Epoxy resin composition, cured resin, resin sheet, power module and motor stator

Abstract

The present disclosure relates to an epoxy resin composition comprising a multifunctional epoxy resin having three or more glycidyl groups and an amino compound having a mesogenic skeleton, the multifunctional epoxy resin having a branch point in the molecule, and having a structure in which at least one atom selected from the group consisting of carbon atoms, nitrogen atoms and oxygen atoms is linearly bonded between the branch point and the epoxy group at the terminal of the glycidyl group. According to the present disclosure, an epoxy resin composition having high thermal conductivity and heat resistance as well as excellent workability can be provided.

Description

[Technical field]

[0001] The present disclosure relates to an epoxy resin composition, and further to a cured resin, a resin sheet, a power module, and a stator for a motor. [Background technology]

[0002] Electrical devices such as motors and power modules are becoming smaller and more powerful. For such devices, efficient heat dissipation to the outside is important for their performance and lifespan, and heat countermeasures are becoming increasingly important. For this reason, insulating materials used in such devices are required to have high heat resistance to withstand heat generation and high thermal conductivity to dissipate the generated heat.

[0003] Resin composite materials, in which thermosetting resin is filled with inorganic fillers, are used as insulating materials. In order to improve the thermal conductivity of materials, inorganic fillers with high thermal conductivity, such as alumina, boron nitride, and aluminum nitride, are widely used. On the other hand, thermosetting resins such as epoxy resins have low thermal conductivity and can become thermal resistance in the heat dissipation path. Therefore, technologies to increase the thermal conductivity of thermosetting resins are being investigated.

[0004] In Japanese Patent No. 5224366 (Patent Document 1) and JP 2021-155586 (Patent Document 2), the application of a highly thermally conductive resin in which a mesogen skeleton such as a biphenyl skeleton is introduced into an epoxy resin is considered.

[0005] In Japanese Patent No. 5737028 (Patent Document 3), application of a highly thermally conductive resin in which a mesogen skeleton is introduced into an amino compound, which is a curing agent, is considered. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5224366 [Patent Document 2] Patent Publication No. 2021-155586 [Patent Document 3] Patent No. 5737028 Summary of the Invention [Problem to be solved by the invention]

[0007] The biphenyl-type epoxy resin cured material having a biphenyl skeleton described in Japanese Patent No. 5224366 and Japanese Patent Publication No. 2021-155586 exhibits a thermal conductivity approximately 1.5 times higher than that of a general-purpose bisphenol A-type epoxy resin cured material. However, the highly thermally conductive epoxy resin having a mesogen skeleton has a high melting point due to its high crystallinity, is solid at room temperature, and is difficult to dissolve in solvents, so it is not satisfactory from the viewpoint of productivity such as workability. In addition, since the molding conditions are limited, the arrangement of the mesogen skeleton does not proceed, and the thermal conductivity does not improve sufficiently.

[0008] In Japanese Patent No. 5737028, no consideration is given to a resin composition aimed at improving the arrangement of mesogen groups in combination with an epoxy resin.

[0009] An object of the present disclosure is to provide an epoxy resin composition that has high thermal conductivity and heat resistance as well as excellent workability. [Means for solving the problem]

[0010] The epoxy resin composition of the present disclosure includes a multifunctional epoxy resin containing three or more glycidyl ether groups and an amino compound having a mesogenic skeleton. The multifunctional epoxy resin has a branching point in the molecule. The multifunctional epoxy resin has a structure in which at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms is linearly bonded between the branching point and the epoxy group at the terminal of the glycidyl group. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide an epoxy resin composition that has high thermal conductivity and heat resistance as well as excellent workability. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a power module according to a fourth embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing the configuration of a stator of a motor according to embodiment 5. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An embodiment of the present invention will be described below.

[0014] Embodiment 1 <Epoxy resin composition> The epoxy resin composition of the present embodiment includes a polyfunctional epoxy resin containing three or more glycidyl groups and an amino compound having a mesogenic skeleton. The polyfunctional epoxy resin has a branch point in the molecule. The polyfunctional epoxy resin has a structure in which at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms is linearly bonded between the branch point and the epoxy group at the end of the glycidyl group (hereinafter also referred to as a linear structure). In particular, it is preferable that the polyfunctional epoxy resin is composed only of a linear structure that does not contain a cyclic structure. Since the epoxy resin composition has a linear structure, in the molecular structure of the cured product in which the epoxy group and the active hydrogen of the amino group react, the structure from the branch point, which is a constraint point in the epoxy resin, to the mesogenic skeleton has a flexible linear structure, so that the arrangement of the mesogenic skeleton is not hindered and high thermal conductivity can be exhibited. In addition, the amine-based curing agent, which has a small molecular weight and contains many amino groups in the molecule, is blended in a smaller proportion to the epoxy resin than the acid anhydride-based curing agent or the phenol-based curing agent. Therefore, even if a hardener that is solid at room temperature is blended, the mixed viscosity of the resin as a whole is unlikely to increase, making it possible to provide an epoxy resin with excellent workability.

