JPH0649263A - Expandable bead of high-impact styrene resin and its production - Google Patents

Abstract

PURPOSE:To provide an expandable bead of a styrene resin having high impact resistance and excellent retention of foaming agent and, accordingly, easily expandable at high expansion ratio. CONSTITUTION:The expandable bead can be produced by impregnating (A) 35-15 pts.wt. of a monomer mixture consisting of 10-55wt.% of a styrene monomer and 90-45wt.% of a conjugated diene monomer in (B) 65-85 pts.wt. of styrene polymer beads, copolymerizing the monomers in the impregnated state and incorporating a foaming agent in the obtained resin beads containing 0.1-35wt.% of gel component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable impact-resistant styrene resin particles and a method for producing the same. The impact-resistant styrene-based resin is a styrene-based resin that has some rubber-like elasticity and thus is hard to be broken by impact.

[0002]

2. Description of the Related Art Expandable particles made of styrene resin are
It is widely used to make foams with complex shapes such as containers. To make the foam, a pre-foaming step and a foam molding step are required. The pre-foaming step is a step of heating expandable styrenic resin particles (hereinafter, referred to as expandable particles) to make particles that have been expanded into pieces. The foam molding process is a process of forming a foamed molded product from disjointed foamed particles, in which the foamed particles are packed in a molding die having the shape of the molded product and steam is filled in the mold. Is blown in to heat the particles to foam the particles and fuse them together in a mold to form a molded body.

As the resin constituting the expandable particles, a homopolymer of styrene was initially used exclusively, and then a copolymer of styrene and a styrene derivative was used. In this case, the styrene derivative is, for example, α-methylstyrene,
Such as α-ethyl styrene and vinyl styrene. However, all of these polymers and copolymers have a high rigidity and therefore have a drawback that they are easily broken by impact. Therefore, a foam made by foaming such a polymer or copolymer has a drawback that it is poor in flexibility and is easily broken by impact.

In many fields, foams that are highly flexible and elastic are required. It is also necessary to make it less likely to be destroyed by impact. Therefore, attempts have been made to modify a styrene polymer or copolymer and add some rubber-like elasticity to it to make the foam somewhat soft and resistant to cracking by impact.

In addition to the styrene-based monomer,
This was done by using a conjugated diene monomer such as butadiene. That is, a conjugated diene monomer is used as a copolymer by copolymerizing with a styrene-based monomer, or a copolymer composed of a conjugated diene monomer is mixed with a styrene homopolymer or copolymer, By using it as a resin composition, it has been attempted to improve impact resistance and use it as expandable particles.

[0006] Many such attempts are shown in the patent publications. For example, Japanese Patent Publication No. 47-17465 discloses
It is described that a block copolymer containing a styrene block and a butadiene block is mixed with a styrene resin to form a resin composition, and a foaming agent is added to the resin composition to form expandable particles. Japanese Patent Application Laid-Open No. 54-158467 describes the same thing. In addition, Japanese Patent Publication No.
Japanese Patent Publication No. 28 describes that a copolymer of styrene and butadiene is mixed with a foaming agent to form expandable particles. In addition, Japanese Patent Publication No. 58-35616 and Japanese Patent Publication No. 58-
No. 35617 discloses that a rubber-like copolymer obtained by copolymerizing a nitrile and a conjugated diene monomer is mixed with a styrene resin to form a resin composition, and a foaming agent is added to the resin composition to form expandable particles. It describes that you do.

However, none of the impact-resistant styrenic expandable particles described in these publications is satisfactory.
That is, when the content of the conjugated diene monomer is increased in order to achieve sufficient impact resistance, the resulting expandable particles suddenly have poor retention of the foaming agent, and therefore, can be expanded at a sufficiently high magnification. lost. On the contrary, when the content of the conjugated diene monomer is reduced to expand the foam at a high magnification, the resulting expandable particles have poor impact resistance, and therefore, the expandable particles with improved impact resistance cannot be obtained. It was

Although it is not an attempt to improve the impact resistance of styrene resins, Japanese Patent Publication No. 52-33678 discloses that styrene and a conjugated diene monomer are used to produce a polymer which is easily decomposed by light. Teaches to polymerize. There, a mixture of a styrene monomer and a conjugated diene monomer was impregnated into particles of a styrenic polymer, and the conjugated diene monomer was polymerized so that a large amount of the conjugated diene monomer gathered on the surface of the particle. It has been shown that the particles are susceptible to decomposition by light. It is also described therein that expandable particles can be obtained by adding a foaming agent to the obtained particles. However, particles that deteriorate with light are not satisfactory as foams.

