Expandable polystyrene resin particles, pre-expanded polystyrene particles, and foamed molded articles

Abstract

The present invention addresses the problem of providing, inter alia, foamable polystyrene resin particles that are suitable for obtaining a foamed molded product capable of easily reducing the generation of rubbing noise, and that can shorten the molding cycle. The present invention provides foamable polystyrene resin particles in which the surface of a foamable polystyrene resin particle body is coated with a fatty oil that is liquid at normal temperatures and a metal salt of a higher fatty acid, and in which the open-cell bubble percentage, for foamed particles obtained by foaming the foamable polystyrene resin particles by a factor of 40, is at least 5%.

Description

[Technical Field]

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

[0002] Foamed molded articles obtained by expanding expandable polystyrene-based resin particles are lightweight and have excellent shock-absorbing and heat-insulating properties, and are therefore widely used as packaging materials (trays) for food containers and the like, various packaging materials, building and civil engineering components, automotive components, and the like.

[0003] However, the foam molded articles have a problem in that they tend to produce an unpleasant squeaking noise (a noise caused by the stick-slip phenomenon) when rubbed against another foam molded article, or against another resin member or a metal such as a steel plate. In particular, in the field of automotive components, vibrations are likely to occur when an automobile is driven on rough roads, and therefore unpleasant scraping noises are likely to occur, which causes a deterioration in the usability.

[0004] To solve this problem, Patent Document 1 proposes expandable polystyrene-based resin particles that are a copolymer of a polysiloxane-containing monomer and a styrene-based monomer, in which polysiloxane is present on the surface of the resin particles. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2016-183255 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques have room for further improvement in terms of productivity.

[0007] An object of one embodiment of the present invention is to provide expandable polystyrene-based resin particles that are suitable for easily obtaining foamed molded articles that can reduce the generation of unpleasant frictional noise and that can shorten the molding cycle, as well as polystyrene-based pre-expanded particles and foamed molded articles. [Means for solving the problem]

[0008] As a result of intensive research into solving the above-mentioned problems, the present inventors independently discovered the following knowledge, which led to the completion of the present invention: expandable polystyrene-based resin particles having a surface coated with oils and a metal salt of a higher fatty acid, wherein the expandable polystyrene-based resin particles are expanded 40 times to produce expanded particles with an open cell ratio of 5% or more, and the oils and fats are liquid at room temperature. This expandable polystyrene-based resin particle is suitable for easily obtaining foamed molded articles that can reduce the generation of unpleasant frictional noise, and can shorten the molding cycle. Furthermore, the present inventors independently discovered the following findings during the course of intensive research: (1) in particular, expandable polystyrene-based resin particles in which the oil or fat comprises an ester of a fatty acid having a specific structure can, surprisingly, further reduce the difference between the static and dynamic friction coefficients of a foamed molded article obtained by expanding the expandable polystyrene-based resin particles; and (2) by applying an amount of the oil or fat to the expandable polystyrene-based resin particles that is equal to or greater than a specific amount, surprisingly, the open cell ratio of the expanded particles can be further increased, and the molding cycle can be significantly shortened.

[0009] In order to reduce the occurrence of unpleasant friction noise (stick-slip phenomenon), it is not enough to simply control the static friction coefficient; it is also necessary to appropriately control the difference between the static friction coefficient and the kinetic friction coefficient. This is a finding that the present inventors have independently discovered.

[0010] That is, one embodiment of the present invention is an expandable polystyrene-based resin particle in which oils and fats and a metal salt of a higher fatty acid are applied to the surface of the expandable polystyrene-based resin particle body, and the expandable polystyrene-based resin particle is expanded 40 times to produce an open cell ratio of 5% or more, and the oils and fats are liquid at room temperature. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide expandable polystyrene-based resin particles, which are suitable for easily obtaining foamed molded articles that can reduce the generation of unpleasant friction noise and can shorten the molding cycle, as well as polystyrene-based pre-expanded particles and foamed molded articles. 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] In this specification, the expandable polystyrene-based resin particle itself (itself) is referred to as the "expandable polystyrene-based resin particle body" or "resin particle body," the expandable polystyrene-based resin particle having oils and fats and metal salts of higher fatty acids applied to its surface is referred to as the "expandable polystyrene-based resin particle," and the particles obtained when the expandable polystyrene-based resin particle is pre-expanded are referred to as the "polystyrene-based pre-expanded particle" or "expanded particle."

[0014] The present inventors have studied the technology described in Patent Document 1 and independently discovered the following: The technology described in Patent Document 1 is prone to problems with fusion between expandable polystyrene-based resin particles having polysiloxane present on the surface. Therefore, the technology described in Patent Document 1 requires an increase in steam pressure during molding of the expandable polystyrene-based resin particles, which tends to lengthen the molding cycle. Therefore, the technology described in Patent Document 1 leaves room for improvement in terms of productivity, which is required for automotive components.

[0015] According to one aspect of the present invention, the difference between the static and dynamic friction coefficients of a foamed molded product obtained by expanding expandable polystyrene-based resin particles can be reduced, and the increase in the open cell ratio of the foamed beads obtained from the expandable polystyrene-based resin particles can be appropriately controlled. Furthermore, in one aspect of the present invention, by expanding and molding the expandable polystyrene-based resin particles according to one embodiment of the present invention using a conventionally known method, a foamed molded product capable of reducing the generation of unpleasant friction noise can be obtained. Therefore, according to one aspect of the present invention, expandable polystyrene-based resin particles suitable for easily obtaining a foamed molded product capable of reducing the generation of unpleasant friction noise and capable of shortening the molding cycle, and a foamed molded product obtained by molding polystyrene-based pre-expanded particles can be obtained.

