Expandable polystyrene resin particles and manufacturing method

Abstract

To provide a foamable polystyrenic resin particle that achieves a high foaming rate and yields a polystyrenic foamed resin molding with high thermal insulation performance.SOLUTION: A foamable polystyrenic resin particle contains a radiation heat transfer inhibitor. The foamable polystyrenic resin particle has a sphericity of 0.985 or less. The foamer contains isobutane. Assuming the total amount of the polystyrenic resin composition and the foamer to be 100 wt.%, the isobutane is more than 2.7 wt.% and 6.0 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to expandable polystyrene resin particles and a method for producing the same. [Background technology]

[0002] Polystyrene-based resin foams are well-balanced foams that have light weight, heat insulating properties, and cushioning properties, and have traditionally been widely used as heat insulating materials for food containers, cooler boxes, cushioning materials, and homes.

[0003] In particular, in recent years, in connection with various problems such as global warming, there has been a trend toward energy conservation by improving the thermal insulation performance of buildings such as houses, and demand for polystyrene-based resin foam molded articles obtained using expandable polystyrene-based resin particles is expected to increase. Therefore, various studies have been conducted on improving the foaming performance and thermal insulation performance of the polystyrene-based resin foam.

[0004] For example, Patent Documents 1 and 2 disclose polystyrene resin foam molded articles that contain a radiation heat transfer inhibitor and a specific amount of isobutane relative to the total amount of pentane and butane, thereby exhibiting excellent foaming performance and heat insulating performance.

[0005] Patent Document 3 discloses that by adjusting the aspect ratio of expandable polystyrene-based resin particles containing a radiation heat transfer inhibitor to 0.95 or less and the sphericity to 0.97 or more, a polystyrene-based resin foam molded article having both a high expansion ratio and high thermal insulation performance can be obtained.

[0006] Patent Document 4 discloses a polystyrene resin foam molded article made of expandable polystyrene resin particles, which are obtained by impregnating a polystyrene resin composition obtained by kneading a polystyrene resin and a radiation heat transfer inhibitor in an aqueous medium with a flame retardant and a blowing agent, so that the flame retardant content (wt%) in the surface layer of the expandable resin particles is 1.05 times or more the flame retardant content (wt%) in the entire particle, and which is impregnated with a pentane content of 15 vol% or more to exhibit stable self-extinguishing properties. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2018-145212 [Patent Document 2] Patent Publication No. 2019-65073 [Patent Document 3] Patent Publication No. 2020-33481 [Patent Document 4] JP 2004-346281 Summary of the Invention [Problem to be solved by the invention]

[0008] The expandable polystyrene resin particles described in Patent Documents 1 to 4 have room for improvement, particularly with regard to increasing the expansion ratio.

[0009] The present invention provides expandable polystyrene resin particles that can be used to obtain a polystyrene resin expansion molded article having both a high expansion ratio and high thermal insulation performance. [Means for solving the problem]

[0010] In general, the use of a radiation heat transfer inhibitor such as graphite in a polystyrene-based resin foam molded product improves the heat insulating performance, but the expansion performance of expandable polystyrene-based resin particles tends to decrease, and there is a problem that the pre-expanded particles shrink when expanded at a high expansion ratio in particular.

[0011] Although Patent Documents 1 and 2 specify that the amount of isobutane should be more than 20% by weight, 50% by weight, or 55% by weight or less relative to 100% by weight of the total amount of pentane and butane, the inventors of the present application have found that a larger amount of isobutane is preferable in order to obtain a polystyrene-based resin foam molded article with a high expansion ratio of 90 or more. From this perspective, the expandable polystyrene-based resin particles of Patent Documents 1 and 2, in which the amount of isobutane is more than 20% by weight and 50% by weight or less, or 55% by weight or less relative to 100% by weight of the total amount of pentane and butane, have room for improvement in order to achieve a higher expansion ratio.

[0012] Patent Document 3 specifies that the aspect ratio of expandable polystyrene-based resin particles must be 0.95 or less and the sphericity must be 0.97 or more, but does not address the blowing agent. The inventors of the present application have found that a small amount of isobutane reduces the expansion ratio of the expandable polystyrene-based resin particles, and in particular, pre-expanded particles may shrink when expanded to a high expansion ratio. From this perspective, there is room for improvement to achieve a higher expansion ratio.

[0013] Patent Document 4 is an invention that exhibits excellent flame retardancy by impregnating the surface layer of polystyrene resin particles with a flame retardant, but there is a concern that the presence of a large amount of flame retardant with a plasticizing effect in the surface layer locally reduces the resin viscosity, promoting the dispersion of the blowing agent and reducing the foaming performance. From this point of view, there is room for improvement in terms of increasing the expansion ratio.

[0014] Therefore, the present inventors conducted research to solve the above-mentioned problems, and by adding a specific amount of isobutane as a blowing agent and controlling the shape of the expandable polystyrene-based resin particles, they succeeded in producing a polystyrene-based resin foam molded article with a high expansion ratio and low thermal conductivity, thereby completing the present invention.

[0015] That is, the present invention relates to expandable polystyrene-based resin particles comprising a polystyrene-based resin composition containing a radiant heat transfer inhibitor and a blowing agent, wherein the expandable polystyrene-based resin particles have a sphericity of 0.985 or less, the blowing agent contains isobutane, and the content of isobutane is more than 2.7% by weight and not more than 6.0% by weight relative to 100% by weight of the total amount of the polystyrene-based resin composition and the blowing agent (hereinafter sometimes referred to as "expandable polystyrene-based resin particles of the present invention"). In the expandable polystyrene-based resin particles of the present invention, the content of the flame retardant is preferably more than 1.0% by weight and not more than 6.0% by weight relative to 100% by weight of the polystyrene-based resin composition. The expandable polystyrene-based resin particles of the present invention preferably contain pentane. In the expandable polystyrene type resin particles of the present invention, it is preferable that the expandable polystyrene type resin particles are pre-expanded to a bulk ratio of 90 times, and the expanded particles satisfy (Formula 1). (Formula 1)(A) / (B)×100≦25.0 (A) Bulk expansion of pre-expanded foam particles to a bulk expansion ratio of 90 times immediately after expansion (B) Bulk expansion ratio after curing the pre-expanded particles at 30°C for 24 hours In the expandable polystyrene-based resin particles of the present invention, the apparent density of the expandable polystyrene-based resin particles is 950 kg / m 3 Super 1200kg / m 3 It is preferable that: In the expandable polystyrene-based resin particles of the present invention, it is preferable that the amount of blowing agent in the pre-expanded particles is 5.0% to 6.0% when the expandable polystyrene-based resin particles are pre-expanded to a bulk expansion ratio of 90 times and then cured at 30°C for 24 hours. In the expandable polystyrene-based resin particles of the present invention, it is preferable that the expandable polystyrene-based resin particles are pre-expanded to a bulk expansion ratio of 90 times and then cured at 30°C for 24 hours, and then the pre-expanded particles are expanded and molded, and the thermal conductivity of the expanded molded product is 0.034 W / m K or less. The pre-expanded particles of the present invention are pre-expanded particles of the expandable polystyrene resin particles of the present invention, and have a bulk expansion ratio of 90 times or more.

[0016] The present invention also relates to a method for producing expandable polystyrene-based resin particles, in which a polystyrene-based resin melt comprising a polystyrene-based resin composition containing a radiant heat transfer inhibitor and a blowing agent is extruded through a die having a plurality of small holes into pressurized circulating water and then cut into particles with a rotary cutter, wherein the blowing agent contains isobutane, and the isobutane content is more than 2.7 wt % and not more than 6.0 wt % relative to 100 wt % of the total amount of the polystyrene-based resin composition and the blowing agent (hereinafter sometimes referred to as the "first production method of the present invention").

[0017] In the first production method of the present invention, the radiation heat transfer inhibitor preferably contains a carbon-based radiation heat transfer inhibitor. In the first production method of the present invention, the blowing agent preferably contains pentane. [Effects of the Invention]

[0018] According to the expandable polystyrene resin particles of the present invention, it is possible to obtain a polystyrene resin foam molded article that has both a high expansion ratio and high heat insulating performance. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Expandable polystyrene resin particles] The expandable polystyrene-based resin particles of the present invention are expandable polystyrene-based resin particles containing a radiation heat transfer inhibitor, i.e., polystyrene-based resin particles containing a radiation heat transfer inhibitor and a blowing agent. The expandable polystyrene-based resin particles of the present invention have a sphericity of 0.985 or less, and contain more than 2.7 wt% and 6.0 wt% or less of isobutane relative to 100 wt% of the total amount of the polystyrene-based resin composition and the blowing agent, thereby making it possible to obtain a polystyrene-based resin foam molded article that achieves both a high expansion ratio and high thermal insulation performance.

