Epoxy adhesive composition, cured product thereof, and laminated core

Abstract

To provide an epoxy adhesive composition that has low viscosity allowing thin-film adhesion and also has heat resistance sufficient to maintain adhesive strength even at high temperature.SOLUTION: An epoxy adhesive composition containing an epoxy resin and a curing agent thereof, wherein the epoxy resin uses a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin in combination, and a glass transition temperature after curing is within a range of 120°C or more and 300°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an epoxy adhesive composition used, for example, to bond soft magnetic members that constitute the laminated core of the motor of an electric vehicle (xEV). In particular, the present invention relates to an epoxy adhesive composition that has a low viscosity that enables thin film bonding and heat resistance that allows adhesive strength to be maintained even at high temperatures, as well as a cured product thereof and a laminated core. [Background technology]

[0002] In recent years, amid calls for the realization of a carbon-free society, the automotive industry has been accelerating the electrification of automobiles in order to break away from dependence on petroleum fuels.While conventional gasoline-powered vehicles are driven by engines, electric vehicles (xEVs) are driven by a motor with a motor core consisting of a rotor and a stator, which converts electrical energy (power) into magnetic energy (magnetic force), and then converts the magnetic energy into kinetic energy (power).In order to contribute to energy savings and reduced carbon dioxide emissions, there is a need for higher efficiency and performance in motors.

[0003] Here, the iron core portion of the rotor or stator that constitutes the motor has conventionally adopted a laminated core formed by laminating hundreds to thousands of electromagnetic steel sheets, each made of steel sheets with an insulating surface, and the processing methods for laminating the electromagnetic steel sheets are generally crimping (dowel lamination) or laser welding (welded lamination). That is, conventional laminated electromagnetic steel sheets have been manufactured by stacking multiple electromagnetic steel sheets with insulating coatings and then fixing and integrating them using crimping or welding.

[0004] However, while reducing iron loss is necessary to increase the efficiency of motors, when electromagnetic steel sheets are stacked by crimping, eddy currents are generated when magnetic flux passes through the crimped area, and the unevenness created by the crimping makes it easy for distortion (mechanical distortion) to occur in the electromagnetic steel sheets, resulting in increased iron loss.Even when the sheets are stacked by welding, there are problems such as increased iron loss due to thermal distortion and damage to the insulating coating of the electromagnetic steel sheets, which reduces their insulation and causes the electromagnetic steel sheets to become conductive to each other.

[0005] Furthermore, in response to demands for higher motor efficiency, there is a trend toward thinner electromagnetic steel sheets in laminated cores in order to reduce eddy current loss. However, thinner electromagnetic steel sheets make it more difficult to crimp or weld them, and also pose problems such as making it more difficult to maintain the shape of the laminated core. In particular, nanocrystalline materials with high magnetic flux density and low iron loss have recently been expected as soft magnetic materials, and attempts have been made to manufacture laminated cores by stacking foils (thin ribbons) of soft magnetic materials such as nanocrystalline materials or their precursors, amorphous alloys. However, foils of soft magnetic materials such as nanocrystalline materials and amorphous alloys are difficult to handle because they are thin and brittle, and it is difficult to secure the laminates by crimping or welding.

[0006] Therefore, instead of laminating and fixing the sheets by crimping or welding, methods of bonding magnetic steel sheets together are attracting attention. Bonding is expected to reduce iron loss because it does not cause processing distortion (mechanical distortion, thermal distortion) caused by crimping or welding. For example, Patent Documents 1 to 4 propose a technique for forming a laminated electromagnetic steel sheet by bonding a plurality of electromagnetic steel sheets together.

[0007] Patent Document 1 discloses a laminated core comprising a plurality of electromagnetic steel sheets stacked on top of each other, in which all pairs of adjacent electromagnetic steel sheets in the stacking direction are fixed together, wherein at least one pair of electromagnetic steel sheets out of all pairs of electromagnetic steel sheets are bonded together by an adhesive joint consisting of a cured product of an adhesive, the adhesive containing an epoxy resin (A) that does not have a glass transition temperature and one or more resins (B) selected from the group consisting of acrylic resins, phenolic resins and urethane resins, the ratio of resin (B) being 1 to 50 parts by mass per 100 parts by mass of epoxy resin (A), and the tensile modulus of elasticity of the adhesive joint at 200°C being 100 to 2500 MPa.

[0008] Patent Document 2 discloses a coating composition for electrical steel sheets containing an epoxy resin, a latent epoxy resin curing agent, and a thermoplastic elastomer, wherein the thermoplastic elastomer has a melting point of 100°C or more and 200°C or less and a flexural modulus of elasticity of more than 5 MPa and 100 MPa or less, and the content of the thermoplastic elastomer is 10 parts by mass or more and less than 40 parts by mass per 100 parts by mass of the total of the epoxy resin and the latent epoxy resin curing agent.

[0009] Patent Document 3 discloses a coating composition for electrical steel sheets, which contains an epoxy resin, a first curing agent made of a phenolic resin containing a phenolic skeleton having either an alkyl group or an alkoxy group, or both, and one or more second curing agents selected from phenolic resole resins and phenolic novolac resins, wherein the content of the first curing agent is 5 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the epoxy resin, and the total content of the first curing agent and the second curing agent is 10 parts by mass or more and 155 parts by mass or less per 100 parts by mass of the epoxy resin.

[0010] Patent Document 4 discloses a coating composition for electrical steel sheets, which contains an epoxy resin, an epoxy resin curing agent, and an elastomer-modified phenolic resin, in which the content of the elastomer-modified phenolic resin is 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the epoxy resin.

[0011] In the technologies of Patent Documents 1 to 4, in addition to the epoxy resin, a specific resin, a specific thermoplastic elastomer, or a specific curing agent is blended to ensure heat resistance that allows the adhesive strength to be maintained even at high temperatures. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent Publication No. 2021-19376 [Patent Document 2] Patent No. 7401820 [Patent Document 3] Patent No. 7360079 [Patent Document 4] Patent No. 7343823 Summary of the Invention [Problem to be solved by the invention]

[0013] Here, in order to improve the efficiency of a motor, it is effective to improve the space factor of soft magnetic members such as electromagnetic steel sheets in order to enhance the magnetic properties of the core, and thin film bonding (thinning of the adhesive layer) is an effective way to improve the space factor of soft magnetic members such as electromagnetic steel sheets, but the formulations of the adhesive compositions in Patent Documents 1 to 4 all result in high viscosity. For this reason, the techniques in Patent Documents 1 to 4 make it difficult to achieve thin film bonding, and there is a limit to how much the space factor of the soft magnetic members can be increased.

[0014] Therefore, an object of the present invention is to provide an epoxy adhesive composition that has a low viscosity that enables thin film adhesion and heat resistance that allows adhesive strength to be maintained even at high temperatures, as well as a cured product thereof and a laminated core. [Means for solving the problem]

[0015] The epoxy adhesive composition of the invention of claim 1 is an epoxy adhesive composition containing an epoxy resin and a curing agent for the epoxy resin, wherein the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the glass transition temperature (Tg) after curing is in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower. The glass transition temperature (also referred to as the glass transition point) is determined by dynamic viscoelasticity measurement (DMA).

[0016] The epoxy adhesive composition of the invention according to claim 2 further contains a reactive diluent.

[0017] The reactive diluent of the epoxy adhesive composition of the invention according to claim 3 is a bifunctional or trifunctional reactive diluent, more preferably a trifunctional reactive diluent.

[0018] The curing agent of the epoxy adhesive composition of the invention according to claim 4 is dicyandiamide.

[0019] The epoxy adhesive composition of the invention of claim 5 is the same as that of claim 4, and further contains an imidazole curing accelerator.

[0020] The epoxy adhesive composition of the invention of claim 6 preferably contains 30 to 1000 parts by mass of the glycidyl amine epoxy resin relative to 100 parts by mass of the bisphenol epoxy resin, more preferably 400 to 900 parts by mass, and even more preferably 500 to 800 parts by mass of the glycidyl amine epoxy resin.

[0021] The epoxy adhesive composition of the invention of claim 7 preferably has a viscosity at 25°C of 1.0 Pa·S or more and 10.0 Pa·S or less, more preferably 1.0 Pa·S or more and 9.5 Pa·S or less, and even more preferably 1.0 Pa·S or more and 8.0 Pa·S or less.

[0022] The cured product of the invention of claim 8 is an adhesive cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and its curing agent, wherein the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and has a glass transition temperature (Tg) in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower.

[0023] The cured product of the invention of claim 9 preferably has a thickness in the range of 0.8 μm or more and 2.5 μm or less, more preferably 0.8 μm or more and 2.0 μm or less, and even more preferably 0.8 μm or more and 1.8 μm or less.

[0024] The laminated core of the invention of claim 10 is a laminated core having a plurality of soft magnetic members and an adhesive layer that bonds the laminated soft magnetic members together, wherein the adhesive layer is made of a cured adhesive product obtained by heat-curing an epoxy-based adhesive composition containing an epoxy resin and its curing agent, the epoxy resin being a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the cured adhesive product of the adhesive layer has a glass transition temperature (Tg) in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower. [Effects of the Invention]

[0025] The epoxy adhesive composition according to the invention of claim 1 contains an epoxy resin and a curing agent for the epoxy resin, and the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower.

[0026] As a result of extensive experimental research, the present inventors have found that an epoxy adhesive composition which uses a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin, and which also contains a curing agent and has a glass transition temperature after curing of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower, has a low viscosity which enables thin film bonding, and the cured product has heat resistance which allows the adhesive strength to be maintained even at high temperatures. Based on this finding, the present invention was completed.