[0009]

As described above, the expandable particles of the styrene resin which have good impact resistance and good retention of the foaming agent and therefore can be easily expanded at a high ratio. Has never been offered. Therefore, the present invention is intended to provide such expandable particles having good impact resistance.

[0010]

DISCLOSURE OF THE INVENTION The inventor of the present invention suspended polystyrene particles in water and allowed the particles to absorb a mixture of styrene and butadiene so that the mixture existed near the surface of the particles. In the above, the mixture was copolymerized to form styrene resin particles, and pentane was pressed into the mixture to prepare expandable styrene resin particles. Then,
It has been found that the expandable particles have good retention of a foaming agent and can be expanded at a high magnification even though impact resistance is improved.

As a result of further investigations based on the above findings, the present inventor found that the polystyrene particles should have good impact resistance and sufficient foaming agent retention in order to have good impact resistance. It has been found that there is a certain relationship between the ratio of and the mixed monomer. That is, it has been found that the polystyrene particles to be the core must account for 65 to 85% by weight in the obtained particles in order for the obtained particles to exhibit sufficient foaming agent retention. Further, in order for the obtained particles to exhibit good impact resistance, in the remaining 35 to 15% by weight of the mixed monomer,
The ratio of the styrene monomer and the butadiene monomer is
It has been found that it must be in the range of 10-55% by weight and 90-45% by weight, respectively. The present invention has been completed based on such knowledge.

The present invention provides, in one aspect, expandable, impact-resistant styrenic resin particles, and in another aspect, a method for producing such particles. The invention relating to expandable impact-resistant styrene-based resin particles is styrene-based resin particles containing a foaming agent, wherein the styrene-based resin is added to 65-85 parts by weight of a particulate styrene-based polymer.
5 to 15 parts by weight of a mixed monomer is impregnated and copolymerized, and the mixed monomer includes 10 to 55 parts by weight of a styrene monomer and a conjugated diene monomer, respectively. %
And 90-45% by weight,
The styrene resin particles contain a gel content of 0.1 to 35% by weight, and the foaming agent is a saturated aliphatic hydrocarbon, an alicyclic hydrocarbon or a hydrocarbon having a boiling point lower than the softening point of the styrene resin. A halogenated aliphatic hydrocarbon, which is a resin 10
It is characterized in that 4 to 12 parts by weight is contained with respect to 0 parts by weight.

Further, the invention relating to the production method is such that 65-85 parts by weight of the particulate styrene-based polymer is dispersed in an aqueous medium, and the styrene-based monomer and the conjugated diene monomer are each by weight. A mixture of 35 to 15 parts by weight of a mixed monomer mixed in a ratio of 10-55% to 90-45% was dispersed with a mixture of a polymerization initiator, and the mixture was impregnated with a particulate styrene polymer. Styrene resin particles are prepared by copolymerizing mixed monomers in the state, or in the course of the copolymerization or thereafter, the saturated aliphatic hydrocarbon having a boiling point lower than the softening point of the styrene resin, It is characterized by containing an alicyclic hydrocarbon or a halogenated aliphatic hydrocarbon.

In the present invention, a particulate styrenic polymer is used as a core, and this is impregnated with a mixed monomer of a styrene monomer and a conjugated diene monomer, and in that state, a mixed monomer is added. The main idea is to copolymerize the body into styrene resin particles. In this regard, Japanese Examined Patent Publication No. 52-33678
The method is similar to the method for producing resin particles which are easily decomposed by light, which is described in Japanese Patent Publication No. 2003-242242.

However, Japanese Examined Patent Publication No. 52-33678 aims at making resin particles that are easily decomposed by light, and for that purpose, a conjugated diene monomer such as butadiene is added to the entire styrene resin particles. 0.5-
It is said that it must occupy 10% by weight. In addition, it is explained that the polystyrene particles, which become the nucleus of the polymerization, should be a small amount of 60% by weight or less in the whole styrene resin particles. Therefore, what this publication teaches is not only related to the purpose of the present invention, but also the constitution of the obtained resin particles is completely different.