[0015] (Multifunctional epoxy resin) The polyfunctional epoxy resin contained in the epoxy resin composition of the present embodiment is a compound having three or more glycidyl groups. The glycidyl group is represented by the following chemical formula: [ka] The term "group" refers to a group represented by the formula:

[0016] The polyfunctional epoxy resin has a branch point in the molecule. The branch point can be at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms. The branch is formed by bonding two or more molecular structures, such as a molecular chain, a group, and another atom that is a branch point, to the atom that is the branch point. One or more linear structures are bonded to the branch point. The atom that is the branch point may be bonded to a molecular structure different from the linear structure, such as a molecular chain and a group.

[0017] Two or more linear structures may be bonded to the branching point. A molecular structure other than the linear structure, such as a cyclic structure, a linear structure having a side chain, or a molecular structure that is a combination of a cyclic structure and a linear structure, may be bonded to the branching point. The side chain may be, for example, a hydroxyl group (-OH). In addition, the molecular structure other than the linear structure may have a glycidyl group at the end opposite to the branching point. Furthermore, when the polyfunctional epoxy resin has two or more branching points, the branching points may be bonded to each other.

[0018] The linear structure may have at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms having a linear structure, and hydrogen atoms bonded to these atoms. The linear structure does not include atoms that constitute branch points. The linear structure does not have a cyclic structure. In addition, the linear structure does not have a side chain. In the molecular structure in the cured product when the epoxy resin and the amino compound react with each other, the structure from the branch point, which is the constraint point in the epoxy resin, to the mesogen skeleton has a flexible linear structure, so that the arrangement of the mesogen skeleton is not hindered and high thermal conductivity can be exhibited. From the viewpoint of workability, it is preferable that the multifunctional epoxy resin is liquid at room temperature.

[0019] Of the three or more glycidyl groups possessed by the multifunctional epoxy resin, two or more glycidyl groups may be bonded to the end opposite to the branch point of the linear structure. The glycidyl group may be directly bonded to the branch point. When the glycidyl group is directly bonded to the branch point, the linear structure has a molecular structure represented by the formula: -CH2-. A glycidyl ether group may be directly bonded to the branch point. When the glycidyl ether group is directly bonded to the branch point, the linear structure has a molecular structure represented by the formula: -O-CH2-.

[0020] Examples of the polyfunctional epoxy resin include polyfunctional aromatic epoxy resin and polyfunctional aliphatic epoxy resin. Examples of the polyfunctional aromatic epoxy resin include triglycidyl paraaminophenol, triglycidyl metaaminophenol, and tetraglycidyl diaminodiphenylmethane. Examples of the polyfunctional aliphatic epoxy resin include glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ethers, sorbitol polyglycidyl ethers, and trimethylolpropane polyglycidyl ethers. Since aliphatic epoxy resins have low viscosity and are excellent in workability even after being mixed with an amino compound, polyfunctional aliphatic epoxy resins are preferred as the polyfunctional epoxy resin in the present invention. These polyfunctional epoxy resins may be used alone or in combination of two or more. In addition, these epoxy resins may be biomass-derived epoxy resins using plant-derived raw materials and the like.

[0021] (Amino Compounds) The amino compound contained in the epoxy resin composition of the present embodiment includes a mesogenic skeleton in its molecular structure. The amino compound has one or more amino groups. Here, the mesogenic skeleton refers to a skeleton exhibiting liquid crystallinity, and examples thereof include biphenyl, cyanobiphenyl, terphenyl, cyanoterphenyl, phenylbenzoate, azobenzene, diazobenzene, aniline benzylidene, azomethine, azoxybenzene, stilbene, phenylcyclohexyl, biphenylcyclohexyl, phenoxyphenyl, benzylideneaniline, benzylbenzoate, phenylpyrimidine, phenyldioxane, benzoylaniline, and derivatives thereof. The amino compound may be a compound containing a primary amino group (-NH2) or a secondary amino group (-NRH). Here, R represents a methyl group, an ethyl group, or the like. Examples of amino compounds containing a mesogenic skeleton include 3,3'-diaminobenzidine, 4,4''-diamino-p-terphenyl, 4,4'-diaminobenzanilide, 4,4'-azodianiline, 4-aminophenyl 4-aminobenzoate, and 4-4'-bis(p-aminophenoxy)biphenyl. Of these, 3,3'-diaminobenzidine is preferred. These amino compounds containing a mesogenic skeleton may be used alone or in combination of two or more.

[0022] The amount of amino compound blended is as follows, per epoxy group in the total epoxy resin: Amino compounds One equivalent of active hydrogen in the amino group reacts. 1 When calculated as an equivalent, the active hydrogen of the amino compound per epoxy group Number of The amount is preferably 1 to 4 equivalents, and more preferably 2 to 4 equivalents in order to improve the alignment of the mesogenic skeleton. If the amount is less than 1 equivalent, the crosslink density is low due to the presence of an epoxy group that does not react with the curing agent, and the heat resistance and thermal conductivity may be insufficient. If the amount is more than 4 equivalents, the crosslink density decreases due to an excess of the curing agent, and the binding force of the alignment of the mesogenic skeleton decreases, causing the alignment to loosen, and the heat resistance and thermal conductivity may be insufficient.