[0020] In general, the use of a radiation heat transfer inhibitor such as graphite in a polystyrene-based resin foam molded body improves its thermal insulation. However, increasing the amount of inorganic substances such as graphite reduces the expandability of expandable polystyrene-based resin particles and leads to the problem of shrinkage of the expanded pre-expanded particles. Although the exact cause is unclear, it is believed that this problem is primarily caused by the inorganic substances, which create holes in the cell membranes of the pre-expanded particles during pre-expansion, making it easier for the blowing agent to escape from the resin during expansion and making it impossible to maintain internal pressure, thereby making shrinkage more likely after expansion. Shrinkage of pre-expanded particles can be restored by curing, but it is predicted that controlling the expansion ratio after curing will be difficult. Furthermore, if the shrinkage is significant, high-temperature curing is required to restore the expansion ratio, which requires additional curing silos capable of high-temperature curing. This requires a large amount of thermal energy during curing, which is costly. In particular, if the shrinkage is even greater, the pre-expanded particles will buckle, making it difficult for the expansion ratio to recover even after curing at high temperatures, and the expansion ratio standard will no longer be met, resulting in a decrease in yield.

[0021] Furthermore, the higher the expansion ratio of expandable polystyrene resin particles containing a radiation heat transfer inhibitor, the more significant the shrinkage of the pre-expanded particles immediately after pre-expansion becomes, making it difficult to achieve a high expansion ratio of 90 times or more.

[0022] Butane has low solubility in polystyrene-based resins, so it is likely to become supersaturated, which is thought to contribute to a high expansion ratio. Furthermore, butane has a smaller molecular weight than pentane, so even a small amount added can contribute to high expansion. In particular, isobutane has a bulkier molecular structure than normal butane, which makes it difficult for the blowing agent to escape from the expandable polystyrene-based resin particles, making it possible to achieve a high expansion ratio. However, even when the blending ratio of pentane and isobutane is controlled as described in Patent Documents 1 and 2, shrinkage may occur immediately after expansion at a high expansion ratio of 90 times or more.

[0023] In general, the higher the sphericity of the expandable polystyrene-based resin particles, the closer they are to a spherical shape, while the lower the sphericity of the expandable polystyrene-based resin particles, the more elliptical they become. Because ellipsoidal shapes have a larger specific surface area than spherical shapes, it is believed that the external additives (anti-blocking agents during pre-expansion and fusion promoters during molding) coated on the surface of the expandable polystyrene-based resin particles effectively work to improve moldability. Furthermore, the amount of external additives used can be reduced, which is thought to lead to cost savings. On the other hand, when expandable polystyrene-based resin particles are expanded at a high expansion ratio of 90 times or more, if the sphericity of the expandable polystyrene-based resin particles is too low, significant shrinkage immediately after expansion is likely to occur.

[0024] Therefore, by setting the sphericity of the expandable polystyrene-based resin particles containing a radiation heat transfer inhibitor to 0.985 or less and setting the amount of isobutane to more than 2.7% by weight relative to 100% by weight of the total amount of the polystyrene-based resin composition and blowing agent, it is possible to obtain a polystyrene-based resin foam molded product that combines a high expansion ratio and high thermal insulation performance.

[0025] Furthermore, since the radiation heat transfer inhibitor, which is an inorganic substance, also acts as a nucleating agent for bubbles, expandable polystyrene-based resin particles containing the radiation heat transfer inhibitor tend to have smaller cell diameters and are more likely to suppress radiation heat, making it possible to achieve better heat insulation performance.

[0026] (Polystyrene resin) The polystyrene resin composition used in the expandable polystyrene resin particles of the present invention contains a polystyrene resin as a base resin. The polystyrene resin may be not only a styrene homopolymer but also a copolymer of styrene with another monomer copolymerizable with styrene or its derivative, provided that the effects of the present invention are not impaired. These may be used alone or in combination of two or more.

[0027] Examples of other monomers copolymerizable with styrene or derivatives thereof include styrene derivatives such as methylstyrene, dimethylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene; polyfunctional vinyl compounds such as divinylbenzene; (meth)acrylic acid ester compounds such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate; cyanide vinyl compounds such as (meth)acrylonitrile; diene compounds or derivatives thereof such as butadiene; unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride; and N-alkyl-substituted maleimide compounds such as N-methylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-(2)-chlorophenylmaleimide, N-(4)-bromophenylmaleimide, and N-(1)-naphthylmaleimide. These may be used alone or in combination of two or more.

[0028] In the present invention, from the viewpoint of impact absorption and heat resistance, for example, diene rubber reinforced polystyrene, acrylic rubber reinforced polystyrene, polyphenylene ether resin, etc. may also be blended.

[0029] The polystyrene-based resin used in the present invention preferably contains a styrene homopolymer, since it is relatively inexpensive, can be foam-molded using low-pressure steam or the like without using a special method, and has an excellent balance of heat insulation performance, flame retardancy, and cushioning performance.

[0030] In the present invention, other resins may be used in combination with the polystyrene resin as the main component, as long as the effects of the present invention are not impaired. Examples of other resins include homopolymers of other monomers copolymerizable with styrene or derivatives thereof, such as polyolefin resins, polyester resins, polycarbonate resins, and acrylic resins, and copolymers thereof.

[0031] (Radiation heat transfer inhibitor) In the present invention, a polystyrene-based resin foam molded article having high thermal insulation performance can be obtained by incorporating a radiation heat transfer inhibitor into expandable polystyrene-based resin particles. Here, the radiation heat transfer inhibitor refers to a material that has the property of reflecting, scattering, or absorbing light in the near-infrared or infrared region (e.g., a wavelength region of about 800 to 3000 nm). While there are no particular limitations on the radiation heat transfer inhibitor, examples include carbon materials, metal particles, metal compounds, and metal oxides. Because metal particles, metal compounds, and metal oxides have low affinity for resins and are prone to reducing foaming performance, it is preferable to incorporate a carbon material, i.e., a carbon-based radiation heat transfer inhibitor.

[0032] Examples of carbon materials include graphite, graphene, carbon black, expanded graphite, activated carbon, carbon nanotubes, and carbon nanofibers. Of these, graphite is preferred from the standpoints of dispersibility in polystyrene resins and cost.

[0033] Examples of graphite include flake graphite, amorphous graphite, spherical graphite, and artificial graphite. In this specification, the term "flake" encompasses scaly, thin, or plate-like graphite. These graphites can be used singly or in combination of two or more. Among these, graphite mixtures primarily composed of flake graphite are preferred, with flake graphite being more preferred, due to their high radiation heat transfer suppression effect. From the viewpoints of high expansion ratio, heat insulating properties, and moldability, the average particle size of the graphite is preferably 1 to 9 μm, and more preferably 2 to 6 μm. The smaller the average particle size of graphite, the higher the production cost. Graphite with an average particle size of less than 1 μm is very expensive due to high production costs, including the cost of pulverization, and the cost of expandable polystyrene-based resin particles tends to be high. On the other hand, if the average particle size exceeds 9 μm, the cell membrane becomes more likely to break when the expandable polystyrene resin particles are used to produce pre-expanded particles and polystyrene resin foam molded articles, which tends to make it difficult to achieve a high expansion ratio, reduce ease of molding, and reduce the compressive strength of the polystyrene resin foam molded articles. The average particle size of graphite here refers to the D50 particle size calculated by a laser diffraction / scattering method based on the Mie theory in accordance with JIS Z8825-1.

[0034] Examples of metal particles include gold, silver, copper, platinum, palladium, zinc, aluminum, and tin.

[0035] Examples of the metal compound include aluminum-based compounds, zinc-based compounds, magnesium-based compounds, titanium-based compounds, antimony-based compounds, calcium-based compounds, and tin-based compounds.

[0036] Examples of metal oxides include aluminum oxide, magnesium oxide, titanium oxide, calcium oxide, copper oxide, zinc oxide, and iron oxide.

