Expandable polystyrene resin particles and method for producing expandable polystyrene resin particles.

Abstract

To provide a foamable styrenic resin particle that has its fluidity kept in a good state, and prevents flaking of powder, while reducing the chargeability of a prefoamed particle.SOLUTION: A foamable styrenic resin particle is prepared by coating the surface of a foamable styrenic resin particle body with a specific liquid material and then coating the surface of the particle body with proper amounts of clay mineral and fusion promoter.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to expandable styrene-based resin particles and a method for producing the same.

Background Art

[0002] Since the expandable styrene-based resin particles are impregnated with a foaming agent (volatile aliphatic hydrocarbons such as butane, pentane, etc.), they are relatively inexpensive and can be foam-molded with steam or the like without using a special method, and a high buffering and heat-insulating effect can be obtained. Therefore, they are socially useful materials. The obtained foam-molded articles are used in a wide range of applications such as buffer materials for fish boxes, agricultural boxes, food containers, household appliances, etc., and heat-insulating materials for building materials.

[0003] As a method for industrially and economically manufacturing an expandable styrene-based resin molded article, (1) expandable styrene-based resin particles are made into pre-expanded particles using a heating medium such as steam, (2) the pre-expanded particles are filled into a closed mold having a desired shape and having a large number of small holes drilled in the wall surface, (3) a heating medium such as steam is introduced from the small holes of the mold to heat the pre-expanded particles to a temperature above their softening point, and the pre-expanded particles are fused to each other to form a shape, and (4) after cooling, the mold is taken out. This method is common.

[0004] In the step of obtaining the pre-expanded particles, by coating the expandable styrene-based resin particles with a powdery external additive such as a blocking inhibitor or a fusion promoter, for example, the state where the pre-expanded particles are bonded to each other (referred to as blocking) is eliminated. For example, in Patent Document 1, it is proposed to prevent blocking in the pre-expansion process by applying a polyether and a powdery inorganic or organic substance such as talc or silica to the surface of the resin particle body.

[0005] Here, when the powdery additive peels off from the expandable styrene-based resin particles, problems such as clogging of the filter of the device used for air transportation of the resin particles, clogging of the small holes of the mold during molding, and a decrease in the strength of the foam-molded article may occur.

[0006] As a method for solving such problems, Patent Document 2 proposes to apply a hardly water-soluble inorganic substance such as magnesium oxide or talc, and a liquid fatty acid triglyceride to the resin particle body to prevent blocking in the pre-foaming step and prevent peeling of the coating agent. Patent Document 3 proposes to apply methylphenyl silicone oil and a metal salt of a higher fatty acid to the surface of the resin particle body to prevent blocking in the pre-foaming step and prevent peeling of the coating agent.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the expandable polystyrene-based resin particles described in Patent Documents 1 to 3 have the following room for improvement. In Patent Document 1, although polyether and silica are applied to the expandable polystyrene-based resin particles, there is a problem that the fusion rate of the foamed molded body, which is the final product, is low. In Patent Document 2, since a liquid fatty acid triglyceride (castor oil) is applied, the surface of the pre-expanded particles is eroded, the cell connection rate (a large number of holes exist on the surface) becomes high, and the practical strength of the foamed molded body decreases. Further, in Patent Document 3, due to the application of methylphenyl polysiloxane, the pre-expanded particles are highly charged, adhere to a net hopper or the like, and are difficult to handle.

[0009] One aspect of the present invention aims to provide expandable polystyrene resin particles suitable for obtaining an expanded molded article that maintains good fluidity of the expandable polystyrene resin particles, suppresses powder peeling and the amount of blocking, suppresses the chargeability of the pre-expanded particles, and has good fusion properties and surface properties.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventor has found that by applying a specific liquid substance, an appropriate amount of clay mineral, and a fusion promoter to the surface of the expandable polystyrene resin particle body, the fluidity of the resin particles is maintained in a good state, powder peeling is suppressed, blocking is prevented, and expandable polystyrene resin particles suitable for obtaining an expanded molded article having better fusion properties and surface properties can be obtained, thus completing the present invention.

