JP6653610B2 - Expandable particles of rubber-modified polystyrene-based resin, expanded particles and expanded molded article, and methods for their production and use - Google Patents

Description

  The present invention relates to a foamed resin article suitable for applications requiring impact resistance and oil resistance, and to expandable particles and foamed particles for producing the same. The invention also relates to a method for their production. The present invention also relates to the use of the foam molded article and the foam particles.

  BACKGROUND ART A foamed molded article made of a polystyrene-based resin has excellent cushioning properties and heat insulating properties, and is easily molded, and thus is widely used as a packaging material and a heat insulating material. However, there is a problem that cracks and chips are easily generated due to insufficient impact resistance and flexibility, and are not suitable for, for example, packaging of precision equipment products. Further, there is a problem that the foam is eroded in an environment where machine oil, edible oil and the like adhere.

  On the other hand, a foamed molded article made of a polypropylene-based resin is excellent in impact resistance and flexibility, but requires extensive equipment when molding the foamed molded article. Also, due to the nature of the resin, it must be transported from the manufacturer to the molding processor in the form of expanded particles. Therefore, there is a problem that the manufacturing cost increases.

  In recent years, foamed molded articles of a rubber-modified polystyrene-based resin have been developed as those which are easy to mold and have improved impact resistance and flexibility compared to polystyrene-based foams. A typical example of the rubber-modified polystyrene resin is a high-impact polystyrene resin (also referred to as a HIPS resin) obtained by modifying a polystyrene resin with butadiene rubber. However, the impact resistance of the HIPS resin is not always sufficient, and various improved techniques have been developed.

For example, in Patent Document 1, the basic resin particles are styrene-based resin particles that can be obtained by graft polymerization of high cis polybutadiene and a styrene-based monomer, and the blowing agent contains n-pentane as a main component, A foamed styrenic resin article is disclosed, wherein the foamed article after foaming has a density of 0.015 to 0.040 g / cm ³ , an average cell diameter of 60 to 300 μm, and a closed cell ratio of 50% or more. ing. According to Patent Literature 1, it is stated that this configuration improves the cell micronization phenomenon of the pre-expanded particles after completion of aging, and provides a highly foamed molded article having excellent elasticity and impact resistance. .

  Patent Document 2 discloses a rubber-modified styrene-based resin in which rubber particles of a diene-based polymer are dispersed in a continuous phase of a styrene-based resin, 85 to 99% by weight, and a volatile foaming agent having a boiling point of 80 ° C. or less 1% by weight. And the weight average molecular weight of the continuous phase is 150,000 to 300,000, the graft ratio of the styrene resin to the diene polymer is 70% to 135%, and 25%. A foamable rubber-modified styrene resin composition characterized in that the degree of swelling of the gel component of the diene polymer in toluene at 12 ° C. is 12 to 25. According to Patent Literature 2, by using a foamable resin composition having this configuration, a foam molded article having a high expansion ratio, excellent impact resistance and flexibility, and excellent appearance can be obtained.

JP-A-7-90105 JP-A-11-147970

  As described above, rubber-modified polystyrene-based resin foam molded articles having improved impact resistance have been proposed. However, the degree of improvement in impact resistance of the conventional foam molded article is not satisfactory.

  Further, Patent Documents 1 and 2 do not mention any technique for improving the oil resistance of a foam molded article.

  An object of the present invention is to provide foamed particles and foamed molded articles of a rubber-modified polystyrene resin having favorable impact resistance and oil resistance, and to provide foamable resin particles for producing the same. .

The present inventors provide the following inventions as means for solving the above problems.
The first aspect of the present invention is:
A continuous phase containing a polystyrene resin, and foamed particles of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
The present invention relates to foamed particles of a rubber-modified polystyrene-based resin, characterized by containing air bubbles having an average diameter of 100 to 300 μm.

  Since the foamed particles of the present invention are excellent in impact resistance and oil resistance, they can be suitably used for producing a resin foam molded article requiring these properties. Further, the expanded particles of the present invention are also useful as a cushion material in a cushion body.

The present invention provides a second aspect,
The present invention relates to a cushion body including a bag and foamed particles of the rubber-modified polystyrene resin filled in the bag.

  The cushion body of the present invention is hardly deformed because the foamed particles of the present invention having excellent impact resistance are used as a cushion material.

The present invention provides a third aspect,
A continuous phase containing a polystyrene resin, a foamed molded article of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
The present invention relates to a foamed molded article of a rubber-modified polystyrene resin, which contains air bubbles having an average diameter of 100 to 300 μm.

  The foam molded article of the present invention has excellent impact resistance and oil resistance. For this reason, the foamed molded article of the present invention is useful for applications requiring impact resistance and oil resistance, for example, for use in shipping containers such as returnable boxes.

According to a fourth aspect of the present invention,
A continuous phase containing a polystyrene resin, a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
And a foaming agent, foamable particles of a rubber-modified polystyrene resin,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
The diene polymer rubber forms particles having an average particle diameter of 2 to 8 μm, and relates to foamable particles of a rubber-modified polystyrene resin.

  The expandable particles of the present invention can be used for producing expanded particles and foamed molded articles having excellent impact resistance and oil resistance.

According to a fifth aspect of the present invention,
The method for producing foamable particles of a rubber-modified polystyrene resin,
In an extruder, kneading the melted rubber-modified polystyrene-based resin and the foaming agent to form a resin foaming agent mixed melt, a mixing and melting step,
Extruding the molten resin foaming agent mixture from the extruder into a cooling liquid and cooling the mixture.

  According to this method of the present invention, the expandable particles impregnated with a blowing agent can be formed in such a manner that relatively large bubbles (preferably having an average cell diameter of 100 to 300 μm) are easily formed during foaming.

The present invention provides a sixth aspect,
The present invention relates to a method for producing expanded particles of a rubber-modified polystyrene resin, including a foaming step of expanding the expandable particles of the rubber-modified polystyrene resin.

  According to this method of the present invention, foamed rubber-modified polystyrene resin particles having excellent impact resistance and oil resistance can be produced.

The present invention provides a seventh aspect,
The foaming step of foaming the foamable particles of the rubber-modified polystyrene resin,
And a molding step of molding the foamed particles of the rubber-modified polystyrene resin obtained in the foaming step in a mold.

  According to this method of the present invention, a rubber-modified polystyrene-based resin foam molded article having excellent impact resistance and oil resistance can be produced.

  According to the present invention, there are provided foamed particles and foamed molded articles of a rubber-modified polystyrene resin having favorable impact resistance and oil resistance, and foamable resin particles for producing the same.

1 is a perspective view showing an example of a foamed resin molded container according to the present invention. FIG. 2 is a sectional view taken along line aa of FIG. 1. It is a figure which shows an example of the reinforcing material used for a foamed resin molding container, FIG. 3: A is a perspective view of the whole, FIG. The figure which shows the state by which the foamed resin molding container by this invention was piled up in multiple stages.

<Rubber-modified polystyrene resin>
In the present invention, the polystyrene resin is a resin containing a polymer obtained by polymerizing a styrene monomer, and may be a resin containing a polymer obtained by copolymerizing a styrene monomer and another monomer. . Examples of the styrene monomer include styrene monomers such as styrene, α-methylstyrene, vinyltoluene, ethylstyrene, i-propylstyrene, t-butylstyrene, dimethylstyrene, bromostyrene, and chlorostyrene; And mixtures of these monomers. The styrene monomer is preferably styrene alone.

  Other monomers include, for example, (meth) acrylic acid (refers to acrylic acid or methacrylic acid; the same applies hereinafter), methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, ( (Meth) acrylic esters such as (meth) butyl acrylate and cetyl (meth) acrylate, alkyl maleates such as (meth) acrylonitrile, dimethyl maleate and diethyl maleate, dimethyl fumarate, diethyl fumarate and ethyl fumarate Alkyl fumarate, maleic anhydride, N-phenylmaleimide, (meth) acrylic acid, and the like.

  The polystyrene resin may be a crosslinked polymer further containing a component derived from a crosslinker. Examples of the crosslinking agent include divinylbenzene, trivinylbenzene, divinyltoluene, divinylxylene, bis (vinylphenyl) methane, bis (vinylphenyl) ethane, bis (vinylphenyl) propane, bis (vinylphenyl) butane, and divinylnaphthalene Compounds having a vinyl group bonded directly to a polyfunctional benzene ring, such as divinylanthracene, divinylbiphenyl, etc .; bifunctional such as ethylene oxide adduct di (meth) acrylate of bisphenol A, propylene oxide adduct di (meth) acrylate of bisphenol A (Poly) alkylene glycol di (meth) acrylate compounds such as (meth) acrylate, ethylene glycol di (meth) acrylate, and diethylene glycol di (meth) acrylate.