[0027] That is, an epoxy adhesive composition that uses a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin in combination as the epoxy resin and has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower, has a low viscosity that enables thin film adhesion and heat resistance that allows adhesive strength to be maintained even at high temperatures.

[0028] According to the epoxy adhesive composition of the invention of claim 2, since it further contains a reactive diluent, in addition to the effect of claim 1, it is possible to further reduce the viscosity.

[0029] According to the epoxy adhesive composition of the invention of claim 3, the reactive diluent is a bifunctional or trifunctional reactive diluent, which not only achieves the effect of claim 1 but also enables a further reduction in viscosity without a significant decrease in heat resistance. More preferably, if a trifunctional reactive diluent is used, the heat resistance of the cured product can be further improved.

[0030] According to the epoxy adhesive composition of the invention of claim 4, the curing agent is dicyandiamide, and therefore in addition to the effect of claim 1, the heat resistance can be further improved.

[0031] The epoxy adhesive composition according to the invention of claim 5 further contains an imidazole curing accelerator, which makes it possible to increase the curing reaction rate and lower the curing temperature in addition to the effect of claim 4, and also makes it possible to further increase heat resistance by using an imidazole curing accelerator.

[0032] According to the epoxy adhesive composition of the invention of claim 6, the glycidyl amine epoxy resin is preferably blended in a range of 30 to 1000 parts by mass, more preferably 400 to 900 parts by mass, and even more preferably 500 to 800 parts by mass per 100 parts by mass of the bisphenol epoxy resin, so in addition to the effect of claim 1, low viscosity can be ensured, and the heat resistance of the cured product can be ensured, as well as moist heat degradation resistance.

[0033] The epoxy adhesive composition of the invention of claim 7 has a viscosity at 25°C of 1.0 Pa·S or more and 10.0 Pa·S or less, more preferably 1.0 Pa·S or more and 9.5 Pa·S or less, and even more preferably 1.0 Pa·S or more and 8.0 Pa·S or less, thereby enabling impregnation bonding in addition to the effect of claim 1.

[0034] According to the cured product of the invention of claim 8, there is provided a cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and its curing agent, wherein the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the glass transition temperature is in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower. An epoxy adhesive composition that uses a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin in combination as the epoxy resin and has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower, has low viscosity, so that the cured product can be used for thin film bonding and has heat resistance that allows it to maintain adhesive strength even at high temperatures.

[0035] According to the cured product of the invention of claim 9, the thickness is preferably in the range of 0.8 μm or more and 2.5 μm or less, more preferably 0.8 μm or more and 2.0 μm or less, and even more preferably 0.8 μm or more and 1.8 μm or less. Therefore, in addition to the effect of claim 8, the space factor between the soft magnetic members in the laminated core can be increased while ensuring adhesive strength.

[0036] According to the laminated core of the invention of claim 10, there is provided a laminated core having a plurality of soft magnetic members and an adhesive layer that bonds the laminated soft magnetic members together, wherein the adhesive layer is made of a cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and its curing agent, the epoxy resin being a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the cured product of the adhesive layer has a glass transition temperature in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower. An epoxy adhesive composition that uses a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin and has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower, has low viscosity, and therefore the adhesive layer made from the cured product is capable of thin film adhesion and has heat resistance that allows it to maintain adhesive strength even at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0037] [Embodiment Mode] Hereinafter, an epoxy adhesive composition according to an embodiment of the present invention will be described. The epoxy adhesive composition according to an embodiment of the present invention is an epoxy adhesive composition for laminated cores, which is used to bond together soft magnetic members, such as plate-shaped or foil-shaped members, made of a soft magnetic material that constitutes the laminated core of a motor mounted on an electric vehicle (xEV) or the like.

[0038] The soft magnetic member constituting the laminated core to be bonded is, for example, an electromagnetic steel sheet (silicon steel sheet), an amorphous alloy foil material (thin ribbon), or a nanocrystalline alloy foil material (thin ribbon). When bonding to an electromagnetic steel sheet, the steel sheet thickness (plate thickness) is, for example, about 0.1 to 1 mm, preferably 0.2 to 0.5 mm, taking into consideration core iron loss and manufacturing costs. When bonding to an amorphous alloy foil material (thin ribbon) or a nanocrystalline alloy foil material (thin ribbon), the thickness of the foil material or ribbon is, for example, about 0.005 to 0.1 mm, preferably 0.01 to 0.1 mm, more preferably 0.01 to 0.05 mm, and even more preferably 0.02 to 0.03 mm.

[0039] Examples of electrical steel sheets include soft iron sheets (electrical steel sheets) with high magnetic flux density, general cold-rolled steel sheets such as SPCC (e.g., those specified in JIS G 3141 (2009)), non-oriented electrical steel sheets containing Si or Al to improve resistivity (e.g., those specified in JIS C 2552:2014), grain-oriented electrical steel sheets (e.g., those specified in JIS C 2553:2019), non-oriented thin electrical steel strips (e.g., those specified in JIS C 2558:2015), and grain-oriented thin electrical steel strips (e.g., those specified in JIS C 2558:2015). While untreated steel sheets can be used, steel sheets that have been subjected to degreasing treatments such as alkaline degreasing or pickling treatments using acids such as hydrochloric acid, sulfuric acid, and phosphoric acid are preferred. Note that electrical steel sheets used to form laminated cores such as the stator core and rotor core of a motor are usually punched or sheared from strip-shaped steel sheets or cut steel sheets.

[0040] Examples of soft magnetic materials having an amorphous structure or a nanocrystalline structure include those composed of at least one magnetic metal selected from the group consisting of Fe, Co, and Ni, and at least one non-magnetic metal selected from the group consisting of B, C, P, Al, Si, Ti, V, Cr, Mn, Cu, Y, Zr, Nb, Mo, Hf, Ta, and W.

[0041] Examples of amorphous materials include FeSi-based (FeAlSi, FeAlSiCr, FeAlSiTiRu, etc.), FeCo-based (FeCo, FeCoV, etc.), FeNi-based (FeNi, FeNiMo, FeNiCr, FeNiSi, etc.), FeTa-based (FeTa, FeTaC, FeTaN, etc.), FeZr-based (FeZrN, etc.), FeAl-based (FeAl, FeAlO, etc.), Fe-Si-B-based, Fe-B-based, Fe-PC-based, Fe-Hf-based, Fe-Ti-based, Co-Si-B-based, Co-Fe-Si-B-based, and Co-B-based alloys. Examples of nanocrystalline materials obtained by crystallizing amorphous materials to nanometer size through heat treatment include Fe-Si-B-Cu-Nb, Fe-B-Cu-Nb, Fe-Zr-B-(Cu), Fe-Zr-Nb-B-(Cu), Fe-Zr-P-(Cu), Fe-Zr-Nb-P-(Cu), Fe-Ta-C, Fe-Al-Si-Nb-B, Fe-Al-Si-Ni-Nb-B, Fe-Al-Nb-B, and Co-Ta-C systems.

[0042] The epoxy adhesive composition according to this embodiment, which is used to bond the soft magnetic members that make up the laminated core of a motor, has a basic composition of an epoxy resin and a curing agent for the epoxy resin, and becomes a three-dimensional hardened product through the reaction between the epoxy resin and the curing agent.The epoxy resins used are a combination of a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin, and the glass transition temperature after hardening is within the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower.

[0043] Here, the bisphenol type epoxy resin is obtained by reacting a phenolic compound such as bisphenol A, bisphenol F, bisphenol S, bisphenol AD, bisphenol AF, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, bisphenol D, bisphenol G, bisphenol M, or bisphenol P with epichlorohydrin, and examples thereof include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AD ​​type epoxy resin, bisphenol AF type epoxy resin, bisphenol AP type epoxy resin, bisphenol B type epoxy resin, bisphenol BP type epoxy resin, bisphenol C type epoxy resin, bisphenol D type epoxy resin, bisphenol G type epoxy resin, bisphenol M type epoxy resin, and bisphenol P type epoxy resin. Note that one type of bisphenol type epoxy resin may be used alone, or two or more types may be used in combination.

[0044] Among bisphenol-type epoxy resins, bisphenol A-type epoxy resins are preferred because they are inexpensively available, have relatively low viscosity, and can form cured products with strength and heat resistance. In particular, bisphenol A diglycidyl ether (DGEBA), which is derived from the reaction of bisphenol A, which has active hydrogen, with epichlorohydrin, is suitable because it is inexpensively available.

[0045] Bisphenol A type epoxy resins and the like are available in a range of forms from liquid to solid depending on the molecular weight, but from the viewpoint of ease of handling and preparation, those with low molecular weights that are liquid to semi-solid at normal temperature (room temperature) are preferably used. The bisphenol A epoxy resin that is liquid at room temperature has a number average molecular weight (Mn) of, for example, 250 to 800, preferably 300 to 700, and more preferably 300 to 600, and an epoxy equivalent of, for example, 120 to 450 g / eq, preferably 130 to 400 g / eq, and more preferably 140 to 300 g / eq. The epoxy equivalent refers to the number of grams of resin containing 1 gram equivalent of epoxy groups (unit: g / eq), and is a value measured in accordance with JIS K7236:2001. In the case of a liquid bisphenol A type epoxy resin, the viscosity is preferably in the range of 150 to 50,000 mPa·s / 25°C, more preferably 5,000 to 40,000 mPa·s / 25°C, and even more preferably 10,000 to 20,000 mPa·s / 25°C.