[0011] That is, one embodiment of the present invention includes the following configurations. [1] Expandable polystyrene resin particles containing a blowing agent, wherein on the surface of the expandable polystyrene resin particle body, with respect to 100 parts by weight of the expandable polystyrene resin particles, a liquid substance (A) containing at least one of polyether and liquid paraffin is 0.3 part by weight or less, a clay mineral (B) is 0.01 part by weight or more and 1 part by weight or less, and a fusion promoter (C) is more than 0 part by weight and 0.5 part by weight or less are applied. Expandable polystyrene resin particles. [2] The liquid substance (A) contains a polyether that is hardly soluble in water. The expandable polystyrene resin particles according to [1], wherein the polyether contains at least one of polypropylene glycol and polyethylene glycol. [3] The expandable polystyrene resin particles according to any one of [1] to [2], wherein the clay mineral (B) contains at least one selected from the group consisting of talc, mica, and kaolin having an average particle size of 30 μm or less. [4] The expandable polystyrene resin particles according to any one of [1] to [3], wherein the fusion promoter (C) contains at least one selected from the group consisting of fatty acid monoglycerides, fatty acid diglycerides, fatty acid triglycerides, and hydroxy fatty acid triglycerides. [5] Pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to any one of [1] to [4]. [6] A foamed molded article obtained by molding the pre-expanded particles according to [5]. [7] A step of obtaining an expandable polystyrene resin particle body containing a foaming agent, and on the surface of the expandable polystyrene resin particle body, a liquid substance (A) containing at least one of polyether and liquid paraffin with respect to 100 parts by weight of the expandable polystyrene resin particle body is 0.3 parts by weight or less, a clay mineral (B) is 0.01 parts by weight or more and 1 part by weight or less, and a fusion promoter (C) is more than 0 part by weight and 0.5 part by weight or less, and a coating step of applying the same. A method for producing expandable polystyrene resin particles.

Effect of the Invention

[0012] According to one aspect of the present invention, it is suitable for obtaining expandable polystyrene resin particles that maintain good fluidity of the resin particles, suppress powder peeling, prevent blocking, and further have good fusion properties and surface properties. A foamed molded article can be obtained. Further, in the polystyrene-based pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles and the foamed molded article obtained by molding the polystyrene-based pre-expanded particles, peeling of the powder from the expandable polystyrene resin particles is suppressed, so that the productivity is improved.

Embodiments for Carrying Out the Invention

[0013] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope indicated in the claims. In addition, embodiments or examples obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, by combining the technical means disclosed in each embodiment, new technical features can be formed. All academic documents and patent documents described in this specification are incorporated herein by reference. In addition, unless otherwise specified in this specification, "A~B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0014] In this specification, the expandable polystyrene resin particles themselves are referred to as "expandable polystyrene resin particle bodies", and those with external additives (antistatic agents, fusion inhibitors, etc.) coated on the surface of the expandable polystyrene resin particle bodies are referred to as "expandable polystyrene resin particles", and particles obtained by pre-expanding (primary foaming) the expandable polystyrene resin particles are referred to as "pre-expanded particles".

[0015] [1. Expandable polystyrene resin particles] [Overview of an embodiment of the present invention] An embodiment of the present invention is expandable polystyrene resin particles obtained by coating on the surface of an expandable polystyrene resin particle body a liquid substance A containing at least one of polyether and liquid paraffin in an amount of 0.3 parts by weight or less, a clay mineral B in an amount of 0.01 part by weight to 1 part by weight, and a fusion promoter C in an amount of more than 0 part by weight and 0.5 part by weight or less, based on 100 parts by weight of the expandable polystyrene resin particles.

[0016] [Expandable polystyrene resin particle body] The expandable polystyrene resin particle body is a particle composed of an expandable resin containing a base resin, a foaming agent, and, if necessary, additives.

[0017] (Base resin) The base resin in this specification includes styrene resins, which may be in the form of resin particles obtained by melt-kneading with additives as appropriate using an extruder, or resin particles obtained by polymerizing styrene monomers in a pressure-resistant container by an aqueous suspension polymerization method or a seed polymerization method. As the styrene resin produced by a polymerization method, it may be a homopolymer of styrene or a copolymer of a styrene monomer and a monomer other than the styrene monomer. Examples of monomers other than the styrene monomer include ethylene, butadiene, acrylonitrile, styrene derivatives, acrylic esters, etc. Examples of the styrene derivatives include α-methylstyrene, paramethylstyrene, t-butylstyrene, chlorostyrene, etc. Examples of the acrylic esters include alkyl acrylates such as methyl acrylate and butyl acrylate. These monomers other than the styrene monomer may be used alone or in combination of two or more.

[0018] (Foaming agent) Known methods for impregnating resin particles with a foaming agent include a method of injecting the foaming agent into the resin melt-kneaded by an extruder (quenching method), a method of impregnating the resin particles obtained by an extruder with the foaming agent at a temperature lower than the resin melting point in a pressure-resistant container (mini pellet post-impregnation method), etc. On the other hand, in the case of production by a polymerization method, known methods such as impregnating the resin particles after polymerization with the foaming agent in a pressure-resistant container are known.

[0019] Examples of the foaming agent include aliphatic hydrocarbons such as propane, butane, and pentane; alicyclic hydrocarbons such as cyclobutane and cyclopentane; halogenated hydrocarbons such as methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane; etc. Among them, butane is more preferable in terms of good foaming power. These foaming agents may be used alone or in combination of two or more.

