Method for producing recycled expandable styrene-based resin particles

Abstract

To provide recycled expandable styrene-based resin particles having energy-saving performance in high yield.SOLUTION: A method for producing recycled expandable styrene-based resin particles, comprises: a step of preparing a solution by dissolving expandable styrene-based resin particles; a step of dispersing the solution into an aqueous medium to form a suspension and initiating polymerization; a step of adding a dispersant when a polymer component ratio in oil droplets of the suspension reaches a predetermined value to obtain recycled styrene-based resin particles; and a step of impregnating the recycled styrene-based resin particles with a blowing agent, wherein the blending amount of the expandable styrene-based resin particles is 15 wt.% or less based on the total amount of the styrene-based monomer and a butyl acrylate monomer, and the base resin contains a predetermined amount of styrene-based monomer units and butyl acrylate monomer units.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled expandable styrene resin particles. [Background technology]

[0002] Expandable styrene resin particles are widely used because they are relatively inexpensive, can be expanded using steam or other methods without special techniques, and offer excellent cushioning and heat insulation. Taking advantage of their insulating properties, they are particularly well-suited for use in refrigerated containers for storing and transporting seafood, vegetables, and fruits. To reduce the energy used in the expansion and molding processes of expandable styrene resin particles, attempts have been made to lower the processing temperature by copolymerizing other monomers that lower the softening point of the styrene monomer. For example, Patent Document 1 discloses that expandable styrene resin particles can be pre-expanded and molded in a mold at low temperatures by copolymerizing a butyl acrylate monomer component with a styrene monomer.

[0003] Incidentally, in recent years, recycling of styrene-based resins has been promoted. For example, as disclosed in Patent Document 2, there is a technique for producing expandable styrene-based resin particles by adding a blowing agent to styrene-based resin particles obtained by dissolving a styrene-based resin in an aqueous medium of a styrene-based monomer and performing suspension polymerization. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-199835 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-193550 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with regard to expandable styrene-based resin particles intended for energy saving during processing as described in Patent Document 1, there is no known technology for dissolving resin particles in a monomer, carrying out suspension polymerization, and then converting them back into energy-saving styrene copolymer resin particles. Also, as described in Patent Document 2, in the method of dissolving used styrene-based resin particles in a styrene monomer and carrying out suspension polymerization, it is difficult to control the particle shape of the resin particles obtained after polymerization, and the yield of particles in a particle size range suitable for use tends to be poor.

[0006] In view of the above circumstances, an object of the present invention is to obtain, with a high yield, recycled expandable styrene resin particles having energy-saving properties. [Means for solving the problem]

[0007] The present inventors have carried out extensive research into polymerization conditions with the aim of overcoming the above-mentioned problems of the prior art, and as a result have completed the present invention.

[0008] That is, one embodiment of the present invention includes the following configuration. [1] A method for producing recycled expandable styrene-based resin particles, comprising the steps of: preparing a solution in which expandable styrene-based resin particles are dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer; dispersing the solution in an aqueous medium to form a suspension and initiating polymerization; adding a dispersant when the polymer component ratio in the oil droplets of the suspension is 30% by weight or more and 50% by weight or less to obtain recycled styrene-based resin particles; and impregnating the recycled styrene-based resin particles with a blowing agent, wherein the styrene-based monomer or the mixture of a styrene-based monomer and a butyl acrylate monomer is dissolved in the expandable styrene-based resin particles. A method for producing recycled expandable styrene-based resin particles, wherein the amount of the expandable styrene-based resin particles dissolved in the monomer mixture is 15% by weight or less based on the total amount of the styrene-based monomer and the butyl acrylate monomer, and the recycled expandable styrene-based resin particles contain styrene-based monomer units and butyl acrylate monomer units as a base resin, and contain 94.5% by weight or more and 98% by weight or less of styrene-based monomer units and 2% by weight or more and 5.5% by weight or less of butyl acrylate monomer units, relative to 100% by weight of the total amount of the styrene-based monomer units and butyl acrylate monomer units contained in the base resin. [2] The method for producing recycled expandable styrene resin particles according to [1], wherein the expandable styrene resin particles to be dissolved in a styrene monomer or a mixture of a styrene monomer and a butyl acrylate monomer are composed of monomer components of 94.5% by weight or more and 98% by weight or less of a styrene monomer and 2% by weight or more and 5.5% by weight or less of a butyl acrylate monomer. [3] The method for producing recycled expandable styrene resin particles according to [1] or [2], in which no plasticizer or solvent is used during suspension polymerization. [4] The method for producing recycled expandable styrene-based resin particles according to any one of [1] to [3], wherein the blowing agent contains butane. [5] A method for producing recycled expandable styrene resin particles according to any one of [1] to [4], wherein the expandable styrene resin particles dissolved in a styrene monomer or a mixture of a styrene monomer and a butyl acrylate monomer contain 100 ppm or less of peroxides having a one-hour half-life temperature of 120°C or less. [Effects of the Invention]

[0009] According to one embodiment of the present invention, recycled expandable styrene resin particles having energy-saving properties can be obtained in high yield. DETAILED DESCRIPTION OF THE INVENTION

[0010] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0011] In the present specification, recycled expandable styrene-based resin particles are recycled styrene-based resin particles impregnated with a blowing agent. The recycled styrene-based resin particles are resin particles obtained by dissolving expandable styrene-based resin particles in a styrene-based monomer, dispersing the resulting solution in an aqueous medium, and polymerizing the solution. The expandable styrene-based resin particles dissolved in the solution may be recycled expandable styrene-based resin particles.

