Method for producing low charging amount foamable styrenic resin particle

Abstract

To provide a method for producing low charging amount foamable styrenic resin particles which can sufficiently express antistatic effects, and prevents stickiness on the surface of foamable styrenic resin particles.SOLUTION: A method for producing low charging amount foamable styrenic resin particles that produces low charging amount foamable styrenic resin particles from foamable styrenic resin particles includes a cleaning step of cleaning the foamable styrenic resin particles with cleaning water, wherein an antistatic agent is added to the foamable styrenic resin particles, in the coexistence of 12 pts.wt. to 100,000 pts.wt. of the cleaning water relative to 100 pts.wt. of the foamable styrenic resin particles, and an addition amount of the antistatic agent relative to 100 pts.wt. of the foamable styrenic resin particles is 0.00010 pt.wt. to 0.00250 pt.wt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing low-charge expandable styrene-based resin particles. [Background technology]

[0002] Expandable styrene resin particles used in cup products, lightweight aggregates, cushion beads, etc. tend to become electrically charged as their average particle size decreases, because their specific surface area increases. Therefore, several technologies have been reported for preventing the static charge of expandable styrene resin particles.

[0003] Expandable polystyrene resin particles for lightweight aggregates have been reported, characterized in that the expandable polystyrene resin particles have an average particle size of 300 to 600 μm and contain 0.1 to 1.0 wt % of zinc stearate on the particle surface in the presence of 0.01 to 1.0 wt % of an antistatic agent, and in the examples, 0.05 wt % of the antistatic agent is used relative to the expandable polystyrene resin particles (Patent Document 1).

[0004] Low-charge expandable particles have been reported, which are at least composed of expandable polystyrene-based resin particles and an antistatic agent that coats the expandable polystyrene-based resin particles, wherein the antistatic agent is a solid or liquid composition at room temperature and contains at least a compound having one amino group and two hydroxyl groups in its molecule, and the compound is contained in an amount of 0.01 to 0.10% by weight relative to the expandable polystyrene-based resin particles, and in the examples, 0.012 to 0.042% by weight of the antistatic agent is used relative to the expandable polystyrene-based resin particles (Patent Document 2).

[0005] A method for producing expandable styrene resin particles has been reported, in which the antistatic agent to be applied to expandable styrene resin particles contains 90% or more of N-hydroxyethyl-N-2-hydroxyalkylamine (the number of carbon atoms in the alkyl group is 14) having one amino group and two hydroxyl groups in the molecule, and the antistatic agent is applied in an amount of 0.005 to 3.0 parts by weight per 100 parts by weight of the expandable styrene resin particles when the moisture content of the expandable styrene resin particles is 0.01 to 5.0% by weight. In the examples, 0.005 to 2.0 parts by weight of N-hydroxyethyl-N-2-hydroxyalkylamine is used as the antistatic agent per 100 parts by weight of the expandable polystyrene resin particles (Patent Document 3).

[0006] However, conventionally, expandable styrene-based resin particles to which an antistatic agent has been added have had problems such as insufficient antistatic effect and the coated antistatic agent causing stickiness on the surface of the expandable styrene-based resin particles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-74242 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-72039 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-114987 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a method for producing low-charge expandable styrene-based resin particles that can fully exhibit antistatic effect and do not cause stickiness on the surface of the expandable styrene-based resin particles. [Means for solving the problem]

[0009] When it is desired to enhance the antistatic effect of the expandable styrene-based resin particles, it is usually considered to apply a large amount of antistatic agent to the expandable styrene-based resin particles. However, when a large amount of antistatic agent is applied to the expandable styrene-based resin particles, the surface of the expandable styrene-based resin particles may become sticky. On the other hand, when it is desired to suppress the stickiness of the surface of the expandable styrene-based resin particles, it is usually considered to reduce the amount of antistatic agent applied to the expandable styrene-based resin particles. However, when the amount of antistatic agent applied to the expandable styrene-based resin particles is reduced, it may become difficult to fully exhibit the antistatic effect.

[0010] Therefore, the present inventors have conducted extensive research into a technology that can achieve a sufficient antistatic effect with a small amount of antistatic agent. As a result, they have focused on a washing step in which expandable styrene-based resin particles are washed with washing water during the production of expandable styrene-based resin particles, and have found that if an antistatic agent is added to the expandable styrene-based resin particles in the presence of the washing water, even a small amount of the antistatic agent can be efficiently and uniformly applied to the entire particle surface, thereby achieving both a sufficient antistatic effect and reduced stickiness on the particle surface.

[0011] [1] A method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention is a method for producing low-charge expandable styrene-based resin particles from expandable styrene-based resin particles, comprising a washing step of washing the expandable styrene-based resin particles with washing water, in which an antistatic agent is added to the expandable styrene-based resin particles in the presence of 12 parts by weight to 100,000 parts by weight of the washing water per 100 parts by weight of the expandable styrene-based resin particles, and the amount of the antistatic agent added per 100 parts by weight of the expandable styrene-based resin particles is 0.00010 parts by weight to 0.00250 parts by weight. [2] In the method for producing low-charge expandable styrene-based resin particles described in [1] above, the expandable styrene-based resin particles may be obtained by impregnating a styrene-based resin with a blowing agent. [3] In the method for producing low-charge expandable styrene-based resin particles according to the above [1] or [2], the antistatic agent may be an anionic surfactant. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for producing low-charge expandable styrene resin particles that can fully exhibit antistatic effects and do not cause stickiness on the surface of the expandable styrene resin particles. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0014] When the expression "weight" appears in this specification, it may be read as "mass," which is a commonly used SI unit indicating weight.

