JP2005097555A - Olefin modified polystyrene-based resin pre-expansion particle, method for producing the same and its foamed molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an olefin modified polystyrene-based pre-expansion particle which can be used to produce a foamed molding having an excellent rigidity, chemical resistance and impact resistance. <P>SOLUTION: The olefin modified polystyrene-based pre-expansion particle comprises a polystyrene-based pre-expansion particle modified by polyolefin-based resin, and a styrene-based monomer is used for forming the polystyrene-based resin in a range of 100-1,000 pts.wt. to a 100 pts.wt. polyolefin-based resin, and the particle has a bulk density of 0.012-0.20 g/cm<SP>3</SP>and an infrared absorption spectrum obtained by infrared spectroscopic analysis of a surface of the particle using ATR-method shows that a ratio of absorbance at 698 cm<SP>-1</SP>and 2,850 cm<SP>-1</SP>(D<SB>698</SB>/D<SB>2850</SB>) is within the range of 0.1-2.5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to olefin-modified polystyrene resin pre-expanded particles, a method for producing the same, and a foam-molded article. According to the olefin-modified polystyrene resin pre-expanded particles of the present invention, it is possible to obtain a foamed molded article having excellent rigidity, chemical resistance and impact resistance.

  Conventionally, polystyrene resin foam molded products obtained by filling polystyrene resin pre-expanded particles in a mold and heating and foaming are excellent in rigidity, heat insulation, light weight, water resistance and foam moldability. It has been known. Therefore, this foaming molding is widely used as a buffer material or a heat insulating material for building materials. However, this foam molded article has a problem that it is inferior in chemical resistance and impact resistance.

  On the other hand, it is known that a foam molded article made of a polyolefin resin such as a polyethylene resin or a polypropylene resin is excellent in chemical resistance and impact resistance. Therefore, this foaming molding is used for automobile-related parts. However, since the polyolefin-based resin is inferior in foaming gas retention, it is necessary to precisely control the foam molding conditions, resulting in a problem that the manufacturing cost is high. In addition, there is a problem that the rigidity is inferior to that of the polystyrene-based resin foam molding.

  In order to solve the problems of the above-mentioned polystyrene resin and polyolefin resin, foam molding in which a polystyrene resin having good rigidity and foam moldability and a polyolefin resin having good chemical resistance and impact resistance are combined. The body has been reported.

  The properties of the composite foamed molded product are greatly influenced by the ratio of the polystyrene resin and the polyolefin resin. That is, the higher the ratio of the polyolefin-based resin, the better the chemical resistance and impact resistance of the foam molded article, but the rigidity and foam moldability are lowered.

  In particular, when foamed molded products are used for automobile-related parts, there is a possibility of contact with chemicals such as gasoline, kerosene, brake oil, vinyl chloride plasticizer, etc. And impact resistance are required. As a method for satisfying this requirement, a method for improving the chemical resistance and impact resistance of a foamed molded article by making the polyolefin resin component in the foamed molded article 50% by weight or more is known. However, in this method, since the amount of the polystyrene-based resin component is relatively reduced, the rigidity and foam moldability of the foam-molded product are greatly reduced. As a result, this foamed molded product could not be widely used for automobile-related parts.

  Therefore, for the purpose of complementing the disadvantages of polystyrene resin and polyolefin resin and making both properties compatible, secondary foaming is possible in which the surface layer is made of expanded polyolefin resin and the core is made of expanded polystyrene resin. Expanded resin particles have been proposed (see Patent Document 1).

  According to this foamed resin particle, it is described that the foaming agent is held in the foamed polystyrene-based resin in the core, and therefore, the moldability is excellent. Furthermore, it is described that the foam molded body obtained from the foamed resin particles is excellent in rigidity, flexibility and low temperature characteristics.

  However, when the present inventors reexamined the above publication, when the resin particles obtained by coating the polystyrene resin particles with the polyolefin resin are impregnated with a foaming agent and pre-foamed, only the polystyrene resin inside is greatly expanded. On the other hand, the polyolefin resin foamed slightly or did not foam. As a result, the polyolefin-based resin layer and the polystyrene-based resin layer were peeled off, and the intended foamed molded product could not be obtained.

In addition to the above method, a method has been proposed in which polyethylene resin particles are impregnated with a styrene monomer in an aqueous medium and polymerized to obtain expanded resin particles obtained by modifying the polystyrene resin with a polyolefin resin ( For example, see Patent Document 2).
However, even with the above method, polystyrene-based resin pre-expanded particles that can provide a foamed molded article that simultaneously achieves high chemical resistance and impact resistance, rigidity, and foam moldability cannot be obtained.

JP 54-119563 A Japanese Patent Publication No.59-3487

Thus, according to the present invention, polystyrene-based resin pre-expanded particles modified with a polyolefin-based resin, and the styrene-based monomer forming the polystyrene-based resin is 100 to 1000 parts by weight with respect to 100 parts by weight of the polyolefin-based resin. The particle has a bulk density of 0.012 to 0.20 g / cm ³ and is obtained from an infrared absorption spectrum of the particle surface measured by ATR infrared spectroscopy, and 698 cm ⁻¹ and 2850 cm. absorbance ratio at ^-1 (D ₆₉₈ / D ₂₈₅₀₎ is an olefin-modified polystyrene-based resin pre-expanded particles is in the range of 0.1 to 2.5 is provided.

Furthermore, according to the present invention, a styrene monomer (100 to 1000 parts by weight with respect to 100 parts by weight of the polyolefin resin particles used) is added to the polyolefin resin particles in an aqueous medium in which the polyolefin resin particles are dispersed. A step (a) of obtaining olefin-modified polystyrene resin particles by polymerizing in the presence of a polymerization initiator while impregnated therein, a step (b) of impregnating the resin particles with a foaming agent, A step (c) of pre-expanding to obtain olefin-modified polystyrene resin pre-expanded particles,
In the step (a), the aqueous medium is stirred with a required power of stirring of 0.06 to 0.8 kw / m ³ , and the impregnation and polymerization of the styrenic monomer has a styrenic monomer content in the polyolefin resin particles of 35. Provided is a method for producing olefin-modified polystyrene-based resin pre-expanded particles, which is performed under the condition of not more than% by weight.

  First, the term “olefin-modified polyolefin resin” means a resin obtained by modifying a polystyrene resin with a polyolefin resin. Hereinafter, the olefin-modified polystyrene resin pre-expanded particles are simply referred to as pre-expanded particles.

The polyolefin resin is not particularly limited, and a resin obtained by a known polymerization method can be used. Moreover, it is preferable to use resin which does not contain a benzene ring in a structure for polyolefin resin. Furthermore, the polyolefin resin may be cross-linked. For example, polyethylene resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers And polypropylene resins such as propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. Of these, branched low-density polyethylene, linear low-density polyethylene, and ethylene-vinyl acetate copolymer are preferable. These low-density polyethylene preferably has a density of 0.91~0.94g / cm ^3, and more preferably has a density of 0.91~0.93g / cm ^3.

  Examples of the polystyrene resin include resins derived from styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, and t-butylstyrene. Furthermore, the polystyrene resin may be a copolymer of a styrene monomer and another monomer copolymerizable with the styrene monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene, and (meth) acrylic acid alkyl esters that do not contain a benzene ring in the structure such as butyl (meth) acrylate. You may use these other monomers in the range which does not exceed 5 weight% substantially with respect to a polystyrene-type resin.

  The z-average molecular weight of the polystyrene-based resin as measured by GPC is preferably 350,000 to 1,100,000, and more preferably 450,000 to 950,000. If the z-average molecular weight is lower than 350,000, the strength of the foamed molded product obtained by foam-molding the pre-foamed particles may decrease, which is not preferable. On the other hand, if it is higher than 1,100,000, the secondary foamability of the pre-foamed particles is lowered, the fusion property between the pre-foamed particles is lowered, and the strength of the foamed molded product may be lowered.

  The polystyrene resin is formed from a styrene monomer in the range of 100 to 1000 parts by weight with respect to 100 parts by weight of the polyolefin resin. The compounding quantity of a preferable styrene-type monomer is 120-800 weight part, and 130-700 weight part is more preferable.

  When the blending amount is more than 1000 parts by weight, the chemical resistance and impact resistance of the foamed molded article obtained by secondary foaming of the pre-foamed particles are unfavorable. On the other hand, when the blending amount is less than 100 parts by weight, the rigidity of the foamed molded product obtained by secondary foaming of the pre-foamed particles is unfavorable.

The pre-expanded particles have a bulk density of 0.012 to 0.20 g / cm ³ . A preferred bulk density is 0.014 to 0.15 g / cm ³ .
If the bulk density is less than 0.012 g / cm ³ , the closed cell ratio of the expanded particles is decreased, and the strength of the expanded molded product obtained by foaming the pre-expanded particles is not preferable. On the other hand, if it is larger than 0.20 g / cm ³ , the weight of the foamed molded product obtained by foaming the pre-foamed particles increases, which is not preferable. In addition, the measuring method of a bulk density is demonstrated in the column of an Example.

