Coating agent for forming etching resist coating film

Abstract

Provided is a coating agent for forming an etching resist coating film, with which it is possible to form an etching resist coating film that is excellent in terms of laser removability, resist characteristics, and separability. A coating agent for forming an etching resist coating film according to the present invention contains, in a solvent, 100 parts by mass of an aqueous alkyd resin, 0.10 part by mass or more and 30 parts by mass or less of a melamine resin, 20 parts by mass or more and 200 parts by mass or less of an aluminum-containing oxide, 10 parts by mass or more and 100 parts by mass or less of a titanium-containing oxide, and 0.10 part by mass or more and 5.0 parts by mass or less of carbon black in terms of solid content, and the total amount of the respective solid contents of these components accounts for 80 mass% or more of the total solid content.

Description

Coating agent for forming etching resist film

[0001] The present invention relates to a coating agent for forming an etching resist film, which is used to form an etching resist film on the surface of a grain-oriented electrical steel sheet.

[0002] Grain-oriented electrical steel sheets have excellent magnetic properties and are primarily used as materials for the iron cores of transformers. To improve the energy efficiency of transformers, it is necessary to reduce the iron loss of grain-oriented electrical steel sheets. One known method for reducing the iron loss of grain-oriented electrical steel sheets is to introduce linear grooves into the surface of the grain-oriented electrical steel sheet. In this method, the width of the magnetic domains is subdivided by forming linear grooves on the surface of the steel sheet, thereby reducing iron loss.

[0003] One known method for forming linear grooves on the surface of a steel sheet is an etching process using an etching resist film. For example, Patent Document 1 describes a method for forming linear grooves on the surface of a steel sheet by uniformly applying a coating agent for forming an etching resist film to the surface of the steel sheet and performing a baking process to form an etching resist film, irradiating the formed etching resist film with a laser to remove the etching resist film in a linear pattern, and then performing an etching process.

[0004] International Publication No. 2017 / 017908

[0005] As a result of independent investigations, the inventors have found that there is room for improvement in the characteristics of the etching resist coating formed on the surface of grain-oriented electrical steel sheets in the above-mentioned prior art. Specifically, when attempting to linearly remove the etching resist coating by irradiating the etching resist coating with a laser, the width of the portion of the etching resist coating removed by the laser irradiation (hereinafter sometimes referred to as the "coating removal portion") may vary significantly, or the width of the coating removal portion may differ significantly from the laser beam diameter. These errors suggest that the etching resist coating's ability to be accurately removed according to the laser irradiation pattern (hereinafter sometimes referred to as "laser removability") is poor. Poor laser removability of the etching resist coating makes it difficult to accurately form the coating removal portion, which may result in difficulty in forming linear grooves in the designed shape on the surface of the grain-oriented electrical steel sheet.

[0006] Furthermore, when electrolytic etching is performed using an etching resist film according to the prior art, a portion of the surface of the etching resist film may discolor, resulting in a change in appearance. The change in color tone of the etching resist film suggests a decrease in the resistance of the etching resist film to the electrolytic etching solution (hereinafter sometimes referred to as "resist properties"). Furthermore, in the prior art, when using a strong alkaline aqueous solution to strip and remove the etching resist film that is no longer needed after the etching process is completed, a portion of the etching resist film may not peel off and remain on the surface of the grain-oriented electrical steel sheet. The remaining etching resist film suggests that the etching resist film is less easily removable (hereinafter sometimes referred to as "separability").

[0007] The present invention has been made in view of the above-mentioned problems of the conventional art, and an object of the present invention is to provide a coating agent for forming an etching resist film, which is capable of forming an etching resist film that is excellent in laser removability, resist properties, and peelability.

[0008] The gist and configuration of the present invention are as follows.

[0009] [1] A coating agent for forming an etching resist film, comprising, in terms of solid content, 100 parts by mass of an aqueous alkyd resin, 0.10 parts by mass or more and 30 parts by mass or less of a melamine resin, 20 parts by mass or more and 200 parts by mass or less of an aluminum-containing oxide, 10 parts by mass or more and 100 parts by mass or less of a titanium-containing oxide, and 0.10 parts by mass or more and 5.0 parts by mass or less of carbon black in a solvent, wherein the total amount of the solid contents of the aqueous alkyd resin, the melamine resin, the aluminum-containing oxide, the titanium-containing oxide, and the carbon black accounts for 80% by mass or more of the total solid content.

[0010] [2] The coating agent for forming an etching resist film according to the above [1], wherein the aqueous alkyd resin is obtained by reacting an alkyd resin with a polymerizable vinyl monomer.

[0011] [3] The coating agent for forming an etching resist film according to the above [1] or [2], wherein the proportion of the total solid content in the coating agent for forming an etching resist is 10 mass % or more and 80 mass % or less.

[0012] [4] The coating agent for forming an etching resist film according to any one of the above [1] to [3], wherein the solvent contains ethylene glycol mono-n-butyl ether.

[0013] The etching resist film formed by applying the coating agent for forming an etching resist film according to the present invention to the surface of a grain-oriented electrical steel sheet and baking it has superior laser removability, resist properties, and peelability compared to conventional techniques.

[0014] The present invention will be described in detail below.

[0015] <Coating Agent for Forming Etching Resist Film> In one embodiment, the present invention relates to a coating agent for forming an etching resist film, which comprises, in terms of solid content, 100 parts by mass of an aqueous alkyd resin, 0.10 to 30 parts by mass of a melamine resin, 20 to 200 parts by mass of an aluminum-containing oxide, 10 to 100 parts by mass of a titanium-containing oxide, and 0.10 to 5.0 parts by mass of carbon black in a solvent, wherein the total solid content of the aqueous alkyd resin, melamine resin, aluminum-containing oxide, titanium-containing oxide, and carbon black accounts for 80 mass% or more of the total solid content. Note that the following description of the coating agent for forming an etching resist film uses a grain-oriented electrical steel sheet as a finished product obtained by completing all processes up to secondary recrystallization annealing as an example of the target to which the coating agent is applied. However, as described below, it should be noted that the target to which the coating agent for forming an etching resist film according to the present invention is applied may also be a steel sheet as an intermediate product during the manufacturing of a grain-oriented electrical steel sheet.