[0023] When the epoxy group of the polyfunctional epoxy resin in the epoxy resin composition is bonded to the amino group of the amino compound containing a mesogenic skeleton, there may be a structure in which 12 or less atoms are bonded in a straight chain between the branch point in the polyfunctional epoxy resin and the mesogenic skeleton in the amino compound. The 12 or less atoms are at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms. If the atoms present between the branch point in the polyfunctional epoxy resin and the mesogenic skeleton in the amino compound are within the above range, the mesogenic skeleton tends to be easily arranged, and the mesogenic skeleton after arrangement tends to be difficult to dissolve. If the number of elements between the branch point in the polyfunctional epoxy resin and the mesogenic skeleton in the amino compound exceeds 12, the molecular mobility between the branch point and the mesogenic skeleton becomes large, the arrangement of the mesogenic skeleton tends to be easily dissolve, and sufficient thermal conductivity and heat resistance may not be obtained. The structure in which 12 or less atoms are bonded in a straight chain does not include a branch point. The structure in which 12 or less atoms are bonded in a straight chain does not have a cyclic structure. Up to 12 atoms may have hydrogen atoms attached and no side chains attached.

[0024] (Polymerizable monomer) The epoxy resin composition of the present embodiment may contain a polymerizable monomer. Examples of the polymerizable monomer include ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, tetrabutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, neopentyl glycol dimethacrylate, ditrimethylolpropane tetraacrylate, trimethylolpropane ethoxy triacrylate, glycerin propoxy triacrylate, tricyclodecane dimethanol diacrylate, and dipropylene glycol diacrylate. In this specification, (meth)acrylate means either acrylate or methacrylate. These polymerizable monomers may be used alone or in combination of two or more. These polymerizable monomers may also be biomass-derived polymerizable monomers using plant-derived raw materials.

[0025] Among these polymerizable monomers, from the viewpoint of heat resistance, preferred are ethyl methacrylate, tetrabutyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, isobornyl (meth)acrylate, ditrimethylolpropane tetraacrylate, trimethylolpropane ethoxy triacrylate, glycerin propoxy triacrylate, tricyclodecane dimethanol diacrylate, dipropylene glycol diacrylate, etc., and more preferred is isobornyl methacrylate. Isobornyl methacrylate has a relatively low viscosity (viscosity at a temperature of 25°C: <10 mPa·s) and a high glass transition temperature (hereinafter also referred to as Tg) (Tg: temperature of 180°C), and therefore tends to facilitate the provision of an epoxy resin composition that exhibits excellent heat resistance while improving workability.

[0026] The content of the polymerizable monomer is preferably within a range that does not interfere with the alignment of the mesogenic skeleton. Specifically, the content is preferably 70% by weight or less based on the polyfunctional epoxy resin (hereinafter also referred to as the base agent), the amino compound containing a mesogenic skeleton (hereinafter also referred to as the curing agent), and the polymerizable monomer. If the content of the polymerizable monomer exceeds 70% by weight, the effect of aligning the mesogenic skeleton is reduced, and there is a risk of impairing heat resistance and thermal conductivity.

[0027] (Polymerization initiator) The epoxy resin composition of the present embodiment may contain a polymerization initiator. The polymerization initiator is a compound capable of initiating polymerization of a polymerizable monomer, and examples thereof include radical initiators that generate active radicals, acids, etc. by the action of light or heat, and redox initiators that generate radicals by utilizing an oxidation-reduction reaction.

[0028] Examples of the polymerization initiator include organic peroxides such as hydroperoxides, dialkyl peroxides, peroxy esters, diacyl peroxides, peroxy carbonates, peroxy ketals, and ketone peroxides, and combinations of these organic peroxides with reducing agents such as metal salts and amines. Among these polymerization initiators, preferred are combinations of hydroperoxides and metal salts, which can efficiently generate radicals even at low temperatures, and combinations of ketone peroxides and metal salts. Examples of the hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. Examples of the ketone peroxides include methyl ethyl ketone peroxide and cyclohexanone peroxide. Examples of the metal salts include cobalt salts such as cobalt naphthenate and cobalt octylate, and vanadium compounds such as vanadium pentoxide.

[0029] The content of the polymerization initiator may be 0.001 to 20 parts by mass, and preferably 0.005 to 10 parts by mass, relative to 100 parts by mass of the polymerizable monomer, depending on the type of the polymerizable monomer used. By setting the content of the polymerization initiator within the above range, the reaction between both the base agent and the curing agent and the polymerizable monomer can be sufficiently promoted, and it tends to be easy to provide an epoxy resin composition having excellent heat resistance.

[0030] (Inorganic filler) The epoxy resin composition of the present embodiment may contain an inorganic filler as a filler. By containing an inorganic filler in the epoxy resin composition, it is possible to obtain an epoxy resin composition having excellent thermal conductivity and insulating properties.

