阅读说明：本技术 用于将电工钢带电绝缘的无铬无磷酸盐涂层 (Chromium-free phosphate-free coating for electrically insulating electrical steel ) 是由 A·德泽尤 T·布赖登 A·阿诺尔德 R·赫希施特拉特 V·盖克 于 2018-12-07 设计创作，主要内容包括：本发明涉及一种通过使用无磷酸盐的含水分散体在电工钢带上提供电绝缘和抗腐蚀的涂层的方法。本发明还涉及这种含水分散体,所述含水分散体特别适用于在电工钢带上提供抗腐蚀和电绝缘的涂层。本发明的含水分散体基本上不含磷酸盐和有机化合物,包含溶解在水中的硅酸盐作为形成涂层的无机粘结剂,以及元素钛和铝的氧化物颜料的混合物。本发明还涉及层合的电工钢带,其由根据本发明制备的电工钢带制成,或由涂布有根据本发明的含水分散体的电工钢带制成。(The invention relates to a method for providing an electrically insulating and corrosion-resistant coating on electrical steel strip by using phosphate-free aqueous dispersions. The invention also relates to such aqueous dispersions which are particularly suitable for providing corrosion-resistant and electrically insulating coatings on electrical steel strip. The aqueous dispersions of the invention are substantially free of phosphates and organic compounds, comprise silicates dissolved in water as inorganic binders for forming coatings, and a mixture of oxide pigments of the elements titanium and aluminum. The invention also relates to a laminated electrical steel strip produced from an electrical steel strip produced according to the invention or produced from an electrical steel strip coated with an aqueous dispersion according to the invention.)

1. A method of coating an electrical steel strip, wherein a wet film of a chromium and phosphate free aqueous composition is applied to at least part of the surface of the electrical steel strip and then dried, wherein the composition comprises:

A) at least 15% by weight, but preferably not more than 40% by weight, of silicates dissolved in water, in the form of SiO₂Calculating;

B) at least 4% by weight, but preferably not more than 15% by weight, calculated as Na, of sodium and/or potassium ions dissolved in water; and

C) at least 1% by weight, but preferably not more than 10% by weight, of at least one water-insoluble oxide pigment.

2. The method according to claim 1, wherein the chromium-free phosphate-free aqueous composition comprises sodium ions or potassium ions alone or as component B), and the Na: K mass ratio is greater than 10:1 or less than 1: 10.

3. The method according to one or both of the preceding claims, characterized in that the chromium-and phosphate-free aqueous composition is obtainable by mixing one or more water glass solutions, each comprising the empirical formula M, with a corresponding amount of the at least one oxide pigment₂O·nSiO₂Wherein n is a natural number of at least 2.5 but not more than 4.5 and M is selected from sodium or potassium.

4. The process according to one or more of the preceding claims, characterized in that as component B) the water-insoluble oxide pigment is selected from the elements Mg, Ca, Al, Si, Mn, Zn, Ti and/or Zr, preferably from the elements Al, Ti and/or Zr, very particularly preferably from the elements Al and/or Ti.

5. The process according to claim 4, characterized in that as component B) the oxide pigment is selected from the group consisting of elemental Ti and elemental Al, Ti: the Al mass ratio is preferably in the range of 70:30 to 30:70, particularly preferably in the range of 60:40 to 40: 60.

6. The method according to one or more of the preceding claims, characterized in that in the chromium-free phosphate-free aqueous composition the proportion of organic compounds having a boiling point below 150 ℃ at 1 atmosphere is below 4 wt. -%, preferably below 1 wt. -%, particularly preferably below 0.5 wt. -%, very particularly preferably below 0.1 wt. -%.

7. The method according to one or more of the preceding claims, characterized in that CO is used₂The proportion of TOC in the chromium-and phosphate-free aqueous composition is calculated to be less than 50g/kg, preferably less than 10g/kg, particularly preferably less than 1 g/kg.

8. The method according to one or more of the preceding claims, characterized in that the wet film is dried by supplying heat, preferably such that a peak metal temperature of at least 200 ℃, particularly preferably at least 250 ℃, but preferably not more than 500 ℃, particularly preferably not more than 400 ℃ is reached.

9. The method according to one or more of the preceding claims, characterized in that the wet film is applied in such an amount that the layer thickness of the dry film after drying amounts to at least 0.5 μm, preferably at least 1 μm, but preferably not more than 5 μm.

10. Method according to one or more of the preceding claims, characterized in that said electrical steel strip is made of steel, wherein the proportion of silicon is in the range of 0.2-4.5% by weight and the proportion of carbon is less than 0.05% by weight.