[0020] The content of the foaming agent in the expandable polystyrene resin particle body is appropriately selected in a timely manner according to the desired magnification of the final foamed molded article. However, it is preferably 3.0 parts by weight or more, more preferably 3.5 parts by weight or more, and preferably 7.0 parts by weight or less, more preferably 5.0 parts by weight or less, based on 100 parts by weight of the expandable polystyrene resin particle body. If the content of the foaming agent is within the above range, it is possible to prevent the heating time from becoming long in the pre-foaming process, suppress blocking, shorten the time required for manufacturing the foamed molded article, and shorten the molding cycle of the molding process.

[0021] (Additive) Examples of the additives appropriately added to the base resin include solvents, plasticizers, nucleating agents, flame retardants, flame retardant aids, and the like.

[0022] Specific examples of the solvent and the plasticizer include aliphatic hydrocarbons having 6 or more carbon atoms such as hexane and heptane; alicyclic hydrocarbons having 6 or more carbon atoms such as cyclohexane and cyclooctane, diisobutyl adipate, dioctyl adipate, dibutyl sebacate, glycerin tristearate, glycerin tricaprylate, coconut oil, palm oil, rapeseed oil; and the like. Specific examples of the nucleating agent include methyl methacrylate-based copolymers, polyethylene wax, talc, fatty acid bisamides, ethylene-vinyl acetate copolymers, and the like. Specific examples of the fatty acid bisamide include, for example, methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, ethylene bisoleic acid amide, and the like.

[0023] As the flame retardant, known flame retardants can be used. Specific examples include halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; brominated phenol derivatives such as tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-diglycidyl ether, and 2,2-bis[4'-(2",3"-dibromoalkoxy)-3',5'-dibromophenyl]-propane; brominated butadiene-vinyl aromatic hydrocarbon copolymers such as brominated styrene-butadiene block copolymer, brominated random styrene-butadiene copolymer, and brominated styrene-butadiene graft copolymer (for example, EMERALD 3000 manufactured by Chemtura, or the copolymer described in JP-T-2009-516019); and the like. As the flame retardant aid, known flame retardant aids can be used. Specific examples include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, and the like.

[0024] These additives may be used alone or in combination of two or more. Alternatively, a foaming styrenic resin particle body having a crack structure formed on the surface of the resin particles may be used by applying and drying a nonionic surfactant to the above-mentioned foaming styrenic resin particle body. By forming the crack structure, the adhesion force of liquid A tends to increase. Specific examples of the liquid nonionic surfactant include polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene laurate, polyoxyethylene palmitate, polyoxyethylene stearate, polyoxyethylene oleate, and the like. These nonionic surfactants may be used alone or in combination of two or more.

[0025] 〔Volume average particle diameter of the expandable polystyrene resin particle body〕 The volume average particle diameter of the expandable polystyrene resin particle body of the present invention can also be said to be the average particle diameter of the expandable polystyrene resin particle body. The volume average particle diameter of the expandable polystyrene resin particles can be appropriately set according to the use of the foamed molded body and the like. Generally, the volume average particle diameter of the resin particles produced by the suspension polymerization method is 0.5 mm or more and 1.2 mm or less, and the particle diameter of the particles produced by the seed polymerization method is 0.2 mm or more and 0.5 mm or less. Also, the particle diameter produced by the quenching method using an extruder is 1.0 mm or more and 1.5 mm or less. In the present specification, the volume average particle diameter of the expandable polystyrene resin particle body is a value measured using an image processing type Microtrac JPA.

[0026] 〔Expandable polystyrene resin particles〕 The expandable polystyrene resin particles of the present invention are obtained by producing the expandable polystyrene resin particle body. As described in the above 〔Expandable polystyrene resin particle body〕, the process for obtaining the expandable polystyrene resin particle body is not particularly limited, and includes known processes such as the process adopted in the quenching method, the process adopted in the post-mini pellet impregnation method, and the process adopted in the polymerization method.

[0027] 〔Production of expandable polystyrene resin particles〕 The expandable polystyrene resin particles of the present invention are obtained by a coating step of applying a liquid material A containing at least one of polyether and liquid paraffin in an amount of 0.3 parts by weight or less, a clay mineral B in an amount of 0.01 parts by weight or more and 1 part by weight or less, and a fusion promoter C in an amount of more than 0 parts by weight and 0.5 parts by weight or less, based on 100 parts by weight of the expandable polystyrene resin particle body, to the surface of the expandable polystyrene resin particle body.

[0028] When a liquid A is applied to the surface of the expandable polystyrene resin particle body, it is preferable that after the liquid A is applied, a clay mineral B and a fusion promoter C are applied. Note that the clay mineral B and the fusion promoter C may be applied simultaneously or separately. Hereinafter, as an embodiment of the present invention, a method for producing expandable polystyrene resin particles in which a liquid A, a clay mineral B, and a fusion promoter C are applied to the surface of the expandable polystyrene resin particle body, and after the liquid A is applied, the clay mineral B and the fusion promoter C are applied will be described. In addition, hereinafter, for convenience of explanation, the step of applying the liquid A is referred to as the first coating step, and the step of applying the clay mineral B and the fusion promoter C is referred to as the second step.