[0046] Commercially available bisphenol A epoxy resins include, but are not limited to, ADEKA RESIN EP-4100, 4100G, 4100E, 4400, 4520S, 4530, EP-4100TX, and EP-4300E from ADEKA CORPORATION, NPEL-127, 127E, 127H, 128, 128E, 128G, 128R, 128S, 134, 134L, 136, and 231 from NAN YA PLASTICS CORPOTATION, EPO (registered trademark) 825 from Oxalis Chemicals Co., Ltd., and jER (registered trademark) 825, 827, 828, 828EL, 828US, 828XA, and 834 from Mitsubishi Chemical Corporation.

[0047] Glycidylamine-type epoxy resins are epoxy resins that contain a glycidylamino group (containing one epoxy group) or a diglycidylamino group (containing two epoxy groups) in the molecule, and include those with aromatic rings such as phenylmethane-type epoxy resins, diaminodiphenyl sulfone-type epoxy resins, diaminodiphenyl ether-type epoxy resins, and aminophenol-type epoxy resins, as well as aliphatic resins such as metaxylylenediamine-type epoxy resins and bisaminomethylcyclohexane-type epoxy resins, glycidylaniline-type resins, tetraglycidylglycoluril-type resins, and triglycidyl isocyanate (TGIC). The glycidylamine-type epoxy resins may be used singly or in combination of two or more.

[0048] Examples of phenylmethane type epoxy resins include tetraglycidyldiaminodiphenylmethane types such as N,N,N',N'-tetraglycidyldiaminodiphenylmethane (TGDDM), N,N,N'-triglycidyl-4,4'-diaminodiphenylmethane, 1,3-phenylenebis(N,N-diglycidylmethanamine), N,N,N',N'-tetraglycidylxylenediamine, N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine), and triphenylmethane triglycidyl ether types such as triphenylmethane triglycidyl ether.

[0049] Diaminodiphenyl sulfone type epoxy resins include N,N,N',N'-tetraglycidyldiaminodiphenyl sulfone. Examples of diaminodiphenyl ether type epoxy resins include N,N-diglycidylamino-1,3-glycidylphenyl ether (DGAGPE), N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether, and tetraglycidyldiaminodiphenyl ether.

[0050] Examples of aminophenol type epoxy resins include p-aminophenol, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, diglycidyl aminophenol, triglycidyl-3-methyl-4-aminophenol, and triglycidyl-p-aminocresol.

[0051] Examples of metaxylylenediamine type epoxy resins include N,N,N',N'-tetraglycidyl-m-xylylenediamine. Examples of bisaminomethylcyclohexane type epoxy resins include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane and tetraglycidylbisaminomethylcyclohexane.

[0052] Examples of the glycidyl aniline type include N,N-diglycidyl aniline, 4,4-methylenebis(N,N-diglycidyl aniline), N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline, diglycidyl toluidine, diglycidyl methoxyaniline, diglycidyl dimethyl aniline, diglycidyl-p-phenoxyaniline, N,N-diglycidyl-4-glycidyl aniline, N,N-diglycidyl-4-glycidyloxyaniline, N,N-diglycidyl-4-oxirane-roxyaniline, diglycidyl trifluoromethyl aniline, N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline, N,N-diglycidyl toluidine, and diglycidyl piperazine.

[0053] The glycidylamine-type epoxy resin is preferably a polyfunctional (difunctional or higher) glycidyl group (epoxy group) having two or more glycidyl groups (epoxy groups) in one molecule, and more preferably a difunctional or trifunctional glycidylamine-type epoxy resin having two or three glycidyl groups (epoxy groups) in one molecule, which can increase the crosslink density of the cured product and further improve heat resistance. Furthermore, the glycidylamine-type epoxy resin preferably has an aromatic ring such as a benzene ring or a naphthalene ring in the molecule, and diaminodiphenylmethane-type epoxy resin or aminophenol-type epoxy resin is preferred, which can increase the crosslink density of the cured product and further improve heat resistance.

[0054] The glycidylamine type epoxy resin has an epoxy equivalent of preferably 30 to 300 g / eq, more preferably 50 to 200 g / eq, and even more preferably 60 to 150 g / eq. When the epoxy equivalent is within this range, the crosslink density of the cured product can be increased, and the heat resistance can be further improved. The glycidylamine type epoxy resin preferably has a weight average molecular weight (Mw) in the range of 100 to 5000, more preferably 250 to 3000, and even more preferably 400 to 1500, and is liquid. Furthermore, liquid glycidylamine-type epoxy resins preferably have a viscosity in the range of 300 to 3000 mPa·s / 25°C, more preferably 400 to 2000 mPa·s / 25°C, and even more preferably 500 to 1000 mPa·s / 25°C. If the viscosity is within this range, an epoxy adhesive composition with a lower viscosity that enables thin film adhesion can be obtained.

[0055] Commercially available glycidylamine type epoxy resins include JER (registered trademark) 604, 630, and 630LSD from Mitsubishi Chemical Corporation, ADEKA Resin EP-3950S, 3950E, 3950L, and 3980S from ADEKA Corporation, TG3DAS from Mitsui Chemicals Fine Co., Ltd., and Epotohto (registered trademark) YH-523, YH-513, and YH-524 from Nippon Steel Chemical & Material Co., Ltd. Examples of epoxy resins include, but are not limited to, SUMIEPOXY (registered trademark) ELM-404, YH-434, YH-434L, Sumiepoxy (registered trademark) ELM-434, ELM-434L, ELM-434VL, ELM-120, ELM-100, ELM-100H from Sumitomo Chemical Co., Ltd., GAN and GOT from Nippon Kayaku Co., Ltd., TETRAD (registered trademark)-X and -C from Mitsubishi Gas Chemical Trading Co., Ltd., TGDDS from Konishi Chemical Co., Ltd., Bakelite EPR494, EPR495, EPR496, and EPR497 from Bakelite AG, and Araldite (registered trademark) MY721, MY720, MY9512, MY9612, MY9634, MY9663, MY0500, MY0600, MY0610, and MY0510 from Huntsman Japan Co., Ltd.

[0056] In the epoxy adhesive composition of this embodiment, the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the glycidylamine-type epoxy resin is preferably blended in an amount of 30 parts by mass or more and 1,000 parts by mass or less, more preferably 400 parts by mass or more and 900 parts by mass or less, and even more preferably 500 parts by mass or more and 800 parts by mass or less, per 100 parts by mass of the bisphenol-type epoxy resin.

[0057] For a total of 100 parts by mass of the epoxy adhesive composition, the bisphenol-type epoxy resin is preferably blended in an amount of 3 parts by mass or more and 90 parts by mass or less, more preferably 4 parts by mass or more and 80 parts by mass or less, and even more preferably 5 parts by mass or more and 70 parts by mass or less, and the glycidylamine-type epoxy resin is preferably blended in an amount of 5 parts by mass or more and 97 parts by mass or less, more preferably 10 parts by mass or more and 90 parts by mass or less, and even more preferably 15 parts by mass or more and 70 parts by mass or less.

[0058] If the amount of bisphenol-type epoxy resin is relatively small and the amount of glycidyl amine-type epoxy resin is relatively large, the resistance to moist heat degradation will decrease. On the other hand, if the amount of glycidyl amine-type epoxy resin is relatively small and the amount of bisphenol-type epoxy resin is relatively large, the viscosity will be high, making it difficult to adhere thin films, and heat resistance will also be impaired. When the blending amounts of the bisphenol type epoxy resin and the glycidylamine type epoxy resin are within the above ranges, low viscosity can be ensured, and the heat resistance of the cured product can be ensured, as well as resistance to moist heat degradation.

[0059] The total content of the bisphenol-type epoxy resin and the glycidyl amine-type epoxy resin is preferably 40 to 95% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass, relative to 100% by mass of the entire epoxy adhesive composition.Within this range, good adhesive strength can be ensured.

[0060] As a curing agent for epoxy resin, a heat-curing type latent curing agent that hardens epoxy resin and has the latency to start the curing reaction by heating to a predetermined temperature is suitable. When epoxy resin is cured with a latent curing agent, the glass transition temperature is increased, and heat resistance can be improved.

[0061] Examples of such heat-curing type latent curing agents include aromatic polyamines (diaminodiphenylmethanes (DDM) such as 4,4'-diaminodiphenylmethane, metaphenylenediamine, metaxylylenediamine (MPDA), diaminodiphenylsulfones (DDS) such as 4,4'-diaminodiphenylsulfone), acid anhydrides (phthalic anhydride, hexahydrophthalic anhydride (HHPA), tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride (MTHPA), methylhexahydrophthalic anhydride such as 4-methylhexahydrophthalic anhydride, maleic anhydride, methylnadic anhydride, chlorendic anhydride, pyromellitic anhydride (PMDA), pyromellitic anhydride, benzophenonetetracarboxylic anhydride (BTD), and the like. A), ethylene glycol bis(anhydrotrimate), methylcyclohexenetetracarboxylic anhydride, trimellitic anhydride (TMA), polyazelaic anhydride, etc.), phenolic hardeners (phenol novolac resin, cresol novolac resin, bisphenol novolac resin, triazine-modified phenol novolac resin, phenol resol resin, cresol naphthol formaldehyde condensate, phenol aralkyl resin, etc.), dicyandiamide (DICY), boron trifluoride-amine complexes (boron trifluoride amine complex salts), organic acid hydrazides (adipic acid dihydrazide, isophthalic acid dihydrazide, sebacic acid dihydrazide, stearic acid dihydrazide, dibasic acid hydrazide, salicylic acid hydrazide, etc.).

[0062] These latent curing agents have an active group (active hydrogen) that reacts with the epoxy group, opening the epoxy group and incorporating the curing agent itself into a part of the resin network structure. As the epoxy resin curing agent, one type may be used alone, or two or more types may be used in combination. Among these, dicyandiamide (DICY) is preferably used from the viewpoint of its ability to form a network structure with high crosslink density through reaction with epoxy resin and to enhance heat resistance. Note that dicyandiamide is insoluble in epoxy resin at room temperature, but dissolves and reacts with epoxy resin when heated.

