JPH07188308A - Three-dimensional polymer fine particle, its production and low-shrinking agent and unsaturated polyester resin composition - Google Patents

Abstract

PURPOSE:To obtain in high yield three-dimensional polymer fine particles (low- shrinking agent) with sharp particle size distribution capable of giving molded products of excellent color and gloss uniformity and low shrinkability. CONSTITUTION:A feedstock mixture comprising styrene-based and/or acrylic monomer having one vinyl group, crosslinking agent, polymerization initiator, aqueous medium and suspending agent is agitated in a vessel equipped with a homogenizer at a shear force of >=5m/sec in terms of the circumferential velocity of the rotary blades of the homogenizer to conduct a high-speed shearing agitation so as to be >=1 in the pass frequency for the mixture to produce a dispersed emulsified liquor, which is, in turn, polymerized, then the aimed three-dimensional polymer fine particles are obtained. The unsaturated polyester resin contains the above polymer fine particles as a low-shrinking agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to three-dimensional polymer fine particles useful as a low-shrinking agent for curable unsaturated polyester resin, a process for producing the same, a low-shrinking agent and an unsaturated polyester resin composition.

[0002]

2. Description of the Related Art Curable unsaturated polyester resin compositions are used in various molded products such as molded products such as SMC, BMC and RIM. This curable unsaturated polyester resin composition is obtained by adding a polymerizable monomer such as styrene to an unsaturated polyester resin, and if necessary, a polymerization initiator, a low shrinkage agent, a reinforcing agent, a release agent, and a filling agent. It contains additives such as agents, thickeners and colorants, and is itself used as a molding material.

The low-shrinking agent added to the curable unsaturated polyester resin is for the purpose of preventing shrinkage during molding or preventing the reinforcing agent from floating on the surface of the molded product. For example, acrylic and styrene resins. Polymerizable monomer solution, resin powder such as thermoplastic nylon and polyethylene, polyvinyl chloride resin powder, three-dimensional acrylic resin and styrene resin powder.

However, conventional low-shrinkage agents have various problems. For example, when a polymerizable monomer solution of an acrylic resin, a styrene resin, or a vinyl acetate resin is used, or when these resin powders are used, a low shrinkage effect is sufficiently obtained, but the dispersibility and its stability are poor. As a result, the composition becomes non-uniform. Further, when mixed, the low-shrinking agent is dissolved in the polymerizable monomer to increase the viscosity, which causes a problem that workability is deteriorated.

When a thermoplastic resin powder such as nylon, polyethylene, or polyvinyl chloride is used as the low-shrinking agent, the composition is excellent in uniform coloring but has low compatibility with the polymerizable monomer. Therefore, there is a problem that the low shrinkage effect is not sufficient. Further, when a three-dimensional acrylic or styrene resin powder is used (Japanese Patent Publication No. 51-1276).
If the crosslink density is less than 0.5%, the resin powder rapidly absorbs the polymerizable monomer and swells, thickens, or aggregates, and a uniform compound cannot be obtained. 5%
In the above case, a uniform compound can be obtained, but there is a problem that a sufficient low shrinkage effect cannot be obtained.

As a means for solving these problems, Japanese Patent Laid-Open No. 148558/1987 discloses a low-shrinking agent having a substance which is not readily soluble in a polymerizable monomer on the surface thereof, and a polymerizable monomer. By using a three-dimensional acrylic-based, styrene-based, vinyl acetate-based resin powder having a swelling degree of 2 to 40 with respect to the body, it has a sufficiently low shrinkage property with respect to the curable unsaturated polyester resin. It is disclosed that it is effective as a material exhibiting uniform colorability, dispersibility, and gloss of a molded article. However, the effect cannot be said to be sufficient. In particular, according to the disclosed method for producing a low-shrinking agent, a product having a sharp particle size distribution cannot be obtained, so that the molded product has insufficient properties such as uniform dispersibility, uniform colorability, and gloss.