[0016] The coating agent for forming an etching resist film according to the present invention is composed primarily of an aqueous alkyd resin, to which a melamine resin crosslinker, an aluminum-containing oxide, a titanium-containing oxide, and carbon black are added, and the resulting mixture is dissolved or mixed in a solvent. The coating agent for forming an etching resist film according to the present invention is applied to the surface of a grain-oriented electrical steel sheet and baked at a predetermined temperature for a predetermined time, resulting in evaporation of the solvent and a crosslinking reaction, forming an etching resist film on the surface of the grain-oriented electrical steel sheet. In this specification, the term "coating agent for forming an etching resist film" refers to a liquid coating agent primarily composed of a resin, which is used to form an etching resist film. In this specification, the term "etching resist film" refers to a solid film formed on the surface of a substrate after the above-described process using the coating agent for forming an etching resist film. The commonly used term "etching resist" can sometimes refer to a coating agent for forming an etching resist film and sometimes to an etching resist film. In this specification, the terms "coating agent for forming an etching resist film" and "etching resist film" are used strictly separately.

[0017] As described above, the coating agent for forming an etching resist film is applied so as to leave continuous or discontinuous linear regions in a direction intersecting the rolling direction as non-coated regions. During the etching treatment, the coated regions protected by the etching resist film prevent contact between the surface of the grain-oriented electrical steel sheet and the etching solution, and corrosion of the grain-oriented electrical steel sheet does not occur. In the non-coated regions, corrosion occurs due to contact of the surface of the grain-oriented electrical steel sheet with the etching solution, forming linear grooves. After the etching treatment is completed, the etching resist film is removed as necessary.

[0018] <Solid Content and Solid Content Equivalent> Before describing each component contained in the coating agent for forming an etching resist film according to the present invention, we will explain how to label the components. In this specification, "solid content" refers to the remaining solid components contained in the coating agent for forming an etching resist film, excluding substances that are lost by evaporation, such as solvents and water. When the coating agent for forming an etching resist film is applied to the surface of a grain-oriented electrical steel sheet and baked, substances such as solvents and water evaporate, and an etching resist film is formed by the remaining solid content.

[0019] As used herein, the term "solids content equivalent" refers to the content of each component in a coating agent for forming an etching resist film being expressed based on the solid content of the component. As described below, the coating agent for forming an etching resist film according to the present invention is prepared by mixing an aqueous alkyd resin, a melamine resin, an aluminum-containing oxide, a titanium-containing oxide, and carbon black in a solvent. The aqueous alkyd resin and melamine resin used in the preparation may themselves contain a solvent. Furthermore, the aluminum-containing oxide, titanium-containing oxide, and carbon black may adsorb moisture from the air. Therefore, when expressing the content of each component, it is appropriate to express the content in terms of solids content, rather than the content of the components actually mixed. Specifically, the solid content of the aqueous alkyd resin contained in the coating agent for forming an etching resist film is defined as 100 parts by mass, and the content is expressed in parts by mass of the solid content of the other components calculated based on this.

[0020] The content of each component expressed in terms of solid content remains unchanged before and after application and baking of the coating agent for forming an etching resist film. Therefore, by quantitatively analyzing the components of the etching resist film after baking, the content of each component, calculated as solid content, contained in the coating agent for forming an etching resist film before baking can be determined.

[0021] <Components of Coating Agent for Forming Etching Resist Film> Hereinafter, each component contained in the coating agent for forming an etching resist film according to the present invention will be described.

[0022] (1) Water-based alkyd resin The coating agent for forming an etching resist film according to the present invention contains 100 parts by mass of water-based alkyd resin in a solvent, calculated as solid content. As described above, the water-based alkyd resin is the main component of the coating agent for forming an etching resist film according to the present invention, and also serves as the main component of the etching resist film after application and baking. Water-based resin is a general term for both water-dispersible resins in which the resin is uniformly dispersed in water, and water-soluble resins that are easily soluble in water.

[0023] As the aqueous alkyd resin, any conventionally known resin can be used without any particular limitation. The alkyd resin, which is the raw material for the aqueous alkyd resin, can be obtained by a dehydration condensation reaction between a polybasic acid, a polyhydric alcohol, and a fat or oil or a processed fat or oil product, and optionally further reacting with a monobasic acid. In a preferred embodiment, the coating agent for forming an etching resist film according to the present invention is an aqueous alkyd resin obtained by reacting an alkyd resin with a polymerizable vinyl monomer. In this preferred embodiment, by using an aqueous alkyd resin obtained by reacting an alkyd resin with a polymerizable vinyl monomer, a coating agent for forming an etching resist film can be obtained that can form an etching resist film with excellent resist properties and removability.

[0024] (Polybasic Acid) Examples of polybasic acids used in the synthesis of alkyd resins include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic acid, succinic acid, maleic acid, adipic acid, sebacic acid, azelaic acid, himic acid, itaconic acid, methylhexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid, methylcyclohexenetricarboxylic acid, pyromellitic acid, and anhydrides thereof. These polybasic acids can be used alone or in combination of two or more.

[0025] (Polyhydric Alcohols) Examples of polyhydric alcohols used in the synthesis of alkyd resins include ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, butanediol, decanediol, diethylene glycol, pentanediol, neopentyl glycol, butylethylpropanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, etc. These polyhydric alcohols can be used alone or in combination of two or more.

[0026] (Oils and fats and processed oil products) Examples of oils and fats used in the synthesis of alkyd resins include tung oil, linseed oil, dehydrated castor oil, safflower oil, soybean oil, castor oil, tall oil, rice bran oil, and their fatty acids, hygienic fatty acids, etc. Furthermore, processed oil products can be obtained using the above-mentioned oils and fats as the main raw material. Examples of such processed oil products include modified oils, isomerized oils, polymerized oils, maleated oils, boiled oils, etc., which are obtained using the above-mentioned oils and fats as the main raw material. These oils and fats and processed oil products can be used alone or in combination of two or more.

[0027] (Monobasic Acid) Examples of monobasic acids optionally used in the synthesis of alkyd resins include benzoic acid, p-t-butylbenzoic acid, methylbenzoic acid, versatic acid, isodecanoic acid, isotridecanoic acid, crotonic acid, non-drying oil fatty acids, etc. These monobasic acids can be used alone or in combination of two or more.

