Surface-coated electrical steel sheets, multi-layer cores, and methods of manufacturing them.

Abstract

The invention relates to an electroplated electroplating system comprising an electroplating and an adhesive coating arranged on at least part of one or both surfaces of the electroplating. The adhesive coating consists of (met)acrylic resin A containing a constituent unit derived from a monomer with self-crosslinking groups, and water-soluble (met)acrylic resin B, and the gel portion of the adhesive coating is greater than 20% by mass and less than or equal to 70% by mass.

Description

Adhesive coated electrical steel sheet and laminated core, and manufacturing method thereof

[0001] This disclosure relates to an adhesive-coated electrical steel sheet and laminated core, and to a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2023-163617, filed on September 26, 2023, the contents of which are incorporated herein by reference.

[0002] Conventionally, cores (i.e., iron cores) used in rotating electrical machines and the like are "laminated cores" in which multiple electromagnetic steel sheets are stacked on top of each other. The multiple electromagnetic steel sheets are fixed by methods such as welding, crimping, bolting, and adhesive bonding. However, fixing multiple electromagnetic steel sheets by welding, crimping, and bolting is prone to mechanical stress, thermal stress, interlayer short circuits, and the like during processing. This deteriorates the magnetic properties of the electromagnetic steel sheets, making it difficult for the laminated core to fully demonstrate its performance.

[0003] On the other hand, when fixing multiple electromagnetic steel sheets by adhesive bonding, electromagnetic steel sheets with an adhesive coating are used, and the adhesive coating is hardened by heating and pressure to develop adhesive properties, thereby bonding the multiple electromagnetic steel sheets together. When fixing multiple electromagnetic steel sheets using adhesive-coated electromagnetic steel sheets, mechanical stress, thermal stress, interlayer short circuits, etc. are less likely to occur during processing. Therefore, the magnetic properties of the electromagnetic steel sheets are less likely to deteriorate, and the performance of the laminated core is more likely to be fully demonstrated. Due to these advantages, various technologies for fixing multiple electromagnetic steel sheets by adhesive bonding have been investigated.

[0004] For example, Patent Document 1 discloses "an adhesive surface-coated electrical steel sheet having on its surface an insulating coating that exhibits adhesive properties when heated and / or pressed, wherein the coating is a mixture of a dispersed epoxy resin or modified epoxy resin having a glass transition point (Tg) of 80°C to 150°C, an epoxy resin curing agent, and a particulate polymer having a particle size of 0.01 μm to 0.5 μm."

[0005] Furthermore, Patent Document 2 discloses "an electromagnetic steel sheet laminate comprising a plurality of electromagnetic steel sheets and a fusion layer located between the plurality of electromagnetic steel sheets, the fusion layer comprising polyethylene acrylate including a repeating unit represented by the following chemical formula 1 and a repeating unit represented by the following chemical formula 2, the polyethylene acrylate containing 65 to 90% by weight of the repeating unit represented by the following chemical formula 1 and 10 to 35% by weight of the repeating unit represented by the following chemical formula 2."

[0006] Furthermore, Patent Document 3 discloses "an electromagnetic steel sheet for lamination, the electromagnetic steel sheet comprising an electromagnetic steel sheet and an adhesive insulating coating having a Martens hardness (HM) of 50 or more and less than 500, the adhesive insulating coating being provided on at least one surface of the electromagnetic steel sheet."

[0007] Furthermore, Patent Document 4 discloses "an electromagnetic steel strip or sheet having at least one thermosetting baked enamel layer, which contains an epoxy resin as a main component, at least one curing agent, and at least one filler, provided on one of its flat surfaces, wherein the filler in the baked enamel layer contains a metal carbonate, a metal sulfate, a metal sulfide, a metal silicate, or a metal phosphate, or any mixture of two or more of these."

[0008] Furthermore, Patent Document 5 discloses "an insulating coated electrical steel sheet having a heat-resistant adhesive insulating coating on one or both sides of the electrical steel sheet, the heat-resistant adhesive insulating coating containing 10 mass % or more of a polycarbonate urethane resin having a softening point of 20 to 200°C, and 10 to 1,000 mass parts of a phenol resin per 100 mass parts of the polycarbonate urethane resin."

[0009] International Publication No. 2004 / 070080 Japanese Patent Publication No. 2023-508140 International Publication No. 2016 / 017132 Japanese Patent Publication No. 2018-518591 Japanese Patent Publication No. 2017-179233

[0010] However, in conventional techniques, including those described in Patent Documents 1 to 5, increasing the adhesive strength of the adhesive coating results in a phenomenon in which the magnetic properties of the electrical steel sheet are reduced. In other words, the adhesive strength of the adhesive coating and the magnetic properties of the electrical steel sheet are in a trade-off relationship, and it is difficult to achieve both. In particular, it is necessary to ensure the adhesive strength of the electrical steel sheet with an adhesive coating at room temperature and at high temperatures, and to ensure the adhesive strength even after the electrical steel sheet with an adhesive coating is stored at high temperatures.

[0011] Therefore, there is a demand for further improvements in adhesive coated electrical steel sheets with respect to adhesive strength at room temperature and high temperature, adhesive strength after high temperature storage, and magnetic properties.

[0012] The object of the present disclosure is to provide an adhesive-coated electrical steel sheet that has excellent adhesive strength at room temperature and high temperature, adhesive strength after high-temperature storage, and magnetic properties, a laminated core using the same, and methods for manufacturing the same.

[0013] Specific means for solving the problems include the following aspects. <1> An adhesive-coated electrical steel sheet according to one aspect of the present disclosure comprises an electrical steel sheet and an adhesive coating provided on at least a portion of one or both sides of the electrical steel sheet, wherein the adhesive coating comprises (meth)acrylic resin particles A containing structural units derived from a monomer having a self-crosslinking group, and a water-soluble (meth)acrylic resin B, and the gel fraction of the adhesive coating is more than 20% by mass and not more than 70% by mass. <2> In the adhesive-coated electrical steel sheet of <1> above, the water-soluble (meth)acrylic resin B may be a (meth)acrylic resin containing structural units derived from a monomer having a self-crosslinking group. <3> In the adhesive-coated electrical steel sheet of <1> or <2> above, the ratio of the mass content of the (meth)acrylic resin particles A to the mass content of the water-soluble (meth)acrylic resin B may be 95 / 5 to 85 / 15. <4> In the adhesive-coated electrical steel sheet according to any one of <1> to <3> above, the self-crosslinking group may be one or more of an N-methylol group, an N-butyrol group, a glycidyl group, and an alkoxymethylamide group. <5> A laminated core according to one aspect of the present disclosure comprises a plurality of adhesive-coated electrical steel sheets according to any one of <1> to <4> above, laminated together, the electrical steel sheets being bonded to one another by a cured film of the adhesive film. <6> In the laminated core according to <5> above, the adhesive film may be an adhesive film comprising the (meth)acrylic resin particles A containing structural units derived from a monomer having a (meth)acrylamide group as the self-crosslinking group-containing monomer, and the water-soluble (meth)acrylic resin B containing structural units derived from a monomer having a hydroxyl group, and the cured film of the adhesive film may have a gel fraction of 70% by mass or more.<7> A method for producing an adhesive coating-coated electrical steel sheet according to one aspect of the present disclosure is the method for producing an adhesive coating-coated electrical steel sheet according to the above item <1>, comprising: a coating step of applying an adhesive coating-forming coating liquid containing (meth)acrylic resin particles A containing structural units derived from a monomer having a self-crosslinking group, and a water-soluble (meth)acrylic resin B, to at least a portion of one or both surfaces of an electrical steel sheet to obtain a coated steel sheet; and a coating step of heating the coated steel sheet to a drying temperature of 100 to 200°C at a heating rate of 6.0°C / second or less, and drying by holding the coated steel sheet from the drying temperature to a temperature in a range from the drying temperature to -10°C for 10 to 60 seconds, thereby forming an adhesive coating on the surface of the electrical steel sheet. <8> In the method for producing an adhesive coating-coated electrical steel sheet according to the above item <7>, the adhesive coating-forming coating liquid may have a ratio of the mass content of the (meth)acrylic resin particles A to the mass content of the water-soluble (meth)acrylic resin B of 95 / 5 to 85 / 15. <9> A manufacturing method for a laminated core according to one aspect of the present disclosure is the manufacturing method for a laminated core according to the above item <5>, and includes: a punching step of punching the adhesive-coated electromagnetic steel sheet to obtain a punched member; a lamination step of stacking a plurality of the punched members to obtain a laminate; and an adhesion step of heating the laminate to a pressing temperature in a temperature range of 200 to 300°C, and holding the laminate for 30 to 60 minutes at a temperature range from the pressing temperature to the pressing temperature minus 10°C while applying a pressure of 0.5 to 10 MPa, thereby curing the adhesive coating and forming the hardened film.

