Casting epoxy resin composition and electrical / electronic parts

Abstract

Provided is an epoxy resin composition for casting which includes a hardener component having excellent storage stability and which has excellent castability at atmospheric pressure.　The epoxy resin composition for casting is characterized by comprising: a main component comprising an epoxy resin and an inorganic filler; and a hardener component comprising a hardener, an inorganic filler, a curing accelerator, and a dispersant comprising a polycarboxylic acid as a main component.

Description

[Technical Field]

[0001] The present invention relates to a cast epoxy resin composition for sealing, coating, insulating, etc. electric and electronic components such as coils and transformers, which comprises a main component containing an inorganic filler and a curing agent component, and which has excellent storage stability of the curing agent component and excellent castability under atmospheric pressure, and to electric and electronic components obtained by casting and curing the composition under atmospheric pressure. [Background technology]

[0002] Conventionally, coils and other components incorporated into electrical and electronic devices have been sealed, coated, insulated, etc. by casting and curing an epoxy resin composition to protect them from the external atmosphere and mechanical shocks. This epoxy resin casting composition is based on an epoxy resin, to which a curing agent, a curing accelerator, and inorganic fillers such as silica and alumina are added to increase thermal conductivity.

[0003] In recent years, electric and electronic parts as cast products have been required to have even greater crack resistance due to factors such as higher internal voltages and thinner walls associated with miniaturization, and attempts have been made to incorporate inorganic fillers not only into the main component but also into the hardener component in order to achieve a high filler ratio.

[0004] Curing agent components containing inorganic fillers have the problem of proneness to settling of the inorganic filler, reducing its storage stability. However, in the past, storage stability has been maintained by reducing the settling rate by reducing the particle size of the inorganic filler, inhibiting settling by imparting thixotropy with fumed silica or polyester ether-type anti-settling agents, and further by reducing the particle size of the inorganic filler, imparting thixotropy with an anti-settling agent, and combining this with vacuum casting (see Patent Documents 1, 2, and 3). However, reducing the particle size of the inorganic filler reduces thermal conductivity, and in the manufacturing process of casting motor coils, thixotropic resins have poor fluidity under atmospheric pressure without a compulsive force such as vacuum pressure, which lengthens the casting time and reduces the productivity of motor parts. Furthermore, vacuum casting requires expensive casting equipment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-012745 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-155394 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-108368 Summary of the Invention

[0006] As described above, it has been difficult with conventional techniques to obtain a cast epoxy resin composition that has excellent storage stability of the curing agent and requires a short casting time when used for casting electric and electronic components such as coils under atmospheric pressure.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an epoxy resin composition which has excellent storage stability of the curing agent component and excellent castability under atmospheric pressure, and an electric / electronic part obtained by casting and curing the epoxy resin composition.

[0008] As a result of intensive research conducted by the present inventors to achieve the above object, they discovered that by blending a dispersant containing a polycarboxylic acid as a main component with a curing agent component containing an inorganic filler whose particle size has been controlled so as to obtain a desired thermal conductivity, an epoxy resin composition can be obtained which has excellent storage stability of the curing agent component and excellent castability under atmospheric pressure, and thus completed the present invention.

[0009] That is, the present invention provides a castable epoxy resin composition comprising a main component containing (A) an epoxy resin and (B) an inorganic filler, and a curing agent component containing (C) an acid anhydride curing agent, (D) an inorganic filler, (E) a curing accelerator, and (F) a dispersing agent mainly composed of a polycarboxylic acid.

[0010] The viscosity of the main component at 40°C is preferably 40 to 120 Pa·s.

[0011] The complex viscosity of the curing agent component at 70°C is preferably 300 Pa·s or less when strain stress is 1 Pa.

[0012] The content of the (F) dispersant containing polycarboxylic acid as a main component in the curing agent component is preferably 0.5% by weight or more and 5.0% by weight or less.

[0013] The acid anhydride curing agent (C) is preferably in a liquid state at room temperature.

[0014] The inorganic filler (D) preferably has an average particle size (D50) of 0.1 to 50 μm and is preferably a single or mixture of aluminum hydroxide, fused silica, and alumina. The amount of the inorganic filler (D) is preferably 250 to 450 parts by weight per 100 parts by weight of the acid anhydride curing agent (C).