[0031] The inorganic filler contained in the epoxy resin of the present embodiment is not particularly limited, and examples thereof include metal oxide particles such as aluminum oxide (alumina), zinc oxide, indium tin oxide (ITO), magnesium oxide, and titanium oxide, metal nitride particles such as boron nitride, silicon nitride, and aluminum nitride, carbon compound particles such as silicon carbide, graphite, diamond, amorphous carbon, carbon black, and carbon fiber, and silica compound powders such as quartz and quartz glass. Among these, aluminum oxide (alumina), zinc oxide, magnesium oxide, titanium oxide, boron nitride, silicon nitride, aluminum nitride, diamond, quartz, and quartz glass are preferable from the viewpoint of insulation.

[0032] The average particle size of the inorganic filler is preferably 0.1 μm to 200 μm, more preferably 1 μm to 100 μm. When the average particle size of the inorganic filler is within the above range, it tends to be advantageous in terms of thermal conductivity, workability, moldability, and storage stability. When the average particle size of the inorganic filler is less than 0.1 μm, it becomes difficult to disperse the inorganic filler in the epoxy resin composition, and there is a risk that the effect of improving thermal conductivity and moldability will decrease. When the average particle size of the inorganic filler exceeds 200 μm, there is a tendency that the strength of the cured product of the epoxy resin composition will decrease and the inorganic filler will easily settle during storage of the epoxy resin composition. In addition, when molded into a sheet, surface roughness will easily occur, and there is a risk that flexibility will decrease.

[0033] The content of the inorganic filler may be, for example, 20 to 80% by volume, preferably 30 to 70% by volume, based on the total volume of the epoxy resin composition. When the content of the inorganic filler is within the above range, it tends to be advantageous in terms of thermal conductivity, workability, and moldability. When the content of the inorganic filler is less than 20% by volume, there is a risk that an epoxy resin composition having sufficient thermal conductivity cannot be obtained. When the content of the inorganic filler is more than 80% by volume, it becomes difficult to disperse the inorganic filler in the epoxy resin composition, and there is a risk that the workability and moldability may be impaired.

[0034] (Coupling Agent) The inorganic filler may be subjected to a coupling treatment with a coupling agent for the purpose of improving the wettability between the inorganic filler and the epoxy resin composition, reinforcing the interface between the inorganic filler and the epoxy resin composition, improving the dispersibility of the inorganic filler, etc. Examples of such coupling agents include γ-glycidoxypropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, etc. These may be used alone or in combination of two or more kinds.

[0035] The content of the coupling agent may be appropriately set depending on the type of inorganic filler and coupling agent used, but is generally 0.01 to 10 parts by mass per 100 parts by mass of the inorganic filler.

[0036] (Cure accelerator) The epoxy resin composition of the present embodiment may contain a curing accelerator (catalyst) as necessary. Examples of the curing accelerator include an imidazole curing accelerator, an amine curing accelerator, and a phosphorus curing accelerator.

[0037] (polymer) The epoxy resin composition of the present embodiment may contain a polymer. The polymer is preferably a thermoplastic resin polymer having a molecular weight of 10,000 or more and a Tg of 100° C. or less. By including such a polymer, an epoxy resin composition having excellent flexibility tends to be obtained. Examples of the polymer include polyethylene resin, polypropylene resin, polyolefin resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyester resin, phenoxy resin, acrylic resin, and the like. These polymers may be used alone or in combination of two or more. When two or more types are used in combination, the combination is not particularly limited. Among these, phenoxy resin and acrylic resin are preferable from the viewpoint of flexibility such as flexibility and coatability. When the molecular weight of the polymer is less than 10,000, the flexibility of the cured product is impaired, the film-forming property when preparing a resin sheet is inferior, and the tackiness of the epoxy resin composition is increased, which may make it difficult to peel off from the substrate, or when the sheets are stacked in a sheet shape, the sheets may stick to each other and become difficult to peel off.

[0038] (Organic solvent) The epoxy resin composition of the present embodiment may contain an organic solvent as necessary. The organic solvent is not particularly limited, and may be appropriately selected from known organic solvents according to the type of epoxy resin, amino compound, inorganic filler, etc., used. Examples of the organic solvent include aromatic hydrocarbons such as toluene, xylene, methoxybenzene, and 1,2-dimethoxybenzene, acetone, ethyl acetate, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, butyronitrile, carbon disulfide, methyl ethyl ketone, cyclohexanone, and cyclopentanone. These organic solvents may be used alone or in combination of two or more. When two or more types are used in combination, the combination is not particularly limited.

[0039] Epoxy resin compositions have high thermal conductivity, heat resistance and insulating properties and are therefore suitable for use in heat dissipation members of power modules and motor stators.

[0040] <Method of producing epoxy resin composition> The method for producing the epoxy resin composition of the present embodiment is not particularly limited, and can be carried out according to a known method. For example, the epoxy resin composition can be obtained by mixing a polyfunctional epoxy resin and an amino compound at room temperature or under heating. In addition, when a polymerizable monomer, a polymerization initiator, an inorganic filler, a coupling agent, a curing accelerator, a polymer, or an organic solvent is used in the epoxy resin composition, it may be added when mixing the polyfunctional epoxy resin and the amino compound. In addition, when a monomer is added, it is preferable to mix at a temperature below the boiling point of the monomer. These mixtures may be kneaded using a device such as a mixer, a three-roll mill, a kneader, or a high-speed stirring device. In addition, the amino compound may be mixed with the polyfunctional epoxy resin after being crushed using, for example, a mortar. This allows the amino compound to dissolve quickly in the polyfunctional epoxy resin or the organic solvent, and to easily react with the polyfunctional epoxy resin.

