JP7616071B2 - Thermosetting resin composition - Google Patents

Description

The present disclosure relates to a thermosetting resin composition, an internal encapsulant for a motor, a motor including a cured product of the thermosetting resin composition, and a method for manufacturing a motor. In particular, the present disclosure relates to a thermosetting resin composition that can be used to encapsulate electric and electronic components such as a motor and a coil, an internal encapsulant for a motor, a motor including a cured product of the thermosetting resin composition, and a method for manufacturing a motor.

Thermosetting resin compositions made by blending unsaturated polyester resin with fiber reinforcing materials, fillers, etc., have good fluidity and give cured products with excellent dimensional accuracy, heat resistance, and mechanical strength, and are therefore widely used in the manufacture of office equipment, chassis for business machines, lamp reflectors for automobile headlamps, enclosed motors, etc.

In particular, in the manufacture of enclosed motors, electric and electronic components such as motors and coils are enclosed, so if the viscosity of the material is high, the enclosed components may move from their initial positions due to the resin pressure during encapsulation, resulting in damage to the enclosed components due to disconnections, short circuits, etc. Patent Document 1 describes an unsaturated polyester resin composition with excellent in-mold flowability.

JP 2001-226573 A

Depending on the application, a low molding shrinkage rate may be required for the thermosetting resin composition. One method for reducing the molding shrinkage rate of a thermosetting resin composition is to blend a low shrinkage agent into the thermosetting resin composition, and polystyrene is generally used as the low shrinkage agent. However, when polystyrene is used as the low shrinkage agent as in Patent Document 1, the viscosity of the thermosetting resin composition does not decrease sufficiently during molding, resulting in poor fluidity and leaving room for improvement in moldability.

On the other hand, depending on the application, carbon black may be blended into the thermosetting resin composition. The present inventors have discovered that blending a saturated polyester resin into a thermosetting resin composition containing carbon black in order to achieve both fluidity and low shrinkage results in the problem of uneven coloring.

The present invention aims to provide a thermosetting resin composition that has good fluidity, low molding shrinkage, and excellent appearance of the cured product.

As a result of intensive research conducted by the inventors to solve the above-mentioned problems, they discovered that by blending an unsaturated polyester resin having a cyclic structure with a saturated polyester resin in a thermosetting resin composition, a thermosetting resin composition can be obtained that has good fluidity, a small molding shrinkage rate, and an excellent appearance of the cured product, and thus completed the present invention.

That is, the present invention includes the following [1] to [13].
[1]
A thermosetting resin composition comprising (A) an unsaturated polyester resin, (B) an ethylenically unsaturated compound, (C) a saturated polyester resin, (D) glass fiber, (E) a filler, and (F) carbon black, wherein at least one of monomer units constituting the unsaturated polyester resin (A) has a cyclic structure, and the content of the monomer unit having the cyclic structure is 2.6 to 10.4 mol %.
[2]
The thermosetting resin composition according to [1], wherein the cyclic structure is an alicyclic or aromatic ring having 6 to 10 carbon atoms.
[3]
The thermosetting resin composition according to [1] or [2], wherein the monomer unit having a cyclic structure is derived from at least one monomer selected from the group consisting of cyclohexanediol, bisphenol A, hydrogenated bisphenol A, phthalic acid, phthalic anhydride, terephthalic acid, and isophthalic acid.
[4]
The thermosetting resin composition according to any one of [1] to [3], wherein the content of a monomer unit having a cyclic structure in the constituent component of the unsaturated polyester resin (A) is 3.0 to 10.0 mol %.
[5]
The thermosetting resin composition according to any one of [1] to [4], wherein the weight average molecular weight of the saturated polyester resin (C) is 3,000 to 25,000.
[6]
The thermosetting resin composition according to any one of [1] to [5], wherein the content of the ethylenically unsaturated compound (B) is 40 to 240 parts by mass per 100 parts by mass of the unsaturated polyester resin (A).
[7]
The thermosetting resin composition according to any one of [1] to [6], wherein the blending amount of the saturated polyester resin (C) is 5 to 20 parts by mass per 100 parts by mass of the unsaturated polyester resin (A).
[8]
The thermosetting resin composition according to any one of [1] to [7], wherein the blending amount of the (D) glass fiber is 50 to 250 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin.
[9]
The thermosetting resin composition according to any one of [1] to [8], wherein the blending amount of the (E) filler is 400 to 1600 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin.
[10]
The thermosetting resin composition according to any one of [1] to [9], wherein the blending amount of the (F) carbon black is 1 to 15 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin.
[11]
An internal encapsulant for a motor, comprising the thermosetting resin composition according to any one of [1] to [10].
[12]
A motor comprising a cured product of the thermosetting resin composition according to any one of [1] to [10].
[13]
A method for manufacturing a motor, comprising: filling a housing having electric and electronic components therein with the thermosetting resin composition according to any one of [1] to [10]; and heat-curing the thermosetting resin composition.

