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

Abstract

The present disclosure pertains to an epoxy resin composition comprising: a polyfunctional epoxy resin having at least three glycidyl groups; and an amino compound having a mesogenic skeleton, wherein the polyfunctional epoxy resin has a branching point in a molecule, and has a structure in which at least one atom selected from the group consisting of a carbon atom, a nitrogen atom, and an oxygen atom is linearly bonded between the branching point and an epoxy group at the terminal of a glycidyl group. The present disclosure can provide an epoxy resin composition having high thermal conductivity and heat resistance and also having excellent workability.

Description

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

[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.

[0002] Electrical devices such as motors and power modules are becoming smaller and more powerful. For these smaller and more powerful devices, efficient heat dissipation to the outside is crucial for their performance and lifespan, making thermal management increasingly important. Therefore, insulating materials used in these 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 resins are filled with inorganic fillers, are used as insulating materials. 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 cause 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 Japanese Patent Laid-Open No. 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), the application of a highly thermally conductive resin in which a mesogen skeleton is introduced into an amino compound, which is a curing agent, is investigated.

[0006] Japanese Patent No. 5224366 Japanese Patent Application Laid-Open No. 2021-155586 Japanese Patent No. 5737028

[0007] Cured biphenyl-type epoxy resins having a biphenyl skeleton, as described in Japanese Patent No. 5224366 and Japanese Patent Laid-Open No. 2021-155586, exhibit thermal conductivity approximately 1.5 times higher than that of general-purpose cured bisphenol A-type epoxy resins. However, highly thermally conductive epoxy resins having a mesogenic skeleton have high melting points due to their high crystallinity, are solid at room temperature, and are difficult to dissolve in solvents, making them unsatisfactory from the standpoint of productivity, such as workability. Furthermore, because molding conditions are limited, the alignment of the mesogenic skeleton does not proceed, and thermal conductivity is not sufficiently improved.

[0008] In Japanese Patent No. 5737028, no consideration is given to a resin composition that aims to improve 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.

[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 terminal epoxy group of the glycidyl group.

[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.

[0012] Fig. 1 is a schematic cross-sectional view showing the configuration of a power module according to embodiment 4. Fig. 2 is a schematic cross-sectional view showing the configuration of a stator of a motor according to embodiment 5.

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

[0014] Embodiment 1. <Epoxy Resin Composition> The epoxy resin composition of this embodiment includes a multifunctional epoxy resin containing three or more glycidyl groups and an amino compound having a mesogenic skeleton. The multifunctional epoxy resin has a branch point within the molecule. The multifunctional epoxy resin has a structure (hereinafter also referred to as a linear 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. In particular, a linear structure without a cyclic structure is preferred. The linear structure of the epoxy resin composition allows the molecular structure of the cured product formed by the reaction of the epoxy groups and the active hydrogen of the amino groups to have a flexible linear structure from the branch point, which serves as a constraint point in the epoxy resin, to the mesogenic skeleton. This does not interfere with the alignment of the mesogenic skeleton, allowing for high thermal conductivity. Furthermore, amine-based curing agents, which have a small molecular weight and contain many amino groups in the molecule, are blended in smaller proportions with epoxy resins than acid anhydride-based curing agents or phenol-based curing agents. Therefore, even when a curing agent that is solid at room temperature is blended, the mixed viscosity of the resin as a whole is unlikely to increase, and an epoxy resin with excellent workability can be provided.

[0015] (Polyfunctional 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: The group represented by the formula:

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

[0017] Two or more linear structures may be bonded to a branch point. A molecular structure other than a 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 a branch point. The side chain may be, for example, a hydroxyl group (—OH). Furthermore, a molecular structure other than a linear structure may have a glycidyl group at the end opposite the branch point. Furthermore, when a polyfunctional epoxy resin has two or more branch points, the branch 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 the 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. Furthermore, the linear structure does not have a side chain. In the molecular structure of the cured product obtained by reacting an epoxy resin with an amino compound, the structure from the branch points, which serve as constraint points 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. 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 polyfunctional epoxy resin, two or more glycidyl groups may be bonded to the terminal opposite to the branch point of the linear structure. The glycidyl groups may be bonded directly to the branch point. When the glycidyl groups are bonded directly to the branch point, the linear structure has the formula: -CH ２ A glycidyl ether group may be directly bonded to a branch point. When a glycidyl ether group is directly bonded to a branch point, the linear structure is represented by the formula: —O—CH ２ The molecular structure is represented by -.

