Thermosetting epoxy resin composition and cured product

Abstract

The purpose of the present invention is to provide a thermosetting epoxy resin composition which is capable of preventing deterioration of reliability due to long-term storage while improving durability against heat generation and vibration after curing.　A thermosetting epoxy resin composition according to the present disclosure is characterized by: containing an epoxy compound (A), an acid anhydride-based curing agent (B), a curing accelerator (C), a silane coupling agent (D), a defoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) is a resin composition that contains spherical silica and amorphous calcium carbonate, and the content of the spherical silica is 50-90 mass% and the content of the amorphous calcium carbonate is 5-50 mass% with respect to the total amount of the resin composition; and being in liquid state at 25°C.

Description

Thermosetting epoxy resin composition and cured product

[0001] This disclosure relates to a thermosetting epoxy resin composition and a cured product thereof. This application claims priority from Japanese Patent Application No. 2024-128100, filed on August 2, 2024, the contents of which are incorporated herein by reference.

[0002] It has been known that epoxy resins and unsaturated polyester resins are used as insulating materials, sealants, and adhesives in EV motors (rotating electric vehicles). Fillers such as silica fillers have been used in these resins to reduce the difference in linear expansion coefficient between the resin and the EV motor, improving durability against heat generation and vibration during high-speed rotation (see, for example, Patent Documents 1 and 2).

[0003] JP 2020-094092 A JP 2016-191031 A

[0004] However, while the use of a filler can reduce the linear expansion coefficient of the resin composition, there have been problems such as the filler settling during long-term storage, which impairs workability during production, and the resin composition becoming non-uniform, which prevents the desired functions from being exerted and reduces reliability.

[0005] Therefore, an object of the present disclosure is to provide a thermosetting epoxy resin composition that can improve durability against heat generation and vibration after curing, while preventing a decrease in reliability due to long-term storage.

[0006] As a result of extensive research to achieve the above-mentioned object, the inventors of the present disclosure have found that a thermosetting epoxy resin composition that is liquid at 25°C, comprising an epoxy compound (A), an acid anhydride curing agent (B), a curing accelerator (C), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) comprises spherical silica and amorphous calcium carbonate, and wherein the contents of the spherical silica and the amorphous calcium carbonate relative to the total amount of the resin composition are within specific ranges, can improve durability against heat generation and vibration after curing while preventing a decrease in reliability due to long-term storage. The present disclosure relates to a composition that has been completed based on these findings.

[0007] That is, the thermosetting epoxy resin composition of the present disclosure is a resin composition comprising an epoxy compound (A), an acid anhydride curing agent (B), a curing accelerator (C), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) comprises spherical silica and amorphous calcium carbonate, and the content of the spherical silica is 50 to 90 mass% and the content of the amorphous calcium carbonate is 10 to 50 mass% relative to the total amount of the resin composition, and the thermosetting epoxy resin composition is liquid at 25°C.

[0008] The thermosetting epoxy resin composition of the present disclosure is a two-component epoxy resin composition comprising a base agent and a curing agent composition, and it is preferred that the base agent contains the epoxy compound (A), the silane coupling agent (D), the antifoaming agent (E), and the inorganic filler (F), and the curing agent composition contains the acid anhydride curing agent (B), the curing accelerator (C), and the inorganic filler (F).

[0009] It is preferable that the content of the spherical silica in the base agent is 50 to 90% by mass, and the content of the amorphous calcium carbonate is 5 to 50% by mass. By having the above-mentioned composition, it can be easily mixed with the hardener composition.

[0010] In addition, it is preferable that the content of the spherical silica in the curing agent composition is 50 to 90% by mass, and the content of the amorphous calcium carbonate is 5 to 50% by mass. By having the above-mentioned configuration, it can be easily mixed with the main agent.

[0011] The base resin and the curing agent composition are poured into a screw tube so that the liquid height is 50 mm, and after storage at 23° C. for one week, it is preferable that the height of the supernatant liquid layer is 3 mm or less.

[0012] The base resin and curing agent composition are poured into a screw tube so that the liquid height is 50 mm, and after storage at 23° C. for one week, it is preferable that the height of the filler precipitate layer is 2 mm or less.

[0013] The present disclosure also provides a cured product of the above-mentioned thermosetting epoxy resin composition.

[0014] The curing agent is preferably used as an insulating material.

[0015] The curing agent is preferably used as an adhesive.

[0016] The curing agent is preferably used as a sealant.

[0017] The thermosetting epoxy resin composition of the present disclosure can improve durability against heat generation and vibration after curing, while preventing a decrease in reliability due to long-term storage.

[0018] [Thermosetting Epoxy Resin Composition] A thermosetting epoxy resin composition according to an embodiment of the present disclosure (hereinafter, may be referred to as the "thermosetting epoxy resin composition of the present disclosure") is a resin composition comprising an epoxy compound (A), an acid anhydride curing agent (B), a curing accelerator (C), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) comprises spherical silica and amorphous calcium carbonate, and the content of the spherical silica is 50 to 90 mass % and the content of the amorphous calcium carbonate is 5 to 50 mass % relative to the total amount of the resin composition, and the thermosetting epoxy resin composition is liquid at 25°C.

[0019] The thermosetting epoxy resin composition of the present disclosure includes spherical silica as the inorganic filler (F), and the content of the spherical silica is 50 to 90 mass% relative to the total amount of the resin composition, thereby reducing the linear expansion coefficient and improving durability. Furthermore, the thermosetting epoxy resin composition includes the acid anhydride curing agent (B), the curing accelerator (C), the silane coupling agent (D), the antifoaming agent (E), and amorphous calcium carbonate as the inorganic filler (F), and the content of the amorphous calcium carbonate is 5 to 50 mass% relative to the total amount of the resin composition, and the inorganic filler (F) is liquid at 25°C, thereby preventing a decrease in reliability due to long-term storage.

[0020] The thermosetting epoxy resin composition of the present disclosure is liquid at 25°C, and therefore exhibits excellent workability, such as impregnation of the material to be impregnated and castability. Furthermore, the viscosity of the thermosetting epoxy resin composition of the present disclosure at 25°C is preferably 30,000 mPa·s or less, more preferably 25,000 mPa·s or less, and even more preferably 15,000 mPa·s or less. A viscosity of 30,000 mPa·s or less improves impregnation and castability, and reduces the likelihood of defects in the cured product due to poor casting. The lower limit may be 100 mPa·s or more. The viscosity of the thermosetting epoxy resin composition of the present disclosure at 25°C can be measured, for example, using an E-type viscometer (trade name "TV-35," manufactured by Toki Sangyo Co., Ltd., rotor: standard 3°×R14, rotation speed: 10 rpm).

[0021] (Epoxy Compound (A)) The epoxy compound (A) is a compound having one or more epoxy groups (oxirane rings). Examples of the epoxy compound (A) include alicyclic epoxy compounds (alicyclic epoxy resins), aromatic epoxy compounds (aromatic epoxy resins), and aliphatic epoxy compounds (aliphatic epoxy resins). Among these, alicyclic epoxy compounds and aromatic epoxy compounds are preferred as the epoxy compound (A). Only one type of epoxy compound (A) may be used, or two or more types may be used.

