阅读说明：本技术 水性涂料组合物及使用所述组合物形成多层涂膜的方法 (Aqueous coating composition and method for forming multilayer coating film using the same ) 是由 中岛久之 H·罗伊特 森聪一 于 2020-03-31 设计创作，主要内容包括：本发明涉及水性涂料组合物,优选着色的水性底色漆组合物,其包含至少一种含有聚氨酯树脂作为核部分和交联的丙烯酸类树脂作为壳部分的核/壳颗粒的分散体和至少一种含有交联的聚氨酯-聚脲颗粒的聚氨酯-聚脲水分散体。此外,本发明涉及使用本发明的水性涂料组合物作为底色漆组合物在基材上形成多层涂层的方法。最后,本发明涉及通过本发明方法制备的多层涂漆体系。(The present invention relates to aqueous coating compositions, preferably pigmented aqueous basecoat compositions, comprising at least one dispersion of core/shell particles containing a polyurethane resin as a core part and a crosslinked acrylic resin as a shell part and at least one aqueous polyurethane-polyurea dispersion containing crosslinked polyurethane-polyurea particles. Furthermore, the present invention relates to a process for forming a multilayer coating on a substrate using the aqueous coating composition of the present invention as a basecoat composition. Finally, the invention relates to a multicoat paint system prepared by the process of the invention.)

1. An aqueous coating composition, preferably a pigmented aqueous basecoat composition, comprising:

(a) an aqueous dispersion of at least one core/shell particle comprising a polyurethane resin as a core portion and a crosslinked acrylic resin as a shell portion, wherein the particle is obtained by:

(i) first an aqueous dispersion of at least one polyurethane resin (P) is added as core part, and then

(ii) Polymerizing a mixture of ethylenically unsaturated monomers in the presence of a polyurethane core portion to obtain a crosslinked acrylic resin (A) shell portion,

wherein:

(ii-1) the polymerization is carried out in the presence of a water-soluble initiator;

(ii-2) metering in the ethylenically unsaturated monomer so that the concentration of the ethylenically unsaturated monomer in the polymerization reaction solution does not exceed 6% by weight, based on the total amount of the ethylenically unsaturated monomer, during the entire polymerization; and is

(ii-3) the mixture of ethylenically unsaturated monomers comprises at least one multi-ethylenically unsaturated monomer, and

(b) at least one aqueous polyurethane-polyurea dispersion comprising polyurethane-polyurea particles having an average particle size of 40-2,000nm and a gel fraction of at least 50%, which polyurethane-polyurea particles comprise in each case the following in reacted form:

● at least one Polyurethane Prepolymer (PP) comprising isocyanate groups and comprising anionic groups and/or groups arranged to be converted into anionic groups, and

● at least one Polyamine (PA) comprising two primary amino groups and one or two secondary amino groups.

2. Aqueous coating composition according to claim 1, wherein the glass transition temperature Tg of the polyurethane resin (P) of the core part is from-80 ℃ to 105 ℃, preferably from-60 ℃ to 80 ℃, more preferably from 50 to 60 ℃, and/or wherein the glass transition temperature Tg of the crosslinked acrylic resin (a) of the shell part is from-60 ℃ to 80 ℃, preferably from-60 ℃ to 20 ℃, according to DIN EN ISO 11357-2: 2013-05.

3. Aqueous coating composition according to claim 1 or 2, wherein the polyurethane resin (P) of the core part has a molecular weight according to DIN EN ISO 2114: an acid number of from 10 to 60mg KOH/g, preferably from 30 to 40mg KOH/g, measured 2002-06, and an OH number of from 20 to 80mg KOH/g, measured according to R.

4. An aqueous coating composition as claimed in any one of the preceding claims, wherein the crosslinked acrylic resin (a) of the shell portion has an OH value of 10 to 140mg KOH/g, measured according to r. Acid number of 0-10mg KOH/g, measured 2002-06.

5. An aqueous coating composition as claimed in any of the preceding claims, wherein the aqueous dispersion (a) has a gel content of from 40 to 97% by weight, preferably from 75 to 90% by weight, based in each case on the solids in the dispersion.

6. The process as claimed in any of the preceding claims, wherein the aqueous coating composition comprises the at least one aqueous dispersion (a) in a total amount of from 0.5 to 50% by weight, preferably from 2 to 40% by weight, more preferably from 3 to 30% by weight, based in each case on the total amount of the aqueous coating composition.

7. An aqueous coating composition as claimed in any of the preceding claims, wherein the aqueous dispersion (b) has a gel fraction of from 70 to 100%, preferably from 80 to 100%, more preferably from 80 to 98%, very preferably from 80 to 90%, in each case based on the solids of the dispersion (b).

8. An aqueous coating composition as claimed in any one of the preceding claims, wherein the Polyurethane Prepolymer (PP) comprises at least one polyester diol which is the product of a diol and a dicarboxylic acid, and wherein at least 50 wt% of the dicarboxylic acid in the preparation of the at least one polyester diol is at least one dimer fatty acid.

9. Aqueous coating composition according to any one of the preceding claims, wherein the Polyurethane Prepolymer (PP) has a molecular weight according to DIN EN ISO 2114: measured 2002-06, an acid number of from 10 to 35mg KOH/g, in particular from 15 to 23mg KOH/g, based on the solids content.

10. Aqueous coating composition according to any one of the preceding claims, wherein the Polyurethane Prepolymer (PP) has an isocyanate content of 0.5 to 6 wt. -%, preferably 1 to 5 wt. -%, particularly preferably 1.5 to 4 wt. -%, according to DIN EN ISO 3251: 2008-06, DIN EN ISO 11909: 2007-05 and DIN EN ISO 14896: 2009-07 measurement.

11. An aqueous coating composition as claimed in any one of the preceding claims, wherein the at least one Polyamine (PA) is at least one selected from diethylenetriamine, 3- (2-aminoethyl) -aminopropylamine, dipropylenetriamine, N1- (2- (4- (2-aminoethyl) piperazin-1-yl) ethyl) ethane-1, 2-diamine, triethylenetetramine and N, N' -bis (3-aminopropyl) ethylenediamine and mixtures thereof.

12. An aqueous coating composition as claimed in any one of the preceding claims, wherein the aqueous coating composition comprises the at least one aqueous dispersion (b) in a total amount of from 10 to 55% by weight, preferably from 15 to 45% by weight, more preferably from 20 to 35% by weight, based in each case on the total amount of aqueous coating composition.

13. An aqueous coating composition as claimed in any one of the preceding claims, wherein the composition comprises the aqueous dispersion of the at least one core-shell particle (a) and the aqueous dispersion of the at least one polyurethane-polyurea (b) in a weight ratio of from 2:1 to 1:15, preferably from 1:1.2 to 1:10, in each case based on the solids content of the dispersion.

14. A method of forming a Multilayer Coating (MC) on a substrate (S), comprising the steps of:

(1) directly applying a first aqueous coating material (X) on a substrate (S) to form an uncured first coating film (X),

(2) directly applying a second aqueous coating material (Y) on the uncured first coating film obtained after step (1) to form an uncured second coating film (Y),

(3) directly applying a clear coating material (Z) on the uncured second coating film obtained after step (2) to form a clear coating film (Z), and then

(4) Curing the three coating films obtained after steps (1) to (3) simultaneously,

the method is characterized in that:

the first aqueous coating (X) and/or the second aqueous coating (Y) are selected from the aqueous coating compositions according to any one of claims 1 to 13.

15. A Multilayer Coating (MC) prepared by the method of claim 14.

Prior Art

Multicoat paint systems on metal or plastic substrates are known, for example in the sector of the automotive industry. Starting from metal substrates, such multicoat paint systems usually comprise an electrocoat film which is cured separately, a film which is applied directly to the electrocoat film and is cured separately (usually called primer), at least one film layer which comprises color pigments and/or effect pigments (usually called basecoat film) and a clearcoat film.

On plastic substrates, which are relevant in the field of components to be mounted in or on vehicles, it is often the same situation that corresponding base paints and clear coating films are applied. In some cases, some primer or adhesion primer is applied prior to the application of the basecoat material.

The basic composition and function of the coatings and of the paints necessary for the formation of these coatings, namely electrocoats, primers, basecoat materials containing color and/or effect pigments and clearcoats, are known. Thus, for example, the basic purpose of an electrophoretically applied electrophoretic coating is to protect the substrate from corrosion. The primary function of the primer coating is to provide protection from mechanical exposure such as stone-chipping and to fill in irregularities of the substrate. The base coat is primarily responsible for producing aesthetic qualities such as color and/or effects such as flocking, while the subsequent clear coat is used in particular for providing a multi-layer paint system with scratch resistance and gloss.

The preparation of these multicoat paint systems generally comprises the electrophoretic deposition or application of an electrocoating, more particularly a cathodic electrocoating, on a metal substrate, such as an automobile body. Prior to depositing the electrocoat, the metal substrate may be subjected to various pretreatments, for example, known conversion coatings, such as phosphate coatings, and more particularly zinc phosphate coatings, may be applied. The operation of depositing the electrophoretic paint is generally carried out in a corresponding electrophoretic bath. After the electrocoat is applied, the coated substrate is removed from the tank and optionally rinsed and flash evaporated and/or intermediate dried, and finally the applied electrocoat is cured. The film thickness of the cured electrocoat should be about 15-25 microns.

The primer material is then applied directly to the cured electrocoat, optionally flash evaporated and/or intermediate dried, followed by curing. In order for the cured primer coating to meet the above objectives, a film thickness of 25-45 microns is required. Applied directly onto the cured primer coating is a basecoat material comprising color and/or effect pigments, and optionally flashed off and/or intermediate dried. The base paint film thus prepared is then coated with a clear coat without separate curing. The clear coat film may be flash evaporated and/or intermediate dried (so-called 2 coat 1 bake (2C1B) process) before the basecoat film and any clear coat film are co-cured. The cured basecoat had a relatively low film thickness of 10-20 microns, while a film thickness of 30-60 microns was used for the cured clearcoat to achieve the described technical application properties. The application of the primer, basecoat and clearcoat can be carried out, for example, by pneumatic and/or electrostatic spraying, as is known to those skilled in the art. Currently, primer and base coat materials are increasingly used in the form of aqueous coatings for environmental reasons.

Multicoat paint systems prepared by the 2C1B process are generally able to meet the requirements of the automotive industry with regard to technical application properties and aesthetic properties. However, increasingly stringent environmental and economic regulations necessitate simplification of the aforementioned relatively complex production operations.

Particularly for metal substrates, there is a method of omitting a separate curing step of a coating composition to be directly applied to a cured electrocoat film (i.e., a coating composition referred to as a primer in the above-mentioned standard method), while optionally reducing the film thickness of a coating film prepared from the coating composition (so-called 3-coat 1-bake (3C1B) method). In this process, the coating film which is not cured separately is generally referred to at this time as a base paint film (no longer a base paint film) or, in order to distinguish it from a second base paint film applied thereon, as a first base paint film. In some cases, it is attempted even to omit the base coat/first base coat film (in which case only one base coat film is prepared directly on the electrophoretic coating film, on which the clearcoat is applied without a separate curing step).

From an environmental and economic point of view, it is very advantageous to avoid a separate curing step of the coating composition applied directly onto the electrocoat film, since this saves energy and allows the production operation to be carried out in significantly less time.

Similar methods are known in the field of plastics processing, wherein no electrocoating is required, so that the electrocoating is omitted. The co-cured system consisting of the first basecoat material, the second basecoat material and the clearcoat material is therefore applied, for example, directly to a plastic substrate which may have been subjected to a surface-activation pretreatment, or to a basecoat film or adhesive basecoat film which is applied first to the substrate.

Also known are refinishing methods for reconstructing multicoat paint systems in which the multicoat paint systems are prepared as described above, but which contain certain disadvantages. The recoating process is carried out, for example, by locally repairing the defect (spot repair) or by completely recoating the initial finish with defects (double finish). In this case, the system consisting of the primer, the basecoat and the clearcoat, or the system consisting of the first basecoat, the second basecoat and the clearcoat, as described above, is usually applied after local grinding of the defect. It is also possible to apply only one basecoat and the clearcoat applied thereto and then to cure them together. In this process, multicoat paint systems having defects (initial finishes) are used as substrates.

Although the technical properties of existing multicoat paint systems are generally already sufficient to meet the specifications of the automobile manufacturers, there is a continuing need to improve them. This need is particularly relevant to the 3C1B process described last for the preparation of multicoat paint systems. However, even the standard methods for producing multicoat paint systems described above can still be optimized in this respect.

For example, omitting the separate curing of the coating film (i.e., the first basecoat material) applied directly onto the electrocoat layer prior to the application of other coatings, such as the second basecoat material and the clearcoat material, may result in the formation of bubbles beneath the surface of the overall paint system, which bubbles may burst during final curing. As a result, the pores formed in the lacquer system (also referred to as pinholes and pop pores) lead to an unfavourable visual appearance. The content of organic solvents and/or water and the amount of air introduced as a result of the application procedure are too great to allow the entire amount to escape from the multicoat paint system without defects during curing. In the case of the 2C1B process, in which the primer film is baked separately and then a generally relatively thin primer film is produced, the total amount of organic solvent, water and air is much lower than in the 3C1B process, and therefore the risk of undesirable bubble formation during the final curing step is itself lower.

However, the described problems of pinholes and popping are often encountered even in the preparation of multicoat paint systems which completely abandon the use of coatings known as primers in standard practice. This is due to the fact that: to achieve the desired properties, the primer film thickness required in this process is generally greater than in the standard 2C1B process. Therefore, the total film thickness of the coating film that must be cured in the final curing step is also significantly higher than in the 2C1B method.

Furthermore, other relevant properties are not always satisfactorily achieved when the multicoat paint systems are constructed using the described 2C1B or 3C1B methods. Thus, challenges are posed in obtaining high-grade overall appearance, which is particularly affected by the good flowability of the coatings used. In this case, the coating must exhibit a suitable rheological behavior (application behavior), in particular a pronounced structural viscosity. This structural viscosity is present when the coating has a low viscosity at the high shear rates present during the application process (typically spraying), but a viscosity that is high enough that the coating is sufficiently sag resistant and does not run off or form a sag on the substrate after application to the substrate. Similar comments apply to mechanical properties such as adhesion. In this regard, obtaining adequate quality is also a challenge.

The environmental properties of multicoat paint systems are also still in need of improvement. In fact, a contribution in this respect has been achieved by replacing a significant fraction of the organic solvent with water in aqueous paints. However, by increasing the solids content of such paints, significant improvements can be achieved. However, especially in aqueous basecoat materials comprising color pigments and/or effect pigments, it is very difficult to increase the solids content while maintaining acceptable storage stability (settling behavior) and suitable rheological properties or a pronounced structural viscosity.

The properties of coatings or paints, such as water-borne base coat materials, are critically determined by the components they contain, such as the polymers used as binders.

Thus, the prior art describes a wide range of specific polymers, their use in coatings and their advantageous effects on various properties of paint systems and coatings.

Patent application JP2004-358462a1 discloses the use of a first aqueous basecoat composition in A3C 1B process, comprising (i) an acrylic resin emulsion having a specific glass transition temperature, acid value and hydroxyl value, (ii) a urethane resin emulsion having a specific acid value and (iii) a curing agent. According to this document, the use of the composition in the 3C1B process results in a multilayer coating having excellent surface smoothness by effectively preventing mixing of the first and second basecoat coating films.

Patent application JP2007-297545a1 discloses the use of a second aqueous basecoat composition in the 3C1B process, comprising (i) a specific amount of an emulsion resin obtained by emulsion polymerizing a specific vinyl monomer mixture, (ii) a water-soluble acrylic resin comprising an amide group, (iii) a urethane resin emulsion, and (iv) a curing agent, which results in excellent appearance and water resistance of the resulting multilayer coating.

Patent application WO2010/082607a1 discloses a first waterborne base coat composition comprising (i) an acrylic resin, (ii) a curing agent and (iii) a urethane resin emulsion, and its use in A3C 1B process for the preparation of multilayer coatings with excellent smoothness, sharpness and chip resistance.

However, when the coating composition disclosed in the above-mentioned patent application is used in the 3C1B method, in which no preheating is performed after the application of the first aqueous base coat composition, layer mixing occurs between the first coating film and the second coating film and it is impossible to obtain a multi-layer coating system having a good appearance.

WO2013/027093a1 describes an aqueous coating composition containing a core/shell type emulsion resin containing an acrylic resin as a core portion and a polyurethane resin as a shell portion, wherein the mass ratio of the core portion and the shell portion in the above core/shell type emulsion resin is 20/80 to 80/20. The coating composition can be used as the first and/or second basecoat composition in the 3C1B process and provides sufficient optical and mechanical resistance. However, if the composition is used in a low bake 3C1B process where curing of all 3 applied layers is carried out at a temperature below 100 ℃, the stone chip resistance, adhesion in recoat applications and resulting hardness of the multilayer coating system are insufficient.

Purpose(s) to

It is therefore an object of the present invention to provide an aqueous coating composition, preferably a pigmented aqueous basecoat composition, which allows advantageous properties to be obtained in paint systems, especially multicoat paint systems, prepared using the aqueous coating composition. The first quality to be achieved should include good optical performance, more particularly good pinhole behavior and good sag resistance. Mechanical properties such as adhesion or stone chip resistance should also be outstanding. Furthermore, the aqueous coating should have good storage stability and should have a high solids content. Despite the high solids content, the rheological behaviour of the coating composition should be outstanding.

It is a further object of the present invention to provide a process for preparing multicoat paint systems in which the coating materials of the present invention are applied directly to a substrate or electrocoat system and are cured in a common curing step together with the other coating films subsequently applied. Despite this simplification of the process, the multicoat paint systems obtained should have outstanding stability with respect to pinholes. Furthermore, a multicoat paint system should be provided in which the coating film disposed between the electrocoat and the clearcoat can have a variable film thickness and in which the problem of pinholes does not occur even at relatively high film thicknesses. The quality obtained with this method should be at least comparable to, and preferably better than, the standard 2C1B method in terms of overall appearance and adhesion.

Technical scheme

It has been found that the stated object is achieved by an aqueous coating composition, preferably a pigmented aqueous basecoat composition, comprising:

(a) an aqueous dispersion of at least one core/shell particle comprising a polyurethane resin as a core portion and a crosslinked acrylic resin as a shell portion, wherein the particle is obtained by:

(i) first an aqueous dispersion of at least one polyurethane resin (P) is added as core part, and then

(ii) Polymerizing a mixture of ethylenically unsaturated monomers in the presence of a polyurethane core portion to obtain a crosslinked acrylic resin (A) shell portion,

wherein:

(ii-1) the polymerization is carried out in the presence of a water-soluble initiator;

(ii-2) metering in the ethylenically unsaturated monomer so that the concentration of the ethylenically unsaturated monomer in the polymerization reaction solution does not exceed 6% by weight, based on the total amount of the ethylenically unsaturated monomer, during the entire polymerization; and is

(ii-3) the mixture of ethylenically unsaturated monomers comprises at least one polyethylenically unsaturated monomer, and (b) at least one aqueous polyurethane-polyurea dispersion comprising polyurethane-polyurea particles having an average particle size of from 40 to 2,000nm and a gel fraction of at least 50%, which polyurethane-polyurea particles comprise in each case in reacted form:

at least one Polyurethane Prepolymer (PP) which contains isocyanate groups and contains anionic groups and/or groups which are arranged to be converted into anionic groups, and

at least one Polyamine (PA) comprising two primary amino groups and one or two secondary amino groups.

