Non-oriented electrical steel sheet, laminated core, and methods for producing same

Abstract

This non-oriented electrical steel sheet has a base material steel sheet and an insulating coating film formed on at least a part of one surface or both surfaces of the base material steel sheet. The insulating coating film contains a crosslinkable acrylic resin and an epoxy resin, has self-fusing ability, has an average thickness of 0.5-3.0 μm, and has a heat distortion temperature of 130-200°C after being heated to 200°C and held for 3 minutes.

Description

Non-oriented Electrical Steel Sheet, Laminated Core, and Methods for Manufacturing the Same

[0001] The present disclosure relates to a non-oriented electrical steel sheet, a laminated core, and methods for manufacturing the same. The present application claims priority based on Japanese Patent Application No. 2025-056028 filed in Japan on March 28, 2025, the content of which is incorporated herein by reference.

[0002] Conventionally, a "laminated core" formed by laminating a plurality of electrical steel sheets on one another has been used for cores (iron cores) employed in rotating electric machines and the like. The plurality of electrical steel sheets are fixed by methods such as welding, caulking, bolt fastening, and adhesion. However, when fixing a plurality of electrical steel sheets by welding, caulking, or bolt fastening, mechanical stress, thermal stress, interlayer short-circuiting, and the like are likely to occur during processing. As a result, the magnetic properties of the electrical steel sheet deteriorate, making it difficult for the performance of the laminated core to be sufficiently exhibited.

[0003] On the other hand, when fixing a plurality of electrical steel sheets by an adhesion method, an electrical steel sheet provided with a coating having adhesive ability is used, and the coating is cured by heating and pressing to develop adhesive ability, thereby bonding the plurality of electrical steel sheets to each other. When fixing a plurality of electrical steel sheets using a coated electrical steel sheet having adhesive ability, mechanical stress, thermal stress, interlayer short-circuiting, and the like are less likely to occur during processing. Therefore, the magnetic properties of the electrical steel sheet are less likely to deteriorate, and the performance of the laminated core is likely to be sufficiently exhibited. Due to such advantages, various techniques have been studied for fixing a plurality of electrical steel sheets by an adhesion method.

[0004] For example, Patent Document 1 discloses "an electrical steel sheet having, on a surface thereof, 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, which is an adhesively surface-coated electrical steel sheet".

[0005] Furthermore, 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."

[0006] Furthermore, 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."

[0007] Furthermore, 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."

[0008] Furthermore, 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."

[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] In recent years, in order to further reduce iron loss in non-oriented electrical steel sheets, there has been a demand for thinner non-oriented electrical steel sheets themselves. Accordingly, there is a demand for thinner insulating coatings as well. Insulating coatings are required to have chemical stability and appropriate adhesive strength. In order to make insulating coatings thin, it is necessary to maintain chemical stability and appropriate adhesive strength while also having good applicability. When laminated cores are used as motors, etc., the adhesive strength of the insulating coating after bonding is required not only at room temperature but also at high temperatures. When trying to ensure adhesive strength even when the insulating coating is made thin, it is conceivable to use resins with a high crosslink density. However, resins with a high crosslink density have poor applicability and impart stress to the base steel sheet due to volume shrinkage during bonding, which degrades the iron loss of the laminated core. Therefore, even when the insulating coating is made thin, it is difficult to obtain non-oriented electrical steel sheets with excellent insulating coating applicability, high insulating coating adhesive strength, and low iron loss.

[0011] This disclosure has been made in view of the above circumstances. The object of this disclosure is to provide a non-oriented electrical steel sheet having excellent coating properties for insulating films, high adhesive strength of insulating films, and low iron loss (especially iron loss when used as a laminated core), a laminated core obtained using this non-oriented electrical steel sheet, and a method for manufacturing these.

[0012] The inventors investigated the influence of the composition of an insulating coating on the applicability and adhesive strength of the insulating coating, as well as on the iron loss of the non-oriented electrical steel sheet and core, based on a non-oriented electrical steel sheet equipped with an insulating coating having self-fusing properties and a core obtained using this non-oriented electrical steel sheet. As a result, they found that by including a crosslinkable acrylic resin and an epoxy resin in the insulating coating, and by setting the heat distortion temperature after crosslinking within a predetermined range, stress due to volume shrinkage can be suppressed, and low iron loss, excellent adhesive strength, and applicability can be obtained simultaneously.