According to the present invention, it is possible to provide a thermosetting resin composition that has good fluidity, a small molding shrinkage rate, and an excellent appearance of the cured product.

Below, exemplary embodiments of the thermosetting resin composition are described in detail. Note that the present invention is not limited to only the embodiments shown below.

In the following description, "ethylenically unsaturated bond" means a double bond formed between carbon atoms other than those forming an aromatic ring, and "ethylenically unsaturated compound" means a compound having an ethylenically unsaturated bond.

"Median size" means the particle size that is the cumulative 50% in the volume-based particle size distribution determined by laser diffraction/scattering method.

"(Meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic" means acrylic or methacrylic.

<1. Thermosetting resin composition>
The thermosetting resin composition comprises at least (A) an unsaturated polyester resin, (B) an ethylenically unsaturated compound, (C) a saturated polyester resin, (D) glass fibers, (E) a filler, and (F) carbon. Includes black.

[(A) Unsaturated polyester resin]

At least one of the monomer units constituting the unsaturated polyester resin has a cyclic structure, and the content of the monomer unit having the cyclic structure is 2.6 to 10.4 mol% based on the entire unsaturated polyester resin. The lower limit is 2.6 mol%, 3.0 mol%, 3.5 mol%, or 3.8 mol%, and the upper limit is 10.4 mol%, 10.0 mol%, 9.0 mol%, 8.0 mol%, 7.0 mol%, or 6.8 mol%, with the range being preferably 3.0 to 10.0 mol%, and more preferably 3.5 to 7.0 mol%. If the content of the monomer unit having a cyclic structure is 2.6 mol% or more, the appearance of the molded product is good. The cause of the uneven color that occurs when carbon black is blended into the thermosetting resin composition is thought to be poor dispersion of the carbon black due to low compatibility between the unsaturated polyester resin and the saturated polyester resin and the carbon black. Without being bound by any theory, when the content of the monomer unit having a cyclic structure is 2.6 mol% or more, the resin skeleton is rigid, so that carbon black is easily dispersed and color unevenness is suppressed. When the content of the monomer unit having a cyclic structure is 10.4 mol% or less, the molding shrinkage rate is good. A plurality of unsaturated polyester resins having or not having a cyclic structure may be blended to set the content of the monomer unit having a cyclic structure in the whole unsaturated polyester resin to the above range. The cyclic structure is a structure containing at least one selected from an alicyclic ring and an aromatic ring, and the monomer unit may have a cyclic structure in the main chain or in the side chain.

Unsaturated polyester resins are polycondensates obtained by polycondensing polyhydric alcohols with unsaturated polybasic acids and, if necessary, saturated polybasic acids. An unsaturated polybasic acid is a polybasic acid that has an ethylenically unsaturated bond, and a saturated polybasic acid is a polybasic acid that does not have an ethylenically unsaturated bond.

The unsaturated polyester resin having a cyclic structure contains a cyclic structure in at least one of the polyhydric alcohol to be polycondensed, the unsaturated polybasic acid, and the saturated polybasic acid used as needed. Of these, it is preferable that at least one of the polyhydric alcohol and the saturated polybasic acid contains a cyclic structure.

Examples of the cyclic structure include an alicyclic ring or aromatic ring having 3 to 14 carbon atoms. From the viewpoint of availability, an alicyclic ring or aromatic ring having 6 to 10 carbon atoms is preferred, and a cyclohexane ring and a benzene ring are more preferred.