[0020] Examples of polyfunctional epoxy resins include polyfunctional aromatic epoxy resins and polyfunctional aliphatic epoxy resins. Examples of polyfunctional aromatic epoxy resins include triglycidyl para-aminophenol, triglycidyl meta-aminophenol, and tetraglycidyl diaminodiphenylmethane. Examples of polyfunctional aliphatic epoxy resins 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 excellent workability even after mixing 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. Furthermore, these epoxy resins may be biomass-derived epoxy resins using plant-derived materials, etc.

[0021] (Amino Compound) The amino compound contained in the epoxy resin composition of the present embodiment contains a mesogenic skeleton in its molecular structure. The amino compound has one or more amino groups. Here, the mesogenic skeleton refers to a skeleton that exhibits 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. In addition, the amino compound contains a primary amino group (-NH ２), or a compound containing 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 the amino compound to be blended should be such that, when one epoxy group in the entire epoxy resin reacts with one active hydrogen equivalent of the amino group, the active hydrogen equivalent of the amino compound per epoxy group is 1 to 4 equivalents, and 2 to 4 equivalents is more preferred in order to improve the alignment of the mesogenic skeleton. If the amount is less than 1 equivalent, there will be epoxy groups that do not react with the curing agent, which may result in low crosslink density and insufficient heat resistance and thermal conductivity. If the amount is more than 4 equivalents, the crosslink density will decrease due to an excess of curing agent, and the binding force on the alignment of the mesogenic skeleton will decrease, causing the alignment to loosen, which may result in insufficient heat resistance and thermal conductivity.

[0023] When the epoxy group of the polyfunctional epoxy resin in the epoxy resin composition is bonded to the amino group of an amino compound containing a mesogenic skeleton, a structure in which 12 or less atoms are bonded in a linear chain between the branch point in the polyfunctional epoxy resin and the mesogenic skeleton in the amino compound is sufficient. The 12 or less atoms are at least one atom selected from the group consisting of carbon atoms, nitrogen atoms, and oxygen atoms. When the number of atoms present between the branch point in the polyfunctional epoxy resin and the mesogenic skeleton in the amino compound is within the above range, the mesogenic skeleton tends to be easily aligned and the aligned mesogenic skeleton tends to be less likely to unravel. 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 increases, the alignment of the mesogenic skeleton tends to be easily unaligned, and sufficient thermal conductivity and heat resistance may not be obtained. The structure in which 12 or less atoms are bonded in a linear chain does not include a branch point. The structure in which 12 or less atoms are bonded in a linear 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 materials, etc.

[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 25°C: <10 mPa s) and a high glass transition temperature (hereinafter also referred to as Tg) (Tg: temperature 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, it is preferably 70% by weight or less relative to the polyfunctional epoxy resin (hereinafter also referred to as the base resin), 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 may be reduced, and heat resistance and thermal conductivity may be impaired.

[0027] (Polymerization initiator) The epoxy resin composition of the present embodiment may contain a polymerization initiator. The polymerization initiator is a compound that can initiate polymerization of polymerizable monomers. Examples of such a polymerization initiator include a radical initiator that generates active radicals, acids, etc. by the action of light or heat, and a redox initiator that generates radicals by utilizing an oxidation-reduction reaction.

[0028] Examples of polymerization initiators include organic peroxides such as hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, peroxycarbonates, peroxyketals, and ketone peroxides, as well as 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, and combinations of ketone peroxides and metal salts, which can efficiently generate radicals even at low temperatures. Examples of hydroperoxides include tert-butyl hydroperoxide and cumene hydroperoxide. Examples of ketone peroxides include methyl ethyl ketone peroxide and cyclohexanone peroxide. Examples of metal salts include cobalt salts such as cobalt naphthenate and cobalt octoate, 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, per 100 parts by mass of the polymerizable monomer, depending on the type of polymerizable monomer used. By setting the content of the polymerization initiator within the above range, the reactions between the main agent and the curing agent and the polymerizable monomer can be sufficiently promoted, which tends to make it easier to provide an epoxy resin composition with 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, an epoxy resin composition having excellent thermal conductivity and insulating properties can be obtained.

[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 preferred from the viewpoint of insulating properties.