The above-mentioned aqueous coating compositions are also referred to below as aqueous coating compositions of the invention and are therefore the subject of the present invention. Preferred embodiments of the aqueous coating composition of the invention are evident from the following description and the dependent claims.

The use of the aqueous coating compositions of the invention makes it possible to obtain outstanding properties of multicoat paint systems prepared using aqueous coating compositions in the 3C1B process, preferably the 3C1B process in which the simultaneous curing step is carried out at a temperature of less than 100 ℃. It is worth mentioning that all of the above are good optical properties, more particularly good pinhole behaviour and good sag stability, as well as good mechanical properties such as adhesion or stone chip resistance. Pinholes are very small holes visible in the final coating. They are one of the most common surface defects in spray paints. The defect known as a pinhole in the specification and in the examples of the subsequent patents is characterized by a funnel-shaped hole continuously entering the cylindrical tube on the order of the pin point indentation, the funnel opening of which has an average diameter of about 300-700 μm and an average tube diameter of about 15-60 μm and passes through the clear coat and the basecoat to the underlying coating. They may be the result of escaping gases such as trapped air or evaporating solvents. The overall appearance and adhesion of these multicoat paint systems is also outstanding and at least at the level of the multicoat paint systems prepared by the standard methods described above. At the same time, the aqueous coating composition exhibits good storage stability. Furthermore, the aqueous coating composition can be prepared in an environmentally advantageous manner, more particularly with a high solids content.

The invention also provides a method for forming a Multilayer Coating (MC) on a substrate (S), comprising the steps of:

(1) directly applying a first aqueous coating material (X) on a substrate (S) to form an uncured first coating film (X),

(2) directly applying a second aqueous coating material (Y) on the uncured first coating film obtained after step (1) to form an uncured second coating film (Y),

(3) directly applying a clear coating material (Z) on the uncured second coating film obtained after step (2) to form a clear coating film (Z), and then

(4) Curing the three coating films obtained after steps (1) to (3) simultaneously,

the method is characterized in that:

the first aqueous coating (X) and/or the second aqueous coating (Y) is selected from the aqueous coating composition of the present invention.

The invention also provides a Multilayer Coating (MC) prepared by the method of the invention.

Detailed Description

If in the context of the present invention an official standard is referred to, this of course means the version of the standard that was passed on the date of application, or the last passed version if no passed version existed on that date.

Aqueous coating composition of the invention:

the expression "aqueous coating composition" is known to the person skilled in the art. It means a system comprising not exclusively or mainly an organic solvent (also referred to as a solvent) as its dispersion medium; instead, it contains a significant fraction of water as its dispersion medium. In the context of the present invention, "aqueous" is understood to mean that the coating composition has a proportion of water of at least 20% by weight, preferably at least 25% by weight, particularly preferably at least 50% by weight, based in each case on the total amount of solvents (i.e. water and organic solvent) present. The proportion of water is preferably from 60 to 100% by weight, in particular from 70 to 98% by weight, particularly preferably from 75 to 95% by weight, based in each case on the total amount of solvent present.

Dispersion of core/shell particles:

the first essential component of the aqueous coating composition is a dispersion of at least one core/shell type particle comprising a polyurethane resin as a core portion and a crosslinked acrylic resin as a shell portion.

The dispersion (a) is characterized by its preparation steps (i) and (ii). In the first production step (i), an aqueous dispersion of the polyurethane resin (P) as a core portion is first added.

Suitable saturated or unsaturated polyurethane resins (P) are described, for example, in DE19948004A1 page 4 line 19 to page 11 line 29 (polyurethane prepolymer B1), EP0228003A1 page 3 line 24 to page 5 line 40, EP0634431A1 page 3 line 38 to page 8 line 9, or WO92/15405 page 2 line 35 to page 10 line 32.

The polyurethane resins (P) are preferably prepared using aliphatic, cycloaliphatic, aliphatic-cycloaliphatic, aromatic, aliphatic-aromatic and/or cycloaliphatic-aromatic polyisocyanates known to the person skilled in the art. Aliphatic and aliphatic-alicyclic urethane resins are particularly preferred.

The alcohol component used for preparing the polyurethane resin (P) is preferably a saturated and unsaturated polyol known to the person skilled in the art, and optionally a minor amount of a monohydric alcohol. In particular diols and optionally small amounts of triols are used to introduce branching. Examples of suitable polyols are saturated or ethylenically unsaturated polyester polyols and/or polyether polyols. The polyols used are, in particular, polyester polyols, in particular those having a number average molecular weight of 400-5,000 g/mol. The number average molecular weight (Mn) is the concentration series at 50 ℃ in toluene with benzophenone as calibration substance for determining the experimental calibration constants of the measuring instrument used, according to E, by means of a vapor pressure permeameter of 10.00 (from Knauer).G.M muller, K. -F.Arndt, "Leitfaden der polymercharakterisinierung", Akademie-Verlag, Berlin, pp.47-54, 1982.

Preferably, the polyurethane resin (P) first added to the aqueous dispersion is a hydrophilic stable polyurethane resin (P). For hydrophilic stabilization or for increasing dispersibility in an aqueous medium, the polyurethane resin (P) may contain the following modifying groups:

functional groups which can be converted into cations by neutralizing and/or quaternizing agents, and/or cationic groups (cationic modification), or

Functional groups which can be converted into anions by neutralizing agents, and/or anionic groups (anionic modification), or

A nonionic hydrophilic group (nonionic modification), or

-combinations of the above groups.

In the context of the present invention, the polyurethane resin (P) is referred to as an ionic or nonionic hydrophilically stabilized polyurethane resin (P). The ionically hydrophilically stabilized polyurethane resin (P) is preferred.

As is known to the person skilled in the art, functional groups for cationic modification are, for example, primary, secondary and/or tertiary amino groups, secondary sulfur groups and/or tertiary phosphine groups, in particular tertiary amino groups and secondary sulfur groups (functional groups which can be converted into cationic groups by neutralizing agents and/or quaternizing agents). Mention should furthermore be made of cationic groups prepared from the abovementioned functional groups, for example primary, secondary, tertiary and/or quaternary ammonium groups, tertiary sulfonium groups and/or quaternary phosphonium groups, using neutralizing and/or quaternizing agents known to the person skilled in the artGroups, especially quaternary ammonium groups and tertiary sulfonium groups.

As is well known, functional groups for anionic modification are, for example, carboxylic, sulfonic and/or phosphonic acid groups, in particular carboxylic acid groups (functional groups which can be converted into anionic groups by neutralizing agents), and anionic groups prepared from the above-mentioned functional groups using neutralizing agents known to the person skilled in the art, such as carboxylates, sulfonates and/or phosphonates.

The functional group for nonionic hydrophilic modification is preferably a polyoxyalkylene group, especially a polyoxyethylene group.

The hydrophilic modification can be introduced, for example, into the polyurethane resin (P) by means of monomers containing ionic or potentially ionic groups, wherein use is made of monomers containing at least one group reactive toward isocyanate groups, preferably at least one hydroxyl group, and also modifying groups. The nonionic modification is introduced into the polyurethane molecule as a side group or end group, for example by introducing a polyethylene oxide polymer. For introducing the nonionic modification, preference is given to using polyether diols and/or alkoxypoly (oxyalkylene) alcohols known to the person skilled in the art.

At least one solvent is preferably added to the initially charged polyurethane dispersion, which solvent is miscible with water in any proportion and with the mixture of ethylenically unsaturated monomers in any proportion. Particularly suitable solvents are N-methylpyrrolidone, N-ethylpyrrolidone and ether alcohols, such as, in particular, methoxypropanol.

As a next preparation step (ii), the polymerization of the ethylenically unsaturated monomer mixture is carried out by free-radical emulsion polymerization in the presence of the polyurethane core part in the presence of at least one polymerization initiator, thereby forming a crosslinked acrylic resin shell part.

The polymerization initiator used must be a water-soluble initiator (ii-1), preferably selected from the group consisting of potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, tert-butyl hydroperoxide, 2 '-azobis (2-acylaminoisopropane) dihydrochloride, 2' -azobis (N, N '-dimethyleneisobutyramidine) dihydrochloride, 2' -azobis (4-cyanovaleric acid) and mixtures thereof. It is also possible to use known redox initiator systems as polymerization initiators. The redox initiator system comprises at least one peroxide-containing compound in combination with a redox co-initiator such as a reducing sulfur compound, for example, a bisulfite, sulfite, thiosulfate, dithionite or tetrathionate salt of an alkali metal and ammonium compound, sodium hydroxymethanesulfinate dihydrate and/or thiourea. For example, a combination of a persulfate with an alkali metal bisulfite or ammonium bisulfite may be used, such as ammonium persulfate and ammonium bisulfite. The weight ratio of peroxide-containing compound to redox coinitiator is preferably 50:1 to 0.05: 1. In combination with the initiator or redox initiator system, it is furthermore possible to use transition metal catalysts, for example iron, nickel, cobalt, manganese, copper, vanadium or chromium salts, for example iron (II) sulfate, cobalt (II) chloride, nickel (II) sulfate, copper (I) chloride, manganese (II) acetate, vanadium (III) acetate, manganese (II) chloride. These transition metal salts are generally used in amounts of from 0.1 to 1000ppm, based on the monomers. For example, a combination of hydrogen peroxide and an iron (II) salt may be used, for example 0.5-30% hydrogen peroxide and 0.1-500ppm Mohr's salt.

The initiator is preferably used in an amount of from 0.05 to 20% by weight, preferably from 0.05 to 10% by weight, more preferably from 0.1 to 5% by weight, based on the total weight of the ethylenically unsaturated monomers used in step (ii).

Due to the use of water-soluble initiators, the ethylenically unsaturated monomers added to the initially charged aqueous dispersion can be reacted immediately to give oligomers. These oligomers have a lower tendency to penetrate into the polyurethane core particles of the initially charged dispersion than the smaller monomers, thus leading to a crosslinked acrylate shell portion. If a water-insoluble initiator is used, the monomer penetrates the polyurethane core prior to forming the oligomer, thus creating a crosslinked acrylate core portion and a polyurethane shell portion.

The polymerization is suitably carried out at a temperature of from 0 to 160 c, preferably from 60 to 95 c.

In this context, preference is given to working with exclusion of oxygen, preferably in a nitrogen stream. Typically, the polymerization is carried out at standard pressure, although lower or higher pressures may also be used, especially when polymerization temperatures above the boiling point of the monomer and/or solvent are used.

The polymers of the invention are prepared by free radical aqueous emulsion polymerization and surfactants or protective colloids can be added to the reaction medium. A list of suitable emulsifiers and protective colloids can be found, for example, in Houben Weyl, Methoden der organischen Chemie, volume XIV/1, Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart 1961, page 411 and subsequent pages.

An important factor in preparing the aqueous dispersion (a) of core/shell-type particles is controlling the polymerization conditions of the mixture of ethylenically unsaturated monomers in the presence of the polyurethane resin (P) as the core portion. This is done in a "starved polymerization" manner. In the context of the present invention, starved polymerization is considered to be emulsion polymerization, in which the residual monomer content in the reaction solution is minimized during the reaction. It is therefore preferred that the ethylenically unsaturated monomer (ii-2) is metered in such that the concentration of ethylenically unsaturated monomer (ii-2) in the reaction solution during the entire polymerization of step (ii) does not exceed 6% by weight, preferably 5% by weight, very preferably 4% by weight, based on the total amount of ethylenically unsaturated monomers. The monomer concentration in the reaction solution can be determined by gas chromatography as described below.

The concentration of the monomer (hereinafter referred to as free monomer) in the reaction solution can be controlled in various ways.

One way of keeping the free monomer concentration low is to select a very low metering rate of the ethylenically unsaturated monomer mixture. It is ensured that the concentration of free monomers is minimized when the metering rate is sufficiently low that all monomers can react very quickly once they have been added to the reaction solution.

In addition to the metering rate, it is important that sufficient free radicals are always present in the reaction solution so that the added monomers can react very quickly. For this purpose, the reaction conditions are preferably selected such that the initiator feed is started already before the metering in of the ethylenically unsaturated monomers. Preferably at least 5 minutes earlier, more preferably at least 10 minutes earlier. Preferably at least 10% by weight, more preferably at least 20% by weight, most preferably at least 30% by weight of initiator, based in each case on the total amount of initiator (ii-1), is added before the start of the metering in of the ethylenically unsaturated monomers.

The amount of the initiator (ii-1) is an important factor for the presence of sufficient radicals in the reaction solution. The amount of initiator should be chosen so that at any time sufficient free radicals are available to allow the added monomer to react. If the amount of initiator is increased, it is also possible to add larger amounts of monomer simultaneously.

Another factor that determines the rate of reaction is the structure of the monomer.

Thus, the concentration of free monomer can be controlled by the amount of initiator, the rate of initiator addition, the interaction of the monomer addition rates, and by the choice of monomer. The slowing of the metering, the increase in the amount of initiator and the early start of the initiator feed therefore serve the purpose of keeping the free monomer concentration below the abovementioned limits.

The concentration of free monomer at any time during the reaction can be determined by gas chromatography. Typical parameters for the assay are as follows: a 50m silica capillary column with a polyethylene glycol phase or a 50m silica capillary column with a polydimethylsiloxane phase, helium carrier gas, split-flow injector 150 ℃, oven temperature 40-220 ℃, flame ionization detector, detector temperature 275 ℃, isobutyl acrylate internal standard.

If any concentration of free monomer is determined in this analysis to be close to the limit of starved polymerization, for example due to the very low reactivity of the ethylenically unsaturated monomer, the above parameters can be used to control the reaction. In this case, for example, the metering rate of the monomers can be reduced or the amount of initiator can be increased.

Suitable ethylenically unsaturated monomers may be mono-or polyethylenically unsaturated.

Examples of suitable monoethylenically unsaturated monomers include (meth) acrylate-based monoethylenically unsaturated monomers, vinyl monoethylenically unsaturated monomers, α, β -unsaturated carboxylic acids, and allyl compounds. The term "(meth) acrylate" refers hereinafter to both acrylates and methacrylates.

The (meth) acrylate-based monoethylenically unsaturated monomers may be, for example, (meth) acrylic acid and esters, nitriles or amides of (meth) acrylic acid.

Preference is given to (meth) acrylates having ethylenically unsaturated R groups of the general formulae (I) and/or (II):

the R groups may be aliphatic or aromatic, preferably aliphatic. The R group may, for example, be an alkyl group, or contain heteroatoms. Examples of heteroatom containing R groups are ethers. The R group is preferably an alkyl group.

If R is an alkyl group, it may be a linear, branched or cyclic alkyl group. In all three cases, the alkyl group can be an unsubstituted alkyl group or an alkyl group substituted with a functional group. The alkyl group preferably has 1 to 20, more preferably 1 to 10 carbon atoms.

Particularly preferred suitable monounsaturated esters of (meth) acrylic acid with unsubstituted alkyl groups are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate, 3, 5-trimethylhexyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, cycloalkyl (meth) acrylates such as cyclopentyl (meth) acrylate, isobornyl (meth) acrylate and cyclohexyl (meth) acrylate, n-butyl and tert-butyl (meth) acrylate and methyl methacrylate being very particularly preferred.

Suitable monounsaturated esters of (meth) acrylic acid with substituted alkyl groups may preferably be substituted with one or more hydroxyl groups.

Particularly preferred suitable monounsaturated esters of (meth) acrylic acid having an alkyl group substituted with one or more hydroxyl groups are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.

The vinyl monounsaturated monomer may be a monomer of formula (III) having an ethylenically unsaturated R' group on the vinyl group:

the R' group may be aliphatic or aromatic, preferably aromatic. The R' group may be a hydrocarbon group or contain heteroatoms. Examples of heteroatom containing R' groups are ethers, esters, amides, nitriles and heterocycles. The R' group is preferably a monovalent group derived from a hydrocarbon, such as methyl or phenyl.

If R' is a hydrocarbyl group, it may be substituted or unsubstituted with heteroatoms, with unsubstituted groups being preferred.

The R' group is preferably an aromatic hydrocarbon group.

Particularly preferred ethylenically unsaturated monomers are vinyl aromatic hydrocarbons, especially vinyl toluene, alpha-methyl styrene, especially styrene. When heteroatoms are present, ethylenically unsaturated monomers are preferred, such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, N-dimethylacrylamide, vinyl acetate, vinyl propionate, vinyl chloride, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinylimidazole and N-vinyl-2-methylimidazoline.

Examples of suitable polyethylenically unsaturated monomers include (meth) acrylates of the general formulae (IV) and/or (V) having an ethylenically unsaturated R' group and allyl ethers of mono-or polyhydric alcohols. The R "group may be allyl or (meth) acrylate.

Preferred polyethylenically unsaturated monomers include ethylene glycol di (meth) acrylate, 1, 2-propylene glycol di (meth) acrylate, 1, 3-propylene glycol di (meth) acrylate, 1, 4-butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 3-methylpentanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, and allyl (meth) acrylate.

Furthermore, preferred polyethylenically unsaturated compounds include acrylic and methacrylic esters of alcohols having more than 2 OH groups, such as trimethylolpropane tri (meth) acrylate or glycerol tri (meth) acrylate, and also trimethylolpropane di (meth) acrylate monoallyl ether, trimethylolpropane (meth) acrylate diallyl ether, pentaerythritol tri (meth) acrylate monoallyl ether, pentaerythritol di (meth) acrylate diallyl ether, pentaerythritol (meth) acrylate triallyl ether, triallyl sucrose and pentaallyl sucrose. Allyl methacrylate and/or hexanediol di (meth) acrylate are particularly preferably used.

The mixture of ethylenically unsaturated monomers comprises at least one multi-ethylenically unsaturated monomer. The mixture of ethylenically unsaturated monomers preferably also comprises one or more monounsaturated esters of (meth) acrylic acid having unsubstituted alkyl groups.

The mixture of ethylenically unsaturated monomers (ii-3) preferably comprises from 0.1 to 6.0 mol%, more preferably from 0.1 to 2.0 mol%, most preferably from 0.1 to 1.0 mol%, of multi-ethylenically unsaturated monomers, in each case based on the total amount of ethylenically unsaturated monomers.

