Coating composition for laminated steel sheet

Abstract

This coating composition for laminated steel sheet comprises (A) a (meth)acrylic resin, (B) an epoxy resin, and (C) a polyamine-based curing agent, wherein the (meth)acrylic resin (A) contains a constituent unit derived from a monomer having a carboxy group at a ratio of 5%-15% by mass with respect to all constituent units, the epoxy resin (B) has an epoxy equivalent of 1000-3000 g / eq, the content of the epoxy resin (B) is 12-120 parts by mass with respect to 100 parts by mass of the (meth)acrylic resin (A), the molar ratio of active hydrogen in the polyamine-based curing agent (C) to the epoxy groups in the epoxy resin (B) is 0.7-3.9, and the molar ratio of the carboxy groups in the (meth)acrylic resin (A) to active hydrogen in the polyamine-based curing agent (C) is 0.4-7.5.

Description

Coating Composition for Laminated Steel Sheets

[0001] The present disclosure relates to a coating composition for laminated steel sheets.

[0002] For motors, high efficiency, miniaturization and high output are important requirements. Motor core materials are required to have high magnetic permeability and low iron loss, and deterioration of core magnetic properties is a problem in core processing. In addition, low noise and low vibration of motors are becoming increasingly important from the perspective of environmental protection, and high-precision positioning control is required for motors. Generally, laminated steel sheets obtained by laminating electrical steel sheets are used for motor cores.

[0003] Conventionally, methods such as welding, caulking, and bolt tightening have been used for fixing electrical steel sheets to each other when manufacturing laminated steel sheets. However, these fixing methods are accompanied by deterioration of magnetic properties. In addition, it is difficult to say that the laminated steel sheets manufactured by these fixing methods have sufficient mechanical rigidity, so there are concerns about the generation of noise and vibration. Therefore, in recent years, a method for manufacturing laminated steel sheets using electrical steel sheets on the surface of which a coating exhibiting adhesiveness by heating and pressing is formed in advance (also referred to as "electrical steel sheet with adhesive coating") has been adopted. In this method, first, a coating agent for forming an adhesive coating on the surface of an electrical steel sheet (also referred to as "coating agent for forming adhesive coating") is applied, then dried at a high temperature (for example, 170°C) to produce an electrical steel sheet with an adhesive coating. After the produced electrical steel sheet with adhesive coating is punched or sheared, it is laminated, and then pressed and fixed at a high temperature (for example, 200°C). Compared with laminated steel sheets manufactured by fixing electrical steel sheets to each other by welding or the like, laminated steel sheets manufactured using electrical steel sheets with adhesive coating have less deterioration of magnetic properties due to processing during fixing, and have higher core rigidity, so problems of noise and vibration tend to be less likely to occur (see Kai Dori, Takeda Kazutoshi, Wakisaka Takeaki, Mizogami Masato, "On Various Properties of Adhesive Electrical Steel Sheet Cores", The Transactions of the Institute of Electrical Engineers of Japan, D, Vol. 119, No. 7, pp. 1010-1015, 1999).

[0004] Various reports have been made on electrical steel sheets with adhesive coatings. For example, Japanese Patent Application Laid-Open No. 7-256206 discloses that on at least one surface of an electrical steel sheet, (A) a resin having a glass transition point of 80°C to 150°C and containing, in the molecule, -OH, -COOH, >NH, -NH ２, and >CH ２ A technique for producing a heat-bondable surface-coated electromagnetic steel sheet is disclosed, comprising applying an aqueous mixture mainly composed of (A) an aqueous solution or emulsion of epoxy resin and / or phenolic resin, (B) an aqueous solution of an aqueous block isocyanate compound whose block groups dissociate upon heating and react with component (A) or both components (A) and (B), and baking the mixture so that the reaction between components (A), (B) and component (C) results in a gelation rate (degree of hardening) of the film after baking being in the range of 10% to 90%.

[0005] In recent years, in order to improve the performance of laminated steel sheets, progress has been made in thinning laminated steel sheets. As one method of thinning laminated steel sheets, the omission of the insulating coating, which was conventionally provided on the electrical steel sheet separately from the adhesive coating, is being considered. Generally, the insulating coating has the functions of insulating and corrosion-resistant properties. Therefore, the adhesive coating used for electrical steel sheets without an insulating coating needs to have the functions of adhesion, insulating, and corrosion-resistant properties. On the other hand, since acrylic resins are resins with relatively high polarity, adhesive coatings whose resin component is acrylic resin tend to have high permeability to moisture and air and poor corrosion resistance. One method to improve corrosion resistance is to increase the crosslinking density of the adhesive coating. Increasing the crosslinking density of the adhesive coating reduces the permeability to moisture and air, thereby improving corrosion resistance. However, increasing the crosslinking density of the adhesive coating can be a factor in reducing the adhesion between adhesive coatings. Therefore, improving the adhesion of the adhesive film and improving its corrosion resistance are mutually exclusive, making it difficult to achieve both simultaneously.

[0006] This disclosure has been made in view of the circumstances described above. One embodiment of this disclosure aims to solve the problem of providing a coating composition for laminated steel sheets that can form a coating film exhibiting high shear adhesion and excellent corrosion resistance, even when used on electrical steel sheets that do not have an insulating coating formed on them.

[0007] The following embodiments are included as specific means for solving the problem: <1> A coating composition for laminated steel sheets comprising: (meth)acrylic resin (A) containing constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total constituent units; epoxy resin (B) having an epoxy equivalent of 1000 g / eq to 3000 g / eq; and a polyamine curing agent (C), wherein the content of the epoxy resin (B) is 12 to 120 parts by mass per 100 parts by mass of the (meth)acrylic resin (A); the ratio of the number of moles of active hydrogen in the polyamine curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is 0.7 to 3.9; and the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) is 0.4 to 7.5. <2> The coating composition for laminated steel sheets according to <1>, wherein the (meth)acrylic resin (A) contains constituent units derived from an alkyl (meth)acrylate monomer. <3> The coating composition for laminated steel sheets according to <1> or <2>, wherein the (meth)acrylic resin (A) contains constituent units derived from a monomer having a ring structure. <4> The coating composition for laminated steel sheets according to <3>, wherein the constituent units derived from the monomer having a ring structure are constituent units derived from styrene. <5> The coating composition for laminated steel sheets according to any one of <1> to <4>, wherein the shape of the (meth)acrylic resin (A) is particulate. <6> The coating composition for laminated steel sheets according to any one of <1> to <5>, wherein the shape of the epoxy resin (B) is particulate. <7> The coating composition for laminated steel sheets according to <5> or <6>, further comprising water.

[0008] According to one embodiment of the present disclosure, a coating composition for laminated steel sheets is provided that can form a coating film exhibiting high shear adhesion and excellent corrosion resistance even when used on electrical steel sheets that do not have an insulating coating formed on them.

[0009] The coating compositions for laminated steel sheets of this disclosure will be described in detail below. The requirements described below may be based on typical embodiments of this disclosure, but this disclosure is not limited to such embodiments and can be modified as appropriate within the scope of the purpose of this disclosure.

[0010] In this disclosure, numerical ranges indicated using "~" mean ranges that include the numerical values ​​before and after "~" as the lower and upper limits, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0011] In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0012] In this disclosure, the amount of each component in the composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition.

[0013] In this disclosure, unless otherwise specified, "solids" means components other than the solvent contained in the composition, and "solvent" means water and organic solvents. For example, if the solvent contained in the composition is only water, then "solids" means components other than water contained in the composition; if the solvent contained in the composition is only an organic solvent, then "solids" means components other than the organic solvent contained in the composition; and if the solvent contained in the composition is both water and an organic solvent, then "solids" means components other than water and organic solvents contained in the composition.