Additionally, pre-expanded particles of the present invention, the surface, from the infrared absorption spectrum obtained by measuring by ATR method infrared spectroscopy, the range of 698cm ^-1 and 2850 cm ^-1 of 0.1 to 2.5 It has an absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ). A preferable absorbance ratio is 0.2 to 2.0, and 0.4 to 2.0 is more preferable. The particle surface includes a region from the surface to a depth of several μm.

  When the absorbance ratio is higher than 2.5, the ratio of the polyolefin resin on the surface of the pre-foamed particles is lowered. As a result, the chemical resistance and impact resistance of the foamed molded product obtained by foaming the pre-expanded particles are unfavorable. When the absorbance ratio is lower than 0.1, the foaming agent dissipates significantly from the surface of the pre-foamed particles, resulting in poor fusion between the particles during molding in the mold, resulting in a decrease in impact resistance. Or the finished appearance of the foamed molded product tends to deteriorate due to shrinkage or the like. In addition, when the pre-expanded particles are produced, the time required for impregnation and polymerization of the styrene monomer into the polyolefin resin particles is increased, and the production efficiency is lowered, which is not preferable.

  Here, the ATR method infrared spectroscopic analysis in the present invention is an analysis method in which an infrared absorption spectrum is measured by a single reflection type ATR method using total reflection absorption (Attenuated Total Reflectance). This analysis method is a method in which an ATR prism having a high refractive index is brought into close contact with a sample, infrared light is irradiated to the sample through the ATR prism, and light emitted from the ATR prism is spectrally analyzed.

  ATR infrared spectroscopic analysis includes organic materials such as polymer materials because of the simplicity of being able to measure the spectrum simply by bringing the sample and the ATR prism into close contact with each other, and the ability to perform surface analysis up to a depth of several μm. It is widely used for surface analysis of various substances.

The absorbance D _{698 at 698} cm ⁻¹ obtained from the infrared absorption spectrum refers to the height of a peak appearing in the vicinity of 698 cm ⁻¹ derived from the out-of-plane deformation vibration of the benzene ring mainly contained in the polystyrene resin. .

Further, the absorbance D _{2850 at 2850} cm ⁻¹ obtained from the infrared absorption spectrum is a peak appearing in the vicinity of 2850 cm ⁻¹ derived from the C—H stretching vibration of the methylene group contained in both the polyolefin resin and the polystyrene resin. The height of

  It is possible to determine the composition ratio of the polystyrene resin and the polyolefin resin from the absorbance ratio. That is, a plurality of types of standard samples obtained by uniformly mixing a polystyrene resin and a polyolefin resin at a predetermined composition ratio are prepared as described below. Each standard sample is subjected to particle surface analysis by ATR infrared spectroscopy to obtain an infrared absorption spectrum. The absorbance ratio is calculated from each of the measured infrared absorption spectra.

  A calibration curve is drawn by taking the composition ratio (weight ratio of polystyrene resin in the standard sample) on the horizontal axis and the absorbance ratio on the vertical axis. Based on this calibration curve, the approximate composition ratio of the polystyrene resin and the polyolefin resin can be determined from the absorbance ratio of the pre-expanded particles of the present invention.

  For example, when the polyolefin resin is an ethylene-vinyl acetate copolymer (trade name “LV-121” manufactured by Nippon Polychem) and the polystyrene resin is polystyrene (trade name “MS142” manufactured by Sekisui Chemical Co., Ltd.), FIG. By using the calibration curve shown, the approximate composition ratio can be known. For example, when the absorbance ratio is 1.0, the polyolefin resin is about 76 to 82% by weight, the polystyrene resin is about 24 to 18% by weight, and when the absorbance ratio is 2.5, the polyolefin resin is about It can be calculated that 51 to 57% by weight and polystyrene resin is about 49 to 43% by weight. The calibration curve is created by the following method.

  The standard sample is obtained by the following method. First, a total of 2 g of the polystyrene resin and the polyolefin resin are precisely weighed so that the composition ratio (polystyrene resin / polyolefin resin) becomes the following ratio. This is heated and kneaded in a small injection molding machine under the following conditions and molded into a cylindrical shape having a diameter of 25 mm and a height of 2 mm to obtain a standard sample. In addition, as a small-sized injection molding machine, what is sold with the brand name "CS-183" from CSI can be used, for example.

Injection molding conditions: heating temperature 200 to 250 ° C., kneading time 10 minutes composition ratio (polystyrene resin / polyolefin resin; weight ratio):
0.5 / 9.5, 1/9, 2/8, 3/7, 4/6, 5/5, 6/4, 7/3, 9/1
The calibration curve in FIG. 9 is obtained by measuring the absorbance ratio of the standard sample having the above ratio and graphing the relationship between the polystyrene amount and the absorbance ratio.

  The pre-expanded particles of the present invention have an absorbance ratio of 0.1 to 2.5. Therefore, the ratio of the polyolefin resin in the vicinity of the surface of the pre-expanded particles is about 50% by weight or more, although it varies depending on the types of the polyolefin resin and the polystyrene resin. In the entire pre-expanded particles, the amount of polyolefin resin is less than or equal to the amount of polystyrene resin, indicating that the polyolefin resin is more abundant than polystyrene resin on the surface of the pre-expanded particles. Understand. In addition, the weight% of polyolefin resin with respect to the total amount of polyolefin resin and polystyrene resin in the whole pre-expanded particle is 9 to 50 wt%. Further, since the absorbance ratio is 0.1 or more, polystyrene resin is present on the surface of the pre-foamed particles, and the polyolefin resin does not reach 100% by weight.

  As described above, pre-expanded particles having a large blending amount of polystyrene-based resin and a large blending amount of polyolefin-based resin on the surface have a special structure that cannot be obtained by a conventional method.

  The form of the pre-expanded particles is not particularly limited as long as it does not affect the subsequent secondary expansion. For example, a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, a prismatic shape and the like can be mentioned. Of these, true spheres and elliptical spheres that can be easily filled into the mold are preferred.

  The average weight of each pre-expanded particle is preferably 0.5 to 5.0 mg, more preferably 0.5 to 3.0 mg. If it is lighter than 0.5 mg, it may be difficult to achieve high foaming, which is not preferable. On the other hand, if it is heavier than 5.0 mg, the pre-expanded particles become too large, the filling property into the mold is lowered, and the appearance of the obtained foamed molded product may be lowered, which is not preferable. In addition, the weight of each pre-expanded particle means the average weight of 200 pre-expanded particles arbitrarily selected.

  The pre-expanded particles may contain an additive. Additives include foaming nucleating agents such as talc, calcium silicate, ethylene bis-stearic acid amide, methacrylic acid ester copolymers, fillers such as synthetic or naturally produced silicon dioxide, hexabromocyclododecane, triallyl Examples include flame retardants such as isocyanurate hexabromide, diisobutyl adipate, liquid paraffin, glycerin diacetomonolaurate, plasticizers such as coconut oil, colorants such as carbon black and graphite, ultraviolet absorbers, antioxidants, and the like. .

Next, the manufacturing method of the pre-expanded particle | grains of this invention is demonstrated.
First, polymerization is performed while impregnating polyolefin resin particles with styrene monomer (100 to 1000 parts by weight with respect to 100 parts by weight of polyolefin resin particles used) in an aqueous medium in which polyolefin resin particles are dispersed. Polymerization is performed in the presence of an initiator to obtain olefin-modified polystyrene resin particles (hereinafter also referred to as modified resin particles) (step (a)).
The styrenic monomer can be continuously or intermittently added to the aqueous medium in order to impregnate the polyolefin resin particles. The styrenic monomer is preferably added gradually to the aqueous medium.
Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol).

Further, the average weight of each polyolefin-based resin particle is preferably 0.10 to 1.5 mg in view of ease of filling into the mold at the time of molding the pre-expanded particles to be produced. The average weight of polyolefin resin particles refers to the average weight of 100 arbitrarily selected polyolefin resin particles. The form of the polyolefin resin particles is not particularly limited. For example, a true spherical shape, an elliptical spherical shape (egg shape), a cylindrical shape, a prismatic shape, and the like can be given.
When the blending amount of the styrene monomer is more than 1000 parts by weight, it is not preferable because particles of the polystyrene resin alone are generated without impregnating the polyolefin resin particles. In addition, the chemical resistance and impact resistance of the foamed molded product obtained by secondary foaming of the pre-expanded particles are not preferable. On the other hand, when the blending amount of the styrene monomer is less than 100 parts by weight, the time required for the impregnation and polymerization of the polyolefin resin particles is shortened, but the ability to retain the foaming agent of the resulting olefin-modified polystyrene resin particles is It is not preferable because it decreases and cannot be highly foamed. In addition, the rigidity of the foamed molded product obtained by secondary foaming of the pre-expanded particles is not preferable.

  In addition, it is preferable to add a dispersant to the aqueous medium. Examples of such a dispersant include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose, magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, and magnesium phosphate. And inorganic dispersants such as magnesium carbonate and magnesium oxide. Of these, inorganic dispersants are preferred.