[0016] [1. Expandable polystyrene resin particles] In one embodiment of the present invention, the expandable polystyrene-based resin particles are formed by coating the surface of the expandable polystyrene-based resin particle body with oils and a metal salt of a higher fatty acid, and the expandable polystyrene-based resin particles are expanded to an expansion ratio of 40 times, resulting in an open cell ratio of 5% or more, and the oil and the like being liquid at room temperature. In this specification, "expansion ratio" refers to "bulk ratio." However, an open cell ratio of 5% or more refers to an open cell ratio of 5.0% or more when rounded to one decimal place.

[0017] The expandable polystyrene-based resin particles according to one embodiment of the present invention have the above-described structure and therefore have the following advantages: (1) The difference between the static friction coefficient and the dynamic friction coefficient of a foamed molded article obtained by expanding the expandable polystyrene-based resin particles according to one embodiment of the present invention can be reduced, and the increase in the open cell ratio of the foamed particles obtained from the expandable polystyrene-based resin particles can be appropriately controlled; (2) The expandable polystyrene-based resin particles according to one embodiment of the present invention are themselves suitable for easily obtaining a foamed molded article that can reduce the generation of unpleasant frictional noise, and can shorten the molding cycle in the production of the foamed molded article; (3) The expandable polystyrene-based resin particles according to one embodiment of the present invention are suitable for easily obtaining a foamed molded article that can reduce the generation of unpleasant friction noise, and can provide pre-expanded polystyrene-based particles that can shorten the molding cycle in the production of the foamed molded article; and (4) The expandable polystyrene resin particles according to one embodiment of the present invention can easily provide a foamed molded article that can reduce the generation of unpleasant friction noise, using a shortened molding cycle.

[0018] Generally, expanded beads are composed of numerous cells, each separated by a cell membrane. Therefore, each cell is independent, and the open cell ratio of expanded beads is generally 2% or less. The more the cell membranes break and the more adjacent cells connect, the higher the open cell ratio. In one embodiment of the expandable polystyrene-based resin beads, the open cell ratio of the expanded beads is thought to be increased by the oil applied to the surface of the expandable polystyrene-based resin beads, which melts and breaks the cell membranes, mainly the outer layer, of the expanded beads during pre-expansion. As a result, the dissipation of the blowing agent from the expanded beads is promoted, significantly shortening the molding cycle. Surprisingly, an open cell ratio of 5% or more reduces the difference between the static and dynamic friction coefficients, preventing the generation of frictional noise. This effect was first discovered by the present inventors. Note that if the amount of oil applied is small, the open cell ratio does not increase, and the aforementioned effect may not be achieved.

[0019] [Expandable polystyrene resin particle body] In one embodiment of the present invention, the styrene-based resin constituting the expandable polystyrene-based resin particle body is preferably a polymer containing 60% by weight or more of styrene as a monomer component. Specific examples of such styrene-based resins include styrene homopolymers, styrene-ethylene copolymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, and styrene-acrylic acid ester copolymers. Any styrene-based resin may be used; for example, one of the above-mentioned polymers may be used alone, or two or more may be used in combination.

[0020] Examples of types of styrene monomers include (a) styrene and (b) styrene derivatives such as α-methylstyrene, paramethylstyrene, t-butylstyrene, chlorostyrene, etc. These styrene monomers may be used alone or in combination of two or more.

[0021] Examples of the acrylic acid ester monomer include alkyl acrylates such as methyl acrylate, butyl acrylate, etc. These acrylic acid ester monomers may be used alone or in combination of two or more.

[0022] The method for producing the expandable polystyrene-based resin particle body (polymerization method) is not particularly limited and may be any known production method. However, when a seed suspension polymerization method is used as the polymerization method, the monomer in the resin particle body that serves as the seed (i.e., the monomer contained in the seed) is also included as the monomer component.

[0023] In addition, the term "monomer component" as used herein refers to a unit (structural unit) derived from a monomer.

[0024] [Oils and fats] In one embodiment of the present invention, the oil or fat is applied to the surface of the expandable polystyrene resin particle body and used as an external additive. The oil or fat is liquid at room temperature. In this specification, room temperature is synonymous with room temperature, and particularly refers to a range of 15°C to 25°C. By applying an oil or fat that is liquid at room temperature to the surface of the expandable polystyrene resin particle body, the open cell ratio of the expanded particles can be effectively increased. This is presumably because oil or fat that is liquid at room temperature has a lower melting point than oil or fat that is solid at room temperature, and therefore the surface of the expanded particles is more likely to melt when heated during pre-expansion. However, the present invention is in no way limited to this presumption.

[0025] The fat or oil preferably comprises an ester of (a) a fatty acid containing 50% by weight or more of a carboxylic acid having 8 or more carbon atoms, which has no hydroxyl group and one or less double bond, and (b) glycerin. This configuration of the expandable polystyrene-based resin particles has the advantage of reducing the difference between the static and dynamic friction coefficients of a foamed molded article obtained by expanding the expandable polystyrene-based resin particles, thereby preventing friction noise. This configuration also has the advantage of shortening the molding cycle when producing a foamed molded article from the expandable polystyrene-based resin particles. In terms of further reducing the difference between the static and dynamic friction coefficients, further preventing friction noise, and further shortening the molding cycle, the fat or oil is particularly preferably a triglyceride of (a) a fatty acid containing 50% by weight or more of a carboxylic acid having 8 or more carbon atoms, which has no hydroxyl group and one or less double bond, and (b) glycerin.

[0026] In addition, the fatty acids constituting castor oil are mainly those having a hydroxyl group. Therefore, castor oil is not preferable as the fat or oil in the present application, and a composition that does not contain castor oil is preferable. In addition, "other external additives" described below as fat or oil that is solid at room temperature are also not considered to be fat or oil in the present application.

