JPH08151471A - Expandable particle for producing impact-resistant foam and production thereof - Google Patents

Abstract

PURPOSE: To provide expandable particles which comprise a resin obtained by grafting a styrene monomer onto an olefin resin and from which a foam excellent in impact resistance can be produced. CONSTITUTION: The particles are obtained by incorporating a foaming agent and 0.1-5wt.% ethylbenzene into particles of a polymer obtained by grafting 50-500 pts.wt. styrene monomer onto 100 pts.wt. olefin resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable particles for producing an impact resistant foam and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Expandable particles are particles of synthetic resin containing a foaming agent. When the expandable particles are heated above the softening point of the synthetic resin, they expand to become expanded particles. The expanded particles are usually called pre-expanded particles. When the pre-expanded particles are put into a mold and heated, the pre-expanded particles further expand to fill the inside of the mold, and the particles are fused to each other under the pressure from the mold wall surface, and are adhered to each other according to the mold. Form a foam. Since steam is usually used for heating, a mold is used in which small holes are formed in the wall surface to allow the steam to pass but not the softened resin. According to this molding method, foams of any complicated shape can be produced all at once, and therefore expandable particles are widely used for producing foams of complicated shape having irregularities.

To make expandable particles, polystyrene has long been used as a synthetic resin. The reason is that polystyrene has a property of retaining a foaming agent for a long time, and has a melt viscosity suitable for foaming over a wide temperature range until it is heated and melted. For this reason, expandable particles made of polystyrene have been widely used to make irregularly shaped foams such as shipping boxes. However, polystyrene foam has the drawback of being vulnerable to impact.

Even if an attempt is made to form the expandable particles as described above by using a resin other than polystyrene, such as polyolefin, it is impossible to form the expandable particles that can be put to practical use. This is because even if a blowing agent such as butane is included in the polyolefin, the blowing agent quickly dissipates from the polyolefin, so the time it can be used as expandable particles is short and it cannot be put to practical use. Because.

Attempts have therefore been made to modify polystyrene to improve its impact resistance and thereby to produce expandable particles which allow the production of impact-resistant foams. The attempt is based on the idea of adding polystyrene properties to polystyrene to improve impact resistance.
Specifically, the styrene resin particles are made to contain a styrene monomer, and the styrene monomer is polymerized in the olefin resin particles to make a graft polymer particle. It is a foamable particle. A method for producing such impact-resistant expandable particles is disclosed in, for example, Japanese Patent Publication No.
No. 9-5135. In this case, as the foaming agent, a foaming agent used for producing expandable particles of polystyrene, that is, an aliphatic hydrocarbon having a low boiling point such as butane or pentane, was exclusively used.

[0006] Generally, in order to produce expandable particles, a method of dispersing particles of synthetic resin in water and pressing a foaming agent therein is adopted. As one of its special modes, a foaming agent is press-fitted in the process of polymerizing a monomer to produce polymer particles. As a foaming agent,
Aliphatic hydrocarbons, cycloaliphatic hydrocarbons, halogenated aliphatic hydrocarbons, inert gases and the like having a boiling point lower than the softening point of the synthetic resin were used. In this case, an attempt was made to add an aromatic hydrocarbon such as benzene or toluene to the monomer in order to uniformly disperse the catalyst for polymerizing the monomer in the monomer. This attempt is made, for example, in Japanese Patent Publication
No. 8-58371. Attempts have also been made to add toluene and xylene into the particles in order to stabilize the foaming rate of the impact-resistant expandable particles. This is described in Japanese Patent Publication No. 58-57453.

Although not intended for impact-resistant styrene, the foaming ability of the regenerated expandable polystyrene particles when the foamed product once foamed is recovered and the expandable particles are to be regenerated from this. Attempts to add toluene, styrene monomer, or ethylbenzene to improve the temperature are also known. This is described in JP-A-5-320406.

[0008]

As described above, the impact-resistant expandable particles obtained by graft-polymerizing a styrene monomer onto an olefin resin contain an olefin resin and thus have a foaming agent content. It had the drawback of poor retention.
In addition, the impact-resistant expandable resin particles have a high impact resistance compared to polystyrene foam, but the impact resistance is still insufficient. There is a drawback that the impact resistance is not sufficient for the purpose of opening. Therefore, it was necessary to improve this point. The present invention aims to remedy such drawbacks.

