Electromagnetic steel sheet, laminated core, and methods for producing same

Abstract

An electromagnetic steel sheet comprising a base material steel sheet and an insulating coating film formed at least partially on one or both surfaces of the base material steel sheet, wherein the insulating coating film has self-fusing ability and contains a crosslinkable acrylic resin containing an acrylic resin that includes a glycidyl group, an acrylic resin that includes a carboxyl group, and an acrylic resin that includes another functional group, and, when the electromagnetic steel sheet having the insulating coating film is subjected to a treatment of being heated to 200°C and held for 5 minutes, the ratio of the gel fraction after the treatment to the gel fraction before the treatment is 1.1-1.4 in the insulating coating film.

Description

Electrical steel sheets and laminated cores, and methods for manufacturing the same.

[0001] This disclosure relates to electrical steel sheets and laminated cores, and methods for manufacturing the same. This application claims priority under Japanese Patent Application No. 2025-055991, filed in Japan on March 28, 2025, the contents of which are incorporated herein by reference.

[0002] Conventionally, cores (iron cores) used in rotating electric machines and the like have been "laminated cores" in which multiple electromagnetic steel sheets are stacked on top of each other. The multiple electromagnetic steel sheets are fixed together by methods such as welding, riveting, bolting, and adhesive bonding. Of these, fixing multiple electromagnetic steel sheets by welding, riveting, and bolting is prone to generating mechanical stress, thermal stress, and interlayer short circuits during processing. As a result, the magnetic properties of the electromagnetic steel sheets deteriorate, and the performance of the laminated core is not fully realized. On the other hand, fixing multiple electromagnetic steel sheets by adhesive bonding is less prone to generating mechanical stress, thermal stress, and interlayer short circuits during processing. As a result, the magnetic properties of the electromagnetic steel sheets are less likely to deteriorate, and the performance of the laminated core is more easily realized. Due to these advantages, various technologies for fixing multiple electromagnetic steel sheets by adhesive bonding have been investigated. As bonding methods, methods using adhesives and methods in which multiple electromagnetic steel sheets with adhesive coatings are laminated, and then heated and pressurized to harden the coatings and bond the sheets together have been proposed.

[0003] For example, Patent Document 1 discloses "an electrical steel sheet having an insulating coating on its surface that exhibits adhesive properties upon heating and / or pressurization, characterized in that the coating is a mixture in which an epoxy resin or epoxy resin modified body having a glass transition temperature (Tg) of 80°C to 150°C, an epoxy resin curing agent, and particulate polymers with a particle size of 0.01 μm to 0.5 μm are dispersed."

[0004] Patent Document 2 discloses "a laminated electromagnetic steel sheet including a plurality of electromagnetic steel sheets and a fusion layer positioned between the plurality of electromagnetic steel sheets, wherein the fusion layer includes polyethylene acrylate containing a repeating unit represented by Chemical Formula 1 and a repeating unit represented by Chemical Formula 2, and the polyethylene acrylate contains 65 to 90% by weight of the repeating unit represented by Chemical Formula 1 and 10 to 35% by weight of the repeating unit represented by Chemical Formula 2".

[0005] Patent Document 3 discloses "a laminated electromagnetic steel sheet, which is an electromagnetic steel sheet for lamination, comprising: an electromagnetic steel sheet; and an adhesive insulating coating provided on at least one surface of the electromagnetic steel sheet and having a Martens hardness (HM) of 50 or more and less than 500".

[0006] Patent Document 4 discloses "an electromagnetic steel strip or electromagnetic steel sheet having at least one thermosetting baking enamel layer containing an epoxy resin as a main component, at least one curing agent and at least one filler provided on one of its planar surfaces, wherein the filler of the baking enamel layer comprises a metal carbonate, a metal sulfate, a metal sulfide, a metal silicate, or a metal phosphate, or any mixture composed of a plurality of these".

[0007] Patent Document 5 discloses "an electromagnetic steel sheet with an insulating coating, which has a heat-resistant adhesive insulating coating on one or both surfaces of the electromagnetic steel sheet, wherein the heat-resistant adhesive insulating coating contains 10% by mass or more of a polycarbonate urethane resin having a softening point of 20 to 200°C, and 10 to 1000 parts by mass of a phenol resin per 100 parts by mass of the polycarbonate urethane resin".