[0022] The alicyclic epoxy compound may be any known or commonly used alicyclic epoxy compound, and is not particularly limited. Examples include: (I) a compound having an epoxy group composed of two adjacent carbon atoms and an oxygen atom that constitute an alicyclic ring in the molecule (referred to as an "alicyclic epoxy group"); (II) a compound in which an epoxy group is directly bonded to an alicyclic ring via a single bond; and (III) a compound having an alicyclic ring and a glycidyl ether group in the molecule (glycidyl ether type epoxy compound).

[0023] The above (I) compound having an alicyclic epoxy group in the molecule includes a compound having a cyclohexene oxide group, for example, a compound represented by the following formula (i).

[0024] In the above formula (i), Y represents a single bond or a linking group (a divalent group having one or more atoms). Examples of the linking group include a divalent hydrocarbon group, an alkenylene group in which some or all of the carbon-carbon double bonds have been epoxidized, a carbonyl group, an ether bond, an ester bond, a carbonate group, an amide group, and groups in which multiple of these are linked together. Note that a substituent such as an alkyl group may be bonded to one or more of the carbon atoms constituting the cyclohexane ring (cyclohexene oxide group) in formula (i).

[0025] Examples of the divalent hydrocarbon group include linear or branched alkylene groups and divalent alicyclic hydrocarbon groups having 1 to 18 carbon atoms. Examples of the linear or branched alkylene groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene. Examples of the divalent alicyclic hydrocarbon group include divalent cycloalkylene groups (including cycloalkylidene groups) such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene.

[0026] Examples of the alkenylene group in the alkenylene group in which some or all of the carbon-carbon double bonds have been epoxidized (sometimes referred to as an "epoxidized alkenylene group") include linear or branched alkenylene groups having 2 to 8 carbon atoms, such as vinylene, propenylene, 1-butenylene, 2-butenylene, butadienylene, pentenylene, hexenylene, heptenylene, and octenylene. In particular, the epoxidized alkenylene group is preferably an alkenylene group in which all of the carbon-carbon double bonds have been epoxidized, and more preferably an alkenylene group having 2 to 4 carbon atoms in which all of the carbon-carbon double bonds have been epoxidized.

[0027] Representative examples of the alicyclic epoxy compound represented by formula (i) above include (3,4,3',4'-diepoxy)bicyclohexyl and compounds represented by formulas (i-1) to (i-10) below. In formulas (i-5) and (i-7) below, l and m each represent an integer of 1 to 30. R' in formula (i-5) below is an alkylene group having 1 to 8 carbon atoms, and among these, a linear or branched alkylene group having 1 to 3 carbon atoms, such as a methylene group, an ethylene group, a propylene group, or an isopropylene group, is preferred. In formulas (i-9) and (i-10) below, n1 to n6 each represent an integer of 1 to 30. Further, other examples of the alicyclic epoxy compound represented by the above formula (i) include 2,2-bis(3,4-epoxycyclohexyl)propane, 1,2-bis(3,4-epoxycyclohexan-1-yl)ethane, 1,2-epoxy-1,2-bis(3,4-epoxycyclohexan-1-yl)ethane, and bis(3,4-epoxycyclohexylmethyl)ether.

[0028] Examples of the compound (II) in which an epoxy group is directly bonded to an alicyclic ring via a single bond include compounds represented by the following formula (ii):

[0029] In formula (ii), R" is a group (p-valent organic group) obtained by removing p hydroxyl groups (-OH) from the structural formula of a p-valent alcohol, and p and n each represent a natural number. p Examples of the compound represented by formula (ii) include polyhydric alcohols (e.g., alcohols having 1 to 15 carbon atoms) such as 2,2-bis(hydroxymethyl)-1-butanol. p is preferably 1 to 6, and n is preferably 1 to 30. When p is 2 or more, the n's in the groups in ( ) (outer parentheses) may be the same or different. Specific examples of the compound represented by formula (ii) include 1,2-epoxy-4-(2-oxiranyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol [for example, trade name "EHPE3150" (manufactured by Daicel Corporation)].

[0030] Examples of the compound (III) having an alicyclic ring and a glycidyl ether group in the molecule include glycidyl ethers of alicyclic alcohols (particularly alicyclic polyhydric alcohols). More specifically, examples include hydrogenated compounds of bisphenol A epoxy compounds such as 2,2-bis[4-(2,3-epoxypropoxy)cyclohexyl]propane and 2,2-bis[3,5-dimethyl-4-(2,3-epoxypropoxy)cyclohexyl]propane (hydrogenated bisphenol A epoxy compounds); bis[o,o-(2,3-epoxypropoxy)cyclohexyl]methane, bis[o,p-(2,3-epoxypropoxy)cyclohexyl]methane, bis[p,p-(2,3-epoxypropoxy)cyclohexyl]methane, bis[3,5-dimethyl-4-

[0033] Examples of the epoxy compounds include hydrogenated compounds of bisphenol F type epoxy compounds such as [(2,3-epoxypropoxy)cyclohexyl]methane (hydrogenated bisphenol F type epoxy compounds); hydrogenated biphenol type epoxy compounds; hydrogenated phenol novolac type epoxy compounds; hydrogenated cresol novolac type epoxy compounds; hydrogenated cresol novolac type epoxy compounds of bisphenol A; hydrogenated naphthalene type epoxy compounds; hydrogenated epoxy compounds of epoxy compounds obtained from trisphenolmethane; and hydrogenated epoxy compounds of other epoxy compounds having an aromatic ring.

[0031] Examples of the aromatic epoxy compounds include epibis-type glycidyl ether epoxy resins (bisphenol-type epoxy compounds such as bisphenol A-type epoxy compounds and bisphenol F-type epoxy compounds) obtained by a condensation reaction of bisphenols [e.g., bisphenol A, bisphenol F, bisphenol S, fluorene bisphenol, etc.] with epihalohydrin; high-molecular-weight epibis-type glycidyl ether epoxy resins obtained by further addition reaction of these epibis-type glycidyl ether epoxy resins with the above-mentioned bisphenols; phenols [e.g., phenol, cresol, xylenol, resol, Examples of suitable epoxy resins include novolak alkyl type glycidyl ether epoxy resins obtained by condensing polyhydric alcohols obtained by condensing polyhydric alcohols [e.g., rusine, catechol, bisphenol A, bisphenol F, bisphenol S, etc.] with aldehydes [e.g., formaldehyde, acetaldehyde, benzaldehyde, hydroxybenzaldehyde, salicylaldehyde, etc.] with epihalohydrin; and epoxy compounds in which two phenol skeletons are bonded to the 9-position of a fluorene ring and a glycidyl group is bonded, directly or via an alkyleneoxy group, to the oxygen atom obtained by removing the hydrogen atom from the hydroxy group of each of the phenol skeletons.