[0029] (First coating step) The first coating step is a step of applying a liquid A containing at least one of polyether and liquid paraffin to the surface of the expandable polystyrene resin particle body. Both polyether and liquid paraffin are poorly soluble in water at room temperature (25°C). Polyether is a derivative from alkylene oxide. Specifically, polypropylene glycol, polyoxypropylene-glycol ether, polyoxypropylene-diglycerol ether, polypropylene-diglycol·sorbitol ether, polybutylene glycol, polyethylene glycol·polypropylene·pentaerythritol ether, polyethylene glycol, etc. can be mentioned. In particular, polypropylene glycol and polyethylene glycol are preferably inexpensive and easy to handle.

[0030] Specific examples of liquid paraffin include saturated hydrocarbons having 15 to 35 carbon atoms.

[0031] Liquid A is preferably a substance that is difficult to erode the surface of expandable styrene resin particles. Since the SP value (solubility parameter) of the styrene resin is 8, substances with widely separated SP values are suitable. For example, the SP values of polyether and liquid paraffin are 10 and 16 respectively, which are difficult to erode the surface of expandable styrene resin particles, suppress the increase in the cell ratio of pre-expanded particles, and result in less reduction in the mechanical strength of the final product. When the SP value is widely separated as in the case of liquid paraffin, the adhesiveness to styrene resin particles tends to decrease. Therefore, polyether is particularly preferred as liquid A.

[0032] It is important that liquid A is poorly soluble in water, so that dissolution of liquid A by the heated steam used in the pre-expansion process and the molding process is less likely to occur, and it is possible to prevent the clay mineral B and the fusion promoter C applied in the second coating process from peeling off. For example, polypropylene glycol with a molecular weight of 1000 or more is poorly soluble in water. Also, the kinematic viscosity (25 °C) of liquid A is 100 mm 2 / S or more and 500 mm 2 / S or less is preferred. If it is less than 100 mm 2 / S, there is a tendency to flow out from the resin particle body, and if it exceeds 500 mm 2 / S, it tends to require a long time for mixing with the resin particles.

[0033] The coating amount of liquid A is more preferably 0.3 parts by weight or less (including 0 parts by weight), preferably 0.25 parts by weight or less, and more preferably 0.2 parts by weight or less, based on 100 parts by weight of the expandable styrene resin particle body. Also, Liquid A may not be applied. When liquid A is applied, it is preferably 0 parts by weight or more, more preferably 0.01 parts by weight or more, and even more preferably 0.02 parts by weight or more, based on 100 parts by weight of the expandable styrene resin particle body.

[0034] If the coating amount of liquid A is within the above range, it can be uniformly mixed with the resin particle body, the fluidity of the resin particles is good, and handling is easy. When the amount of liquid A is 0 parts by weight, although the clay mineral B and the fusion accelerator C applied in the second coating step tend to be easily peeled off, the electrostatic attraction between the positively charged clay mineral B and the negatively charged polystyrene-based resin suppresses powder separation. When the coating amount exceeds 0.3 parts by weight, the fluidity (angle of repose) of the resin particles deteriorates, and blocking during pre-expansion increases.

[0035] (Second coating step) The second coating step is a step carried out after the first coating step, and is a step of applying the clay mineral B and the fusion accelerator C to the surface of the expandable polystyrene resin particle body. Specifically, the clay mineral B is a silicate mineral, and a substance located in the positive charge of the charging list is preferable. This is because when the clay mineral B is a positively charged substance, it electrostatically attracts the negatively charged polystyrene-based resin particle body, making it difficult to peel off. On the other hand, silica (SiO2), which is not a negatively charged silicate mineral, and fatty acid metal salts (zinc stearate) generally used as antiblocking agents tend to be easily peeled off because they electrostatically repel the polystyrene-based resin particle body.

[0036] In addition, the inventors have newly found that by applying the clay mineral B to the surface of the expandable polystyrene resin particle body, the charging of the pre-expanded particles obtained by expanding the expandable polystyrene resin particles is suppressed. Here, if the pre-expanded particles are charged, not only is it difficult to handle due to adhesion to a net hopper or the like, but when the pre-expanded particles move through a pipe while being transported or dried by air transportation, the pre-expanded particles containing the styrene-based resin are highly electrically insulating and thus tend to be charged by friction. Therefore, there is a possibility of ignition and explosion of the hydrocarbon used as the blowing agent due to the discharge of static electricity derived from charging. In the present invention, by applying the clay mineral B to the surface of the expandable polystyrene resin particle body, not only can blocking be suppressed, but also the charging of the pre-expanded particles can be suppressed. Specific examples of clay mineral B include silicate minerals such as kaolinite, mica, talc, zeolite, chlorite, glauconite, smectite, etc. in powder form with an average particle size of 30 μm or less, preferably 20 μm or less and 1 μm or more. More preferably, they are kaolinite, mica, and talc which are inexpensive and easily available. These clay minerals may be used alone or in combination of two or more.

