JP3001360B2 - Method for producing expandable copolymer resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing expandable copolymer resin particles.

[0002]

2. Description of the Related Art Expandable polystyrene particles are widely used because they can easily produce a foamed molded article of any shape. However, foamed molded articles made of expandable polystyrene particles have a disadvantage of poor heat resistance. That is, the polystyrene foam has a drawback that when it is exposed to hot water at 90 ° C., it is softened and deformed. Therefore, an attempt was made to produce heat-resistant foamable resin particles by using another resin instead of polystyrene.

[0003] It is not easy to find a resin suitable for making heat-resistant foamable resin particles. This is because resins that replace polystyrene must have heat resistance and easily foam in contact with water vapor, and have the property of fusing together with foaming to form a foam. Because it must be. This is because a resin having such a property does not exist in a dark cod.

JP-A-63-37139 discloses a method for producing the above-mentioned heat-resistant foamable resin particles. The method comprises the N- aryl maleimide compound 0.5 to 30 parts by weight, alpha-methyl styrene 40-70
Parts by weight, 10 to 40 parts by weight of acrylonitrile, and 0 to 20 parts by weight of other vinyl monomers copolymerizable therewith, and a vinyl cyanide content of 10 to 50 parts is separately prepared. The vinyl cyanide copolymer particles having the same size by weight are dispersed in an aqueous medium to form a suspension, and the monomer mixture is gradually added to the suspension to form the monomer mixture. Absorbed by the copolymer particles, the monomer mixture is copolymerized in the presence of a polymerization initiator using the copolymer particles as nuclei, and the monomer mixture is 95 to 5 to 70 parts by weight of the copolymer particles. This is a method of producing resin particles copolymerized at a ratio of about 30 parts by weight, and impregnating the resin particles obtained in the course of the copolymerization with an organic foaming agent to produce heat-resistant foamable resin particles.

[0005]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. 63-3713
According to the method disclosed in Japanese Patent Application Publication No. 9-203, heat-resistant foamable particles are obtained. However, it has been found that these heat-resistant foamable particles have a disadvantage. The disadvantage is that when the expandable particles are heated and expanded, pre-expanded particles having a hollow inside are liable to be produced. In particular, the styrene content of the core vinyl cyanide copolymer is about 70%. % Is more likely to be hollow. For this reason, when the obtained pre-expanded particles are placed in a molding die and steam-heated and molded, the resulting expanded molded article has poor mechanical strength and has slightly reduced other physical properties. It turned out that there was a drawback. Therefore, a need has arisen to improve this disadvantage.

[0006]

The present inventor has sought to remedy the above disadvantages. For this reason, the inventor has studied in detail why the above drawbacks occur. As a result, the reason for the above drawbacks is that the expandable particles have a structure in which the vinyl cyanide copolymer is the core and the surface is covered with the copolymer obtained by copolymerizing the monomer mixture. This was considered to be because the inside and the surface exhibited differences in glass transition point and foaming property.

More specifically, in general, a thermoplastic resin foams well when it is in a suitable softened state, and when heated further beyond this state, melts to collapse the bubbles and become non-foamed. An appropriate softening state is exhibited when the temperature is slightly higher than the glass transition point of the resin, and the temperature suitable for foaming differs from resin to resin and changes with the glass transition point. Since the glass transition point of the vinyl cyanide copolymer is lower than the glass transition point of the copolymer obtained from the monomer mixture in the expandable particles considered here, when the expandable particles are heated, the former, namely, The vinyl cyanide copolymer foams first, and the latter, the copolymer obtained from the mixture, foams later. Then, when the temperature of the latter becomes suitable for foaming, the former has already passed the appropriate foaming temperature and is in a state where air bubbles are crushed. For this reason, it was considered that the foamable particles formed with the former as a nucleus would have a cavity inside when prefoamed.

Based on this idea, it is considered that the formation of voids in the pre-expanded particles is an inevitable result of the resin used, and it cannot be fundamentally eliminated unless the resin is changed. Was done. However, it has been found that the formation of the cavities is, surprisingly, virtually inconspicuous by further processing of the expandable particles, and thus can be effectively solved.