[0041] Embodiment 2 <Resin sheet> The resin sheet of the present embodiment contains the epoxy resin composition of embodiment 1. For example, it may be a sheet of the epoxy resin composition of embodiment 1. In the present embodiment, the resin sheet refers to a sheet-like epoxy resin composition that is not completely cured.

[0042] <Method of manufacturing resin sheet> The resin sheet of the present embodiment can be produced by applying the epoxy resin composition described in the first embodiment to a substrate.

[0043] For example, the epoxy resin composition is applied to a substrate that has been subjected to a release treatment using, for example, a doctor blade, a roll coater, a comma coater, a die coater, or the like.

[0044] The substrate is not particularly limited, and examples thereof include a resin sheet such as polyethylene terephthalate (PET) and a metal sheet such as copper foil.

[0045] The applied epoxy resin composition may be dried as necessary, and the drying temperature and time may be appropriately set depending on the type of organic solvent used.

[0046] The resin sheet obtained by drying may be pressurized. Voids may remain in the resin sheet, which reduces the thermal conductivity and insulating properties. Therefore, by applying pressure, it is possible to suppress the remaining voids in the resin sheet.

[0047] The conditions of pressure, temperature, time, etc. during pressurization may be appropriately set depending on the polyfunctional epoxy resin and amino compound used. For example, the pressure may be 0.1 to 40 MPa. If the pressure is too low, voids may not be sufficiently removed, and if the pressure is too high, the epoxy resin composition may flow out. The temperature may be 40 to 250°C, and the time may be 1 minute to 10 hours.

[0048] The resin sheet of this embodiment may be manufactured as follows. That is, the manufacturing method of the thermally conductive sheet of this embodiment may include a step of mixing a polyfunctional epoxy resin, an amino compound, etc., with an organic solvent to form a slurry (slurry formation step), a step of applying the slurry to a substrate (application step), and a step of removing the organic solvent in the slurry by heat drying (heat drying step). The heat drying is preferably performed at a temperature equal to or higher than the volatilization temperature of the organic solvent. Each step will be described below.

[0049] (Slurry formation process) In this step, for example, a multifunctional epoxy resin, an amino compound, etc. are mixed using an organic solvent, and an inorganic filler is added as necessary to form a slurry. The mixing method is as described in the first embodiment.

[0050] (Coating process) In this step, the slurry can be applied to, for example, a release-treated substrate. The application method and substrate are as described above.

[0051] (heat drying process) In this step, the organic solvent in the slurry is removed by heat drying to obtain a resin sheet. Heat drying is preferably performed at a temperature equal to or higher than the volatilization temperature of the organic solvent. By performing heat drying in such a temperature range, the organic solvent can be efficiently removed. Here, the volatilization temperature of the organic solvent is defined as the temperature at which the weight of the slurry begins to decrease by thermogravimetry. The temperature and time in this step may be appropriately set depending on the types of polyfunctional epoxy resin, amino compound, organic solvent, etc. used.

[0052] (Crushing process) The method for producing a resin sheet according to the present embodiment may include a pulverizing step of pulverizing the amino compound before the slurry forming step. The pulverizing method is as described in the first embodiment.

[0053] (Pressure process) The method for producing a resin sheet according to the present embodiment may further include a pressurizing step after the heat drying step. The conditions for this step are as described above.

[0054] Embodiment 3 <Cured resin> The cured resin product of the present embodiment is obtained by curing the epoxy resin composition of the first embodiment or the resin sheet of the second embodiment.

[0055] <Method of manufacturing cured resin> The cured resin of this embodiment is obtained by heating the epoxy resin composition of embodiment 1 or the resin sheet of embodiment 2. However, from the viewpoint of suppressing deterioration of the substrate and the cured resin, it is preferable to heat at 300°C or less. When curing the resin sheet, pressure treatment may be performed simultaneously with heating. Furthermore, this pressure treatment may be performed under vacuum. Voids may remain in the cured resin, which reduces the thermal conductivity and insulation. Therefore, the voids in the cured resin can be removed by performing vacuum degassing treatment or pressure treatment.

[0056] The conditions of the pressure treatment, such as pressure, temperature and time, may be appropriately set depending on the polyfunctional epoxy resin and amino compound used. For example, the pressure may be 0.1 to 40 MPa. If the pressure is too low, the voids may not be sufficiently removed, and if the pressure is too high, the epoxy resin composition may flow out. The temperature may be 40 to 300°C, and the time may be 1 minute to 10 hours.

[0057] The cured resin of the present embodiment can also be obtained by applying the epoxy resin composition of the first embodiment to a substrate and heating the applied composition. The application method and substrate are as described in the second embodiment. Pressurization may be performed simultaneously with heating. The conditions for the pressurization are as described above.

[0058] Embodiment 4 The power module of the present embodiment includes a power semiconductor element mounted on one heat dissipation member, the other heat dissipation member capable of dissipating heat generated by the power semiconductor element to the outside, and the cured resin material according to the third embodiment capable of transferring heat generated by the power semiconductor element from the one heat dissipation member to the other heat dissipation member. The power module of the present embodiment will be described below with reference to FIG. 1.