[0015] The present invention also provides an electric / electronic part obtained by casting the above-mentioned epoxy resin composition for casting under atmospheric pressure and curing it.

[0016] According to the present invention, it is possible to provide a cast epoxy resin composition which has a desired thermal conductivity, excellent storage stability of the curing agent component, and excellent castability under atmospheric pressure, and to provide an electric / electronic part obtained by casting and curing the epoxy resin composition under atmospheric pressure. DETAILED DESCRIPTION OF THE INVENTION

[0017] The cast epoxy resin composition of the present invention (hereinafter also referred to simply as "resin composition") comprises a main component containing (A) an epoxy resin and (B) an inorganic filler, and a curing agent component containing (C) an acid anhydride curing agent, (D) an inorganic filler, (E) a curing accelerator, and (F) a dispersing agent mainly composed of a polycarboxylic acid.

[0018] The main component of the resin composition of the present invention will be described. The epoxy resin (A) used in the present invention is not particularly limited in terms of molecular structure, molecular weight, etc., as long as it has two or more epoxy groups in one molecule, and any commonly used epoxy resin can be used. Examples include aromatic epoxy resins such as bisphenol type, novolak type, and biphenyl type, glycidyl ether type of polycarboxylic acid, and alicyclic epoxy resins obtained by epoxidation of cyclohexane derivatives, etc., and these can be used alone or in combination of two or more types. In addition to these, a liquid monoepoxy resin or the like can be used as a co-component as needed to adjust the viscosity of the resin composition, and further, when flame retardancy is to be imparted, an epoxy resin modified with a halogen compound, a phosphorus compound, or the like can also be used. The amount of the epoxy resin (A) in the resin composition is preferably 10 to 50 mass %, more preferably 20 to 40 mass %, and even more preferably 25 to 35 mass %, from the viewpoint of obtaining good curability and cured physical properties.

[0019] The inorganic filler (B) used in the present invention is blended to improve the thermal conductivity and crack resistance of the cured product. As inorganic fillers, calcium carbonate, aluminum hydroxide, fused silica, alumina, boron nitride, aluminum nitride, and other commonly used inorganic fillers can be used without particular limitation as long as they provide the desired physical properties. Examples of commercially available products include Kalfain 200M (light calcium carbonate, manufactured by Maruo Calcium Co., Ltd.), C-301N (aluminum hydroxide, manufactured by Sumitomo Chemical Co., Ltd.), Fuselex RY (fused silica, manufactured by Tatsumori Co., Ltd.), LS-210B (alumina, manufactured by Nippon Light Metal Co., Ltd.), Shinano Random GP (silicon carbide, manufactured by Shin-Etsu Electric Smelting Co., Ltd.), Denka Boron Nitride HGP (boron nitride, manufactured by Denka Company, Limited), and Toyal Tech Filler TFZ-N05P (aluminum nitride, manufactured by Toyo Aluminum Co., Ltd.). Among these inorganic fillers, from the viewpoint of improving the thermal conductivity of the cured product, fused silica, alumina, silicon carbide, boron nitride, and aluminum nitride are preferred, with fused silica and alumina being more preferred. Furthermore, from the viewpoint of ease of mixing with resin and resistance to viscosity increase, calcium carbonate, aluminum hydroxide, fused silica, and alumina are preferred, with aluminum hydroxide, fused silica, and alumina being more preferred. Furthermore, from the viewpoint of stable product quality due to the large volume of distribution in the market, calcium carbonate, aluminum hydroxide, fused silica, and alumina are preferred, with aluminum hydroxide, fused silica, and alumina being more preferred.

[0020] The blending amount of (B) inorganic filler used in the present invention is preferably in the range of 150 to 250 parts by weight per 100 parts by weight of (A) epoxy resin, from the viewpoint of obtaining good thermal conductivity. It is desirable to use a mixture of inorganic fillers (B) with different particle sizes, for example, 10 to 30 parts by weight of an inorganic filler with an average particle size (D50) of 10 μm to 30 μm, 40 to 70 parts by weight of an inorganic filler with an average particle size (D50) of 4 μm to 10 μm, and 60 to 100 parts by weight of an inorganic filler with an average particle size (D50) of 1 μm to 4 μm. It is preferable to use a mixture of fused silica and alumina.

