阅读说明：本技术 多层涂膜的形成方法 (Method for forming multilayer coating film ) 是由 领木贵之 今中健二 于 2019-03-19 设计创作，主要内容包括：本发明涉及多层涂膜的形成方法,其中进行以下步骤：形成底漆涂膜的步骤；形成基础涂膜的步骤；形成透明涂膜的步骤；以及使这些涂膜同时固化的步骤。此方法至少满足：(A)在涂覆制品和底漆涂膜之间的界面处的异氰酸酯量是1.5质量份或更少,基于100质量份的在底漆涂料中的树脂固含量计；或(B)在底漆涂膜和基础涂膜之间的界面处的异氰酸酯量是3.5质量份或更少,基于100质量份的在基础涂料中的树脂固含量计。(The present invention relates to a method for forming a multilayer coating film, wherein the following steps are performed: a step of forming a primer coating film; a step of forming a base coating film; a step of forming a transparent coating film; and a step of simultaneously curing these coating films. The method at least satisfies the following conditions: (A) the amount of isocyanate at the interface between the coated article and the primer coating film is 1.5 parts by mass or less based on 100 parts by mass of the resin solid content in the primer coating; or (B) the amount of isocyanate at the interface between the primer coating film and the base coating film is 3.5 parts by mass or less based on 100 parts by mass of the resin solid content in the base coating material.)

1. A method for forming a multilayer coating film, comprising sequentially performing the steps of:

step (1): applying a primer coating composition (X) to an article, thereby forming an uncured primer coating film;

step (2): applying a base coating composition (Y) onto the uncured primer coating film obtained in step (1), thereby forming an uncured base coating film;

and (3): applying a solvent-based two-component clear coating composition (Z) containing a hydroxyl group-containing resin and a polyisocyanate compound onto the uncured base coating film obtained in step (2), thereby forming an uncured clear coating film; and

and (4): heating the uncured primer coating film formed in step (1), the uncured base coating film formed in step (2), and the uncured clear coating film formed in step (3) to simultaneously cure these coating films,

wherein at least one of the following (A) and (B) is satisfied:

(A) an amount of isocyanate at an interface between the article and the cured primer coating film is 1.5 parts by mass or less based on 100 parts by mass of a resin solid content in the primer coating composition (X), wherein the amount of isocyanate is detected by attenuated total reflection infrared spectroscopy; and

(B) the amount of isocyanate at the interface between the cured primer coating film and the cured base coating film, which is detected by attenuated total reflection infrared spectroscopy, is 3.5 parts by mass or less based on 100 parts by mass of the resin solid content in the base coating composition (Y).

2. The method for forming a multilayer coating film according to claim 1, wherein at least one of the primer coating composition (X) and the base coating composition (Y) contains an imino-containing melamine resin having a weight average molecular weight of 400-4000.

3. The method for forming a multilayer coating film according to claim 1 or 2, wherein at least one of the primer coating composition (X) and the base coating composition (Y) contains a matte pigment.

4. The method for forming a multilayer coating film according to any one of claims 1 to 3, wherein the polyisocyanate compound has a viscosity at 25 ℃ of 0.35 to 5 Pa-s.

5. The method for forming a multilayer coating film according to any one of claims 1 to 4, wherein at least one of the primer coating composition (X) and the base coating composition (Y) is a solvent-based coating composition.

Technical Field

The present invention relates to a method for forming a multilayer coating film.

Background

In the manufacturing specifications of vehicles, glass elements, such as windshields, are typically fixed by adhesion of multiple coating films formed on the outer panel portion of the vehicle, the multiple coating films including an undercoat coating film, a base coating film, and a clear coating film. In the case of the above-mentioned outer panel, particularly a plastic member, the undercoat coating composition used for forming the above-mentioned undercoat coating film may be referred to as a primer coating composition.

As a multilayer coating film containing an undercoat coating film formed from an undercoat coating composition, patent document 1 discloses a multilayer coating material comprising: a multicoat paint system (a) containing at least one basecoat coating film (a1) formed from a basecoat paint composition containing at least one melamine resin, and at least one clear paint film (a2) as the outermost layer of the multicoat paint system; and an adhesive layer (B) formed from a moisture-curable isocyanate-based adhesive and located directly on/above the cured clear coat layer of the uppermost layer of the multicoat paint system, wherein (i) all of the aminoplast resins contained in the basecoat paint composition are fully methylolated and fully etherified melamine resins in which at least 90% of the etherified methylol groups are etherified with butanol; and (ii) the base coat coating composition contains at least 1.0 mass% of at least one polyester binder having a hydroxyl value of at least 240mg KOH/g and an acid value of at most 10mg KOH/g, based on the total mass of the base coat coating composition.

Patent document 2 discloses a method of forming a multilayer coating film in which the following steps (1) to (5) are sequentially performed on/over a vehicle body member coated via electrodeposition: a step (1) of applying an intermediate coating composition (X) onto the electrodeposition coating film to form an intermediate coating film; a step (2) of applying an aqueous base coating composition (Y) onto the intermediate coating film formed in the above step (1) to form a base coating film; a step (3) of applying a clear coating composition (Z) containing a hydroxyl group-containing acrylic resin and a polyisocyanate compound onto the base coating film formed in the above step (2) to form a clear coating film; step (4) of thermally curing the intermediate coating film formed in the step (1), the base coating film formed in the step (2), and the clear coating film formed in the step (3); and a step (5) of forming an adhesive layer on the clear coating film, wherein the above-mentioned intermediate coating composition (X) contains a hydroxyl group-containing polyester resin (A), a melamine resin (B), a pyrazole-terminated polyisocyanate compound (C), a pigment (D) and an organic solvent (E), the ratio (B/C) between the content of the above-mentioned melamine resin (B) and the content of the above-mentioned pyrazole-terminated polyisocyanate compound (C) is 5/35 to 20/15 in terms of a solid content ratio, the Pigment Weight Concentration (PWC) of the pigment (D) is 40 to 60%, and the cured coating film obtained by thermally curing the above-mentioned intermediate coating film has an elongation at break at 20 ℃ of 40 to 90%, a Young's modulus of 600-1600MPa and a Tukon hardness of 3 to 9.

Patent document 3 discloses an aqueous primer coating composition comprising a non-aqueous conductive chlorinated polyolefin resin (a), an aqueous polyurethane resin (B), an aqueous epoxy resin (C) and an internally crosslinked acrylic particle emulsion (D), wherein the content of the above (a) is 15 to 60 mass%, the content of the above (B) is 10 to 50 mass%, the content of the above (C) is 20 to 50 mass%, and the content of the above (D) is 5 to 20 mass% based on the total amount (100 mass%) of the above (a), (B), (C) and (D); and the above (A) is an aqueous polypropylene resin having a crystallinity of 35 to 55% and a weight average molecular weight of 50,000 to 200,000.

Patent document 4 discloses a cutting primer coating composition containing a styrene-ethylene-butene copolymer having a hydroxyl group, a melamine curing agent and a pigment, wherein the pigment contains highly conductive carbon black, and the ratio between the highly conductive carbon black and other pigments is 5: 1 to 1: 30, the Pigment Weight Concentration (PWC) of the highly conductive carbon black is 0.1 to 9.0 mass%, and the styrene-ethylene-butene copolymer having a hydroxyl group has a hydroxyl value of 1 to 10 and a number average molecular weight of 40,000 to 100,000.

Reference list

Patent document

Patent document 1: JP-A-2012-524673

Patent document 2: JP-A-2017-

Patent document 3: JP-A-2008-56914

Patent document 4: JP-A-2009-102452

Disclosure of Invention

Technical problem

The undercoat coating composition used in patent document 1 and the intermediate coating composition used in patent document 2 are suitable for coating metal members, but cannot coat plastic members due to, for example, adhesion problems.

In addition, with the primer coating compositions disclosed in patent documents 3 and 4, when a glass member such as a windshield is adhered to an article having a primer coating film formed from the primer coating composition, the adhesion between the primer coating film and the article is insufficient.

An object of the present invention is to provide a method for forming a multilayer coating film, whereby a multilayer coating film having excellent adhesion to an article can be formed on the article, for example, a plastic member.

Solution scheme

In order to achieve the above object, the present invention includes the following subject matters.

<1> a method for forming a multilayer coating film, which comprises sequentially carrying out the steps of:

step (1): applying a primer coating composition (X) to an article, thereby forming an uncured primer coating film;

step (2): applying a base coating composition (Y) onto the uncured primer coating film obtained in step (1), thereby forming an uncured base coating film;

and (3): applying a solvent-based two-component clear coating composition (Z) containing a hydroxyl group-containing resin and a polyisocyanate compound onto the uncured base coating film obtained in step (2), thereby forming an uncured clear coating film; and

and (4): heating the uncured primer coating film formed in step (1), the uncured base coating film formed in step (2), and the uncured clear coating film formed in step (3) to simultaneously cure these coating films,

wherein at least one of the following (A) and (B) is satisfied:

(A) an amount of isocyanate at an interface between the article and the cured primer coating film is 1.5 parts by mass or less based on 100 parts by mass of a resin solid content in the primer coating composition (X), wherein the amount of isocyanate is detected by attenuated total reflection infrared spectroscopy; and

(B) the amount of isocyanate at the interface between the cured primer coating film and the cured base coating film, which is detected by attenuated total reflection infrared spectroscopy, is 3.5 parts by mass or less based on 100 parts by mass of the resin solid content in the base coating composition (Y).