[0014] In this disclosure, "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group. In this disclosure, "(meth)acrylic resin" means a resin that contains constituent units derived from a (meth)acrylic monomer, and in which the proportion of constituent units derived from a (meth)acrylic monomer is 50% by mass or more.

[0015] In this disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic," "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate," and "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl."

[0016] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0017] In this disclosure, "constituent units derived from monomers" means constituent units formed by the addition polymerization of monomers.

[0018] In this disclosure, "mass%" and "weight%" are synonymous, and "parts by mass" and "parts by weight" are synonymous. Also, in this disclosure, "monomer" and "monomer" are synonymous, and "polymer" and "polymer" are synonymous.

[0019] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved.

[0020] [Coating Composition for Laminated Steel Sheets] The coating composition for laminated steel sheets of the present disclosure (hereinafter also simply referred to as "coating composition") comprises a (meth)acrylic resin (A) containing constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total constituent units, an epoxy resin (B) having an epoxy equivalent of 1000 g / eq to 3000 g / eq, and a polyamine curing agent (C), wherein the content of the epoxy resin (B) is 12 to 120 parts by mass per 100 parts by mass of the (meth)acrylic resin (A), the ratio of the number of moles of active hydrogen in the polyamine curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is 0.7 to 3.9, and the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) is 0.4 to 7.5. The coating composition of this disclosure is a coating composition for use on laminated steel sheets, and more specifically, a composition for coating the surface of electrical steel sheets used in the manufacture of laminated steel sheets. Having the above-described configuration, the coating composition of this disclosure enables the formation of a coating film exhibiting high shear adhesion and excellent corrosion resistance, even when used on electrical steel sheets that do not have an insulating film formed on them.

[0021] [(meth)acrylic resin (A)] The coating composition of this disclosure contains a (meth)acrylic resin (A) which contains constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total constituent units. In this disclosure, "(meth)acrylic resin (A) which contains constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total constituent units" is also simply referred to as "(meth)acrylic resin (A)". The coating composition of this disclosure may contain one type of (meth)acrylic resin (A) alone, or it may contain two or more types.

[0022] In the coating composition of this disclosure, the (meth)acrylic resin (A) may exist dissolved in the medium or dispersed in the medium. When the (meth)acrylic resin (A) is dispersed in the medium, the shape of the (meth)acrylic resin (A) may be particulate. Generally, when the resin in a coating composition exists in particulate form, voids tend to form between the resin particles when a coating film is formed. When voids form between resin particles, water and air can easily permeate, which reduces the corrosion resistance of the coating film. In contrast, the coating composition of this disclosure can form a coating film that exhibits excellent corrosion resistance even when the shape of the (meth)acrylic resin (A) is particulate.

[0023] <Constituent units derived from monomers having carboxyl groups> The (meth)acrylic resin (A) contains constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total number of constituent units. The type of monomer having carboxyl groups is not particularly limited. Examples of monomers having carboxyl groups include monomers having at least one carboxyl group and an ethylenically unsaturated group in one molecule. Examples of ethylenically unsaturated groups include vinyl groups, allyl groups, vinylphenyl groups, (meth)acrylamide groups, and (meth)acryloyl groups.

[0024] Specific examples of monomers having a carboxyl group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≈2) monoacrylate], and succinic acid derivatives (e.g., 2-acryloyloxyethyl succinic acid). The monomer having a carboxyl group preferably contains (meth)acrylic acid, more preferably (meth)acrylic acid, and even more preferably methacrylic acid.

[0025] The (meth)acrylic resin (A) may contain one or more constituent units derived from monomers having a carboxyl group.

[0026] The content of constituent units derived from monomers having carboxyl groups in (meth)acrylic resin (A) is 5% to 15% by mass relative to the total constituent units of (meth)acrylic resin (A). When the content of constituent units derived from monomers having carboxyl groups in (meth)acrylic resin (A) is 5% by mass or more relative to the total constituent units of (meth)acrylic resin (A), the adhesion between the coating film and the electrical steel sheet becomes sufficiently high. In addition, when the electrical steel sheets are heat-pressed together (for example, pressed together at 200°C), the reaction between carboxyl groups derived from (meth)acrylic resin (A) and epoxy groups derived from epoxy resin (B), and the reaction between carboxyl groups derived from (meth)acrylic resin (A) and amino groups derived from polyamine-based curing agent (C) occur, resulting in a sufficiently high crosslink density of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. From this viewpoint, the content of constituent units derived from monomers having carboxyl groups in (meth)acrylic resin (A) is preferably 8% by mass or more, and more preferably 10% by mass or more, relative to the total constituent units of (meth)acrylic resin (A). When the content of constituent units derived from monomers having carboxyl groups in (meth)acrylic resin (A) is 15% by mass or less relative to the total constituent units of (meth)acrylic resin (A), the crosslinking reaction does not proceed excessively when the coating composition is dried at a high temperature (e.g., 170°C), and a coating film with appropriate softness is formed. Because the coating film has appropriate softness, the coating films fuse together sufficiently when the electrical steel sheets are heat-pressed together (e.g., pressed together at 200°C). Therefore, the coating film tends to exhibit high shear adhesion. From this viewpoint, the content of constituent units derived from monomers having carboxyl groups in (meth)acrylic resin (A) is preferably 13% by mass or less relative to the total constituent units of (meth)acrylic resin (A). In one embodiment, the content of constituent units derived from monomers having a carboxyl group in the (meth)acrylic resin (A) may be 8% to 15% by mass, 8% to 13% by mass, or 10% to 15% by mass, relative to the total constituent units of the (meth)acrylic resin (A).

[0027] <Constituent units derived from (meth)acrylate alkyl ester monomers> The (meth)acrylic resin (A) preferably contains constituent units derived from (meth)acrylate alkyl ester monomers, for example, from the viewpoint of adjusting the glass transition temperature of the (meth)acrylic resin (A). In this disclosure, "(meth)acrylate alkyl ester monomer" refers to an (meth)acrylate alkyl ester monomer that does not have a carboxyl group. In other words, in this disclosure, "(meth)acrylate alkyl ester monomer having a carboxyl group" is classified as a monomer having a carboxyl group.

[0028] The type of alkyl (meth)acrylate monomer is not particularly limited. The alkyl (meth)acrylate monomer may be an alkyl acrylate monomer or an alkyl methacrylate monomer. The alkyl group of the alkyl (meth)acrylate monomer may be unsubstituted or substituted, but it is preferable that it be unsubstituted. The alkyl group of the alkyl (meth)acrylate monomer may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate monomer is preferably 1 to 18, more preferably 1 to 12, even more preferably 1 to 8, and particularly preferably 1 to 4.

[0029] Specific examples of alkyl (meth)acrylate monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

[0030] The alkyl (meth)acrylate monomer preferably contains at least one of methyl methacrylate and n-butyl acrylate, more preferably at least one of methyl methacrylate and n-butyl acrylate, and even more preferably methyl methacrylate and n-butyl acrylate.

[0031] If the (meth)acrylic resin (A) contains constituent units derived from alkyl (meth)acrylate monomers, it may contain one type of constituent unit derived from alkyl (meth)acrylate monomers alone, or it may contain two or more types.

[0032] When the (meth)acrylic resin (A) contains constituent units derived from alkyl (meth)acrylate monomers, the content of constituent units derived from alkyl (meth)acrylate monomers in the (meth)acrylic resin (A) is not particularly limited, but for example, it is preferably 35% to 95% by mass, more preferably 45% to 80% by mass, and even more preferably 50% to 60% by mass, relative to the total constituent units of the (meth)acrylic resin (A).

[0033] <Other constituent units> The (meth)acrylic resin (A) may contain constituent units that do not fall under either the constituent units derived from monomers having a carboxyl group or the constituent units derived from alkyl (meth)acrylate monomers (so-called other constituent units).