[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 filler in the epoxy resin composition, which may reduce the effect of improving thermal conductivity and moldability. When the average particle size of the inorganic filler exceeds 200 μm, the strength of the cured product of the epoxy resin composition tends to decrease, and the inorganic filler is more likely to settle during storage of the epoxy resin composition. Furthermore, when molded into a sheet, surface roughness is more likely to occur, which may reduce flexibility.

[0033] The content of the inorganic filler may be, for example, 20 to 80% by volume, and 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. If the content of the inorganic filler is less than 20% by volume, an epoxy resin composition with sufficient thermal conductivity may not be obtained. If the content of the inorganic filler is more than 80% by volume, it may become difficult to disperse the inorganic filler in the epoxy resin composition, and 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 purposes of improving the wettability of the inorganic filler with 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 types.

[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 inorganic filler.

[0036] (Curing Accelerator) The epoxy resin composition of the present embodiment may contain a curing accelerator (catalyst) as needed. 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. The inclusion of such a polymer tends to facilitate the production of an epoxy resin composition with excellent flexibility. Examples of polymers include polyethylene resin, polypropylene resin, polyolefin resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyester resin, phenoxy resin, and acrylic resin. 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 preferred from the viewpoint of flexibility, such as flexibility and coatability. If the molecular weight of the polymer is less than 10,000, the flexibility of the cured product may be impaired, film-forming properties may be poor when preparing a resin sheet, and the tackiness of the epoxy resin composition may increase, making it difficult to peel from the substrate, or when sheets are stacked, the sheets may stick to each other and be difficult to peel.

[0038] (Organic Solvent) The epoxy resin composition of the present embodiment may contain an organic solvent as needed. The organic solvent is not particularly limited, and a known organic solvent may be appropriately selected depending on the type of epoxy resin, amino compound, inorganic filler, etc. used. Examples of organic solvents 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 organic solvents 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 for power modules and motor stators.

[0040] <Method for Producing Epoxy Resin Composition> The method for producing the epoxy resin composition of this embodiment is not particularly limited and can be carried out according to a known method. For example, an epoxy resin composition can be obtained by mixing a multifunctional epoxy resin and an amino compound at room temperature or under heating. 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, these may be added when mixing the multifunctional epoxy resin and the amino compound. When a monomer is added, it is preferable to mix the monomer at a temperature below the boiling point of the monomer. This mixture may be kneaded using a device such as a mixer, a three-roll mill, a kneader, or a high-speed stirrer. The amino compound may be pulverized using, for example, a mortar and then mixed with the multifunctional epoxy resin. This allows the amino compound to dissolve quickly in the multifunctional epoxy resin or the organic solvent, facilitating reaction with the multifunctional epoxy resin.

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

[0042] <Method for Producing Resin Sheet> The resin sheet of the present embodiment can be produced by applying the epoxy resin composition described in embodiment 1 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 needed, 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 thermal conductivity and insulating properties. Therefore, pressurization can suppress the remaining voids in the resin sheet.

[0047] The conditions for pressurization, 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, 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 also be manufactured as follows. That is, the method for manufacturing the thermally conductive sheet of this embodiment can include a step of mixing a polyfunctional epoxy resin, an amino compound, or the like 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 Step) 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 needed to form a slurry. The mixing method is as described in the first embodiment.

[0050] (Coating Step) In this step, the slurry can be coated onto, for example, a substrate that has been subjected to a release treatment. The coating method and substrate are as described above.

[0051] (Heat drying step) In this step, the organic solvent in the slurry is removed by heat drying, thereby obtaining a resin sheet. Heat drying is preferably carried out at a temperature equal to or higher than the volatilization temperature of the organic solvent. By carrying out heat drying in this 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] (Pulverization Step) The method for producing a resin sheet according to the present embodiment may include a pulverization step of pulverizing the amino compound before the slurry formation step. The pulverization method is as described in the first embodiment.

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

[0054] Embodiment 3 <Cured Resin Product> The cured resin product of this embodiment is obtained by curing the epoxy resin composition of Embodiment 1 or the resin sheet of Embodiment 2.

[0055] <Method for producing cured resin> The cured resin of this embodiment can be 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 may reduce thermal conductivity and insulation. Therefore, voids in the cured resin can be removed by performing vacuum degassing or pressure treatment.

[0056] The pressure, temperature, time, and other conditions for the pressure treatment 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 300°C, and the time may be 1 minute to 10 hours.