<2> the method for forming a multilayer coating film according to <1>, wherein at least one of the primer coating composition (X) and the base coating composition (Y) contains an imino-containing melamine resin having a weight average molecular weight of 400-4000.

<3> the method for forming a multilayer coating film according to <1> or <2>, wherein at least one of the primer coating composition (X) and the base coating composition (Y) contains a matte pigment.

4. The method for forming a multilayer coating film according to any one of <1> to <3>, wherein the polyisocyanate compound has a viscosity of 0.35-5Pa · s at 25 ℃.

5. The method of forming a multilayer coating film according to any of <1> to <4>, wherein at least one of the primer coating composition (X) and the base coating composition (Y) is a solvent-based coating composition.

Advantageous effects of the invention

By the method for forming a multilayer coating film of the present invention, a multilayer coating film having excellent adhesion to an article, such as a plastic member, can be formed on the article. Such multilayer coating films are particularly effective, for example, when a glass member such as a windshield is bonded to an article having the multilayer coating film.

Detailed description of the preferred embodiments

Hereinafter, the method of forming a multilayer coating film of the present invention is described in detail.

The method for forming a multilayer coating film comprises the following steps in order:

step (1): applying a primer coating composition (X) to an article, thereby forming an uncured primer coating film;

step (2): applying a base coating composition (Y) onto the uncured primer coating film obtained in step (1), thereby forming an uncured base coating film;

and (3): applying a solvent-based two-component clear coating composition (Z) containing a hydroxyl group-containing resin and a polyisocyanate compound onto the uncured base coating film obtained in step (2), thereby forming an uncured clear coating film; and

and (4): heating the uncured primer coating film formed in step (1), the uncured base coating film formed in step (2), and the uncured clear coating film formed in step (3) to simultaneously cure these coating films,

wherein at least one of the following (A) and (B) is satisfied:

(A) an amount α of isocyanate at an interface between the article and the cured primer coating film, which is detected by attenuated total reflection infrared spectroscopy, is 1.5 parts by mass or less based on 100 parts by mass of a resin solid content in the primer coating composition (X); and

(B) the amount of isocyanate β at the interface between the cured primer coating film and the cured base coating film, which is detected by attenuated total reflection infrared spectroscopy, is 3.5 parts by mass or less based on 100 parts by mass of the resin solid content in the base coating composition (Y).

In the case where at least one of the isocyanate amount α and the isocyanate amount β is within the above range, the primer coating film can be prevented from becoming too hard due to the isocyanate, and a multilayer coating film having sufficient adhesion can be obtained.

From the viewpoint of the adhesion of the resulting coating film, the amount of the isocyanate α is preferably 0.01 to 1.0 part by mass, more preferably 0.01 to 0.5 part by mass, based on 100 parts by mass of the resin solid content in the primer coating composition (X).

From the viewpoint of the adhesion of the resulting coating film, the amount of isocyanate β is preferably 0.01 to 2.0 parts by mass, more preferably 0.01 to 1.0 part by mass, based on 100 parts by mass of the resin solid content in the base coating composition (Y).

In the present invention, the amount of isocyanate at the interface between the article and the primer coating film and the amount of isocyanate at the interface between the primer coating film and the base coating film are defined by a value detected by attenuated total reflection infrared spectroscopy (hereinafter referred to as ATR-IR).

First, a method of detecting the amount α of isocyanate at the interface between the article and the primer coating film is described.

The primer coating composition (X) is applied onto an article such as "KOBE polyshue" (trade name, produced by standardtest Corporation, polypropylene sheet), thereby having a cured film thickness of 10 μm. Next, the base coating composition (Y) was applied thereon, thereby having a cured film thickness of 15 μm. Then, a solvent-based two-component clear coating composition (Z) was applied thereon, thereby having a cured film thickness of 30 μm. Then, the obtained coating film was baked at 80 ℃ for 30 minutes to obtain a multilayer coating film. The multilayer coating film was cut at any position, and peeled off from the article.

ATR-IR detection was performed on the surface of the multilayer coating film, on the side of the multilayer coating film in contact with the article, under the following conditions. Detecting at 1730cm^-1The intensity of the infrared absorption peak derived from the ester bond at (A) and (B) at 1670cm^-1Intensity of infrared absorption peak derived from urethane bond at (b). The numerical value of the peak area ratio (area of urethane bond/area of ester bond) was used in a calibration curve obtained in advance to estimate the amount α of isocyanate.

The calibration curve is obtained by plotting the above peak area ratios of samples obtained by adding a polyisocyanate compound (e.g., "DURANATE TLA 100" (trade name, manufactured by Asahi Kasei Corporation, polyisocyanate compound)) contained in the solvent-based two-component clear coating composition (Z) to a primer coating composition (X) (e.g., "SOFLEX 3100CD PRIMER GRAY L50" (trade name, manufactured by Kansai Paint co., ltd.).

(detection conditions of ATR-IR)

Equipment: fourier transform Infrared Spectroscopy "FT/IR 610", manufactured by JASCO Corporation,

detection mode: ATR method (prism: zinc selenide, incident angle: 45 degree)

Resolution ratio: 4cm^-1，

Cumulative number: the number of the times of the treatment is 16,

wavelength range: 400cm^-1To 4000cm^-1。

A method of detecting the amount of isocyanate β at the interface between the primer coating film and the base coating film is described below.

The method for detecting the amount of isocyanate β is the same as the method for detecting the amount of isocyanate α described above, except that: (i) a multilayer coating film for detection was obtained as follows: applying the base coating composition (Y) to the article to have a cured film thickness of 15 μm, followed by applying the solvent-based two-component clear coating composition (Z) thereto to have a cured film thickness of 30 μm, and then baking at 80 ℃ for 35 minutes; and (ii) a calibration curve is obtained by plotting the above peak area ratios of samples obtained by adding a polyisocyanate compound (e.g., "DURANATE TLA 100" (trade name, polyisocyanate compound manufactured by Asahi Kasei Corporation)) contained in the solvent-based two-component clear coating composition (Z) to the base coating composition (Y).

It is assumed that the value measured by the ATR-IR described above is a value obtained by detecting the infrared light that has penetrated 1.2 μm from the surface of the above multilayer coating film on the side where the above multilayer coating film is in contact with the article. The depth of penetration of the infrared light into the sample depends on the angle of incidence of the infrared light on the sample, the refractive index of the crystal used for detection, and the wavelength of the infrared light, and is calculated as in equation 1 below.

[ mathematical formula 1]

dp: depth of penetration

λ: wavelength of infrared light

θ: incident angle of infrared light to sample

n₁: refractive index of crystal for detection

n₂: refractive index of the sample.

1. Step (1)

Step (1) is to apply the primer coating composition (X) to an article, thereby forming an uncured primer coating film.

[ article ]

There is no particular limitation on the article used in the present invention, and examples of the article include plastic members and the like.

As the plastic member, for example, particularly preferred is a plastic member containing a polyolefin resin obtained by polymerizing (copolymerizing) at least one or two or more kinds of olefins having 2 to 10 carbon atoms, such as ethylene, propylene, butene and hexene. In addition, plastic parts containing polycarbonate, Acrylonitrile Butadiene Styrene (ABS) resin, polyurethane resin, and polyamide may also be used.

Plastic elements are used for exterior panel parts of automobiles, such as bumpers, deflectors, grills and fenders, and exterior panel parts of household appliances.

Among the above articles, plastic elements are preferable in view of the adhesiveness of the obtained coating film. The method of forming a multilayer coating film of the present invention can be preferably used for molding materials such as a molding film and a molding sheet, each of which includes these plastic elements.

Before the primer coating composition (X) is applied, the above-mentioned article may be subjected to degreasing treatment, washing treatment, and the like as appropriate by a method known per se.

[ primer coating composition (X) ]

The primer coating composition (X) may be used without any particular limitation as long as it is a primer coating composition that can satisfy at least one condition of the above-described (a) and (B).

As the primer coating composition (X), preferred is a coating composition in which an organic solvent and/or water is used as a main solvent, and resin components such as a base resin and a curing agent, and a pigment are contained. The primer coating composition (X) is preferably a solvent-based coating composition in which an organic solvent is used as a main solvent, from the viewpoint of the adhesion of the resulting coating film.

(base resin)

In the primer coating composition (X), a base resin used for a coating composition which is common per se in the prior art may be used as the base resin, and examples of the base resin include acrylic resins, polyester resins, alkyd resins, polyurethane resins, polyolefin resins, and the like. These base resins preferably have crosslinkable functional groups such as hydroxyl groups, carboxyl groups and epoxy groups in the molecule thereof. One of these base resins may be used alone, or two or more thereof may be used in combination.