[0007]

SUMMARY OF THE INVENTION The present invention is particularly directed to sharpening the particle size distribution of the resin fine particles used as the low-shrinking agent so as to obtain those characteristics, that is, uniform dispersibility, uniform colorability and gloss of the molded product. For the purpose of improving properties such as transparency and transparency, and further, a method for producing polymer fine particles in a high yield, three-dimensional polymer fine particles obtained by this production method, and a low shrinkage agent comprising these fine particles. And an unsaturated polyester resin composition using the low-shrinking agent.

[0008]

[Means for Solving the Problems] That is, the present invention provides a raw material mixed solution containing a styrene-based and / or acrylic-based monomer having one vinyl group, a crosslinking agent, a polymerization initiator, an aqueous medium, and a suspending agent. In a container equipped with a homogenizer, with a rotor blade peripheral speed of the homogenizer being agitated with a shearing force of 5 m / sec or more, and high-speed shearing agitation such that the number of passes of the mixed solution was 1 or more, to obtain a dispersion emulsion. And a method for producing three-dimensional polymer fine particles, a three-dimensional polymer fine particle obtained by the production method, a low-shrinking agent comprising the same, an unsaturated polyester resin, and the low-shrinking agent. And an unsaturated polyester resin composition containing

The styrene-based and / or acrylic-based monomers having one vinyl group used in the present invention include the following. As the styrene-based monomer, besides styrene, α-methylstyrene, vinyltoluene, pt
There are styrene derivatives such as butyl styrene.

Acrylic monomers include acrylic acid and acrylic acid derivatives such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, and acrylic. Octyl acid, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, glycidyl acrylate, methoxyethyl acrylate, propoxyethyl acrylate, butoxyethyl acrylate, methoxydiethylene glycol acrylate, ethoxydiethylene glycol acrylate, acrylic acid Methoxyethylene glycol, butoxytriethylene glycol acrylate, methoxydipropylene glycol acrylate, phenoxyethyl acrylate, phenoxydiacrylate Glycol, acrylic acid phenoxy tetraethylene glycol, benzyl acrylate, cyclohexyl acrylate, tetrahydrofurfuryl acrylate, acrylic acid dicyclopentenyl, dicyclopentenyloxyethyl acrylate, N-
Vinyl-2-pyrrolidone, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, 2-hydroxy-3-phenyloxypropyl acrylate, glycidyl acrylate, acrylonitrile, acrylamide, N-methylol acrylamide, diacetone acrylamide, Methacrylic acid, derivatives of methacrylic acid, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate,
Heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, glycidyl methacrylate, methoxyethyl methacrylate, propoxyethyl methacrylate, butoxyethyl methacrylate, methoxydiethylene glycol methacrylate, methacrylic acid Ethoxydiethylene glycol, methoxyethylene glycol methacrylate, butoxytriethylene glycol methacrylate, methoxydipropylene glycol methacrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol methacrylate, phenoxytetraethylene glycol methacrylate, benzyl methacrylate, cyclohexyl methacrylate, methacrylic acid Tetrahydrofurfuryl, metac Dicyclopentenyl methacrylate, dicyclopentenyl oxyethyl methacrylate, N-vinyl-2-pyrrolidone methacrylate, methacrylonitrile, methacrylamide, N-methylol methacrylamide, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, methacrylic acid Acid hydroxybutyl, 2-hydroxy-3-phenyloxypropyl methacrylate,
A vinyl-based monomer having one vinyl group in one molecule, such as vinylpyridine, may be mentioned. These can be used alone or in combination of two or more.

The crosslinking agent used in the present invention may be any monomer having two or more vinyl groups in one molecule, but one having two vinyl groups in one molecule is preferable. . Examples of the preferred monomer include divinylbenzene, a reaction product of glycol and methacrylic acid or acrylic acid, such as ethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4- Butanedioldi (meta)
Acrylate, 1,5-pentanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, diethylene glycol di (meth) acrylate,
There are triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, etc.
It is not limited to these. The amount added is 0.02 with respect to 100 parts by weight of the monomer having one vinyl group.
-5 parts by weight is preferred. When the amount added is less than 0.02 parts by weight, the degree of swelling of the resulting polymer fine particles with respect to the polymerizable monomer exceeds 40, and the effect of low shrinkage becomes small. On the other hand, when it exceeds 5 parts by weight, the degree of swelling of the resulting polymer fine particles with respect to the polymerizable monomer is less than 2, and the effect of low shrinkage becomes small. Since the amount of the cross-linking agent added and the cross-linking density differ depending on the type, as a guideline, the degree of swelling of the resulting polymer fine particles with respect to the polymerizable monomer is 2 to 40, particularly 5 to 20. It is preferable to adjust the addition amount of the crosslinking agent.