[0063] Furthermore, when an acid anhydride-based, phenol novolac resin-based, or dicyandiamide-based epoxy resin curing agent is used, a curing accelerator (co-curing agent) is preferably used in combination to increase the curing reaction rate or lower the curing temperature.

[0064] Curing accelerators include tertiary amines (N,N-dimethylpiperazine, triethylenediamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, etc.), tertiary amine salts, imidazole compounds, phosphines, phosphonium salts, and urea compounds (urea derivatives such as 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethyl)urea, 3-(p-chlorophenyl)-1,1-dimethylurea, and N,N-dimethyl-N'-phenylurea). As the curing accelerator for dicyandiamide, urea-based accelerators and imidazoles are preferably used because they can lower the curing temperature, thereby reducing thermal shrinkage during curing and making it difficult for stress distortion and hysteresis loss to occur in the soft magnetic members that make up the laminated core. Among them, imidazoles are more preferred from the viewpoint of increasing the pot life (storage stability) and the glass transition temperature and heat resistance of the cured product.

[0065] Examples of imidazoles as curing accelerators include imidazole, 2-methylimidazole, 2-undecylimidazole (C11Z), 2-ethyl-4-methylimidazole, 2-heptadecylimidazole (C17Z), 1,2-dimethylimidazole (1,2DMZ), 2-phenylimidazole (2PZ), 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl- 2-Methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2'-methylimidazolyl(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazole 2,4-Diamino-6-[2'-ethyl-4-methylimidazolyl(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4-methylimidazolyl(1')]-ethyl-s-triazine, isocyanuric acid adduct of 2,4-diamino-6-[2'-methylimidazolyl(1')]-ethyl-s-triazine, isocyanuric acid adduct of 2-phenylimidazole, isocyanuric acid adduct of 2-methylimidazole, 2-phenyl-4,5-dihydroxydimethylimidazole, 2-phenyl-4-methyl- Examples of suitable imidazole compounds include 5-hydroxymethylimidazole, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-methylimidazoline, and 2-phenylimidazoline; and adducts of imidazole compounds with epoxy resins. Of these, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 1-benzyl-2-phenylimidazole are preferably used.

[0066] The amount of the curing agent to be added is appropriately determined depending on the epoxy resin (epoxy equivalent, etc.) used, the curing conditions, etc. For example, in the case of dicyandiamide, the amount is set based on its amine equivalent and epoxy equivalent, and is about 0.5 to 0.9 equivalents relative to the epoxy equivalent, preferably about 0.5 to 0.7 equivalents. Also, in the case of imidazoles, the amount is blended in the range of, for example, 0 to 8 parts by mass, more preferably 0.5 to 6 parts by mass, and more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the entire epoxy resin (total amount, total amount). For example, the amount of the curing agent is in the range of 1 to 30 parts by mass, preferably 3 to 25 parts by mass, and more preferably 5 to 20 parts by mass, and the amount of the curing accelerator is in the range of 0 to 20 parts by mass, preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the total epoxy resin.

[0067] Commercially available dicyandiamide curing agents include, but are not limited to, DICY7 and DICY15 from Mitsubishi Chemical Corporation, DICYANEX1400F from Evonik, DDA5, DDA10, DDA50, and DDA100 from the OMICURE (registered trademark) series from CVC Thermoset Specialties, CG-325G, CG-1200G, and CG-1400 from the Amicure (registered trademark) series from Air Products and Chemicals, Inc., and DYHARD (registered trademark) 100 from AlzChem. Commercially available imidazole curing accelerators include, but are not limited to, 2MZA-PW and 2PHZ-PW from Evonik, and P200-H50 from Mitsubishi Chemical Corporation.

[0068] The epoxy adhesive composition of the present embodiment may further contain an epoxy reactive diluent. The epoxy-based reactive diluent has an epoxy group in its molecule and is incorporated into part of the resin network structure during the curing process of the epoxy resin. Preferably, a bifunctional reactive diluent (bifunctional group type) and / or a trifunctional reactive diluent (trifunctional group type) is used. A bifunctional or trifunctional reactive diluent allows the viscosity of the epoxy adhesive composition to be reduced without significantly impairing heat resistance, allowing the cured product to have a thinner film. More preferably, a trifunctional reactive diluent allows the viscosity of the epoxy adhesive composition to be reduced while maintaining higher heat resistance of the cured product.

[0069] Trifunctional epoxy-based reactive diluents are compounds made from epichlorohydrin and have three epoxy groups (reactive groups) in their molecules. Examples include aliphatic triglycidyl ethers such as trimethylolpropane polyglycidyl ether, and aliphatic tetraglycidyl ethers. The trifunctional reactive diluent preferably has a viscosity in the range of 100 to 1000 mPa·s / 25° C., more preferably 500 to 800 mPa·s / 25° C. The trifunctional reactive diluent also preferably has an epoxy equivalent in the range of 50 g / eq to 400 g / eq, more preferably 50 g / eq to 200 g / eq.

[0070] Bifunctional reactive epoxy diluents are compounds derived from epichlorohydrin and have two epoxy groups (reactive groups) in their molecules, such as glycidyl ether types, specifically 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, neopentyl glycol glycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, and dimer acid diglycidyl ester. Diepoxy diluents with an alkyl and branched structure are preferred, as they can maintain a high glass transition temperature of the cured product. The bifunctional reactive epoxy-based reactive diluent preferably has a viscosity in the range of 5 to 200 mPa·s / 25°C, more preferably 10 to 150 mPa·s / 25°C. The bifunctional reactive diluent also preferably has an epoxy equivalent in the range of 50 g / eq to 500 g / eq, more preferably 50 g / eq to 400 g / eq.

[0071] Commercially available trifunctional reactive diluents include, for example, Denacol (registered trademark) EX-321, 321L from Nagase ChemteX Corporation and Adeka Glycirol ED-505 from ADEKA Corporation, but are not limited to these. Commercially available bifunctional reactive diluents include, but are not limited to, Denacol (registered trademark) EX-810, 810P, 811, 850, 851, 830, 832, 841, 861, 201, 211, 212, 252, and 931 from Nagase ChemteX Corporation, Adeka Glycirol ED-503, 506, and 523T from ADEKA Corporation, DER732 from DOW (registered trademark), Epogosey (registered trademark) PT, PG400, BD, NPG, HD, HD(M), and HD(D) from Yokkaichi Chemical Co., Ltd., YED216M and 216D from Mitsubishi Chemical Corporation, NPER-032 from NAN YA PLASTICS CORPOTATION, and Epiol (registered trademark) 100LC from NOF Corporation.

[0072] The epoxy-based reactive diluent is preferably blended in an amount of 0 to 50 parts by mass, more preferably 5 to 40 parts by mass, and even more preferably 15 to 30 parts by mass, relative to 100 parts by mass of the total epoxy resin. The epoxy-based reactive diluent is preferably contained in an amount of 0 to 40 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 25 parts by mass, relative to 100 parts by mass of the total epoxy adhesive composition. Within the above range, the viscosity can be reduced without reducing the heat resistance or adhesive strength.

[0073] When carrying out the present invention, other components may be blended as necessary, such as emulsifiers, antifoaming agents, surfactants, neutralizing agents, rust inhibitors, lubricants, antioxidants, organic solvents (for example, ketones such as acetone, methyl ethyl ketone, dipropyl ketone, and diisobutyl ketone; alcohols such as methanol, ethanol, isopropanol, and butanol; aromatic hydrocarbons such as toluene and xylene; and esters such as methyl propionate, ethyl propionate, butyl propionate, methyl butanoate, ethyl butanoate, butyl butanoate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate).

[0074] The epoxy adhesive composition of the present embodiment, which contains at least a bisphenol-type epoxy resin, a glycidylamine-type epoxy resin, and a curing agent, has a glass transition temperature (Tg) after curing of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower. If the glass transition temperature (Tg) is too low, the heat resistance required to maintain adhesive strength will not be achieved even at high temperatures (for example, around 160°C) when the laminated core of a motor, for example, is in operation. If the glass transition temperature (Tg) is too high, residual stress is likely to occur due to cure shrinkage or differences in the coefficient of linear thermal expansion with the substrate, resulting in large hysteresis loss during lamination. If the glass transition temperature of the cured product is within the above range, hysteresis loss can be suppressed, and heat resistance can be ensured that good adhesive strength can be maintained even at high temperatures (e.g., about 160°C) when a laminated core of a motor for an automobile or the like is driven. In particular, by blending a glycidylamine type epoxy resin, the crosslink density of the cured product can be increased because the glycidylamine type epoxy resin is polyfunctional, and therefore the glass transition temperature (Tg) can be increased, and heat resistance can be improved.

[0075] The epoxy adhesive composition of this embodiment, which contains such a bisphenol-type epoxy resin, a glycidyl amine-type epoxy resin, and a curing agent, is used to bond soft magnetic members constituting a laminated core, such as a rotor core or stator core constituting a drive motor for an electric vehicle. That is, in a laminated core formed by stacking multiple soft magnetic members, such as plate-shaped or foil-shaped soft magnetic members, in the stacking direction, the composition is used to bond the stacked soft magnetic members together. This forms a laminated core having multiple soft magnetic members and an adhesive layer made of a cured product of the epoxy adhesive composition containing an epoxy resin and its curing agent. Note that the epoxy adhesive composition using a latent curing agent cures upon heating to exhibit adhesive properties.