[0012] The present inventors have found that conventional methods for producing expandable polystyrene resin particles by recycling styrene resins have room for improvement in terms of obtaining energy-saving recycled expandable styrene resin particles with a high yield. Specifically, in the method of dissolving a styrene resin in a styrene monomer and performing suspension polymerization, it is difficult to control the average particle size of the styrene resin particles obtained after polymerization, and the particle size distribution tends to be broad, resulting in a poor yield of particles in a suitable particle size range. In addition, when attempting to produce styrene resin particles with energy-saving moldability by adding a copolymerizable component copolymerizable with the styrene monomer to the styrene monomer during suspension polymerization, there are problems such as increased blocking during foaming and a narrower range of molding conditions depending on the ratio of the styrene monomer to the copolymerizable component.

[0013] Therefore, the present inventors have conducted extensive research with the aim of providing a production method for obtaining recycled expandable styrene resin particles having energy-saving moldability with a high yield.

[0014] A method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention comprises the steps of: preparing a solution in which expandable styrene-based resin particles are dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer; dispersing the solution in an aqueous medium to form a suspension and initiating polymerization; adding a dispersant when the polymer component ratio in the oil droplets of the suspension is 30% by weight or more and 50% by weight or less to obtain recycled styrene-based resin particles; and impregnating the recycled styrene-based resin particles with a blowing agent. The amount of the expandable styrene-based resin particles dissolved in the mixture of styrene-based monomers and butyl acrylate monomers is 15% by weight or less based on the total amount of the styrene-based monomers and butyl acrylate monomers, and the recycled expandable styrene-based resin particles contain styrene-based monomer units and butyl acrylate monomer units as a base resin, and contain 94.5% by weight or more and 98% by weight or less of styrene-based monomer units and 2% by weight or more and 5.5% by weight or less of butyl acrylate monomer units based on 100% by weight of the total amount of the styrene-based monomer units and butyl acrylate monomer units contained in the base resin.

[0015] Examples of styrene-based monomers used in this production method include styrene and styrene derivatives such as α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. These styrene-based monomers may be used alone or in combination of two or more. Among these, styrene is preferably selected from the viewpoints of foamability and energy-saving moldability.

[0016] In one embodiment of the present invention, expandable styrene-based resin particles are dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer. When preparing a solution by dissolving the expandable styrene-based resin particles in a styrene-based monomer alone, the solution is charged separately from the butyl acrylate monomer at the start of suspension polymerization to obtain recycled styrene-based resin particles. When preparing a solution by dissolving the expandable styrene-based resin particles in a mixture of a styrene-based monomer and a butyl acrylate monomer, the solution is charged at the start of suspension polymerization to obtain recycled styrene-based resin particles. The expandable styrene-based resin particles are not foamed or molded. Specifically, resin particles with a density of 2 g / ml or less are used before being fed into a pre-expansion machine or molding machine. This is because foamed particles and foamed molded articles after being fed into a pre-expansion machine or molding machine are susceptible to contamination by foamed particles of different quality, and their bulk tends to make dissolution difficult.

[0017] The expandable styrene-based resin particles to be dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer are not particularly limited as long as they contain a blowing agent, but it is preferable to use resin particles that are not suitable for use (non-standard particles).For example, in the suspension polymerization method, the size (particle diameter) of the resulting resin particles is distributed, so the produced expandable styrene-based resin particles are usually sieved into a particle diameter range suitable for use to produce the product, and resin particles that are determined to be unsuitable for use by this sieving are non-standard particles.When non-standard particles are used as the expandable styrene-based resin particles to be dissolved in a styrene-based monomer, there is an advantage that the composition of the raw material to be reused is easier to control than when recovering foamed molded products on the market.

[0018] The expandable styrene-based resin particles to be dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer are preferably those that do not use external additives or coating agents on the particle surface. When expandable styrene-based resin particles using external additives or coating agents are used, the dispersant is consumed by the external additives or coating agents in the suspension polymerization process, which tends to make it difficult to control the average particle size and particle size distribution of the recycled styrene-based resin particles.

[0019] The recycled expandable styrene-based resin particles according to one embodiment of the present invention are obtained by suspension polymerization in an aqueous medium using a styrene-based monomer as the main component. The amount of expandable styrene-based resin particles used in the suspension polymerization is 15% by weight or less relative to the total amount of the styrene-based monomer and butyl acrylate monomer used in the suspension polymerization. If the amount exceeds 15% by weight, it takes a long time for the resin particles to dissolve in the styrene-based monomer, and the viscosity of the monomer droplets at the initial stage of the suspension polymerization increases, making it difficult to control the particle size of the recycled styrene-based resin particles obtained by suspension polymerization. To balance particle size stability and recyclability of non-standard particles, the amount of expandable styrene-based resin particles used is preferably 1% by weight to 10% by weight, more preferably 2% by weight to 5% by weight.

[0020] In one embodiment of the present invention, the recycled styrene-based resin particles are obtained by so-called suspension polymerization, in which a solution in which expandable styrene-based resin particles are dissolved in a styrene-based monomer is dispersed in an aqueous medium to form a suspension, and a polymerization reaction is carried out. An example of suspension polymerization is given below.

