Expandable polystyrene resin particles, pre-expanded particles thereof, expanded molded article, and method for producing expandable polystyrene resin particles

Abstract

To provide a foamable polystyrene resin particle that can suppress damage to a compact surface while satisfying moldabilities under a wide range of molding conditions in a molding process, and is suitable for stable production.SOLUTION: The foamable polystyrene resin particle includes: a base resin that contains a styrene unit, or a styrene unit and a butyl acrylate unit; and a foaming agent, as constituent units. A surface of 100 pts.wt. of a body of the foamable polystyrene resin particle is coated with 0.015 pts.wt. or more and 0.035 pts.wt. or less of a polyoxyethylene alkyl ester type of nonionic surfactant of which the HLB value is 8-15, and the solidification point is 0°C or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to expandable polystyrene resin particles, pre-expanded polystyrene resin particles, foamed molded articles, and a method for producing expandable polystyrene resin particles. [Background technology]

[0002] Expandable polystyrene resin particles are a socially useful material because they are relatively inexpensive, can be expanded using steam or other methods without the need for special methods, and provide high cushioning and heat insulation effects.

[0003] Expandable polystyrene-based resin particles are produced, for example, by a method of impregnating polystyrene resin particles with a blowing agent (i.e., a volatile aliphatic hydrocarbon, such as butane or pentane, that only slightly swells the particles) in an aqueous suspension. The expandable polystyrene-based resin particles produced in this manner are used as a raw material for producing polystyrene-based resin foamed molded articles.

[0004] A common method for industrially and economically producing polystyrene-based resin molded articles of a desired shape is to (1) convert expandable polystyrene-based resin particles into pre-expanded particles using a heating medium such as steam, (2) fill the pre-expanded particles into a closed mold of the desired shape with a large number of small holes in its wall, (3) introduce a heating medium such as steam through the small holes in the mold to heat the pre-expanded particles to a temperature above their softening point, thereby fusing the pre-expanded particles to form a molded article, and (4) cool the mold and then remove it from the mold. Expanded polystyrene-based resin molded articles, especially in-mold foam molded articles, have advantages such as ease of producing molded articles of a desired shape, and are therefore used as packaging materials (trays) for food containers and the like, and transport packaging materials for fish boxes and the like because they are lightweight and have excellent thermal insulation properties.

[0005] When producing foamed polystyrene resin articles using the above method, a large amount of steam is required to turn the expandable polystyrene resin particles into foamed articles. However, in recent years, in response to the increasing demand for greater energy conservation, resins that can be foamed and molded with less steam have been developed. In many cases, the above problem is solved by lowering the softening point of the resin, making it possible to foam and mold at a lower temperature.

[0006] For example, Patent Document 1 discloses that low-temperature molding is possible by adding butyl acrylate, a plasticizer, and a foaming aid. However, while this enables low-temperature molding, the softened resin tends to clog the small holes in the mold during molding. This clogged resin impedes steam flow, resulting in reduced steam-saving properties and scratches on the foamed product during demolding. Furthermore, there is a problem of the tendency for aggregation (blocking) to occur during pre-expansion, which can lead to reduced productivity. Patent Document 2 describes a method for suppressing blocking and resin clogging in the mold by combining a nonionic surfactant, a methylphenylpolysiloxane with a refractive index of 1.41 to 1.44, a fatty acid metal salt, and a fusion accelerator. However, methylphenylpolysiloxane with a refractive index of 1.41 to 1.44 is prone to generating static electricity, which can cause problems with the foamed particles' ability to fill the mold and adhesion to silo walls. Patent Document 3 describes a method for improving steam-saving properties and surface appearance during molding by treating expandable styrene resin particles with a nonionic surfactant. However, the polyoxyethylene alkyl ether used in the examples and comparative examples has a melting point higher than 0°C, and is therefore often solid when used, which makes it difficult to treat the resin surface uniformly, resulting in unstable quality during production. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-203042 [Patent Document 2] Japanese Patent Application Publication No. 2019-65074 [Patent Document 3] Japanese Patent Publication No. 2020-152843 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of one aspect of the present invention is to provide expandable polystyrene resin particles, polystyrene pre-expanded particles, and expanded molded articles that are suitable for stable production while maintaining moldability over a wide range of molding conditions during molding, and that can suppress scratches on the surface of the molded article. [Means for solving the problem]

[0009] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by applying a nonionic surfactant having an ester bond with an HLB value of 8 to 15 and a freezing point of 0°C or lower to the surface of expandable styrene-based resin particles.

[0010] That is, one embodiment of the present invention includes the following configuration. [1] The expandable polystyrene-based resin particles include a base resin containing a styrene unit or a styrene unit and a butyl acrylate unit as a constituent unit, and a blowing agent, The base resin contains, as constituent units, 97 to 100 parts by weight of the styrene unit and 0 to 3 parts by weight of the butyl acrylate unit (provided that the total of the styrene unit and the butyl acrylate unit is 100 parts by weight), and the expandable polystyrene-based resin particles have 100 parts by weight of the expandable polystyrene-based resin particle body coated on the surface with 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or lower. [2] The expandable polystyrene-based resin particles of [1] are further coated on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body with 0.01 to 0.20 parts by weight of a metal stearate and 0.005 to 0.013 parts by weight of a cationic surfactant. [3] The expandable polystyrene-based resin particles of [2] are further coated on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body with 0.01 to 0.10 parts by weight of methylphenylpolysiloxane having a refractive index of 1.47 or more. [4] Polystyrene-based resin particles according to [1] to [3], containing, relative to 100 parts by weight of the base resin, 3.0 parts by weight or more but less than 8.0 parts by weight of the foaming agent, 1.5 parts by weight or more but less than 2.5 parts by weight of an aliphatic hydrocarbon having a boiling point of 60°C or more but less than 100°C as a foaming aid, and 0 part by weight or more but less than 1.0 part by weight of a plasticizer having a boiling point of 100°C or more. [5] Pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles of [1] to [4] [6] [5] A foamed molded article obtained by molding the polystyrene resin pre-expanded particles. [7] a first step of impregnating a foaming agent in an aqueous medium and dehydrating the resulting particles to obtain expandable polystyrene-based resin particle bodies; a second step of applying 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or lower to the surface of 100 parts by weight of the expandable polystyrene-based resin particle bodies, followed by heating; a third step of sieving the obtained expandable polystyrene-based resin particles; A method for producing expandable polystyrene-based resin particles, comprising: [8] [7] The manufacturing method according to [7], wherein the second step is heating at a temperature of 45°C or higher and 65°C or lower. [9] The manufacturing method according to [7] or [8], wherein the nonionic surfactant is dispersed in water at a concentration of 1% by weight or more and 5% by weight or less and applied to the expandable polystyrene resin particle body.