[0027] This section describes a case where the surface of the expandable polystyrene-based resin particles is coated with the following oils and fats: (a) an ester of a fatty acid containing 50% or more by weight of a carboxylic acid having two or more double bonds in its molecule; (b) an ester of a fatty acid containing 50% or more by weight of a carboxylic acid having a hydroxyl group; (c) an ester of a fatty acid containing 50% or more by weight of a carboxylic acid having less than 8 carbon atoms; and / or (d) an ester of a fatty acid containing less than 50% by weight of a carboxylic acid having 8 or more carbon atoms and no more than one double bond and no hydroxyl group. In this case, it tends to be difficult to appropriately control (reduce) the difference between the static and dynamic coefficients of friction of the foamed molded article obtained by expanding the expandable polystyrene-based resin particles. Furthermore, in this case, the open cell ratio of the expanded particles obtained from the expandable polystyrene-based resin particles tends to be low, resulting in an insufficient shortening of the molding cycle.

[0028] The phrase "having one or less double bonds" means that the carboxylic acid has no double bonds or one double bond. In other words, the carboxylic acid is preferably a saturated carboxylic acid or a monovalent unsaturated carboxylic acid.

[0029] The number of carbon atoms in the carboxylic acid is preferably 12 or more, since it reduces the difference between the static and dynamic friction coefficients, prevents friction noise, and shortens the molding cycle. It is presumed that when the carboxylic acid has 12 or more carbon atoms, the oil does not infiltrate the expandable polystyrene-based resin particle body, and the concentration of the oil present on the surface of the expandable polystyrene-based resin particle body does not decrease, allowing the surface of the expanded beads to be sufficiently dissolved during pre-expansion, resulting in a high open cell ratio of the expanded beads. However, the present invention is not limited to this presumption.

[0030] Specific examples of the carboxylic acid include (a) saturated fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, and lignoceric acid; and (b) monounsaturated fatty acids such as palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, and erucic acid. Among these, the carboxylic acid is preferably one or more selected from the group consisting of oleic acid, lauric acid, and myristic acid. This configuration has the advantages of reducing the difference between the static and dynamic friction coefficients of the foamed molded article, preventing friction noise, and shortening the molding cycle. These carboxylic acids may be used alone or in combination.

[0031] Specific examples of the fats and oils include olive oil (oleic acid: approximately 78% by weight) and / or coconut oil (lauric acid: approximately 48% and myristic acid: approximately 19%), which can reduce the difference between the static and dynamic coefficients of friction of the foamed molded article, prevent friction noise, and shorten the molding cycle. These fats and oils may be used alone or in combination of two or more. The fats and oils may be natural (vegetable oils) or synthetic, but natural (vegetable oils) are more preferred due to their ease of availability. In the examples of fats and oils, the fatty acid in parentheses and its weight percentage indicate the type of fatty acid used as the raw material for the fats and oils, and the amount of the fatty acid used relative to 100% by weight of the total fatty acids used as the raw material for the fats and oils.

[0032] In one embodiment of the present invention, the amount of oil applied is preferably 0.15 to 0.80 parts by weight, more preferably 0.20 to 0.60 parts by weight, even more preferably 0.20 to 0.50 parts by weight, and particularly preferably 0.20 to 0.45 parts by weight, relative to 100 parts by weight of the expandable polystyrene-based resin particle body. When the amount of oil applied is 0.15 parts by weight or more, (a) the effect of the applied oil is fully exerted, the difference between the static and dynamic friction coefficients of the foamed molded body tends to be small, and the effect of reducing the generation of friction noise tends to be sufficient, and / or (b) the open cell ratio tends to be large, and the molding cycle tends to be shortened. When the amount of oil applied is 0.80 parts by weight or less, the expandable polystyrene-based resin particles tend to be easily expanded to a predetermined expansion ratio (40 times or more).

[0033] There are various methods for applying oil to the surfaces of expandable polystyrene-based resin particle bodies, specifically, methods for adding oil to the expandable polystyrene-based resin particle bodies and mixing the oil to apply the oil to the surfaces, such as a method of thoroughly mixing the expandable polystyrene-based resin particle bodies and the oil using a mixing device such as a blender.

[0034] The oil and fat applied to the expandable polystyrene resin particle body is substantially entirely attached to the expandable polystyrene resin particle body and acts as an external additive.

[0035] [Metal salts of higher fatty acids] The metal salt of a higher fatty acid in one embodiment of the present invention is applied to the surface of the expandable polystyrene-based resin particle body and used as an external additive. The metal salt of a higher fatty acid has an alkyl group having preferably 12 to 20 carbon atoms, more preferably 16 to 18 carbon atoms.

[0036] Specific examples of the metal salts of higher fatty acids include (a) metal stearates such as zinc stearate, calcium stearate, magnesium stearate, and aluminum stearate; (b) metal oleates such as zinc oleate and magnesium oleate; and (c) metal laurates such as zinc laurate and calcium laurate. Among these, metal stearates are more preferred because they have superior affinity with styrene-based resins and exhibit a melting point suitable for application. Furthermore, zinc stearate is even more preferred as the metal salt of higher fatty acids, as it is less likely to inhibit the fusion of expanded beads during molding. These metal salts of higher fatty acids may be used alone or in combination of two or more.

[0037] In one embodiment of the present invention, the coating amount of the metal salt of a higher fatty acid is preferably 0.20 to 0.40 parts by weight, more preferably more than 0.20 to 0.40 parts by weight, and more preferably 0.25 to 0.35 parts by weight, relative to 100 parts by weight of the expandable polystyrene resin particle body. When the coating amount of the metal salt of a higher fatty acid is 0.20 parts by weight or more, blocking of the expanded beads (bonding and aggregation of expanded beads) during pre-expansion (primary expansion) in which the expandable polystyrene resin particles are expanded to form expanded beads tends to be reduced. When the coating amount of the metal salt of a higher fatty acid is 0.40 parts by weight or less, the fusion properties of the expanded molded article when the expandable polystyrene resin particles are expanded to form an expanded molded article tend to be good.