The inventor of the present invention has used a heat-resistant expandable particle obtained by the method described in JP-A-63-37139 as a raw material, and further repeating the method to obtain a copolymer formed from a monomer mixture. Made many expandable particles. That is, the heat-resistant expandable particles obtained by the teaching of the above publication are dispersed again in an aqueous medium to form a suspension, and a monomer mixture of maleimide, α -methylstyrene, and acrylonitrile is gradually added thereto. The resin particles were adhered to the particle surface and polymerized to prepare resin particles having a high copolymer content obtained from the monomer mixture, which were impregnated with a blowing agent to prepare large expandable particles. When this was pre-expanded by steam heating, it was found that the obtained pre-expanded particles had no cavities, or even if they had cavities, their size was small and inconspicuous. Furthermore, they have found that when the pre-expanded particles are placed in a mold, steam is blown therein and heated to form a molded article having no voids. The present invention has been completed based on such knowledge.

[0010] The present invention is briefly described in Japanese Patent Application Laid-Open
The foamable copolymer resin particles obtained by the method disclosed in Japanese Patent Publication No. 37139 are used as a raw material, and this is dispersed in an aqueous medium to form a suspension. In addition to the suspension, the method of producing expandable particles is repeated, in which a monomer mixture is copolymerized with the above resin particles as nuclei, and an organic blowing agent is impregnated during the copolymerization process. The present invention is disclosed in
The blowing agent-containing copolymer resin particles obtained according to the teaching of JP-A-37139 can be used as a raw material, but the starting material can also be a copolymer resin particle containing no organic blowing agent. .

In Japanese Patent Application Laid-Open No. 63-37139, it is necessary to use, as polymer particles, those containing 10 to 50% by weight of a vinyl cyanide monomer in order to produce expandable copolymer resin particles. It had been. However, the raw material used in the present invention does not need to be made of a vinyl cyanide copolymer, but should be made of styrene-based polymers, that is, styrene homopolymers and copolymers. There was found.

Accordingly, the present invention relates to a method for producing an N-arylmaleimide comprising 0.5 to 30% by weight of α -methylstyrene and
70% by weight, acrylonitrile 10 to 40% by weight,
95 to 30 parts by weight of a monomer mixture comprising 0 to 20% by weight of another vinyl monomer copolymerizable therewith is added to 5 to 7 parts by weight.
Copolymer resin particles of uniform size obtained by copolymerization on the surface of 0 parts by weight of styrene-based polymer particles are dispersed in an aqueous medium to form a suspension. The same monomer mixture was gradually added, and the monomer mixture was copolymerized on the surface of the copolymer resin particles in the presence of a polymerization initiator, and the copolymerization ratio was 5 to 70 by weight. The present invention relates to a method for producing expandable copolymer resin particles, characterized in that the monomer mixture is 95 to 30 parts per part, and the resin particles are impregnated with an organic blowing agent in the course of the copolymerization.

The copolymer resin particles used as a raw material in the present invention are those produced according to the teachings described in JP-A-63-37139. However, the copolymer resin particles that can be used in the present invention are different from those taught in the above publication in the following two points. First, in the above publication, 10 to 5 polymer particles are first used to prepare a suspension.
Although it is necessary to use a copolymer containing 0% by weight of vinyl cyanide, the copolymer resin particles that can be used in the present invention are those made from a vinyl cyanide copolymer as described above. However, the present invention is not limited to this, and it is widely possible to use those made of styrene resins.
Second, the above publication requires that the copolymer resin particles be impregnated with an organic blowing agent, but the copolymer resin particles that can be used in the present invention do not necessarily need to contain a blowing agent. Is a point.