By the way, the impact resistant styrene resin particles according to the present invention are constituted as described below. That is, it has a structure in which 65-85 parts by weight of a particulate styrenic polymer is used as a core, 35-15 parts by weight of a mixed monomer are impregnated into the core, and the mixed monomer is copolymerized in this state. . The mixed monomer in this case is a mixture of a styrene-based monomer and a conjugated diene monomer. The mixing ratio of the styrene-based monomer is 10-55% by weight,
The ratio of the conjugated diene monomer is 90-45% by weight.

The styrenic monomer that can be used in the present invention contains styrene derivative in addition to styrene. The styrene derivative is, for example, α-methylstyrene,
Examples include α-ethylstyrene, α-chlorostyrene, vinylstyrene and the like. These styrenic monomers can be used alone or as a mixture.

The conjugated diene monomer that can be used in the present invention contains isoprene, chloroprene, 1,4-pentadiene, 1,5-hexadiene and the like in addition to the above-mentioned butadiene. These conjugated diene monomers can be used alone or as a mixture. Of these, it is preferable to use butadiene.

The styrenic polymer which can be used in the present invention includes homopolymers or copolymers of styrenic monomers and copolymers of styrenic monomers and other monomers. I'm out. As described above, the styrene-based monomer includes a styrene derivative such as α-methylstyrene in addition to styrene. The above-mentioned copolymer of the styrene-based monomer and the other monomer must contain the styrene-based monomer in a larger amount by weight than the other monomer. . Other monomers include acrylic acid,
Unsaturated aliphatic organic acids such as methacrylic acid and maleic anhydride, butyl acrylate, unsaturated aliphatic esters such as methyl methacrylate, N-phenylmaleimide, acrylonitrile and the like can be used.

The styrenic polymer may be obtained by polymerizing or copolymerizing a styrenic monomer by any method. For example, any of a suspension polymerization method, an emulsion polymerization method, a solution polymerization method and a bulk polymerization method may be used. Further, the shape of the polymer is required to be particulate, but the specific shape may be pellet or spherical. The particle size is preferably within the range of 0.1-10 mm.

The expandable impact-resistant styrenic resin particles according to the present invention are, as described above, copolymerized with the mixed monomer in a state where the particulate styrene polymer is impregnated with the mixed monomer. It was made. When impregnating the particles of the styrene polymer with the mixed monomer, it takes time for the mixed monomer to penetrate to the center of the polymer particles. Therefore, the mixed monomer is inevitably copolymerized in a state where it exists near the surface of the polymer particles. Therefore, the copolymer produced by copolymerizing the mixed monomers is collected on the surface of the styrene polymer particles. As a result, the particles obtained by copolymerizing the mixed monomer have a structure such as a coated particle in which the central portion is a styrene-based polymer and the vicinity of the skin is a copolymer of the mixed monomer. I will have. However, unlike the coated particles, the boundary between the inside and the epidermis is not clear, and the bond between the inside and the surface is extremely strong.

Since the mixed monomer contains the conjugated diene monomer and the amount of the conjugated diene monomer is relatively large, the conjugated diene monomer acts as a cross-linking agent and the solvent It becomes easy to form an insoluble gel. Therefore, the obtained resin particles contain a solvent-insoluble gel component. This gel content can be grasped as an insoluble portion remaining after the generated resin particles are extracted with boiling toluene. According to actual measurement, the resin particles according to the present invention are 0.1
It contains a wide range of toluene insolubles ranging from -35% by weight. This gel content includes the polymerization temperature, the type and amount of the polymerization initiator,
It can be adjusted by the amount of the chain transfer agent, and especially 0.1-
A preferable range is 10% by weight.

The resin particles according to the present invention contain a foaming agent. As the foaming agent, one which has been used as a foaming agent for polystyrene has been used. The foaming agents are roughly classified into three types, saturated aliphatic hydrocarbons, alicyclic hydrocarbons, and halogenated aliphatic hydrocarbons. Among them, the saturated aliphatic hydrocarbons are, for example, propane, butane and pentane, the alicyclic hydrocarbons are, for example, cyclohexane, and the halogenated aliphatic hydrocarbons are, for example, methyl chloride and dichlorodifluoromethane. All of these foaming agents have a boiling point of 100 ° C. or less under normal pressure, and have a boiling point lower than the softening point of the styrene resin. Further, these foaming agents can be easily impregnated in the styrene resin.