The polyhydric alcohol is not particularly limited as long as it is a compound having two or more hydroxyl groups, and examples thereof include ethylene glycol, propylene glycol, butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, pentanediol, hexanediol, neopentanediol, tetraethylene glycol, polyethylene glycol, 2-methyl-1,3-propanediol, cyclohexanediol such as 1,4-cyclohexane-dimethanol, alkylene glycol such as hydrogenated bisphenol A; alkylene oxide-modified bisphenol A such as ethylene oxide adduct of bisphenol A and propylene oxide adduct of bisphenol A; bisphenol A and glycerin. Of these, cyclohexanediol, hydrogenated bisphenol A, alkylene oxide-modified bisphenol A, and bisphenol A are polyhydric alcohols having a cyclic structure. Among these, propylene glycol, neopentanediol, hydrogenated bisphenol A, and bisphenol A are preferred from the viewpoints of heat resistance, mechanical strength, and resin fluidity during molding of the cured product, and propylene glycol is 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 is a compound having an ethylenically unsaturated bond and two or more carboxy groups or an acid anhydride thereof, and examples thereof include maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, chloromaleic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. Of these, 4-cyclohexene-1,2-dicarboxylic acid is an unsaturated polybasic acid having a cyclic structure. Among these, maleic anhydride and fumaric acid are preferred from the viewpoints of the heat resistance and mechanical strength of the cured product and the resin fluidity during molding. The unsaturated polybasic acids may be used alone or in combination of two or more kinds.

The saturated polybasic acid is not particularly limited as long as it does not have an ethylenically unsaturated bond and has two or more carboxy groups, or an acid anhydride thereof. For example, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, halogenated phthalic anhydrides such as tetrachlorophthalic anhydride and tetrabromophthalic anhydride, and aromatic saturated polybasic acids such as nitrophthalic acid or anhydrides thereof; succinic acid, adipic acid, sebacic acid, oxalic acid, malonic acid, azelaic acid, glutaric acid, hexahydroterephthalic acid, hexahydrophthalic acid, and hexahydrophthalic anhydride, aliphatic saturated polybasic acids or anhydrides thereof, etc. Among these, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, halogenated phthalic anhydrides, nitrophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, and hexahydrophthalic anhydride are saturated polybasic acids having a cyclic structure. Among these, phthalic anhydride and isophthalic acid are preferred from the viewpoints of heat resistance and mechanical strength of the cured product, resin fluidity during molding, etc. The saturated polybasic acids may be used alone or in combination of two or more kinds.

Preferred polyhydric alcohols, unsaturated polybasic acids, and saturated polybasic acids having a cyclic structure include cyclohexanediol, bisphenol A, hydrogenated bisphenol A, phthalic acid, phthalic anhydride, terephthalic acid, and isophthalic acid, and more preferably hydrogenated bisphenol A, phthalic anhydride, and isophthalic acid.

Preferred combinations of raw materials used in the synthesis of unsaturated polyester resins include propylene glycol, hydrogenated bisphenol A and maleic anhydride, propylene glycol, phthalic anhydride and maleic anhydride, and propylene glycol, isophthalic acid and maleic anhydride.

Unsaturated polyester resins may be used alone or in combination of two or more types.

The unsaturated polyester resin can be synthesized by a known method using the raw materials as described above. Various conditions in the synthesis of the unsaturated polyester resin can be set appropriately depending on the raw materials used and their amounts, but generally, an esterification reaction can be performed in an inert gas stream such as nitrogen gas at a temperature of 140 to 230°C under normal pressure, pressure, or reduced pressure. 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 may be used alone or in combination of two or more types.

The weight average molecular weight (Mw) of the unsaturated polyester resin is not particularly limited. The weight average molecular weight of the unsaturated polyester resin is preferably 3,000 to 25,000, more preferably 5,000 to 20,000, and even more preferably 7,000 to 18,000. If the weight average molecular weight is 3,000 to 25,000, the moldability of the thermosetting resin composition will be further improved. In addition, in the present disclosure, the "weight average molecular weight" means a value measured at room temperature (23 ° C.) using gel permeation chromatography (GPC) under the following conditions and obtained using a standard polystyrene calibration curve.
Apparatus: Shodex (registered trademark) GPC-101 manufactured by Showa Denko K.K.
Column: LF-804 manufactured by Showa Denko K.K.
Column temperature: 40°C
Sample: 0.2% by mass solution of the object to be measured in tetrahydrofuran Flow rate: 1 mL/min Eluent: tetrahydrofuran Detector: RI-71S

The degree of unsaturation of the unsaturated polyester resin 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 is better. The degree of unsaturation of the 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

[(B) Ethylenically unsaturated compound]
The ethylenically unsaturated compound can be used without any particular limitation as long as it has an ethylenically unsaturated bond capable of radical copolymerization with the unsaturated polyester resin. The ethylenically unsaturated group may be one or more. Examples of the ethylenically unsaturated compound include aromatic monomers such as styrene, vinyl toluene, α-methyl styrene, and divinyl benzene; acrylic monomers such as 2-hydroxyethyl methacrylate, diacrylate of polyalkylene oxide, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, ethyl (meth)acrylate, and methyl (meth)acrylate; monomers having alkenyl groups such as diallyl phthalate, triallyl isocyanurate, and diallyl phthalate prepolymer; and oligomers in which a plurality of the above monomers are bonded. Among these, styrene and methyl methacrylate are preferred from the viewpoint of reactivity with the unsaturated polyester resin, and styrene is particularly preferred. The ethylenically unsaturated compound may be used alone or in combination of two or more kinds.

