Non-oriented electromagnetic steel sheet, laminated core, and method for producing these

Abstract

This non-oriented electromagnetic steel sheet is characterized by having a base material steel sheet and an insulating coating film provided on at least a part of one surface or both surfaces of the base material steel sheet, the insulating coating film containing a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150-250°C.

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. 2025-055548 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 as a core (i.e., an iron core) for use in rotating electric machines and the like. The plurality of electrical steel sheets are fixed by methods such as welding, caulking, bolting, and adhesion. However, when fixing a plurality of electrical 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 electrical steel sheet deteriorate, and it is 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 an adhesive coating is used, and the adhesive coating having insulating properties (also referred to as an insulating coating) is cured by heating and pressing to develop adhesive ability, thereby bonding the plurality of electrical steel sheets to one another. When fixing a plurality of electrical steel sheets using an electrical steel sheet provided with an adhesive coating, mechanical stress, thermal stress, interlayer short-circuiting and the like are less likely to occur during processing. As a result, 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 adhesive surface-coated electrical steel sheet".

[0005] 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 the following chemical formula 1 and repeating units represented by the following chemical formula 2, and the polyethylene acrylate contains 65 to 90% by weight of the repeating units represented by the following chemical formula 1 and 10 to 35% by weight of the repeating units represented by the following chemical formula 2."

[0006] 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] 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] 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 1,000 parts by mass of a phenolic 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] Insulating coatings are required to have chemical stability and adequate adhesive strength. Furthermore, insulating coatings are also required to have good applicability. However, Patent Documents 1 to 5 do not consider the applicability of insulating coatings.

[0011] When laminated cores are used in motors and the like, the adhesive strength of the insulating coating must be good not only at room temperature but also at high temperatures. To ensure the adhesive strength of the insulating coating at high temperatures, it is effective to use a resin with a high crosslinking density. However, resins with a high crosslinking density have poor applicability and can impart stress to the base steel plate due to volume shrinkage during bonding, which can degrade the iron loss of the laminated core. Therefore, it is difficult to achieve both excellent applicability and low iron loss in the insulating coating.

[0012] Furthermore, the corrosion resistance of non-oriented electrical steel sheets deteriorates in areas where the insulating coating is applied thinly. Poor corrosion resistance of non-oriented electrical steel sheets is undesirable because it degrades the product's appearance, such as causing rust to form on the top and bottom surfaces of the laminated core. Adding rust inhibitors to the insulating coating to improve corrosion resistance may reduce the adhesive strength of the insulating coating. Therefore, non-oriented electrical steel sheets are required to have excellent corrosion resistance and adhesive strength.

[0013] This disclosure has been made in view of the above circumstances. The purpose of this disclosure is to provide a non-oriented electrical steel sheet characterized by high adhesive strength at room temperature and high temperature, excellent coatability and corrosion resistance, and excellent iron loss when used as a laminated core, a laminated core using this non-oriented electrical steel sheet, and a method for manufacturing the same.

[0014] The gist of this disclosure is as follows: [1] A non-oriented electrical steel sheet comprising a base steel sheet and an insulating coating provided on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating comprises a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C. [2] The non-oriented electrical steel sheet according to [1], wherein the aqueous rust inhibitor is an amine-based rust inhibitor. [3] The non-oriented electrical steel sheet according to [1] or [2], wherein the insulating coating has self-fusing ability. [4] A laminated core comprising a base steel sheet and an insulating coating provided on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating comprises a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C, and is formed by laminating two or more non-oriented electrical steel sheets. [5] The laminated core according to [4], characterized in that the aqueous rust inhibitor is an amine-based rust inhibitor. [6] A method for manufacturing a non-oriented electrical steel sheet according to any one of [1] to [3], characterized in that a coating liquid is applied to at least a part of one or both sides of a base steel sheet, the coating liquid comprising the crosslinkable acrylic resin, the thermosetting epoxy resin, and the aqueous rust inhibitor having a boiling point of 150 to 250°C, wherein the thermosetting epoxy resin is contained in an amount of 10 to 80 parts by weight per 100 parts by weight of the crosslinkable acrylic resin, and the aqueous rust inhibitor is contained in an amount of 0.5 to 5.0 parts by weight per 100 parts by weight of the crosslinkable acrylic resin to form a coating film, and the insulating film is formed by drying the coating film. A method for manufacturing a laminated core according to [7], [4], or [5], characterized in that the non-oriented electrical steel sheets are laminated with the insulating coating interposed between each other's base steel sheets to form a laminate, and the insulating coating is cured by heating and pressurizing the laminate.