[0038] There are various methods for applying a metal salt of a higher fatty acid to the surface of the expandable polystyrene-based resin particle body, specifically, a method for adding a metal salt of a higher fatty acid to the expandable polystyrene-based resin particle body and mixing the same to apply it to the surface. For example, there is a method for thoroughly mixing the expandable polystyrene-based resin particle body and the metal salt of a higher fatty acid using a mixing device such as a blender.

[0039] The metal salt of the higher fatty acid applied to the expandable polystyrene resin particle body is substantially entirely attached to the expandable polystyrene resin particle body and acts as an external additive.

[0040] [Additives, etc.] The expandable polystyrene-based resin particles in one embodiment of the present invention may contain additives such as solvents, plasticizers, blowing agents, cell regulators, nucleating agents, flame retardants, flame retardant assistants, or monomer components, to the extent that the effects of one embodiment of the present invention are not impaired. These additives may be added to the expandable polystyrene-based resin particle bodies, for example, during the production of the expandable polystyrene-based resin particle bodies. The timing and / or method of adding these additives to the expandable polystyrene-based resin particle bodies are not particularly limited.

[0041] The monomer components remaining in the expandable polystyrene-based resin particles according to one embodiment of the present invention, i.e., the monomer components contained in the expandable polystyrene-based resin particles, are preferably less than 0.3 parts by weight, more preferably less than 0.1 parts by weight, and even more preferably less than 0.03 parts by weight, per 100 parts by weight of the expandable polystyrene-based resin particles themselves. The monomer components remaining in the expandable polystyrene-based resin particles tend to volatilize from the foamed molded article obtained by expanding and molding the expandable polystyrene-based resin particles. Therefore, expandable polystyrene-based resin particles having less than 0.3 parts by weight of the monomer components remaining in the expandable polystyrene-based resin particles are suitable for use in the medical field, packaging materials such as food containers that come into direct contact with food, the automotive field, and the construction field.

[0042] The solvent preferably has a boiling point of 50° C. or higher. Specific examples of the solvent include (a) aliphatic hydrocarbons having 6 or more carbon atoms, such as toluene, hexane, and heptane; and (b) alicyclic hydrocarbons having 6 or more carbon atoms, such as cyclohexane and cyclooctane. These solvents may be used alone or in combination of two or more.

[0043] The plasticizer is added (used) during the production (polymerization) of the expandable polystyrene resin particle body. The plasticizer is preferably a compound generally used as a plasticizer and having a boiling point of 200°C or higher, and one type may be used, or two or more types may be used in combination.

[0044] Specific examples of the blowing agent include volatile blowing agents such as (a) aliphatic hydrocarbons having 3 to 5 carbon atoms, such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; and (b) fluorocarbons with an ozone depletion potential of zero, such as difluoroethane and tetrafluoroethane. These blowing agents may be used alone or in combination of two or more. The amount of blowing agent used is preferably 4 to 10 parts by weight, more preferably 5 to 9 parts by weight, per 100 parts by weight of the expandable polystyrene-based resin particle body. When the amount of blowing agent used is 4 parts by weight or more, it tends to be easier to obtain a desired expansion ratio. When the amount of blowing agent used is 10 parts by weight or less, aggregation of the expandable polystyrene-based resin particle body tends to be less likely to occur during the process of impregnating the blowing agent.

[0045] Specific examples of the cell regulator include (a) aliphatic bisamides such as methylene bisstearic acid amide and ethylene bisstearic acid amide; and (b) polyethylene wax. These cell regulators may be used alone or in combination of two or more.

[0046] Specific examples of the nucleating agent include methyl methacrylate copolymers, polyethylene wax, talc, fatty acid bisamides, ethylene-vinyl acetate copolymers, etc. Specific examples of fatty acid bisamides include methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, ethylene bisoleic acid amide, etc. These nucleating agents may be used alone or in combination of two or more.

[0047] Specific examples of the flame retardant include: (a) halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; (b) brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; and (c) tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-diglycerides. and (d) brominated phenol derivatives such as brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers (e.g., EMERALD3000 manufactured by Chemtura or the copolymers described in JP-A-2009-516019). Other known flame retardants than those mentioned above can also be used as the flame retardant. These flame retardants may be used alone or in combination of two or more.

[0048] Specific examples of the flame retardant aid include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane. Known flame retardant aids other than those mentioned above can also be used as the flame retardant aid. These flame retardant aids may be used alone or in combination of two or more.

[0049] [Other external additives] The expandable polystyrene-based resin particles in one embodiment of the present invention may further contain known external additives such as antiblocking agents, antistatic agents, water repellents, and fusion accelerators, provided that the effects of one embodiment of the present invention are not impaired. For example, fusion accelerators are solid at room temperature, and examples include castor wax (hydroxystearic acid triglyceride), sorbitan stearate esters, and other triesters, diesters, and monoesters of higher fatty acids, as well as sucrose esters. Since these external additives are solid at room temperature, they do not fall under the definition of oils and fats in the present application. The timing of adding (using) these external additives is not particularly limited. When other external additives are solid at room temperature, it is preferable to add them to the expandable polystyrene-based resin particle body after the application of the oil and fat has been completed, as this provides good fluidity. In this specification, the term "external additive" refers to additives, particularly those applied to the surface of the expandable polystyrene-based resin particle body.

[0050] [Mixing equipment] In one embodiment of the present invention, to add fats and oils, metal salts of higher fatty acids, etc. to the expandable polystyrene-based resin particle bodies, mix them, and then coat the surfaces of the particles, it is preferable to use a mixer that can uniformly mix the fats and oils. Examples of such mixers include (a) mixers such as Super Mixers, Nauta Mixers, Universal Mixers, Proshare Mixers, Apex Mixers, Henschel Mixers, and Loedige Mixers; and (b) blenders such as ribbon blenders and tumbler blenders. The mixing conditions, such as the mixing time, of the mixer can be adjusted taking into consideration (a) mixing capacity and (b) the amount of fats and oils, metal salts of higher fatty acids, etc. to be coated.

