JP3240319B2 - Spherical expandable resin particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to spherical expandable resin particles having excellent heat resistance and good foamability and moldability, and an industrially advantageous method for producing the same.

[0002]

2. Description of the Related Art Conventionally, expandable polystyrene resins have been widely used because of their inexpensiveness, and foamed polystyrene resins are industrially produced and used because mold foamed products can be easily obtained from the expandable polystyrene resins. Have been. However, since the polymer constituting the foam molded product is a styrene resin, it cannot be used as a heat insulating material at a relatively high temperature, such as a heat insulating material for a roof, an automobile member, a heat insulating material for a solar system, and the like. is there.

On the other hand, foamable resins having excellent heat resistance include foamable resin compositions obtained by blending an unsaturated dicarboxylic acid imide derivative or an unsaturated dicarboxylic acid imide derivative with another thermoplastic resin in a polystyrene resin. Are known. For example, JP-A-60-184546,
JP-A-62-235340 discloses that a maleimide polymer and a resin having compatibility such as acrylonitrile / butadiene / styrene copolymer resin are mixed with a Henschel mixer, and then kneaded with an extruder or the like to be integrated, Disclosed is a foamable resin composition which is formed into a pellet and then impregnated with a foaming agent.

[0004] However, the production process of these pellet-shaped foamable resins is complicated because two or more kinds of raw materials are mechanically mixed and kneaded by extrusion. It is a large columnar particle (pellet) with a minimum diameter of 0.8 to 1 mm or more. When filling in a mold and foaming, the filling property does not become dense, so the obtained foam molded product has a grain of surface. There are drawbacks that it is coarse and unattractive, and that it is difficult to produce a molded product having a dense structure and a thin molded product.

[0005]

The present inventors have conducted intensive studies to improve the above-mentioned drawbacks of the conventional pellet-shaped foamable resin, and as a result, have sufficient heat resistance for practical use, Succeeded in obtaining a novel spherical expandable resin particles and a method for producing the same, which can obtain a dense foam molded article,
The present invention has been made.

[0006]

That is, the present invention provides
Rubber polymer 0 to 40% by weight, aromatic vinyl monomer residue 3
0 to 70% by weight, unsaturated dicarboxylic acid imide monomer residue
30 to 60% by weight, residual unsaturated dicarboxylic anhydride monomer
0-20% by weight of the group and other vinyl monomer residues 0
40% by weight of unsaturated dicarboxylic imide derivative residue
In the presence of 10 to 60 parts by weight of a copolymer (A) containing a group,
Aromatic vinyl monomer, vinyl cyanide monomer and this
One selected from vinyl monomers copolymerizable with
A suspension polymerization of 40 to 90 parts by weight of two or more monomers (B) is carried out.
During the polymerization of the resin particles,
Is a volatile foaming agent based on 100 parts by weight of resin particles after polymerization.
Spherical foamable resin particles impregnated with 2 to 15 parts by weight
It is.

Further , the present invention relates to a rubbery polymer having 0 to 40
%, Aromatic vinyl monomer residue 30 to 70% by weight, unsaturated
30-60% by weight of the dicarboxylic acid imide monomer residue,
0-20% by weight of saturated dicarboxylic acid anhydride monomer residues and
And other vinyl monomer residues from 0 to 40% by weight.
Copolymer containing saturated dicarboxylic imide derivative residue
(A) An aromatic vinyl monomer in the presence of 10 to 60 parts by weight
, Vinyl cyanide monomer and copolymerizable with them
One or more monomers selected from vinyl monomers
(B) Suspension polymerization of 40 to 90 parts by weight to produce resin particles
During or after polymerization of the resin particles,
Impregnated with 2 to 15 parts by weight of a volatile foaming agent per part by weight
The method for producing spherical expandable resin particles, characterized in that
is there.

[0008]

[0009]

Hereinafter, the present invention will be described in detail. The present invention dissolves a copolymer containing an unsaturated dicarboxylic acid imide derivative residue such as a styrene / maleimide polymer known as a heat resistance modifier for a synthetic resin in a vinyl monomer, and suspends and dissolves the copolymer. It has been found that the purpose can be achieved by forming spherical resin particles which are substantially integrated by polymerization and by adding an easily volatile foaming agent to the resin particles.