[0013] This disclosure has been made in view of the above findings. The outline of this disclosure is as follows: [1] An unoriented 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 sides of the base steel sheet, wherein the insulating coating contains a crosslinkable acrylic resin and an epoxy resin, has self-fusing ability, has an average thickness of 0.5 to 3.0 μm, and has a heat distortion temperature of 130 to 200°C after being heated to 200°C and held for 3 minutes. [2] In the unoriented electrical steel sheet according to [1], the insulating coating may contain 10 to 70 parts by weight of the epoxy resin per 100 parts by weight of the crosslinkable acrylic resin. [3] In the unoriented electrical steel sheet according to [1] or [2], the epoxy resin may be one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and phenol resin. [4] A method for manufacturing a non-oriented electrical steel sheet according to another aspect of the present disclosure comprises a coating step of applying an insulating coating liquid to at least a portion of one or both sides of an electrical steel sheet that will be a base steel sheet, and a coating step of drying the electrical steel sheet coated with the insulating coating liquid after the coating step to obtain a non-oriented electrical steel sheet with an insulating film formed on its surface, wherein the insulating coating liquid comprises a crosslinkable acrylic resin and an epoxy resin, with the epoxy resin being 5 to 90 parts by weight per 100 parts by weight of the crosslinkable acrylic resin. [5] In the method for manufacturing a non-oriented electrical steel sheet according to [4], the epoxy resin may be one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and phenol resin. [6] In the method for manufacturing a non-oriented electrical steel sheet according to [4] or [5], the insulating coating liquid may contain a curing agent. [7] A laminated core according to another embodiment of the present disclosure comprises two or more non-oriented electrical steel sheets, each having a base steel sheet and an insulating coating formed on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating comprises a crosslinkable acrylic resin and an epoxy resin, and has a heat distortion temperature of 130 to 200°C.[8] A method for manufacturing a laminated core according to another aspect of the present disclosure comprises: a coating step of applying an insulating coating liquid to at least a portion of one or both sides of an electromagnetic steel sheet that will be a base steel sheet; a coating forming step of drying the electromagnetic steel sheet coated with the insulating coating liquid after the coating step to obtain a non-oriented electromagnetic steel sheet with an insulating film formed on its surface; a punching step of punching out the non-oriented electromagnetic steel sheet to obtain punched members; a lamination step of stacking a plurality of punched members to obtain a laminate; and an adhesion step of heating the laminate to a pressurized temperature in the temperature range of 200 to 300°C and holding it for 1 to 60 minutes while applying a pressurized pressure of 0.5 to 10 MPa in the range of the pressurized temperature to the pressurized temperature - 10°C, wherein the insulating coating liquid comprises a crosslinkable acrylic resin and an epoxy resin, with the epoxy resin being 5 to 90 parts by weight per 100 parts by weight of the crosslinkable acrylic resin.

[0014] According to the above embodiments of this disclosure, it is possible to provide a non-oriented electrical steel sheet having excellent coating properties for insulating films, high adhesive strength of insulating films, and low iron loss (especially iron loss when used as a laminated core), a laminated core obtained using this non-oriented electrical steel sheet, and a method for manufacturing the same.

[0015] This is a schematic diagram showing an example of a non-oriented electrical steel sheet (electrical steel sheet with adhesive coating) of the present disclosure. This is a schematic diagram showing an example of a laminated core of the present disclosure.

[0016] The following describes this disclosure. The requirements described below may be based on typical embodiments of this disclosure, but this disclosure is not limited to such embodiments and may be modified as appropriate within the scope of the purposes of this disclosure.

[0017] In this disclosure, numerical ranges indicated using "~" mean ranges that include the numerical values ​​before and after "~" as the lower and upper limits, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0018] In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0019] In this disclosure, the amount of each component in the insulating coating liquid means the total amount of the multiple substances present in the insulating coating liquid, unless otherwise specified, if there are multiple substances corresponding to each component in the insulating coating liquid.

[0020] In this disclosure, "mass%" and "weight%" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

[0021] This document describes an unoriented electrical steel sheet (also referred to as the unoriented electrical steel sheet according to this embodiment), a laminated core (also referred to as the laminated core according to this embodiment) according to this embodiment, and a method for manufacturing them. The unoriented electrical steel sheet 10 according to this embodiment has, as shown in Figure 1, a base steel sheet 10A and insulating coatings 10B and 10C formed on the surface of the base steel sheet 10A. Each of these will be described.

[0022] [Non-oriented electrical steel sheet] <Base steel sheet> The base steel sheet is the steel sheet on which the insulating coating is formed, and there are no particular restrictions as long as it is a non-oriented electrical steel sheet. Specifically, for example, non-oriented electrical steel sheets of JIS C 2552:2014 and non-oriented thin electrical steel sheets of JIS C 2558:2021 can be used. The thickness of the base steel sheet is preferably 0.20 to 0.35 mm.

[0023] <Insulating Coating> The insulating coating is provided on at least a portion of one or both sides of the non-oriented electrical steel sheet, which is the base steel sheet. The insulating coating may be formed on only one side. That is, it may be either insulating coating 10B or insulating coating 10C alone. The insulating coatings 10B and 10C do not need to be formed on the entire surface, but only on at least a portion. For example, they may be provided in a pattern such as a staggered arrangement. However, it is preferable that the insulating coating covers 60% or more of the area of ​​one side of the base steel sheet, more preferably 80% or more, and may cover 100%.