[0034] Other constituent units include, for example, monomers having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and N-(2-hydroxyethyl)(meth)acrylamide; constituent units having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; constituent units having an alkoxyalkyl (meth)acrylate, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; constituent units having an aromatic monovinyl, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; and constituent units having a vinyl ester, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0035] Other preferred structural units include, for example, those derived from monomers having a ring structure, from the viewpoint of the strength and gloss of the coating film. Examples of structural units derived from monomers having a ring structure include those derived from (meth)acrylate having the above-mentioned aromatic ring, and those derived from the above-mentioned aromatic monovinyl. Of the structural units derived from monomers having a ring structure, those derived from styrene are preferred, for example, from the viewpoint of the strength of the coating film.

[0036] If the (meth)acrylic resin (A) contains other constituent units, it may contain one type of other constituent unit alone or two or more types.

[0037] If the (meth)acrylic resin (A) contains other constituent units, the content of the other constituent units in the (meth)acrylic resin (A) can be set appropriately within a range that does not impair the effect of the coating composition of this disclosure. For example, if the (meth)acrylic resin (A) contains constituent units derived from monomers having a ring structure as other constituent units, the content of constituent units derived from monomers having a ring structure in the (meth)acrylic resin (A) may be 20% to 40% by mass relative to the total constituent units of the (meth)acrylic resin (A).

[0038] <<Glass transition temperature of (meth)acrylic resin (A)>> The glass transition temperature of (meth)acrylic resin (A) is not particularly limited, but from the viewpoint of the cohesive force of (meth)acrylic resin (A) and fusion during thermocompression bonding, it is preferably 70°C to 105°C, and more preferably 80°C to 100°C.

[0039] In this disclosure, the glass transition temperature of the (meth)acrylic resin is measured using a differential scanning calorimetry (DSC). The specific measurement method is as follows: A liquid containing the (meth)acrylic resin is applied to release paper using a 4 mil (101.6 μm) applicator. The applied liquid containing the (meth)acrylic resin is then dried (drying temperature: 105°C, drying time: 10 minutes) to obtain a dried (meth)acrylic resin product. 10 mg of this dried product is placed in an aluminum sample pan (e.g., Tzero Pan (product name) manufactured by T.A. Instrument Japan Co., Ltd.), sealed with an aluminum lid (e.g., Tzero Hermetic Lid (product name) manufactured by T.A. Instrument Japan Co., Ltd.), and the glass transition temperature is measured using a differential scanning calorimetry under the following measurement conditions. In this measurement, the glass transition temperature is defined as the temperature at the intersection of a straight line extending the low-temperature baseline of the obtained DSC curve toward the high-temperature side and a tangent line drawn at the point where the slope of the curve representing the stepwise transition of the glass transition is maximum. As a differential scanning calorimeter, for example, a differential scanning calorimeter manufactured by T.A. Instruments Japan Co., Ltd. (product name: Discovery DSC 2500) can be used. However, the differential scanning calorimeter is not limited to this.

[0040] -Measurement Conditions- Atmosphere: Under air Measurement temperature range: -50°C to 150°C Heating rate: 10°C / min Standard material: Empty sample pan

[0041] The glass transition temperature of (meth)acrylic resin (A) can be adjusted to a desired value, for example, by changing the type and proportion of monomers used as raw materials for (meth)acrylic resin (A).

[0042] <<Content of (meth)acrylic resin (A)>> The content of the (meth)acrylic resin (A) in the coating composition of the present disclosure is not particularly limited. For example, it is preferably from 40% by mass to 88% by mass, more preferably from 50% by mass to 80% by mass, and even more preferably from 60% by mass to 70% by mass, relative to the total solid content in the coating composition.

[0043] In the present disclosure, the "total solid content in the coating composition" means the mass of the residue obtained by removing the solvent from the coating composition.

[0044] [Method for producing (meth)acrylic resin (A)] The method for producing the (meth)acrylic resin (A) is not particularly limited as long as the above-described (meth)acrylic resin (A) can be produced. The (meth)acrylic resin (A) can be produced, for example, by an emulsion polymerization method. Examples of the emulsion polymerization method for producing the (meth)acrylic resin (A) include the methods [1] to [3] shown below. In the present disclosure, a monomer that forms a constituent unit of the (meth)acrylic resin (A) is also referred to as a "monomer component".

[0045] [1] A method in which a monomer component, a surfactant, and water are charged into a reactor equipped with a thermometer, a stirrer, a raw material introduction pipe, a reflux condenser, a nitrogen introduction pipe, and the like, the temperature is raised while stirring under a nitrogen stream, then a polymerization initiator, a reducing agent, and the like are added as appropriate to allow an emulsion polymerization reaction to proceed (a so-called batch charging method). [2] A method in which a surfactant and water are charged into a reactor equipped with a thermometer, a stirrer, a raw material introduction pipe, a reflux condenser, a nitrogen introduction pipe, and the like, the temperature is raised while stirring under a nitrogen stream, then a monomer component is added dropwise, and a polymerization initiator, a reducing agent, and the like are added as appropriate to allow an emulsion polymerization reaction to proceed (a so-called monomer dropping method). [3] After putting a monomer component into a container, the mixture is stirred to prepare a monomer mixture. After putting water and a surfactant into another container, the mixture is stirred to prepare an aqueous surfactant solution. A pre-emulsion is prepared by stirring and emulsifying while adding the mixture of the monomer component to the prepared aqueous surfactant solution. A part of the pre-emulsion and water are charged into a reactor equipped with a thermometer, a stirrer, a raw material introduction pipe, a reflux condenser, a nitrogen introduction pipe, and the like, and the temperature is raised while stirring under a nitrogen stream. After the temperature in the reactor is stabilized, the remaining pre-emulsion is added dropwise while appropriately adding a polymerization initiator, a reducing agent and the like dropwise into the reactor to allow an emulsion polymerization reaction to proceed (a so-called emulsified monomer dropping method). Among these, as the emulsion polymerization method for producing the (meth)acrylic resin (A), for example, from the viewpoint of industrial productivity, the emulsified monomer dropping method of the above [3] is preferred.

[0046] The (meth)acrylic resin (A) obtained by the above emulsion polymerization method is obtained in the form of a dispersion dispersed in a medium containing at least water and a surfactant.

[0047] Since details of the monomer component are as described above, and details of water and the surfactant are as described below, descriptions thereof are omitted here.

[0048] Polymerization initiators are not particularly limited as long as they are used in ordinary emulsion polymerization. Examples of polymerization initiators include persulfates, organic peroxides, and azo compounds. Specific examples of persulfates include ammonium persulfate (also called "ammonium peroxodisulfate"), sodium persulfate, and potassium persulfate. Specific examples of organic peroxides include t-butyl hydroperoxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and t-butyl peroxypivalate. Specific examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitride), and 2,2'-azobis(isobutyric acid)dimethyl.

[0049] In the emulsion polymerization method for producing (meth)acrylic resin (A), one polymerization initiator may be used alone, or two or more may be used.

[0050] The polymerization initiator is used in the amount typically used. The amount of polymerization initiator used is preferably 0.05 parts by mass to 1.00 parts by mass per 100 parts by mass of the total monomer components.

[0051] The reducing agent is not particularly limited, as long as it is one that is commonly used in emulsion polymerization. Examples of reducing agents include sodium metabisulfite, sodium sulfite, sodium bisulfite, sodium pyrosulfite, sodium pyrophosphate, sodium hydroxymethanesulfinate, thioglycolic acid, and sodium thiosulfate.

[0052] In the emulsion polymerization method for producing (meth)acrylic resin (A), one reducing agent may be used alone, or two or more reducing agents may be used.