[0009]

The inventor has found that, as an impact resistant resin, 50 to 500 parts by weight of a styrene-based monomer is contained in 100 parts by weight of an olefin-based resin, and the monomer is polymerized. To the graft polymer obtained by
We found that when a small amount of ethylbenzene was added to the particles when making expandable particles with a foaming agent such as butane, the resulting expandable particles retained the expanding agent well. It was At the same time, it has been found that the expandable particles have further improved impact resistance. The present invention has been completed based on such knowledge.

The present invention, in one aspect, provides expandable particles for the production of impact resistant foams. The expandable particles are formed of synthetic resin particles containing, as a foaming agent, an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin. A graft polymer obtained by polymerizing 100 parts by weight of a resin containing 50 to 500 parts by weight of a styrene-based monomer, in which ethylbenzene together with the above-mentioned blowing agent is added to the graft polymer. It is characterized by containing 1 to 5% by weight.

The present invention also provides, in another aspect, a method for producing expandable particles for producing an impact resistant foam. The production method is such that olefin resin particles are dispersed in an aqueous medium in the presence of a dispersant, and a styrene monomer is added thereto to add 50 to 100 parts by weight of olefin resin particles.
500 parts by weight of styrene-based monomer was added, and the styrene-based monomer was polymerized in this state with the aid of a polymerization initiator dissolved in the styrene-based monomer. It is characterized by containing ~ 5 wt% of ethylbenzene and also containing an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the graft polymer.

In the present invention, the styrene-based monomer is polymerized in the state where the styrene-based monomer is contained in the particles of the olefin-based resin in a specific ratio, and ethylbenzene is included in the graft polymer thus produced. That is the greatest feature. The above-mentioned graft polymer has a different softening point depending on the kind and mixing ratio of the olefin resin and the styrene monomer, but the softening point is approximately in the range of 85 to 110 ° C. On the other hand, ethylbenzene is an aromatic hydrocarbon having a boiling point of 136 ° C. Therefore, ethylbenzene cannot act as a blowing agent for mixed resins.

The graft polymer used in the present invention is obtained by adding 50 to 500 parts by weight of a styrene monomer to 100 parts by weight of an olefin resin and polymerizing the styrene monomer in this state. The method for producing such a graft polymer is already known. The graft polymer used in this invention can also be prepared according to this method. One of the methods is to first disperse 100 parts by weight of olefin resin particles in an aqueous medium, add 50 to 500 parts by weight of a styrene monomer, and add the styrene monomer to the olefin resin. The particles are evenly absorbed, and then the styrene monomer is polymerized with the aid of a polymerization initiator that dissolves in the styrene monomer to form a graft polymer.

As the above-mentioned olefin resin, low density polyethylene, medium density polyethylene, high density polyethylene, ethylene / vinyl acetate copolymer and the like can be used.

Further, as the above-mentioned styrene-based monomer,
In addition to styrene, styrene derivatives such as α-methylstyrene, vinyltoluene and chlorostyrene can be used. Moreover, as the styrene-based monomer, not only the styrene-based monomer but also a mixture of the styrene-based monomer and another monomer can be used. As the other monomer, acrylonitrile, butyl acrylate, or the like can be used.

The aqueous medium for polymerizing the styrenic monomer is composed of water and an appropriate amount of dispersant. Examples of the dispersant include partially saponified polyvinyl alcohol, polyacrylic acid salts, polyvinylpyrrolidone, carboxymethylcellulose, methylcellulose, calcium stearate, ethylenebisstearoamide, and other organic compounds, as well as calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium carbonate. Inorganic compounds such as magnesium phosphate, magnesium pyrophosphate, and magnesium oxide, which are fine powders which are hardly soluble in water, can be used. In the present invention, when an inorganic compound is used as the dispersant, it is preferable to use a surfactant such as sodium dodecylbenzenesulfonate together. These dispersants are generally used by adding 0.01 to 5% by weight to water.

In order to make particles of the graft polymer, it is necessary to absorb the styrene monomer in the particles of the olefin resin and polymerize the styrene monomer in this state with the aid of the polymerization initiator. To be done. As the polymerization initiator, one that is soluble in the styrene-based monomer is used, and generally, the polymerization initiator used when suspension-polymerizing the styrene monomer is used. For example, benzoyl peroxide, t-butyl peroxybenzoate, etc. are used. In addition, dicumyl peroxide can be used as a crosslinking agent.