[0015] According to the above embodiments of this disclosure, it is possible to provide a non-oriented electrical steel sheet characterized by high adhesive strength at room temperature and high temperature, excellent coatability and corrosion resistance, and excellent iron loss when used as a laminated core, a laminated core using this non-oriented electrical steel sheet, and a method for manufacturing the same.

[0016] This is a schematic diagram showing an example of a non-oriented electrical steel sheet related to this disclosure. This is a schematic diagram showing an example of a laminated core related to this disclosure.

[0017] As a result of the inventors' investigation into means to solve the above problems, the inventors obtained the following findings. The insulating coating of non-oriented electrical steel sheets is in a semi-cured state, and subsequent heating and pressurization harden it, bonding the base steel sheets together. In order to improve the corrosion resistance when manufactured into laminated cores, it is necessary to further improve the corrosion resistance of the insulating coating in the semi-cured state. In particular, when an environmentally friendly water-based resin is used as a rust inhibitor in the insulating coating, the water content of the insulating coating in the semi-cured state is high, which may reduce corrosion resistance. If a large amount of water-based rust inhibitor is included to improve corrosion resistance, the rust inhibitor evaporates during heating and pressurization, causing the insulating coating to shrink, stress is applied to the base steel sheets, and the iron loss of the laminated core deteriorates. Therefore, the inventors focused on the thermal properties of water-based rust inhibitors during the application and drying of insulating coatings and found that by incorporating a water-based rust inhibitor having a predetermined boiling point into the insulating coating together with a crosslinkable acrylic resin and a thermosetting epoxy resin, excellent corrosion resistance and high adhesive strength can be obtained in non-oriented electrical steel sheets.

[0018] The non-oriented electrical steel sheets and laminated cores related to this disclosure are described below. The numerical limits indicated by "~" below include both a lower limit and an upper limit. Numerical values ​​indicated as "less than" or "greater than" are not included in the numerical range.

[0019] As shown in Figure 1, the non-oriented electrical steel sheet 10 according to this disclosure comprises a base steel sheet 10A and an insulating coating 10B provided on at least a portion of one or both sides of the base steel sheet 10A. The insulating coating 10B includes a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C. Each component will be described in detail below. Reference numerals in the drawings will be omitted in the following description.

[0020] The base steel sheet is a steel sheet on which an insulating coating is formed, and there are no particular restrictions on its type. As the base steel sheet, for example, a non-oriented electrical steel strip of JIS C 2552:2014 or a non-oriented thin electrical steel strip of JIS C 2558:2021 cut to a predetermined length can be used.

[0021] The insulating coating is provided on at least a portion of one or both sides of the base steel plate. The insulating coating may, for example, be provided on the entire surface of one or both sides of the base steel plate, or it may be provided on one or both sides of the base steel plate in a pattern such as a staggered arrangement (an arrangement that is alternately shifted up, down, left, and right). However, it is preferable that the insulating coating covers 60% or more, 80% or more, or 100% of the area of ​​one side of the base steel plate.

[0022] The insulating coating comprises a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C.

[0023] Crosslinkable acrylic resin is an acrylic resin having crosslinkable groups. From the viewpoint of environmental performance, it is preferable that the crosslinkable acrylic resin is a water-soluble resin. A water-soluble resin is a resin whose solubility in water at 25°C is 5 g or more per 100 g of water. The insulating film may contain only one type of crosslinkable acrylic resin, or it may contain two or more types.

[0024] 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. It is preferable that the crosslinkable groups exhibit crosslinking properties upon heating.

[0025] 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.

[0026] The crosslinkable acrylic resin may be either a vinyl-based thermoplastic resin or a non-vinyl-based thermoplastic resin. Examples of non-vinyl-based thermoplastic resins include (meth)acrylic resins. Examples of vinyl-based thermoplastic resins include (meth)acrylic acid monomers (e.g., (meth)acrylic acid, alkyl (meth)acrylate esters, etc.). "(meth)acrylic acid monomer" refers to a monomer having a (meth)acryloyl group. "(meth)acrylic acid monomer" 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. "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic".

