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

Abstract

This electrical steel sheet has: a base steel sheet; and an insulating coating formed on at least a part of one or both surfaces of the base steel sheet. The insulating coating has self-fusing properties and includes: a water-dispersible acrylic resin containing carboxyl groups in an amount of 5 to 25 mg KOH / g; and an epoxy resin curing agent. The epoxy resin curing agent is present in an amount of 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin. The insulating coating has a Δ105 / Δ300 ratio of 0.005 to 0.400, where Δ105 is the weight loss after heating to 105°C and Δ300 is the weight loss after heating to 300°C.

Description

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

[0001] The present disclosure relates to an electromagnetic steel sheet, a laminated core, and methods for producing the same. The present application claims priority based on Japanese Patent Application No. 2025-056058 filed in Japan on March 28, 2025, the content of which is incorporated herein by reference.

[0002] Conventionally, for cores (iron cores) used in rotating electrical machinery and the like, a "laminated core" in which a plurality of electromagnetic steel sheets are laminated on each other has been used. The plurality of electromagnetic steel sheets are fixed by methods such as welding, caulking, bolting, and adhesion. Among these, when fixing a plurality of electromagnetic steel sheets by welding, caulking, or bolting, mechanical stress, thermal stress, interlayer short-circuiting, and the like are likely to occur during processing. As a result, the magnetic properties of the electromagnetic steel sheets deteriorate, and it is difficult for the performance of the laminated core to be sufficiently exhibited. On the other hand, when fixing a plurality of electromagnetic steel sheets by an adhesion method, mechanical stress, thermal stress, interlayer short-circuiting, and the like 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 likely to be sufficiently exhibited. Due to such advantages, various technologies have been studied for fixing a plurality of electromagnetic steel sheets by an adhesion method. As adhesion methods, a method using an adhesive, and a method in which after laminating electromagnetic steel sheets with a coating having adhesive ability, heating and pressing are performed to cure the coating and adhere the plurality of electromagnetic steel sheets to each other, have been proposed.

[0003] For example, Patent Document 1 discloses "an adhesive surface-coated electromagnetic steel sheet characterized in that it is an electromagnetic steel sheet having on the surface an insulating coating that exhibits adhesive ability by heating and / or pressing, wherein the coating is a mixture in which an 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 diameter of 0.01 µm to 0.5 µm are dispersed."

[0004] Patent Document 2 discloses "a laminate of electrical steel sheets comprising a plurality of electrical steel sheets and a fusion layer located between the plurality of electrical steel sheets, wherein the fusion layer comprises polyethylene acrylate containing repeating units represented by chemical formula 1 and repeating units represented by chemical formula 2, and the polyethylene acrylate contains 65 to 90% by weight of the repeating units represented by chemical formula 1 and 10 to 35% by weight of the repeating units represented by chemical formula 2."

[0005] Patent Document 3 discloses "a laminated electrical steel sheet comprising an electrical steel sheet and an adhesive insulating coating provided on at least one side of the electrical steel sheet, having a Martens hardness (HM) of 50 or more and less than 500."

[0006] Patent Document 4 discloses "an electrical steel strip or electrical steel sheet having at least one thermosetting baked enamel layer provided on one of its planes, comprising an epoxy resin main component, at least one curing agent, and at least one filler, characterized in that the filler of the baked enamel layer includes a metal carbonate, a metal sulfate, a metal sulfide, a metal silicate, or a metal phosphate, or any mixture of a plurality thereof."

[0007] Patent Document 5 discloses "an insulating coated electromagnetic steel sheet having a heat-resistant adhesive insulating coating on one or both sides 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 Patent Publication No. 2023-508140; International Publication No. 2016 / 017132, Japanese Patent Publication No. 2018-518591; Japanese 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.