The copolymer resin particles obtained by the method described in JP-A-63-37139 are resin particles obtained by copolymerizing a monomer mixture on the surface of vinyl cyanide copolymer particles. Among these, as the vinyl cyanide copolymer particles, resin particles obtained by copolymerizing vinyl cyanide with aromatic vinyl, acrylate, methacrylate, vinyl carboxylic acid, maleimide and the like can be used. As the above-mentioned vinyl cyanide, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, fumaronitrile and the like can be used. Among them, acrylonitrile and methacrylonitrile are preferably used.

In preparing a vinyl cyanide copolymer, aromatic vinyl used for copolymerization with vinyl cyanide includes styrene, α-methylstyrene and t-methylstyrene.
-Butyl styrene, vinyl toluene, vinyl xylene,
Monochlorostyrene, dichlorostyrene and the like can be used, and among them, styrene and α-methylstyrene are preferable. In addition, methyl acrylate, ethyl acrylate, and butyl acrylate can be used as the acrylate. Methyl methacrylate, ethyl methacrylate and the like can be used as methacrylate, acrylic acid and methacrylic acid can be used as vinyl carboxylic acid, and laurylmaleimide, phenylmaleimide, methylphenylmaleimide and the like can be used as maleimide.

Styrene-based polymer particles that can be used in the present invention, including the above-mentioned vinyl cyanide copolymer, include:
It preferably has a spherical or pellet shape. It is preferable that the size is set within a range of a diameter of 0.2 to 1.2 mm. When styrene-based polymer particles are usually produced by a suspension polymerization method, particles having a diameter in the range of 0.1 to 2 mm are obtained. Therefore, the styrene-based polymer used as the nucleus of the polymerization does not use the particles obtained by the suspension polymerization method as it is, but has an appropriate particle size, for example, 0.1 g.
It is preferable to select and use one having a thickness of 2 to 1.2 mm.

The monomer mixture needs to contain three kinds of monomers of N-arylmaleimide, α -methylstyrene and acrylonitrile in a certain ratio. In addition, the monomer mixture may contain, as an optional component, other vinyl monomers copolymerizable with the above three kinds of monomers to a certain ratio.

N-arylmaleimides are disclosed in
No. 37139, a compound abbreviated as N-aromatic maleimide,

[0019]

Embedded image It is a compound represented by these. Here, Ar represents an aryl group. The aryl group may be substituted with one or more halogen atoms or lower alkyl groups. Of these, N-phenylmaleimide and N-methylphenylmaleimide are preferably used in terms of availability. The N-arylmaleimide is required to account for 0.5 to 30% by weight of the monomer mixture. The reason for this is that if the N-arylmaleimide is less than 0.5% by weight, the heat resistance of the obtained particles will not be improved remarkably.
If the content is more than 10% by weight, the softening temperature of the obtained particles becomes too high, so that pre-expansion becomes difficult. Among them, the content is preferably 5 to 20% by weight.

The amount of α-methylstyrene affects the foamability of the copolymer resin particles. That is, if the amount of α-methylstyrene is less than 40% by weight, the retention of the foaming agent in the expandable copolymer resin particles decreases, and if it exceeds 70% by weight, unreacted α-methyl The amount of styrene increases and the heat resistance decreases. For this reason, α-methylstyrene is set to 40 to 70% by weight in the monomer mixture. Of these, the content is preferably 50 to 70% by weight.

Acrylonitrile is used in the monomer mixture at 1
It is necessary to account for 0 to 40% by weight for the following reasons. If the amount of acrylonitrile is less than 10% by weight, the obtained foamed molded article becomes brittle, and the chemical resistance and oil resistance are reduced. The molded product is colored and the heat resistance is reduced. Within the above-mentioned range, it is particularly preferred to be 20 to 30% by weight.

Vinyl monomers that can be added as optional components to the monomer mixture are aromatic vinyls other than α-methylstyrene, for example, halogenated styrene, and methacrylates, for example, methyl methacrylate. Among these, it is preferable to use a monomer whose glass transition point of the homopolymer is higher than that of polystyrene (100 ° C.). The optional vinyl monomer is required to be 20% by weight or less in the monomer mixture.
The reason is that if it exceeds 20% by weight, the heat resistance of the obtained copolymer resin will be reduced.