[0059] FIG. 1 is a schematic cross-sectional view of a power module according to the present embodiment. In FIG. 1, the power module 1 includes a power semiconductor element 4 mounted on a lead frame 3, which is one of the heat dissipation members, a heat sink 5, which is the other of the heat dissipation members, and a cured resin 2 disposed between the lead frame 3 and the heat sink 5. The cured resin 2 is a cured thermally conductive resin. Furthermore, the power semiconductor element 4 and the control semiconductor element 6, and the power semiconductor element 4 and the lead frame 3 are wire-bonded with metal wires 7. Moreover, the lead frame 3 is sealed with a sealing resin 8 except for the end portion and the heat sink 5 except for the portion for external heat dissipation.

[0060] In this power module 1, the epoxy resin cured material of the first embodiment can be used for either or both of the resin cured material 2 and the sealing resin 8 that serve as heat dissipation members. Materials other than these heat dissipation members are not particularly limited, and materials known in the relevant technical field can be used. The power module 1 having such a configuration includes either or both of the resin cured material 2 and the sealing resin 8 that have excellent thermal conductivity and insulation properties, and therefore tends to have excellent heat dissipation properties and insulation properties.

[0061] <Embodiment 5> The motor stator according to the present embodiment includes a stator core made of a magnetic material, a coil formed by winding a wire, and the epoxy resin composition according to the first embodiment or the cured resin according to the third embodiment.

[0062] Fig. 2 is a schematic cross-sectional view of a motor stator according to the present embodiment. In Fig. 2, a cured resin material 10 is interposed between a coil 11 and a stator core 12. The motor stator 9 is manufactured by disposing the insulating cured resin material 10 and the coil 11 in slots provided in the stator core 12, and then fusing the insulating cured resin material 10 to both the coil 11 and the stator core 12 by heat treatment.

[0063] Alternatively, the motor stator according to this embodiment may be obtained by placing a stator core 12 equipped with a coil 11 in a molding die, and pouring or integrally molding the epoxy resin composition 13 described in embodiment 1 into the molding die.

[0064] In this motor stator 9, the resin cured material 10 and / or the epoxy resin composition 13 may be the resin cured material described in the third embodiment or the epoxy resin composition of the first embodiment. The members other than the resin cured material or the epoxy resin composition are not particularly limited, and any member known in the art may be used. A motor stator having such a configuration includes an epoxy resin cured material having excellent thermal conductivity and insulation, and therefore tends to have excellent heat dissipation and insulation properties. EXAMPLES

[0065] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited thereto. In the examples, "parts" refers to parts by mass unless otherwise specified.

[0066] <Example 1> Base agent 1 (polyfunctional aliphatic epoxy resin, polyglycerol polyglycidyl ether, "EX521" manufactured by Nagase ChemteX Corporation), curing agent 1 (diaminobenzidine having a mesogenic skeleton) and polymerizable monomer were prepared, and each was placed in a mortar in the amounts shown in Table 1, pulverized and mixed uniformly to obtain an epoxy resin composition. The obtained epoxy resin composition was heated at a temperature of 160°C for 3 hours and at a temperature of 180°C for 3 hours, respectively, to obtain a cured resin.

[0067] <Examples 2, 3, and 4> An epoxy resin composition and a cured product thereof were obtained in the same manner as in Example 1, except that the amount of Curing Agent 1 was changed to the amount shown in Table 1.

[0068] <Example 5> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 2 (polyfunctional aromatic epoxy resin, "EX313" manufactured by Nagase ChemteX Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0069] <Example 6> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 3 (polyfunctional aromatic epoxy resin, "EX614B" manufactured by Nagase ChemteX Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0070] <Example 7> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 4 (polyfunctional aromatic epoxy resin, "jER604" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0071] <Example 8> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 5 (polyfunctional aromatic epoxy resin, "jER630" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0072] <Example 9> An epoxy resin composition and a cured product thereof were obtained in the same manner as in Example 1, except that curing agent 2 (diaminobenzanilide having a mesogenic skeleton) was used instead of curing agent 1 in Example 1, and the amount of curing agent 2 was set to the amount shown in Table 1.

[0073] <Examples 10 and 11> The main agent 1 and the curing agent 1 were prepared, and the amounts shown in Table 1 were taken in a mortar, crushed, and mixed uniformly. Furthermore, a polymerizable monomer [isobornyl methacrylate (IBOMA)] mixed with a polymerization initiator in advance was mixed in the amount shown in Table 1. As the polymerization initiator, a curing agent 328E (manufactured by Nouryon Co., Ltd.) and a redox initiator of cobalt octylate were used, and 0.2 parts by mass was mixed with 100 parts by mass of the polymerizable monomer to obtain an epoxy resin composite composition. The obtained epoxy resin composition was heated at 80°C for 5 hours to polymerize and cure while suppressing the volatilization of the monomer components, and then heated at 160°C for 3 hours and at 180°C for 3 hours, respectively, to obtain a resin cured product.