[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 comprises a water-dispersible acrylic resin having self-fusing ability and containing carboxyl groups in a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resins, wherein the amount of the curing agent for epoxy resins is 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin, and the ratio of the weight loss after heating to 105°C, Δ105 / Δ300, to the weight loss after heating to 300°C, Δ300, is 0.005 to 0.400. [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, the coating liquid being 0.5 to 20 parts by mass of the epoxy resin curing agent, wherein the amount of the coating liquid after the coating step is 0.5 to 20 parts by mass of the epoxy resin curing agent, and the coating liquid being 0.5 to 20 parts by mass of the epoxy resin curing agent, 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 drying temperature is 100 to 200°C and the drying time is 10 to 90 seconds. [3] A laminated core according to another aspect of the present disclosure is a laminated core comprising a plurality of electromagnetic steel sheets laminated with an insulating coating in between, wherein the space factor of the laminated core is 96 to 98%, and the insulating coating comprises a water-dispersible acrylic resin containing carboxyl groups at a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resins, wherein the amount of the curing agent for epoxy resins is 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin. [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 1 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 provided on the electromagnetic steel sheet according to this embodiment contains a water-dispersible acrylic resin and a curing agent for epoxy resins, wherein the water-dispersible acrylic resin contains carboxyl groups at a ratio of 5 to 25 mg KOH / g. It may also consist substantially of a water-dispersible acrylic resin and a curing agent for epoxy resins (the inclusion of various additives such as preservatives, wetting agents, and defoaming agents is permitted). In the insulating coating, the epoxy resin curing agent is contained in a ratio of 0.5 to 20 parts by mass per 100 parts by mass of water-dispersible acrylic resin. By including a water-dispersible acrylic resin containing carboxyl groups and an epoxy resin curing agent in a predetermined ratio, heat resistance (for example, Δ105 / Δ300 as described later) is ensured by crosslinking of the carboxyl groups, and excellent magnetic properties are obtained in the main chain portion of the acrylic by relaxation of compressive stress. If the ratio of the epoxy resin curing agent to the water-dispersible acrylic resin is small, curing will be insufficient and heat resistance will be inferior, and if it is large, the insulating coating will become too hard and magnetic properties will be inferior. For epoxy resins, dicyandiamide is preferable as the curing agent due to its latent properties. Furthermore, if the proportion of carboxyl groups in the water-dispersible acrylic resin is small, curing will be insufficient and heat resistance will be poor. On the other hand, if the proportion of carboxyl groups is large, the insulating film will become too hard, resulting in poor magnetic properties.

[0020] Furthermore, the insulating coating on the electromagnetic steel sheet according to this embodiment has a ratio (Δ105 / Δ300) of Δ105 (weight loss after heating to 105°C) to Δ300 (weight loss after heating to 300°C), which is 0.005 to 0.400. When Δ105 / Δ300 is within the above range, a particularly good balance between adhesive strength and magnetic properties is achieved. Δ105 is the weight loss due to moisture, and Δ300 is the weight loss due to moisture and decomposed resin. Therefore, Δ105 / Δ300 is an index for evaluating the weight loss of resin excluding the effect of moisture. If Δ105 / Δ300 is less than 0.005, the curing by thermocompression bonding is insufficient, resulting in inferior adhesive strength. Preferably, Δ105 / Δ300 is 0.010 or higher. Preferably, Δ105 / Δ300 is 0.030 or higher. On the other hand, if Δ105 / Δ300 exceeds 0.400, hardening progresses too much after thermocompression bonding, resulting in high internal stress and inferior magnetic properties. Preferably, Δ105 / Δ300 is 0.350 or less, or 0.300 or less.

[0021] 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 combining infrared spectroscopy, nuclear magnetic resonance, and gas chromatography. The amount of epoxy resin curing agent per 100 parts by mass of water-dispersible acrylic resin is determined by a similar method.