[0057] The cured resin product of this embodiment can also be obtained by applying the epoxy resin composition of embodiment 1 to a substrate and heating the applied composition. The application method and substrate are as described in embodiment 2. Pressure treatment may be carried out simultaneously with heating. The conditions for pressure treatment are as described above.

[0058] Embodiment 4. A power module of this embodiment comprises a power semiconductor element mounted on one heat dissipation member, another heat dissipation member capable of dissipating heat generated by the power semiconductor element to the outside, and the cured resin according to embodiment 3 capable of transferring heat generated by the power semiconductor element from one heat dissipation member to the other heat dissipation member. The power module of this 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 heat dissipation member; a heat sink 5, which is the other heat dissipation member; and a cured resin 2 disposed between the lead frame 3 and the heat sink 5. The cured resin 2 is a 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 by metal wires 7. Furthermore, the lead frame 3 is sealed with a sealing resin 8, except for the ends thereof and the portion of the heat sink 5 for external heat dissipation.

[0060] In this power module 1, the cured epoxy resin of embodiment 1 can be used for either or both of the cured resin 2 and the sealing resin 8, which 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 cured resin 2 and the sealing resin 8, which have excellent thermal conductivity and insulating properties, and therefore tends to have excellent heat dissipation properties and insulating properties.

[0061] <Embodiment 5> A motor stator according to this embodiment includes a stator core made of a magnetic material, a coil formed by winding a wire, and the epoxy resin composition described in embodiment 1 or the cured resin material described in embodiment 3.

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

[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 then pouring or integrally molding the epoxy resin composition 13 described in embodiment 1 into the molding die.

[0064] In this motor stator 9, the cured resin material 10 and / or the epoxy resin composition 13 may be the cured resin material described in embodiment 3 or the epoxy resin composition of embodiment 1. The components other than the cured resin material or the epoxy resin composition are not particularly limited, and materials known in the relevant technical field may be used. A motor stator having such a configuration includes a cured epoxy resin material with excellent thermal conductivity and insulating properties, and therefore tends to have excellent heat dissipation properties and insulating properties.

[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" means 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 a polymerizable monomer were prepared, and each was placed in a mortar in the amounts shown in Table 1, pulverized, and uniformly mixed 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 Epoxy resin compositions and cured products 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 a cured product thereof were obtained in the same manner as in Example 1, except that main agent 2 (a polyfunctional aromatic epoxy resin, "EX313" 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.

[0069] Example 6 An epoxy resin composition and a cured product thereof were obtained in the same manner as in Example 1, except that main component 3 (a polyfunctional aromatic epoxy resin, "EX614B" manufactured by Nagase ChemteX Corporation) was used instead of main component 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 a cured product thereof were obtained in the same manner as in Example 1, except that main component 4 (a polyfunctional aromatic epoxy resin, "jER604" manufactured by Mitsubishi Chemical Corporation) was used instead of main component 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 a cured product thereof were obtained in the same manner as in Example 1, except that main agent 5 (a polyfunctional aromatic epoxy resin, "jER630" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 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 blending amount of curing agent 2 was changed to the amounts shown in Table 1.

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

[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 in parts by mass, and mixed uniformly using a twin-screw Raikai mashine, so that the total epoxy resin composition was 60 parts by volume, thereby obtaining an epoxy resin composite composition.

[0075] Comparative Examples 1 to 4 Epoxy resin compositions and cured products thereof 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, 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 a cured product thereof were obtained in the same manner as in Example 1, except that main agent 7 (a polyfunctional phenol novolac epoxy resin, "jER1032H60" manufactured by Mitsubishi Chemical Corporation) was used instead of main agent 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 a cured product thereof 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 blending 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 [diaminodiphenyl sulfone (DDs)] was used instead of curing agent 1 in Example 1, and the blending amount of curing agent 4 was changed to the amount shown in Table 1.

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

[0081] Comparative Example 10 An epoxy resin composite composition and a cured product thereof were obtained in the same manner as in Example 12, 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 12, and the blending 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 method.

[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 material in the thickness direction was measured by a laser flash method. The results of this thermal conductivity measurement are shown in Table 1 as a relative value of the thermal conductivity obtained for the cured resin material of each Example or Comparative Example (the value of [thermal conductivity obtained for the cured resin material of each Example or Comparative Example] / [thermal conductivity obtained for the cured resin material of Comparative Example 1 or 10]) with the thermal conductivity obtained for the cured resin material of Comparative Example 1 and Comparative Example 10 as the standard.