[0021] An aqueous medium containing water, a dispersant, an initiator, and optionally a nucleating agent, plasticizer, and flame retardant is stirred in an autoclave to produce a dispersion. A solution of expandable styrene-based resin particles dissolved in styrene-based monomer and butyl acrylate monomer are then added to the dispersion to produce a suspension containing a styrene-based monomer component containing butyl acrylate monomer dispersed in an aqueous medium. Alternatively, instead of adding the butyl acrylate monomer separately from the solution of expandable styrene-based resin particles dissolved in styrene-based monomer, the expandable styrene-based resin particles may be dissolved in a mixture of styrene-based monomer and butyl acrylate monomer and then added to the suspension. After reducing the oxygen content in the autoclave by evacuation or nitrogen substitution, the temperature is raised to the polymerization temperature and maintained for a predetermined time (polymerization time) to allow the polymerization reaction to proceed. The polymerization temperature and time depend on the type and amount of polymerization initiator used, but the polymerization is carried out at a polymerization temperature of 80°C to 100°C for 3 to 6 hours to produce styrene-based resin particles.

[0022] In the method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention, plasticizers and solvents can be used as needed to adjust the expandability and moldability. While plasticizers and solvents are typically introduced into the dispersion during suspension polymerization, components that affect radical polymerization, such as aliphatic hydrocarbons, are preferably introduced during the blowing agent impregnation process after suspension polymerization. Examples of plasticizers include diisobutyl adipate, dioctyl adipate, dibutyl sebacate, glycerin tristearate, glycerin tricaprylate, coconut oil, palm oil, and rapeseed oil. While the use of plasticizers can further adjust energy efficiency, they tend to narrow the range of molding conditions, so it is preferable not to use plasticizers. Examples of solvents include aliphatic hydrocarbons with C6 or more, such as hexane and heptane, alicyclic hydrocarbons with C6 or more, such as cyclohexane and cyclooctane, and toluene. While the use of solvents can help maintain expandability over time after production, they tend to require a longer cooling time during molding. Therefore, from an energy-saving perspective, it is preferable not to use solvents.

[0023] The dispersant may function to disperse monomer droplets, resin particles, and / or expandable resin particles in an aqueous suspension. Examples of dispersants include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone, and sparingly soluble inorganic substances such as calcium triphosphate and magnesium pyrophosphate. When using sparingly soluble inorganic substances, the suspension stabilization effect can be enhanced by using them in combination with an anionic surfactant such as sodium dodecylbenzenesulfonate. Using a water-soluble polymer in combination with a sparingly soluble inorganic substance is also effective.

[0024] In one embodiment of the present invention, a method for producing recycled expandable styrene-based resin particles includes dispersing a solution of expandable styrene-based resin particles in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer in an aqueous medium to form a suspension, and then initiating polymerization. The method then includes adding a dispersant to the suspension at least once during polymerization to control particle size and stabilize polymerization. This process allows for the production of recycled styrene-based resin particles. The dispersant should be added during polymerization when the polymer component ratio in the oil droplets of the suspension is between 30% and 50% by weight. Introducing the dispersant at this timing ensures stable production of the target particle size and stable dispersion of the monomer. In other words, adding or not adding a dispersant when the polymer component ratio is less than 30% and / or more than 50% can result in failure to achieve the target particle size, particle size enlargement, or dispersion anomalies. To obtain the desired particle size more stably, it is preferable to introduce the dispersant when the polymer component ratio in the oil droplets is 35% by weight or more and 45% by weight or less, more preferably 40% by weight or more and 45% by weight or less. The dispersant added at this time is preferably a sparingly soluble inorganic substance, and tribasic calcium phosphate is particularly preferable.

[0025] In one embodiment of the present invention, in the method for producing recycled expandable styrene-based resin particles, a polymerization initiator may be added to an aqueous medium to form a suspension, or the polymerization initiator may be dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer. Among these, the polymerization initiator is preferably added to an aqueous medium to form a suspension. A radical-generating polymerization initiator generally used in the production of thermoplastic polymers can be used as the polymerization initiator. Representative examples of the polymerization initiator include azo compounds such as azobisisobutyronitrile, and peroxides such as benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, lauroyl peroxide-t-butylperoxyisopropyl carbonate, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxybenzoate, and t-butylperoxy-2-ethylhexyl carbonate. These polymerization initiators may be used alone or in combination of two or more.

[0026] The amount of the polymerization initiator used is preferably 0.01 to 3 parts by weight based on 100 parts by weight of the total weight of the monomers. If the amount of the polymerization initiator used is less than 0.01 part by weight, the polymerization rate tends to be slow, whereas if it exceeds 3 parts by weight, the polymerization reaction tends to be rapid and difficult to control.

[0027] In one embodiment of the present invention, the base resin constituting the recycled expandable styrene-based resin particles contains a styrene unit and a butyl acrylate unit from the viewpoints of energy saving during foaming and molding and the quality of the resulting foamed molded article. In other words, the monomers used in producing the recycled expandable styrene-based resin particles must contain a styrene monomer and a butyl acrylate monomer.

[0028] The recycled expandable styrene-based resin particles obtained according to one embodiment of the present invention must contain a base resin primarily composed of a styrene-butyl acrylate copolymer, with a monomer composition of 94.5 to 98% by weight of styrene-based monomer and 2 to 5.5% by weight of butyl acrylate-based monomer, based on 100% by weight of the total amount of styrene-based monomer and butyl acrylate monomer. A monomer composition containing less than 2% by weight of butyl acrylate monomer units tends to result in insufficient energy conservation. A monomer composition containing more than 5.5% by weight of butyl acrylate monomer units lowers the softening point of the base resin too much, narrowing the range of molding conditions and making the foam prone to shrinkage during molding. From the standpoint of energy conservation and the range of molding conditions, the butyl acrylate monomer units in the monomer composition are preferably 4 to 5% by weight, more preferably 4.5 to 5% by weight. The base resin constituting the recycled expandable styrene-based resin particles may contain only styrene-based monomer units and butyl acrylate monomer units, or may contain other monomer components in addition to the styrene-based monomer units and butyl acrylate monomer units. From the viewpoint of energy saving during foaming and molding, the proportion of the styrene-based monomer units and butyl acrylate monomer units in 100% by weight of the base resin component is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more.