The mixture of ethylenically unsaturated monomers (ii-3) preferably comprises from 0.1 to 6.0 mol%, more preferably from 0.1 to 2.0 mol%, most preferably from 0.1 to 2.0 mol% of allyl methacrylate and/or hexanediol di (meth) acrylate. More preferably, no other multi-ethylenically unsaturated monomers are present in the mixture in addition to allyl methacrylate and/or hexanediol di (meth) acrylate, which means that the mixture comprises 0% by weight, based on the total amount of ethylenically unsaturated monomers, of other multi-ethylenically unsaturated monomers in addition to allyl methacrylate.

The mixture of ethylenically unsaturated monomers (ii-3) preferably comprises <10.0 wt.%, more preferably <5.0 wt.%, very preferably 0 wt.% of vinylarene, based on the total amount of ethylenically unsaturated monomers.

In a preferred embodiment, the mixture of ethylenically unsaturated monomers (ii-3) comprises, based on the total amount of ethylenically unsaturated monomers:

98.0 to 99.5% by weight of one or more monounsaturated esters of (meth) acrylic acid having unsubstituted alkyl groups, where the alkyl groups have a length of 1 to 10, preferably 3 to 5, carbon atoms, and

from 0.5 to 2.0% by weight of one or more polyunsaturated esters of (meth) acrylic acid, preferably allyl (meth) acrylate and/or hexanediol di (meth) acrylate.

Preferably, at least one solvent is added to the mixture of ethylenically unsaturated monomers (ii-3), which solvent is miscible with water in any proportion and with the mixture of ethylenically unsaturated monomers in any proportion. Particularly suitable solvents are N-methylpyrrolidone, N-ethylpyrrolidone and ether alcohols, for example methoxypropanol.

The aqueous dispersion (a) of core/shell type particles is obtained only by the above-described production method. The core-shell structure is characterized in that the core comprises at least one polyurethane resin (P) and the shell comprises a crosslinked acrylic resin (A) obtained by polymerization of ethylenically unsaturated monomers in the presence of the polyurethane core.

The core-shell structure is achieved by the specific reaction conditions of the starved polymerization and the use of water-soluble initiators. During the entire reaction, there is no large amount of ethylenically unsaturated monomer that can penetrate into the initially charged polyurethane resin (P). Since the free radicals, which are provided by the water-soluble initiator, are continuously present during the addition of the monomers to the aqueous phase, oligomers are formed immediately upon addition of the monomers. These oligomers can no longer penetrate into the polyurethane core (P) and therefore polymerize on the surface of the polyurethane core (P) to give the crosslinked acrylic shell (a).

The glass transition temperature Tg of the urethane resin (P) of the core portion and/or the glass transition temperature Tg of the crosslinked acrylic resin (a) of the shell portion are preferably within a specific range. The glass transition temperature Tg of the polyurethane resin (P) of the core portion is preferably-80 ℃ to 105 ℃, more preferably-60 ℃ to 80 ℃, even more preferably 50-60 ℃, and/or the glass transition temperature Tg of the crosslinked acrylic resin (a) of the shell portion is preferably-80 ℃ to 20 ℃, more preferably-60 ℃ to 20 ℃, according to DIN EN ISO 11357-2: 2013-05. Specific examples of Tg's for the polyurethane core (P) include-75, -70, -65, -60, -55, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5,0, 5, 10, 15, 20 ℃. Specific examples of the Tg of the acrylic shell (A) include-55, -50, -45, -40, -35, -30, -25, -20, -15, -10, -5,0, 5, 10, 15, 20 ℃. It is desirable for the polyurethane core to have a lower Tg than the crosslinked acrylic shell in view of improved hardness and repair adhesion, as well as improved stone chip resistance.

In addition to the glass transition temperatures Tg of the core part and the shell part, it is also preferred that the core/shell particles in the aqueous dispersion (a) have a glass transition temperature of from-50 ℃ to 30 ℃ in accordance with DIN EN ISO 11357-2: 2013-05.

For the purposes of the present invention, the glass transition temperature Tg is in accordance with DIN 51005: 2005-08 and DIN EN ISO 11357-2: 2013-05 were determined experimentally. This involves weighing out 10mgSample into a sample pan and introduce it into a DSC instrument. The instrument was cooled to the starting temperature, followed by an inert gas purge (N) at 50 ml/min₂) The 1 st and 2 nd round measurements were then carried out at a heating rate of 10K/min, with cooling again to the starting temperature between the measuring rounds. The measurement is typically performed at a temperature range of from about 50 ℃ below the expected glass transition temperature to about 50 ℃ above the glass transition temperature. According to DIN EN ISO 11357-2: 2013-05, the glass transition temperature for the purposes of the present invention is the temperature at which half the change in specific heat capacity (0.5 Δ cp) is reached in round 2 measurements. The temperature is determined from the DSC diagram (curve of heat flow versus temperature) and is the temperature at the intersection of the central line between the extrapolated baselines and the measured curve before and after the glass transition.

All the values reported above for the glass transition temperature Tg of the acrylic shell portion relate to the specific polymer formed when the corresponding monomer mixture (ii-3) is polymerized in the absence of the aqueous dispersion of the polyurethane resin (P).

To purposefully estimate the expected glass transition temperature, the Fox equation can be used:

tg: the glass transition temperature (kelvin) of the resulting copolymer,

X₁，X₂，…，X_n: monomer component 1,2, …, weight fraction of n,

Tg₁，Tg₂，…，Tg_n: glass transition temperature (kelvin) of the homopolymer of monomer component 1,2, …, n.

Since the Fox equation represents only an approximation based on the glass transition temperature of the homopolymer and its weight fraction, and does not include molecular weight, it can be used as a tool or objective index for those skilled in the art in synthesis. However, the glass transition temperature values relevant to the description of the present invention are those measured as described above.

The urethane resin (P) forming the core portion has a sufficient amount of the above-mentioned hydrophilic group so as to be capable of water dispersibility. The acid number of the polyurethane resin (P) of the core part is therefore preferably from 10 to 60mg KOH/g, very preferably from 30 to 40mg KOH/g, in accordance with DIN EN ISO 2114: 2002-06. The OH number of the polyurethane resin (P) is preferably from 20 to 80mg KOH/g, measured in accordance with R. -P.Kr ü ger, R.Gnauck and R.Algeier, Plaste und Kautschuk, 20, 274 (1982). If the acid value is less than 10mg KOH/g or the OH value is less than 20mg KOH/g, the emulsion stability of the polyurethane resin (P) in an aqueous medium is lowered; if the acid value exceeds 60mg KOH/g or the OH value exceeds 80mg KOH/g, the water solubility of the polyurethane resin (P) becomes too high. In both cases, discrete core/shell particles can no longer be obtained by the aforementioned methods. The OH number can be determined on the basis of R.P.Krueger, R.Gnauck and R.Algeier, Plaste und Kautschuk, 20, 274(1982) in the presence of 4-dimethylaminopyridine as catalyst in Tetrahydrofuran (THF)/Dimethylformamide (DMF) solution at room temperature with the aid of acetic anhydride and after acetylation the residual excess acetic anhydride is completely hydrolyzed and the acetic acid is subjected to potentiometric back-titration with alcoholic potassium hydroxide solution. The acid number can be based on DIN EN ISO 2114: 2002-06 was measured in a homogeneous solution of THF/water (9 parts by volume of THF and 1 part by volume of distilled water) and an ethanolic solution of potassium hydroxide.

In terms of appearance of the coating film and adhesion of the coating film to the object to be coated, it is desirable that the crosslinked acrylic resin (A) of the shell portion has an OH value of 10 to 140mg KOH/g, measured in accordance with R. -P.Krueger, R.Gnauck and R.Algeier, plant und Kautschuk, 20, 274(1982), and an acid value of 0 to 10mg KOH/g, in accordance with DIN EN ISO 2114: 2002-06. If the OH value is less than 10mg KOH/g, the adhesion to the object to be coated may decrease, and if the hydroxyl value exceeds 140mg KOH/g, the polarity of the shell part becomes too high, thus increasing the risk of undesired layer mixing between the first water-based paint and the second water-based paint or between the second water-based paint and the clear paint in the multilayer coating method. Such layer mixing can result in a negative impact on the appearance of the multilayer coating. If the acid value of the acrylic resin (A) exceeds 10mg KOH/g, core/shell type particles may not be obtained in the aforementioned production method.

In addition to the acid and OH values described above for the core and shell parts, it is also advantageous for the core/shell particles in the aqueous dispersion (a) to have a specific acid and OH value. It is therefore preferred that the core-shell particles in the aqueous dispersion (a) have an acid number of from 10 to 30mg KOH/g solids and/or an OH number of from 20 to 50mg KOH/g solids, determined as described above.

In a preferred embodiment, the weight ratio of the polyurethane core portion to the crosslinked acrylic shell portion is from 80:20 to 20:80, more preferably from 60:40 to 40: 60. The microstructure of the core/shell type particles can be examined by transmission electron microscopy as described in US2016/0152862a 1.

The core/shell particles in the aqueous dispersion (a) preferably have a particle size (z-average) of 60 to 250nm, more preferably 60 to 115nm, as measured by photon correlation spectroscopy at 25 ± 1 ℃ using Malvern Nano S90 (available from Malvern Instruments). The unit was equipped with a 4mWHe-Ne laser with a wavelength of 633nm, covering a size range of 1-3,000 nm.

Preferably, the acid value of the core/shell particles in the aqueous dispersion (a) is from 0 to 220mg KOH/g solid resin, more preferably from 0 to 40mg KOH/g solid resin, and very preferably from 0 to 25mg KOH/g solid resin. The OH number is preferably less than 70mg KOH/g solid resin, more preferably less than 20mg KOH/g solid resin. Acid number and OH number were determined as described previously.

The core-shell particles in the aqueous dispersion (a) preferably have a weight-average molar mass of 3 x 10⁷g/mol to 8.5 x 10⁹g/mol, more preferably 3 x 10⁷g/mol to 5 x 10¹⁰g/mol, wherein the weight average molar mass can be determined by small-angle laser light scattering.

The solids content of the aqueous dispersion (a) is preferably from 20 to 45% by weight, very preferably from 25 to 40% by weight, in accordance with DIN EN ISO 3251: 2008-06. Solids content is understood to mean the proportion by weight which remains as residue on evaporation concentration under fixed conditions. The solids were determined according to DIN EN ISO 3251 at 130 ℃ for 60 minutes, starting with a weight of 1.0 g.

The core/shell particles are crosslinked. The gel content of the aqueous dispersion (a) is preferably from 40 to 97% by weight, more preferably from 75 to 90% by weight, based in each case on the solids in the dispersion. The gel content can be determined gravimetrically, including freeze drying the dispersion, determining the total mass of the freeze dried polymer, and then extracting the polymer in excess tetrahydrofuran (tetrahydrofuran to freeze dried polymer ratio 300:1) at 25 ℃ for 24 hours. The insoluble fraction was removed and dried in an air circulating oven at 50 ℃ for 4 hours. Subsequently, the dried insoluble fraction was weighed and given a quotient to the total mass of the freeze-dried polymer. The values obtained correspond to the gel content.

According to a preferred embodiment of the present invention, the aqueous coating composition comprises said at least one aqueous dispersion (a) in a specific mass ratio. Preferably, the aqueous coating composition comprises the at least one aqueous dispersion (a) in a total amount of from 0.5 to 50% by weight, more preferably from 2 to 40% by weight, very preferably from 3 to 30% by weight, in each case based on the total amount of the aqueous coating composition. The use of the aqueous dispersion (a) in the stated amounts leads to good optical properties, more particularly good pinhole behavior and good sag resistance, and also good mechanical properties such as high adhesion and/or chip resistance.

Aqueous polyurethane-polyurea dispersion (b):

the aqueous coating composition of the present invention further comprises, in addition to the aqueous dispersion (a) described above, an aqueous polyurethane-polyurea dispersion (b) containing polyurethane-polyurea particles. This means that the polymer particles present in the dispersion are based on polyurethane-polyureas.

The polyurethane-polyurea particles present in the aqueous polyurethane-polyurea dispersion (b) have a gel fraction of at least 50% (for the measurement method, see examples section). Thus, dispersion (b) is a microgel dispersion in which the polyurethane-polyurea polymer is present in the form of smaller particles (i.e. microparticles) which are at least partially intramolecularly crosslinked. The latter means that the polymer structure of the particles corresponds to a typical macroscopic network with a three-dimensional network structure. Although the particles may be partially crosslinked, the system is still a dispersion of discrete particles having a measurable average particle size.

For example, the fraction of cross-linking can be determined after removal of water and any organic solvent and subsequent extraction. The phenomenon utilized here is that microgel particles, initially soluble in a suitable organic solvent, retain their internal network structure after separation and behave like a macroscopic network in the solid. Crosslinking can be verified by experimentally available gel fraction. The gel fraction is ultimately the fraction of polymer from the dispersion that cannot be molecularly dissolved in the solvent. This insoluble fraction in turn corresponds to the fraction of polymer or the fraction of particles present in the dispersion in the form of intramolecularly crosslinked particles, provided that a further increase in the gel fraction caused by the crosslinking reaction after separation of the polymer solids is avoided.

The polyurethane-polyurea particles present in the aqueous polyurethane-polyurea dispersion (b) preferably have a gel fraction of at least 60%, more preferably at least 70%, particularly preferably at least 80%. Thus, the gel fraction may reach 100% or about 100%, e.g. 99% or 98%. In this case, all or almost all of the polyurethane-polyurea polymer is present in the form of crosslinked particles. Specific ranges include 60-100%, 70-100%, 80-99%, 80-98%, 80-95%, 80-90%, or 85-95%.

The polyurethane-polyurea particles present in the dispersion (b) preferably have an average particle size of from 40 to 1,500nm, more preferably from 50 to 1,000nm, more preferably from 60 to 500nm, even more preferably from 120 to 300 nm. A particularly preferred range is 70-210 nm. Particle size was measured by Photon Correlation Spectroscopy (PCS) at 25 ± 1 ℃ (for the measurement method, see the examples section).

The polyurethane-polyurea particles present in the dispersion (b) comprise in each case at least one specific Polyurethane Prepolymer (PP) and at least one specific Polyamine (PA) in reacted form. The term "comprising certain components in reacted form" means that these components are used as starting materials in the preparation of the corresponding polymer particles. In the preparation of the polyurethane-polyurea particles, the components (PP) and (PA) react with one another by reaction of the isocyanate groups of (PP) with the amino groups of (PA), wherein urea bonds are formed. Since the starting materials remain unchanged except for the reacted isocyanate and amino groups, the particles comprise two components (PP) and (PA). Thus, the meaning of the expression "the polymer comprises the component (X) in reacted form" can be equivalent to the meaning of the expression "the component (X) is used in the preparation of the polymer".

The polyurethane-polyurea particles preferably consist of two components (PP) and (PA); in other words, they are prepared using only these two components.

The aqueous dispersion (b) can be obtained by a specific three-stage process. In a first step (I) of the process, a specific composition (Z) is prepared, which is dispersed in an aqueous phase in a second step (II). In step (III) of the process, the at least one Organic Solvent (OS) is at least partially removed from the dispersion obtained in step (II). In the context of the description of the process, preferred embodiments of components (PP) and (PA) are also mentioned.

The composition (Z) prepared in the first step (I) comprises at least one, preferably exactly one specific intermediate (I1) which contains isocyanate groups and has a blocked primary amino group.

The preparation of the intermediate (I1) comprises reacting at least one Polyurethane Prepolymer (PP) which comprises isocyanate groups and comprises anionic groups and/or groups which can be converted into anionic groups, with at least one polyamine (PA-a) which is derived from a Polyamine (PA) which comprises two blocked primary amino groups and one or two free secondary amino groups.

Polyurethane polymers which contain isocyanate groups and contain anionic groups and/or groups which can be converted into anionic groups are known in principle. For the purposes of the present invention, component (PP) is referred to as prepolymer since it serves as starting component for the preparation of another component, in particular intermediate (I1).

Prepolymers (PP) are prepared by reacting polyisocyanates with polyols, more particularly diols, usually to form urethanes and/or polyamines. US 2018/0002476a1 describes polyisocyanates, polyols and polyamines which can suitably be used for the synthesis of prepolymers (PP). Preferably, the prepolymer (PP) is prepared by using at least one polyester diol which is the product of a diol and a dicarboxylic acid, and wherein at least 50 wt.% of the dicarboxylic acid in the preparation of the at least one polyester diol is at least one dimer fatty acid. Dimer fatty acids or dimer fatty acids are mixtures prepared by dimerizing unsaturated fatty acids and may be obtained, for example, under the trade names Radiacid (available from Oleon) or Pripol (available from Croda).

The prepolymer (PP) comprises anionic groups and/or groups convertible to anionic groups, such as carboxylic, sulfonic and/or phosphonic groups, preferably carboxylic acid groups, as well as anionic groups derived from the above-mentioned functional groups, such as more particularly carboxylate, sulfonate and/or phosphonate, preferably carboxylate. It is known that the introduction of such groups can increase dispersibility in water. Depending on the amount of neutralizing agent present, the groups may be present as free acid groups (e.g., carboxylic acids) or as salified groups (e.g., carboxylates). However, regardless of the form in which the groups are present, in the context of the present invention, a uniform nomenclature is often chosen for easier understanding. If there is any difference in this respect, such difference is handled, for example, using a degree of neutralization.

For introducing the groups, starting materials comprising groups capable of forming urethane linkages, preferably hydroxyl groups (PP), as well as the above groups (e.g. carboxylic acid groups) can be used to prepare prepolymers suitable starting materials for introducing the preferred carboxylic acid groups are polyether polyols and/or polyester polyols comprising carboxylic acid groups. However, in the preparation of the prepolymer (PP), it is preferred to use a low molecular weight compound, preferably a monomeric compound, having at least one carboxylic acid group and at least one functional group reactive with isocyanate groups, such as a hydroxyl group. The term "low molecular weight compounds" is understood to mean that the molecular weight of the corresponding compounds is less than 300 g/mol. The preferred range is 100-200 g/mol.

Preferred compounds in this context are monocarboxylic acids comprising two hydroxyl groups, such as dihydroxypropionic acid, dihydroxysuccinic acid and dihydroxybenzoic acid. Very particular compounds are α, α -dimethylolalkanoic acids, such as 2, 2-dimethylolacetic acid, 2-dimethylolpropionic acid, 2-dimethylolbutyric acid and 2, 2-dimethylolpentanoic acid, especially 2, 2-dimethylolpropionic acid.

According to a preferred embodiment, the Polyurethane Prepolymer (PP) comprises carboxylic acid groups. The prepolymer (PP) therefore preferably has an acid number of from 10 to 35mg KOH/g, more preferably from 15 to 23mg KOH/g, based on solid content, in accordance with DIN EN ISO 2114: 2002-06.

The number average molecular weight Mn of the prepolymer (PP) can vary within wide limits and lies, for example, in the range from 2,000-20,000g/mol, preferably 3,500-6,000g/mol, measured with a vapor pressure permeameter of 10.00 using benzophenone as calibration substance (see above).