  When an inorganic dispersant is used, it is preferable to use a surfactant in combination. Examples of such surfactants include dodecyl benzene sulfonic acid soda and α-olefin sulfonic acid soda.

Here, the impregnation and polymerization steps of the styrenic monomer may be performed separately as long as the impregnation is performed first, but it is preferable to proceed simultaneously.
When proceeding simultaneously, impregnation and polymerization are carried out by adjusting the addition rate of the styrene monomer or adjusting the polymerization temperature so that the content of the styrene monomer in the polyolefin resin particles is maintained at 0 to 35% by weight. It is preferable to do. When the addition, impregnation and polymerization steps are carried out continuously, the content is preferably 0.5 to 35% by weight, more preferably 0.5 to 30% by weight.

  In addition, the polyolefin resin particle in the case of calculating said content means the particle | grains comprised from the polyolefin resin, the styrene-type monomer impregnated, and the polystyrene-type resin already impregnated and impregnated.

  When the content of the styrenic monomer is more than 35% by weight, pre-expanded particles having an absorbance ratio in a predetermined range may not be obtained even if the required power for stirring (Pv) is adjusted within the range described later. Absent.

In the present invention, an aqueous medium containing polyolefin resin particles and a styrene monomer is stirred under predetermined conditions. Specifically, the power required for stirring (Pv) required to stir the aqueous medium 1m ³ including the polyolefin resin particles, the styrene monomer, and, if necessary, other dispersion and dissolved matter is 0.06. It is the stirring conditions adjusted so that it might become -0.8kw / m < ³ >. The power required for stirring is preferably 0.08 to 0.7 kw / m ³ . This required power for stirring corresponds to the net energy per unit volume received by the contents in the reaction vessel.

Conventionally, when a polyolefin resin particle is impregnated with a styrene monomer in an aqueous medium and polymerized, the stirring of the aqueous medium is not noted, and it is performed under conditions that allow the aqueous medium to be sufficiently stirred. The conventional stirring power is estimated to be about 1 to 2 kw / m ³ . On the other hand, in the production method of the present invention, by lowering the power required for stirring than before, the polyolefin resin is localized in the vicinity of the surface of the modified resin particles with the polymerization of the styrene monomer, and in the vicinity of the surface. It has been surprisingly found that modified resin particles rich in polyolefin-based resin can be obtained.

  By adjusting the power required for stirring to a predetermined range and adjusting the content of the styrene monomer in the polyolefin resin particles to a predetermined amount, the styrene monomer is sufficiently impregnated near the center of the polyolefin resin particles. It becomes possible to make it. As a result, it is possible to obtain a state in which a large amount of styrene monomer is present at the center of the polyolefin resin particles, and to gradually reduce the amount of styrene monomer from the center of the polyolefin resin particles toward the surface.

  Furthermore, since the styrene monomer is sequentially absorbed into the polystyrene resin produced in the polyolefin resin particles and polymerized, the polyolefin resin particles come closer to the center as the polystyrene resin is produced. The larger the diameter, the larger the polystyrene resin.

  As a result, the pre-expanded particles obtained in the manner described below contain a high percentage of polystyrene resin at the center, and the polyolefin resin is dispersed in layers in the polystyrene resin. On the other hand, in the vicinity of the surface, the polyolefin resin is contained in a high ratio, and the polystyrene resin is in a state of being finely dispersed in the polyolefin resin while gradually decreasing and decreasing the ratio as it approaches the particle surface. The particle surface is in a state where there is almost no polystyrene resin and polyolefin resin is present at a higher ratio.

If the power required for stirring is lower than 0.06 kw / m ^3, the dispersion of the styrene monomer in the aqueous medium becomes insufficient, and it is difficult to sufficiently impregnate the styrene monomer in the center of the polyolefin resin particles. is there. Therefore, the polymerization of the styrene monomer proceeds in the vicinity of the surface of the polyolefin resin particles, and the composition ratio of the polyolefin resin in the vicinity of the surface of the resulting modified resin particles decreases. As a result, the chemical resistance and impact resistance of the foamed molded article obtained by foaming the modified resin particles are lowered.

On the other hand, when the power required for stirring is higher than 0.8 kw / m ³ , the mixing of the styrene monomer and the polyolefin resin in the modified resin particles proceeds, and the modified resin containing the polyolefin resin rich in the vicinity of the surface Particles are difficult to obtain. In addition, the polyolefin resin particles impregnated with the styrene monomer and softened may be deformed into a flat shape. In that case, it becomes difficult to obtain pre-expanded particles having sufficient secondary foaming power.

Here, the power required for stirring refers to that measured in the following manner.
That is, an aqueous medium containing polyolefin resin particles, styrene monomers, and other dispersions and dissolved substances as necessary is supplied into a polymerization vessel of a polymerization apparatus, and a stirring blade is rotated at a predetermined rotational speed to form an aqueous medium. Stir the medium. At this time, the rotational driving load necessary to rotate the stirring blade is measured as a current value A ₁ (ampere). A value obtained by multiplying the current value A ₁ by an effective voltage (volts) is defined as P ₁ (watts).

Then, the stirring blade of the polymerization apparatus is rotated at the same rotation speed as described above in an empty state of the polymerization vessel, and the rotational driving load required to rotate the stirring blade is measured as a current value A ₂ (ampere). The value obtained by multiplying the current value A ₂ by the effective voltage (volt) is P ₂ (watts), and the required power for stirring can be calculated by the following equation 2. V (m ³ ) is the volume of the entire aqueous medium including the polyolefin resin particles, the styrene monomer, and other dispersions and dissolved substances as required.
Power required for stirring (Pv) = (P ₁ −P ₂ ) / V Equation 2

The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for the polymerization of styrene monomers.
The stirring blade is not particularly limited as long as the power required for stirring can be set within a predetermined range. Specifically, paddle blades such as V-type paddle blades, inclined paddle blades, flat paddle blades, fiddler blades, pull margin blades, turbine blades such as turbine blades and fan turbine blades, propeller blades such as marine propeller blades, etc. Can be mentioned. Of these stirring blades, paddle blades are preferable, and V-type paddle blades, inclined paddle blades, flat paddle blades, Ferdler blades, and pull margin blades are more preferable. The stirring blade may be a single-stage blade or a multi-stage blade.
Also, the size of the stirring blade is not particularly limited as long as the required power for stirring can be set within a predetermined range.
Furthermore, you may provide a baffle plate (baffle) in the superposition | polymerization container.

  Moreover, as a polymerization initiator, the polymerization initiator currently used widely for superposition | polymerization of a styrene-type monomer can be used. For example, benzoyl peroxide, lauroyl peroxide, t-amyl peroxy octoate, t-butyl peroxybenzoate, t-amyl peroxybenzoate, t-butyl peroxybivalate, t-butyl peroxyisopropyl carbonate, t- Butyl peroxyacetate, t-butylperoxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t-butylperoxybutane, dicumyl peroxide And an azo compound such as azobisisobutyronitrile and azobisdimethylvaleronitrile. In addition, a polymerization initiator may be used independently or may be used together.

  The method for adding the polymerization initiator to the aqueous medium is not particularly limited, but is preferably performed according to the following procedure. That is, the polymerization initiator may be added in an amount of 0.02 to 2.0% by weight of the total amount of polyolefin resin particles and styrene monomer used until the amount of styrene monomer used reaches 90% by weight of the total amount used. preferable. The polymerization initiator is more preferably added until it reaches 85% by weight, particularly 80% by weight of the total amount used. Moreover, the more preferable addition amount of a polymerization initiator is 0.10-1.50 weight% with respect to the total amount used.

  According to the said addition point, the polymerization rate of the styrene-type monomer in polyolefin-type resin particle can be improved, and the composition ratio of polyolefin-type resin in the surface vicinity part of the modified resin particle obtained can be increased. As a result, it is possible to improve the strength of the foam molded body obtained by foam molding the modified resin particles.

  Furthermore, the addition of the polymerization initiator is preferably performed up to the predetermined amount via a styrene monomer containing the polymerization initiator. As the remaining styrenic monomer, a monomer containing no polymerization initiator can be used.

The reason why the styrene monomer containing the polymerization initiator is used is considered as follows.
That is, by allowing the styrene monomer to contain the polymerization initiator and absorbing it in the polyolefin resin particles, the polymerization initiator and the styrene monomer can be effectively impregnated in the center of the polyolefin resin particles. Therefore, from the early stage of the styrene monomer polymerization process, a polymerization initiator in an amount necessary for the polymerization of the styrene monomer can be preferentially supplied to the central part of the polyolefin resin particles. As a result, the styrene monomer can be preferentially polymerized at the center of the polyolefin resin particles.

  Next, when a styrene monomer that does not contain a polymerization initiator is added to the aqueous medium, the polyolefin resin is sequentially absorbed by the polystyrene resin formed at the center of the polyolefin resin particles. Polymerization is smoothly performed under a polymerization initiator that is abundant in the center of the particle. Therefore, the resulting modified resin particles are in a state of being rich in polystyrene resin in the central portion from near the surface.