[0021] The curing agent component of the resin composition of the present invention will now be described. The complex viscosity of the curing agent component of the present invention is 300 Pa·s or less at 70°C with a strain stress of 1 Pa, preferably 300 Pa·s or less, more preferably 100 Pa·s or less, and even more preferably 80 Pa·s or less. If the viscosity of the curing agent component in the extremely low shear region of strain stress of 1 Pa is 300 Pa·s or less, the resin will exhibit sufficient fluidity even under atmospheric pressure when mixed with the main component, thereby making it possible to obtain a resin composition with excellent castability.

[0022] The acid anhydride curing agent (C) used in the present invention is not particularly limited as long as it has an acid anhydride group in the molecule, and examples thereof include hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, nadic anhydride, and methylnadic anhydride. These can be used alone or in combination of two or more. Among these acid anhydride curing agents, acid anhydride curing agents that are liquid at room temperature are preferred, and their viscosity at 25°C is preferably 30 to 500 mPa·s, more preferably 50 to 300 mPa·s. From this perspective, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, dodecenylsuccinic anhydride, and methylhimic anhydride are preferred, and methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and methylnadic anhydride are more preferred.

[0023] From the viewpoint of obtaining good curing properties and cured physical properties, the (C) acid anhydride curing agent is preferably contained in an amount of 80 to 90 parts by weight per 100 parts by weight of the (A) epoxy resin.

[0024] Examples of the inorganic filler (D) contained in the curing agent component of the present invention include the same inorganic fillers as those (B) contained in the main component, and preferred inorganic fillers are also the same.

[0025] The blending amount of (D) inorganic filler used in the present invention is preferably in the range of 250 to 450 parts by weight relative to (C) acid anhydride curing agent, from the viewpoint of obtaining good thermal conductivity. The inorganic filler (D) preferably has an average particle size (D50) of 15 μm or less, more preferably 10 μm or less. It is desirable to use a mixture of fillers with different particle sizes. For example, it is preferable to mix 100 to 200 parts by weight of fillers with an average particle size (D50) of 5 μm to 10 μm and 100 to 350 parts by weight of fillers with an average particle size (D50) of 1 μm to 5 μm. It is preferable to use a mixture of aluminum hydroxide, fused silica and alumina.

[0026] The curing accelerator (E) used in the present invention can be any accelerator that accelerates the reaction between the epoxy resin (A) and the acid anhydride curing agent (C). Examples of such accelerators include imidazoles such as 1-butyl-2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-phenyl-4-methylimidazole, and tertiary amines such as 2-(dimethylaminomethyl)phenol, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU), and benzyldimethylamine (BDMA). These accelerators can be used alone or in combination.

[0027] The amount of (E) curing accelerator blended is preferably 0.1 to 2.0 parts by weight, more preferably 0.3 to 1.5 parts by weight, per 100 parts by weight of (C) acid anhydride curing agent, from the viewpoint of obtaining good curability, an appropriate pot life, and good physical properties of the cured product.

[0028] The polycarboxylic acid-based dispersant (F) used in the present invention can be widely used without particular limitations, as long as it has an adsorbing group that promotes wetting of the inorganic filler particle surface, adsorbs to the inorganic filler particles, stabilizing the dispersion state of the inorganic filler, and suppressing secondary aggregation of the inorganic filler due to steric hindrance caused by affinity with the resin component. Preferred polycarboxylic acid-based dispersants are ester compounds of α-olefin-maleic anhydride copolymers with monohydric alcohols (sometimes referred to as "carboxyl group-containing polymer modified products"). Such ester compounds have a controlled arrangement of hydrophobic moieties, such as hydrocarbon groups derived from α-olefins, and hydrophilic moieties, such as carboxyl groups formed by ring-opening addition of maleic anhydride groups derived from maleic anhydrides. The α-olefins constituting these ester compounds are not particularly limited as long as they are linear or branched unsaturated hydrocarbons having 6 or more carbon atoms, but are preferably unsaturated hydrocarbons having 6 to 30 carbon atoms, such as 1-dodecene, 1-tetradecene, and mixtures thereof. Examples of monohydric alcohols include aliphatic alcohols, aromatic alcohols, and polyalkylene glycol monoalkyl ethers. Examples of aliphatic alcohols include cetyl alcohol and stearyl alcohol. Examples of aromatic alcohols include 1-phenyl-1-propanol and α-phenoxy-2-propanol. Examples of polyalkylene glycol monoalkyl ethers include polyethylene glycol monoalkyl ethers having a molecular weight of approximately 400 to 700. The weight-average molecular weight, calculated using standard polystyrene, is preferably in the range of 1,000 to 20,000, more preferably 3,000 to 15,000, and even more preferably 5,000 to 10,000. The acid value is preferably in the range of 10 to 100 mgKOH / g, and more preferably 15 to 60 mgKOH / g. Examples of commercially available products include FLOWLEN G-700 and FLOWLEN GW-1500 (both manufactured by Kyoeisha Chemical Co., Ltd.).