[0014] According to the above aspects of the present disclosure, there are provided an adhesive-coated electrical steel sheet having excellent adhesive strength at room temperature and high temperature, excellent adhesive strength after high-temperature storage, and excellent magnetic properties, a laminated core using the same, and methods for manufacturing the same.

[0015] 1 is a schematic diagram showing an example of an adhesive coated electrical steel sheet according to the present disclosure; 2 is a schematic diagram showing an example of a laminated core according to the present disclosure;

[0016] The present disclosure will be described below. The following description of the requirements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented by making appropriate modifications within the scope of the purpose of the present disclosure.

[0017] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples.

[0018] In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.

[0019] In the present disclosure, when a plurality of substances corresponding to each component are present in the coating composition for laminated steel sheets, the amount of each component in the coating composition for laminated steel sheets means the total amount of the plurality of substances present in the coating composition for laminated steel sheets, unless otherwise specified.

[0020] In the present disclosure, the term "(meth)acrylic monomer" refers to a monomer having a (meth)acryloyl group. In the present disclosure, the term "(meth)acrylic resin" refers to a resin that contains structural units derived from a (meth)acrylic monomer and in which the proportion of structural units derived from the (meth)acrylic monomer is 50 mass% or more.

[0021] In the present disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic," "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate," "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl," and "(meth)acrylamide" is a term that encompasses both "acrylamide" and "methacrylamide."

[0022] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0023] In the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

[0024] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0025] [Adhesive-Coated Electrical Steel Sheet] The adhesive-coated electrical steel sheet of the present disclosure comprises an electrical steel sheet and an adhesive coating provided on at least a portion of one or both sides of the electrical steel sheet (see FIG. 1). The adhesive coating comprises (meth)acrylic resin particles A, which are derived from an adhesive coating-forming coating liquid and contain structural units derived from a monomer having a self-crosslinking group, and a water-soluble (meth)acrylic resin B. The gel fraction of the adhesive coating is greater than 20% by mass and not more than 70% by mass. In FIG. 1, 10 denotes the adhesive-coated electrical steel sheet, 10A denotes the electrical steel sheet, and 10B and 10C denote the adhesive coatings.

[0026] Due to the above-mentioned configuration, the adhesive coated electrical steel sheet of the present disclosure has excellent adhesive strength at room temperature (normal temperature) and high temperatures, adhesive strength after high-temperature storage, and magnetic properties (it also has excellent magnetic properties as a laminated core. In this disclosure, "room temperature (normal temperature)" refers to 25°C, and "high temperature" refers to 150°C. The reason for this is presumed to be as follows. Acrylic resins are chemically stable because their main chains are composed of carbon-carbon bonds, and by setting the gel fraction of the adhesive coating within a specific range, adhesive strength after high-temperature storage is guaranteed. Furthermore, acrylic resin particles A having self-crosslinking groups have enhanced adhesive strength from room temperature to high temperatures as a result of the self-crosslinking groups bonding. It is presumed that the addition of water-soluble acrylic resin B evenly distributes the stress applied to the electrical steel sheet across the adhesive surface, resulting in excellent magnetic properties.

[0027] Hereinafter, the adhesive-coated electrical steel sheet of the present disclosure will be described in detail.

[0028] (Electromagnetic steel sheet) The 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 directional electromagnetic steel sheet. Specifically, as the electromagnetic steel sheet, for example, a non-oriented electromagnetic steel strip according to JIS C 2552:2014, a directional electromagnetic steel strip according to JIS C 2553:2019, a non-oriented thin electromagnetic steel strip according to JIS C 2558:2021, or a directional thin electromagnetic steel strip cut to a predetermined length can be used.

[0029] (Adhesive Coating) The adhesive coating is provided on at least a portion of one or both sides of the electromagnetic steel sheet (see FIG. 1 ). That is, the adhesive coating may be provided, for example, on the entire surface of one or both sides of the electromagnetic steel sheet, or may be provided on one or both sides of the electromagnetic steel sheet in a pattern such as a staggered arrangement (an arrangement in which the layers are alternately shifted up, down, left, and right). However, it is preferable that the adhesive coating be provided over 60% or more, 80% or more, or 100% of the area of ​​one side of the electromagnetic steel sheet.

[0030] - Gel fraction - The gel fraction of the adhesive coating is greater than 20% by mass and not greater than 70% by mass. If the gel fraction of the adhesive coating is 20% by mass or less, sufficient adhesive strength cannot be ensured after high-temperature storage. In addition, the appearance deteriorates. If the gel fraction of the adhesive coating is greater than 70% by mass, sufficient adhesive strength cannot be ensured at high temperatures. Furthermore, if the gel fraction of the adhesive coating is increased too much, the adhesive strength becomes excessively high and the adhesive coating becomes too hard, resulting in deterioration of the magnetic properties. Therefore, the gel fraction of the adhesive coating is set within the above range. The gel fraction of the adhesive coating is preferably 30% by mass or more, and more preferably 40% by mass or more. The gel fraction of the adhesive coating is preferably 60% by mass or less, and more preferably 50% by mass or less.

[0031] The gel fraction of the adhesive coating is the proportion of solvent-insoluble matter measured using ethyl acetate as the extraction solvent. Specifically, the gel fraction of the adhesive coating is measured as follows. First, an adhesive-coated electrical steel sheet was cut to a size of 60 mm x 60 mm to obtain two sample pieces. Next, the adhesive coating was removed from one of the sample pieces. The sample piece from which the adhesive coating was removed was designated Sample X1, and the mass of Sample X1 was designated A. The other sample piece (i.e., the sample piece with the adhesive coating) was designated Sample X2, and the mass of Sample X2 was designated B. Next, Sample X2 was placed in a glass bottle containing 80 g of ethyl acetate and the lid was closed. Next, the glass bottle containing Sample X2 was left in an environment with an ambient temperature of 23°C and 50% RH for 3 days. Next, Sample X2 was removed from the glass bottle and washed with a small amount of ethyl acetate. Next, Sample X2 was dried at a drying temperature of 100°C for 24 hours. The mass of Sample X2 after drying was accurately measured using a precision balance. This mass is designated as D (unit: g). Next, the gel fraction is calculated using the following formula: Gel fraction [mass %] = (D - (B - A)) / (B - A) x 100

[0032] The gel fraction of the adhesive coating can be adjusted, for example, by appropriately setting the heating temperature, heating time, cooling rate, etc. of the coating film when forming the adhesive coating.