[0024] The insulating coating of the non-oriented electrical steel sheet according to this embodiment contains a crosslinkable acrylic resin and an epoxy resin, has self-fusing properties, and its heat distortion temperature after heating to 200°C and holding for 3 minutes is 130 to 200°C.

[0025] (Crosslinkable Acrylic Resin) A crosslinkable acrylic resin is an acrylic resin having crosslinkable groups. A water-dispersible resin is preferable for environmental reasons. The insulating coating may contain only one type of crosslinkable acrylic resin, or it may contain two or more types.

[0026] In a crosslinkable acrylic resin, the crosslinkable groups may be crosslinkable groups that can crosslink even in the absence of a crosslinking agent (i.e., self-crosslinkable groups that crosslink through the reaction of other crosslinkable groups), or they may be crosslinkable groups that can crosslink through reaction with a crosslinking agent. The crosslinkable groups are preferably groups that can exhibit crosslinking properties upon heating.

[0027] Examples of crosslinkable groups include N-methylol group, N-butyrol group, glycidyl group, alkoxymethylamide group, alkoxysilyl group, hydroxyl group, phenolic hydroxyl group, carboxyl group, thiol group, and amino group.

[0028] Crosslinkable acrylic resins contain constituent units derived from (meth)acrylic acid monomers. "(meth)acrylic acid monomer" refers to a monomer having a (meth)acryloyl group. "Crosslinkable acrylic resin" refers to a resin in which the proportion of constituent units derived from (meth)acrylic acid monomers is 50% by mass or more of the total constituent units.

[0029] Crosslinkable acrylic resin is included to obtain the effect of preventing creep. In the case of acrylic resin without crosslinkable groups, creep occurs after lamination, causing gradual shifting of the laminated surface and failing to prevent vibration. Furthermore, even with resins that have crosslinkable groups, if they are not acrylic resins, they impart stress to the steel sheet, degrading core iron loss. Generally, if high-temperature adhesive strength is to be ensured, epoxy resin is preferred, and crosslinkable acrylic resin is not selected. However, in the non-oriented electrical steel sheet according to this embodiment, by including both crosslinkable acrylic resin and epoxy resin and setting the heat distortion temperature after crosslinking within a predetermined range, stress imparted due to volume shrinkage caused by the curing reaction can be suppressed, and low iron loss, excellent adhesive strength, and coatability can be obtained simultaneously.

[0030] (Epoxy Resin) Any epoxy resin having two or more epoxy groups in one molecule can be used without particular restriction. To ensure adhesive strength while obtaining the heat distortion temperature described later, the epoxy resin is preferably included in an amount of 5 to 90 parts by weight, and more preferably in an amount of 10 to 70 parts by weight, per 100 parts by weight of the crosslinkable acrylic resin. The epoxy resin does not have to be a thermosetting epoxy resin, as it can be cured by adding a curing agent, but a thermosetting epoxy resin is preferable because it can be cured in the same heating process as the crosslinkable acrylic resin. Examples of thermosetting epoxy resins include bisphenol A type epoxy resin, phenol resin, bisphenol F type epoxy resin, triphenylmethane type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, alicyclic epoxy resin, glycidyl ester type epoxy resin, glycidylamine type epoxy resin, hydantoin type epoxy resin, isocyanurate type epoxy resin, acrylic acid modified epoxy resin (epoxy acrylate), phosphorus-containing epoxy resin, and halogens thereof (brominated epoxy resin, etc.) and hydrogenated products. These thermosetting epoxy resins may be used individually or in combination of two or more. Preferably, the thermosetting epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, or phenol resin. The epoxy resin is included to obtain the effect of improving the adhesive strength at 150°C. If an epoxy resin is not used, there is a risk that it will react at room temperature and the adhesive strength at room temperature will decrease.

[0031] (Curing agent) The insulating coating may contain a curing agent to enhance the effects during heating and pressurization. The curing agent is not limited as long as it is a latent curing agent. Examples include resol-type phenolic resins, dicyandiamides, and diamine diphenylethanes. When a curing agent is included, it is preferable that the amount of curing agent is 0.3 to 5.0 parts by weight per 100 parts by weight of thermosetting epoxy resin.

[0032] The components of the insulating coating are identified by measuring the weight-average molecular weight using GPC and then analyzing the functional groups using FT-IT.

[0033] The weight-average molecular weight of the insulating coating components is measured by GPC (Gel Permeation Chromatography). The components of the insulating coating are identified from the molecular weight distribution obtained by GPC. Samples for analysis can be obtained by cutting out the coating portion with a precision cutter. In the case of a laminated core, several sheets of electrical steel are peeled off from the laminated core before sampling using the above method.