The content of the ethylenically unsaturated compound is preferably 40 parts by mass or more per 100 parts by mass of the unsaturated polyester resin. This allows the thermosetting resin composition to have a viscosity that is easy to handle. From this perspective, the content of the ethylenically unsaturated compound is more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more.

The content of the ethylenically unsaturated compound is preferably 240 parts by mass or less per 100 parts by mass of the unsaturated polyester resin. This allows the mechanical strength of the cured product of the thermosetting resin composition to be increased. From this perspective, the content of the ethylenically unsaturated compound is more preferably 230 parts by mass or less, and even more preferably 220 parts by mass or less.

[(C) Saturated polyester resin]
By using a saturated polyester resin, it is possible to reduce the molding shrinkage rate of the thermosetting resin composition and at the same time obtain a low viscosity of the thermosetting resin composition during molding. Without being bound by any theory, this is because a general saturated polyester resin has a small molecular weight and a low viscosity compared to polystyrene, which is generally used as a low shrinkage agent, and therefore can improve the fluidity of the thermosetting resin composition, and further, because it has good compatibility with unsaturated polyester resins, a sphere group structure is formed during curing, which reduces the transmission of the shrinkage force of the saturated polyester resin and reduces the shrinkage of the entire system.

The saturated polyester resin is a polycondensation product of a polyhydric alcohol having no ethylenically unsaturated bond and a saturated polybasic acid, and is not particularly limited. The saturated polybasic acid is a polybasic acid having no ethylenically unsaturated bond. The saturated polyester resin may be used alone or in combination of two or more kinds.

Examples of the polyhydric alcohol include alkylene glycols such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, pentanediol, hexanediol, neopentanediol, hydrogenated bisphenol A, bisphenol A, and glycerin. Among these, propylene glycol, neopentanediol, hydrogenated bisphenol A, and bisphenol A are preferred, and propylene glycol is more preferred, from the viewpoints of heat resistance and mechanical strength of the cured product and resin fluidity during molding. The polyhydric alcohols may be used alone or in combination of two or more kinds.

Examples of saturated polybasic acids include aromatic saturated polybasic acids or their anhydrides, such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrachlorophthalic anhydride, and tetrabromophthalic anhydride; and aliphatic saturated polybasic acids, such as succinic acid, adipic acid, and sebacic acid. Among these, phthalic anhydride and isophthalic acid are more preferred from the viewpoints of heat resistance, mechanical strength, and resin fluidity during molding of the cured product. The saturated polybasic acids may be used alone or in combination of two or more.

Preferred combinations of polyhydric alcohols and saturated polybasic acids include propylene glycol and isophthalic acid, propylene glycol and adipic acid, and propylene glycol, isophthalic acid and adipic acid.

Saturated polyester resins can be synthesized in the same manner as unsaturated polyester resins using the raw materials described above.

The weight average molecular weight (Mw) of the saturated polyester resin is not particularly limited. The weight average molecular weight of the saturated polyester resin is preferably 3,000 to 25,000, more preferably 5,000 to 20,000, and even more preferably 7,000 to 18,000. If the weight average molecular weight is 3,000 to 25,000, the moldability of the thermosetting resin composition will be even better.

The amount of saturated polyester resin blended is preferably 5 to 20 parts by weight, more preferably 8 to 16 parts by weight, and even more preferably 10 to 14 parts by weight, per 100 parts by weight of unsaturated polyester resin. If the amount of saturated polyester resin blended is 5 parts by weight or more, the molding shrinkage rate is good. On the other hand, if the amount of saturated polyester resin blended is 20 parts by weight or less, the saturated polyester resin, low shrinkage agent, carbon black, etc. can be dispersed more uniformly.

[(D) Glass fiber]
The thermosetting resin composition further contains (D) glass fiber. The glass fiber is not particularly limited, and any glass fiber known in the technical field of the present invention can be used. Chopped strand glass cut to a fiber length of 3 to 25 mm is preferably used.

The amount of glass fiber blended is preferably 50 to 250 parts by mass, more preferably 50 to 180 parts by mass, and even more preferably 50 to 100 parts by mass, per 100 parts by mass of unsaturated polyester resin. If the amount of glass fiber blended is 50 parts by mass or more, the mechanical properties of the molded body will be better. On the other hand, if the amount of glass fiber blended is 250 parts by mass or less, the glass fibers will be more uniformly dispersed in the thermosetting resin composition, allowing the production of a homogeneous molded body.

