JP2024066874A - Thermosetting resin composition and molded article - Google Patents

Abstract

To provide a thermosetting resin composition which has good storage stability and gives a cured product having good thermal conductivity.SOLUTION: The thermosetting resin composition contains (A) a thermosetting resin, (B) an ethylenically unsaturated monomer, (C) a shrinkage-reducing agent, (D) an inorganic filler, (E) a thermal polymerization initiator, and (F) glass fibers. The thermosetting resin (A) contains (A-1) an unsaturated polyester resin. The unsaturated polyester resin (A-1) has an acid value of 2.5 mg KOH/g or less. The content of the inorganic filler (D) in the thermosetting resin composition is 60-90 mass%. The content of magnesium oxide in the inorganic filler (D) is 60 mass% or more.SELECTED DRAWING: None

Description

The present invention relates to a thermosetting resin composition, a molded article containing a cured product of the thermosetting resin composition, a method for manufacturing the molded article, an electric/electronic component, and a method for manufacturing the electric/electronic component.

In electronic devices such as motors, coils, and electronic control units mounted on automobiles, etc., in order to protect the wiring board and the electronic components mounted on the wiring board, a structure is required that can fix the components to prevent damage to the components due to vibration and prevent the intrusion of water, corrosive gases, etc. In such cases, a structure in which the entire electronic components are sealed and fixed with a material called a sealant is generally used. As a sealant, a thermosetting resin composition is widely used in which additives according to the purpose are added to a thermosetting resin such as an unsaturated polyester resin or a vinyl ester resin, and the mixture is kneaded in a kneading machine. Among such thermosetting resin compositions, bulk molding compounds (hereinafter abbreviated as "BMC"), which are resin compositions in a bulk form, can be made into molded products by molding methods such as compression molding, transfer molding, and injection molding.

In recent years, electronic components have become more powerful (higher density) and smaller (lighter), which means that large amounts of heat tend to accumulate inside the electronic components. This causes a problem in that the operating efficiency of the electronic components decreases due to this heat. To solve this problem, there is a demand for thermosetting resin compositions, particularly BMCs, that have excellent thermal conductivity.

As a method for imparting thermal conductivity to a thermosetting resin composition, a technique of adding a highly thermally conductive inorganic filler, such as boron nitride, aluminum nitride, aluminum oxide (alumina), magnesium oxide, magnesium carbonate, etc., to the thermosetting resin composition is known. Patent Document 1 discloses an unsaturated polyester resin composition containing magnesium oxide, an inorganic filler that has the advantages of relatively high thermal conductivity, no anisotropy, and low cost. Patent Document 2 discloses a thermosetting resin composition containing calcium carbonate, aluminum hydroxide, and magnesium oxide as inorganic fillers.

JP 2004-027019 A JP 2020-132737 A

The magnesium oxide used as an inorganic filler in the thermosetting resin compositions of Patent Documents 1 and 2 acts as a thickener for the unsaturated polyester resin, so when magnesium oxide is used in a thermosetting resin composition containing an unsaturated polyester resin, there is a problem in that the storage stability of the thermosetting resin composition is insufficient.

The present invention aims to provide a thermosetting resin composition that has good storage stability and produces a cured product with good thermal conductivity.

The present invention includes the following aspects.
[1]
(A) a thermosetting resin,
(B) an ethylenically unsaturated monomer,
(C) a low shrinkage agent,
(D) an inorganic filler;
A thermosetting resin composition comprising: (E) a thermal polymerization initiator; and (F) a glass fiber, wherein the (A) thermosetting resin contains (A-1) an unsaturated polyester resin, the (A-1) unsaturated polyester resin has an acid value of 2.5 mgKOH/g or less, the (D) inorganic filler is contained in the thermosetting resin composition in a content of 60 to 90 mass%, and the (D) inorganic filler has a magnesium oxide content of 60 mass% or more.
[2]
The thermosetting resin composition according to [1], wherein the acid value of the unsaturated polyester resin (A-1) is 0.5 mg KOH/g or more.
[3]
The thermosetting resin composition according to [1] or [2], further comprising a release agent (G).
[4]
Relative to 100 parts by mass of the (A) thermosetting resin,
The (B) ethylenically unsaturated monomer is contained in an amount of 1 to 150 parts by mass,
The composition contains 1 to 100 parts by mass of the (C) low shrinkage agent,
The (D) inorganic filler is contained in an amount of 500 to 1600 parts by mass,
The composition contains 0.1 to 20 parts by mass of the thermal polymerization initiator (E),
The thermosetting resin composition according to any one of [1] to [3], comprising 10 to 300 parts by mass of the glass fiber (F).
[5]
A molded article comprising a cured product of the thermosetting resin composition according to any one of [1] to [4].
[6]
A method for producing a molded article, comprising a step of curing the thermosetting resin composition according to any one of [1] to [4] by heating and pressurizing.
[7]
An electric/electronic part comprising a cured product of the thermosetting resin composition according to any one of [1] to [4].
[8]
A method for producing an electric/electronic component, comprising: a step of compressing, transferring, or injecting the thermosetting resin composition according to any one of [1] to [4] to encapsulate components of the electric/electronic component; and a step of heating and curing the thermosetting resin composition.

According to the present invention, it is possible to provide a thermosetting resin composition that has good storage stability and can give a cured product with good thermal conductivity. Furthermore, it is possible to provide a molded article containing a cured product of the above-mentioned thermosetting resin composition and a manufacturing method thereof, as well as an electric/electronic part containing a cured product of the above-mentioned thermosetting resin composition and a manufacturing method thereof.

The following describes in detail the embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

In this specification, "(meth)acrylic acid" means methacrylic acid or acrylic acid, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acryloyloxy" means acryloyloxy or methacryloyloxy.

In this specification, the term "thermosetting resin" refers to a resin that hardens by forming a crosslinked structure when heated, and refers to the resin in its pre-hardened state.

In this specification, "ethylenically unsaturated bond" means a double bond formed between carbon atoms other than those forming an aromatic ring, and "ethylenically unsaturated monomer" means a monomer having an ethylenically unsaturated bond.

In this specification, the term "acid value" refers to the number of milligrams of potassium hydroxide required to neutralize the resin acid (carboxy group) contained in 1 g of a sample (thermosetting resin), and is a value calculated from the amount required for neutralization by dissolving the sample (thermosetting resin) in a solvent, adding phenolphthalein as an indicator, and titrating with an ethanolic solution of potassium hydroxide (neutralization titration method) using the following calculation formula:
Acid value (mgKOH/g) = [B x f x 5.611] / S
B: Amount of 0.1M potassium hydroxide-ethanol solution used (mL)
f: factor of 0.1M potassium hydroxide-ethanol solution S: amount of sample taken (g)

In this specification, the terms "weight average molecular weight" and "number average molecular weight" refer to values measured at room temperature (23° C.) under the following conditions using gel permeation chromatography (GPC) and determined using a standard polystyrene calibration curve.
Apparatus: Shodex (registered trademark) GPC-101 (Showa Denko K.K.)
Column: Shodex (registered trademark) LF-804 (Showa Denko K.K.)
Column temperature: 40°C
Sample: 0.2% by mass solution of sample in tetrahydrofuran Flow rate: 1 mL/min Eluent: tetrahydrofuran Detector: Shodex (registered trademark) RI-71S (Showa Denko K.K.)