[0034] The measurement conditions are as follows: Measurement device: High-speed GPC (HLC-8220GPC, manufactured by Tosoh Corporation) Detector: Differential refractive index detector (RI) (integrated into HLC-8220, manufactured by Tosoh Corporation) Column: Four TSK-gel GMHXL columns (manufactured by Tosoh Corporation) Column temperature: 40°C Eluent: Tetrahydrofuran sample solution Injection volume: 100 μL Flow rate: 0.8 mL / min

[0035] The functional groups of the resin components of the insulating coating are analyzed by FT-IR (Fourier transform infrared spectrum meter). The obtained spectrum is converted to a form similar to a normal absorbance spectrum by Kramers-Kronig analysis. The functional groups are identified from the obtained absorbance spectrum. The measurement conditions are as follows: Measurement device: Spotlight 400 (manufactured by Perkin Elmer) Measurement method: Specular reflection method (background: gold plating) Resolution: 2 cm －１ Scans: 16 times

[0036] (Heat Distortion Temperature) As a result of the inventors' investigations, it was found that the viscosity during bonding affects the adhesive strength and iron loss after lamination in an insulating coating that has adhesive properties on a non-oriented electrical steel sheet. Specifically, it was found that with an insulating coating that has high viscosity, the fusion during bonding is insufficient and the adhesive strength decreases, while if the viscosity is too low, excessive stress is applied to the steel sheet when it hardens. Further investigations revealed that by using a crosslinkable acrylic resin and an epoxy resin and setting the heat distortion temperature after crosslinking to 130 to 200°C, it is possible to suppress the application of stress due to volume shrinkage, achieve both magnetic properties and high-temperature adhesive strength (adhesion strength at 150°C), and ensure good coating amount and the properties of an insulating coating. Therefore, the insulating coating on the non-oriented electrical steel sheet according to this embodiment has a heat distortion temperature of 130 to 200°C after crosslinking (typically, after heating to 200°C, the temperature at which the epoxy resin hardens, and holding for 3 minutes). Since crosslinking does not proceed further even if heated for more than 3 minutes, the holding time may be more than 3 minutes. If the heat distortion temperature is below 130°C, the high-temperature adhesive strength will be inferior, and if it is above 200°C, the adhesive strength at room temperature will be low.

[0037] The heat distortion temperature is measured by the following method: A non-oriented electrical steel sheet with an insulating coating is heated to 200°C and held for 3 minutes. The insulating coating is then scraped off with a cutter or file and collected as a powder sample. In the case of a laminated core after heating, a core piece is cut out, the insulating coating is scraped off and collected as a powder sample. The collected powder sample is heated to 80°C while being pressurized at 3 MPa using a press and held for 10 minutes to solidify it. After removing it from the press, a solid test piece measuring 5 mm × 2 mm × 2 mm is prepared. The heat distortion temperature of this solid test piece is measured using a Hitachi High-Tech Science TMA / SS6100 or equivalent device. Specifically, the displacement of the solid test piece is measured while heating it from room temperature to 300°C at a heating rate of 5°C / min. The temperature at which a rapid displacement occurs, or the intersection of the extensions of the straight lines on the high-temperature and low-temperature sides of the TMA curve, is calculated as the heat distortion point.

[0038] (Self-fusing ability) The insulating coating has self-fusing ability. Whether or not self-fusing ability is present is determined by measuring the adhesive strength using the following method. Two single-sheet test pieces measuring 30 mm x 60 mm are cut from a non-oriented electrical steel sheet. The edges of the two single-sheet test pieces, measuring 30 mm x 10 mm, are overlapped with the insulating coatings facing each other. A sample is obtained by heating and pressurizing the overlapped body under the following conditions: steel sheet temperature: 250°C, pressurized pressure (pressure applied to the overlapping surface): 2 MPa, heating and pressurizing time: 1 minute. With the steel sheet temperature at room temperature (25°C), the sample is mounted on a tensile testing machine and the tensile shear adhesive strength (shear adhesive strength) is measured at a tensile speed of 50 mm / min in accordance with JIS K 6850:1999. The adhesive strength is obtained by dividing the obtained tensile shear adhesive strength value by the adhesive area of ​​the two single-sheet test pieces. If the adhesive strength exceeds 5.0 MPa, the base steel plates can be considered to have bonded together. Therefore, it is determined that the insulating coating has self-fusing properties.

[0039] (Average Thickness) The average thickness of the insulating coating is 0.5 to 3.0 μm. If the average thickness is less than 0.5 μm, non-adhering areas will occur, resulting in inferior room-temperature strength. On the other hand, if it exceeds 3.0 μm, the stress applied to the steel plate increases, resulting in inferior core iron loss. The average thickness of the insulating coating is preferably 1.0 μm or more, or 2.0 μm or more. It is also preferably 2.5 μm or less.