[(E) Filler]
As the filler, organic fillers and inorganic fillers known in the technical field of the present invention can be used. Among them, inorganic fillers are preferred. Examples of inorganic fillers include calcium carbonate, silica, aluminum oxide, aluminum hydroxide, barium sulfate, calcium sulfate, calcium hydroxide, calcium oxide, magnesium oxide, magnesium hydroxide, wollastonite, clay, kaolin, mica, gypsum, silicic anhydride, and glass powder. Among these, calcium carbonate, aluminum oxide, and aluminum hydroxide are preferred because they are inexpensive, and calcium carbonate, aluminum oxide, and aluminum hydroxide are more preferred. The filler may be used alone or in combination of two or more.

From the viewpoint of the viscosity of the thermosetting resin composition during molding, the median diameter of the filler is preferably 1 to 100 μm, more preferably 1 to 60 μm, and even more preferably 1 to 50 μm. If the median diameter of the filler is 1 μm or more, aggregation of the filler can be suppressed. On the other hand, if the median diameter of the filler is 100 μm or less, the moldability of the thermosetting resin composition is good.

The shape of the filler is not particularly limited. Examples of the shape of the filler include nearly spherical, ellipsoidal, scaly, and amorphous.

The amount of filler is preferably 400 to 1600 parts by mass, more preferably 600 to 1200 parts by mass, and even more preferably 800 to 1000 parts by mass per 100 parts by mass of unsaturated polyester resin. If the amount of filler is 400 parts by mass or more, the mechanical properties of the cured product are better. If the amount of filler is 1600 parts by mass or less, the filler is more uniformly dispersed in the thermosetting resin composition, allowing the production of a homogeneous molded product.

[(F) Carbon Black]
The thermosetting resin composition further contains (F) carbon black. Examples of carbon black include polymer charcoal, carbon fiber, and acetylene black. The amount of carbon black is preferably 1 to 15 parts by mass, more preferably 1 to 13 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of the unsaturated polyester resin. When the amount of carbon black is 1 part by mass or more, the coloring of the thermosetting resin composition is good. When the amount of carbon black is 15 parts by mass or less, the carbon black is more uniformly dispersed in the thermosetting resin composition, and a molded product with a good appearance without color unevenness can be obtained.

From the viewpoint of the viscosity of the thermosetting resin composition during molding, the median diameter of the carbon black is preferably 1 to 50 nm, more preferably 1 to 40 nm, and even more preferably 1 to 30 nm. If the median diameter of the carbon black is 1 nm or more, particle aggregation can be suppressed. On the other hand, if the median diameter of the carbon black is 50 nm or less, the moldability of the thermosetting resin composition is good.

[(G) Low Shrinkage Agent]
The thermosetting resin composition may contain (G) a low shrinkage agent in addition to (C) the saturated polyester resin. The low shrinkage agent is not particularly limited, and any agent known in the technical field of the present invention may be used. Examples of low shrinkage agents include polystyrene, polyethylene, polymethyl methacrylate, polyvinyl acetate, polycaprolactone, and styrene-butadiene rubber. The low shrinkage agents to be added may be used alone or in combination of two or more.

The amount of low shrinkage agent is preferably 10 to 100 parts by mass, more preferably 20 to 80 parts by mass, and even more preferably 30 to 70 parts by mass, per 100 parts by mass of unsaturated polyester resin. The amount of low shrinkage agent does not include saturated polyester resin. If the amount of low shrinkage agent is 10 parts 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. On the other hand, if the amount of low shrinkage agent is 100 parts by mass or less, the fluidity of the thermosetting resin composition is better.

[(H) Curing Agent]
The thermosetting resin composition may contain a curing agent (H). The curing agent is not particularly limited as long as it is a radical initiator capable of polymerizing ethylenically unsaturated bonds, and any curing agent known in the technical field of the present invention may be used. Examples of the curing agent include peroxides such as diacyl peroxides, peroxy esters, hydroperoxides, dialkyl peroxides, ketone peroxides, peroxy ketals, alkyl peresters, and percarbonates. Among these peroxides, t-butyl peroxy octoate, t-butyl peroxy 2-ethylhexanoate, benzoyl peroxide, 1,1-di-t-butyl peroxy 3,3,5-trimethylcyclohexane, t-butyl peroxy isopropyl carbonate, t-butyl peroxy benzoate, dicumyl peroxide, and di-t-butyl peroxide are preferred. The curing agent may be used alone or in combination of two or more kinds.