[0029] The composition ratio of the styrene monomer unit and the butyl acrylate monomer unit contained in the base resin of the recycled expandable styrene resin particles can be calculated from the monomer composition of the dissolving expandable styrene resin particles and the number of parts used, the amount of the styrene monomer used to dissolve the expandable styrene resin particles, and the amount of the butyl acrylate monomer used. When the number of parts used and the composition ratio are unknown, they can be determined from the peak intensity of the structure derived from each monomer component by 1H-NMR or 13C-NMR.

[0030] In one embodiment of the present invention, in order to balance energy saving and the quality of the resulting foamed molded article, the composition ratio of the base resin constituting the expandable styrene-based resin particles to be dissolved is preferably 94.5% by weight to 98% by weight of styrene-based monomer units and 2% by weight to 5.5% by weight of butyl acrylate monomer units. If the ratio of styrene-based monomer units exceeds 98%, energy saving tends to decrease, and if the ratio of butyl acrylate monomer units is 5% by weight or more, the range of molding conditions tends to narrow. The ratio of butyl acrylate monomer units constituting the expandable styrene-based resin particles to be dissolved is preferably 4% by weight to 5% by weight, more preferably 4.5% by weight to 5% by weight. Furthermore, the composition ratio of the expandable styrene-based resin particles to be dissolved is preferably the same as that of the resulting recycled expandable styrene-based resin particles. Furthermore, since the absolute amount of the dissolving expandable styrene-based resin particles is small relative to the recycled expandable styrene-based resin particles, they may contain plasticizer components and solvent components that affect the molding conditions. However, in the composition of the recyclable expandable styrene-based resin particles of the present invention, the presence of plasticizer components and solvent components may increase the amount of blocking that occurs during foaming or narrow the range of molding conditions, so it is most preferable that the recyclable expandable styrene-based resin particles do not contain plasticizer components or solvent components.

[0031] The amount of peroxide with a one-hour half-life temperature of 120°C or less in the expandable styrene-based resin particles dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer is preferably 100 ppm or less. 20 ppm or less is more preferable. Residual peroxide affects the polymerization rate during suspension polymerization, making it difficult to control particle size and molecular weight. The amount of peroxide in the expandable styrene-based resin particles to be dissolved can be estimated from the amount of peroxide used in preparing the resin particles to be dissolved and the thermal history, or can be determined by measuring the amount of active oxygen in the resin particles by titration.

[0032] In one embodiment of the present invention, the method for producing recycled expandable styrene-based resin particles preferably contains a thickener in the aqueous medium used during suspension polymerization, and preferably uses a thickener at a concentration of 4 ppm to 9 ppm relative to the water. Using a thickener in the aqueous medium can suppress the generation of fine particles during suspension polymerization, resulting in a sharper particle size distribution and improved product yield. Examples of thickeners that can be used include water-soluble polysaccharides such as rhamsan gum, curdlan, xanthan gum, welan gum, and xanthan gum, with xanthan gum being particularly effective and preferred. If the thickener concentration in water is less than 4 ppm, it is difficult to achieve sufficient fine particle reduction effects, while if it exceeds 9 ppm, it promotes the coalescence of oil droplets during polymerization, resulting in increased particle size and an unstable dispersion. The thickener concentration in water is more preferably 6 ppm to 8 ppm.

[0033] In a method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention, the aqueous medium used in suspension polymerization preferably contains a polymeric nonionic surfactant, and it is preferable to use a molecular nonionic surfactant at a concentration of 15 ppm to 30 ppm relative to the water. The use of a polymeric nonionic surfactant sharpens the particle size distribution and improves product yield. As the polymeric nonionic surfactant, it is preferable to use a polyoxyethylene polyoxypropylene glycol-based surfactant. If the concentration of the polymeric nonionic surfactant relative to the water is less than 15 ppm, it is difficult to achieve the effect of sharpening the particle size distribution, while if the concentration of the polymeric nonionic surfactant exceeds 30 ppm, polymerization stability tends to decrease. The concentration of the polymeric nonionic surfactant relative to the water is more preferably 15 ppm to 25 ppm.

[0034] In the method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention, any blowing agent that can be used in the production of expandable styrene-based resin particles can be used appropriately. Examples of blowing agents include aliphatic hydrocarbons such as propane, butane, and pentane; alicyclic hydrocarbons such as cyclobutane and cyclopentane; and halogenated hydrocarbons such as methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane. These blowing agents may be used alone or in combination of two or more. Among these blowing agents, butane is preferred due to its excellent foaming power, and it is even more preferred to use a blowing agent in which the ratio of normal butane to isobutane is 50 / 50 to 80 / 20.

[0035] The content of the blowing agent in the recycled expandable styrene-based resin particles of the present invention is 3.0% by weight or more and less than 10.0% by weight, preferably 5.0% by weight or more and less than 9.0% by weight, and more preferably 6.0% by weight or more and less than 8.0% by weight, relative to 100% by weight of the recycled expandable styrene-based resin particles.

[0036] If the foaming agent content is less than 3% by weight, the pre-expansion time tends to be long and it is difficult to obtain a sufficient expansion ratio.If the foaming agent content is 8% by weight or more, the cooling time during molding tends to be long and energy saving tends to be poor.