From the viewpoint of the adhesiveness of the resulting coating film, the base resin preferably contains a polyolefin resin, more preferably contains a chlorinated polyolefin resin and an acrylic-modified chlorinated polyolefin resin (a1) and/or an acrylic-modified non-chlorinated polyolefin resin (a2) (hereinafter may be simply referred to as component (a)). One of these base resins may be used alone, or two or more thereof may be used in combination.

As the polyolefin resin, for example, a polyolefin resin obtained by polymerizing (copolymerizing) at least one olefin having 2 to 10 carbon atoms, for example, selected from the group consisting of ethylene, propylene, butene, hexene, octene and decene, particularly an olefin having 2 to 4 carbon atoms, can be used. Resins obtained by graft polymerization of a polyolefin resin with an unsaturated carboxylic acid such as maleic acid, fumaric acid, itaconic acid and (meth) acrylic acid, preferably an unsaturated monocarboxylic acid or dicarboxylic acid or an anhydride of such an unsaturated carboxylic acid, in a manner known per se, can be used. In particular, polyolefin resins modified with maleic anhydride are preferred. In addition, the unsaturated carboxylic acid or acid anhydride-modified polyolefin resin may be modified with an amine or modified with an alcohol. As the amine and the alcohol, one of the conventional amine and the conventional alcohol may each be used alone, or two or more thereof may each be used in combination.

In the case where a polyolefin resin is used in the primer coating composition (X), the content of the polyolefin resin is preferably 15 to 70% by mass, more preferably 25 to 60% by mass, based on the total amount of the resin solid content of the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

Chlorinated polyolefin resins are chlorides of polyolefin resins. Examples of the polyolefin resin used as the chlorinated polyolefin resin base include radical homopolymers or copolymers of at least one olefin selected from the group consisting of ethylene, propylene, butene, methylbutene and isoprene, and radical copolymers of the olefin with vinyl acetate, butadiene, acrylate or methacrylate.

The chlorinated polyolefin resin preferably has a weight average molecular weight in the range of 30,000 to 200,000, more preferably a weight average molecular weight in the range of 50,000 to 150,000.

The chlorine content in the chlorinated polyolefin resin is preferably in the range of 10 to 40 mass%. In the case where the chlorine content is within the above range, the solubility of the multilayer coating film in a solvent is not reduced. Therefore, atomization during spray coating is sufficient, and the solvent resistance of the multilayer coating film is not lowered. The chlorine content is more preferably in the range of 12 to 35 mass%.

The chlorinated polyolefin resin is preferably chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, chlorinated ethylene-vinyl acetate copolymer, or the like.

In the case of using a chlorinated polyolefin resin in the primer coating composition (X), the content thereof is preferably 15 to 70% by mass, more preferably 25 to 60% by mass, based on the total amount of the resin solid content of the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

The above-mentioned component (a) is obtained by modifying a chlorinated and/or non-chlorinated polyolefin resin with an acrylic resin, and contains an acryloyl moiety and a chlorinated and/or non-chlorinated polyolefin moiety.

Examples of the method for obtaining the acrylic-modified chlorinated polyolefin resin (a1) include a method in which a polyolefin resin is graft-copolymerized with an α, β -unsaturated carboxylic acid and/or an anhydride thereof to obtain an acid-modified polyolefin resin (a11), then the acid-modified polyolefin resin (a11) is chlorinated to obtain an acid-modified chlorinated polyolefin resin (a12), and then a polymerizable unsaturated monomer including a hydroxyl group-containing (meth) acrylate ester is graft-polymerized in the presence of a polymerization initiator to achieve acrylic modification. In addition, examples of the method include a method in which a hydroxyl group-containing (meth) acrylate is reacted with an acid-modified chlorinated polyolefin resin (a12) to effect esterification, and a double bond is introduced into the acid-modified chlorinated polyolefin resin (a12) to obtain a double bond-introduced chlorinated polyolefin resin, and then a polymerizable unsaturated monomer is graft-copolymerized with the double bond-introduced chlorinated polyolefin resin to effect acrylic modification.

Examples of the method for obtaining the acrylic-modified non-chlorinated polyolefin resin (a2) include a method in which a polyolefin resin is graft-copolymerized with an α, β -unsaturated carboxylic acid and/or an anhydride thereof to obtain an acid-modified polyolefin resin (a11), and then a polymerizable unsaturated monomer including a hydroxyl group-containing (meth) acrylate is graft-polymerized in the presence of a polymerization initiator to effect acrylic modification. In addition, examples of the method include a method in which a hydroxyl group-containing (meth) acrylate is reacted with the acid-modified polyolefin resin (a11) to effect esterification, and a double bond is introduced into the acid-modified polyolefin resin (a11) to obtain a double bond-introduced polyolefin resin, and then a polymerizable unsaturated monomer is graft-copolymerized with the double bond-introduced polyolefin resin to effect acrylic modification.

In the present specification, the term "(meth) acrylate" means acrylate or methacrylate, and the term "(meth) acrylic acid" means acrylic acid or methacrylic acid.

Examples of the polyolefin resin used for preparing the above-mentioned component (a) include resins obtained by polymerization (copolymerization) of at least one olefin selected from olefins having 2 to 10 carbon atoms such as ethylene, propylene, butene, hexene, octene and decene, particularly from olefins having 2 to 4 carbon atoms.

Examples of the α, β -unsaturated carboxylic acid and/or an anhydride thereof include unsaturated carboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, and (meth) acrylic acid, or anhydrides of these unsaturated carboxylic acids. Of these, maleic acid and maleic anhydride are particularly preferred. One of these may be used alone, or two or more thereof may be used in combination.

Examples of the hydroxyl group-containing (meth) acrylate include (meth) acrylates having one hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and polypropylene glycol (meth) acrylate. Among them, 2-hydroxyethyl (meth) acrylate is particularly preferable. One of these may be used alone, or two or more thereof may be used in combination.

Examples of polymerizable unsaturated monomers include: alkyl esters of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate; acrylic monomers such as (meth) acrylic acid, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylamide, and (meth) acrylonitrile; styrene; and so on. Among them, butyl (meth) acrylate, hexyl (meth) acrylate and cyclohexyl (meth) acrylate are particularly preferable. One of these may be used alone, or two or more thereof may be used in combination.

The graft copolymerization and the esterification reaction can be carried out by methods known per se.

As the polymerization initiator, a peroxide-based initiator such as benzoyl peroxide and an azo-based initiator such as azobisisobutyronitrile can be preferably used.

In the acrylic-modified chlorinated polyolefin resin (a1), the glass transition temperature of the acryloyl moiety is preferably from-50 ℃ to 0 ℃, more preferably from-45 ℃ to-5 ℃, still more preferably from-35 ℃ to-15 ℃ from the viewpoint of the adhesiveness of the resulting coating film. In the acrylic-modified chlorinated polyolefin resin (a1), the solid content mass ratio between the acryloyl moiety and the chlorinated polyolefin moiety is preferably 7:3 to 2:8, more preferably 6.5:3.5 to 2.5:7.5, still more preferably 6:4 to 3:7, from the viewpoint of the adhesiveness of the resulting coating film.

In the above component (a), the glass transition temperature of the acryloyl moiety may be adjusted by the composition of the polymerizable unsaturated monomer.

In the present specification, the glass transition temperature Tg is a value calculated by the following formula:

1/Tg(K)＝W1/T1+W2/T2+…Wn/Tn

Tg(℃)＝Tg(K)–273

in the above formula, W1, W2, … Wn are the mass fractions of the respective monomers, and T1, T2, … Tn are the glass transition temperatures tg (k) of the homopolymers of the respective monomers.

The glass transition temperature of the homopolymer of each monomer is a value described in "POLYMER HANDBOOK (POLYMER HANDBOOK)" 4 th edition, edited by J.Brandrup, E.h.Immergut and E.A.Grulke (1999). The glass transition temperature of a homopolymer of each monomer not described in this document is a value obtained in the following manner. A homopolymer of the monomers was synthesized to have a weight average molecular weight of about 50,000, and the glass transition temperature of the homopolymer was detected by differential scanning calorimetry.

In the primer coating composition (X), the content of the above-mentioned component (a) is preferably 10 to 50% by mass, more preferably 12 to 45% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

In the present specification, unless otherwise specified, the resin contains a base resin and a curing agent.

As described above, it is preferable that the base resin, such as the polyester resin and the acrylic resin, have a crosslinkable functional group, such as a hydroxyl group, in the molecule thereof. The hydroxyl group-containing polyester resin and the hydroxyl group-containing acrylic resin are as follows.

For example, the hydroxyl group-containing polyester resin can be obtained by esterification reaction of a polybasic acid and a polyhydric alcohol with an excess of hydroxyl groups according to a method known per se.

The polybasic acid is a compound having two or more carboxyl groups in one molecule thereof, and examples of the polybasic acid include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 1, 4-cyclohexanedicarboxylic acid, pyromellitic acid, itaconic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, dimer acid, humic acid, succinic acid, chlorendic acid, anhydrides thereof and the like.

The polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule thereof, and examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, neopentyl glycol, butanediol, hexanediol, 2-ethyl-2-butyl-1, 3-propanediol, cyclohexanedimethanol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol, and the like.

The esterification reaction having an excess of hydroxyl groups can be carried out by using, in combination, for example, a polyol having at least three hydroxyl groups in one molecule. As the hydroxyl group-containing polyester resin, a fatty acid-modified polyester resin obtained by modification with a fatty acid such as soybean oil fatty acid, castor oil fatty acid and dehydrated castor oil fatty acid can also be used. In addition, if necessary, the hydroxyl group-containing polyester resin may be modified with an epoxy compound such as butyl glycidyl ether, alkylphenyl glycidyl ether and glycidyl neodecanoate.

From the viewpoint of the adhesion of the resulting coating film, the hydroxyl value of the hydroxyl group-containing polyester resin is preferably in the range of 10 to 150mgKOH/g, more preferably 50 to 85 mgKOH/g. The acid value of the hydroxyl group-containing polyester resin is preferably in the range of 0 to 50mg KOH/g, more preferably 1 to 30mg KOH/g, from the viewpoint of the adhesiveness of the resulting coating film. The number average molecular weight of the hydroxyl group-containing polyester resin is preferably in the range of 1,500 to 100,000, more preferably 2,000 to 30,000, from the viewpoint of the adhesiveness of the resulting coating film.

In the primer coating composition (X), in the case of using a hydroxyl group-containing polyester resin, the amount thereof is preferably 5 to 15% by mass, more preferably 7 to 20% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

The hydroxyl group-containing acrylic resin can be obtained, for example, by polymerizing a hydroxyl group-containing polymerizable unsaturated monomer, an alkyl (meth) acrylate monomer and optionally other polymerizable unsaturated monomers according to a conventional polymerization method, such as a solution polymerization method and the like.

The hydroxyl group-containing polymerizable unsaturated monomer is a compound having a hydroxyl group and a polymerizable unsaturated group, and examples of the hydroxyl group-containing polymerizable unsaturated monomer include monoester products of (meth) acrylic acid and a diol having 2 to 10 carbon atoms, such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl (meth) acrylate; and caprolactone-modified products of compounds having these hydroxyl groups, (meth) acryloyl groups and polymerizable unsaturated groups, and the like.

Examples of the alkyl (meth) acrylate monomer include monoester products of (meth) acrylic acid and monohydric alcohols having 1 to 20 carbon atoms, such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and the like.

Other polymerizable unsaturated monomers are compounds having a polymerizable unsaturated group, which are different from the hydroxyl group-containing polymerizable unsaturated monomer and the alkyl (meth) acrylate monomer, and examples thereof include carboxyl group-containing polymerizable unsaturated monomers such as (meth) acrylic acid and maleic acid; epoxy group-containing polymerizable unsaturated monomers such as glycidyl (meth) acrylate; and (meth) acrylamide, acrylonitrile, styrene, vinyl acetate, and vinyl chloride.

From the viewpoint of the adhesion of the resulting coating film, the hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 10 to 100mgKOH/g, more preferably 50 to 90 mgKOH/g. The acid value of the hydroxyl group-containing acrylic resin is preferably in the range of 0 to 50mgKOH/g, more preferably 2 to 30mgKOH/g, from the viewpoint of the adhesion of the resulting coating film. The weight average molecular weight of the hydroxyl group-containing acrylic resin is preferably in the range of 2,000 to 100,000, more preferably 3,000 to 50,000, from the viewpoint of the adhesiveness of the resulting coating film.

In the primer coating composition (X), in the case of using a hydroxyl group-containing acrylic resin, the amount thereof is preferably 5 to 20% by mass, more preferably 7 to 15% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

(curing agent)

In the primer coating composition (X), a reagent capable of reacting with the functional group of the above-mentioned base resin may be used as the curing agent. Examples of such curing agents include melamine resins, epoxy resins, polyisocyanate compounds, blocked polyisocyanate compounds, polycarbodiimide compounds, and the like. One of these curing agents may be used alone, or two or more thereof may be used in combination.

In particular, the weight average molecular weight of the above melamine resin is preferably in the range of 400 to 4000, more preferably 600 to 3000, from the viewpoint of the adhesion of the resulting coating film.

The melamine resin preferably contains an imino-containing melamine resin. The number of imino groups per triazine nucleus in the above melamine resin is preferably 1 or more, more preferably in the range of 1.2 to 2.

In the primer coating composition (X), when an imino-containing melamine resin having a weight average molecular weight of 400 to 4000 is used, the melamine resin supplements the isocyanate. Therefore, the isocyanate amount α can be reduced.

In the primer coating composition (X), in the case of using an imino-containing melamine resin having a weight average molecular weight of 400 to 4000, the content thereof is preferably 2.5 to 15% by mass, more preferably 3 to 10% by mass, based on the total amount of the resin solid content of the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

Examples of the above epoxy resin include: bisphenol a based epoxy resins; bisphenol F based epoxy resins; a novolac type epoxy resin; hydrogenated bisphenol a based epoxy resins; aliphatic epoxy resins such as ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl hexahydrophthalate, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, and polyglycerol polyglycidyl ether; a biphenyl-based epoxy resin; dicyclopentadiene based epoxy resins, and the like. One of these epoxy resins may be used alone, or two or more thereof may be used in combination.

Examples of commercially available products of the above-mentioned Epoxy Resins include bisphenol A-based Epoxy Resins such as "jER 827", "jER 828", "jER 828 EL", "jER 828 XA", "jER 834" (each produced by Japan Epoxy Resins Co., Ltd.), "EPICLON 840", "EPICLON 840-S", "EPICLON 850", "EPICLON 850-S", "EPICLON 850-CRP", "EPICLON 850-LC" (each produced by DIC Corporation), "Epotohto YD-127", "Epotohto YD-128" (each produced by Tohto Kasei Co., Ltd.), "Rika Chemical BPO-20E", and "Rika Chemical Resin O-60E" (each produced by New Japan Co., Ltd.); bisphenol F-based Epoxy Resins such as "jER 806", "jER 807" (both produced by Japan Epoxy Resins co., ltd.), "EPICLON 830", "EPICLON 830-S", "EPICLON 835" (both produced by DIC Corporation), and "epohto YDF-170" (produced by Tohto Kasei co., ltd.); novolac type Epoxy Resins such as "jER 152" (manufactured by Japan Epoxy Resins co., ltd.); hydrogenated bisphenol a-based Epoxy resins such as "jERYX 8000", "jERYX 8034" (both produced by Japan Epoxy resins co., ltd.), "epohto ST-3000" (produced by Tohto Kasei co., ltd.), "Rika Resin HBE-100" (produced by New Japan Chemical co., ltd.), "Denacol EX-252" (produced by Nagase chemtexin corporation), and "SR-HBA" (produced by Sakamoto Yakuhin Kogyo co., ltd.); and aliphatic Epoxy Resins such as "YED 205", "YED 216M", "YED 216D" (each produced by Japan Epoxy Resins Co., Ltd., "Epotohto YH-300", "Epotohto YH-301", "Epotohto YH-315", "Epotohto YH-324", "Epotohto YH-325" (each produced by Tohto Kasei Co., Ltd., "Denacol EX-211", "Denacol EX-212", "Denacol EX-212L", "Denacol EX-214L", "Denacol EX-216L", "Denacol EX-313", "Denacol EX-314", "Denacol EX-321", "Denacol EX-321L", "Denacol EX-411", "Denacol EX-421 Denacol EX-512", "Denacol EX-521", "Denacol EX-614", "and" Denacol EX-321 ", "Denacol EX-614B", "Denacol EX-622", "Denacol EX-810", "Denacol EX-811", "Denacol EX-850", "Denacol EX-850L", "Denacol EX-851", "Denacol EX-821", "Denacol EX-830", "Denacol EX-832", "Denacol EX-841", "Denacol EX-861", "Denacol EX-911", "Denacol EX-941", "Denacol EX-920", "Denacol EX-931" (each produced by NagaChese exmtcorporation), "SR-NPG", "SR-16H", "SR-16 HL", "SR-TMP", "SR-PG", "SR-TPG", "SR-4 PG", "SR-2 EG", "SR-8 EG", "SR-8 EGS", "SR-GLG", "SR-DGE", "SR-DGE", "SR-4 GL", "SR-4 GLS" and "SR-SEP" (all produced by Sakamoto Yakuhin Kogyo Co., Ltd.).

The epoxy equivalent of the epoxy resin is preferably in the range of 170-4000 g/equivalent, more preferably in the range of 220-2700 g/equivalent, from the viewpoint of the adhesion of the resulting coating film.

From the viewpoint of the adhesion of the resulting coating film, the molecular weight of the epoxy resin is preferably in the range of 170-. The epoxy resin preferably has a hydroxyl group in view of the adhesiveness of the resulting coating film.