It is necessary to disperse the above-mentioned styrene polymer particles or the copolymer resin particles obtained according to the teaching of JP-A-63-37139 in an aqueous medium. Examples of the aqueous medium include water-soluble organic compounds such as polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium pyrophosphate, magnesium phosphate, and magnesium oxide. What disperse | distributed the hardly soluble inorganic fine powder in water is used. When using the above-mentioned inorganic powder, it is preferable to add a small amount of a surfactant such as sodium dodecylbenzenesulfonate.

According to the method of the present invention, JP-A-63-3713
No. 9, styrene-based polymer particles 5
On 70 to 70 parts by weight of the surface, the above monomer mixture 95-3
A copolymer resin particle obtained by copolymerizing 0 parts by weight is used as a material, and this is dispersed in the above-mentioned aqueous medium to form a suspension. Separately, the above-mentioned monomer mixture is prepared, and this is gradually added to the above-mentioned suspension. In this case, the ratio of the monomer mixture to the copolymer resin particles is 95 to 30 parts by weight based on 5 to 70 parts by weight of the resin particles. The reason is that if the resin particles are less than 5 parts by weight, it is difficult to uniformly absorb the monomer mixture into the resin particles, and therefore the monomer mixture separates from the resin particles and copolymerizes alone. On the other hand, if the content of the resin particles exceeds 70 parts by weight, the improvement in heat resistance becomes insufficient, and the productivity also deteriorates.

As the polymerization initiator for copolymerizing the monomer mixture, those generally used as a polymerization initiator for styrene can be used. For example, benzoyl peroxide, lauroyl peroxide, t
-Butylperoxybenzoate, t-butylperoxyisobutyrate, t-butylperoxylaurate,
Organic peroxides such as di-t-butyl peroxide and di-t-butyl peroxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile can be used. These polymerization initiators can be used alone, but also
More than one species can be used in combination. These polymerization initiators may be added to the suspension, may be added to the monomer mixture, or may be added by dissolving only specific monomers separately from these.

In the method of the present invention, the monomer mixture is gradually added to the suspension of the copolymer resin particles, and the mixture is adhered to the surface of the resin particles by gentle stirring. At this time, the suspension is maintained at a temperature of 60 to 150 ° C., so that the monomer mixture is easily affected by the polymerization initiator to cause copolymerization. If the temperature is lower than 60 ° C., the speed of the copolymerization is slow and it takes time until the copolymerization is completed.
If the average particle size exceeds, the suspension becomes unstable and the particles tend to aggregate.

As described above, the monomer mixture added to the suspension is well absorbed by the copolymer resin particles,
Copolymerization is carried out in the presence of a polymerization initiator to obtain copolymer resin particles. In this process, the resin particles are impregnated with an organic foaming agent. The impregnation with the organic foaming agent may be performed before the copolymerization is performed, during the copolymerization is being performed, or after the copolymerization is completed.

Examples of the organic blowing agent include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane and n-hexane, methyl chloride, ethyl chloride, dichlorodifluoromethane, and trichlorofluorocarbon. Halogenated hydrocarbons such as methane can be used. These foaming agents may be used alone or in combination of two or more. The content of the blowing agent is
It is suitable that the ratio is 1 to 10% by weight based on the obtained copolymer resin particles.

In the method of the present invention, in addition to the above-mentioned materials, a well-known bubble regulator, lubricant, flame retardant, coloring agent, antistatic agent and the like can be added. Further, the suspension, the dropping of the monomer mixture, and the separation can be further repeated.