[0008] International Publication No. 2004 / 070080 Japanese National Publication of Translated Version No. 2023-508140 International Publication No. 2016 / 017132 Japanese National Publication of Translated Version No. 2018-518591 Japanese Unexamined Patent Publication No. 2017-179233

[0009] In recent years, there has been a demand for improved adhesive strength (sometimes simply referred to as adhesive strength) between laminated steel sheets used in the automotive sector, and in particular, for improved adhesive strength at high temperatures ranging from room temperature to approximately 150°C. However, in conventional technologies, including those described in Patent Documents 1 to 5, increasing the adhesive strength of the adhesive film results in a decrease in the magnetic properties of the electrical steel sheet. This is thought to be because resins with high adhesive strength tend to have a high Young's modulus, which causes distortion in the steel sheet due to curing shrinkage, leading to a deterioration of magnetic properties. While it is known that reducing the thickness of the film mitigates the decrease in magnetic properties, this also reduces the adhesive strength, making it undesirable from the perspective of magnetic properties. In other words, it has been difficult to simultaneously improve both adhesive strength and magnetic properties with conventional technologies.

[0010] Given this background, there is a need for electrical steel sheets with an adhesive coating that exhibit excellent adhesive strength and magnetic properties. Therefore, the object of this disclosure is to provide electrical steel sheets equipped with an adhesive coating that exhibit excellent magnetic properties and adhesive strength at room temperature to 150°C, laminated cores obtained by laminating these electrical steel sheets, and methods for manufacturing these.

[0011] In view of the above findings, the inventors investigated how to achieve both magnetic properties and adhesive strength at room temperature to 150°C. As a result, they found that it is possible to achieve both magnetic properties and adhesive strength in an electrical steel sheet with an insulating coating formed by compounding an acrylic resin having a predetermined functional group.

[0012] This disclosure has been made in view of the above findings. The gist of this disclosure is as follows: [1] An electrical steel sheet according to one aspect of this disclosure comprises a base steel sheet and an insulating coating formed on at least a portion of one or both surfaces of the base steel sheet, wherein the insulating coating is made of a crosslinkable acrylic resin having self-fusing ability and containing an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups, and when the electrical steel sheet having the insulating coating is heated to 200°C and held for 5 minutes, the ratio of the gel fraction after the treatment to the gel fraction before the treatment in the insulating coating is 1.1 to 1.4. [2] A method for manufacturing an electrical steel sheet according to another aspect of the present disclosure includes a coating step of applying a coating liquid to at least a portion of one or both sides of a steel sheet that will be a base steel sheet, and a film forming step of drying the coating liquid after the coating step to form an insulating film on the surface of the base steel sheet, wherein the coating liquid contains 10 parts by mass or more of acrylic resin containing glycidyl groups, 20 parts by mass or more of acrylic resin containing carboxyl groups, and 10 parts by mass or more of acrylic resin containing other functional groups, when the total resin content is 100 parts by mass. [3] A laminated core according to another aspect of the present disclosure is a laminated core in which a plurality of electrical steel sheets are laminated with an insulating film in between, wherein the gel fraction of the insulating film is 60 to 90% by mass, and the insulating film is made of a crosslinkable acrylic resin containing acrylic resin containing glycidyl groups, acrylic resin containing carboxyl groups, and acrylic resin containing other functional groups. [4] A method for manufacturing a laminated core according to another aspect of the present disclosure includes the step of stacking a plurality of electromagnetic steel sheets as described in [1] to form a laminated body, and holding the laminated body at a temperature of 200 to 300°C and a pressure of 0.5 to 10 MPa for 5 to 60 minutes.

[0013] According to the above-described aspects of this disclosure, it is possible to provide an electrical steel sheet having a coating with adhesive properties (self-fusing properties) and excellent adhesive strength and magnetic properties (particularly the rate of deterioration of magnetic properties after lamination), a laminated core obtained by laminating this electrical steel sheet, and a method for manufacturing the same.

[0014] This is a schematic diagram showing an example of an electrical steel sheet of the present disclosure. This is a schematic diagram showing an example of a laminated core of the present disclosure.

[0015] An electrical steel sheet (electrical steel sheet according to this embodiment), a laminated core (laminated core according to this embodiment), and a method for manufacturing these according to one embodiment of this disclosure will be described.