The foaming agent is 4-1 with respect to 100 parts by weight of the resin.
Include 2 parts by weight. The reason is that it is difficult to expand the expandable particles to a high expansion ratio when the amount is less than 4 parts by weight, and conversely, when the expansion amount exceeds 12 parts by weight, the expandable particles abruptly expand upon heating to control the expansion ratio. It is difficult to do so.

The above-mentioned gel component facilitates foaming of particles. That is, when the amount is such that there is no gel content and the amount is less than 0.1% by weight, the resin has too much flexibility due to the copolymerization of the conjugated diene monomer and immediately after foaming. The expanded particles will greatly contract. On the other hand, if the gel content is large and exceeds 35% by weight,
The resin becomes hard, and it becomes difficult to foam at a high magnification, and it becomes difficult to mutually fuse the foamed particles. However, when the gel content is 0.1 to 35% by weight, appearance of the above-mentioned defects is suppressed, and good expandable particles are obtained.

[0026]

[Effects of the Invention for Expandable Particles] The expandable particles according to the present invention are obtained by impregnating a particulate styrene polymer having a resin therein of 65-85 parts by weight with 35-15 parts by weight of a mixed monomer. In this state, the mixed monomer is copolymerized, and the mixed monomer contains 10-55% by weight and 90-4% by weight of the styrene monomer and the conjugated diene monomer, respectively.
Since it is mixed at a ratio of 5% by weight, a styrenic polymer is used as a core, and a skin made of a copolymer of a styrene monomer and a conjugated diene monomer is integrally formed around the core. It has a different structure. Since the core of these particles is composed of a styrene-based polymer and the core occupies 65 to 85 parts by weight, the holding power of the foaming agent is large, and thus the foaming ability is large. On the other hand, the skin has a sufficient impact resistance because it is composed of a copolymer of a styrene monomer and a conjugated diene monomer and the skin occupies 35 to 15 parts by weight. Furthermore, by including the conjugated diene monomer in the above proportion, a gel content of 0.1-35 wt% is produced in the particles. As described above, this gel content is effective in giving a good molded product that is foamed at a high magnification. The expandable particles according to the present invention provide the above advantages.

[0027]

[Description of Invention of Manufacturing Method] Next, a method of manufacturing the expandable particles according to the present invention will be described. In the production method, in addition to the styrene polymer particles, the mixed monomer, and the foaming agent, which have already been described, an aqueous medium and a polymerization initiator are required. Therefore, these are first described.

The aqueous medium is an aqueous solution in which a dispersant or the like is dissolved in water. Ion-exchanged water is usually used as the water must not contain impurities. Various dispersants can be used. For example,
Polymer protective colloids such as partially saponified polyvinyl alcohol and polyvinylpyrrolidone, poorly water-soluble inorganic salts such as magnesium pyrophosphate and calcium phosphate, and anionic surfactants such as sodium dodecylbenzene sulfonate and sodium lauryl sulfate. Can be used alone or in combination. The dispersant is about 2% by weight or less with respect to water.

The polymerization initiator is for copolymerizing the mixed monomers. As the polymerization initiator, it is possible to use the polymerization initiator which has been used so far for suspension polymerization of styrene. For example, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, 2,2-di (t-butylperoxy) butane, t-
Butyl peroxy benzoate etc. can be used.

To carry out the method of the present invention, for example, the following is carried out. First, an aqueous medium having a volume of ½ to ⅓ of its internal volume is placed in an autoclave, and a particulate styrene polymer is placed therein. The styrene polymer is
It is 50-100% by weight of the weight of the aqueous medium. After adding the styrene polymer, the aqueous medium is thoroughly stirred.

Separately, a styrene monomer and a conjugated diene monomer are mixed to prepare a mixed monomer. The mixing ratio at this time is such that the styrene-based monomer is 10-55% by weight and the conjugated diene monomer is 90-45% by weight. Also,
A polymerization initiator is added to this mixed monomer. The amount of the polymerization initiator is 1 to 0.1% by weight based on the mixed monomer. The mixed monomer containing the polymerization initiator is immediately added to the autoclave. The ratio of the mixed monomer to be added is 35-15 parts by weight with respect to 65-85 parts by weight of the styrene polymer so that the total amount becomes 100 parts by weight.