[0033] (Average Thickness of Adhesive Coating) The average thickness of the adhesive coating is preferably 1.0 to 6.0 μm. The average thickness of the adhesive coating is more preferably 1.5 μm or more, or 2.0 μm or more. The average thickness of the adhesive coating is more preferably 4.0 μm or less, or 3.0 μm or less. In the adhesive-coated electrical steel sheet according to the present disclosure, even when the average thickness of the adhesive coating is reduced to 1.0 to 6.0 μm, the adhesive strength at room temperature and high temperature, and the adhesive strength and magnetic properties after high-temperature storage are all excellent.

[0034] The method for measuring the average thickness of the adhesive coating is as follows: The adhesive coated electrical steel sheet to be measured is cut along the thickness direction to obtain a test specimen with the cut surface as the observation surface. The observation surface of the test specimen is observed using a scanning electron microscope (SEM), and the thickness of the adhesive coating at any three locations is measured. The thicknesses of the adhesive coating at the three locations are then arithmetically averaged to obtain the average thickness of the adhesive coating. Note that the adhesive coating and the electrical steel sheet can be easily distinguished by the difference in brightness, and the layer present in the center in the thickness direction is considered to be the electrical steel sheet, and the layers present on the surface and back side in the thickness direction are considered to be the adhesive coating.

[0035] (Components of Adhesive Coating) The adhesive coating contains (meth)acrylic resin particles A (hereinafter also referred to as "specific (meth)acrylic resin particles A") containing structural units derived from a monomer having a self-crosslinkable group, and a water-soluble (meth)acrylic resin B. The adhesive coating is an insulating coating that exhibits adhesive properties when heated and pressurized, as crosslinking of at least the specific (meth)acrylic resin particles A progresses and the adhesive coating hardens.

[0036] [Specific (meth)acrylic resin particles A] The specific (meth)acrylic resin particles A contain structural units derived from a monomer having a self-crosslinking group, specifically, the specific (meth)acrylic resin particles A contain structural units derived from a monomer having a carboxy group and structural units derived from a monomer having a self-crosslinking group. The adhesive coating may contain only one type of specific (meth)acrylic resin particle A, or may contain two or more types.

[0037] <Constituent units derived from monomers having a carboxy group> The specific (meth)acrylic resin particles A preferably contain constituent units derived from monomers having a carboxy group in a proportion of 1% by mass or more and less than 20% by mass of all constituent units. In the present disclosure, "constituent units derived from monomers having a carboxy group" means constituent units formed by addition polymerization of monomers having a carboxy group.

[0038] Examples of the monomer having a carboxy group include a monomer having at least one carboxy group and an ethylenically unsaturated group in one molecule. The ethylenically unsaturated group is not particularly limited, and examples thereof include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. The ethylenically unsaturated group is preferably a (meth)acryloyl group.

[0039] Specific examples of the monomer having a carboxy 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). As the monomer having a carboxy group, a (meth)acrylic monomer having a carboxy group is preferred, (meth)acrylic acid is more preferred, and methacrylic acid is even more preferred.

[0040] The specific (meth)acrylic resin particles A may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types.

[0041] The content of structural units derived from monomers having a carboxy group in the specific (meth)acrylic resin particles A is preferably 1% by mass or more and less than 20% by mass, relative to the total structural units of the specific (meth)acrylic resin particles A. When the content of structural units derived from monomers having a carboxy group in the specific (meth)acrylic resin particles A is 1% by mass or more, relative to the total structural units of the specific (meth)acrylic resin particles A, the appearance, adhesive strength, and magnetic properties tend to all be excellent. From this perspective, the content of structural units derived from monomers having a carboxy group in the specific (meth)acrylic resin particles A is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and particularly preferably 10% by mass or more, relative to the total structural units of the specific (meth)acrylic resin particles A.

[0042] <Constituent units derived from monomers having self-crosslinking groups> The specific (meth)acrylic resin particles A preferably contain constituent units derived from monomers having self-crosslinking groups in a proportion of 0.1% by mass or more and 7% by mass or less of all constituent units. In the present disclosure, the term "constituent units derived from monomers having self-crosslinking groups" refers to constituent units formed by addition polymerization of monomers having self-crosslinking groups.

[0043] In the present disclosure, the term "self-crosslinking" refers to the property of being able to crosslink even in the absence of a crosslinking agent.

[0044] The self-crosslinking group in the present disclosure can exhibit self-crosslinking properties by heating. The temperature at which the self-crosslinking group exhibits self-crosslinking properties varies depending on the type of self-crosslinking group. The self-crosslinking group may exhibit self-crosslinking properties at a temperature at which the magnetic steel sheets are bonded together, and the temperature at which the self-crosslinking group exhibits self-crosslinking properties is not particularly limited.

[0045] Specific examples of the self-crosslinking group include an N-methylol group, an N-butyrol group, a glycidyl group, and an alkoxymethylamide group. The self-crosslinking group is preferably at least one selected from the group consisting of an N-methylol group, an N-butyrol group, and a glycidyl group.

[0046] Specific examples of monomers having a self-crosslinking group include N-hydroxyalkyl(meth)acrylamide, N,N-dihydroxyalkyl(meth)acrylamide, glycidyl(meth)acrylate, and N-alkoxymethyl(meth)acrylamide. Examples of N-hydroxyalkyl(meth)acrylamides include N-methylolacrylamide (NMAM), N-butyrolacrylamide (NBMA), and hydroxyethylacrylamide (HEAA). Examples of N,N-dihydroxyalkyl(meth)acrylamides include dimethylol(meth)acrylamide. Examples of N-alkoxymethyl(meth)acrylamides include N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide. The monomer having a self-crosslinking group is preferably at least one selected from the group consisting of N-methylolacrylamide (NMAM), N-butyrolacrylamide (NBMA), and hydroxyethylacrylamide (HEAA), and more preferably hydroxyethylacrylamide (HEAA).

[0047] The specific (meth)acrylic resin particles A may contain only one type of structural unit derived from a monomer having a self-crosslinking group, or may contain two or more types.

[0048] The content of the structural units derived from the monomer having a self-crosslinking group in the specific (meth)acrylic resin particles A is preferably 0.1% by mass or more and 7% by mass or less, relative to the total structural units of the specific (meth)acrylic resin particles A. In one embodiment, the content of the structural units derived from the monomer having a self-crosslinking group in the specific (meth)acrylic resin particles A may be in the range of 0.1% by mass or more and 6% by mass or less, 0.1% by mass or more and 5% by mass or less, 1% by mass or more and 7% by mass or less, 1.5% by mass or more and 6% by mass or less, or 1.9% by mass or more and 5% by mass or less.

[0049] <Constituent Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The specific (meth)acrylic resin particles A preferably contain constituent units derived from (meth)acrylic acid alkyl ester monomers. In the present disclosure, the term "constituent units derived from (meth)acrylic acid alkyl ester monomers" refers to constituent units formed by addition polymerization of (meth)acrylic acid alkyl ester monomers. Note that the "(meth)acrylic acid alkyl ester monomer" in the specific (meth)acrylic resin particles A does not include monomers corresponding to monomers having a carboxy group or monomers corresponding to monomers having a self-crosslinking group.

[0050] The type of (meth)acrylic acid alkyl ester monomer is not particularly limited. The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding a carboxy group, a self-crosslinkable group, and a hydroxyl group), but is preferably unsubstituted. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group contained in the (meth)acrylic acid alkyl ester monomer is, for example, preferably 1 to 18, more preferably 1 to 12, and even more preferably 1 to 8.

[0051] Specific examples of the (meth)acrylic acid alkyl ester monomer 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. The (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of n-butyl acrylate, methyl methacrylate, and 2-ethylhexyl acrylate.

[0052] <Constituent units derived from other monomers> The specific (meth)acrylic resin particles A may contain constituent units derived from monomers (so-called other monomers) that do not fall into any of the following categories: a monomer having a carboxy group, a monomer having a self-crosslinking group, and a (meth)acrylic acid alkyl ester monomer. In the present disclosure, the term "constituent units derived from other monomers" refers to constituent units formed by addition polymerization of other monomers.

