JP5033576B2 - Thermosetting resin composition, cured product and high thermal conductive coil - Google Patents

Description

  The present invention relates to a thermosetting resin composition, a cured product, and a high thermal conductive coil having the cured product as an insulating layer. More specifically, a thermosetting resin composition having a high thermal conductivity of the cured product, a cured product obtained by curing the thermosetting resin composition, and a high thermal conductive coil excellent in heat dissipation having the cured product as an insulating layer. In particular, this high thermal conductive coil is used by being incorporated in a drive motor or a generator mounted on a hybrid car, an electric vehicle or the like that is attracting attention especially for environmental measures.

Conventionally, hardened products of varnish and molding resin have been used to insulate rotating electrical equipment that generates large vibrations during operation, such as generators and drive motors. These materials include unsaturated polyester resins and Vinyl ester resins are known.
In recent years, these electric devices have been improved in performance, and improvement in performance and reliability has been demanded more than ever, and in particular, measures for heat dissipation during operation have become important.
Conventionally, as a heat dissipation measure, a method of improving the thermal conductivity by mixing an inorganic filler in a resin has been adopted. In particular, in molding resins, techniques have been used in which windings are molded with a thermosetting resin composition containing a large amount of an inorganic filler such as aluminum hydroxide or titanium oxide (for example, Patent Documents 1 and 2). Since these fillers have high hardness, there is a problem of causing wear of equipment used at the time of manufacturing or molding the resin composition.
Magnesium oxide, on the other hand, has high thermal conductivity and low hardness, but is a compound that is generally used as an esterification catalyst. When mixed in unsaturated polyester resin or vinyl ester resin, the resin thickens and increases the filling rate. There is a disadvantage that the stability cannot be achieved (for example, Patent Document 3).
In order to improve this, it has been proposed to prevent thickening of a resin composition comprising an unsaturated polyester resin and a curing agent by using an inert magnesium oxide subjected to high heat treatment (for example, Patent Document 4). ).
However, high heat treatment of magnesium oxide not only increases the cost but also makes it difficult to obtain a resin composition having sufficient fluidity.
Furthermore, it is proposed to improve the heat dissipation from the coil by molding the winding with a varnish containing an unsaturated polyester resin composition containing a large amount of a specific inorganic filler in order to prevent high costs. (For example, Patent Document 5).
However, coils that are incorporated in motors, generators, and the like for use in vehicles are designed to have a large number of turns and a high line factor because they are used with high output and high voltage. The above-mentioned proposed varnish containing a large amount of inorganic filler (resin, inorganic filler and solvent and / or reactive diluent as a main component) has a problem that the winding is poorly impregnated and the reliability of the coil is lowered. There is.
Therefore, there is a demand for a resin composition in which the varnish has an appropriate viscosity and gelation time, and the cured product can form an insulating layer with high thermal conductivity and high reliability.
JP-A-9-204828 JP 11-346450 A JP-A-9-102409 JP 2001-234050 A JP 2004-91515 A

  The present invention has been proposed under such circumstances, and the curable resin composition used for the high heat conductive coil having excellent heat dissipation has an appropriate viscosity (flowability) and curability (gel). A thermosetting resin composition that can form an insulating layer having a high thermal conductivity and high reliability (particularly, the volume resistance value after boiling does not decrease so much). It is intended to provide.

That is, the present invention provides the following (1) to ( 4 ).
(1) Thermal conductivity measured by thin wire heating method of cured product containing vinyl ester resin and / or unsaturated polyester resin (A), curing agent (B) and magnesium oxide (C) , and crystalline silica (D) Is a high thermal conductive resin composition having an acid value of 10 mgKOH / g or less and an equivalent ratio of an epoxy resin and an unsaturated acid used as a raw material for the vinyl ester resin ( The epoxy group / carboxyl group) is 1.05 / 1 to 1.50 / 1, and the equivalent ratio (hydroxyl group / carboxyl group) of the alcohol component and acid component used as the raw material of the unsaturated polyester resin is 1.05 / 1. 1 to 1.50 / 1, comprising 15 to 60 parts by mass of magnesium oxide (C ) and 50 to 200 parts by mass of crystalline silica (D) with respect to 100 parts by mass of the resin (A). Thermosetting resin composition,
(2) The thermosetting resin composition according to (1), which includes the curing agent (B) at a ratio of 0.5 to 5 parts by mass with respect to 100 parts by mass of the resin (A).
( 3 ) A highly heat conductive coil having a cured product obtained by curing the thermosetting resin composition described in (1) or (2 ) above and ( 4 ) an insulating layer made of the cured product described in ( 3 ) above. It is to provide.