[0040] The average thickness of the insulating coating is measured by the following method: The non-oriented 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 with a scanning electron microscope (SEM), and the thickness of the insulating coating is measured at three locations separated by at least 3 mm from each other. The average thickness of the insulating coating is then obtained by taking the arithmetic mean of the thicknesses of the three insulating coating locations. The insulating coating and the base steel sheet can be easily distinguished by the difference in brightness, and the layer located in the center in the thickness direction is considered to be the base steel sheet, while the layers located on the surface and back in the thickness direction are considered to be the insulating coating.

[0041] [Laminated Core] The laminated core according to this embodiment is made by laminating two or more non-oriented electrical steel sheets, each having a base steel sheet and an insulating coating formed on at least a portion of one or both sides of the base steel sheet. The insulating coating contains a crosslinkable acrylic resin and an epoxy resin, and has a heat distortion temperature of 130 to 200°C. With the above configuration, even if the adhesive strength between the laminated non-oriented electrical steel sheets is high, the stress applied is small, resulting in good iron loss. In the insulating coating of the non-oriented electrical steel sheet according to this embodiment, crosslinking of the crosslinkable acrylic resin progresses by heating and pressurizing, and adhesive ability is exhibited. Therefore, by processing the non-oriented electrical steel sheet according to this embodiment into a predetermined shape, laminating multiple sheets (two or more), and then heating and pressurizing them, a laminated core according to this embodiment having the above characteristics can be obtained.

[0042] The laminated core according to this embodiment can be used as a core (iron core) for rotating electric machines and the like. Figure 2 is a schematic diagram showing an example of the laminated core of this disclosure. As shown in Figure 2, the laminated core 100 is formed as a laminated body 13 by connecting eight punched members 11 of adhesive-coated electromagnetic steel sheets in an annular shape and stacking the annularly connected punched members 11 in eight layers. The punched members 11 of adhesive-coated electromagnetic steel sheets are punched out of the adhesive-coated electromagnetic steel sheet and have an arc-shaped yoke portion 17 and teeth portions 15 that protrude radially inward from the inner circumferential surface of the yoke portion 17. The laminated core 100 is not limited to the shape, number, and number of layers of punched members 11 that form the laminated core 100 shown in Figure 2, and can be designed according to the purpose.

[0043] The laminated core according to this embodiment has a laminate formed by stacking punched members of non-oriented electrical steel sheets according to this embodiment. Therefore, iron loss is low. The iron loss of the core laminate can be evaluated by cutting out a 55 mm x 55 mm sample using wire cutting or the like to avoid processing distortion, and then measuring this laminate sample using the single-sheet magnetic measurement method in accordance with JIS C 2556:2015. However, if the size of the laminate is small and one side of the sample is less than 55 mm, multiple samples can be taped together with cellophane tape or the like to form a 55 mm square for measurement.

[0044] [Manufacturing Method] Regardless of the manufacturing method, the non-oriented electrical steel sheet according to the present embodiment and the laminated core according to the present embodiment exhibit the above-described effects as long as they have the above characteristics, and can be obtained, for example, by a manufacturing method including the following steps. Specifically, the non-oriented electrical steel sheet according to the present embodiment is obtained by a manufacturing method including the following steps (I) and (II): (I) A coating step of applying a coating liquid for forming an insulating coating to at least a part of one surface or both surfaces of an electrical steel sheet serving as a base steel sheet; (II) A coating forming step of drying the electrical steel sheet coated with the coating liquid for forming an insulating coating after the coating step to obtain a non-oriented electrical steel sheet having an insulating coating formed on a surface thereof.

[0045] Further, the laminated core according to the present embodiment is obtained by subjecting the non-oriented electrical steel sheet obtained by the manufacturing method including steps (I) and (II) to the following steps (III) to (V): (III) A punching step of punching a non-oriented electrical steel sheet to obtain a punched member; (IV) A laminating step of laminating a plurality of the punched members to obtain a laminate; (V) 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 1 to 60 minutes while applying a pressing force of 0.5 to 10 MPa within a range from the pressing temperature to (the pressing temperature - 10°C). Each step will be described below. For steps and conditions not described, known conditions can be applied.