[0015] In this specification, the term "(meth)acrylic" means "acrylic and / or methacrylic", the term "(meth)acrylate" means "acrylate and / or methacrylate", the term "(meth)acryloyl" means "acryloyl and / or methacryloyl", the term "(meth)allyl" means "allyl and / or methallyl", and the term "(meth)acrolein" means "acrolein and / or methacrolein".

[0016] <<A. Method for producing low-charge expandable styrene-based resin particles>> The method for producing low-charge-amount foamed styrene resin particles according to an embodiment of the present invention is a method for producing low-charge-amount foamed styrene resin particles from foamed styrene resin particles, and includes a washing step of washing the foamed styrene resin particles with washing water. An antistatic agent is added to the foamed styrene resin particles in the coexistence of 12 parts by weight to 100,000 parts by weight of the washing water with respect to 100 parts by weight of the foamed styrene resin particles, and the addition amount of the antistatic agent with respect to 100 parts by weight of the foamed styrene resin particles is 0.00010 parts by weight to 0.00250 parts by weight.

[0017] ≪A-1. Foamed styrene resin particles≫ In the method for producing low-charge-amount foamed styrene resin particles according to an embodiment of the present invention, low-charge-amount foamed styrene resin particles are produced from foamed styrene resin particles. The foamed styrene resin particles may be only one kind or two or more kinds.

[0018] As the foamed styrene resin particles, any appropriate foamed styrene resin particles can be adopted as long as the effects of the present invention are not impaired. Such foamed styrene resin particles are typically obtained by impregnating a styrene resin with a foaming agent.

[0019] The weight average molecular weight of the foamed styrene resin particles is preferably 100,000 to 600,000, more preferably 150,000 to 550,000, still more preferably 180,000 to 500,000, and even more preferably 200,000 to 450,000.

[0020] <A-1-1. Styrene resin> The styrene resin can be obtained by polymerizing a monomer component containing a styrene-based monomer.

[0021] The weight average molecular weight of the styrene resin is preferably 100,000 to 600,000, more preferably 150,000 to 550,000, still more preferably 180,000 to 500,000, and even more preferably 200,000 to 450,000.

[0022] The styrene-based monomer includes styrene or a styrene derivative. Examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene. The styrene-based monomer may be one type or two or more types.

[0023] The styrene-based monomer preferably contains at least styrene. The content of styrene relative to the total amount of the styrene-based monomer is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0024] The monomer component may contain other monomers as long as it contains a styrene-based monomer as the main component. In this specification, the "main component" means that the content of the component in all components is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0025] The other monomers typically include vinyl monomers.

[0026] Examples of the vinyl monomer include a polyfunctional monomer, a (meth)acrylic acid ester monomer, a maleic acid ester monomer, and a fumaric acid ester monomer. The vinyl monomer may be one type or two or more types.

[0027] Examples of polyfunctional monomers include divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene; and alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate. By using a polyfunctional monomer, a branched structure can be imparted to the styrene-based resin. The content of the polyfunctional monomer in the monomer components constituting the styrene-based resin is preferably 0% by weight to 0.1% by weight.

[0028] Examples of (meth)acrylic acid ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and hexyl (meth)acrylate. Among these (meth)acrylic acid ester monomers, butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate are preferred, and butyl acrylate is more preferred. By using a (meth)acrylic acid ester monomer, the glass transition temperature (Tg) of the styrene-based resin can be lowered. The content of the acrylic acid ester monomer in the monomer components constituting the styrene-based resin is preferably 0% by weight to 4.0% by weight.

[0029] An example of the maleate monomer is dimethyl maleate.

[0030] Examples of fumarate monomers include dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

[0031] The styrene-based resin may be a non-recycled styrene-based resin, such as general-purpose styrene resin (GPPS), commercially available styrene-based resin, or a styrene-based resin newly prepared by a method such as suspension polymerization, or may be a recycled styrene-based resin. The recycled material may typically be a used foamed styrene-based resin. The recycled material may be a material obtained by recovering food packaging trays, fish boxes, cushioning materials for home appliances, etc., and regenerating them using a limonene dissolution method or a thermal volume reduction method. The recycled material may also be a material obtained by crushing non-foamed styrene-based resin molded bodies separated and recovered from home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.) or office equipment (e.g., copiers, facsimiles, printers, etc.), melt-kneading them, and re-pelletizing them.

[0032] The styrenic resin may be a composite resin of a styrenic resin and an olefinic resin. The content ratio of the styrenic resin to the olefinic resin in the composite resin (styrenic resin / olefinic resin: weight ratio) is preferably 50 / 50 to 90 / 10, more preferably 60 / 40 to 85 / 15. If the content of the styrenic resin is too low, the foaming property and / or the molding processability may become insufficient. If the content of the styrenic resin is too high, the impact resistance and / or the flexibility may become insufficient.

[0033] As the olefinic resin, any suitable olefinic resin can be adopted as long as the effects of the present invention are not impaired. The olefinic resin may be only one kind or two or more kinds. Examples of the olefinic resin include polyethylene-based resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers; polypropylene-based resins such as propylene homopolymer, propylene-vinyl acetate copolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. Among these olefinic resins, preferably, an ethylene-vinyl acetate copolymer, high-density polyethylene, linear low-density polyethylene, and mixtures thereof. The low density is preferably 0.91 g / cm ~0.94 g / cm 3 and more preferably 0.91 g / cm 3 ~0.93 g / cm 3 The high density is preferably 0.95 g / cm 3 ~0.97 g / cm 3 and more preferably 0.95 g / cm 3 ~0.96 g / cm 3 The medium density is the density between the low density and the high density.

