JP2010084098A - Styrene-based resin prefoamed particle and method for manufacturing the same, and styrene-based resin foam molded article composed of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide styrene-based resin prefoamed particles which provide a foam molded article with light weight and with transparency on the surface. <P>SOLUTION: In the styrene-based resin prefoamed particles, the average air bubble diameter is 400 to 1,500 μm, and the number of small air bubbles existing in the surface layer is 0 to 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a styrene resin pre-expanded particle from which a foamed molded article having a light weight and a transparent surface can be obtained.

  Conventionally, foam molded articles have been widely used as building materials, distribution materials, automobile materials, etc. utilizing food packaging materials such as various trays and containers, heat insulation properties, buffering properties, etc. by taking advantage of lightness. Among them, styrene resin foam moldings are widely used because they are lightweight, have good heat insulating properties, buffer properties, water resistance, and are inexpensive. In addition to these requirements, the surface aesthetics of the styrene resin foam molded article are strongly demanded, and among them, a styrene resin foam molded article having a transparent feeling on the surface is particularly demanded. For this reason, various studies have been made on styrene resin foam molded products having a transparent surface.

  For example, Patent Document 1 discloses that an organic-inorganic composite foam composed of pre-expanded particles obtained by pre-expanding organic-inorganic composite particles composed of a styrene monomer and an organosilicon compound has excellent transparency. It is disclosed. However, since the technique disclosed in Patent Document 1 requires polymerization of styrene and polycondensation of organosilicic acid and the reaction is complicated, a simpler method is required.

  In addition, as a prior art referring to the cell structure of the styrene resin expanded particle, Patent Document 2 has 2 to 35 large cells having a diameter of 100 μm or more in the particle, and the particle size is 0.5 to 20 mm. And the thermoplastic resin pre-expanded particle | grains whose film thickness of a particle | grain outer skin is 5-100 micrometers are disclosed.

  Furthermore, in Patent Document 3, the average cell diameter is different between the surface layer portion and the center portion of the expanded particles obtained by foaming to 40 times the bulk ratio, the average cell diameter of the surface layer portion is 25 μm or less, A styrene-based resin foam having a thickness of 75 μm or less, an average cell diameter in the range from 80 μm to 800 μm, and a foam group in which bubbles having an average cell diameter in the range of 30 μm to 70 μm are present in the expanded particles. Particles are disclosed.

  Patent Document 4 is obtained by suspension polymerization of an aromatic vinyl unit and a vinyl cyanide unit in the presence of a copolymer comprising an aromatic vinyl unit, an unsaturated dicarboxylic anhydride unit, and an N-alkyl-substituted maleimide unit. A method using spherical resin particles made of a thermoplastic resin composition is disclosed. However, Patent Document 4 discloses a heat-resistant foamed molded article.

Patent Documents 5 and 6 disclose a foamable resin composition in which a maleimide polymer and an acrylonitrile / styrene copolymer are mixed and a foaming agent is added, but injection foam molding and extrusion foam molding are disclosed. The technical field is different from the present application relating to a thermoplastic resin foam molded article obtained by in-mold foam molding of thermoplastic resin pre-expanded particles.
JP 2004-256653 A JP-A-2-107646 JP 2007-262345 A Japanese Patent Laid-Open No. 4-345639 JP-A-60-184546 JP-A-62-235340

  An object of the present invention is to provide pre-expanded styrenic resin particles that can provide a foamed molded article that is lightweight and has a transparent surface.

  As a result of intensive studies, the present inventors have found that the average cell diameter of the styrene resin pre-expanded particles is relatively large and that there are few small bubbles in the surface layer of the pre-expanded particles. As a result, it was found that a foamed molded article having a transparent surface and a beautiful surface could be obtained, and the present invention was completed.

  That is, the first of the present invention relates to styrene resin pre-expanded particles having an average cell diameter of 400 μm or more and 1500 μm or less and 0 to 5 small bubbles present in the surface layer portion.