[0076] In this case, the epoxy adhesive composition may be applied to the soft magnetic member (thin plate, foil material) that serves as the core member (for example, by application means such as a roll coater, flow coater, spray coater, knife coater, bar coater, die coater, gravure coater, or casting), and the soft magnetic members may then be laminated in this state, and the epoxy adhesive composition may be cured by heating to bond the laminated soft magnetic members together. Alternatively, the soft magnetic members (thin plate, foil material) may be laminated first, and the epoxy adhesive composition may be impregnated between the soft magnetic members in this laminated state, and then cured by heating to bond the soft magnetic members together. The heating means used here is not particularly limited, and examples include heating in a high-temperature bath, electric furnace, hot air drying oven, or induction heating furnace using hot air, infrared heating, or induction heating. The heating conditions are, for example, 100°C or higher, preferably 150°C or higher, for approximately 10 to 20 minutes. In particular, the epoxy adhesive composition of this embodiment uses a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin together as the epoxy resin, which allows it to have a low viscosity (10 [Pa·s / 20°C] or less) that allows for impregnation and adhesion between the soft magnetic members that make up the laminated core, making it suitable for full-surface adhesion.

[0077] Methods for impregnating and bonding between the soft magnetic members that make up the laminated core include vacuum impregnation, which involves reducing the pressure of the atmosphere, atmospheric impregnation (atmospheric pressure impregnation) based on the principle of capillary action (normal pressure impregnation), dip impregnation (immersion), and a method of supplying the adhesive using a dropper tube. Preferably, the impregnation and bonding is by vacuum impregnation, which allows the epoxy adhesive composition to easily penetrate between the laminated soft magnetic members and provides stable adhesive strength.

[0078] In the vacuum impregnation method, for example, multiple soft magnetic members constituting the laminated core are stacked and the stacked state is fixed with a jig or the like. Then, the laminate fixed with the jig and the epoxy adhesive composition are placed in a tank (made of stainless steel, for example) so that the entire laminate fixed with the jig is immersed in the epoxy adhesive composition. Next, the air in the tank is sucked out with a vacuum pump, and this state is continued until all air bubbles generated from the epoxy adhesive composition in the tank disappear. Alternatively, the air in the tank is sucked out until a predetermined vacuum level is reached. This allows the epoxy adhesive composition to be impregnated between the soft magnetic members of the laminate. The laminate is then removed from the tank, and the epoxy adhesive composition adhering to the front, back, and end faces of the laminate is removed. The laminate is then heated to harden the epoxy adhesive composition and bond the soft magnetic members together. The heat treatment is carried out, for example, at a temperature of 100°C or higher, preferably 150°C or higher, for about 10 to 20 minutes, using, for example, an electric furnace, a hot air drying furnace, an infrared heating furnace, an induction heating furnace, or the like.

[0079] The epoxy adhesive composition of the present embodiment is a one-component type that uses a latent curing agent, and therefore can be stored at room temperature. When the epoxy adhesive composition in the tank runs low, it can be replenished, making it suitable for mass production.

[0080] In particular, when constructing a laminated core using a soft magnetic material with an amorphous structure or a nanocrystalline structure, even if the number of laminated sheets increases because the thickness is thinner than that of electromagnetic steel sheets, bonding can be performed using an impregnation bonding method, which improves workability and productivity. That is, according to the epoxy adhesive composition of this embodiment, by using a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin in combination as the epoxy resin, the composition has a low viscosity at room temperature, which allows it to penetrate into the gaps between stacked soft magnetic members, filling the gaps between the laminations, and harden between the laminations to bond the soft magnetic members together, that is, it is possible to impregnate and bond the soft magnetic members that make up the laminated core. The low viscosity allows the composition to fill and impregnate the gaps between the laminations in a short time, which shortens the process time for adhering the epoxy adhesive composition to the soft magnetic members, thereby enabling the work efficiency and productivity of adhesive lamination to be improved.

[0081] The epoxy adhesive composition of this embodiment uses a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin in combination as the epoxy resin, resulting in low viscosity. This allows the thickness of the cured product, which is thermally cured by heating to bond the soft magnetic members together, to be thin. This allows for the miniaturization of laminated cores and, ultimately, motors. Furthermore, the thinning of the cured product allows for a higher space factor between the soft magnetic members in the laminated core, thereby improving magnetic properties. Furthermore, a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin are used in combination as the epoxy resin, and the glass transition temperature (Tg) is within the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, and more preferably 140°C or higher and 250°C or lower, so that adhesive strength can be maintained even at high temperatures and heat resistance is achieved. That is, in addition to having good adhesive strength at room temperature, the adhesive also has heat resistance that allows that adhesive strength to be exerted even at high temperatures. Therefore, the adhesive cured product used to bond soft magnetic members constituting a laminated core, which becomes hot during operation of a drive motor or the like for an electric vehicle, can maintain sufficient adhesive strength even when exposed to high temperatures during operation.

[0082] That is, the epoxy adhesive composition of this embodiment uses a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin in combination as the epoxy resin, and therefore has low viscosity at room temperature, making it possible to apply a thin film to the soft magnetic members that make up the laminated core, or to impregnate the spaces between the soft magnetic members. Therefore, the adhesive cured product obtained by heat-curing the epoxy adhesive composition interposed between the soft magnetic members is thin. In particular, the low viscosity makes it easy to form an adhesive layer with a consistent thickness between the soft magnetic members, and the adhesive layer has good film thickness accuracy, facilitating full-surface adhesion. Even when a large number of soft magnetic members are laminated, flatness is ensured, resulting in stable precision in the laminated core and reducing vibration, noise, and the like.

[0083] In this case, the thickness (average thickness) of the cured product obtained by heat-curing the epoxy adhesive composition interposed between the soft magnetic members constituting the laminated core is preferably in the range of 0.5 μm or more and 2.5 μm or less, more preferably 0.8 μm or more and 2.0 μm or less, and even more preferably 0.8 μm or more and 1.8 μm or less. If the thickness of the cured product is too thin, the desired adhesive strength cannot be obtained, while if it is too thick, the space factor of the soft magnetic member in the laminated core decreases, and magnetic properties such as core loss deteriorate. If the thickness of the cured product is within the above range, the adhesive strength for bonding the soft magnetic members together can be ensured, and the space factor of the soft magnetic members in the laminated core can be increased, thereby improving the magnetic properties.

[0084] Furthermore, laminated cores made of soft magnetic materials bonded with the epoxy adhesive composition of this embodiment are used, for example, in stator cores and iron cores of motors for vehicles such as automobiles. Such automobile motors may be exposed to high-temperature atmospheres of, for example, about 160°C, and adhesives for laminated cores used in such motors are required to be able to maintain stable adhesive strength even in high-temperature atmospheres. As will be described later, the epoxy adhesive composition of this embodiment has good shear adhesive strength at room temperature and at 160°C of the cured product, and has heat resistance that allows the adhesive strength to be maintained even at high temperatures without a significant decrease in adhesive strength.

[0085] In addition, the cured adhesive obtained by thermally curing the epoxy adhesive composition of this embodiment has insulating properties and exhibits insulating performance between adjacent soft magnetic members in the stacking direction. Therefore, even if the epoxy adhesive composition of this embodiment is applied to soft magnetic members without an insulating coating and thermally cured to bond the soft magnetic members together, it is possible to reduce eddy current loss without preventing electrical conduction and deteriorating magnetic properties.

[0086] In particular, the epoxy adhesive composition of this embodiment has low viscosity, making it suitable for full-surface bonding between soft magnetic members, and its insulating properties enable thin-film bonding between soft magnetic members that are not insulated. This allows for the miniaturization of laminated cores, an increase in the space factor of the soft magnetic members in the laminated core, and the elimination of the need for insulating the soft magnetic members, thereby improving the productivity of laminated cores.

[0087] Furthermore, a laminated core in which soft magnetic members are bonded together with an adhesive layer made of a cured product formed by applying the epoxy-based adhesive composition of this embodiment to the soft magnetic members and then stacking the soft magnetic members, or by impregnating the spaces between the stacked soft magnetic members with the epoxy-based adhesive composition and then heating to thermally cure the epoxy-based adhesive composition, is less susceptible to the effects of processing distortion compared to soft magnetic members bonded together by crimping or welding, and therefore can reduce deterioration of magnetic properties and core iron loss, contributing to higher motor efficiency. That is, adhesive lamination, in which laminated soft magnetic members are bonded and fixed together by thermal curing of an epoxy-based adhesive composition, is less likely to cause processing distortion or conduction, as occurs with fixation by crimping or welding, thereby reducing core iron loss. Furthermore, because processing distortion is less likely to occur, it is also possible to laminate and fix soft magnetic members such as thinned electromagnetic steel sheets, amorphous alloy materials, and nanocrystalline alloy materials. In particular, when forming a laminated core using extremely thin soft magnetic members such as amorphous alloy ribbons and nanocrystalline alloy ribbons, which are effective in reducing iron loss, fixing the soft magnetic members by crimping or welding is difficult and results in insufficient strength. However, when the soft magnetic members of the laminated core are bonded together by curing and adhesion using the epoxy-based adhesive composition according to this embodiment, stress is prevented from being applied to the soft magnetic members. This makes it suitable for fixing soft magnetic members with a thickness of 0.2 mm or less, which are difficult to fix by crimping or welding, such as extremely thin soft magnetic members (e.g., approximately 25 μm), such as amorphous alloy ribbons and nanocrystalline alloy ribbons.