[0053] The reducing agent is used in the amount typically used. Preferably, the amount of reducing agent used is 0.05 parts by mass to 1.00 parts by mass per 100 parts by mass of the total monomer components.

[0054] In the emulsion polymerization method for producing (meth)acrylic resin (A), the polymerization temperature is, for example, 50°C to 80°C, preferably 60°C to 70°C. The polymerization time is, for example, 5 hours to 9 hours, preferably 6 hours to 8 hours.

[0055] [Epoxy resin (B)] The coating composition of this disclosure comprises epoxy resin (B) having an epoxy equivalent of 1,000 g / eq to 3,000 g / eq. In this disclosure, "epoxy resin (B) having an epoxy equivalent of 1,000 g / eq to 3,000 g / eq" is also simply referred to as "epoxy resin (B)".

[0056] In the coating composition of this disclosure, the epoxy resin (B) may exist in a dissolved state in the medium or in a dispersed state in the medium. When the epoxy resin (B) is dispersed in the medium, the epoxy resin (B) may take the form of particulate matter. Generally, when the resin in a coating composition exists in particulate matter, voids tend to form between the resin particles when a coating film is formed. When voids form between resin particles, water and air can easily permeate, which reduces the corrosion resistance of the coating film. In contrast, the coating composition of this disclosure can form a coating film that exhibits excellent corrosion resistance even when the epoxy resin (B) is in particulate matter.

[0057] The epoxy resin (B) has an epoxy equivalent of 1000 g / eq to 3000 g / eq. When the epoxy equivalent of epoxy resin (B) is 1000 g / eq or more, the crosslinking reaction does not proceed excessively when the coating composition is dried at a high temperature (e.g., 170°C), and a coating film with appropriate softness is formed. Because the coating film has appropriate softness, when electrical steel sheets are heat-pressed together (e.g., pressed together at 200°C), the coating films fuse together sufficiently. Therefore, the coating film tends to exhibit high shear adhesion. From this viewpoint, the epoxy equivalent of epoxy resin (B) is preferably 1200 g / eq or more, and more preferably 1500 g / eq or more. When the epoxy equivalent of epoxy resin (B) is 3000 g / eq or less, when electrical steel sheets are heat-pressed together (for example, pressed at 200°C), reactions occur between epoxy groups derived from epoxy resin (B) and carboxyl groups derived from (meth)acrylic resin (A), and between epoxy groups derived from epoxy resin (B) and amino groups derived from polyamine curing agent (C), resulting in a sufficiently high crosslink density of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. From this viewpoint, the epoxy equivalent of epoxy resin (B) is preferably 2600 g / eq or less, more preferably 2500 g / eq or less, and even more preferably 2200 g / eq or less. In one embodiment, the epoxy equivalent of epoxy resin (B) may be 1200 g / eq to 2600 g / eq, 1200 g / eq to 2500 g / eq, 1200 g / eq to 2200 g / eq, 1500 g / eq to 2600 g / eq, 1500 g / eq to 2500 g / eq, or 1500 g / eq to 2200 g / eq.

[0058] In this disclosure, the epoxy equivalent of the epoxy resin is measured by a method in accordance with JIS K 7236:2009. When using a commercially available epoxy resin, the epoxy equivalent of the epoxy resin shall be based on the catalog value of the commercially available product.

[0059] The type of epoxy resin (B) is not particularly limited as long as it satisfies the epoxy equivalent requirement. Examples of epoxy resin (B) include glycidyl ether type epoxy resins obtained by the reaction of a compound having a hydroxyl group in its molecule with epichlorohydrin; glycidyl ester type epoxy resins obtained by the reaction of a compound having a carboxyl group in its molecule with epichlorohydrin; glycidylamine type epoxy resins obtained by the reaction of a compound having an amino group in its molecule with epichlorohydrin; and the like. Examples of glycidyl ether type epoxy resins include bisphenol type epoxy resins obtained by the reaction of bisphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, and hydrogenated bisphenol A with epichlorohydrin; novolac type epoxy resins obtained by the reaction of novolac resins such as phenol novolac and o-cresol novolac with epichlorohydrin; and the like. Examples of glycidyl ester type epoxy resins include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl dimer acid. Examples of glycidylamine-type epoxy resins include tetraglycidyldiaminodiphenylmethane, tetraglycidylxylenediamine, bis(diglycidylaminomethyl)cyclohexane, and triglycidyl isocyanurate.

[0060] Commercially available epoxy resins can be used as epoxy resin (B). Examples of commercially available epoxy resins (B) include "BECKOPOX EP2307w / 45WAMP" (epoxy equivalent: 1775 g / eq) manufactured by Daicel Ornex Co., Ltd., and "YUKAREZIN NE-307T" (epoxy equivalent: 2250 g / eq) manufactured by Yoshimura Oil Chemical Co., Ltd. "BECKOPOX," "YUKAREZIN," and "ADEKARESIN" are all registered trademarks.

[0061] The coating composition of this disclosure may contain one epoxy resin (B) alone or two or more epoxy resins.

[0062] The epoxy resin (B) content in the coating composition of this disclosure is 12 to 120 parts by mass per 100 parts by mass of (meth)acrylic resin (A). When the epoxy resin (B) content in the coating composition of this disclosure is 12 parts by mass or more per 100 parts by mass of (meth)acrylic resin (A), when the electrical steel sheets are heat-pressed together (for example, pressed at 200°C), reactions occur between epoxy groups derived from epoxy resin (B) and carboxyl groups derived from (meth)acrylic resin (A), and between epoxy groups derived from epoxy resin (B) and amino groups derived from polyamine curing agent (C), resulting in a sufficiently high crosslink density of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. Furthermore, if the epoxy resin (B) content in the coating composition of this disclosure is 12 parts by mass or more per 100 parts by mass of (meth)acrylic resin (A), when the coating composition is dried at a high temperature (for example, 170°C), reactions occur between epoxy groups derived from epoxy resin (B) and carboxyl groups derived from (meth)acrylic resin (A), and between epoxy groups derived from epoxy resin (B) and amino groups derived from polyamine curing agent (C), resulting in a sufficiently high crosslink density of the coating film. As a result, the coating film tends to exhibit excellent corrosion resistance. From the above viewpoint, it is preferable that the epoxy resin (B) content in the coating composition of this disclosure is 15 parts by mass or more per 100 parts by mass of (meth)acrylic resin (A). If the epoxy resin (B) content in the coating composition of this disclosure is 120 parts by mass or less per 100 parts by mass of (meth)acrylic resin (A), the crosslinking reaction does not proceed excessively when the coating composition is dried at a high temperature (for example, 170°C), and a coating film with appropriate softness is formed. The coating film has a moderate degree of flexibility, which allows it to fuse sufficiently with other electrical steel sheets when they are heat-pressed together (for example, at 200°C). As a result, the coating film tends to exhibit high shear adhesion.From this viewpoint, the content of epoxy resin (B) in the coating composition of the present disclosure is preferably 100 parts by mass or less, and more preferably 80 parts by mass or less, per 100 parts by mass of (meth)acrylic resin (A). In some embodiments, the content of epoxy resin (B) in the coating composition of the present disclosure may be 15 to 120 parts by mass, 15 to 100 parts by mass, or 15 to 80 parts by mass, per 100 parts by mass of (meth)acrylic resin (A).

[0063] [Polyamine-based curing agent (C)] The coating composition of this disclosure comprises a polyamine-based curing agent (C). The polyamine-based curing agent (C) forms a crosslinked structure with the (meth)acrylic resin (A) and the epoxy resin (B).

[0064] In this disclosure, a polyamine-based curing agent refers to an amine compound having two or more active hydrogens and two or more amino groups in one molecule, wherein the amino groups of the amine compound preferably include at least one of a primary amino group and a secondary amino group, and more preferably include a primary amino group.