  In the second aspect of the present invention, a styrene resin, a foaming agent, and 0 to 0.05 parts by weight of a nucleating agent with respect to 100 parts by weight of the styrene resin are melt-kneaded together using an extruder and cooled. The styrenic resin as described above, wherein the extruded foam obtained by performing extrusion foaming from a nozzle of a die through the process or by completing foaming is cut with a rotary cutter before or after foaming is completed. The third aspect of the present invention relates to a method for producing pre-expanded particles, and relates to a styrene-based resin foam-molded product obtained by molding the above-mentioned styrene-based resin pre-expanded particles in a mold.

  Since the styrene resin pre-expanded particles of the present invention have a large average cell diameter and almost no small bubbles in the surface layer of the pre-expanded particles, the styrene resin has a light and transparent surface when subjected to in-mold foam molding. A foamed molded article can be provided.

  The styrene resin pre-expanded particles of the present invention have an average cell diameter of 400 μm to 1500 μm, preferably 400 μm to 1400 μm. In addition, the number of small bubbles present in the surface layer portion of the styrene-based resin pre-expanded particles is 0 or more and 5 or less, preferably 4 or less, and it is most preferable that no small bubbles exist in the surface layer portion. preferable.

  In the present invention, the average cell diameter of the styrene resin pre-expanded particles is obtained by photographing the cell structure with an optical microscope, calculating the length per cell in accordance with ASTM: D3576-94, and multiplying by 1.5. Was the average cell diameter.

  The surface layer part of the styrene resin pre-expanded particles corresponds to ¼ of the radius from the outermost surface to the center when cut so as to pass through the central part of the pre-expanded particles. It is a part to do. The small bubbles referred to in the present invention are cut so as to pass through the center of the pre-expanded particles, and when the bubble structure is observed with an optical microscope or an electron microscope, a straight line from the outermost surface to the center is drawn and the line is drawn. It is a bubble having an average bubble diameter of 200 μm or less that exists in a portion corresponding to ¼ of the radius from the top surface to the center.

  A styrene resin foam molded article obtained by in-mold foam molding using styrene resin pre-expanded particles as described above becomes a foam molded article that is lightweight and transparent on the surface.

  The styrene resin of the present invention refers to a polymer containing aromatic vinyl as a monomer. Examples of the aromatic vinyl include styrene, α-methyl styrene, ethyl styrene, isopropyl styrene, dimethyl styrene, bromo styrene, chloro styrene, vinyl toluene, and vinyl xylene. Of these, from the viewpoint of ease of polymerization, it is preferable to use styrene or α-methylstyrene as the aromatic vinyl, and it is preferable to use styrene which is inexpensive in price.

  These aromatic vinyl single polymers, copolymers and copolymer blends may also be used. Examples of the single polymer include polystyrene, recycled polystyrene, α-methyl polystyrene, ethyl polystyrene, isopropyl polystyrene, dimethyl polystyrene, bromopolystyrene, chloropolystyrene, and the like. Of these, styrene and recycled styrene are particularly preferred from the viewpoint of ease of polymerization and environmental problems. Recycled polystyrene is a recycled product obtained by partially or completely dissolving a recovered product such as a styrene-based resin foam molded product such as a food tray, fish box, or home appliance packaging in a solvent such as limonene and then removing the solvent. Examples thereof include recycled polystyrene obtained by melting and kneading polystyrene or a pulverized product of the styrenic resin foam molding in an extruder.

  As the copolymer, vinyl monomers other than aromatic vinyl may be copolymerized. Examples of vinyl monomers copolymerizable with aromatic vinyl include vinyl cyanide, unsaturated dicarboxylic anhydride, N-alkyl substituted maleimide, vinyl halide, and alkyl methacrylate. Among these, a copolymer composed of vinyl cyanide, unsaturated dicarboxylic acid anhydride, and N-alkyl-substituted maleimide is preferable.

  Examples of vinyl cyanide include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and the like. Among them, acrylonitrile is preferably used.

  Examples of the unsaturated dicarboxylic acid anhydride include maleic anhydride, itaconic anhydride, citraconic anhydride, and the like. Of these, maleic anhydride is preferably used from the viewpoint of aromatic vinyl units, ease of polymerization, and low cost.

  Examples of the N-alkyl-substituted maleimide include N-methylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-4-diphenylmaleimide, N-2-chlorophenylmaleimide, N-4-bromophenyl Maleimide, N-1-naphthylmaleimide and the like can be mentioned. Among these, N-phenylmaleimide is preferably used from the viewpoint of ease of polymerization and low cost.