The prepolymer (PP) contains isocyanate groups. Preferably, it has an isocyanate content of from 0.5 to 6% by weight, preferably from 1 to 5% by weight, particularly preferably from 1.5 to 4% by weight, based on the solids content, in accordance with DIN EN ISO 3251: 2008-06, DIN EN ISO 11909: 2007-05 and DIN EN ISO 14896: 2009-07 measurement.

Since the prepolymer (PP) contains isocyanate groups, the hydroxyl value of the prepolymer (PP) is very low. The hydroxyl number of the prepolymer is preferably less than 15mg KOH/g, more preferably less than 10mg KOH/g, very preferably less than 5mg KOH/g, based on solids content, determined in accordance with R. -P.Krueger, R.Gnack and R.Algeier, Plaste und Kautschuk, 20, 274 (1982).

The prepolymer (PP) can be prepared in bulk or in solution by known and widely used methods, preferably by reacting the starting compounds in an organic solvent such as methyl ethyl ketone at a temperature of from 60 to 120 ℃ and optionally using catalysts customary in urethane preparation. Such catalysts are known to the person skilled in the art, an example being dibutyltin laurate. The preparation is preferably carried out in an Organic Solvent (OS) as described later, since in any case this solvent must be present in the composition (Z) prepared in step (I) of the process.

As already mentioned above, the anionic groups in the prepolymer (PP) can also be partially salified by using neutralizing agents. In this way, the water dispersibility of the prepolymer (PP) and hence of the intermediate (I1) can be adjusted.

Neutralizing agents include in particular the known basic neutralizing agents, for example alkali metal and alkaline earth metal carbonates, bicarbonates or hydroxides, for example LiOH, NaOH, KOH or Ca (OH)₂. Also suitable for neutralization and preferred for use in the context of the present invention are nitrogen-containing organic bases, such as amines, e.g. ammonia, trimethylamine, N-dimethylformamide,Triethylamine, tributylamine, dimethylaniline, triphenylamine, dimethylethanolamine, methyldiethanolamine, triethanolamine, and mixtures thereof.

The neutralization of the prepolymer (PP) with a neutralizing agent, more particularly with a nitrogen-containing organic base, can be carried out after the prepolymer (PP) has been prepared in the organic phase, more particularly in the solvent (OS) as described below. The neutralizing agent can of course also be added during or before step (II), in which case the carboxylic acid group-containing starting compound is neutralized. The prepolymer (PP) is preferably neutralized as described after its preparation and before use in the preparation of intermediate (I1).

If it is desired to neutralize groups which can be converted into anionic groups, more particularly carboxylic acid groups, the neutralizing agent can be added in an amount such that a proportion of the groups of from 35 to 65% are neutralized (degree of neutralization). Preferably 40-60% (for the calculation method, see examples).

The preparation of the intermediate (I1) described herein comprises the reaction of the prepolymer (PP) described above with at least one, preferably exactly one, polyamine (PA-a) derived from a Polyamine (PA).

The polyamine (PA-a) comprises two blocked primary amino groups and one or two free secondary amino groups. Blocked amino groups are those in which a hydrogen residue on a nitrogen is replaced by a blocking agent that can be removed under specific reaction conditions. After blocking, the amino groups cannot react by condensation or addition reactions, as do the free amino groups, and are therefore non-reactive in this respect, distinguishing them from the free amino groups. The blocked amino group can only react after removal of the blocking agent, thereby generating a free amino group. Thus, the principle is similar to that of blocked or blocked isocyanates, which are likewise known in the field of polymer chemistry.

The primary amino groups of the polyamine (PA-a) can be blocked with blocking agents known per se, for example with ketones and/or aldehydes. The use of these blocking agents leads to ketimines and/or aldimines which no longer contain any nitrogen-hydrogen bonds, so that typical condensation or addition reactions of amino groups with other functional groups, such as isocyanate groups, are no longer possible.

Reaction conditions for preparing such blocked primary amines, e.g., ketimines, are known. This blocking can be achieved by introducing heat into a mixture of a primary amine with an excess of a ketone, which at the same time acts as a solvent for the amine. The water formed during this reaction is preferably removed to prevent the reverse reaction (deblocking). The conditions for the deblocking reaction for blocking primary amino groups are also known per se. For example, the addition of a blocked amine to the aqueous phase is sufficient to shift the equilibrium to the side of the free amino group and free ketone, as the water exerts a concentration pressure.

From the above, it can be seen that in the context of the present invention, there is a clear distinction between blocked amino groups and free amino groups. However, an amino group is a free amino group if it is not designated as either blocked or free.

The preferred reagent for blocking the primary amino group of the Polyamine (PA) is a ketone. Among the ketones, particularly preferred are those which can also be used as an Organic Solvent (OS) described later. The reason is that these solvents (OS) must in any case be present in the composition (Z) prepared according to said process step (I). It has already been pointed out above that the preparation of the corresponding primary amines blocked with ketones gives particularly good results in the case of an excess of ketone. By using ketones for blocking and as Organic Solvent (OS), expensive and inconvenient removal of the blocking agent is not required if its presence is not desired in a subsequent step of the process. Instead, the solution of the blocked amine can be used directly to prepare intermediate (I1). Preferred blocking agents and Organic Solvents (OS) are acetone, methyl ethyl ketone, methyl isobutyl ketone, diisopropyl ketone, cyclopentanone or cyclohexanone, particularly preferred blocking agents are ketones, methyl ethyl ketone and methyl isobutyl ketone.

Preferred blocking with ketones and/or aldehydes, more particularly ketones, and the concomitant preparation of ketimines and/or aldimines, has the advantage of selectively blocking primary amino groups. The secondary amino groups present are not blocked and therefore remain free. Thus, polyamines (PA-a) which contain one or two free secondary amino groups in addition to two blocked primary amino groups can easily be prepared from Polyamines (PA) having one or two secondary and two primary amino groups by using ketones and/or aldehydes as blocking agents.

Finally suitable are all aliphatic, aromatic or araliphatic (mixed aliphatic-aromatic) Polyamines (PA) known per se having two primary amino groups and one or two secondary amino groups. This means that in addition to the amino group, any aliphatic, aromatic or araliphatic group may be present per se. For example, monovalent groups located as end groups on secondary amino groups, or divalent groups located between two amino groups, are possible. Aliphatic in the context of the present invention means the residue of all organic groups which are not aromatic. For example, the groups present in addition to the amino group may be aliphatic hydrocarbon groups, in other words groups consisting only of carbon and hydrogen and which are not aromatic. These aliphatic hydrocarbon groups may be linear, branched or cyclic, and may be saturated or unsaturated. These groups may of course also comprise cyclic and straight-chain or branched moieties. The aliphatic group may also comprise heteroatoms, more particularly in the form of bridging groups, such as ether, ester, amide and/or carbamate groups. Possible aromatic groups are likewise known and do not require further explanation.

The polyamine (PA-a) preferably has two blocked primary amino groups and one or two free secondary amino groups. Preferably, the polyamine (PA-a) has a total of 3 or 4 amino groups, these groups being selected from blocked primary amino groups and free secondary amino groups. Particularly preferred polyamines (PA-a) are those which consist of two blocked primary amino groups, one or two free secondary amino groups and an aliphatic saturated hydrocarbon group. Similar preferred embodiments apply to Polyamines (PA) which consist of one or two secondary amino groups, two primary amino groups and an aliphatic saturated hydrocarbon group.

Examples of preferred Polyamines (PA) which can be prepared by blocking primary amino groups are: (a) polyamines (PA) comprising one secondary amino group and two primary amino groups for blocking, such as diethylenetriamine, 3- (2-aminoethyl) aminopropylamine, dipropylenetriamine, N1- (2- (4- (2-aminoethyl) piperazin-1-yl) ethyl) ethane-1, 2-diamine, (b) amines (PA) comprising two secondary amino groups and two primary amino groups for blocking, such as triethylenetetramine and N, N' -bis (3-aminopropyl) ethylenediamine, and (c) mixtures thereof.

For reasons relating to the pure technical synthesis, the blocking of the primary amino groups of the Polyamine (PA) is not always quantitative, which means that not all available primary amino groups of the Polyamine (PA) are completely blocked by the blocking agent. In the context of the present invention, if more than 95 mol% of the primary amino groups present in the amount of Polyamine (PA) used are blocked (determinable by IR spectroscopy; see example section), the polyamine (PA-a) has blocked primary amino groups, which means that the major fraction of the total amount of Polyamine (PA) used for blocking does in fact contain only blocked primary amino groups, in particular exactly two blocked primary amino groups.

The preparation of intermediate (I1) involves the reaction of the isocyanate groups of prepolymer (PP) with the free secondary amino groups of polyamine (PA-a) to form urea linkages without deblocking the primary amino groups. It is therefore clear that no other amines having free or blocked secondary amino groups or free or blocked primary amino groups or reaction conditions leading to the deblocking of primary amino groups are used in the preparation of intermediate (I1). Intermediate (I1) can be prepared in bulk or in solution by known and widely used techniques, preferably by reacting (PP) with (PA-a) in an organic solvent that is not reactive with the functional groups of (PP) and (PA-a). As solvent, it is preferred to use an Organic Solvent (OS), as described later, especially methyl ethyl ketone, at least in proportion, since this solvent must in any case be present in the composition (Z) prepared in step (I) of the process. The intermediate (I1) is preferably prepared by mixing a solution of the prepolymer (PP) in the solvent (OS) with a solution of the polyamine (PA-a) in the solvent (OS).

Of course, the intermediate (I1) thus prepared can be neutralized during or after preparation in the same manner as described above for the prepolymer (PP) using the neutralizing agent already described above. Preferably, however, the prepolymer (PP) is neutralized in the manner described above before being used for the preparation of intermediate (I1). Therefore, in this case, the degree of neutralization of the prepolymer (PP) may be equal to that of the intermediate (I1). Thus, the degree of neutralization of the polymer present in the finally prepared aqueous dispersion (b) can also be equal to that of the prepolymer (PP), when no further neutralizing agent is added at all in the context of the process of the present invention.

Thus, intermediate (I1) contains a blocked primary amino group as well as an isocyanate group. Therefore, in the reaction of (PP) and (PA-a), the proportions of these components must be chosen such that the product, i.e.intermediate (I1), contains isocyanate groups. Since only the free secondary amino groups in (PA-a) react with the isocyanate groups in (PP), the molar ratio of isocyanate groups of (PP) to free secondary amino groups in (PA-a) must be higher than 1. In this preferred embodiment, the molar amounts (n) of isocyanate groups, free secondary amino groups and blocked primary amino groups satisfy the following condition: [ n (isocyanate group from (PP))) -n (free secondary amino group from (PA-a))/n (blocked primary amino group from (PA-a)) 1.2/1 to 4/1, preferably 1.5/1 to 3/1, very preferably 1.8/1 to 2.2/1, even more preferably 2/1.

In this preferred embodiment, the intermediate (I1) formed by reacting the isocyanate group of (PP) with the free secondary amino group of (PA-a) has an excess of isocyanate groups relative to the blocked primary amino group. This excess is finally achieved by selecting the molar ratio of the isocyanate groups of (PP) to the sum of the free secondary and blocked primary amino groups of (PA-a) to be sufficiently large that, even after preparation of (I1) and corresponding consumption of isocyanate groups by reaction with free secondary amino groups, a corresponding excess of isocyanate groups is still present. For example, if the polyamine (PA-a) has one free secondary amino group and two blocked primary amino groups, in a particularly preferred embodiment the molar ratio of the isocyanate groups of (PP) to the polyamine (PA-a) is set at 5/1. At this point, the consumption of one isocyanate group in the reaction with a free secondary amino group means that 4/2 (or 2/1) is achieved for the above conditions.

The fraction of intermediates (I1) is from 15 to 65% by weight, preferably from 25 to 60% by weight, more preferably from 30 to 55% by weight, very preferably from 35 to 52.5% by weight, and in a very particular embodiment from 40 to 50% by weight, in each case based on the total amount of the composition (Z). The fraction of intermediate (I1) corresponds to the solids content of composition (Z), since this composition contains only intermediate (I1) and organic solvent (for the determination of the solids content, see the examples section)

The composition (Z) further comprises at least one specific Organic Solvent (OS).

The solubility of the solvent (OS) in water at a temperature of 20 ℃ does not exceed 38% by weight (for the measurement method, see the examples section). The solubility in water at 20 ℃ is preferably less than 30% by weight. A preferred range is 1 to 30% by weight. Thus, the solvent (OS) has a rather moderate solubility in water, in particular is not completely miscible with water or has no infinite solubility in water. When the solvent can be mixed with water in any ratio without separation, it is completely miscible with water.

Examples of solvents (OS) are methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, diethyl ether, dibutyl ether, dipropylene glycol dimethyl ether, ethylene glycol diethyl ether, toluene, methyl acetate, ethyl acetate, butyl acetate, propylene carbonate, cyclohexanone or mixtures of these solvents. Preference is given to methyl ethyl ketone, whose solubility in water at 20 ℃ is 24% by weight. In contrast, acetone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, tetrahydrofuran, diAlkanes, N-formylmorpholine, dimethylformamide or dimethyl sulfoxide do not have the required water solubility and are therefore unsuitable as solvents (OS).

A particular effect of selecting a specific solvent (OS) having only limited solubility in water is that when the composition (Z) is dispersed in the aqueous phase in step (II) of the process, a homogeneous solution is not formed. It is believed that the dispersion present allows the crosslinking reaction in step (II) (addition reaction of free primary amino groups of intermediate (I1) and isocyanate groups) to take place in a limited volume, ultimately resulting in the formation of microparticles as defined above.

In addition to the above water solubility, preferred solvents (OS) have a boiling point of not more than 120 ℃, more preferably not more than 90 ℃ (at 1.013 bar). This has the advantage that, in step (III) of the process, the at least one Organic Solvent (OS) can be at least partially removed from the dispersion prepared in step (II) by distillation without simultaneously removing a significant amount of the water introduced in step (II) of the process. Thus, there is no need to laboriously re-add water to maintain the aqueous character of dispersion (b).

The fraction of the at least one Organic Solvent (OS) is from 35 to 85% by weight, preferably from 40 to 75% by weight, more preferably from 45 to 70% by weight, particularly preferably from 47.5 to 65% by weight, and in a very particular embodiment from 50 to 60% by weight, in each case based on the total amount of the composition (Z).

By combining specific amounts of intermediate (I1) and selecting a specific solvent (OS) in composition (Z), it is possible to provide a polyurethane-polyurea dispersion comprising polyurethane-polyurea particles having the required particle size and gel fraction.

The components (I1) and (OS) preferably together represent at least 90% by weight of the composition (Z). Preferably, the two components constitute at least 95% by weight, more particularly at least 97.5% by weight, of the composition (Z). Very particularly preferably, the composition (Z) consists of these two components. It should be noted in this context that when the above-mentioned neutralizing agents are used, these neutralizing agents are assigned to the intermediates when calculating the amount of intermediate (I1).

When composition (Z) comprises further components in addition to components (I1) and (OS), these further components are preferably exclusively organic solvents. Thus, the solids content of composition (Z) preferably corresponds to the fraction of intermediate (I1) in composition (Z). The solids content of the composition (Z) is therefore preferably from 15 to 65% by weight, preferably from 25 to 60% by weight, more preferably from 30 to 55% by weight, very preferably from 35 to 52.5% by weight, and in a particularly preferred embodiment from 40 to 50% by weight, based on the total amount of the composition (Z). Thus, particularly preferred compositions (Z) comprise at least 90% by weight of components (I1) and (OS) in total and comprise, in addition to intermediate (I1), only organic solvents.

The composition (Z) has the advantage that it can be used without using eco-unfriendly and health-hazardous organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, bis (methyl pyrrolidone)Alkane, tetrahydrofuran and N-ethyl-2-pyrrolidone. Thus, it is preferred that composition (Z) comprises less than 10% by weight, preferably less than 5% by weight, more preferably less than 2.5% by weight, very preferably 0% by weight of a compound selected from N-methyl-2-pyrrolidone, dimethylformamideAn organic solvent of an alkane, tetrahydrofuran and N-ethyl-2-pyrrolidone.

In the second step (II) of the process, the composition (Z) is dispersed in an aqueous phase. This dispersion leads to deblocking of the blocked primary amino group of intermediate (I1) to form a free primary amino group. The resulting free primary amino group is then reacted with the isocyanate group also present in intermediate (I1) by addition reaction to form a urea bond. In addition to the above-described reaction of the isocyanate groups with unblocked primary amino groups, these isocyanate groups of intermediate (I1) can also react with water with elimination of carbon dioxide, so that free primary amino groups are formed, which can then react with the isocyanate groups still present. These reactions and conversions described above are carried out in parallel with each other. As a result of intermolecular and intramolecular reactions or crosslinking, dispersions are formed which comprise polyurethane-polyurea particles having a defined average particle size and degree of crosslinking or gel fraction.

Preferably, the dispersion is prepared by stirring into an aqueous phase a composition (Z) which, after preparation, has a temperature of, for example, 20 to 25 ℃ or an elevated temperature of 30 to 60 ℃. Preferably, the aqueous phase has room temperature. The dispersion can be carried out in pure water (deionized water), which means that the aqueous phase preferably consists only of water. In addition to water, the aqueous phase may also contain typical auxiliaries, such as emulsifiers and protective colloids. A compilation of suitable emulsifiers and protective colloids is found, for example, in Houben Weyl, Methoden der organischen Chemie, volume XIV/1, Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart 1961, page 411 and subsequent pages.

Advantageously, in step (II) of the process, the weight ratio of organic solvent to water is chosen such that the resulting dispersion has a weight ratio of water to organic solvent of greater than 1, preferably from 1.05 to 2/1, particularly preferably from 1.1 to 1.5/1.

In step (III) of the process, the at least one Organic Solvent (OS) is at least partially removed from the dispersion obtained in step (II). Of course, step (III) of the process may also require removal of other solvents, for example in composition (Z). The removal of the at least one Organic Solvent (OS) and any other organic solvents may be done in any known manner, e.g. by vacuum distillation at slightly elevated temperature relative to room temperature, e.g. 30-60 ℃. The resulting polyurethane-polyurea dispersions (b) are therefore aqueous (see above for a basic definition of "aqueous").

The polyurethane-polyurea particles present in dispersion (b) preferably have an acid number of from 10 to 35mg KOH/g, more particularly from 15 to 23mg KOH/g, based on the solids content, in accordance with DIN EN ISO 2114: 2002-06.

The polyurethane-polyurea particles present in the dispersion (b) preferably have little or no hydroxyl groups. The OH number of the particles is preferably less than 15mg KOH/g, more particularly less than 10mg KOH/g, very preferably less than 5mg KOH/g, based on the solids content, measured in accordance with R. -P.Krueger, R.Gnauck and R.Algeier, Plaste und Kautschuk, 20, 274 (1982).

The fraction of polyurethane-polyurea particles in the dispersion (b) is preferably from 25 to 55% by weight, preferably from 30 to 50% by weight, more preferably from 35 to 45% by weight, based in each case on the total amount of the dispersion (determined via solids content).