First, a copolymer containing an unsaturated dicarboxylic acid imide derivative residue of the component (A) (hereinafter, referred to as a copolymer of the component (A)) and a method for producing the same will be described.

As a first method for producing the copolymer of the component (A), an aromatic vinyl monomer, an unsaturated dicarboxylic acid imide monomer, and an unsaturated vinyl monomer are used in the presence of a rubbery polymer, if necessary. A method for copolymerizing a dicarboxylic anhydride monomer and a vinyl monomer mixture copolymerizable therewith. As a second production method, an aromatic vinyl monomer and an unsaturated vinyl monomer are used in the presence of a rubbery polymer if necessary. A polymer obtained by copolymerizing a dicarboxylic anhydride monomer and a vinyl monomer mixture copolymerizable therewith is reacted with ammonia and / or a primary amine (imidation reaction) to form an acid anhydride group. A method of converting part or all of the compound into an imide group can be given.

The aromatic vinyl monomer includes, for example, styrene monomers such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene and the like, and substituted monomers thereof. Styrene is particularly preferred.

Examples of the unsaturated dicarboxylic imide monomer include maleimide, N-methylmaleimide, N-butylmaleimide, N-phenylmaleimide, N-methylphenylmaleimide, N-hydroxyphenylmaleimide, N-methoxyphenylmaleimide, N-chlorophenylmaleimide, N-carboxyphenylmaleimide,
Maleimide derivatives such as N-nitrophenylmaleimide, N-cyclohexylmaleimide and N-isopropylmaleimide, and itaconic imide derivatives such as N-methylitaconimide and N-phenylitaconimide are exemplified. N-phenylmaleimide is particularly preferred.

The unsaturated dicarboxylic anhydride monomer includes, for example, anhydrides such as maleic acid, itaconic acid, citraconic acid and aconitic acid, and maleic anhydride (maleic anhydride) is particularly preferred.

Further, a vinyl monomer copolymerizable therewith may be copolymerized. Examples of the copolymerizable vinyl monomer include acrylonitrile, methacrylonitrile,
vinyl cyanide monomers such as α-chloroacrylonitrile, acrylate monomers such as methyl acrylate and ethyl acrylate, methacrylate monomers such as methyl methacrylate and ethyl methacrylate, acrylic acid,
Examples thereof include vinyl carboxylic acid monomers such as methacrylic acid, acrylic acid amide, and methacrylic acid amide. Among these, monomers such as acrylonitrile, methacrylic acid ester, acrylic acid, and methacrylic acid are preferable.

Examples of the rubbery polymer include a butadiene polymer, a copolymer of a vinyl monomer copolymerizable with butadiene, an ethylene-propylene copolymer, an ethylene-propylene-diene copolymer, and a butadiene. A block copolymer with aromatic vinyl, an acrylate polymer, a copolymer of an acrylate ester and a vinyl monomer copolymerizable therewith, and the like are used.

In the second production method, the ammonia and the primary amine used for the imidization reaction may be in any of anhydrous and aqueous solutions. Examples of the primary amine include alkylamines such as methylamine, ethylamine, butylamine and cyclohexylamine, and aromatic amines such as chloro- or bromo-substituted alkylamines, aniline, tolylamine and naphthylamine, and chloro- or bromo-amines. Examples include halogen-substituted aromatic amines such as substituted anilines, and among them, aniline is particularly preferable.

Further, when the imidization reaction is carried out in a solution state or a suspension state, it is preferable to use a usual reaction vessel, for example, an autoclave, and when the imidization reaction is carried out in a bulk molten state, an extruder equipped with a devolatilizer is used. May be used.
In addition, a catalyst may be present at the time of imidization, and for example, a tertiary amine or the like is preferably used.

The temperature of the imidation reaction is usually about 80-3.
The temperature is 50 ° C, preferably 100 to 300 ° C. 8
When the temperature is lower than 0 ° C., the reaction speed is slow, and the reaction requires a long time, which is not practical. On the other hand, when the temperature is higher than 350 ° C., the physical properties are deteriorated due to thermal decomposition of the polymer.