[0028] (Polymerizable vinyl monomer) In a preferred embodiment of the present invention, as the polymerizable vinyl monomer to be reacted with the alkyd resin to obtain the aqueous alkyd resin, any conventionally known polymerizable vinyl monomer can be used without any particular limitation. Examples of polymerizable vinyl monomers used in the reaction with the alkyd resin include (meth)acrylic acid ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, ethylcyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, toluyl (meth)acrylate, and glycidyl (meth)acrylate; aromatic polymerizable unsaturated monomers such as styrene, α-methylstyrene, chlorostyrene, vinyltoluene, vinylnaphthalene, phenyl (meth)acrylate, benzyl (meth)acrylate, and vinyl benzoate; vinyl monomers such as vinyl acetate and vinyl propionate; N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylate. N-alkoxy-substituted amide monomers such as diethyl(meth)acrylamide; fluorine-containing vinyl monomers such as perfluoroethylene, perfluoropropylene, and vinylidene fluoride; silicon-containing vinyl monomers such as vinyltrimethoxysilane and vinyltriethoxysilane; dialkyl esters of maleic acid and fumaric acid; alkenes such as ethylene and propylene; conjugated dienes such as butadiene and isoprene; monomers such as vinyl chloride and allyl chloride; (meth)acrylic acid, itaconic acid, maleic acid monomethyl ester, maleic acid monobutyl ester, itaconic acid monobutyl ester, sulfonic acid group-containing (meth)acrylates, phosphoric acid group-containing (meth)acrylates, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate;Lactone adducts of 2-hydroxyethyl (meth)acrylate, ring-opening adducts of ethylene oxide to 2-hydroxyethyl (meth)acrylate or 2-hydroxypropyl (meth)acrylate, ring-opening adducts of propylene oxide to 2-hydroxyethyl (meth)acrylate or 2-hydroxypropyl (meth)acrylate, dimers and trimers of 2-hydroxyethyl (meth)acrylate or 2-hydroxypropyl (meth)acrylate, N,N-dimethylaminoethyl ... Examples of the polymerizable vinyl monomer include N,N-methylethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dipropylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-methylpropylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, N,N-dipropylaminopropyl (meth)acrylate, N,N-dimethylaminopropyl acrylamide, and N,N-diethylaminopropyl acrylamide. These polymerizable vinyl monomers can be used alone or in combination of two or more.

[0029] The aqueous alkyd resin may be commercially available or synthesized from raw materials. When using a commercially available product, it is preferable to use one synthesized using one of the compounds listed above as raw materials. When synthesizing an aqueous alkyd resin from raw materials, the following procedure is preferably used. First, a predetermined amount of polybasic acid, polyhydric alcohol, oil or fat or processed oil product, and optionally a monobasic acid are charged into a reaction vessel, and the contents are heated while stirring to cause a dehydration condensation reaction. When the acid value of the solids reaches 3 to 30 mgKOH / g, heating is stopped and the mixture is cooled. The acid value of the solids is preferably measured in accordance with Japanese Industrial Standard JIS K 0070. Next, a solvent is added to the resulting reaction mixture to form an alkyd resin solution. The alkyd resin solution is heated with stirring, and a previously prepared mixture of polymerizable vinyl monomer and polymerization initiator is added dropwise. After the dropwise addition is complete, the polymerization initiator is further added dropwise to the reaction mixture, and the mixture is stirred and allowed to react. Furthermore, a neutralizing agent and a solvent are added to the reaction mixture and mixed to obtain a solution containing a water-based alkyd resin.

[0030] The aqueous alkyd resin synthesized by the above procedure preferably has an acid value of 30 mgKOH / g or more and 80 mgKOH / g or less, a hydroxyl value of 50 mgKOH / g or more and 150 mgKOH / g or less, a number average molecular weight of 2,000 or more and 10,000 or less, and a weight average molecular weight of 10,000 or more and 50,000 or less.

[0031] The solvent used in synthesizing the water-based alkyd resin is not particularly limited. Preferred solvents include glycol ethers such as ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-t-butyl ether, dipropylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, and t-butyl cellosolve; and alcohols such as isopropyl alcohol and butyl alcohol.

[0032] The polymerization initiator used in synthesizing the water-based alkyd resin is not particularly limited, but preferred examples of the polymerization initiator include dibenzoyl peroxide and 2,2'-azobisbutyronitrile.

[0033] The neutralizing agent used in synthesizing the water-based alkyd resin is not particularly limited, but preferred neutralizing agents include, for example, triethylamine and diethylethanolamine.

[0034] (2) Melamine Resin The coating agent for forming an etching resist according to the present invention contains 0.10 parts by mass or more and 30 parts by mass or less of a melamine resin in a solvent, calculated as solid content. The melamine resin is contained in the coating agent for forming an etching resist as a crosslinking agent that crosslinks the aqueous alkyd resin. The inclusion of the melamine resin improves adhesion between the etching resist film and the grain-oriented electrical steel sheet. Examples of the melamine resin that can be used include methylated melamine and butylated melamine.

[0035] When the solvent contains 0.10 parts by mass or more of melamine resin per 100 parts by mass of the aqueous alkyd resin, calculated as solid content, the adhesion between the formed etching resist film and the grain-oriented electrical steel sheet is enhanced, and the resist properties are improved. On the other hand, when the melamine resin is contained in an amount of 30 parts by mass or less, the crosslink density does not increase excessively. As a result, the etching resist film maintains appropriate hardness and adhesion, and the removability of the etching resist film does not deteriorate. Therefore, the content of the melamine resin is set to 0.10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the aqueous alkyd resin, calculated as solid content. The content of the melamine resin is preferably 1.0 part by mass or more, and more preferably 2.0 parts by mass or more. The content of the melamine resin is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less.

[0036] (3) Aluminum-Containing Oxide The coating agent for forming an etching resist film according to the present invention contains 20 parts by mass or more and 200 parts by mass or less of an aluminum-containing oxide in a solvent, calculated as solid content. The type of aluminum-containing oxide is not particularly limited, and various known oxides can be used; for example, alumina, alumina-coated silica, kaolinite, etc. are preferably used. By including an aluminum-containing oxide whose thermal conductivity is higher than that of the aqueous alkyd resin, the thermal conductivity of the etching resist film is increased, improving its laser removability. These aluminum-containing oxides can be used alone or in combination of two or more.

[0037] Alumina is also called alumina sol, and its shape is not particularly limited and may be, for example, granular or fibrous. Regarding size, in the case of granular, the average particle size is preferably 5.0 nm or more and 100 nm or less, and in the case of fibrous, the length is preferably 50 nm or more and 200 nm or less, from the viewpoint of the mixability of the coating agent and the appearance of the coating. By setting the size of the alumina within the above range, it becomes easy to mix the alumina uniformly into the coating agent for forming an etching resist film, and the stability of the coating agent can be improved. Here, "stability of the coating agent" specifically refers to the stability as a paint, such as the absence of precipitation of the aluminum-containing oxide and deterioration of quality when used as a coating agent for forming an etching resist film.