[0037] The content of the radiation heat transfer inhibitor in the expandable polystyrene-based resin particles of the present invention is preferably 2 to 40 wt% based on 100 wt% of the polystyrene-based resin composition. From the viewpoint of easy control of the target expansion ratio and a balance of the thermal conductivity reduction effect, etc., the content is more preferably 3 to 30 wt%, and even more preferably 3 to 20 wt%. A content of the radiation heat transfer inhibitor of 2 wt% or more provides a sufficient thermal conductivity reduction effect. On the other hand, a content of 40 wt% or less makes it easier to achieve a high expansion ratio and to control the expansion ratio because the cell membrane is less likely to break when producing pre-expanded particles and polystyrene-based resin foam molded articles from the expandable polystyrene-based resin particles. Here, the term "polystyrene-based resin composition" as used herein refers to a component composition constituting the expandable polystyrene-based resin particles, but does not include a blowing agent.

[0038] In the present invention, two or more types of radiation heat transfer inhibitors may be added in combination as long as the effects of the present invention are not impaired.

[0039] (foaming agent) The expandable polystyrene resin particles of the present invention contain butane as a blowing agent. Isobutane is essential as the butane. From the viewpoints of achieving a high expansion ratio by suppressing shrinkage immediately after pre-expansion and production stability, the isobutane content is more than 2.7 wt% and not more than 6.0 wt% relative to 100 wt% of the total amount of the polystyrene resin composition and the blowing agent. The isobutane content relative to 100 wt% of the total amount of the polystyrene resin composition and the blowing agent is preferably 2.75 wt% or more, more preferably 2.8 wt% or more, and particularly preferably 2.9 wt% or more. On the other hand, the isobutane content relative to 100 wt% of the total amount of the polystyrene resin composition and the blowing agent is preferably 5.0 wt% or less, more preferably 4.5 wt% or less, and particularly preferably 4.2 wt% or less. If the isobutane content exceeds 2.7% by weight, a high expansion ratio can be achieved. On the other hand, if the content is 6.0% by weight or less, when produced by melt extrusion, expansion during the production of expandable polystyrene-based resin particles can be suppressed, cutting becomes possible, die clogging is suppressed, and the collection of expandable polystyrene-based resin particles is stabilized.

[0040] In addition to isobutane, other hydrocarbon-based blowing agents having 4 to 5 carbon atoms may also be used as the blowing agent in the present invention. Examples include hydrocarbons such as normal pentane, isopentane, normal butane, neopentane, and cyclopentane. When isobutane is used in combination with other hydrocarbon-based blowing agents having 4 to 5 carbon atoms, the amount of the other hydrocarbon-based blowing agent having 4 to 5 carbon atoms added is preferably 1 to 8 parts by weight per 100 parts by weight of the polystyrene-based resin composition. From the viewpoints of improved productivity due to a shortened heating time during pre-expansion and improved flame retardancy, the amount is more preferably 2 to 6 parts by weight. Furthermore, since pentane has a stronger effect of plasticizing polystyrene-based resins than isobutane, it is preferable to use isobutane and pentane in combination to shorten the heating time during pre-expansion. Therefore, when isobutane and pentane are used in combination, the amount of pentane added is preferably 1 to 8 parts by weight per 100 parts by weight of the polystyrene-based resin composition. From the viewpoints of improved productivity due to a shortened heating time during pre-expansion and improved flame retardancy, the amount is more preferably 2 to 6 parts by weight. As the pentane, normal pentane and isopentane are preferably used as a mixture, and more preferably normal pentane and isopentane are used in a weight ratio (normal pentane / isopentane) of 100 / 0 to 60 / 40. From the viewpoint of expansion recovery and self-extinguishing properties of the pre-expanded particles after curing at 30°C for 24 hours, a weight ratio of 98 / 2 to 60 / 40 is more preferred.

[0041] The amount of blowing agent added is preferably 2.8 to 15 parts by weight per 100 parts by weight of the polystyrene resin composition. When the amount of blowing agent added is 2.8 parts by weight or more, the foaming power is sufficient, making it easy to achieve a high expansion ratio, and it becomes easy to produce a polystyrene resin foam molded article with a high expansion ratio. Furthermore, when the amount of blowing agent is 15 parts by weight or less, the flame retardant performance is less likely to deteriorate, and the production time (molding cycle) for producing a polystyrene resin foam molded article is shortened, thereby reducing production costs. The amount of blowing agent added is more preferably 3 to 12 parts by weight, and even more preferably 4 to 10 parts by weight per 100 parts by weight of the polystyrene resin composition.

[0042] The expandable polystyrene-based resin particles of the present invention contain a polystyrene-based resin, a radiation heat transfer inhibitor, and a blowing agent, and may optionally contain at least one optional component selected from the group consisting of a flame retardant, a heat stabilizer, a radical generator, an external additive, and other additives. The expandable polystyrene-based resin particles of the present invention preferably contain a polystyrene-based resin, a radiation heat transfer inhibitor, a blowing agent, an external additive, and a flame retardant, and may optionally contain at least one of the above-mentioned optional components excluding the flame retardant. More preferably, the expandable polystyrene-based resin contains a polystyrene-based resin, a radiation heat transfer inhibitor, a blowing agent, an external additive, a flame retardant, and a heat stabilizer, and may optionally contain at least one of the above-mentioned optional components excluding the flame retardant and the heat stabilizer. Even more preferably, the expandable polystyrene-based resin contains a polystyrene-based resin, a radiation heat transfer inhibitor, a blowing agent, an external additive, a flame retardant, a heat stabilizer, and a nucleating agent, and may optionally contain at least one of the above-mentioned optional components excluding the flame retardant, the heat stabilizer, and the nucleating agent.

[0043] (Flame retardant) The flame retardant that can be used in the present invention is not particularly limited, and any known flame retardant that has been conventionally used in polystyrene resin foam moldings can be used, but among them, bromine-based flame retardants that have a high flame retardancy-imparting effect are preferred. Examples of brominated flame retardants that can be used in the present invention include brominated bisphenol compounds such as 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane (also known as tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether)) and 2,2-bis[4-(2,3-dibromopropoxy)-3,5-dibromophenyl]propane (also known as tetrabromobisphenol A-bis(2,3-dibromopropyl ether)); brominated butadiene-vinyl aromatic hydrocarbon copolymers such as brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers (disclosed, for example, in JP-T-2009-516019); and tetrabromocyclooctane. These brominated flame retardants may be used alone or in combination of two or more.

[0044] The content of the flame retardant is preferably more than 1.0 wt% and not more than 6.0 wt%, and more preferably more than 1.0 wt% and not more than 4.0 wt%, based on 100 wt% of the polystyrene resin composition, from the viewpoints of easy control of the expansion ratio to the desired level and of the balance of flame retardancy when a radiant heat transfer inhibitor is added. If the content is more than 1.0 wt%, the flame retardancy imparting effect is not reduced, and if it is not more than 6.0 wt%, the strength of the obtained polystyrene resin expansion molded article is less likely to decrease.

[0045] (heat stabilizer) In the expandable polystyrene-based resin particles of the present invention, by further using a heat stabilizer in combination, it is possible to suppress deterioration of the expandable polystyrene-based resin particles and deterioration of the flame retardant due to decomposition of the flame retardant during the production process.

[0046] The heat stabilizers in the present invention can be used in appropriate combination depending on the type of polystyrene resin used, the type and content of the foaming agent, the type and content of the radiant heat transfer inhibitor, the type and content of the flame retardant, etc.

[0047] The heat stabilizer used in the present invention is preferably a hindered amine compound, a phosphorus-based compound, or an epoxy compound, since it allows for the 1% weight loss temperature of the polystyrene resin composition to be arbitrarily controlled in thermogravimetric analysis. The heat stabilizers can be used alone or in combination of two or more.

[0048] The amount of the heat stabilizer is preferably 0.5 to 3 wt% per 100 wt% polystyrene resin composition, from the viewpoints of easy control of the expansion ratio to the desired level and of the balance of flame retardancy when a radiation heat transfer inhibitor is added. If the amount is 0.5 wt% or more, the flame retardant is less likely to decompose and the flame retardancy-imparting effect is not reduced, and if the amount is 3 wt% or less, the strength of the resulting polystyrene resin expansion molded article is less likely to decrease.