[0065] Examples of polyamine-based curing agents (C) include aliphatic amine compounds such as diethylenetriamine, triethylenetetramine, and 4,4'-diaminodicyclohexylmethane; and aromatic amine compounds such as diethyltoluenediamine, dimethylthiotoluenediamine, and 3,3'-diethyl-4,4'-diaminodiphenylmethane.

[0066] The active hydrogen equivalent of the polyamine-based curing agent (C) is not particularly limited, but is preferably 90 g / eq to 400 g / eq, more preferably 100 g / eq to 300 g / eq, and even more preferably 150 g / eq to 200 g / eq. In some embodiments, the active hydrogen equivalent of the polyamine-based curing agent (C) may be 90 g / eq to 200 g / eq, 100 g / eq to 180 g / eq, or 120 g / eq to 160 g / eq. When the active hydrogen equivalent of the polyamine-based curing agent (C) is within the above range, the amino groups derived from the polyamine-based curing agent (C) tend to react appropriately with the carboxyl groups derived from the (meth)acrylic resin (A) and the epoxy groups derived from the epoxy resin (B), forming a crosslinked structure.

[0067] In this disclosure, the active hydrogen equivalent of the polyamine curing agent is calculated based on the amine value measured in accordance with the potentiometric titration method described in JIS K 7237:1995. When using a commercially available polyamine curing agent, the catalog value of the commercially available product is given priority for determining the active hydrogen equivalent of the polyamine curing agent.

[0068] Commercially available polyamine-based curing agents (C) can be used. Examples of commercially available polyamine-based curing agents (C) include "Fujicure FXH-940" manufactured by T&K TOKA Corporation, "BECKOPOX EH616W / 67WA" manufactured by Daicel Ornex Corporation, and "Yukarezin HD-03" manufactured by Yoshimura Oil Chemical Co., Ltd. "Fujicure," "BECKOPOX," and "Yukarezin" are all registered trademarks.

[0069] The coating composition of this disclosure may contain one polyamine-based curing agent (C) alone, or may contain two or more.

[0070] <<Ratio of moles of active hydrogen in polyamine-based curing agent (C) to moles of epoxy groups in epoxy resin (B)>> The coating composition of this disclosure has a ratio of 0.7 to 3.9 of moles of active hydrogen in the polyamine-based curing agent (C) to moles of epoxy groups in epoxy resin (B) [i.e., moles of active hydrogen in the polyamine-based curing agent (C) / moles of epoxy groups in epoxy resin (B)]. When the ratio of moles of active hydrogen in the polyamine-based curing agent (C) to moles of epoxy groups in epoxy resin (B) is 0.7 or higher, when electrical steel sheets are heat-pressed together (for example, pressed at 200°C), a reaction occurs between the epoxy groups derived from the epoxy resin (B) and the amino groups derived from the polyamine-based curing agent (C), resulting in a sufficiently high crosslink density of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. Furthermore, if the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is 0.7 or higher, when the coating composition is dried at a high temperature (for example, 170°C), a reaction occurs between the epoxy groups derived from the epoxy resin (B) and the amino groups derived from the polyamine-based curing agent (C), resulting in a sufficiently high crosslink density of the coating film. As a result, the coating film tends to exhibit excellent corrosion resistance. From the above viewpoint, the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is preferably 1.0 or higher, and more preferably 1.2 or higher. In addition, the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) may be 1.3 or higher, or 1.6 or higher. When the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is 3.9 or less, the crosslinking reaction does not proceed excessively when the coating composition is dried at a high temperature (e.g., 170°C), and a coating film with appropriate flexibility is formed. Because the coating film has appropriate flexibility, the coating films fuse together sufficiently when electrical steel sheets are heat-pressed together (e.g., pressed at 200°C). Therefore, the coating film tends to exhibit high shear adhesion.From this viewpoint, the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is preferably 3.3 or less, and more preferably 3.0 or less. Furthermore, the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) may be 2.5 or less. In some embodiments, the ratio of the number of moles of active hydrogen in the polyamine-based curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) may be 1.0 to 3.0, 1.2 to 3.0, 1.0 to 2.5, 1.2 to 2.5, 1.3 to 3.9, 1.6 to 3.9, 1.3 to 3.3, or 1.6 to 3.3.

[0071] <<Ratio of moles of carboxyl groups in (meth)acrylic resin (A) to moles of active hydrogen in polyamine curing agent (C)>> The coating composition of this disclosure has a ratio of moles of carboxyl groups in (meth)acrylic resin (A) to moles of active hydrogen in polyamine curing agent (C) [i.e., moles of carboxyl groups in (meth)acrylic resin (A) / moles of active hydrogen in polyamine curing agent (C)] of 0.4 to 7.5. When the ratio of moles of carboxyl groups in (meth)acrylic resin (A) to moles of active hydrogen in polyamine curing agent (C) is 0.4 or higher, when electrical steel sheets are heat-pressed together (for example, pressed at 200°C), a reaction occurs between carboxyl groups derived from (meth)acrylic resin (A) and amino groups derived from polyamine curing agent (C), resulting in a sufficiently high crosslink density of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. From this perspective, the ratio of moles of carboxyl groups in the (meth)acrylic resin (A) to moles of active hydrogen in the polyamine curing agent (C) is preferably 0.5 or higher, more preferably 0.6 or higher, even more preferably 0.8 or higher, and particularly preferably 0.9 or higher. Furthermore, the ratio of moles of carboxyl groups in the (meth)acrylic resin (A) to moles of active hydrogen in the polyamine curing agent (C) may be 1.2 or higher. When the ratio of moles of carboxyl groups in the (meth)acrylic resin (A) to moles of active hydrogen in the polyamine curing agent (C) is 7.5 or lower, a decrease in the crosslinking density of the coating film due to an excessive amount of carboxyl groups is less likely to occur when the electrical steel sheets are heat-pressed together (for example, pressed at 200°C), resulting in sufficiently high cohesive force of the coating film. Therefore, the coating film tends to exhibit high shear adhesion. Furthermore, if the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) is 7.5 or less, when the coating composition is dried at a high temperature (for example, 170°C), the number of uncrosslinked carboxyl groups remaining in the coating film will decrease, thus reducing the hydrophilicity of the coating film and suppressing the penetration of water into the electrical steel sheet.Therefore, the coating film tends to exhibit excellent corrosion resistance. From the above viewpoint, the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) is preferably 6.3 or less, more preferably 5.1 or less, even more preferably 5.0 or less, and particularly preferably 3.9 or less. In one embodiment, the ratio of moles of carboxyl groups in the (meth)acrylic resin (A) to moles of active hydrogen in the polyamine curing agent (C) may be 0.8 to 5.0, 1.2 to 5.0, 0.5 to 6.3, 0.5 to 5.1, 0.5 to 3.9, 0.6 to 6.3, 0.6 to 5.1, 0.6 to 3.9, 0.8 to 6.3, 0.8 to 5.1, 0.8 to 3.9, 0.9 to 6.3, 0.9 to 5.1, or 0.9 to 3.9.

[0072] The number of moles of carboxyl groups in (meth)acrylic resin is calculated using the following formula (1): Number of moles of carboxyl groups in (meth)acrylic resin = [Content of constituent units derived from monomers containing carboxyl groups in (meth)acrylic resin (unit: mass%)] / 100 × [Amount of (meth)acrylic resin blended (unit: g)] / [Molecular weight of constituent units derived from monomers containing carboxyl groups (unit: g / mol)] × [Number of carboxyl groups in constituent units derived from monomers containing carboxyl groups] ... (1)

[0073] The molecular weights of the constituent units derived from monomers containing a carboxyl group are, for example, 72.06 g / mol for acrylic acid and 86.09 g / mol for methacrylic acid.