<Thermosetting Resin Composition>
The thermosetting resin composition contains (A) a thermosetting resin, (B) an ethylenically unsaturated monomer, (C) a shrinkage reducing agent, (D) an inorganic filler, (E) a thermal polymerization initiator, and (F) glass fibers. The thermosetting resin composition may further contain (G) a mold release agent, if necessary.

[(A) Thermosetting resin]
From the viewpoints of moldability, fluidity, and cure shrinkage, the (A) thermosetting resin contains (A-1) unsaturated polyester resin as an essential component, and the acid value of the (A-1) unsaturated polyester resin is 2.5 mgKOH/g or less. If necessary, other thermosetting resins generally used for sealing material applications can also be used in combination. As the other thermosetting resin, a resin having a functional group capable of forming a crosslinked structure when heat-cured as a thermosetting resin composition is preferred. In particular, a resin having a plurality of ethylenically unsaturated groups as functional groups from the viewpoint of being able to react with the (B) ethylenically unsaturated monomer and (H) ethylenically unsaturated group-containing phosphate ester compound that can be added as necessary, and having no carboxy group from the viewpoint of storage stability, is preferred. Specific examples of the other thermosetting resin include (A-2) vinyl ester resin, (A-3) urethane (meth)acrylate resin, (A-4) diallyl phthalate resin, (A-5) epoxy resin, and the like. The other thermosetting resins may be used alone or in combination of two or more.

The inventors have found that when the acid value of the (A-1) unsaturated polyester resin is 2.5 mgKOH/g or less, the storage stability of the thermosetting resin composition containing the unsaturated polyester resin is good, and the change (increase) in viscosity over time in a room temperature atmosphere can be suppressed. The smaller the acid value of the (A-1) unsaturated polyester resin, the better the storage stability of the thermosetting resin composition. However, in order to reduce the acid value of the (A-1) unsaturated polyester resin to as close to zero as possible in synthesis, advanced reaction control is required, which increases the production cost, so the acid value is preferably 0.5 mgKOH/g or more. A more preferred acid value is 0.8 mgKOH/g or more and 2.3 mgKOH/g or less, and an even more preferred range is 1.0 mgKOH/g or more and 2.0 mgKOH/g or less.

In this disclosure, when the (A) thermosetting resin also falls under the category of the optional component (H) ethylenically unsaturated group-containing phosphate ester compound described below, it is treated as (H) ethylenically unsaturated group-containing phosphate ester compound.

<(A-1) Unsaturated polyester resin>
The unsaturated polyester resin (A-1) is a polycondensate of a polyhydric alcohol and an unsaturated polybasic acid, or a polycondensate of a polyhydric alcohol, an unsaturated polybasic acid, and a saturated polybasic acid, and is not particularly limited.

The unsaturated polyester resin (A-1) may be used alone or in combination of two or more types. By using the unsaturated polyester resin (A-1), a cured product having excellent mechanical strength and heat resistance can be obtained.

In this disclosure, styrene monomers and the like contained in commercially available unsaturated polyester resins are classified as (B) ethylenically unsaturated monomers.

The polyhydric alcohol is not particularly limited as long as it is a compound having two or more hydroxyl groups. Examples of the polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, pentanediol, hexanediol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), tetraethylene glycol, polyethylene glycol, 2-methyl-1,3-propanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, and the like; bisphenol A; alkylene oxide-modified bisphenol A such as an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of bisphenol A; and glycerin. From the viewpoints of the heat resistance and mechanical strength of the cured product and the fluidity of the thermosetting resin composition during molding, propylene glycol, dipropylene glycol, neopentyl glycol, hydrogenated bisphenol A, and bisphenol A are preferred, and propylene glycol and neopentyl glycol are more preferred. The polyhydric alcohols may be used alone or in combination of two or more kinds.

The unsaturated polybasic acid is not particularly limited as long as it has an ethylenically unsaturated bond and has two or more carboxy groups, or an acid anhydride thereof, and known compounds can be used. In particular, unsaturated polybasic acids having 4 to 6 carbon atoms or an acid anhydride thereof are preferred because they are less expensive and can provide a thermosetting resin composition having excellent mechanical strength and heat resistance of the cured product. Examples of unsaturated polybasic acids include maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, and chloromaleic acid. More preferred are unsaturated polybasic acids selected from fumaric acid, maleic acid, maleic anhydride, and itaconic acid. The unsaturated polybasic acids may be used alone or in combination of two or more.

Preferred combinations of polyhydric alcohols and unsaturated polybasic acids include, for example, a combination of fumaric acid and neopentyl glycol, a combination of maleic acid and dipropylene glycol, a combination of maleic anhydride and propylene glycol, a combination of fumaric acid and propylene glycol, a combination of fumaric acid, hydrogenated bisphenol A and propylene glycol, and a combination of maleic anhydride, propylene glycol and neopentyl glycol. The combinations of fumaric acid and propylene glycol, fumaric acid, hydrogenated bisphenol A and propylene glycol, and maleic anhydride, propylene glycol and neopentyl glycol are preferred because they are less expensive and produce a thermosetting resin composition with a higher heat distortion temperature of the cured product and superior mechanical strength and heat resistance.

The saturated polybasic acid is not particularly limited as long as it is a compound or an acid anhydride thereof that does not have an ethylenically unsaturated bond and has two or more carboxy groups, and known compounds can be used. Examples of the saturated polybasic acid include aromatic saturated polybasic acids or acid anhydrides thereof, such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, nitrophthalic acid, and halogenated phthalic anhydride; aliphatic saturated polybasic acids, such as succinic acid, adipic acid, sebacic acid, oxalic acid, malonic acid, azelaic acid, and glutaric acid; and cyclic aliphatic saturated polybasic acids, such as hexahydrophthalic anhydride. The saturated polybasic acids may be used alone or in combination of two or more.

The weight average molecular weight (Mw) of the (A-1) unsaturated polyester resin is not particularly limited. The weight average molecular weight of the (A-1) unsaturated polyester resin is preferably 2,000 to 50,000, more preferably 3,000 to 40,000, and even more preferably 3,500 to 30,000. If the weight average molecular weight is 2,000 to 50,000, the moldability of the thermosetting resin composition will be even better.