[0046] <Coating Step> In the coating step, a coating liquid for forming an insulating coating (sometimes simply referred to as coating liquid) is applied to at least a part of one or both surfaces of an electrical steel sheet serving as a base steel sheet. The coating liquid for forming an insulating coating contains a crosslinkable acrylic resin and an epoxy resin, and may further contain a curing agent if necessary. In the coating liquid for forming an insulating coating, the epoxy resin is preferably 5 to 90 parts by weight, more preferably 10 to 70 parts by weight, relative to 100 parts by weight of the crosslinkable acrylic resin. After applying this coating liquid for forming an insulating coating and drying, an insulating coating containing the crosslinkable acrylic resin and the epoxy resin can be obtained. By adopting the above composition in the coating liquid for forming an insulating coating, the aforementioned preferred composition can be obtained even when the insulating coating is formed. The epoxy resin is preferably a thermosetting epoxy resin, and particularly preferably one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and phenol resin. When a curing agent is contained, the curing agent is preferably 0.3 to 5.0 parts by weight relative to 100 parts by weight of the thermosetting epoxy resin. The solid content concentration of the coating liquid is preferably 5 to 40% by mass, more preferably 10 to 25% by mass.

[0047] The type of water in the coating liquid for forming an insulating coating is not particularly limited. As water, for example, from the viewpoint of low impurity content, distilled water, deionized water (also referred to as "ion-exchanged water"), and pure water are preferred. The content of water is preferably 35 to 50% by mass, more preferably 40 to 45% by mass, relative to the total mass of the coating liquid.

[0048] The insulating coating liquid may contain components other than those described above (so-called "other components") as necessary, to the extent that it does not impair its effectiveness. 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 may include various additives such as chain preservatives, wetting agents, and defoamers.

[0049] The insulating coating liquid is obtained, for example, by gradually mixing a water-dispersible acrylic resin, an epoxy resin, and a curing agent (in a way that prevents heat generation and temperature rise during mixing). One mixing method is, for example, stirring. A general stirring device or apparatus can be used for stirring. The stirring temperature is not particularly limited, but is preferably, for example, 20 to 30°C.

[0050] The method of applying the coating solution is not limited, and well-known coating methods such as the roll coater method and the spray method are given as examples.

[0051] <Coating Formation Process> In the coating formation process, the electrical steel sheet coated with the insulating coating liquid after the coating process is heated and dried (baked) to obtain a non-oriented electrical steel sheet with an insulating coating formed on its surface. The drying conditions are not limited, but the drying temperature (target temperature) is preferably 100 to 200°C, and more preferably 120 to 160°C. The holding time at the target temperature is preferably 10 to 90 seconds. The drying (baking) method is preferably a radiant heating furnace, but a hot air furnace or other method may also be used.

[0052] <Punching Process> In the punching process, a non-oriented electrical steel sheet having an insulating coating is punched out to obtain a component with a predetermined shape (punched component). The punching method is not limited.

[0053] <Lamination Process> In the lamination process, multiple punched-out members are stacked to obtain a laminate. During this process, an insulating coating is interposed between the base steel sheets (so that the base steel sheets do not come into direct contact with each other). This is how the laminate is obtained.

[0054] <Bonding Process> In the bonding process, the laminate is heated to a pressurized temperature in the temperature range of 200 to 300°C, and held for 1 to 60 minutes under a pressurized pressure of 0.5 to 10 MPa in the range of pressurized temperature to pressurized temperature - 10°C. This promotes the crosslinking of the crosslinkable acrylic resin in the insulating film and hardens the insulating film. As a result, the insulating film develops adhesive properties, the non-oriented electrical steel sheets are bonded to each other, and a laminated core is obtained. If the pressurized temperature is below 200°C, the crosslinking of the crosslinked acrylic does not proceed, resulting in inferior high-temperature adhesive strength. If the pressurized temperature is above 300°C, oxidation of the organic resin progresses, resulting in inferior adhesive strength at room temperature and high temperatures. If the pressurized force is below 0.5 MPa, there is a risk of unbonded areas, and if it is above 10 MPa, there is a risk of the organic resin flowing and overflowing from the edges. If the holding time (the time during which the material temperature is maintained between the pressurized temperature - 10°C and the pressurized temperature) is less than 1 minute, the hardener may not fully cure, and if it exceeds 60 minutes, the acrylic resin may oxidize. When there are many layers, it is preferable to set the holding time to 5 minutes or more, or 30 minutes or more.

[0055] The effects of one aspect of this disclosure will be further explained by the examples, but the conditions in the examples are just one example of conditions adopted to confirm the feasibility and effectiveness of this disclosure, and this disclosure is not limited to this one example of conditions. This disclosure may adopt various conditions as long as they do not depart from the gist of this disclosure and achieve the objectives of this disclosure.

[0056] First, a non-oriented electrical steel sheet with a thickness of 0.25 mm and a width of 100 mm was prepared, containing, by mass percent, Si: 3.0%, Mn: 0.2%, Al: 0.5%, with the remainder being Fe and impurities.