[10] a fourth step of applying 0.005 to 0.013 parts by weight of a cationic surfactant to the surface of 100 parts by weight of the expandable polystyrene resin particle body, The manufacturing method according to any one of [7] to [9], wherein the fourth step is carried out before the third step.

[11] a fifth step of applying 0.01 to 0.20 parts by weight of a metal stearate to the surface of 100 parts by weight of the expandable polystyrene resin particle body, The manufacturing method according to

[10] , wherein the fifth step is carried out after the fourth step.

[12] a sixth step of coating 0.01 to 0.10 parts by weight of methylphenylpolysiloxane having a refractive index of 1.47 or higher on the surface of 100 parts by weight of the expandable polystyrene resin particle body, The manufacturing method of

[11] , wherein the fourth step, the fifth step, and the sixth step are carried out in the order of the fourth step, the sixth step, and the fifth step. [Effects of the Invention]

[0011] According to one aspect of the present invention, expandable polystyrene-based resin particles can be obtained that are suitable for stable production and can suppress scratches on the surface of a molded product while achieving moldability under a wide range of molding conditions during molding processing. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0013] The polystyrene-based expandable resin particles of the present invention are expandable polystyrene-based resin particles containing a base resin containing styrene units or styrene units and butyl acrylate units as constituent units, and a blowing agent. The base resin constituting the polystyrene-based expandable resin particles of the present invention is obtained by polymerization of a styrene-based monomer as the main component (specifically, 97 parts by weight or more of the styrene-based monomer per 100 parts by weight of the total amount of the monomer components).

[0014] Furthermore, butyl acrylate may be copolymerized as an acrylic acid ester monomer in an amount of up to 3 parts by weight per 100 parts by weight of the total amount of the monomer components. By using butyl acrylate as a copolymerization component, the foaming rate tends to increase and the appearance of the molded product tends to improve, but if the amount exceeds 3 parts by weight per 100 parts by weight of the total amount of the monomer components, mold contamination tends to occur.

[0015] In addition, when seed suspension polymerization is used as the polymerization method, the monomer composition of the base resin also includes the monomer composition in the seed resin particles. In this specification, "styrene units" refer to units derived from styrene-based monomers, and "butyl acrylate units" refer to units derived from butyl acrylate as a monomer. Both are sometimes referred to as "monomer components."

[0016] In addition to the foaming agent, a solvent having a boiling point of 60°C or higher but lower than 100°C can be used in the polystyrene-based expandable resin particles of the present invention as needed to adjust the foaming properties and moldability, and a plasticizer having a boiling point of 100°C or higher can be used in combination with the solvent.

[0017] Examples of solvents with a boiling point of 60° C. or higher and lower than 100° C. include aliphatic hydrocarbons with C6 or higher such as hexane and heptane, and alicyclic hydrocarbons such as cyclohexane.

[0018] The content of the solvent having a boiling point of 60°C or higher but lower than 100°C in the expandable polystyrene-based resin particles of the present invention is preferably 1.5 parts by weight or higher but lower than 2.5 parts by weight per 100 parts by weight of the base resin. If it is less than 1.5 parts by weight, the effect of improving expandability is not fully exerted, and if it is more than 2.5 parts by weight, the bubbles during expansion are unstable, and the appearance and strength of the expanded molded product are likely to deteriorate. The content of the solvent having a boiling point of 60°C or higher but lower than 100°C in the expandable polystyrene-based resin particles is more preferably 1.8 parts by weight or higher but lower than 2.3 parts by weight per 100 parts by weight of the base resin, and within this range, it is easy to achieve both expandability and good molded product appearance. The solvent functions as a foaming aid.

[0019] Furthermore, the plasticizer used in this specification is not particularly limited as long as it has a boiling point of 100°C or higher and has a plasticizing effect on the base resin. Examples of plasticizers having a boiling point of 100°C or higher that can be used in the present invention include toluene, xylene, diisobutyl adipate, dioctyl adipate, dibutyl sebacate, glycerin tristearate, glycerin tricaprylate, coconut oil, palm oil, and rapeseed oil. Among these plasticizers, when used in the medical field or in the field of packaging materials that come into direct contact with food, edible oils are preferred, and coconut oil, palm oil, and rapeseed oil are more preferred.

[0020] The content of the plasticizer having a boiling point of 100°C or higher is preferably less than 1.0 part by weight (including 0 part by weight) per 100 parts by weight of the base resin, and preferably 0 part by weight or more (including 0 part by weight) but less than 0.5 part by weight. If the amount of plasticizer having a boiling point of 100°C or higher used is 1.0 part by weight or more, the molded product tends to shrink when expanded at a high expansion ratio, damaging the appearance of the molded product. In addition, fusion within the molded product tends to vary, making the strength insufficient. If the amount is less than 1.0 part by weight, the above problems are less likely to occur, and the effects of improving foaming power and improving surface aesthetics during molding are more likely to be achieved. If the amount is 0 part by weight or more but less than 0.5 part by weight, the effects tend to be even more pronounced.

[0021] In the present invention, a solvent having a boiling point of 60° C. or higher but lower than 100° C. or a plasticizer having a boiling point of 100° C. or higher may be added during the polymerization step of polystyrene resin particles, the step of impregnating with a blowing agent, or the like.

[0022] The content of the blowing agent in the expandable polystyrene resin particles of the present invention is preferably 3.0 parts by weight or more and less than 8.0 parts by weight, more preferably 5.0 parts by weight or more and 7.0 parts by weight or less, per 100 parts by weight of the base resin.

[0023] If the foaming agent content is less than 3 parts by weight, the foaming power during pre-expansion is low, making it difficult to obtain polystyrene-based pre-expanded particles with a bulk ratio of 65 times. If the foaming agent content is 8 parts by weight or less, the molded product tends to shrink when highly expanded, damaging its appearance. In addition, the foaming power becomes high during pre-expansion, making the cell membrane more likely to tear. As a result, the adhesive surfaces between the pre-expanded particles tend to weaken, reducing the strength and fracture displacement. If the foaming agent content is 5.0 parts by weight or more and 7.0 parts by weight or less, a good balance of expandability and moldability is achieved.

[0024] Examples of the blowing agent used in the present invention include aliphatic hydrocarbons such as propane, butane, and pentane; alicyclic hydrocarbons such as cyclobutane and cyclopentane; and halogenated hydrocarbons such as methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane. These blowing agents may be used alone or in combination of two or more. Among these blowing agents, butane is preferred because of its good blowing power.

[0025] The weight average molecular weight Mw of the expandable polystyrene resin particles in the present invention is preferably 250,000 to 320,000, and more preferably 270,000 to 300,000.