[0030]

EFFECTS OF THE INVENTION The present invention method, and 0.5 to 30 wt% N-aryl maleimides, alpha-methyl styrene 40
70% by weight, acrylonitrile 10 to 40% by weight,
Since the monomer mixture was composed of 0 to 20% by weight of other vinyl monomers copolymerizable therewith, this monomer mixture has an affinity for the styrene-based polymer, The resulting copolymer is easy to impregnate with an organic foaming agent, and the copolymer containing the foaming agent easily foams upon heating and has the property of fusing together, and is more heat-resistant than styrene-based polymers Rich in sex. Therefore, copolymer resin particles obtained by copolymerizing 95 to 30 parts by weight of the monomer mixture on the surface of 5 to 70 parts by weight of the styrene-based polymer particles,
It is suitable for use as heat-resistant foamed particles. However, when the foamed particles were made to contain an organic foaming agent, when the foamed particles were heated and pre-foamed, the obtained pre-foamed particles had cavities inside, and had excellent mechanical strength. It cannot be made into a foamed molded product. On the other hand, according to the method of the present invention, the copolymer resin particles which already have good properties in terms of heat resistance are used as the material, which is again suspended, and the monomer mixture is added thereto. Since the process of copolymerizing the monomer mixture with the particles as nuclei was repeatedly applied, in the obtained copolymer resin particles, the copolymer formed from the monomer mixture was far more than the styrene-based polymer particles. Therefore, when this is expanded, even if the cells of the styrene polymer are crushed, the expansion by the copolymer is sufficiently performed, and as a result, good heat-resistant expandable particles are obtained. . As described above, the method of the present invention provides a great advantage in that foamable particles having good heat resistance can be provided.

Hereinafter, the advantages of the method of the present invention will be specifically described with reference to examples and comparative examples. In the following, simply “parts” means parts by weight.

[0032]

Example 1 (Production of raw material) As a vinyl cyanide copolymer, a styrene-acrylonitrile copolymer obtained by copolymerizing acrylonitrile at a ratio of 30% by weight and styrene at a ratio of 70% by weight was used. First, copolymer resin particles were prepared according to the teaching of JP-A-37139. The details are as follows.

In a 5 liter autoclave, water 2
An aqueous medium was prepared by adding 200 g, 132 g of tricalcium phosphate and 0.35 g of sodium dodecylbenzenesulfonate. In this, the particle diameter is 0.343-0.575m
The above-mentioned styrene-acrylonitrile copolymer (550 g) adjusted to m was added and uniformly dispersed in an aqueous medium to form a suspension. The suspension was stirred at a stirring speed of 340 rpm to keep the suspension.

Separately, 10 parts of N-phenylmaleimide, α-
A monomer mixture was prepared by mixing 58 parts of methylstyrene, 22 parts of acrylonitrile and 10 parts of styrene. As a polymerization initiator, 6.3 g of di-t-butyl peroxyhexahydroterephthalate and t-butyl perbenzoate 2.
5 g of the above monomer mixture 165
0 g, and this solution was added to the autoclave.

Prior to the addition, the suspension in the autoclave was heated to 95 ° C., and while maintaining the temperature, the above solution was gradually dropped into the suspension so that the addition was completed in 5 hours. Thereafter, the temperature was raised to 120 ° C. and maintained at this temperature for 3 hours to complete the copolymerization. Thereafter, the temperature was cooled to 30 ° C. to obtain copolymer particles. The copolymer particles were used as a raw material for the method of the present invention.

(Execution of the method of the present invention) 2200 g of water, 132 g of tribasic calcium phosphate and 0.35 of sodium dodecylbenzenesulfonate were placed in the 5-liter autoclave.
g was added to prepare the same aqueous medium as above, and 550 g of the copolymer particles obtained above were added thereto, and stirred under the same conditions as above to form a suspension.

The suspension is heated to 95 ° C., and the monomer mixture containing the above-mentioned polymerization initiator is added dropwise while maintaining the temperature. And then raise the temperature to 120 ° C. for 3 hours at 120 ° C.
, And 88 g of butane was injected as a blowing agent under pressure, followed by stirring at 120 ° C. for 6 hours to impregnate the resin particles with the blowing agent to obtain expandable copolymer resin particles.

(Performance of the obtained expandable particles) After the obtained expandable particles were stored for a while, they were brought into contact with steam at 150 ° C to obtain pre-expanded particles having a multiple of 5 times. After being left for a while, the pre-expanded particles are
mm into a mold, and steam was blown into the mold to obtain a foam molded article.