[0053] Examples of the structural units derived from other monomers include structural units derived from styrene. When the specific (meth)acrylic resin particles A contain structural units derived from styrene, gloss can be imparted to the adhesive coating film formed.

[0054] Furthermore, examples of structural units derived from other monomers include structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from vinyl cyanide, such as acrylonitrile and methacrylonitrile; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0055] When the specific (meth)acrylic resin particles A contain a structural unit derived from another monomer, they may contain only one type of structural unit derived from another monomer, or may contain two or more types of structural units derived from another monomer.

[0056] When the specific (meth)acrylic resin particles A contain structural units derived from other monomers, the content of the structural units derived from other monomers can be set appropriately within a range that does not impair the effects of the coating composition of the present disclosure.

[0057] <<Content of Specific (Meth)acrylic Resin Particles A>> The content of the specific (meth)acrylic resin particles A is not particularly limited, but is, for example, preferably 85 to 95% by mass, more preferably 87 to 93% by mass, and even more preferably 89 to 91% by mass, relative to the adhesive coating.

[0058] [Water-soluble (meth)acrylic resin B] The adhesive coating contains a water-soluble (meth)acrylic resin B. The adhesive coating may contain only one type of water-soluble (meth)acrylic resin B, or may contain two or more types.

[0059] Here, the term "water-soluble (meth)acrylic resin" refers to a (meth)acrylic resin having a solubility in water at 25°C of 50 mg or more per 100 g of water.

[0060] <Constituent units derived from monomers having a self-crosslinking group> The water-soluble (meth)acrylic resin B may contain constituent units derived from monomers having a self-crosslinking group. When the water-soluble (meth)acrylic resin B contains constituent units derived from monomers having a self-crosslinking group, the adhesive strength at high temperatures tends to be excellent. Note that the water-soluble (meth)acrylic resin B does not necessarily have to contain constituent units derived from monomers having a self-crosslinking group. In other words, the water-soluble (meth)acrylic resin B may be a non-crosslinkable resin.

[0061] Specific examples of the self-crosslinking group in the water-soluble (meth)acrylic resin B are the same as the specific examples of the self-crosslinking group in the specific (meth)acrylic resin particles A. The self-crosslinking group is preferably at least one selected from the group consisting of an N-methylol group, an N-butyrol group, and a glycidyl group.

[0062] Specific examples of the monomer having a self-crosslinkable group in the water-soluble (meth)acrylic resin B are the same as the specific examples of the monomer having a self-crosslinkable group in the specific (meth)acrylic resin particles A. As the monomer having a self-crosslinkable group, at least one selected from N-methylolacrylamide (NMAM) and hydroxyethylacrylamide (HEAA) is preferred.

[0063] When the water-soluble (meth)acrylic resin B contains a structural unit derived from a monomer having a self-crosslinking group, it may contain only one type of structural unit derived from a monomer having a self-crosslinking group, or it may contain two or more types of structural units derived from a monomer having a self-crosslinking group.

[0064] When the water-soluble (meth)acrylic resin B contains a structural unit derived from a monomer having a self-crosslinking group, the content of the structural unit derived from the monomer having a self-crosslinking group is not particularly limited, but is, for example, preferably 0.1% by mass to 10.0% by mass, more preferably 1.0% by mass to 5.0% by mass, and even more preferably 1.5% by mass to 2.0% by mass, relative to all structural units of the water-soluble (meth)acrylic resin B. When the content of the structural unit derived from the monomer having a self-crosslinking group in the water-soluble (meth)acrylic resin B relative to all structural units of the water-soluble (meth)acrylic resin B is within the above range, the adhesive coating formed tends to exhibit higher adhesive strength under the high-temperature conditions used when bonding electrical steel sheets together.

[0065] <Constituent units derived from monomers having hydroxyl groups> The water-soluble (meth)acrylic resin B preferably contains constituent units derived from monomers having hydroxyl groups. In the present disclosure, the term "constituent units derived from monomers having hydroxyl groups" refers to constituent units formed by addition polymerization of monomers having hydroxyl groups. In the present disclosure, the hydroxyl groups constituting part of the self-crosslinking groups are not included in the hydroxyl groups in the monomers having hydroxyl groups.

[0066] Examples of the monomer having a hydroxyl group include a monomer having at least one hydroxyl group and an ethylenically unsaturated group in one molecule. The ethylenically unsaturated group is not particularly limited, and examples thereof include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. The ethylenically unsaturated group is preferably a (meth)acryloyl group.

[0067] Specific examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate. As the monomer having a hydroxyl group, a hydroxyalkyl(meth)acrylate is preferred, a hydroxyalkyl(meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is more preferred, 2-hydroxyethyl(meth)acrylate is even more preferred, and 2-hydroxyethyl methacrylate is particularly preferred.

[0068] When the water-soluble (meth)acrylic resin B contains a structural unit derived from a monomer having a hydroxyl group, it may contain only one type of structural unit derived from a monomer having a hydroxyl group, or it may contain two or more types of structural units derived from a monomer having a hydroxyl group.

[0069] When the water-soluble (meth)acrylic resin B contains structural units derived from monomers having a hydroxyl group, the content of the structural units derived from monomers having a hydroxyl group is not particularly limited, but is preferably 5% to 30% by mass, more preferably 10% to 25% by mass, and even more preferably 15% to 25% by mass, relative to the total structural units of the water-soluble (meth)acrylic resin B. When the content of structural units derived from monomers having a hydroxyl group in the water-soluble (meth)acrylic resin B is 5% by mass or more relative to the total structural units of the water-soluble (meth)acrylic resin B, the appearance, adhesive strength, and magnetic properties all tend to be excellent. When the content of structural units derived from monomers having a hydroxyl group in the water-soluble (meth)acrylic resin B is 30% by mass or less relative to the total structural units of the water-soluble (meth)acrylic resin B, the production stability of the water-soluble (meth)acrylic resin B tends to be more excellent.

[0070] <Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The water-soluble (meth)acrylic resin B preferably contains structural units derived from (meth)acrylic acid alkyl ester monomers. Note that the "(meth)acrylic acid alkyl ester monomer" in the water-soluble (meth)acrylic resin B does not include monomers corresponding to monomers having a self-crosslinkable group or monomers corresponding to monomers having a hydroxyl group.

[0071] The type of (meth)acrylic acid alkyl ester monomer is not particularly limited. The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding a carboxy group, a self-crosslinkable group, and a hydroxyl group), but is preferably unsubstituted. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group contained in the (meth)acrylic acid alkyl ester monomer is, for example, preferably 1 to 12, more preferably 1 to 8, and even more preferably 1 to 4.

[0072] Specific examples of the (meth)acrylic acid alkyl ester monomer in the water-soluble (meth)acrylic resin B are the same as the specific examples of the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic resin particles (A). From the viewpoint of water solubility, the (meth)acrylic acid alkyl ester monomer preferably contains at least one selected from the group consisting of n-butyl acrylate, methyl methacrylate, and ethyl acrylate, more preferably contains at least one selected from methyl methacrylate and ethyl acrylate, and even more preferably contains methyl methacrylate.

[0073] When the water-soluble (meth)acrylic resin B contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, it may contain only one type of structural unit derived from a (meth)acrylic acid alkyl ester monomer, or it may contain two or more types of structural units derived from a (meth)acrylic acid alkyl ester monomer.

[0074] When the water-soluble (meth)acrylic resin B contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural unit derived from a (meth)acrylic acid alkyl ester monomer in the water-soluble (meth)acrylic resin B is not particularly limited, but is, for example, preferably 40% by mass to 90% by mass, more preferably 40% by mass to 80% by mass, and even more preferably 40% by mass to 70% by mass, relative to all structural units of the water-soluble (meth)acrylic resin B.