[0038] Kaolinite is a hydrous silicate of aluminum, also known as kaolin, and contains alumina and silica. From the viewpoint of the stability of the coating agent, the particle size of the kaolinite is preferably 1.0 μm or more and 30 μm or less.

[0039] Alumina-coated silica is a mixture of alumina and silica. Alumina-coated silica has a form in which alumina is unevenly distributed on the surface of the silica, and is therefore preferable from the viewpoint of the stability of the coating agent. The particle diameter of the alumina-coated silica is preferably 1.0 μm or more and 30 μm or less from the viewpoint of the stability of the coating agent.

[0040] When the solvent contains 20 parts by mass or more of an aluminum-containing oxide per 100 parts by mass of the solid content of the aqueous alkyd resin, the laser removability and resist properties are improved. On the other hand, when the solvent contains 200 parts by mass or less of an aluminum-containing oxide, the adhesion of the etching resist film is improved. Therefore, the content of the aluminum-containing oxide is set to 20 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the aqueous alkyd resin, converted into solid content. The content of the aluminum-containing oxide is preferably 30 parts by mass or more. The content of the aluminum-containing oxide is preferably 150 parts by mass or less.

[0041] (4) Titanium-Containing Oxide The coating agent for forming an etching resist film according to the present invention contains a titanium-containing oxide in a solvent in an amount of 10 parts by mass or more and 100 parts by mass or less, calculated as solids. The type of titanium-containing oxide is not particularly limited, and various known titanium-containing oxides can be used. For example, titania (rutile type) and titania (anatase type) are preferably used. By including a titanium-containing oxide having a higher thermal conductivity than that of the aqueous alkyd resin, the thermal conductivity of the etching resist film is increased, improving its laser removability. These titanium-containing oxides can be used alone or in combination of two or more types.

[0042] When the solvent contains 10 parts by mass or more of titanium-containing oxide per 100 parts by mass of the solid content of the aqueous alkyd resin, the laser removability and resist properties are improved. On the other hand, when the titanium-containing oxide is contained in an amount of 100 parts by mass or less, the titanium-containing oxide can be easily mixed uniformly into the coating agent, improving adhesion. Therefore, the content of titanium-containing oxide is set to 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the aqueous alkyd resin, converted into solid content. The content of titanium-containing oxide is preferably 15 parts by mass or more. The content of titanium-containing oxide is preferably 80 parts by mass or less.

[0043] (5) Carbon Black The coating agent for forming an etching resist film according to the present invention contains 0.10 parts by mass or more and 5.0 parts by mass or less of carbon black in terms of solid content in a solvent. The inclusion of an appropriate amount of carbon black improves laser removability. That is, the carbon black in the present invention is not contained as a pigment for coloring the etching resist film, but is contained for the purpose of improving the laser removability of the etching resist film, similar to the aluminum-containing oxide and titanium-containing oxide. The type of carbon black is not particularly limited, and various known carbon blacks can be used.

[0044] When the solvent contains 0.10 parts by mass or more of carbon black per 100 parts by mass of the solids content of the aqueous alkyd resin, the laser removability is improved. On the other hand, when the solvent contains 5.0 parts by mass or less of carbon black, it becomes easier to uniformly mix the carbon black into the coating agent, improving the stability of the coating agent and the laser removability. Therefore, the carbon black content is set to 0.10 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the aqueous alkyd resin, converted into solids. The carbon black content is preferably 1.0 part by mass or more. The carbon black content is preferably 3.0 parts by mass or less.

[0045] Although the details of why the laser removability is further improved when the solvent for the coating agent for forming an etching resist according to the present invention contains carbon black in addition to an aluminum-containing oxide and a titanium-containing oxide are unknown, the inventors believe the following: As described above, the inclusion of an aluminum-containing oxide and a titanium-containing oxide in the solvent increases the thermal conductivity of the etching resist film. In contrast, although the thermal conductivity of graphite, which constitutes carbon black, is higher than that of aqueous alkyd resin, the content of carbon black in the solvent in the present invention is lower than that of the aluminum-containing oxide and the titanium-containing oxide. Furthermore, the particle size of carbon black is very fine. Therefore, the inclusion of carbon black does not significantly improve the thermal conductivity of the etching resist film.

[0046] On the other hand, the emissivity of carbon black is higher than that of aluminum-containing oxides and titanium-containing oxides. Furthermore, as mentioned above, when the carbon black is contained in an amount of 5.0 parts by mass or less, the carbon black can be uniformly mixed in the coating agent. Therefore, when a laser is irradiated onto the surface of an etching resist film containing a predetermined amount of carbon black, the carbon black particles uniformly dispersed on the surface radiate heat only within the laser-irradiated area. This is thought to further improve the property of the etching resist film to be accurately removed according to the laser irradiation pattern, i.e., laser removability, compared to a film not containing carbon black.

[0047] As shown in the examples below, the inventors' investigations have shown that the above-mentioned unique effects of carbon black are achieved when the solvent contains 0.10 parts by mass or more of carbon black per 100 parts by mass of aqueous alkyd resin. This is thought to be because, even at trace amounts, the carbon black is uniformly dispersed on the surface of the etching resist film, thereby achieving the above-mentioned heat radiation effect. On the other hand, when the solvent contains more than 5.0 parts by mass of carbon black per 100 parts by mass of aqueous alkyd resin, laser removability actually decreases. This is because, as mentioned above, it becomes difficult to uniformly mix the carbon black into the coating agent. Thus, the preferred range of the carbon black content in the present invention is significantly different from the preferred range when carbon black is added simply as a pigment for coloring.

[0048] As described above, in the coating agent for forming an etching resist according to the present invention, the aluminum-containing oxide, the titanium-containing oxide, and the carbon black are all components that contribute to improving laser removability. However, the aluminum-containing oxide and the titanium-containing oxide, which are metal oxides, and the carbon black, which is a non-metallic substance, have significantly different mechanisms of contribution to laser removability and preferred ranges of content. In the present invention, by containing optimal amounts of the metal oxide and the carbon black, which have different properties, it is possible to achieve better laser removability than when only one of them is contained.