[0026] If the weight-average molecular weight Mw of the expandable styrene-based resin particles is less than 250,000, not only will the strength of the expanded molded article be low, but the surface of the molded article will tend to melt easily, which will impair the appearance of the molded article and increase the number of scratches on the surface of the molded article.If the weight-average molecular weight Mw of the expandable polystyrene-based resin particles is 320,000 or more, the expandability will tend to be low and the moldability will tend to deteriorate, that is, the heating temperature required to obtain pre-expanded particles with the desired expansion ratio and the molding temperature required to obtain a molded article with excellent properties will tend to be high.

[0027] The Z-average molecular weight Mz of the expandable polystyrene resin particles in the present invention is preferably from 600,000 to 950,000, and more preferably from 650,000 to 800,000.

[0028] If the Z-average molecular weight Mz of the expandable styrene resin particles is less than 600,000, not only will the strength of the foamed molded article be low, but the surface of the molded article will be more likely to melt, impairing the appearance and increasing scratches on the surface of the molded article, while if it is 950,000 or more, the expandability will be low and moldability will be poor (the heating temperature required to obtain pre-expanded particles with the desired expansion ratio and the molding temperature required to obtain a molded article with excellent fusion properties will be high). Within the range of 600,000 or more and less than 950,000, the balance between expandability and moldability tends to be good.

[0029] The weight-average molecular weight Mw and the Z-average molecular weight Mz can be controlled by adjusting the amount of initiator used and the polymerization temperature when polymerizing the polystyrene-based resin particles. For example, Mw and Mz can be reduced by increasing the amount of initiator used and / or increasing the polymerization temperature.

[0030] Here, the weight average molecular weights Mw and Mz of the expandable polystyrene resin particles in the present invention are values measured using a gel permeation chromatograph (hereinafter sometimes abbreviated as "GPC") under the conditions described below.

[0031] The expandable polystyrene-based resin particles of the present invention can be produced by either a method of impregnating particles obtained by suspension polymerization in an aqueous medium with a blowing agent, or a method of impregnating pellets produced by bulk polymerization or the like in an aqueous medium with a blowing agent.

[0032] Among these, suspension polymerization is preferred because it can obtain spherical resin particles and, further, expandable polystyrene-based resin particles can be obtained by continuously performing the polymerization step and the blowing agent impregnation step, and therefore has good industrial productivity. That is, as a method for producing expandable polystyrene-based resin particles, a method is preferred in which various monomers constituting a base resin (including a styrene-based monomer, or a styrene-based monomer and an acrylic acid ester-based monomer) are polymerized in the presence of a suspending agent, a polymerization initiator, and, if necessary, other additives, and a blowing agent is added during suspension polymerization, or the particles are impregnated with a blowing agent after polymerization.

[0033] Examples of suspending agents used in the suspension polymerization method of the present invention include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone, and sparingly soluble inorganic substances such as calcium triphosphate and magnesium pyrophosphate. When using a sparingly soluble inorganic substance, the suspension stabilizing effect can be enhanced by using it in combination with an anionic surfactant such as sodium dodecylbenzenesulfonate. It is also effective to use a water-soluble polymer in combination with a sparingly soluble inorganic substance.

[0034] The polymerization initiator used in the suspension polymerization method of the present invention can be a radical-generating polymerization initiator commonly used in the production of polystyrene-based polymers. Representative examples of polymerization initiators include azo compounds such as azobisisobutyronitrile, and peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, lauroyl peroxide-t-butylperoxyisopropyl carbonate, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxybenzoate, and t-butylperoxy-2-ethylhexyl carbonate. These polymerization initiators can be used alone or in combination of two or more.

[0035] Additives that can be added during the suspension polymerization of the present invention include nucleating agents, flame retardants, flame retardant auxiliaries, external additives, etc., within limits that do not impair the effects of the present invention.

[0036] The average chord length of the cells in the cross section of the foam can be controlled by the amount of nucleating agent used: for example, more nucleating agent will decrease the average chord length, and less nucleating agent will increase the average chord length.

[0037] Nucleating agents used in the present invention include, for example, methyl methacrylate copolymers, polyethylene wax, talc, fatty acid bisamides, and ethylene-vinyl acetate copolymer resins. Specific examples of fatty acid bisamides include methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, and ethylene bisoleic acid amide. The nucleating agent can adjust the average chord length of the cells on the cross section of the foamed molded article obtained by pre-expansion and molding. The average chord length of the cells is preferably 80 to 120 μm, and more preferably 90 to 110 μm. The preferred amount of nucleating agent is 0.03 to 0.10 parts by weight per 100 parts by weight of polystyrene-based expandable resin particles. If the amount is less than 0.03 parts by weight, the average chord length of the cells is likely to exceed 120 μm and the cell diameter will be non-uniform. If the amount is more than 0.10 parts by weight, the average chord length of the cells will likely be 80 μm or less.

[0038] If the average chord length is less than 80 μm, the membrane thickness of the cells constituting the foam will be thin, which will tend to increase the occurrence of blocking during pre-expansion, and will result in internal fusion and a poor surface appearance.If the average chord length is more than 120 μm, the fracture displacement of the fracture strength (for example, flexural strength in JIS A9511 or tensile strength of box-shaped molded body) will be short, and the molded body will tend to be brittle.

[0039] In the present invention, a flame retardant or a flame retardant aid may be added to impart flame retardancy depending on the application. Known and commonly used flame retardants and flame retardant aids can be used. The flame retardant is preferably a bromine-based compound, and specific examples include halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether). Examples of suitable flame retardants include brominated phenol derivatives such as aryl-A-diglycidyl ether and 2,2-bis[4'(2",3"-dibromoalkoxy)-3',5'-dibromophenyl]-propane, brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers, etc. (e.g., EMERALD3000 manufactured by Chemtura or those disclosed in JP-T-2009-516019). These flame retardants may be used alone or in combination of two or more.

[0040] The flame retardant aid is preferably a compound that generates radicals when heated, such as a peroxide. Specific examples of initiators that may be used include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane.

[0041] The expandable polystyrene-based resin particles of the present invention are obtained by coating the surface of 100 parts by weight of the expandable polystyrene-based resin particle body with 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or lower.