[0074] <Example 12> An epoxy resin composite composition and a cured resin were obtained in the same manner as in Example 10, except that no polymerizable monomer was added, and that inorganic filler 1 and inorganic filler 2 were blended as fillers in a ratio of 7:3 by mass, mixed uniformly using a twin-screw Raikai mashine, and blended so that the total volume of the epoxy resin composition became 60 parts by volume to obtain an epoxy resin composite composition.

[0075] <Comparative Examples 1 to 4> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 6 (difunctional bisphenol A type epoxy resin, "jER828US" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0076] <Comparative Example 5> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 7 (a multifunctional phenol novolac type epoxy resin, "jER1032H60" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0077] <Comparative Example 6> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 8 (difunctional aliphatic epoxy resin, "EX810" manufactured by Nagase ChemteX Corporation) was used instead of main agent 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0078] <Comparative Example 7> An epoxy resin composition and a cured product thereof were obtained in the same manner as in Example 1, except that curing agent 3 [diaminodiphenylmethane (DDM)] was used instead of curing agent 1 in Example 1, and the amount of curing agent 3 was changed to the amount shown in Table 1.

[0079] <Comparative Example 8> An epoxy resin composition and a cured product thereof were obtained in the same manner as in Example 1, except that curing agent 4 [diaminodiphenylsulfone (DDS)] was used instead of curing agent 1 in Example 1, and the amount of curing agent 4 was set to the amount shown in Table 1.

[0080] <Comparative Example 9> An epoxy resin composition and its cured product were obtained in the same manner as in Example 1, except that main agent 9 (polyfunctional aliphatic epoxy resin, epoxidized castor oil) was used instead of main agent 1 in Example 1, and the amount of curing agent 1 was changed to the amount shown in Table 1.

[0081] <Comparative Example 10> An epoxy resin composite composition and its cured product were obtained in the same manner as in Example 12, except that in Example 12, main agent 6 (difunctional bisphenol A type epoxy resin, "jER828US" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 1, and the amounts of curing agent 1, inorganic filler 1 and inorganic filler 2 were changed to the amounts shown in Table 1.

[0082] The evaluation was carried out by the following methods.

[0083] <Glass transition temperature (Tg)> The Tg of the cured resin was measured by dynamic mechanical analysis (DMA). The peak top temperature of tan δ in this measurement was taken as Tg and is shown in Table 1. The higher the Tg, the more excellent the heat resistance tends to be.

[0084] <Thermal conductivity> The thermal conductivity of the cured resin in the thickness direction was measured by a laser flash method. The results of the thermal conductivity measurements are shown in Table 1 as a relative value of the thermal conductivity of the cured resin of each Example or Comparative Example (value of [thermal conductivity obtained in the cured resin of each Example or Comparative Example] / [thermal conductivity obtained in the cured resin of Comparative Example 1 or 10]) based on the thermal conductivity obtained in the cured resin of Comparative Example 1 and Comparative Example 10.

[0085] [Table 1]

[0086] [Main ingredient] Base 1: Polyglycerol polyglycidyl ether, "EX521" manufactured by Nagase Chemtex Corporation Base 2: Glycerol polyglycidyl ether, "EX313" manufactured by Nagase Chemtex Corporation Base 3: Sorbitol polyglycidyl ether, "EX614B" manufactured by Nagase Chemtex Corporation Main agent 4: Tetraglycidyldiaminodiphenylmethane, "jER604" manufactured by Mitsubishi Chemical Corporation Main ingredient 5: Triglycidyl paraaminophenol, "jER630" manufactured by Mitsubishi Chemical Corporation Base 6: Bisphenol A type epoxy resin, "jER828US" manufactured by Mitsubishi Chemical Corporation Base 7: Phenol novolac epoxy resin, "jER1032H60" manufactured by Mitsubishi Chemical Corporation Base 8: Ethylene glycol diglycidyl ether, "EX810" manufactured by Nagase Chemtex Corporation Base 9: Epoxidized castor oil

[0087] [Hardening agent] Hardener 1: Diaminobenzidine Hardener 2: Diaminobenzanilide Hardener 3: Diaminodiphenylmethane (DDM) Hardener 4: Diaminodiphenylsulfone (DDS) [Polymerizable Monomer] Isobornyl methacrylate (IBOMA) [Inorganic filler] Inorganic filler 1: Spherical alumina with an average particle size of 48 μm, "DAW-45" manufactured by Denka Co., Ltd. Inorganic filler 2: Spherical alumina with an average particle size of 6 μm, "DAW-05" manufactured by Denka Co., Ltd.

[0088] As shown in Table 1, the epoxy resin cured products of the Examples had excellent thermal conductivity, exhibiting a thermal conductivity that was about 1.3 to 1.7 times that of the benchmark Comparative Example 1. Furthermore, compared to Example 1, in which the active hydrogen in the amino compound was blended in an equivalent amount to the epoxy group, Examples 2 and 3, in which the active hydrogen was 2 to 4 equivalents, had superior thermal conductivity. This is believed to be because, by reducing the blending ratio of the epoxy resin, the network of the epoxy resin bonded to the amino group does not interfere with the arrangement of the mesogen skeleton, improving the packing property.