There are no cavities inside the pre-expanded particles, and the obtained foam molded article has a beautiful surface and a fusion rate of 100%.
%, And the bending strength was 51.2 kg / cm ² .
Also, when the heating dimensional change rate of the molded body was measured, the heating dimensional change rate was −0.39 at 100 ° C. × 168 h,
The value was −0.31 at 110 ° C. × 168 h, and the dimensional change was small. Therefore, these expandable particles expand well,
A good molded product was obtained.

[0040]

Example 2 (Production of raw material) This example was carried out in the same manner as in Example 1, except that styrene containing no acrylonitrile was used instead of the styrene-acrylonitrile copolymer used in the production of the raw material. A copolymer particle to be used as a raw material was obtained in exactly the same manner as in Example 1 except that the homopolymer was used.

(Execution of the method of the present invention) Using the copolymer particles obtained above, expandable copolymer resin particles were obtained in exactly the same manner as in Example 1.

(Performance of the Expandable Resin Particles Obtained) When pre-expanded particles were produced in exactly the same manner as in Example 1, no void was formed inside. Further, when a foam molded article was produced in exactly the same manner as in Example 1, the molded article had a beautiful surface, a fusion rate of 90%, and a flexural strength of 47.5 kg / cm ^2.
And the heating dimensional change rate was −0.0 at 100 ° C. × 168 h.
The dimensional change was small at -0.56 at 45.degree. Therefore, the expandable particles foamed well to give a good foam molded article.

[0043]

Example 3 (Production of raw material) This example was carried out in the same manner as in Example 1, except that 80% by weight of styrene was used instead of the styrene-acrylonitrile copolymer used in the production of the raw material.
Copolymer particles were obtained in exactly the same manner as in Example 1 except that a styrene / α-methylstyrene copolymer of 20% by weight of α-methylstyrene was used.

(Implementation of the method of the present invention) Using the copolymer particles obtained above, the same procedure as in Example 1 was carried out to obtain expandable copolymer resin particles.

(Performance of the Expandable Resin Particles Obtained) When pre-expanded particles were produced in exactly the same manner as in Example 1, no void was formed inside. Further, when a foam molded article was produced in exactly the same manner as in Example 1, the appearance of the molded article was beautiful, the fusion rate was 90%, and the bending strength was 48.2 kg / cm ^2.
And the heating dimensional change rate was −0.0 at 100 ° C. × 168 h.
43, the dimensional change was small at -0.45 at 110 ° C. for 168 h. Therefore, the expandable particles foamed well to give a good foam molded article.

[0046]

Comparative Example 1 (Production of Expandable Resin Particles)
This is the case where expandable copolymer particles are prepared according to the teaching of JP 37139. That is, 88 g of butane as a foaming agent was added to the copolymer particles obtained in (Production of Raw Material) in Example 1, and the foaming agent was impregnated with stirring at 120 ° C. for 6 hours, and then cooled to 30 ° C. Thus, expandable copolymer particles were obtained.

(Performance of the Expandable Particles Obtained) The expandable particles obtained above were treated in exactly the same manner as in Example 1 to produce pre-expanded particles. Some have become. When a foam molded article was produced in exactly the same manner as in Example 1, the appearance of the molded article was beautiful and the fusion rate was 95%, which was good, but the bending strength was 30.6 kg.
/ Cm ² was slightly inferior. The heating dimensional change rate of the molded body is 10
-0.20 at 0 ° C x 168h,-at 110 ° C x 168h
0.10 was good. However, there was a cavity inside the pre-expanded particles, and the bending strength was inferior.

[0048]

Comparative Example 2 This comparative example is the same as Comparative Example 1
This is a case where expandable copolymer particles are prepared according to the teaching of JP-A-3-37139. That is, 88 g of butane was added as a foaming agent to the copolymer particles obtained in (Production of Raw Material) in Example 2 as in Comparative Example 1, and stirring was continued at 120 ° C. for 6 hours to impregnate the foaming agent. Thereafter, the mixture was cooled to 30 ° C. to obtain expandable copolymer particles.