  The amount of the styrene monomer not containing the polymerization initiator is preferably 10 to 60% by weight, more preferably 15 to 60% by weight, and particularly preferably 20 to 55% by weight of the total amount of the styrene monomer used. If the addition amount is less than 10% by weight, the ratio of the polystyrene resin in the vicinity of the surface of the modified resin particles may increase, which is not preferable. In this case, the impact resistance and chemical resistance of the foamed molded product obtained by secondary foaming of pre-expanded particles obtained from the modified resin particles may decrease. On the other hand, when the amount is more than 60% by weight, the polymerization rate of the styrene monomer is decreased, and a large amount of the styrene monomer may remain in the modified resin particles.

Various methods are mentioned as a method of adding the styrene monomer containing a polymerization initiator to an aqueous medium. For example,
(1) A method in which a polymerization initiator is dissolved and contained in a styrene monomer in a container different from the polymerization container, and the styrene monomer is supplied to an agitated aqueous medium in the polymerization container.
(2) A polymerization initiator is dissolved in a part of a styrene monomer, a solvent or a plasticizer to prepare a solution. A method of simultaneously supplying this solution and a predetermined amount of a styrenic monomer to a stirred aqueous medium in a polymerization vessel;
(3) A dispersion in which a polymerization initiator is dispersed in an aqueous medium is prepared. Examples thereof include a method of simultaneously supplying the dispersion and the styrene monomer to the stirred aqueous medium in the polymerization vessel.

  Further, the temperature of the aqueous medium when polymerizing the styrene monomer in the polyolefin resin particles is not particularly limited, but is preferably in the range of −30 to + 10 ° C. of the melting point of the polyolefin resin. More specifically, 70-140 degreeC is preferable and 80-130 degreeC is more preferable. Furthermore, the temperature of the aqueous medium may be a constant temperature from the start to the end of the polymerization of the styrenic monomer, or may be increased stepwise. When raising the temperature of the aqueous medium, it is preferable to raise the temperature stepwise at a rate of temperature rise of 0.1 to 2 ° C./min.

  Furthermore, when using particles comprising a crosslinked polyolefin resin, the crosslinking may be performed in advance before impregnating the styrene monomer, or by impregnating and polymerizing the styrene monomer in the polyolefin resin particles. It may be performed while the polyolefin resin particles are impregnated with a styrene monomer and polymerized.

  Examples of the crosslinking agent used for crosslinking the polyolefin resin include 2,2-di-t-butylperoxybutane, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy. An organic peroxide such as hexane may be mentioned. In addition, a crosslinking agent may be individual or may use 2 or more types together. Moreover, the usage-amount of a crosslinking agent has preferable 0.05-1.0 weight part normally with respect to 100 weight part of polyolefin resin particles.

  As a method for adding a crosslinking agent, for example, a method in which a crosslinking agent is directly added to a polyolefin resin, a method in which a crosslinking agent is dissolved in a solvent, a plasticizer, or a styrene monomer, and a crosslinking agent is dispersed in water. For example, a method of adding after adding them. Among these, the method of adding after dissolving a crosslinking agent in a styrene-type monomer is preferable.

  The modified resin particles are impregnated with a foaming agent (step (b)). The method of impregnating the modified resin particles with the foaming agent can be appropriately changed according to the type of the foaming agent. For example, a method in which a foaming agent is pressed into an aqueous medium in which the modified resin particles are dispersed to impregnate the modified resin particles with the foaming agent, the modified resin particles are supplied to a rotary mixer, Examples thereof include a method in which a foaming agent is injected and the modified resin particles are impregnated with the foaming agent. In addition, the temperature which makes a modified resin particle impregnate a foaming agent is 50-140 degreeC normally.

  Here, examples of the foaming agent include volatile foaming agents such as propane, butane, pentane, and dimethyl ether. A foaming agent may be used independently or may be used together. The addition amount of the foaming agent is preferably 5 to 25 parts by weight with respect to 100 parts by weight of the modified resin particles.

  Furthermore, you may use a foaming adjuvant with a foaming agent. Examples of such foaming aids include solvents such as toluene, xylene, ethylbenzene, cyclohexane, and D-limonene, and plasticizers (high boiling point solvents) such as diisobutyl adipate, diacetylated monolaurate, and coconut oil. . In addition, as addition amount of a foaming adjuvant, 0.1-2.5 weight part is preferable with respect to 100 weight part of modified resin particles.

Further, a surface treatment agent such as a binding inhibitor, a fusion accelerator, an antistatic agent, or a spreading agent may be added to the modified resin particles.
The anti-bonding agent plays a role of preventing coalescence of the pre-expanded particles when the modified resin particles are pre-expanded. Here, coalescence means that a plurality of pre-expanded particles are united and integrated. Specific examples include talc, calcium carbonate, zinc stearate, aluminum hydroxide, ethylene bis stearamide, tricalcium phosphate, dimethylpolysiloxane and the like.

  The fusion accelerator plays a role of promoting fusion between the pre-foamed particles when the pre-foamed particles are subjected to secondary foam molding. Specific examples include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, sorbitan stearate, and the like.

Examples of the antistatic agent include polyoxyethylene alkylphenol ether and stearic acid monoglyceride.
Examples of the spreading agent include polybutene, polyethylene glycol, and silicone oil.

  The total amount of the surface treatment agent is preferably 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the modified resin particles.

  If the modified resin particles impregnated with the volatile foaming agent are heated using a heating medium such as water vapor and pre-foamed to a predetermined bulk density, pre-foamed particles can be obtained (step (c)).

  Furthermore, the pre-expanded particles are filled in a mold of a molding machine, heated and subjected to secondary foaming, and the pre-expanded particles are fused and integrated with each other to obtain a foam-molded article having a desired shape. As said molding machine, the molding machine used when manufacturing a foaming molding from a polystyrene-type resin pre-expanded particle can be used.

  As described above, the pre-expanded particles contain a high percentage of polystyrene resin at the center and a high percentage of polyolefin resin near the surface.

  Accordingly, when the pre-expanded particles are subjected to secondary foaming, the pre-expanded particles can be strongly heat-bonded and integrated with each other by the polyolefin resin contained in a large amount on the surface thereof. In addition, the excellent foam moldability resulting from the polystyrene-based resin contained in a large amount at the center of the pre-expanded particles can be exhibited.

  The entire surface of the obtained foamed molded article contains a high proportion of polyolefin resin derived from the polyolefin resin in the vicinity of the surface of the pre-foamed particles. In other words, the foam-molded article has excellent chemical resistance and impact resistance because it has a surface containing a high percentage of polyolefin resin.

  Moreover, the inside of each expanded particle constituting the expanded molded body is formed by foaming the central part of the pre-expanded particle and contains a high proportion of polystyrene resin. Is also provided.

  The foamed molded body obtained as described above is used for various purposes such as vehicle bumper core materials, vehicle cushioning materials such as door interior cushioning materials, electronic parts, various industrial materials, food containers and the like. Can do. In particular, it can be suitably used as a vehicle cushioning material.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the following examples, the bulk density, absorbance ratio, maximum content of styrene monomer, z average molecular weight by GPC measurement of polystyrene resin, fusion rate, compressive strength, impact resistance, chemical resistance are measured. Below.
(Maximum content of styrene monomer)
A portion of the polyolefin resin particles impregnated with styrene monomer and polymerizing is taken out from the polymerization vessel and separated from the aqueous medium, and then the moisture on the surface of the polyolefin resin particles is removed with gauze to obtain a measurement sample. .

  Then, 0.08 g was precisely weighed from the measurement sample and immersed in 40 ml of toluene for 24 hours to extract the styrene monomer. Titrate the sample by adding 10 ml of Wis reagent, 30 ml of 5 wt% potassium iodide aqueous solution and about 30 ml of 1 wt% starch aqueous solution to the styrene monomer extracted solution, and titrating with N / 40 sodium thiosulfate solution. A number (milliliter). The Wies reagent was prepared by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.

  Further, the measurement sample was titrated in the same manner as described above without immersing the sample in toluene to obtain a blank titer (milliliter). And content of the styrene-type monomer in polyolefin-type resin particle was computed based on the following formula.

  Styrenic monomer content (% by weight) = 0.1322 × (blank drop constant−sample drop constant) / weight of measurement sample (g)

  The above measurement was performed every 20 minutes from the start of adding the styrenic monomer to the aqueous medium, and the content of the most styrenic monomer was defined as the maximum content of the styrenic monomer.

(The bulk density)
The bulk density of the pre-expanded particles is measured as follows.
First, pre-expanded particles are filled in a 500 cm ³ graduated cylinder to a scale of 500 cm ³ .

When the graduated cylinder is visually observed from the horizontal direction and any pre-expanded particles reach a scale of 500 cm ³ , the filling of the pre-expanded particles into the graduated cylinder is terminated at that point.