The degree of unsaturation of the unsaturated polyester resin (A-1) is preferably 50 to 100 mol%, more preferably 60 to 100 mol%, and even more preferably 70 to 100 mol%. When the degree of unsaturation is within the above range, the moldability of the thermosetting resin composition containing the unsaturated polyester resin (A-1) is improved.

The degree of unsaturation of the (A-1) unsaturated polyester resin can be calculated by the following formula using the number of moles of the unsaturated polybasic acid and the saturated polybasic acid used as raw materials.
Degree of unsaturation (mol %)={(number of moles of unsaturated polybasic acid×number of ethylenically unsaturated bonds per molecule of unsaturated polybasic acid)/(number of moles of unsaturated polybasic acid+number of moles of saturated polybasic acid)}×100

((A-1) Method for synthesizing unsaturated polyester resin)
The unsaturated polyester resin (A-1) can be synthesized by a known method using the above-mentioned raw materials. The various conditions for synthesizing the unsaturated polyester resin (A-1) are appropriately set depending on the raw materials used and their amounts.

In general, the esterification reaction can be carried out at a temperature of 140°C to 230°C in a stream of an inert gas such as nitrogen gas (atmospheric pressure), or under pressure or reduced pressure. The pressure during the reaction can be constant, or the pressure can be changed over time. The esterification reaction time can be, for example, 5 to 15 hours, but is not limited to this range. In the esterification reaction, an esterification catalyst can be used as necessary. Examples of the esterification catalyst include known catalysts such as manganese acetate, dibutyltin oxide, stannous oxalate, zinc acetate, and cobalt acetate. The esterification catalyst can be used alone or in combination of two or more types.

The unreacted unsaturated polybasic acid remaining after synthesis of the (A-1) unsaturated polyester resin is considered to be the (B) ethylenically unsaturated monomer described below.

In order to increase the molecular weight of the (A-1) unsaturated polyester resin by improving the reaction rate and to improve storage stability by reducing the acid value, it is preferable that the equivalent weight of the hydroxyl group of the polyhydric alcohol is in the range of 0.9 to 1.2 relative to the total amount of the carboxyl groups of the unsaturated polybasic acid and any saturated polybasic acid. The acid value of the unsaturated polyester resin can be adjusted (reduced) by reacting a compound having a glycidyl group (glycidyl (meth)acrylate, phenyl glycidyl ether, n-butyl glycidyl ether, etc.) with the carboxyl group at the end of the unsaturated polyester resin in the presence of a known catalyst that can be used in the ring-opening reaction of a carboxylic acid with an epoxy compound, such as diazabicycloundecene or 2,4,6-tris(dimethylaminomethyl)phenol. It is preferable to use a compound having a C=C bond (carbon-carbon double bond) such as glycidyl (meth)acrylate as the compound having a glycidyl group, because it is possible to obtain a cured product with a higher elastic modulus (higher heat resistance).

(A-1) Unreacted unsaturated polybasic acid and any saturated polybasic acid remaining after synthesis of the unsaturated polyester resin may be present in the thermosetting resin composition without being removed.

The content of the (A-1) unsaturated polyester resin in the (A) thermosetting resin is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. When the content of the (A-1) unsaturated polyester resin is 75% by mass or more, appropriate moldability, fluidity, and cure shrinkage can be ensured. There is no particular upper limit to the content of the (A-1) unsaturated polyester resin in the (A) thermosetting resin. For example, it may be 100% by mass, 97% by mass, or 95% by mass.

<(A-2) Vinyl ester resin>
(A-2) vinyl ester resin is generally a compound having an ethylenically unsaturated bond obtained by a ring-opening reaction between (a) an epoxy group in an epoxy compound having two or more epoxy groups and (b) a carboxy group of an unsaturated monobasic acid having an ethylenically unsaturated bond and a carboxy group. (A-2) vinyl ester resin is described, for example, in Polyester Resin Handbook (published by The Nikkan Kogyo Shimbun, Ltd. in 1988).

(A-2) Vinyl ester resin may be used alone or in combination of two or more kinds. (A-2) Vinyl ester resin is generally used after dilution with (B) ethylenically unsaturated monomer for ease of handling. By using (A-2) Vinyl ester resin, it is possible to reduce the material cost of the thermosetting resin composition and obtain a cured product with excellent adhesiveness.

The number average molecular weight (Mn) of the vinyl ester resin (A-2) can be adjusted according to the desired physical properties, but from the standpoint of handling, a range of 500 to 5,000 is preferable.

((a) Epoxy Compound)
The (a) epoxy compound is not particularly limited as long as it is a compound having two or more epoxy groups. It is preferably at least one selected from the group consisting of bisphenol-type epoxy compounds and novolac phenol-type epoxy compounds, and more preferably a bisphenol-type epoxy compound. By using the (A-2) vinyl ester resin using the (a) epoxy compound as a raw material, the mechanical strength and corrosion resistance of the cured product are further improved.

Examples of bisphenol type epoxy compounds include those obtained by reacting a bisphenol compound such as bisphenol A, bisphenol F, bisphenol S, and tetrabromobisphenol A with epichlorohydrin and/or methylepichlorohydrin; and those obtained by reacting a compound obtained by glycidyl etherifying one or more of the above bisphenol compounds with a condensate of one or more of the above bisphenol compounds with epichlorohydrin and/or methylepichlorohydrin. From the viewpoint of durability, a reaction product of a bisphenol compound with epichlorohydrin is preferred, and a reaction product of bisphenol A with epichlorohydrin is more preferred.

Novolak phenol type epoxy compounds include, for example, those obtained by reacting phenol novolak or cresol novolak with epichlorohydrin and/or methyl epichlorohydrin.

((b) Unsaturated monobasic acid)
The unsaturated monobasic acid (b) is not particularly limited as long as it is a monocarboxylic acid having an ethylenically unsaturated bond. Preferred are methacrylic acid, acrylic acid, crotonic acid, cinnamic acid, etc., more preferably acrylic acid or methacrylic acid, and even more preferably methacrylic acid from the viewpoint of the corrosion resistance of the cured product.

((A-2) Method for synthesizing vinyl ester resin)
The vinyl ester resin (A-2) can be synthesized by a known synthesis method, for example, a method in which an unsaturated monobasic acid (b) is added in the presence of an esterification catalyst and an epoxy compound (a) in a reaction vessel capable of being heated and stirred, and the reaction is carried out at 70 to 150°C, preferably 80 to 140°C, and more preferably 90 to 130°C.

The unreacted (b) unsaturated monobasic acid remaining after synthesis of (A-2) vinyl ester resin is considered to be (B) ethylenically unsaturated monomer, which will be described later.

As the esterification catalyst, for example, known catalysts such as tertiary amines such as triethylamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, diazabicyclooctane, triphenylphosphine, diethylamine hydrochloride, etc. can be used.