[0027] Thermosetting epoxy resins can be used without particular limitations as long as they are thermosetting epoxy resins having two or more epoxy groups in one molecule. Examples of such thermosetting epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, triphenylmethane type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, alicyclic epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, hydantoin type epoxy resins, isocyanurate type epoxy resins, acrylic acid modified epoxy resins (epoxy acrylates), phosphorus-containing epoxy resins, and halogens thereof (brominated epoxy resins, 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 resins, phenol novolac type epoxy resins, and cresol novolac type epoxy resins. The thermosetting epoxy resin is preferably included in an amount of 10 to 80 parts by weight per 100 parts by weight of the crosslinkable acrylic resin.

[0028] Water-based rust inhibitors are necessary components for imparting corrosion resistance to insulating coatings. It is preferable that the water-based rust inhibitor be included in an amount of 0.5 to 5.0 parts by weight per 100 parts by weight of crosslinkable acrylic resin.

[0029] The type of water-based rust inhibitor is not limited as long as it is water-soluble, but those consisting of an organic acid and a base are preferred. Examples of organic acids include carboxylic acids such as octanoic acid, oleic acid, dimer acid, and naphthenic acid, sulfonic acids such as alkylbenzene sulfonic acid and alkylnaphthalene sulfonic acid, and alkyl phosphoric acids. An example of alkylnaphthalene sulfonic acid is dinolylnaphthalene sulfonic acid. Examples of bases include amine-based rust inhibitors containing water-soluble amines such as ammonia, ethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, and diethylethanolamine. The preferred water-based rust inhibitor can be obtained by arbitrarily selecting and combining one type each of these organic acids and bases. Furthermore, a mixture of one type of organic acid arbitrarily selected from these and two or more types of bases arbitrarily selected from these, or a mixture of two or more types of organic acids arbitrarily selected from these and one type of base arbitrarily selected from these, is also acceptable. And a mixture of two or more types of organic acids and two or more types of bases is also acceptable. The aqueous rust inhibitor is preferably an amine-based rust inhibitor. Examples of amine-based rust inhibitors include monoethanolamine-based (boiling point: 171°C), aminoethylethanolamine-based (boiling point: 243°C), and hexamethylenediamine-based (boiling point: 160°C). Among these, the aminoethylethanolamine-based rust inhibitor (boiling point: 243°C) is preferred because it has a high boiling point and is prone to residue. The type of amine-based rust inhibitor can be determined by gas chromatography-mass spectrometry (GC-MS). For example, the analytical conditions can be a Shimadzu QP-2010 Ultra, column UA-5, carrier gas He, column flow rate of 1.2 ml / min, and mass range m / z = 29.0 to 550.0.

[0030] 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-IR.

[0031] 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. 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

[0032] The functional groups of the insulating coating components 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

[0033] When the insulating coating contains, for example, a crosslinkable acrylic resin such as a (meth)acrylic resin, the weight-average molecular weight is 80,000 to 300,000, and N-methylol groups, glycidyl groups, carboxyl groups, or amino groups are detected. When the thermosetting epoxy resin contains a cresol novolac type epoxy resin, the weight-average molecular weight is 1,000 to 20,000, and phenolic hydroxyl groups are detected. When the aqueous rust inhibitor contains an amine-based rust inhibitor, the weight-average molecular weight is 60 to 200, and amino groups are detected.

[0034] Water-based rust inhibitors have a boiling point of 150 to 250°C. If the boiling point of a water-based rust inhibitor is outside this range, it will evaporate excessively during heating and pressurization, leading to deterioration of the iron loss in the laminated core. By identifying the water-based rust inhibitor using the method described above, its boiling point can be determined.

[0035] The insulating coating has self-fusing properties. The presence or absence of self-fusing properties 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 overlapping body under the following conditions: steel sheet temperature: 250°C, pressure: 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 is measured at a tensile speed of 50 mm / min. The adhesive strength is calculated by dividing the obtained tensile shear adhesive strength value by the adhesive area of ​​the two single-sheet test pieces. If the adhesive strength is greater than 5.0 MPa, the base steel sheets can be considered to have bonded to each other. Therefore, it can be determined that the insulating coating has self-fusing properties.

[0036] The average thickness of the insulating film is preferably 0.7 to 6.0 μm. More preferably, the average thickness of the insulating film is 1.0 μm or more, or 2.0 μm or more. Furthermore, it is more preferable that the average thickness of the insulating film is 4.0 μm or less, or 3.0 μm or less.

[0037] 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 arbitrary locations. The average thickness of the insulating coating is then obtained by taking the arithmetic mean of the thicknesses of the three insulating coating locations. Note that 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.