[0037] If the average particle size of clay mineral B is within the above range, blocking during pre-foaming can be suppressed. However, if the average particle size exceeds 30 μm, the coverage rate of clay mineral B on the surface of the resin particle body becomes small, and the amount of blocking tends to increase. If it is less than 1 μm, although the coverage rate increases and the amount of blocking decreases, the strength of the foam molded body tends to decrease. The coating amount of clay mineral B is 0.01 part by weight or more and 1 part by weight or less, preferably 0.05 part by weight or more and 0.6 part by weight or less, more preferably 0.05 part by weight or more and 0.4 part by weight or more, based on 100 parts by weight of the expandable styrene resin particle body. If the addition amount of clay mineral B is within the above range, blocking during pre-foaming and the chargeability of the pre-foamed particles can be suppressed, and a foam molded body with practical strength that does not easily break can be obtained. Since clay mineral B acts as a fusion inhibitor, if it exceeds 0.6 part by weight, the foam molded body will easily break. If it is less than 0.01 part by weight, blocking will increase, and the obtained pre-foamed particles will be charged and adhere to the wall surface of the storage hopper, making handling difficult.

[0038] Examples of the fusion promoter C include fatty acid glycerides in powder form with a melting point upper limit of 120 °C or less, more preferably 100 °C or less, at room temperature (25 °C). If the melting point upper limit exceeds 120 °C, it will not fuse during molding processing and tends to impair the fusion promoting effect. Specifically, fatty acid triglycerides such as tricaprin, tristearin, trilinolein, and triglyceride hydroxystearate; fatty acid diglycerides such as dilaurin, distearin, and dilinolein; fatty acid monoglycerides such as monolaurin, monostearin, and monolinolein; vegetable oils (hydroxy fatty acid triglycerides) such as hydrogenated castor oil (triglyceride hydroxystearate), etc. These fatty acid glycerides may be used alone or in combination of two or more. Among them, hydrogenated castor oil (melting point 84°C) is suitable for suppressing the erosion of the surface of polystyrene resin particles and promoting the fusion of the foam molded body.

[0039] The coating amount of the fusion promoter C is more than 0 part by weight and 0.5 part by weight or less, more preferably 0 part by weight or more and 0.1 part by weight or less, and still more preferably 0.5 part by weight or more and 0.4 part by weight or less, based on 100 parts by weight of the expandable styrene resin particle body. If the addition amount of the fusion promoter is within the above range, blocking during pre-expansion can be suppressed, and the practical strength of the foam molded body can be exhibited. When the amount of the fusion promoter exceeds 0.5 part by weight, the blocking amount during pre-expansion increases, and the foam breakage of the surface film of the pre-expanded particles is promoted.

[0040] The clay mineral B and the fusion promoter C used in the second coating step are preferably powdery substances that are hardly soluble in water. Thereby, dissolution and peeling due to the heated steam used in the pre-expansion step and the molding step can be prevented. In the first coating step and / or the second coating step of manufacturing the expandable polystyrene resin particles of the present invention, further additives may be applied to the surface of the expandable polystyrene resin particle body according to the required performance. Furthermore, the method for manufacturing the expandable polystyrene resin particles of the invention may include additional coating steps other than the first coating step and the second coating step according to the required performance. Note that after applying the liquid A in the first coating step, applying the powdery clay mineral B and the fusion promoter C in the second coating step can coat the agent (additive) applied to the surface of the expandable polystyrene resin particle body more uniformly.

[0041] In the method for manufacturing the expandable polystyrene resin particles of the present invention, as a method for applying the liquid A, the clay mineral B, and the fusion promoter C to the surface of the expandable polystyrene resin particle body, it is only necessary to be able to mix the expandable polystyrene resin particle body and various additives, and various known methods can be used. In order to uniformly mix the expandable polystyrene resin particle body and various additives, it is preferable to use mixing equipment in the first coating step and the second coating step. Examples of the mixing equipment used in the manufacturing method of the present invention include mixers such as super mixers, Nauta mixers, universal mixers, Proshear mixers, Apex mixers, Henschel mixers, and Lodige mixers; blenders such as ribbon blenders and tumbler-type blenders. The mixing equipment can be appropriately selected in consideration of the coating amount of the additive and the like.

[0042] The mixing time in each of the above steps is not particularly limited and can be appropriately adjusted according to the mixing ability of the mixing equipment.

[0043] 〔2. Pre-expanded particles〕 The pre-expanded particles according to an embodiment of the present invention are obtained by pre-expanding (primary foaming) the above-described expandable polystyrene resin particles.

[0044] As a method for pre-expanding, for example, a normal method such as using a cylindrical pre-expansion device and heating and expanding the expandable thermoplastic resin particles using a heating medium such as steam can be adopted.

[0045] The pre-foaming device and the conditions of the pre-foaming process may be appropriately set according to the type of the base resin of the expandable polystyrene resin particle body, the desired pre-foaming ratio, etc., and are not particularly limited.