Next, the weight of the pre-expanded particles filled in the measuring cylinder is weighed with two significant figures after the decimal point, and the weight is defined as W (g). Then, the bulk density of the pre-expanded particles is calculated by the following formula.
Bulk density (g / cm ³ ) = W / 500

(Absorbance ratio)
The absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is measured as follows. That is, the surface of each of 10 randomly selected pre-expanded particles is subjected to particle surface analysis by ATR infrared spectroscopy to obtain an infrared absorption spectrum. An absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is calculated from each infrared absorption spectrum, and the minimum absorbance ratio and the maximum absorbance ratio are excluded. The arithmetic average of the remaining 8 absorbance ratios is taken as the absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ). The absorbance ratio (D ₆₉₈ / D ₂₈₅₀ ) is measured using, for example, a measuring apparatus sold by Nicolet under the trade name “Fourier transform infrared spectrophotometer MAGMA 560”.

(Z average molecular weight of polystyrene resin)
About 60 mg of pre-expanded particles were collected, and each pre-expanded particle was divided into two using a cutter, and then immersed in 10 ml of chloroform at room temperature for 24 hours.

  Thereafter, chloroform was filtered through a non-aqueous 0.45 · m chromatographic disk, and the z-average molecular weight in terms of polystyrene was measured using GPC (gel permeation chromatograph).

Measuring apparatus: Product name “HPLC Detector 484, Pump 510” manufactured by Water
Measurement conditions Column: Showa Denko Co., Ltd., trade name “Shodex GPC K-806L (diameter 8.0 × 300 mm)” Column temperature: 40 ° C., mobile phase: chloroform, mobile phase flow rate: 1.2 ml / min Pump temperature: room temperature, measurement time: 25 minutes, detection: ultraviolet 254 nm
Injection amount: 50 microliters Standard polystyrene for calibration curve Product name “Shodex” molecular weight: 1030000 made by Showa Denko KK
Tosoh Corporation molecular weight: 5480000, 3840000, 355000, 102000, 37900, 9100, 2630, 495

(Fusion rate)
A 300 mm long and 5 mm deep score line was placed on the surface of a rectangular parallelepiped foam molded body having a length of 400 mm × width of 300 mm × height of 50 mm with a cutter, and the foam molded body was divided into two along this score line. . Then, on the divided surface of the foam molded body, the number of expanded particles (a) broken in the expanded particles and the number of expanded particles (b) broken at the interface between the expanded particles were measured, and based on the following formula: The fusing rate was calculated.
Fusing rate (%) = 100 × (a) / [(a) + (b)]

(Compressive strength)
A flat rectangular test piece having a length of 50 mm, a width of 50 mm, and a thickness of 25 mm was cut out from the foamed molded article, and the 5% compressive strength of the test piece was measured in accordance with JIS K6767. The compression speed was 10 mm / min.

(Impact resistance)
A flat rectangular test piece having a length of 215 mm, a width of 40 mm, and a thickness of 20 mm was cut out from the foam molded article. Then, in accordance with JIS K7211, a test piece was installed between a pair of fulcrums arranged at intervals of 150 mm, and a steel ball of 321 g was dropped, and a falling ball impact value, that is, a 50% breaking height was obtained. It calculated based on the following formula. However, the maximum height of the hard sphere was 120 cm.

50% fracture height H ₅₀ = Hi + d [Σ (i × ni) /N±0.5]
However, H ₅₀ : 50% fracture height (cm)
Hi: the height (cm) of the test piece when the height level (i) is 0,
Height at which the specimen is expected to break d: Height interval (cm) when raising and lowering the height of the specimen
i: Height level when Hi is 0, and the height level increases or decreases by 1
(i = ...- 3, -2, -1, 0, 1, 2, 3, ...)
ni: number of test pieces destroyed (or not destroyed) at each level N: total number of test pieces destroyed (or not destroyed) (N = Σni)
Use whichever data is greater
In case of the same number, either one may be adopted. ± 0.5: Negative when using destroyed data,
Take positive when using unbroken data

(chemical resistance)
Three flat rectangular plate-shaped test pieces having a length of 100 mm, a width of 100 mm, and a thickness of 20 mm were cut out from the foamed molded article and allowed to stand for 24 hours at 23 ° C. and a humidity of 50%. The test piece was cut out from the foam molded body so that the entire upper surface of the test piece was formed from the surface of the foam molded body.

Next, 1 g of different chemicals (gasoline, kerosene, dibutyl phthalate (DBP)) was uniformly applied to each of the upper surfaces of the three test pieces and left for 60 minutes under the conditions of 23 ° C. and 50% humidity. Then, the chemical | medical agent was wiped off from the upper surface of the test piece, the upper surface of the test piece was observed visually, and it judged based on the following reference | standard.
○: Good No change △: Slightly bad surface softening ・: Bad Surface depression (shrinkage)

(Example 1)
Ethylene-vinyl acetate copolymer (EVA) (trade name “NUC-3221” manufactured by Nippon Unicar Co., Ltd., vinyl acetate content: 5 wt%, melting point: 107 ° C., melt flow rate: 0.5 g / 10 min, density: 0.93 g / cm ³ ) 100 parts by weight and 0.5 parts by weight of synthetic hydrous silicon dioxide are supplied to an extruder, melt-kneaded, granulated by an underwater cutting method, and oval (egg-like) polyolefin resin particles Got. The average weight of the polyolefin resin particles was 0.60 mg. In addition, the melt flow rate and density of an ethylene-vinyl acetate copolymer are the values measured based on JIS K6992-2.

In a polymerization vessel 3 having an inner diameter of 1800 mm, a straight body length of 1890 mm, and an internal volume of 6.4 m ³ , a V-shaped paddle blade 4 (3 stirring blades, stirring blade radius d ₁ : 585 mm, stirring blade width d ₂ : 315 mm) was prepared. In the polymerization vessel of this polymerization apparatus, 100 parts by weight of water at 70 ° C., 0.8 part by weight of magnesium pyrophosphate and 0.02 part by weight of sodium dodecylbenzenesulfonate were supplied while stirring with a V-type paddle blade 4 to form an aqueous solution. The medium. Thereafter, 40 parts by weight of the polyolefin-based resin particles were suspended in an aqueous medium while stirring with the V-type paddle blade 4. Then, after the aqueous medium was heated to 85 ° C., the rotation speed of the V-type paddle blade 4 was adjusted so that the power required for the subsequent stirring was maintained at 0.20 kw / m ³ .

  As shown in FIG. 7, the polymerization vessel 3 of the polymerization apparatus has a cylindrical peripheral wall portion 32 projecting upward from the outer peripheral edge of the bottom surface portion 31 having a convex arcuate cross section. Further, the upper end opening of the peripheral wall 32 is closed by a ceiling 33 having a convex arcuate cross section. A V-type paddle blade 4 is attached as a stirring blade to the lower end portion of the rotating shaft 33a suspended from the ceiling portion 33 of the polymerization vessel 3.

The V-shaped paddle blade 4 includes a mounting portion 41 for mounting on the rotating shaft 33a and three side parallelogram stirring blades integrally provided at equal intervals in the horizontal direction on the outer peripheral surface of the mounting portion 41. 42. Each stirring blade 42 is directed obliquely outward at the top.
In FIG. 7, 61 is a motor for rotating the V-type paddle blade 4, 62 is an inverter for controlling the rotational speed of the motor, 63 is an ammeter for measuring the load current value of the motor, and 64 is a power source. Means.

  On the other hand, 0.15 parts by weight of benzoyl peroxide and 0.01 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and 0.25 parts by weight of dicumyl peroxide as a crosslinking agent and 20 parts by weight of styrene monomer (St). The first styrene-based monomer was prepared by dissolving in the solution. In addition, a second styrene monomer was prepared by dissolving 0.05 parts by weight of ethylenebisstearic acid amide as a bubble regulator in 40 parts by weight of styrene monomer (St).

  The first styrene monomer is continuously dropped into the aqueous medium at a rate of 10 parts by weight per hour, and the styrene monomer, the polymerization initiator and the crosslinking agent are impregnated in the polyolefin resin particles, Was polymerized in polyolefin resin particles.

  Next, after the addition of the first styrene monomer to the aqueous medium is completed, the second styrene monomer is continuously dropped into the aqueous medium at a rate of 20 parts by weight per hour to adjust the styrene monomer and the bubbles. While impregnating the agent into the polyolefin resin particles, the styrene monomer was polymerized in the polyolefin resin particles.

  Further, while stirring the aqueous medium, the dropping of the second styrene monomer to the aqueous medium was allowed to stand for 1 hour, and then the aqueous medium was heated to 140 ° C. and held for 3 hours. Thereafter, the polymerization vessel was cooled to obtain modified resin particles.

Subsequently, 100 parts by weight of the modified resin particles, 1.0 part by weight of water, 0.15 part by weight of stearic acid monoglyceride and 0.5 part by weight of diisobutyl adipate are supplied to a pressure-resistant V-type rotary mixer having an internal volume of 1 m ^3. Then, 14 parts by weight of butane was press-fitted at room temperature while rotating. Then, the inside of the rotary mixer was heated to 70 ° C. and held for 4 hours, and then cooled to 25 ° C. to obtain expandable modified resin particles.

The obtained foamable modified resin particles are immediately supplied to a pre-foaming machine (trade name “SKK-70” manufactured by Sekisui Koki Seisakusho Co., Ltd.) and pre-foamed using steam at a pressure of 0.02 MPa to obtain a bulk density. 0.06 g / cm ³ of pre-expanded particles were obtained.