In the primer coating composition (X), in the case of using the above epoxy resin, the content thereof is preferably 1 to 20% by mass, more preferably 5 to 15% by mass, based on the total amount of the solid content of the resin in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

In particular, the epoxy resin preferably contains a polysulfide-modified epoxy resin from the viewpoint of the adhesion of the resulting coating film. The polysulfide-modified epoxy resin is a bisphenol-based epoxy resin having a compound having a bisphenol skeleton and a polysulfide skeleton in its molecular main chain.

Examples of the compound having the above bisphenol skeleton include an epoxy resin based on bisphenol a, an epoxy resin based on bisphenol AD, an epoxy resin based on halogenated bisphenol a, an epoxy resin based on bisphenol F, an epoxy resin based on halogenated bisphenol F, and the like. Among them, bisphenol F-based epoxy resins are particularly preferable from the viewpoint of the adhesion of the resulting coating film.

From the viewpoint of the adhesion of the resulting coating film, the number average molecular weight of the polysulfide-modified epoxy resin is preferably in the range of 350-. From the viewpoint of the adhesion of the resulting coating film, the epoxy equivalent of the polysulfide-modified epoxy resin is preferably in the range of 110-500 g/equivalent, more preferably 130-400 g/equivalent, still more preferably 150-350 g/equivalent.

From the viewpoint of ease of handling, the polysulfide-modified epoxy resin preferably has a viscosity of 3000 poise or less at 25 ℃ and more preferably has a viscosity of 100 poise-300 poise at 25 ℃.

Examples of commercially available products of polysulfide-modified epoxy resins include "FLEP-10", "FLEP-50", "FLEP-60", "FLEP-65", "FLEP-80", "FLEP-120X", "FLEP-125X", "FLEP-410C", "FVD-103X", "FVD-105X", "FVD-423C" (all trade names, manufactured by Toray Fine Chemicals Co., Ltd.), and the like.

In the primer coating composition (X), in the case of using the above polysulfide-modified epoxy resin, the content thereof is preferably 5 to 25% by mass, more preferably 7 to 20% by mass, still more preferably 10 to 18% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

The polyisocyanate compound is a compound having at least two isocyanate groups in one molecule. The blocked polyisocyanate compound is a polyisocyanate compound in which an isocyanate group in its molecule is blocked with a blocking agent.

Examples of the polyisocyanate compound include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, araliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, derivatives of these polyisocyanate compounds, and the like. One of these polyisocyanate compounds may be used alone, or two or more thereof may be used in combination.

Examples of the above-mentioned aliphatic polyisocyanate compounds include aliphatic diisocyanate compounds such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1, 2-propylene diisocyanate, 1, 2-butylene diisocyanate, 2, 3-butylene diisocyanate, 1, 3-butylene diisocyanate, 2,4, 4-or 2,2, 4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and methyl 2, 6-diisocyanatohexanoate (common name: lysine diisocyanate); aliphatic triisocyanate compounds such as 2-isocyanatoethyl 2, 6-diisocyanatohexanoate, 1, 6-diisocyanate 3-isocyanatomethylhexane, 1,4, 8-triisocyanatooctane, 1,6, 11-triisocyanatoundecane, 1, 8-diisocyanato-4-isocyanatomethyloctane, 1,3, 6-triisocyanatohexane and 2,5, 7-trimethyl-1, 8-diisocyanato-5-isocyanatomethyloctane, etc.

Examples of the above alicyclic polyisocyanate compounds include alicyclic diisocyanate compounds such as 1, 3-cyclopentene diisocyanate, 1, 4-cyclohexane diisocyanate, 1, 3-cyclohexane diisocyanate, 3-isocyanatomethyl-3, 5, 5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2, 4-cyclohexane diisocyanate, methyl-2, 6-cyclohexane diisocyanate, 1, 3-or 1, 4-bis (isocyanatomethyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis (1, 4-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI) and norbornane diisocyanate; alicyclic triisocyanate compounds, for example 1,3, 5-triisocyanatocyclohexane, 1,3, 5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2, 6-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatoethyl) -3- (3-isocyanatomethyl) heptane Propyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane and the like.

Examples of the above-mentioned araliphatic polyisocyanate compounds include araliphatic diisocyanate compounds such as methylenebis (1, 4-phenylene) diisocyanate (common name: MDI),1, 3-or 1, 4-xylylene diisocyanate or a mixture thereof, ω, ω' -diisocyanato-1, 4-diethylbenzene, and 1, 3-or 1, 4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof, araliphatic triisocyanate compounds such as 1,3, 5-triisocyanatomethylbenzene, and the like.

Examples of the above aromatic polyisocyanate include aromatic diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4 ' -diphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 2, 4-or 2, 6-toluene diisocyanate or a mixture thereof, 4,4 ' -ditoluene diisocyanate and 4,4 ' -diphenyl ether diisocyanate; aromatic triisocyanates, such as triphenylmethane-4, 4', 4 "-triisocyanate, 1,3, 5-triisocyanate benzene and 2,4, 6-triisocyanate toluene; aromatic tetraisocyanates such as 4,4 ' -diphenylmethane-2, 2 ', 5,5 ' -tetraisocyanate and the like.

Examples of the derivatives of the polyisocyanates include dimers, trimers, biurets, allophanates, uretdiones, allophanates, isocyanurates, uretdiones, uretonimines, isocyanurates, uretdiones, and the like of the above-mentioned polyisocyanate compounds,

Diazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI; polymeric MDI) and crude TDI.

The polyisocyanate compound is preferably an alicyclic diisocyanate or a derivative of an alicyclic diisocyanate, and more preferably an alicyclic diisocyanate, from the viewpoint of the adhesion of the resulting coating film.

In the primer coating composition (X), in the case where the above polyisocyanate compound is used, the content thereof is preferably 1 to 25% by mass, more preferably 5 to 20% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

The blocked polyisocyanate compound can be obtained, for example, by adding a blocking agent to the isocyanate group of the above polyisocyanate compound. The blocked polyisocyanate compound is stable at ordinary temperatures, but when heated at the baking temperature of the coating film (usually about 90 to 200 ℃), it is desirable that the blocking agent is dissociated to produce free isocyanate groups.

Examples of the blocking agent satisfying these requirements include the following blocking agents: phenol-based blocking agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based blocking agents, such as caprolactam, -valerolactam, gamma-butyrolactam and beta-propiolactam; aliphatic alcohol-based capping agents such as methanol, ethanol, propanol, butanol, pentanol and lauryl alcohol; ether-based blocking agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid; glycolic acid ester-based capping agents, such as methyl glycolate, ethyl glycolate, and butyl glycolate; lactate-based capping agents such as lactic acid, methyl lactate, ethyl lactate, and butyl lactate; alcohol-based blocking agents such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; oxime-based blocking agents such as formamide oxime, acetamide oxime, acetyl oxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime and cyclohexane oxime; blocking agents based on dialkyl malonates, such as dimethyl malonate, diethyl malonate, diisopropyl malonate, di-n-butyl malonate, diethyl methylmalonate, benzylmethyl malonate, and diphenyl malonate; acetoacetate-based blocking agents, such as methyl acetoacetate, ethyl acetoacetate, isopropyl acetoacetate, n-propyl acetoacetate, benzyl acetoacetate, phenyl acetoacetate; active methylene-based capping agents, such as acetylacetone; thiol-based blocking agents such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophene, methylthiophene, and ethylthiophene; amide-based blocking agents such as acetanilide, methoxyacetanilide, N-acetyltoluidine, acrylamide, methacrylamide, acetic acid amide, stearic acid amide and benzamide; imide-based capping agents, such as succinimides, phthalimides and maleimides; amine-based blocking agents such as diphenylamine, phenylnaphthylamine, dimethylaniline, N-phenyldimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine and butylphenylamine; imidazole-based capping agents such as imidazole and 2-ethylimidazole; pyrazole-based capping agents, such as 3, 5-dimethylpyrazole; urea-based blocking agents such as urea, thiourea, ethylene urea, ethylene thiourea and diphenylurea; urethane-based blocking agents, such as phenyl N-phenyl carbamate; imine-based blocking agents such as aziridine and 2-methylaziridine; sulfite-based blocking agents such as sodium bisulfite and potassium bisulfite; and so on. Among the above-mentioned blocking agents, those based on active methylene are particularly preferred from the viewpoint of low-temperature curability and adhesion of the resulting coating film.

In the primer coating composition (X), in the case where the above-mentioned blocked polyisocyanate compound is used, the content thereof is preferably in the range of 1 to 25% by mass, more preferably 5 to 20% by mass, based on the total amount of the solid content of the resin in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

The polycarbodiimide compound is a compound having at least two carbodiimide groups in one molecule.

Examples of commercially available products of the polycarbodiimide compounds include "Carbodilite SV-02", "Carbodilite V-02", "Carbodilite V-02-L2", "Carbodilite V-04", "Carbodilite E-01", and "Carbodilite E-02" (both produced by Nisshinbo).