[0034] <A-1-2. Foaming agent> The foaming agent may be only one kind or two or more kinds.

[0035] As the foaming agent, any suitable foaming agent can be used as long as the effects of the present invention are not impaired. The foaming agent is preferably an organic compound having a boiling point below the softening point of the styrene resin and being gaseous or liquid at normal pressure. Examples of the foaming agent include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane or neopentane), n-hexane, etc.; alicyclic hydrocarbons such as cyclopentane, cyclopentadiene, etc.; ketones such as acetone, methyl ethyl ketone, etc.; alcohols such as methanol, ethanol, isopropyl alcohol, etc.; low-boiling ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, etc.; halogen-containing hydrocarbons such as trichloromonofluoromethane, dichlorodifluoromethane, etc. Inorganic gases such as carbon dioxide gas, nitrogen, ammonia, etc. may be used as the foaming agent. Among these, aliphatic hydrocarbons are preferred as the foaming agent. This is because it can prevent the destruction of the ozone layer and can quickly replace with air, so that the change with time of the styrene resin foam molded body can be suppressed. More preferably, the foaming agent is propane, n-butane, isobutane, n-pentane, isopentane, and combinations thereof.

[0036] The content of the foaming agent can be appropriately set according to the purpose. The content of the foaming agent is preferably 2 parts by weight to 20 parts by weight, more preferably 2 parts by weight to 18 parts by weight, still more preferably 3 parts by weight to 16 parts by weight, particularly preferably 3 parts by weight to 14 parts by weight, and most preferably 4 parts by weight to 12 parts by weight, based on 100 parts by weight of the styrene resin.

[0037] <A-1-3. Impregnation of the Foaming Agent into the Styrene Resin> As a method for impregnating the styrene resin with the foaming agent, a conventionally known method can be adopted. For example, (1) A method of continuously or intermittently supplying a monomer component containing a styrene monomer into an aqueous medium and polymerizing it in the presence of a polymerization initiator, and adding and impregnating the foaming agent during and / or after the polymerization (one-step method), (2) A method (two-stage method) in which, without adding a blowing agent, a monomer component containing a styrene-based monomer is polymerized in the presence of a polymerization initiator to produce styrene-based resin particles, which are sieved as necessary to obtain styrene-based resin particles having a required particle size range, the temperature of a reaction vessel to which the styrene-based resin particles, water, and a dispersant have been supplied is raised to prepare a dispersion, and a blowing agent is added to the dispersion to impregnate the particles with the blowing agent; (3) A method (seed polymerization method) in which small styrene resin particles (seed particles), water, and a dispersant are supplied to a reaction vessel and heated to prepare a dispersion, and then a monomer component in which a polymerization initiator is dissolved is continuously supplied to the reaction vessel, and further monomer components are continuously supplied as necessary, to carry out polymerization, and a blowing agent is added during and / or after the completion of polymerization to impregnate the particles and grow them to the desired particle size; Examples include:

[0038] The temperature for impregnation with the blowing agent can be any appropriate temperature within a range that does not impair the effects of the present invention, and is, for example, 40°C to 150°C, preferably 50°C to 140°C, more preferably 60°C to 130°C, even more preferably 70°C to 120°C, and particularly preferably 80°C to 115°C.

[0039] Any suitable polymerization initiator can be used as long as it does not impair the effects of the present invention. Examples of such polymerization initiators include organic peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexyl monocarbonate, dicumyl peroxide, t-butylperoxypivalate, t-butylperoxyisopropyl carbonate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylhexanoate, and di-t-butylperoxyhexylhydroterephthalate; and azo compounds such as azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination of two or more.

[0040] As the polymerization initiator, in order to adjust the molecular weight and reduce the amount of residual monomer, a polymerization initiator having a decomposition temperature in the range of 50°C to 80°C to obtain a 10-hour half-life and a polymerization initiator having a decomposition temperature in the range of 80°C to 120°C to obtain a 10-hour half-life may be used in combination. The polymerization initiator is preferably added in a suspended or emulsified state in an aqueous medium, or dissolved in a small amount of a styrene-based monomer, to which a dispersant is added, to form an aqueous suspension.

[0041] The polymerization initiator is preferably added by dissolving it in a monomer component containing a styrene-based monomer or in a solvent. Examples of the solvent include aromatic hydrocarbons such as ethylbenzene and toluene; and aliphatic hydrocarbons such as heptane and octane. When a solvent is used, it is usually used in an amount of 10% by weight or less based on the monomer component.

[0042] The amount of the polymerization initiator used may be any appropriate amount within the range that does not impair the effects of the present invention, and is preferably 0.1 to 1.0% by weight based on the monomer component.

[0043] As the dispersant, any appropriate dispersant can be used as long as it does not impair the effects of the present invention. Examples of such dispersants include suspension stabilizers and anionic surfactants. These may be used alone or in combination of two or more.

[0044] Examples of the suspension stabilizer include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone; and sparingly soluble inorganic metal salts such as calcium triphosphate, magnesium pyrophosphate, and magnesium oxide. When a sparingly soluble inorganic metal salt is used, an anionic surfactant may be used in combination.

[0045] Examples of anionic surfactants include alkyl sulfates such as sodium lauryl sulfate; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate; higher fatty acid salts such as sodium oleate; and β-tetrahydroxynaphthalene sulfonates.