[0049] (6) Total Solids Content In the coating agent for forming an etching resist film according to the present invention, the total solid content of the aqueous alkyd resin, melamine resin, aluminum-containing oxide, titanium-containing oxide, and carbon black accounts for 80% by mass or more of the total solids content. In this specification, "total solids content" refers to the total solid content of all components contained in the coating agent for forming an etching resist film. When the total solid content of the aqueous alkyd resin, melamine resin, aluminum-containing oxide, titanium-containing oxide, and carbon black accounts for 80% by mass or more of the total solids content, the components of the etching resist film formed by the coating agent for forming an etching resist film are not significantly diluted by the other components described below. Therefore, the effects of the present invention exhibited by the etching resist film are not impaired. There is no particular upper limit on the total solid content of the aqueous alkyd resin, melamine resin, aluminum-containing oxide, titanium-containing oxide, and carbon black, and this total content may be 100% by mass or less.

[0050] (7) Solvent The coating agent for forming an etching resist film according to the present invention contains a water-based alkyd resin, a melamine resin, an aluminum-containing oxide, a titanium-containing oxide, and carbon black in a solvent. The solvent functions to uniformly dissolve the resin and uniformly mix the pigment, and also facilitates application of the coating agent for forming an etching resist film. In addition, from the viewpoint of affinity with the water-based alkyd resin, the solvent preferably contains ethylene glycol mono-n-butyl ether.

[0051] The solvent can be used by mixing with a hydrophilic solvent. Specific examples of hydrophilic solvents include glycol ethers such as diethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-butyl ether, propylene glycol mono-t-butyl ether, dipropylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, and t-butyl cellosolve, as well as alcohols such as isopropyl alcohol and butyl alcohol. These solvents can be used alone or in combination of two or more.

[0052] The solvent may be mixed with a hydrophobic solvent such as toluene, xylene, etc. These hydrophobic solvents may be used alone or in combination of two or more.

[0053] The proportion of the solvent in the coating agent for forming an etching resist film is not particularly limited, but is preferably 20% by mass or more and 90% by mass or less. In other words, the proportion of the total solids in the coating agent for forming an etching resist film is preferably 10% by mass or more and 80% by mass or less. When the amounts of the solvent and total solids in the coating agent for forming an etching resist film are within the above ranges, the storage stability of the coating agent for forming an etching resist film and the workability when applying it to a grain-oriented electrical steel sheet are good.

[0054] (8) Other Components In a preferred embodiment, the coating agent for forming an etching resist film according to the present invention further contains one or more components selected from surfactants, rust inhibitors, lubricants, leveling agents, neutralizing agents, antifoaming agents, antioxidants, and coloring pigments in a solvent. These components are added to further improve the performance and uniform application of the etching resist film. These other components can be used alone or in combination of two or more. When the total amount of the solid content of these other components is 20 mass% or less of the total solid content, the performance of the etching resist film can be sufficiently maintained.

[0055] <Method for Producing a Coating Agent for Forming an Etching Resist Film> Next, a method for producing a coating agent for forming an etching resist film according to the present invention will be described. The method for producing a coating agent for forming an etching resist film is not particularly limited, but preferably follows the procedure below. First, a portion of a solution containing an aqueous alkyd resin is placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, etc., and an aluminum-containing oxide, a titanium-containing oxide, and carbon black, as well as a hydrophilic solvent as needed, are added to uniformly disperse the mixture. Next, the remainder of the solution containing the aqueous alkyd resin and a melamine resin are added and dispersed to obtain a dispersion. A leveling agent, a neutralizing agent, an antifoaming agent, and a solvent or water are added to the obtained dispersion as needed to obtain a coating agent for forming an etching resist film.

[0056] <Method for producing steel sheet with etching resist film> Next, a preferred method for producing a steel sheet with an etching resist film using the coating agent for forming an etching resist film according to the present invention will be described. However, the method for producing a steel sheet with an etching resist film using the coating agent for forming an etching resist film according to the present invention is not limited to the method described here.

[0057] (1) Steel Sheet First, a steel sheet to which a coating agent for forming an etching resist film is applied is prepared. The steel sheet to which the coating agent for forming an etching resist film is applied is any steel sheet that will eventually become a grain-oriented electrical steel sheet and has been hot-rolled. Grain-oriented electrical steel sheets are generally manufactured by the following process: a steel slab is hot-rolled to form a hot-rolled steel sheet; the hot-rolled steel sheet or the hot-rolled annealed steel sheet obtained by hot-rolling the hot-rolled steel sheet is then cold-rolled once or twice or more times with intermediate annealing between them to form a cold-rolled steel sheet; the cold-rolled steel sheet is then subjected to primary recrystallization annealing to form a primary recrystallized sheet; and the primary recrystallized sheet is then subjected to secondary recrystallization annealing to obtain a secondary recrystallized sheet.

[0058] When a grain-oriented electrical steel sheet is manufactured using a steel sheet with an etching resist coating, the components and composition of the final grain-oriented electrical steel sheet are not particularly limited. The thickness of the grain-oriented electrical steel sheet is also not particularly limited. While thinner steel sheets reduce iron loss, excessively thin steel sheets not only deteriorate shape stability but also increase the manufacturing costs of the steel sheet. Therefore, the thickness of the grain-oriented electrical steel sheet is preferably 50 μm or more. Furthermore, as the sheet thickness increases, iron loss also increases. Therefore, the thickness of the grain-oriented electrical steel sheet is preferably 0.50 mm or less, and more preferably 0.30 mm or less.

[0059] In the present invention, there are two types of steel sheets to which the coating agent for forming an etching resist film is applied. One is a grain-oriented electrical steel sheet as a finished product obtained by completing all processes up to the secondary recrystallization annealing described above. The other is a steel sheet as an intermediate product during the manufacturing of a grain-oriented electrical steel sheet. Specific examples of the latter include a hot-rolled steel sheet after hot rolling, a hot-rolled annealed sheet obtained by hot-rolling a hot-rolled steel sheet, a cold-rolled steel sheet after cold rolling in a single cold rolling process, a cold-rolled steel sheet before or after intermediate annealing or a cold-rolled steel sheet after intermediate annealing in a case where cold rolling is performed in two or more processes with an intermediate annealing in between, and a primary recrystallized sheet after primary recrystallization annealing. In the present invention, the steel sheet to which the coating agent for forming an etching resist film is applied is collectively referred to as a "steel sheet" regardless of whether it is a finished product or an intermediate product.

[0060] In the present invention, the target to be subjected to the etching treatment by applying the coating agent for forming an etching resist film may be either the above-mentioned finished steel sheet or an intermediate steel sheet. However, if the intermediate steel sheet is subjected to the etching treatment to form grooves on the surface thereof and then further rolled, the grooves formed by the etching treatment may disappear. Therefore, when an intermediate steel sheet is used, it is preferable to use a cold-rolled steel sheet or a primary recrystallized steel sheet after all cold rolling has been completed.