In the primer coating composition (X), in the case of using the above polycarbodiimide compound, the content thereof is preferably 1 to 25% by mass, more preferably 5 to 20% by mass, based on the total amount of the solid content of the resin in the primer coating composition (X), from the viewpoint of the adhesion of the obtained coating film.

(pigment)

In the primer coating composition (X), conventional pigments may be used as the pigment without limitation, and a matte pigment is preferably used.

In the primer coating composition (X), when a matte pigment is used, the matte pigment physically inhibits the movement of isocyanate. Therefore, the isocyanate amount α can be reduced.

Examples of matte pigments include mica, alumina, talc, silica, aluminum flakes, and the like. These matte pigments may be used alone, or two or more thereof may be used in combination. Examples of mica include mica, alumina coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, and the like.

Among the above-mentioned matte pigments, from the viewpoint of the adhesiveness of the resulting coating film, it is preferable to use a matte pigment having an average particle diameter of 8 μm or more.

In the case where the primer coating composition (X) contains the above-mentioned matte pigment, the content of the matte pigment is preferably in the range of 1 to 20% by mass, more preferably 2 to 15% by mass, and still more preferably 3 to 12% by mass, based on the total amount of the solid content of the resin (100 parts by mass) in the primer coating composition (X).

As for the pigment, in addition to the matt pigment, a colored pigment, an extender pigment and a conductive pigment may be used as the pigment.

Examples of colored pigments include titanium oxide, carbon black, chrome yellow, loess, yellow iron oxide, hansa yellow, pigment yellow, chrome orange, chrome cinnabar, permanent orange, amber pigment, permanent red, brilliant carmine, sun violet, methyl violet lake, ultramarine, ferric blue, cobalt blue, phthalocyanine blue, pigment green, naphthol green, and the like. Among these colored pigments, titanium oxide and carbon black are particularly preferable. One of these colored pigments may be used alone, or two or more thereof may be used in combination.

In the case where the primer coating composition (X) contains titanium oxide as the above-mentioned colored pigment, the content of titanium oxide is preferably 100-150% by mass, more preferably 110-140% by mass, based on the total amount of the resin solid content in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

Examples of extender pigments include calcium carbonate, barium sulfate, zinc white (zinc oxide), and the like. One of these extender pigments may be used alone, may be used in combination, or two or more thereof.

In the case where the primer coating composition (X) contains the above extender pigment, the content of the above extender pigment is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, based on the total amount of the solid content of the resin in the primer coating composition (X), from the viewpoint of the adhesion of the obtained coating film.

The conductive pigment is not particularly limited as long as it can impart conductivity to the coating film to be formed, and any particle shape, flake shape, and fiber (including whisker) shape may be used.

Specific examples of the conductive pigment include conductive carbon such as conductive carbon, carbon nanotube, carbon nanofiber and microcarbon roll; and metals such as silver, nickel, copper, graphite, and aluminum. Examples of the conductive pigment further include: antimony-doped tin oxide, phosphorus-doped tin oxide, tin oxide and/or acicular titanium oxide, the surface of which is coated with antimony, antimony oxide, zinc antimonate and indium tin oxide; a pigment in which the whisker surface of carbon or graphite is coated with tin oxide; pigments in which the surface of the flake mica is coated with a conductive metal oxide, such as tin oxide or antimony doped tin oxide; a conductive pigment composed of titanium oxide particles containing tin oxide and phosphorus on the surface thereof, and the like. One of these conductive pigments may be used alone, or two or more thereof may be used in combination. Among these conductive pigments, conductive carbon can be particularly preferably used.

In the case where the primer coating composition (X) contains conductive carbon as the above-mentioned conductive pigment, the content of the conductive carbon is preferably 1 to 10% by mass, more preferably 2 to 7% by mass, based on the total amount of the solid content of the resin in the primer coating composition (X), from the viewpoint of the adhesion of the resulting coating film.

(organic solvent)

As described above, in the primer coating composition (X), the organic solvent is mainly used as the solvent.

The organic solvent is not particularly limited as long as it can dissolve or disperse the above base resin and the above curing agent by mixing; examples of the organic solvent include solvents such as aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, alcohol-based solvents, ester-based solvents, and ketone-based solvents.

(other Components)

The primer coating composition (X) may further contain additives for coating compositions such as silane coupling agents, thickeners, defoaming agents, surface conditioning agents and film forming aids, if necessary.

Examples of the silane coupling agent include 2- (3, 4-epoxycyclohexyl) ethyltrialkoxysilane, 3-glycidoxypropyltrialkoxysilane, 3-glycidoxypropylmethyldialkoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldialkoxysilane, N-2- (aminoethyl) -3-aminopropyltrialkoxysilane, 3-aminopropylmethyldialkoxysilane, 3-mercaptopropylmethyldialkoxysilane, 3-mercaptopropyltrialkoxysilane, N-phenyl-3-aminopropyltrialkoxysilane, 3-ureidopropyltrialkoxysilane, 3-chloropropyltrialkoxysilane, bis (trialkoxysilylpropyl) tetrasulfide, 3-isocyanatopropyltrialkoxysilane, and the like. One of these silane coupling agents may be used alone, or two or more thereof may be used in combination.

From the viewpoint of the adhesion of the obtained coating film, the primer coating composition (X) preferably further contains a curing catalyst.

Examples of curing catalysts include quaternary catalysts such as tetraethylammonium bromide, tetrabutylammonium bromide, tetraethylammonium chloride, tetrabutylammonium bromideAnd IIIPhenylbenzyl chloride

And amines such as triethylamine and tributylamine.

(method of preparing primer coating composition (X))

The primer coating composition (X) can be prepared by a conventional method. The primer coating composition (X) can be prepared, for example, by dissolving or dispersing the base resin, the curing agent, the pigment and, if necessary, the above-mentioned other components in an organic solvent.

(application of primer coating composition (X))

The primer coating composition (X) can be applied to the above-mentioned article by air spraying, airless spraying, dipping, brushing, etc. to have a cured film thickness of preferably 1 to 20 μm, more preferably 3 to 15 μm. After application of the primer coating composition (X), the resulting primer coating film surface may be left to stand at room temperature for a period of about 30 seconds to about 60 minutes, if necessary.

2. Step (2)

Step (2) is to apply the base coating composition (Y) onto the uncured primer coating film obtained in step (1), thereby forming an uncured base coating film.

[ base coating composition (Y) ]

The base coating composition (Y) may be used without any particular limitation as long as it is a base coating composition that can satisfy at least one of the conditions of (a) and (B) described above.

As the base coating composition (Y), preferred is a coating composition in which an organic solvent and/or water is used as a main solvent, and resin components such as a base resin and a curing agent, and a pigment are contained. The base coating composition (Y) is preferably a solvent-based coating composition in view of the adhesion of the resulting coating film, and among them, an organic solvent is preferably used as a main solvent.

(base resin)

Examples of the base resin used in the base coating composition (Y) include resins such as acrylic resins, polyester resins, and alkyd resins, which have reactive functional groups such as hydroxyl groups, epoxy groups, carboxyl groups, and silanol groups. Among them, hydroxyl group-containing acrylic resins and hydroxyl group-containing polyester resins are preferable from the viewpoint of the adhesiveness of the resulting coating film.

As the hydroxyl group-containing acrylic resin, the same resins as described above with respect to the primer coating composition (X) can be used.

The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 10 to 100mg KOH/g, more preferably in the range of 50 to 90mg KOH/g, from the viewpoint of the adhesion of the resulting coating film. The acid value of the hydroxyl group-containing acrylic resin is preferably in the range of 0 to 50mgKOH/g, more preferably in the range of 2 to 30mgKOH/g, from the viewpoint of the adhesiveness of the resulting coating film. The weight average molecular weight of the hydroxyl group-containing acrylic resin is preferably in the range of 2,000 to 100,000, more preferably in the range of 3,000 to 50,000, from the viewpoint of the adhesiveness of the resulting coating film.

In the base coating composition (Y), in the case of using a hydroxyl group-containing acrylic resin, the amount thereof is preferably 20 to 70% by mass, more preferably 30 to 65% by mass, based on the total amount of the resin solid content in the base coating composition (Y), from the viewpoint of the adhesion of the resulting coating film.

As the hydroxyl group-containing polyester resin, the same resins as described above with respect to the primer coating composition (X) can be used.

The hydroxyl value of the hydroxyl group-containing polyester resin is preferably in the range of 10 to 150mg KOH/g, more preferably in the range of 50 to 85mg KOH/g, from the viewpoint of the adhesion of the resulting coating film. The acid value of the hydroxyl group-containing polyester resin is preferably in the range of 0 to 50mg KOH/g, more preferably in the range of 1 to 30mg KOH/g, from the viewpoint of the adhesiveness of the resulting coating film. The number average molecular weight of the hydroxyl group-containing polyester resin is preferably in the range of 1,500 to 100,000, more preferably in the range of 2,000 to 30,000, from the viewpoint of the adhesiveness of the resulting coating film.