The polymerization initiator used in the present invention includes
Peroxide radical initiators are preferred, for example benzoyl peroxide, 2-ethylhexyl perbenzoate, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide. , Methyl ethyl ketone peroxide,
Peroxidation of 4,4,6-trimethylcyclohexanone di-tert-butylperoxyketal, cyclohexanone peroxide, methylcyclohexanone peroxide, acetylacetone peroxide, cyclohexanone di-tert-butylperoxyketal, acetone di-tert-butylperoxyketal, diisopropylhydroperoxide, etc. Physical radical polymerization initiators. The polymerization initiator is preferably used in an amount of 0.05 to 10 parts by weight based on 100 parts by weight of the monomer having one vinyl group. If the amount used is less than 0.05 parts by weight, the polymerization time tends to be long and the particle size distribution of the polymer particles tends to be broad. On the other hand, when the amount used exceeds 10 parts by weight, not only the polymerization initiator is wasted but also the crosslinking density is difficult to increase.

At the time of polymerization, a chain transfer agent can be added appropriately. Examples of the chain transfer agent include alkyl mercaptans such as t-dodecyl mercaptan, lower alkyl xanthogens such as diisopropyl xanthogen, carbon tetrachloride, carbon tetrabromide and the like. When these are used, a monomer having one vinyl group is used. It is preferable to add 0.1 part by weight or less to 100 parts by weight. It is preferable to adjust the addition amount of these in consideration of the degree of swelling.

Water is mainly used as the aqueous medium, but a hydrophilic organic solvent such as alcohol, acetone or methyl ethyl ketone may be used together. The amount of the aqueous medium used in the present invention is basically 80 to 400 parts by weight with respect to 100 parts by weight of a monomer having one vinyl group in order to emulsify and disperse oil droplets to a desired size. Preferably. 8
If the amount is less than 0 part by weight, the viscosity of the emulsion dispersion is increased, and it is difficult to adjust desired oil droplets. If the amount is more than 400 parts by weight, productivity is deteriorated.

The suspending agent used in the present invention is preferably a substance which is not readily soluble in the polymerizable monomer, and examples thereof include hydroxyapatite, tricalcium phosphate, calcium hydroxide and calcium carbonate. , Titanium oxide and silica are preferred, and others, red iron oxide, carbon black, glass, metal powder, starch powder, cellulose powder, polyacrylonitrile, metal salts of polyacrylic acid,
A metal salt of polymethacrylic acid, polyacrylamide and the like can also be used. Among them, particularly preferable suspending agents are hydroxyapatite and tricalcium phosphate, which are excellent in stability of oil droplets and sharp particle size distribution of fine particle powder.

The amount of the suspending agent used is specifically determined according to the average particle diameter of the desired three-dimensional polymer fine particles, and is based on 100 parts by weight of the monomer having one vinyl group. On the other hand, it is preferably 0.1 to 20 parts by weight. 0.1
If it is less than 20 parts by weight, the desired polymer fine particles are difficult to obtain, while if it exceeds 20 parts by weight, the suspending agent is wasted.

Some of the above-mentioned suspending agents exhibit the function of the suspending agent alone, and those that do not exhibit the function of the suspending agent. As the suspension aid, generally known surfactants, cationic, anionic,
Nonionic surfactants are used, of which anionic surfactants are particularly preferred. Examples of the anionic surfactant include sodium alkylbenzene sulfonate,
Examples include sodium α-olefin sulfonate, sodium alkyl sulfonate, and metal salts thereof. The anionic surfactant is 1 × 10 ^{−4 to} 0.
It is preferably added at 1% by weight. If it is less than 1 × 10 ^-4 % by weight, the function as a suspension aid is difficult to appear, and if it exceeds 0.1% by weight, it itself functions as a suspending agent or an emulsifier, and good suspension polymerization cannot be performed. There is a tendency.