[0061] In the present invention, the etching resist film formed on the surface of the steel sheet may be burned or altered at high temperatures when the steel sheet is subjected to heat treatment. Therefore, when the intermediate product described above is used as the steel sheet to which the coating agent for forming an etching resist film is applied, it is preferable to apply the coating agent for forming an etching resist film, followed by baking, laser irradiation, and etching in succession, and then carry out the subsequent steps involving heat treatment. Note that the number of times this series of steps for forming grooves on the surface of the steel sheet is carried out may be one or more.

[0062] (2) Application of Coating Agent for Forming an Etching Resist Film Next, the coating agent for forming an etching resist film according to the present invention is uniformly applied to the surface of the steel sheet. The method for applying the coating agent for forming an etching resist film is not particularly limited, and it can be applied by methods such as roll coating, flow coating, knife coating, or spray coating. The surface to which the coating agent for forming an etching resist film is applied may be one surface of the steel material, or both surfaces of the steel material.

[0063] (3) Baking Treatment of Coating Agent for Forming Etching Resist Film Next, the steel sheet coated with the coating agent for forming an etching resist film is baked. The method for performing the baking treatment is not particularly limited, and commonly used baking treatments such as hot air, infrared heating, and induction heating can be applied.

[0064] The baking temperature of a steel sheet coated with the coating agent for forming an etching resist film according to the present invention is preferably 120°C or higher and 350°C or lower in terms of the maximum steel sheet temperature. In this specification, "maximum steel sheet temperature" refers to the temperature measured on the surface of the steel sheet and the maximum temperature reached in the heat treatment process. If the maximum steel sheet temperature is 120°C or higher, the curing of the coating agent for forming an etching resist film proceeds sufficiently. The maximum steel sheet temperature is more preferably 150°C or higher, and even more preferably 170°C or higher. If the maximum steel sheet temperature is 350°C or lower, thermal decomposition of the etching resist film can be prevented. The maximum steel sheet temperature is more preferably 300°C or lower, and even more preferably 260°C or lower.

[0065] The baking time in the baking treatment, i.e., the time from the start of heating until the steel sheet temperature reaches the maximum, is not particularly limited. However, from the viewpoint of sufficiently volatilizing the solvent component in the coating agent for forming an etching resist film to form a film, the baking time is preferably 3 seconds or more. On the other hand, when the baking treatment is performed by induction heating, the baking time is preferably 30 seconds or less from the viewpoint of suppressing the occurrence of cell-like unevenness in the coating component called Benard cells. Furthermore, when the baking treatment is performed by a method other than induction heating, the baking time is preferably 60 seconds or less from the viewpoint of productivity.

[0066] The amount of etching resist film attached to one side was 0.50 g / m ２ The adhesion amount of the etching resist film is preferably 0.50 g / m or more. ２ By setting the above, it is possible to provide a steel sheet with an etching resist film having particularly excellent resist properties. ２ It is more preferable that the amount of the etching resist film deposited on one side is 20 g / m or more. ２ The deposition amount of the etching resist film is preferably 20 g / m or less. ２The amount of the etching resist film deposited on one side can be determined by dissolving and removing only the etching resist film from the steel sheet with the etching resist film after baking treatment using a hot alkali or the like, and measuring the change in weight of the steel sheet before and after removal.

[0067] (4) Laser irradiation Next, the surface of the steel sheet coated with the etching resist film is irradiated with a laser while scanning the laser in a direction intersecting the rolling direction of the steel sheet. This laser irradiation locally heats and removes the etching resist film in the irradiated areas, resulting in the formation of film-removed areas where the surface of the steel sheet is exposed. The film-removed areas are selectively etched in the etching step described below, forming linear grooves in the surface of the steel sheet. The arrangement and dimensions of the linear grooves formed by etching affect the final magnetic properties of the grain-oriented electrical steel sheet, so the pattern of the etching resist film, i.e., the arrangement and dimensions of the film-removed areas, can be determined in consideration of the magnetic properties of the grain-oriented electrical steel sheet.

[0068] The linear coating-removed portions are provided in a direction that intersects with the rolling direction, and the angle between the rolling direction and the direction in which the linear coating-removed portions are provided is preferably 50° or more, more preferably 60° or more, and most preferably 90°. The coating-removed portions may be provided linearly in a continuous manner or discontinuously. The coating-removed portions may be provided at equal intervals or may not be provided at equal intervals. The width of the coating-removed portions may be, for example, 0.20 mm.

[0069] In the laser irradiation step, laser scanning is preferably performed periodically in the rolling direction of the steel sheet. In this case, the interval between the linear coating removal portions in the rolling direction of the steel sheet is preferably 1.0 mm or more and 30 mm or less. The laser light source may be any laser capable of removing the etching resist coating, but from the viewpoint of output, a solid-state laser such as a fiber laser or a CO ２It is preferable to use a laser, etc. The laser output, irradiation energy per unit scanning length, scanning speed, beam diameter, and beam long / short axis ratio may be determined taking into consideration the shape of the coating removal portion, productivity, cost, etc.

[0070] (5) Etching Treatment Next, the steel sheet with the etching resist film after laser irradiation is etched to form grooves on the surface of the steel sheet in the coating-removed areas. By forming etched grooves on the surface of the steel sheet, the width of the magnetic domains is narrowed, and iron loss is reduced. The etching method is not particularly limited, but can be, for example, electrolytic etching. When electrolytic etching is performed, the electrolyte is preferably NaCl, KCl, CaCl ２ , NaNO ３ It is preferable to use a current density of 5 to 50 A / dm ２ The electrolysis time is preferably about 5 to 20 seconds. The conditions of the etching process are preferably adjusted so that, in a cross section perpendicular to the extension direction of the groove formed by the etching process, the angle between the sidewall of the groove and the plate thickness direction is 60 degrees or less, and the height of the convex portion formed at the bottom of the groove is 1 / 2 or less of the maximum depth of the groove. By adjusting the shape of the groove in this way, the effect of reducing iron loss is increased. The depth of the groove can be, for example, 20 μm.

[0071] In the method for producing grain-oriented electrical steel sheet, after the etching treatment, the remaining treatments required to convert the steel sheet into a grain-oriented electrical steel sheet are appropriately carried out depending on the treatment stage of the steel sheet in the above-mentioned manufacturing process of the grain-oriented electrical steel sheet, thereby making it possible to produce a grain-oriented electrical steel sheet with reduced iron loss.