  The diene polymer rubber is a rubber formed by polymerizing a diene monomer such as 1,3-butadiene and isoprene (2-methyl-1,3-butadiene). The diene polymer rubber is a high cis diene polymer rubber containing 70% or more of 1,4 cis structure, and more preferably contains 80% or more, more preferably 90% or more of 1,4 cis structure. When the ratio of the 1,4 cis structure is in this range, a crosslinking reaction of molecules due to heating hardly occurs, and flexible expanded particles and expanded molded articles can be obtained. A high cis diene polymer rubber containing 70% or more of 1,4 cis structure is produced by a known production method. For example, it can be produced by polymerizing a diene monomer using an organoaluminum compound and a catalyst containing cobalt or nickel.

  The rubber-modified polystyrene-based resin used in the present invention includes a continuous phase containing a polystyrene-based resin, and a diene-based polymer rubber dispersed in the continuous phase. Such a rubber-modified polystyrene-based resin is used in the presence of a diene-based polymer rubber to convert the monomers (styrene-based monomer and, if necessary, the other monomers) constituting the polystyrene-based resin. It can be produced by graft polymerization. Specifically, the method described in JP-B-61-11965 can be mentioned. This method is a method of polymerizing the monomers constituting the polystyrene resin by a bulk polymerization method or a bulk-suspension two-stage polymerization method in the presence of a diene polymer rubber. And a polystyrene-based resin to form a graft polymer. A preferred embodiment of the method is illustrated below.

  First, the diene-based polymer rubber and the monomer constituting the polystyrene-based resin are mixed, heated and melted at 60 to 80 ° C, and further heated and stirred at 90 to 120 ° C. Bulk polymerization is performed until the polymerization rate reaches 10 to 40%. This step is called a pre-polymerization step, during which the diene polymer rubber is dispersed into particles by the action of stirring.

  The average particle size of the particles formed by the diene-based polymer rubber in the rubber-modified polystyrene-based resin, which will be described later, can be achieved by appropriately adjusting the stirring conditions in the prepolymerization step.

  After the preliminary polymerization step, the bulk polymerization may be continued, or the polymerization may be suspended in an aqueous phase containing a suspending agent such as tribasic calcium phosphate to perform granular polymerization. The polymerization is usually carried out up to a polymerization rate of about 100%, but may be carried out by performing a polymerization at a low polymerization rate, for example, 50 to 80%, and distilling off the unreacted monomer. This polymerization step after the preliminary polymerization step is referred to as a main polymerization step.

If necessary, a recovery step is performed after the main polymerization step.
If necessary, after the main polymerization step or the recovery step, a heating step may be performed after heating is continued in a state where substantially no monomer is present. The post-heating step may be performed in the presence of an organic peroxide if necessary. Examples of the organic peroxide include dicumyl peroxide, ditertiary butyl peroxide, 2,5-dimethyl-2,5 (dibutyl tertiary butylperoxy) hexane, and the like. When the total weight of the united rubber and the monomer is 100 parts, the amount can be 0.01 to 0.50 part.

  As defined in the present invention, the graft ratio of the diene polymer rubber with a polystyrene resin, such as the degree of gel swelling of the diene polymer rubber, each property of the rubber-modified polystyrene resin is the polymerization rate of the main polymerization step, It can be controlled by appropriately adjusting the reached polymerization rate, the processing temperature in the post-heating step, the processing time, the amount of the organic peroxide decomposed in the post-heating step, and the like.

  When the whole process is performed by bulk polymerization, the rubber-modified polystyrene-based resin obtained as described above can be pelletized by performing an extrusion process after the above treatment. When the main polymerization step and subsequent steps are performed by suspension polymerization, the slurry is dewatered, and the beads are separated and dried. The beads may be used as they are, or may be extruded with an extruder and pelletized.

  In addition, the rubber-modified polystyrene resin used in the present invention, the additional rubber-like substance for the modification, not less than 10 parts by weight with respect to 100 parts by weight of the rubber-modified polystyrene-based resin, as long as the object of the present invention is not hindered. May be added by melting and mixing. Such additional rubbery materials include styrene-butadiene block copolymers, styrene-butadiene random copolymers, styrene-isoprene block copolymers, styrene-isoprene random copolymers, low cis polybutadienes and hydrogenated versions thereof. And the like.

The rubber-modified polystyrene resin having the properties specified in the present invention may be purchased from a commercial product and used.
The molecular weight of the styrene-based resin in the rubber-modified polystyrene-based resin used in the present invention is not particularly limited, but typically, the rubber-modified polystyrene-based resin is dissolved in chloroform and filtered to remove the rubber component, and is contained in the solution. When the Z + 1 average molecular weight of the resin (which is considered to be a styrene-based resin forming a continuous phase) is measured, it is from 400,000 to 800,000, preferably from 400,000 to 700,000. When the styrene-based resin has this molecular weight, it is possible to prevent breakage of the cell membrane due to heating during molding, and to obtain a foamed molded article having excellent buffering properties and chemical resistance.

  The content of the diene polymer rubber in the rubber-modified polystyrene resin used in the present invention is preferably 9 to 15% by mass. The content of the diene-based polymer rubber was determined by dissolving the rubber-modified polystyrene-based resin in chloroform, adding a fixed amount of an iodine monochloride / carbon tetrachloride solution, and leaving the mixture in a dark place for a predetermined time, as described in Examples. A potassium iodide solution was added, and excess iodine monochloride was titrated with a known concentration of sodium thiosulfate / ethanol aqueous solution, the amount of iodine monochloride added was calculated, the rubber mass was calculated from the amount of iodine monochloride, and rubber-modified polystyrene was used. The rubber mass relative to the mass of the system resin is determined as a rubber content (% by mass). When the content of the diene polymer rubber is 9% by mass or more, the effect of improving the impact resistance and oil resistance of the diene polymer rubber is sufficiently exhibited. Double bonds contained in the rubber component cause discoloration and deterioration, that is, deterioration of weather resistance. However, when the content of the diene polymer rubber is 15% by mass or less, the double bond is contained in the rubber-modified polystyrene resin. The number of double bonds contained is sufficiently small, and deterioration of weather resistance due to double bonds contained in the rubber component can be avoided.

  In the rubber-modified polystyrene resin used in the present invention, the diene polymer rubber preferably forms particles. The particles of the diene polymer rubber may have an occlusion structure or a salami structure. The occlusion structure is a structure in which polystyrene resin particles are present alone in diene polymer rubber particles, and the salami structure is a structure in which a plurality of small polystyrene resin particles are contained in diene polymer rubber particles. Indicates a structure in which a plurality is included.

  In a more preferred embodiment, in the rubber-modified polystyrene resin used in the present invention, the diene polymer rubber forms particles having an average particle diameter of 2 to 8 μm. Particles of the diene-based polymer rubber in the rubber-modified polystyrene-based resin, when foamed resin particles or foamed molded articles are formed, spread thinly in the direction of the film surface inside the resin film constituting the partition walls between the bubbles, It is considered that the foamed particles or foamed articles are given impact resistance, flexibility, and oil resistance. When the average particle size of the particles of the diene polymer rubber in the rubber-modified polystyrene resin is within this range, sufficient impact resistance, flexibility, and oil resistance are imparted to the foamed particles or foamed molded article of the resin. preferable. The average particle size of the particles of the diene polymer rubber is calculated from morphological observation with a transmission electron microscope (TEM). Specifically, the average particle diameter can be determined by the procedure described in the examples.

The graft ratio of the diene polymer rubber with the polystyrene resin is preferably 137 to 160%. When the graft ratio is large, the affinity of the diene-based polymer rubber with the styrene-based resin is high, and the diene-based polymer rubber easily expands and expands during foaming.On the other hand, when the graft ratio is too large, the Since the double bond is insufficient, the elasticity and flexibility of the diene polymer rubber tend to deteriorate. When the graft ratio is set to 137 to 160%, when the foamed particles or foamed molded article of the rubber-modified polystyrene resin is formed, the diene-based polymer rubber is formed inside the resin film constituting the partition wall between the bubbles. Thus, it is considered that the foamed particles or foamed molded article are provided with impact resistance, flexibility, and oil resistance. The graft ratio is calculated by the following formula.
Graft ratio (%) = 100 × (gel content−rubber content) / rubber content The method for calculating the rubber content is as described above.