[0046] The reaction liquid (typically a suspension or dispersion) used in the production of expandable styrene-based resin particles may contain any appropriate additives as long as the effects of the present invention are not impaired. Examples of such additives include radiant heat transfer suppressing components, resins other than styrene-based resins, crosslinking agents, plasticizers, fillers, colorants, cell regulators, weathering agents, antioxidants, anti-fogging agents, and fragrances. The type, number, combination, content, etc. of the additives can be appropriately set depending on the purpose. The additives may be one type only or two or more types.

[0047] When producing expandable styrene-based resin particles, a foaming aid may be used together with the foaming agent. Examples of the foaming aid include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil. The foaming aid may be one type or two or more types.

[0048] When producing expandable styrene-based resin particles, a flame retardant or a flame retardant aid may be used in addition to the blowing agent. Examples of flame retardants include tetrabromocyclooctane, hexabromocyclododecane, hexabromocyclohexane, tris(dibromopropyl phosphate), tetrabromobisphenol A, tetrabromobisphenol F, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-diglycidyl ether, and 2,2-bis[4'(2'',3''-dibromoalkoxy)-3',5'-dibromophenyl]-propane. Examples of flame retardant aids include cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, 2,3-dimethyl-2,3-diphenylbutane, and 3,4-dimethyl-3,4-diphenylhexane. The flame retardant may be of only one kind or may be of two or more kinds. The flame retardant synergist may be of only one kind or may be of two or more kinds.

[0049] Expandable styrene resin particles may be produced by melt extrusion. In the melt extrusion method, styrene resin pellets are fed into a resin supply device, a blowing agent is injected into the molten styrene resin in the resin supply device, and the molten resin containing the blowing agent is extruded through a small hole in a die attached to the tip of the resin supply device and then cooled to obtain expandable styrene resin particles. The hot-cut method involves directly extruding the resin through a small hole in the die into a cooling liquid, cutting the extrudate with a rotary blade immediately after extrusion, and cooling the cut particles in the cooling liquid. The strand-cut method (cold-cut method) involves extruding the resin through a small hole in the die into the air in the form of a strand, introducing the strand into a cooling water bath before foaming, cooling the strand in the cooling water bath, and then cutting the strand into cylindrical particles. Expandable styrene resin particles can be produced by either the hot-cut method or the strand-cut method (cold-cut method).

[0050] <A-2. Cleaning process> A method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention includes a washing step of washing the expandable styrene-based resin particles with washing water, and adding an antistatic agent to the expandable styrene-based resin particles in the presence of the washing water.

[0051] The washing step typically includes an operation of adding washing water to the expandable styrene-based resin particles (hereinafter, sometimes referred to as the "washing water adding operation"), and an operation of washing the expandable styrene-based resin particles by stirring, ultrasonic irradiation, or the like (hereinafter, sometimes referred to as the "washing operation").

[0052] In the washing step, when a series of operations including a washing water addition operation and a washing operation is considered as one washing cycle, this washing cycle may be performed only once or may be performed two or more times (for example, two to five times). When this washing cycle is performed two or more times, an operation of removing washing water (hereinafter, sometimes referred to as a "washing water removal operation") is usually included between the washing operation and the washing water addition operation of the next washing cycle. For example, when there are two washing cycles, the washing step will be performed as follows: washing water addition operation (first cycle), washing operation (first cycle), washing water removal operation, washing water addition operation (second cycle), and washing operation (second cycle).

[0053] Unlike the dehydration step described below, the wash water removal operation does not require substantially complete removal of the wash water using a dehydrator or the like. The amount of wash water (remaining wash water) immediately after the wash water removal operation can be any appropriate amount as long as the effects of the present invention are not impaired. From the viewpoint of enhancing the cleaning effect in the next washing cycle following the wash water removal operation, the amount of wash water (remaining wash water) immediately after the wash water removal operation is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 10 parts by weight or less, particularly preferably 5 parts by weight or less, and most preferably 1 part by weight or less, relative to 100 parts by weight of the expandable styrene-based resin particles. From the viewpoint of enhancing the cleaning effect in the next washing cycle following the wash water removal operation, the lower limit of the amount of wash water (remaining wash water) immediately after the wash water removal operation is usually the less the better, for example, 0% by weight or more. However, as mentioned above, unlike the dehydration step described below, the wash water removal operation does not require substantially complete removal of the wash water using a dehydrator or the like. The wash water removal operation can be carried out, for example, by separating and draining using a screen or the like.

[0054] The amount of washing water may be any appropriate amount within a range that does not impair the effects of the present invention. The amount of washing water is preferably 12 to 100,000 parts by weight, more preferably 15 to 10,000 parts by weight, even more preferably 20 to 1,000 parts by weight, particularly preferably 30 to 200 parts by weight, and most preferably 40 to 150 parts by weight, per 100 parts by weight of the expandable styrene-based resin particles in one washing cycle.

[0055] The temperature of the washing water may be any appropriate temperature within a range that does not impair the effects of the present invention. The temperature of such washing water is preferably 1°C to 37°C, more preferably 3°C to 35°C, even more preferably 5°C to 33°C, particularly preferably 6°C to 31°C, and most preferably 7°C to 30°C.

[0056] The washing time in the washing operation can be set to any appropriate time within a range that does not impair the effects of the present invention. Taking into consideration production costs, etc., the washing time in one washing cycle is preferably 90 minutes or less, more preferably 60 minutes or less.