[0037] The recycled expandable styrene resin particles produced by the manufacturing method of one embodiment of the present invention preferably contain less than 0.3% by weight of monomer components. The contained monomer components tend to volatilize from the foamed molded article obtained by expanding the recycled expandable styrene resin particles, and a monomer content of 0.3% by weight or more is particularly undesirable for use as a direct food packaging material. Furthermore, it is preferable that the content be less than 0.03% by weight when used for building interiors and less than 0.01% by weight when used as automotive components.

[0038] The amount of the monomer component contained in the recycled expandable styrenic resin particles produced by the production method of one embodiment of the present invention can be controlled by a combination of the amount of initiator used and the polymerization temperature when polymerizing the recycled expandable styrenic resin particles. For example, the amount of the monomer component can be reduced by increasing the amount of initiator used or the polymerization temperature.

[0039] The molecular weight of the recycled expandable styrene-based resin particles produced by the production method according to one embodiment of the present invention is preferably a weight-average molecular weight Mw of 220,000 or more but less than 320,000, and more preferably 250,000 or more but less than 300,000. If the weight-average molecular weight Mw of the recycled expandable styrene-based resin particles is less than 220,000, not only will the strength of the foamed molded article decrease, but the surface of the molded article will tend to melt, impairing the appearance. If the weight-average molecular weight Mw is 320,000 or more, the foaming ability will decrease and moldability will tend to deteriorate.

[0040] The weight-average molecular weight Mw can be controlled by the combination of the amount of initiator used and the polymerization temperature when polymerizing the recycled styrene-based resin particles. For example, the weight-average molecular weight Mw can be reduced by increasing the amount of initiator used and / or increasing the polymerization temperature.

[0041] Here, the weight average molecular weight Mw of the recycled expandable styrene resin particles can be measured using a gel permeation chromatograph (hereinafter sometimes abbreviated as "GPC").

[0042] The average particle diameter of the recycled expandable styrene-based resin particles produced by the production method of one embodiment of the present invention is preferably 0.7 mm or more and 1.2 mm or less, and more preferably 0.85 mm or more and 1.0 mm or less. If the average particle diameter of the recycled expandable styrene-based resin particles is less than 0.7 mm, a long heating time is required to achieve the desired expansion ratio during pre-expansion, and energy-saving moldability tends to deteriorate. Furthermore, if the average particle diameter exceeds 1.0 mm, filling properties during molding into box shapes and the like tend to deteriorate, and a long cooling time is likely to be required during molding, resulting in a longer molding cycle and reduced molding productivity. Furthermore, the particle size distribution index (UT) of the recycled expandable styrene-based resin particles is preferably 3.0 or less, more preferably 2.8 or less. A high particle size distribution index (UT) results in a high proportion of large and small particles, which tends to reduce product yield.

[0043] In one embodiment of the present invention, the content of the blowing agent in the pre-expanded particles in the method for producing recycled expandable styrene-based resin particles is preferably 2.5% by weight or more and 4.5% by weight or less, and more preferably 3% by weight or more and 4.3% by weight or less, relative to 100% by weight of the pre-expanded particles.

[0044] In order to control the bubble diameter when the recycled expandable styrene-based resin particles are pre-expanded, a nucleating agent can be introduced into the aqueous medium. Examples of nucleating agents include methyl methacrylate copolymers, polyethylene wax, talc, fatty acid bisamides, and ethylene-vinyl acetate copolymer resins. Specific examples of fatty acid bisamides include methylene bisstearylamide, ethylene bisstearylamide, hexamethylene bispalmitic acid amide, and ethylene bisoleic acid amide. The bubble diameter can also be controlled by the amount of nucleating agent. For example, increasing the amount of nucleating agent reduces the bubble diameter, while decreasing the amount of nucleating agent increases the bubble diameter.

[0045] The cell diameter of the pre-expanded particles obtained by pre-expanding the recycled expandable styrene-based resin particles obtained by the method for producing recycled expandable styrene-based resin particles in one embodiment of the present invention is preferably such that the average chord length of the cells on the cross section of the expanded molded article obtained from the recycled expandable styrene-based resin particles is 70 μm or more and less than 120 μm, more preferably 80 μm or more and less than 110 μm.

[0046] If the average chord length is less than 70 μm, the thickness of the cells constituting the foam will be thin, and internal fusion and surface roughness will tend to be reduced.If the average chord length is 120 μm or more, the fracture displacement of the fracture strength (for example, bending strength in JIS A9511 or bottom split strength of box-shaped molded body) will be short, and the molded body will tend to be brittle.

[0047] In the method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention, additives that can be added include external additives, adhesives, flame retardants, flame retardant assistants, etc., within the scope that does not impair the effects of the present invention.

[0048] As the flame retardant and the flame retardant aid, known and commonly used ones can be used. Specific examples of the flame retardant include halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane, brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-diglycerides. Examples of suitable flame retardants include brominated phenol derivatives such as brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers, such as brominated butadiene-vinyl aromatic hydrocarbon copolymers (e.g., EMERALD3000 manufactured by LANXESS or those disclosed in JP-A-2009-516019). These flame retardants may be used alone or in combination of two or more.

[0049] Specific examples of the flame retardant aid that may be used include initiators such as cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane.

[0050] The flame retardant and the flame retardant aid may be added together with the styrene monomer and the dispersant before the start of suspension polymerization, or may be added after suspension polymerization and before the addition of the blowing agent.