[0032] Examples of the aliphatic epoxy compound include glycidyl ethers of q-valent alcohols (q is a natural number) that do not have a cyclic structure; glycidyl esters of monovalent or polyvalent carboxylic acids [for example, acetic acid, propionic acid, butyric acid, stearic acid, adipic acid, sebacic acid, maleic acid, itaconic acid, etc.]; epoxidized products of fats and oils having double bonds, such as epoxidized linseed oil, epoxidized soybean oil, and epoxidized castor oil; and epoxidized products of polyolefins (including polyalkadiene), such as epoxidized polybutadiene. Examples of the q-valent alcohol not having a cyclic structure include monohydric alcohols such as methanol, ethanol, 1-propyl alcohol, isopropyl alcohol, and 1-butanol; dihydric alcohols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, and polypropylene glycol; and trihydric or higher polyhydric alcohols such as glycerin, diglycerin, erythritol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, and sorbitol. The q-valent alcohol may be a polyether polyol, a polyester polyol, a polycarbonate polyol, a polyolefin polyol, or the like.

[0033] The content of the epoxy compound (A) is preferably 3 to 30 mass%, more preferably 5 to 25 mass%, and even more preferably 10 to 20 mass%, relative to the total amount (100 mass%) of the thermosetting epoxy resin composition of the present disclosure.

[0034] The thermosetting epoxy resin composition of the present disclosure may also contain a curable compound other than the epoxy compound (A). Examples of the curable compound include a compound that is more reactive with the acid anhydride curing agent (B). The content of the epoxy compound (A) is preferably 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass, based on the total amount (100% by mass) of the curable compounds.

[0035] (Acid anhydride curing agent (B)) The acid anhydride curing agent (B) is a compound that reacts with the epoxy compound (A) to cure the epoxy compound. In addition, by using the acid anhydride curing agent (B) as a curing agent for the epoxy compound (A), the viscosity of the thermosetting epoxy resin composition of the present disclosure can be reduced. Only one type of acid anhydride curing agent (B) may be used, or two or more types may be used.

[0036] As the acid anhydride curing agent (B), known or conventional acid anhydride curing agents can be used, and are not particularly limited. Examples thereof include methyltetrahydrophthalic anhydride (4-methyltetrahydrophthalic anhydride, 3-methyltetrahydrophthalic anhydride, etc.), methylhexahydrophthalic anhydride (4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, etc.), dodecenyl succinic anhydride, methyl-endo-methylenetetrahydrophthalic anhydride, phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, Examples of suitable carboxylic acid anhydrides include phthalic acid, methylcyclohexene dicarboxylic anhydride, pyromellitic anhydride, trimellitic anhydride, benzophenone tetracarboxylic anhydride, nadic anhydride, methyl nadic anhydride, hydrogenated methyl nadic anhydride, 4-(4-methyl-3-pentenyl)tetrahydrophthalic anhydride, succinic anhydride, adipic anhydride, sebacic anhydride, dodecanedioic anhydride, methylcyclohexene tetracarboxylic anhydride, vinyl ether-maleic anhydride copolymer, and alkylstyrene-maleic anhydride copolymer.

[0037] Among the acid anhydride curing agents (B), from the viewpoint of handleability, acid anhydrides that are liquid at 25° C., such as methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, dodecenylsuccinic anhydride, and methyl-endomethylenetetrahydrophthalic anhydride, are preferred. On the other hand, for acid anhydrides that are solid at 25° C., for example, by dissolving the acid anhydride in an acid anhydride that is liquid at 25° C. to form a liquid mixture, the handleability of the curing agent in the thermosetting epoxy resin composition of the present disclosure tends to be improved.

[0038] The content of the acid anhydride curing agent (B) in the thermosetting epoxy resin composition of the present disclosure is not particularly limited, but is preferably 50 to 200 parts by mass, more preferably 80 to 150 parts by mass, relative to the total amount (100 parts by mass) of the epoxy compound (A). More specifically, it is preferably used in a proportion of 0.5 to 1.5 equivalents, more preferably 0.8 to 1.1 equivalents, and even more preferably 0.9 or more and less than 1.0 equivalents per equivalent of epoxy groups in the epoxy compound (A). When the content of the acid anhydride curing agent (B) is 50 parts by mass or more, curing can proceed sufficiently and the viscosity tends to be lowered, further improving handleability. When the content of the acid anhydride curing agent (B) is 200 parts by mass or less, coloration tends to be suppressed, and a cured product with excellent hue tends to be obtained.

[0039] The thermosetting epoxy resin composition of the present disclosure may also contain a curing agent other than the acid anhydride curing agent (B). The content of the acid anhydride curing agent (B) is preferably 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass, based on the total amount (100% by mass) of the curing agents contained in the thermosetting epoxy resin composition of the present disclosure.

[0040] (Curing Accelerator (C)) The curing accelerator (C) is a compound that has the function of accelerating the reaction rate when the epoxy compound (A) reacts with the acid anhydride curing agent (B). As the curing accelerator (C), one type may be used alone, or two or more types may be used.

[0041] As the curing accelerator (C), known or conventional curing accelerators can be used, but amine-based curing accelerators are particularly preferred. By using the amine-based curing accelerator, a cured product with excellent heat resistance can be formed. Examples of amine-based curing accelerators include imidazole-based curing accelerators and strongly basic compound-based curing accelerators.

[0042] As the imidazole curing accelerator, known or conventional imidazole curing accelerators can be used, and examples thereof include, but are not limited to, 1-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-(2-hydroxypropyl)imidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimid ... Examples of imidazole compounds include decyl imidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2-methylimidazolium isocyanurate, 2-phenylimidazolium isocyanurate, a compound (1:1) of 6-[2-(2-methyl-1H-imidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine and 1,3,5-triazinane-2,4,6-trione, 2,4-diamino-6-[2-ethyl-4-methylimidazolyl-(1)]-ethyl-s-triazine, and 2,4-diamino-6-(2'-methylimidazolyl)ethyl-1,3,5-triazine.

[0043] The imidazole curing accelerator may also be a derivative of an imidazole compound, such as an amine adduct of the imidazole compound (e.g., an amine adduct with an epoxy compound). Examples of the epoxy compound include those exemplified and explained as the epoxy compound (A). Only one type of the epoxy compound may be used, or two or more types may be used.

[0044] Among these, from the viewpoint of further improving the heat resistance of the cured product, the imidazole curing accelerator preferably contains at least 1-methylimidazole, 2-methylimidazole, 1-(2-hydroxypropyl)imidazole, a compound (1:1) of 6-[2-(2-methyl-1H-imidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine and 1,3,5-triazinane-2,4,6-trione, 2,4-diamino-6-(2'-methylimidazolyl)ethyl-1,3,5-triazine, or an amine adduct thereof (particularly, an amine adduct with an epoxy compound, more preferably an amine adduct with a bisphenol-type epoxy compound). Among these, from the viewpoint of superior long-term stability (shelf life) when mixed with the acid anhydride curing agent (B), 2-methylimidazole, 1-(2-hydroxypropyl)imidazole, a compound (1:1) of 6-[2-(2-methyl-1H-imidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine and 1,3,5-triazinane-2,4,6-trione, 2,4-diamino-6-(2'-methylimidazolyl)ethyl-1,3,5-triazine, or amine adducts of these epoxy compounds are preferred.