[0074] The number of moles of epoxy groups in epoxy resin is calculated using the following formula (2): Number of moles of epoxy groups in epoxy resin (unit: mol) = [Amount of epoxy resin (unit: g)] / [Epoxy equivalent of epoxy resin (unit: g / eq)] ... (2)

[0075] The number of moles of active hydrogen in a polyamine-based curing agent is calculated using the following formula (3): Number of moles of active hydrogen in polyamine-based curing agent (unit: mol) = [Amount of polyamine-based curing agent (unit: g)] / [Equivalent amount of active hydrogen in polyamine-based curing agent (g / eq)] ... (3)

[0076] [Water] The coating compositions of this disclosure may contain water. If the coating compositions of this disclosure contain water, the (meth)acrylic resin (A) and epoxy resin (B) may be present in the coating composition in the form of dispersed particles. The water is not particularly limited, but from the viewpoint of having fewer impurities, for example, deionized water, distilled water, and purified water are preferred.

[0077] If the coating composition of this disclosure contains water, the water content is not particularly limited and can be set as appropriate depending on the purpose, as long as it does not impair the effect of the coating composition of this disclosure.

[0078] [Organic Solvents] The coating compositions of this disclosure may contain organic solvents. If the coating compositions of this disclosure contain organic solvents, the (meth)acrylic resin (A) and epoxy resin (B) may be present in the coating composition in the form of dispersed particles and / or dissolved particles. Examples of organic solvents include water-miscible organic solvents and water-immiscible organic solvents. The organic solvent may be a water-miscible organic solvent, a water-immiscible organic solvent, or a mixed solvent of a water-miscible organic solvent and a water-immiscible organic solvent.

[0079] Examples of water-miscible organic solvents include monohydric alcohol compounds such as methanol, ethanol, propanol, and isopropanol; polyhydric alcohol compounds such as glycerin, ethylene glycol, diethylene glycol, and propylene glycol; and glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

[0080] Examples of water-immiscible organic solvents include aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirits, petroleum naphtha, and turpentine oil; ester compounds such as methyl acetate, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; and ketone compounds such as acetone, methyl ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone.

[0081] If the coating composition of this disclosure contains an organic solvent, it may contain one organic solvent alone or two or more organic solvents.

[0082] If the coating composition of this disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be set as appropriate depending on the purpose, as long as it does not impair the effect of the coating composition of this disclosure.

[0083] [Surfactants] The coating compositions of this disclosure may contain surfactants. The type of surfactant is not particularly limited. Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. When the shape of the (meth)acrylic resin (A) is particulate, the surfactant is preferably at least one of anionic surfactants and nonionic surfactants, and more preferably anionic surfactants and nonionic surfactants, from the viewpoint of the manufacturing stability of the (meth)acrylic resin (A).

[0084] Examples of anionic surfactants include polyoxyalkylene polycyclic phenyl ether sulfates, such as polyoxyethylene distyrenated phenyl ether sulfate ammonium; polyoxyalkylene polycyclic phenyl ether sulfates, such as polyoxyethylene distyrenated phenyl ether sulfate ammonium; polyoxyalkylene alkyl phenyl ether sulfates, such as polyoxyethylene nonylphenyl ether sulfate sodium; polyoxyalkylene alkyl ether sulfates, such as polyoxyethylene lauryl ether sulfate sodium; polyoxyalkylene alkyl ether sulfates; alkyl phosphate esters; and others. Examples of nonionic surfactants include polyoxyalkylene alkyl ethers, such as polyoxyethylene oleyl ether and polyoxyethylene lauryl ether; and polyoxyalkylene styrene-derived phenyl ethers, such as polyoxyethylene styrene-derived phenyl ether.

[0085] Commercially available surfactants can be used. Examples of commercially available surfactants include "Neoperex G-65," an anionic surfactant manufactured by Kao Corporation; "Neugen EA-197D," a nonionic surfactant manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; and "Emulgen A-60," a nonionic surfactant manufactured by Kao Corporation. "Neoperex," "Neugen," and "Emulgen" are all registered trademarks.

[0086] If the coating composition of this disclosure contains a surfactant, it may contain one surfactant alone or two or more surfactants.

[0087] If the coating composition of this disclosure contains a surfactant, the surfactant content is not particularly limited and can be set as appropriate depending on the purpose, as long as it does not impair the effect of the coating composition of this disclosure.

[0088] [Other Components] The coating composition of this disclosure may contain components other than those described above (so-called other components) as necessary, to the extent that it does not impair its effect. Examples of other components include various additives such as preservatives, wetting agents, and defoaming agents. Other components may include resins such as (meth)acrylic resins other than (meth)acrylic resin (A), epoxy resins other than epoxy resin (B), and curing agents other than curing agent (C).

[0089] [Gel fraction of coating composition after heating] The coating composition of this disclosure preferably has a gel fraction of 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, after being heated at 170°C for 90 seconds and then at 200°C for 60 seconds, from the viewpoint of forming a coating film that exhibits high shear adhesion. The upper limit is not particularly limited and may be, for example, 100% by mass.

[0090] The coating composition of the present disclosure preferably has a gel fraction of 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, after heating at 170°C for 90 seconds and before heating at 200°C for 60 seconds, from the viewpoint of forming a coating film exhibiting excellent corrosion resistance. Furthermore, the coating composition of the present disclosure preferably has a gel fraction of 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, after heating at 170°C for 90 seconds and before heating at 200°C for 60 seconds, from the viewpoint of forming a coating film exhibiting high shear adhesion. In one embodiment, the coating composition of the present disclosure may have a gel fraction of 5% by mass to 50% by mass, 15% by mass to 40% by mass, or 20% by mass to 40% by mass, after heating at 170°C for 90 seconds and before heating at 200°C for 60 seconds.

[0091] The gel fraction of the coating composition after heating according to this disclosure is the proportion of solvent-insoluble matter measured using tetrahydrofuran as the extraction solvent. In this disclosure, the gel fraction of the coating composition after heating is measured by the following method: The coating composition is applied to release paper to form a coating film. The formed coating film is then dried at room temperature (25°C) for 24 hours, and then heated and dried at a predetermined temperature for a predetermined time to obtain a resin film with release paper. The release paper is then peeled off from the resin film with release paper to obtain a resin film. Next, 0.2 g ± 0.01 g of the resin film is weighed into a glass container. Next, 20 g of tetrahydrofuran (THF) is added to the glass container containing the resin film, and the container is sealed. The container is then left to stand for 3 days in an environment of 23°C and 50% RH to immerse the resin film in THF. The sample obtained from this immersion is used as the measurement sample. Next, the measurement sample is filtered using a 1000-mesh stainless steel mesh. Next, the wire mesh used to filter the sample is dried at 100°C for 3 hours. Then, the mass of the dried wire mesh is measured. The gel fraction of the resin film is then calculated using the following formula. In the following formula, A is the mass of the weighed resin film (in g), B is the mass of the wire mesh before filtering the sample (in g), and C is the mass of the wire mesh after filtering the sample (in g). Gel fraction of resin film [unit: mass %] = (C - B) / A × 100

[0092] [Applications of the Coating Composition] The coating composition of this disclosure is a composition used to coat the surface of electrical steel sheets used in the manufacture of laminated steel sheets. The coating composition of this disclosure can form a coating film that exhibits high shear adhesion and excellent corrosion resistance even when used on electrical steel sheets that do not have an insulating film formed on them. A specific application is to fix electrical steel sheets together when manufacturing laminated steel sheets. The coating composition of this disclosure is suitable, for example, as a composition for forming an adhesive film on electrical steel sheets with an adhesive film used in the manufacture of laminated steel sheets.