[0051] As the external additive used in the present invention, known and commonly used ones can be used.Specific examples of external additives include fatty acid triglycerides such as lauric triglyceride, stearic triglyceride, linoleic triglyceride, fatty acid diglycerides such as lauric diglyceride, stearic diglyceride, linoleic diglyceride, fatty acid monoglycerides such as lauric monoglyceride, stearic monoglyceride, linoleic monoglyceride, fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, calcium laurate, nonionic surfactants such as polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene laurate, polyoxyethylene palmitate, polyoxyethylene stearate, polyoxyethylene oleate, silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, castor wax, vegetable oils such as castor oil and olive oil. These external additives may be used alone or in combination of two or more. These external additives may be added to the aqueous system during the foaming agent impregnation, or may be added and coated after dehydration or drying. The coating method is not particularly limited, but a preferred coating method is to apply the additives after drying and mix and stir to coat.

[0052] The amount of external additives used is preferably 0.10 to 0.20 parts by weight of zinc stearate as an anti-blocking agent relative to 100 parts by weight of the base resin component, and 0.03 to 0.10 parts by weight of castor wax as a fusion accelerator. If the amount of anti-blocking agent is less than 0.10 parts by weight, blocking, in which the expanded particles adhere to each other, is likely to occur during pre-expansion, while if it exceeds 0.20 parts by weight, fusion properties during molding are likely to deteriorate. If the amount of fusion accelerator is less than 0.03 parts by weight, fusion properties are likely to deteriorate when the heating conditions during molding are low, and if it exceeds 0.10 parts by weight, blocking is likely to increase.

[0053] The pre-expanded particles according to one embodiment of the present invention are obtained by expanding the recycled expandable styrene-based resin particles according to the present invention. That is, the pre-expanded particles according to one embodiment of the present invention can be obtained by expanding (pre-expanding) the recycled expandable styrene-based resin particles according to the present invention by a known method.

[0054] As a pre-expansion method, for example, a conventional method can be used, such as using a cylindrical pre-expansion device to heat and expand with steam or the like.

[0055] The foaming temperature (temperature inside the can) during pre-foaming is adjusted appropriately by the blown steam pressure and the amount of air, but is usually preferably about 97 to 105°C.

[0056] The foamed molded article according to one embodiment of the present invention is produced by molding the pre-expanded particles of the present invention in a mold. That is, the foamed molded article according to one embodiment of the present invention can be obtained by expanding the recycled expandable styrene-based resin particles of the present invention to produce pre-expanded particles, and then performing foam molding using the pre-expanded particles by a known method.

[0057] As a method for foam-molding the pre-expanded particles, a conventional method can be used, such as the so-called in-mold foam molding method, in which the pre-expanded particles are filled into a mold and heated by blowing steam or the like to obtain a foamed molded article.

[0058] The steam pressure during molding in the mold is usually about 0.03 to 0.09 MPa, and the temperature inside the mold is preferably 105°C to 130°C. The foamed molded article can be suitably used in fields where styrene resin foams are used. For example, it can be suitably used as a cold storage container such as a fish box or vegetable box, or as a cushioning material. [Example]

[0059] Examples and comparative examples are given below, but the present invention is not limited to these. The polymer ratio, average particle size, and energy-saving moldability when a dispersant was added in the examples and comparative examples were measured by the following methods. Note that "parts" and "%" are by weight unless otherwise specified.

[0060] <Polymer ratio when adding dispersant during the production of recycled expandable styrene resin particles> During suspension polymerization in the process of producing recycled styrene-based resin particles, the contents of the autoclave were sampled when additional calcium phosphate was added. The contents were filtered through filter paper, and the oil layer was scooped up from the residue remaining on the filter paper with a spoon and weighed out 2 g. The scooped oil layer was placed in a dryer at 150°C for 30 minutes to volatilize the monomer content, and the polymer ratio was calculated from the weight of the remaining solid using the formula below.

[0061] Polymer ratio (%) = Weight of solids after drying (g) / Weight of oil layer weighed before drying (g) × 100 <Average particle size and particle size distribution index (UT) of recycled expandable styrene resin particles> Using 100 g of the expandable styrene-based resin particles obtained by the production method of the present invention, a weight-based cumulative passing distribution curve was obtained using an image analysis type particle distribution measuring device (Militrack JPA, manufactured by Nikkiso Co., Ltd.).

[0062] From the obtained cumulative passing distribution curve, the particle diameter at the point corresponding to a cumulative weight of 50% by weight on the cumulative passing distribution curve based on the weight of the ellipse minor axis of the resin particles was determined as the average particle diameter (mm).

[0063] In addition, the particle size at the point where the cumulative weight corresponds to 10% by weight (U10), 40% by weight (U40), 60% by weight (U60), and 90% by weight (U90) were determined, and the particle size molecule number (UT) was calculated using the following formula.

[0064] Particle size distribution index UT=U90 / U40+U60 / U10 <Energy-saving molding performance evaluation and molding cycle evaluation> The recycled expandable styrene resin particles obtained in the <Production of Recycled Expandable Styrenic Resin Particles> described below were sieved to 0.6 mm to 1.4 mm. 100 parts by weight of the obtained recycled expandable styrene resin particles of 0.6 mm to 1.4 mm were mixed with 0.15 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corporation) and 0.05 parts by weight of caster wax (Castarwax A Powder, manufactured by NOF Corporation) and stirred together with the resin particles to form a coating. The mixture was placed in a pre-expander [manufactured by Daikai Kogyo, CH-100] and blown in at a steam pressure of 0.1 kgf / cm. 2 The foaming was continued until the foaming ratio reached 65 times.