[0045] The imidazole curing accelerator may be incorporated as a latent curing accelerator. Use of a latent curing accelerator can improve the long-term stability of the thermosetting epoxy resin composition of the present disclosure. Examples of latent curing accelerators include imidazole curing accelerators that have been microencapsulated (microencapsulated latent curing agents).

[0046] The microcapsule-type latent curing agent contains, for example, a core and a shell covering the surface of the core, the core containing an imidazole-based curing accelerator, and the shell containing an organic polymer and / or an inorganic compound. Note that when the shell is an inorganic compound, the microcapsule-type latent curing agent does not fall under the category of inorganic filler (F).

[0047] The content of the shell is preferably 0.01 to 100 parts by mass, more preferably 0.1 to 80 parts by mass, even more preferably 1 to 60 parts by mass, and particularly preferably 5 to 50 parts by mass, per 100 parts by mass of the core. When the content of the shell is within the above range, both excellent long-term stability and curability can be achieved.

[0048] Examples of the organic polymer include natural polymers such as cellulose, synthetic resins, etc. Among these, synthetic resins are preferred from the viewpoints of long-term stability, ease of destruction of the shell during curing, and uniformity of the physical properties of the cured product.

[0049] Examples of the synthetic resin include epoxy resin, acrylic resin, polyester resin, phenolic resin, polyethylene resin, nylon resin, polystyrene resin, urea resin, urethane resin, and mixtures and copolymers thereof.

[0050] Examples of the inorganic compound include boron compounds such as boron oxide and boric acid esters, silicon dioxide, calcium oxide, etc. Among these, boron oxide is preferred from the viewpoint of superior film stability and ease of destruction when heated.

[0051] The strongly basic compound-based curing accelerator is preferably a curing accelerator containing a strongly basic compound having a pKa of 10 or more, more preferably a pKa of 11 or more, even more preferably a pKa of 11 to 16, and particularly preferably a pKa of 11 to 14. The pKa is the pKa in water. The strongly basic compound is preferably a nitrogen-containing cyclic compound having the above pKa. Specific examples of the strongly basic compound include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) and salts thereof (e.g., phenol salt, octylate salt, 2-ethylhexanoate, p-toluenesulfonate, formate salt, tetraphenylborate salt, etc.), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN) and salts thereof (e.g., phenol salt, octylate salt, p-toluenesulfonate, formate salt, tetraphenylborate salt, etc.), tetramethylguanidine (TMG) and salts thereof, 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,5,7-triazabicyclo[4.4.0]decene-5 (TBD) and salts thereof, and 7-methyl-1,5,7-triazabicyclo[4.4.0]decene-5 (MTBD) and salts thereof. Among these, DBU and its salts are more preferred as the strongly basic compound.

[0052] The content of the curing accelerator (C) in the curable epoxy composition is not particularly limited, but is preferably 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and even more preferably 0.1 to 1% by mass, relative to the total amount (100% by mass) of the curable compounds. When the content of the curing accelerator (C) is 0.01% by mass or more, heat resistance tends to be further improved and a more efficient curing acceleration effect tends to be obtained. When the content of the curing accelerator (C) is 5% by mass or less, coloration tends to be suppressed and a cured product with excellent hue tends to be obtained. Furthermore, the proportion of the amine-based curing accelerator in the curing accelerator (C) is preferably 50% by mass or more, and may be 60% by mass or more, 75% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more, relative to the total amount (100% by mass) of the curing accelerator.

[0053] (Silane Coupling Agent (D)) The thermosetting epoxy resin composition of the present disclosure contains a silane coupling agent (D) in order to impart excellent properties such as adhesion, weather resistance, heat resistance, etc. to the cured product. Only one type of silane coupling agent (D) may be used, or two or more types may be used.

[0054] Examples of the silane coupling agent (D) include 3-trimethoxysilylpropyl (meth)acrylate, 3-triethoxysilylpropyl (meth)acrylate, 3-dimethoxymethylsilylpropyl (meth)acrylate, 3-diethoxymethylsilylpropyl (meth)acrylate, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, etc. When a silane coupling agent whose functional group is a (meth)acryloyloxy group is used, a small amount of a radical polymerization initiator may be added.

[0055] The content of the silane coupling agent (D) is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 4 parts by mass, relative to the total amount (100 parts by mass) of the epoxy compound (A).

[0056] (Antifoaming Agent (E)) The thermosetting epoxy resin composition of the present disclosure contains an antifoaming agent (E) to prevent the generation and residual bubbles and improve durability after curing. As the antifoaming agent (E), one type may be used alone, or two or more types may be used.

[0057] Examples of the antifoaming agent (E) include oxyalkylene-based antifoaming agents, silicone-based antifoaming agents, alcohol-based antifoaming agents, mineral oil-based antifoaming agents, fatty acid-based antifoaming agents, and fatty acid ester-based antifoaming agents.

[0058] Examples of the oxyalkylene antifoaming agent include polyoxyalkylenes such as (poly)oxyethylene (poly)oxypropylene adducts; (poly)oxyalkylene alkyl ethers such as diethylene glycol heptyl ether, polyoxyethylene oleyl ether, polyoxypropylene butyl ether, polyoxyethylene polyoxypropylene 2-ethylhexyl ether, and oxyethylene oxypropylene adducts to higher alcohols having 8 or more carbon atoms or secondary alcohols having 12 to 14 carbon atoms; (poly)oxyalkylene (alkyl)aryl ethers such as polyoxypropylene phenyl ether and polyoxyethylene nonylphenyl ether; alkylenes adducts to acetylene alcohols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,5-dimethyl-3-hexyne-2,5-diol, and 3-methyl-1-butyn-3-ol. (poly)oxyalkylene fatty acid esters such as diethylene glycol oleate, diethylene glycol laurate, and ethylene glycol distearate; (poly)oxyalkylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan trioleate; (poly)oxyalkylene alkyl (aryl) ether sulfate salts such as polyoxypropylene methyl ether sodium sulfate and polyoxyethylene dodecylphenol ether sodium sulfate; (poly)oxyalkylene alkyl phosphates such as (poly)oxyethylene stearyl phosphate; (poly)oxyalkylene alkyl amines such as polyoxyethylene laurylamine; and polyoxyalkylene amides.

[0059] Examples of the silicone-based defoaming agents include dimethylsilicone oil, silicone paste, silicone emulsion, modified polysiloxane, fluorosilicone oil, and mixtures thereof with silicic acid. Examples of the alcohol-based defoaming agents include octyl alcohol, 2-ethylhexyl alcohol, hexadecyl alcohol, acetylene alcohol, glycols, and the like. Examples of the mineral oil-based defoaming agents include kerosene and liquid paraffin. Examples of the fatty acid-based defoaming agents include oleic acid, stearic acid, and alkylene oxide adducts thereof. Examples of the fatty acid ester-based defoaming agents include glycerin monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, and natural wax. Among these, a mixture of dimethylsilicone oil and silicic acid is preferably used because it is effective against each component of the present disclosure.