11. The method of claim 12 wherein said electrical steel strip is non-grain oriented.

12. An aqueous dispersion comprising:

A) at least 15% but not more than 40% by weight of silicates dissolved in water, in the form of SiO₂Calculating;

B) at least 4% but not more than 15% by weight of sodium and/or potassium ions dissolved in water, calculated as Na;

C) at least 1 wt.% in total but not more than 10 wt.% in total of a water-insoluble oxide pigment comprising an oxide pigment of the element Ti and the element Al;

D) less than 10mg/kg of phosphate as PO₄Calculating;

E) TOC content of less than 10g/kg, in CO₂Calculating the amount of (c);

the aqueous dispersion is preferably obtained by mixing one or more water glass solutions, each comprising the empirical formula M, with a corresponding amount of the water-insoluble oxide pigment₂O·nSiO₂Wherein n is a natural number of at least 2.5 but not more than 4.5, and M is selected from sodium or potassium.

13. Laminated electrical steel strip comprising a plurality of electrical steel strip portions which are laid one on top of the other and welded to each other at least on one side, preferably on both sides, and which are provided with a coating consisting of silicates and oxide pigments of the elements Ti and Al, wherein the coating on the electrical steel strip portions is preferably obtainable by a process according to one or more of the preceding claims 5-11.

Technical Field

The invention relates to a method for providing an electrically insulating and corrosion-resistant coating on electrical steel strip (electrical steelstrip) by using a phosphate-free aqueous dispersion. The invention further relates to aqueous dispersions which are particularly suitable for providing electrical insulation and corrosion-resistant coatings on electrical steel strips. The aqueous dispersions of the invention are substantially free of phosphates and organic compounds, comprise silicates dissolved in water as inorganic binders for forming coatings, and a mixture of oxide pigments of the elements titanium and aluminum. The subject of the invention is also a laminated electrical steel strip produced from an electrical steel strip produced according to the process of the invention or produced from an electrical steel strip coated with an aqueous dispersion according to the invention.

Background

In terms of quantity and value, electrical steel sheets (electrical steel sheet) are the most important soft magnetic material with an annual production of about 1000 ten thousand tons in the world. They can be subdivided into non-grain oriented and grain oriented materials according to their properties. Electrical steel sheets and strips refer in the narrow sense to cold-rolled strips made of iron-silicon alloys and to laminations (laminations) cut or punched from them for the production of the magnetic circuits of electrical machines, i.e. the iron cores of generators, motors, transformers, relays, contactors, chokes, ignition coils, electricity meters and controllable deflection magnets. Grain-oriented electrical steel strip is an important material in the production of energy-saving transformers. Grain-oriented electrical steel strip can be found in layered, wound or stamped form as the core material for power distribution and power transformers. On the other hand, non-grain oriented electrical steel strip is used without the need for anisotropic soft magnetic properties and particularly low core losses. The non-grain oriented steel strip is mainly used for generators, motors, contactors, relays and miniature transformers.

The production of grain-oriented electrical steel strip is described in various ways in the prior art, for example in european patent application EP 1752548 a 1. Typically, the final annealed cold rolled strip is typically corrosion protected prior to storage and shipping to the customer. Numerous pretreatment methods are known in the prior art which provide suitable coatings for transport protection.

Coating compositions for electrically insulating grain-oriented electrical steel strip are known in the art and typically comprise chromium and optionally additional inorganic or organic binders which may be selected from phosphates, silicates and/or resins. Chromium-containing compositions are described in published application DE 2247269 and are also suitable for pretreatment to improve coating adhesion prior to application of organic coatings to electrical steel strip for the production of stamped laminated cores, as is evident from published application DE 2146344. It is also available to formulate compositions completely free of chromium for environmental hygiene reasons, as described for example in EP 1967612 a1, in which they are present in the form of compositions with organic resins and based on polysiloxane copolymers, as coatings on electrical steel strips, imparting both corrosion resistance and high electrical resistance.

More recently, purely inorganic compositions for applying electrically insulating and corrosion-resistant coatings to electrical steel strips without the use of chromium compounds or water-soluble phosphates have also been described. For example, EP 2752503 a1 describes a completely chromate-free, water-based formulation consisting of a mixture of silanes comprising at least one silane having at least one non-hydrolyzable functional group, and preferably particulate silica. Such compositions have the advantage that they are largely free of problems from an environmental hygiene point of view, since they contain neither chromium compounds nor phosphates, or organic solvents, or components released into the environment during application or baking.