The water fraction in the dispersion (b) is preferably from 45 to 75% by weight, preferably from 50 to 70% by weight, more preferably from 55 to 65% by weight, based in each case on the total amount of dispersion.

It is essential that dispersion (b) consists of at least 90% by weight, preferably at least 92.5% by weight, very preferably at least 95% by weight, more preferably at least 97.5% by weight of polyurethane-polyurea particles and water (relevant figures are obtained by adding together the amount of particles (i.e. polymer, determined by solids content) and the amount of water). Despite this low fraction of other components, in particular organic solvents for example, the storage stability of dispersion (b) is very good.

Even more preferably, dispersion (b) comprises, in addition to the polymer, only water and organic solvent, e.g. residual fractions which are not completely removed in step (III) of the process. The solids content of the dispersion (PD) is therefore preferably from 25 to 55% by weight, preferably from 30 to 50% by weight, more preferably from 35 to 45% by weight, still more preferably equal to the fraction of particles in the dispersion, based on the total amount of dispersion (b).

The advantage of the dispersion (b) is that it can be used without using ecologically unfriendly and healthily harmful organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, bis (methyl pyrrolidone)Alkane, tetrahydrofuran and N-ethyl-2-pyrrolidone. Thus, dispersion (b) preferably comprises less than 7.5% by weight, preferably less than 5% by weight, more preferably less than 2.5% by weight, very preferably 0% by weight of a compound selected from the group consisting of N-methyl-2-pyrrolidone, dimethylformamideAn organic solvent of an alkane, tetrahydrofuran and N-ethyl-2-pyrrolidone.

According to a preferred embodiment of the present invention, the aqueous coating composition comprises a specific amount of the at least one aqueous dispersion (b). Preferably, the aqueous coating composition comprises the at least one aqueous dispersion (b) in a total amount of from 10 to 55% by weight, more preferably from 15 to 45% by weight, very preferably from 20 to 35% by weight, in each case based on the total amount of the aqueous coating composition. The use of the aqueous dispersion (b) in the stated amounts leads to good optical properties, more particularly good pinhole behavior and good sag resistance, and also good mechanical properties, such as high adhesion and/or chip resistance.

Furthermore, it is preferred that the aqueous coating composition comprises the at least one aqueous dispersion of core/shell particles (a) and the at least one aqueous dispersion of polyurethane-polyurea (b) in a specific weight ratio. The aqueous coating composition therefore preferably comprises the at least one aqueous dispersion of core-shell particles (a) and the at least one aqueous polyurethane-polyurea dispersion (b) in a weight ratio of from 2:1 to 1:15, very preferably from 1:1.2 to 1:10, in each case based on the solids content of the dispersion. The use of dispersions (a) and (b) in this weight ratio leads to good optical and mechanical properties and also to a high storage stability of the aqueous coating composition.

The solids content of the aqueous coating composition of the invention may vary depending on the requirements of the situation at hand. The solids content is determined primarily by the viscosity required for application, more particularly spray application. It is of particular advantage that the aqueous coating compositions of the invention, despite having a relatively high solids content, have a viscosity which allows for proper application. The solids content of the aqueous coating compositions of the invention is preferably from 5 to 80% by weight, more preferably from 10 to 75% by weight, very preferably from 15 to 65% by weight, based on the total amount of the coating composition, in accordance with DIN EN ISO 3251: 2008-06 measurement.

At said solids content, preferred aqueous coating compositions of the invention have a viscosity of from 40 to 150 mPas, more particularly from 70 to 85 mPas, at 23 ℃ at a shear rate of 10001/s (see the examples section for further details on the measurement method). For the purposes of the present invention, a viscosity in this range at the stated shear rate is referred to as the spray viscosity (working viscosity). As is known, coatings are applied at spray viscosity, which means that under the conditions present at the time (high shear load), they have a viscosity that allows efficient application. This means that the setting of the spray viscosity is important to allow the aqueous coating composition to be applied by the spray method, and to ensure that a complete, uniform coating film can be formed on the substrate to be coated. It is a particular advantage that the aqueous coating composition of the invention has a high solids content even when adjusted to the spray viscosity.

Other components of the aqueous coating composition:

the aqueous coating composition of the present invention may comprise other components than the dispersions (a) and (b).

The aqueous coating composition of the present invention preferably further comprises at least one known typical crosslinking agent. It preferably comprises polycarbodiimides, aminoplast resins, polyisocyanates, blocked polyisocyanates and mixtures thereof as crosslinking agents, especially polycarbodiimides. As the polycarbodiimide, hydrophilic carbodiimide is preferable. Examples of the hydrophilic polycarbodiimide include compounds obtained by reacting a polycarbodiimide compound having at least two isocyanate groups per molecule with a polyol having a hydroxyl group at a molecular terminal in a ratio of NCO/OH molar ratio of more than 1, and then reacting the resulting reaction product with a hydrophilizing agent having an active hydrogen atom and a hydrophilic moiety.

In the present invention, in the case of using a polycarbodiimide compound as a curing agent, the molar ratio NCN/COOH in the aqueous coating composition is preferably 0.5 to 2, more preferably 0.8 to 1.5. These ratios result in good film appearance and adhesion to the substrate to be coated or to the underlying film layer.

In this connection, the proportion of crosslinking agent, more particularly polycarbodiimide, is preferably from 0.5 to 20% by weight, more preferably from 3 to 15% by weight, very preferably from 6 to 11% by weight, based in each case on the total weight of the aqueous coating composition of the invention.

The crosslinker is preferably present if the aqueous coating composition of the invention is used as the first basecoat composition (also referred to as CP1 composition) in the 3C1B process to produce a multilayer coating.

If the aqueous coating composition of the invention is used as a second basecoat composition (also referred to as CP2 composition) in the 3C1B process to produce a multilayer coating, the aqueous coating composition is preferably free of crosslinkers, meaning that the composition comprises 0 wt.% total crosslinker, based on the total amount of aqueous coating composition.

The aqueous coating composition of the present invention preferably further comprises a curable binder different from the above dispersions (a) and (b). "binders" in the context of the present invention and according to DIN EN ISO 4618 are the non-volatile components of the coating composition, excluding pigments and fillers. However, in the following, the expression is mainly used in relation to specific physically curable polymers, which optionally may also be thermally curable, examples being polyurethanes, polyesters, polyacrylates and/or copolymers of said polymers. In the context of the present invention, copolymer refers to polymer particles formed from different polymers. This expressly includes polymers which are covalently bonded to one another and those in which different polymers are bonded to one another by adhesion. The definition also covers combinations of both types of binding.

In the context of the present invention, the term "physical solidification" means the formation of a film by evaporation of a solvent from a polymer solution or polymer dispersion. Typically, no crosslinking agent is required for such curing.

In the context of the present invention, the term "thermally cured" means that self-crosslinking binders or a combination of a separate crosslinker and binder (external crosslinking) are used to thermally initiate crosslinking of the coating film. The crosslinking agent contains reactive functional groups complementary to the reactive functional groups present in the binder so as to form a macroscopically crosslinked coating film upon reaction of the binder and the crosslinking agent.

The binder component present in the coating composition of the present invention always exhibits at least a proportion of physical cure. Thus, if it is said that the coating composition comprises a heat-curable binder component, this of course does not exclude that curing also includes a proportion of physical curing.

The aqueous coating composition of the invention preferably further comprises at least one binder different from the polymers present in dispersions (a) and (b), more particularly at least one binder selected from polyurethanes, polyesters, polyacrylates, copolymers of these polymers and mixtures of these polymers, more particularly polyacrylates and/or polyurethane polyacrylates. Preferred polyesters are described, for example, in DE 4009858A1 at column 6, line 53 to column 7, line 61 and column 10, line 24 to column 13, line 3. Preferred polyurethane-polyacrylate copolymers (acrylated polyurethanes) and their preparation are described, for example, in WO 91/15528A1, page 3, line 21 to page 20, line 33, DE 4437535A1, page 2, line 27 to page 6, line 22 and EP0649865A 1. Preferred polyacrylates can be obtained, for example, by free-radical emulsion polymerization of at least 50% by weight of methyl methacrylate, at least 10% by weight of butyl acrylate and 5% by weight or less, in each case based on the total amount of monomers, of a mixture of butyl methacrylate, hydroxyethyl methacrylate, ethylene glycol di (meth) acrylate and methacrylic acid. The binder may be hydroxyl functional, preferably having an OH number of 20 to 200mg KOH/g, more preferably 40 to 150mg KOH/g. The aqueous coating composition of the present invention more preferably comprises at least one hydroxyl-functional polyurethane-polyacrylate copolymer, at least one hydroxyl-functional polyacrylate and at least one acid-functional polyurethane-polyacrylate copolymer.

The proportion of the further polymers as binders can vary within wide limits and is preferably in the range from 0.5 to 40% by weight, more preferably from 1 to 30% by weight, very preferably from 1.5 to 20% by weight, based in each case on the total weight of the aqueous coating composition of the invention, based in each case on the binder solids.

The aqueous coating composition of the present invention is preferably a pigmented aqueous coating composition. Therefore, it is preferred that the coating composition further comprises at least one pigment selected from the group consisting of a coloring pigment, an effect pigment, and a mixture thereof. Such coloring pigments and effect pigments are known to the person skilled in the art and are described, for example, inLexikon Lacke and Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, pages 176 and 451. The terms "colored pigment" and "color pigment" are interchangeable, as are the terms "visual effect pigment" and "effect pigment".

Useful effect pigments are, for example, platelet-shaped metallic effect pigments, such as lamellar aluminum pigments, gold bronzes, bronze oxides and/or iron oxide-aluminum pigments; pearlescent pigments, such as pearlescent powders, basic lead carbonate, bismuth oxychloride and/or metal oxide-mica pigments; and/or other effect pigments, such as flake graphite, flake iron oxide, multilayer effect pigments consisting of PVD films, and/or liquid crystal polymer pigments. Particularly preferred are the flake-like metallic effect pigments, more particularly the flake-like aluminum pigments.

Typical colored pigments include inorganic colored pigments, for example, white pigments such as titanium dioxide, zinc white, zinc sulfide or lithopone; black pigments such as carbon black, iron manganese black or spinel black; color pigments, such as chromium oxide, hydrated chromium oxide green, cobalt green or ultramarine green, cobalt blue, ultramarine blue or manganese blue, ultramarine violet or cobalt violet and manganese violet, iron oxide red, cadmium sulfoselenide, molybdate-chromium red or ultramarine red; brown iron oxide, mixed brown, spinel phase and corundum phase or chromium orange; or yellow iron oxide, nickel titanium yellow, chrome titanium yellow, cadmium sulfide, cadmium zinc sulfide, chrome yellow or bismuth vanadate; and mixtures of these pigments. In addition, typical color pigments also include organic color pigments such as monoazo pigments; disazo pigments, anthrone pigments, quinacridone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, bisOxazine pigments, indanthrone pigments, isoindolinone pigments, metal complex pigments, perinone pigments, perylene pigments, phthalocyanine pigments, nigrosine azomethine pigments, and mixtures thereof.

The fraction of the at least one pigment is preferably present in a total amount of from 1 to 30% by weight, more preferably from 1.5 to 20% by weight, very preferably from 2 to 15% by weight, in each case based on the total weight of the aqueous coating composition.

Preferably, the coating composition of the invention additionally comprises at least one thickener selected from the group consisting of phyllosilicates, (meth) acrylic acid- (meth) acrylate copolymers, hydrophobic polyurethanes, ethoxylated polyurethanes, polyamides and mixtures thereof.

Suitable thickeners are inorganic thickeners selected from phyllosilicates such as lithium magnesium aluminum silicate. However, coating compositions whose rheological spectrum is determined by the predominant or overwhelming use of the inorganic thickener can only be formulated at a well-defined low solids content, e.g., less than 20%, without adversely affecting important properties. A particular advantage of the aqueous coating composition of the present invention is that it can be formulated without or without a large fraction of this inorganic phyllosilicate acting as a thickener. Thus, the fraction of inorganic phyllosilicate used as thickener is preferably less than 0.5 wt.%, more preferably less than 0.25 wt.%, very preferably less than 0.05 wt.%, based on the total weight of the aqueous coating composition. Very particularly preferably, the aqueous coating composition comprises 0% by weight of the inorganic phyllosilicate thickener, which means that it is completely free of this thickener.

In contrast, the aqueous coating composition preferably comprises at least one organic thickener, such as a (meth) acrylic acid- (meth) acrylate copolymer thickener, a polyurethane thickener or a polyamide thickener. Associative thickeners, such as associative polyurethane thickeners, are preferably used. Associative thickeners are water-soluble polymers which have strongly hydrophobic groups at the chain ends or in the side chains and/or whose hydrophilic chains contain hydrophobic blocks or monomers in their main chain. Thus, these polymers have surfactant properties and can form micelles in the aqueous phase. Like surfactants, hydrophilic regions remain in the aqueous phase, while hydrophobic regions enter the particles of the polymer dispersion, adsorb on the surface of other solid particles, such as pigments and/or fillers, and/or form micelles in the aqueous phase. Such thickeners are commercially available, for example under the trade name Adekanol (available from Adeka Corporation). Polyamide thickeners are commercially available under the trade name Disparlon (available from Kusumoto Chemicals Ltd).

The proportion of the at least one thickener is preferably present in a total amount of from 0.01 to 2% by weight, more preferably from 0.05 to 1% by weight, very preferably from 0.1 to 0.6% by weight, in each case based on the total weight of the aqueous coating composition.

In addition, the aqueous coating composition of the present invention may further comprise at least one auxiliary. Examples of such auxiliaries are thermally decomposable salts which can be decomposed residue-free or substantially residue-free, polymers which are binders which can be cured physically, thermally and/or with actinic radiation and are different from the polymers already stated as binders, further crosslinkers, organic solvents, acids or bases, reactive diluents, transparent pigments, fillers, molecularly disperse soluble dyes, nanoparticles, light stabilizers, antioxidants, degassing agents, emulsifiers, slip additives, inhibitors, free-radical polymerization initiators, tackifiers, flow regulators, film-forming auxiliaries, Sag Control Agents (SCA), flame retardants, corrosion inhibitors, waxes, desiccants, biocides and matting agents. Such auxiliaries are used in conventional and known amounts.

The invention method comprises the following steps:

the aqueous coating composition of the present invention can be used as a basecoat composition to produce a multilayer coating in the 3C1B process.

In the method of the invention, a multilayer coating is built up on a substrate (S) by the following steps:

(1) directly applying a first aqueous coating material (X) on a substrate (S) to form an uncured first coating film (X),

(2) directly applying a second aqueous coating material (Y) on the uncured first coating film obtained after step (1) to form an uncured second coating film (Y),

(3) directly applying a clear coating material (Z) on the uncured second coating film obtained after step (2) to form a clear coating film (Z), and then

(4) Curing the three coating films obtained after steps (1) to (3) simultaneously,

wherein the first aqueous coating (X) and/or the second aqueous coating (Y) is selected from the aforementioned aqueous coating compositions of the present invention.

The substrate (S) is preferably selected from the group consisting of metal substrates, metal substrates coated with a cured electrocoat, plastic substrates and substrates comprising metal and plastic components, particularly preferably from the group consisting of metal substrates coated with a cured electrocoat.

In this connection, preferred metal substrates (S) are selected from the group consisting of iron, aluminum, copper, zinc, magnesium and alloys thereof, and steel. Preferred substrates are those of iron and steel, examples being those used in the automotive industry sector. The substrate itself may be of any shape, i.e. for example a simple metal sheet or a complex part, such as an automobile body and parts thereof.

Preferred plastic substrates (S) are essentially substrates comprising or consisting of: (i) polar plastics such as polycarbonates, polyamides, polystyrenes, styrene copolymers, polyesters, polyphenylene ethers and blends of these plastics, (ii) synthetic resins such as polyurethanes RIM, SMC, BMC, and (iii) polyolefin substrates of the polyethylene and polypropylene type having a high rubber content, such as PP-EPDM, and surface-activated polyolefin substrates. Furthermore, the plastic may be fiber reinforced, in particular using carbon fibers and/or metal fibers.

Preferred substrates are metal substrates that are coated by electrophoretically applying an electrocoat to the substrate, followed by curing the electrocoat to produce a cured electrocoat on the metal substrate. Suitable electrocoats and their curing are described, for example, in WO 2017/088988A 1. The film thickness of the cured electrophoretic coating is, for example, 10 to 40 micrometers, preferably 15 to 25 micrometers.

The substrate (S) may be pretreated, i.e. cleaned and/or provided with a known conversion coating, prior to step (1) of the process of the invention or prior to applying the electrocoat in any conventional manner. Cleaning may be done mechanically, e.g., by wiping, sanding, and/or polishing, and/or chemically by an acid wash process, by incipient wet etching in an acid or alkaline bath, e.g., by hydrochloric or sulfuric acid. Of course, cleaning with organic solvents or aqueous detergents is also possible. The pretreatment can likewise be carried out by applying a conversion coating, more particularly by phosphating and/or chromizing, preferably phosphating. In any case, the metal substrate is preferably conversion coated, more particularly phosphated, preferably provided with a zinc phosphate coating. Step (1):

in step (1) of the method of the present invention, an uncured first coating film (X) is prepared by applying the first aqueous coating material (X) directly onto the substrate (S). The first aqueous coating (X) may be applied by Electrostatic Spraying (ESTA). The direct application of the coating (X) on the substrate (S) results in the coating film (X) being in direct contact with the substrate (S). Therefore, there is no other coating layer between the coating film (x) and the substrate (S).

In a preferred embodiment, in step (1) of the process of the present invention, no pre-drying or curing is carried out after the application of the first aqueous coating (X). In contrast, it is preferable that the first aqueous coating material (X) directly applied on the substrate (S) is flash-evaporated before the second aqueous coating material (Y) is applied in step (2).

"flash" or "flash off" is to be understood as meaning the passive or active evaporation of organic solvent and/or water from the coating material (X), preferably at from 15 to 35 ℃ in a period of from 0.5 to 30 minutes. Thus, after the flash stage, the coating film (X) contains less water and/or solvent than the applied coating (X), but is not yet in service ready. Although it is no longer flowable, it is still soft and/or tacky and only partially dry. In particular, as described later, the coating film (x) has not yet been cured.

By contrast, predrying is understood to mean passive or active evaporation of organic solvent and/or water from the coating (X) at a temperature higher than the temperature used for flash evaporation, for example at 40 to 90 ℃ for 1 to 60 minutes. During pre-drying, the applied coating (X) will also lose a certain fraction of organic solvent and/or water. Thus, the pre-drying is performed at a higher temperature than the flash evaporation, which means that there is also a higher fraction of organic solvent and/or water escaping from the applied coating (X). However, predrying does not result in a ready-to-service coating film, i.e., a cured coating film as described below.