  As the copolymer blend, it is sufficient that two or more copolymers are compatible, and in particular, a copolymer composed of aromatic vinyl-unsaturated dicarboxylic acid-N-alkyl-substituted maleimide (hereinafter sometimes referred to as copolymer A). And a copolymer of aromatic vinyl-vinyl cyanide (hereinafter sometimes referred to as copolymer B) are preferable from the viewpoint of compatibility. The blending amount of copolymer A composed of aromatic vinyl, unsaturated dicarboxylic anhydride, N-alkyl-substituted maleimide and copolymer B composed of aromatic vinyl and vinyl cyanide in the styrene resin is styrene resin 100. In the parts by weight, the copolymer composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide is preferably 30 parts by weight or more and 80 parts by weight or less, more preferably 35 parts by weight or more and 75 parts by weight. Or less, more preferably 40 parts by weight or more and 70 parts by weight or less. The copolymer B composed of aromatic vinyl and vinyl cyanide is preferably 20 to 70 parts by weight, more preferably 25 to 65 parts by weight, in 100 parts by weight of the styrenic resin. More preferably, it is 30 parts by weight or more and 60 parts by weight or less. If it is the said compounding quantity, the styrene-type resin foaming molding which is lightweight and has a transparent feeling on the surface can be obtained easily.

  As long as the characteristics are not impaired, the styrene resin may contain a thermoplastic resin other than the styrene resin. Examples of the thermoplastic resin that can be mixed include polyethylene terephthalate resin, polycarbonate resin, polyether ether ketone resin, and phenylene ether resin.

  In the present invention, a nucleating agent can be further added to the styrene resin. Examples of the nucleating agent include talc, alumina, silica, polyethylene wax, polypropylene wax, ethylene bisstearylamide, and one or more of these can be used. Moreover, various additives can be used as needed. The addition amount of the nucleating agent is preferably 0 part by weight or more and 0.05 part by weight or less with respect to 100 parts by weight of the styrene resin.

  In this invention, a well-known method is employable as a method of adding a nucleating agent and an additive in a styrene resin. Generally, when a styrene resin is melt-kneaded with an extruder, a method of adding a nucleating agent or an additive and melt-kneading with the styrene resin can be mentioned.

  Examples of the method for making the styrene resin in the present invention into pre-expanded styrene resin particles include, for example, (1) styrenic resin is made into styrene resin particles with a pelletizer and the like, impregnated with a foaming agent, and expanded styrene. (2) Melting and kneading together styrene resin, foaming agent and nucleating agent using an extruder. Then, the extruded foam obtained before or after completion of foaming, which is obtained by extrusion foaming from the nozzle of the die through a cooling process or after completion of foaming, is cut with a rotary cutter to obtain pre-expanded styrene resin particles. Method, (3) The foamable styrene obtained by impregnating and impregnating a foaming agent during melt kneading with an extruder and impregnating the styrenic resin, cutting it into a certain size with a pelletizer or the like without foaming Method by heating the system resin particles and styrene resin pre-expanded particles of any bulk magnification, and the like.

  Specifically, the method (1) can be performed as follows. Styrenic resin melted and kneaded in an extruder is extruded into air through a die having a hole with a fixed diameter, cooled, and then cooled to a fixed size with a pelletizer. Or after extruding into water through a die, the styrenic resin particles are once produced by cutting the styrenic resin into a certain size with a pelletizer or the like. The size of the obtained styrene resin particles is preferably 0.5 mg or more and 1.5 mg or less, and more preferably 0.8 mg or more and 1.2 mg or less. If the styrene resin particles have a size within the above range, when the expandable styrene resin particles are pre-expanded, they tend to be pre-expanded styrene resin particles having excellent fusing property and surface appearance of the foam molded article. is there. The styrene resin particles thus obtained are dispersed in an aqueous solvent to which a dispersant is added, a foaming agent is added, and preferably heated at a temperature of 100 ° C. or higher and 130 ° C. or lower and heated for 6 hours or longer and 24 hours or shorter. By stirring, the foaming styrene resin particles impregnated with 100 parts by weight of styrene resin particles, preferably 2 parts by weight or more and 15 parts by weight or less, are taken out, washed with water, and dried. And a method of heating the expandable styrene resin particles to obtain pre-expanded styrene resin particles.