(Performance of the Expandable Particles Obtained) The expandable particles obtained above were treated in exactly the same manner as in Example 1 to produce pre-expanded particles. Became. When a foam molded article was produced in exactly the same manner as in Example 1, the molded article had a poor surface appearance, a poor fusion rate of 30%, and a poor bending strength of 8.5 kg / cm ^2. Was. The heating dimensional change rate of the molded body is 100 ° C. × 1
−0.41 at 68 h, −0.52 at 110 ° C. × 168 h
Was good. However, since the pre-expanded particles contained voids inside and were inferior in appearance and flexural strength, they were evaluated as poor overall.

[0050]

Comparative Example 3 (Production of Expandable Particles) In this comparative example, as in Comparative Examples 1 and 2, foamable copolymer particles were produced according to the teachings of JP-A-63-37139. That is, 88 g of butane as a foaming agent was added to the copolymer particles obtained in (Production of Raw Material) in Example 3, and the foaming agent was impregnated with stirring at 120 ° C. for 6 hours, and then cooled to 30 ° C. Expandable copolymer particles were obtained.

(Performance of Obtained Expandable Particles) When the expandable particles obtained above were treated in the same manner as in Example 1 to produce pre-expanded particles, most of the pre-expanded particles became hollow. Was. Further, when a foamed molded article was produced in exactly the same manner as in Example 1, the molded article had a poor surface appearance, and the fusion rate was 20%.
And the bending strength was inferior at 7.6 kg / cm ² . The heating dimensional change rate of the molded body is 100 ° C. × 168 hours.
, And -0.55 at 110 ° C for 168 h. However, the pre-expanded particles contain cavities inside,
Since appearance and bending strength were inferior, it was evaluated as inferior as a whole.

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Claims (2)

(57) [Claims] 1. 0.5 to 30% by weight of N-arylmaleimide, 40 to 70% by weight of α -methylstyrene, 10 to 40% by weight of acrylonitrile and other vinyl monomers copolymerizable therewith. 95 to 30 parts by weight of a monomer mixture consisting of styrene polymer particles 5
A copolymer resin particle having a uniform size obtained by copolymerization on a surface of about 70 parts by weight is dispersed in an aqueous medium to form a suspension, and the same monomer as described above is added to the suspension. The mixture was gradually added, and the monomer mixture was copolymerized on the surface of the copolymer resin particles in the presence of a polymerization initiator. 9 body mixtures
A method for producing expandable copolymer resin particles, comprising 5 to 30 parts, and impregnating the resin particles with an organic foaming agent in the course of the copolymerization. 2. 0.5 to 30% by weight of N-arylmaleimide, 40 to 70% by weight of α -methylstyrene, 10 to 40% by weight of acrylonitrile and other vinyl monomers copolymerizable therewith. -20% by weight of a monomer mixture, and separately , vinyl cyanide copolymer particles are dispersed in an aqueous medium to form a suspension. The monomer mixture is gradually added to the suspension. In addition, the monomer mixture is copolymerized on the surface of the vinyl cyanide copolymer particles in the presence of the polymerization initiator, and the copolymerization ratio is 5 to 70 parts by weight based on the weight ratio of the vinyl cyanide copolymer particles. 95-3 of the monomer mixture
0 parts, and thus obtained copolymer resin particles are again dispersed in an aqueous medium to form a suspension, and a monomer mixture similar to the above is gradually added again to the suspension, and The mixture is copolymerized on the surface of the copolymer resin particles in the presence of a polymerization initiator, and the copolymerization ratio is determined by the weight ratio of the copolymer resin particles 5.
A method for producing expandable copolymer resin particles, characterized in that the monomer mixture is 95 to 30 parts per 70 to 70 parts, and the resin particles are impregnated with an organic blowing agent in the course of the copolymerization.