[0038] The thickness of the non-oriented electrical steel sheet is preferably 0.20 to 0.35 mm. The thickness of the non-oriented electrical steel sheet is measured using the same method as the average thickness of the insulating coating.

[0039] The laminated core according to this disclosure comprises a base steel sheet and an insulating coating provided on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating is formed by laminating two or more non-oriented electrical steel sheets containing a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C. The description of components that overlap with the non-oriented electrical steel sheet is omitted.

[0040] An example of a laminated core according to this disclosure is a laminated core formed by punching out punched members from a non-oriented electrical steel sheet according to this disclosure, stacking the punched members, and then heating and pressurizing them to form an integrated core. Figure 2 is a schematic diagram showing an example of a laminated core according to this disclosure. As shown in Figure 2, the laminated core 100 (stator 100) is formed as a laminated body 13 by connecting eight punched members 11 of non-oriented electrical steel sheets in an annular shape, and stacking the annularly connected punched members 11 in eight layers to form an integrated core. The punched member 11 of the non-oriented electrical steel sheet 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 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.

[0041] The laminated core according to this disclosure is formed by laminating two or more non-oriented electrical steel sheets containing a water-based rust inhibitor with a boiling point of 150 to 250°C in an insulating coating. Therefore, volume shrinkage when bonding the base steel sheets by heating and pressurizing is suppressed, and iron loss is reduced (improved). Furthermore, although some of the water-based rust inhibitor may evaporate during the manufacturing of the laminated core, the remainder remains in the insulating coating. As a result, the laminated core can exhibit excellent corrosion resistance even when its upper or lower surfaces are exposed to the external environment.

[0042] Manufacturing method for non-oriented electrical steel sheets The insulating coating of a non-oriented electrical steel sheet is formed by applying a coating liquid to at least a portion of one or both sides of a base steel sheet and drying the coating film. In this disclosure, unless otherwise specified, the amount of each component in the coating liquid refers to the total amount of the multiple substances present in the coating liquid when there are multiple substances corresponding to each component.

[0043] The coating liquid according to the present disclosure contains, for example, a crosslinkable acrylic resin, a thermosetting epoxy resin, an aqueous rust inhibitor having a boiling point of 150 to 250°C, and a medium containing water. In the coating liquid according to the present disclosure, the crosslinkable acrylic resin and the thermosetting epoxy resin exist in a state where particles of the crosslinkable acrylic resin and particles of the thermosetting epoxy resin are dispersed in the medium containing water. The aqueous rust inhibitor exists in a dissolved state in the medium containing water.

[0044] In the coating liquid, the content of the thermosetting epoxy resin is 10 to 80 parts by weight relative to 100 parts by weight of the crosslinkable acrylic resin, and the content of the aqueous rust inhibitor is preferably 0.5 to 5.0 parts by weight relative to 100 parts by weight of the crosslinkable acrylic resin.

[0045] The type of water in the coating liquid is not particularly limited. As water, for example, distilled water, deionized water (also referred to as "ion-exchanged water"), and pure water are preferred from the viewpoint of low impurity content. The content of water is preferably 35 to 50 mass%, more preferably 40 to 45 mass%, relative to the total mass of the coating liquid.

[0046] The coating liquid according to the present disclosure may optionally contain components other than the components described above (so-called other components) within a range that does not impair the effects thereof.

[0047] Examples of the other components include aqueous media other than water. Examples of the aqueous media other than water include water-miscible organic solvents. Examples of the 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. Further, examples of the other components include various additives such as chain preservatives, wetting agents and antifoaming agents.

[0048] The coating solution according to this disclosure is obtained, for example, by mixing a dispersion of crosslinkable acrylic resin particles and thermosetting epoxy resin particles in water with an aqueous solution of an aqueous rust inhibitor. A mixing method may include, for example, mixing by 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°C to 30°C.

[0049] Formation of an insulating film using the coating liquid according to this disclosure can be achieved by applying the coating liquid to the surface of a base steel sheet using a well-known coating method such as a roll coater or spray method, and then baking the coating film. The solid content concentration of the coating liquid is preferably 5 to 40% by mass, and more preferably 10 to 25% by mass. The temperature reached during baking is preferably 100 to 200°C, and the holding time at the reached temperature is preferably 10 to 90 seconds. The baking method is preferably one using a copy-type heating furnace, but a hot air furnace or other method may also be used.