Curing of the coating film is therefore understood to be the conversion of the film into a ready-to-service state, i.e. a state in which the substrate to which the coating film is decorated can be transported, stored and used in its intended manner. Therefore, the cured coating film is no longer soft or tacky but is adjusted to a solid coating film, and its properties such as hardness or adhesion to a substrate do not show any significant change even if further exposed to curing conditions as described later.

The first aqueous coating material (X) is applied so that the film thickness of the first coating film (X) is preferably 5 to 35 μm, preferably 10 to 30 μm. All film thicknesses reported in the context of the present invention are to be understood as dry film thicknesses. It is therefore the thickness of the cured film in each case. Therefore, when it is reported that the coating material is applied at a specific film thickness, this means that the coating material is applied in such a manner as to produce the film thickness after curing.

In a particularly preferred embodiment of the process of the present invention, a coating composition according to the present invention as described hereinbefore is used as the first aqueous coating composition (X).

In order to obtain good optical properties, more particularly good pinhole behaviour and good sag resistance stability, as well as good mechanical properties, it is advantageous to use a first aqueous coating composition (X) comprising an aqueous dispersion (a) of core-shell particles and an aqueous polyurethane-polyurea dispersion (b) in a specific weight ratio. It is therefore preferred that in the first aqueous coating material (X) the weight ratio of the aqueous dispersion of the at least one core-shell-type particles (a) to the aqueous dispersion of the at least one polyurethane-polyurea (b) is from 10:1 to 1:30, preferably from 1:1.6 to 1:10, in each case based on the solids content of the dispersion.

In terms of the excellent mechanical properties and hardness of the resulting multilayer coatings, it has also proven advantageous to use, in step (1) of the process of the present invention, a first aqueous coating material (X) which preferably comprises the at least one aqueous dispersion (a) in a total amount of from 0.5 to 40% by weight, more preferably from 2 to 30% by weight, very preferably from 3 to 25% by weight, based in each case on the total amount of coating material (X).

Furthermore, it is preferred that the first aqueous coating material (X) comprises at least one of the aforementioned crosslinkers, very preferably in the aforementioned amounts.

Step (2):

in step (2) of the method of the present invention, the uncured second coating film (Y) is prepared by applying the second aqueous coating material (Y) directly onto the uncured first coating film (x). The second aqueous coating (Y) may also be applied by Electrostatic Spraying (ESTA). The coating material (Y) is directly applied on the uncured first coating film (x), which results in the coating film (Y) being in direct contact with the coating film (x). Therefore, no other coating layer is provided between the coating films (x) and (y).

According to a preferred embodiment, the second aqueous coating material (Y) is preheated after application, preferably at 40 to 90 ℃ for 5 to 60 minutes.

The second aqueous coating material (Y) is applied so that the film thickness of the second coating film (Y) after curing in step (4) is preferably 5 to 35 μm, more preferably 10 to 30 μm.

In a particularly preferred embodiment of the process of the present invention, a coating composition of the present invention as described hereinbefore is used as the second aqueous coating composition (Y). Very preferably, the coating composition of the invention as described before is used in step (1) and step (2) of the process of the invention. However, this does not necessarily mean that the same aqueous coating composition is used in the first and second steps of the process of the present invention. This merely means that the coating compositions (X) and (Y) used in steps (1) and (2) of the process of the present invention each comprise at least the essential components (a) and (b) as described, but may differ in the optional components present in the compositions (X) and (Y).

In a further preferred embodiment, the second aqueous coating composition (Y) further comprises an aqueous dispersion (a) of core/shell-type particles and an aqueous polyurethane-polyurea dispersion (b) in a specific weight ratio. This weight ratio is particularly preferably less than the weight ratio of the two components in the aqueous coating composition (X). Thus, in the second aqueous coating material (Y), the weight ratio of the aqueous dispersion of the at least one core-shell-type particle (a) to the aqueous dispersion of the at least one polyurethane-polyurea (b) is preferably from 2:1 to 1:10, very preferably from 1:1.2 to 1:5, in each case based on the solids content of the dispersion. The weight ratio results in high flexibility of the coating (Y) and thus in an increased chip resistance.

The use of coating compositions comprising components (a) and (b) in different weight ratios in steps (1) and (2) of the process of the present invention results in excellent optical and mechanical behavior, especially if the curing in step (4) of the process of the present invention is carried out at a temperature below 100 ℃.

The second aqueous coating material (Y) preferably comprises the at least one aqueous dispersion (a) in a total amount of from 1 to 45% by weight, more preferably from 5 to 35% by weight, very preferably from 10 to 25% by weight, based in each case on the total amount of coating material (Y).

The use of coating compositions comprising different amounts of component (a) in steps (1) and (2) of the process of the present invention results in excellent optical and mechanical behavior, especially if the curing in step (4) of the process of the present invention is carried out at a temperature below 100 ℃.

Although it is preferred that the aqueous coating composition (X) comprises at least one crosslinker, the aqueous coating composition (Y) preferably does not comprise at least one crosslinker, i.e. the crosslinkers are present in a total amount of 0 wt. -%, based on the total amount of the coating (Y). The multilayer coatings obtained by the present invention have excellent hardness even if the second aqueous coating is not chemically crosslinked.

And (3):

in step (3) of the process of the present invention, a clear coating film (z) is prepared directly on the uncured second coating film (y). The preparation is carried out by applying the clear coat (Z) accordingly. The direct application of the clear coat (Z) on the uncured second coating film (y) results in direct contact of the coating film (y) and the clear coating film (Z). Therefore, no other coating layer is provided between the coating films (y) and (z).

The clear coat (Z) can be any desired clear coat known to the person skilled in the art. By "clear" is meant that the film formed with the coating is not opaquely pigmented, but has the underlying color-visible structure of the basecoat system. However, as is known, this does not exclude the possibility of including pigments in the clear coat, which pigments may, for example, support the color depth of the entire system.

The clear coats (Z) are aqueous or solvent-borne clear coats which can be formulated not only as one-component but also as two-component or multi-component coatings. Powder slurry clearcoats are also suitable. Solvent borne clearcoats are preferred.

In particular, the clearcoats (Z) used may be thermochemically curable and/or photochemically curable. In particular, they are thermochemically curable and externally cross-linked. Two-component transparent coatings which can be cured thermally are preferred.

Thus, typically and preferably, the clear coat comprises at least one (first) polymer having functional groups as binder, and at least one crosslinker having functional groups complementary to the functional groups of the binder. Preferably, at least one hydroxy-functional poly (meth) acrylate polymer is used as binder and free and/or blocked polyisocyanates are used as crosslinking agents.

Suitable clear coats are described, for example, in WO 2006/042585a1, WO 2009/077182a1 and WO 2008/074490a 1.

The clear coat (Z) is applied by methods known to the person skilled in the art for applying liquid coatings, for example by dipping, knife coating, spraying, roller coating, etc. Spraying methods such as compressed air spraying (pneumatic application) and Electrostatic Spraying (ESTA) are preferably used.

After application, the clear coat (Z) or the corresponding clear coat film (Z) is flashed off and/or intermediate-dried, preferably at from 15 to 35 ℃ for from 0.5 to 30 minutes. These flash and intermediate drying conditions are particularly suitable for the preferred case in which the clear coating (Z) comprises a thermochemically curable two-component coating. This does not exclude that the clear coat (Z) is a coat which can be cured in other ways and/or that other flash evaporation and/or intermediate drying conditions are used.

The clear coat (Z) is applied so that the film thickness of the clear coat film after curing in step (4) is, for example, 15 to 80 μm, preferably 20 to 65 μm, and very preferably 25 to 60 μm.

The process of the invention does not exclude the presence of other coating materials, for example applying other clear coating materials after the application of clear coating material (Z) and preparing other clear coating films in this way. Then, these other coating films are similarly cured in step (4) described below. However, it is preferred to apply only one clear coat (Z) and then cure as described in step (4).

And (4):

in step (4) of the method of the present invention, co-curing of the uncured first coating film (x), the uncured second coating film (y) and the clear coating film (z) is carried out.

The co-curing is preferably carried out at a temperature of 60-90 c, more preferably 85 c, for a period of 5-60 minutes, very preferably 15-25 minutes. Since waterborne coatings (X) and (Y) are thermochemically curable one-component coatings, these conditions are typically required to achieve the cure. In the case of clear coatings (Z), which are, for example, likewise thermochemically curable one-component coatings, the corresponding clear coating films (Z) are, of course, likewise cured under these conditions. The same is true for the preferred case in which the clear coating (Z) is a thermochemically curable two-component coating.

However, the above statements do not exclude that the aqueous coating materials (X) and (Y) and also the clear coating material (Z) may additionally be cured under other curing conditions.

The process of the present invention allows the preparation of multilayer coatings on substrates without the need for a separate curing step. However, the application of the process of the invention results in a multilayer coating exhibiting excellent stability to pinholes, which means that even relatively high film thicknesses of the respective first and second coating films (x) and (y) can be established without loss of aesthetic quality. Properties such as adhesion or overall appearance are also outstanding.

The description of the coating composition according to the invention applies mutatis mutandis to other preferred embodiments of the process according to the invention, in particular to preferred embodiments of the first and second aqueous coating compositions (X) and (Y) used in steps (1) and (2) of the process according to the invention.

Multilayer coating of the invention:

the result after the end of step (4) of the process of the invention is a Multilayer Coating (MC) of the invention.

The statements made above with respect to the coating composition of the invention and the process of the invention apply, mutatis mutandis, to further preferred embodiments of the multilayer coating of the invention.

In particular, the invention is described by the following embodiments:

according to a first embodiment, the present invention relates to an aqueous coating composition, preferably a pigmented aqueous basecoat composition, comprising:

(a) an aqueous dispersion of at least one core/shell particle comprising a polyurethane resin as a core portion and a crosslinked acrylic resin as a shell portion, wherein the particle is obtained by:

(i) first an aqueous dispersion of at least one polyurethane resin (P) is added as core part, and then

(ii) Polymerizing a mixture of ethylenically unsaturated monomers in the presence of a polyurethane core portion to obtain a crosslinked acrylic resin (A) shell portion,

wherein:

(ii-1) the polymerization is carried out in the presence of a water-soluble initiator;

(ii-2) metering in the ethylenically unsaturated monomer so that the concentration of the ethylenically unsaturated monomer in the polymerization reaction solution does not exceed 6% by weight, based on the total amount of the ethylenically unsaturated monomer, during the entire polymerization; and is

(ii-3) the mixture of ethylenically unsaturated monomers comprises at least one multi-ethylenically unsaturated monomer, and

(b) at least one aqueous polyurethane-polyurea dispersion comprising polyurethane-polyurea particles having an average particle size of 40-2,000nm and a gel fraction of at least 50%, which polyurethane-polyurea particles comprise in each case the following in reacted form:

at least one Polyurethane Prepolymer (PP) which contains isocyanate groups and contains anionic groups and/or groups which are arranged to be converted into anionic groups, and

at least one Polyamine (PA) comprising two primary amino groups and one or two secondary amino groups.

According to a second embodiment, the present invention relates to an aqueous coating composition according to embodiment 1, wherein the water-soluble initiator (ii-1) is selected from the group consisting of potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, 2 '-azobis (2-amidoisopropane) dihydrochloride, 2' -azobis (N, N '-dimethyleneisobutyramidine) dihydrochloride, 2' -azobis (4-cyanovaleric acid), and mixtures thereof.

According to a third embodiment, the present invention relates to an aqueous coating composition according to embodiment 1 or 2, wherein the ethylenically unsaturated monomers (ii-2) are metered in such that the concentration of ethylenically unsaturated monomers in the reaction solution during the entire polymerization does not exceed 6% by weight, preferably 5% by weight, very preferably 4% by weight, based on the total amount of ethylenically unsaturated monomers.

According to a fourth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the ethylenically unsaturated monomer mixture (ii-3) comprises from 0.1 to 6 mol%, preferably from 0.1 to 2 mol%, of at least one polyethylenically unsaturated monomer, in each case based on the total amount of ethylenically unsaturated monomers.

According to a fifth embodiment, the present invention relates to an aqueous coating composition according to embodiment 6, wherein the at least one multi-ethylenically unsaturated monomer is selected from allyl (meth) acrylate and/or hexanediol di (meth) acrylate and/or a mixture of ethylenically unsaturated monomers does not comprise any other multi-ethylenically unsaturated monomer.

According to a sixth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the ethylenically unsaturated monomer mixture (ii-3) comprises 98 to 99.5 wt.% of one or more monounsaturated esters of (meth) acrylic acid having an unsubstituted alkyl group, wherein the alkyl group has a length of 1 to 10, preferably 3 to 5, carbon atoms, and 0.5 to 2 wt.% of one or more polyunsaturated esters of (meth) acrylic acid, preferably allyl (meth) acrylate and/or hexanediol di (meth) acrylate, in each case based on the total amount of ethylenically unsaturated monomers.

According to a seventh embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the ethylenically unsaturated monomer mixture (ii-3) comprises from 0 to less than 10 wt. -%, preferably from 0 to less than 5 wt. -%, more preferably 0 wt. -% of the vinyl aromatic monomer, in each case based on the total amount of ethylenically unsaturated monomers.

According to an eighth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the glass transition temperature Tg of the polyurethane resin (P) of the core part is from-80 ℃ to 105 ℃, preferably from-60 ℃ to 80 ℃, even more preferably from 50 to 60 ℃, and/or wherein the glass transition temperature Tg of the crosslinked acrylic resin (a) of the shell part is from-60 ℃ to 80 ℃, preferably from-60 ℃ to 20 ℃, according to DIN EN ISO 11357-2: 2013-05.

According to a ninth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the polyurethane resin (P) of the core part has a molecular weight according to DIN EN ISO 2114: an acid number of from 10 to 60mg KOH/g, preferably from 30 to 40mg KOH/g, measured 2002-06 and an OH number of from 20 to 80mg KOH/g, measured according to R.

According to a tenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the crosslinked acrylic resin (a) of the shell part has an OH value of 10 to 140mg KOH/g measured according to r. -p.kr ü ger, r.gnauck and r.algeier, plant und Kautschuk, 20, 274(1982) and a molecular weight distribution according to DIN EN ISO 2114: acid number of 0-10mg KOH/g, measured 2002-06.

According to an eleventh embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the core/shell particles in the aqueous dispersion (a) have a core to shell weight ratio of from 80:20 to 20:80, preferably from 60:40 to 40: 60.

According to a twelfth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the core/shell particles in the aqueous dispersion (a) have a glass transition temperature of-50 ℃ to 30 ℃ according to DIN EN ISO 11357-2: 2013-05.

According to a thirteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the core/shell particles in the aqueous dispersion (a) have a particle size according to DIN EN ISO 2114: an acid number of 10-30mg KOH/g solid measured 2002-06 and/or an OH number of 20-50mg KOH/g solid measured according to R.

According to a fourteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the core/shell particles in the aqueous dispersion (a) have a particle size (z-average) of 60-250nm, preferably 60-115nm, measured by Photon Correlation Spectroscopy (PCS) at 25 ± 1 ℃.

According to a fifteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the core/shell particles in the aqueous dispersion (a) have a particle size according to DIN EN ISO 2114: an acid number, measured 2002-06, of 0-220mg KOH/g solid resin, preferably 0-40mg KOH/g solid resin, more preferably 0-25mg KOH/g solid resin, and an OH number, measured according to R. -P.Krueger, R.Gnauck and R.Algeier, Plaste und Kautschuk, 20, 274(1982), of less than 70mg KOH/g solid resin, preferably less than 20mg KOH/g solid resin.

According to a sixteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the weight average molar mass of the core-shell particles in the aqueous dispersion (a) is 3 x 10⁷g/mol to 8.5 x 10⁹g/mol, preferably 3X 10⁷g/mol to 5 x 10¹⁰g/mol, measured by small angle laser light scattering.

According to a seventeenth embodiment, the present invention is directed to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous dispersion (a) has a composition according to DIN EN ISO 3251: a solids content of 20 to 45 wt%, preferably 25 to 40 wt%, measured 2008-06.

According to an eighteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous dispersion (a) has a gel content of from 40 to 97% by weight, preferably from 75 to 90% by weight, in each case based on the solids in the dispersion.

According to a nineteenth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous coating composition comprises the at least one aqueous dispersion (a) in a total amount of from 0.5 to 50% by weight, preferably from 2 to 40% by weight, more preferably from 3 to 30% by weight, in each case based on the total amount of the aqueous coating composition.

According to a twentieth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous dispersion (b) has a gel fraction of from 70 to 100%, preferably from 80 to 100%, more preferably from 80 to 98%, very preferably from 80 to 90%, in each case based on the solids of dispersion (b).

According to a twenty-first embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the polyurethane-polyurea particles in dispersion (b) have an average particle size (volume average) of 50 to 1,000nm, more preferably 60 to 500nm, even more preferably 120-300nm, especially preferably 70-210nm, measured by Photon Correlation Spectroscopy (PCS) at 25 ± 1 ℃.

According to a twenty-second embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the Polyurethane Prepolymer (PP) comprises at least one polyester diol which is the product of a diol and a dicarboxylic acid, and wherein at least 50 wt.% of the dicarboxylic acid in the preparation of the at least one polyester diol is at least one dimer fatty acid.

According to a twenty-third embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the Polyurethane Prepolymer (PP) comprises carboxylic acid groups.

According to a twenty-fourth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the Polyurethane Prepolymer (PP) has an acid number of from 10 to 35mg KOH/g, in particular from 15 to 23mg KOH/g, based on solid content, according to DIN EN ISO 2114: 2002-06.

According to a twenty-fifth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the number average molecular weight of the Polyurethane Prepolymer (PP) is 2,000-20,000g/mol, preferably 3,500-6,000g/mol, measured with a vapour pressure permeameter of 10.00 with benzophenone as calibration substance.

According to a twenty-sixth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the isocyanate content of the Polyurethane Prepolymer (PP) is from 0.5 to 6 wt. -%, preferably from 1 to 5 wt. -%, particularly preferably from 1.5 to 4 wt. -%, according to DIN EN ISO 3251: 2008-06, DIN EN ISO 11909: 2007-05 and DIN EN ISO 14896: 2009-07 measurement.

According to a twenty-seventh embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the Polyurethane Prepolymer (PP) has an OH value of from 0 to less than 15mg KOH/g, more particularly from 0 to less than 10mg KOH/g, even more preferably from 0 to less than 5mg KOH/g, measured according to r.

According to a twenty-eighth embodiment, the present invention is directed to an aqueous coating composition according to any one of the preceding embodiments, wherein the at least one Polyamine (PA) consists of one or two secondary amino groups, two primary amino groups and an aliphatic saturated hydrocarbon group.

According to a twenty-ninth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the at least one Polyamine (PA) is at least one selected from the group consisting of diethylenetriamine, 3- (2-aminoethyl) -aminopropylamine, dipropylenetriamine, N1- (2- (4- (2-aminoethyl) piperazin-1-yl) ethyl) ethane-1, 2-diamine, triethylenetetramine and N, N' -bis (3-aminopropyl) ethylenediamine, and mixtures thereof.