[0075] <Structural Units Derived from Other Monomers> The water-soluble (meth)acrylic resin B may contain structural units derived from monomers (so-called other monomers) that do not fall into any of the categories of monomers having a self-crosslinkable group, monomers having a hydroxyl group, and alkyl (meth)acrylate monomers.

[0076] Examples of structural units derived from other monomers include structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from vinyl cyanide, such as acrylonitrile and methacrylonitrile; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0077] When the water-soluble (meth)acrylic resin B contains a structural unit derived from another monomer, it may contain only one type of structural unit derived from another monomer, or may contain two or more types of structural units derived from another monomer.

[0078] When the water-soluble (meth)acrylic resin B contains a structural unit derived from another monomer, the content of the structural unit derived from the other monomer can be set appropriately within a range that does not impair the effects of the coating composition of the present disclosure.

[0079] <<Content of Water-Soluble (Meth)acrylic Resin B>> With regard to the content of water-soluble (meth)acrylic resin B in the adhesive coating, the ratio of the mass content of specific (meth)acrylic resin particles A to the mass content of water-soluble (meth)acrylic resin B [mass content of specific (meth)acrylic resin particles A / mass content of water-soluble (meth)acrylic resin B] is preferably 95 / 5 to 85 / 15. When the ratio of the mass content of specific (meth)acrylic resin particles A to the mass content of water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15, the appearance, adhesive strength, and magnetic properties all tend to be excellent. From these viewpoints, the ratio of the mass content of specific (meth)acrylic resin particles A to the mass content of water-soluble (meth)acrylic resin B is preferably 95 / 5 to 90 / 10.

[0080] [Other Components] The adhesive coating may contain components other than those already described (so-called other components) as needed, provided that the adhesive coating's effects are not impaired.

[0081] The adhesive coating of an adhesive-coated magnetic steel sheet or a laminated core obtained by laminating adhesive-coated magnetic steel sheets can be qualitatively analyzed for its components using infrared spectroscopy, nuclear magnetic resonance, or gas chromatography, followed by a weight distribution of the fragments using TOFMS to estimate the component ratio. Analytical samples of adhesive-coated magnetic steel sheets can be obtained by cutting out the coating portion with a precision cutter. Furthermore, in the case of a laminated core, several magnetic steel sheets are peeled off from the laminated core and then sampled using the above-mentioned method.

[0082] (Method for Manufacturing Adhesive-Coated Magnetic Steel Sheet) (Method for Forming Adhesive Coating) The adhesive-coated magnetic steel sheet of the present disclosure exhibits its effects as long as it has the above-mentioned characteristics, regardless of the manufacturing method. For example, it can be obtained by a manufacturing method including the following steps: (I) a coating step in which an adhesive coating-forming coating liquid is applied to at least a portion of one or both sides of an magnetic steel sheet to obtain a coated steel sheet; (II) a coating-forming step in which the coated steel sheet is heated to a drying temperature of 100 to 200°C at a heating rate of 6.0°C / sec or less and then held in a temperature range from the drying temperature to the drying temperature minus 10°C for 10 to 60 seconds to dry, thereby forming an adhesive coating on the surface of the magnetic steel sheet. Note that in the present disclosure, when the adhesive coating-forming coating liquid contains multiple substances corresponding to each component, the amount of each component in the adhesive coating-forming coating liquid refers to the total amount of the multiple substances present in the adhesive coating-forming coating liquid, unless otherwise specified. Each step will be described below.

[0083] - Coating Step - In the coating step, a coating liquid for forming an adhesive coating (hereinafter also referred to as "the coating liquid of the present disclosure" or "the coating composition of the present disclosure") is applied to at least a portion of one or both sides of an electrical steel sheet to obtain a coated steel sheet.

[0084] The coating liquid (coating composition) of the present disclosure contains (meth)acrylic resin particles A, a water-soluble (meth)acrylic resin B, and a medium containing water. In the coating liquid of the present disclosure, the specific (meth)acrylic resin particles A are present in a dispersed state in the medium containing water. Furthermore, the water-soluble (meth)acrylic resin B is present in a dissolved state in the medium containing water. By applying such a coating liquid and then drying it, the adhesive coating according to the present embodiment described above can be obtained.

[0085] [Water] The coating liquid of the present disclosure contains water. The type of water is not particularly limited. As the water, for example, distilled water, deionized water (also called "ion-exchanged water"), and pure water are preferred from the viewpoint of having few impurities.

[0086] The water content in the coating solution of the present disclosure is not particularly limited, but is preferably 35% by mass to 50% by mass, and more preferably 40% by mass to 45% by mass, relative to the total mass of the coating composition.

[0087] [Other Components] The coating fluid of the present disclosure may contain components (so-called other components) other than the components described above, as necessary, within the scope that does not impair the effects of the coating fluid.

[0088] Examples of other components include aqueous media other than water. Examples of aqueous media other than water include water-miscible organic solvents. Examples of water-miscible organic solvents include monohydric alcohol compounds such as methanol and ethanol; polyhydric alcohol compounds such as glycerin, ethylene glycol, and propylene glycol; and glycol derivatives such as ethylene glycol monoethyl ether and propylene glycol monobutyl ether. Examples of other components include various additives such as preservatives, wetting agents, and antifoaming agents.

[0089] (Gel Fraction of Coating Composition) In the coating fluid of the present disclosure, for example, the gel fraction at a temperature higher than the temperature at which crosslinking by the self-crosslinking groups contained in the specific (meth)acrylic resin particles A proceeds is preferably greater than the gel fraction at a temperature lower than the temperature at which crosslinking by the self-crosslinking groups contained in the specific (meth)acrylic resin particles A proceeds. When the gel fraction of the coating fluid of the present disclosure satisfies the above-mentioned requirements, the coating fluid of the present disclosure tends to achieve a good balance between excellent coating on the surface of the electrical steel sheet and the formation of an adhesive coating that exhibits high adhesive strength under high-temperature conditions when bonding electrical steel sheets together.

[0090] The gel fraction of the coating solution of the present disclosure is measured in the same manner as in the above-described method for measuring the gel fraction of an adhesive coating, except that the object of measurement is a coating composition.

[0091] [Method for Producing Coating Fluid] The method for producing the coating fluid (coating composition) of the present disclosure is not particularly limited. The coating fluid of the present disclosure can be produced, for example, by mixing a dispersion of specific (meth)acrylic resin particles A and an aqueous solution of water-soluble (meth)acrylic resin B.

[0092] The mixing method is not particularly limited. For example, mixing by stirring can be used. A general stirring tool or stirring device can be used for stirring. The stirring temperature is not particularly limited, but is preferably, for example, 20°C to 30°C.