The mixing ratio of the (a) epoxy compound and the (b) unsaturated monobasic acid is preferably such that the total amount of the carboxyl groups of the (b) unsaturated monobasic acid is 0.3 to 1.2 moles per mole of the total amount of epoxy groups of the (a) epoxy compound, more preferably 0.4 to 1.1 moles, and even more preferably 0.5 to 1.0 moles. When the total amount of the carboxyl groups of the (b) unsaturated monobasic acid is 0.3 moles or more, a cured product having sufficient hardness can be obtained when the thermosetting resin composition is cured. On the other hand, when the total amount of the carboxyl groups of the (b) unsaturated monobasic acid is 1.2 moles or less, the amount of unreacted (b) unsaturated monobasic acid can be reduced when synthesizing the (A-2) vinyl ester resin, and thus a cured product having excellent mechanical strength can be obtained.

After synthesis of the vinyl ester resin (A-2), the unreacted (b) unsaturated monobasic acid can be used as it is as the ethylenically unsaturated monomer (B) of the thermosetting resin composition without being removed. When the thermosetting resin composition is heat-cured, the unreacted (b) unsaturated monobasic acid may volatilize or bleed out, affecting the adhesiveness of the cured product, so it is better to reduce the content of the unreacted (b) unsaturated monobasic acid as much as possible. For example, the content of the unreacted (b) unsaturated monobasic acid is preferably 5% by mass or less, more preferably 3% by mass or less, based on the total amount of the vinyl ester resin (A-2) and the unreacted (b) unsaturated monobasic acid.

The content of the vinyl ester resin (A-2) in the thermosetting resin (A) can be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. There is no particular upper limit to the content of the vinyl ester resin (A-2) in the thermosetting resin (A). For example, it may be 25% by mass, 20% by mass, or 10% by mass.

<(A-3) Urethane (meth)acrylate resin>
As the urethane (meth)acrylate resin (A-3), for example, a resin obtained by introducing (meth)acryloyl groups into the hydroxyl groups or isocyanato groups at both ends of a polyurethane obtained by reacting a polyisocyanate with a polyhydric alcohol can be used.

As the polyhydric alcohol, the compounds described above as raw materials for the (A-1) unsaturated polyester resin can be used without any particular restrictions.

Examples of polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, lysine triisocyanate, and trimethylhexane diisocyanate; cyclic aliphatic polyisocyanates such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4 (or 2,6)-diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), and 1,3-(isocyanatomethyl)cyclohexane; aromatic polyisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, and triphenylmethane triisocyanate; and adducts, isocyanurates, and biurets of these polyisocyanates. The polyisocyanates may be used alone or in combination of two or more.

When introducing a (meth)acryloyl group, for example, a method can be used in which a terminal isocyanato group is reacted with a hydroxyl group-containing (meth)acrylic compound, or a method can be used in which a terminal hydroxyl group is reacted with an isocyanato group-containing (meth)acrylic compound such as 2-(meth)acryloyloxyethyl isocyanate, 2-(meth)acryloyloxypropyl isocyanate, or 1,1-bis(acryloyloxymethyl)ethyl isocyanate. Examples of hydroxyl group-containing (meth)acrylic compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, caprolactone-modified hydroxyalkyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, tris(hydroxyethyl)isocyanuric acid di(meth)acrylate, pentaerythritol tri(meth)acrylate, glycerin mono(meth)acrylate, and hydroxyethylacrylamide, with 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, caprolactone-modified hydroxyalkyl (meth)acrylate, and hydroxyethylacrylamide being preferred. The isocyanato group-containing (meth)acrylic compounds and hydroxyl group-containing (meth)acrylic compounds may each be used alone or in combination of two or more.

In addition, any unreacted hydroxyl group-containing (meth)acrylic compound or unreacted isocyanato group-containing (meth)acrylic compound remaining after synthesis of (A-3) urethane (meth)acrylate resin is considered to be (B) ethylenically unsaturated monomer, which will be described later.

The content of the urethane (meth)acrylate resin (A-3) in the thermosetting resin (A) can be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. There is no particular upper limit to the content of the urethane (meth)acrylate resin (A-3) in the thermosetting resin (A). For example, it may be 25% by mass, 20% by mass, or 10% by mass.

<(A-4) Diallyl phthalate resin>
The diallyl phthalate resin (A-4) is an oligomer obtained by an esterification reaction between diallyl phthalate and a polyhydric alcohol, and a conventionally known one can be used without particular limitation. The diallyl phthalate resin (A-4) may be used alone or in combination of two or more kinds.

In addition, after synthesizing the (A-4) diallyl phthalate resin, any unreacted diallyl phthalate may be present in the thermosetting resin composition without being removed.

(A-4) Any unreacted diallyl phthalate remaining after synthesis of diallyl phthalate resin is considered to be (B) an ethylenically unsaturated monomer, as described below.

The content of the (A-4) diallyl phthalate resin in the (A) thermosetting resin can be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. There is no particular upper limit to the content of the (A-4) diallyl phthalate resin in the (A) thermosetting resin. For example, it may be 25% by mass, 20% by mass, or 10% by mass.

<(A-5) Epoxy resin>
As the epoxy resin (A-5), the compounds described in the section (a) Epoxy compounds can be used. The epoxy resin (A-5) may be used alone or in combination of two or more kinds.

The content of the epoxy resin (A-5) in the thermosetting resin (A) can be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more. There is no particular upper limit to the content of the epoxy resin (A-5) in the thermosetting resin (A). For example, it may be 25% by mass, 20% by mass, or 10% by mass.

[(B) Ethylenically unsaturated monomer]
The ethylenically unsaturated monomer (B) is not particularly limited as long as it is a monomer having an ethylenically unsaturated bond and does not fall under the category of the ethylenically unsaturated group-containing phosphate ester compound (H) which is an optional component described later. The ethylenically unsaturated monomer (B) may be used alone or in combination of two or more kinds.

Specifically, vinyl compounds (compounds having a vinyl group) such as styrene, vinyltoluene, t-butylstyrene, methoxystyrene, divinylbenzene, and vinylnaphthalene; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, furfuryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, phenyl (meth)acrylate, benzene Examples of the methacrylate include aryl (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, allyl (meth)acrylate, isobornyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecanol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and cyclic unsaturated compounds such as acenaphthylene and norbornene. (A) From the viewpoint of copolymerizability with the thermosetting resin, vinyl compounds are preferred, and one or more selected from styrene, vinyl toluene, t-butyl styrene, and methoxystyrene are more preferred, and styrene is even more preferred.

The content of the (B) ethylenically unsaturated monomer is preferably 1 to 150 parts by mass, more preferably 50 to 130 parts by mass, and even more preferably 80 to 120 parts by mass, per 100 parts by mass of the (A) thermosetting resin. When the (B) ethylenically unsaturated monomer content is 1 part by mass or more, the viscosity of the thermosetting resin composition can be adjusted to an appropriate range, and therefore moldability is good. When the (B) ethylenically unsaturated monomer content is 150 parts by mass or less, the mechanical strength of the cured product is good.