[0057] <A-3. Addition of antistatic agent> In the method for producing low-charge expandable styrene resin particles according to an embodiment of the present invention, an antistatic agent is added to the expandable styrene resin particles in the presence of the washing water.

[0058] In the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention, typically, an antistatic agent is added to the expandable styrene-based resin particles in the presence of the washing water during the washing step. In a preferred embodiment of the present invention, during a washing step in which the number of washing cycles is n (n is an integer of 1 or more), after washing water is added in the n-th washing water adding operation, the antistatic agent is added to the expandable styrene-based resin particles in the presence of the washing water until the end of the n-th washing operation.

[0059] When an antistatic agent is added to the expandable styrene-based resin particles, the amount of washing water present with the expandable styrene-based resin particles is typically 12 to 100,000 parts by weight, preferably 15 to 10,000 parts by weight, more preferably 25 to 5,000 parts by weight, even more preferably 30 to 500 parts by weight, even more preferably 40 to 200 parts by weight, even more preferably 50 to 180 parts by weight, particularly preferably 55 to 160 parts by weight, and most preferably 60 to 140 parts by weight, per 100 parts by weight of the expandable styrene-based resin particles. If the amount of washing water is too small outside the above range, the antistatic agent may not be efficiently and uniformly applied to the entire particle surface. If the amount of washing water is too large outside the above range, the antistatic agent may be easily removed by the excess washing water, and a sufficient amount of antistatic agent may not be applied to the particle surface.

[0060] As an embodiment of the addition of the antistatic agent, any appropriate embodiment can be adopted as long as the antistatic agent is added to the expandable styrene-based resin particles in the presence of washing water, as long as the effects of the present invention are not impaired. (1) In a cleaning step with one cleaning cycle, an antistatic agent is added after the cleaning water addition operation, and then the cleaning operation is performed. (2) In a cleaning step having one cleaning cycle, a cleaning operation is performed after a cleaning water addition operation, and an antistatic agent is added during the cleaning operation. (3) In a cleaning step having n cleaning cycles (n is an integer of 2 or more), an antistatic agent is added after the n-th cleaning water addition operation, and then the n-th cleaning operation is performed. (4) In a cleaning process having n cleaning cycles (n is an integer of 2 or more), the nth cleaning operation is performed after the nth cleaning water addition operation, and the antistatic agent is added during the nth cleaning operation. In the present specification, the operation of adding an antistatic agent to expandable styrene resin particles in the presence of washing water and then stirring the mixture is referred to as a "washing operation."

[0061] In the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention, the amount of antistatic agent added per 100 parts by weight of the expandable styrene-based resin particles is typically 0.00010 to 0.00250 parts by weight, preferably 0.00050 to 0.00230 parts by weight, more preferably 0.00080 to 0.00210 parts by weight, particularly preferably 0.00100 to 0.00200 parts by weight, and most preferably 0.00100 to 0.00200 parts by weight. In the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention, even if the amount of antistatic agent added is very small, the antistatic agent can be efficiently and uniformly applied to the entire particle surface, thereby achieving both sufficient antistatic effect and reduced stickiness on the particle surface. If the amount of antistatic agent added is too small, outside the above range, sufficient antistatic effect may not be achieved. If the amount of the antistatic agent added is too large and outside the above range, the surface of the expandable styrene resin particles may become sticky, or the antistatic agent may not be applied efficiently and uniformly to the entire particle surface.

[0062] The antistatic agent may be added by any appropriate method as long as the effects of the present invention are not impaired. For example, the antistatic agent may be added as an aqueous solution or as is.

[0063] The antistatic agent may be one type or two or more types. As the antistatic agent, any appropriate antistatic agent may be used as long as it does not impair the effects of the present invention. Examples of such antistatic agents include anionic surfactants, cationic surfactants, and nonionic surfactants.

[0064] Examples of anionic surfactants include alkyl sulfates such as sodium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, higher fatty acid salts such as sodium oleate, and β-tetrahydroxynaphthalene sulfonates.

[0065] Examples of cationic surfactants include alkylammonium acetate salts, alkyldimethylbenzylammonium salts, alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylpyridinium salts, oxyalkylene alkylamines, and polyoxyalkylene alkylamines.

[0066] Examples of nonionic surfactants include fatty acid diethanolamides, silicone surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene-polyoxypropylene glycols, and polyether-modified silicones.

[0067] In the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention, an anionic surfactant is preferred as the antistatic agent, as it can more effectively exhibit the effects of the present invention.

[0068] ≪A-4. Dehydration process≫ The method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention may include a dehydration step after the washing step. In the dehydration step, the washing water coexisting with the expandable styrene-based resin particles at the end of the washing step is dehydrated. The method for dehydrating the washing water in the dehydration step can be any appropriate method as long as it can remove substantially all of the washing water coexisting with the expandable styrene-based resin particles at the end of the washing step. An example of such a dehydration method is dehydration using a dehydrator.

[0069] The amount of washing water present together with the expandable styrene resin particles after substantially all of the washing water has been removed is preferably less than 12 parts by weight, more preferably less than 6.0 parts by weight, even more preferably 0 to 3.0 parts by weight, even more preferably 0 to 1.0 parts by weight, still more preferably 0 to 0.1 parts by weight, particularly preferably 0 to 0.01 parts by weight, and most preferably 0 to 0.009 parts by weight, relative to 100 parts by weight of the expandable styrene resin particles.