[0057] Next, the acrylic resins A1 to A4, epoxy resins E1 to E5, and curing agents C1 to C3 were mixed in the proportions shown in Table 1 and stirred to prepare insulating coating liquids (coating liquids (No. 1 to 15)). Water was used as the solvent, and the solid content concentration of the coating liquid was 30% by mass. A1: Crosslinkable acrylic resin (crosslinkable group is N-methylol group) A2: Crosslinkable acrylic resin (crosslinkable group is glycidyl group) A3: Crosslinkable acrylic resin (crosslinkable group is carboxyl group) A4: Non-crosslinkable acrylic resin E1: Bisphenol A type epoxy resin E2: Phenol novolac type epoxy resin E3: Phenolic resin E4: Polyurethane-based thermosetting resin E5: Non-aqueous epoxy resin C1: Resol type phenolic resin C2: Dicyandiamide C3: Diamine diphenylethane

[0058] One of the coating liquids was applied to the entire surface of both sides of a non-oriented electrical steel sheet, which served as the base steel sheet, so that the average thickness of the insulating film on each side was as shown in Table 2. The non-oriented electrical steel sheet coated with the coating liquid was dried under the conditions of the temperature reached and holding time shown in Table 1, and the insulating film was baked on. As a result, a non-oriented electrical steel sheet with an insulating film formed on the surface of the base steel sheet was obtained.

[0059]

[0060] The non-oriented electrical steel sheets obtained, with an insulating coating formed on their surface, were evaluated for the applicability of the insulating coating (coating liquid), the thermal distortion temperature of the insulating coating, the adhesive strength (at room temperature and high temperature), and the iron loss in the laminate, according to the following procedure. The results are shown in Table 2. Although not shown in the table, a component analysis of the insulating coating revealed that it contained acrylic resin, epoxy resin, elastomer, and curing agent in the same proportions as the coating liquid in Table 1.

[0061] <Heat Distortion Temperature> A non-oriented electrical steel sheet with an insulating coating was heated to 200°C and held for 3 minutes. The insulating coating portion was then scraped off with a cutter and file and collected as a powder sample. The collected powder sample was heated to 80°C under pressure of 3 MPa using a press and held for 10 minutes to solidify it. After removing it from the press, a solid test piece measuring 5 mm × 2 mm × 2 mm was prepared. Using a Hitachi High-Tech Science TMA / SS6100, the solid test piece was heated from room temperature to 300°C at a heating rate of 5°C / min, and the amount of displacement was measured. The temperature at which a rapid amount of displacement occurred, or the intersection of the extensions of the straight lines on the high-temperature and low-temperature sides of the TMA curve, was calculated as the heat distortion temperature. A heat distortion temperature of 130 to 200°C was considered preferable.

[0062] <Room Temperature Bonding Strength> Two test pieces measuring 30 mm x 60 mm were taken from a non-oriented electrical steel sheet. Next, the two test pieces were arranged so that only one side of each piece (30 mm x 10 mm) overlapped, and then heated to 200°C. At that temperature, pressure was applied to 3 MPa and held for 1 minute. After releasing the pressure and cooling to room temperature (25°C), the shear bonding strength was measured at 25°C using a tensile testing apparatus (Autograph AGX-V2 manufactured by Shimadzu Corporation) in accordance with JIS K 6850:1999. The value obtained by dividing the shear bonding strength by the bonding area was defined as the room temperature bonding strength. If the room temperature bonding strength was 5 MPa or higher, it was judged that sufficient bonding strength was present.

[0063] <High-Temperature Bonding Strength> Two test pieces measuring 60 mm x 30 mm were taken from a non-oriented electrical steel sheet. Next, the two test pieces were arranged so that only one side of each piece (30 mm x 10 mm) overlapped, and then heated to 200°C. At that temperature, pressure was applied to 3 MPa and held for 1 minute. After releasing the pressure and allowing the material to cool to room temperature (25°C), the shear bonding strength was measured in a 150°C atmosphere using a tensile testing apparatus (Shimadzu Autograph AGX-V2) in accordance with JIS K 6850:1999. The value obtained by dividing the shear bonding strength by the bonding area was defined as the bonding strength at 150°C (high-temperature bonding strength). A high-temperature bonding strength of 1.0 MPa or higher was considered to indicate sufficient bonding strength.

[0064] <Applicability> Three 5mm square samples were cut from a non-oriented electrical steel sheet, and the applicability was evaluated as follows based on the percentage of coating defects observed at three locations on each sample (3 x 3 = 9 fields of view in total) at 100x magnification using a scanning electron microscope. A or B was considered to indicate excellent applicability. A (Excellent): No coating defects such as cracks, fissures, or peeling were observed. B (Good): The area percentage of coating defects was less than 10%. C (Poor): The area percentage of coating defects was 10% or more but less than 30%. D (Bad): The area percentage of coating defects was 30% or more. The percentage of coating defects was calculated by dividing the area of ​​the defect (a rectangle with dimensions equal to the length and width of the defect) by the total area of ​​the field of view, with the entire field of view being considered 100%. Coating defects were judged by visual inspection.