[0093] - Adhesive Coating Formation Method - In the coating formation process, an electrical steel sheet (coated steel sheet) coated with a coating liquid is heated to a drying temperature (maximum temperature reached by the material) of 100 to 200°C at a heating rate of 6.0°C / second or less, and then held at a temperature range of from the drying temperature to (drying temperature -10°C) for 10 to 60 seconds, thereby drying the sheet and forming an adhesive coating on the surface of the electrical steel sheet. The drying time (the time during which the material temperature is held from the drying temperature -10°C to the drying temperature) is preferably 30 to 60 seconds. The heating rate is calculated from the time required to reach the drying temperature (maximum temperature reached by the material). If the drying temperature exceeds 200°C, the curing reaction may proceed excessively, resulting in a decrease in adhesive strength. Furthermore, if the drying temperature is too high, the resin may oxidize. If the drying temperature is less than 100°C or the drying time is less than 10 seconds, sufficient drying is not achieved. If the drying time exceeds 60 seconds, the curing reaction may proceed excessively, resulting in a decrease in adhesive strength. Furthermore, if the temperature rise rate exceeds 6.0°C / sec, the film will not be formed properly and the adhesive strength will be insufficient. Generally, slowing the temperature rise rate requires increasing the furnace length or reducing the line speed, which is considered undesirable in terms of equipment constraints and productivity. However, in the manufacturing method of an adhesive-coated electrical steel sheet according to this embodiment, the temperature rise rate is deliberately slowed based on the new finding that the above-mentioned effects can be achieved by slowing the temperature rise rate. Formation of an adhesive coating film using the coating liquid of the present disclosure can be achieved by applying the coating liquid to the surface of the electrical steel sheet using a well-known coating method, such as a roll coater or spray method, followed by drying. The solids concentration of the coating liquid is preferably 5 to 40% by mass, more preferably 10 to 25% by mass. The drying method is preferably a method using a copying oven, but may also be a hot air oven or other method.

[0094] [Laminated Core] The laminated core of the present disclosure is formed by stacking a plurality of adhesive-coated magnetic steel sheets of the present disclosure, with the magnetic steel sheets being bonded to one another by a cured film of the adhesive film. Here, the cured film of the adhesive film is a film that develops adhesive properties by heating and pressurizing the laminated adhesive-coated magnetic steel sheets, as a result of crosslinking of the (meth)acrylic resin particles A in the adhesive film progressing and hardening.

[0095] Specifically, examples of the laminated core of the present disclosure include a laminated core obtained by punching out an adhesive-coated magnetic steel sheet of the present disclosure to produce punched members, and then laminating and integrating the punched members.

[0096] FIG. 2 is a schematic diagram illustrating an example of a laminated core according to the present disclosure. As shown in FIG. 2 , the laminated core 100 is formed as a laminate 13 in which eight punched members 11 made of adhesive-coated electromagnetic steel sheets are connected in an annular shape and the annularly connected punched members 11 are stacked into eight layers. The punched members 11 made of adhesive-coated electromagnetic steel sheets are punched out of the adhesive-coated electromagnetic steel sheets, and include a circular arc-shaped yoke portion 17 and teeth portions 15 protruding radially inward from the inner peripheral surface of the yoke portion 17. The shape, number, and number of laminations of the punched members 11 forming the laminated core 100 shown in FIG. 2 are not limited, and the laminated core 100 may be designed according to the purpose.

[0097] (Manufacturing Method of Laminated Core) The laminated core of the present disclosure is manufactured, for example, by the following steps: (III) A punching step in which an adhesive-coated magnetic steel sheet of the present disclosure is punched to obtain a punched member; (IV) A lamination step in which a plurality of the punched members are stacked to obtain a laminate; (V) A bonding step in which the laminate is heated to a pressing temperature in the temperature range of 200 to 300°C, and maintained at a temperature in the range of the pressing temperature to the pressing temperature minus 10°C while applying a pressure of 0.5 to 10 MPa for 30 to 60 minutes. Each step will be described below.

[0098] -Punching Step- In the punching step, the adhesive coated magnetic steel sheet is punched to obtain a member (punched member) having a predetermined shape. There are no limitations on the punching method.

[0099] -Laminating Process- In the laminating process, the punched members are laminated with adhesive coatings interposed between the magnetic steel sheets, thereby obtaining a laminate.

[0100] - Bonding Process - In the bonding process, the laminate is heated to a pressing temperature (the maximum temperature reached by the material) in the temperature range of 200 to 300°C, and maintained at a pressure of 0.5 to 10 MPa within a range of from the pressing temperature to the pressing temperature minus 10°C for 30 to 60 minutes. This promotes crosslinking of the (meth)acrylic resin particles A in the adhesive coating, hardening the adhesive coating. This allows the cured adhesive coating to exhibit adhesive properties, bonding the magnetic steel sheets together. These operations result in the laminated core of the present disclosure. The magnetic steel sheets with adhesive coatings may be bonded together with the cured adhesive coatings of the magnetic steel sheets facing each other, or may be bonded together with the cured adhesive coating of one magnetic steel sheet facing the surface of the other magnetic steel sheet not carrying the adhesive coating. The pressing temperature is preferably 200 to 300°C, the pressure is preferably 0.5 to 10 MPa, and the holding time is preferably 30 to 60 minutes.

[0101] (Gel Fraction of Cured Adhesive Coating) In the laminated core of the present disclosure, the gel fraction of the cured adhesive coating is preferably 70% by mass or more, more preferably 85% by mass or more, and even more preferably 85% by mass or more. When the gel fraction of the cured adhesive coating is within the above range, both the adhesive strength and magnetic properties tend to be excellent. Here, when the gel fraction of the cured adhesive coating is 70% by mass or more, the adhesive coating preferably contains (meth)acrylic resin particles A containing structural units derived from a monomer having a (meth)acrylamide group as a self-crosslinking group-containing monomer, and a water-soluble (meth)acrylic resin B containing structural units derived from a monomer having a hydroxyl group. The gel fraction of the cured adhesive coating is measured using the same method as for the gel fraction of the adhesive coating on an adhesive-coated electrical steel sheet.

[0102] (Applications of Laminated Core) The laminated core of the present disclosure can be used as a core (i.e., iron core) used in a rotating electric machine or the like.

[0103] The coating composition of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as it does not depart from the gist of the disclosure.

[0104] Example 1 1. Production of (meth)acrylic resin particles A A monomer mixture was prepared by mixing 168 parts by mass of methyl methacrylate [MMA; methacrylic acid alkyl ester monomer], 56 parts by mass of n-butyl acrylate [n-BA; acrylic acid alkyl ester monomer], 128 parts by mass of styrene [St; other monomer], 40 parts by mass of methacrylic acid [MAA; monomer having a carboxy group], and 8 parts by mass of hydroxyethyl acrylamide [HEAA; monomer having a self-crosslinkable group] in a stainless steel container. Next, 172.0 parts by mass of deionized water, 2.7 parts by mass of the nonionic surfactant Noigen (registered trademark) EA-197D (Dai-ichi Kogyo Seiyaku Co., Ltd.), 4.1 parts by mass of Emulgen (registered trademark) A-60 (Kao Corporation), and 2.7 parts by mass of the anionic surfactant Neopelex (registered trademark) G-65 (Kao Corporation) were placed in a separate stainless steel container and stirred to dissolve, thereby preparing 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, thereby preparing a pre-emulsion. This prepared pre-emulsion was used for polymerization. The polymerization was carried out in a thermostatic chamber equipped with a 7 L (liter; the same applies hereinafter) flask, a reflux condenser, a stirrer, a nitrogen gas inlet pipe, a pre-emulsion dropping pump (trade name: Hi-Cera Pump V-10, manufactured by Iwaki Corporation), and a polymerization initiator adding device (trade name: Metering Pump MP-2000, manufactured by Tokyo Rikakikai Co., Ltd.). Specifically, the polymerization was carried out as follows. 162.4 parts by mass of deionized water was placed in the flask, and then a portion (17.5 parts by mass) of the pre-emulsion prepared above 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: 240 rpm (revolutions per minute; the same applies hereinafter)). After the internal temperature stabilized, 2.3 parts by mass of a 24% by mass aqueous solution of ammonium peroxodisulfate (polymerization initiator) and 2.3 parts by mass of a 20% by mass aqueous solution of sodium hydrogen sulfite (reducing agent) were added, and the flow rate of nitrogen gas was adjusted to 50 ml / min.After confirming the temperature increase in the flask, the remaining pre-emulsion (564 parts by mass) was added dropwise over 270 minutes, and 63.4 parts by mass of a 2.4% by mass aqueous solution of ammonium peroxodisulfate (polymerization initiator) and 63.4 parts by mass of a 2.0% by mass aqueous solution of sodium hydrogen sulfite (reducing agent) were added dropwise over 360 minutes. Thirty minutes after the completion of the dropwise addition of the aqueous solution of ammonium peroxodisulfate and sodium hydrogen sulfite, 6.4 parts by mass of a 6.9% by mass aqueous solution of t-butyl hydroperoxide (polymerization initiator) and 6.4 parts by mass of a 4.4% by mass aqueous solution of sodium hydroxymethanesulfinate (reducing agent) were added dropwise over 30 minutes. The polymerization reaction was terminated 150 minutes after the completion of the dropwise addition of the pre-emulsion by cooling to 30°C. To the emulsion polymer obtained by the polymerization reaction, 1.3 parts by mass of a preservative (trade name: Topside 350, manufactured by Permakem Asia Co., Ltd.) and 1.3 parts by mass of a wetting agent (trade name: Surfynol (registered trademark) 440, manufactured by Nissin Chemical Industry Co., Ltd.) were added to obtain an aqueous dispersion of (meth)acrylic resin particles A.