[0093] [Electromagnetic Steel Sheet] An electromagnetic steel sheet is a steel sheet on which an adhesive coating is formed, and is not particularly limited. The electromagnetic steel sheet may be a non-oriented electromagnetic steel sheet or a grain-oriented electromagnetic steel sheet. Specifically, as the electromagnetic steel sheet, for example, a non-oriented electromagnetic steel sheet of JIS C 2552:2014, a grain-oriented electromagnetic steel sheet of JIS C 2553:2019, or a non-oriented thin electromagnetic steel sheet or a grain-oriented thin electromagnetic steel sheet of JIS C 2558:2015 can be used.

[0094] [Method for Manufacturing the Coating Composition] The method for manufacturing the coating composition of the present disclosure is not particularly limited. For example, the coating composition of the present disclosure can be manufactured by mixing a (meth)acrylic resin (A), an epoxy resin (B) in a ratio of 12 to 120 parts by mass per 100 parts by mass of (meth)acrylic resin (A), and a polyamine curing agent (C) such that the ratio of the number of moles of active hydrogen in the polyamine curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) [i.e., moles of active hydrogen in the polyamine curing agent (C) / moles of epoxy groups in the epoxy resin (B)] is 0.7 to 3.9, and the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) [i.e., moles of carboxyl groups in the (meth)acrylic resin (A) / moles of active hydrogen in the polyamine curing agent (C)] is 0.4 to 7.5.

[0095] The mixing method is not particularly limited. For example, mixing can be done by stirring. A general stirring device or agitator can be used for stirring. The stirring temperature is not particularly limited, but is preferably 20°C to 30°C.

[0096] The coating compositions of this disclosure will be described in more detail below with reference to examples. This disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0097] In the following examples, the glass transition temperature (Tg) of the (meth)acrylic resin was measured using a differential scanning calorimeter (product name: Discovery DSC 2500) manufactured by T.A. Instrument Japan Co., Ltd., by the method described above. The epoxy equivalent of the epoxy resin and the active hydrogen equivalent of the polyamine curing agent were both catalog values. The number of moles of carboxyl groups in the (meth)acrylic resin was determined by formula (1) described above. The number of moles of epoxy groups in the epoxy resin was determined by formula (2) described above. The number of moles of active hydrogen in the polyamine curing agent was determined by formula (3) described above.

[0098] [Production of (meth)acrylic resin] [Production example A-1] 54.4 parts by mass of n-butyl acrylate [n-BA; alkyl acrylate monomer], 169.6 parts by mass of methyl methacrylate [MMA; alkyl methacrylate monomer], 128.4 parts by mass of styrene [St; other monomers], 40.0 parts by mass of methacrylic acid [MAA; monomer having a carboxyl group], and 7.6 parts by mass of N-(2-hydroxyethyl)acrylamide [HEAA; other monomers] were placed in a stainless steel container, and then stirred to prepare a monomer mixture. Next, in a separate stainless steel container, 261.1 parts by mass of deionized water, 2.7 parts by mass of the nonionic surfactant Neugen EA-197D (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 4.1 parts by mass of the nonionic surfactant Emulgen (registered trademark) A-60 (manufactured by Kao Corporation), and 5.4 parts by mass of the anionic surfactant Neoperex G-65 (manufactured by Kao Corporation) were added and stirred to prepare an aqueous surfactant solution. Next, the monomer mixture prepared above was gradually added to the aqueous surfactant solution while stirring with a stirrer to emulsify and prepare a preemulsion. This prepared preemulsion was used for polymerization. Polymerization was carried out in a constant temperature bath using a 7 L (liter; the same applies hereafter) flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet tube, a pre-emulsion dropper pump (product name: Highcera Pump V-10, manufactured by Iwaki Co., Ltd.), and a polymerization initiator addition device (product name: Quantitative Liquid Delivery Pump MP-2000, manufactured by Tokyo Rika Kikai Co., Ltd.). Specifically, polymerization was carried out as follows: 162.4 parts by mass of deionized water were placed in the flask, and then a portion of the pre-emulsion prepared above (20.2 parts by mass) was added. Nitrogen gas was blown into the flask at a flow rate of 300 ml / min, and the internal temperature of the flask was raised to a desired reaction temperature (standard conditions: 62°C) while stirring at a desired rotation speed (standard conditions: 150 rpm (revolutions per minute; the same applies hereafter)). After the internal temperature stabilized, 3.1 parts by mass of an 18% by mass aqueous solution of ammonium peroxodisulfate [polymerization initiator] and 3.1 parts by mass of a 15% by mass aqueous solution of sodium bisulfite [reducing agent] were added, and the nitrogen gas flow rate was adjusted to 50 ml / min.After confirming the temperature rise in the flask, the remaining pre-emulsion (653.1 parts by mass) was added dropwise over 180 minutes, while 84.5 parts by mass of 1.8% by mass ammonium peroxodisulfate aqueous solution [polymerization initiator] and 84.5 parts by mass of 1.5% by mass sodium bisulfite aqueous solution [reducing agent] were added dropwise over 240 minutes. Thirty minutes after the completion of the addition of ammonium peroxodisulfate aqueous solution and sodium bisulfite, 6.4 parts by mass of 6.9% by mass t-butyl hydroperoxide aqueous solution [polymerization initiator] and 6.4 parts by mass of 4.4% by mass sodium hydroxymethanesulfinate aqueous solution [reducing agent] were added dropwise over 30 minutes. The polymerization reaction was completed by cooling to 30°C 150 minutes after the completion of the pre-emulsion addition. To the emulsion polymer obtained by polymerization, 1.3 parts by mass of a preservative [product name: Topside 350, manufactured by Permachem Asia Co., Ltd.] and 1.3 parts by mass of a wetting agent [product name: Surfinol® 440, manufactured by Nisshin Chemical Industry Co., Ltd.] were added to obtain an aqueous dispersion of (meth)acrylic resin A-1 with a solid content concentration of 40.0% by mass. Visual observation of the obtained aqueous dispersion confirmed that particulate (meth)acrylic resin A-1 was present in a dispersed state in water.

[0099] [Production Examples A-2 to A-6] In Production Examples A-2 to A-6, aqueous dispersions of (meth)acrylic resin A-2 to A-6, each with a solid content concentration of 40.0% by mass, were obtained in the same manner as in Production Example A-1, except that the monomer composition of the (meth)acrylic resin was changed to the monomer composition shown in Table 1.

[0100] Of the (meth)acrylic resins A-1 to A-6, (meth)acrylic resins A-1 to A-3 and A-6 correspond to (meth)acrylic resin (A) in this disclosure.

[0101]

[0102] In Table 1, "-" indicates that the monomer corresponding to that column is not included.

[0103] Details of each monomer listed in Table 1 are as follows: "n-BA": n-butyl acrylate (alkyl acrylate monomer) "MMA": methyl methacrylate (alkyl methacrylate monomer) "St": styrene (other monomer) "MAA": methacrylic acid (monomer with a carboxyl group) "HEAA": N-(2-hydroxyethyl) acrylamide (other monomer)

[0104] [Production of Coating Composition] [Example 1] 253.8 parts by mass (100.0 parts by mass as resin solids; 100.0 g) of an aqueous dispersion of (meth)acrylic resin A-1 obtained above, 222.2 parts by mass (100.0 parts by mass as resin solids; 100.0 g) of epoxy A [product name: BECKOPOX EP2307w / 45WAMP, manufactured by Daicel Ornex Co., Ltd.], and 13.1 parts by mass (10.1 parts by mass as solids; 10.1 g) of curing agent A [product name: Fujicure FXH-940, manufactured by T&K Toka Co., Ltd.] were mixed, and then an appropriate amount of deionized water was added to obtain a coating composition with a solid content concentration of 32.0% by mass.