  The thermosetting resin composition of the present invention has appropriate curability (gelation time), the cured product has high thermal conductivity, and the high thermal conductive coil of the present invention having an insulating layer made of the cured product is excellent. High heat dissipation and high reliability.

Hereinafter, the thermosetting resin composition, the cured product, and the high thermal conductive coil of the present invention will be described in detail. As the component (A) that is a curable component in the thermosetting resin composition of the present invention, a vinyl ester resin and / or an unsaturated polyester resin is used.
In the present invention, the vinyl ester resin and unsaturated polyester resin used as component (A) are required to have an acid value of 10 mgKOH / g or less.
A normal vinyl ester resin or unsaturated polyester resin has an acid value of 8 to 30 mgKOH / g, but when the acid value exceeds 10 mgKOH / g, it is a catalyst when mixing magnesium oxide which is component (C) described later. As a result, the viscosity of the resin composition rises, and there arises a disadvantage that a large amount of magnesium oxide or filler cannot be filled. The lower limit of the acid value is not particularly limited, but is usually about 3 mgKOH / g because the molecular weight of the resin increases during the synthesis reaction and eventually gels. The acid value is preferably 9 mgKOH / g or less, and more preferably 8.5 mgKOH / g or less.
First, the vinyl ester resin which is one of the components (A) will be described.
Vinyl ester resins are made from unsaturated acids and epoxy resins.
Examples of unsaturated acids that can be used include acrylic acid, methacrylic acid, crotonic acid, sorbic acid, hydroxyethyl methacrylate monophthalate, hydroxyethyl methacrylate monomaleate, hydroxyethyl acrylate monomaleate, hydroxypropyl acrylate monomaleate, and dicyclopentadiazine. Examples thereof include unsaturated monobasic acids such as enil monomalate. If necessary, use an unsaturated dibasic acid such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, etc. Can do. The amount of the unsaturated dibasic acid used in combination is 2/1 or less in molar ratio to the unsaturated monobasic acid. By setting it to 2/1 or less, it becomes possible to adjust the curing with the curing agent which is the component (B). By using an unsaturated dibasic acid in combination, surface drying during curing drying is accelerated.

  As an epoxy resin, as long as it has two or more epoxy groups in one molecule, it can be widely used without being limited by molecular structure, molecular weight or the like. Specific examples include epoxy resins having bisphenol type, novolak type, and biphenyl type aromatic groups, glycidyl esters of polycarboxylic acids, and alicyclic epoxy resins obtained by epoxidation of cyclohexane derivatives. These epoxy resins can be used individually or in mixture of 2 or more types. Furthermore, in addition to the above epoxy resin having two or more epoxy groups, a liquid monoepoxy compound can be used in combination as required. The amount of the monoepoxy compound used in combination is 0.5 / 1 or less in terms of a molar ratio with respect to an epoxy resin having two or more epoxy groups. By setting it to 0.5 / 1 or less, the strength of the synthesized vinyl ester resin is ensured. By using a monoepoxy compound in combination, the viscosity of the resin composition can be lowered. When it is larger than 0.5 / 1, the cured product properties such as bending strength are deteriorated.

The molar ratio of unsaturated acid to epoxy resin is adjusted so that the equivalent ratio of epoxy group / carboxyl group is 1.05 / 1 to 1.50 / 1, preferably 1.05 / 1 to 1.20 / 1. To do.
By setting the equivalent ratio to 1.50 / 1 or less, the residual amount of epoxy groups in the system is prevented from being increased more than necessary (relatively unsaturated and the amount of carboxyl groups are decreased), and radical polymerization Can be cured in a short time.
By setting the equivalent ratio to 1.05 / 1 or more, it is possible to prevent unreacted unsaturated acid from remaining more than necessary, and to prevent the acid value of the resin from exceeding 10 mgKOH / g.