The gel content can be determined by the procedure described in the examples. Specifically, a rubber-modified polystyrene resin is precisely weighed (W), a 50% methyl ethyl ketone / 50% acetone mixed solution is added and dissolved in a volume ratio, and the solution is centrifuged to precipitate insoluble components. The supernatant is removed by filtration to obtain an insoluble matter, the insoluble matter is dried, and the mass G of the dried insoluble matter is measured to determine the gel content by the following formula.
Gel content (% by mass) = (G / W) × 100

In the rubber-modified polystyrene resin used in the present invention, the diene polymer rubber preferably has a gel swelling degree of 13 to 20. The degree of gel swelling means the ease of swelling of the diene polymer rubber with toluene, and reflects the high flexibility of the diene polymer rubber and the small number of double bonds in the rubber. Since the flexibility of the diene polymer rubber is higher as the gel swelling degree is higher, the diene polymer rubber is easily spread thinly in the film surface direction inside the resin film constituting the partition wall between the bubbles, and the expanded particles or It is considered that impact resistance, flexibility, and oil resistance are imparted to the foam molded article. On the other hand, if the degree of gel swelling is too high, it means that the double bonds of the diene polymer rubber are too large, which causes deterioration of weather resistance. Since the gel swelling degree of the diene polymer rubber in the rubber-modified polystyrene resin is 13 to 20, the foamed particles or molded foam formed using the resin have sufficient impact resistance, flexibility, and oil resistance. It is considered to have high weather resistance and sufficient weather resistance. The gel swelling ratio is a swelling ratio of a gel component with toluene at a room temperature of 25 ° C. The gel swelling degree can be determined according to the method described in Examples. That is, a rubber-modified polystyrene-based resin is precisely weighed, a sufficient amount of toluene (25 ° C.) is added and dissolved, the solution is centrifuged to precipitate insoluble components, and the supernatant is removed by decantation. The mass S of the insoluble portion swollen in the step is measured. The operation so far is performed at 25 ° C. Subsequently, after drying the insoluble matter swollen with toluene at 25 ° C., the dry mass D of the insoluble matter can be measured and determined as follows.
Swelling degree SI = S / D

  The rubber-modified polystyrene resin used in the present invention preferably has a residual monomer content of preferably 1000 ppm or less, more preferably 500 ppm or less. When the amount of the residual monomer is in this range, the heat resistance of the foamed molded product is further improved, the foam film is prevented from being broken during molding, and a foamed molded product excellent in impact resistance is obtained.

  The melt index (MI) of the rubber-modified polystyrene resin used in the present invention is preferably 2 or more and 5 or less, more preferably 3 or more and 4 or less. When the MI is in this range, even if the density of the foam molded article is reduced, a good foam molded article which does not cause shrinkage or the like can be obtained. MI is the weight (g / 10 min) of a rubber-modified polystyrene resin melted at 200 ° C. and flowing for 10 minutes from an orifice diameter of 2.09 mm when a load of 5 kg is applied.

  The Vicat softening point of the rubber-modified polystyrene resin used in the present invention is preferably 95 ° C. or lower, more preferably 90 ° C. or lower. When the Vicat softening point is within this range, shrinkage during molding can be prevented.

<Expandable particles of rubber-modified polystyrene resin>
The foamable particles of the rubber-modified polystyrene-based resin of the present invention are, as described above, a rubber-modified polystyrene-based resin containing a continuous phase containing a polystyrene-based resin and a diene-based polymer rubber dispersed in the continuous phase, and a foaming agent. And By expanding the expandable particles according to the present invention, it is possible to produce expanded resin particles and foamed resin molded articles having impact resistance and oil resistance.

  The particle size of the expandable particles of the present invention is not particularly limited, but the average particle size is preferably from 0.2 mm to 4 mm, more preferably from 0.5 mm to 2.5 mm. The average particle diameter is determined using a sieve having a JISZ8801-1 standard sieve opening, and the particle diameter at which the cumulative mass becomes 50% is defined as the average particle diameter based on the cumulative weight distribution curve.

  In the present invention, the foaming agent is not particularly limited, and any known one can be used. As the foaming agent, a physical foaming agent or a chemical foaming agent can be used, and two or more physical foaming agents and / or chemical foaming agents may be used in combination. Particularly preferred blowing agents are those containing at least a physical blowing agent, and may further comprise a chemical blowing agent.

  As the physical foaming agent, a gaseous or liquid organic compound having a boiling point equal to or lower than the softening point of the styrene-based resin and at normal pressure is particularly suitable. For example, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, n-hexane, hydrocarbons such as petroleum ether, ketones such as acetone and methyl ethyl ketone, methanol, ethanol, isopropyl alcohol and the like Low-boiling ether compounds such as alcohols, dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane; and inorganic gases such as carbon dioxide, nitrogen, and ammonia. No. These physical foaming agents may be used alone or in combination of two or more. Of these, the use of hydrocarbons is preferred from the viewpoint of preventing the destruction of the ozone layer and of rapidly replacing the air with air to suppress the temporal change of the foamed molded product. Among the hydrocarbons, hydrocarbons having a boiling point of −45 to + 40 ° C. are more preferable, and propane, n-butane, isobutane, n-pentane, isopentane and the like are further preferable. Particularly preferred physical blowing agents are n-pentane or isopentane, and may be a mixture of n-pentane and isopentane. The mixing mass ratio is not particularly limited.

  The content of the physical foaming agent is preferably in the range of 3 to 15% by mass based on the whole foamable particles. When the content is 3% by mass or more, a foam molded article having a desired density can be easily obtained from the expandable particles. In addition, the effect of increasing the secondary foaming force during in-mold foam molding is sufficient, and the appearance of the foam molded article tends to be good. When the content is 15% by mass or less, the time required for the cooling step in the production process of the foam molded article is sufficiently short, and the productivity is good. A more preferred content is 4 to 12% by mass, and a still more preferred content is 4 to 10% by mass.

  Examples of the chemical blowing agent include azodicarbonamide, dinitrosopentamethylenetetramine, hydrazoyldicarbonamide, sodium bicarbonate, and sodium bicarbonate citric acid derivative.

  A foaming aid may be used in combination with a foaming agent. Foaming aids include diisobutyl adipate, styrene, toluene, cyclohexane, ethylbenzene and the like.

  The foamable particles may contain other additives as necessary. Other additives include a plasticizer, a flame retardant, a flame retardant auxiliary, an antistatic agent, a spreading agent, a bubble regulator, an infrared attenuator, a filler, a colorant, a weathering agent, an antioxidant, a lubricant, and a protective agent. Examples include fogging agents, fragrances, dyes, pigments and the like.

  Examples of the plasticizer include aromatic hydrocarbons such as styrene, toluene, and xylene; aliphatic hydrocarbons such as cyclohexane, hexane, and heptane; adipates such as diisobutyl adipate, dioctyl adipate, and diisononyl adipate; Examples include glycerin fatty acid esters such as laurate, phthalic acid esters such as dioctyl phthalate, diisononyl phthalate and diisobutyl phthalate, and high boiling compounds such as liquid paraffin and white oil.

  Examples of the flame retardant include tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, tetrabromobisphenol A-bis (2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-bis (2,3-dibromopropyl ether) and the like.

  Examples of the flame retardant aid include 2,3-dimethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, dicumyl peroxide, organic peroxides of cumene hydroperoxide, biscumyl and the like. Is mentioned.

  Examples of the antistatic agent include polyoxyethylene alkylphenol ether, stearic acid monoglyceride, polyethylene glycol, glycerin, propylene glycol and the like.

  Examples of the spreading agent include polybutene, polyethylene glycol, glycerin, silicone oil, propylene glycol and the like.

  As the foam control agent, talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, Metal soaps such as barium sulfate, glass beads, polytetrafluoroethylene, tribasic calcium phosphate, magnesium pyrophosphate, zinc stearate, magnesium stearate, bisamide compounds such as ethylene bisstearic amide and methylene bisstearic acid amide, stearic amide And amide compounds such as 12-hydroxystearic acid amide; fatty acid glycerides such as stearic acid triglyceride and stearic acid monoglyceride.

  As a lubricant, zinc stearate, metal soap such as magnesium stearate, ethylene bis stearamide, bisamide compounds such as methylene bis stearamide, stearamide, amide compounds such as 12-hydroxy stearamide, stearic triglyceride, Fatty acid glycerides such as stearic acid monoglyceride and hydroxystearic acid triglyceride, polyethylene wax, liquid paraffin, white oil and the like can be mentioned.

  The infrared attenuating agent may be an infrared reflecting material or an infrared absorbing material, or both, and may be added as long as the object of the present invention is not hindered. Examples are metal powders such as aluminum, copper, silver and gold, carbon materials such as graphite, graphene, activated carbon and carbon black, metal oxides such as titanium oxide and tin oxide, or silica, flakes Mica and the like.

Examples of the method for producing the expandable particles include a melt extrusion method and a suspension method.
(1) Melt extrusion method
In an extruder, a molten rubber-modified polystyrene resin and a foaming agent are kneaded to form a resin foaming agent mixed melt, a mixing and melting step,
An extruding step of extruding the molten resin foaming agent mixture from the extruder into a cooling liquid and cooling it.

  The present inventors have surprisingly found that the expandable particles produced by the melt extrusion method tend to form relatively large bubbles during foaming.

  In the mixing and melting step, preferably, a foaming agent is pressed into the melted rubber-modified polystyrene-based resin in an extruder and kneaded to form a resin foaming agent mixed melt.

  More specifically, in the melt extrusion method, as the mixing and melting step, a rubber-modified polystyrene resin is supplied to an extruder, and a foaming agent is pressed and kneaded into the resin melted in the extruder. As a step, a molten resin containing a foaming agent is extruded into a cooling liquid through small holes of a die provided at the tip of the extruder, and solidified by cooling to obtain foamable particles.