[0042] A method for producing expandable polystyrene-based resin particles according to one embodiment of the present invention includes the following steps: a first step of impregnating the expandable polystyrene-based resin particles with a blowing agent in an aqueous medium and dehydrating the particles to obtain expandable polystyrene-based resin particle bodies; a second step of applying 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or below to the surface of 100 parts by weight of the expandable polystyrene-based resin particle bodies, followed by heating; and a third step of sieving the resulting expandable polystyrene-based resin particles. Specifically, the present invention includes the steps of obtaining expandable polystyrene-based resin particle bodies in an aqueous medium by suspension polymerization or by impregnating pellets with a blowing agent, followed by dehydration and coating with a nonionic surfactant. The nonionic surfactant is applied to the surface of the expandable polystyrene-based resin particle bodies, and acts on the surface of the expandable polystyrene-based resin particles after heat treatment, thereby improving the surface aesthetics of the resulting expanded molded article. In order for a nonionic surfactant to act on expandable styrene resin particles, it is necessary for the HLB (hydrophile-lipophile balance) value to be 8 to 15.

[0043] Nonionic surfactants with an HLB value of less than 8 tend to be more oil-soluble and have a stronger plasticizing effect, which tends to increase blocking during pre-expansion (primary expansion). Nonionic surfactants with an HLB value of more than 15 tend to be more hydrophilic and make it difficult to uniformly cover the surfaces of the resin particles themselves, which tends to worsen the fusion properties of the foamed molded article and may not be effective enough to smooth the surface of the foamed molded article.

[0044] Examples of nonionic surfactants having an HLB value of 8 to 15 include water-soluble and water-dispersible polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl diesters, polyoxyethylene sorbitan alkylates, etc. Among these, in order to stably apply the surfactant uniformly to the surface of the expandable polystyrene resin particles during production and to obtain an effect of improving the surface aesthetics with little variation, the nonionic surfactant must have a freezing point of 0°C or lower and must have an ester bond.

[0045] Specific examples of usable nonionic surfactants include polyoxyethylene monooleate having an HLB value of 8.3.9 to 11.6, polyoxyethylene sorbitan monooleate having an HLB value of 15.7, etc. These nonionic surfactants may be used alone or in combination of two or more.

[0046] The HLB value of a nonionic surfactant can be measured by the method described on pages 307-327 of Sangyo Tosho's "Surfactant Handbook."

[0047] In the present invention, the amount of nonionic surfactant applied must be 0.015 to 0.035 parts by weight, and more preferably 0.020 to 0.030 parts by weight, per 100 parts by weight of the expandable styrene-based resin particles. If the amount of nonionic surfactant applied is less than 0.015 parts by weight, the effect of improving the surface aesthetics of the foamed molded article will be insufficient. If the amount of nonionic surfactant applied exceeds 0.035 parts by weight, the blowing agent will be more likely to dissipate and the fluidity of the resin particles will be reduced, resulting in increased blocking during pre-expansion.

[0048] In the present invention, it is preferable to add the nonionic surfactant dispersed in water to the expandable polystyrene resin particle bodies and mix them to coat the surfaces. By adding the nonionic surfactant in the form of an aqueous solution or a dispersion in water, the nonionic surfactant can be uniformly applied to coat the surfaces of the expandable polystyrene resin particle bodies. In this case, the weight concentration of the nonionic surfactant is preferably 1% by weight or more and 5% by weight or less per 100 parts by weight of water.

[0049] If the concentration of the nonionic surfactant dispersion is less than 1% by weight, the nonionic surfactant tends to be applied unevenly and the effect of smoothing the surface of the foamed molded article tends to be reduced. The water is removed during the process of obtaining the final foamed molded article. If the concentration of the nonionic surfactant exceeds 5% by weight, it becomes difficult to remove the water, which can lead to poor resin fluidity due to insufficient water removal or excessive drying due to water removal, resulting in increased blocking during pre-foaming.

[0050] There are various methods for adding a nonionic surfactant to the expandable polystyrene-based resin particle body, mixing the particles, and then coating the surface. For example, a method is used in which the expandable polystyrene-based resin particle body and an aqueous dispersion of a nonionic surfactant are thoroughly mixed using a mixing device such as a blender. Another advantageous method is to dehydrate the expandable polystyrene-based resin particle body impregnated with a blowing agent in an aqueous suspension, for example, using a centrifugal dehydrator, and then add the nonionic surfactant, or an aqueous solution or dispersion thereof, to the expandable polystyrene-based resin particle body using a mixing device such as a blender, mixing the particles, and then coating the surface. In this case, the nonionic surfactant also has an antistatic effect, and if necessary, other antistatic agents may be mixed and applied.

[0051] After applying the nonionic surfactant, the product must be heated and dried. Drying after application of the nonionic surfactant removes moisture adhering to the surface of the expandable polystyrene-based resin particles, and the nonionic surfactant acts on the surface of the expandable polystyrene-based resin particles, causing cracks only in the surface layer. The cracks allow the formation of a layer with less blowing agent and higher hardness in the surface layer, improving the surface appearance of the foamed molded product. The heating temperature is preferably 45°C or higher and 65°C or lower. Heating temperatures below 45°C tend to make it difficult for the nonionic surfactant to act on the surface of the expandable polystyrene-based resin particles, making it difficult to obtain a foamed molded product with a beautiful surface. Heating temperatures above 65°C tend to result in poor foamability due to increased loss of blowing agent caused by cracks.

[0052] The drying method is, for example, a method of drying the moisture adhering to the surface of the expandable polystyrene resin particle body together with the nonionic surfactant, but is not particularly limited thereto, for example, by using a groove-type or cylindrical agitator dryer, a box-type or band-type through-air dryer, a fluidized bed dryer, etc.

[0053] Although the nonionic surfactant acts as an antistatic agent, to stabilize the production process, a method for producing expandable polystyrene-based resin particles according to one embodiment of the present invention preferably includes a fourth step in which a cationic surfactant is further applied to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body at a weight ratio of 0.005 to 0.013 parts by weight. If the amount is 0.0050 parts by weight or less, the pre-expanded particles tend to become highly charged, especially when used in combination with a silicone-based external additive (described below). If the amount exceeds 0.013 parts by weight, the fluidity of the resin particles deteriorates, making blocking during expansion more likely. The cationic surfactant is preferably applied immediately before or simultaneously with the application of the nonionic surfactant, as this also helps to suppress static electricity during the subsequent heating step. That is, the fourth step in which a cationic surfactant is further applied to the surface of the expandable polystyrene-based resin particle body is preferably performed before the heating step included in the second step. In this case, the fourth step may be performed either before the second step or during the second step. The fourth step is preferably carried out before the third step of sieving the obtained expandable polystyrene resin particles.

[0054] The expandable polystyrene resin particles that have undergone the heating process are sieved to the desired particle size depending on the application. Normally, they are sieved to a particle size of 0.5 mm to 1.4 mm, and for use as regular food containers and packaging materials, sieving to a particle size of 0.6 mm to 1.2 mm is preferable, as it provides a good balance between expansion ratio and ease of molding.