In the base coating composition (Y), in the case of using a hydroxyl group-containing polyester resin, the amount thereof is preferably 15 to 45% by mass, more preferably 20 to 40% by mass, based on the total amount of the solid content of the resin in the base coating composition (Y), from the viewpoint of the adhesiveness of the resulting coating film.

(curing agent)

The preferred amounts of curing agent and curing agent in the base coating composition (Y) are the same as described above for the primer coating composition (X).

In the base coating composition (Y), a reagent capable of reacting with the functional group of the above-mentioned base resin may be used as the curing agent. Examples of such curing agents include melamine resins, epoxy resins, polyisocyanate compounds, blocked polyisocyanate compounds, polycarbodiimide compounds, and the like. One of these curing agents may be used alone, or two or more thereof may be used in combination.

In particular, the weight average molecular weight of the melamine resin is preferably in the range of 400 to 4000, more preferably 600 to 3000, from the viewpoint of the adhesion of the resulting coating film.

The melamine resin preferably contains an imino-containing melamine resin. The number of imino groups per triazine nucleus in the above melamine resin is preferably 1 or more, more preferably in the range of 1.2 to 2.

In the base coating composition (Y), when an imino-containing melamine resin having a weight average molecular weight of 400 to 4000 is used, the melamine resin is supplemented with an isocyanate. Therefore, the isocyanate amount β can be reduced.

In the base coating composition (Y), in the case of using an imino group-containing melamine resin having a weight average molecular weight of 400 to 4000, the content thereof is 2.5 to 15% by mass, preferably 3 to 10% by mass, based on the total amount of the resin solid content of the base coating composition (Y), from the viewpoint of the adhesion of the resulting coating film.

(pigment)

The preferred amounts of pigment and pigment in the base coating composition (Y) are the same as described above for the primer coating composition (X).

In the base coating composition (Y), conventional pigments may be used as the pigment without limitation, and a matte pigment is preferably used.

In the base coating composition (Y), when a matte pigment is used, the matte pigment physically inhibits the movement of isocyanate. Therefore, the isocyanate amount β can be reduced.

Examples of matte pigments include mica, alumina, talc, silica, aluminum flakes, and the like. These matte pigments may be used alone, or two or more thereof may be used in combination. Examples of mica include mica, alumina coated with titanium oxide or iron oxide, mica coated with titanium oxide or iron oxide, and the like.

Among the above-mentioned matte pigments, from the viewpoint of the cutting resistance of the resulting coating film, it is preferable to use a matte pigment having an average particle diameter of 8 μm or more.

In the case where the base coating composition (Y) contains the above-mentioned matte pigment, the mixing amount of the matte pigment is usually in the range of 1 to 20 parts by mass, preferably in the range of 2 to 15 parts by mass, more preferably in the range of 3 to 12 parts by mass, based on the total amount (100 parts by mass) of the solid content of the resin in the base coating composition (Y).

Among the pigments, in addition to the matte pigment, a colored pigment, an extender pigment, and the like may be used as the pigment. As the pigment and extender pigment, the same pigments as described above with respect to the primer coating composition (X) may be used.

(organic solvent)

As described above, in the base coating composition (Y), an organic solvent is preferably used as the main solvent.

The organic solvent is not particularly limited as long as it can dissolve or disperse the above base resin and the above curing agent by mixing; examples thereof include solvents such as aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, alcohol-based solvents, ester-based solvents, and ketone-based solvents.

(other Components)

The base coating composition (Y) may further contain, if necessary, additives for coating compositions such as curing catalysts, ultraviolet absorbers, paint surface conditioners, rheology control agents, antioxidants, defoaming agents, waxes and preservatives.

(method of preparing base coating composition (Y))

The base coating composition (Y) can be prepared by a conventional method. The base coating composition (Y) can be prepared by dissolving or dispersing, for example, a base resin, a curing agent, a pigment and, if necessary, the above-mentioned other components in an organic solvent.

(application of base coating composition (Y))

The base coating composition (Y) may be applied to the above-mentioned uncured primer coating film by air spraying, airless spraying, dipping, brushing, etc. so as to have a cured film thickness of preferably 5 to 50 μm, more preferably 5 to 30 μm, still more preferably 10 to 20 μm. After the application of the base coating composition (Y), the surface of the resulting base coating film may be allowed to stand at room temperature for about 1 to 60 minutes, if necessary.

3. Step (3)

Step (3) is to apply a solvent-based two-component clear coating composition (Z) containing a hydroxyl group-containing resin and a polyisocyanate compound onto the uncured base coating film obtained in step (2), thereby forming an uncured clear coating film.

[ solvent-based two-component clear coating composition (Z) ]

The solvent-based two-component clear coating composition (Z) is a two-component clear coating composition which contains a hydroxyl group-containing resin as a main agent and a polyisocyanate compound as a curing agent.

(hydroxyl group-containing resin)

As the hydroxyl group-containing resin used as the base material, any conventional resin in the art may be used without particular limitation so long as it contains a hydroxyl group. Examples of the hydroxyl group-containing resin include hydroxyl group-containing acrylic resins, hydroxyl group-containing polyester resins, hydroxyl group-containing polyether resins, hydroxyl group-containing polyurethane resins, and the like. Preferred are hydroxyl-containing acrylic resins and hydroxyl-containing polyester resins, and particularly preferred are hydroxyl-containing acrylic resins.

The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably in the range of 80 to 200mgKOH/g, more preferably in the range of 100-180 mgKOH/g. In the case where the hydroxyl value is 80mg KOH/g or more, the crosslinking density is high, and therefore the scratch resistance of the multilayer coating film is sufficient. In the case where the hydroxyl value is 200mg KOH/g or less, the water resistance of the multilayer coating film can be satisfied.

The weight average molecular weight of the hydroxyl group-containing acrylic resin is preferably in the range of 2,500 to 40,000, more preferably in the range of 5,000 to 30,000. In the case where the weight average molecular weight is 2,500 or more, the properties of the multilayer coating film, such as acid resistance, can be satisfied. In the case where the weight average molecular weight is 40,000 or less, the smoothness of the multilayer coating film is sufficient, thereby satisfying the coating properties of the multilayer coating film.

In the present specification, each of the weight average molecular weight and the number average molecular weight is a numerical value determined from a chromatogram by gel permeation chromatography based on the molecular weight of standard polystyrene. As the gel permeation chromatography, "HLC 8120 GPC" (manufactured by Tosoh Corporation) can be used. As the column for chromatography, four columns, that is, "TSKgel G-4000 HXL", "TSKgel G-3000 HXL", "TSKgel G-2500HXL", and "TSKgel G-2000 HXL" (trade names, all produced by TosoH corporation) can be used, and this detection can be carried out in the case where the mobile phase is tetrahydrofuran, the detection temperature is 40 ℃ and the flow rate is 1cc/min, and the detector is RI.

The glass transition temperature of the hydroxyl group-containing acrylic resin is preferably in the range of-40 ℃ to 20 ℃, more preferably in the range of-30 ℃ to 10 ℃. In the case where the glass transition temperature is-40 ℃ or higher, the hardness of the multilayer coating film is sufficient. In addition, in the case where the glass transition temperature is 20 ℃ or less, the smoothness of the coating surface of the multilayer coating film can be satisfied.

(polyisocyanate Compound)

The polyisocyanate compound used as the curing agent is a compound having at least two isocyanate groups in one molecule thereof. Examples of the polyisocyanate compound include: aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, araliphatic polyisocyanate compounds, aromatic polyisocyanate compounds, derivatives of any of these polyisocyanate compounds, and the like.

Examples of the above aliphatic polyisocyanate compounds include: aliphatic diisocyanate compounds such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1, 2-propylene diisocyanate, 2, 3-butylene diisocyanate, 1, 3-butylene diisocyanate, 2,4, 4-or 2,2, 4-trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and methyl 2, 6-diisocyanatohexanoate (common name: lysine diisocyanate); aliphatic triisocyanate compounds such as 2-isocyanatoethyl-2, 6-diisocyanatohexanoate, 1, 6-diisocyanate 3-isocyanatomethylhexane, 1,4, 8-triisocyanatooctane, 1,6, 11-triisocyanatoundecane, 1, 8-diisocyanato-4-isocyanatomethyloctane, 1,3, 6-triisocyanatohexane and 2,5, 7-trimethyl-1, 8-diisocyanato-5-isocyanatomethyloctane, and the like.

Examples of the above alicyclic polyisocyanate compounds include alicyclic diisocyanate compounds such as 4, 4' -methylenebis (cyclohexyl isocyanate), 1, 3-cyclopentene diisocyanate, 1, 4-cyclohexane diisocyanate, 1, 3-cyclohexane diisocyanate, 3-isocyanatomethyl-3, 5, 5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1, 3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1, 3-cyclohexylene diisocyanate, 1, 3-or 1, 4-bis (isocyanatomethyl) cyclohexane (common name: hydrogenated xylylene diisocyanate) or a mixture thereof, methylenebis (4, 1-cyclohexanediyl) diisocyanate (common name: hydrogenated MDI), and norbornane diisocyanate; alicyclic triisocyanate compounds, for example 1,3, 5-triisocyanatocyclohexane, 1,3, 5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 2- (3-isocyanatopropyl) -2, 6-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 3- (3-isocyanatopropyl) -2, 5-bis (isocyanatomethyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatoethyl) -3- (3-isocyanatomethyl) heptane Propyl) -bicyclo (2.2.1) heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) -heptane, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -bicyclo (2.2.1) heptane; and so on.