[(C) Shrinkage reducing agent]
The (C) shrinkage reducing agent is not particularly limited, and any agent known in the technical field of the present invention can be used. The (C) shrinkage reducing agent is preferably a thermoplastic resin. Examples of the (C) shrinkage reducing agent include polystyrene, polyethylene, polymethyl methacrylate, polyvinyl acetate, saturated polyester, polycaprolactone, styrene-butadiene rubber, and styrene-modified vinyl acetate block polymer. The (C) shrinkage reducing agent may be used alone or in combination of two or more.

The content of the (C) low shrinkage agent is preferably 1 to 100 parts by mass, more preferably 15 to 90 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of the (A) thermosetting resin. If the content of the (C) low shrinkage agent is 1 part by mass or more, the shrinkage rate of the cured product is small, and the desired dimensional accuracy can be obtained in the molded product. If the content of the (C) low shrinkage agent is 100 parts by mass or less, the moldability of the thermosetting resin composition and the mechanical properties of the cured product are better.

[(D) Inorganic filler]
As the inorganic filler (D), a particulate material known in the technical field of the present invention can be used. The inorganic filler (D) contains magnesium oxide as an essential component. The inorganic filler (D) may contain other inorganic fillers as necessary. By using the inorganic filler (D), the molding shrinkage rate of the molded product can be reduced, the viscosity of the thermosetting resin composition can be adjusted to improve workability, or the strength of the molded product can be improved. By using the inorganic filler (D) containing magnesium oxide as an essential component, the thermal conductivity of the molded product can be increased. The content of the inorganic filler (D) in the thermosetting resin composition is 60 to 90 mass%, preferably 65 to 85 mass%, and more preferably 70 to 80 mass%. When the content of the inorganic filler (D) in the thermosetting resin composition is 60 to 90 mass%, a thermoset product having good mechanical strength can be obtained.

As described above, the inorganic filler (D) contains magnesium oxide as an essential component, and the content of magnesium oxide in the inorganic filler (D) is 60% by mass or more. Magnesium oxide has high thermal conductivity and is low cost. By using a thermosetting resin composition containing 60% by mass or more of magnesium oxide in the inorganic filler (D), a cured product of the thermosetting resin composition having good thermal conductivity can be produced at low cost. Examples of other inorganic fillers that can be used in combination with magnesium oxide include calcium carbonate, silica, aluminum oxide, aluminum hydroxide, barium sulfate, calcium sulfate, calcium hydroxide, calcium oxide, magnesium hydroxide, anhydrous magnesium carbonate, wollastonite, clay, kaolin, mica, gypsum, anhydrous silicic acid, and glass powder. Calcium carbonate, aluminum oxide, and aluminum hydroxide are preferable because they are inexpensive. The other inorganic fillers may be used alone or in combination of two or more.

The average particle size of the inorganic filler (D) is preferably 1 to 100 μm, more preferably 1 to 60 μm, and even more preferably 1 to 50 μm. If the average particle size of the inorganic filler (D) is 1 μm or more, particle aggregation can be suppressed. On the other hand, if the average particle size of the inorganic filler (D) is 100 μm or less, the moldability of the thermosetting resin composition is good.

In this specification, the term "average particle size" refers to the 50% particle size (D50) in a volume-based cumulative particle size distribution measured by a laser diffraction/scattering type particle size distribution measuring device (manufactured by Microtrack-Bell Co., Ltd., _FRA ).

(D) The shape of the inorganic filler is not particularly limited. Examples include nearly spherical, ellipsoidal, scaly, amorphous, etc.

The amount of the inorganic filler (D) containing magnesium oxide is preferably 500 to 1600 parts by mass, more preferably 600 to 1400 parts by mass, and even more preferably 800 to 1200 parts by mass, relative to 100 parts by mass of the thermosetting resin (A). If the amount of the inorganic filler (D) is 500 parts by mass or more, the mechanical properties of the cured product are better. If the amount of the inorganic filler (D) is 1600 parts by mass or less, the inorganic filler (D) is more uniformly dispersed in the thermosetting resin composition, and a homogeneous molded product can be produced. From the viewpoint of thermal conductivity, the content of magnesium oxide in the inorganic filler (D) is 60% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of the content of magnesium oxide in the inorganic filler (D) is not particularly limited, but may be, for example, 100% by mass, 99% by mass, or 98% by mass.

[(E) Thermal Polymerization Initiator]
The thermal polymerization initiator (E) is not particularly limited as long as it is a polymerization initiator that generates radicals by heating, and examples thereof include organic peroxides such as diacyl peroxides, peroxy esters, hydroperoxides, dialkyl peroxides, ketone peroxides, peroxy ketals, alkyl peresters, and percarbonates.

Among these peroxides, the following are preferred as the thermal polymerization initiator (E): 1,1-di-t-hexylperoxy-cyclohexane, t-hexylperoxyisopropylcarbonate, t-butylperoxyoctoate, t-butylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-amylperoxy-2-ethylhexanoate, benzoyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, t-butylperoxyisopropylcarbonate, t-butylperoxybenzoate, dicumyl peroxide, and di-t-butyl peroxide. The thermal polymerization initiator (E) may be used alone or in combination of two or more.

The amount of (E) thermal polymerization initiator is preferably 0.1 to 20 parts by mass, more preferably 3 to 15 parts by mass, and even more preferably 4 to 10 parts by mass, per 100 parts by mass of (A) thermosetting resin. When the amount of (E) thermal polymerization initiator is 0.1 part by mass or more, the curing reaction during molding of the thermosetting resin composition proceeds uniformly, and the physical properties and appearance of the cured product become good. When the amount of (E) thermal polymerization initiator is 20 parts by mass or less, the storage stability of the thermosetting resin composition becomes good, and handling properties are improved.

[(F) Glass fiber]
The glass fiber (F) is not particularly limited as long as it is a fibrous material having an aspect ratio of 3 or more. A specific example is chopped strand glass.

The fiber length of (F) the glass fiber is preferably 20 mm or less, more preferably 10 mm or less, and even more preferably 5.0 mm or less. When the fiber length is 20 mm or less, the moldability of the thermosetting resin composition is good, and the appearance of the cured product is good. The fiber length is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1.0 mm or more. When the fiber length is 0.1 mm or more, the strength of the cured product is good. The average fiber diameter of (F) the glass fiber is preferably 3 to 100 μm, and more preferably 5 to 30 μm.