The amount of curing agent is preferably 1 to 20 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, per 100 parts by mass of unsaturated polyester resin. If the amount of curing agent is 1 part by mass or more, the curing reaction during molding occurs uniformly, and the physical properties and appearance of the cured product are good. On the other hand, if the amount of curing agent is 20 parts by mass or less, the storage stability of the thermosetting resin composition is good and handling is improved.

[(I) Release Agent]
The thermosetting resin composition may contain a release agent (I). The release agent is not particularly limited, and any release agent known in the technical field of the present invention may be used. Examples of the 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 release agent may be used alone or in combination of two or more kinds.

The amount of release agent is preferably 5 to 40 parts by weight, more preferably 5 to 35 parts by weight, and even more preferably 5 to 30 parts by weight, per 100 parts by weight of unsaturated polyester resin. If the amount of release agent is 5 parts by weight 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 amount of release agent is 40 parts by weight or less, the surface of the cured product will not be contaminated by excess release agent, and a cured product with a good appearance can be obtained.

[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 thickener, a colorant other than carbon black (hereinafter also simply referred to as a colorant), a polymerization inhibitor, and a viscosity reducer, within a range that does not impair the effects of the present invention.

The thickener is a compound other than the (E) filler that exhibits a thickening effect, such as an isocyanate compound. The thickener may be used alone or in combination of two or more types. The amount of thickener added can be adjusted appropriately depending on the handleability, flowability, etc. required for the thermosetting resin composition.

Colorants are used when coloring the cured product. Various inorganic or organic pigments can be used as colorants. The 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. Thermosetting resin compositions allow the colorant to be uniformly dispersed, and can give molded products without color unevenness.

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 curable resin composition, the curing conditions, etc.

2. Method for producing thermosetting resin composition
The thermosetting resin composition can be produced by mixing (A) an unsaturated polyester resin, (B) an ethylenically unsaturated compound, (C) a saturated polyester resin, (D) glass fiber, (E) a filler, (F) carbon black, and, if necessary, optional components such as (G) a low shrinkage agent, (H) a curing agent, (I) a release agent or additive, or a combination of two or more of these. An example of a mixing method is kneading. There is no particular restriction on the kneading method, and for example, a kneader, a disperser, a planetary mixer, or the like can be used. The kneading temperature is preferably 5°C to 40°C, more preferably 10°C to 30°C.

There is no particular restriction on the order in which the components are mixed when producing a thermosetting resin composition. For example, it is preferable to mix the unsaturated polyester resin and some or all of the ethylenically unsaturated compound before mixing 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 ethylenically unsaturated compound may be mixed in advance with the unsaturated polyester resin so that it acts as a solvent, dispersion medium, etc.

3. Method of using the thermosetting resin composition
The thermosetting resin composition can be used as an encapsulant for a motor. In one embodiment, there is provided an encapsulant for a motor comprising the thermosetting resin composition.

4. Method for curing thermosetting resin composition
The thermosetting resin composition can be molded into a desired shape and cured to produce a molded article containing a cured product of the thermosetting resin composition. The molding and curing methods are not particularly limited, and methods commonly used in the technical field of the present invention, such as compression molding, transfer molding, injection molding, etc., can be used.

The molding and curing process of the thermosetting resin composition is not particularly limited, but examples include a method of opening the mold and pouring the resin composition into the mold, a method of applying pressure from outside the mold, or a method such as injection molding, in which the resin composition is injected from the outside into a closed mold through a hole in the mold such as a sprue, by reducing the pressure inside the mold. The conditions for curing the thermosetting resin composition in the mold can be set appropriately depending on the material used, and an example of preferred conditions is a temperature of 120 to 180°C and a curing time of 1 to 30 minutes.

In one embodiment, a motor is provided that includes a cured product of a thermosetting resin composition. The motor can be manufactured, for example, by a method that includes encapsulating the thermosetting resin composition in a housing having electric and electronic components therein and curing the thermosetting resin composition by heating.

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.

<1. Ingredients>
An example of the synthesis of the unsaturated polyester resin (A) is shown below.