An esterification catalyst may be used to prepare a vinyl ester resin by reacting an epoxy resin with an unsaturated acid.
Examples of esterification catalysts include aminophenols such as 2,4,6-tris (dimethylaminomethyl) phenol, phosphorus compounds such as triphenylphosphine and tributylphosphine, N-benzyldimethylamine, N-benzyldiphenylamine, and triethylamine. Various tertiary amines, quaternary ammonium salts, quaternary phosphonium salts, various quaternary compounds such as quaternary pyridinium salts, metal chlorides such as zinc chloride, aluminum chloride and tin chloride, metal oxides such as magnesium oxide, tetra Organometallic compounds such as butyl titanate and lithium methacrylate can be used. These can be used alone or in admixture of two or more.
The usage-amount of an esterification catalyst is 0.05-2 mass parts normally with respect to 100 mass parts of epoxy resins, Preferably it is 0.1-1 mass part. By setting the amount to 0.1 parts by mass or more, the esterification reaction proceeds smoothly, and by setting the amount to 1 parts by mass or less, a side reaction is prevented from occurring in the esterification reaction and an appropriate pot for the thermosetting resin composition Life can be secured.

Next, the unsaturated polyester resin as another component (A) will be described.
The unsaturated polyester resin can be produced by an esterification reaction between an acid component containing an unsaturated dibasic acid and an alcohol component.
A dibasic acid and a monobasic acid are used as the acid component. Dibasic acids include aliphatic saturated dibasic acids such as adipic acid, aliphatic unsaturated dibasic acids such as maleic acid, fumaric acid, itaconic acid or their anhydrides, phthalic acid, isophthalic acid, terephthalic acid, etc. Examples thereof include aromatic dibasic acids or anhydrides thereof, alicyclic unsaturated dibasic acids such as tetrahydrophthalic acid and anhydrides, and alicyclic saturated dibasic acids such as hexahydrophthalic acid and anhydrides thereof. Among these dibasic acids, aliphatic unsaturated dibasic acids or aromatic unsaturated dibasic acids are used as essential components, and mixed with aliphatic saturated dibasic acids and alicyclic dibasic acids as appropriate. Is done.
Examples of monobasic acids include a mixture of a plurality of types of fatty acids such as soybean oil fatty acid, linseed oil fatty acid, coconut oil fatty acid, tall oil fatty acid, rice bran oil fatty acid.
The acid component can be used alone or in combination.

As alcohol components, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,6-cyclohexanedi Dihydric alcohols such as methanol, glycerin monoallyl ether, trimethylolpropane monoallyl ether, pentaerythritol diallyl ether, trivalent or higher valents such as glycerin, trimethylolpropane, tris-2-hydroxyethyl isocyanurate, pentaerythritol monoallyl ether Although alcohol etc. are mentioned, it is not limited to these. Moreover, these can be used individually or in mixture of 2 or more types.
Saturated polyester resin having an acid value of 10 mgKOH / g or less by charging the above dibasic acid and alcohol so that the molar ratio of hydroxyl group / carboxyl group is 1.05 / 1 to 1.50 / 1 Can be obtained. An esterification catalyst as described above may be used for the esterification reaction.
The vinyl ester resin and unsaturated polyester resin obtained as described above have an acid value of 10 mgKOH / g or less in the present invention.

  The compounding amount in the thermosetting resin composition of the vinyl ester resin or unsaturated polyester resin as component (A) is the compounding amount of components (B) and (C) described later and other components optionally blended. It is decided by its own relationship. The vinyl ester resin and the unsaturated polyester resin as the component (A) may be appropriately mixed as long as the acid value is 10 mgKOH / g or less.

  Next, the curing agent which is the component (B) in the thermosetting resin composition of the present invention will be described. As the curing agent, organic peroxides, specifically, butyl peroxybenzoate, tertiary butyl peroxybenzoate, benzoyl peroxide, tertiary butyl peroxide, 1,1-bis (t-butylperoxy)- 3,3,5-trimethylcyclohexane, t-butyl peroxyoctoate, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butylperoxy-2-ethylhexyl monocarbonate, Acetyl peroxide, methyl ethyl ketone peroxide, cumene peroxide, etc. are mentioned, These can be used individually or in mixture of 2 or more types.