[0072] In the method for producing grain-oriented electrical steel sheet, after grooves are formed by etching, the etching resist film remains on the steel sheet coated with the etching resist film. This etching resist film may or may not be peeled off after the etching process. If the etching resist film is not peeled off, it can also function as an insulating tension film. When the etching resist film is removed, the method for the removal process is not particularly limited, and any well-known method can be used. For example, the etching resist film can be removed by immersing the steel sheet in an alkaline solution such as an aqueous NaOH solution to soften the etching resist film, and then rinsing and removing the etching resist film with a brush.

[0073] The effects of the present invention will be specifically explained below based on examples, but the present invention is not limited to these examples.

[0074] Example 1 (1) Production of a coating agent for forming an etching resist film The resin, melamine resin, aluminum-containing oxide, titanium-containing oxide, carbon black, and other components shown in Table 1 were prepared as starting materials. Of the starting materials shown in Table 1, the water-based alkyd resin indicated by symbol a1 was produced by the method described below. The other starting materials used were those manufactured by the manufacturers and with trade names shown in Table 1.

[0075]

[0076] The aqueous alkyd resin designated by symbol a1 in Table 1 was produced by the following method. First, 75 parts by mass of linseed oil, 16 parts by mass of glycerin, 40 parts by mass of phthalic anhydride, 1 part by mass of maleic anhydride, 20 parts by mass of pentaerythritol, and 5 parts by mass of xylene were placed in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dehydrator, and nitrogen gas inlet tube. The mixture was stirred and heated under a nitrogen atmosphere until the temperature of the mixture reached 220°C. The reaction was continued until the acid value of the solid content of the mixture reached 8 mgKOH / g, and then the mixture was cooled. The acid value of the solid content was measured in accordance with Japanese Industrial Standard JIS K 0070. Next, 72 parts by mass of ethylene glycol mono-n-butyl ether was added as a solvent to the obtained reaction mixture and mixed to obtain an alkyd resin solution having an oil length of 55%, an acid value of 8 mgKOH / g, a hydroxyl value of 120 mgKOH / g, a heating residue of 65%, a number average molecular weight of 3,200, and a weight average molecular weight of 19,500.

[0077] Next, 150 parts by mass of the obtained alkyd resin solution was charged into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, etc., and stirred while heating. Once the temperature of the solution reached 110°C, a mixture obtained by pre-mixing 16 parts by mass of styrene, 16 parts by mass of methyl methacrylate, 4 parts by mass of acrylic acid, and 1 part by mass of dibenzoyl peroxide as a polymerization initiator was added dropwise over 4 hours to carry out a dehydration condensation reaction. After completion of the dropwise addition, while maintaining the reaction mixture at 110°C, a mixture of 0.5 parts by mass of dibenzoyl peroxide and 5 parts by mass of ethylene glycol mono-n-butyl ether as a polymerization initiator was further added dropwise over 3 hours, and the reaction was continued with stirring at 110°C for 2 hours, followed by cooling. Next, 14 parts by mass of triethylamine was added to the obtained reaction mixture and stirred, and then 5 parts by mass of ethylene glycol mono-n-butyl ether was added and mixed to obtain a solution containing an aqueous alkyd resin having an oil length of 38, an acid value of 56 mgKOH / g, a hydroxyl value of 84 mgKOH / g, a heating residue of 65%, a number average molecular weight of 3,200, and a weight average molecular weight of 25,700 (symbol a1 in Table 1).

[0078] Next, the starting materials shown in Table 1 were mixed according to the following procedure to prepare a coating agent for forming an etching resist film having the components and solids content shown in Table 2. First, a portion of the resin-containing solution was placed in a disperser, and aluminum-containing oxide, titanium-containing oxide, carbon black, an organic pigment (f1 or f2) among the other components, and ethylene glycol mono-n-butyl ether (10% by mass of the total) as a solvent were added and uniformly dispersed. A particle gauge was used to confirm that the particle diameter of components other than the resin or solvent was 10 μm or less. Next, the remaining resin and melamine resin were added and dispersed to obtain a dispersion. Furthermore, to improve film-forming properties, 0.5% by mass of a surfactant (f3 or f4) among the other components was added to the resulting dispersion. Furthermore, triethylamine was added as a neutralizing agent and ethylene glycol mono-n-butyl ether was added as a solvent to adjust the pH of the coating agent for forming an etching resist film to 9.0 and the proportion of total solids in the coating agent for forming an etching resist film to 63.0% by mass.

[0079] The components and solid content equivalents of the resulting coating materials for forming etching resist films, No. 1 to No. 33, which have different component compositions, are shown in Table 2. The content of each component shown in Table 2, expressed in mass %, is the proportion of the solid content of each component to the total solid content. Furthermore, the content expressed in parts by mass is the mass parts of the other components based on 100 parts by mass of the resin (symbol a1, a2, or a3). It should be noted that, among the coating agents for forming etching resist films shown in Table 2, No. 33, which is a comparative example, uses a water-based epoxy resin (symbol a3) as the resin, rather than a water-based alkyd resin.

[0080]

[0081] (2) Production of Steel Sheet with Etching Resist Coating A steel sheet measuring 150 mm wide and 300 mm long was cut out from a grain-oriented electrical steel sheet with a thickness of 0.23 mm and used as a test material. The coating agent for forming an etching resist film produced by the above method was uniformly applied to the entire surface of one side of this test material using a roll coater. Next, the test material coated with the coating agent for forming an etching resist film was baked in a hot air oven at the maximum steel sheet temperature and drying time shown in Table 3, and then allowed to cool to room temperature to obtain a steel sheet with an etching resist coating.

[0082] Next, the properties of the steel sheets with etching resist films Nos. 1 to 33 manufactured by the above method were evaluated by the following methods. The evaluation results are shown in Table 3.

[0083]

[0084] <Adhesion Weight> The adhesion weight of the etching resist film after baking was measured by a gravimetric method. Specifically, the etching resist film alone was dissolved and removed from the test material using a heated potassium hydroxide solution, and the weight change of the steel sheet before and after dissolution and removal was measured. The adhesion weight was calculated by dividing the measured weight change by the area of ​​one side of the test material.