[0049] (external additives) The external additive that can be used in the present invention is not particularly limited, and any of the known external additives that have been conventionally used for expandable polystyrene-based resin particles can be used. By coating the expandable polystyrene-based resin particles with an external additive, it is possible to suppress blocking (adhesion between expanded particles) during pre-expansion and promote fusion during molding. Examples of external additives include fatty acid triglycerides such as lauric acid triglyceride, stearic acid triglyceride, and linoleic acid triglyceride; fatty acid diglycerides such as lauric acid diglyceride, stearic acid diglyceride, and linoleic acid diglyceride; fatty acid monoglycerides such as lauric acid monoglyceride, stearic acid monoglyceride, and linoleic acid monoglyceride; fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, and calcium laurate; and nonionic surfactants such as polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene laurate, polyoxyethylene palmitate, polyoxyethylene stearate, and polyoxyethylene oleate. These external additives may be used alone or in combination of two or more. A preferred coating method for these external additives is to apply them after drying and mix them to coat. A preferred external additive is a combination of zinc stearate and hydroxystearic acid triglyceride, which is preferred because it is easy to achieve both suppression of blocking during pre-expansion and promotion of fusion during molding.

[0050] (Other additives) The polystyrene resin composition of the expandable polystyrene resin particles of the present invention may optionally contain one or more additives selected from the group consisting of radical generators, processing aids, light resistance stabilizers, nucleating agents, foaming aids, antistatic agents, and colorants such as pigments, as long as the effects of the present invention are not impaired. Examples of radical generators include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, and poly-1,4-isopropylbenzene. Examples of processing aids include sodium stearate, magnesium stearate, calcium stearate, zinc stearate, barium stearate, and liquid paraffin. Examples of light resistance stabilizers include the above-mentioned hindered amines, phosphorus-based stabilizers, and epoxy compounds, as well as phenolic antioxidants, nitrogen-based stabilizers, sulfur-based stabilizers, and benzotriazoles. Examples of nucleating agents include inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, calcium carbonate, sodium bicarbonate, and talc; polymeric compounds such as methyl methacrylate copolymers and ethylene-vinyl acetate copolymer resins; olefin waxes such as polyethylene wax; and fatty acid bisamides such as methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, and ethylene bisoleic acid amide. Examples of foaming aids that can be used include solvents with a boiling point of 200°C or less at atmospheric pressure, such as aromatic hydrocarbons such as styrene, toluene, ethylbenzene, and xylene; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and acetate esters such as ethyl acetate and butyl acetate. Antistatic agents and colorants that are used in various resin compositions can be used without particular limitation. These other additives can be used alone or in combination of two or more.

[0051] The sphericity of the expandable polystyrene-based resin particles of the present invention is 0.985 or less. In order for the external additive to function effectively, the sphericity is preferably 0.983 or less, and more preferably 0.980 or less. It is presumed that when the sphericity of the expandable polystyrene-based resin particles is 0.985 or less, the external additive functions effectively, improving moldability, thereby producing an expanded molded article with a high expansion ratio. On the other hand, the sphericity of the expandable polystyrene-based resin particles is preferably 0.900 or more, more preferably 0.920 or more, and particularly preferably 0.940 or more. When the sphericity of the expandable polystyrene-based resin particles is 0.900 or more, the shape is not extremely distorted, and the significant shrinkage that occurs during high-expansion expansion can be alleviated.

[0052] In the expandable polystyrene resin particles of the present invention, the shrinkage percentage of the expanded particles pre-expanded to a bulk ratio of 90 is preferably 25.0 or less, more preferably 22.0 or less, and particularly preferably 20.0 or less. The shrinkage percentage of the pre-expanded particles is calculated by the following formula: (Formula) Shrinkage rate of pre-expanded particles (%) = (A) / (B) x 100 (A) Bulk expansion of pre-expanded foam particles to a bulk expansion ratio of 90 times immediately after expansion (B) Bulk expansion ratio after curing the pre-expanded particles at 30°C for 24 hours When the shrinkage ratio of the pre-expanded particles calculated from the above formula (1) is 25.0 or less, the expansion ratio after 24 hours of curing at 30° C. is high and the expansion ratio is easily restored. If the shrinkage ratio of the pre-expanded particles is greater than 25.0, the cells of the pre-expanded particles will buckle, making it difficult to restore the expansion ratio even after curing at high temperatures. However, since the expandable polystyrene resin particles of the present invention have suppressed shrinkage, there is no need to cure the pre-expanded particles at high temperatures, and control of the expansion ratio after curing becomes easier.

[0053] The expandable polystyrene resin particles of the present invention have an apparent density of 950 kg / m 3 Super 1200kg / m 3 From the viewpoint of foaming property, it is preferable that the viscosity is 980 kg / m or less. 3 More preferably, it is greater than 1000 kg / m 3On the other hand, from the viewpoint of heat insulation performance, it is more preferable that the density is 1150 kg / m or more. 3 It is preferable that the saturation is 1100 kg / m or less. 3 More preferably, it is 1080 kg / m or less. 3 The following are particularly preferred: Here, the density of a typical polystyrene resin is 1050 kg / m 3 ~1060kg / m 3 However, if the polystyrene resin composition contains a high-density inorganic substance as a radiation heat transfer inhibitor, and thus foaming during extrusion in producing expandable polystyrene resin particles can be suppressed, the density of 1050 kg / m 3 ~1060kg / m 3 The density of the expandable polystyrene resin particles should be higher than that of the expandable polystyrene resin particles. 3 Super 1200kg / m 3 It is believed that foaming during extrusion of a polystyrene-based resin melt comprising a polystyrene-based resin composition and a foaming agent is suppressed by the following: By obtaining expandable polystyrene-based resin particles in which foaming during extrusion is suppressed, the closed cell ratio in the pre-expanded particles increases, and the strength of the cell structure increases, making it possible to suppress shrinkage immediately after pre-expansion and achieve a high expansion ratio.

[0054] In the expandable polystyrene resin particles of the present invention, the amount of blowing agent remaining in the pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles is preferably 5.0 to 6.0% by weight, more preferably 5.2 to 5.8% by weight, after the pre-expanded particles are cured for 24 hours at 30° C. A blowing agent amount of 5.0% by weight or more in the pre-expanded particles facilitates molding, while a blowing agent amount of 6.0% by weight or less shortens the molding cycle and provides excellent productivity for foamed molded articles.

[0055] In the expandable polystyrene resin particles of the present invention, the pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles preferably have a bulk expansion ratio of 90 or more after curing at 30°C for 24 hours. When the bulk expansion ratio of the pre-expanded particles is 90 or more, the density of the polystyrene resin foam molded article obtained by molding the pre-expanded particles decreases, making it possible to produce a lighter polystyrene resin foam molded article. In addition, increasing the bulk expansion ratio allows for a reduction in the amount of resin used, leading to cost reductions.

[0056] [Method for producing expandable polystyrene resin particles] The expandable polystyrene-based resin particles of the present invention can be obtained by a known melt-kneading method. Specifically, the polystyrene-based resin, the radiation heat transfer inhibitor, and the blowing agent are melt-kneaded in an extruder (melt-kneading step), and the melt-kneaded mixture is extruded through a die with small holes attached to the tip of the extruder into a chamber filled with pressurized circulating water (extrusion step), and the melt-kneaded mixture immediately after extrusion is cut with a rotary cutter and cooled and solidified with pressurized circulating water (cooling step). This manufacturing method makes it easy to obtain expandable polystyrene-based resin particles with a sphericity of 0.985 or less. Preferably, the expandable polystyrene-based resin particles of the present invention can be obtained by the following manufacturing method.

[0057] The method for producing expandable polystyrene-based resin particles of the present invention comprises extruding a polystyrene-based resin melt comprising a polystyrene-based resin composition containing a radiant heat transfer inhibitor and a blowing agent through a die having a plurality of small holes into pressurized circulating water, and cutting the melt into particles with a rotary cutter, wherein the blowing agent contains isobutane, and the amount of isobutane is more than 2.7 wt % and not more than 6.0 wt % relative to 100 wt % of the total amount of the polystyrene-based resin composition and the blowing agent (hereinafter, may be referred to as the "production method of the present invention").

[0058] Of the components in the production method of the present invention, the components described above in the section [Expandable polystyrene resin particles] can also be applied to the production method of the present invention.