  Next, the pre-expanded particles were allowed to stand at room temperature for 7 days, and then filled in a mold of a molding machine (trade name “ACE-3SP” manufactured by Sekisui Koki Co., Ltd.). And water vapor | steam was supplied in the metal mold | die and the pre-expanded particle was secondary-foamed, and the rectangular parallelepiped foaming molding of length 400mm x width 300mm x height 50mm was manufactured.

(Example 2)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that the power required for stirring was maintained at 0.08 kw / m ³ .

(Example 3)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that the power required for stirring was maintained at 0.50 kw / m ³ .

Example 4
Example 1 except that the amount of styrene monomer in the first styrene monomer was changed from 20 parts by weight to 40 parts by weight, and the amount of styrene monomer in the second styrene monomer was changed from 40 parts by weight to 20 parts by weight. Thus, pre-foamed particles and a foam-molded product were obtained.

(Example 5)
15 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.25 parts by weight of benzoyl peroxide and 0.02 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.15 parts by weight of dicumyl peroxide in 30 parts by weight of styrene monomer, and the first styrene monomer was dropped into the aqueous medium at a rate of 10 parts by weight per hour. Then, 0.14 parts by weight of ethylene bis-stearic acid amide as a foam regulator is dissolved in 55 parts by weight of styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 15 parts by weight per hour. Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that it was dropped into the medium.

(Example 6)
10 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.30 part by weight of benzoyl peroxide and 0.02 part by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.10 parts by weight of dicumyl peroxide in 30 parts by weight of a styrene monomer, and the first styrene monomer was dropped into an aqueous medium at a rate of 10 parts by weight per hour. Then, 0.14 parts by weight of ethylene bis-stearic acid amide as a foam regulator is dissolved in 60 parts by weight of styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 20 parts by weight per hour. Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that it was dropped into the medium.

(Example 7)
The foamable modified resin particles obtained in Example 5 were put into a prefoaming machine and prefoamed using water vapor at a pressure of 0.04 MPa, so that the prefoaming with a bulk density of 0.015 g / cm ³ was performed. Particles were obtained. Then, it carried out similarly to Example 1, and obtained the foaming molding.

(Example 8)
The foamable modified resin particles obtained in Example 1 were put into a prefoaming machine and prefoamed with water vapor at a pressure of 0.01 MPa, so that prefoaming with a bulk density of 0.15 g / cm ³ was performed. Particles were obtained. Then, it carried out similarly to Example 1, and obtained the foaming molding.

Example 9
100 parts by weight of linear low density polyethylene (LLDPE) (trade name “TUF-2032” manufactured by Nippon Unicar Co., Ltd., melting point: 125 ° C., melt flow rate: 0.9 g / 10 min, density: 0.923 g / cm ³ ) And 0.3 parts by weight of talc was supplied to an extruder, melted and kneaded, and granulated by an underwater cutting method to obtain oval (egg-like) polyolefin resin particles. The average weight of the polyolefin resin particles was 0.50 mg. The melt flow rate and density of the linear low density polyethylene were measured according to JIS K6767.

Using the same polymerization apparatus as in Example 1, 100 parts by weight of water at 70 ° C., 0.8 part by weight of magnesium pyrophosphate and 0.02 part by weight of sodium dodecylbenzenesulfonate were added to the polymerization vessel 3 of this polymerization apparatus. An aqueous medium was supplied while stirring with a mold paddle blade 4. Thereafter, 35 parts by weight of the polyolefin-based resin particles were suspended in an aqueous medium while stirring with the V-type paddle blade 4. Then, after heating the aqueous medium to 125 ° C., the rotational speed of the V-type paddle blade 4 was adjusted so that the power required for stirring thereafter would be maintained at 0.20 kw / m ³ .

  On the other hand, 0.15 part by weight of dicumyl peroxide as a polymerization initiator was dissolved in 20 parts by weight of styrene monomer to prepare a first styrene monomer.

  Then, the first styrene monomer is continuously dropped into the aqueous medium at a rate of 10 parts by weight per hour, and the styrene monomer and the polymerization initiator are impregnated in the polyolefin resin particles, while the styrene monomer is added to the polyolefin system. Polymerization was performed in the resin particles.

  Next, after the addition of the first styrene monomer to the aqueous medium is completed, 45 parts by weight of the styrene monomer is continuously dropped into the aqueous medium at a rate of 20 parts by weight per hour, and the styrene monomer is added to the polyolefin-based medium. While impregnating the resin particles, the styrene monomer was polymerized in the polyolefin resin particles. This styrene monomer is shown in the column of the second styrene monomer for convenience in Table 1.

  Further, while stirring the aqueous medium, the dropping of the styrene monomer to the aqueous medium was allowed to stand for 1 hour, and then the aqueous medium was heated to 140 ° C. and held for 1 hour. Thereafter, the polymerization vessel was cooled to obtain modified resin particles.

Subsequently, 100 parts by weight of the modified resin particles, 0.15 parts by weight of stearic acid monoglyceride and 0.5 parts by weight of diisobutyl adipate are supplied to a pressure resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated at room temperature. 14 parts by weight of butane was press-fitted. Then, the inside of the rotary mixer was heated to 80 ° C. and held for 3 hours, and then cooled to 25 ° C. to obtain expandable modified resin particles. The foamed modified resin particles were immediately pre-foamed using water vapor to obtain pre-foamed particles having a bulk density of 0.06 g / cm ³ .

  Next, the pre-expanded particles were allowed to stand at room temperature for 7 days, and then filled in a mold of a molding machine (trade name “ACE-3SP” manufactured by Sekisui Koki Co., Ltd.). And water vapor | steam was supplied in the metal mold | die and the pre-expanded particle was secondary-foamed, and the rectangular parallelepiped foaming molding of length 400mm x width 300mm x height 50mm was manufactured.

(Example 10)
In the polymerization vessel, instead of the V-shaped paddle blade, a downflow type 45 ° inclined paddle blade 5 (4 stirring blades, stirring blade radius d ₁ : 550 mm, stirring blade width d ₂ as shown in FIG. 8) : 280 mm) using a polymerization apparatus having two upper and lower stages, and the number of revolutions of the inclined paddle blade 5 immediately before dropping the first styrene monomer into the aqueous medium is completed. Until then, pre-expanded particles and a foam-molded article were obtained in the same manner as in Example 1 except that they were kept constant.

  Here, the polymerization vessel 3 of the polymerization apparatus has the same structure as that of Example 1, and each of the lower end portion of the rotating shaft 33a suspended from the ceiling portion 33 of the polymerization vessel 3 and the central portion in the vertical direction. Further, a downflow type 45 ° inclined paddle blade 5 is attached as a stirring blade.

The downflow type 45 ° inclined paddle blade 5 includes a mounting portion 51 for mounting on the rotating shaft 33a and four laterally long rectangular rectangles integrally provided on the outer peripheral surface of the mounting portion 51 at equal intervals in the horizontal direction. And a stirring blade 52 in the form of a ring. Each agitating blade 52 is oriented in the horizontal direction and is inclined by 45 ° obliquely forward from the upper end toward the lower end with respect to the rotational traveling direction.
Further, a baffle plate 7 is installed in the polymerization container 3. The baffle plates 7 are installed on the side wall of the polymerization vessel 3 so as to have a 90 ° positional relationship with each other when viewed from the upper surface of the polymerization vessel 3. The baffle plate 7 has a width of 100 mm and a length of 1890 mm.

The power required for stirring immediately before dropping the first styrene monomer into the aqueous medium (initial power required for stirring) is 0.20 kw / m ³ , and stirring is required when the production of the modified resin particles is completed. The power (final stirring required power) was 0.29 kw / m ³ .

(Example 11)
100 parts by weight of branched low density polyethylene (LDPE) (trade name “DFDJ-6775” manufactured by Nippon Unicar Co., Ltd., melting point: 112 ° C., melt flow rate: 0.2 g / 10 min, density: 0.92 g / cm ³ ) 0.5 parts by weight of synthetic hydrous silicon dioxide was supplied to an extruder, melted and kneaded, and granulated by an underwater cutting method to obtain elliptical spherical (egg-like) polyolefin resin particles. The average weight of the polyolefin resin particles was 0.75 mg. The melt flow rate and density of the branched low density polyethylene were measured according to JIS K6767. Pre-expanded particles and an expanded molded body were obtained in the same manner as in Example 10 except that the polyolefin resin particles were used. The initial required power for stirring was 0.20 kw / m ³ and the final required power for stirring was 0.29 kw / m ³ .

(Example 12)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 11 except that the initial power required for stirring was adjusted to 0.08 kw / m ³ . The final power required for stirring was 0.13 kw / m ³ .

(Example 13)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 11 except that the initial power required for stirring was adjusted to 0.45 kw / m ³ . The final power required for stirring was 0.68 kw / m ³ .

(Comparative Example 1)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 1 except that the power required for stirring was 0.04 kw / m ³ .