[0070] ≪A-5. Drying process≫ The method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention may include a drying step of drying the particles obtained through the washing step. Any appropriate drying conditions may be set as long as the effects of the present invention are not impaired. The drying step may be performed, for example, after the dehydration step.

[0071] <A-6. Surface modification process> The method for producing low-charge expandable styrene resin particles according to an embodiment of the present invention may include a surface modification step of modifying the surfaces of the expandable styrene resin particles with a surface additive other than an antistatic agent. The surface modification step can appropriately modify the surface properties of the expandable styrene resin particles depending on the purpose.

[0072] In the surface modification step, a surface additive is added (typically coated) to the surface of the expandable styrene resin particles. The surface additive may be of one type only, or of two or more types.

[0073] Surface additives include, for example, spreading agents, anti-binding agents, adhesion promoters, and lubricants.

[0074] The amount of the surface additive may be any appropriate amount within the range that does not impair the effects of the present invention. The amount is typically preferably 0.05 to 3.0 parts by weight, more preferably 0.05 to 2.0 parts by weight, and even more preferably 0.1 to 1.6 parts by weight, relative to 100 parts by weight of the expandable styrene-based resin particles.

[0075] <<B. Low-charge expandable styrene resin particles>> The low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention can exhibit both a sufficient antistatic effect and reduced stickiness on the particle surface, even if only a small amount of antistatic agent is used, as the antistatic agent is efficiently and uniformly applied to the entire particle surface.

[0076] The low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention can have any suitable shape as long as the effects of the present invention are not impaired. Specific examples of such shapes include spherical, approximately spherical, oval-spherical (egg-shaped), cylindrical, and approximately cylindrical shapes.

[0077] The average particle diameter of the low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention can be any appropriate average particle diameter depending on the purpose. The low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention can exhibit both sufficient antistatic effect and reduced stickiness on the particle surface, and this effect can be more effectively achieved with particles having a small average particle diameter. Such an average particle diameter is preferably 0.20 mm to 0.95 mm, more preferably 0.20 mm to 0.90 mm, even more preferably 0.20 mm to 0.85 mm, even more preferably 0.20 mm to 0.80 mm, even more preferably 0.20 mm to 0.75 mm, even more preferably 0.20 mm to 0.70 mm, particularly preferably 0.20 mm to 0.65 mm, and most preferably 0.20 mm to 0.60 mm. The average particle diameter can be measured in accordance with JIS Z 8815. Specifically, the average particle size is the value measured as the particle size at 50% of the cumulative value from the particle size distribution according to the sieving test of JIS Z 8815.

[0078] The low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention can exhibit a sufficient antistatic effect, and for example, the absolute value of the charge amount measured by the measurement method described below is preferably 5.0 kV or less, more preferably 4.0 kV or less, even more preferably 3.5 kV or less, particularly preferably 3.0 kV or less, and most preferably 2.5 kV or less.

[0079] <<C. Pre-expanded styrene resin particles>> The pre-expanded styrene-based resin particles are obtained by pre-expanding low-charge expandable styrene-based resin particles.

[0080] Pre-expansion involves expanding low-charge expandable styrene-based resin particles to a desired bulk expansion ratio (bulk density) using steam or the like. The bulk expansion ratio of the pre-expanded styrene-based resin particles is preferably 2 to 150 times, more preferably 5 to 100 times. When the bulk expansion ratio of the pre-expanded styrene-based resin particles is within the above range, blocking during expansion and molding can be more effectively prevented, and further, electrostatic charge during expansion and molding can be further suppressed while exhibiting better fusion properties and surface properties, making it possible to mold a styrene-based resin foam molded article with less static electricity. Bulk density is the reciprocal of the bulk expansion ratio. The bulk expansion ratio and bulk density can be determined, for example, as follows.

[0081] A measurement sample of W (g) of expandable styrene resin particles is collected. This measurement sample is allowed to fall naturally into a measuring cylinder, and the volume of the measurement sample dropped into the measuring cylinder is V (cm 3 ) is measured using an apparent density measuring instrument conforming to JIS K 6911. From the weight and volume of the measurement sample, the bulk expansion ratio and bulk density can be calculated according to the following formula. Bulk foaming ratio (times = cm 3 / g) = Volume of measurement sample (V) / Weight of measurement sample (W) Bulk density (g / cm 3 ) = weight of measurement sample (W) / volume of measurement sample (V)

[0082] In one representative embodiment, the pre-expanded styrene-based resin particles can be used to form a styrene-based resin foamed molded article. In another embodiment, the pre-expanded styrene-based resin particles can be used as they are as a buffer material, a heat insulating material, etc. When the pre-expanded styrene-based resin particles are used as they are, the pre-expanded styrene-based resin particles can preferably be used as a packed body in which a large number of the pre-expanded styrene-based resin particles are filled into a bag.

[0083] <<D. Styrene-based resin foam molded body>> One embodiment of the styrene-based resin foam molded article is a styrene-based resin foam molded article molded from low-charge expandable styrene-based resin particles. Another embodiment of the styrene-based resin foam molded article is a styrene-based resin foam molded article molded from pre-expanded styrene-based resin particles.

[0084] The styrene-based resin foam molded article typically contains expanded styrene-based resin particles (hereinafter sometimes simply referred to as "expanded particles") obtained by further expanding pre-expanded styrene-based resin particles.

[0085] A styrene-based resin foam molded article is typically composed of a plurality of foam particles fused together.