  In this case, the amount of the foaming agent used at the time of stirring is preferably 2 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the styrene resin particles, although it varies depending on the capacity of the container to be used. Within this range, the amount of foaming agent in the obtained expandable styrene resin particles tends to be easily 2 parts by weight or more and 15 parts by weight or less per 100 parts by weight of the styrene resin particles.

  The dispersant may be a known dispersant, for example, a water-soluble polymer compound such as polyvinyl alcohol, polyvinyl pyrrolidone, or methyl cellulose, or a water-insoluble or hardly soluble inorganic compound such as calcium phosphate, magnesium pyrophosphate, magnesium carbonate, or kaolin. Is used. The concentration of the dispersant in the aqueous solvent is preferably in the range of 0.1 to 0.5% by weight. Moreover, a water-soluble surfactant can be used as needed, and the concentration is preferably 0.001 to 0.01% by weight in an aqueous solvent. As the heating means, for example, water vapor, hot air or the like can be used. When the softening point of the expandable styrene resin particles is high, pre-expansion can be performed by using pressurized steam or superheated steam. The pre-foaming conditions vary depending on the softening point temperature of the expandable styrene-based resin particles, but are preferably a temperature of 80 ° C. or higher and 200 ° C. or lower and a time of 10 seconds or longer and 300 seconds or shorter. Furthermore, after pre-expanding the styrene resin pre-expanded particles obtained by pre-expanding the expandable styrene resin particles to a volume ratio lower than the target bulk magnification, the styrene resin pre-expanded particles are treated in high-temperature and high-pressure air for a certain period of time, and then discharged under atmospheric pressure Styrenic resin pre-expanded particles having a target bulk magnification can be obtained. The bulk magnification is the volume obtained by measuring the weight of expandable styrene resin particles and dividing by the density of the base resin, and the styrene resin pre-expanded particles obtained by pre-expanding the expandable styrene resin particles Is a value obtained by dividing the volume when the measuring cylinder is filled.

  Specifically, the method (2) can be performed as follows. While melt-kneading a styrene resin with an extruder, the foaming agent is injected under high-pressure conditions and melt-kneaded, then extruded and foamed into a low-pressure region through a die, and cut and cooled by a cutter immediately after foaming. It can be set as the styrene-type resin pre-expanded particle of a bulk magnification.

  Alternatively, a styrene resin is dispersed in an aqueous solvent to which a dispersant is added, a foaming agent is added, and 100 parts by weight of the styrene resin is impregnated with the foaming agent, preferably 2 parts by weight or more and 15 parts by weight or less. After obtaining foamable styrenic resin by taking out, washing and drying, it is put into an extruder, melt kneaded, extruded into a low pressure region through a die, foamed, cut by a cutter immediately after foaming and cooled Styrenic resin pre-expanded particles having an arbitrary bulk magnification can be obtained. In this case, the temperature of the extruder varies depending on the softening point temperature of the resin used, but is preferably 100 ° C. or higher and 250 ° C. or lower.

  The amount of the foaming agent to be press-fitted is preferably 1 part by weight or more and 40 parts by weight or less, more preferably 2 parts by weight or more and 30 parts by weight or less, with respect to 100 parts by weight of the styrene resin. Part or less is more preferable. If the amount of the foaming agent is within this range, the foamability is good.

  Examples of the blowing agent in the present invention include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, and cyclopentane; air, nitrogen, oxygen, carbon dioxide, argon, helium, and the like Inorganic gas; water and the like. Moreover, these can be used in combination of 2 or more types as a foaming agent.

  The styrene resin pre-expanded particles of the present invention are obtained as described above. The obtained pre-expanded styrenic resin particles can be subjected to in-mold foam molding by a general method to obtain a styrene resin foam molded article. For example, styrene resin pre-expanded particles are filled in a mold and steam is blown into the mold to heat the styrene resin pre-expanded particles. When the styrene resin pre-expanded particles are heated by the steam, the styrene resin pre-expanded particles expand, but the volume in the mold remains unchanged, so the styrene resin pre-expanded particles adhere to each other and fuse together. Then, the desired styrenic resin foam molded article is obtained by cooling, taking out, and drying with water or the like. The styrene resin foam molded article thus obtained is a foam molded article having excellent energy absorption performance.