[0016] <Electromagnetic Steel Sheet> As shown in Figure 1, the electromagnetic steel sheet 10 according to this embodiment has a base steel sheet 10A and an insulating coating 10B formed on the surface of the base steel sheet 10A. In Figure 1, the insulating coating 10B is formed on the entire surface (front and back) of both surfaces (front and back) of the base steel sheet 10A, but it is sufficient if it is formed on at least a part of at least one or both surfaces. The base steel sheet 10A and the insulating coating 10B are as follows.

[0017] [Base Steel Sheet] The base steel sheet is the steel sheet on which the insulating coating is formed. After the insulating coating is formed, it is sufficient for it to become an electrical steel sheet with an insulating coating, and there are no particular restrictions on the base steel sheet as long as it is an electrical steel sheet. The electrical steel sheet that becomes the base steel sheet may be a non-oriented electrical steel sheet or a grain-oriented electrical steel sheet. For example, non-oriented electrical steel sheet of JIS C 2552:2014, grain-oriented electrical steel sheet of JIS C 2553:2019, non-oriented thin electrical steel sheet or grain-oriented thin electrical steel sheet of JIS C 2558:2015 can be used.

[0018] [Insulating Coating] In the electrical steel sheet according to this embodiment, the insulating coating is formed on the surface of the base steel sheet. This insulating coating has self-fusing properties (i.e., it is an adhesive coating with so-called adhesive properties). Because it has self-fusing properties, when stacking and fixing multiple sheets, the use of adhesives or the like is unnecessary. In the electrical steel sheet according to this embodiment, steel sheets are stacked on top of each other via the insulating coatings they each have, and after being held (pressed) for 5 minutes at a steel sheet temperature of 250°C and a pressure (pressure applied to the stacking surface) of 2 MPa, if the adhesive strength (shear adhesive strength) measured at room temperature in accordance with JIS K 6850:1999 is 3.0 MPa or higher, it is determined that the insulating coating has self-fusing properties.

[0019] Furthermore, the insulating coating on the electrical steel sheet according to this embodiment is made of a crosslinkable acrylic resin containing an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups. (However, the inclusion of various additives other than resin, such as preservatives, wetting agents, and defoaming agents, is permitted.) In addition, when this insulating coating is subjected to a treatment in which it is heated to 200°C and held for 5 minutes, the ratio of the gel fraction after treatment to the gel fraction before treatment (sometimes simply called the gel fraction ratio) is 1.1 to 1.4. The reason for making the insulating coating out of a crosslinkable acrylic resin is that it is possible to improve heat resistance through crosslinking and to relax internal stress by polymer chains. When internal stress is relaxed, the stress on the steel sheet is reduced and iron loss is decreased. With other resins, there is a risk that adhesive strength and magnetic properties cannot be achieved at a desirable level or higher. Furthermore, by including an acrylic resin containing a glycidyl group and an acrylic resin containing a carboxyl group as the crosslinkable acrylic resin, the adhesive strength at high temperatures becomes stronger. While epoxy resin is commonly used to increase adhesive strength, coatings using acrylic resin emulsion have fewer reaction bonding sites compared to epoxy resin coatings, meaning they have a lower curing shrinkage rate, thus reducing the stress on the steel sheet due to film shrinkage. As a result, the deterioration of magnetic properties (especially hysteresis loss) can be mitigated. Therefore, the above-mentioned acrylic resin is used in the electrical steel sheet according to this embodiment. The above effect cannot be obtained without including an acrylic resin having any of the functional groups. In addition, acrylic resins having other functional groups (other than glycidyl and carboxyl groups, for example, N-methylol group, N-butyrol group, amino group, hydroxyl group, alkoxymethylamide group) are included to ensure fluidity during heat-press bonding. By including the three types of resin in a balanced manner, a synergistic effect is obtained, making it possible to achieve both adhesive strength and magnetic properties. If the gel fraction ratio of the crosslinkable acrylic resin is less than 1.1, crosslinking will be insufficient and sufficient adhesive strength cannot be obtained. On the other hand, if the gel fraction ratio exceeds 1.4, the magnetic properties will deteriorate. The gel fraction ratio can be controlled by controlling the proportion of acrylic resin containing glycidyl groups, acrylic resin containing carboxyl groups, and acrylic resin containing other functional groups in the coating.Since it is not easy to accurately measure the proportion of these resins in an insulating coating, in this embodiment, it is defined by the gel fraction ratio.