[0065] The resulting pre-expanded particles were filled into a flat mold (400 mm long x 300 mm wide x 25 mm thick) using a molding machine [Daika Kogyo KR-57]. The mold was then molded under an initial pressure of 0.5 MPa and a steam pressure of 0.05-0.07 MPa to obtain a molded foam plate. The heating and cooling timer conditions were mold heating for 2 seconds, one-sided heating for 3 seconds, reverse one-sided heating for 4 seconds, double-sided heating for 5 seconds, heat retention for 3 seconds, water cooling for 3 seconds, and air cooling for 5 seconds. The mold was then allowed to cool in a vacuum until the surface pressure of the molded product reached 0.03 MPa.

[0066] The energy-saving moldability of the obtained polystyrene foam molded articles was evaluated by the following method. ◎: A compact with almost no interparticle gaps on the surface can be obtained at an injection steam pressure of 0.05 MPa. ○: A compact with almost no interparticle gaps on the surface was obtained at an injection steam pressure of 0.06 MPa. △: A compact with almost no interparticle gaps on the surface was obtained at a blown steam pressure of 0.07 MPa. ×: A molded product with few interparticle gaps on the surface cannot be obtained even with a blown steam pressure of 0.07 MPa. Alternatively, a molded product with few interparticle gaps on the surface cannot be obtained because the expanded particles constituting the molded product shrink and deform at a blown steam pressure of 0.05 MPa.

[0067] The molding cycle of the obtained polystyrene foam molded article was evaluated by the time required for cooling in vacuum when molded under the condition of a blown steam pressure of 0.06 MPa. 〇: Less than 120 seconds △: Less than 180 seconds ×: 180 seconds or more <Preparation of Expandable Styrenic Resin Particles Dissolving in Styrene Monomers> (Method for producing expandable styrene resin particles A) A 6L autoclave equipped with a stirrer was charged with 100 parts by weight of purified water, 0.15 parts by weight of tricalcium phosphate, 0.007 parts by weight of sodium dodecylbenzenesulfonate, 0.47 parts by weight of salt, 0.25 parts by weight of benzoyl peroxide and 0.18 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as initiators, and 0.04 parts by weight of polyethylene wax as a nucleating agent. Next, while stirring at 250 rpm, 95 parts by weight of styrene monomer and 5 parts by weight of butyl acrylate were charged, and the autoclave was purged with nitrogen (a process of pressurizing with nitrogen at 0.1 MPa and purging was repeated three times). The temperature was then raised to 98°C and maintained at 98°C for 1.5 hours. Then, 0.05 parts by weight of calcium phosphate was added, and the mixture was maintained for an additional 2.25 hours to obtain styrene-based resin particles.

[0068] Next, 6.8 parts by weight of butane as a blowing agent was pressurized into the autoclave, and the temperature was raised again to 120°C. After maintaining the temperature at 120°C for 2 hours, the autoclave was cooled to room temperature, and the polymerized slurry was removed from the autoclave. The removed polymerized slurry was washed, dehydrated, and dried to obtain expandable styrene-based resin particles. The resulting expandable styrene-based resin particles were classified using a 0.6 mm sieve to obtain expandable styrene-based resin particles A of 0.6 mm or less. The amount of peroxide in expandable styrene-based resin particles A was calculated using the Arrhenius equation based on the polymerization and blowing agent impregnation temperature and time, and the 1-minute half-life temperature, 1-hour half-life temperature, and 10-hour half-life temperature and activation energy of the peroxide, and was found to be less than 10 ppm.

[0069] (Method for producing expandable styrene resin particles B) A 6L autoclave equipped with a stirrer was charged with 100 parts by weight of purified water, 0.15 parts by weight of tricalcium phosphate, 0.007 parts by weight of sodium dodecylbenzenesulfonate, 0.47 parts by weight of table salt, 0.20 parts by weight of benzoyl peroxide and 0.18 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as initiators, 0.04 parts by weight of polyethylene wax as a nucleating agent, and 0.4 parts by weight of coconut oil as a plasticizer. Next, while stirring at 250 rpm, 100 parts by weight of styrene monomer was added, and the autoclave was then purged with nitrogen (a process of pressurizing with 0.1 MPa of nitrogen and purging was repeated three times). The mixture was then heated to 98°C and held at 98°C for 1.5 hours. Then, 0.05 parts by weight of calcium phosphate was added and held for an additional 2.25 hours to obtain styrene-based resin particles.

[0070] Next, 2.1 parts by weight of cyclohexane as a solvent and 6.8 parts by weight of butane as a blowing agent were pressure-charged into the autoclave, and the temperature was again raised to 120°C. After maintaining the temperature at 120°C for 2 hours, it was cooled to room temperature, and the polymerized slurry was removed from the autoclave. The removed polymerized slurry was washed, dehydrated, and dried to obtain expandable styrene-based resin particles. The obtained expandable styrene-based resin particles were classified using a 0.6 mm sieve to obtain expandable styrene-based resin particles B of 0.6 mm or less. The amount of peroxide in expandable styrene-based resin particles B was calculated from the temperature and time of polymerization and blowing agent impregnation and the half-life temperature of the peroxide, and was found to be less than 10 ppm.

[0071] (Method for producing expandable styrene resin particles C) In the method for producing expandable styrene-based resin particles A, instead of classifying them into particles of 0.6 mm or less by sieving, expandable styrene-based resin particles classified into particles of 0.6 mm or more and 1.2 mm or less were collected, and 0.15 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corporation), 0.05 parts by weight of castor wax (Castarwax A Powder, manufactured by NOF Corporation), and 0.10 parts by weight of fatty acid triglyceride (Rikemal VT, manufactured by Riken Vitamin Co., Ltd.) were applied to 100 parts by weight of the collected expandable styrene-based resin particles to obtain expandable styrene-based resin particles C.