[0051] [Method for producing expandable polystyrene resin particles] In one embodiment of the present invention, a method for producing expandable polystyrene-based resin particles is, for example, to add expandable polystyrene-based resin particle bodies and oils and fats (and additives and external additives, if necessary) to a mixer and mix them to coat the surfaces of the resin particles with oils and fats, and then add a metal salt of a higher fatty acid (and additives and external additives, if necessary) and mix them to further coat the surfaces with a metal salt of a higher fatty acid. This method is preferred in that it can prevent friction noise, shorten the molding cycle, and achieve good fluidity in the expandable polystyrene-based resin particles.

[0052] A method for producing expandable polystyrene-based resin particles in one embodiment of the present invention may be configured as follows: (i) a step of charging expandable polystyrene-based resin particle bodies and grease (and, if necessary, additives and external additives) into a mixer and mixing the expandable polystyrene-based resin particle bodies and grease (and, if necessary, additives and external additives) to apply grease to the surfaces of the resin particles (grease application step); (ii) A method for producing expandable polystyrene-based resin particles, comprising a step (metal salt application step) of further applying a metal salt of a higher fatty acid to the surface of the expandable polystyrene-based resin particle body to which at least a grease has been applied, by adding a metal salt of a higher fatty acid (and, if necessary, additives and external additives) to a mixing device and mixing the expandable polystyrene-based resin particle body to which at least a grease has been applied with the metal salt of a higher fatty acid (and, if necessary, additives and external additives).

[0053] The above-described manufacturing method has the following advantages: (a) the foamed molded article obtained by expanding and molding the resulting expandable polystyrene-based resin particles can prevent friction noise; (b) the molding cycle for producing the foamed molded article can be shortened; and (c) good fluidity can be exhibited in the expandable polystyrene-based resin particles.

[0054] However, the method for producing expandable polystyrene-based resin particles in one embodiment of the present invention is not particularly limited as long as it is a method that can apply the oil and fat and the metal salt of a higher fatty acid to the surface of the expandable polystyrene-based resin particle body in the amounts described above.

[0055] In one embodiment of the present invention, an appropriate amount of oil or grease is first applied to the surface of the expandable polystyrene-based resin particle body, and then an appropriate amount of a metal salt of a higher fatty acid can be efficiently applied to the surface (at least the surface of the expandable polystyrene-based resin particle body coated with the oil or grease). This makes it possible to obtain expandable polystyrene-based resin particles suitable for easily producing expanded molded products that can reduce the generation of unpleasant frictional noise, without applying a large amount of external additives or causing contamination of equipment such as a pre-expansion machine and / or a molding die.

[0056] [2. Polystyrene-based pre-expanded particles] 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.

[0057] The polystyrene-based pre-expanded particles according to one embodiment of the present invention have the above-described structure and therefore have the following advantages: (1) The polystyrene-based pre-expanded particles according to one embodiment of the present invention can easily provide a foamed molded article that can reduce the generation of unpleasant friction noise without applying a large amount of external additives or causing contamination of equipment such as a molding die; (2) The polystyrene pre-expanded particles according to one embodiment of the present invention can reduce the difference between the static and dynamic friction coefficients of an expanded molded article obtained by molding the polystyrene pre-expanded particles, and have an open cell ratio of 5% or more; (3) The polystyrene-based pre-expanded particles according to one embodiment of the present invention are themselves suitable for easily obtaining a foamed molded article that can reduce the generation of unpleasant frictional noise, and can shorten the molding cycle in the production of the foamed molded article; and (4) The polystyrene-based pre-expanded particles according to one embodiment of the present invention can easily provide a foamed molded article that can reduce the generation of unpleasant frictional noise through a shortened molding cycle.

[0058] Here, when obtaining a foamed molded article from expandable polystyrene-based resin particles, the expandable polystyrene-based resin particles may first be expanded to obtain polystyrene-based expanded particles, and then the polystyrene-based expanded particles may be molded to obtain a foamed molded article. Therefore, in the process of obtaining a foamed molded article from expandable polystyrene-based resin particles, expanding the expandable polystyrene-based resin particles may be referred to as "pre-expanding," and the obtained polystyrene-based expanded particles may be referred to as "polystyrene-based pre-expanded particles." In other words, "polystyrene-based pre-expanded particles in one embodiment of the present invention" can also be referred to as "polystyrene-based expanded particles in one embodiment of the present invention."

[0059] The method for pre-expanding the expandable polystyrene-based resin particles can be a conventional method, such as using a cylindrical pre-expansion device and heating the expandable polystyrene-based resin particles with a heating medium such as steam to expand them. The device used for pre-expansion and the pre-expansion conditions can be appropriately set depending on the composition of the expandable polystyrene-based resin particle body and / or the desired pre-expansion ratio, and are not particularly limited.

[0060] The polystyrene-based expanded beads according to one embodiment of the present invention may have the following configuration: That is, the polystyrene-based expanded beads according to another embodiment of the present invention are polystyrene-based expanded beads obtained by expanding expandable polystyrene-based resin beads, in which the expandable polystyrene-based resin beads have oils and fats and metal salts of higher fatty acids applied to the surfaces of the expandable polystyrene-based resin beads, and the expansion ratio of the polystyrene-based expanded beads is 40 times, and the open cell ratio of the polystyrene-based expanded beads is 5% or more.

[0061] [3. Foam Molded Product] The foamed molded article in one embodiment of the present invention is obtained by heat-expanding (secondary expansion) the above-mentioned polystyrene-based pre-expanded particles. It can also be said that the foamed molded article in one embodiment of the present invention is obtained by molding the above-mentioned polystyrene-based pre-expanded particles.