[Synthesis Example 1]
In a four-neck flask equipped with a thermometer, a stirrer, a nitrogen gas inlet and a reflux condenser, 98.0 parts by mass of maleic anhydride and 76.0 parts by mass of propylene glycol (100 moles per 100 moles of maleic anhydride) were placed, and the mixture was heated to 210°C while being stirred under a nitrogen gas stream, and an esterification reaction was carried out by a conventional procedure to obtain an unsaturated polyester resin A1 (0 moles of monomer units having a cyclic structure, weight average molecular weight 10,000, degree of unsaturation 100 moles). Next, 0.015 parts by mass of hydroquinone was added per 100 parts by mass of the reactant, and the mixture was cooled to 160°C, and then styrene monomer was further added to obtain a styrene solution containing 70% by mass of unsaturated polyester resin A1.

[Synthesis Example 2]
A styrene solution containing unsaturated polyester resin A2 (10.5 mol% of monomer units having a cyclic structure, weight average molecular weight 10,000, degree of unsaturation 100 mol%) was obtained in the same manner as in Example 1, except that 60.0 parts by mass of propylene glycol, 50.4 parts by mass of hydrogenated bisphenol A, and 98.0 parts by mass of maleic anhydride were used and the molar ratio of propylene glycol:hydrogenated bisphenol A:maleic anhydride was changed to 79:21:100.

[Synthesis Example 3]
A styrene solution containing unsaturated polyester resin A3 (2.5 mol% of monomer units having a cyclic structure, weight average molecular weight 10,000, degree of unsaturation 95 mol%) was obtained in the same manner as in Example 1, except that 76.0 parts by mass of propylene glycol, 7.4 parts by mass of phthalic anhydride, and 93.1 parts by mass of maleic anhydride were used and the molar ratio of propylene glycol:phthalic anhydride:maleic anhydride was set to 100:5:95.

[Synthesis Example 4]
A styrene solution containing unsaturated polyester resin A4 (12.5 mol% of monomer units having a cyclic structure, weight average molecular weight 10,000, degree of unsaturation 100 mol%) was obtained in the same manner as in Example 1, except that 76.0 parts by mass of propylene glycol, 41.5 parts by mass of isophthalic acid, and 73.5 parts by mass of maleic anhydride were used and the molar ratio of propylene glycol:isophthalic acid:maleic anhydride was 100:25:75.

(C) An example of the synthesis of saturated polyester resin is shown below.

[Synthesis Example 5]
In a four-neck flask equipped with a thermometer, a stirrer, a nitrogen gas inlet and a reflux condenser, 83.0 parts by mass of isophthalic acid, 73.0 parts by mass of adipic acid and 76.0 parts by mass of propylene glycol were put, and the molar ratio of propylene glycol: isophthalic acid: adipic acid was set to 100: 50: 50, and the mixture was heated to 210 ° C. while being stirred under a nitrogen stream, and an esterification reaction was carried out by a conventional procedure to obtain a saturated polyester resin C1. Next, 0.1 parts by mass of hydroquinone was added to 100 parts by mass of the reactant, and the mixture was cooled to 160 ° C., and then a styrene monomer was further added to obtain a styrene solution containing 70% by mass of saturated polyester resin C1 (weight average molecular weight 10,000).

(D) Glass fiber: chopped strand glass ECS03B-173 (manufactured by Nitto Boseki Co., Ltd.), fiber length 3 mm
(E) Filler: Tankal G-100 (calcium carbonate, manufactured by Sankyo Flour Milling Co., Ltd., median diameter 65 μm), B-103 (aluminum hydroxide, manufactured by Nippon Light Metal Co., Ltd., median diameter 8 μm)
(F) Carbon black: MA-100R (manufactured by Mitsubishi Chemical Industries, Ltd., median diameter 24 nm)
(G) Low shrinkage agent: MS-200 (polystyrene, manufactured by Sekisui Chemical Co., Ltd.), Asaprene (registered trademark) T-411G (styrene-butadiene block polymer, manufactured by Asahi Kasei Corporation)
(H) Hardener: Perbutyl (registered trademark) I-75 (t-butylperoxyisopropyl carbonate, manufactured by NOF Corporation)
(I) Release agent: calcium stearate (manufactured by NOF Corporation)

2. Preparation of thermosetting resin composition
Examples 1 to 5, Comparative Examples 1 to 8
The ingredients shown in Table 1, except for the glass fiber, were put into a twin-arm kneader and kneaded for 30 minutes. Then, the glass fiber was added and kneaded for 10 minutes to obtain the thermosetting resin compositions of Examples 1 to 5 and Comparative Examples 1 to 8.

3. Evaluation method of thermosetting resin composition
The thermosetting resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 8 were subjected to various evaluations by the following test methods. The evaluation results are shown in Table 1.