In the extrusion step, a method in which the extrudate is directly extruded through a small hole of a die into a cooling liquid, and the extrudate is cut with a rotary blade immediately after the extrusion, and the cut particles are cooled in the cooling liquid is called a hot cut method. . According to the hot cut method, there is an advantage that substantially spherical expandable particles can be obtained.
The cooling liquid typically includes water.

  In the hot cutting method, for example, the following manufacturing apparatus can be used. That is, an extruder, a die having a number of small holes attached to the tip of the extruder, a raw material supply hopper for charging raw materials into the extruder, and a foaming agent being pressed into the molten resin in the extruder through a foaming agent supply port. A high-pressure pump, and a cooling chamber provided to contact the cooling liquid with the resin discharge surface in which the small holes of the die are perforated. (High-speed rotating blades) rotatably provided in the cutting chamber so that the resin can be cut off, and the expandable particles carried along with the flow of the cooling liquid from the cutting chamber are separated from the cooling liquid and dried. A dryer with a solid-liquid separation function to obtain expandable particles, a tank for storing the cooling liquid separated by the dryer with a solid-liquid separation function, and a high-pressure port for sending the cooling liquid in this tank to the cutting chamber. Flop and include manufacturing apparatus and a storage container for storing the dried effervescent grains at the solid-liquid separation function dryer.

  An example of a procedure for producing expandable particles using the above production apparatus will be described. First, a rubber-modified polystyrene resin as a raw material is charged into an extruder from a raw material supply hopper. The raw material rubber-modified polystyrene resin may be pelletized or granulated, mixed well in advance, and then charged from one raw material supply hopper, or supplied, for example, for each lot when a plurality of lots are used. The raw materials may be fed from a plurality of raw material supply hoppers whose amounts have been adjusted and mixed in an extruder. When using multiple lots of recycled raw materials in combination, the raw materials of multiple lots are mixed well in advance, and foreign substances are removed by appropriate sorting means such as magnetic sorting, sieving, specific gravity sorting, and blast sorting. It is preferable to keep it.

  After feeding the raw materials into the extruder, the rubber-modified polystyrene resin is heated and melted, and while the molten resin is being transferred to the die side, the blowing agent is pressed in from the blowing agent supply port by a high-pressure pump to mix the blowing agent into the molten resin. Then, the melt is moved to the tip side while further kneading through a screen for removing foreign substances provided in the extruder as needed, and the melt containing the foaming agent is added to the extruder at the tip of a small hole of the die. Extrude from

  The resin discharge surface in which the small holes of the die are drilled is arranged in a cutting chamber in which the cooling liquid is circulated and supplied into the chamber, and the cutting chamber can cut the resin extruded from the small holes of the die. A cutter is rotatably provided. When the melt with the blowing agent added is extruded from the small holes of the die attached to the tip of the extruder, the melt is cut into granules, and at the same time, is contacted with a cooling liquid and quenched to solidify while suppressing foaming. Into foamable particles.

  When other additives are added to the expandable particles, the timing of addition is not particularly limited, but is preferably added to the extruder together with the raw materials.

(2) Suspension method The rubber-modified polystyrene-based resin is impregnated with a foaming agent by a suspension method in a state where the rubber-modified polystyrene-based resin is suspended in an aqueous medium during or after polymerization of the rubber-modified polystyrene-based resin in a pressure-resistant closed container. This is a method for press-fitting a foaming agent.

  The impregnation of the foaming agent using an aqueous medium in the suspension method is usually performed at a temperature of 100 ° C to 150 ° C, preferably 110 ° C to 130 ° C.

In the suspension method, the impregnation time of the foaming agent varies depending on the size (volume) of the rubber-modified polystyrene resin as the raw material, and is not particularly limited. For example, in the case of particles having a volume of about 1.0 mm ³ , the time is 4 hours or more, preferably 6 hours or more. When the impregnation time is short, an unimpregnated portion called a core is formed at the center portion of the resin particles, and when the foamed particles are formed, the foamed portion and the unfoamed portion are mixed in one foamed particle, and obtained from the foamed particles. In some cases, the obtained foamed molded article does not have desired physical properties.

  In the suspension method, if necessary, the above-mentioned other additives can be added to the expandable particles by adding the above-mentioned other additives to the aqueous medium.

  The aqueous medium may contain a suspension stabilizer for stabilizing the dispersion of monomer droplets and seed particles. The suspension stabilizer is not particularly limited as long as it has been conventionally used for suspension polymerization of a monomer.

<Expanded particles of rubber-modified polystyrene resin>
The expanded particles of the present invention,
A continuous phase containing a polystyrene resin, and foamed particles of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
It is characterized by containing air bubbles having an average diameter of 100 to 300 μm.

  The expanded particles of the present invention can be produced by expanding (pre-expanding) the expandable particles of the present invention. The expanded particles of the present invention can be used not only as pre-expanded particles for producing the expanded molded article of the present invention described below, but also as a cushion material of the cushion body of the present invention.

  The rubber-modified polystyrene resin contained in the expanded particles of the present invention can be the same as the rubber-modified polystyrene resin in the expandable particles of the present invention. However, the shape of the diene polymer rubber in the rubber-modified polystyrene resin differs before and after foaming. In the state before foaming, that is, when the rubber-modified polystyrene resin in the foamable particles of the present invention contains a diene-based polymer rubber having the above particle shape, the foamable particles are obtained by foaming the foamable particles. In the expanded particles, the diene polymer rubber is stretched and spreads in a thin sheet. As a result, a sheet-like diene-based polymer rubber spreads in the film surface direction inside the resin film constituting the partition wall between the bubbles, and the foamed particles or foamed molded article have impact resistance, flexibility, and oil resistance. It is considered to be granted.

  The foamed particles of the present invention are characterized by containing bubbles having an average diameter of 100 to 300 μm. Assuming that the size and expansion ratio of the foamed particles are the same, the smaller the cell diameter in the foamed particles, the thinner the partition walls between the cells, and the lower the impact resistance and oil resistance. In the foamed particles of the present invention, when the average diameter of the cells (hereinafter sometimes referred to as “average cell diameter”) is 100 μm or more, the partition walls between the cells are sufficiently thick, and the impact resistance and the oil resistance are excellent. On the other hand, if the bubble diameter is too large, the impact resistance of the bubbles tends to be poor. The expanded particles of the present invention have sufficient impact resistance when the average cell diameter is 300 μm or less. The average bubble diameter is more preferably 110 to 300 µm, more preferably 130 to 300 µm, and more preferably 170 to 300 µm.

Here, the average cell diameter can be measured in accordance with the test method of ASTM D3576-77.
Specifically, an arbitrary part of the expanded particles is used to obtain a cross section of the expanded particles using a razor blade. Using a scanning electron microscope (JSM-6360LV manufactured by NEC Corporation), the cut surface is enlarged (for example, magnified 30 times) to create an image.

Next, a straight line of 60 mm is drawn at an arbitrary position in the cross section of the expanded bead on the image of the cut surface. The number of bubbles on the straight line is counted, and the average chord length (t) of the bubbles is calculated by the following equation.
Average chord length t (mm) = 60 / (number of bubbles x magnification of image)

  In drawing a straight line, the straight line should penetrate the bubble as much as possible without making point contact. In addition, when some of the bubbles make a point contact with a straight line, this bubble is also included in the number of bubbles, and furthermore, when both ends of the straight line do not penetrate the bubble and are located in the bubble. Includes the bubbles at both ends of the straight line in the number of bubbles.

The average cell diameter (D) of the cells is calculated by the following equation.
Average bubble diameter D (mm) = t / 0.616
The above operation is performed with N number 5 or more, and the average value is defined as the average bubble diameter.

  The expanded particles of the present invention themselves have high impact resistance and oil resistance. Further, the foamed molded article obtained by molding the foamed particles of the present invention also has high impact resistance and oil resistance. These advantageous properties of the expanded particles of the present invention result from a combination of the above-mentioned effects of the properties of the rubber-modified polystyrene resin and the above-mentioned effects of the range of the average cell diameter.

  The method of producing the expanded particles by expanding the expandable particles of the present invention is not particularly limited, but typically, the expandable particles of the present invention are housed in a pre-expanding device, and steam is introduced into the device. This can be done by press-fitting.

The pressure of the steam is, for example, preferably from 0.03 to 0.07 MPa, more preferably from 0.04 to 0.06 MPa. In the present invention, the pressure means a gauge pressure. The heating time is preferably from 60 to 180 seconds, more preferably from 90 to 120 seconds.
The above average bubble diameter can be achieved by appropriately adjusting the pressure of steam and the heating time.

  The particle diameter of the expanded particles of the present invention is not particularly limited, but the average particle diameter is preferably 0.5 mm or more and 15 mm or less, more preferably 2 mm or more and 10 mm or less. The average particle diameter is determined using a sieve having a JISZ8801-1 standard sieve opening, and the particle diameter at which the cumulative mass becomes 50% is defined as the average particle diameter based on the cumulative weight distribution curve.