[0086] Styrenic resin foam molded articles can typically be produced by placing pre-expanded styrene-based resin particles in a mold having a predetermined shape depending on the purpose and performing in-mold foam molding. More specifically, in-mold foam molding includes (i) filling pre-expanded styrene-based resin particles into a closed mold having a large number of small holes, (ii) heating and expanding the pre-expanded styrene-based resin particles with a heat medium (e.g., pressurized steam, etc.) to obtain expanded particles, and (iii) filling the voids between the expanded particles and fusing the expanded particles together to integrate them by the heat expansion. The density of the styrene-based resin foam molded article can be appropriately set depending on the purpose. The density of the styrene-based resin foam molded article can be adjusted, for example, by previously adjusting the bulk expansion ratio of the pre-expanded styrene-based resin particles to be filled in the mold or by adjusting the amount of pre-expanded styrene-based resin particles filled in the mold.

[0087] The heat-foaming temperature (substantially the temperature of the heat transfer medium) is preferably 90°C to 150°C, more preferably 110°C to 130°C. The heat-foaming time is preferably 5 to 50 seconds, more preferably 10 to 50 seconds. The molding vapor pressure of the heat-foaming (gauge pressure of the heat transfer medium blown in) is preferably 0.04 MPa to 0.1 MPa, more preferably 0.06 MPa to 0.08 MPa. Heat-foaming under these conditions allows the expanded particles to be well fused to each other.

[0088] If necessary, the pre-expanded styrene-based resin particles may be aged before molding into a styrene-based resin expansion molded article. The aging temperature of the pre-expanded styrene-based resin particles is preferably 20°C to 60°C. If the aging temperature is too low, an excessively long aging time may be required. If the aging temperature is too high, the blowing agent in the pre-expanded styrene-based resin particles may dissipate, resulting in a decrease in moldability.

[0089] The bulk expansion ratio of the expanded beads in the styrene-based resin expansion molded article is preferably 2 to 150 times, and more preferably 5 to 100 times. [Example]

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring and evaluating each property are as follows.

[0091] <Evaluation of charge amount and charge amount variation> 500 g of the expandable styrene resin particles (1) to (10) and (C1) to (C6) obtained in the Examples and Comparative Examples were placed in a polyethylene bag (OK bag No. 15, manufactured by Okura Kogyo Co., Ltd.) and dried for 24 hours in an open environment at 23°C and 10% humidity. The bag was then tied and shaken up and down 100 times. The polyethylene bag was then opened, and the surface charge of the expandable styrene resin particles was measured five times using a static electricity meter (FMX-003, manufactured by Simco Japan Co., Ltd.). The average value of the measurement results was recorded as the charge amount. The difference between the maximum and minimum values ​​among the five measurements was recorded as the charge amount variation. The smaller the variation in charge amount, the better, and it is preferably 1.0 kV or less, more preferably 0.7 kV or less, even more preferably 0.5 kV or less, still more preferably 0.3 kV or less, even more preferably 0.3 kV or less, particularly preferably 0.25 kV or less, and most preferably 0.2 kV or less.

[0092] <Evaluation of stickiness of resin particles> The expandable styrene resin particles (1) to (10) and (C1) to (C6) obtained in the Examples and Comparative Examples were filled to the brim in a stainless steel cylindrical container with an inner diameter of 71 mm and a height of 100 mm, and the container was covered with a large vinyl chloride plate. The container was then turned upside down with the lid still on, and the cylindrical container was raised 100 mm over one second. The maximum diameter of the expandable styrene resin particles when expanded was measured, and a maximum diameter of 200 mm or greater was evaluated as ◯, and a maximum diameter of less than 200 mm was evaluated as ×. The maximum diameter was defined as the maximum length, as viewed from above in the planar direction, between the intersection of a line passing through the center of the circle on the bottom surface of the stainless steel cylindrical container and the end of the expanded expandable styrene resin particles.

[0093] [Example 1] <Preparation of Expandable Styrene-Based Resin Particles> Into a 100-liter autoclave equipped with a stirrer, 82 g of magnesium pyrophosphate, 2.4 g of sodium dodecylbenzenesulfonate, 106 g of benzoyl peroxide, 24 g of t-butylperoxy-2-ethylhexyl monocarbonate, 40 kg of ion-exchanged water, and 40 kg of styrene monomer were fed, and the stirring blade was rotated so that the average particle diameter became 0.45 mm, to prepare a suspension. Next, while stirring the suspension, the temperature of the autoclave was raised to 90°C and maintained at 90°C for 6 hours and 50 minutes, and then the temperature inside the autoclave was raised to 125°C and maintained at 125°C for 2 hours to carry out suspension polymerization. Thereafter, the temperature inside the autoclave was cooled to 25°C, and the polymer was removed from the autoclave. The obtained polymer was washed and dehydrated several times, then dried and sieved to obtain styrene-based resin particles (A) having a weight-average molecular weight of 300,000. Next, 2 kg of ion-exchanged water, 15 g of magnesium oxide, 1.6 g of polyoxyethylene-polyoxypropylene glycol, 0.6 g of dilauryl-3,3'-thiodipropionate, and 0.8 g of ethylene bisstearic acid amide were charged into a 5-liter autoclave, and 2 kg of the styrene-based resin particles (a) obtained above was added to this aqueous medium and stirred at 300 rpm. Next, the temperature inside the autoclave was raised to 110°C, and while maintaining this temperature, 55 g of butane and 151 g of pentane were pressure-injected and impregnated for 1 hour and 30 minutes, after which the autoclave was cooled to 25°C to produce expandable styrene-based resin particles (A). Then, 100 mL of 20% diluted hydrochloric acid was poured into the autoclave, and the mixture was stirred for 25 minutes, after which the liquid portion was separated. 97 parts by weight of washing water was added to 100 parts by weight of the remaining expandable styrene resin particles (A), and the mixture was stirred for 25 minutes to wash. After that, the washing water was almost completely removed by separation and draining. This operation was repeated once, and then 97 parts by weight of washing water was added to 100 parts by weight of the remaining expandable styrene resin particles (A). While stirring, an antistatic agent (anionic surfactant, NOF Corporation, product name: Newlex R-25L, diluted aqueous solution with 25% active ingredient) was added to the expandable styrene resin particles (A) that were coexisting with the washing water so that the amount of active ingredient was 0.00010 parts by weight per 100 parts by weight of the expandable styrene resin particles (A). The mixture was stirred for a total of 25 minutes, and then dehydrated in a dehydrator. The expandable styrene resin particles (A) were then dried by pumping with sufficiently dry air. In this way, expandable styrene resin particles (1) were obtained. The results are shown in Table 1.