  The compounding amount of the curing agent in the thermosetting resin composition is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass with respect to 100 parts by mass of the component (A). By setting it to 0.5 parts by mass or more, an appropriate curability of the curable resin composition is ensured, and by setting it to 5 parts by mass or less, an appropriate gelation time is secured without being too early, and at the time of injection molding It is possible to prevent clogging of the nozzles and prevent deterioration of the mechanical properties of the cured product due to excessive blending.

Next, magnesium oxide which is the component (C) in the thermosetting resin composition of the present invention will be described.
As magnesium oxide, as long as it is a substance represented by the chemical formula MgO, physical properties such as particle diameter and specific surface area are not particularly limited, and commercially available products having a purity of about 95% can be used.
The blending amount of magnesium oxide in the thermosetting resin composition is preferably 15 to 60 parts by mass, more preferably 30 to 50 parts by mass with respect to 100 parts by mass of the component (A). By setting it to 15 parts by mass or more, moderate thermal conductivity of the cured product is secured, and by setting it to 40 parts by mass or less, the fluidity of the thermosetting resin composition of the present invention is secured and the magnesium oxide has. A decrease in electrical properties (volume resistivity) of the cured product due to hygroscopicity can be prevented, and a decrease in mechanical properties of the cured product due to excessive blending can be prevented.

  The curable resin composition of the present invention comprising the components (A), (B) and (C) may contain other components such as a polymerizable monomer and a curing accelerator as necessary unless the object of the present invention is contrary. It is preferable to add a polymerization inhibitor, a low expansion resin (low shrinkage material), a filler, a release agent, a colorant, an antifoaming agent, a leveling agent, etc., which are preferably added when an agent or a polymerizable monomer is used. Can do.

Examples of polymerizable monomers include ethylene polymerizable monomers such as styrene, vinyl toluene, vinyl pyrrolidone, diallyl phthalate, diallyl isophthalate, triallyl isocyanurate, methyl (meth) acrylate, phenoxyethyl (meth) acrylate, 1,6- Examples include (meth) acrylic monomers such as hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and 2-hydroxyethyl (meth) acrylate, and phenylmaleimide. A mixture of more than one species can be used.
The compounding amount of the polymerizable monomer is preferably 20 to 350 parts by mass with respect to 100 parts by mass of the component (A). By setting it as 20-350 mass parts, the fluidity | liquidity and sclerosis | hardenability of the thermosetting resin composition of this invention can be kept moderate.
In the examples described later, a solution in which the component (A) is dissolved in a polymerizable monomer is referred to as a varnish.

Examples of the curing accelerator include naphthenic acid or octylic acid metal (cobalt, zinc, zirconium, manganese, calcium, copper, etc.) salts, organic titanates, etc., and these can be used alone or in combination of two or more. .
The blending amount of the curing accelerator is preferably 0.5 to 25 parts by mass with respect to 100 parts by mass of the component (B), and the thermosetting resin composition of the present invention is made such a blending amount. The curability of can be arbitrarily adjusted.

  Preferable polymerization inhibitors to be added when a polymerizable monomer is used include phenols such as hydroquinone, methoquinone, paratertiary butyl catechol, pyrogallol, and these are used alone or in combination of two or more. be able to. The blending amount of the polymerization inhibitor is preferably 0.02 to 0.8 parts by weight with respect to 100 parts by weight of the polymerizable monomer, and the thermosetting resin composition of the present invention is made by such blending amount. The curability and pot life of the product can be adjusted.

Examples of the low expansion resin (low shrinkage material) include thermoplastic polymers generally used as low shrinkage materials such as polystyrene, polyethylene, saturated polyester, polymethyl methacrylate, polyvinyl acetate, and styrene-butadiene rubber. Can be used alone or in combination.
The compounding amount of the low expansion resin (low shrinkage material) is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the component (A). Shrinkage that occurs when the resin composition is molded to produce a cured product can be alleviated.

As filler, crystalline silica, fused silica, alumina, hydrated alumina, titanium oxide, bengara, calcium carbonate, calcium hydroxide, magnesium hydroxide, silicon nitride, boron nitride, barium sulfate, aluminum fluoride, calcium fluoride , Magnesium fluoride, antimony trioxide, silicon carbide, talc, gypsum, kaolin clay, dolomite, mica, glass fiber and the like, and these can be used alone or in combination.
The blending amount of the filler is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the component (A), and the mechanical properties of the cured product can be adjusted by using such a blending amount. .