[0065] <Measurement of Iron Loss> Single-sheet test pieces measuring 55 mm x 55 mm were taken from non-oriented electrical steel sheets, and two of these test pieces were stacked so that their entire surfaces overlapped to obtain a laminated sample. This laminated sample was heated to 200°C, a pressure of 2 MPa was applied, and the pressure was maintained for 1 minute. Then, in accordance with JIS C 2556:2015, the iron loss W10 / 400 in the rolling direction and the direction perpendicular to the rolling direction was measured using the single-sheet magnetic measurement method, and the average value was taken as the iron loss value for each laminated sample. If the iron loss was 12.0 W / kg or less, it was judged to be low iron loss.

[0066]

[0067] As can be seen from Tables 1 and 2, in Samples No. 1 to 8, which are examples of the present invention, the thickness of the insulating film was 0.5 to 3.0 μm, and the heat distortion temperature of the insulating film after heating to 200°C and holding for 3 minutes was 130 to 200°C, and it was excellent in terms of room temperature adhesive strength, adhesive strength at 150°C, applicability, and iron loss. On the other hand, in Comparative Example Sample No. 9, which did not contain crosslinkable acrylic resin, the heat distortion temperature was outside the range of the present invention, and the adhesive strength at 150°C was inferior. In Comparative Example Sample No. 10, which did not contain epoxy resin, the adhesive strength at 150°C was inferior. Furthermore, in Comparative Examples Samples No. 11 to 12, the heat distortion temperature was outside the range of the present invention, and the applicability and iron loss were inferior.

[0068] This disclosure provides a non-oriented electrical steel sheet having excellent coating properties for insulating films, high adhesive strength for insulating films, and low iron loss (especially when used as a laminated core), as well as a laminated core obtained using this non-oriented electrical steel sheet, and methods for manufacturing these. These have high industrial applicability.

[0069] 10 Non-oriented electrical steel sheet 10A Base steel sheet 10B Insulating coating 10C Insulating coating 11 Punched member 13 Laminate 15 Teeth section 17 Yoke section 100 Laminated core

Claims

1. A non-oriented electrical steel sheet comprising a base steel sheet and an insulating coating formed on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating contains a crosslinkable acrylic resin and an epoxy resin, has self-fusing ability, has an average thickness of 0.5 to 3.0 μm, and has a heat distortion temperature of 130 to 200°C after being heated to 200°C and held for 3 minutes.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that the insulating coating contains 10 to 70 parts by weight of the epoxy resin with respect to 100 parts by weight of the crosslinkable acrylic resin.

3. The non-oriented electrical steel sheet according to claim 1 or 2, characterized in that the epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and phenol resin.

4. A method for manufacturing a non-oriented electrical steel sheet, comprising: a coating step of applying an insulating coating liquid to at least a portion of one or both sides of an electrical steel sheet that will be a base steel sheet; and a coating formation step of drying the electrical steel sheet coated with the insulating coating liquid after the coating step to obtain a non-oriented electrical steel sheet with an insulating film formed on its surface, wherein the insulating coating liquid comprises a crosslinkable acrylic resin and an epoxy resin, and the epoxy resin is 5 to 90 parts by weight per 100 parts by weight of the crosslinkable acrylic resin.

5. The method for manufacturing non-oriented electrical steel sheets according to claim 4, characterized in that the epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, and phenol resin.

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 4 or 5, characterized in that the coating liquid for forming an insulating film contains a curing agent.

7. A laminated core characterized by comprising two or more non-oriented electrical steel sheets, each having a base steel sheet and an insulating coating formed on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating contains a crosslinkable acrylic resin and an epoxy resin, and has a heat distortion temperature of 130 to 200°C.

8. A method for manufacturing a laminated core, comprising: a coating step of applying an insulating coating liquid to at least a portion of one or both sides of an electrical steel sheet that will be a base material steel sheet; a coating forming step of drying the electrical steel sheet coated with the insulating coating liquid after the coating step to obtain a non-oriented electrical steel sheet with an insulating film formed on its surface; a punching step of punching out the non-oriented electrical steel sheet to obtain punched members; a lamination step of stacking a plurality of punched members to obtain a laminate; and an adhesion step of heating the laminate to a pressurized temperature in the temperature range of 200 to 300°C and holding it for 1 to 60 minutes while applying a pressurized pressure of 0.5 to 10 MPa in the range of the pressurized temperature to the pressurized temperature - 10°C, wherein the insulating coating liquid comprises a crosslinkable acrylic resin and an epoxy resin, and the epoxy resin is 5 to 90 parts by weight per 100 parts by weight of the crosslinkable acrylic resin.

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