[0105] [Examples 2-15] The coating compositions of Examples 2-15 were obtained in the same manner as in Example 1, except that the composition of the coating composition other than the preservative and wetting agent was as shown in Table 2.

[0106] [Comparative Examples 1-9] Each of the coating compositions in Comparative Examples 1-9 was obtained in the same manner as in Example 1, except that the composition of the coating composition other than the preservative and wetting agent was as shown in Table 3.

[0107]

[0108]

[0109] The ingredient amounts listed in Tables 2 and 3 are all based on solid content. In Table 3, "-" indicates that there is no corresponding entry in that column.

[0110] Details of each component listed in Tables 2 and 3 are as follows: "Epoxy A": BEKOPOX EP2307w / 45WAMP (product name), manufactured by Daicel Ornex Co., Ltd. "Epoxy B": Yucaresin NE-307T (product name), manufactured by Yoshimura Oil Chemical Co., Ltd. "Epoxy C": BEKOPOX VEP2381w / 55WA (product name), manufactured by Daicel Ornex Co., Ltd. "Epoxy D": Yucaresin NE-320 (product name), manufactured by Yoshimura Oil Chemical Co., Ltd. "Hardening agent A": Fujicure FXH-940 (product name; polyamine-based hardening agent), manufactured by T&K TOKA Corporation

[0111] [Measurement and Evaluation] 1. Measurement of Gel Fraction (1) Preparation of Resin Film with Release Paper (1-1) Resin Film X with Release Paper The coating composition was applied onto release paper using an 8 mil (203.2 μm) applicator to form a coating film. The formed coating film was then dried at room temperature (25°C) for 24 hours, and then further dried at 170°C for 90 seconds to obtain Resin Film X with Release Paper.

[0112] (1-2) A resin film Y with release paper was coated onto release paper using an 8 mil (203.2 μm) applicator to form a coating film. The formed coating film was then dried at room temperature (25°C) for 24 hours, then dried at 170°C for 90 seconds, and then dried at 200°C for 60 seconds to obtain a resin film Y with release paper.

[0113] (2) Measurement of Gel Fraction The release paper was peeled off from resin film X and resin film Y with release paper to obtain resin film X and resin film Y. The gel fraction was measured using the obtained resin film X and resin film Y. In the following measurements, "resin film X and resin film Y" will be collectively referred to as "resin film". 0.2 g ± 0.01 g of resin film was weighed into a glass bottle. Next, 20 g of tetrahydrofuran (THF) was added to the glass bottle containing the resin film, and after sealing, the bottle was left to stand for 3 days in an environment of ambient temperature of 23°C and 50% RH, immersing the resin film in THF. The material obtained from this immersion is called the sample. Next, the sample was filtered using a 1000 mesh stainless steel wire mesh. Next, the wire mesh after filtering the sample was dried at 100°C for 3 hours. Next, the mass of the wire mesh after drying was measured. The gel fraction was then calculated using the following formula. In the following formula, A is the mass of the weighed resin film (in g), B is the mass of the wire mesh before filtering the sample (in g), and C is the mass of the wire mesh after filtering the sample (in g). Gel fraction of the resin film [in mass %] = (C - B) / A × 100

[0114] 2. Shear Adhesion Strength Two 2cm x 10cm electrical steel sheets [insulating coating: none, manufactured by Nippon Steel Corporation] were prepared. A coating composition was applied to the surface of the two prepared electrical steel sheets. The amount of coating composition applied was such that the film thickness after drying was 2 μm. Next, the applied coating composition was dried by heating it at 170°C for 90 seconds using a hot air circulation dryer to produce two coated electrical steel sheets. Next, the two produced coated electrical steel sheets were arranged so that the overlapping area of ​​the coating films was 2cm x 2cm, and thermocompression bonding (temperature: 200°C, time: 60 seconds, pressure: 3 MPa) was performed to obtain a laminate. The obtained laminate was used as an evaluation sample. Next, a tensile shear adhesion strength test was performed on the evaluation sample in an environment of 155°C. The tensile shear adhesion strength test was performed in accordance with JIS K 6850:1999. The measured shear adhesion strengths obtained are shown in Table 4. A shear adhesion strength of 0.50 MPa or higher was considered acceptable for practical use.

[0115] 3. Corrosion Resistance An electrical steel sheet measuring 2 cm x 10 cm [insulating coating: none, manufactured by Nippon Steel Corporation] was prepared. A coating composition was applied to the surface of the prepared electrical steel sheet. The amount of coating composition applied was such that the film thickness after drying was 2 μm. Next, the applied coating composition was dried by heating it at 170°C for 90 seconds using a hot air circulation dryer to produce an electrical steel sheet with a coating film. Next, in order to prevent saltwater from entering through the gap between the electrical steel sheet and the coating film, the four sides of the electrical steel sheet with the coating film were sealed with odorless beeswax [manufactured by Turner Colour Works, Inc.] to prepare a test specimen. The prepared test specimen was placed in a salt spray test machine [product name: STP-90V, manufactured by Suga Test Instruments Co., Ltd.] set to a temperature of 35°C, and a salt spray test was performed by spraying a 5% by mass sodium chloride aqueous solution onto the test specimen. At one hour and two hours after the start of the salt spray test, the surface of the electrical steel sheet of the test specimen was visually inspected to check for rust. Based on the results of the inspection, an evaluation was performed according to the evaluation criteria below. The evaluation results are shown in Table 4. In the evaluation criteria below, "A" and "B" are at a level that does not pose a practical problem, and "A" is the most preferable.

[0116] -Evaluation Criteria- A: No rust was observed 2 hours after the start of the salt spray test. B: No rust was observed 1 hour after the start of the salt spray test, but rust was observed after 2 hours. C: Rust was observed 1 hour after the start of the salt spray test.

[0117]

[0118] Table 4 shows the results, which indicate that the coating film formed by the coating composition of the example exhibits higher shear adhesion and superior corrosion resistance compared to the coating film formed by the coating composition of the comparative example when used on electrical steel sheets without an insulating film.

[0119] The disclosures of Japanese Patent Application No. 2025-056958, filed on 28 March 2025, and Japanese Patent Application No. 2026-005410, filed on 15 January 2026, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted.

Claims

1. A coating composition for laminated steel sheets comprising: a (meth)acrylic resin (A) containing constituent units derived from monomers having carboxyl groups in a proportion of 5% to 15% by mass relative to the total constituent units; an epoxy resin (B) having an epoxy equivalent of 1000 g / eq to 3000 g / eq; and a polyamine curing agent (C), wherein the content of the epoxy resin (B) is 12 to 120 parts by mass per 100 parts by mass of the (meth)acrylic resin (A); the ratio of the number of moles of active hydrogen in the polyamine curing agent (C) to the number of moles of epoxy groups in the epoxy resin (B) is 0.7 to 3.9; and the ratio of the number of moles of carboxyl groups in the (meth)acrylic resin (A) to the number of moles of active hydrogen in the polyamine curing agent (C) is 0.4 to 7.

5.

2. The coating composition for laminated steel sheets according to claim 1, wherein the (meth)acrylic resin (A) comprises constituent units derived from an alkyl (meth)acrylate monomer.

3. The coating composition for laminated steel sheets according to claim 1, wherein the (meth)acrylic resin (A) comprises constituent units derived from monomers having a ring structure.

4. The coating composition for laminated steel sheets according to claim 3, wherein the constituent units derived from the monomer having a ring structure are constituent units derived from styrene.

5. The coating composition for laminated steel sheets according to claim 1, wherein the shape of the (meth)acrylic resin (A) is particulate.

6. The coating composition for laminated steel sheets according to claim 1, wherein the epoxy resin (B) is in the form of particles.

7. The coating composition for laminated steel sheets according to claim 5 or claim 6, further comprising water.

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