When the particles of the graft polymer are prepared, it is preferable to start the polymerization of the styrene-based monomer after the styrene-based monomer is uniformly absorbed by the olefin-based resin particles. They are heated to accelerate the polymerization,
The degree of heating is preferably 60 to 120 ° C. The temperature is maintained for 2 to 12 hours to accelerate the polymerization of the styrenic monomer. Then, in order to carry out the polymerization more completely, it is preferable to raise the temperature at the end and maintain the temperature at 100 to 150 ° C. for 1 to 10 hours.

Thus, particles of the graft polymer are obtained. The particles are grown using the olefin resin particles used at the beginning as nuclei. Therefore, in order to obtain fine particles of the graft polymer, it is necessary that the olefin resin particles to be initially charged be fine, and in order to obtain mixed resin particles having a uniform particle size. It is necessary that the olefin resin particles to be initially charged have the same size.

In the present invention, in order to make the particles of the graft polymer obtained as described above expandable, a foaming agent is contained therein. As the foaming agent, those which have been used so far for imparting foamability to the styrene resin can be used. The blowing agent is an aliphatic or cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the graft polymer.
For example, the ones belonging to the aliphatic hydrocarbon are:
Propane, isobutane, n-butane, pentane and the like, and those belonging to the cycloaliphatic group are cyclopentane, cyclohexane and the like. These can be used alone or in combination.

In the present invention, the foaming agent is contained in an amount of 2% by weight or more based on the graft polymer. The reason for setting the content to 2% by weight or more is that if the content is less than 2% by weight, the graft polymer will not satisfactorily foam even if the graft polymer containing the same is heated. Generally, as the amount of foaming agent included increases,
Although it tends to foam at a high ratio, if it exceeds a certain level, it will not foam at a higher ratio. However, the upper limit is not set here because it is difficult to clearly define the limit at which foaming does not occur at high magnification.

In the present invention, ethylbenzene is added to improve the properties of the graft polymer. The foaming agent used in the present invention is limited to an aliphatic or cycloaliphatic hydrocarbon, but ethylbenzene is a compound belonging to an aromatic compound and is not a foaming agent. Moreover, since the boiling point of ethylbenzene is about 136 ° C., it is more clear that ethylbenzene does not act as a blowing agent, in contrast to the softening point of the graft polymer being within the range of about 85 to 110 ° C. Becomes

In the present invention, it is necessary that the graft polymer contains 0.1 to 5% by weight of ethylbenzene as described above. The reason is that when the ethylbenzene content is less than 0.1% by weight, the resulting expandable particles do not sufficiently improve the ability to retain the foaming agent, and the foam obtained by expanding the expandable particles is , Because it does not show sufficient impact resistance. On the other hand, when ethylbenzene exceeds 5% by weight in the graft polymer, both the foaming agent retaining ability and the impact resistance are improved, but the heat resistance of the obtained foam is lowered, and the foam becomes more volatile with the passage of time. This is because it causes another defect such as a large shrinkage.

Ethylbenzene includes benzene, toluene,
Although it is likely to be considered to be similar to xylene and styrene, it is greatly different from benzene, toluene, xylene and styrene in relation to the graft polymer used in the present invention. Of these, styrene is a highly unsaturated unsaturated compound, so it is a unique compound and, therefore, if it is excluded, benzene, toluene, and xylene are all listed in the Special and Deleterious Substances Order. , Only ethylbenzene is not regulated. Further, when these are added to the above graft polymer, ethylbenzene alone greatly improves the ability to retain a foaming agent such as butane and the impact resistance of the foam when formed into a foam, but benzene, toluene, Xylene or the like does not significantly improve the retaining ability of the foaming agent and the impact resistance of the foam. This point will later clarify the difference in performance between the example and the comparative example.