[0020] The composition of the insulating coating is determined by identifying the components, types of functional groups, main chain structure, monomer residues, decomposition products, curing agents, and plasticizers, for example, by using a combination of infrared spectroscopy, nuclear magnetic resonance, and gas chromatography.

[0021] Furthermore, the gel fraction of the insulating coating is the proportion of solvent-insoluble matter measured using ethyl acetate as the extraction solvent. Therefore, the gel fractions before and after treatment can be determined for both the electromagnetic steel sheet before and after treatment by the following method. First, two sample pieces are obtained from an electromagnetic steel sheet on which an insulating coating has been formed on the surface of the base steel sheet, cut to a size of 60 mm x 60 mm. Next, the insulating coating is removed from one of the sample pieces by cutting. The sample piece from which the insulating coating has been removed is designated as sample X1, and its mass is A. The other sample piece (i.e., the sample piece with the insulating coating) is designated as sample X2, and its mass is B. Next, sample X2 is placed in a glass bottle containing 80 g of ethyl acetate and the lid is closed. Next, the glass bottle containing sample X2 is left in an environment with an ambient temperature of 23°C and 50% RH for 3 days. Next, sample X2 is removed from the glass bottle and washed with a small amount of ethyl acetate. Next, sample X2 is dried at a drying temperature of 100°C for 24 hours. The mass of the dried sample X2 is accurately measured using a precision balance. This mass is denoted as D (in grams). Next, the gel fraction is calculated using the following formula (1): Gel fraction [mass %] = (D - A) / (B - A) × 100 (1)

[0022] The average thickness of the insulating coating is preferably 1.0 to 6.0 μm, and more preferably 1.5 to 3.0 μm. Even when the average thickness of the insulating coating is within the above range, the electromagnetic steel sheet according to this embodiment exhibits excellent adhesive strength and magnetic properties.

[0023] The method for measuring the average thickness of the insulating coating is as follows: The insulating coated electrical steel sheet to be measured is cut along the thickness direction to obtain a test piece with the cut surface as the observation surface. The observation surface of the test piece is observed at a magnification of 2000x using a scanning electron microscope (SEM), and the thickness of the insulating coating is measured at three locations at least 10 mm apart. Then, the arithmetic mean of the thicknesses of the insulating coating at the three locations is taken to determine the average thickness of the insulating coating.

[0024] <Laminated Core> The laminated core according to this embodiment is obtained by laminating multiple electromagnetic steel sheets according to this embodiment, which have been cut to a predetermined shape as needed, and then heating and pressurizing them. As a result, multiple electromagnetic steel sheets are laminated with an insulating coating in between (without the base steel sheets directly contacting each other). It also has the characteristic of having superior rigidity and magnetic properties compared to a crimped core. In the laminated core, the insulating coating is an insulating coating obtained as a result of the crosslinking of the crosslinkable acrylic resin in the insulating coating of the electromagnetic steel sheet according to this embodiment progressing and hardening due to heating and pressurizing. This insulating coating is obtained using the electromagnetic steel sheet according to this embodiment and has a gel fraction of 60 to 90% by mass. The insulating coating is made of a crosslinkable acrylic resin that includes an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups. As a result, in the laminated core according to this embodiment, the adhesive strength between the electromagnetic steel sheets is high due to the crosslinking of the acrylic resin, and the gel fraction after bonding is lower compared to laminated cores bonded with a self-fusing insulating coating using a thermosetting resin such as epoxy resin, thus reducing internal stress and resulting in lower iron loss.

[0025] The gel fraction of the insulating coating in a laminated core can be determined in the same way as for electrical steel sheets after peeling off several sheets from the laminated core.

[0026] Figure 2 is a schematic diagram showing an example of a laminated core of the present disclosure. Figure 2 shows a laminated core formed by punching out punched members from an electromagnetic steel sheet and then laminating and integrating these punched members. The laminated core 100 according to this embodiment is not limited to the shape, number, or number of layers of punched members 11 that form the laminated core 100, and can be designed according to the purpose. For example, in the case of Figure 2, the laminated core 100 is formed as a laminated body 13 by connecting eight punched members 11 of electromagnetic steel sheets (electromagnetic steel sheets according to this embodiment) in an annular shape, and laminating the annularly connected punched members 11 in eight layers. The punched member 11 includes an arc-shaped yoke portion 17 and a teeth portion 15 that protrudes radially inward from the inner circumferential surface of the yoke portion 17. The laminated core according to this embodiment can be used as a core (iron core) for use in rotating electric machines and the like.