[0055] The method for producing expandable polystyrene-based resin particles according to one embodiment of the present invention may further include a step of applying an external additive to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body. The external additive used in the present invention may be any known or commonly used one. The external additive described below is usually applied after a heating step and sieving to a desired particle size.

[0056] Specific examples of external additives include fatty acid triglycerides such as lauric acid triglyceride, stearate triglyceride, and linoleic acid triglyceride, fatty acid diglycerides such as lauric acid diglyceride, stearate diglyceride, and linoleic acid diglyceride, fatty acid monoglycerides such as lauric acid monoglyceride, stearate monoglyceride, and linoleic acid monoglyceride, fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, and calcium laurate, silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane, castor wax, and vegetable oils such as castor oil and olive oil. These external additives may be used alone or in combination of two or more. Among these, it is preferable to use zinc stearate alone in an amount of 0.01 to 0.020 parts by weight per 100 parts by weight of expandable styrene-based resin particles, or to combine zinc stearate with 0.01 to 0.10 parts by weight of methylphenyl silicone with a refractive index of 1.47 or higher. If the amount of zinc stearate is less than 0.05 parts by weight, blocking is likely to occur during pre-expansion, while if it exceeds 0.20 parts by weight, it is difficult to obtain fusion-like properties for the foamed molded product. While applying methylphenyl silicone with a refractive index of 1.47 or higher can prevent peeling of solid external additives such as zinc stearate, using more than 0.10 parts by weight can reduce fluidity, increasing blocking during pre-expansion and increasing the electrostatic charge of the pre-expanded particles. If the refractive index of the methylphenyl silicone is less than 1.47, the fusion-like properties of the foamed molded product are likely to deteriorate and the pre-expanded particles are likely to become electrostatically charged. These external additives may be added to the aqueous system during the foaming agent impregnation, or may be added and coated after dehydration or drying, regardless of the coating method. A preferred coating method is to apply the coating by mixing and stirring after drying.That is, the method for producing expandable polystyrene-based resin particles according to one embodiment of the present invention may include a step (fifth step) of applying 0.01 to 0.20 parts by weight of a metal stearate to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, or a step (sixth step) of applying 0.01 to 0.10 parts by weight of a methylphenylpolysiloxane having a refractive index of 1.47 or more to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body. When the fifth step of applying a metal stearate to the surface of the expandable polystyrene-based resin particle body is performed, it is preferable that the fifth step be performed after the fourth step of further applying a cationic surfactant to the surface of the expandable polystyrene-based resin particle body, and it is more preferable that the fourth step, the second step of drying the expandable polystyrene-based resin particle body by heating, and the fifth step be performed in that order. Furthermore, when the sixth step of applying methylphenylpolysiloxane to the surface of the expandable polystyrene-based resin particle body is further carried out, it is preferable to carry out the steps in the order of the fourth step of further applying a cationic surfactant to the surface of the expandable polystyrene-based resin particle body, the sixth step, and the fifth step of applying a metal stearate, and it is more preferable to carry out the steps in the order of the fourth step, the second step of drying the expandable polystyrene-based resin particle body by heating, the sixth step, and the fifth step.

[0057] The content of the monomer component in the expandable polystyrene resin particles of the present invention is preferably less than 0.3% by weight. The contained monomer component tends to volatilize from the foamed molded article obtained by expanding the expandable polystyrene resin particles. In particular, if the content of the monomer component is 0.3% by weight or more, it is not preferable for use in the medical field, in the field of packaging materials that come into direct contact with food, or as automotive or building components. In addition, the surface appearance tends to deteriorate.

[0058] The amount of the monomer component contained can be controlled by a combination of the amount of initiator used and the polymerization temperature when polymerizing the polystyrene-based resin particles. For example, the amount of the monomer component contained can be reduced by increasing the amount of initiator used or the polymerization temperature.

[0059] The pre-expanded polystyrene particles in one embodiment of the present invention are obtained by pre-expanding (primary expanding) the expandable polystyrene resin particles described above.

[0060] As a method for pre-expanding, a conventional method can be adopted, for example, using a cylindrical pre-expanding device and heating the expandable polystyrene-based resin particles with a heating medium such as steam to cause expansion. The device used for pre-expanding and the pre-expanding conditions can be appropriately set depending on the composition of the expandable polystyrene-based resin particles, the desired pre-expansion ratio, etc., and are not particularly limited.

[0061] The foamed molded article according to one embodiment of the present invention is obtained by heating and foaming (secondary foaming) the above-described polystyrene-based pre-expanded particles.

[0062] The method for heat-expanding the polystyrene-based pre-expanded particles can be, for example, a conventional method such as an in-mold foam molding method in which the pre-expanded particles are filled into a mold and heated by blowing in a heating medium such as steam. The apparatus used for heat-expanding and the conditions for heat-expanding can be appropriately set depending on the composition of the expandable polystyrene-based resin particle body, the desired expansion ratio, etc., and are not particularly limited. Foamed molded products, particularly in-mold foamed molded products, have the advantage of being easy to produce molded products of desired shapes, and are therefore suitable for use as, for example, packaging materials (trays) for food containers and the like, and transport packaging materials for fish boxes and the like. [Example]

[0063] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measurement and evaluation methods were as follows.

[0064] <Preparation of pre-expanded particles> Expandable polystyrene resin particles were placed in a pressurized pre-expander (Daika Kogyo Co., Ltd., BHP-1800) equipped with a stirrer, and pre-expanded (primary expansion) by heating using steam as a heating medium at a blowing steam pressure of 0.09 MPa, resulting in polystyrene pre-expanded particles with a bulk expansion ratio (apparent expansion ratio) of 65 times.

[0065] <Evaluation of blocking during pre-foaming> In the above pre-expansion, when the polystyrene pre-expanded particles were taken out of the pre-expansion machine, the pre-expanded particles were passed through a mesh with a mesh size of 1 cm, and the pre-expanded particles that did not pass through the mesh were collected and weighed to obtain the amount of blocking. ◎ Blocking rate is less than 0.01% by weight Blocking occurs at a rate of 0.01% by weight or more but less than 0.02% by weight △ Blocking rate is 0.02% by weight or more and less than 0.10% by weight × Blocking amount is 0.10% by weight or more

[0066] <Evaluation of electrostatic charge of pre-expanded particles> The expanded particles obtained in the pre-expansion were dried and left overnight in a thermostatic chamber at 23°C and 50% humidity. 15 g of the expanded particles were weighed and placed in a polyethylene bag (OK bag No. 15, Okura Kogyo Co., Ltd.), which was then shaken 100 times with the bag closed. The polystyrene bag was then opened with the top facing downwards, and the styrene-based pre-expanded particles were allowed to fall freely and removed. The weight of the expanded particles remaining in the polyethylene bag was measured, and the following evaluation was performed. ◎ Less than 0.5% by weight of foam particles remain in the polyethylene bag ○ The amount of foam particles remaining in the polyethylene bag is 0.5% by weight or more and less than 1.0% by weight △ The amount of foam particles remaining in the polyethylene bag is 1.0% by weight or more and less than 3.0% by weight × The amount of foam particles remaining in the polyethylene bag is 3.0% by weight or more