After the mixed monomer is added, the inside of the autoclave is well stirred so that the mixed monomer and the styrene polymer are well dispersed in the aqueous medium. The autoclave is then heated with continued stirring. The heating maintains the temperature in the autoclave at the desired temperature in the range 60-180 ° C. In this way, heating is continued while stirring for a suitable time, and the mixed monomer is copolymerized with the styrene-based polymer impregnated with the mixed monomer. When the copolymerization is complete, the autoclave is cooled. The resin particles thus obtained are impact resistant styrene resin particles.

The mixed monomer is prepared by mixing the styrene-based monomer and the conjugated diene monomer in a container separate from the autoclave as described above, or by adding the styrene-based monomer in the autoclave. There is also a method in which a monomer and a conjugated diene monomer are added separately and mixed in an autoclave. In this case, the styrene-based monomer may be added first, and then the conjugated diene monomer may be added later. Conversely, the conjugated diene monomer may be added first, and then the styrene-based monomer may be added. May be. The addition method of these monomers may be batch, continuous or intermittent.

In the step of copolymerizing the above-mentioned mixed monomers or after the copolymerization, a foaming agent is pressed into the autoclave. Then, the foaming agent is absorbed by the styrene-based polymer and the mixed monomer, or the generated styrene-based resin particles, whereby the expandable particles are obtained.

[0035]

According to the present invention,
As the mixed monomer, a mixture of a styrene-based monomer and a conjugated diene monomer in a proportion of 10-55% and 90-45% by weight is used, respectively, so that they are well dissolved in each other, By applying a slight pressure to the mixed monomer, the mixed monomer can be handled as a uniform liquid. Further, the mixed monomer is easily absorbed by the particulate styrenic polymer, and thus the mixed monomer has a viscosity of 65-85 in an aqueous medium.
Since 35 parts by weight of the particulate styrenic polymer is dispersed and 35-15 parts by weight of the mixed monomer are dispersed, the mixed monomer is easily adsorbed uniformly on the surface of each particle of the styrene polymer. Most of the mixed monomer that has been adsorbed in this manner remains on the surface of the particles. At this time, since the mixed monomer contains the polymerization initiator, it is copolymerized to form a skin. Since this skin is composed of a mixture of styrene-based monomer and conjugated diene monomer in the proportions of 10-45% and 90-45%, respectively, the styrene-based polymer has appropriate flexibility and elasticity. Will be given. When a foaming agent selected from saturated aliphatic hydrocarbons, alicyclic hydrocarbons or halogenated aliphatic hydrocarbons is included in the particles after the copolymerization process or after the copolymerization, these foaming agents are incorporated into the skin. It was obtained because it was well retained in the styrene-based polymer having a better retention of the blowing agent than the polymer, and the styrene-based polymer occupies a large amount of 65-85 parts by weight in the particles. The particles have a large foaming ability when heated. Thus, according to this method, it is possible to efficiently produce the expandable particles having a flexible elasticity and a large foaming ability. The present invention provides such benefits.

Hereinafter, the reason why the method of the present invention is excellent will be specifically described with reference to Examples and Comparative Examples.

The resin particles obtained in Examples and Comparative Examples were (a) gel fraction, (b) maximum foaming bulk ratio as a foaming agent retention evaluation, and (c) compressive strength as an elasticity evaluation. In addition, (d) compression strain recovery rate and (e) falling ball value are measured for impact resistance evaluation, and the physical properties thereof are measured as follows. (A) Gel fraction: Styrene-based resin particles were placed in a Soxhlet extractor, extracted with boiling toluene for 24 hours, filtered through a wire mesh of 80 mesh, and the weight of the toluene-insoluble portion remaining on the wire mesh was measured. It was measured and the ratio was defined as the gel fraction. Foaming agent retention evaluation (b) Maximum expansion bulk ratio: 20 after producing expandable particles
After storing at ℃ for 21 days and aging, put the particles in an unsealed foaming tank, blow steam at 100 ℃ into the tank to foam, and put the resulting expanded particles in a container with an internal volume of 500 ml. The weight Wg of the expanded particles that could be filled and placed in the container was determined, and the quotient obtained by dividing 500 by W was taken as the bulk ratio (ml / g) to determine the maximum bulk ratio. Elasticity evaluation: After the expandable particles were produced, they were stored at 20 ° C for 7 days for aging and then put into a pre-expanding machine to be pre-expanded to a bulk ratio of 40 (ml / g). After leaving the pre-expanded particles at room temperature for 24 hours, 400 mm × 3
It is filled in a mold of 00 mm x 100 mm and 0.5 kg /
cm ² G of steam was blown into the mold to foam and fuse the particles to obtain a foamed molded body. A test piece of 50 mm × 50 mm × 50 mm was cut out from this foamed molded body, and the compression strength and the compression strain restoration rate of the test piece were determined. (C) Compressive strength: According to the test method specified in JIS K-6767, the above test piece was compressed at a speed of 10 mm / min to give a stress (kg / c) when a compressive strain of 25% was generated.
m ² ) was calculated. (D) Restoration rate of compressive strain: According to the test method specified in JIS K-6767, the above test piece was compressed at a speed of 10 mm / min to generate a compressive strain of 80%, and then the test piece was taken out. Then, the dimension L after restoration in the compression direction was measured, and L ÷ 50 × 100 was taken as the restoration rate (%). Impact resistance evaluation (e) Falling ball value 20 mm × 40 mm × 200 from the foamed molded product described above
mm test pieces were cut out and spaced 150 mm apart 2
A test piece was placed between two fulcrums, and a 198 g steel ball was dropped from the support point, and the height at which 50% of the test piece was broken was measured to determine the falling ball value (cm).