The copolymer of the component (A) is a rubbery polymer 0
-40% by weight, preferably 0-30% by weight, aromatic vinyl monomer residue 30-70% by weight, preferably 40-70% by weight.
% By weight, unsaturated dicarboxylic acid imide monomer residue 30 to 6
0% by weight, preferably 30 to 55% by weight, 0 to 20% by weight, preferably 0 to 20% by weight of unsaturated dicarboxylic anhydride monomer residues.
~ 15% by weight, and other vinyl monomer residues 0 ~
It is a copolymer composed of 40% by weight.

Next, the component (B) in the present invention comprises one or two or more monomers selected from aromatic vinyl monomers, vinyl cyanide monomers and vinyl monomers copolymerizable therewith. Is a monomer.

Examples of the aromatic vinyl monomer include styrene monomers such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, chlorostyrene and the like, and substituted monomers thereof. And monomers such as styrene and α-methylstyrene are particularly preferred.

Examples of the vinyl cyanide monomer include, for example, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, etc., and acrylonitrile is particularly preferred.

The vinyl monomers copolymerizable therewith include acrylate monomers such as methyl acrylate, ethyl acrylate and butyl acrylate, and methacrylate monomers such as methyl methacrylate and ethyl methacrylate. And vinyl carboxylic acid monomers such as acrylic acid and methacrylic acid, acrylamide, and methacrylamide. Of these, methyl methacrylate, acrylic acid, and methacrylic acid are particularly preferable.

The preferred composition of the monomer (B) is, for example, one composed of styrene, styrene-acrylonitrile and α-methylstyrene-acrylonitrile.

The spherical resin particles of the present invention are prepared by subjecting the monomer of the component (B) to suspension polymerization in the presence of the copolymer of the component (A).
Although the amount of the copolymer of the component (A) contained in the resin particles is determined by the desired heat resistance, it is usually 1%.
The amount is in the range of 0 to 60 parts by weight, preferably 10 to 40 parts by weight. When the amount is less than 10 parts by weight, the heat resistance is slightly improved, and when the amount exceeds 60 parts by weight, the component (B) is dissolved in the monomer. In this case, the viscosity of the solution becomes too high, and suspension polymerization becomes difficult. Further, in order to obtain heat resistance of 100 ° C. with a foam molded product of 30 to 50 times, an amount of the copolymer of the component (A) in the range of 15 to 25 parts by weight is required, and a foam molded product of 5 to 15 times is required. In order to obtain a heat resistance of 110 ° C., the copolymer (A)
Quantities in the range of 0 to 30 parts by weight are required.

On the other hand, (B) contained in spherical resin particles
The amount of the monomer component is usually in the range of 40 to 90 parts by weight, preferably 40 to 80 parts by weight. If the amount is less than 40 parts by weight, suspension polymerization becomes difficult. It is not preferable because it is sufficient.

In order to impart oil resistance to the foam, it is useful to use acrylonitrile among the monomers of the component (B).

Further, it is also useful to add a polyfunctional monomer such as divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate for modifying the foam. The amount of the polyfunctional monomer to be added is 0.0 to 100 parts by weight of the monomer (B).
The range is 1 to 3 parts by weight.

Next, the spherical expandable resin particles of the present invention are:
In the presence of the copolymer of component (A), the component (B)
Resin particles obtained by impregnating a resin particle obtained by suspension polymerization of a monomer with a volatile foaming agent.

The volatile volatile blowing agents usable in the present invention include aliphatic hydrocarbons such as propane, butane and pentane;
Examples thereof include cycloaliphatic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane, and halogenated hydrocarbons such as 1-chloro-1,1-difluoroethane, 1,1-dichloro-1-fluoroethane, and chlorodifluoromethane. The amount of these volatile foaming agents varies depending on the desired expansion ratio, but is usually 2 to 100 parts by weight of the resin particles.
To 15 parts by weight to obtain a 2 to 60-fold foam. Preferably it is in the range of 3 to 10 parts by weight.

The spherical resin particles and expandable resin particles of the present invention are produced by a suspension polymerization method.