[0029] Dispersants whose main component is polycarboxylic acid have adsorption groups that promote wetting of inorganic filler particle surfaces, which adsorb to the inorganic filler particles, stabilizing the dispersion of the inorganic filler. Furthermore, the steric hindrance caused by affinity with the resin component inhibits secondary aggregation of the inorganic filler, delaying the settling of the inorganic filler, which can reduce the storage stability of the curing agent component. Therefore, even if the complex viscosity at a strain stress of 1 Pa is 100 Pa·s or less at 70°C, the dispersion of the inorganic filler is stabilized, resulting in excellent storage stability of the curing agent component. In addition, typical anti-settling agents inhibit the settling of inorganic filler particles by thixotropy, which occurs when a polymer incorporating functional groups with affinity for inorganic filler particles adsorbs through the particles' adsorption groups, forming a crosslinked structure, and by the thickening effect of polymer chain entanglement. In contrast, dispersants primarily composed of polycarboxylic acids do not exhibit thixotropy or thickening effects for the reasons mentioned above. Furthermore, even when the viscosity of the curing agent component is 100 Pa·s or less in the extremely low shear region of strain stress (1 Pa), there is no settling of the inorganic filler, and when mixed with the base component, the resin exhibits sufficient fluidity even at atmospheric pressure, resulting in a resin composition with excellent castability.

[0030] The blending amount of the dispersant (F) containing a polycarboxylic acid as a main component is preferably 0.1 to 10 mass %, more preferably 0.3 to 5.0 mass %, and even more preferably 0.5 to 3.0 mass %, of the curing agent components, from the viewpoint of balancing the sedimentation property and cured physical properties of the inorganic filler.

[0031] In addition to the above-mentioned components, other components such as coupling agents, leveling agents, antifoaming agents, pigments, and flame retardants may be added to the cast epoxy resin composition of the present invention as needed, provided that the effects of the present invention are not impaired. These may be used alone or in combination of two or more.

[0032] To prepare the cast epoxy resin composition of the present invention as a casting material, first, (A) epoxy resin, (B) inorganic filler, and various additives as needed are thoroughly degassed and mixed to form the main component. Next, (C) acid anhydride curing agent, (D) inorganic filler, (E) curing accelerator, (F) polycarboxylic acid-based dispersant, and various additives as needed are thoroughly degassed and mixed to form the curing agent component. Then, 90 to 110 parts by weight of the curing agent component are mixed with 100 parts by weight of the resulting main component to form the cast epoxy resin composition. That is, the composition of the present invention is a two-part type in which the main component and the curing agent component are stored separately and mixed before casting.

[0033] The epoxy resin composition for casting thus obtained can impart excellent properties and reliability when used for sealing, coating, insulating, etc. electric and electronic parts such as coils and transformers.

[0034] In the present invention, electric and electronic parts such as coils and transformers are sealed, coated, insulated and protected by casting the epoxy resin composition of the present invention under normal atmospheric pressure and curing it. [Example]

[0035] The present invention will now be described in detail with reference to examples. However, the present invention is not limited to these examples. In the following examples and comparative examples, "parts" means "parts by weight."

[0036] The abbreviations used in the examples and comparative examples are as follows: [Epoxy resin in the main component] A1: Bisphenol A liquid epoxy resin (Nippon Steel Chemical & Material Co., Ltd., Epotohto YD-128, epoxy equivalent 187 g / eq., viscosity 12,000 mPa·s at 25°C) A2: Bisphenol F solid epoxy resin (Nippon Steel Chemical & Material Co., Ltd., Epotohto YDF-2001, epoxy equivalent 485 g / eq., softening point 60°C) A3: Bisphenol F liquid epoxy resin (Nippon Steel Chemical & Material Co., Ltd., Epotohto YDF-170, epoxy equivalent 167 g / eq., viscosity 3,000 mPa·s at 25°C)