In the present invention, a raw material mixture containing the above materials is emulsified and dispersed in a container equipped with a homogenizer. The homogenizer referred to in the present invention is a device that mixes and disperses two liquid layers by a mechanical treatment to form a dispersion emulsion, and has a shape in which a rotary blade is housed in a fixed blade, and the mixed liquid is generated by interaction of both blades. A material having a function of dispersing and emulsifying is used. The homogenizer that can be used in the present invention is a commercially available TK homomixer (Tokushu Kika Kogyo Co., Ltd.).
Made), Line Flow Homo Mixer (Tokushu Kika Kogyo Co.
Manufactured by Silverson Co., Ltd., and a Polytron homogenizer (manufactured by Polytron, Switzerland). Preferred is a shape with a screw rotor for high viscosity, such as T
A K homomixer can be used. The high shear stirring speed of the homogenizer requires a shearing force of 5 m / sec or more as the blade peripheral speed of the rotary blade. If it is less than 5 m / sec, a desired oil droplet average particle diameter with a sharp particle diameter distribution cannot be obtained.
7-2 from the viewpoint of sharpness of particle size distribution and economical efficiency
0 m / sec is preferred.

Further, in the present invention, when the above-mentioned raw material mixed solution is subjected to high-speed shear stirring with a homogenizer, the number of passes (average circulation number) when the mixed solution is calculated by the following formula may be one or more. is necessary.

[Equation 1] Here, when the number of passes is less than 1, even if the desired oil droplet average particle size is obtained, the particle size distribution of the three-dimensional polymer fine particles after the polymerization reaction becomes broad, and the target sharp distribution is I can't get it. From the viewpoint of sharp particle size distribution and economical efficiency, it is preferably 3 to 350 times. When the capacity of the homogenizer is small and the number of passes cannot be obtained once or more, a method may be used in which several homogenizers are installed in the raw material mixed solution and one or more passes are obtained from the total discharge amount of each rotor. The discharge amount of the rotary blade may be measured, but may be calculated by the following formula.

[Equation 2] The discharge coefficient differs depending on the rotor blade shape. For example, T
In the case of K homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), a high-viscosity rotary blade has 0.15, a low-viscosity rotary blade has 0.20, and both have both (DH). It can be calculated as 0.20.

The average particle diameter of the oil droplet particles obtained by high-speed shear stirring is preferably adjusted to 1 to 100 μm. Outside this range, it is difficult to obtain a good low-contraction agent. The obtained dispersion emulsion is preferably reacted at a temperature of 70 to 95 ° C. according to a usual suspension polymerization. Since it exhibits good properties as a low-shrinking agent, it has an average particle diameter of 3
It is preferable to obtain dimensional polymer particles.

The resulting three-dimensional polymer fine particles are contained in the unsaturated polyester resin composition of the present invention as a low-shrinking agent. As the unsaturated polyester resin, a known one produced by a known method can be used. Examples of the acid component used as a raw material of the unsaturated polyester resin include unsaturated dibasic acids such as maleic acid, fumaric acid, itaconic acid and mesaconic acid or their anhydrides, as well as isophthalic acid, terephthalic acid, phthalic anhydride and succinic acid. Further, polybasic acids such as adipic acid and sebacic acid can also be used. As the alcohol component, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol,
A diol such as butanediol and neopentyl glycol and a triol such as trimethylolpropane are used. The reaction conditions of the acid and alcohol are appropriately selected according to a conventional method.