[0046] 〔3. Foamed molded body〕 The foamed molded body according to an embodiment of the present invention is obtained by heating and foaming (secondary foaming) the above-described pre-foamed particles and then molding them.

[0047] As a method of heating and foaming the pre-foamed particles and then molding them, for example, an ordinary method such as an in-mold foaming molding method in which the pre-foamed particles are filled into a mold and a heating medium such as steam is blown in for heating can be adopted.

[0048] As a specific in-mold foaming molding method, there is a method in which the pre-foamed particles are filled into a mold that can be closed but not airtight, and the pre-foamed particles are heated and fused by a heating medium to form an in-mold foamed molded body.

[0049] The device used for heating and foaming and the conditions of heating and foaming may be appropriately set according to the composition of the expandable polystyrene resin particle body, the desired foaming ratio, etc., and are not particularly limited.

[0050] The above foamed molded body, particularly the in-mold foamed molded body, is suitable for, for example, packaging materials (trays) such as food containers, transport packaging materials such as fish boxes, and particularly cushioning materials for household appliances and precision parts that require low charging performance, etc., because of advantages such as being easy to produce a molded body of a desired shape.

Examples

[0051] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, "parts" and "%" are based on weight unless otherwise specified.

[0052] The various measurement methods and evaluation methods for the expandable polystyrene resin particles and the foamed molded articles in the examples and comparative examples are as follows.

[0053] <Evaluation of the fluidity of expandable polystyrene resin particles> The fluidity of the expandable polystyrene resin particles was evaluated in the following 5 grades using an evaluation apparatus of an angle of repose measuring instrument. The larger the numerical value, the better the fluidity, and a value of "3" or more was judged as passing.

[0054] The angle of repose was measured by the following method. First, a box with one side serving as a weir was prepared, and the expandable polystyrene resin particles were put into the box until it was full. After putting them in, the weir was removed and the expandable polystyrene resin particles were allowed to spill out naturally. Then, the angle of the expandable polystyrene resin particles remaining in the box was measured, and that angle was taken as the angle of repose (degrees).

[0055] 5: The angle of repose is 25 degrees or less, the fluidity is good, and the resin particles roll well. 4: The angle of repose exceeds 25 degrees and is 30 degrees or less. The resin particles roll, but the flow is slow. 3: The angle of repose exceeds 30 degrees and is 35 degrees or less. The fluidity is good, and the resin particles roll, but there are irregularities remaining on a part of the slope. 2: The angle of repose exceeds 35 degrees and is 40 degrees or less. The fluidity is good, but a vibrator is required to roll the resin particles. 1: The angle of repose exceeds 40 degrees, the fluidity is very poor, and the resin particles do not roll. An angle of repose of 35 degrees or less was considered passing.

[0056] <Evaluation of powder separation of expandable polystyrene resin particles> Weigh 1 kg of expandable polystyrene resin particles and sieve them for 2 minutes using a screen (aperture: 355 μm, 42 mesh, φ750 mm) attached to an electric sieve (DY-50). Then, collect the powder that has passed through the screen (if there is resin mixed in, remove the resin), weigh its weight, and use it as the peeling amount. And calculate the peeling rate of the external additive based on the following calculation formula: (peeling rate [wt%]) = (peeling amount [g]) / (total amount of external additives added to the expandable polystyrene resin particles [g]) × 100. Expandable polystyrene resin particles with a peeling rate of 10 wt% or less were evaluated as qualified.

[0057] <Measurement of blocking rate> Put expandable polystyrene resin particles into a pressure-type pre-expander (manufactured by Daikai Kogyo Co., Ltd., CH-100) equipped with a stirrer, use steam as the heating medium, heat with a blowing steam pressure of 0.1 MPa to perform pre-expansion (primary expansion), and obtain polystyrene pre-expanded particles with a bulk expansion ratio (apparent expansion ratio) of 65 times. And when taking out the polystyrene pre-expanded particles from the pre-expander, pass the pre-expanded particles through a screen with an aperture of 1 cm, collect the pre-expanded particles that did not pass through the screen, weigh its weight, and use it as the blocking amount. And calculate the blocking rate based on the following calculation formula: blocking rate [wt%] = blocking amount [g] / total amount of polystyrene pre-expanded particles [g] × 100. Polystyrene pre-expanded particles with a blocking rate of 2.0 wt% or less were evaluated as qualified.

[0058] <Charge amount of pre-expanded particles> Put 10 g of the pre-expanded particles obtained above into a polyethylene bag, let it stand in a dryer at 40 °C for 1 hour, and then perform about 100 hand shakes. After hand shaking, pour it out onto a hat, and measure the charge amount with an electrostatic measuring instrument Statiron DZ4 type (manufactured by Shishido Electrostatic Co., Ltd.).

[0059] <Evaluation of foamed molded body> After drying the foamed molded body obtained by the manufacturing method described in Example 1 below at room temperature for 24 hours, evaluate the fusion rate and surface elongation.