[0072] (Method for producing foamed molded product D) The expandable styrene resin particles C were placed in a pre-expansion machine [manufactured by Daikai Kogyo, CH-100] and blown in at a steam pressure of 0.1 kgf / cm. 2 The mixture was foamed until the foaming ratio reached 60 times.

[0073] The resulting pre-expanded particles were filled into a flat mold (400 mm long x 300 mm wide x 150 mm thick) using a molding machine (Daika Kogyo, KR-57) at an initial pressure of 0.5 MPa and a steam injection pressure of 0.06 MPa to obtain a foamed molded plate. The heating and cooling timer conditions were: mold heating 2 seconds, one-sided heating 10 seconds, reverse one-sided heating 8 seconds, double-sided heating 8 seconds, heat retention 5 seconds, water cooling 10 seconds, air cooling 10 seconds, and vacuum cooling 600 seconds. The resulting foamed molded plate was sliced ​​into approximately 5 cm squares using a hot-wire slicer to facilitate dissolution into the styrene-based monomer.

[0074] <Production of recycled expandable styrene resin particles> Example 1 Five parts by weight of the expandable styrene resin particles A were dissolved in 90.5 parts by weight of styrene monomer to prepare a monomer solution in which the expandable styrene resin particles were dissolved.

[0075] A 6-liter autoclave equipped with a stirrer was charged with 100 parts by weight of purified water, 0.15 parts by weight of tricalcium phosphate, 0.007 parts by weight of sodium dodecylbenzenesulfonate, 0.47 parts by weight of salt, 0.25 parts by weight of benzoyl peroxide and 0.18 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as initiators, and 0.04 parts by weight of polyethylene wax as a nucleating agent. Next, while stirring at 250 rpm, 95.5 parts by weight of a solution containing the expandable styrene resin particles (listed as "Parts of Solution" in the table) and 4.5 parts by weight of butyl acrylate monomer were added, and the autoclave was then purged with nitrogen (the process of pressurizing with nitrogen to 0.1 MPa and purging was repeated three times). The temperature was then raised to 98°C, and the mixture was maintained at 98°C for 1.5 hours, after which 0.05 parts by weight of calcium phosphate was added (sometimes referred to as "when the dispersant is added" in this example), and the mixture was maintained for a further 2.25 hours to obtain recycled styrene-based resin particles. Sampling was performed when the dispersant was added, and the polymer ratio at the time of adding the dispersant was measured.

[0076] Next, 7.0 parts by weight of butane as a blowing agent was injected into the autoclave, and the temperature was again raised to 120°C. After that, the temperature was maintained at 120°C for 2 hours, and then cooled to room temperature, and the polymerized slurry was removed from the autoclave. The removed polymerized slurry was washed, dehydrated, and dried to obtain recycled expandable styrene-based resin particles.

[0077] The obtained recycled expandable styrene resin particles were evaluated for average particle size, particle size distribution index (UT), energy-saving moldability, and molding cycle. The evaluation results are shown in Table 1. The resin composition of the base resin that makes up the recycled expandable styrene resin particles can be calculated from the monomer composition of the dissolving expandable styrene resin particles and the number of parts used, the amount of styrene monomer used to dissolve the expandable styrene resin particles, and the amount of butyl acrylate monomer used.

[0078] (Examples 2 to 9, Comparative Examples 1 to 6) In <Production of recycled expandable styrene-based resin particles>, the type and number of dissolving expandable styrene-based resin particles, the number of parts of monomer used in suspension polymerization, and the timing of adding additional dispersant were changed as shown in Table 1, and the same operations as in Example 1 were carried out to obtain recycled expandable styrene-based resin particles, pre-expanded particles, and foamed molded articles. The evaluation results are shown in Table 1.

[0079] [Table 1]

Claims

1. In a method for producing recycled expandable styrene resin particles, a step of preparing a solution in which expandable styrene-based resin particles are dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer; a step of dispersing the solution in an aqueous medium to form a suspension and initiating polymerization; a step of adding a dispersant when the polymer component ratio in the oil droplets of the suspension is 30% by weight or more and 50% by weight or less to obtain recycled styrene-based resin particles; impregnating the recycled styrene-based resin particles with a blowing agent; Equipped with the amount of the expandable styrene-based resin particles dissolved in the styrene-based monomer or the mixture of the styrene-based monomer and the butyl acrylate monomer is 15% by weight or less based on the total amount of the styrene-based monomer and the butyl acrylate monomer; The recycled expandable styrene-based resin particles contain styrene-based monomer units and butyl acrylate monomer units as a base resin, and contain 94.5% by weight or more and 98% by weight or less of styrene-based monomer units and 2% by weight or more and 5.5% by weight or less of butyl acrylate monomer units relative to 100% by weight of the total amount of the styrene-based monomer units and butyl acrylate monomer units contained in the base resin. A method for producing recycled expandable styrene resin particles.

2. The expandable styrene-based resin particles to be dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer are composed of a monomer component of 94.5% by weight or more and 98% by weight or less of a styrene-based monomer and 2% by weight or more and 5.5% by weight or less of a butyl acrylate monomer. A method for producing the recycled expandable styrene resin particles according to claim 1.

3. 3. The method for producing recycled expandable styrene resin particles according to claim 1, wherein no plasticizer or solvent is used during suspension polymerization.

4. 3. The method for producing recycled expandable styrene-based resin particles according to claim 1, wherein the foaming agent contains butane.

5. the expandable styrene-based resin particles dissolved in a styrene-based monomer or a mixture of a styrene-based monomer and a butyl acrylate monomer contain 100 ppm or less of peroxides having a one-hour half-life temperature of 120°C or less; The method for producing the recycled expandable styrene resin particles according to claim 1 or 2.

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