[0088] [Example] Next, examples of the epoxy adhesive composition according to the embodiment of the present invention will be described. The epoxy adhesive compositions of Examples 1 and 2 comprised a liquid bisphenol A epoxy resin (bisphenol A diglycidyl ether: DGEBA, trade name "Nan Ya EPOXY RESIN NPEL-128" from Nan Ya Plastics Corporation, epoxy equivalent: 180 to 190 g / eq, viscosity: 12,000 to 15,000 mPa·s / 25°C) as the bisphenol epoxy resin, a liquid p-aminophenol epoxy resin (trade name "ADEKA DILENE EP-3950E" from ADEKA CORPORATION), which is a glycidylamine trifunctional epoxy resin, epoxy equivalent: 97 g / eq, viscosity: 800 mPa·s / 25°C) as the glycidylamine epoxy resin, and dicyandiamide (CVC Thermoset) as the curing agent. It is a blend of 2-phenyl-4,5-dihydroxymethylimidazole (trade name "CUREZOL (registered trademark) 2PHZ-PW" from Evonik), an imidazole curing accelerator as a dicyandiamide curing accelerator, and trimethylolpropane triglycidyl ether (trade name "ADEKA GLYCILOR ED-505" from ADEKA Corporation, epoxy equivalent: 180-190 g / eq, viscosity: 150 mPa·s / 25°C), a trifunctional reactive epoxy reactive diluent.

[0089] The epoxy adhesive composition of Example 3 contains the same materials as those of Examples 1 and 2, except that no epoxy reactive diluent is added. Unlike Examples 1 and 2, Example 4 used a bifunctional reactive diluent, polypropylene glycol glycidyl ether (ADEKA Corporation, trade name "ADEKA GLYCIROL ED-506", epoxy equivalent: 300 g / eq, viscosity: 60 mPa·s / 25°C), as the epoxy-based reactive diluent. The other components were blended with the same materials as in Examples 1 and 2. In Examples 1 to 4, the above materials were mixed at room temperature using a universal mixer until homogeneous, and then degassed to prepare an epoxy adhesive composition. Each of the epoxy adhesive compositions of Examples 1 to 4 was applied to a substrate (steel plate) and heated (170°C for 2 hours) to form a cured product. The glass transition temperatures (Tg) of the cured products were determined by differential scanning calorimetry (DSC) in accordance with JIS K7121-1987 using a dynamic viscoelasticity measuring device (DMA850 manufactured by TA Instruments, measurement mode: single cantilever, frequency: 1.0 Hz, strain: 0.05%, heating rate: 2.0°C / min). The cured product had a glass transition temperature (Tg) of 166°C for the epoxy adhesive composition of Example 1, 152°C for the epoxy adhesive composition of Example 2, 160°C for the epoxy adhesive composition of Example 3, and 131°C for the epoxy adhesive composition of Example 4.

[0090] [Comparative Example] For comparison, an epoxy adhesive composition according to a comparative example was also prepared. Comparative Example 1 did not contain any glycidylamine-type epoxy resin, but contained the same materials as in Example 3. That is, only a bisphenol-type epoxy resin was used as the epoxy resin, and the other materials were the same as in Example 3, containing a dicyandiamide curing agent and an imidazole-based curing accelerator. Comparative Example 2 did not contain any glycidylamine-type epoxy resin, but contained the same materials as in Examples 1 and 2. That is, only a bisphenol-type epoxy resin was used as the epoxy resin, and the other materials were the same as in Examples 1 and 2, containing a trifunctional reactive diluent, a dicyandiamide curing agent, and an imidazole-based curing accelerator.

[0091] In Comparative Example 3, a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin were used in combination as the epoxy resin, but unlike the Examples, a monofunctional reactive diluent, glycidyl (3-methylphenyl) ether (ADEKA Corporation, trade name "ADEKA Glycirol ED-529", epoxy equivalent: 180 g / eq, viscosity: 20 mPa·s / 25°C), was used as the reactive diluent. Other than that, like the Examples, a dicyandiamide curing agent and an imidazole curing accelerator were blended.

[0092] In Comparative Examples 1 to 3, the above materials were mixed at room temperature using a universal mixer until uniform, and then degassed to prepare an epoxy adhesive composition. Each of the epoxy adhesive compositions of Comparative Examples 1 to 3 was applied to a substrate (steel plate) and cured by heating (170°C for 2 hours). The glass transition temperatures (Tg) of these cured products were measured in the same manner as in the above examples. The cured product of the epoxy adhesive composition of Comparative Example 1 had a glass transition temperature of 113°C, the cured product of the epoxy adhesive composition of Comparative Example 2 had a glass transition temperature of 115°C, and the cured product of the epoxy adhesive composition of Comparative Example 3 had a glass transition temperature of 110°C.

[0093] The blending compositions of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in the upper part of Table 1. The blending compositions shown in the upper part of Table 1 are in parts by mass.

[0094] [Table 1]

[0095] As shown in Table 1, the epoxy adhesive composition of Example 1 was prepared by blending 7 parts by mass of bisphenol A epoxy resin as the bisphenol epoxy resin, 60 parts by mass of p-aminophenol epoxy resin as the glycidylamine epoxy resin, 20 parts by mass of trimethylolpropane triglycidyl ether, which is a trifunctional reactive epoxy reactive diluent as the epoxy reactive diluent, 10 parts by mass of dicyandiamide as the curing agent, and 3 parts by mass of an imidazole curing accelerator. In this Example 1, the content of bisphenol A type epoxy resin as the bisphenol type epoxy resin and the content of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin were 7 mass % and 60 mass %, respectively, relative to 100 mass % of the total epoxy adhesive composition, and the blending ratio of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin was 857 mass parts per 100 mass parts of bisphenol A type epoxy resin as the bisphenol type epoxy resin.

[0096] The epoxy adhesive composition of this Example 2 was prepared by blending 60 parts by mass of bisphenol A epoxy resin as a bisphenol epoxy resin, 20 parts by mass of p-aminophenol epoxy resin as a glycidylamine epoxy resin, 10 parts by mass of trimethylolpropane triglycidyl ether, which is a trifunctional reactive diluent, as an epoxy reactive diluent, 9 parts by mass of dicyandiamide as a curing agent, and 1 part by mass of an imidazole curing accelerator. In Example 2, the content of bisphenol A type epoxy resin as the bisphenol type epoxy resin and the content of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin were 60 mass % and 20 mass %, respectively, relative to 100 mass % of the total epoxy adhesive composition, and the blending ratio of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin was 33 mass parts per 100 mass parts of bisphenol A type epoxy resin as the bisphenol type epoxy resin.

[0097] The epoxy adhesive composition of this Example 3 was a blend of 60 parts by mass of bisphenol A type epoxy resin as a bisphenol type epoxy resin, 30 parts by mass of p-aminophenol type epoxy resin as a glycidylamine type epoxy resin, 9 parts by mass of dicyandiamide as a curing agent, and 1 part by mass of an imidazole type curing accelerator. In this Example 3, the content of bisphenol A type epoxy resin as the bisphenol type epoxy resin and the content of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin were 60 mass % and 30 mass %, respectively, relative to 100 mass % of the total epoxy adhesive composition, and the blending ratio of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin was 50 mass parts per 100 mass parts of bisphenol A type epoxy resin as the bisphenol type epoxy resin.

[0098] The epoxy adhesive composition of Example 4 was prepared by blending 57 parts by mass of bisphenol A epoxy resin as a bisphenol epoxy resin, 20 parts by mass of p-aminophenol epoxy resin as a glycidylamine epoxy resin, 15 parts by mass of polypropylene glycol glycidyl ether, which is a bifunctional reactive diluent, as an epoxy reactive diluent, 7 parts by mass of dicyandiamide as a curing agent, and 1 part by mass of an imidazole curing accelerator. In Example 4, the content of bisphenol A type epoxy resin as the bisphenol type epoxy resin and the content of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin were 57 mass% and 20 mass%, respectively, relative to 100 mass% of the total epoxy adhesive composition, and the blending ratio of p-aminophenol type epoxy resin as the glycidylamine type epoxy resin was 35 mass parts per 100 mass parts of bisphenol A type epoxy resin as the bisphenol type epoxy resin.

[0099] On the other hand, the epoxy adhesive composition of Comparative Example 1 was a blend of 90 parts by mass of bisphenol A epoxy resin as a bisphenol epoxy resin, 8 parts by mass of dicyandiamide as a curing agent, and 2 parts by mass of an imidazole curing accelerator, and did not contain any glycidylamine epoxy resin. The epoxy adhesive composition of Comparative Example 2 was a blend of 72 parts by mass of bisphenol A epoxy resin as a bisphenol epoxy resin, 20 parts by mass of trimethylolpropane triglycidyl ether as a trifunctional reactive epoxy reactive diluent as an epoxy reactive diluent, 7 parts by mass of dicyandiamide as a curing agent, and 1 part by mass of an imidazole curing accelerator, and did not contain any glycidylamine epoxy resin.

[0100] The epoxy adhesive composition of Comparative Example 3 was a blend of 57 parts by mass of bisphenol A epoxy resin as a bisphenol epoxy resin, 20 parts by mass of p-aminophenol epoxy resin as a glycidylamine epoxy resin, 15 parts by mass of glycidyl (3-methylphenyl) ether, which is a monofunctional reactive diluent, as an epoxy reactive diluent, 7 parts by mass of dicyandiamide as a curing agent, and 1 part by mass of an imidazole curing accelerator.

[0101] The viscosity of each of the one-component thermosetting epoxy adhesive compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 3 was measured and evaluated, and the thickness, heat resistance, and heat aging resistance of the cured products were also measured and evaluated.