Examples of the above-mentioned araliphatic polyisocyanate compounds include araliphatic diisocyanate compounds such as methylenebis (4, 1-phenylene) diisocyanate (common name: MDI),1, 3-or 1, 4-xylylene diisocyanate or a mixture thereof, ω, ω' -diisocyanato-1, 4-diethylbenzene, and 1, 3-or 1, 4-bis (1-isocyanato-1-methylethyl) benzene (common name: tetramethylxylylene diisocyanate) or a mixture thereof; araliphatic triisocyanate compounds such as 1,3, 5-triisocyanatomethylbenzene; and so on.

Examples of the above aromatic polyisocyanate compounds include aromatic diisocyanate compounds such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4 ' -diphenyl diisocyanate, 1, 5-naphthalene diisocyanate, 2, 4-toluene diisocyanate (common name: 2,4-TDI) or 2, 6-toluene diisocyanate (common name: 2,6-TDI) or a mixture thereof, 4,4 ' -toluidine diisocyanate and 4,4 ' -diphenyl ether diisocyanate; aromatic triisocyanate compounds such as triphenylmethane-4, 4', 4 "-triisocyanate, 1,3, 5-triisocyanatobenzene and 2,4, 6-triisocyanatotoluene; aromatic tetraisocyanate compounds such as 4,4 ' -diphenylmethane-2, 2 ', 5,5 ' -tetraisocyanate; and so on.

Examples of the derivatives of the above polyisocyanate compounds include dimers, trimers, biurets, allophanates, uretdiones, allophanates, isocyanurates, uretdiones, allophanates, uretdiones, uretonimines, isocyanurates, uretdiones, uretonimines, and the like of the above polyisocyanate compounds,Diazinetrione, polymethylene polyphenyl polyisocyanate (crude MDI; polymeric MDI) and crude TDI.

One of the above polyisocyanate compounds and derivatives thereof may be used alone, or two or more thereof may be used in combination.

Among the above polyisocyanate compounds and derivatives thereof, preferred are aliphatic diisocyanate compounds and derivatives thereof, and alicyclic diisocyanate compounds and derivatives thereof. Among the aliphatic diisocyanate compounds and derivatives thereof, hexamethylene diisocyanate and derivatives thereof are more preferable. Among the alicyclic diisocyanate compounds and derivatives thereof, 4' -methylenebis (cyclohexyl isocyanate) is more preferable. Among the above polyisocyanate compounds and derivatives thereof, the derivatives of hexamethylene diisocyanate are most preferable from the viewpoint of adhesion and compatibility.

As the above polyisocyanate compound, a prepolymer obtained by reacting the above polyisocyanate compound and derivatives thereof with a compound capable of reacting with the polyisocyanate compound and derivatives thereof in the case where an excess of isocyanate groups is used can be used. The compounds capable of reacting with the polyisocyanate compound and derivatives thereof include, for example, compounds having active hydrogen groups such as hydroxyl groups and amino groups. Examples of the compound having an active hydroxyl group include polyols, low molecular weight polyester resins, amines, water and the like.

The viscosity of the polyisocyanate compound at 25 ℃ is preferably in the range of 0.35 to 5 pas, more preferably in the range of 0.4 to 4 pas, and still more preferably in the range of 0.45 to 2 pas, from the viewpoint of the adhesiveness of the multilayer coating film.

When the polyisocyanate compound having a viscosity within the above range is used, the movement of isocyanate within the polyisocyanate compound is restricted, and the amount of isocyanate α and the amount of isocyanate β can be reduced.

(other Components)

The solvent-based two-component clear coating composition (Z) may suitably contain a solvent such as an organic solvent, and additives such as a curing catalyst, a defoaming agent and an ultraviolet absorber, if necessary.

The solvent-based two-component clear coating composition (Z) may suitably contain a color pigment as long as the transparency of the multilayer coating film is not impaired. As the colored pigment, a conventional pigment used in the art for ink or coating compositions may be used alone, or two or more thereof may be used in combination. The addition amount of the color pigment may be suitably determined, and is preferably 30 parts by mass or less, more preferably 0.01 to 10 parts by mass, based on 100 parts by mass of the medium resin composition in the solvent-based two-component clear coating composition (Z).

(method for preparing solvent-based two-component clear coating composition (Z))

The solvent-based two-component clear coating composition (Z) can be prepared by conventional methods. The solvent-based two-component clear coating composition (Z) can be prepared by mixing the hydroxyl group-containing resin used as the main agent, the polyisocyanate compound used as the curing agent, and the above-mentioned other components as required immediately before use.

From the viewpoint of curability and scratch resistance of the multilayer coating film, the mixing ratio of the hydroxyl group-containing resin and the polyisocyanate compound is preferably such that the equivalent ratio (NCO/OH) between the isocyanate group of the polyisocyanate compound and the hydroxyl group of the hydroxyl group-containing resin is in the range of 0.5 to 2, more preferably in the range of 0.8 to 1.5.

The solid content concentration of the solvent-based two-component clear coating composition (Z) is preferably in the range of about 30 to 70% by mass, more preferably in the range of about 40 to 60% by mass.

The solvent-based two-component clear coating composition (Z) is used as an organic solvent-based coating composition. As the organic solvent used in this case, various organic solvents used for the coating composition, such as aromatic or aliphatic hydrocarbon-based solvents, ester-based solvents, ketone-based solvents, and ether-based solvents, can be used. In the case where an organic solvent is used during the preparation of the hydroxyl group-containing resin, the organic solvent may be used as it is, or may be appropriately added.

(application of solvent-based two-component clear coating composition (Z))

The above-mentioned solvent-based two-component clear coating composition (Z) is applied to the above-mentioned uncured base coating film. There is no particular limitation on the method of applying the solvent-based two-component clear coating composition (Z). The coating operation may be carried out in the same manner as described above with respect to the primer coating composition (X) and the base coating composition (Y), and may be carried out by coating methods such as air spraying, airless spraying, rotary atomization and curtain coating.

When these coating methods are carried out, the solvent-based two-component clear coating composition (Z) can be applied electrostatically, if desired. In the case of electrostatically coating the solvent-based two-component clear coating composition (Z), a rotary atomization coating based on electrostatic coating is preferable.

In the operation of applying the solvent-based two-component clear coating composition (Z), the viscosity of the solvent-based two-component clear coating composition (Z) is preferably adjusted to a viscosity range suitable for the coating method. For example, in the case of rotary atomization coating based on electrostatic coating, it is preferable to suitably adjust the viscosity of the solvent-based two-component clear coating composition (Z) to a range of about 15 to 60 seconds by using a solvent, such as an organic solvent, which is measured at 20 ℃ with a Ford Cup (Ford Cup) No.4 viscometer.

The solvent-based two-component clear coating composition (Z) is preferably applied in such an amount that the cured film thickness is about 10 to 50 μm.

After the solvent-based two-component clear coating composition (Z) is applied to form a clear coating film, the clear coating film may be left to stand, for example, at room temperature for about 1 to 60 minutes to promote volatilization of volatile components.

4. Step (4)

Step (4) is heating the uncured primer coating film formed in step (1), the uncured base coating film formed in step (2), and the uncured clear coating film formed in step (3) to simultaneously cure these coating films.

The heating operation may be carried out by a conventional method. For example, a curing oven such as a hot air oven, an electric oven, and an infrared induction heating oven can be used. The heating temperature is preferably in the range of 60 to 95 deg.C, more preferably in the range of 70 to 90 deg.C. The heating time is not particularly limited, and is preferably in the range of 20 to 40 minutes, more preferably in the range of 25 to 35 minutes.

In the present invention, at least one of the primer coating composition (X) and the base coating composition (Y) preferably contains an imino-containing melamine resin having a weight average molecular weight of 400-4000. At least one of the primer coating composition (X) and the base coating composition (Y) preferably contains a matte pigment. At least one of the primer coating composition (X) and the base coating composition (Y) is preferably a solvent-based coating composition.

In the present invention, an adhesive layer having an adhesive may be provided on the resulting multilayer coating film. The adhesive is not particularly limited, and for example, an adhesive containing a moisture-curable isocyanate is preferably generally used in order to bond glass members such as windshields.

Windshields are window elements for vehicles, including, for example, front windows, rear windows, sun screens, and the like. The glass member may be inorganic glass, or may be plexiglass. Examples of the resin glass include those made of a transparent resin such as a polycarbonate resin or an acrylic resin. Examples of vehicles include any type of vehicle such as automobiles and trains, airplanes, submarines, and the like.