[0060] The content of the antifoaming agent (E) is preferably 0.001 to 1 mass%, and more preferably 0.01 to 0.1 mass%, relative to the total amount (100 mass%) of the thermosetting epoxy resin composition of the present disclosure. When the content of the antifoaming agent (E) is 0.001 mass% or more, the generation and residual bubbles in the thermosetting epoxy resin composition of the present disclosure are prevented, and durability after curing is likely to be improved.

[0061] (Inorganic Filler (F)) The inorganic filler (F) includes spherical silica and amorphous calcium carbonate. The thermosetting epoxy resin composition of the present disclosure includes spherical silica as the inorganic filler (F), which reduces the linear expansion coefficient upon curing and provides durability. Furthermore, the inclusion of amorphous calcium carbonate disperses the spherical silica, providing excellent reliability even after long-term storage. In the present disclosure, "spherical" particles refer to particles including true spheres, nearly spherical particles, and spheroids. They also include non-spherical particles whose corners have been rounded by crushing, polishing, or the like. Furthermore, "irregular" particles refer to particles that do not have a uniform shape, such as fragments, plates, scales, or needles. The spherical silica may be used alone or in combination of two or more types, and the amorphous calcium carbonate may be used alone or in combination of two or more types. Furthermore, inorganic fillers other than spherical silica and amorphous calcium carbonate may be used as the inorganic filler (F).

[0062] The spherical silica is not particularly limited, and may be any known or commonly used silica, such as fused silica, crystalline silica, high-purity synthetic silica, etc. The spherical silica may also be one that has been subjected to a known or commonly used surface treatment, such as a surface treatment with a metal oxide, a silane coupling agent, a titanium coupling agent, an organic acid, a polyol, or a silicone.

[0063] The spherical silica may be hydrophilic or hydrophobic. Hydrophobic silica is preferred because it inhibits sedimentation of the solid components of the thermosetting epoxy resin composition of the present disclosure, thereby improving dispersibility, and also imparts thixotropy to the curable epoxy composition, thereby improving workability such as impregnation and casting properties.

[0064] Above-mentioned hydrophobic silica is the silica that hydrophilic silica is subjected to hydrophobic treatment.The treating agent used for hydrophobic treatment can be, for example, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, hexamethyldisilazane, methyltrialkoxysilane, dimethyldialkoxysilane, trimethylalkoxysilane, ethyltrichlorosilane, propyltrichlorosilane, hexyltrichlorosilane, long-chain alkyltrichlorosilane, ethyltrialkoxysilane, propyltrialkoxysilane, hexyltrialkoxysilane, long-chain alkyltrialkoxysilane, methacrylsilane, fluoroalkylsilane, perfluoroalkylsilane and other organic silyl compounds; dimethylpolysiloxane (silicone oil), methylphenylpolysiloxane, methylhydrogenpolysiloxane, amino-modified silicone and other polysiloxanes and other silicone compounds.Among them, the hydrophobic treatment by polysiloxane is preferred. The hydrophobic treatment can be carried out using a known method, such as a liquid phase method, a gas phase method, an autoclave method, or the like.

[0065] The median particle size of the spherical silica is not particularly limited, but from the viewpoint of improving the low linear expansion, strength, and crack resistance of the cured product, it is preferably 0.1 to 100 μm, more preferably 1 to 50 μm. Furthermore, from the viewpoint of reducing the viscosity and improving the flowability of the thermosetting epoxy resin composition of the present disclosure, it is preferable to use a combination of spherical silica particles with different median particle sizes. Specifically, it is preferable to use a combination of large-particle-size spherical silica particles with a median particle size of 10 to 100 μm and small-particle-size spherical silica particles with a median particle size of 0.1 to 10 μm. The median particle size refers to the particle size (median diameter) at 50% of the integrated value in the particle size distribution measured by laser diffraction / scattering.

[0066] The content of the spherical silica is 50 to 90% by mass, preferably 55 to 80% by mass, and more preferably 57 to 70% by mass, based on the total amount (100% by mass) of the thermosetting epoxy resin composition of the present disclosure. By having a spherical silica content of 50% by mass or more, the linear expansion coefficient can be reduced and durability can be improved. Furthermore, by having a content of 90% by mass or less, precipitation of the spherical silica can be suppressed and reliability can be improved.

[0067] The amorphous calcium carbonate is preferably heavy calcium carbonate, and the median particle size of the amorphous calcium carbonate is preferably 0.1 to 50 μm, more preferably 1 to 30 μm.

[0068] The content of the amorphous calcium carbonate is 5 to 50% by mass, preferably 12 to 40% by mass, and more preferably 14 to 30% by mass, relative to the total amount (100% by mass) of the thermosetting epoxy resin composition of the present disclosure. By ensuring that the content of amorphous calcium carbonate is 5% by mass or more, precipitation of spherical silica can be suppressed, improving reliability. Furthermore, by ensuring that the content is 50% by mass or less, the linear expansion coefficient can be reduced, improving durability.

[0069] The content of the amorphous calcium carbonate is 5 to 50% by mass, preferably 8 to 45% by mass, and more preferably 10 to 40% by mass, relative to the total amount (100% by mass) of the inorganic filler (F). When the content of the amorphous calcium carbonate relative to the inorganic filler (F) is within the above range, thixotropy can be easily imparted.

[0070] As the inorganic filler (F) other than the spherical silica and the amorphous calcium carbonate, any known or conventional inorganic filler can be used, and is not particularly limited. Examples thereof include powders of silica other than the spherical silica, alumina, zircon, calcium silicate, calcium phosphate, calcium carbonate other than the amorphous calcium carbonate, magnesium carbonate, silicon carbide, silicon nitride, aluminum nitride, boron nitride, aluminum hydroxide, iron oxide, zinc oxide, zirconium oxide, magnesium oxide, titanium oxide, aluminum oxide, calcium sulfate, barium sulfate, fosterite, steatite, spinel, clay, kaolin, dolomite, hydroxyapatite, nepheline cyanoite, cristobalite, wollastonite, diatomaceous earth, talc, and the like, or molded products thereof.

[0071] The shape of the other inorganic filler (F) is not particularly limited, but examples thereof include powder, spheres, crushed particles, fibers, needles, and scales. Among these, a spherical shape is preferred from the viewpoint of dispersibility. The median particle size of the other inorganic filler (F) is preferably 0.1 to 50 μm, and more preferably 1 to 30 μm.

[0072] The content of the inorganic filler (F) in the thermosetting epoxy resin composition of the present disclosure is preferably 60 to 90 mass% and more preferably 70 to 80 mass% relative to the total amount (100 mass%) of the thermosetting epoxy resin composition of the present disclosure. When the content of the inorganic filler (F) is 60 mass% or more, the linear expansion coefficient of the thermosetting epoxy resin composition of the present disclosure is reduced, and durability during curing is likely to be improved. Furthermore, when the content is 90 mass% or less, precipitation of spherical silica is suppressed, and reliability is likely to be improved.