[0105] 2. Preparation of Water-Soluble (Meth)acrylic Resin B 126 parts by mass of methyl methacrylate [MMA; methacrylic acid alkyl ester monomer], 60 parts by mass of acrylic acid [AA; monomer having a carboxy group], 48 parts by mass of ethyl acrylate [EA; acrylic acid alkyl ester monomer], 60 parts by mass of 2-hydroxyethyl methacrylate [2HEMA; monomer having a hydroxyl group], and 6 parts by mass of hydroxyethyl acrylamide [HEAA; monomer having a self-crosslinkable group] were mixed in a stainless steel container to prepare a monomer mixture. Next, 121.0 parts by mass of deionized water and 4.5 parts by mass of the anionic surfactant Latemul (registered trademark) E-118B [Kao Corporation] were added to another stainless steel container and stirred to dissolve, preparing 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, thereby preparing a pre-emulsion. This prepared pre-emulsion was used for polymerization. The polymerization was carried out in a thermostatic chamber equipped with a 7 L flask equipped with a reflux condenser, a stirrer, a nitrogen gas inlet pipe, a pre-emulsion drip pump (trade name: Hi-Cera Pump V-10, manufactured by Iwaki Corporation), and a polymerization initiator addition device (trade name: Metering Pump MP-2000, manufactured by Tokyo Rikakikai Co., Ltd.). Specifically, the polymerization was carried out as follows. 415 parts by mass of deionized water and 7.0 parts by mass of an anionic surfactant, Latemul (registered trademark) E-118B (Kao Corporation), were placed in a flask, and then a portion (8.5 parts by mass) of the pre-emulsion prepared above was added. Nitrogen gas was blown into the flask at a flow rate of 300 ml / min, and while stirring at a desired rotation speed (standard conditions: 150 rpm), the internal temperature of the flask was raised to a desired reaction temperature (standard conditions: 60°C), and then 1.0 part by mass of a 69.0% by mass aqueous solution of t-butyl hydroperoxide (polymerization initiator) and 2.5 parts by mass of a 10.0% by mass aqueous solution of sodium hydroxymethanesulfinate (reducing agent) were added. After the internal temperature stabilized, the flow rate of the nitrogen gas was adjusted to 50 ml / min.After the adjustment, the remaining pre-emulsion (456.6 parts by mass) was added dropwise over 180 minutes, and 24.5 parts by mass of a 6.9% by mass aqueous solution of t-butyl hydroperoxide (polymerization initiator), 24.5 parts by mass of a 1.2% by mass aqueous solution of sodium hydroxymethanesulfinate (reducing agent), and 39.6 parts by mass of 14.7% by mass 2-mercaptoethanol (chain transfer agent) were added dropwise over 180 minutes to obtain an aqueous dispersion of (meth)acrylic resin particles. 58 parts by mass of 25.0% by mass aqueous ammonia (basic aqueous solution) was added to the obtained aqueous dispersion of (meth)acrylic resin particles to solubilize the (meth)acrylic resin particles, thereby obtaining an aqueous solution of water-soluble (meth)acrylic resin B.

[0106] 3. Preparation of Coating Fluid (Coating Composition) 300.0 parts by mass (137.1 parts by mass as solids) of an aqueous dispersion of (meth)acrylic resin particles A and 48.1 parts by mass (15.2 parts by mass as solids) of an aqueous solution of water-soluble (meth)acrylic resin B were mixed, and then an appropriate amount of deionized water was added to obtain a coating fluid with a solids concentration of 43.5% by mass. The "solids concentration" here refers to the total mass proportion of the (meth)acrylic resin particles A and the water-soluble (meth)acrylic resin B in the coating composition. The same applies to the coating fluids prepared below.

[0107] 4. Preparation of Adhesive-Coated Electrical Steel Sheet First, a non-oriented electrical steel sheet with a thickness of 0.25 mm and a width of 100 mm was prepared. The resulting coating liquid was then applied to the entire surface of one side of the electrical steel sheet, and the electrical steel sheet was then heated in a heating furnace for 3 minutes to dry the coating. During heating, the electrical steel sheet was heated until the temperature (heating temperature) of the steel sheet surface reached a range of 140 to 170°C, and then held at that temperature for 30 seconds. The electrical steel sheet was then cooled to room temperature at a cooling rate of 2.5°C / s to form a 2.5 μm-thick adhesive coating. In this manner, an adhesive-coated electrical steel sheet was obtained.

[0108] Examples 2 to 9, Comparative Examples 1 to 7 A coating composition having a solids concentration of 43.5% by mass was obtained by the same procedure as in Example 1, except that the monomer compositions of the (meth)acrylic resin particles A and the water-soluble (meth)acrylic resin B were set to those shown in Table 1, and the mass ratio [A / B] of the (meth)acrylic resin particles A to the water-soluble (meth)acrylic resin B was set to the mass ratio shown in Table 1. Then, using the obtained coating liquid, an electrical steel sheet with an adhesive coating was obtained in the same manner as in Example 1. However, the heating temperature, heating temperature, and cooling rate of the coating film were adjusted so that the gel fraction of the adhesive coating would have the value shown in Table 1. In Comparative Example 5, a coating composition not containing the (meth)acrylic resin particles A was obtained. In Comparative Example 6, a coating composition not containing the water-soluble (meth)acrylic resin B was obtained.

[0109] Comparative Example 7 An adhesive coating-coated electrical steel sheet was obtained in the same manner as in Example 1, except that an epoxy resin composition prepared by mixing bisphenol A, epichlorohydrin, and a latent curing agent was used as the coating liquid, except that the coating film of the epoxy resin composition was heated to a temperature of 170°C on the steel sheet surface, and the average thickness of the adhesive coating was 6 µm.

[0110] [Evaluation] (Gel Fraction) The gel fraction of the adhesive coating in each example of the adhesive-coated electrical steel sheet was measured according to the method described above. Two 60 mm x 60 mm single-plate test pieces were cut out from each example of the adhesive-coated electrical steel sheet. The two single-plate test pieces were then stacked with the adhesive coatings facing each other. The stack was heated and pressed under conditions of a steel sheet temperature of 250°C, a pressure of 3 MPa, and a heating and pressing time of 60 minutes to obtain a laminate sample. The gel fraction of the cured adhesive coating in the laminate sample was measured according to the method described above.

[0111] (Adhesive Strength) Two 30 mm × 60 mm veneer test pieces were cut out from each adhesive-coated electrical steel sheet. The 30 mm × 10 mm ends of the two veneer test pieces were overlapped with the adhesive coatings facing each other. The overlapped two veneer test pieces were heated and pressed at a temperature of 250°C, a pressure of 2 MPa, and a holding time (heating and pressing) of 1 minute to obtain bonded plates for measuring adhesive strength.