The expanded particles of the present invention preferably have a flatness of 0.6 to 0.8. Here, the flatness is calculated from the minor axis and major axis of the expanded particles by the following method.
Flatness = average minor axis of expanded particles / average major axis of expanded particles

  The average minor axis and average major axis of the expanded particles can be calculated as an average value by measuring the minor axis and major axis of an appropriate number (for example, 50 or more) of the expanded particles.

  When the flatness is in the above-mentioned range, it is excellent in fixing an object when used as a cushion core material, while maintaining good filling of the foamed particles in the mold during molding.

The bulk density of the expanded beads of the present invention is preferably in a range of 0.010~0.100g / cm ^3, more preferably in the range of 0.012~0.050g / cm ^3, 0.014~0 It is more preferably in the range of 0.025 g / cm ³ .
The bulk expansion multiple of the expanded particles of the present invention is preferably 10 to 100 times, more preferably 20 to 80 times, and even more preferably 40 to 70 times.

  In addition, in the present invention, the bulk density of the expanded particles refers to a value measured in accordance with JIS K6911: 1995 “General Method for Testing Thermosetting Plastics”. For example, it can be measured as follows.

Method for measuring the bulk density of expanded particles:
The mass (W) g of the expanded particles is weighed to two decimal places. Next, the weighed foamed particles are filled into the measuring cylinder by natural falling, and the volume (V) cm ³ of the foamed particles dropped into the measuring cylinder is measured using an apparent density measuring device based on JIS K6911. . Then, the bulk density of the expanded particles is determined based on the following equation.
Bulk density (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)

The bulk expansion multiple of the expanded particles is a numerical value calculated by the following equation.
Bulk foaming factor = 1 / bulk density (g / cm ³ )

<Rubber-modified polystyrene resin foam molded article>
The foam molded article of the present invention,
A continuous phase containing a polystyrene resin, a foamed molded article of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
It is characterized by containing air bubbles having an average diameter of 100 to 300 μm.

  The foamed molded article of the present invention can be produced by a molding step of molding the foamed particles of the present invention in a mold. In the molding step, specifically, the foamed particles of the present invention described above are filled in a closed mold having a large number of small holes, heated and foamed with a heating medium (for example, pressurized steam, etc.), This is a step of filling the voids and fusing the foamed particles together to integrate them. At this time, the density of the foamed molded article can be adjusted by, for example, adjusting the filling amount of the foamed particles in the mold.

  The heating and foaming can be performed, for example, by heating with a heating medium at 110 to 150 ° C. for 5 to 50 seconds. Under these conditions, good fusion between the foamed particles can be ensured. More preferably, the heat foam molding can be performed by heating with a heat medium (for example, steam) at a molding vapor pressure (gauge pressure) of 0.06 to 0.08 MPa and 90 to 120 ° C. for 10 to 50 seconds. .

  The rubber-modified polystyrene resin contained in the expanded particles of the present invention can be the same as the rubber-modified polystyrene resin in the expandable particles of the present invention. However, the shape of the diene polymer rubber in the rubber-modified polystyrene resin differs before and after foaming. In the state before foaming, that is, when the rubber-modified polystyrene resin in the foamable particles of the present invention contains a diene-based polymer rubber having the above particle shape, the foamable particles are foamed and molded in a mold. In the foam molded article obtained by the above, the diene polymer rubber is stretched and spreads in a thin sheet shape. As a result, it is thought that the sheet-like diene-based polymer rubber spreads in the film surface direction inside the resin film constituting the partition wall between the bubbles, and imparts impact resistance, flexibility, and oil resistance to the foam molded article. Can be

  In the foamed molded article of the present invention, the average cell diameter is 100 to 300 μm. Assuming that the size and expansion ratio of the foamed molded article are the same, the smaller the cell diameter in the foamed molded article, the thinner the partition wall between the cells, and the lower the impact resistance and oil resistance. In the foam molded article of the present invention, when the average cell diameter is 100 μm or more, the partition walls between the cells are sufficiently thick, and the impact resistance and the oil resistance are excellent. On the other hand, if the bubble diameter is too large, the impact resistance of the bubbles tends to be poor. The foam molded article of the present invention has sufficient impact resistance when the average cell diameter is 300 μm or less. The average bubble diameter is more preferably from 130 to 300 μm, more preferably from 150 to 300 μm, and more preferably from 200 to 300 μm.

  Here, the average cell diameter can be measured in accordance with the test method of ASTM D3576-77. Specifically, a cross section of the foam molded article is obtained from any part of the foam molded article using a razor blade. Using a scanning electron microscope (JSM-6360LV manufactured by NEC Corporation), the cut surface is enlarged (for example, magnified 30 times) to create an image. Using this image, the average chord length and the average cell diameter are determined according to the same procedure as described for the average cell diameter of the expanded particles. This is performed with N number 5 or more, and the average value is defined as the average bubble diameter.

  The foam molded article of the present invention has high impact resistance and oil resistance. These advantageous properties of the foamed molded article of the present invention arise from the combination of the above-mentioned effects due to the properties of the rubber-modified polystyrene-based resin and the above-mentioned effects due to the range of the average cell diameter.

The density of the foamed molded article of the present invention is preferably in a range of 0.010~0.100g / cm ^3, more preferably in the range of 0.012~0.050g / cm ^3, 0.014~0.025g / Cm ³ is more preferable.

  The foaming multiple of the foamed molded article of the present invention is preferably 10 to 100 times, more preferably 20 to 80 times, and still more preferably 40 to 70 times.

<The density of the foamed molded article>
In the present invention, the density of the foamed molded article is a density measured by a method described in JIS K7122: 1999 “Expanded plastic and rubber-Measurement of apparent density”, and specifically, can be measured by the following method. it can.

A test piece of 50 cm ³ or more (100 cm ³ or more in the case of a semi-hard or soft material) was cut without changing the original cell structure of the material, and its mass was measured and calculated by the following equation.
Density (g / cm ³ ) = test piece mass (g) / test piece volume (cm ³ )

  A test piece for condition adjustment and measurement of a test piece was cut out from a sample 72 hours or more after molding, and subjected to an atmosphere condition of 23 ° C. ± 2 ° C. × 50% ± 5% or 27 ° C. ± 2 ° C. × 65% ± 5%. It has been left for more than an hour.

<Foaming multiple>
The “foaming multiple” of the foam molded article is a numerical value calculated by the following equation.
Foaming factor = 1 / density (g / cm ³ )

  In the embodiment in which the foamed molded article of the present invention is made of thermally fused foamed particles, the fusion rate between the foamed particles is preferably 90% or more. The fusion rate is expressed on the cross section when the foam molded article is bent and fractured, and is expressed as a percentage of the number of the foamed particles that are fractured inside the particles, among the total number of foamed particles. is there. The measurement of the fusion rate can be specifically performed according to the following procedure. A sample of a 400 mm × 300 mm × 50 mm rectangular parallelepiped foam molded body is prepared, and a cutting line having a depth of about 5 mm is formed with a cutter knife along a line connecting the centers of a pair of long sides of one of the 400 mm × 300 mm surfaces. Put in. Thereafter, the foam molded body is manually divided into two along the cut line. Regarding the expanded particles in the fractured surface, the number (A) of all the particles and the number (B) of the particles broken in the particles are counted in an arbitrary range of 100 to 150. The value obtained by substituting the result into the formula [(B) / (A)] × 100 is defined as the fusion rate (%).

<Cushion body>
Further embodiments of the present invention include:
A bag,
The present invention relates to a cushion body including the foamed particles of the present invention filled in the bag body.

  Since the foamed particles of the present invention have excellent impact resistance as described above, the cushion body of the present invention containing it as a cushioning material has the effect of being hardly deformed even after long-term use. The cushion body of the present invention having this effect is particularly useful when used in a mode in which a load is applied to the cushion body such as a bed, a mattress, a pillow, a cushion, and a chair.

  The expanded particles of the present invention to be filled in the cushion body preferably contain a lubricant for promoting flow. Specific examples of the lubricant are as described for the expandable particles. The lubricant functions to suppress abnormal noise generated when the foamed particles flow and rub. Examples of the content of the lubricant include 0.4 to 1.5 parts by weight per 100 parts by weight of the foamed particles of the present invention.

  The bag may or may not have elasticity, but preferably has elasticity. Examples of the bag having elasticity include a bag having 30 to 300% elasticity. As the stretchable material, for example, spandex (polyurethane elastic yarn) having elasticity is most preferable. The elasticity can be determined by the following method.

A test piece having a tensile interval of 10 cm and a width of 2.5 cm is stretched at a rate of 30 cm / min using a Tensilon universal testing machine UCT-10T (manufactured by ORIENTEC CORPORATION), and the elongation under a 9.8 N load is measured. This measurement is performed in the vertical and horizontal directions of the test piece, and the average value of the elongation is defined as the elasticity.
Elongation (%) = {length of test specimen under load of 9.8 N (cm) −10} 10 × 100

  Use of the above bag has the following effects. That is, by using a stretchable material for the bag, when a part of the cushion body is compressed, the filled particles move from the compression part to another part, and the volume of the moved particles becomes another. Since it is permissible that the bag located at the site extends and deforms, the permissible range of the movement of the particles can be further increased. The synergistic effect of these effects of the foamed particles and the bag of the present invention can provide a cushion having a better touch.