[0050] Manufacturing Method of Laminated Core The laminated core according to this disclosure is manufactured, for example, by the following method. Non-oriented electrical steel sheets according to this disclosure are laminated with an insulating coating interposed between each other. The laminate of non-oriented electrical steel sheets is heated and pressurized to promote crosslinking of the crosslinkable acrylic resin in the insulating coating and to exhibit the self-fusing ability of the insulating coating. As a result, the base steel sheets are bonded to each other. These operations yield the laminated core according to this disclosure. In the laminated core, the insulating coatings of the non-oriented electrical steel sheets may be facing each other and bonded, or the insulating coating of one base steel sheet may be facing the surface of the other base steel sheet where no insulating coating is formed and bonded to each other. Preferably, the heating temperature is 200 to 300°C, the pressurizing pressure is 0.5 to 10 MPa, and the heating and pressurizing time is 30 to 60 minutes.

[0051] (Applications of the laminated core) The laminated core of this disclosure can be used as a core (i.e., an iron core) used in rotating electric machines and the like.

[0052] 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.

[0053] A coating solution was prepared containing the types and amounts (parts by mass) shown in Manufacturing Table 1 of the coating solution, with a solid content concentration of 40% by mass. Underlined items in the table indicate that they are outside the scope of this disclosure, that the manufacturing conditions are undesirable, or that the properties are undesirable. "Solid content concentration" refers to the total mass percentage of the crosslinkable acrylic resin, thermosetting epoxy resin, and aqueous rust inhibitor in the coating solution.

[0054] A base steel sheet with a thickness of 0.25 mm and a width of 100 mm was manufactured, with the mass percentage of non-oriented electrical steel sheets being Si: 3.0%, Mn: 0.2%, Al: 0.5%, and the remainder being Fe and impurities. Next, a coating solution was applied to the entire surface of one side of the base steel sheet, and then an insulating film with an average thickness of 2.0 μm was formed using the baking conditions shown in Table 1. Non-oriented electrical steel sheets were manufactured by these methods.

[0055] Two 30 mm x 60 mm single-sheet test pieces were cut from each example of non-oriented electrical steel sheet for adhesive strength. The 30 mm x 10 mm edges of the two single-sheet test pieces were overlapped with their insulating coatings facing each other. The overlapped body was heated and pressurized under the following conditions: steel sheet temperature: 250°C, pressurized pressure: 2 MPa, heating and pressurizing time: 1 minute, to obtain a sample.

[0056] With the steel plate temperature at room temperature (25°C), the sample was mounted on a tensile testing machine, and the tensile shear bond strength was measured at a tensile speed of 50 mm / min. The obtained tensile shear bond strength value was divided by the bonding area of ​​the two single-plate test specimens to determine the bond strength at room temperature.

[0057] Furthermore, the sample was placed in a 150°C atmosphere, and the tensile shear bond strength was measured using the same method as described above while the steel plate temperature was at 150°C. The obtained tensile shear bond strength value was divided by the bonding area of ​​the two single-plate test specimens to determine the bond strength at 150°C.

[0058] If the adhesive strength at room temperature exceeded 5.0 MPa and the adhesive strength at 150°C exceeded 1.0 MPa, it was judged to have high adhesive strength at both room temperature and high temperature, and was deemed to pass. On the other hand, if either of these conditions was not met, it was deemed to fail.

[0059] Three 5 mm square test pieces were cut from each example of non-oriented electrical steel sheet to obtain test specimens. The insulating coating surface of each test specimen was observed at three locations using a scanning electron microscope at a magnification of 100x. A total of nine fields of view were observed. The specimens were then evaluated according to the following evaluation criteria. If the result was S or A, it was judged to have excellent coating properties and was judged to pass. On the other hand, if the result was B or C, it was judged to have poor coating properties and was judged to fail. S: No coating defects such as cracks, fissures, or peeling were observed. A: Area percentage with coating defects is 10% or less. B: Area percentage with coating defects is more than 10% but less than 30%. C: Area percentage with coating defects is 30% or more.