[0073] The total content of the spherical silica and the irregular calcium carbonate in the inorganic filler (F) is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass, based on the total amount (100% by mass) of the inorganic filler (F). That is, the inorganic filler (F) may consist of the spherical silica and the irregular calcium carbonate.

[0074] The thermosetting epoxy resin composition of the present disclosure may contain components other than the above-described components. Examples of such components include conventional additives such as flame retardants, colorants, antioxidants, UV absorbers, ion adsorbents, colorants, fluorescent materials, mold release agents, thickeners, dispersants, rust inhibitors, corrosion inhibitors, freezing point depressants, anti-wear additives, and wettability modifiers. Only one of the above-described other components may be used, or two or more may be used. Furthermore, the content of the above-described other components is preferably 5% by mass or less, more preferably 1% by mass or less, and even 0% by mass, relative to the total amount (100% by mass) of the thermosetting epoxy resin composition of the present disclosure.

[0075] The thermosetting epoxy resin composition of the present disclosure may be prepared by stirring and mixing the above-described components in a heated state as needed, without any particular limitation. The thermosetting epoxy resin composition of the present disclosure may be used as a one-component composition in which the components are premixed and used as is, or may be used as a multi-component composition in which, for example, two or more components stored separately are mixed before use. From the viewpoint of improving storage stability and achieving long-term reliability, the thermosetting epoxy resin composition of the present disclosure is preferably a two-component composition comprising a base component and a curing agent composition.

[0076] When the thermosetting epoxy resin composition of the present disclosure is a two-component composition, the main component preferably contains an epoxy compound (A), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F). The main component may also contain an acid anhydride curing agent (B), a curing accelerator (C), and the other components described above as needed, but is preferably substantially free of the acid anhydride curing agent (B) and the curing accelerator (C). In this specification, "substantially free" means that the content is 1% by mass or less relative to the total amount (100% by mass) of the comparative object.

[0077] The curing agent composition preferably contains an acid anhydride curing agent (B), a curing accelerator (C), and an inorganic filler (F). The curing agent composition may contain an epoxy compound (A), a silane coupling agent (D), an antifoaming agent (E), and the other components as needed, but is preferably substantially free of the epoxy compound (A), the silane coupling agent (D), and the antifoaming agent (E).

[0078] The base agent preferably contains the spherical silica and the amorphous calcium carbonate as inorganic fillers (F) to facilitate mixing with the curing agent composition. When the base agent contains the spherical silica, its content is preferably 50 to 90% by mass, more preferably 55 to 80% by mass, and even more preferably 57 to 70% by mass, based on the total amount (100% by mass) of the base agent. When the base agent contains the amorphous calcium carbonate, its content is preferably 5 to 50% by mass, more preferably 12 to 40% by mass, and even more preferably 14 to 30% by mass, based on the total amount (100% by mass) of the base agent.

[0079] Furthermore, the curing agent composition preferably contains the spherical silica and the amorphous calcium carbonate as inorganic fillers (F) to facilitate mixing with the main agent. When the spherical silica is contained, its content is preferably 50 to 90% by mass, more preferably 55 to 80% by mass, and even more preferably 57 to 70% by mass, based on the total amount (100% by mass) of the curing agent composition. When the amorphous calcium carbonate is contained, its content is preferably 5 to 50% by mass, more preferably 12 to 40% by mass, and even more preferably 14 to 30% by mass, based on the total amount (100% by mass) of the curing agent composition.

[0080] The mixing mass ratio of the base agent to the curing agent composition [base agent:curing agent composition] is preferably 100:90 to 100:130, more preferably 100:100 to 100:120. After preparing the base agent, storing it at room temperature preferably results in a stable dispersion of the inorganic filler (F) throughout the base agent. However, some of the inorganic filler (F) may precipitate, resulting in the formation of two or more layers selected from the group consisting of a transparent supernatant liquid layer, a filler dispersion layer in which the inorganic filler (F) is dispersed, and a filler precipitate layer in which the inorganic filler (F) has precipitated, resulting in layer separation. For this reason, after storing a container containing the base agent to a liquid height of 50 mm at 23°C for one week, the height of the supernatant liquid layer is preferably 3 mm or less, and more preferably, the supernatant liquid layer is not visually visible. By having the above configuration, the physical properties tend to be less susceptible to change even when stored at room temperature for a long period of time, and the reliability tends to be excellent.

[0081] Furthermore, after a container into which the base agent is poured to a liquid height of 50 mm is stored at 23°C for one week, it is preferable that the height of the filler precipitate layer at the bottom of the container is 2 mm or less, and it is more preferable that no filler precipitate layer is observed. By having the above-mentioned configuration, the physical properties tend to be less susceptible to change even when stored at room temperature for a long period of time, and reliability tends to be excellent. The height of the filler precipitate layer can be measured, for example, by the method described in the Examples below.

[0082] As with the base agent, storage of the curing agent composition at room temperature may result in the formation of two or more layers selected from the group consisting of the supernatant liquid layer, the filler dispersion layer, and the filler precipitate layer, resulting in layer separation. After storing a container containing the curing agent composition at a liquid height of 50 mm at 23°C for one week, it is preferable that the height of the supernatant liquid layer is 3 mm or less, and it is more preferable that the supernatant liquid layer is not visually confirmed. By having the above-mentioned configuration, the physical properties are less likely to change even when stored at room temperature for a long period of time, and reliability tends to be excellent.

[0083] Furthermore, after storing a container into which the curing agent composition has been poured to a liquid height of 50 mm at 23°C for one week, it is preferable that the height of the filler precipitate layer at the bottom of the container is 2 mm or less, and it is preferable that no filler precipitate layer is observed. By having the above configuration, the physical properties tend to be less susceptible to change even when stored at room temperature for a long period of time, and reliability tends to be excellent. The height of the filler precipitate layer can be measured, for example, by the method described in the Examples below.

[0084] The base agent preferably has a ratio of shear viscosity measured at a shear rate of 1.0 [1 / s] to that measured at a shear rate of 10.0 [1 / s] at 25°C (thixotropy index (TI) value) of 1.3 or more, more preferably 1.5 or more. A TI value of 1.3 or more can prevent settling of the filler during storage. The upper limit is not particularly limited, but may be 20 or less.

[0085] The curing agent composition preferably has a ratio of the shear viscosity measured at a shear rate of 1.0 [1 / s] to the shear viscosity measured at a shear rate of 10.0 [1 / s] at 25°C (TI value: thixotropy index) of 1.3 or more, more preferably 1.5 or more. A TI value of 1.3 or more can prevent settling of the filler during storage. The upper limit is not particularly limited, but may be 20 or less.

[0086] [Cured Product] One embodiment of the present disclosure includes a cured product obtained by curing the thermosetting epoxy resin composition of the present disclosure (hereinafter, the cured product may be referred to as the "cured product of the present disclosure"). Known or conventional methods, such as heat treatment, can be used to cure the thermosetting epoxy resin composition to produce the cured product of the present disclosure. The temperature (curing temperature) for curing by heating is not particularly limited, but is preferably 45 to 220°C, more preferably 50 to 200°C, and even more preferably 55 to 190°C. The heating time (curing time) for curing is also not particularly limited, but is preferably 5 to 600 minutes, more preferably 10 to 540 minutes, and even more preferably 30 to 480 minutes. A curing temperature of 45°C or higher ensures sufficient curing, while a temperature of 220°C or lower can suppress decomposition of the resin components. The curing conditions depend on various factors, but can be appropriately adjusted, for example, by shortening the curing time when the curing temperature is increased, or by lengthening the curing time when the curing temperature is decreased. The curing can be carried out in one step or in two or more steps.