  In the cushion body of the present invention, it is preferable that the foamed particles are sealed so as to have a volume of 1.1 to 3.5 times the internal volume of the bag body having elasticity. By enclosing foamed particles having a volume equal to or larger than the inner volume of the bag as a filler in a bag made of an extensible material, it is possible to further improve the sitting comfort and the effect of preventing deformation of the cushion. Here, if the foamed particles are less than 1.1 times the inner volume of the bag body, a feeling of bottoming is generated at the time of sitting, and if it is more than 3.5 times, the sitting comfort is unfavorably deteriorated. A more preferred range is 1.3 to 2.5 times. Here, the filling ratio indicates a multiple of the bulk volume of the expanded beads to be filled when the internal volume of the bag is set to 1. The inner volume of the bag is prepared by cutting a bag of the same size as the cushion of the cushion body from a 0.05 mm thick polyethylene bag manufactured by Yamajix Co., Ltd., and air is applied to the polyethylene bag at an internal pressure of 0.01 MPa. The air in the bag is then placed in a graduated cylinder submerged in water, and the amount of air can be used as the internal volume of the bag.

  In addition, in order to suppress the generation of abnormal noise, express a suitable feel, and satisfy permanent cushioning properties, double openable fasteners are provided so that these fillers do not leak from the bag body. It is a more preferred embodiment that the structure is changed. It is also effective that the bag itself has a double structure.

  Furthermore, it is also possible to adopt a configuration in which a plurality of bags in which the expanded particles of the present invention are sealed are put in one large bag. In this case, the fillers in the plurality of bags may have different feels.

<Transport container>
The foamed molded article of the present invention is excellent in impact resistance and oil resistance, so that it is likely to receive an impact, and is suitable for use as a transport container that may come into contact with edible oil or machine oil. I have. That is, the foam molded article of the present invention is preferably in the form of a transport container. The foamed molded article of the present invention in the form of a transport container may be referred to as a “transport container of the present invention” in the following description.

  The transport container of the present invention is particularly suitable for use as a returnable box that is repeatedly used for a long time because of its excellent impact resistance and oil resistance.

  The transport container of the preferred embodiment of the present invention is more preferably a container of the foamed molded article of the present invention in which a step portion as a handle is formed on the outer surface of the peripheral wall, and at least an upper end region portion of the step portion Is covered with a reinforcing material preformed in its shape, and a portion of the reinforcing material that is continuous with the covering surface is embedded in the peripheral wall.

It is more preferable that the upper end surface of the step portion is an inclined surface in which the outer surface becomes lower toward the inside from the outer surface of the peripheral wall.
It is preferable that the reinforcing material has a convex portion or a concave portion which serves as a locking portion to a molding die.

  The reinforcing material is a surface region portion covering the upper end region portion of the step portion of the container of the foam molded article of the present invention, a peripheral surface portion entering the peripheral wall of the container from the surface region portion, and an end of the peripheral surface portion. It is preferable to have a skirt portion that spreads, and that the peripheral surface portion and the skirt portion be embedded in the peripheral wall.

It is preferable that the resin type of the foam molded article of the present invention and the resin type of the reinforcing material are the same rubber-modified polystyrene resin.
This preferred embodiment of the transport container of the present invention will be described more specifically with reference to the drawings.

  Hereinafter, preferred embodiments of the transport container of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of the transport container of the present invention, and FIG. 2 is a sectional view taken along line aa of FIG. FIG. 3 shows an example of a reinforcing material used in the shipping container of the present invention. FIG. 4 shows a state in which shipping containers according to a preferred embodiment of the present invention are stacked.

  In this example, the transport container 1 is composed of a container body 2 and a lid 3 which are the above-described foam molded article of the present invention. The container main body 2 has a step 22 as a handle on the outer surface of two opposing side walls 21 constituting the peripheral wall (side peripheral wall) (note that only the step 22 formed on one side wall 21 in FIG. Shown). The step portion 22 includes an upper end surface 23, left and right side wall portions 24 and 25, and a bottom wall portion 26, and the container bottom surface 27 side of the step portion 22 is open downward. Further, the periphery of the bottom surface 4 of the container body 2 is formed with a notch 28.

  The upper end region of the step portion 22 in the container body 2, that is, the upper end surface 23 of the step portion 22, the left and right side wall portions 24, 25, the vicinity of the upper end surface 23 of the bottom wall portion 26, and the side wall 21 The peripheral portion is covered with the reinforcing material 4 according to the present invention.

  In this example, the reinforcing material 4 is a non-foamed sheet of a polystyrene resin formed in advance, and has a thickness of about 0.3 mm. As shown in FIG. 3, the reinforcing member 4 includes a surface region portion 41 formed along the upper end region portion of the step portion 22 formed in the container main body 2, a peripheral surface portion 42 entering rearward from the periphery thereof, A skirt portion 43 is provided which extends from the rear end of the peripheral surface portion 42 in the substantially same direction as the surface region portion 41.

  3, a portion 41a covers the upper end surface 23 of the surface region portion 41, a portion 41b covers the left and right side walls 24 and 25, a portion 41c covers the bottom wall portion 26, and 41d. Is a portion covering the peripheral portion of the side wall 21. Further, in this example, a concave hole 41e is formed in the portion 41a, and is used for temporarily fixing in a molding die as described later. Then, as shown in FIG. 2, other portions except the surface region portion 41, that is, a peripheral surface portion 42 entering rearward from the periphery of the surface region portion 41 and a skirt portion 43 following the peripheral portion 42 are formed inside the side wall 21 of the container body 2. The reinforcing member 4 is integrated with the container body 2 in a state of being embedded in the container body 2.

  The lid 3 has a convex portion (not shown in the figure) on the back surface that is fitted into the container main body 2, a peripheral bank portion 31 corresponding to the notch 28 on the bottom surface of the container main body 2, and a peripheral wall (side). A step portion 33 as a handle is formed on the outer side surface of the two opposing side walls 32 constituting the peripheral wall). In this example, no special covering is applied to the step portion 33, but a reinforcing material may be provided in the same manner as the step portion 22 of the container body 2.

  In the transport container 1 according to the preferred embodiment of the present invention, since the step portion serving as the handle is covered with the reinforcing material 4, as shown in FIG. Even when the operator puts his / her finger on the stepped portion, particularly on the upper end region thereof, when separating the containers 1 individually, it is possible to effectively avoid the destruction or breakage of the portion. The reinforcing member 4 is in a state in which the peripheral surface portion 42 and the skirt portion 43 following the skirt portion 43 are embedded in the side wall 21 of the container main body 2. No peeling occurs. Therefore, long-term repeated use as a return box or the like can be performed in a stable state.

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. Each operation described below was performed at room temperature of 23 ° C. unless otherwise specified.
<Example 1>
(Production of expandable rubber-modified polystyrene resin particles)
As the base resin, the diene rubber particles have a high cis structure in which the ratio of 1,4-cis structure is 93%, the rubber content is 12% by mass, the average particle diameter of the rubber particles is 5 μm, the graft ratio of styrene is 140%, and the gel swells. A rubber-modified polystyrene resin having a degree of 16 was used. A mixture of 100 parts by mass of this rubber-modified polystyrene-based resin and 0.5 parts by mass of polyslen ES405 (manufactured by Eiwa Kasei Co., Ltd.) as a chemical foaming agent was continuously supplied at 150 kg per hour to a single-screw extruder having a diameter of 90 mm. The maximum temperature in the extruder was set at 210 ° C., and after melting the resin, 6 parts by mass of pentane (isopentane: normal pentane = 20: 80 (mass ratio) with respect to 100 parts by mass of the resin) as a foaming agent. Was injected from the middle of the extruder. The resin and the foaming agent are kneaded and cooled in the extruder, and the resin temperature at the extruder tip is maintained at 180 ° C., the pressure at the resin inlet of the die is maintained at 15 MPa, and the land length is 0.6 mm and the land length is 3 mm. At the same time as extruding the blowing agent-containing molten resin into a cutting chamber connected to the discharge side of this die and circulating water at 40 ° C. from a die in which 200 small holes having a diameter of 200 mm are arranged, 10 pieces of the resin are circumferentially placed. The extrudate was cut by a high-speed rotary cutter having a blade. While cooling the cut particles with circulating water, the cut particles were conveyed to a particle separator to separate the particles from the circulating water. Further, the collected particles were dehydrated and dried to obtain expandable polystyrene resin particles. The foamable polystyrene resin particles obtained were substantially spherical and had an average particle diameter of about 1.1 mm without deformation, whiskers and the like, and foamable rubber-modified polystyrene resin particles were obtained.

  When the obtained expandable rubber-modified polystyrene resin particles were measured, they had a high cis structure in which the ratio of 1,4-cis structure was 93%, the rubber content was 12% by mass, the graft ratio of styrene was 140%, and the gel swelling degree was 16 Met.