[0112] The shear adhesive strength was measured as follows when the steel plate temperature was room temperature (25°C). The adhesive strength measurement sample was attached to a tensile tester, and the shear adhesive strength was measured at a tensile speed of 50 mm / min. The obtained shear adhesive strength value was then divided by the adhesive area of ​​the two single-plate test pieces to determine the room-temperature adhesive strength. An adhesive strength of 6 MPa or more was determined to be sufficient.

[0113] Separately, two 30 mm x 60 mm veneer test pieces were cut from each adhesive-coated electrical steel sheet of each example, and the 30 mm x 10 mm ends were overlapped with the adhesive coatings facing each other. The two overlapping veneer test pieces were placed in a 150°C atmosphere, and the shear bond strength was measured at a steel sheet temperature of 150°C under the same conditions as at room temperature. The obtained shear bond strength value was then divided by the bond area of ​​the two veneer test pieces to determine the 150°C bond strength. An adhesive strength of 0.5 MPa or more was considered to be sufficient.

[0114] Separately, two 30 mm x 60 mm veneer test pieces were cut from each adhesive-coated electrical steel sheet, and the 30 mm x 10 mm edges were overlapped with the adhesive coatings facing each other. The overlapped two veneer test pieces were left for one week in an atmosphere at 50°C and 85% humidity. Thereafter, the shear bond strength was measured under the same conditions as at room temperature, with the steel sheet temperature at room temperature (25°C). The obtained shear bond strength value was then divided by the adhesive area of ​​the two veneer test pieces to determine the room-temperature bond strength after aging. A bond strength of 5.5 MPa or higher was considered to be sufficient.

[0115] (Magnetic Properties) A ​​single sheet test piece measuring 55 mm x 55 mm was cut from each adhesive-coated electrical steel sheet. Two single sheet test pieces were then stacked with their adhesive coatings facing each other. The stack was heated and pressed at a temperature of 250°C, a pressure of 2 MPa, and a holding time (heating and pressing) of 1 minute to obtain a laminate sample. The iron losses in the rolling direction and the direction perpendicular to the rolling direction of the obtained laminate sample were measured using the single sheet magnetic measurement method specified in JIS C2556:2015, and the average values ​​of the iron losses W10 / 400 in the rolling direction and the direction perpendicular to the rolling direction were calculated. A sample with an iron loss of 10.9 W / Kg or less was determined to have excellent magnetic properties.

[0116] (Appearance) Three 5 mm square test pieces were cut out from each adhesive coated electrical steel sheet to obtain test pieces. The adhesive coating surface of each test piece was observed at three locations using a scanning electron microscope at 100x magnification. A total of nine fields of view were observed. Evaluation was then performed according to the following evaluation criteria, with A and B being considered acceptable. A: No coating defects such as cracks, fissures, or peeling were observed. B: The area ratio of coating defects was 10% or less. C: The area ratio of coating defects was more than 10% but less than 30%. D: The area ratio of coating defects was 30% or more.

[0117] Details of the abbreviations for each monomer listed in Table 1 are as follows: <Monomers having a self-crosslinking group> "NMAM": N-methylolacrylamide "NBMA": N-butylolacrylamide <Monomers having a self-crosslinking group and a hydroxyl group> "HEAA": hydroxyethylacrylamide <Monomers having a carboxyl group> "MAA": methacrylic acid "AA": acrylic acid <Monomers having a hydroxyl group> "2HEMA": 2-hydroxyethyl methacrylate <(meth)acrylic acid alkyl ester monomers> "n-BA": n-butyl acrylate "MMA": methyl methacrylate "2EHA": 2-ethylhexyl acrylate "EA": ethyl acrylate <Other monomers> "St": styrene

[0118] In Table 1, blank spaces in the monomer composition column mean that the corresponding monomer was not used. All values ​​in the monomer composition column in Table 1 are solid content equivalent values ​​(parts by mass).

[0119]

[0120]

[0121] From the above results, it can be seen that the present example is superior to the comparative example in appearance, adhesive strength after high-temperature storage, and magnetic properties.

[0122] According to the above aspects of the present disclosure, there are provided an adhesive-coated electrical steel sheet having excellent adhesive strength at room temperature and high temperature, excellent adhesive strength after high-temperature storage, and excellent magnetic properties, a laminated core using the same, and methods for manufacturing the same.

[0123] 10: Adhesive coated electromagnetic steel sheet 10A: Electromagnetic steel sheet 10B: Adhesive coating 10C: Adhesive coating 11: Punched member of adhesive coated electromagnetic steel sheet 100: Laminated core

Claims

1. An adhesive coating-coated electromagnetic steel sheet, comprising: an electromagnetic steel sheet; and an adhesive coating provided on at least a portion of one or both sides of the electromagnetic steel sheet, the adhesive coating comprising (meth)acrylic resin particles A containing structural units derived from a monomer having a self-crosslinking group, and a water-soluble (meth)acrylic resin B, the adhesive coating having a gel fraction of more than 20 mass% and not more than 70 mass%.

2. An adhesive-coated electrical steel sheet as described in claim 1, wherein the water-soluble (meth)acrylic resin B is a (meth)acrylic resin containing a structural unit derived from a monomer having a self-crosslinking group.

3. An adhesive coated electrical steel sheet according to claim 1, wherein the ratio of the mass content of the (meth)acrylic resin particles A to the mass content of the water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15.

4. An adhesive coated electrical steel sheet according to claim 1, wherein the self-crosslinking group is at least one of an N-methylol group, an N-butyrol group, a glycidyl group, and an alkoxymethylamide group.

5. A laminated core in which a plurality of magnetic steel sheets with an adhesive coating according to any one of claims 1 to 4 are laminated together, the magnetic steel sheets being bonded to one another by the hardened film of the adhesive coating.

6. A laminated core as described in claim 5, wherein the adhesive coating is an adhesive coating containing the (meth)acrylic resin particles A which contain structural units derived from a monomer having a (meth)acrylamide group as the monomer having the self-crosslinking group, and the water-soluble (meth)acrylic resin B which contains structural units derived from a monomer having a hydroxyl group, and wherein the gel fraction of the cured film of the adhesive coating is 70 mass% or more.

7. A method for producing an adhesive coated electromagnetic steel sheet according to claim 1, comprising: a coating step of applying an adhesive coating forming coating liquid, which contains (meth)acrylic resin particles A containing structural units derived from a monomer having a self-crosslinking group, and water-soluble (meth)acrylic resin B, to at least a portion of one or both sides of an electromagnetic steel sheet to obtain a coated steel sheet; and a coating step of heating the coated steel sheet to a drying temperature of 100 to 200°C at a heating rate of 6.0°C / sec or less, and drying by holding the coated steel sheet from the drying temperature to a temperature in the range of -10°C from the drying temperature for 10 to 60 seconds, thereby forming an adhesive coating on the surface of the electromagnetic steel sheet.

8. A method for producing an adhesive coated electrical steel sheet as described in claim 7, characterized in that in the coating liquid for forming an adhesive coating, the ratio of the mass content of the (meth)acrylic resin particles A to the mass content of the water-soluble (meth)acrylic resin B is 95 / 5 to 85 / 15.

9. A method for manufacturing a laminated core as claimed in claim 5, comprising: a punching step of punching the adhesive-coated electromagnetic steel sheet to obtain a punched member; a lamination step of stacking a plurality of the punched members to obtain a laminate; and a bonding step of heating the laminate to a pressurizing temperature in the temperature range of 200 to 300°C, and holding the laminate for 30 to 60 minutes at a pressure of 0.5 to 10 MPa in a range from the pressurizing temperature to the pressurizing temperature - 10°C, thereby hardening the adhesive coating and forming the hardened film.

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