Thus, there remains a need for inexpensive, alternative chromium-and phosphate-free coating compositions that, inter alia, do not use organic binders and can therefore be formulated completely without solvents. It is also important that these compositions have high electrical conductivity, good coatability, and good weldability, particularly for producing laminated iron cores, as coatings on electrical steel strips.

Disclosure of Invention

The inventors of the present invention have now surprisingly found that by comprising an aqueous dispersion of a specific silicate dissolved in water in the presence of a water-insoluble oxide pigment, the desired required properties can be met.

Accordingly, in a first aspect, the present invention relates to a method of coating an electrical steel strip, wherein a wet film of a chromium and phosphate free water based composition is applied to at least part of the surface of the electrical steel strip, followed by drying, wherein the composition comprises:

A. at least 15% by weight, but preferably not more than 40% by weight, of silicates dissolved in water, in the form of SiO₂Calculating;

B. at least 4% by weight, but preferably not more than 15% by weight, calculated as Na, of sodium and/or potassium ions dissolved in water; and

C. at least 1% but preferably not more than 10% by weight of at least one water-insoluble oxide pigment.

According to the invention, the term "electrical steel strip" includes those types of steel in strip form, which, due to their alloy composition of silicon and/or aluminium and their specific production method, have a coercive field strength of less than 1000A/m and are therefore considered soft magnetic. In a preferred embodiment of the method according to the invention, the electrical steel strip is made of steel, wherein the proportion of silicon is in the range of 0.2-4.5 wt.% and the proportion of carbon is less than 0.05 wt.%. In DIN EN 10106: the 2016-03 standard, in the context of the present invention, makes it particularly preferable for the treated electrical steel strip to be non-grain oriented.

In the context of the present invention, a composition is "aqueous-based" if its components are dissolved or dispersed in an aqueous phase and the water content is at least 40% by weight.

In the context of the present invention, if the composition comprises less than 1g/kg, preferably less than 01g/kg, particularly preferably less than 0.01g/kg, of phosphate (as PO)₄Calculated), the composition is "phosphate-free".

In the context of the present invention, a composition is "chromium-free" if it contains less than 1g/kg, preferably less than 0.1g/kg, particularly preferably less than 0.01g/kg, of chromium compounds, calculated as Cr.

In particular, water glass and water glass solutions can be used as a source of silicate according to component a), which is dissolved in water and contained in the chromium-free phosphate-free aqueous composition according to the method of the invention, i.e. a glassy, i.e. amorphous, water-soluble silicate solidified from the melt or an aqueous solution thereof. Thus, in a preferred embodiment of the process according to the invention, a chromium-and phosphate-free aqueous composition is obtained by mixing one or more water glass solutions, each comprising the empirical formula M, with a corresponding amount of at least one oxide pigment₂O·nSiO₂Wherein n is a natural number of at least 2.5, preferably at least 3.0, particularly preferably at least 3.5, but not more than 4.5, preferably not more than 4.0, and M is selected from sodium or potassium. This ensures optimal cross-linking of the inorganic binder matrix and optimal embedding of the oxide particles, which results in a uniform coating with low surface conductivity but easy soldering. It is also possible to include an amount of lithium water glass without adversely affecting the binder matrix, but their presence is not preferred from an economic point of view, in a preferred embodiment the proportion of lithium in the chromium-free phosphate-free aqueous composition is less than 1% by weight, particularly preferably less than 0.1% by weight, very particularly preferably less than 0.01% by weight.

For this purpose, it is also advantageous if the oxide pigments have a D90 value of not more than 500nm, preferably not more than 300nm, particularly preferably not more than 200 nm. The D90 value represents the particle size of 90% by volume of the dispersed oxide pigment below the stated value as a 1% by weight aqueous dispersion in ammonia buffer (pH 10). The D90 value is determined from a volume-weighted cumulative particle size distribution, where the particle size distribution curve can be measured using static light scattering methods.

According to the invention, the term "oxide pigment" covers all pigments which, in addition to metallic or semimetallic elements, also consist essentially of oxygen, wherein the qualifier "essentially" allows the pigment to comprise up to 10 at% but preferably less than 5 at% of other non-metallic elements.

In the process according to the invention, the oxide pigment contained in the chromium-free phosphate-free aqueous composition is "water-insoluble", i.e. at a temperature of 60 ℃, per kg of deionized water (k)<1μScm^-1) Less than 1 gram of pigment may be dissolved. The oxide pigment is preferably water-insoluble and alkali-resistant, i.e. its solubility in aqueous ammonia buffer solution (pH 10) is less than 1g pigment/kg buffer solution at a temperature of 60 ℃.