[0059] In the production method of the present invention, from the viewpoint of dispersibility of the polystyrene resin and the various components, it is preferable to prepare a kneaded mixture in advance by kneading the polystyrene resin and the various components under load using a kneading device equipped with a twin-screw agitator (for example, a Banbury mixer), and then feed the obtained kneaded mixture and the polystyrene resin into an extruder to melt-knead them, and then cut them into particles.

[0060] In a preferred embodiment of the production method of the present invention, a polystyrene-based resin and a radiation heat transfer inhibitor are kneaded in a kneading device equipped with a twin-screw agitator such as a Banbury mixer to prepare a masterbatch as a kneaded product, and the prepared masterbatch, a new polystyrene-based resin, a blowing agent, and, if necessary, other components such as a flame retardant, are melt-kneaded in an extruder, and the resulting resin melt is extruded through a die having small holes attached to the tip of the extruder into a cutter chamber filled with pressurized circulating water, cut with a rotary cutter immediately after extrusion, and cooled and solidified by the pressurized circulating water. In this case, the melt-kneading in the extruder can be performed using a single extruder, a plurality of extruders connected together, or an extruder in combination with a second kneading device such as a static mixer or an agitator without a screw, and can be selected as appropriate.

[0061] The polystyrene resin and the radiation heat transfer inhibitor are preferably kneaded using a kneading device equipped with a twin-screw agitator, such as an intensive mixer, internal mixer, or Banbury mixer, which can knead the resin under load, to prepare a masterbatch. While the concentration of the masterbatch is not particularly limited, a radiation heat transfer inhibitor concentration of 20% to 80% by weight is preferred for balancing kneadability and cost. The prepared masterbatch, polystyrene resin, blowing agent, and optionally flame retardant, thermal stabilizer, and other additives are melt-kneaded in a first extruder and, if necessary, a second kneading device attached to the extruder. The resulting resin melt is cooled to a predetermined temperature and then extruded through a die with small holes into a cutter chamber filled with pressurized circulating water. Immediately after extrusion, the resin is cut into pellets using a rotary cutter, and the resulting pellets (resin particles) are cooled and solidified using pressurized circulating water to obtain expandable polystyrene resin particles. Similarly, for other additives such as a flame retardant and a heat stabilizer, a masterbatch of the polystyrene resin and the other additives may be prepared in advance and then charged into an extruder, etc. Furthermore, for the radiation heat transfer inhibitor, flame retardant, heat stabilizer, and other additives, the raw materials may be directly charged into an extruder without preparing them into a masterbatch.

[0062] When pentane and butane are used in combination as the blowing agent, the method of addition is not particularly limited as long as pentane and butane are added, and they may be added simultaneously, or one may be added first and then the other.

[0063] The amount of isobutane used in the production method of the present invention is more than 2.7 wt% and not more than 6.0 wt%, based on 100 wt% of the total amount of the polystyrene resin composition and the blowing agent. When produced by melt extrusion, if the amount of isobutane exceeds 6.0 wt%, it becomes difficult to suppress foaming during the production of expandable polystyrene resin particles, causing blockage of the die and making it difficult to stably obtain expandable polystyrene resin particles.

[0064] In the production method of the present invention, isobutane and pentane may be used in combination, and when isobutane and pentane are used in combination, the amount of pentane added is preferably 1 to 8 parts by weight per 100 parts by weight of the polystyrene resin composition, and more preferably 2 to 6 parts by weight from the viewpoints of improving productivity by shortening the heating time during pre-expansion and of flame retardancy.

[0065] The temperature set in the melt-kneading section of the extruder is preferably 100°C to 250°C. Furthermore, the residence time in the extruder from when the polystyrene resin and various components are fed to the extruder until the end of melt-kneading is preferably 10 minutes or less. If the temperature set in the melt-kneading section of the extruder is 250°C or less and / or the residence time in the extruder until the end of melt-kneading is 10 minutes or less, the flame retardant added will not decompose, and the desired flame retardancy can be obtained. There is also no need to add an excessive amount of flame retardant to impart the desired flame retardancy. On the other hand, if the temperature set in the melt-kneading section of the extruder is 100°C or more, the load on the extruder will not be large, resulting in stable extrusion and good dispersibility of the added components.

[0066] Here, the melt-kneading section of the extruder means the section from the feed section to the tip of the final downstream extruder when the extruder is configured with a single or twin screw. When a second kneading device such as a static mixer or a mixer without a screw is used in conjunction with the first extruder, it means the section from the feed section of the first extruder to the tip of the second kneading device.

[0067] The water pressure of the pressurized circulating water is preferably 1.0 MPa or more and 2.0 MPa or less, and more preferably 1.1 MPa or more and 1.8 MPa or less. If the water pressure is 1.0 MPa or more, foaming can be suppressed, the bulk density of the expandable polystyrene resin particles increases, and a decrease in the expansion ratio and transport efficiency is less likely to occur. On the other hand, if the water pressure is 2.0 MPa or less, the rotary cutter is not pushed back by the water pressure, and the extruded molten resin does not wrap around the rotary cutter, allowing for stable production.

[0068] The temperature of the pressurized circulating water is preferably 45°C or higher and 80°C or lower, and more preferably 50°C or higher and 70°C or lower. If the water temperature is 45°C or higher, blockage of the die due to cooling can be suppressed. On the other hand, if the water temperature is 80°C or lower, foaming in the pressurized circulating water can be suppressed, the bulk density of the expandable polystyrene resin particles increases, and a decrease in transport efficiency is less likely to occur.

[0069] The die used in the present invention is not particularly limited, but examples thereof include those having small holes with a diameter of 0.3 mm to 2.0 mm, preferably 0.4 mm to 1.5 mm.

[0070] The cutting device for cutting the molten resin extruded into the pressurized circulating water is not particularly limited, but examples thereof include a device in which the molten resin is cut into small pellets by a rotary cutter that comes into contact with a die lip, and then transported to a centrifugal dehydrator where it is dehydrated and collected.

[0071] The method for coating the external additive used in the present invention is not particularly limited, but a preferred coating method is, for example, a method in which the additive is applied after drying and then mixed to coat the surface.

[0072] [Polystyrene resin foam molding] The expandable polystyrene-based resin particles of the present invention are not particularly limited, but can be expanded to a predetermined expansion ratio to form pre-expanded particles, and a polystyrene-based resin foam molded article can be produced by a pre-expanding method in which the expandable polystyrene-based resin particles are expanded to a predetermined expansion ratio to form pre-expanded particles, and these pre-expanded particles are used for molding.

[0073] Since the higher the expansion ratio of a polystyrene-based resin foam molded article, the less the amount of expandable polystyrene-based resin particles used as the raw material is, the less expensive it is. According to the present invention, a polystyrene-based resin foam molded article with a high expansion ratio can be produced at a lower cost. It should be noted that high-expansion expansion was difficult with conventional expandable polystyrene-based resin particles containing graphite. However, with the expandable polystyrene-based resin particles of the present invention and the expandable polystyrene-based resin particles obtained by the production method of the present invention, high-expansion expansion is possible by controlling the isobutane content contained in the expandable polystyrene-based resin particles, and a lightweight, easy-to-handle, and more inexpensive thermal insulating material can be provided.

[0074] The expandable polystyrene resin particles of the present invention are subjected to a known pre-expansion process, for example, by expanding them with steam to 10 to 120 times their original size to form pre-expanded particles (pre-expansion process), and after curing for a certain period of time as necessary, the pre-expanded particles are molded with steam using a known molding machine to produce a polystyrene resin foam molded article. Depending on the shape of the mold used, a molded article with a complex shape or a block-like molded article can be obtained.

[0075] (Pre-foaming process) The pre-expansion step can be carried out using a pre-expansion machine in the same manner as in the pre-expansion of conventional expandable polystyrene resin particles.

[0076] Any known pre-expanding machine can be used, for example, a pre-expanding machine equipped with a stirrer, a can in which expandable polystyrene resin particles are accommodated, a steam chamber disposed below the can for supplying steam to the can, and a pre-expanded particle outlet.