Further, as a component of the unsaturated polyester resin composition, styrene monomers such as styrene, α-methylstyrene, vinyltoluene and divinylbenzene, lower alkyl esters of acrylic acid or methacrylic acid, diallyl phthalate and diallyl iso A polymerizable monomer such as phthalate can be used in an amount usually used. In addition, if necessary, fillers such as calcium carbonate and alumina, thickeners such as magnesium oxide, magnesium hydroxide and calcium oxide, curing catalysts such as various organic peroxides, colorants such as various dyes and pigments, etc. Various additives can be used. The polyester resin composition obtained is SM
It is used for various molded products by C, BMC, RIM, etc.

[0023]

EXAMPLES Examples will be described below. In addition, a part means a weight part. Example 1 65 equipped with a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd., HV-O type (high viscosity type), rotor blade diameter d = 4.3 cm)
Styrene 18 kg (100 parts), divinylbenzene 0.09 kg (0.5 parts), benzoyl peroxide 0.09 kg (0.5 parts), water 21.3 kg (about 118) in a liter container.
Part), hydroxyapatite (Super Tight 10, manufactured by Nippon Kagaku Kogyo Co., Ltd.) 6.3 kg (3.5 parts in solid content, water content about 32 parts) and 90 g of 1% sodium dodecylbenzenesulfonate aqueous solution were charged. The liquid mixture was dispersed and emulsified for 10 minutes at a rotation speed of TK homomixer of 8,000 rpm (discharge rate: 95 liter / min) (20 passes), and then transferred to a 50 liter reaction kettle equipped with a stirrer. The dispersion emulsion was sampled, and the average particle diameter of the oil droplet particles was measured with a Coulter counter to find that it was 25 μm. Fifty
The temperature of the liter reaction kettle was raised to 80 ° C., and the reaction was completed at 80 ° C. for 8 hours. After cooling, dehydration with a centrifugal dehydrator, 80 ℃
It was dried in a drier to obtain three-dimensional polystyrene fine particles. The yield of fine particles having a particle diameter of 128 μm or less was 95%, which was a high yield. Further, when the particle size distribution of the fine particles was measured, the average particle diameter was 43 μm and the sharpening degree was 0.5, which was considerably sharp. The degree of swelling of the fine particles was 8, which was 8.

The evaluation method of the polymer fine particles is shown below. (1) Method for measuring particle size distribution of polymer fine particles and oil droplet fine particles A Coulter counter was used as a measuring instrument. As the coulter counter, ZM type manufactured by Nikkaki Co., Ltd. was used. As the electrolytic solution, Isoton II manufactured by Nikkaki Co., Ltd. was used. The method of measuring the particle size distribution was measured according to the manual. (2) How to obtain the sharpening degree (Cv value) in the particle size distribution It was obtained by the following method based on the data of the particle size distribution measured with a Coulter counter.

[Equation 3] (3) Method of measuring degree of swelling 0.5 g of a sample is precisely weighed in a 20 ml graduated cylinder made of colorless glass, having an inner diameter of 14 mm, a height of 135 mm, graduation of 0.2 ml, and tapping several times. After that, gently put the styrene monomer on the wall and put it on the scale of 20 ml. Let stand for 16 to 24 hours at room temperature, read the height of swollen gel in ml,

[Equation 4] The swelling degree is calculated by.

Examples 2 to 10 and Comparative Examples 1 to 4 Polymer fine particles were obtained in the same manner as in Example 1 except that the composition and conditions shown in Table 1 were changed.

[0026]

[Table 1]

[Production of polyester resin composition and S
Manufacture of MC Molded Product and BMC Molded Product] (1) Manufacture of Unsaturated Polyester Resin Composition An unsaturated polyester resin (polyset PS-9195, maleic acid, terephthalic acid, and propylene glycol is used as a raw material in a container equipped with a stirrer. Mixture of unsaturated polyester resin and styrene monomer, manufactured by Hitachi Chemical Co., Ltd.
6.3 kg, pigment (Ivory, manufactured by Tokyo Ink Co., Ltd.),
A curing agent (Perbutyl Z, manufactured by NOF CORPORATION) was mixed in the proportions shown in Table 2 and uniformly dissolved. Thereafter, zinc stearate, aluminum hydroxide and polymer fine particles of the examples and comparative examples of the present invention are added and uniformly dispersed, and then magnesium oxide is added. The magnesium oxide was sufficiently dispersed until the grains were removed to obtain unsaturated polyester resin compositions (A) and (B).