The content of the (F) glass fiber is preferably 10 to 300 parts by mass, more preferably 30 to 250 parts by mass, and even more preferably 40 to 210 parts by mass, per 100 parts by mass of the (A) thermosetting resin. If the content of the (F) glass fiber is 10 parts by mass or more, the mechanical properties of the molded article obtained from the thermosetting resin composition are better. If the content of the (F) glass fiber is 300 parts by mass or less, the (F) glass fiber is more uniformly dispersed in the thermosetting resin composition, and a homogeneous molded article can be produced.

[(G) Release Agent]
The thermosetting resin composition may contain a (G) mold release agent as necessary. The (G) mold release agent is not particularly limited, and any agent known in the technical field of the present invention may be used. Examples of the (G) mold release agent include stearic acid, oleic acid, zinc stearate, calcium stearate, aluminum stearate, magnesium stearate, stearic acid amide, oleic acid amide, silicone oil, and synthetic wax. The (G) mold release agent may be used alone or in combination of two or more kinds.

When (G) release agent is used, its content is preferably 0.1 to 40 parts by mass, more preferably 2 to 30 parts by mass, and even more preferably 4 to 25 parts by mass, per 100 parts by mass of (A) thermosetting resin. If the content of (G) release agent is 0.1 parts by mass or more, the release properties of the cured product when molded are good, and the productivity of the product is good. On the other hand, if the content of (G) release agent is 40 parts by mass or less, the surface of the cured product is not contaminated by excess release agent, and a cured product with a good appearance can be obtained.

[(H) Ethylenically unsaturated group-containing phosphate ester compound]
The thermosetting resin composition may contain (H) an ethylenically unsaturated group-containing phosphate ester compound as necessary. The (H) ethylenically unsaturated group-containing phosphate ester compound is not particularly limited as long as it is a compound having an ethylenically unsaturated group and a phosphate ester structure. By using the (H) ethylenically unsaturated group-containing phosphate ester compound, the adhesive strength of the cured product of the thermosetting resin composition to metal is improved. The (H) ethylenically unsaturated group-containing phosphate ester compound can be obtained by, for example, esterification reaction of a phosphorus compound such as phosphoric acid, polyphosphoric acid, phosphorus pentoxide, phosphorus oxychloride, etc. with an organic compound having an ethylenically unsaturated group and an alcoholic hydroxyl group or an epoxy group.

Examples of organic compounds having an ethylenically unsaturated group and an alcoholic hydroxyl group or an epoxy group include hydroxyalkyl (meth)acrylates such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, methyl-α-hydroxymethylacrylate, ethyl-α-hydroxymethylacrylate, n-butyl-α-hydroxymethylacrylate, and 2-ethylhexyl-α-hydroxymethylacrylate, and their alkylene oxide adducts, (meth)acrylates such as glycidyl (meth)acrylate and N-methylol (meth)acrylamide, and unsaturated alcohols such as allyl alcohol, crotyl alcohol, and isocrotyl alcohol, and their alkylene oxide adducts. Among these, from the viewpoint of adhesive strength, hydroxyalkyl (meth)acrylates such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, methyl-α-hydroxymethyl acrylate, ethyl-α-hydroxymethyl acrylate, n-butyl-α-hydroxymethyl acrylate, and 2-ethylhexyl-α-hydroxymethyl acrylate are preferred, and from the viewpoint of combination with other ethylenically unsaturated monomers that affect strength and dispersibility, hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate are more preferred.

From the viewpoints of adhesion and dispersibility in resin, the (H) ethylenically unsaturated group-containing phosphate ester compound is preferably one or more selected from monoesters and diesters, and is more preferably a compound having one or two ethylenically unsaturated groups. From the viewpoints of adhesion and dispersibility in resin, the (H) ethylenically unsaturated group-containing phosphate ester compound is preferably a phosphate ester having a (meth)acryloyloxy group. Specific examples of such compounds include 2-(meth)acryloyloxyethyl acid phosphate, di[2-(meth)acryloyloxyethyl]acid phosphate, etc.

When the (H) ethylenically unsaturated group-containing phosphate ester compound is used, the content of the (H) ethylenically unsaturated group-containing phosphate ester compound is preferably 0.1 to 70 parts by mass, more preferably 0.8 to 50 parts by mass, even more preferably 1 to 30 parts by mass, and even more preferably 5 to 30 parts by mass, relative to 100 parts by mass of the (A) thermosetting resin. When the (H) ethylenically unsaturated group-containing phosphate ester compound is 0.1 parts by mass or more, the adhesive strength of the cured product of the thermosetting resin composition to metal is good. When the (H) ethylenically unsaturated group-containing phosphate ester compound is 70 parts by mass or less, the releasability from the mold during molding is good.

[Other additives]
In addition to the above components, the thermosetting resin composition may contain components known in the technical field of the present invention, such as a viscosity reducer (viscosity modifier), a colorant, a polymerization inhibitor, and a molding aid, within a range that does not impair the effects of the present invention.

A viscosity reducer is a compound that exhibits a viscosity reducing effect when blended with a thermosetting resin composition. For example, BYK-W9011, available commercially as a wetting dispersant from BYK Corporation, can be mentioned. Viscosity reducers may be used alone or in combination of two or more types. The amount of viscosity reducer added can be adjusted as appropriate depending on the handleability, fluidity, etc. required for the thermosetting resin composition.

Colorants are used when coloring the cured product. As colorants, various dyes, inorganic pigments, or organic pigments can be used. Colorants may be used alone or in combination of two or more. The amount of colorant added can be adjusted appropriately depending on the degree of coloration desired in the cured product.

Examples of polymerization inhibitors include hydroquinone, trimethylhydroquinone, p-benzoquinone, naphthoquinone, t-butylhydroquinone, catechol, p-t-butylcatechol, and 2,6-di-t-butyl-4-methylphenol. The polymerization inhibitors may be used alone or in combination of two or more. The amount of polymerization inhibitor added can be appropriately adjusted depending on the storage environment and period of the thermosetting resin composition, the curing conditions, etc.

<Method for producing thermosetting resin composition>
The thermosetting resin composition can be produced by mixing (A) a thermosetting resin, (B) an ethylenically unsaturated monomer, (C) a low shrinkage agent, (D) an inorganic filler, (E) a thermal polymerization initiator, and (F) glass fibers, and, as necessary, optional components such as (G) a release agent, (H) an ethylenically unsaturated group-containing phosphate ester compound, and other additives.

An example of a mixing method is kneading. There are no particular limitations on the kneading method, and for example, a kneader, a disperser, a planetary mixer, etc. can be used. The kneading temperature is preferably 5°C to 50°C, and more preferably 10°C to 40°C.

There are no particular restrictions on the order in which the components are mixed when producing a thermosetting resin composition. For example, it is preferable to mix the (A) thermosetting resin with some or all of the (B) ethylenically unsaturated monomer and then mix the other components, since this makes it easier to obtain a thermosetting resin composition in which the components are sufficiently dispersed or uniformly mixed. At least a portion of the (B) ethylenically unsaturated monomer may be mixed in advance with the (A) thermosetting resin so that it acts as a solvent, dispersion medium, etc.