(1) Fluidity Fluidity was evaluated by the flow length (spiral flow value) in a spiral flow test. Specifically, a semicircular spiral flow mold with a cross section of φ3 mm was attached to a 70 ton transfer molding machine, and the spiral flow value (cm) of the thermosetting resin composition was measured under the conditions of a raw material charge amount of 50 g, a molding temperature of 150° C., and a molding pressure of 10 MPa.

(2) Appearance: The thermosetting resin composition was molded under the following conditions and then visually observed. Those without unevenness in appearance were rated as "good", and those with unevenness in appearance were rated as "poor".
Molding machine: 150-ton compression molding machine (manufactured by Osaka Jack Manufacturing Co., Ltd.)
Mold: 320 x 220 mm t3 mm flat plate mold Mold temperature: 160°C top and bottom
Molding pressure: 80 kgf/ ^cm2
Pressurization time: 300 seconds Sample amount: 400 g

(3) Molding shrinkage rate According to JIS K6911:1995 5.7, a shrink disk (φ90 mm×11 mm) was compression molded (using a compression molding machine manufactured by Technomaruch Co., Ltd.) under conditions of a molding temperature of 120° C., a molding pressure of 5 MPa, and a molding time of 5 minutes, and the molding shrinkage rate was calculated.

(4) Flame retardancy 340 g of the thermosetting resin composition was molded into a 320 mm x 220 mm x 3 mm flat plate in a compression molding die heated to 140 ° C. under the conditions of a pressurization time of 5 minutes and a molding pressure of 10 MPa. After post-curing under the conditions of 150 ° C. and 60 minutes, the molded product was removed from the die and a test piece of (125 ± 5) mm x (13 ± 0.5) mm x 3 mm was cut out. These test pieces were evaluated in a vertical combustion test according to the UL94 V-0 standard, and in the following Table 1, those that met the V-0 standard were shown as acceptable, and those that did not meet the V-0 standard were shown as unacceptable.

As can be seen from Table 1, the thermosetting resin compositions of Examples 1 to 5, in which the content of monomer units having a cyclic structure is within the range of 2.6 to 10.4 mol%, have good fluidity, small molding shrinkage, and good appearance and flame retardancy. On the other hand, Comparative Examples 1, 3, and 8, which do not contain (C) saturated polyester resin, had poor fluidity. Comparative Examples 2, 4, and 7, in which the content of monomer units having a cyclic structure is less than 2.6 mol%, had poor appearance, and Comparative Examples 5 and 6, in which the content of monomer units having a cyclic structure is more than 10.4 mol%, had large molding shrinkage.

Claims (7)

A thermosetting resin composition comprising (A) an unsaturated polyester resin, (B) an ethylenically unsaturated compound (excluding the (A) unsaturated polyester resin) , (C) a saturated polyester resin, (D) glass fiber, (E) a filler, and (F) carbon black, wherein at least one of monomer units constituting the (A) unsaturated polyester resin has a cyclic structure, and the content of the monomer unit having the cyclic structure is 3.0 to 9.0 mol % ,
The content of the ethylenically unsaturated compound (B) is 40 to 240 parts by mass based on 100 parts by mass of the unsaturated polyester resin (A),
the blending amount of the (C) saturated polyester resin is 5 to 20 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin,
the blending amount of the (D) glass fiber is 50 to 250 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin,
the blending amount of the (E) filler is 400 to 1600 parts by mass per 100 parts by mass of the (A) unsaturated polyester resin,
The thermosetting resin composition according to claim 1, wherein the blending amount of the carbon black (F) is 1 to 15 parts by mass per 100 parts by mass of the unsaturated polyester resin (A) . The thermosetting resin composition according to claim 1, wherein the cyclic structure is an alicyclic or aromatic ring having 6 to 10 carbon atoms. The thermosetting resin composition according to claim 1 or 2, wherein the monomer unit having a cyclic structure is derived from at least one monomer selected from the group consisting of cyclohexanediol, bisphenol A, hydrogenated bisphenol A, phthalic acid, phthalic anhydride, terephthalic acid, and isophthalic acid. The thermosetting resin composition according to any one of claims 1 to 3 , wherein the weight average molecular weight of the saturated polyester resin (C) is 3,000 to 25,000. An internal encapsulant for a motor comprising the thermosetting resin composition according to any one of claims 1 to 4 . A motor comprising a cured product of the thermosetting resin composition according to any one of claims 1 to 4 . A method for producing a motor, comprising: filling a housing having electric and electronic components therein with the thermosetting resin composition according to any one of claims 1 to 4 ; and heat-curing the thermosetting resin composition.