  Hereinafter, although the specific example of the styrene-type resin foam molding of this invention is demonstrated in detail, this invention is not limited only to this Example. Unless otherwise specified, “part” and “%” are based on weight.

<Transparency evaluation of styrene resin foam molding>
The appearance of the foamed molded product was visually evaluated.
◎: Transparency is sufficient ○: Transparency ×: No transparency

Example 1
As a general-purpose polystyrene resin, PS Japan Co., Ltd., trade name: GPPS G9401 is added to a 100 L pressure vessel with a stirrer, 100 parts by weight of resin, 200 parts by weight of pure water, 0.3 parts of calcium phosphate, α-olefin sulfonic acid After adding 0.006 part of sodium and 1 part of sodium chloride and raising the temperature to 120 ° C., 8 parts of n-pentane was added as a foaming agent, and the foaming agent was impregnated by heating and stirring for 3 hours. Then, after cooling to 40 degreeC, it took out, wash | cleaned, and dried and obtained foamable styrene resin. Next, this foamable styrene resin is put into a single-screw extruder having a diameter of 40 mm, heated and melted at a temperature of 160 ° C., extruded and foamed into the atmosphere through a die, cut with a rotary cutter, and a bulk magnification of 7 times. Styrenic resin pre-expanded particles were obtained. After curing the obtained styrene resin pre-expanded resin particles for 24 hours, the styrene resin preliminary foam was put into a 300 mm long × 400 mm wide × 40 mm thick mold using a KD-345 molding machine manufactured by Daisen Industry Co., Ltd. Filled with foamed resin particles, and steam was blown into the mold to obtain a flat styrene resin foam molded article. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

(Example 2)
0.02 part of Talcan powder manufactured by Hayashi Kasei Co., Ltd. was added to 100 parts by weight of the expandable styrenic resin obtained in Example 1, mixed well, and then charged into a single screw extruder having a diameter of 40 mm. It was melted by heating at a temperature of 0 ° C., extruded and foamed into the atmosphere through a die, and cut using a rotary cutter to obtain styrene resin pre-expanded particles having a bulk magnification of 15 times. After curing the obtained styrene resin pre-expanded resin particles for 24 hours, the styrene resin preliminary foam was put into a 300 mm long × 400 mm wide × 40 mm thick mold using a KD-345 molding machine manufactured by Daisen Industry Co., Ltd. Filled with foamed resin particles, and steam was blown into the mold to obtain a flat styrene resin foam molded article. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

(Example 3)
A resin having a composition of 100% by weight of recycled polystyrene is used as a base resin, and a styrene resin containing 4% of pentane as a foaming agent is put into a single screw extruder having a diameter of 40 mm, heated and melted at a temperature of 160 ° C., Extruded and foamed into the atmosphere through a die and cut using a rotary cutter to obtain styrene resin pre-expanded particles having a bulk magnification of 10 times. After curing the obtained styrene resin pre-expanded resin particles for 24 hours, the styrene resin preliminary foam was put into a 300 mm long × 400 mm wide × 40 mm thick mold using a KD-345 molding machine manufactured by Daisen Industry Co., Ltd. Filled with foamed resin particles, and steam was blown into the mold to obtain a flat styrene resin foam molded article. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