[0087] The linear expansion coefficient of the cured product is preferably 30 ppm / °C or less, more preferably 25 ppm / °C or less, and even more preferably 20 ppm / °C or less. When the linear expansion coefficient is 30 ppm / °C or less, the linear expansion coefficient of the cured product of the present disclosure can be sufficiently reduced, resulting in excellent durability. The linear expansion coefficient can be measured using, for example, a thermomechanical analyzer.

[0088] The thermosetting epoxy resin composition and cured product of the present disclosure are preferably used in components included in rotating electrical machines (rotating electrical machine applications), and because they have excellent durability, they are particularly suitable for use in automotive components such as EV motors. Specific uses of the cured product of the present disclosure include insulating materials, coating materials, sealants, adhesives, etc. Furthermore, the thermosetting epoxy resin composition of the present disclosure is resistant to changes in physical properties even at room temperature and has excellent long-term reliability, making it suitable for use in processes such as atmospheric pressure impregnation, reduced-pressure impregnation, pressure impregnation, and dipping.

[0089] Examples of the above-mentioned rotating electric machine applications include applications for protecting rotor wires, impregnation and casting of stator coils, insulation and sealing of coil ends, impregnation and casting to cover the entire stator, magnet fixing applications in rotors and / or stators for fixing magnets inserted into holes provided in the rotor core or stator core to the inner walls of the holes, and filling gaps between the holes and the magnets.

[0090] Preferred uses of the thermosetting epoxy resin composition of the present disclosure and the cured product of the present disclosure include, among others, coil impregnation applications such as impregnation and casting of coils (wires, windings) in stators and rotors of rotating electrical machines, and insulation and sealing of coil ends.

[0091] Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of configurations are possible as appropriate within the scope of the gist of the present invention. The present disclosure is not limited to the embodiments.

[0092] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0093] Example 1 (Preparation of Main Component) The epoxy compound (A), silane coupling agent (D), antifoaming agent (E), and inorganic filler (F) were mixed in the blending ratios (unit: parts by mass) shown in Table 1, and the mixture was uniformly mixed using a variable rotation / revolution mixer (product name "MAZERUSTAR KK-400W", manufactured by Kurabo Industries Ltd.), followed by degassing to prepare the main component of the thermosetting epoxy resin composition of Example 1.

[0094] (Preparation of Curing Agent Composition) The acid anhydride curing agent (B), the curing accelerator (C), and the inorganic filler (F) were added in the blending ratios (unit: parts by mass) shown in Table 1, and the mixture was uniformly mixed using a variable rotation / revolution mixer (product name "MAZERUSTAR KK-400W", manufactured by Kurabo Industries Ltd.), and further degassed to prepare the curing agent composition for the thermosetting epoxy resin composition of Example 1.

[0095] (Preparation of Cured Product) The base resin and the curing agent composition were mixed by hand in a mass ratio of 100:120 to prepare a thermosetting epoxy resin composition. The thermosetting epoxy resin composition was then filled into a mold and heated in an oven at 100°C for 120 minutes and then at 180°C for 120 minutes, thereby preparing the cured product of Example 1.

[0096] Examples 2 to 16 and Comparative Examples 1 to 3 (Preparation of Base Agent) Base agents for the thermosetting epoxy resin compositions of Examples 2 to 16 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the compositions were changed as shown in Table 1.

[0097] (Preparation of Curing Agent Compositions) Curing agent compositions for the thermosetting epoxy resin compositions of Examples 2 to 16 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the compositions were changed as shown in Table 1.

[0098] (Preparation of Cured Products) Thermosetting epoxy resin compositions were prepared in the same manner as in Example 1, and then subjected to heat treatment to prepare cured products of Examples 2 to 16 and Comparative Examples 1 to 3.

[0099] <Evaluation> The main components of the thermosetting epoxy resin compositions, the curing agent compositions of the thermosetting epoxy resin compositions, and the cured products obtained in the Examples and Comparative Examples were subjected to the following evaluation tests.

[0100] (1) Coefficient of Linear Expansion The coefficient of linear expansion of the cured products of Examples 1 to 16 and Comparative Examples 1 to 3 was measured using a thermomechanical analyzer (model name "TMA / SS7100", manufactured by Hitachi High-Tech Science Corporation).

[0101] (2) Filler Settling Property: After stirring, the base resin and curing agent compositions of Examples 1 to 16 and Comparative Examples 1 to 3 were each transferred to a screw tube so that the liquid height was 50 mm. The height of the precipitate (filler sediment layer) at the bottom of the screw tube immediately after stirring was measured as the initial filler settling height, and the height of the clear supernatant liquid (supernatant liquid layer) was measured as the initial supernatant liquid height. The filler settling height and supernatant liquid height were also measured after one week of storage at 23°C. The supernatant liquid height was measured visually, and the filler settling height was measured using a universal physical property tester (trade name "Texture Analyzer TA-XT-plus," manufactured by Eiko Seiki Co., Ltd.) at the position where a 100 g load could be detected when a measurement probe was inserted from the top surface of the liquid toward the bottom. If the measurement probe did not detect a 100 g load and reached the bottom of the screw tube, the filler settling height was deemed not to have been confirmed. Among these, a supernatant liquid height of 3 mm or less was rated as O, a height exceeding 3 mm was rated as X, a filler sedimentation height of 2 mm or less was rated as O, and a filler sedimentation height exceeding 2 mm was rated as X. When the height of the supernatant liquid and the filler sedimentation height of the evaluation target were both rated as O, the filler sedimentation was rated as O, and when at least one of the height of the supernatant liquid and the filler sedimentation height was rated as X, the filler sedimentation was rated as X.

[0102] (3) TI (Thixotropy Index) For the base agent and curing agent compositions of Examples 1 to 16 and Comparative Examples 1 to 3, the shear viscosity was measured at 25° C. using a rheometer ("MCR302e" manufactured by Anton Paar) while changing the shear rate from 0.01 [1 / s] to 300 [1 / s]. From the obtained measurement data, the ratio of the shear viscosity at a shear rate of 1.0 [1 / s] to the shear viscosity at a shear rate of 10.0 [1 / s] [shear viscosity at 1.0 [1 / s] / shear viscosity at 10.0 [1 / s]] was calculated as the TI value.