<Method for producing the cured product>
The thermosetting resin composition can be cured by heating. The conditions for curing the thermosetting resin composition can be appropriately set depending on the materials used and the decomposition temperature of the thermal polymerization initiator (E). One example of preferred conditions is a temperature of 120 to 180°C, more preferably a temperature of 120 to 160°C, and a curing time of 1 to 30 minutes.

<Method of manufacturing molded products>
The thermosetting resin composition can be molded into a desired shape and heated to produce a molded article containing a cured product of the thermosetting resin composition. The molding and curing method is not particularly limited, and methods commonly used in the technical field of the present invention, such as compression molding, transfer molding, and injection molding, can be used.

More specific examples of methods for molding and curing a thermosetting resin composition include a method of opening a mold, pouring a thermosetting resin composition into the mold, and curing the composition, and a method of injecting a thermosetting resin composition into a closed mold from the outside through a hole in the mold such as a sprue while the mold is under reduced pressure or under pressure from the outside, as in injection molding, and curing the composition. The conditions for curing the thermosetting resin composition in the mold can be set appropriately depending on the material used. One example of preferred conditions is a temperature of 120 to 180°C, more preferably a temperature of 120°C to 160°C, and a curing time of 1 to 30 minutes.

In one embodiment, an electric/electronic component is provided that includes a cured product of the thermosetting resin composition. The electric/electronic component can be manufactured, for example, by encapsulating components of the electric/electronic component with the thermosetting resin composition and then curing the thermosetting resin composition by heating. The components of the electric/electronic component can be encapsulated, for example, by injecting the thermosetting resin composition into a housing having the components therein.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

(A) An example of the synthesis of a thermosetting resin is shown below.

[Synthesis Example 1] (A-1-1) Synthesis of Unsaturated Polyester Resin In a four-neck flask equipped with a thermometer, a stirrer, an inert gas inlet, and a reflux condenser, 1.72 kg (17.5 mol) of maleic anhydride (manufactured by Nippon Shokubai Co., Ltd.), 0.67 kg (8.8 mol) of propylene glycol (manufactured by Arc Co., Ltd.), and 0.91 kg (8.8 mol) of neopentyl glycol (manufactured by LG Chemical Co., Ltd.) were charged. The temperature was raised to 200°C while heating and stirring under a nitrogen gas flow, and an esterification reaction was carried out for 8 hours. After cooling the reaction liquid to 160°C, 0.21 kg (1.5 mol) of glycidyl methacrylate (manufactured by NOF Corporation) and 0.003 kg of diazabicycloundecene (manufactured by Tokyo Chemical Industry Co., Ltd.) were added and reacted for 30 minutes. After the reaction was completed, styrene monomer was added so that the amount was 37% by mass relative to the total of the unsaturated polyester resin and the styrene monomer, and a mixture of unsaturated polyester resin and styrene was obtained. The resulting unsaturated polyester resin had a degree of unsaturation of 100 mol %, an acid value of 1.4 mgKOH/g and a weight average molecular weight of 10,000.

[Synthesis Example 2] Synthesis of unsaturated polyester resin (A-1-2) After obtaining an unsaturated polyester resin by the same process as the synthesis of unsaturated polyester resin (A-1-1) above, except that glycidyl methacrylate and diazabicycloundecene were not added, styrene monomer was added in an amount of 43.5 mass% based on the total amount of the unsaturated polyester resin and the styrene monomer to obtain a mixture of the unsaturated polyester resin and styrene. The obtained unsaturated polyester resin had an unsaturation degree of 100 mol%, an acid value of 16.0 mgKOH/g, and a weight average molecular weight of 10,000.

[Synthesis Example 3] Synthesis of unsaturated polyester resin (A-1-3) A mixture of unsaturated polyester resin and styrene was obtained by the same process as in the synthesis of unsaturated polyester resin (A-1-1) above, except that the amount of glycidyl methacrylate added was changed to 0.28 kg (2.0 mol). The unsaturated polyester resin obtained had an unsaturation degree of 100 mol%, an acid value of 1.0 mgKOH/g, and a weight average molecular weight of 10,000.

[Synthesis Example 4] Synthesis of unsaturated polyester resin (A-1-4) A mixture of unsaturated polyester resin and styrene was obtained by the same process as in the synthesis of unsaturated polyester resin (A-1-1) above, except that the amount of glycidyl methacrylate added was changed to 0.14 kg (1.0 mol). The unsaturated polyester resin obtained had an unsaturation degree of 100 mol%, an acid value of 2.5 mgKOH/g, and a weight average molecular weight of 10,000.

[Synthesis Example 5] Synthesis of unsaturated polyester resin (A-1-5) A mixture of unsaturated polyester resin and styrene was obtained by the same process as in the synthesis of unsaturated polyester resin (A-1-1) above, except that the amount of glycidyl methacrylate added was changed to 0.11 kg (0.8 mol). The unsaturated polyester resin obtained had an unsaturation degree of 100 mol%, an acid value of 4.1 mgKOH/g, and a weight average molecular weight of 10,000.

[Synthesis Example 6] Synthesis of unsaturated polyester resin (A-1-6) A mixture of unsaturated polyester resin and styrene was obtained by the same process as in the synthesis of unsaturated polyester resin (A-1-1) above, except that the amount of glycidyl methacrylate added was changed to 0.09 kg (0.6 mol). The unsaturated polyester resin obtained had an unsaturation degree of 100 mol%, an acid value of 8.2 mgKOH/g, and a weight average molecular weight of 10,000.

The other ingredients used were as follows:

(B) Ethylenically unsaturated monomer:
- Styrene (Idemitsu Kosan Co., Ltd.)

(C) Low shrinkage agent:
・Modiper (registered trademark) S-501 (styrene-modified vinyl acetate block polymer, manufactured by NOF Corporation)

(D) Inorganic filler:
・Starmag SL-WR (magnesium oxide, average particle size 8.6 μm, manufactured by Konoshima Chemical Co., Ltd.)
Softon 1200BM (calcium carbonate, average particle size 1.80 μm, manufactured by Bihoku Funka Kogyo Co., Ltd.)
B53 (aluminum hydroxide, average particle size 55 μm, manufactured by Nippon Light Metal Co., Ltd.)
・Mixture of Magthermo (registered trademark) MS-PS (anhydrous magnesium carbonate, average particle size 15 μm, manufactured by Konoshima Chemical Co., Ltd.) and Magthermo (registered trademark) MS-S (anhydrous magnesium carbonate, average particle size 1.5 μm, manufactured by Konoshima Chemical Co., Ltd.) ・Magseeds EP3 (magnesium hydroxide, average particle size 5.6 μm, manufactured by Konoshima Chemical Co., Ltd.)