[0027] <Manufacturing Method> Regardless of the manufacturing method, the electrical steel sheet according to this embodiment will have the above-described characteristics and effects. A method including the following steps is preferable because it allows the electrical steel sheet according to this embodiment to be obtained: (I) A coating step of applying a coating liquid containing a crosslinkable acrylic resin to at least a portion of one or both sides of a steel sheet that will become a base material steel sheet; (II) A film forming step of drying the coating liquid after the coating step to form an insulating film on the surface of the base material steel sheet. Each step will be described below.

[0028] (Coating Process) In the coating process, a coating liquid containing a predetermined crosslinkable acrylic resin is applied to at least a portion of one or both sides of the steel sheet that will become the base material. The coating method is not limited, and well-known coating methods such as the roll coater method and the spray method can be applied. This coating liquid contains an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups. When the total resin content is 100 parts by mass, the acrylic resin containing a carboxyl group is 20 parts by mass or more, and the acrylic resin containing a glycidyl group and the acrylic resin containing other functional groups are each 10 parts by mass or more. It is preferable that the acrylic resin containing a glycidyl group is 20 parts by mass or more. The solid content concentration of the coating liquid is preferably 5 to 40% by mass, and more preferably 10 to 25% by mass. If the proportion of the acrylic resin containing a glycidyl group and the acrylic resin containing a carboxyl group is low, the crosslinking reaction during bonding will not proceed sufficiently, the gel fraction will be low, and the adhesive strength at 150°C will be inferior. If the proportion of acrylic resin containing other functional groups is small, the fluidity during heat-press bonding will be insufficient, preventing sufficient fusion of the insulating films, resulting in inferior adhesive strength at room temperature. The type of water in the coating liquid for forming insulating films is not particularly limited. As for the water, for example, distilled water, deionized water (also called "ion-exchanged water"), and pure water are preferred from the viewpoint of having fewer impurities. The coating liquid for forming insulating films may contain components other than those described above (so-called other components) as needed, to the extent that it does not impair its effect. 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; glycol derivatives such as ethylene glycol monoethyl ether and propylene glycol monobutyl ether; and other organic solvents. Other components include various additives such as preservatives, wetting agents, and defoamers.The insulating coating liquid is obtained, for example, by gradually mixing various acrylic resins (in a way that prevents heat generation and temperature rise during mixing). One mixing method is, for example, stirring. General stirring equipment or devices can be used for stirring. The stirring temperature is not particularly limited, but is preferably, for example, 20 to 30°C.

[0029] (Coating Formation Process) In the coating formation process, the coating liquid after the coating process is dried. This forms an insulating coating on the surface of the base steel sheet. The drying conditions are not limited, but the drying temperature is preferably 100 to 200°C, and the drying time is preferably 10 to 90 seconds. If the drying temperature exceeds 200°C, there is a concern that the resin may oxidize. If the drying temperature is less than 100°C, or the drying time is less than 10 seconds, the coating may not dry sufficiently. If the drying time exceeds 90 seconds, the productivity will be inferior. The drying method is preferably a radiant heating furnace, but a hot air furnace or other method may also be used.

[0030] The laminated core according to this embodiment can be manufactured by a manufacturing method that further includes the following steps: (III) Prepare a plurality of electrical steel sheets according to this embodiment, overlap them so that an insulating film is interposed between the base steel sheets to form a laminated body, and hold this laminated body at a temperature of 200 to 300°C and a pressure of 0.5 to 10 MPa for 5 to 60 minutes (heating and pressurizing). Under the above conditions, heating and pressurizing promotes crosslinking of the crosslinkable acrylic resin (thermoplastic resin) in the insulating film, and the insulating film hardens. As a result, the hardened insulating film (cured film) exhibits adhesive properties, and the electrical steel sheets are bonded to each other. If the temperature during pressurization is less than 200°C, hardening will be insufficient, and if it exceeds 300°C, the resin will oxidize. If the pressure is less than 0.5 MPa, unbonded areas are likely to occur, and if it exceeds 10 MPa, the steel sheets will be distorted. If the holding time is less than 5 minutes, hardening will be insufficient, and if it exceeds 60 minutes, productivity will be inferior. When many sheets are to be stacked, it is preferable to extend the holding time to ensure uniform heating. For example, 10 minutes or more, or 30 minutes or more. The electromagnetic steel sheets to be stacked according to this embodiment may be cut and processed into a predetermined shape. For example, they may have a shape with teeth and a yoke. Also, if the laminated core is a segmented core, multiple stacked bodies may be combined to form the core. These operations will yield the laminated core according to this embodiment. When stacking with an insulating coating interposed between the base steel sheets, the insulating coatings of the electromagnetic steel sheets may face each other, or the insulating coating of one electromagnetic steel sheet may face the base steel sheet of the other electromagnetic steel sheet.