[0022] The weight loss (Δ105, Δ300) and its ratio (Δ105 / Δ300) after heating to 105°C or 300°C are measured by the following method. First, two sample pieces are obtained from an electrical steel sheet with an insulating coating formed on the surface of the base steel sheet, cut to a size of 60 mm x 60 mm. One of these sample pieces is designated as sample A for 105°C, and the other as sample B for 300°C. Next, the mass of the sample (untreated) is measured. The mass of sample A is designated as A1 (unit: g), and the mass of sample B is designated as B1 (unit: g). Next, under a dry nitrogen atmosphere (dew point: -65°C or below, N ２Sample A is heated to 105°C and Sample B to 300°C (at 100% volume), and both are held at these temperatures for 1 hour. After cooling to room temperature, the masses of Sample A and Sample B are measured, with the mass of Sample A being A2 (in g) and the mass of Sample B being B2. Using these A1, A2, B1, and B2, the weight loss ratio is then calculated using the following formulas (1) to (3): Δ105 [g] = (A1 - A2) (1) Δ300 [g] = (B1 - B2) (2) Weight loss ratio (Δ105 / Δ300) [-] = (A1 - A2) / (B1 - B2) (3)

[0023] 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.

[0024] 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.

[0025] <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. The laminated core according to this embodiment is manufactured using the electromagnetic steel sheet according to this embodiment, and high adhesive strength can be obtained even with a thin adhesive layer, so the packing ratio is 96 to 98%. The insulating coating also contains a water-dispersible acrylic resin containing carboxyl groups at a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resin, with the amount of the epoxy resin curing agent being 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin.

[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 to at least a portion of one or both sides of a steel sheet that will become a base steel sheet, the coating liquid being 0.5 to 20 parts by mass of the epoxy resin curing agent, which contains a water-dispersible acrylic resin with carboxyl groups in a ratio of 5 to 25 mg KOH / g, with the amount of the water-dispersible acrylic resin being 0.5 to 20 parts by mass of the epoxy resin curing agent per 100 parts by mass of the water-dispersible acrylic resin; (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 steel sheet. Each step will be described below.

[0028] (Coating Process) In the coating process, a predetermined coating liquid 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 a water-dispersible acrylic resin containing carboxyl groups at a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resin, and is prepared so that the amount of epoxy resin curing agent is 0.5 to 20 parts by mass per 100 parts by mass of water-dispersible acrylic resin. The solid content concentration of the coating liquid is preferably 5 to 40% by mass, and more preferably 10 to 25% by mass. The type of water in the coating liquid for forming an insulating film is not particularly limited. As water, for example, distilled water, deionized water (also called "ion-exchanged water"), and pure water are preferred from the viewpoint of having few impurities. The coating liquid for forming an insulating film may contain components other than those described above (so-called other components) as needed, to the extent that it does not impair its effect. Other components include, for example, aqueous media other than water. Examples of aqueous media other than water include, for example, 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, for example, various additives such as preservatives, wetting agents, and defoamers. The insulating coating liquid is obtained, for example, by gradually mixing a water-dispersible acrylic resin and an epoxy resin curing agent (so as not to generate heat and raise the temperature during mixing). A mixing method can be, for example, by stirring. A general stirring device or stirring apparatus 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 a drying temperature of 100 to 200°C and a drying time of 10 to 90 seconds. If the drying temperature exceeds 200°C, there is a concern that the resin will 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, it will be disadvantageous in terms of productivity. The drying method is preferably a radiant heating furnace, but a hot air furnace or other methods 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 electromagnetic 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 1 to 60 minutes (heat and pressurize).