The spherical resin particles of the present invention can be obtained by using the above (A)
In the presence of 10 to 60 parts by weight of the component copolymer, (B)
Suspend 40 to 90 parts by weight of one or more monomers selected from aromatic vinyl monomers, vinyl cyanide monomers and vinyl monomers copolymerizable therewith , constituting Obtained by polymerization.

Examples of the dispersant used in the suspension polymerization method of the present invention include water-soluble polymer compounds such as polyvinyl alcohol, polyvinyl pyrrolidone, and methylcellulose; and water-insoluble or water-insoluble compounds such as calcium phosphate, magnesium pyrophosphate, and magnesium carbonate. Insoluble inorganic compounds are used. The concentration of the dispersant in the aqueous dispersion medium is 0.01 to 2
% By weight. Further, a water-soluble surfactant can be used if necessary.

The polymerization initiator used in the suspension polymerization method of the present invention is not particularly limited, and general organic peroxides such as benzoyl peroxide and t-butylperoxybenzoate are used. Organic peroxides such as 1,1-di-t-butylperoxy-3,
3,5-trimethylcyclohexane, di-t-butylperoxyhexahydroterephthalate, tris (t-
Butylperoxy) triazine and the like can also be used. Further, diazo compounds such as azobisisobutylnitrile and azobis 1-cyclohexanecarbonitrile can be used. These polymerization initiators may be used alone, but a method in which several kinds having different decomposition temperatures are used in combination is preferable in that the time required for polymerization can be shortened. The amount of the polymerization initiator used is in the range of 0.1 to 2 parts by weight based on 100 parts by weight of the total amount of the vinyl monomer.

The polymerization temperature in the suspension polymerization method of the present invention can be varied over a wide range based on the decomposition temperature of the polymerization initiator to be used. The first half of the polymerization is 1
A method in which the polymerization is carried out at a temperature of not higher than 00 ° C. and the latter half at a temperature of not lower than 100 ° C. is advantageous.

In addition, the spherical expandable resin particles of the present invention include:
In the presence of 10 to 60 parts by weight of the copolymer of the component (A), an aromatic vinyl monomer, a vinyl cyanide monomer, and a vinyl monomer copolymerizable therewith , constituting the component (B). One or more monomers 40 to 9 selected from monomers
0 parts by weight are subjected to suspension polymerization to produce resin particles, and the resin particles are obtained by impregnating 100 parts by weight of the resin particles with 2 to 15 parts by weight of a volatile foaming agent during or after the polymerization of the resin particles. Thus, the easily volatile foaming agent for imparting foaming property may be added at any time during or after the polymerization. Also, once the resin particles are taken out, sieved into particles of a size according to the purpose, a volatile foaming agent is added again in a state of being suspended in an aqueous dispersion medium, and the resin particles are impregnated. Good.

Further, in order to adjust the foaming speed of the resin and the like, a solvent such as toluene and xylene or a plasticizer such as a phthalic acid ester can be added. When these are added, a method of preliminarily mixing and polymerizing with a monomer or a method of impregnating simultaneously with a foaming agent may be used, but the latter method is generally employed. The addition amount is in the range of 0.1 to 2 parts by weight based on 100 parts by weight of the resin particles.

As described above, the spherical expandable resin particles obtained by the method of the present invention are pre-foamed by heating with steam, hot air or the like, and then filled into a mold that can be closed but cannot be sealed. Then, by heating again with steam or the like, a foamed molded article having desired heat resistance and oil resistance can be obtained.

Further, the spherical resin particles of the present invention constitute the component (B) in the presence of the copolymer of the component (A) .
That, aromatic vinyl monomers, vinyl cyanide monomers and mixtures polymer particles obtained by suspension polymerization of a copolymerizable with these selected from vinyl monomers one or two or more monomers May be. Furthermore, as spherical expandable resin particles,
Resin particles obtained by impregnating the polymer particles with a volatile foaming agent during or after the polymerization of the mixed polymer particles may be used.

Further, an antioxidant, a flame retardant, an antistatic agent, an ultraviolet absorber, a plasticizer, a lubricant, a coloring agent, and the like can be further added to the expandable resin particles of the present invention according to the purpose. is there.