[0031] The coating liquids of this disclosure will be described in more detail below with reference to examples. This disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0032] A coating solution was prepared by mixing and stirring one or more of the following: crosslinkable acrylic resins A to E, thermoplastic resins, and thermosetting resins, in the proportions (parts by mass) shown in Table 1. A blank space in Table 1 indicates that the corresponding resin was not present. Water was used as the solvent during preparation, and the solid content concentration of the coating solution was 20% by mass. Crosslinkable acrylic resins A to E are as follows: Crosslinkable acrylic resin A: Acrylic resin containing glycidyl groups; Crosslinkable acrylic resin B: Acrylic resin containing carboxyl groups; Crosslinkable acrylic resin C: Acrylic resin containing N-methylol groups; Crosslinkable acrylic resin D: Acrylic resin containing amino groups; Crosslinkable acrylic resin E: Acrylic resin containing hydroxyl groups.

[0033] Furthermore, a non-oriented electrical steel sheet with a thickness of 0.25 mm and a width of 100 mm was prepared, consisting of Si: 3.0%, Mn: 0.2%, Al: 0.5% by mass, with the remainder being Fe and impurities. The coating solution obtained above was applied to the entire surface of one side of this non-oriented electrical steel sheet, and it was heated to the drying temperature shown in Table 1 and held for the drying time. This resulted in an electrical steel sheet (non-oriented electrical steel sheet) with an insulating film formed on the entire surface of one side.

[0034]

[0035] For each example of electrical steel sheet, the ratio of the gel fraction after treatment to the gel fraction before treatment when heated to 200°C and held for 5 minutes, the adhesive strength at room temperature (25°C) and high temperature (150°C) after holding the steel sheet at a temperature of 250°C and a pressure of 2 MPa for 5 minutes, and the magnetic degradation rate before and after treatment at a temperature of 250°C and a pressure of 2 MPa for 5 minutes were evaluated in the following manner.

[0036] (Ratio of Gel Fractions) For each example of electrical steel sheet, the gel fraction of the insulating coating was measured using the method described above. This was defined as the gel fraction G1 before treatment. The obtained electrical steel sheet was then heated to 200°C and held for 5 minutes, and the gel fraction of the insulating coating was measured using the method described above. This was defined as the gel fraction G2 after treatment. The ratio of G2 to G1 was defined as the gel fraction ratio. The results are shown in Table 2.

[0037] ​(Adhesive Strength - Room Temperature) Two single-sheet test pieces measuring 25 mm x 100 mm were cut from each example of electrical steel sheet. The 25 mm x 12.5 mm edges of the two single-sheet test pieces were overlapped with their insulating coatings facing each other. The overlapped body was held (heated and pressurized) for 5 minutes at a steel sheet temperature of 250°C and a pressure of 2 MPa to obtain a sample for adhesive strength measurement. With the sample temperature at room temperature (25°C), the sample was mounted on a tensile testing machine and the shear adhesive strength (tensile shear adhesive strength) measured in accordance with JIS K 6850:1999 was defined as the room temperature adhesive strength. An adhesive strength of 9.0 MPa or higher was considered to indicate excellent adhesive strength.

[0038] (Adhesive Strength - High Temperature) Two single-sheet test pieces measuring 25 mm x 100 mm were cut from each example of electrical steel sheet. The 25 mm x 12.5 mm edges of the two single-sheet test pieces were overlapped with their insulating coatings facing each other. The overlapped body was held at a steel sheet temperature of 250°C and a pressure of 2 MPa for 5 minutes (heated and pressurized) to obtain a sample for adhesive strength measurement. This laminated sample was placed in a 150°C atmosphere, and with the sample temperature at 150°C, the sample was attached to a tensile testing machine and measured in accordance with JIS K 6850:1999. The shear adhesive strength was taken as the adhesive strength at high temperature (150°C). If the adhesive strength was 3.0 MPa or higher, it was judged that excellent adhesive strength had been obtained.