[0028]

[Table 2]

(2) Manufacture of SMC molded product The unsaturated polyester resin composition (A) was set in an SMC machine so that the glass fiber content was 25% by weight to prepare an SMC sheet. In order to prevent the scattering of styrene, it was packed with a polyester film and the SMC was aged at 40 ° C. for 2 days. Next, size 250 x 500 x
800 g of SMC aged in a 3 mm mold was taken, and an SMC molded product was manufactured under the conditions of a molding temperature of 140 ° C., a molding pressure of 130 kgf / cm ² , and a molding time of 3 minutes. (3) Production of BMC molded product The unsaturated polyester resin composition (B) was blended so that the content of the 1.5 mm glass fiber was 3% by weight, and kneaded well with a kneader for 10 minutes to prepare a compound. . Next, in order to prevent the scattering of styrene, it was packed with a polyester film, and the compound was aged at 40 ° C. for 20 hours. Take 700g of this and measure 220 x 220 (mm)
Put in the mold, molding temperature 140 ℃, molding pressure 100kg
A BMC molded product having a thickness of 6 mm was manufactured under the conditions of f / cm ² and molding time of 9 minutes. (4) Evaluation of Molded Product-Low Shrinkage The length of the side of the obtained SMC molded product corresponding to a mold length of 500 mm was measured and evaluated according to the following criteria. Good: Shrinkage rate is 0.02% or less. A little: Shrinkage exceeds 0.02% and 0.05% or less. None: Shrinkage rate exceeds 0.05%. -Coloring and uneven gloss The obtained molded product was visually judged. -Transparency Using visible light from a turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd., the transmittance is 100% when there is no sample, and 0% when the sample part is shielded. After making this correction, B
The MC molded product is put in the sample part, and the transmittance of the molded product is measured. Table 3 shows the above evaluation results.

[0030]

[Table 6]

[0031]

EFFECTS OF THE INVENTION According to the present invention, three-dimensional polymer fine particles having a sharp particle size distribution and a high yield can be obtained, and an unsaturated polyester resin using the three-dimensional polymer fine particles as a low-shrinking agent. The composition can ensure uniformity in coloring and gloss of the SMC molded product, and exhibits sufficient low shrinkage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yugo Kumagai 4-13-1, Higashimachi, Hitachi, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Factory

Claims (8)

[Claims] 1. A styrene-based resin having one vinyl group and / or
Alternatively, a raw material mixture containing an acrylic monomer, a crosslinking agent, a polymerization initiator, an aqueous medium, and a suspending agent is placed in a container equipped with a homogenizer, and the peripheral speed of the rotor blade of the homogenizer is 5 m / sec or more with a shearing force. A method for producing three-dimensional polymer fine particles, which comprises stirring and performing high-speed shear stirring such that the number of passes of the mixed solution is one or more to produce a dispersion emulsion and polymerizing the dispersion emulsion. 2. The average particle size of oil droplets of the dispersed emulsion is 1-10.
The method for producing three-dimensional polymer particles according to claim 1, wherein the particle size is 0 μm. 3. The suspending agent is selected from hydroxyapatite, tricalcium phosphate, calcium hydroxide, calcium carbonate, titanium oxide and silica.
Alternatively, the method for producing three-dimensional polymer fine particles according to item 2. 4. Three-dimensional polymer fine particles obtained by the production method according to claim 1, 2 or 3. 5. The three-dimensional polymer fine particles according to claim 4, wherein the degree of swelling is 2 to 40. 6. The three-dimensional polymer fine particles according to claim 4, which have an average particle diameter of 1 to 100 μm. 7. A low-shrinkage agent comprising the three-dimensional polymer fine particles according to claim 4, 5 or 6. 8. An unsaturated polyester resin composition containing an unsaturated polyester resin and the low-shrinking agent according to claim 7.