(Comparative Example 2)
Pre-expanded particles were obtained in the same manner as in Example 1 except that the power required for stirring was 0.90 kw / m ³ . However, since the modified resin particles were flat, it was not possible to obtain the pre-expanded particles and the expanded molded body.

(Comparative Example 3)
The power required for stirring was 0.04 kw / m ³ , 0.15 parts by weight of benzoyl peroxide and 0.01 parts by weight of t-butylperoxybenzoate as a polymerization initiator without using a second styrene monomer, and crosslinking A first styrene monomer was prepared by dissolving 0.25 parts by weight of dicumyl peroxide as an agent and 0.05 parts by weight of ethylenebisstearic acid amide as a foam regulator in 60 parts by weight of a styrene monomer. Pre-expanded particles and an expanded molded article were obtained in the same manner as in Example 1 except that one styrene monomer was dropped into the aqueous medium at a rate of 15 parts by weight per hour.

(Comparative Example 4)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Comparative Example 3 except that the power required for stirring was 0.20 kw / m ³ .

(Comparative Example 5)
60 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.1 part by weight of benzoyl peroxide and 0.01 part by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.35 parts by weight of dicumyl peroxide in 10 parts by weight of a styrene monomer, and the first styrene monomer was dropped into an aqueous medium at a rate of 10 parts by weight per hour. Then, 0.04 part by weight of ethylenebisstearic acid amide as a foam regulator is dissolved in 30 parts by weight of the styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 15 parts by weight per hour. Pre-expanded particles were obtained in the same manner as in Example 1 except that it was dropped into the medium.

  Then, a foamed molded article was obtained in the same manner as in Example 1 except that the pre-expanded particles were allowed to stand for 1 day at room temperature.

(Comparative Example 6)
8 parts by weight of polyolefin resin particles suspended in an aqueous medium, 0.32 parts by weight of benzoyl peroxide and 0.02 parts by weight of t-butylperoxybenzoate as a polymerization initiator, and as a crosslinking agent A first styrene monomer was prepared by dissolving 0.10 parts by weight of dicumyl peroxide in 30 parts by weight of a styrene monomer, and the first styrene monomer was dropped into an aqueous medium at a rate of 10 parts by weight per hour. Then, 0.12 part by weight of ethylenebisstearic acid amide as a foam regulator is dissolved in 62 parts by weight of styrene monomer to prepare a second styrene monomer, and the second styrene monomer is aqueous at a rate of 21 parts by weight per hour. Pre-expanded particles and a foamed molded article were obtained in the same manner as in Example 1 except that it was dropped into the medium.

(Comparative Example 7)
Pre-expanded ethylene-propylene random copolymer particles (ethylene-random copolymer: ethylene component = 3.5 wt%, average weight: 2 mg) having a bulk density of 0.06 g / cm ³ are gold-coated using a high-pressure molding machine. Secondary foaming was performed in the mold to obtain a foamed molded product. In Table 2, the ethylene-propylene random copolymer is expressed as “PP”.

(Comparative Example 8)
Expandable polystyrene particles (trade name “Eslen Beads HDS” manufactured by Sekisui Plastics Co., Ltd.) were pre-expanded to a bulk density of 0.06 g / cm ³ in the same manner as in Example 1 to obtain polystyrene pre-expanded particles. Then, the polystyrene pre-expanded particles were subjected to secondary foaming in the same manner as in Example 1 to obtain a foam molded article. In Table 2, polystyrene was expressed as “PSt”.

(Comparative Example 9)
Pre-expanded particles and a foamed molded product were obtained in the same manner as in Example 11 except that the initial power required for stirring was adjusted to 0.04 kw / m ³ . The final power required for stirring was 0.06 kw / m ³ .

(Comparative Example 10)
Pre-expanded particles were obtained in the same manner as in Example 11, except that the initial stirring power was adjusted to 0.90 kw / m ³ . However, since the obtained modified resin particles were flat, it was not possible to obtain pre-foamed particles and foamed molded products. The final power required for stirring (Pv) was 1.25 kw / m ³ .

In Examples 1 to 13 and Comparative Examples 1 to 10, the absorbance ratio of the pre-expanded particles (D ₆₉₈ / D ₂₈₅₀ ), the z-average molecular weight by GPC measurement of the polystyrene resin in the pre-expanded particles, and during the polymerization of the styrene monomer Tables 1 to 3 show the maximum content of the styrene monomer in the polyolefin resin particles, the fusion rate of the foamed molded product, the compressive strength, the impact resistance, and the chemical resistance.

The following can be seen from Tables 1 to 3.
(1) By Examples 1-8 and Comparative Examples 5-6, if the compounding quantity of polystyrene-type resin is the range of 1-10 times with respect to the compounding quantity of polyolefin resin, it is foam molding of a favorable characteristic. It can be seen that pre-expanded particles that can provide a body are obtained.
(2) According to Examples 1 to 8 and Comparative Examples 1 and 3 to 4, pre-expanded particles capable of providing a foamed molded article having good characteristics are obtained if the absorbance ratio is in the range of 0.1 to 2.5. You can see that
(3) According to Examples 1 to 8 and Comparative Examples 1 to 2, and Examples 11 to 13 and Comparative Examples 9 to 10, if the required power for stirring is in the range of 0.06 to 0.8 kW / m ³ , good. It can be seen that pre-expanded particles can be obtained that can provide a foamed molded article having various characteristics.
(4) According to Examples 1 to 8 and Comparative Examples 1 and 3 to 4, pre-expanded particles capable of providing a foamed molded article having good characteristics are obtained if the maximum content of the styrene monomer is 35% by weight or less. You can see that
(5) It can be seen from Examples 1 to 8 and Example 9 that even if the type of the polyolefin resin particles is changed, pre-expanded particles that can provide a foamed molded article having good characteristics can be obtained.
(6) From Examples 1 to 9 and Comparative Examples 7 to 8, it is understood that the pre-expanded particles made of polystyrene resin modified with polyolefin resin can provide a foam molded article having good characteristics.
(7) Even if the shape of the stirring blade is different between Examples 1 to 9 and Examples 10 to 13, if the required power for stirring is in the range of 0.06 to 0.8 kw / m ³ , foaming with good characteristics It turns out that the pre-expanded particle which can provide a molded object is obtained.

(Electron micrograph)
FIG. 1 is an electron micrograph obtained by photographing the surface of the pre-expanded particles obtained in Example 1 using a SEM at a magnification of 1500 times.
FIG. 2 is an electron micrograph obtained by photographing the cross-section near the surface of the pre-expanded particles obtained in Example 1 at a magnification of 20,000 using a TEM.
FIG. 3 is an electron micrograph of a cross section near the surface of the pre-expanded particles obtained in Example 1 taken at a magnification of 100,000 using a TEM.
FIG. 4 is an electron micrograph of a cross section of the central portion of the pre-expanded particles obtained in Example 1 taken at a magnification of 20,000 using a TEM.
FIG. 5 is an electron micrograph obtained by subjecting the pre-expanded particles obtained in Example 1 to polystyrene resin extraction, and then photographing the surface of the pre-expanded particles after processing at a magnification of 1500 times using SEM. .
FIG. 6 is an electron micrograph of the pre-expanded particles obtained in Comparative Example 3 taken with a polystyrene resin, and the surface of the pre-expanded particles after processing was photographed using a SEM at a magnification of 1500 times. .

2 to 4 were taken as follows.
That is, the pre-expanded particles obtained in Example 1 were divided into two. Then, the cross-section of the pre-expanded particles was entirely covered with a room temperature curing type epoxy resin (embedding resin) and then dyed with ruthenium tetroxide (RuO ₄ ).

  Next, the pre-expanded particles were sliced into a thin film using an ultramicrotome to prepare a test piece. This test piece was photographed at a predetermined magnification using a TEM.

Moreover, in FIGS. 5-6, the extraction process of the polystyrene-type resin was performed in the following way.
The pre-expanded particles were immersed in 40 ml of tetrahydrofuran and stirred at 23 ° C. for 3 hours to extract a polystyrene resin from the pre-expanded particles.

  Next, the pre-expanded particles after extraction were taken out from the tetrahydrofuran, and the tetrahydrofuran adhering to or penetrating the surface of the pre-expanded particles was removed by natural drying to obtain pre-expanded particles from which polystyrene resin was extracted.

  As shown in FIG. 2 and FIG. 3, in the vicinity of the surface of the pre-expanded particles, the polyolefin resin 1 is contained in a high ratio, while the polystyrene resin 2 gradually decreases as it approaches the particle surface. And the size is getting smaller. The surface of the pre-expanded particles is generally formed from the polyolefin resin 1.

  Further, as shown in FIG. 4, in the cell membrane at the center of the pre-expanded particles, the polystyrene resin 2 is contained in a high ratio, and the polyolefin resin 1 is dispersed in a layered manner in the polystyrene resin 2. It has become.

  Furthermore, FIG.1 and FIG.5 represents the particle | grain surface before and behind extracting polystyrene-type resin from the pre-expanded particle | grains of Example 1. FIG. On the other hand, FIG. 6 shows the particle surface after extracting the polystyrene resin from the pre-expanded particles of Comparative Example 3.