[0067] <Production of foam molded product> Using a molding machine (Daisen Co., Ltd., KR-57), a box-shaped mold (550 mm long x 350 mm wide x 120 mm high, 30 mm thick bottom and 25 mm thick sidewalls) was filled with the polystyrene pre-expanded particles, which had been pre-expanded 65 times using the method described above. The molding conditions were as follows: steam (water vapor) was used as the heating medium, the blowing pressure was 0.09 MPa, cracking time was 1 mm, mold heating time was 2 seconds, one-sided heating time was 6 seconds, reverse one-sided heating time was 2 seconds, both-sided heating time was 4 seconds, supplementary heating time was 5 seconds, water cooling time was 2 seconds, air cooling time was 5 seconds, and vacuum cooling time was 80 seconds. The resulting foam molded product was dried at room temperature for 24 hours.

[0068] <Evaluation of surface aesthetics of molded products> The surface condition of the foamed molded article obtained under the above molding conditions was visually observed and evaluated according to the following criteria. ◎: No gaps found 〇: There are some gaps in some areas, but overall it is acceptable △: The gap is noticeable ×: There are many gaps, and it is not acceptable as a product.

[0069] <Evaluation of resin clogging in mold slits> Using a molding machine (Daisen Co., Ltd., KR-57), a box-shaped mold (550mm long x 350mm wide x 120mm high, 30mm thick bottom and 25mm thick sides) was filled with polystyrene pre-expanded particles pre-expanded 65 times using the method described above. Ten consecutive in-mold foam moldings were performed using steam (water vapor) as the heating medium. The injection pressure was 0.09 MPa, the cracking time was 1mm, mold heating was 2 seconds, one-sided heating was 8 seconds, reverse one-sided heating was 0 seconds, both-side heating was 10 seconds, supplementary heating was 5 seconds, water cooling was 3.5 seconds, air cooling was 5 seconds, and the vacuum cooling time was 50 seconds. Afterwards, the mold's slit steam holes were visually inspected for clogging with resin. ◎: Almost no resin clogging is found 〇: There are small resin clogs in places, but no large resin clogs are found. △: Large resin clogs are present in some places ×: Large resin clogging has occurred throughout the entire area

[0070] <Weight average molecular weight measurement> 0.02 g of the obtained expandable polystyrene resin particles was dissolved in 20 ml of tetrahydrofuran (hereinafter sometimes abbreviated as "THF"), and then gel permeation chromatography (GPC) was performed under the following conditions to obtain a GPC measurement chart, weight average molecular weight (Mw), and number average molecular weight (Mn). The obtained values are relative values converted into polystyrene. Measurement equipment: Tosoh Corporation, high-speed GPC equipment HLC-8220 Columns used: Tosoh Corporation, SuperHZM-H x 2, SuperH-RC x 2 Column temperature: 40°C, mobile phase: THF (tetrahydrofuran) Flow rate: 0.35ml / min, injection volume: 10μl Detector: RI.

[0071] <Nonionic surfactants used> O-3: Polyoxyethylene monooleate, HLB 10.2, freezing point -8°C (product name: Nonion O-3, manufactured by NOF Corporation) O-2: Polyoxyethylene monooleate, HLB 8.3, freezing point -20°C (product name: Nonion O-2, manufactured by NOF Corporation) P-208: Polyoxyethylene cetyl ether, HLB 11.9, freezing point 25°C (product name: Nonion P-208, manufactured by NOF Corporation) S-4: Polyoxyethylene monostearate, HLB 11.6, freezing point 30-40°C (product name: Nonion S-4, manufactured by NOF Corporation) K-220: Polyoxyethylene lauryl ether, HLB 9.7, freezing point 15°C (product name: Nonion K-220, manufactured by NOF Corporation) S-202: Polyoxyethylene stearyl ether, HLB 4.9, freezing point 40°C (product name: Nonion S-202, manufactured by NOF Corporation)

[0072] <Methylphenylpolysiloxane used> KF-54: methylphenylpolysiloxane, viscosity (25°C): 400 mm 2 / s, refractive index (25°C): 1.505 (manufactured by Shin-Etsu Chemical Co., Ltd.) KF-50: methylphenylpolysiloxane, viscosity (25°C): 1000 mm 2 / s, refractive index (25°C): 1.427 (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0073] Example 1 <Production of Expandable Polystyrene Resin Particles> A 6-L autoclave equipped with a stirrer was charged with 100 parts by weight of purified water, 0.15 parts by weight of tricalcium phosphate, 0.005 parts by weight of sodium dodecylbenzenesulfonate, 0.0005 parts by weight of polyoxyethylene polypropylene glycol (ADEKA Pluronic F-108, manufactured by ADEKA Corporation), 0.0004 parts by weight of xanthan gum (KELZAN S PLUS, manufactured by Sansho Co., Ltd.), 0.18 parts by weight of benzoyl peroxide and 0.25 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as initiators, 0.4 parts by weight of coconut oil as plasticizer, and 0.04 parts by weight of polyethylene wax as a nucleating agent. Subsequently, 100 parts by weight of styrene monomer was added while stirring at 250 rpm, and the temperature was raised to 98°C. The mixture was then held at 98°C for 4 hours to obtain polystyrene resin particles.

[0074] Next, 1.9 parts by weight of cyclohexane as a blowing aid and 6.9 parts by weight of butane as a blowing agent were pressurized into the autoclave and heated again to 120°C. After maintaining the temperature at 120°C for 2 hours, the mixture was cooled to room temperature, and the polymerized slurry was removed from the autoclave. The removed polymerized slurry was washed and dehydrated to obtain expandable polystyrene-based resin particle bodies. 0.009 parts by weight of N-hydroxyethyl-N-(2-hydroxyalkyl)amine was applied to 100 parts by weight of the obtained expandable polystyrene-based resin particle bodies. Polyoxyethylene monooleate (Nonion O-3) was then prepared into a 3% by weight dispersion in water, and 0.02 parts by weight of the dispersion (pure polyoxyethylene monooleate) was added and stirred to uniformly coat the surface of the expandable polystyrene-based resin particle bodies. The mixture was then dried in an airflow dryer and heated at 50°C for 20 minutes in a box-type ventilated dryer (manufactured by Tanaka Chemical Machinery Co., Ltd.) to obtain expandable polystyrene-based resin particles.