[0085] <Adhesion> A test material was cut into a size of 30 mm in width and 50 mm in length, and a cellophane adhesive tape 24 mm in width and 50 mm in length was attached to the surface of the cut test material on which the etching resist film was formed (the test surface). Next, the test material was bent 180° using a round rod with a diameter of 5 mm, with the test surface as the compression side, and then the cellophane adhesive tape was peeled off. The area ratio of the etching resist film that had adhered to the cellophane adhesive tape and peeled off was calculated, and the adhesion was evaluated according to the following criteria. A rating of A or B was considered to be pass, and F was considered to be fail. (Evaluation criteria) A: Area ratio is 5.0% or less B: Area ratio is more than 5.0% and 10% or less F: Area ratio is more than 10%

[0086] <Scratch Resistance> Two test pieces of each type were prepared by cutting the test material into a size of 100 mm in width and 200 mm in length. For each of the two test pieces, the test surfaces on which the etching resist film was formed were placed together, and a pressure of 196 kPa (2 kgf / cm) was applied in the direction normal to the test surfaces. ２ ) while applying a pressure of 1000 kJ / s, the specimen was slid lengthwise at a relative speed of 2 cm / s for 10 seconds. Next, scratches on the surface of the test surface were visually observed to calculate the scratch occurrence area ratio, and scratch resistance was evaluated according to the following criteria. A rating of A, B, or C was considered to be pass, and F was considered to be fail. (Evaluation criteria) A: Almost no scratches were observed B: Only a few scratches were observed C: Clear scratches were observed F: Scratches were observed to the extent that the base steel was exposed

[0087] <Laser removability> The laser removability of the etching resist film was evaluated as follows. First, a steel plate with an etching resist film was irradiated with a laser. The output of the light source used for laser irradiation was 2.0 kW, the beam diameter was 50 μm, and the long / short axis ratio of the beam was 1.02. The scanning speed was 10 m / s. The laser irradiation conditions were set so that the width of the film-removed portion would be approximately 40 μm. Next, the width of the film-removed portion after laser irradiation was measured using an optical microscope and evaluated according to the following criteria. A rating of A or B was considered acceptable, and F was considered unacceptable. (Evaluation criteria) A: The width of the film-removed portion was in the range of 30 μm or more and 50 μm or less. B: The width of the film-removed portion was in the range of 20 μm or more and 60 μm or less. F: The width of the film-removed portion varied beyond the range of 20 μm or more and 60 μm or less.

[0088] <Resist Properties> The test material was cut into a size of 30 mm in width and 250 mm in length and subjected to electrolytic etching. The appearance of the surface of the etched resist film after electrolytic etching was visually observed, and the area ratio of the part where discoloration was observed was calculated to evaluate the resist properties. A 20% aqueous NaCl solution was used as the electrolyte for electrolytic etching. The conditions for electrolytic etching were an electrolyte temperature of 25°C, a current density of 8 A / dm ２The current was applied for 3 minutes. The resist characteristics were evaluated according to the following criteria. A rating of A or B was considered to be pass, and F was considered to be fail. (Evaluation criteria) A: The area ratio of the area where discoloration was observed was 0.0% or less. B: The area ratio of the area where discoloration was observed was greater than 0.0% and less than 5.0%. F: The area ratio of the area where discoloration was observed was greater than 5.0%.

[0089] <Removability> The test material for which the resist properties were evaluated above was immersed in a 15% aqueous sodium hydroxide solution at 50°C for 10 seconds, then removed and washed with water to remove the etching resist film. The test surface of the test material after the etching resist film had been removed was visually observed, and the area ratio of the peeled portion of the etching resist film was calculated to evaluate the removability. The removability was evaluated according to the following criteria. A rating of A or B was considered to be pass, and F was considered to be fail. (Evaluation criteria) A: The area ratio of the peeled portion was 100% B: The area ratio of the peeled portion was 90% or more but less than 100% F: The area ratio of the peeled portion was less than 90%

[0090] According to the evaluation results shown in Table 3, the etching resist films formed using the coating agent for forming an etching resist film according to the present invention passed the property evaluation results for all evaluation items. On the other hand, the test materials Nos. 24 to 32, in which the content of the coating agent for forming an etching resist film in terms of solid content did not satisfy the numerical range of the content specified in the present invention, and the test material No. 33, in which a water-based epoxy resin was used as the resin, failed the property evaluation results for one of the evaluation items.

[0091] Example 2 Using the same method as in Example 1, the starting materials shown in Table 1 were mixed to prepare coating agents for forming etching resist films having the components and solids-equivalent contents shown in Table 4. As in Example 1, the proportion of total solids in the coating agents for forming etching resist films was adjusted to 63.0 mass% at all levels. However, unlike in Example 1, the proportions of the aqueous alkyd resin and melamine resin in the coating agents for forming etching resist films were not fixed, but were adjusted to the proportions shown in Table 4. The components and solids-equivalent contents of the resulting coating materials for forming etching resist films Nos. 34 to 59, which had different component compositions, are shown in Table 4.

[0092]

[0093] Next, steel sheets with etching resist coatings were produced in the same manner as in Example 1, and the properties of the produced steel sheets with etching resist coatings No. 34 to 59 were evaluated in the same manner as in Example 1. However, a hot air oven or an induction heating oven was used for the baking treatment. The evaluation results are shown in Table 5.

[0094]

[0095] According to the evaluation results shown in Table 5, the etching resist film formed using the coating agent for forming an etching resist film according to the present invention passed the property evaluation results for all evaluation items.

Claims

1. In the solvent, in terms of solid content, 100 parts by mass of aqueous alkyd resin, 0.10 parts by mass or more and 30 parts by mass or less of melamine resin, Aluminum-containing oxide, 20 parts by mass or more and 200 parts by mass or less. 10 parts by mass or more and 100 parts by mass or less of titanium-containing oxide, and Carbon black: 0.10 parts by mass or more, and 5.0 parts by mass or less It contains, A coating agent for forming an etching resist film, wherein the total amount of solids of the aqueous alkyd resin, the melamine resin, the aluminum-containing oxide, the titanium-containing oxide, and the carbon black accounts for 80% by mass or more of the total solids.

2. The etching resist film forming coating agent according to claim 1, wherein the aqueous alkyd resin is an aqueous alkyd resin obtained by reacting an alkyd resin with a polymerizable vinyl monomer.

3. The etching resist film forming coating agent according to claim 1 or 2, wherein the proportion of the total solid content in the etching resist film forming coating agent is 10% by mass or more and 80% by mass or less.

4. The etching resist coating agent according to claim 1 or 2, wherein the solvent comprises ethylene glycol mono-n-butyl ether.

5. The coating agent for forming an etching resist film according to claim 3, wherein the solvent comprises ethylene glycol mono-n-butyl ether.