[0077] The internal pressure (cage pressure) during the introduction of steam is not particularly limited, but is preferably 0.001 to 0.15 MPa, more preferably 0.01 to 0.10 MPa, and even more preferably 0.03 to 0.08 MPa. When the internal pressure is 0.01 MPa or higher, the time for introducing steam during pre-expansion can be set to 500 seconds or less when a high expansion ratio is desired. When the internal pressure is 0.15 MPa or lower, it is not necessary to increase the pressure of steam, the occurrence of blocking phenomenon decreases, and the pre-expansion yield increases.

[0078] The pre-expansion step can be carried out either continuously or batchwise.

[0079] The continuous method is a method in which expandable polystyrene resin particles are continuously fed into a can and pre-expanded particles are continuously discharged from a discharge port provided at the top of the can. The expansion ratio of the pre-expanded particles can be adjusted, for example, by appropriately selecting the amount (weight) of expandable polystyrene resin particles fed into the can per unit time. In the case of the continuous method, the residence time in the pre-expanding machine can from the time the expandable polystyrene resin particles are fed into the can until the pre-expanded particles are discharged is defined as the steam feeding time.

[0080] In addition, the batch method is a method in which a predetermined amount of expandable polystyrene resin particles is placed in a can, and after pre-expanding them to a predetermined expansion ratio, the supply of steam is stopped, and then air is blown into the can as needed to cool and dry the pre-expanded particles, which are then removed from the can. The expansion ratio of the pre-expanded particles can be adjusted by appropriately selecting the amount (weight) of expandable polystyrene resin particles placed in the can per batch. Since the batch method is a method in which the placed expandable polystyrene resin particles are pre-expanded to a predetermined volume, the smaller the amount placed per batch, the higher the expansion ratio of the resulting pre-expanded particles.

[0081] It is also advisable to cure the pre-expanded particles immediately after pre-expansion. Water vapor is present within the expanded particles during pre-expansion, but the water vapor condenses into water during the cooling process after expansion, resulting in a reduced pressure inside the pre-expanded particles immediately after pre-expansion. If the cell wall strength of the pre-expanded particles is low during this reduced pressure state, shrinkage may readily occur. Furthermore, if the closed cell ratio of the pre-expanded particles is low, the strength of the cell structure decreases, making them more susceptible to shrinkage. Therefore, a curing process in which the interior of the pre-expanded particles is replaced with air and returned to atmospheric pressure is effective. Since shrinkage immediately after pre-expansion is suppressed in the pre-expanded particles of the polystyrene-based resin expandable particles of the present invention, the curing process can restore the desired expansion ratio.

[0082] The temperature during curing is not particularly limited, but is preferably 20 to 80°C, more preferably 25 to 70°C, and even more preferably 30 to 60°C. If the curing temperature is 20°C or higher, air is easily introduced into the pre-expanded particles, which have been in a reduced pressure state, and the pressure inside the expanded particles is easily returned to atmospheric pressure. If the curing temperature is 80°C or lower, the blowing agent present in the pre-expanded particles is less likely to escape, and the expandability is not reduced, and the surface beauty of the molded article is not reduced.

[0083] The polystyrene resin foam molded article of the present invention can be used for various purposes, such as building insulation materials used for floors, walls, roofs, etc., agricultural and marine product boxes such as boxes for transporting marine products such as fish and boxes for transporting agricultural products such as vegetables, bathroom insulation materials, and hot water tank insulation materials. [Example]

[0084] The present invention will be specifically explained below based on Reference Examples, Examples and Comparative Examples, but the present invention is not limited to these.

[0085] The measurement and evaluation methods used in the following Reference Examples, Examples, and Comparative Examples are as follows.

[0086] (Method for measuring sphericity of expandable polystyrene resin particles) (1) Measuring device: Retsch Technology CAMSIZER P4 (2) Setting conditions: The feeder and funnel parameters were set to the following conditions. Control level when moving forward quickly: 55 Maximum time for fast forward movement [sec]: 60 Start level: 50 Maximum Control Level: 75 Target coverage area [%]: 0.5 Feeder width [mm]: 60 Use the guidance sheet The following conditions were used as measurement data. Basic camera coverage area [%] < 3 Zoom camera coverage area [%] < 5 However, particles that met the following conditions in the photographed projection were excluded from the measurement data. Convexity ≧ 0.99 If particles fall onto each other at the projection measurement point, the shape of each particle cannot be accurately evaluated, so the feeder and funnel parameters were set to the above conditions. Similarly, if a large number of particles fall at the same time, it may be impossible to accurately evaluate the shape of each particle. For this reason, if the number of particles falling exceeds the set coverage area, the projection data for that particle was excluded.

[0087] Furthermore, to eliminate the influence of minute foreign matter such as dust, data with a convexity (surface roughness) of 0.99 or more was excluded from the analysis. (3) Measurement method: A projection image of approximately 50 g of expandable polystyrene resin particles was photographed using the CAMSIZER P4 set as described above, and the perimeter and area of ​​the projection image of each expandable polystyrene resin particle obtained were measured. The average sphericity was calculated from the perimeter and area of ​​the projection image of each expandable polystyrene resin particle obtained using the following formula.

number

[0088] However, in the above formula, Si is the area of ​​the i-th particle (mm 2 ), R i Let be the perimeter (mm) of the ith particle.

[0089] (Method for measuring the apparent density of expandable polystyrene resin particles) W (kg) of expandable polystyrene resin particles was collected as a measurement sample, and this measurement sample was allowed to fall naturally into a measuring cylinder containing ethanol, and its mass (kg) and volume (m 3 ) was measured, and the apparent density was calculated based on the following formula:

[0090] Apparent density (kg / m 3 ) = weight of measured sample (W) / volume of measured sample (V).

[0091] (Method for measuring bulk magnification of pre-expanded particles) Each pre-expanded particle was collected as a measurement sample, W (g), and the measurement sample was allowed to fall naturally into a measuring cylinder. The measuring cylinder was then struck to determine the apparent volume V (cm 3 ) is constant, and its mass (g) and volume (cm 3 ) was measured, and the bulk magnification was calculated based on the following formula.

[0092] Bulk magnification (cm 3 / g) = Volume of measurement sample (V) / Weight of measurement sample (W) The bulk expansion ratio of pre-expanded particles measured within 5 to 10 minutes after the pre-expanded particles were discharged from the pre-expanding machine is defined as the bulk expansion ratio immediately after expansion, when shrinkage occurs after pre-expansion.

[0093] The bulk expansion ratio of the pre-expanded particles measured after curing at 30°C for 24 hours after shrinkage is defined as the bulk expansion ratio after curing.

[0094] (Calculation method for shrinkage rate of pre-expanded particles) The value calculated by the following formula is defined as the shrinkage rate of the pre-expanded particles.

[0095] Formula:(A) / (B)×100 (A) Bulk expansion of pre-expanded foam particles to a bulk expansion ratio of 90 times immediately after expansion (B) Bulk expansion ratio after curing the pre-expanded particles at 30°C for 24 hours (Method for measuring the amount of blowing agent in pre-expanded particles) The expandable polystyrene resin particles were pre-expanded, and after curing at 30°C for 24 hours, the weight W1 (g) of the expanded particles was measured, heated in an oven at 150°C for 30 minutes, then cooled at room temperature in a desiccator for 30 minutes, and the weight W2 (g) was measured again. The value calculated using the following formula was used as the amount of blowing agent in the pre-expanded particles.

[0096] Amount of foaming agent in pre-expanded particles (wt%) = (W1 - W2) / W1 x 100 (Expansion ratio of polystyrene resin foam molded body) The polystyrene resin foam molded body was removed from the mold and dried at 30°C for 24 hours. The weight (g) of the foam molded body was then measured, and the length, width, and thickness of the foam molded body were measured using a vernier caliper. The volume (cm3) of the polystyrene resin foam molded body was calculated from the measured dimensions. 3 ) was calculated, and the expansion ratio was calculated according to the following formula. Foaming ratio (cm 3 / g) = test piece volume (cm 3 ) / test piece weight (g) The expansion ratio of polystyrene resin foam moldings is conventionally expressed as "cm 3 It is also expressed as " / g".

[0097] (Method for measuring the thermal conductivity of polystyrene-based resin foam molded products) It is generally known that the higher the average temperature at which thermal conductivity is measured, the greater the thermal conductivity value, and so it is necessary to determine the average measurement temperature in order to compare thermal insulation properties. In this specification, the standard used is 23°C, as specified in JIS A9511:2006R, the standard for foamed plastic insulation materials.