The inclusion of ethylbenzene and the blowing agent in the graft polymer is carried out in a state where these are suspended in an aqueous medium. For this, first, 100 parts by weight of an aqueous medium is placed in a container which can be closed, and then 100 parts by weight of the graft polymer particles are added thereto, and well stirred to suspend them in the aqueous medium. Then, the container is closed, and a predetermined amount of ethylbenzene and a foaming agent are press-fitted into this while stirring. Then, while continuing stirring, the container is heated to keep the temperature of the aqueous medium at 40 to 130 ° C., and this state is continued for 1 hour or more. Then, it is cooled and the graft polymer particles are taken out from the container, washed and dried to obtain expandable particles. Since this method uses an aqueous medium, it can be called a wet impregnation method.

On the other hand, by the dry impregnation method, that is, without using an aqueous medium, the graft polymer may be impregnated with a foaming agent and ethylbenzene to obtain expandable particles. For example, in a pressure tight sealed rotatable mixer
Add 0 parts by weight of graft polymer particles and close the mixer. While rotating the mixer, a predetermined amount of ethylbenzene and blowing agent are added. Furthermore, while rotating the mixer, it is heated to a temperature of 40 to 85 ° C., and this rotation and heating are continued for 1 hour or more. Then, the mixer is cooled, and the graft polymer particles are taken out from the mixer to obtain expandable particles.

Since the expandable particles thus obtained contain a foaming agent, when they are brought into contact with water vapor and heated to a temperature above the softening point of the graft polymer, they expand and expand in proportion to the content of the foaming agent. Becomes a foam of. This is the pre-expanded particles. After leaving the pre-expanded particles at room temperature for several days, put them in a molding die with small holes in the wall of the mold cavity, blow steam into the mold to heat the expanded particles, and the particles will swell further. The inside of the mold cavity is filled with the mold cavity, and when it is still expanded, it receives pressure from the wall surface of the mold cavity and fuses with each other, thereby forming a foam-molded article as the mold cavity.

In the foamed molded product thus obtained, the foamed particles are strongly fused to each other, and the surface is in close contact with the wall surface of the mold, so that the size and shape of the mold can be obtained. It is a molded body with. No matter how complicated the shape of the mold is, it is possible to obtain the foam-molded article exactly as the mold. In this way, the foamable particles are a valuable foam molding material like no other in that a foam having a complicated shape can be obtained all at once.

[0029]

According to the present invention, 50 to 50 parts by weight of the olefin resin is used as the resin constituting the expandable particles.
Since the graft polymer obtained by polymerizing in the state that 0 part by weight of styrene-based monomer is contained, the foamed molded product obtained by foaming this is compared to the polystyrene foam. It has excellent impact resistance. Moreover, in the present invention, since the expandable particles contain 0.1 to 5% by weight of ethylbenzene with respect to the graft polymer, the obtained foamed molded product is a foamed molded product obtained by using only the graft polymer. It is more shock resistant than the body. For this reason, the expandable particles are used in fields requiring large impact resistance, such as automobile bumpers,
It is suitable for applications such as transport boxes and tatami cores.

Further, since the expandable particles contain 0.1 to 5% by weight of ethylbenzene with respect to the graft polymer, the ability to retain the foaming agent is large. If the foaming agent has a poor retention capacity, it is made into expandable particles, and the foaming agent dissipates during storage for a while to reduce the foaming ability, so the usable period as expandable particles is short, and therefore the expandable particles are However, a product having a large foaming agent retaining ability withstands long-term storage and can be used when necessary after storage, so that the commercial value is greatly improved.

In addition, ethylbenzene facilitates the inclusion of a blowing agent in the graft polymer and facilitates the expansion of the expandable particles when heated, as found in conventional benzene, toluene and xylene. It also brings various effects. From these points, the effect of the expandable particles according to the present invention is great.

The method for producing expandable particles according to the present invention is advantageous in that expandable particles having the above-mentioned advantages can be obtained safely, efficiently and easily.

Next, the reason why the effect of the present invention is excellent will be specifically described with reference to Examples and Comparative Examples. In the following, simply "parts" means "parts by weight". In addition, in Examples and Comparative Examples, the bead binding, the pot life of expanded beads, and the impact resistance were measured, which were measured by the following methods. (A) Bead binding is a measure of the degree of binding of expandable particles after impregnation. (B) Impact resistance is 40% by dropping a 321 g steel ball onto a foamed molded body having a size of 215 × 40 × 20 mm.
The height at which the steel ball was dropped at the time of fracture was expressed in cm (based on JIS K 6745), which was considered to have fractured when a break having a length of mm or more occurred. (C) Foamed particle life: Immediately after the impregnation, the expandable particles are contacted with steam at 101 ° C. to prepare pre-expanded particles expanded to a bulk ratio of 55 times, and the pre-expanded particles are allowed to stand at a temperature of 20 ° C. for 25 days, and thereafter. The pre-expanded particles were placed in a molding die having a mold cavity of 400 × 300 × 100 mm, and steam at 110 ° C. was blown into the foamed mold to make a foamed body approximately 50 times, and the quality of the molded body was judged.