In the process according to the invention, preferred oxide pigments are oxide pigments of the elements Mg, Ca, Al, Si, Mn, Zn, Ti and/or Zr, particularly preferably of the elements Al, Ti and/or Zr, very particularly preferably of the elements Al and/or Ti, selected, for example, from at least 90% by weight of Al₂O₃And/or TiO₂The pigment of the composition. In particular, the mixture of oxide pigments of the elements Ti and Al gives the coating produced according to the process of the invention very good weldability at sufficiently high electrical resistances. In the context of the present invention, it is therefore preferred that in the process according to the invention the chromium-free phosphate-free composition comprises as component B) an oxide pigment of the elements Ti and Al, preferably the proportion of the elements Ti and Al is at least 50 at.%, particularly preferably at least 80 at.%, very particularly preferably at least 90 at.%, based on the total amount of metallic and semimetallic elements in the oxide pigment; the mass ratio of Ti to Al is preferably in the range of 70:30 to 30:70, particularly preferably in the range of 60:40 to 40: 60.

In the process according to the invention, for good solderability of the coatings obtained from the chromium-and phosphate-free aqueous composition, it is preferred that the composition comprises sodium ions or potassium ions alone or as component B) and that the mass ratio Na: K is greater than 10:1 or less than 1: 10. Such compositions are preferably obtained by mixing various water glass solutions, using solutions containing the empirical formula Na₂O·nSiO₂And a water glass solution containing a silicate of the empirical formula K₂O·nSiO₂Wherein n is a natural number of at least 2.5, preferably at least 3.0, particularly preferably at least 3.5, but not more than 4.5, in particular not more than 4.0.

The chromium-free phosphate-free composition for use in the method according to the present invention can be formulated without a solvent, and also does not require the addition of an organic resin to improve the properties with respect to weldability and low surface conductivity or to increase coatability. In order to improve the latter properties, it may be advantageous to add only organosilanes, so that it may be preferred that the chromium-free phosphate-free aqueous composition in the process according to the invention additionally comprises at least one organosilane having at least one hydrolyzable substituent and at least one non-hydrolyzable substituent.

During the condensation and/or hydrolysis, the hydrolyzable substituents of the organosilane cleave off an alcohol which preferably has a boiling point of 100 ℃ at an atmospheric pressure of 1 bar. Thus, in a preferred embodiment, in the composition according to the invention, the hydrolysable substituents of the organosilane are selected from methoxy, ethoxy and/or propoxy groups, in particular methoxy groups.

The non-hydrolyzable substituent has a Si-C covalent bond on the silicon atom. Suitable organosilanes may have one or more alkyl groups, one or more glycidoxyalkyl groups, or one or more amino groups (preferably primary amino groups). Particularly suitable representatives of organosilanes are selected from aminosilanes having the general structural formula (I):

H₂N-[(CH₂)_mNH]_y(CH₂)_n-Si-X₃(I)

wherein the substituents X are each, independently of one another, selected from alkoxy groups having not more than four, preferably not more than two, carbon atoms, where m and n are each, independently of one another, an integer from 1 to 4 and y is an integer from 0 to 8, preferably from 1 to 5, such as, for example, 3- (diethylenetriamine) propyltrimethoxysilane, 3- (ethylenediamine) propyltrimethoxysilane, 3-amino-propyltrimethoxysilane, 3- (diethylenetriamine) propyltriethoxysilane, 3- (ethylenediamine) propyltriethoxysilane and 3-aminopropyltriethoxysilane, particularly preferably 3- (diethylenetriamine) propyl-trimethoxysilane.

However, in the process according to the invention, it is still preferred, where possible, to use a chromium-and phosphate-free aqueous composition which does not release any volatile organic compounds during crosslinking and curing of the coating. In a preferred embodiment of the process according to the invention, the proportion of organic compounds having a boiling point below 150 ℃ at 1 atmosphere in the chromium-free phosphate-free aqueous composition is less than 4% by weight, preferably less than 1% by weight, particularly preferably less than 0.5% by weight, very particularly preferably less than 0.1% by weight.

In the context of the present invention, the process according to the invention is also preferably carried out with CO in an aqueous composition in which no chromium or phosphate is present₂The calculated proportion of TOC ("Total Organic carbon") is less than 50g/kg, preferably less than 10g/kg, particularly preferably less than 1g/kg, wherein the proportion of TOC can be determined by NIR analysis after combustion at 900 ℃ in a nitrogen stream and in the presence of a copper oxide catalyst. The preferred low TOC content indicates that the chromium-and phosphate-free aqueous composition ensures adequate coatability and passivation of the electrical steel strip to be coated in the process according to the invention without the addition of organic binders.