[0060] (1) Evaluation of fusion rate The obtained foam molded body was broken and its fracture surface was observed, and the ratio (fusion rate) at which the foam particles were broken rather than the foam particle interface was determined. When the fusion rate was 80% or more, it was evaluated as passing.

[0061] (2) Surface elongation The surface states of four parts of the obtained foam molded body were visually observed and evaluated in the following five grades. The average value of these four parts was taken as the score for surface elongation. The larger the numerical value, the smaller the gap between the foam particles and the more beautiful the surface state, and it was determined that a score of "4" or more was passing.

[0062] 5: No gap is found. 4: There are gaps in some parts, but they are hardly noticeable. 3: There are gaps here and there, but it is acceptable as a whole. 2: The gaps are prominent. 1: There are many gaps.

[0063] The coating agents used in the examples and comparative examples are described below.

[0064] <Liquid A> · A(1); Polypropylene glycol: D-2000, manufactured by NOF Corporation · A(2); Liquid paraffin: K-350, manufactured by Kaneda Co., Ltd. · A(3); Methylphenylpolysiloxane: KF50, manufactured by Shin-Etsu Chemical Co., Ltd.

[0065] <Clay mineral B> · B(1); Talc: PK-S, particle size 11 μm, manufactured by Hayashi Kasei Co., Ltd. · B(2); Mica: AB-25S, particle size 10 μm, manufactured by Yamaguchi Mica Co., Ltd. · B(3); Kaolin: ASP170, particle size 0.4 μm, manufactured by San-Es Gypsum Co., Ltd.

[0066] <Fusion inhibitor (fatty acid metal)> · B(4) Zinc stearate: particle size 12 μm, manufactured by NOF Corporation

[0067] <Fusion promoter> ·C: Triglyceride hydroxystearate (hydrogenated castor oil): Castor wax, manufactured by NOF Corporation

[0068] 〔Example 1〕 (Expandable polystyrene resin particle body) Uncoated expandable polystyrene resin particles (Kaneparl TG, volume average particle diameter 0.9 mm, manufactured by Kaneka Corporation) were used as the expandable polystyrene resin particle body (base resin). The expandable polystyrene resin particle body is a styrene-butyl acrylate copolymer obtained by copolymerizing styrene and butyl acrylate at a weight ratio of 95:5.

[0069] (Production of expandable polystyrene resin particles) 100 parts by weight of the above expandable polystyrene resin particle body was put into a universal mixer (manufactured by TSMS Co., Ltd., EM-15B type), 0.06 part by weight of liquid A(1) was added over 6 seconds, and stirred for 30 seconds to complete the first coating step. Next, 0.15 part by weight of clay mineral B(1) and 0.05 part by weight of fusion promoter C were added, and further stirred for 30 seconds to complete the second coating step, obtaining expandable polystyrene resin particles.

[0070] (Production of pre-expanded particles) The expandable polystyrene resin particles obtained above were put into a pressure-type pre-expander (manufactured by Dai-Kai Kogyo Co., Ltd., CH-100) equipped with a stirrer, and pre-expanded (primary expansion) using steam (injected steam pressure 60 kPa) as a heating medium to obtain pre-expanded particles with a bulk expansion ratio (apparent expansion ratio) of 65 times. Next, the obtained pre-expanded particles were left at room temperature for 24 hours for curing and drying.

[0071] (Production of foamed molded body) The pre-expanded particles after curing and drying were heated for 10 seconds using a molding machine (KR-57, manufactured by Daisen Co., Ltd.) and a mold (box-shaped with a length of 450 mm, a width of 300 mm, and a depth of 25 mm), with steam (injected steam pressure: 80 kPa) as the heating medium. Subsequently, they were cooled with water for 2 seconds and then cooled under vacuum. When the surface pressure gauge (pressure of the foamed molded body) provided in the mold reached 30 kPa, the mold was opened and the foamed molded body was taken out.

[0072] The resin fluidity (angle of repose) of the foamed polystyrene resin particles obtained above and the powder release evaluation were carried out, and the charge amount of the pre-expanded particles, the fusion rate of the foamed molded body, and the evaluation test of the surface elongation were also conducted. The evaluation results are shown in Table 1.

[0073] [Examples 2~ 7. Reference Examples 8 and 9 , Comparative Examples 1~3, 6~8 Using the foamed polystyrene resin particle body (Kaneparl TG, manufactured by Kaneka Corporation) produced in Example 1, with the liquid A, clay mineral B, fusion promoter C, and fusion inhibitor (zinc stearate) added in the amounts shown in Tables 1 and 2, and using the same method as in Example 1, foamed polystyrene resin particles, pre-expanded particles, and foamed molded bodies were obtained. The evaluation results are shown in Table 1 (Examples) and Table 2 (Comparative Examples).