10 kg of the expandable rubber-modified polystyrene resin particles were coated with 5 g of zinc stearate, 5 g of 12-hydroxystearic acid triglyceride, 5 g of monoglyceride stearate, and 5 g of polyethylene glycol. Subsequently, the expandable polystyrene-based resin particles were supplied to a cylindrical batch-type prefoaming machine, and heated with steam having a blowing pressure of 0.05 MPa to obtain expanded particles. The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 202 μm, and a flatness of 0.66.

  When the obtained expanded particles were measured, they had a high cis structure in which the ratio of 1,4 cis structure was 93%, the rubber content was 12% by mass, the graft ratio of styrene was 140%, and the gel swelling degree was 16.

Subsequently, after leaving the obtained foamed particles in a room temperature atmosphere for 24 hours, the foamed particles are filled in a molding die having a rectangular cavity of 400 mm in length × 300 mm in width × 50 mm in height, and steam is formed. Molding was performed under the conditions of a pressure of 0.07 MPa (gauge pressure), a mold heating of 5 seconds, a heating of 10 seconds, a double-sided heating of 10 seconds, a water cooling of 10 seconds, and a set extraction surface pressure of −0.02 MPa. The obtained foamable form had a density of 0.020 g / cm ³ (expansion factor 50 times) and an average cell diameter of 230 μm.

  When the obtained foamed molded article was measured, it had a high cis structure in which the ratio of the 1,4-cis structure was 93%, the rubber content was 12% by mass, the graft ratio of styrene was 140%, and the gel swelling degree was 16.

(Rubber content)
The foamed particles or the foamed molded article were allowed to stand in a constant temperature bath at 70 ° C. for 24 hours to remove the foaming agent contained in the foamed particles or the foamed molded article, and then used as a rubber-modified polystyrene resin sample.

  A rubber-modified polystyrene resin is dissolved in chloroform, a fixed amount of an iodine monochloride / carbon tetrachloride solution is added, and the mixture is allowed to stand in a dark place for about 1 hour. Then, a potassium iodide solution is added, and excess iodine monochloride is added to 0.1N thione. Titrate with sodium sulfate / ethanol aqueous solution to determine the amount of iodine monochloride added. The mass of rubber was calculated from the amount of iodine monochloride, and the mass of rubber relative to the mass of rubber-modified polystyrene resin was determined as the rubber content (% by mass).

(1,4 cis structure ratio)
The foamed particles or the foamed molded article were allowed to stand in a constant temperature bath at 70 ° C. for 24 hours to remove the foaming agent contained in the foamed particles or the foamed molded article, and then used as a rubber-modified polystyrene resin sample.

About 0.1 g of a rubber-modified polystyrene resin was dissolved in about 20 mL of toluene, a film was formed on a hot plate, and infrared analysis was performed. The peak height was obtained from the obtained chart, and the ratio (% by mass) of the 1,4-trans structure to the mass of the rubber-modified polystyrene resin was calculated from the calibration curve.
Apparatus: Thermo Fourier Transform Infrared Spectrophotometer Resolution: 4 cm ^-1
Number of scans: 32
Detector: DTGS KBr

The ratio (%) of the 1,4 cis structure was calculated by the following equation.
Ratio of 1,4-cis structure (%) = [[Rubber content (% by mass)] − [Ratio of 1,4 trans structure (% by mass)]] / [Rubber content (% by mass)] × 100

(Rubber particle diameter)
The average particle size of the dispersed particles of butadiene rubber in the present invention is a value obtained by measuring the particle size (the longest width of each particle) of 100 to 200 rubber particles in a transmission electron micrograph and calculating by the following formula.
Average particle size = ΣN _i D ² / ΣN _i D
(Note that _Ni is the number of rubber particles, and D is the particle size of the rubber particles.)

(Gel content)
The foamed particles or the foamed molded article were allowed to stand in a constant temperature bath at 70 ° C. for 24 hours to remove the foaming agent contained in the foamed particles or the foamed molded article, and then used as a rubber-modified polystyrene resin sample.

A rubber-modified polystyrene-based resin having a mass of 1.00 g was precisely weighed (W), 35 ml of a 50% methyl ethyl ketone / 50% acetone mixed solution was added and dissolved in a volume ratio, and the solution was centrifuged (K-SAN H-2000B). (Rotor: H)), centrifuged at 10,000 rpm for 30 minutes to precipitate insolubles, and the supernatant was removed by decantation to obtain insolubles, which were pre-dried in a safety oven at 90 ° C. for 2 hours. Furthermore, after drying under reduced pressure at 120 ° C. for 1 hour in a vacuum dryer and cooling in a desiccator for 20 minutes, the mass G of the dried insoluble matter can be measured and determined as follows.
Gel content (% by mass) = (G / W) × 100

(Graft rate)
The foamed particles or the foamed molded article were allowed to stand in a constant temperature bath at 70 ° C. for 24 hours to remove the foaming agent contained in the foamed particles or the foamed molded article, and then used as a rubber-modified polystyrene resin sample.

The graft ratio of the rubber-like dispersed particles of the rubber-modified polystyrene resin is determined from the gel content (% by mass) in the rubber-modified polystyrene resin and the rubber content (% by mass) in the rubber-modified polystyrene resin as follows. be able to.
Graft ratio = 100 × (gel content−rubber content) / rubber content

(Gel swelling degree)
The foamed particles or the foamed molded article were allowed to stand in a constant temperature bath at 70 ° C. for 24 hours to remove the foaming agent contained in the foamed particles or the foamed molded article, and then used as a rubber-modified polystyrene resin sample.

1.00 g of the rubber-modified polystyrene-based resin is precisely weighed and dissolved by adding 30 ml of toluene at 25 ° C., and the solution is centrifuged at 10,000 rpm by a centrifuge (H-2000B (Rotor: H) manufactured by Kokusan). After centrifugation for minutes, the insoluble matter was sedimented, the supernatant was removed by decantation, and the mass S of the insoluble matter swollen with toluene was measured. The operations so far were performed at 25 ° C. Subsequently, the insoluble matter swollen with toluene at 25 ° C. was preliminarily dried at 90 ° C. for 2 hours in a safety oven, further dried under reduced pressure at 120 ° C. for 1 hour in a vacuum dryer, and dried in a desiccator for 20 minutes. The dry mass D per minute can be measured and determined as follows.
Swelling degree SI = S / D

(Evaluation of fusion rate)
A cut line having a depth of about 5 mm is formed by a cutter knife along a straight line connecting the centers of a pair of long sides to a molded product having a length of 400 mm, a width of 300 mm and a height of 50 mm, and then a foam molded article is formed along the cut line. Is divided into two by hand, and the number of all particles (A) and the number of particles (B) broken in the particles are counted in an arbitrary range including 100 to 150 particles of the foamed particles in the fractured surface. The fusion rate (%) was calculated by the following equation.
Fusion rate = (B) × 100 / (A)
The following evaluation criteria: 90% or more was evaluated as ○, and less than 90% was evaluated as poor (x).

(Evaluation of average bubble diameter)
Using a scanning electron microscope (trade name “JSM-6360LV” manufactured by JOEL) as a measuring device, the measurement was performed according to the test method of ASTM D3576-77. Specifically, the foamed molded product is cut with a razor tooth on a plane passing through an arbitrary position, and the cut surface is magnified 30 times using a scanning electron microscope (trade name “JSM-6360LV” manufactured by JOEL). Shoot.

Next, the photographed image is printed on A4 paper, a straight line having a length of 60 mm is drawn at an arbitrary position in the cross section of the foamed molded product, and the average chord length (t) of the bubbles is determined from the number of bubbles existing on the straight line. Is calculated by the following equation.
Average chord length t (mm) = 60 / (number of bubbles x magnification of photograph)

  In drawing a straight line, the straight line should penetrate the bubble as much as possible without making point contact. In addition, when some of the bubbles make a point contact with a straight line, this bubble is also included in the number of bubbles, and furthermore, when both ends of the straight line do not penetrate the bubble and are located in the bubble. Includes the bubbles at both ends of the straight line in the number of bubbles.

The average bubble diameter (D) can be calculated by the following equation based on the calculated average chord length t.
Average bubble diameter D (mm) = t / 0.616

Further, the average cell diameter is calculated in the same manner as described above at any five places in the photographed image, and the arithmetic mean value of these average cell diameters is defined as the average cell diameter of the foam molded article.
The average cell diameter of the expanded particles was determined in the same procedure.

(50% breaking height)
In accordance with JIS K-7211, a 255 g steel ball was dropped on a sample in which a foam molded article was adjusted to a size of 200 mm in length, 40 mm in width, and 25 mm in thickness, and a 50% breaking height (cm) was obtained.
45 cm or more was evaluated as ○, and less than 45 cm was evaluated as x.

(Solvent resistance)
The salad oil was applied to the surface of the foamed particles or the foamed molded product, left at room temperature for 1 hour, and then visually evaluated for appearance.
The sample having no change was marked with "O", and the sample with change such as depression was marked with "X".