According to a thirtieth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the polyurethane-polyurea particles in dispersion (b) have a particle size according to DIN EN ISO 2114: an acid number of 10 to 35mg KOH/g, more particularly 15 to 23mg KOH/g, measured 2002-06.

According to a thirty-first embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the polyurethane-polyurea particles in dispersion (b) have an OH-value of 0 to less than 15mg KOH/g, more particularly 0 to less than 10mg KOH/g, more preferably 0 to less than 5mg KOH/g, measured according to r.

According to a thirty-second embodiment, the present invention relates to an aqueous coating composition as claimed in any one of the preceding embodiments, wherein the aqueous dispersion (b) has a content of polyurethane-polyurea particles of from 25 to 55% by weight and water of from 45 to 75% by weight, and wherein the total fraction of polyurethane-polyurea particles and water in the dispersion (b) is at least 90% by weight, preferably 95% by weight, in each case based on the total amount of dispersion (b).

According to a thirty-third embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous dispersion (b) comprises polyurethane-polyurea particles in a total amount of from 25 to 55% by weight, preferably from 30 to 50% by weight, more preferably from 35 to 45% by weight, in each case based on the total amount of dispersion (b).

According to a thirty-fourth embodiment, the present invention relates to an aqueous coating composition as described in any one of the preceding embodiments, wherein the aqueous dispersion (b) comprises from 0 to less than 7.5 wt. -%, preferably from 0 to less than 5 wt. -%, more preferably from 0 to less than 2.5 wt. -%, very preferably 0 wt. -% of an organic solvent selected from N-methyl-2-pyrrolidone, dimethylformamideAlkanes, tetrahydrofuran and N-ethyl-2-pyrrolidone and mixtures thereof.

According to a thirty-fifth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous coating composition comprises the at least one aqueous dispersion (b) in a total amount of from 10 to 55 wt. -%, preferably from 15 to 45 wt. -%, more preferably from 20 to 35 wt. -%, in each case based on the total amount of the aqueous coating composition.

According to a thirty-sixth embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the composition comprises the aqueous dispersion of the at least one core-shell particle (a) and the aqueous dispersion of the at least one polyurethane-polyurea (b) in a weight ratio of from 2:1 to 1:15, preferably from 1:1.2 to 1:10, in each case based on the solid content of the dispersion.

According to a thirty-seventh embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous coating composition has a solid content of 5 to 80 wt. -%, more preferably of 10 to 75 wt. -%, very preferably of 15 to 65 wt. -%, based on the total amount of the coating composition, according to DIN EN ISO 3251: 2008-06 measurement.

According to a thirty-eighth embodiment, the present invention is directed to an aqueous coating composition as described in any one of the preceding embodiments, wherein the composition further comprises at least one crosslinking agent selected from the group consisting of polycarbodiimides, aminoplast resins, polyisocyanates, blocked polyisocyanates, and mixtures thereof, especially polycarbodiimides.

According to a thirty-ninth embodiment, the present invention relates to an aqueous coating composition according to embodiment 38, wherein the crosslinking agent, preferably at least one carbodiimide, is present in a total amount of 0.5 to 20 wt. -%, more preferably 3 to 15 wt. -%, very preferably 6 to 11 wt. -%, based on the total amount of the aqueous coating composition.

According to a fortieth embodiment, the present invention relates to an aqueous coating composition according to embodiments 1-37, wherein the composition comprises a total amount of 0 wt.% of crosslinker, based on the total amount of aqueous coating composition.

According to a forty-first embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein said aqueous coating composition further comprises at least one binder different from the aqueous dispersions (a) and (b), selected from polyurethanes, polyesters, polyacrylates, copolymers of these polymers and mixtures of these polymers, more particularly polyacrylates and/or polyurethane polyacrylates.

According to a forty-second embodiment, the present invention relates to an aqueous coating composition according to embodiment 41, wherein the at least one binder is present in a total amount of 0.5 to 40 wt% binder solids, more preferably 1 to 30 wt% binder solids, very preferably 1.5 to 20 wt% binder solids, in each case based on the total weight of the aqueous coating composition.

According to a forty-third embodiment, the present invention relates to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous coating composition further comprises at least one pigment selected from the group consisting of a coloring pigment, an effect pigment, and mixtures thereof.

According to a forty-fourth embodiment, the present invention relates to an aqueous coating composition according to embodiment 43, wherein the at least one pigment is present in a total amount of 1 to 30 wt. -%, preferably 1.5 to 20 wt. -%, more preferably 2 to 15 wt. -%, in each case based on the total weight of the aqueous coating composition.

According to a forty-fifth embodiment, the present invention is directed to an aqueous coating composition according to any one of the preceding embodiments, wherein the aqueous coating composition further comprises at least one thickener selected from the group consisting of phyllosilicates, (meth) acrylic acid- (meth) acrylate copolymers, hydrophobic polyurethanes, ethoxylated polyurethanes, polyamides and mixtures thereof.

According to a forty-sixth embodiment, the present invention relates to an aqueous coating composition according to embodiment 45, wherein the at least one thickener is present in a total amount of 0.01 to 2 wt. -%, preferably 0.05 to 1 wt. -%, more preferably 0.1 to 0.6 wt. -%, in each case based on the total weight of the aqueous coating composition.

According to a forty-seventh embodiment, the present invention relates to a method for forming a Multilayer Coating (MC) on a substrate (S), comprising the steps of:

(1) directly applying a first aqueous coating material (X) on a substrate (S) to form an uncured first coating film (X),

(2) directly applying a second aqueous coating material (Y) on the uncured first coating film obtained after step (1) to form an uncured second coating film (Y),

(3) directly applying a clear coating material (Z) on the uncured second coating film obtained after step (2) to form a clear coating film (Z), and then

(4) Curing the three coating films obtained after steps (1) to (3) simultaneously,

the method is characterized in that:

the first aqueous coating (X) and/or the second aqueous coating (Y) is selected from the aqueous coating compositions described in embodiments 1 to 44.

According to a forty-eighth embodiment, the present invention relates to the method according to embodiment 47, wherein the substrate (S) is selected from the group consisting of metal substrates, metal substrates coated with a cured electrocoat, plastic substrates and substrates comprising metal and plastic components, particularly preferably from the group consisting of metal substrates coated with a cured electrocoat.

According to a forty-ninth embodiment, the present invention relates to the method of embodiment 48, wherein the metal substrate is selected from the group consisting of iron, aluminum, copper, zinc, magnesium and alloys thereof and steel.

According to a fifty-first embodiment, the present invention relates to the method of embodiments 47-49, wherein no pre-drying or curing is performed after step (1).

According to a fifty-first embodiment, the present invention relates to the process according to embodiments 47 to 50, wherein in the first aqueous coating (X) the weight ratio of the aqueous dispersion of the at least one core/shell-type particle (a) to the aqueous dispersion of the at least one polyurethane-polyurea (b) is from 10:1 to 1:30, preferably from 1:1.6 to 1:10, in each case based on the solid content of the dispersion.

According to a fifty-second embodiment, the present invention relates to the process according to embodiments 47 to 51, wherein the first aqueous coating (X) comprises the at least one aqueous dispersion (a) in a total amount of 0.5 to 40 wt. -%, preferably 2 to 30 wt. -%, more preferably 3 to 25 wt. -%, in each case based on the total amount of coating (X).

According to a fifty-third embodiment, the present invention relates to the process according to embodiments 47 to 52, wherein in the second aqueous coating (Y) the weight ratio of the aqueous dispersion of the at least one core/shell-type particle (a) to the aqueous dispersion of the at least one polyurethane-polyurea (b) is from 2:1 to 1:10, preferably from 1:1.2 to 1:5, in each case based on the solid content of the dispersion.

According to a fifty-fourth embodiment, the present invention relates to the process according to embodiments 47 to 53, wherein the second aqueous coating (Y) comprises the at least one aqueous dispersion (a) in a total amount of 1 to 45% by weight, preferably 5 to 35% by weight, more preferably 10 to 25% by weight, in each case based on the total amount of coating (Y).

According to a fifty-fifth embodiment, the present disclosure is directed to the method of embodiments 47-54, wherein the second aqueous coating (Y) comprises a total amount of 0 wt.% of crosslinker, based on the total amount of coating (Y).

According to a fifty-sixth embodiment, the present disclosure relates to the method of embodiments 47 to 55, wherein the clearcoat (Z) is a solvent-based 1K or 2K clearcoat.

According to a fifty-seventh embodiment, the present invention relates to the method according to embodiments 47 to 56, wherein the clear coat (Z) comprises at least one binder chosen from hydroxy-functional polyacrylates and at least one crosslinker chosen from blocked and/or unblocked polyisocyanates.

According to a fifty-eighth embodiment, the invention relates to the method according to embodiments 47 to 57, wherein the simultaneous curing (4) is carried out at a temperature of 60 to 90 ℃, preferably 85 ℃, for a time of 5 to 60 minutes, preferably 15 to 25 minutes.

According to a fifty-ninth embodiment, the present invention relates to a Multilayer Coating (MC) prepared by the method of any one of embodiments 47-58.

Examples

The invention will now be described in more detail using working examples, to which the invention is in no way limited. In addition, "parts", "percentages", and "ratios" in the examples represent "parts by mass", "% by mass", and "mass ratio", respectively, unless otherwise indicated.

The determination method comprises the following steps:

1. solid content (solids, non-volatiles)

Unless otherwise stated, the solids content, also referred to below as solids fraction, is determined in accordance with DIN EN ISO 3251 at 130 ℃ and 60 minutes, initial mass 1.0 g.

2. Isocyanate content

The isocyanate content, hereinafter also referred to as NCO content, is determined by adding an excess of a 2% solution of N, N-dibutylamine in xylene to a homogeneous solution of the sample in acetone/N-ethylpyrrolidone (1: 1% by volume), by potentiometric titration of the excess amine with 0.1N hydrochloric acid, in a method based on DIN EN ISO 3251, DIN EN ISO 11909 and DIN EN ISO 14896. The NCO content (based on solids) of a polymer can be calculated from the fraction of polymer in solution (solids content).

3. Hydroxyl number

The hydroxyl number is determined on the basis of R.P.Krueger, R.Gnauck and R.Algeier, Plaste und Kautschuk, 20, 274(1982) by means of acetic anhydride in the presence of 4-dimethylaminopyridine as catalyst in Tetrahydrofuran (THF)/Dimethylformamide (DMF) solution at room temperature by completely hydrolyzing the excess acetic anhydride remaining after acetylation and carrying out a potentiometric back-titration of the acetic acid with an alcoholic potassium hydroxide solution. In all cases, an acetylation time of 60 minutes was sufficient to ensure complete conversion.

4. Acid value

The acid number is determined on the basis of DIN EN ISO 2114 in a homogeneous solution of Tetrahydrofuran (THF)/water (9 parts by volume of THF and 1 part by volume of distilled water) and potassium hydroxide in ethanol.

5. Glass transition temperature Tg (DSC)

Unless otherwise stated, the glass transition temperature (also known as Tg (DSC)) is determined according to DIN EN ISO 11357-2 by a second heating run with a heating rate of 10K/min between-80 ℃ and 150 ℃.

6. Viscosity of the oil

Unless otherwise stated, the viscosity is determined according to DIN 53014 using a cylindrical rotary viscometer at 23 ℃ and 1000s^-1Measured at a shear rate of (a).

7. Content of solvent

The amount of organic solvent in the mixture, e.g. in an aqueous dispersion, is determined by gas chromatography (Agilent 7890A, 50m silica capillary column with a polyethylene glycol phase or 50m silica capillary column with a polydimethylsiloxane phase, helium carrier gas, 250 ℃ split-flow injector, oven temperature 40-220 ℃, flame ionization detector, 275 ℃ detector temperature, n-propylene glycol as internal standard).

8. Average particle size

In the context of the present invention, the average particle size of the particles present in dispersions (a) and (b) is determined by Photon Correlation Spectroscopy (PCS).

Specific for the measurement was Malvern Nano S90 (available from Malvern Instruments) at 25. + -. 1 ℃. The instrument covers a size range of 3-3,000nm and is equipped with a 633nm 4mW He-Ne laser. Dispersions (a) and (b) were diluted with particle-free deionized water as dispersion medium and then measured in a 1ml polystyrene cell with the appropriate scattering intensity. The evaluation was performed using a digital correlator with the aid of Zetasizer analysis software version 6.32 (available from Malvern Instruments). The measurement was performed five times and the measurement was repeated for a second freshly prepared sample. The standard deviation of 5 times of measurement is less than or equal to 4 percent. The reported mean particle size (volume average) is the arithmetic mean of the mean particle sizes (volume averages) of the respective formulations, while the Z-means is the intensity weighted mean size. The validation was performed using polystyrene standards with certified particle sizes of 50-3,000 nm.

9. Fraction of gel

In the context of the present invention, the gel fraction of the particles present in dispersions (a) and (b) is determined gravimetrically. First, the corresponding polymer was isolated by freeze-drying from a sample of the aqueous dispersion (a) or (b) (initial mass 1.0 g). After determination of the solidification temperature, i.e. the temperature above which the electrical resistance of the sample does not show any further change when the temperature is further reduced, the completely frozen sample is subjected to its main drying at a drying temperature which is 10 ℃ below the solidification temperature, typically in the range of a drying vacuum pressure of 5 mbar to 0.05 mbar. Rapid freeze-drying of the polymer was achieved by gradually raising the temperature of the heated surface below the polymer to 25 ℃; after a drying time of typically 12 hours, the amount of isolated polymer (solids, determined by freeze-drying) is constant and does not undergo any change even with prolonged freeze-drying. Subsequent drying at a surface temperature below the polymer of 30 ℃ and reduction of the ambient pressure to a maximum value (typically between 0.05 and 0.03 mbar) results in optimum drying of the polymer.

The isolated polymer was then sintered in a forced air oven at 130 ℃ for 1 minute and then extracted in excess tetrahydrofuran (tetrahydrofuran to solids ratio 300:1) at 25 ℃ for 24 hours. The insoluble fraction of the isolated polymer (gel fraction) was then separated off on a suitable frit, dried in a forced-air oven at 50 ℃ for 4 hours and subsequently weighed again.

It was further determined that the gel fraction of the microgel particles was found to be independent of the sintering time at sintering temperatures of 130 ℃ with sintering times varying between 1 and 20 minutes. Thus, crosslinking reactions after separation of the polymer solids can be excluded to further increase the gel fraction.

The gel fraction determined in this way according to the invention is also referred to as gel fraction (freeze-dried).

In parallel, the gel fraction (solids content), also referred to below as gel fraction (130 ℃) is determined gravimetrically by separating a polymer sample from an aqueous dispersion (initial mass 1.0g) at 130 ℃ for 60 minutes. The mass of the polymer was determined and the polymer was then extracted in excess tetrahydrofuran at 25 ℃ for 24 hours analogously to the procedure described above, after which the insoluble fraction (gel fraction) was separated off, dried and weighed again.

10. Solubility in water

The solubility of the organic solvent in water was determined at 20 ℃ as follows. The respective organic solvents and water were combined in a suitable glass vessel, mixed and the mixture was subsequently equilibrated. The amounts of water and solvent are chosen such that two phases separated from each other are obtained after equilibration. After equilibration, a sample was taken from the aqueous phase (i.e. the phase containing more water than organic solvent) with a syringe and diluted with tetrahydrofuran at a ratio of 1/10, the fraction of solvent being determined by gas chromatography (for conditions, see section 8, solvent content).

The solvent may be miscible with water in any weight ratio if two phases are not formed regardless of the amount of water and solvent. This solvent infinitely soluble in water (e.g. acetone) is therefore not a solvent (OS) anyway.

11. Preparation of the multilayer coating

A cationic electrodeposition paint (product name "CathoGuard 800", produced by BASF Coatings) was applied by electrostatic deposition on a zinc phosphate-treated low carbon steel plate in a dried film thickness of 20 μm. Then, the plate was baked at 175 ℃ for 25 minutes to obtain an electrodeposition-coated plate for evaluation (hereinafter referred to as "electrodeposition plate").

To prepare the multilayer coating, the electrodeposition sheet was coated using a rotary atomizing type cup coater (product name "Metallic bell RB-1000 bell", manufactured by ABB) at a temperature of 25 ℃ and a relative humidity of 75%, as follows:

the first aqueous coating material (X) was applied to an electrodeposition plate so that the film thickness after drying was 20 μm. The plate was kept at room temperature for 5 minutes and then coated with the second aqueous coating material (Y) so that the film thickness after drying was 12 μm. The plates were kept at room temperature for 5 minutes and then dried at 80 ℃ for 5 minutes. After the plate was cooled to room temperature, a clear coat (product name "Evergloss", manufactured by BASF Coatings) was applied to the plate so that the film thickness after drying was 40 μm. After coating, the panels were kept at room temperature for 10 minutes and then baked at 85 ℃ for 25 minutes to prepare panels coated with the multilayer coating of the invention.

12. Test measurements

The coated panels were subjected to the following tests:

12.1 evaluation of chipping resistance

The resulting sheet having a size of 70mm × 150mm was set at an angle of 45 ° in a gravelernet (manufactured by Suga Shikenki co.) under an environment of-20 ℃, and at 4kg/crn²Air pressure of 50g of No. 7 crushed stone was sprayed on the paint film surface. Then, the area of the paint film that had peeled off was evaluated. A smaller value indicates a higher chipping resistance. If the peel-off is not more than 1.0mm²/cm²The board has satisfactory chip resistance.

12.2 evaluation of film appearance

The short wave value (SW value) and the long wave value (LW value) were measured by using a wave scanner DOI manufactured by BYK Co. The smaller the value, the better the appearance. If SW is not greater than 10 and LW is not greater than 3, the test board passes the test.

12.3 evaluation of adhesiveness

Initial adhesion test:

the coated panels were divided into 100 grid cells measuring 2mm x 2mm using a cutter knife. Sellotape was firmly bonded to the grid cell and the edges of the tape were peeled off at a 45 ° angle in a single movement, followed by observation of the film appearance of the grid cell and evaluation as follows:

well: no peeling of the coating film was observed.

Not good: peeling of the coating film was observed.

Adhesion test after Water resistance:

the coated panels were soaked in warm water at 40 ℃ for 20 days and then subjected to an initial adhesion test. Adhesion test of recoated sheets:

the first aqueous coating (X), the second aqueous coating (Y) and the clear coating are applied to the electrodeposition sheet according to the method described in point 11. However, after application of the clear coating composition, the panels were baked at 100 ℃ for 25 minutes. Next, the coated board was recoated with the first aqueous coating (X), the second aqueous coating (Y) and the clear coating, and then the recoated board was baked at 80 ℃ for 25 minutes. The resulting recoated panels were subjected to an initial adhesion test.

12.4 evaluation of pinhole count

An electrodeposition sheet having a size of 450mm × 300mm was prepared. The first aqueous coating (X), the second aqueous coating (Y) and the clear coating are applied as described at point 11. However, the thickness of the first aqueous coating material (X) after drying was 30 μm, and the thickness of the second aqueous coating material (Y) after drying was 20 μm.