[0098] The thermal conductivity was measured by leaving the polystyrene resin foam molded body at 70°C for 96 hours, cutting out a sample for measuring the thermal conductivity, and leaving it at 23°C for 24 hours.

[0099] More specifically, the polystyrene resin foam molded article was left to stand at 70°C for 96 hours, and then a sample measuring 300 mm long x 300 mm wide x 50 mm was cut out. The sample was then left to stand at 23°C for 24 hours, and then its thermal conductivity was measured at an average temperature of 23°C and a temperature difference of 20°C by the heat flow meter method using a thermal conductivity measuring device (HC-074, manufactured by Eiko Seiki Co., Ltd.) in accordance with JIS A1412-2:1999.

[0100] (Flame retardancy evaluation of polystyrene resin foam moldings) Flame retardancy was measured by cutting out a sample from a polystyrene foam molded article after leaving it at 70°C for 96 hours, and then leaving it at 23°C for 24 hours. Flame retardancy was evaluated in accordance with JISA9511:2006R (measurement method A). The flame extinction time was calculated as the average of the measurement results for five test pieces, and the flame retardancy of the polystyrene foam molded article was evaluated based on the following criteria.

[0101] 〇: Consumed within 3 seconds ×: Burning continues for 3 seconds or more (Fusion evaluation of polystyrene resin foam moldings) The obtained polystyrene resin foam molded article was broken, and the fracture surface was visually observed to determine the area of ​​the entire fracture surface where the particles themselves, not the particle interfaces, were broken, and the percentage (%) of the area where the particles themselves were broken relative to the entire fracture surface area was calculated. The fusion of the polystyrene resin foam molded article was evaluated based on the following criteria.

[0102] 〇: Over 80% fusion △: Fusion: Over 60% and up to 80% ×: Fusion 60% or less The raw materials used in the Reference Examples, Examples, and Comparative Examples are shown below.

[0103] (styrene resin) (A) Styrene homopolymer [PS Japan Co., Ltd., 680] (graphite) (B) Graphite [Marutoyo Foundry Manufacturing Co., Ltd., flake graphite SGP-40B] (Brominated flame retardants) (C) 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane [manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., SR-130, bromine content = 66 wt%].

[0104] (heat stabilizer) (D1) Tetrakis(2,2,6,6-tetramethylpiperidyloxycarbonyl)butane [ADEKA Corporation, LA-57] (D2) Bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite [PEP-36 manufactured by ADEKA Corporation].

[0105] (foaming agent) (E1) Normal pentane [Wako Pure Chemical Industries, Ltd., reagent grade] (E2) Isopentane [Wako Pure Chemical Industries, Ltd., reagent grade] (E3) Isobutane [Mitsui Chemicals, Inc.] (Other additives) (F) Ethylene bisstearic acid amide [NOF Corporation, Alflow H-50S].

[0106] (Production Example 1) (Graphite Masterbatch (G)) The raw materials were fed into a Banbury mixer so that the total weight (A+B+F) of 49% by weight of polystyrene resin (A), 50% by weight of graphite (B), and 1% by weight of ethylene bisstearamide (F) was 100% by weight, and the mixture was mixed at 5 kgf / cm 2 The mixture was kneaded for 20 minutes under a load of 1000 kJ / s without heating or cooling. The resin temperature was measured and found to be 180°C. The resin was fed to a ruder and extruded at 250 kg / hr through a die with small holes attached to the tip. The strand-shaped resin was cooled and solidified in a water bath at 30°C, and then cut to obtain masterbatch (G). The graphite content in masterbatch (G) was 50% by weight.

[0107] (Production Example 2) (Masterbatch (H) of a mixture of a brominated flame retardant and a heat stabilizer) After feeding polystyrene resin (A) into a twin-screw extruder and melt-kneading it, a mixture of brominated flame retardant (C) and heat stabilizers (D1) and (D2) was fed midway through the extruder and further melt-kneaded. The weight ratio of each material was (A):(C):(D1):(D2) = 70:28.5:0.6:0.9, with (A) + (C) + (D1) + (D2) = 100 wt%. Strands of resin extruded at 300 kg / hr through a die with small holes attached to the tip of the extruder were cooled and solidified in a water bath at 20°C and then cut to obtain a masterbatch (H) of a mixture of brominated flame retardant and heat stabilizer. The extruder temperature was set to 170°C.

[0108] (Production Example 3) (Mixture (I) of Brominated Flame Retardant and Heat Stabilizer) Brominated flame retardant (C), heat stabilizers (D1) and (D2) were mixed in a mixer to obtain a mixture (I) of brominated flame retardant and heat stabilizer, with the weight ratio of each material being (C):(D1):(D2) = 100:2.1:3.2, and (C) + (D1) + (D2) = 100 wt%.

[0109] (Reference example 1) [Preparation of polystyrene resin particles] The polystyrene resin (A), the masterbatch (H), and the graphite masterbatch (G) were each placed in a blender and blended for 10 minutes to obtain a resin mixture.

[0110] The weight ratio of each material was (A):(H):(G) = 83.65:8.35:8.00, with (A) + (H) + (G) = 100% by weight. The resulting resin mixture was fed into a 40mm co-rotating twin-screw extruder and melt-kneaded at a set temperature of 190°C and a screw speed of 230 rpm. The extruder tip was fitted with a die equipped with 30 small holes, each 1.4mm in diameter, and the extruded resin strands were cooled and solidified in a 20°C water bath. The strands were then cut with a strand cutter to obtain styrene resin particles. The resin temperature at the extruder tip was 220°C.

[0111] [Preparation of expandable polystyrene resin particles] Next, 100 parts by weight of the resulting styrene-based resin particles were charged into a 6-L autoclave equipped with a stirrer with 200 parts by weight of deionized water, 1 part by weight of tricalcium phosphate, 0.03 parts by weight of sodium dodecylbenzenesulfonate, and 1 part by weight of sodium chloride, and the pressure vessel was sealed. The vessel was then heated to 105°C over one hour, and 7 parts by weight of mixed pentane (a mixture of 80% normal pentane and 20% isopentane) and 1.5 parts by weight of isobutane were added to the pressure vessel over 30 minutes. The vessel was then heated to 115°C over 10 minutes and held there for four hours. After cooling to room temperature, the resin particles impregnated with the blowing agent were removed from the autoclave, pickled with hydrochloric acid, washed with water, dehydrated in a centrifuge, and then dried to remove moisture adhering to the resin particle surface in an airflow dryer. The resulting expandable polystyrene-based resin particles had a sphericity of 0.988 and an apparent density of 1,030 kg / m. 3 It was.

[0112] Example 1 [Preparation of expandable polystyrene resin particles] Polystyrene resin (A), graphite (B), and a mixture of brominated flame retardant and thermal stabilizer (I) were fed into a tandem two-stage extruder consisting of a 40mm diameter co-rotating twin-screw extruder (extruder 1) and a 90mm diameter single-screw extruder (extruder 2) connected in series. The 40mm diameter extruder was set at a temperature of 190°C and a rotation speed of 167 rpm. The weight ratio of (A):(B):(I) was 93:4.5:2.5, and the total feed rate was 55.7 kg / h. A 40 mm diameter extruder (first extruder) was injected with 5.2 parts by weight of mixed pentane [a mixture of 80% by weight of normal pentane (E1) and 20% by weight of isopentane (E2)] per 100 parts by weight of the melted resin mixture (resin composition), and 3.0 parts by weight of isobutane (E3) per 100 parts by weight of the resin composition, for a total of 8.2 parts by weight of blowing agent. The mixture was then fed to a 90 mm diameter extruder (second extruder) through a continuation pipe set at 200°C.

[0113] The molten resin was cooled to a resin temperature of 160°C in a 90mm diameter extruder (second extruder) and then extruded through a die equipped with 60 small holes, each 0.65mm in diameter and 5.0mm in length, attached to the tip of the second extruder, set at 250°C, into pressurized circulating water at 62°C and 1.3MPa. The extruded molten resin was cut and granulated using a rotating cutter with six blades that contacted the die, and then transferred to a centrifugal dehydrator to obtain expandable polystyrene resin particles. The residence time in the first extruder was 2 minutes, and the residence time in the second extruder was 5 minutes.