[0075] 100 parts by weight of the obtained expandable polystyrene resin particles were sieved to separate expandable polystyrene resin particles with particle diameters of 0.6 mm to 1.2 mm. 100 parts by weight of the separated expandable polystyrene were mixed with 0.18 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corp.) and 0.06 parts by weight of castor wax (Castarwax A, manufactured by NOF Corp.) as external additives, and the mixture was stirred for 60 seconds in a super mixer (SMV-20, manufactured by Kawata Corp.).

[0076] Pre-expanded particles and foaming specimens were prepared according to the procedures described in <Preparation of pre-expanded particles> and <Preparation of foamed molded products>, and various evaluations were carried out.

[0077] The evaluation results are shown in Table 1.

[0078] Example 2 In the <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 2.3 parts by weight of cyclohexane was used. The evaluation results are shown in Table 1.

[0079] Example 3 In the <Production of Expandable Polystyrene-Based Resin Particles>, the amount of styrene monomer added was 98 parts by weight, the amount of butyl acrylate monomer added was 2 parts by weight, the amount of coconut oil added was 0 parts by weight, the amount of cyclohexane added was 1.8 parts by weight, the amount of butane added was 6.5 parts by weight, and the external additives were methylphenylpolysiloxane (KF-54) 0.06 parts by weight, zinc stearate (Zinc Stearate GF-200, NOF Corp.) 0.10 parts by weight, and castor wax (Castarwax A, NOF Corp.) 0 parts by weight. Expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0080] Example 4 In <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the external additives were changed to 0.06 parts by weight of methylphenylpolysiloxane (KF-54), 0.10 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corp.), and 0 parts by weight of castor wax (Castarwax A, manufactured by NOF Corp.). The evaluation results are shown in Table 1.

[0081] Example 5 In the <Production of Expandable Polystyrene-Based Resin Particles>, the amount of styrene monomer added was 98 parts by weight, the amount of butyl acrylate monomer added was 2 parts by weight, the amount of coconut oil added was 0 parts by weight, the amount of cyclohexane added was 1.4 parts by weight, the amount of butane added was 6.5 parts by weight, and the external additives were methylphenylpolysiloxane (KF-54) 0.06 parts by weight, zinc stearate (Zinc Stearate GF-200, NOF Corp.) 0.10 parts by weight, and castor wax (Castarwax A, NOF Corp.) 0 parts by weight. Expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0082] Example 6 In <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that in the production of expandable polystyrene-based resin particles, the amount of styrene monomer charged was 98 parts by weight, the amount of butyl acrylate monomer charged was 2 parts by weight, the amount of coconut oil added was 0 parts by weight, the amount of cyclohexane charged was 2.6 parts by weight, and the amount of butane charged was 6.5 parts by weight. The evaluation results are shown in Table 1.

[0083] Example 7 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the amount of coconut oil added was 0.9 parts by weight. The evaluation results are shown in Table 1.

[0084] Example 8 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the amount of coconut oil added was 1.2 parts by weight. The evaluation results are shown in Table 1.

[0085] Example 9 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-2) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). The evaluation results are shown in Table 1.

[0086] Example 10 In the preparation of expandable polystyrene-based resin particles, 98 parts by weight of styrene monomer, 2 parts by weight of butyl acrylate monomer, 0 parts by weight of coconut oil, 1.8 parts by weight of cyclohexane, and 6.5 parts by weight of butane were used. 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-2) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). 0.06 parts by weight of methylphenylpolysiloxane (KF-54), 0.10 parts by weight of zinc stearate (Zinc Stearate GF-200, NOF Corp.), and 0 parts by weight of castor wax (Castarwax A, NOF Corp.) were used as external additives. Expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0087] Example 11 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that polyoxyethylene monooleate (Nonion O-3) was used in an amount of 0.03 parts by weight. The evaluation results are shown in Table 1.

[0088] Example 12 In <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the concentration of polyoxyethylene monooleate (Nonion O-3) when preparing the dispersion was 7%. The evaluation results are shown in Table 1.

[0089] Example 13 In the <Production of Expandable Polystyrene-Based Resin Particles>, the amount of styrene monomer added was 98 parts by weight, the amount of butyl acrylate monomer added was 2 parts by weight, the amount of coconut oil added was 0 parts by weight, the amount of cyclohexane added was 1.8 parts by weight, the amount of butane added was 6.5 parts by weight, and the external additives were methylphenylpolysiloxane (KF-50) 0.05 parts by weight, zinc stearate (Zinc Stearate GF-200, NOF Corp.) 0.05 parts by weight, and castor wax (Castarwax A, NOF Corp.) 0.05 parts by weight. Expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0090] Example 14 In the <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the amount of N-hydroxyethyl-N-(2-hydroxyalkyl)amine applied was 0.004 parts by weight. The evaluation results are shown in Table 1.

[0091] Example 15 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the amount of N-hydroxyethyl-N-(2-hydroxyalkyl)amine applied was 0.015 parts by weight. The evaluation results are shown in Table 1.

[0092] Example 16 In <Production of expandable polystyrene resin particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corp.) was used in an amount of 0.21 parts by weight. The evaluation results are shown in Table 1.

[0093] Example 17 In <Production of expandable polystyrene resin particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the external additives were changed to 0.12 parts by weight of methylphenylpolysiloxane (KF-54), 0.10 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corp.), and 0 parts by weight of castor wax (Castarwax A, manufactured by NOF Corp.). The evaluation results are shown in Table 1.

[0094] Example 18 In <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the heating temperature after application of polyoxyethylene monooleate (Nonion O-3) was set to 40° C. The evaluation results are shown in Table 1.

[0095] Example 19 In <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the heating temperature after application of polyoxyethylene monooleate (Nonion O-3) was set to 70° C. The evaluation results are shown in Table 1.

[0096] (Comparative Example 1) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that polyoxyethylene monooleate (Nonion O-3) was not used. The evaluation results are shown in Table 2.

[0097] (Comparative Example 2) In <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that polyoxyethylene monooleate (Nonion O-3) was used in an amount of 0.01 parts by weight. The evaluation results are shown in Table 2.

[0098] (Comparative Example 3) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that polyoxyethylene monooleate (Nonion O-3) was used in an amount of 0.04 parts by weight. The evaluation results are shown in Table 2.

[0099] Comparative Example 4 In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene cetyl ether (Nonion P-208) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). The evaluation results are shown in Table 2.

[0100] (Comparative Example 5) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene monostearate (Nonion S-4) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). The evaluation results are shown in Table 2.

[0101] (Comparative Example 6) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene lauryl ether (Nonion K-220) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). The evaluation results are shown in Table 2.