[0102] The viscosity (apparent viscosity) of the epoxy adhesive composition was measured after 1 minute of rotation using a B-type viscometer in accordance with JIS-K2220 under the measurement conditions of a rotation speed of 20 rpm, rotor H5, and room temperature (20°C). If the viscosity was 10.0 Pa·s or less, it was judged to be low enough to allow for impregnation adhesion and was rated as passing (〇 or ◎); in particular, if it was 5.0 Pa·s or less, it was judged to be a sufficiently low viscosity and was rated as ◎ (excellent, passing); if it was over 5.0 Pa·s but not more than 10.0 Pa·s, it was rated as 〇 (fair, passing); and if it exceeded 10.0 Pa·s, it was rated as × (unacceptable, failing).

[0103] Regarding the thickness, ten sheets of amorphous alloy foil material were stacked, and an epoxy adhesive composition was applied between the layers to form a laminate, which was then heated and pressurized in a heat press (pressure conditions: 3.2 MPa, temperature: 170°C, time: 2 hours), and the average thickness of the cured adhesive layer that bonded the steel sheets together was measured. The thickness of the adhesive layer was measured by cutting the laminate and measuring the cross-sectional thickness of the adhesive layer between the layers using a microscope. If the thickness of the epoxy adhesive composition after curing, i.e., the thickness of the cured product, was 2.5 μm or less, it was judged to be effective in increasing the space factor of the soft magnetic components because the thickness of the cured adhesive that bonds the soft magnetic components that make up the laminated core was thin and a thin film was bonded, and it was judged to be pass (◯ or ◎).In particular, if the thickness was 1.5 μm or less, it was judged to be sufficiently thin and was rated as ◎ (excellent, pass).If it was more than 1.5 μm and 2.5 μm or less, it was rated as ◯ (fair, pass), and if it was more than 2.5 μm, it was rated as × (unacceptable, fail).

[0104] Heat resistance was evaluated by measuring shear strength at temperatures of 20°C and 160°C. The shear strength was measured in accordance with the tensile shear adhesive strength test method for rigid adherends of JIS K6850 (1999). Specifically, two 100mm x 25mm x 1.6mm steel substrates were prepared as test panels for the adherends. An epoxy adhesive composition was applied to one of the test panels at a thickness of 10mm over a predetermined length from one longitudinal end of the test panel. The epoxy adhesive composition was then applied to one end of the other test panel, and the panels were then linearly stacked. The stacked test panels were then heated in a hot air oven at 170°C for 2 hours to produce test specimens (adhesive layer thickness: 2mm) cured and bonded by the epoxy adhesive composition. Using a tensile tester (manufactured by Shimadzu Corporation), both ends of the test specimen were pulled longitudinally at a pulling rate of 5mm / min at initial temperatures of 20°C (room temperature) and 160°C, and the breaking force (N) at the time of fracture of the test specimen was measured. The breaking force (N) was then calculated based on the shear cross-sectional area (mm). 2 ) to obtain the tensile shear strength (MPa).

[0105] If the shear strength measured under the temperature conditions of 20°C and 160°C was 8.0 MPa or higher, it was judged that there was sufficient adhesive strength to bond the soft magnetic components that make up the laminated core, and it was rated as pass (◯); if it was less than 8.0 MPa, it was judged that the adhesive strength was insufficient, and it was rated as × (fail). The adhesive strength retention rate was then calculated by calculating the ratio of the shear strength under a temperature condition of 160°C to the initial shear strength under a temperature condition of 20°C (shear strength under a temperature condition of 160°C / shear strength under a temperature condition of 20°C x 100). If the adhesive strength retention rate was 50% or higher, it was judged that the adhesive strength was maintained even at high temperatures and that the material had sufficient heat resistance, and was rated as O (pass). If the adhesive strength retention rate was less than 50%, it was judged that the material lacked heat resistance and was rated as × (fail).

[0106] Furthermore, heat aging resistance was evaluated by measuring shear strength after heat degradation. That is, the same test pieces as those used in the heat resistance measurement test were prepared, and the test pieces were left (exposed) for 1000 hours to age at 200°C. After natural cooling, the aged test pieces were stretched in the longitudinal direction at a tensile speed of 5 mm / min at 20°C. The breaking force (N) at break was measured, and the shear strength (MPa) was determined in the same manner as above. The adhesive strength retention after thermal degradation was then determined by calculating the ratio of the shear strength at 20°C after thermal degradation to the shear strength at the initial 20°C temperature (shear strength after thermal degradation / initial shear strength × 100). If the adhesive strength retention rate after heat degradation was 40% or more, it was judged to have heat aging resistance and was rated as ○ (pass), and if the adhesive strength retention rate after heat degradation was less than 40%, it was judged to lack heat aging resistance and was rated as × (fail).

[0107] The results of measuring and evaluating the viscosity, thickness of the cured product, heat resistance, and heat aging resistance of the epoxy adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in the lower part of Table 1.

[0108] As shown in Table 1, in Comparative Example 1, which did not contain a glycidylamine epoxy resin as the epoxy resin but used only a bisphenol epoxy resin, the adhesive strength significantly decreased after heating at 160°C, the adhesive strength retention rate after heating was poor, and the heat resistance was poor, resulting in a rating of x. Furthermore, in Comparative Example 1, the viscosity of the epoxy adhesive composition was high, resulting in a rating of x, and the thickness of the cured product was also large, resulting in a rating of x.

[0109] In Comparative Example 2, in which only a bisphenol-type epoxy resin was used as the epoxy resin without blending a glycidylamine-type epoxy resin and further blending a trifunctional reactive diluent, the addition of the trifunctional reactive diluent resulted in a lower viscosity than in Comparative Example 1, and although the viscosity was rated as good, the thickness of the cured product was rated as bad. Furthermore, the shear strength at 160°C decreased significantly compared to the shear strength at 20°C, and the adhesive strength retention rate after heating and the adhesive strength retention rate after heat aging were also rated as bad, indicating a lack of heat resistance and heat aging resistance.

[0110] In Comparative Example 3, which used a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin but added a monofunctional reactive diluent, the viscosity was lower than in Comparative Examples 1 and 2 due to the addition of the monofunctional reactive diluent, and the viscosity was rated as ⊚, and the thickness of the cured product was rated as ⊚. However, the glass transition temperature of the cured product was less than 120°C, and the shear strength at 160°C was significantly lower than that at 20°C, and the adhesive strength retention after heating and after heat aging was also poor, resulting in an x ​​rating, indicating a lack of heat resistance and heat aging resistance.

[0111] In contrast, in Examples 1 and 2, which used a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin and also contained a trifunctional reactive diluent, the glass transition temperature of the cured adhesive was in the range of 120 to 300°C, there was less decrease in shear strength at a temperature of 160°C compared to the shear strength at a temperature of 20°C, and the retention of adhesive strength after heating was significantly improved to 70% or more, rated ○, compared to Comparative Examples 1 to 3. The retention of adhesive strength after heat aging was also high, rated ○, and the heat resistance and heat aging resistance were good. Furthermore, the viscosity of the adhesive composition was low, rated ◎ or ○, and the cured product was thin, rated ◎ or ○.

[0112] Furthermore, in Example 3, in which a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin were used in combination as the epoxy resin and no reactive diluent was added, the glass transition temperature of the cured product was in the range of 120 to 300°C, there was little decrease in shear strength at a temperature of 160°C compared to the shear strength at a temperature of 20°C, and the retention of adhesive strength after heating was significantly improved to over 70% and was rated as ○ compared to Comparative Examples 1 to 3. The retention of adhesive strength after heat aging was also high and was rated as ○, and the heat resistance and heat aging resistance were good. Furthermore, the viscosity of the adhesive composition was low and was rated as ○, and the cured product was thin and was rated as ○.

[0113] In Example 4, which used a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin and blended a bifunctional reactive diluent, the glass transition temperature of the cured product was in the range of 120 to 300°C, there was less decrease in shear strength at a temperature of 160°C compared to the shear strength at a temperature of 20°C, and the adhesive strength retention after heating was improved to 50% or more and was rated as ○ compared to Comparative Examples 1 to 3. The adhesive strength retention after heat aging was also high and was rated as ○, and the heat resistance and heat aging resistance were good. Furthermore, the viscosity of the adhesive composition was low and was rated as ○, and the cured product was thin and was rated as ○.

[0114] In this way, the epoxy adhesive compositions of Examples 1 to 4, which use a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin, and further contain a dicyandiamide curing agent and an imidazole-based curing accelerator, and have a glass transition temperature after curing in the range of 120 to 300°C, have low viscosity, cure to a thin film, and provide heat-resistant cured products.

[0115] Generally, the higher the crosslink density of the epoxy resin network and the more rigid the network chains are, with lower molecular mobility, the better the heat resistance. However, such a rigid molecular structure tends to result in high viscosity. However, a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin as the epoxy resin can achieve both low viscosity that enables thin film adhesion and heat resistance. Furthermore, in order to further reduce the viscosity, it is effective to add a reactive diluent, and if a bifunctional or trifunctional reactive diluent is used, the viscosity can be further reduced without impairing the heat resistance.

[0116] Thus, the epoxy adhesive compositions of Examples 1 to 4 above are epoxy adhesive compositions containing an epoxy resin, dicyandiamide as its curing agent, and an imidazole curing accelerator as its curing accelerator, and the epoxy resin is a combination of a bisphenol A epoxy resin as a bisphenol epoxy resin and a p-aminophenol epoxy resin as a glycidylamine epoxy resin, and has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower. The combination of a bisphenol A epoxy resin and a p-aminophenol epoxy resin and a glass transition temperature after curing in the range of 120°C to 300°C results in a low viscosity that enables thin film adhesion, heat resistance that allows adhesive strength to be maintained even at high temperatures, and heat aging resistance.