[0114] [Preparation of pre-expanded particles] The resulting expandable polystyrene-based resin particles were stored at 15°C for at least one week, and then dry-blended with 0.04 parts by weight of zinc stearate and 0.1 parts by weight of hydroxystearic acid triglyceride as external additives. 220 g of the expandable polystyrene-based resin particles containing the external additives were placed in a pre-expander [batch-type pre-expander manufactured by Daikai Kogyo Co., Ltd.], and the internal pressure was set to 0.05 kg / cm. 2 ~0.15kg / cm 2 Steam at 0.10 MPa was introduced into the pre-expander to expand the mixture to a bulk expansion ratio of 90 times, thereby obtaining pre-expanded particles.

[0115] [Preparation of polystyrene resin foam molded body] The resulting pre-expanded particles were cured at 30°C for 24 hours and then loaded into an in-mold molding die (400 mm long x 400 mm wide x 50 mm thick) attached to a polystyrene foam molding machine (Daisen Industrial Co., Ltd., KR-57). Steam at 0.06 MPa was introduced to cause in-mold foaming, followed by cooling by spraying water onto the mold. The polystyrene foam molded body was held in the mold until the pressure pushing the mold down to 0.01 MPa (gauge pressure), after which it was removed to obtain a polystyrene foam molded body. The resulting polystyrene foam molded body had an expansion ratio of 90.5 times, and its thermal conductivity, measured using the above-mentioned method, was 0.03084 W / m·K.

[0116] The properties of the produced expandable polystyrene resin particles and pre-expanded particles were measured and evaluated using the above-mentioned measurement and evaluation methods. The measurement results and evaluation results for the expandable polystyrene resin particles and pre-expanded particles are shown in Table 1.

[0117] Example 2 A polystyrene resin foam molded article was produced in the same manner as in Example 1, except that in [Preparation of expandable polystyrene resin particles], the amount of isobutane (E3) was changed to 3.2 parts by weight per 100 parts by weight of the resin composition. The expansion ratio of the obtained polystyrene resin foam molded article was 92.6 times, and the thermal conductivity, measured by the above-mentioned measuring method, was 0.03078 W / m K.

[0118] The various properties of the resulting expandable polystyrene resin particles and pre-expanded particles were measured and evaluated in the same manner as in Example 1. The measurement results and evaluation results are shown in Table 1.

[0119] Example 3 A polystyrene resin foam molded article was produced in the same manner as in Example 1, except that in [Preparation of expandable polystyrene resin particles], the amount of isobutane (E3) was changed to 3.7 parts by weight per 100 parts by weight of the resin composition, and the resin composition was extruded into pressurized circulating water at 1.38 MPa. The expansion ratio of the obtained polystyrene resin foam molded article was 92.6 times, and the thermal conductivity, measured by the above-mentioned measurement method, was 0.03088 W / m K.

[0120] The various properties of the resulting expandable polystyrene resin particles and pre-expanded particles were measured and evaluated in the same manner as in Example 1. The measurement results and evaluation results are shown in Table 1.

[0121] (Comparative Example 1) A polystyrene resin foam molded article was produced in the same manner as in Example 1, except that in [Preparation of expandable polystyrene resin particles], the amount of isobutane (E3) was changed to 2.5 parts by weight per 100 parts by weight of the resin composition, and the resin composition was extruded into pressurized circulating water at 1.25 MPa. The expansion ratio of the obtained polystyrene resin foam molded article was 92.1 times, and the thermal conductivity, measured by the above-mentioned measurement method, was 0.03130 W / m K.

[0122] The various properties of the resulting expandable polystyrene resin particles and pre-expanded particles were measured and evaluated in the same manner as in Example 1. The measurement results and evaluation results are shown in Table 1.

[0123] (Comparative Example 2) A polystyrene resin foam molded article was produced in the same manner as in Example 1, except that in [Preparation of expandable polystyrene resin particles], the amount of isobutane (E3) was changed to 2.8 parts by weight per 100 parts by weight of the resin composition, and the resin composition was extruded into pressurized circulating water at 1.25 MPa. The expansion ratio of the obtained polystyrene resin foam molded article was 92.2 times, and the thermal conductivity, measured by the above-mentioned measuring method, was 0.03101 W / m K.

[0124] The various properties of the resulting expandable polystyrene resin particles and pre-expanded particles were measured and evaluated in the same manner as in Example 1. The measurement results and evaluation results are shown in Table 1.

[0125] (Comparative Example 3) A polystyrene resin foam molded article was produced in the same manner as in Example 1, except that in [Preparation of Expandable Polystyrene Resin Particles], the weight ratio of polystyrene resin (A): graphite (B): mixture of brominated flame retardant and heat stabilizer (I) was changed to 95:4.5:0.5, the amount of isobutane (E3) was changed to 2.5 parts by weight per 100 parts by weight of the resin composition, and the extrusion was carried out into pressurized circulating water at 1.25 MPa. The expansion ratio of the obtained polystyrene resin foam molded article was 90.6 times, and the thermal conductivity, measured by the above-mentioned measurement method, was 0.03255 W / m K.

[0126] The various properties of the resulting expandable polystyrene resin particles and pre-expanded particles were measured and evaluated in the same manner as in Example 1. The measurement results and evaluation results are shown in Table 1.

[0127] [Table 1]

Claims

1. Expandable polystyrene-based resin particles comprising a polystyrene-based resin composition containing a radiation heat transfer inhibitor and a blowing agent, the sphericity of the expandable polystyrene-based resin particles is 0.985 or less, the blowing agent comprises isobutane; the content of isobutane is more than 2.7% by weight and 6.0% by weight or less relative to 100% by weight of the total amount of the polystyrene-based resin composition and the blowing agent, the content of the radiation heat transfer inhibitor is 2 to 40% by weight based on 100% by weight of the polystyrene-based resin composition; The total amount of the foaming agent is 2.8 to 15 parts by weight based on 100 parts by weight of the polystyrene resin composition.

2. the polystyrene-based resin composition contains a flame retardant, The expandable polystyrene-based resin particles according to claim 1 , wherein the content of the flame retardant is more than 1.0% by weight and not more than 6.0% by weight, based on 100% by weight of the polystyrene-based resin composition.

3. The expandable polystyrene-based resin particles according to claim 1 or 2, wherein the blowing agent comprises pentane.

4. The expandable polystyrene resin particles have an apparent density of 950 kg / m ３ Super 1200kg / m ３ The expandable polystyrene-based resin particles according to any one of claims 1 to 3, wherein:

5. The expandable polystyrene-based resin particles according to any one of claims 1 to 4, wherein the amount of blowing agent in the pre-expanded particles when the expandable polystyrene-based resin particles are pre-expanded to a bulk expansion ratio of 90 times and then aged at 30°C for 24 hours is 5.0% by weight to 6.0% by weight.

6. The expandable polystyrene-based resin particles according to any one of claims 1 to 5, wherein the expandable polystyrene-based resin particles are pre-expanded to a bulk expansion of 90 times and then cured at 30°C for 24 hours, and the pre-expanded particles are then expanded and molded, resulting in an expansion molded body having a thermal conductivity of 0.034 W / m K or less.

7. 7. Pre-expanded particles of the expandable polystyrene-based resin particles according to claim 1, having a bulk expansion ratio of 90 times or more.

8. A method for producing expandable polystyrene-based resin particles, comprising extruding a polystyrene-based resin melt comprising a polystyrene-based resin composition containing a radiation heat transfer inhibitor and a blowing agent through a die having a plurality of small holes into pressurized circulating water, and cutting the melt into particles with a rotary cutter, the blowing agent comprises isobutane; isobutane is contained in an amount of more than 2.7% by weight and not more than 6.0% by weight relative to 100% by weight of the total amount of the polystyrene-based resin composition and the blowing agent, the content of the radiation heat transfer inhibitor is 2 to 40% by weight based on 100% by weight of the polystyrene-based resin composition; The method for producing expandable polystyrene-based resin particles, wherein the total amount of the foaming agent is 2.8 to 15 parts by weight based on 100 parts by weight of the polystyrene-based resin composition.

9. The method for producing expandable polystyrene-based resin particles according to claim 8 , wherein the radiative heat transfer inhibitor comprises a carbon-based radiative heat transfer inhibitor.

10. The method for producing expandable polystyrene-based resin particles according to claim 8 or 9, wherein the blowing agent contains pentane.

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