[0085]

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

[0087] [Curing agents] Curing agent 1: diaminobenzidine Curing agent 2: diaminobenzanilide Curing agent 3: diaminodiphenylmethane (DDM) Curing agent 4: diaminodiphenylsulfone (DDS) [Polymerizable monomer] Isobornyl methacrylate (IBOMA) [Inorganic filler] Inorganic filler 1: spherical alumina with an average particle size of 48 μm, manufactured by Denka Co., Ltd. "DAW-45" Inorganic filler 2: spherical alumina with an average particle size of 6 μm, manufactured by Denka Co., Ltd. "DAW-05"

[0088] As shown in Table 1, the cured epoxy resin products of the Examples had excellent thermal conductivity, exhibiting thermal conductivity approximately 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 blended in an equivalent amount to the epoxy group, had superior thermal conductivity. This is thought 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 alignment of the mesogenic skeleton, improving packing properties.

[0089] Furthermore, all of the resins exhibited heat resistance with a glass transition temperature (hereinafter also referred to as Tg) of 100°C or higher, but Example 2 had an improved Tg compared to Example 1, suggesting that the dense packing structure suppresses the movement of molecular chains. As in Examples 1 to 3, Examples 5 and 6, which used a polyfunctional aliphatic epoxy resin, also yielded cured resin products exhibiting high thermal conductivity and high heat resistance.

[0090] In Example 4, in which the equivalent weight was set to 0.5, the thermal conductivity was superior to that of Comparative Example 1, but was lower than that of Examples 1 to 3, and the Tg was also low, which suggests that the amount of curing agent was excessive and alignment did not proceed 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 thermal conductivity.

[0092] In Example 9, an amino compound having a different mesogenic skeleton was used, and although the thermal conductivity was inferior to that of Examples 1 to 3 having a biphenyl skeleton, it exhibited 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. Furthermore, 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 main component.

[0095] In Comparative Examples 1 to 3, a bifunctional bisphenol A epoxy resin was used as the base resin, but the thermal conductivity did not change even when the equivalent weight was changed, suggesting that the alignment of the mesogenic skeleton was not sufficiently advanced. Furthermore, in Comparative Example 4, where the equivalent weight was set to 0.5, the thermal conductivity and Tg were significantly reduced, suggesting that a sufficient network structure was not formed.

[0096] Comparative Example 5 shows the results of using a phenolic novolac epoxy resin containing a cyclic structure between the branching point and the mesogen skeleton as the base resin. Because it contains a rigid structure, the Tg of the cured product is excellent, but improvement in 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, resulting in no improvement in packing properties.

[0097] The aliphatic bifunctional epoxy resin used in Comparative Example 6 had a flexible molecular chain, but did not form a sufficient network structure, resulting in a lower Tg than those of Examples 1 to 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 mesogenic skeleton exceeded 12. It is believed that the flexible molecular chain from the branch point in the epoxy resin to the mesogenic skeleton was long, which increased the molecular mobility between the branch point and the mesogenic skeleton, making it easy for the arrangement of the mesogenic skeleton to unravel, and thus making it impossible to obtain sufficient thermal conductivity and heat resistance.

[0100] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. 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.

[0101] REFERENCE SIGNS LIST 1 Power module, 2, 10 Resin cured product, 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 an amino compound having a mesogenic skeleton, wherein the multifunctional epoxy resin has a branching point in the molecule, and has 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 branching point and the epoxy group at the terminal of the glycidyl group.

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

3. The epoxy resin composition according to claim 1 or 2, wherein the amino compound is an amino compound having a mesogenic skeleton in which amino groups are bonded to two adjacent carbon atoms.

4. The epoxy resin composition according to any one of claims 1 to 3, wherein the active hydrogen equivalent of the amino group of the amino compound is 1 to 4 equivalents.

5. The epoxy resin composition according to any one of claims 1 to 4, comprising a polymerizable monomer and a polymerization initiator.

6. The epoxy resin composition according to any one of claims 1 to 5, which contains a filler.

7. A resin sheet comprising the epoxy resin composition according to any one of claims 1 to 6.

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

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

10. A motor stator comprising the epoxy resin composition according to any one of claims 1 to 6 or the cured resin according to claim 8.

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