The number of pinholes in the coated panels was counted visually. A smaller number of pinholes is desirable.

Preparation of aqueous dispersions (a) and (b) and aqueous coating compositions

1. Aqueous dispersion (a)

Aqueous dispersions (a) of core/shell particles were prepared as described in points 1.1 to 1.3, based on WO 2015/007427a 1.

1.1 aqueous Dispersion of core/Shell particles (PD-A1)

Preparation of dispersion of unsaturated polyester carbamate with allyl group (allyl-PD):

based on patent specification WO 2015/007427a1, page 24, example D-P1, polyurethane dispersions of allyl-containing polyester urethanes (allyl-PD) were prepared, with the following modifications: the polyester-urethane contains allyl groups, completely replacing the methyl ethyl ketone with N-methylpyrrolidone. The synthesis proceeds as follows:

in a reaction vessel equipped with a stirrer, an internal thermometer, a reflux condenser and an electric heater, 440.0 parts by weight of a linear polyester polyol and 71.0 parts by weight of dimethylolpropionic acid (available from GEO specialty Chemicals) were dissolved under nitrogen in 425.4 parts by weight of methyl ethyl ketone. The linear polyester polyol has been previously prepared from dimer fatty acid(s) ((s))1012, available from Uniqema), isophthalic acid (available from Uniqema)BP Chemicals) and 1, 6-hexanediol (obtained from BASF SE) (starting material: dimer fatty acid to isophthalic acid to 1, 6-hexanediol in a weight ratio of 54.00:30.02:15.98) and having a hydroxyl number of 73mg KOH/g solid and a number average molar mass of 1379 g/mol.

294.2 parts by weight of isophorone diisocyanate having an isocyanate content of 37.75% by weight (I.S.)I, obtained from BASF SE). After the exothermic reaction subsided, the reaction mixture was gradually heated to 80 ℃ with stirring. Stirring was continued at this temperature until the isocyanate content of the solution was 3.3% by weight. The reaction mixture was then cooled to 65 ℃ while a mixture of 9.4 parts by weight of allyl alcohol (from LyondellBasell), 22.2 parts by weight of trimethylolpropane (from BASF SE) and 21.3 parts by weight of methyl ethyl ketone was added. The resulting reaction mixture was stirred at 65 ℃ until the isocyanate content of the solution had dropped to 1.0% by weight. Then, 22.6 parts by weight of diethanolamine (from BASF SE) were added and the content of isocyanate groups was monitored until no free isocyanate groups could be detected anymore. The resulting dissolved polyurethane was mixed with 28.8 parts by weight of methyl ethyl ketone, 142.3 parts by weight of methoxypropanol and 45.5 parts by weight of triethylamine (obtained from BASF SE). 30 minutes after the addition of triethylamine, the temperature of the solution was lowered to 60 ℃, and then 1977 parts by weight of deionized water was added over 30 minutes with stirring. Methyl ethyl ketone was distilled from the resulting dispersion under reduced pressure at 60 ℃. Thereafter, any loss of solvent and water is compensated.

The allyl-containing polyester urethane dispersion thus obtained had a solids content of 29.0% by weight, an acid number of 34.6mg KOH/g solids, a hydroxyl number of 27.7mg KOH/g solids and a pH of 7.1 (measured at 23 ℃). The level of methoxypropanol was 3.6 wt% (GC) and the level of methyl ethyl ketone was 0.1 wt% (GC).

Preparation of an aqueous dispersion of core/shell type particles (PD-A1):

an aqueous dispersion of core/shell particles (PD-a1) was prepared on the basis of patent specification WO 2015/007427a1, page 34, example D-B1, with the following modifications: the polyester urethane polymer has allyl groups, n-butyl methacrylate and 2-hydroxyethyl acrylate are used as monomers, and the final dispersion is pyrrolidone-free. The aqueous dispersion (PD-a1) was obtained as follows:

to prepare a primary dispersion of a polyester urethane-polyacrylate copolymer, 1961.2 parts by weight of the previously prepared allyl-PD was diluted with 43.3 parts by weight of methoxypropanol and 744.4 parts by weight of deionized water under a nitrogen atmosphere, neutralized with 3.6 parts by weight of triethylamine (obtained from BASF SE) and heated to 80 ℃. After heating the reactor contents to 80 ℃, 0.6 parts by weight ammonium persulfate dissolved in 35.7 parts by weight deionized water was added to the reactor at standard pressure. Subsequently, a mixture of 538.3 parts by weight of n-butyl methacrylate, 26.3 parts by weight of 2-hydroxyethyl acrylate, 4.2 parts by weight of allyl methacrylate and 70.0 parts by weight of butyl glycol (from BASF SE) was added uniformly over a period of 5 hours while stirring was continued. At the beginning of the monomer mixture addition, a solution of 1.1 parts by weight ammonium persulfate in 71.3 parts by weight deionized water was also added over a period of 5 hours.

The content of free monomers was determined by gas chromatography at 30 minute intervals during the free-radical polymerization, after 30 minutes the maximum total monomer content based on the dispersion was determined to be 0.5% by weight (3.1% by weight based on vinyl monomers).

After the simultaneous metering-in of monomers and initiator had ended, the reaction mixture obtained was stirred at 80 ℃ for a further 1 hour and then cooled to room temperature.

After cooling to room temperature (23 ℃), the dispersion was filtered through a filter with a pore size of 25 μm. The polyester urethane-polyacrylate copolymer dispersion (PD-a1) had no coagulum. The stable, milky-white aqueous dispersion of the core/shell particles (PD-a1) thus obtained had the following characteristics:

content of solvent

1.2 aqueous dispersions of core/Shell particles (PD-A2)

An aqueous dispersion of core/shell particles (PD-A2) was prepared analogously to the preparation of PD-A1. However, the polyester urethane content was reduced to 33.3 wt%:

to prepare a primary dispersion of a polyester urethane-polyacrylate copolymer, 1372.8 parts by weight of the allyl-PD prepared in point 1.1 was diluted with 64.4 parts by weight of methoxypropanol and 1106.9 parts by weight of deionized water, neutralized with 5.1 parts by weight of triethylamine (obtained from BASF SE) and heated to 80 ℃ under a nitrogen atmosphere. After post-heating the reactor contents to 80 ℃, 0.7 parts by weight ammonium persulfate dissolved in 46.4 parts by weight deionized water was added to the reactor at standard pressure. Subsequently, a mixture of 697.7 parts by weight of n-butyl methacrylate, 36.2 parts by weight of 2-hydroxyethyl acrylate, 5.5 parts by weight of allyl methacrylate (all monomers obtained from BASF SE) and 70.0 parts by weight of butyl glycol (obtained from BASF SE) was added uniformly over a period of 5 hours while stirring was continued. At the start of the monomer mixture addition, a solution of 1.5 parts by weight ammonium persulfate in 92.7 parts by weight deionized water was also added over a period of 5 hours.

The content of free monomers was determined by gas chromatography at 30 minute intervals during the free-radical polymerization, after 30 minutes the maximum total monomer content based on the dispersion was determined to be 0.5% by weight (2.4% by weight based on vinyl monomers).

After the simultaneous metering-in of monomers and initiator had ended, the reaction mixture obtained was stirred at 80 ℃ for a further 1 hour and then cooled to room temperature.

After cooling to room temperature (23 ℃), the dispersion was filtered through a filter with a pore size of 25 μm. The stable, milky-white aqueous dispersion of the core/shell particles (PD-a2) thus obtained had the following characteristics:

content of solvent

1.3 aqueous dispersions of core/Shell particles (PD-A3)

An aqueous dispersion of core/shell particles (PD-A3) was prepared analogously to the preparation of PD-A1. However, n-butyl acrylate, 4-hydroxybutyl acrylate and allyl methacrylate were used as monomers:

to prepare a primary dispersion of a polyester urethane-polyacrylate copolymer, 1961.2 parts by weight of the allyl-PD prepared in point 1.1 was diluted with 46.3 parts by weight of methoxypropanol and 795.8 parts by weight of deionized water, neutralized with 3.5 parts by weight of triethylamine (obtained from BASF SE) and heated to 80 ℃ under a nitrogen atmosphere. After heating the reactor contents to 80 ℃, 0.3 parts by weight ammonium persulfate dissolved in 17.8 parts by weight deionized water was added to the reactor at standard pressure. Subsequently, a mixture of 495.1 parts by weight of n-butyl acrylate, 68.9 parts by weight of 4-hydroxybutyl acrylate, 4.8 parts by weight of allyl methacrylate (all monomers from BASF SE) and 70.0 parts by weight of butyl glycol (from BASF SE) was added uniformly over a period of 5 hours while stirring was continued. At the start of the monomer mixture addition, a solution of 0.6 parts by weight of ammonium persulfate in 35.7 parts by weight of deionized water was also added over a period of 5 hours.

The content of free monomers was determined by gas chromatography at 30 minute intervals during the free-radical polymerization, after 30 minutes the maximum total monomer content based on the dispersion was determined to be 0.4% by weight (2.5% by weight based on vinyl monomers).

After the simultaneous metering-in of monomers and initiator had ended, the reaction mixture obtained was stirred at 80 ℃ for a further 1 hour and then cooled to room temperature.

After cooling to room temperature (23 ℃), the dispersion was filtered through a filter with a pore size of 25 μm. The stable, milky-white aqueous dispersion of core/shell particles thus obtained had the following characteristics:

content of solvent

2. Aqueous dispersions (PD-B) of polyurethane-polyurea particles (B)

An aqueous dispersion of polyurethane-polyurea particles (b) was prepared according to the synthesis example "PD" of WO 2016/177514A1, pages 72 to 74.

3. Preparation of water-based base paint material

Regarding the formulation ingredients and their amounts, the contents shown in the following table should be considered. When referring to a commercial product or a preparation protocol described elsewhere, the reference is to the commercial product or the product prepared with the referenced protocol exactly, independent of the primary name chosen for the ingredient in question.

Thus, when a formulation ingredient has the primary name "melamine-formaldehyde resin" and when the ingredient is represented by a commercial product, the melamine-formaldehyde resin is used precisely in the form of the commercial product. Therefore, if conclusions are to be drawn about the amount of active substance (melamine-formaldehyde resin), any other ingredients present in the commercial product, such as solvents, must be taken into account.

Thus, if a preparation scheme of the formulation ingredients is mentioned and if the preparation results, for example, in a polymer dispersion having a defined solids content, the dispersion is used precisely. The most important factor is not whether the main name chosen is the term "polymer dispersion" or merely an active substance, for example "polymer", "polyester" or "polyurethane-modified polyacrylate". This must be taken into account if conclusions are to be drawn about the amount of active substance (polymer).

All proportions shown in the table are parts by weight.

3.1 preparation of Black paste P1

From 25 parts by weight of an acrylated polyurethane dispersion (prepared according to WO 91/15528 base Dispersion A), 10 parts by weight of carbon black, 0.1 parts by weight of methyl isobutyl ketone, 1.36 parts by weight of dimethylethanolamine (10% strength in DI water), 2 parts by weight of a commercially available polyether(s) (II)P900, obtained from BASF SE) and 61.45 parts by weight of deionized water. The black paste had a pigment content of 10 parts by weight and a resin solids content of 10 parts by weight.

3.2 preparation of the white paste P2

A white paste was prepared from 43 parts by weight of acrylated polyurethane dispersion (prepared according to WO 91/15528 base stock dispersion a), 50 parts by weight of rutile 2310, 3 parts by weight of 1-propoxy-2-propanol and 4 parts by weight of deionized water. The white paste had a pigment content of 50 parts by weight and a resin solids content of 17.2 parts by weight.

3.3 preparation of the first aqueous coating (X):

the components 1 to 9 listed in table 1 were stirred together in the stated order to obtain a first aqueous coating material (X). After addition, the first aqueous coating (X) was stirred for 30 minutes and adjusted to pH 8.5 with N, N-dimethylethanolamine (obtained from BASF SE) (component 10). Then, the viscosity was adjusted to 100 mPas at 1000s by adding deionized water (component 11)^-1Under shear loading (using a rotational viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at 23 ℃).

Table 1: first Water-based paints (X-I1) to (X-I6) and (X-C1) to (X-C2)

Aqueous coating composition of the invention

The ratio of the aqueous dispersion of core/shell particles (a) to the aqueous polyurethane-polyurea dispersion (b), based on the solids content of the respective dispersion

The water-borne coatings X-I1 to X-I6 of the invention are stable after storage for 4 weeks at 40 ℃. They show no tendency to settle at all and have a low shear viscosity (1 s)^-1The shear load of (a) was not significantly changed (less than 15%) at 23 ℃ with a rotational viscometer (Rheomat RM 180 instrument from Mettler-Toledo).

3.4 preparation of the second aqueous coating (Y):

the components listed under "aqueous phase" in table 2 were added in the order stated to give an aqueous mixture. The aqueous mixture was stirred for 60 minutes. In the next step, the components listed under "organic phase" were added to prepare an organic mixture. The organic mixture was added to the aqueous mixture and stirred for 30 minutes. And adjusted to pH 8.0 with N, N-dimethylethanolamine (obtained from BASF SE). Subsequently, the viscosity was adjusted to 100 mPas at 1000s with deionized water^-1Measured at 23 ℃ using a rotational viscometer (Rheomat RM 180 instrument from Mettler-Toledo). The corresponding amounts of N, N-dimethylethanolamine and water required to adjust the pH and viscosity are listed under "adjuvant" in Table 2.

Table 2: second Water-based paints (Y-I1) to (Y-I6) and (Y-C1) to (Y-C2)

An aqueous coating composition of the invention;

¹⁾3% by weight ofRD (lithium magnesium sodium layered silicate, Rockwood Additives) and 3% by weightAn aqueous solution of P900 (BASF SE);

²⁾aluminum Pigments (Eckart Effect Pigments);

³⁾aluminum Pigments (Eckart Effect Pigments);

⁴⁾prepared according to DE 4009858a1 example D (column 16, lines 37-59);

the ratio of the aqueous dispersion of core/shell particles (a) to the aqueous polyurethane-polyurea dispersion (b), based on the solids content of the respective dispersion.

The water-borne coatings Y-I1 to Y-I6 of the invention are stable after storage for 4 weeks at 40 ℃. They show no tendency to settle at all and have a low shear viscosity (1 s)^-1The shear load of (a) was not significantly changed (less than 15%) at 23 ℃ with a rotational viscometer (Rheomat RM 180 instrument from Mettler-Toledo).

Results

1. Multilayer coatings MC-I1 to MCI-6, MC-C1 and MC-C2

The multilayer coatings MC-I1 to MC-I6 according to the invention were prepared as described above using the first aqueous coating materials X-I1 to X-I6 according to the invention and the second aqueous coating materials Y-I1 to Y-I6 according to the invention (see Table 3 for the combinations used for the first and second coating materials) (see point 11 of the "determination method"). In addition, comparative multilayer coatings MC-C1 and MC-C2 were prepared as described above using the first aqueous paints X-C1 and X-C2 and the second aqueous paints Y-C1 and Y-C2, respectively (see point 11 of "determination methods"). The multilayer coatings of the invention, MC-I1 to MC-I6, were then compared with comparative multilayer coatings, MC-C1 and MC-C2, with respect to chip resistance, film appearance, adhesion and pinhole resistance. The results obtained are shown in table 3.

Table 3: multi-layer coatings MC-I1 to MC-I7, MC-C1 and MC-C2 were prepared and the test results of the multi-layer coatings

The comparative multilayer coatings MC-C1 prepared from coatings (X) and (Y) comprising only aqueous dispersions (a) of core/shell particles have lower chip resistance, film appearance and pinhole resistance than the inventive multilayer coatings MC-I1 to MC-I6 prepared from coatings (X) and (Y) comprising the claimed combination of dispersions (a) and (b). Furthermore, the comparative multilayer coating MC-C1 showed lower adhesion after immersion in water.

The use of the polyurethane-polyurea dispersion (b) in the aqueous coating materials (X) and (Y) (comparative multilayer coating material MC-C2) leads to improved chip resistance and adhesion after immersion in water compared to the multilayer coating material MC-C1. However, recoat adhesion is significantly reduced.

In contrast, the use of the combination of the aqueous dispersion (a) of core/shell-type particles and the aqueous dispersion (b) of polyurethane-polyurea to prepare the multilayer coatings MC-I1 to MC-I7 of the present invention results not only in excellent chip resistance, film appearance and pinhole resistance, but also in excellent adhesion even after immersion in water or when used for recoating.

2. Multilayer coatings MC-I7 to MC-I12, MC-C3 and MC-C4

First aqueous paints X-I1 to X-I6 and X-C1 and X-C2 were mixed with carbodiimide hardener (Carbodilite v-02-l2 available from Nisshinbo Chemical, solids: 40% by weight) in a 100:10 ratio of first aqueous paint to carbodiimide hardener to prepare first aqueous paints X-I7 to X-I12, X-C3 and X-C4.

Then, as described above (see "measuring method" at point 11), multilayer coatings MC-I7 to MC-I12, MC-C3 and MC-C4 were prepared using each of the first water borne paints and each of the second water borne paints containing carbodiimide described in Table 4. The multilayer coatings of the invention MC-I7 to MC-I12 were compared with comparative multilayer coatings MC-C3 and MC-C4 with respect to chip resistance, film appearance, adhesion and pinhole resistance. The results obtained are shown in Table 4.

Multi-layer coatings MC-I7 to MC-I12, MC-C3 and MC-C4 prepared in Table 4 and test results of the multi-layer coatings

The comparative multilayer coatings MC-C3 prepared from coatings (X) and (Y) comprising only aqueous dispersions (a) of core/shell particles have lower chip resistance, film appearance and pinhole resistance than the inventive multilayer coatings MC-I7 to MC-I12 prepared from coatings (X) and (Y) comprising the claimed combination of dispersions (a) and (b). Furthermore, the comparative multilayer coating MC-C3 showed lower adhesion after immersion in water.

The use of the polyurethane-polyurea dispersion (b) in the aqueous coating materials (X) and (Y) (comparative multilayer coating material MC-C4) leads to improved chip resistance and adhesion after immersion in water compared to the multilayer coating material MC-C3. However, recoat adhesion is significantly reduced.

In contrast, the use of the combination of the aqueous dispersion (a) of core/shell-type particles and the aqueous dispersion (b) of polyurethane-polyurea to prepare the multilayer coatings MC-I7 to MC-I12 of the present invention results not only in excellent chip resistance, film appearance and pinhole resistance, but also in excellent adhesion even after immersion in water or when used for recoating. Furthermore, the chip resistance of the multilayer coatings MC-I7 to MC-I12 of the present invention can be further improved by adding a carbodiimide hardener to the first aqueous coating material, as compared with the multilayer coatings MC-I1 to MC-I6 of the present invention prepared without mixing a carbodiimide hardener with the first aqueous coating material.