[0037] [Inorganic fillers in the main component] B1: Fused silica (Tatsumori Co., Ltd., Fuslex SY, D50 = 20 μm, D98 = 96 μm) B2: Alumina (Nippon Light Metal Co., Ltd., LS-210B, BET specific surface area = 1.4 m 2 / g, D50=5μm, D98=48μm) B3: Alumina (Nippon Light Metal Co., Ltd., SLS-130, BET specific surface area = 1.4 m 2 / g, D50=3μm, D98=32μm)

[0038] [Other additives in the main ingredient] G1: Antifoaming agent (Momentive Performance Materials Japan, TSA720) G2: Wetting and dispersing agent (BYK-110, manufactured by BYK-Chemie) G3: Silane coupling agent (Momentive Performance Materials Japan, TSL-8350) G4: Colorant (Mitsubishi Chemical Corporation, MA-8)

[0039] [Curing agent in the curing agent component] C1:3 or 4-methyl-1,2,3,6-tetrahydrophthalic anhydride (Hitachi Chemical Co., Ltd., HN-2200R, viscosity at 25°C = 70 mPa·s)

[0040] [Inorganic filler in hardener component] D1: Aluminum hydroxide (Sumitomo Chemical Co., Ltd., C-301N, BET specific surface area = 4.0 m 2 / g, D50=1.5μm, D98=64μm) D2: Fused silica (Tatsumori Co., Ltd., Fuslex RD-20, D50 = 7 μm, D98 = 32 μm) D3: Fused silica (Tatsumori Co., Ltd., Fuslex RD-X, D50 = 2 μm, D98 = 18 μm) D4: Alumina (Nippon Light Metal Co., Ltd., SLS-130, BET specific surface area = 1.4 mm 2 / g, D50=3μm, D98=32μm) D5: Alumina (Nippon Light Metal Co., Ltd., V325F, BET specific surface area = 0.8 mm 2 / g, D50=12μm, D98=48μm)

[0041] [Curing accelerator in hardener component] E1: 1-benzyl-2-methylimidazole (Shikoku Chemicals Corporation, Curesol 1B2MZ)

[0042] [Dispersant containing polycarboxylic acid as the main component in the hardener] F1: Carboxyl group-containing modified polymer (Florene G-700, manufactured by Kyoeisha Chemical Co., Ltd., weight average molecular weight 7,500, acid value 60 mg KOH / g) F2: Carboxyl group-containing modified polymer (Kyoeisha Chemical Co., Ltd., FLOWLEN GW-1500, weight average molecular weight 7,500, acid value 55 mg KOH / g)

[0043] [Anti-settling agent in hardener components] (Reference example) H1: Hydrophobic fumed silica (Nippon Aerosil Co., Ltd., Aerosil RY-200, BET specific surface area = 100 m 2 / g, average primary particle size D50 = 12 nm) H2: Polyether ester anti-settling agent (Kusumoto Chemicals, Disparlon 3600N, weight-average molecular weight 19,500)

[0044] Example 1 A mixture of 82 parts A1 and 18 parts A2 as epoxy resins, 22 parts B1, 56 parts B2, and 84 parts B3 as inorganic fillers, and 0.2 parts G1, 1.9 parts G2, 1.5 parts G3, and 1 part G4 as other additives, was vacuum-kneaded at 50°C for 1 hour to obtain the base component. Separately, a mixture of 100 parts C1 as acid anhydride, 12 parts D1, 139 parts D2, and 150 parts D3 as inorganic fillers, 0.6 parts E1 as a curing accelerator, and 6.1 parts F1 as a carboxyl group-containing modified polymer was vacuum-kneaded at room temperature for 1 hour to obtain the curing agent component. The base component and curing agent component were uniformly mixed before casting to obtain a castable epoxy resin composition.

[0045] Examples 2 to 8, Comparative Examples 1 to 4 Using the amounts (parts) of each raw material shown in Table 1, the same procedures as in Example 1 were carried out to obtain epoxy resin compositions for casting.

[0046] [Table 1]

[0047] The viscosity of the base component and the complex viscosity and storage stability of the curing agent component obtained in Examples 2 to 8 and Comparative Examples 1 to 4 were evaluated, and the castability and thermal conductivity of the cast epoxy resin compositions in which the base component and the curing agent component were uniformly mixed were measured. The results are shown in Table 2.