[0038]

Example 1 10 g of magnesium pyrophosphate and 0.4 g of sodium dodecylbenzene sulfonate were dissolved in 2000 g of ion-exchanged water to obtain an aqueous medium having an internal volume of 5.
It was placed in a 5 liter autoclave. Next, 1400 g of polystyrene particles having a particle size of 0.7-0.8 mm were put in this aqueous medium and well stirred to disperse the particles in the medium.

Separately, 240 g of styrene monomer and 360 g of butadiene were mixed under pressure to prepare a liquid mixed monomer, and 2 g of benzoyl peroxide as a polymerization initiator and t-butyl peroxybenzoate (0.1 g) were added thereto as a polymerization initiator. 5 g was added to form a mixture.

The above mixture was added to the above autoclave, the mixture was dispersed together with polystyrene particles in an aqueous medium, and the dispersion liquid was stirred at 60 ° C. for 2 hours so that the mixture was absorbed by the polystyrene particles. Continuously, the dispersion liquid at 90 ° C
Was kept for 4 hours and then at 125 ° C. for 2 hours to copolymerize styrene and butadiene. After that, 100 ℃
After cooling to 0, a part of the particles formed in the container was taken out and the gel fraction was measured.

Then, pentane 20 was placed in the autoclave.
0 g was press-fitted and kept at 100 ° C. for 6 hours to impregnate the particles with the foaming agent. Then, it was cooled to 30 ° C., and the resin particles produced from the dispersion were taken out, washed with water and dried to obtain expandable particles.

When the physical properties of the thus-obtained expandable particles were measured as described above, the gel fraction was 5.4.
%, The maximum expansion bulk ratio was 59 ml / g, the compression strength in the elasticity test was 0.7 kg / cm ² , the recovery rate was 94%, and the impact resistance was a falling ball value of 40.5 cm. From this, it was confirmed that the expanded beads had a good foaming agent retention and excellent elasticity and impact resistance.

[0043]

Example 2 This example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, expandable particles were obtained in the same manner as in Example 1 except that 1500 g of polystyrene particles, 200 g of styrene monomer and 300 g of butadiene were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 3.
The foaming ratio was 7%, the maximum expansion bulk ratio was 71 ml / g, the compression strength in the elasticity test was 1.0 kg / cm ² , the restoration rate was 91%, and the falling ball value was 33.5 cm. From this, it was confirmed that the expanded beads have very good foaming agent retention and excellent elasticity and impact resistance.

[0045]

Example 3 This example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, expandable particles were obtained in the same manner as in Example 1 except that 1600 g of polystyrene particles, 160 g of styrene monomer and 240 g of butadiene were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 1.
The maximum expansion bulk ratio was 75 ml / g, the compressive strength in the elasticity test was 1.2 kg / cm ² , the recovery rate was 89%, and the falling ball value was 27.5 cm. From this, it was confirmed that the expanded beads have very good foaming agent retention and excellent elasticity and impact resistance.

[0047]

Example 4 This example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, expandable particles were obtained in the same manner as in Example 1 except that 1500 g of polystyrene particles, 150 g of styrene monomer and 350 g of butadiene were used.