  Examples of the mold release agent include conventionally known mold release agents, for example, aliphatic metal soaps such as zinc stearate and calcium stearate, and the blending amount is based on 100 parts by mass of the component (A). And preferably 0.1 to 5 parts by mass.

The thermosetting resin composition of the present invention is prepared as follows.
That is, vinyl ester resin or unsaturated polyester resin (A), curing agent (B), essential component of magnesium oxide (C) and polymerizable monomer, curing accelerator, polymerization inhibitor, low expansion added as necessary After thoroughly mixing each component such as resin (low shrinkage material), filler, mold release agent, colorant, antifoaming agent, leveling agent, etc. according to a conventional method, further, using a disperser, kneader, three roll mill, etc. It can be easily manufactured by performing a kneading process and then degassing under reduced pressure. At this time, in order to mix each component efficiently, it is preferable to mix the reinforcing material last.

A cured product is obtained by molding and curing the thermosetting resin composition obtained as described above. This molding and curing can be performed by, for example, heat compression molding, transfer molding, or the like.
The heating performed for curing is preferably performed at a mold temperature of 100 ° C. or higher and 200 ° C. or lower, more preferably 130 ° C. or higher and 160 ° C. or lower in consideration of productivity. Moreover, it is preferable that the heat conductivity of the obtained hardened | cured material is 1.5 W / mK or more.

  After impregnating the coil with the thermosetting resin composition of the present invention obtained as described above, the coil is cured at the above temperature, and a cured product having a thermal conductivity of 1.5 W / mK or more is used as an insulating layer. The high heat conductive coil has excellent heat dissipation and high reliability.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these examples. In the following examples, “parts” and “%” mean “parts by mass” and “% by mass” unless otherwise specified.

<Example 1>
40 parts of hydroxyethyl methacrylate monophthalate obtained by reacting 100 parts of 2-hydroxyethyl methacrylate and 100 parts of tetrahydrophthalic anhydride at 100 ° C. for 2 hours in a reaction vessel equipped with a thermometer, a stirrer and a raw material charging nozzle 30 parts of bisphenol A type epoxy resin (EP4100, manufactured by ADEKA) having an epoxy equivalent of 190 and 0.1 part of 2,4,6-tris (dimethylaminomethyl) phenol were charged and heated at 100 ° C. for 12 hours with stirring. The reaction was continued until the acid value became 10 mgKOH / g or less. 30 parts of styrene was added thereto to make a varnish.
A uniform thermosetting resin composition was obtained by mixing 100 parts of this varnish, 30 parts of polystyrene as a low shrinkage material, 2 parts of butyl peroxybenzoate as a curing agent, 30 parts of magnesium oxide, and 40 parts of crystalline silica as a filler. .