[0103]

[0104] The components listed in Table 1 are explained below. (Epoxy compound (A)) CELLOXIDE 2021P: Trade name "CELLOXIDE 2021P" (3,4-epoxycyclohexylmethyl (3,4-epoxy) cyclohexanecarboxylate), manufactured by Daicel Corporation jER806: Trade name "jER806", bisphenol F type liquid epoxy compound, manufactured by Mitsubishi Chemical Corporation (Acid anhydride-based curing agent (B)) MH-700: Trade name "Ricadit MH-700", a mixture of 4-methylhexahydrophthalic anhydride and hexahydrophthalic anhydride, manufactured by New Japan Chemical Co., Ltd. (Curing accelerator (C)) MY-H: Trade name "Ajicure MY-H", an amine adduct-based latent curing accelerator, manufactured by Ajinomoto Fine-Techno Co., Inc. HXA3792: ​​Trade name "Novacure HXA3792", a microcapsule-type imidazole-based curing accelerator, manufactured by Asahi Kasei Corporation 2MZA-PW: Trade name "2MZA-PW", a compound of 6-[2-(2-methyl-1H-imidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine and 1,3,5-triazinane-2,4,6-trione (1:1), manufactured by Shikoku Chemical Industry Co., Ltd. 2MAOK-PW: Trade name "2MAOK-PW", 2,4-diamino-6-(2'-methylimidazolyl)ethyl-1,3,5-triazine, manufactured by Shikoku Chemical Industry Co., Ltd. (silane coupling agent (D)) KBM-403: Trade name "KBM403", manufactured by Shin-Etsu Chemical Co., Ltd. (defoaming agent (E)) KS-69: Trade name "KS-69", manufactured by Shin-Etsu Chemical Co., Ltd. (inorganic filler (F)) FB-40R: Trade name "FB-40R", fused spherical silica, D50: 41.0 μm, manufactured by Denka Co., Ltd. FB-5D: Trade name "FB-5D", fused spherical silica, D50: 4.7 μm, manufactured by Denka Co., Ltd. SL-100: Trade name "SL-100", amorphous heavy calcium carbonate powder, manufactured by Takehara Kogyo Co., Ltd. SL-1000: Trade name "SL-1000", amorphous heavy calcium carbonate powder, manufactured by Takehara Kogyo Co., Ltd. SL-2200: Trade name "SL-2200", amorphous heavy calcium carbonate powder, manufactured by Takehara Kogyo Co., Ltd.

[0105] The thermosetting epoxy resin compositions of the Examples had a low coefficient of linear expansion, were evaluated as having excellent durability against heat generation and vibration after curing, and were also evaluated as being able to prevent filler settling even after long-term storage, preventing a decrease in reliability due to long-term storage. On the other hand, when amorphous calcium carbonate was not included as a filler, filler settling due to long-term storage could not be prevented, resulting in poor reliability (Comparative Examples 1 to 3).

[0106] Variations of the present disclosure are described below. [Appendix 1] A thermosetting epoxy resin composition that is liquid at 25°C, comprising an epoxy compound (A), an acid anhydride curing agent (B), a curing accelerator (C), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) comprises spherical silica and amorphous calcium carbonate, and wherein the content of the spherical silica is 50 to 90 mass% and the content of the amorphous calcium carbonate is 5 to 50 mass% relative to the total amount of the resin composition. [Appendix 2] The thermosetting epoxy resin composition according to Appendix 1, comprising a two-component epoxy resin composition comprising a base component and a curing agent composition, wherein the base component comprises the epoxy compound (A), the silane coupling agent (D), the antifoaming agent (E), and the inorganic filler (F), and wherein the curing agent composition comprises the acid anhydride curing agent (B), the curing accelerator (C), and the inorganic filler (F). [Appendix 3] The thermosetting epoxy resin composition according to Appendices 2, wherein the content of the spherical silica in the base resin is 50 to 90% by mass and the content of the amorphous calcium carbonate is 5 to 50% by mass. [Appendix 4] The thermosetting epoxy resin composition according to Appendices 2 or 3, wherein the content of the spherical silica in the curing agent composition is 50 to 90% by mass and the content of the amorphous calcium carbonate is 5 to 50% by mass. [Appendix 5] The thermosetting epoxy resin composition according to any one of Appendices 2 to 4, wherein the base resin and the curing agent composition are poured into a screw tube to a liquid height of 50 mm, and after storage at 23°C for one week, the height of the supernatant liquid layer is 3 mm or less. [Appendix 6] The thermosetting epoxy resin composition according to any one of Appendices 2 to 5, wherein the base resin and the curing agent composition are poured into a screw tube to a liquid height of 50 mm, and after storage at 23°C for one week, the height of the filler precipitate layer is 2 mm or less. [Appendix 7] The thermosetting epoxy resin composition according to any one of Appendices 2 to 6, wherein the base agent and the curing agent composition have a thixotropy index (TI) value of 1.3 or more. [Appendix 8] A cured product of the thermosetting epoxy resin composition according to any one of Appendices 1 to 7. [Appendix 9] The cured product according to Appendices 8, which is used as an insulating material. [Appendix 10] The cured product according to Appendices 8, which is used as an adhesive.[Appendix 11] The cured product according to Appendix 8, which is used as a sealant.

Claims

1. A thermosetting epoxy resin composition that is liquid at 25°C, comprising an epoxy compound (A), an acid anhydride curing agent (B), a curing accelerator (C), a silane coupling agent (D), an antifoaming agent (E), and an inorganic filler (F), wherein the inorganic filler (F) comprises spherical silica and amorphous calcium carbonate, and the content of the spherical silica is 50 to 90 mass% and the content of the amorphous calcium carbonate is 5 to 50 mass% relative to the total amount of the resin composition.

2. The thermosetting epoxy resin composition according to claim 1, which is a two-component epoxy resin composition comprising a base agent and a curing agent composition, wherein the base agent contains the epoxy compound (A), the silane coupling agent (D), the antifoaming agent (E), and the inorganic filler (F), and the curing agent composition contains the acid anhydride curing agent (B), the curing accelerator (C), and the inorganic filler (F).

3. A thermosetting epoxy resin composition according to claim 2, wherein the content of the spherical silica in the base resin is 50 to 90% by mass, and the content of the amorphous calcium carbonate is 5 to 50% by mass.

4. The thermosetting epoxy resin composition according to claim 2, wherein the content of the spherical silica in the curing agent composition is 50 to 90 mass % and the content of the amorphous calcium carbonate in the curing agent composition is 5 to 50 mass %.

5. The thermosetting epoxy resin composition according to claim 2, wherein the base and curing agent compositions are poured into a screw tube so that the liquid height is 50 mm, and after storage at 23°C for one week, the height of the supernatant liquid layer is 3 mm or less.

6. The thermosetting epoxy resin composition according to claim 2, wherein the base and curing agent composition are poured into a screw tube so that the liquid height is 50 mm, and after storage at 23°C for one week, the height of the filler precipitate layer is 2 mm or less.

7. The thermosetting epoxy resin composition according to claim 2, wherein the base resin and the curing agent composition have a thixotropy index (TI) value of 1.3 or more.

8. A cured product of the thermosetting epoxy resin composition according to any one of claims 1 to 7.

9. The cured product according to claim 8, which is used as an insulating material.

10. The cured product according to claim 8, which is used as an adhesive.

11. The cured product according to claim 8, which is used as a sealant.

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