Physical properties of the resulting expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 6.
0%, the maximum expansion bulk ratio was 68 ml / g, the compression strength in the elasticity test was 0.8 kg / cm ² , the restoration rate was 92%, and the falling ball value was 35.5 cm. From this, it was confirmed that the expanded beads have very good foaming agent retention and excellent elasticity and impact resistance.

[0049]

Example 5 This example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, expandable particles were obtained in the same manner as in Example 1 except that 1500 g of polystyrene particles, 100 g of styrene monomer and 400 g of butadiene were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 9.
3%, the maximum expansion bulk ratio was 66 ml / g, the compressive strength in the elasticity test was 0.7 kg / cm ² , the restoration rate was 92%, and the falling ball value was 36.5 cm. From this, it was confirmed that the expanded beads have very good foaming agent retention and excellent elasticity and impact resistance.

[0051]

Comparative Example 1 This comparative example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, the amount of polystyrene particles used is reduced to 800 g.
(40 parts by weight), and using 480 g of styrene monomer and 720 g of butadiene, the same procedure as in Example 1 was carried out to obtain expandable particles.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 1
It was 8.5% and the maximum expansion bulk ratio was 19 ml / g, and it was not possible to obtain a foamed molded product. From this, it was found that when the amount of the polystyrene particles used was less than 65 parts by weight, the foaming agent retaining property was poor and it could not be put to practical use.

[0053]

Comparative Example 2 This comparative example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, this comparative example was carried out in accordance with the teaching of Japanese Examined Patent Publication No. 52-32678, except that the amount of polystyrene particles and butadiene used was reduced to 800 g of polystyrene particles, 1080 g of styrene monomer, and 120 g of butadiene. The same procedure as in Example 1 was carried out to obtain expandable particles.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 0.
%, The maximum expansion bulk ratio is 52 ml / g, the compressive strength in the elasticity test is 1.7 kg / cm ² , the restoration rate is 75%, and the falling ball value is 1.
It was 6.5 cm. As a result,
The use amount of polystyrene particles taught in Japanese Patent Publication No. 8 is 65
Less than 4 parts by weight and the butadiene ratio in the mixed monomer is 4
It was found that the expandable particles of less than 5% by weight have good foaming agent retention, but poor elasticity and impact resistance.

[0055]

Comparative Example 3 This comparative example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, 1000 g (50 parts by weight) of polystyrene particles,
Expandable particles were obtained in the same manner as in Example 1 except that 400 g of styrene monomer and 600 g of butadiene were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 1
1.2%, the maximum expansion bulk ratio was 34 ml / g, and a foamed molded product could not be obtained. From this, it was found that when the amount of the polystyrene particles used was less than 65 parts by weight, the foaming agent retention property was poor and it could not be put to practical use.

[0057]

Comparative Example 4 This comparative example was carried out in exactly the same manner as in Example 1 except that the amounts of polystyrene particles, styrene monomer and butadiene used in Example 1 were changed. That is, 1800 g (90 parts by weight) of polystyrene particles,
Expandable particles were obtained in the same manner as in Example 1 except that 80 g of styrene monomer and 120 g of butadiene were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was found to be 0.
2%, the maximum expansion bulk ratio was 77 ml / g, the compressive strength in the elasticity test was 1.7 kg / cm ² , the restoration rate was 75%, and the falling ball value was 15.5 cm. From this, it was found that when the amount of polystyrene particles used exceeds 85 parts by weight, the modifying effect of butadiene does not appear and only those having poor elasticity and impact resistance can be obtained.

[0059]

Comparative Example 5 This comparative example was carried out in exactly the same manner as in Example 1 except that the amounts of styrene monomer and butadiene used were changed. That is, expandable particles were obtained in exactly the same manner as in Example 1 except that 420 g of styrene monomer and 180 g of butadiene (ratio of butadiene in the mixed monomer was 30% by weight) were used.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 0.
7%, the maximum expansion bulk ratio was 62 ml / g, the compressive strength in the elasticity test was 1.5 kg / cm ² , the recovery rate was 80%, and the falling ball value was 16.5 cm. From this, it was found that when the ratio of butadiene in the mixed monomer was less than 45 parts by weight, the modifying effect was not exhibited and only those having poor elasticity and impact resistance were obtained.