[0048] The main component, the curing agent component, and the epoxy resin composition for casting were evaluated by the following methods.

[0049] (1) Viscosity: Using a B-type viscometer (TVB-10U model, manufactured by Toki Sangyo Co., Ltd.), the viscosity of the main component was measured at a measurement temperature of 40°C, rotor number No. 7, rotor rotation speed of 50 rpm, and measurement time of 1 minute.

[0050] (2) Complex viscosity: Using a rheometer (RS-600, manufactured by HAAKE), measurements were taken under the conditions of a cone rotor diameter of 20 mm, a cone rotor angle of 0°, and a measurement temperature of 70°C, while varying the strain stress in the range of 0.1 to 1,000 Pa, and the complex viscosity of the curing agent component at 1 Pa was read.

[0051] (3) Storage stability: 250g of the obtained hardener component was placed in a 110mL, 35mm diameter glass bottle and left at 100℃ for 2 hours. The difference between the resin height measured by placing a metal ruler on the outside of the glass bottle and the resin surface height when the metal ruler was inserted into the resin (the amount of penetration of the metal ruler) was taken as the sedimentation and accumulation height (mm) of the inorganic filler. For example, when the amount of penetration of the metal ruler = the resin height (sedimentation and accumulation height 0mm), the storage stability is the best.

[0052] (4) Castability: 150 g of a cast epoxy resin composition, which was a homogeneous mixture of the base component and the curing agent component, was heated to 70°C and immediately poured vertically under normal pressure into a mold (gap 4 mm, dimensions 160 mm x 180 mm) preheated to 90°C, and the time (minutes) until the composition was completely poured into the mold was measured. If the composition was not poured at all, it was marked as "x."

[0053] (5) Thermal conductivity: A castable epoxy resin composition was prepared by uniformly mixing the main component and the curing agent component, and cured at 110°C for 4 hours. The thermal conductivity of the cured product at 25°C was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).

[0054] [Table 2]

[0055] From Tables 1 and 2, it was confirmed that the epoxy resin composition for casting of the present invention is excellent in storage stability of the curing agent component and in casting ability under normal pressure.

[0056] As is clear from the above explanation and the results in Tables 1 and 2, according to the present invention, by blending a dispersant whose main component is polycarboxylic acid with an epoxy resin curing agent component, it is possible to obtain a cast epoxy resin composition which has excellent storage stability of the curing agent component and excellent castability under normal pressure.If this composition is used to seal, coat, insulate, etc. cast parts such as coils and transformers, it is possible to obtain electric / electronic parts which have improved electrical properties and excellent crack resistance in thin-walled products. [Industrial Applicability]

[0057] The present invention is useful as a cast epoxy resin composition for sealing, coating, insulating, etc. electric and electronic parts such as coils and transformers.

Claims

1. A castable epoxy resin composition comprising: a main component containing (A) an epoxy resin and (B) an inorganic filler; and a curing agent component containing (C) an acid anhydride curing agent, (D) an inorganic filler, (E) a curing accelerator, and (F) a dispersant comprising an ester compound of an α-olefin-maleic anhydride copolymer and a monohydric alcohol.

2. 2. The epoxy resin composition for casting according to claim 1, wherein the viscosity of the main component at 40° C. is 40 to 120 Pa·s.

3. 2. The epoxy resin composition for casting according to claim 1, wherein the complex viscosity of the curing agent component at 70°C is 300 Pa·s or less at a strain stress of 1 Pa.

4. 2. The epoxy resin composition for casting according to claim 1, wherein the content of the dispersant (F) in the curing agent component is 0.5% by weight or more and 5.0% by weight or less.

5. 2. The castable epoxy resin composition according to claim 1, wherein the acid anhydride curing agent (C) is liquid at room temperature.

6. 2. The epoxy resin composition for casting according to claim 1, wherein the inorganic filler (D) has an average particle size of 0.1 to 50 μm and is selected from aluminum hydroxide, fused silica, and alumina, either singly or as a mixture, and the amount of the inorganic filler (D) is 250 to 450 parts by weight per 100 parts by weight of the acid anhydride curing agent (C).

7. An electric / electronic part obtained by casting the epoxy resin composition for casting according to any one of claims 1 to 6 under atmospheric pressure and curing it.

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