[0117] The epoxy adhesive compositions of Examples 1 to 4 have low viscosity, allowing for thin-film curing by impregnation or application to bond the soft magnetic members constituting the laminated core together. This allows for thin-film bonding, thereby enabling the miniaturization of the entire laminated core and, ultimately, the motor. Furthermore, the space factor between the soft magnetic members in the laminated core can be increased, thereby improving the magnetic properties of the soft magnetic members. Furthermore, the cured products of the epoxy adhesive compositions of Examples 1 to 4 have insulating properties, allowing for thin-film bonding between uninsulated soft magnetic members while insulating the soft magnetic members from each other, thereby enabling the formation of laminated cores that reduce eddy current loss. Additionally, while laminated cores for motors are exposed to high-temperature environments (e.g., approximately 160°C), the epoxy adhesive compositions of Examples 1 to 4 maintain their adhesive strength and are resistant to degradation even in such high-temperature environments. This prevents the heat generated when the motor is running from reducing adhesive strength, resulting in gaps between the lamination surfaces and deformation of the laminated core. Furthermore, since the adhesive strength can be maintained even at high temperatures and the adhesive strength retention rate is high, it is also possible to suppress the stress distortion that is applied to the soft magnetic member.

[0118] The epoxy adhesive compositions of Examples 1 to 4 have a low viscosity of 1 to 10 Pa·S, so that even if the gaps between the laminated soft magnetic members of a laminated core are as narrow as 1 to 50 μm, the laminated soft magnetic members can be bonded together by impregnating the gaps between the laminated soft magnetic members with the epoxy adhesive composition by, for example, the above-mentioned vacuum impregnation or pressure impregnation, and then heating and thermosetting. This impregnation bonding method requires less time and effort than constructing a laminated core by stacking soft magnetic members coated with an adhesive composition, and enables bonding with thinner films.

[0119] Thus, the epoxy adhesive compositions of Examples 1 to 4 described above can be made to have a low viscosity that enables thin film adhesion, and even when the thickness is thin, they are heat resistant, maintain adhesive strength even at high temperatures, and exhibit insulating properties. As a result, it is possible to increase the space factor, which is the ratio of the soft magnetic material to the laminated core, and to increase the magnetic flux density of the soft magnetic material.

[0120] However, if the amount of bisphenol-type epoxy resin blended is relatively too small and the amount of glycidyl amine-type epoxy resin blended is relatively large, the resistance to moist heat degradation will decrease. On the other hand, if the amount of glycidyl amine-type epoxy resin blended is relatively small and the amount of bisphenol-type epoxy resin blended is relatively large, the viscosity will increase, making it difficult to adhere thin films, and the heat resistance will also decrease. According to the experimental research of the present inventors, it has been confirmed that when the glycidylamine type epoxy resin is blended in an amount within the range of preferably 30 parts by mass or more and 1,000 parts by mass or less, more preferably 400 parts by mass or more and 900 parts by mass or less, and even more preferably 500 parts by mass or more and 800 parts by mass or less, per 100 parts by mass of bisphenol type epoxy resin, a low viscosity that enables thin film adhesion can be ensured, and the heat resistance of the cured product and resistance to moist heat degradation can be ensured.

[0121] As explained above, the epoxy adhesive composition of the above embodiment is an epoxy adhesive composition containing an epoxy resin and a curing agent for the epoxy resin, wherein the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the glass transition temperature after curing, as measured by dynamic mechanical analysis (DMA), is in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower.

[0122] According to the epoxy adhesive composition of the above embodiment, a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin are used in combination as the epoxy resin, and the glass transition temperature after curing is within the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower. This results in low viscosity, allowing for impregnation bonding and thin film coating, thin film bonding and thin film curing, and heat resistance that allows the adhesive strength to be maintained even at high temperatures.

[0123] The glycidyl amine epoxy resin preferably has a viscosity at 25°C of 300 mPa·S or more and 5000 mPa·S or less, more preferably 300 mPa·S or more and 2500 mPa·S or more, and even more preferably 300 mPa·S or more and 1000 mPa·S or less. If the viscosity is within this range, it is possible to obtain an epoxy adhesive composition with a low viscosity that enables impregnation bonding.

[0124] In the epoxy adhesive composition of the above embodiment, if a reactive diluent is further contained, the viscosity can be further reduced. Furthermore, when the reactive diluent is a bifunctional or trifunctional reactive diluent, the viscosity can be further reduced without significantly reducing the heat resistance of the cured product. More preferably, when the reactive diluent is a trifunctional reactive diluent, the heat resistance of the cured product can be further increased.

[0125] In the epoxy adhesive composition of the above embodiment, if the curing agent is dicyandiamide, the heat resistance can be further improved. Furthermore, when an imidazole curing accelerator is contained, the curing reaction rate can be increased and the curing temperature can be lowered. In addition, when the curing accelerator is an imidazole, the heat resistance can be further increased.

[0126] In the epoxy adhesive composition of the above embodiment, when the glycidyl amine epoxy resin is blended in an amount of preferably 30 to 1000 parts by mass, more preferably 400 to 900 parts by mass, and even more preferably 500 to 800 parts by mass per 100 parts by mass of the bisphenol epoxy resin, low viscosity can be ensured, and the heat resistance of the cured product can be ensured, as well as resistance to moist heat degradation.

[0127] In the epoxy adhesive composition of the above embodiment, when the viscosity at 25°C is in the range of 1 Pa·S or more and 10.0 Pa·S or less, more preferably 1.0 Pa·S or more and 9.5 Pa·S or less, and even more preferably 1.0 Pa·S or more and 8.0 Pa·S or less, impregnation adhesion is possible.

[0128] The above-described embodiment can also be understood as an invention of a cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and its curing agent, in which the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the glass transition temperature of the cured product is in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower. According to the cured product of the above embodiment, the epoxy resins used are a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, and the epoxy adhesive composition has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower, and therefore has low viscosity. Therefore, the cured product is capable of thin film bonding and has heat resistance that allows it to maintain adhesive strength even at high temperatures.

[0129] In the cured product of the above embodiment, the thickness is in the range of 0.8 μm or more and 2.5 μm or less, more preferably 0.8 μm or more and 2.0 μm or less, and even more preferably 0.8 μm or more and 1.8 μm or less. Therefore, while ensuring adhesive strength, the space factor between the soft magnetic members in the laminated core can be increased, and the magnetic properties can be improved.

[0130] Furthermore, the description of the above embodiment can also be interpreted as an invention of a laminated core having a plurality of soft magnetic members and an adhesive layer that bonds the laminated soft magnetic members together, wherein the adhesive layer is made of a cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and its curing agent, the epoxy resin being a combination of a bisphenol-type epoxy resin and a glycidyl amine-type epoxy resin, and the cured product of the adhesive layer has a glass transition temperature in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower. According to the laminated core of the above embodiment, a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin are used in combination as the epoxy resin, and the epoxy adhesive composition has a glass transition temperature after curing in the range of 120°C or higher and 300°C or lower, preferably 130°C or higher and 280°C or lower, more preferably 140°C or higher and 250°C or lower, and particularly preferably 150°C or higher and 200°C or lower, and therefore has a low viscosity.Therefore, the adhesive layer made of the cured product is capable of thin film adhesion and has heat resistance that allows it to maintain adhesive strength even at high temperatures.

[0131] When carrying out the present invention, the configuration, ingredients, blending, manufacturing method, etc. of the epoxy adhesive composition, the cured product, and other parts of the laminated core are not limited to those of the above-mentioned embodiments and examples. It should be noted that not all of the numerical values ​​given in the embodiments and examples of the present invention indicate critical values, and some numerical values ​​are determined based on factors such as manufacturing costs and ease of manufacturing, and indicate suitable values ​​suitable for implementation. Therefore, even if the numerical values ​​are slightly changed within the allowable range, this does not negate the implementation.

Claims

1. An epoxy adhesive composition containing an epoxy resin and a curing agent for the epoxy resin, The epoxy resin is a combination of a bisphenol type epoxy resin and a glycidyl amine type epoxy resin, An epoxy adhesive composition characterized in that the glass transition temperature after curing is in the range of 120°C or higher and 300°C or lower.

2. 2. The epoxy adhesive composition according to claim 1, further comprising a reactive diluent.

3. 2. The epoxy adhesive composition according to claim 1, wherein the reactive diluent is a difunctional or trifunctional reactive diluent.

4. 2. The epoxy adhesive composition according to claim 1, wherein the curing agent is dicyandiamide.

5. 5. The epoxy adhesive composition according to claim 4, further comprising an imidazole curing accelerator.

6. 2. The epoxy adhesive composition according to claim 1, wherein the glycidyl amine epoxy resin is blended in an amount ranging from 30 parts by mass to 1,000 parts by mass relative to 100 parts by mass of the bisphenol epoxy resin.

7. 2. The epoxy adhesive composition according to claim 1, wherein the epoxy resin composition has a viscosity at 25°C in the range of 1.0 Pa·S or more and 10.0 Pa·S or less.

8. A cured product obtained by heat-curing an epoxy adhesive composition containing an epoxy resin and a curing agent for the epoxy resin, the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, A cured product having a glass transition temperature in the range of 120°C or higher and 300°C or lower.

9. 9. The adhesive cured product according to claim 8, wherein the cured product has a thickness in the range of 0.8 μm or more and 2.5 μm or less.

10. A laminated core having a plurality of soft magnetic members and an adhesive layer that bonds the laminated soft magnetic members together, the adhesive layer is made of a cured product obtained by heat-curing an epoxy-based adhesive composition containing an epoxy resin and a curing agent for the epoxy resin; the epoxy resin is a combination of a bisphenol-type epoxy resin and a glycidylamine-type epoxy resin, A laminated core characterized in that the glass transition temperature of the cured product of the adhesive layer is in the range of 120°C or higher and 300°C or lower.

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