The particle size of the resin particles and expandable resin particles produced by the suspension polymerization method of the present invention is determined depending on the purpose of use. Generally, the average particle size is 0.1 to 2.5 mm, preferably 0.4 to 1.2 mm
And retains a spherical shape even when impregnated with a volatile foaming agent. In addition, since it is manufactured by a suspension polymerization method, the manufacturing process is simple and suitable for obtaining spherical particles.When the obtained spherical expandable resin particles are filled in a mold and foamed, In addition, the filling property is increased, and the obtained foamed molded product has a smooth surface, and a molded product having a dense structure and a thin molded product can be obtained. further,
The particle size of the obtained resin particles and expandable resin particles can be determined according to the purpose.

[0044]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the scope of the present invention is not limited by these examples. However, unless otherwise specified, parts are parts by weight.

Example 1 (1) Maleimide copolymer (A-1) 60 parts of styrene and 50 parts of methyl ethyl ketone were charged into an autoclave equipped with a stirrer, and the system was purged with nitrogen gas. ℃ to 40 ℃, maleic anhydride 40
And a solution prepared by dissolving 0.15 parts of benzoyl peroxide in 250 parts of methyl ethyl ketone were continuously added over 8 hours. After the addition, the temperature was kept at 85 ° C. for a further 3 hours.

A portion of the viscous reaction solution was sampled, and the degree of polymerization was determined by gas chromatography. As a result, it was found to be 99% styrene and 99% maleic anhydride.
To the copolymer solution obtained here, 34 parts of aniline and 0.3 part of triethylamine were added at 0.90 molar equivalents relative to maleic anhydride, and the mixture was reacted at 140 ° C. for 7 hours. 200 parts of methyl ethyl ketone was added to the reaction solution, cooled to room temperature, poured into 1500 parts of vigorously stirred methanol, precipitated, separated by filtration and dried to obtain an imidized copolymer. C-13N
According to MR analysis, the maleic anhydride monomer residue was 3.1% by weight.
Met. This was designated as copolymer A-1.

(2) Production of expandable resin particles A monomer obtained by mixing 60 parts of styrene and 20 parts of acrylonitrile was added to a maleimide copolymer (A-
1) 20 parts were added and then heated to 40 ° C. to dissolve the maleimide-based copolymer (A-1) (hereinafter, this is abbreviated as a monomer solution). After cooling the monomer solution to room temperature, 0.1 part of benzoyl peroxide, 1,1-di-
0.2 parts of t-butylperoxy-3,3,5-trimethylcyclohexane was added.

In an autoclave equipped with a stirrer, 100
Parts, 0.2 parts of calcium phosphate and 0.002 parts of sodium dodecylbenzenesulfonate. The monomer solution is suspended in the aqueous dispersion medium, and the suspension is stirred for 3 hours.
Temperature to 100 ° C. for 1 hour, then 1 hour at 100 ° C.
The polymerization was carried out by heating at 110 ° C. for 1 hour.

A part of the obtained resin particles was taken out and subjected to JI
As a result of sieving with an S standard sieve, most of the diameter is 2.
The spherical particles ranged from 38 to 0.25 mm. Once
After cooling to 100 ° C., 6 parts of butane was added and impregnated at this temperature for 5 hours to obtain spherical expandable resin particles.

The spherical expandable resin particles have a diameter of 1.19 to
Heated with steam, prefoamed to an apparent magnification of 10 times, filled in a mold that can be closed but not sealed, and heated again with steam to obtain a 15 cm × 15 cm × 1 cm. A dense plate-shaped foam molded product having a surface of was obtained. Table 1 shows the dimensional change after heating this plate-like foam molded article in a hot air circulation type dryer for one week in accordance with JIS K6767.

Examples 2 to 4 Spherical expandable resin particles were obtained in the same manner as in Example 1 except that the components constituting the polymer were as shown in Table 1. The obtained spherical expandable resin particles were prefoamed in the same manner as in Example 1 and then molded to obtain a foam molded article, which was evaluated in the same manner.
The results are shown in Table 1.

The resin particles before impregnation with the foaming agent are as follows:
Most of them were spherical particles having a diameter of 2.38 to 0.25 mm.

Comparative Examples 1 to 3 Except that the components constituting the polymer were as shown in Table 1, foamed molded articles were obtained in the same manner as in Example 1. Table 1 shows the results of the evaluation performed in the same manner as in Example 1.