Example 4
Copolymer A, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: DENKA IP (grade name: MS-NA, N-phenylmaleimide / styrene / maleic anhydride monomer ratio of 50/49/1, respectively) Toyo Styrene Co., Ltd., trade name: Toyo AS (grade name: AS-XGS, acrylonitrile / styrene monomer ratio of 25/75 each) mixed at a ratio of 30/70 as a blender B as a blend B In a 100 L pressure vessel with 100 parts by weight of resin, 150 parts by weight of pure water, 0.3 part of calcium phosphate, 0.006 part of sodium α-olefin sulfonate and 1 part of sodium chloride were added, and the temperature was raised to 120 ° C. 7 parts of n-pentane was added as a foaming agent, and the foaming agent was impregnated by heating and stirring for 9.5 hours. Then, after cooling to 40 degreeC, it took out, wash | cleaned, and dried and obtained foamable styrene resin. Next, this expandable styrene resin is put into a single screw extruder having a diameter of 40 mm, heated and melted at a temperature of 200 ° C., extruded and foamed into the atmosphere through a die, cut with a rotary cutter, and bulk ratio of 20 times. Styrenic resin pre-expanded particles were obtained. After the obtained styrene-based pre-expanded resin particles were cured for 24 hours, the styrene-based pre-expanded resin particles were molded into a 300 mm long × 400 mm wide × 40 mm thick mold using a KD-345 molding machine manufactured by Daisen Kogyo Co., Ltd. The particles were filled and steam was blown into the mold to obtain a flat styrene-based resin foam molding. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

(Comparative Example 1)
After adding 0.1 parts of Hayashi Kasei Co., Ltd. Talcan powder to 100 parts by weight of the expandable styrenic resin obtained in Example 1, and thoroughly mixing it, it was put into a single screw extruder having a diameter of 40 mm. It was melted by heating at a temperature of 0 ° C., extruded and foamed into the atmosphere through a die, and cut using a rotary cutter to obtain styrene resin pre-expanded particles having a bulk magnification of 15 times. The obtained styrene resin pre-expanded particles were cured for 24 hours, and then styrene-based resin pre-expanded into a mold having a length of 300 mm, a width of 400 mm, and a thickness of 40 mm using a KD-345 molding machine manufactured by Daisen Industry Co., Ltd. The particles were filled and steam was blown into the mold to obtain a flat styrene-based resin foam molding. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

(Comparative Example 2)
A resin having a composition of 100% by weight of polystyrene is used as a base resin, and pre-expanded particles of styrene resin having a bulk magnification of 20 times containing 5% of industrial butane (normal / iso = 70/30) as a blowing agent are used. A flat styrene resin foam molded article having a length of 450 × width of 300 × thickness of 40 mm was obtained using a KR-57BMC molding machine manufactured by Kogyo Co., Ltd. The obtained styrenic resin foam molded article was dried at 50 ° C. for 24 hours. Table 1 shows the average cell diameter and the transparency evaluation results of the styrene resin foam molded article obtained.

(Comparative Example 3)
A resin having a composition of 100 parts by weight of the styrene resin described in Example 4 was used as a base resin, and styrene resin pre-expanded particles having a bulk ratio of 25 times containing 4% of n-butane / pentane as a foaming agent were used. A flat styrene-based resin foam molded body having a length of 300, a width of 400, and a thickness of 40 mm was obtained using a KD-345 molding machine manufactured by Kogyo Co., Ltd. The obtained styrenic resin foam molded article was dried at 70 ° C. for 24 hours. Table 1 shows the average cell diameter and transparency evaluation results of the foamed molded products obtained.

  Styrenic resin foam molded article, wherein the styrene resin pre-foamed particles forming the styrenic resin foam molded article have an average cell diameter of 400 μm or more and 1500 μm or less, and there are small bubbles in the surface layer of the pre-foamed particles It can be seen that the styrene-based resin foam molded article that is not used is a foam molded article having a transparent feeling.

2 is a cross-sectional photograph of styrene resin pre-expanded particles of Example 1. FIG. 3 is a cross-sectional photograph of styrene resin pre-expanded particles of Example 2. FIG. 4 is a cross-sectional photograph of styrene resin pre-expanded particles of Comparative Example 2.

Claims (3)

  Styrenic resin pre-expanded particles having an average cell diameter of 400 μm or more and 1500 μm or less, and 0 or more and 5 or less small cells present in the surface layer portion.   A styrene resin, a foaming agent, and a nucleating agent of 0 to 0.05 part by weight with respect to 100 parts by weight of the styrenic resin are melted and kneaded together using an extruder, and from a die nozzle through a cooling step. 2. The production of pre-expanded styrenic resin particles according to claim 1, wherein the extruded foam obtained by completion of foaming or after completion of foaming is cut with a rotary cutter before or after completion of foaming. Method.   A styrene resin foam molded article obtained by molding the styrene resin prefoamed particles according to claim 1 in a mold.