[0039] (Magnetic Properties - Magnetic Degradation Rate) Single-sheet test pieces measuring 55 mm x 55 mm were cut from each example of electrical steel sheet with insulating coating. Two single-sheet test pieces were then stacked with their insulating coatings facing each other. The iron loss (W10 / 400) in the rolling direction and the direction perpendicular to rolling of the obtained stacked sample was measured using the single-sheet magnetic measurement method specified in JIS C 2556:2015. Iron loss was measured in two directions, the rolling direction and the direction perpendicular to rolling, and the average of these was taken as the iron loss W1 of the stacked sample. Subsequently, the stacked body was held (heated and pressurized) for 5 minutes at a steel sheet temperature of 250°C and a pressure of 2 MPa to obtain an adhesive laminate sample. The iron loss (W10 / 400) in the rolling direction and the direction perpendicular to rolling of the obtained adhesive laminate sample was measured in the same manner as above. The average of these was taken as the iron loss W2 of the adhesive laminate sample. The magnetic (iron loss) degradation rate of the adhesive laminate relative to the superimposed body was determined using the following formula (2): (W2 - W1) / W1 × 100 Formula (2) If the magnetic degradation rate was 10.0% or less, it was judged to be a low magnetic degradation rate.

[0040]

[0041] As can be seen from Tables 1 and 2, in cases where the insulating film is made of a crosslinkable acrylic resin containing glycidyl groups, carboxyl groups, and other functional groups, and the gel fraction ratio of the insulating film is 1.1 to 1.4, the adhesive strength at room temperature and 150°C was high, and the magnetic degradation rate was low. (Judgment A) On the other hand, in cases where the insulating film is not made of the specified acrylic resin, the gel fraction ratio of the insulating film is outside the range of the present invention, and one or more of the adhesive strength at room temperature, adhesive strength at 150°C, and magnetic degradation rate are inferior. (Judgment B or C) In particular, if any one of the following falls within the range: adhesive strength at room temperature is 4.5 MPa or less, adhesive strength at 150°C is 0.5 MPa or less, or magnetic degradation rate is 20.0% or more, the judgment is C.

[0042] According to this disclosure, it is possible to provide electrical steel sheets having a coating with adhesive properties (self-fusing properties) and excellent adhesive strength and magnetic properties (particularly the rate of degradation of magnetic properties after lamination), laminated cores obtained by laminating these electrical steel sheets, and methods for manufacturing the same. These have high potential for industrial application.

[0043] 10 Electrical steel sheet 10A Base steel sheet (electrical steel sheet) 10B Insulating coating 11 Punched member 13 Laminate 15 Teeth part 17 Yoke part 100 Laminated core

Claims

1. An electrical steel sheet comprising: a base steel sheet; and an insulating coating formed on at least a portion of one or both surfaces of the base steel sheet, wherein the insulating coating is made of a crosslinkable acrylic resin having self-fusing ability and containing an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups, and wherein when the electrical steel sheet having the insulating coating is heated to 200°C and held for 5 minutes, the ratio of the gel fraction after the treatment to the gel fraction before the treatment in the insulating coating is 1.1 to 1.

4.

2. A method for manufacturing an electrical steel sheet, comprising: a coating step of applying a coating liquid to at least a portion of one or both sides of a steel sheet that will become a base steel sheet; and a film forming step of drying the coating liquid after the coating step to form an insulating film on the surface of the base steel sheet, wherein the coating liquid contains, when the total resin content is 100 parts by mass, 10 parts by mass or more of acrylic resin containing glycidyl groups, 20 parts by mass or more of acrylic resin containing carboxyl groups, and 10 parts by mass or more of acrylic resin containing other functional groups.

3. A laminated core comprising a plurality of electromagnetic steel sheets laminated with an insulating coating in between, wherein the gel fraction of the insulating coating is 60 to 90% by mass, and the insulating coating is made of a crosslinkable acrylic resin containing an acrylic resin containing a glycidyl group, an acrylic resin containing a carboxyl group, and an acrylic resin containing other functional groups.

4. A method for manufacturing a laminated core, characterized by comprising the steps of stacking a plurality of electromagnetic steel sheets as described in claim 1 to form a laminated body, and holding the laminated body at a temperature of 200 to 300°C and a pressure of 0.5 to 10 MPa for 5 to 60 minutes.

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