[0031] Under the above conditions, heating and pressurizing promotes crosslinking of the crosslinkable acrylic resin (thermoplastic resin) in the insulating coating, causing the insulating coating to harden. As a result, the hardened insulating coating (cured film) exhibits adhesive properties, and the electrical steel sheets are bonded to each other. If the pressurizing temperature is below 200°C, hardening will be insufficient, and if it exceeds 300°C, the resin will oxidize. If the pressurizing force is below 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 1 minute, hardening will be insufficient, and if it exceeds 60 minutes, productivity will be poor. When many sheets are to be stacked, it is preferable to increase the holding time to ensure uniform heating. For example, 5 minutes or more, or 30 minutes or more. The electrical steel sheets according to this embodiment to be stacked may be cut and processed into a predetermined shape. For example, they can be shaped to have teeth and yoke portions. Also, if the laminated core is a segmented core, multiple stacked bodies may be combined to form the core. Through these operations, a laminated core according to this embodiment is obtained. When superimposing two base steel sheets with an insulating coating in between, the insulating coatings of the two electrical steel sheets may face each other, or the insulating coating of one electrical steel sheet may face the base steel sheet of the other electrical steel sheet.

[0032] 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.

[0033] A coating solution containing water-dispersible acrylic resins A to C and epoxy resin curing agents A to B in the proportions (parts by mass) shown in Table 1, with a solid content concentration of 20% by mass, was prepared. A blank space in Table 1 indicates the absence of the corresponding resin. During preparation, the acrylic resin and epoxy resin curing agent were mixed immediately before coating. Water-dispersible acrylic resins A to C and epoxy resin curing agents A to B are as follows: Water-dispersible acrylic resin A: Water-dispersible acrylic resin containing carboxyl groups; Water-dispersible acrylic resin B: Water-dispersible acrylic resin without crosslinking groups; Water-dispersible acrylic resin C: Water-dispersible acrylic resin containing glycidyl groups; Epoxy resin curing agent A: Dicyandiamide; Epoxy resin curing agent B: Resol-type phenolic resin

[0034] 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 liquid obtained above was applied to the entire surface of one side of this non-oriented electrical steel sheet, heated to the drying temperature shown in Table 1, and held for the drying time. From this, an electrical steel sheet (electrical steel sheet with insulating coating) was obtained in which an insulating coating was formed on the surface of the electrical steel sheet, which was the base steel sheet.

[0035]

[0036] The resin content was measured for each example of electrical steel sheet. The results showed that the resin content was the same as the resin content in the coating solution.

[0037] Furthermore, for each example of electrical steel sheet, measurements were taken for Δ105 / Δ300 using the method described above. The results are shown in Table 2.

[0038] Furthermore, for each example of electrical steel sheet, the adhesive strength at room temperature and 150°C after heat-pressing the overlapping body at the heating (thermocompression) temperature, pressing (thermocompression) force, and holding (thermocompression) time shown in Table 1, as well as the magnetic degradation rate after heat-pressing the overlapping body at the heating (thermocompression) temperature, pressing (thermocompression) force, and holding (thermocompression) time shown in Table 1, were evaluated in the following manner.

[0039] (Adhesive Strength - Room Temperature) Two 25 mm x 100 mm single-sheet test pieces 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 heat-pressed using the heating (thermocompression) temperature, pressing (thermocompression) force, and holding (thermocompression) time shown in Table 1 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.

[0040] (Adhesive Strength - High Temperature) Two 25 mm x 100 mm single-sheet test pieces 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 heat-compressed using the heating (thermocompression) temperature, pressing (thermocompression pressing) force, and holding (thermocompression) time shown in Table 1 to obtain a sample for measuring adhesive strength. 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. The shear adhesive strength measured in accordance with JIS K 6850:1999 was defined as the adhesive strength at high temperature (150°C). An adhesive strength of 3.0 MPa or higher was considered to indicate excellent adhesive strength.