(Flatness of expanded particles)
The minor axis and major axis of 100 arbitrary expanded particles were measured, and the average value was calculated by the following equation.
Flatness = average minor axis of expanded particles / average major axis of expanded particles Each of the examples and comparative examples was evaluated by the above method.

<Example 2>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of 1,4-cis structure is 93%, the rubber content is 12% by mass, the average particle diameter of the rubber particles is 3 μm, the graft ratio of styrene is 144%, and the gel swells. Except for using a rubber-modified polystyrene resin having a degree of 15, a foamed particle and a foamed molded product were obtained in the same manner as in Example 1.

The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 219 μm, a flatness of 0.72, a high cis structure with a 1,4 cis structure ratio of 93%, and a rubber content. The ratio was 12% by mass, the graft ratio of styrene was 144%, and the gel swelling degree was 15.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor 50 times), an average cell diameter of 250 μm, a high cis structure having a 1,4 cis structure ratio of 93%, a rubber content of 12% by mass, and styrene graft. Rate of 144% and gel swelling of 15.

<Example 3>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of the 1,4-cis structure is 93%, the rubber content is 12% by mass, the average particle diameter of the rubber particles is 7 μm, the graft ratio of styrene is 155%, and the gel swells. Except for using a rubber-modified polystyrene resin having a degree of 16, a foamed particle and a foamed molded product were obtained in the same manner as in Example 1.

The obtained expanded particles have a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 215 μm, a flatness of 0.71, a high cis structure with a 1,4 cis structure ratio of 93%, and a rubber content. The ratio was 12% by mass, the graft ratio of styrene was 155%, and the degree of gel swelling was 16.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor: 50 times), an average cell diameter of 245 μm, a high cis structure having a 1,4 cis structure ratio of 93%, a rubber content of 12% by mass, and styrene graft. The ratio was 155%, and the gel swelling degree was 16.

<Example 4>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of the 1,4-cis structure is 93%, the rubber content is 12% by mass, the average particle diameter of the rubber particles is 7 μm, the graft ratio of styrene is 155%, and the gel swells. Except for using a rubber-modified polystyrene resin having a degree of 16 and using 1.0 part by mass of Polyslen ES405, foamed particles and a foamed molded product were obtained in the same manner as in Example 1.

The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 114 μm, a flatness of 0.78, a high cis structure with a 1,4 cis structure ratio of 93%, and a rubber content. The ratio was 12% by mass, the graft ratio of styrene was 155%, and the degree of gel swelling was 16.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor: 50 times), an average cell diameter of 130 μm, a high cis structure having a 1,4 cis structure ratio of 93%, a rubber content of 12% by mass, and styrene graft. The ratio was 155%, and the gel swelling degree was 16.
The average bubble diameter obtained was as small as 130 μm.

<Comparative Example 1>
As the base resin, the diene rubber particles have a low cis structure in which the ratio of 1,4-cis structure is 60%, the rubber content is 6% by mass, the average particle diameter of the rubber particles is 0.1 μm, the graft ratio of styrene is 120%, Except for using a rubber-modified polystyrene resin having a gel swelling degree of 15, foamed particles and foamed molded articles were obtained in the same manner as in Example 1.

The foamed particles obtained had a bulk density of 0.020 g / cm ³ (bulk foaming multiple of 50 times), an average cell diameter of 79 μm, a flatness of 0.54, a low cis structure with a 1,4 cis structure ratio of 60%, and a rubber content. The ratio was 6% by mass, the graft ratio of styrene was 120%, and the gel swelling degree was 15.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor: 50 times), an average cell diameter of 90 μm, a low cis structure having a ratio of 1,4 cis structure of 60%, a rubber content of 6% by mass, and a graft of styrene. The ratio was 120% and the gel swelling degree was 15.
The resulting foam had a small average cell diameter, a 50% breaking height, and poor solvent resistance.

<Comparative Example 2>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of 1,4-cis structure is 85%, the rubber content is 10% by mass, the average particle diameter of the rubber particles is 3 μm, the graft ratio of styrene is 133%, and the gel swells. Except that a rubber-modified polystyrene resin having a degree of 9 was used, foamed particles and foamed molded articles were obtained in the same manner as in Example 1.

The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 82 μm, a flatness of 0.85, a high cis structure with a 1,4 cis structure ratio of 85%, and a rubber content. 10% by mass, the graft ratio of styrene was 133%, and the gel swelling degree was 9.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor: 50 times), an average cell diameter of 94 μm, a high cis structure having a ratio of 1,4 cis structure of 85%, a rubber content of 10% by mass, and styrene graft. Rate 133% and gel swelling degree 9
The resulting foam had a small average cell diameter, a 50% breaking height, and poor solvent resistance.

<Comparative Example 3>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of 1,4-cis structure is 80%, the rubber content is 10% by mass, the average particle diameter of the rubber particles is 1 μm, the graft ratio of styrene is 167%, and the gel swells. Except for using a rubber-modified polystyrene resin having a degree of 12, a foamed particle and a foamed molded product were obtained in the same manner as in Example 1.

The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 75 μm, a flatness of 0.56, a high cis structure with a 1,4 cis structure ratio of 80%, and a rubber content. The ratio was 10% by mass, the graft ratio of styrene was 167%, and the gel swelling degree was 12.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor: 50 times), an average cell diameter of 85 μm, a high cis structure having a 1,4 cis structure ratio of 80%, a rubber content of 10% by mass, and styrene graft. Rate was 167% and gel swelling degree was 12.
The obtained foam had a small average cell diameter, and was inferior in the fusion rate, the 50% breaking height, and the solvent resistance.

<Comparative Example 4>
As the base resin, the diene rubber particles have a high cis structure in which the ratio of 1,4-cis structure is 93%, the rubber content is 12% by mass, the average particle diameter of the rubber particles is 3 μm, the graft ratio of styrene is 144%, and the gel swells. A foamed particle and a foamed molded product were obtained in the same manner as in Example 1 except that a rubber-modified polystyrene resin having a degree of 15 was used, and polystyrene ES405 was not used.

The obtained expanded particles had a bulk density of 0.020 g / cm ³ (bulk expansion multiple of 50 times), an average cell diameter of 307 μm, a flatness of 0.53, a high cis structure with a 1,4 cis structure ratio of 93%, and a rubber content. The ratio was 12% by mass, the graft ratio of styrene was 144%, and the gel swelling degree was 15.

The obtained foamed molded article had a density of 0.020 g / cm ³ (expansion factor 50 times), an average cell diameter of 350 μm, a high cis structure having a 1,4 cis structure ratio of 93%, a rubber content of 12% by mass, and styrene graft. Rate of 144% and gel swelling of 15.
The obtained foam had a large average cell diameter of 350 μm and was inferior to a 50% breaking height.

<Result>
The evaluation results of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in the following table.

Claims (9)

A continuous phase containing a polystyrene resin, and foamed particles of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
Look including a bubble average diameter of 100~300μm,
A foamed particle of a rubber-modified polystyrene resin, wherein the gel swelling degree of the diene polymer rubber is 13 to 20 . Flatness is 0.6 to 0.8, foamed particles of the rubber-modified polystyrene-based resin according to claim 1. A bag,
A cushion body comprising: the foamed particles of the rubber-modified polystyrene-based resin according to claim 1 or 2 filled in the bag body. A continuous phase containing a polystyrene resin, a foamed molded article of a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
Look including a bubble average diameter of 100~300μm,
A foam molded article of a rubber-modified polystyrene resin, wherein the diene-based polymer rubber has a gel swelling degree of 13 to 20 . The foamed molded article of the rubber-modified polystyrene resin according to claim 4 , which is in the form of a transport container. A continuous phase containing a polystyrene resin, a rubber-modified polystyrene resin containing a diene polymer rubber dispersed in the continuous phase,
And a foaming agent, foamable particles of a rubber-modified polystyrene resin,
The diene polymer rubber contains 70% or more of 1,4 cis structure,
The content of the diene polymer rubber in the rubber-modified polystyrene resin is 9 to 15% by mass,
A polystyrene resin is graft-bonded to the diene polymer rubber, and a graft ratio is 137 to 160%.
The diene polymer rubber forms particles having an average particle diameter of 2 to 8 μm ,
Expandable particles of a rubber-modified polystyrene resin, wherein the diene-based polymer rubber has a gel swelling degree of 13 to 20 . A method for producing expandable particles of a rubber-modified polystyrene resin according to claim 6 ,
In an extruder, kneading the melted rubber-modified polystyrene resin and the blowing agent to form a resin foaming agent mixed melt, a mixing and melting step,
Extruding said resin foaming agent mixed melt from said extruder into a cooling liquid and cooling. A method for producing expanded particles of a rubber-modified polystyrene resin, comprising a foaming step of expanding the expandable particles of the rubber-modified polystyrene resin according to claim 6 . A foaming step of foaming foamable particles of the rubber-modified polystyrene resin according to claim 6 ,
And forming the foamed particles of the rubber-modified polystyrene resin obtained in the foaming step in a mold.

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