(E) Thermal polymerization initiator:
Perhexyl (registered trademark) I (t-hexylperoxyisopropyl carbonate, manufactured by NOF Corporation)

(F) Glass fiber:
Glass chop (fiber length 1.5 mm, fiber diameter 11 μm, manufactured by Nitto Boseki Co., Ltd.)

(G) Release agent:
・Calcium stearate (NOF Corporation)

Example 1
(Preparation of Thermosetting Resin Composition)
(A) Thermosetting resin and (B) 159 parts by mass of a mixture of the unsaturated polyester resin (A-1-1) obtained in Synthesis Example 1 as an ethylenically unsaturated monomer and styrene (100 parts by mass of unsaturated polyester resin, 59 parts by mass of styrene), (C) 31 parts by mass of Modiper S-501 as a low shrinkage agent, (D) 894 parts by mass of magnesium oxide as an inorganic filler, (E) 4 parts by mass of Perhexyl (registered trademark) I as a thermal polymerization initiator, (F) 39 parts by mass of glass chop as glass fiber, and (G) 4 parts by mass of calcium stearate as a mold release agent were charged into a twin-arm kneader (manufactured by Moriyama Seisakusho Co., Ltd.) and kneaded for 30 minutes at 30° C. to prepare a thermosetting resin composition.

(Viscosity change rate)
The viscosity (η1 and η8, respectively) of the thermosetting resin composition was measured after storage in an air atmosphere at 23 ° C. for 1 day (24 hours) and after storage in an air atmosphere at 23 ° C. for 8 days (168 hours) using a flow tester viscosity measuring instrument (measuring instrument: Shimadzu Corporation CFT-500D) after preparation of the thermosetting resin composition. Specifically, the thermosetting resin composition after storage for a predetermined time was placed in a cylinder sample insertion hole heated to 90 ° C. with a die having a diameter of 1.2 mm and a thickness of 10 mm, and the piston was pressurized at a pressure of 5 MPa after preheating for 60 seconds, and the thermosetting resin composition was allowed to flow out from the nozzle of the die, and the viscosity of the thermosetting resin composition was obtained from the point where the linearity of the relationship between time and stroke was good, and the viscosity change rate was calculated by the following formula. The results are shown in Table 1. If the viscosity change rate is 150% or less, it can be determined that the storage stability is good.
Viscosity change rate = (η8/η1) x 100 (%)

(Thermal conductivity)
The prepared thermosetting resin composition was molded using a 50t hydraulic press (manufactured by Press Machinery Co., Ltd.) as a molding machine under conditions of a molding temperature of 150°C, a molding time of 10 minutes, and a molding pressure of 15 MPa to obtain a cured product having a thickness of 20 mm, a width of 50 mm, and a length of 110 mm as a test piece for evaluation. The thermal conductivity of the obtained test piece was measured at 23°C using a rapid thermal conductivity meter QTM-500 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.). The results are shown in Table 1.

<Examples 2 to 5, Comparative Examples 1 to 7>
A thermosetting resin composition was prepared in the same manner as in Example 1, except that the type and composition of the raw materials were changed as shown in Table 1. The amount of styrene used to dilute the thermosetting resin (A) was excluded from the amount of component (A) and was listed in the amount of ethylenically unsaturated monomer (B). Next, various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

From Examples 1, 4, and 5 and Comparative Examples 1 to 3, it is observed that the viscosity change rate of the thermosetting resin composition tends to increase as the acid value of the unsaturated polyester resin used as the (A) thermosetting resin increases. Since the viscosity change rate of Example 5, which used an unsaturated polyester resin with an acid value of 2.5 mgKOH/g, was 147%, it is suggested that a thermosetting resin composition with a viscosity change rate of 150% or less can be obtained by using an (A-1) unsaturated polyester resin with an acid value of 2.5 mgKOH/g or less. In other words, it can be said that a thermosetting resin composition with good storage stability and a viscosity change rate of 150% or less can be obtained by setting the acid value of the unsaturated polyester resin contained in the thermosetting resin composition to 2.5 mgKOH/g or less. Note that the thermal conductivity of the thermosetting resin composition of Example 4 has not been evaluated, but it is sufficiently suggested that it has a thermal conductivity equivalent to that of Examples 1 and 5. (D) In Comparative Examples 4 to 7, in which magnesium-containing particles other than magnesium oxide (magnesium hydroxide or anhydrous magnesium carbonate) or particles containing other metal elements (calcium carbonate or aluminum hydroxide) were used alone as the inorganic filler, the thermal conductivity was insufficient.

According to the present invention, a thermosetting resin composition is provided that has good storage stability and can give a cured product with good thermal conductivity. Furthermore, according to the present invention, a molded article containing a cured product of the thermosetting resin composition, specifically an electric/electronic component containing a cured product of the thermosetting resin composition, is provided. The thermosetting resin composition can be preferably used as a sealant for electric/electronic components.

Claims (8)

(A) a thermosetting resin,
(B) an ethylenically unsaturated monomer,
(C) a low shrinkage agent,
(D) an inorganic filler;
A thermosetting resin composition comprising: (E) a thermal polymerization initiator; and (F) a glass fiber, wherein the (A) thermosetting resin contains (A-1) an unsaturated polyester resin, the (A-1) unsaturated polyester resin has an acid value of 2.5 mgKOH/g or less, the (D) inorganic filler is contained in the thermosetting resin composition in a content of 60 to 90 mass%, and the (D) inorganic filler has a magnesium oxide content of 60 mass% or more. The thermosetting resin composition according to claim 1, wherein the acid value of the unsaturated polyester resin (A-1) is 0.5 mg KOH/g or more. The thermosetting resin composition according to claim 1 or 2, further comprising (G) a release agent. Relative to 100 parts by mass of the (A) thermosetting resin,
The (B) ethylenically unsaturated monomer is contained in an amount of 1 to 150 parts by mass,
The composition contains 1 to 100 parts by mass of the (C) low shrinkage agent,
The (D) inorganic filler is contained in an amount of 500 to 1600 parts by mass,
The composition contains 0.1 to 20 parts by mass of the thermal polymerization initiator (E),
3. The thermosetting resin composition according to claim 1, comprising 10 to 300 parts by mass of the glass fiber (F). A molded article comprising a cured product of the thermosetting resin composition according to claim 1 or 2. A method for producing a molded product comprising a step of curing the thermosetting resin composition according to claim 1 or 2 by heating and pressurizing it. An electric/electronic part comprising a cured product of the thermosetting resin composition according to claim 1 or 2. A method for producing an electric/electronic component, comprising: a step of compressing, transferring, or injecting the thermosetting resin composition according to claim 1 or 2 to encapsulate components of the electric/electronic component; and a step of heating and curing the thermosetting resin composition.