[0062] The foam molded article according to one embodiment of the present invention has the above-described structure, which has the advantage of being able to reduce the generation of unpleasant friction noise.Furthermore, the foam molded article according to one embodiment of the present invention has the above-described structure, which has the advantage of being able to be easily provided in a shortened molding cycle without causing contamination of equipment such as molding dies during production.

[0063] 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. Among foam-molded products, in-mold foam-molded products in particular have advantages such as ease of producing a molded product of a desired shape, and are lightweight and have excellent cushioning and heat insulation properties, making them suitable for use as, for example, packaging materials (trays) for food containers and the like, various packaging materials, building and civil engineering components, automotive components, etc.

[0064] [4.Characteristics] [Static and dynamic friction coefficients] In one embodiment of the present invention, the expandable polystyrene-based resin particles preferably exhibit a difference between the static and dynamic friction coefficients of less than 0.050 when foamed molded articles obtained by expanding the expandable polystyrene-based resin particles to an expansion ratio (bulk ratio) of 40 times are rubbed against each other under conditions of a load of 40 N, a reciprocating distance of 50 mm, and a sliding speed of 1.0 mm / s. The difference between the static and dynamic friction coefficients is more preferably 0.04 or less, even more preferably 0.03 or less, and most preferably 0.00 (below the detection limit). When the difference between the static and dynamic friction coefficients is 0.04 or less, the foamed molded articles are less likely to catch when rubbed against each other, thereby effectively reducing the generation of unpleasant friction noise. The difference between the static and dynamic friction coefficients can be easily controlled by varying the amount of oil or fat applied to the surface of the expandable polystyrene-based resin particle body and the amount of metal salt of higher fatty acid within the above-mentioned ranges, depending on the composition of the expandable polystyrene-based resin particle body. In addition, the foamed molded article obtained by expanding expandable polystyrene-based resin particles to an expansion ratio (bulk ratio) of 40 times may also be a foamed molded article obtained by molding expanded particles obtained by expanding expandable polystyrene-based resin particles, as long as the expansion ratio is 40 times.

[0065] [Open cell rate] In one embodiment of the present invention, the expandable polystyrene-based resin particles are expanded to an expansion ratio (bulk ratio) of 40 times, and the expanded particles have an open cell ratio of 5% or more. The expansion conditions for expanding the expandable polystyrene-based resin particles to an expansion ratio (bulk ratio) of 40 times are not particularly limited. For example, it is preferable to heat the expandable polystyrene-based resin particles using steam as a heating medium at a blowing steam pressure of 0.08 to 0.12 MPa. The open cell ratio is preferably 6% or more, more preferably 8% or more, and particularly preferably 20% or less. The surface condition (skin layer condition) of a foamed molded article produced using expanded beads with an open cell ratio in this range is uneven compared to the surface condition of a foamed molded article produced using expanded beads with an open cell ratio of less than 5% (e.g., the foamed molded article of Comparative Example 6 in this specification). This unevenness can be confirmed by observing the surface of the foamed molded article with a scanning electron microscope. It is believed that the unevenness of the surface of the foamed molded article is one factor in suppressing the generation of friction noise.

[0066] When the open cell ratio of the expanded beads is 5% or more, the effect of preventing friction noise and shortening the molding cycle is good. Furthermore, when the open cell ratio of the expanded beads is 20% or less, the expandable polystyrene resin beads have sufficient expandability. The present inventors have surprisingly independently discovered that the open cell ratio can be easily controlled by changing the amount of oil or fat applied to the surface of the expandable polystyrene resin beads.

[0067] [5. Automotive Components] An automotive component according to one embodiment of the present invention comprises the foam molded article according to one embodiment of the present invention described in the above section [3. Foam molded article]. It can also be said that an automotive component according to one embodiment of the present invention includes the foam molded article according to one embodiment of the present invention described in the above section [3. Foam molded article].

[0068] The automotive component according to one embodiment of the present invention has the above-described configuration, and therefore has the advantage of being able to reduce the generation of unpleasant scraping noise.

[0069] Specific examples of the automobile component according to one embodiment of the present invention include, but are not limited to, tibia pads, floor spacers, bumper core materials, and tool boxes.

[0070] That is, one embodiment of the present invention includes the following configuration.

[0071] [1] Expandable polystyrene-based resin particles having a surface coated with oils and a metal salt of a higher fatty acid, wherein the expandable polystyrene-based resin particles are expanded 40 times to produce expanded particles with an open cell ratio of 5% or more, and the oils and the metal salts are liquid at room temperature.

[0072] [2] Expandable polystyrene resin particles according to [1], characterized in that when foamed molded articles obtained by expanding the expandable polystyrene resin particles 40 times are rubbed against each other under conditions of a load of 40 N, a reciprocating distance of 50 mm, and a sliding speed of 1.0 mm / s, the difference between the static friction coefficient and the dynamic friction coefficient is less than 0.050.

[0073] [3] Expandable polystyrene-based resin particles according to [1] or [2], characterized in that the oil or fat is an ester of glycerin and a fatty acid containing 50% by weight or more of a carboxylic acid having 8 or more carbon atoms, which has no hydroxyl group and one or less double bond.

[0074] [4] Expandable polystyrene resin particles according to any one of [1] to [3], characterized in that the oil is olive oil and / or coconut oil.

[0075] [5] Expandable polystyrene-based resin particles according to any one of [1] to [4], characterized in that 0.15 to 0.80 parts by weight of the oil or fat is applied to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

[0076] [6] Expandable polystyrene-based resin particles according to any one of [1] to [5], characterized in that 0.20 to 0.40 parts by weight of the metal salt of the higher fatty acid is applied to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body.

[0077] [7] Expandable polystyrene resin particles according to any one of [1] to [6], characterized in that the metal salt of a higher fatty acid is zinc stearate.

[0078] [8] Pre-expanded polystyrene particles, characterized by being obtained by pre-expanding the expandable polystyrene resin particles according to any one of [1] to [7].

[0079] [9] A foamed molded article obtained by molding the polystyrene pre-expanded particles according to [8].