The pH of the chromium-and phosphate-free aqueous composition is preferably alkaline, particularly preferably greater than 8.5, but preferably less than 11, particularly preferably less than 10.5. In the context of the present invention, the pH corresponds to the negative decimal logarithm of the hydronium ion activity determined directly in the composition with a pH sensitive glass electrode at 20 ℃.

In the process according to the invention, the chromium and phosphate-free aqueous composition is applied as a wet film and then dried, preferably by supplying heat. For this purpose, the electrical steel strip is brought into contact with the composition. Contacting the composition with the surface of the electrical steel strip can be accomplished by all known methods including, but not limited to, spraying, dipping, rolling or roll-coating, and printing. The layer thickness of the wet film is preferably 0.5 to 10 μm. In particular, the wet film is applied in such an amount that the layer thickness of the dry film after drying amounts to at least 0.5 μm, preferably at least 1 μm, but preferably not more than 5 μm. The wet film is preferably dried by heating the electrical steel strip so as to reach a peak metal temperature of at least 200 ℃, particularly preferably at least 250 ℃, but preferably not more than 500 ℃, particularly preferably not more than 400 ℃. The peak metal temperature is preferably maintained for 1 to 200 seconds, preferably 10 to 60 seconds. The low baking temperature and the possibility of formulating a chromium-free phosphate-free aqueous composition without the need for organic binder components provide a methodical advantage in that the desired peak metal temperature, and hence high heating rate, can be quickly achieved at high furnace temperatures without fear of long furnace downtime during short process shutdowns in continuous operation of the coating system and without fear of coating quality degradation due to degradation of any organic binder components when the peak metal temperature eventually rises.

For producing, for example, cores for rotors, stators or generators, steel sheets are punched out of the coated electrical steel strip as described above, pressed together in a stack and welded. The invention therefore also comprises a laminated electrical steel strip comprising a multiplicity of electrical steel strip portions which are arranged one on top of the other and are welded to one another at least on one side, preferably on both sides, and are provided with a coating which consists of a silicate and oxide pigments of the elements Ti and Al, wherein the coating on the electrical steel strip portions is preferably obtainable by the above-described process according to the invention using a chromium-and phosphate-free aqueous composition comprising oxide pigments of the elements Ti and Al as component B).

In another aspect, the present invention relates to an aqueous dispersion which is particularly suitable for application to electrical steel strip in order to form an electrically insulating coating having excellent weldability. Such aqueous dispersions according to the invention comprise:

A. at least 15% but not more than 40% by weight of silicates dissolved in water, in the form of SiO₂Calculating;

B. at least 4% but not more than 15% by weight of sodium and/or potassium ions dissolved in water, calculated as Na; and

C. at least 1 wt.% but not more than 10 wt.% total of a water-insoluble oxide pigment of elemental Ti and elemental Al;

D. less than 10mg/kg of phosphate as PO₄Calculating;

E. TOC content of less than 10g/kg, in CO₂Calculating the amount of (c);

the aqueous dispersion is preferably obtainable by mixing one or more water glass solutions, each comprising the empirical formula M, with the corresponding amount of water-insoluble oxide pigment₂O·nSiO₂Wherein n is a natural number of at least 2.5 but not more than 4.5, and M is selected from sodium or potassium.

Further preferred embodiments of the aqueous dispersion can be found in the chromium and phosphate free aqueous composition described in the context of the first aspect of the present invention.

Practical examples:

table 1 lists formulations used to provide an insulating coating on non-grain oriented steel sheets (M700-50A) and the solderability and volume resistance of these formulations were determined.

The compositions were prepared by dispersing the corresponding pigments into a liquid base formulation consisting of sodium and/or potassium waterglass and applied to steel panels using rollers at a wet film thickness of 1.4 μm, then dried in an oven at 350 ℃ until a peak metal temperature of 250 ℃ was reached.

It has been shown that only the pigmented water glass formulations according to the invention have a sufficiently high volume resistance; surprisingly, solderability was still provided (see E1-E5 in comparison to CE1-CE 3). Furthermore, those formulations in which a certain amount of pigmentary titanium oxide is contained are advantageous for weldability (see E3 in comparison with E4 and E5). In addition, formulations consisting of only one water glass have a higher volume resistance as a coating on steel plates and are therefore better than mixtures of water glasses (see E1 and E2 in comparison with E5).