  From FIG. 1 and FIG. 5, the surface of the pre-expanded particles of Example 1 is formed with only a few voids after the polystyrene resin extraction, whereas as can be seen from FIG. It can be seen that innumerable voids after the polystyrene resin extraction are formed on the surface of the pre-expanded particles 3.

  The pre-expanded particles of the present invention contain a high percentage of polyolefin resin in the vicinity of the surface. On the other hand, the ratio of the polystyrene resin decreases as the particle surface is approached. Moreover, the ratio of the polystyrene-based resin gradually increases toward the inside of the particles, and is contained in a high ratio at the center. Further, the polystyrene resin is finely dispersed in the polyolefin resin in the vicinity of the surface.

  Therefore, the pre-expanded particles of the present invention have excellent foam moldability due to the central portion containing the polystyrene resin in a high ratio. As a result, a foamed molded product having a desired shape can be easily produced.

  In addition, the vicinity of the surface of the pre-expanded particles is in a state where most of the polyolefin-based resin is occupied. Therefore, when the pre-expanded particles are filled in the mold and subjected to secondary foaming, the particles are well fused and integrated with each other, and a foamed molded article having excellent strength and appearance can be obtained.

  In addition, the obtained foamed molded article has excellent chemical resistance and impact resistance because the surface thereof is generally coated with a polyolefin resin. On the other hand, the inside of the foamed particles constituting the foamed molded article is in a state in which a polystyrene resin is contained in a high ratio, and therefore has excellent rigidity.

  Moreover, when the z average molecular weight by GPC measurement of a polystyrene-type resin is 350,000-1.1 million, the secondary foamability of a pre-expanded particle can be improved. In addition, a foamed molded article having excellent strength can be obtained.

  Furthermore, according to the method for producing pre-expanded particles of the present invention, the pre-expanded particles having the excellent characteristics as described above can be easily produced without using a special apparatus.

  In the method for producing pre-expanded particles, the ratio of the polyolefin resin in the vicinity of the surface of the pre-expanded particles can be further increased by adding a predetermined amount of the polymerization initiator by a predetermined time. As a result, it is possible to obtain a foamed molded article having more excellent strength from the pre-expanded particles.

  Further, a styrene monomer containing a predetermined amount of a polymerization initiator is polymerized in an aqueous medium, and then a styrene monomer not containing a polymerization initiator is polymerized in an aqueous medium, whereby a polyolefin in the vicinity of the surface of the pre-expanded particles is obtained. The ratio of the resin can be reliably increased. As a result, it is possible to obtain a foamed molded article having further excellent strength from the pre-expanded particles.

  The foamed molded article of the present invention is useful for vehicle bumper cores, vehicle cushioning materials such as door interior cushioning materials, electronic parts, various industrial materials, food containers and the like.

2 is an electron micrograph of the surface of pre-foamed olefin-modified polystyrene resin particles obtained in Example 1 taken using an SEM. It is the electron micrograph which image | photographed the surface vicinity part cross section of the olefin modification polystyrene-type resin pre-expanded particle obtained in Example 1 using TEM. It is the electron micrograph which image | photographed the surface vicinity part cross section of the olefin modification polystyrene-type resin pre-expanded particle obtained in Example 1 using TEM. 2 is an electron micrograph of a cross section of the central portion of the olefin-modified polystyrene resin pre-expanded particles obtained in Example 1 taken using a TEM. It is the electron micrograph which image | photographed the surface of the olefin modification polystyrene-type resin pre-expanded particle (Example 1) after performing the extraction process of a polystyrene-type resin using SEM. It is the electron micrograph which image | photographed the surface of the olefin modification polystyrene-type resin pre-expanded particle (comparative example 3) after performing the extraction process of a polystyrene-type resin using SEM. 2 is a schematic cross-sectional view of a polymerization vessel used in Example 1. FIG. 3 is a schematic cross-sectional view of a polymerization vessel used in Example 10. FIG. It is a calibration curve showing the relationship between the amount of polystyrene resin and the absorbance ratio.

Explanation of symbols

1 Polyolefin resin 2 Polystyrene resin 3 Polymerization vessel 4 V-type paddle blade 5 Inclined paddle blade

Claims (19)

A styrene monomer comprising polystyrene resin pre-expanded particles modified with a polyolefin resin and forming a polystyrene resin is used in a range of 100 to 1000 parts by weight with respect to 100 parts by weight of the polyolefin resin. with a bulk density of particles is 0.012~0.20g / cm ^3, the absorbance ratio at 698cm ^-1 and 2850 cm ^-1 obtained from an infrared absorption spectrum of the measured particle surface by ATR method infrared spectroscopy ( D ₆₉₈ / D ₂₈₅₀ ) olefin-modified polystyrene resin pre-expanded particles in the range of 0.1 to 2.5.   The olefin-modified polystyrene resin pre-expanded particles according to claim 1, wherein the absorbance ratio is in the range of 0.4 to 2.0. The olefin-modified polystyrene resin pre-expanded particles according to claim 1, wherein the bulk density is in a range of 0.014 to 0.15 g / cm ³ .   The olefin-modified polystyrene resin pre-expanded particles according to claim 1, wherein the polyolefin-based resin is present more on the surface than in the center of the pre-expanded particles.   2. The olefin-modified polystyrene resin pre-expanded particles according to claim 1, wherein the polystyrene-based resin has a z-average molecular weight of 350,000 to 1.1 million as measured by GPC.   2. The olefin-modified polystyrene-based resin reserve according to claim 1, wherein the polyolefin-based resin is a branched low-density polyethylene, a linear low-density polyethylene, or an ethylene-vinyl acetate copolymer, and the polystyrene-based resin is a polystyrene resin. Expanded particles. Polymerization initiator while impregnating polyolefin resin particles with styrene monomer (100 to 1000 parts by weight with respect to 100 parts by weight of polyolefin resin particles used) in an aqueous medium in which polyolefin resin particles are dispersed. The step (a) of obtaining olefin-modified polystyrene resin particles by polymerizing in the presence of olefin, the step (b) of impregnating the resin particles with a foaming agent, and pre-foaming the foaming agent-impregnated resin particles to produce olefin-modified polystyrene A step (c) of obtaining a resin-based pre-expanded particle,
In the step (a), the aqueous medium is stirred with a required power of stirring of 0.06 to 0.8 kw / m ³ , and the impregnation and polymerization of the styrenic monomer has a styrenic monomer content in the polyolefin resin particles of 35. A process for producing olefin-modified polystyrene-based resin pre-expanded particles, which is carried out under a condition of not more than% by weight. In step (a), the amount of the styrenic monomer used reaches 90% by weight of the total amount used.
The method for producing olefin-modified polystyrene resin pre-expanded particles according to claim 7, wherein the polymerization initiator is added in an amount of 0.02 to 2.0% by weight based on the total amount of the polyolefin resin particles and the styrene monomer used. In step (a), the amount of the styrenic monomer used reaches 90% by weight of the total amount used.
The olefin modification according to claim 7, wherein the polymerization initiator is added in an amount of 0.02 to 2.0% by weight of the total amount of the polyolefin resin particles and the styrene monomer, and then the styrene monomer not containing the polymerization initiator is added. For producing pre-expanded polystyrene resin particles.   The olefin-modified polystyrene resin pre-expanded particles according to claim 9, wherein the addition amount of the styrene monomer not containing a polymerization initiator is in the range of 10 to 60 wt% with respect to the total amount of the styrene monomer used. Method.   The method for producing pre-expanded olefin-modified polystyrene resin particles according to claim 7, wherein the polymerization of the styrene monomer is performed in a temperature range of -30 to + 10 ° C of the melting point of the polyolefin resin particles.   The olefin-modified polystyrene according to claim 7, wherein the polyolefin resin particles are branched low density polyethylene, linear low density polyethylene, or ethylene-vinyl acetate copolymer particles, and the styrene monomer is a styrene monomer. For producing resin-based pre-expanded particles. The method for producing olefin-modified polystyrene resin pre-expanded particles according to claim 7, wherein the power required for stirring is in the range of 0.08 to 0.7 kw / m ³ .   The olefin-modified polystyrene resin pre-foaming according to claim 7, wherein the impregnation and polymerization of the styrene monomer are performed under a condition that the content of the styrene monomer in the polyolefin resin particles is in the range of 0 to 30% by weight. Particle production method.   The method for producing olefin-modified polystyrene resin pre-expanded particles according to claim 7, wherein the step (b) is performed with stirring by a paddle type stirring blade.   The method for producing olefin-modified polystyrene resin pre-expanded particles according to claim 7, wherein the total amount of the styrene monomer used is in the range of 130 to 700 parts by weight with respect to 100 parts by weight of the polyolefin resin particles.   The method for producing olefin-modified polystyrene resin pre-expanded particles according to claim 7, wherein the styrene monomer contains a crosslinking agent.   A foam-molded product obtained by filling the olefin-modified polystyrene resin pre-expanded particles according to claim 1 into a mold and foam-molding.   The foaming molding of Claim 18 used as a shock absorbing material for vehicles.