[0054]

[Table 1]

Examples 5 to 6 The compositions constituting the polymer were as shown in Table 2, and 0.2 parts of benzoyl peroxide and 1,1-
0.4 parts of di-t-butylperoxy-3,3,5-trimethylcyclohexane and 0.05 parts of t-butylperoxybenzoate were used, 10 parts of butane was used as a blowing agent, and the solvent was added simultaneously with impregnation with the blowing agent. As toluene 1.2
In the same manner as in Example 1 except that a part was added, spherical expandable resin particles having a diameter mostly in the range of 2.38 to 0.25 mm were obtained.

The obtained spherical expandable resin particles were adjusted to have a diameter of 1.1.
The particles in the range of 9 to 0.59 mm were mixed, heated with steam and prefoamed to an apparent magnification of 40 times, then filled in a mold that could be closed but could not be sealed, and heated again with steam to obtain 15 cm × A 15 cm × 1 cm plate-like foam molded product was obtained. This foam molded article was evaluated in the same manner as in Example 1.
The results are shown in Table 2.

[0057]

[Table 2]

Example 7 Expandable spherical resin particles were obtained in the same manner as in Example 5, except that the polymer composition was changed to 20 parts of a maleimide copolymer, 80 parts of styrene, and 0.1 part of ethylene glycol dimethacrylate. . Most were spherical particles ranging in diameter from 2.38 to 0.25 mm. Thereafter, a foam molded article was produced in the same manner as in Example 5, and evaluated. The dimensional change after heating at 100 ° C. for one week was -1.1%.

[0059]

As described above, according to the spherical expandable resin particles of the present invention, it is possible to obtain a foam molded article having sufficient heat resistance for practical use and a dense surface. Can be

Further, according to the production method of the present invention, spherical resin particles and expandable resin particles can be easily obtained by a simple production process of the suspension polymerization method.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 9/16

Claims (4)

(57) [Claims] 1. A rubbery polymer of 0 to 40% by weight, an aromatic vinyl monomer residue of 30 to 70% by weight, an unsaturated dicarboxylic acid imide monomer residue of 30 to 60% by weight, and an unsaturated dicarboxylic anhydride. (A) 10 to 60 parts by weight of a copolymer containing an unsaturated dicarboxylic acid imide derivative residue consisting of 0 to 20% by weight of a monomer residue and 0 to 40% by weight of another vinyl monomer residue Below, 40 to 90 parts by weight of one or more monomers (B) selected from an aromatic vinyl monomer, a vinyl cyanide monomer and a vinyl monomer copolymerizable therewith are suspended. Spherical foamed resin particles obtained by impregnating spherical resin particles obtained by turbid polymerization with 2 to 15 parts by weight of a volatile foaming agent per 100 parts by weight of resin particles during or after polymerization of the resin particles . 2. The spherical resin particles comprise a copolymer (A)
Is obtained by dissolving in the monomer (B) and subjecting to suspension polymerization.
The spherical expandable resin particles according to claim 1. 3. A rubbery polymer of 0 to 40% by weight, an aromatic vinyl monomer residue of 30 to 70% by weight, an unsaturated dicarboxylic acid imide monomer residue of 30 to 60% by weight, and an unsaturated dicarboxylic anhydride. (A) 10 to 60 parts by weight of a copolymer containing an unsaturated dicarboxylic acid imide derivative residue consisting of 0 to 20% by weight of a monomer residue and 0 to 40% by weight of another vinyl monomer residue Below, 40 to 90 parts by weight of one or more monomers (B) selected from an aromatic vinyl monomer, a vinyl cyanide monomer and a vinyl monomer copolymerizable therewith are suspended. Spherical foaming resin particles characterized by impregnating with 2 to 15 parts by weight of a readily volatile blowing agent with respect to 100 parts by weight of resin particles during or after polymerization of the resin particles by turbid polymerization to produce resin particles. Manufacturing method. 4. The copolymer (A) is dissolved in the monomer (B).
4. The method according to claim 3, wherein the resin particles are disintegrated and subjected to suspension polymerization to produce resin particles.
A method for producing spherical expandable resin particles.