[0060] The corrosion resistance of corrosion-resistant non-oriented electrical steel sheets was evaluated by performing a neutral salt spray test for 2 hours in accordance with JIS Z 2371:2015. 30 mm x 60 mm samples were taken from the non-oriented electrical steel sheets, and the sample edges were treated with rust prevention agents such as beeswax. The samples were then placed in the corrosion test apparatus at a 30° angle from the vertical, ensuring that the samples did not overlap. The resulting rust was evaluated according to the following criteria based on the area percentage of the rust: 1: 0.00–0.10%; 2: greater than 0.10% and 0.50% or less; 3: greater than 0.50% and 2.50% or less; 4: greater than 2.50% and 10.00% or less; 5: greater than 10.00%.

[0061] Single-sheet test pieces measuring 55 mm x 55 mm were cut from non-oriented electrical steel sheets of each example of magnetic properties. Two single-sheet test pieces were stacked with their insulating coatings facing each other. The stacked body was heated and pressurized under the conditions of steel sheet temperature: 250°C, pressurizing pressure: 3 MPa, and heating and pressurizing time: 1 minute to obtain a laminated sample. The iron loss in the obtained laminated sample in the rolling direction and the direction perpendicular to the rolling direction was measured using the single-sheet magnetic measurement method specified in JIS C 2556:2015, and the average value of the iron loss in the rolling direction and the direction perpendicular to the rolling direction was determined. If the obtained average value of iron loss was 12.0 W / kg or less, it was judged to have excellent magnetic properties and was judged to pass. On the other hand, if the obtained average value of iron loss was greater than 12.0 W / kg, it was judged to not have excellent magnetic properties and was judged to fail.

[0062] The details of the materials used, as listed in Table 1, are as follows: A1: Crosslinkable acrylic resin A2: Crosslinkable acrylic resin A3: Crosslinkable acrylic resin A4: Non-crosslinkable acrylic resin E1: Cresol novolac type epoxy resin E2: Phenol novolac type epoxy resin E3: Bisphenol A type epoxy resin B1: Monoethanolamine type (boiling point: 171°C) B2: Aminoethylethanolamine type (boiling point: 243°C) B3: Hexamethylenediamine type (boiling point: 160°C) B4: Ethylenediamine type (boiling point: 117°C) B5: Triethanolamine type (boiling point: 360°C)

[0063]

[0064]

[0065] From the above results, it can be seen that the present invention, compared to the comparative example, has high adhesive strength at room temperature and high temperature, as well as excellent coatability and corrosion resistance, and also exhibits excellent iron loss when used as a laminated core.

[0066] According to the above embodiments of this disclosure, it is possible to provide a non-oriented electrical steel sheet that has high adhesive strength at room temperature and high temperature, as well as excellent coatability and corrosion resistance, and excellent iron loss when used as a laminated core, a laminated core using this non-oriented electrical steel sheet, and a method for manufacturing the same.

[0067] 10 Non-oriented electrical steel sheet 10A Base steel sheet 10B Insulating coating 10C Insulating coating 11 Punched member 100 Laminated core

Claims

1. A non-oriented electrical steel sheet comprising a base steel sheet and an insulating coating provided on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating comprises a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that the aqueous rust inhibitor is an amine-based rust inhibitor.

3. The non-oriented electrical steel sheet according to claim 1 or 2, characterized in that the insulating coating has self-fusing ability.

4. A laminated core comprising a base steel sheet and an insulating coating provided on at least a portion of one or both sides of the base steel sheet, wherein the insulating coating is formed by laminating two or more non-oriented electrical steel sheets containing a crosslinkable acrylic resin, a thermosetting epoxy resin, and an aqueous rust inhibitor having a boiling point of 150 to 250°C.

5. The laminated core according to claim 4, characterized in that the aqueous rust inhibitor is an amine-based rust inhibitor.

6. A method for manufacturing a non-oriented electrical steel sheet according to any one of claims 1 to 3, characterized in that a coating liquid is applied to at least a portion of one or both sides of a base steel sheet, the coating liquid comprising the crosslinkable acrylic resin, the thermosetting epoxy resin, and the aqueous rust inhibitor having a boiling point of 150 to 250°C, wherein the thermosetting epoxy resin is contained in an amount of 10 to 80 parts by weight per 100 parts by weight of the crosslinkable acrylic resin, and the aqueous rust inhibitor is contained in an amount of 0.5 to 5.0 parts by weight per 100 parts by weight of the crosslinkable acrylic resin to form a coating film, and the insulating film is formed by drying the coating film.

7. A method for manufacturing a laminated core according to claim 4 or 5, characterized in that the non-oriented electrical steel sheets are laminated with the insulating coating interposed between each other, and the insulating coating is cured by heating and pressurizing the laminate.

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