[0080]

[10] An automobile component made of the foam molded article according to [9]. [Example]

[0081] 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.

[0082] The manufacturing methods, measurement methods, and evaluation methods for the polystyrene pre-expanded particles and foamed molded articles in the examples and comparative examples are as follows. Furthermore, "parts" and "%" are by weight unless otherwise specified.

[0083] <Production of Polystyrene-Based Pre-Expanded Particles> Expandable polystyrene resin particles classified to a predetermined particle size using a sieve were placed in a pressure pre-expansion machine (manufactured by Daikai Kogyo Co., Ltd., BHP). The expandable polystyrene resin particles were heated using steam as a heating medium at a blowing steam pressure of 0.08 to 0.12 MPa, thereby pre-expanding (primary expansion) the expandable polystyrene resin particles. The resulting pre-expanded polystyrene particles were then left at room temperature for 24 hours to obtain pre-expanded polystyrene particles with an expansion ratio of 40 times.

[0084] <Measurement of foaming ratio> The expansion ratio of the polystyrene pre-expanded particles was calculated by carrying out the following steps (1) to (3) in order: (1) 10 g of the expanded particles was weighed out and 3 (2) The volume of 10 g of expanded beads was measured from the scale of the measuring cylinder; (3) The expansion ratio of the polystyrene pre-expanded beads was calculated using the following formula: Foaming ratio (cm 3 / g): Volume of foam particles (cm 3 ) / 10g.

[0085] <Measurement of blocking property> Polystyrene pre-expanded particles with an expansion ratio (bulk ratio) of 40 times were produced by the above-mentioned method. During the production of these polystyrene pre-expanded particles (pre-expansion ratio: 40 times), when the polystyrene pre-expanded particles were removed from the pre-expansion machine, the polystyrene pre-expanded particles were placed on a mesh with a mesh opening of 1 cm. Next, the polystyrene pre-expanded particles that did not pass through the mesh were collected and their weight was measured to obtain the amount of blocking. The blocking ratio was calculated based on the following formula, and the blocking property was evaluated using the following four-point scale.

[0086] Blocking rate [wt%] = Blocking amount [g] / Total amount of polystyrene pre-expanded particles removed from the pre-expanding machine [g] × 100 A smaller blocking rate indicates a better blocking state, and a rating of "◯ (good)" or higher was judged to be acceptable.

[0087] ◎ (Excellent): Blocking rate is 0.10% by weight or less ◯ (Good): Blocking rate is greater than 0.10% by weight and less than 0.15% by weight △ (poor): Blocking rate is greater than 0.15% by weight and less than 0.20% by weight × (very poor): Blocking rate exceeds 0.20% by weight.

[0088] <Open cell rate> Using the method described above, polystyrene pre-expanded particles with an expansion ratio (bulk ratio) of 40 were produced. Using 0.8 g of the obtained polystyrene pre-expanded particles (pre-expansion ratio: 40), the closed cell volume (V0) of the polystyrene pre-expanded particles was determined using an air-comparison hydrometer (Beckman, Model 930). The ethanol-immersed volume (V1) of the same sample was also determined separately. The ethanol-immersed volume (V1) was calculated by submerging the polystyrene pre-expanded particles in ethanol in a measuring cylinder containing ethanol, and then calculating the rise in the ethanol level in the measuring cylinder. The open cell ratio (%) was calculated from the obtained closed cell volume (V0) and ethanol-immersed volume (V1) using the following formula: Open cell rate (%)=((V1-V0) / V1)×100.

[0089] <Production of foam molded products and molding cycle> The foamed molded articles were produced using a mold measuring 450 mm long, 300 mm wide, and 25 mm deep and a molding machine (Daisen, KR-57). Specifically, the process was as follows: (1) the mold was filled with the polystyrene pre-expanded particles produced by the method described above. (2) In-mold foaming was performed using steam as the heating medium under the following molding conditions: a steam injection time of 18 seconds, and a steam injection pressure of 0.06 MPa. This resulted in a 40x expansion ratio (bulk ratio) (secondary expansion). (3) After 3 seconds of water cooling, the product was vacuum-cooled. The vacuum cooling was terminated when the surface pressure reached 0.3 MPa or less. (4) The resulting product was removed from the mold to obtain a foamed molded article. The resulting foamed molded article was dried at room temperature for 24 hours and used to evaluate the fusion rate, friction noise, and static and dynamic friction coefficients.

[0090] The molding cycle was measured as the time required for the steps from filling the mold with the expanded beads to removing the expanded molded article from the mold (the steps (1) to (4) above).

[0091] <Evaluation of fusion properties> The foamed molded article was broken and the fracture surface was observed. The number of foamed beads where the foamed beads were broken, but not at the foamed bead interface, relative to the total number of foamed beads (100%) present on the fracture surface (percentage; %) was calculated and evaluated on the following four-point scale. The greater the percentage of broken foamed beads, the better the fusion strength, and a rating of "○ (good)" or better was judged to be acceptable.

[0092] ◎ (Excellent): The rate of broken foam particles is 90% or more. Good: The percentage of foam particles broken is 80% or more but less than 90%. △ (Poor): The percentage of foam particles broken is 70% or more but less than 80% × (very poor): The rate of broken foam particles is less than 70%.

[0093] <Method for measuring static and dynamic friction coefficients> The foam molded article was cut into pieces measuring 60 mm in length, 60 mm in width, and 4 mm in thickness using a vertical slicer (Sakura Engineering Co., Ltd.). Multiple test specimens were prepared, each with a skin layer on one side (the surface of the foam molded article that was in direct contact with the inner surface of the mold). The test specimens were then placed in a constant temperature and humidity chamber at 23°C and 50% humidity for 12 hours. Then, under the same conditions, the skin layers of two test specimens were rubbed together five times using a surface property tester (Shinto Scientific Co., Ltd., HEIDON Type: 14FW) under conditions of a load of 40 N, a reciprocating distance of 50 mm, and a sliding speed of 1.0 mm / s. The static and kinetic friction coefficients were measured after each rub. The average static and kinetic friction coefficients were calculated over the five rubs, and the difference between the average static and kinetic friction coefficients was calculated. In the table, the difference between the average value of the static friction coefficient and the average value of the dynamic friction coefficient is expressed as "difference between static friction coefficient and dynamic friction coefficient."