[0034]

Example 1 In an autoclave having an internal volume of 100 liters, 100 parts of pure water as an aqueous medium, 0.45 part of magnesium pyrophosphate, sodium dodecylbenzenesulfonate of 0.
Add 02 parts of the mixture, and add 3 parts of polyethylene resin particles (Sumitomo Chemical Co., Ltd., trade name EvaTate D-1042) 3
0 part was added, and the mixture was stirred at a rotation speed of 250 rpm and suspended in an aqueous medium.

Separately, 0.3 part of benzoyl peroxide as a polymerization initiator, 0.01 part of t-butylperoxybenzoate, and 70 parts of 0.25 part of dicumyl peroxide as a crosslinking agent of a styrene monomer. To prepare a monomer solution, which was added to the aqueous medium to be absorbed by polyethylene resin particles, and maintained at a temperature of 85 ° C. for 4 hours for polymerization. Thereafter, the temperature was raised to 143 ° C., the temperature was maintained for 3 hours to complete the polymerization, and then the mixture was cooled to obtain graft polymer particles.

Next, 100 parts of water and 0.03 part of sodium dodecylbenzene sulfonate were put into an autoclave having an internal volume of 10 liters to prepare an aqueous medium, and 100 parts of the particles of the above graft polymer were put therein. The mixture was stirred and dispersed, and then 1 part of ethylbenzene as a modifier was added and the mixture was stirred and dispersed. Then, the autoclave was closed and 15 parts of butane as a foaming agent was pressed into this aqueous medium while continuing stirring. Then, the temperature of the aqueous medium was raised to 70 ° C., the temperature was maintained at this temperature for 3 hours with stirring to impregnate the resin particles with the foaming agent, and then the particles were cooled to obtain expandable particles.
At this time, the particles retained their original shape and no lumps were formed.

Thereafter, the expandable particles thus obtained were pre-expanded at a bulk ratio of 55 times. After leaving the pre-expanded particles at room temperature for 7 days, the pre-expanded particles are placed in a molding die having a size of 400 × 300 × 100 mm, and steam having a gauge pressure of 0.5 kg / cm ² is introduced for 1 minute and heated, and then for 20 minutes. After cooling, the foamed molded product was taken out.

The foamed molded product obtained above was placed in a drying chamber at 50 ° C.
When the foam molded article was sun-dried and dried, the impact resistance of the foamed molded article was measured. As a result, the falling ball value was 38.5 mm, and the impact resistance was good.

On the other hand, the pre-expanded particles obtained above were treated at 20 ° C.
After leaving it for 25 days under the temperature of 400 × 300 × 1
A foam molding having a size of 00 mm was produced. Since this foamed molded product had good moldability and also had a good appearance, it was confirmed that the life of the foamed particles was sufficient.

[0040]

Examples 2 to 5 These Examples 2 to 5 were carried out in the same manner as in Example 1 using the graft polymer particles obtained in Example 1, except that the amount of ethylbenzene used was 100%. 1.0, 1.0, 0.1,
In addition to 5.0 parts, the temperature when impregnating the foaming agent in the autoclave is 40, 130, 70, 7 respectively.
The operation was carried out while maintaining the temperature at 0 ° C. to obtain expandable particles.

Using the resulting expandable particles, Example 1
A foamed molded product was prepared by the same procedure as above. The obtained foamed molded product had good bonding of the expandable particles (hereinafter, referred to as bead bonding) and moldability, and had a sufficient expanded particle life. The falling ball values are 27.5 and 29.
It was 5, 23.5, 32.5 cm, and the impact resistance was also excellent.

[0042]

Examples 6-10 In Examples 6-10, the aqueous medium was not used to form the expandable particles, and ethylbenzene and the blowing agent were dried at the temperatures of 70 and 4, respectively, as described above.
Impregnation at 0, 85, 70, and 70 ° C., the content of ethylbenzene was 1.0, 1.0, and
Effervescent particles containing 1.0, 0.1 and 5.0% by weight were obtained.