[0102] (Comparative Example 7) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene stearyl ether (Nonion S-202) was used instead of 0.02 parts by weight of polyoxyethylene monooleate (Nonion O-3). The evaluation results are shown in Table 2.

[0103] (Comparative Example 8) In the preparation of expandable polystyrene-based resin particles, the amounts of styrene monomer, butyl acrylate monomer, coconut oil, cyclohexane, butane were changed to 95 parts by weight, 0 parts by weight, benzoyl peroxide, 1,1-bis(t-butylperoxy)cyclohexane, 0.25 parts by weight, 0.17 parts by weight, methylphenylpolysiloxane (KF-54), zinc stearate (Zinc Stearate GF-200, NOF Corp.), 0.10 parts by weight, castor wax (Castarwax A, NOF Corp.), and polyoxyethylene monooleate (Nonion O-3) were used. The same procedures as in Example 1 were used to obtain expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles. The evaluation results are shown in Table 2.

[0104] (Comparative Example 9) In the preparation of expandable polystyrene-based resin particles, the amounts of styrene monomer, butyl acrylate monomer, coconut oil, cyclohexane, butane were changed to 95 parts by weight, 0 parts by weight, benzoyl peroxide, 1,1-bis(t-butylperoxy)cyclohexane, 0.25 parts by weight, 0.17 parts by weight, methylphenylpolysiloxane (KF-54), zinc stearate (Zinc Stearate GF-200, NOF Corp.), and caster wax (Castarwax A, NOF Corp.), respectively. The same procedures as in Example 1 were repeated to obtain expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles. The evaluation results are shown in Table 2.

[0105] (Comparative Example 11) In the <Production of Expandable Polystyrene-Based Resin Particles>, expandable polystyrene-based resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that the amounts of styrene monomer, butyl acrylate monomer, coconut oil, cyclohexane, butane, benzoyl peroxide, and 1,1-bis(t-butylperoxy)cyclohexane were changed to 96 parts by weight, 4 parts by weight, 0.5 parts by weight, 0.25 parts by weight, and 0.17 parts by weight, respectively. The evaluation results are shown in Table 2.

[0106] (Comparative Example 12) In the <Production of Expandable Polystyrene-Based Resin Particles>, the number of parts by weight of styrene monomer charged was 95, the number of parts by weight of butyl acrylate monomer charged was 5, the number of parts by weight of added coconut oil was 0, the number of parts by weight of cyclohexane charged was 0, the number of parts by weight of butane charged was 7, benzoyl peroxide was 0.25, 1,1-bis(t-butylperoxy)cyclohexane was 0.17, and polyoxyethylene monooleate (Nonion O-3) was 0.02. Expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed articles were obtained in the same manner as in Example 1, except that 0.02 parts by weight of polyoxyethylene cetyl ether (Nonion P-208) was used instead of 0.02 parts by weight of methylphenylpolysiloxane (KF-54), 0.06 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corp.), 0.08 parts by weight of castor wax (Castarwax A, manufactured by NOF Corp.) were used as external additives. The evaluation results are shown in Table 2.

[0107] [Table 1]

[0108] [Table 2]

Claims

1. The expandable polystyrene-based resin particles include a base resin containing a styrene unit or a styrene unit and a butyl acrylate unit as a constituent unit, and a blowing agent, the base resin contains, as structural units, 97 parts by weight or more and 100 parts by weight or less of the styrene unit and 0 part by weight or more and 3 parts by weight or less of the butyl acrylate unit (provided that the total of the styrene unit and the butyl acrylate unit is 100 parts by weight); Expandable polystyrene-based resin particles, in which 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or lower is coated on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

2. The expandable polystyrene-based resin particles according to claim 1, further comprising a coating of 0.01 to 0.20 parts by weight of a metal stearate and 0.005 to 0.013 parts by weight of a cationic surfactant on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

3. The expandable polystyrene-based resin particles according to claim 2, further comprising a coating of 0.01 to 0.10 parts by weight of methylphenylpolysiloxane having a refractive index of 1.47 or more on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

4. For 100 parts by weight of the base resin, The foaming agent is 3.0 parts by weight or more and less than 8.0 parts by weight, 1.5 parts by weight or more and less than 2.5 parts by weight of an aliphatic hydrocarbon having a boiling point of 60°C or more and less than 100°C as a foaming aid, and A plasticizer with a boiling point of 100°C or higher is contained in an amount of 0 part by weight or more and less than 1.0 part by weight. The expandable polystyrene-based resin particles according to claim 1 , comprising:

5. Pre-expanded particles obtained by pre-expanding the expandable polystyrene-based resin particles according to any one of claims 1 to 4.

6. A foamed molded article obtained by molding the pre-expanded particles according to claim 5.

7. a first step of impregnating a foaming agent in an aqueous medium and dehydrating the resulting foamed polystyrene-based resin particles to obtain expandable polystyrene-based resin particle bodies; a second step of applying 0.015 to 0.035 parts by weight of a polyoxyethylene alkyl ester-type nonionic surfactant having an HLB value of 8 to 15 and a freezing point of 0°C or lower to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, followed by heating; a third step of sieving the obtained expandable polystyrene-based resin particles; Including, the expandable polystyrene-based resin particle body contains a base resin, a base resin containing, as constituent units, 97 parts by weight or more and 100 parts by weight or less of the styrene units and 0 parts by weight or more and 3 parts by weight or less of the butyl acrylate units (provided that the total of the styrene units and the butyl acrylate units is 100 parts by weight);

8. The method of claim 7, wherein the second step involves heating at a temperature of 45°C or higher and 65°C or lower.

9. 9. The method according to claim 7, wherein the nonionic surfactant is dispersed in water at a concentration of 1% by weight to 5% by weight and then applied to the expandable polystyrene resin particle bodies.

10. a fourth step of applying 0.005 parts by weight or more and 0.013 parts by weight or less of a cationic surfactant to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, The manufacturing method according to claim 7 , wherein the fourth step is carried out before the third step.

11. a fifth step of applying 0.01 part by weight or more and 0.20 part by weight or less of a metal stearate to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, The manufacturing method according to claim 10 , wherein the fifth step is performed after the fourth step.

12. a sixth step of coating 0.01 to 0.10 parts by weight of methylphenylpolysiloxane having a refractive index of 1.47 or more on the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, The manufacturing method according to claim 11 , wherein the fourth step, the fifth step, and the sixth step are performed in the order of the fourth step, the sixth step, and the fifth step.

13. A manufacturing method described in any one of claims 7 to 9, further comprising a step of applying 0.01 parts by weight or more and 0.10 parts by weight or less of methylphenylpolysiloxane having a refractive index of 1.47 or more to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

Images