[0094] <Evaluation of Rubbing Noise> When measuring the static and dynamic friction coefficients, the level of discomfort felt by the rubbing noise was evaluated on the following four-point scale, depending on the volume of the rubbing noise generated when the skin layers of the two test pieces were rubbed against each other. The smaller the rubbing noise, the less uncomfortable the experience, and a rating of "○ (good)" or higher was judged to be acceptable.

[0095] ◎ (Excellent): No friction noise at all Good: Almost no rubbing noise △ (bad): A loud rubbing noise occurs when rubbing together × (very poor): A loud scraping noise occurs just by bringing the skin layers into contact with each other.

[0096] Example 1 Product name: Kanepearl (registered trademark) VF (manufactured by Kaneka Corporation, amount of blowing agent: 6.5 parts by weight per 100 parts by weight of expandable polystyrene resin particles) was classified using a sieve to obtain particles with a particle diameter of 0.6 mm to 1.12 mm, which were used as the expandable polystyrene resin particles. Kanepearl VF is a styrene homopolymer.

[0097] Olive oil (manufactured by Gokyo Sangyo Co., Ltd.) was used as the fat and oil. Zinc stearate (manufactured by NOF Corporation) was used as the metal salt of a higher fatty acid.

[0098] 100 parts by weight of expandable polystyrene-based resin particle bodies were charged into a Nauta mixer (manufactured by Hosokawa Micron Corporation), then 0.20 parts by weight of oil was charged into the Nauta mixer over 120 seconds, and the raw materials in the Nauta mixer were stirred for 30 minutes. Thereafter, 0.25 parts by weight of a metal salt of a higher fatty acid was charged into the Nauta mixer, and the raw materials in the Nauta mixer were stirred for an additional 15 minutes, thereby obtaining expandable polystyrene-based resin particles in which the oil and metal salt of a higher fatty acid were applied to the surfaces of the expandable polystyrene-based resin particle bodies.

[0099] According to the above-mentioned <Production of Polystyrene Pre-Expanded Beads> and <Production of Foam Molded Articles and Molding Cycle>, polystyrene pre-expanded beads and foam molded articles were produced using the obtained expandable polystyrene resin beads. The molding cycle was 110 seconds. The fusion properties and friction noise of the obtained foam molded articles were evaluated. In addition, the static and dynamic friction coefficients were measured, and the difference between the average static and dynamic friction coefficients was calculated. The results are shown in Table 1, along with the composition of the expandable polystyrene resin beads and other evaluation results.

[0100] [Examples 2 to 5, Comparative Examples 1 to 6] Expandable polystyrene resin particles, pre-expanded polystyrene particles, and foamed molded articles were obtained in the same manner as in Example 1, except that the type of expandable polystyrene resin particle body, the type and application amount of oil and fat, and the type and application amount of metal salt of higher fatty acid were changed to the types and application amounts shown in Tables 1 and 2. The results are shown in Tables 1 and 2.

[0101] Palm oil (manufactured by Kaneka Corporation) was used as the fat and oil in Examples 3 and 5 and Comparative Example 3. In Comparative Example 6, castor oil (manufactured by Ito Oil Mills Co., Ltd.) was used as the fat and oil.

[0102] In Examples 4 and 5 and Comparative Example 4, particles with a particle diameter of 0.6 to 1.4 mm obtained by classifying Kanepearl (registered trademark) CI (manufactured by Kaneka Corporation, amount of blowing agent: 4.0 parts by weight per 100 parts by weight of expandable polystyrene resin particles) using a sieve were used as the expandable polystyrene resin particles. Kanepearl CI is a copolymer of styrene monomer / acrylonitrile monomer / α-methylstyrene monomer.

[0103] In Comparative Example 7, stearic acid triglyceride derived from hydrogenated soybean oil was used as the fat and oil. [Table 1] [Table 2]

Claims

1. Expandable polystyrene-based resin particles having a surface coated with oils and fats and a metal salt of a higher fatty acid, The expandable polystyrene resin particles are expanded 40 times to produce expanded particles with an open cell ratio of 5% or more, and the oil or fat is liquid at room temperature, 0.15 to 0.80 parts by weight of the oil or fat are applied to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, 0.20 to 0.40 parts by weight of the metal salt of the higher fatty acid is applied to the surface of 100 parts by weight of the expandable polystyrene-based resin particle body, The expandable polystyrene-based resin particles, wherein the metal salt of a higher fatty acid is zinc stearate.

2. The expandable polystyrene-based resin particles according to claim 1, characterized in that when foamed molded articles obtained by expanding the expandable polystyrene-based resin particles 40 times are rubbed against each other under conditions of a load of 40 N, a reciprocating distance of 50 mm, and a sliding speed of 1.0 mm / s, the difference between the static friction coefficient and the dynamic friction coefficient is less than 0.

050.

3. Expandable polystyrene-based resin particles according to claim 1 or 2, characterized in that the oil or fat is an ester of glycerin and a fatty acid containing 50% by weight or more of a carboxylic acid having 8 or more carbon atoms, which does not have a hydroxyl group and has one or less double bonds.

4. 4. The expandable polystyrene resin particles according to claim 1, wherein the oil is olive oil and / or coconut oil.

5. 5. Pre-expanded polystyrene particles, characterized in that they are obtained by pre-expanding the expandable polystyrene resin particles according to any one of claims 1 to 4.

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

7. An automobile component made of the foam molded article according to claim 6.

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