[0074] Reference Example 10 , Example 11, Comparative Examples 4, 9 An uncoated product of foamed polystyrene resin particles (Kaneparl NSG, volume average particle diameter 0.9 mm, manufactured by Kaneka Corporation) was used as the foamed polystyrene resin particle body (base resin). The resin particle body is a styrene homopolymer, and an aqueous solution of a nonionic surfactant polyoxyethylene - monooleate (O-3, manufactured by NOF Corporation) was applied to the resin particle body and dried, with cracks formed on the surface of the resin particle body.

[0075] ​To this resin particle body, clay mineral B, fusion promoter C, and fusion inhibitor were added in the amounts shown in Tables 1 and 2 using the same method as in Example 1 to obtain expandable styrene resin particles, pre-expanded particles, and a foamed molded body. The evaluation results are shown in Table 1 (Examples) and Table 2 (Comparative Examples).

[0076] 〔Examples 12, Comparative Examples 5, 10〕 Uncoated expandable styrene resin particles (Kaneparl FQ, volume average particle diameter 0.9 mm, manufactured by Kaneka Corporation) were used as the expandable styrene resin particle body (base resin). The expandable polystyrene resin particles are a terpolymer of styrene, acrylonitrile, and α-methylstyrene copolymerized at a weight ratio of 71:24:5. To this resin particle body, liquid A, clay mineral B, fusion promoter C, and fusion inhibitor were added in the amounts shown in Table 1 using the same method as in Example 1 to obtain expandable thermoplastic resin particles, pre-expanded particles, and a foamed molded body. The evaluation results are shown in Table 1 (Examples) and Table 2 (Comparative Examples).

[0077]

Table 1

[0078]

Table 2

[0079] As shown in Table 1, the expandable styrene resin particles of Examples 1 to 7. Reference Examples 8 - 10, Examples 11 and 12 showed good fluidity (angle of repose) and were excellent in suppressing powder separation. Also, the blocking rate in the production of pre-expanded particles was low, the chargeability of the pre-expanded particles was suppressed, and the foamed molded body had good fusion properties and surface elongation.

[0080] In contrast, Comparative Example 1 without the fusion promoter C had a poor fusion rate of the foamed molded body. Comparative Example 2 with 0.4 parts by weight of liquid A applied had poor fluidity of the resin and a high blocking rate.

[0081] In Comparative Examples 3 to 5 using zinc stearate instead of the clay mineral, clay mineral B was used. Reference Compared with Examples 8, 9, and 10, the powder separation rate is high, and the pre-expanded particles are highly negatively charged. This is considered to be an increase in powder separation due to electrostatic repulsion caused by the negative charge of the polystyrene resin particles and zinc stearate. Also, in Comparative Example 6 using zinc stearate instead of the talc of Example 1, the pre-expanded particles are highly negatively charged. In Comparative Examples 7 to 10 using silicone oil for Liquid A, the pre-expanded particles are negatively charged. This is considered to be because the silicone oil itself is highly negatively charged.

[0082] From these results, expandable styrene resin particles obtained by applying Liquid A containing at least one of polyether and liquid paraffin, clay mineral B, and fusion promoter C to the surface of the expandable styrene resin particle body can maintain good fluidity and suppress powder separation, and furthermore, can suppress the chargeability of the pre-expanded particles.

Claims

1. Expandable polystyrene resin particles containing a foaming agent, wherein on the surface of the expandable polystyrene resin particle body, based on 100 parts by weight of the expandable polystyrene resin particle body, a liquid substance (A) containing at least one of polyether and liquid paraffin is 0.01 part by weight or more and 0.3 part by weight or less, a clay mineral (B) is 0.01 part by weight or more and 1 part by weight or less, and a fusion promoter (C) is more than 0 part by weight and 0.5 part by weight or less, is applied to form expandable polystyrene resin particles.

2. The liquid substance (A) contains a polyether that is poorly soluble in water, The polyether contains at least one of polypropylene glycol and polyethylene glycol, and the expandable polystyrene resin particles according to claim 1.

3. The expandable polystyrene resin particles according to any one of claims 1 to 2, wherein the clay mineral (B) contains at least one selected from the group consisting of talc, mica, and kaolin having an average particle diameter of 30 μm or less.

4. The expandable polystyrene resin particles according to any one of claims 1 to 3, wherein the fusion promoter (C) contains at least one selected from the group consisting of fatty acid monoglycerides, fatty acid diglycerides, fatty acid triglycerides, and hydroxy fatty acid triglycerides.

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

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

7. A step of obtaining an expandable polystyrene resin particle body containing a foaming agent, and on the surface of the expandable polystyrene resin particle body, based on 100 parts by weight of the expandable polystyrene resin particle body, a liquid substance (A) containing at least one of polyether and liquid paraffin is 0.01 part by weight or more and 0.3 part by weight or less, a clay mineral (B) is 0.01 part by weight or more and 1 part by weight or less, and a fusion promoter (C) is more than 0 part by weight and 0.5 part by weight or less, A manufacturing method of expandable polystyrene resin particles including an application step of applying.

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