[0061]

COMPARATIVE EXAMPLE 6 This comparative example is the same as Example 1 except that the amount of polystyrene particles used is increased and that styrene monomer and butadiene are not used at all.
It carried out exactly like the above. That is, polystyrene particles 2
000 g was dispersed in an aqueous medium, and 200 g of pentane was immediately pressed in without heating for copolymerization and held at 100 ° C. for 6 hours for impregnation of pentane to obtain expandable particles.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 0.
%, The maximum expansion bulk ratio is 70 ml / g, the compressive strength in the elasticity test is 1.9 kg / cm ² , the restoration rate is 73%, and the falling ball value is 1.
It was 4.5 cm. Therefore, ordinary expanded polystyrene particles have poor elasticity and impact resistance and are inferior.

[0063]

Comparative Example 7 In this Comparative Example, a resin composition obtained by mixing the polymers instead of polymerizing the monomer with the polymer particles as the core was used. The details are as follows.

Styrene-butadiene random copolymer (butadiene content 76.5%) 2 in 80 parts of polystyrene 2
After mixing 0 parts of the mixture, the mixture was put into an extruder and melt-kneaded. Then, the mixture was extruded into a string shape, water-cooled, and cut into pellets having a length of about 1 mm and a diameter of 0.7 mm.

Expandable particles were obtained in the same manner as in Comparative Example 6 except that the above pellets were used instead of the polystyrene particles in Comparative Example 6.

Physical properties of the obtained expandable particles were measured in exactly the same manner as in Example 1. The gel fraction was 0.
%, The maximum expansion bulk ratio is 38 ml / g, the compression strength in the elasticity test is 1.4 kg / cm ² , the restoration rate is 78%, and the falling ball value is 1.
It was 6.5 cm. Therefore, the expanded particles are poor in elasticity and impact resistance and are inferior as a whole, and mechanical mixing of the rubber-like copolymer with polystyrene resin results in
It has been found that the objectives of the invention are not achieved.

In order to make the above results easier to understand, Table 1 shows the examples and Table 2 shows the comparative examples. However, the judgment criteria are as follows. Foaming agent retention: Maximum foaming bulk ratio (ml / g) 60 or more ◎ 40 or more and less than 60 ○ 20 or more and less than 40 △ Less than 20 × Elasticity evaluation: 25% compressive strength (kg / cm ² ) less than 1.2 ◎ 1 1.2 or more and less than 1.5 ○ 1.5 or more and less than 1.8 △ 1.8 or more × compression strain recovery rate (%) 90 or more ◎ 85 or more and less than 90 ○ 80 or more and less than 85 △ less than 80 × impact resistance evaluation Falling ball value (cm) 30 or more ◎ 25 or more and less than 30 ○ 20 or more and less than 25 △ less than 20 ×

[0068]

[Table 1]

[0069]

[Table 2]

Claims (2)

[Claims] 1. Styrene-based resin particles containing a foaming agent, wherein the styrene-based resin comprises 65-85 parts by weight of a particulate styrene-based polymer impregnated with 35-15 parts by weight of a mixed monomer. Particles obtained by copolymerizing in a state of
The mixed monomer contains 10-55% by weight and 90-45% by weight of a styrene-based monomer and a conjugated diene monomer, respectively.
The styrenic resin particles contain a gel content of 0.1-35% by weight, and the foaming agent is a saturated aliphatic resin having a boiling point lower than the softening point of the styrenic resin. Hydrocarbons, alicyclic hydrocarbons or halogenated aliphatic hydrocarbons, 4-12 per 100 parts by weight of resin
Expandable, impact-resistant styrene-based resin particles, characterized in that they are contained in parts by weight. 2. 65-85 parts by weight of a particulate styrene-based polymer is dispersed in an aqueous medium, and the styrene-based monomer and the conjugated diene monomer are each 10-by weight.
In a state where a mixture of 35-15 parts by weight of a mixed monomer mixed at a ratio of 55% and 90-45% and a polymerization initiator was dispersed, and the mixture was impregnated with a particulate styrene-based polymer, Styrene-based resin particles are prepared by copolymerizing mixed monomers, and after the copolymerization process, the particles have a saturated aliphatic hydrocarbon or alicyclic group having a boiling point lower than the softening point of the styrene-based resin. A method for producing expandable, impact-resistant styrene-based resin particles, which comprises containing a hydrocarbon or a halogenated aliphatic hydrocarbon.