Each characteristic in the table was measured by the following method.
《Varnish acid value》
The acid value of component (A) in the varnish [mixture of component (A) and polymerizable monomer, the same applies hereinafter] was measured in accordance with JIS2103.
<< Varnish viscosity >>
The viscosity of the varnish was measured at 25 ° C. using a B-type viscometer (Bismometron, manufactured by Shibaura System Co., Ltd., hereinafter the same) (unit: dPa · s).
<< Varnish viscosity after mixing with magnesium oxide >>
After mixing the varnish so that magnesium oxide was 20%, the viscosity was measured at 50 ° C. using a B-type viscometer (unit is dPa · s).
<< Double varnish viscosity time after mixing with magnesium oxide >>
After mixing the varnish with 20% magnesium oxide, continuously measure the change in viscosity at 50 ° C using a B-type viscometer and measure the time until the viscosity reaches twice the initial value. did.
《Gelification time》
A thermosetting resin composition having 10 g of each example shown in Table 1 (all components described in the blending column) and a glass rod were placed in a test tube and left in an oil bath at 130 ° C. The glass rod was pulled up every hour and the time until the test tube was lifted together with the glass rod was measured (unit: hours).
<< disc growth >>
Weigh 5 g of the same thermosetting resin composition used for the gelation time measurement, place it on a smooth iron plate heated to 165 ° C., sandwich it with an iron plate heated to the same temperature, and apply a load of 40 kg / cm ² from above. The average length of the major axis and minor axis of the resin that was taken out after 45 seconds and spread in an elliptical shape was measured (unit: mm).
《Mold shrinkage》
The same thermosetting resin composition as that used for the gelation time measurement was molded under the molding conditions of 165 ° C., 1 minute, 40 kg / cm ² to produce a test piece having a thickness of 76 mmφ and a thickness of 3 mm, in accordance with JIS K6911. Measured.
"Thermal conductivity"
The same thermosetting resin composition used for the gelation time measurement is molded under the same conditions to produce a resin plate having a thickness of about 2 mm, and a thermal conductivity measuring instrument (QTM-500) manufactured by Kyoto Electronics Industry Co., Ltd. Was used to measure the thermal conductivity by the hot wire method (thin wire heating method) (unit: W / mK).
《Volume resistivity ・ Normal state》
The same thermosetting resin composition as that used for the gelation time measurement is molded under the same conditions, a 2 mm thick resin plate is prepared, and measured according to JIS K6911 using a super insulation meter (manufactured by Yokogawa HP). (Unit: MΩ · m).
<Volume resistivity after boiling>
The test piece after volume resistivity / normal measurement was immersed in boiling water for 1 hour and then measured in the same manner (unit: MΩ · m).
《Bending strength》
The same curable resin composition as that used for the gelation time measurement was molded under the same conditions to prepare a 10 mm × 4 mm × 100 mm test piece and measured according to JIS K6911 (unit: MPa).
《Bending elastic modulus》
A 10 mm × 4 mm × 100 mm test piece was prepared and measured according to JIS K6911 as in the case of bending strength (unit: GPa).
"Tensile strength"
A dumbbell-shaped test piece was prepared according to JIS K6911 and measured according to JIS K6911 (unit: MPa).

<Examples 2-6 and Comparative Examples 1-5>
Each of the above characteristics was measured for a varnish, a thermosetting resin composition, and a cured product obtained by curing the thermosetting resin composition in the same manner as in Example 1 except that the composition shown in Table 1 was used. In Comparative Examples 1, 3 and 5, the heating time was changed at 100 ° C. to adjust the acid values to 12.0, 6.2 and 6.7, respectively. The results are also shown in Table 1.

  As is apparent from Table 1, the thermosetting resin composition of the present invention has appropriate fluidity and curability, the cured product has high thermal conductivity, and the present invention has an insulating layer made of the cured product. It can be seen that the high thermal conductive coil has excellent heat dissipation and high reliability (particularly, the volume resistance value after boiling does not decrease so much).

  The thermosetting resin composition of the present invention is excellent in curability, and a high heat conductive coil having an insulating layer made of a cured product obtained by curing the resin composition is mounted on a hybrid car or an electric vehicle. If incorporated in a generator or the like, it can be used as a highly reliable coil.

Claims (4)

The thermal conductivity measured by the thin wire heating method of the cured product containing vinyl ester resin and / or unsaturated polyester resin (A), curing agent (B), magnesium oxide (C) , and crystalline silica (D) is 1. It is a high thermal conductive resin composition of 5 W / mK or more, wherein the acid value of the resin (A) is 10 mg KOH / g or less, and the equivalent ratio of epoxy resin to unsaturated acid used as a raw material for vinyl ester resin (epoxy group / Carboxyl group) is 1.05 / 1 to 1.50 / 1, and the equivalent ratio (hydroxyl group / carboxyl group) of the alcohol component and acid component used as the raw material of the unsaturated polyester resin is 1.05 / 1 to 1. 50/1, and thermosetting property comprising 15 to 60 parts by mass of magnesium oxide (C ) and 50 to 200 parts by mass of crystalline silica (D) with respect to 100 parts by mass of the resin (A). Resin composition.   The thermosetting resin composition of Claim 1 which contains the said hardening | curing agent (B) in the ratio of 0.5-5 mass parts with respect to 100 mass parts of said resins (A). A cured product obtained by curing the thermosetting resin composition according to claim 1 or 2. A high thermal conductive coil having an insulating layer made of the cured product according to claim 3 .