[0089] In addition, the glass transition temperature (hereinafter also referred to as Tg) of each of the resins shows heat resistance of 100°C or higher, but the Tg of Example 2 is higher than that of Example 1, and it is presumed that the movement of molecular chains is suppressed by the dense packing structure. Similarly to Examples 1 to 3, Examples 5 and 6, which use a multifunctional aliphatic epoxy resin, also produce cured resin products with high thermal conductivity and high heat resistance.

[0090] In Example 4, in which the equivalent was set to 0.5, the thermal conductivity was superior to that of Comparative Example 1, but was lower than those of Examples 1 to 3, and the Tg was also low. There are epoxy groups that do not react with the amino groups of the hardener. , it is believed that the sequence has not progressed sufficiently.

[0091] In Examples 7 and 8, a polyfunctional aromatic epoxy resin was used as the base resin, and thus a high Tg was exhibited in addition to a high thermal conductivity.

[0092] Example 9 used an amino compound having a different mesogenic skeleton, and although its thermal conductivity was inferior to that of Examples 1 to 3 having a biphenyl skeleton, it showed a higher thermal conductivity than the comparative examples.

[0093] In Examples 10 and 11, IBOMA, a polymerizable monomer with a high homopolymer Tg, was blended, and the monomer was polymerized during the epoxy resin curing process. This reduced the resin viscosity before curing, while also increasing the thermal conductivity of the cured product compared to Comparative Example 1. Although the Tg was lower than in Example 2, which did not contain a polymerizable monomer, it was still high at 180°C or higher.

[0094] In Example 12, an inorganic filler was blended. The thermal conductivity was 1.4 times higher than that of Comparative Example 10, in which an inorganic filler was blended with a bisphenol A type epoxy resin as the base resin.

[0095] In Comparative Examples 1 to 3, bifunctional bisphenol A type epoxy resin is used as the base resin, but the thermal conductivity does not change even if the equivalent weight is changed, and it is considered that the arrangement of the mesogen skeleton is not sufficiently advanced. In Comparative Example 4, in which the equivalent weight is set to 0.5, the thermal conductivity and Tg are significantly decreased, and it is presumed that a sufficient network structure is not formed.

[0096] Comparative Example 5 shows the results of using a phenol novolac type epoxy resin containing a cyclic structure between the branch point and the mesogen skeleton as the main component. Since it contains a rigid structure, the Tg of the cured product is excellent, but the improvement of thermal conductivity is not expected. This is thought to be because the inclusion of a rigid structure makes it difficult for mesogens to approach each other, and the packing property is not improved.

[0097] The aliphatic difunctional epoxy resin used in Comparative Example 6 had a flexible molecular chain, but did not form a sufficient network structure, and thus had a lower Tg than those of Examples 1-3.

[0098] Although the curing agents used in Comparative Examples 7 and 8 were amino compounds, they did not have a mesogenic skeleton and therefore did not align, resulting in lower thermal conductivity and Tg compared to Examples 1 to 3 which used the same base resin.

[0099] In Comparative Example 9, a polyfunctional aliphatic epoxy resin was used in which the number of atoms from the branch point in the epoxy resin to the mesogen skeleton exceeds 12. It is considered that the flexible molecular chain from the branch point in the epoxy resin to the mesogen skeleton is long, which increases the molecular mobility between the branch point and the mesogen skeleton, making it easy for the arrangement of the mesogen skeleton to dissolve, and thus making it difficult to obtain sufficient thermal conductivity and heat resistance.

[0100] The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0101] 1 power module, 2, 10 cured resin, 3 lead frame, 4 power semiconductor element, 5 heat sink, 6 control semiconductor element, 7 metal wire, 8 sealing resin, 9 motor stator, 11 coil, 12 stator core, 13 epoxy resin composition.

Claims

1. An epoxy resin composition comprising a multifunctional epoxy resin having three or more glycidyl groups and diaminobenzidine, The polyfunctional epoxy resin has a branching point in the molecule, an epoxy resin composition having a structure in which at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms is bonded in a linear chain between the branch point and the epoxy group at the terminal of the glycidyl group.

2. when the polyfunctional epoxy resin and the diaminobenzidine are bonded to each other, a structure is formed in which 12 or less atoms are bonded in a linear chain between the branch points and the mesogenic skeleton of the diaminobenzidine, 2. The epoxy resin composition according to claim 1, wherein the 12 or less atoms are at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms.

3. 2. The epoxy resin composition according to claim 1, wherein the active hydrogen equivalent of the amino group of the diaminobenzidine is 1 to 4 equivalents.

4. 2. The epoxy resin composition according to claim 1, comprising a polymerizable monomer and a polymerization initiator.

5. The epoxy resin composition of claim 1 , further comprising a filler.

6. A resin sheet comprising the epoxy resin composition according to claim 1.

7. A cured resin product comprising the epoxy resin composition according to any one of claims 1 to 5 or the cured resin sheet according to claim 6.

8. A power module comprising the cured resin according to claim 7.

9. A stator for a motor, comprising the epoxy resin composition according to any one of claims 1 to 5.

10. A stator for a motor, comprising the resin cured product described in claim 7.

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