[0094] [Examples 2 to 10, Comparative Examples 1 and 2] The same procedure as in Example 1 was carried out, except that the amount of washing water present per 100 parts by weight of the expandable styrene-based resin particles (A) when the antistatic agent was added to the expandable styrene-based resin particles (A) and the amount of the antistatic agent added (amount of active ingredient) in the washing water per 100 parts by weight of the expandable styrene-based resin particles (A) were adjusted to the amounts shown in Table 1, to obtain expandable styrene-based resin particles (2) to (10), (C1), and (C2). The results are shown in Table 1.

[0095] Comparative Example 3 In the same manner as in Example 1, expandable styrene-based resin particles (A) were prepared. Then, 100 mL of 20% diluted hydrochloric acid was poured into the autoclave. After stirring for 25 minutes, the liquid portion was separated. 97 parts by weight of washing water was added to 100 parts by weight of the remaining expandable styrene-based resin particles (A), and the mixture was stirred for 25 minutes to wash. After this, the washing water was almost completely removed by separation and deliquoring. This operation was repeated once, and then 97 parts by weight of washing water was added to 100 parts by weight of the remaining expandable styrene-based resin particles (A), and the mixture was stirred for 25 minutes to wash. The mixture was then dehydrated using a spin dryer. An antistatic agent (anionic surfactant, NOF Corporation, trade name: Newlex R-25L, diluted aqueous solution with 25% active ingredient) was added to 100 parts by weight of the expandable styrene-based resin particles (A) in an amount of 0.00005 parts by weight of the active ingredient, and the mixture was applied to the surfaces of the expandable styrene-based resin particles (A). Thereafter, the particles were sent out in sufficiently dry air to dry the expandable styrene resin particles (A). Furthermore, analysis by coulometric titration using a trace moisture analyzer (Mitsubishi Chemical Analytech, Model CA-310) confirmed that the amount of washing water remaining in the expandable styrene resin particles (A) dehydrated by the above-mentioned dehydrator was 10 parts by weight per 100 parts by weight of the expandable styrene resin particles (A). In this way, expandable styrene-based resin particles (C3) were obtained. The results are shown in Table 1.

[0096] [Comparative Examples 4 to 6] The same procedure as in Comparative Example 3 was carried out, except that an antistatic agent was added to 100 parts by weight of the dehydrated expandable styrene-based resin particles (A) so that the amount of the active ingredient was the amount shown in Table 1, to obtain expandable styrene-based resin particles (C4) to (C6). The results are shown in Table 1.

[0097] [Table 1] [Industrial Applicability]

[0098] The low-charge expandable styrene-based resin particles obtained by the method for producing low-charge expandable styrene-based resin particles according to an embodiment of the present invention, and pre-expanded styrene-based resin particles and styrene-based resin foam molded articles obtained therefrom are suitable for use as insulation materials for homes and automobiles, thermal insulation materials for building materials, transport packaging materials such as fish boxes and food containers, cushioning materials, etc. More specifically, the expandable styrene-based resin particles, pre-expanded styrene-based resin particles, and styrene-based resin foam molded articles according to an embodiment of the present invention are suitable for use as wall insulation materials, floor insulation materials, roof insulation materials, automotive insulation materials, hot water tank insulation materials, piping insulation materials, solar system insulation materials, water heater insulation materials, containers for food and industrial products (e.g., food containers such as fish boxes, returnable containers), cushioning materials, floats, blocks, packaging materials for fish and agricultural products, etc., embankment materials (e.g., embankment molded articles and embankment blocks), tatami mat core materials, cushion core materials, concrete aggregate, etc.

Claims

1. A method for producing low-charge expandable styrene-based resin particles from expandable styrene-based resin particles, comprising: a washing step of washing the expandable styrene-based resin particles with washing water, adding an antistatic agent to the expandable styrene-based resin particles in the presence of 12 to 100,000 parts by weight of the washing water relative to 100 parts by weight of the expandable styrene-based resin particles; the amount of the antistatic agent added is 0.00010 parts by weight to 0.00250 parts by weight based on 100 parts by weight of the expandable styrene-based resin particles; A method for producing low-charge expandable styrene-based resin particles.

2. The method for producing low-charge expandable styrene-based resin particles according to claim 1 , wherein the expandable styrene-based resin particles are obtained by impregnating a styrene-based resin with a blowing agent.

3. The method for producing low-charge expandable styrene-based resin particles according to claim 1 , wherein the antistatic agent is an anionic surfactant.

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