Using the resulting expandable particles, Example 1
A foamed molded product was prepared by the same procedure as above. The resulting foamed molded article has good bead binding and moldability,
Foam grain life was also sufficient. The falling ball values are 28.5, 27.5, 29.5, 23.5, 31.5c, respectively.
m, and the impact resistance was also excellent.

[0044]

Comparative Examples 1 to 4 Comparative Examples 1 to 4 were wet-impregnated with the graft polymer particles obtained in Example 1 as in Example 1, except that the amount of ethylbenzene used or the impregnation temperature was changed. Was changed and carried out. Specifically, in Comparative Examples 1 to 4, the impregnation temperatures were 70, 70, 135 and 35 ° C., respectively,
Ethylbenzene content of 0.05, 6.0,
1.0, 1.0 wt% expandable particles were obtained.

Using the resulting expandable particles, Example 1
A foamed molded product was produced in exactly the same manner as in. Although the bead binding of all the obtained molded articles was good, the moldability of Comparative Example 2 and Comparative Example 3 was rather poor, and Comparative Example 1 and Comparative Example 4 were extremely poor, and therefore the foamed grain life was low. Was recognized as less than 25 days. Further, the falling ball values showing the scale of impact resistance were 18.5, 26.5, 26.5 and 21.5 cm, respectively.

[0046]

Comparative Examples 5 to 12 In Comparative Examples 5 to 8, the mixed resin particles obtained in Example 1 were used to dry-impregnate ethylbenzene and a foaming agent in the same manner as in Examples 6 to 10. In Comparative Examples 9 and 10, toluene was used instead of ethylbenzene, and in Comparative Examples 11 and 12, xylene and benzene were used instead of ethylbenzene, respectively, and a blowing agent was impregnated in a dry manner. At that time, in Comparative Examples 5 to 12, the impregnation temperatures were 70, 70, 90, 35, 70, 70, 70, 7 respectively.
0 ℃, ethylbenzene content of 0.05, 6.0,
1.0, 1.0, 1.0 (however, toluene instead of ethylbenzene), 1.5 (however, toluene instead of ethylbenzene), 1.0 (however, xylene instead of ethylbenzene), 1.0 (However, benzene instead of ethylbenzene) was included to obtain expandable particles.

The expandable particles thus obtained were treated in exactly the same manner as in Example 1 to prepare a foamed molded product. The bead binding of the obtained foamed molded article was poor in Comparative Example 7, but the others were good, and the moldability was poor in Comparative Examples 6, 9, 11 and 12, and Comparative Examples 5, 7, and 8 were Only Comparative Example 10 was extremely bad and good. Further, the foamed granule life was good only in Comparative Example 7, and was poor in all other cases. Moreover, the falling ball values showing the impact resistance are 16.5, 26.5 and 2, respectively.
It was 8.5, 21.5, 20.5, 24.5, 18.5 and 21.5 cm.

Examples 1 to 10 and Comparative Examples 1 to 12 described above
The results are shown in Table 1 below.

[0049]

[Table 1]

Claims (2)

[Claims] 1. A foamable particle comprising a synthetic resin particle containing, as a foaming agent, an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin, wherein the resin is an olefin. 50 to 500 per 100 parts by weight of the base resin
It is a graft polymer obtained by polymerizing in a state of containing styrene type monomer in an amount of 1 part by weight, in which ethylbenzene together with the above-mentioned foaming agent is 0.1 to 5 relative to the graft polymer.
Expandable particles for producing an impact resistant foam, characterized in that the expandable particles are contained in a weight percentage. 2. An olefin resin particle is dispersed in an aqueous medium in the presence of a dispersant, and a styrene monomer is added to the olefin resin particle to add 50 to 500 to 100 parts by weight of the olefin resin particle.
By adding styrene-based monomer in an amount of 1 part by weight, the styrene-based monomer is polymerized in this state with the aid of a polymerization initiator that dissolves in the styrene-based monomer. Impact-resistant foam, characterized in that it contains ~ 5% by weight of ethylbenzene and also contains an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the graft polymer. For producing expandable particles for automobiles.