[0041] (Magnetic Properties - Magnetic Deterioration Rate) A single-plate test piece with a size of 55 mm × 55 mm was cut out from the electromagnetic steel sheet with an insulating coating of each example. Then, two single-plate test pieces were 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 by the single-plate magnetic measurement method specified in JIS C 2556:2015. Iron loss was measured in two directions, namely the rolling direction and the direction perpendicular to rolling, and the average of these measurements was taken as the iron loss W₁ of the stacked sample. Subsequently, the stacked body was thermocompression-bonded under the heating (thermocompression) temperature, pressing (thermocompression pressing) force, and holding (thermocompression) time shown in Table 1 to obtain a bonded laminate sample. The iron loss (W₁₀ / ₄₀₀) in the rolling direction and the direction perpendicular to rolling of the obtained bonded laminate sample was measured in the same manner as described above. The average of these measurements was taken as the iron loss W₂ of the bonded laminate sample. The magnetic (iron loss) deterioration rate of the bonded laminate relative to the stacked body was obtained by the following formula (4). (W₂ - W₁) / W₁ × 100 Formula (4) When the magnetic deterioration rate was 10% or less, it was judged that the magnetic deterioration rate was low.

[0042] (Space Factor) Thirty test pieces of 30 × 300 mm were cut out from the electromagnetic steel sheet with an insulating coating of each example, these thirty test pieces were laminated, and the laminated thickness when a pressure of 1.00 ± 0.05 MPa was applied in the direction perpendicular to the surface of the test pieces was measured. The space factor was calculated in accordance with JIS C 2550-5:2020 Testing methods for electrical steel strip — Part 5: Methods of measurement for resistivity, density and space factor of electrical steel strip.

[0043]

[0044] As can be seen from Tables 1 and 2, in the case where a water-dispersible acrylic resin containing carboxyl groups at a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resins were included, with a ratio of 0.5 to 20 parts by mass of epoxy resin per 100 parts by mass of water-dispersible acrylic resin, and the Δ105 / Δ300 of the insulating film being 0.005 to 0.400, the adhesive strength at room temperature and high temperature was high, and the magnetic degradation rate was low. (Judgment A) On the other hand, in the case where the ratio of carboxyl groups contained in the water-dispersible acrylic resin and the ratio of water-dispersible acrylic resin to epoxy resin were outside the range of the present invention, the Δ105 / Δ300 of the insulating film was outside the range of 0.005 to 0.400, and one or more of the adhesive strength at room temperature and high temperature and the magnetic degradation rate were inferior. (Judgment B or C) In particular, if any one of the following conditions is met, such as a room temperature adhesive strength of 4.0 MPa or less, an adhesive strength at 150°C of 0.5 MPa or less, or a magnetic degradation rate of 20% or more, the judgment is C.

[0045] 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.

[0046] 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 comprises a water-dispersible acrylic resin having self-fusing ability and containing carboxyl groups in a ratio of 5 to 25 mg KOH / g, and a curing agent for epoxy resins, wherein the amount of the curing agent for epoxy resins is 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin; and the ratio of the weight loss after heating to 105°C, Δ105 / Δ300, to the weight loss after heating to 300°C, Δ300, is 0.005 to 0.

400.

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 be a base material steel sheet, the coating liquid being 0.5 to 20 parts by mass of the epoxy resin curing agent per 100 parts by mass of the water-dispersible acrylic resin, the coating liquid being 0.5 to 20 parts by mass of the epoxy resin curing agent, the coating liquid being 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin; 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 material steel sheet, wherein the drying temperature in the film forming step is 100 to 200°C and the drying time is 10 to 90 seconds.

3. A laminated core comprising a plurality of electromagnetic steel sheets laminated with an insulating coating in between, wherein the space factor of the laminated core is 96 to 98%, and the insulating coating comprises a water-dispersible acrylic resin containing carboxyl groups at a ratio of 5 to 25 mg KOH / g and a curing agent for epoxy resins, wherein the amount of the epoxy resin curing agent is 0.5 to 20 parts by mass per 100 parts by mass of the water-dispersible acrylic resin.

4. A method for manufacturing a laminated core, characterized by comprising the steps of stacking a plurality of electromagnetic steel sheets according to 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 1 to 60 minutes.

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