Method for producing recycled expandable styrene-based resin particles

Abstract

To perform suspension polymerization using off-grade particles of expandable styrene-based resin particles, thereby providing expandable styrene-based resin particles 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 in a styrene-based monomer; a step of dispersing the solution into an aqueous medium containing a bromine-based flame retardant and a flame retardant aid to form a suspension and initiating polymerization; a step of adding a dispersant when a polymer component ratio in oil droplets of the suspension becomes 30 wt.% or more and 50 wt.% or less 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 to be dissolved in the styrene-based monomer is 15 wt.% or less based on the total of the styrene-based monomer and the expandable styrene-based resin particles, and a predetermined amount of the bromine-based flame retardant and the flame retardant aid is charged into the aqueous medium.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 foamed using steam or the like without using any special methods, and provide high cushioning and heat insulation effects. In recent years, the recycling of styrene resins has been progressing, and as shown in Patent Documents 1 and 2, for example, there is a technology for producing expandable styrene resin particles by incorporating a blowing agent into styrene resin particles obtained by dissolving a styrene resin in a styrene monomer in an aqueous medium and carrying out suspension polymerization, or by dissolving a styrene resin in an aqueous medium of a styrene monomer and carrying out suspension polymerization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-89728 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-193550 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when attempting to obtain flame-retardant expandable styrene-based resin particles, the above-mentioned conventional techniques have room for improvement in terms of productivity.

[0005] In view of the above circumstances, an object of the present invention is to provide a method for producing recycled expandable styrene resin particles with good productivity. [Means for solving the problem]

[0006] 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.

[0007] That is, one embodiment of the present invention includes the following configuration. [1] A method for producing recycled expandable styrenic resin particles, comprising: a step of preparing a solution in which expandable styrenic resin particles are dissolved in a styrenic monomer; a step of dispersing the solution in an aqueous medium prepared by adding a brominated flame retardant and a flame retardant aid to water 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 between 30% and 50% by weight to obtain recycled styrenic resin particles; and a step of impregnating the recycled styrenic resin particles with a blowing agent, wherein the blending amount of the expandable styrenic resin particles dissolved in the styrenic monomer is 15% by weight or less based on the total amount of the expandable styrenic resin particles and the styrenic monomer, the amount of the brominated flame retardant added to the aqueous medium is 0.7 parts by weight or more per 100 parts by weight of the recycled expandable styrenic resin particles, and the amount of the flame retardant aid added to the aqueous medium is 0.4 parts by weight or more per 100 parts by weight of the recycled expandable styrenic resin particles. [2] The method for producing recycled expandable styrene resin particles according to [1], wherein the expandable styrene resin particles to be dissolved in the styrene monomer contain 0.7 parts by weight or more of a bromine-based flame retardant per 100 parts by weight of the base resin of the expandable styrene resin particles. [3] The method for producing recycled expandable styrene-based resin particles according to [1] or [2], wherein the aqueous medium contains a thickener, and the concentration of the thickener in water is 4 ppm or more and 9 ppm or less. [4] The method for producing recycled expandable styrene-based resin particles according to any one of [1] to [3], wherein the aqueous medium contains a polymeric nonionic surfactant, and the concentration of the polymeric nonionic surfactant in water is 15 ppm or more and 30 ppm or less. [5] A method for producing recycled expandable styrene resin particles according to any one of [1] to [4], wherein the content of peroxides having a one-hour half-life temperature of 120°C or less in the expandable styrene resin particles dissolved in a styrene monomer is 100 ppm or less. [Effects of the Invention]

[0008] According to one embodiment of the present invention, the yield of recycled expandable styrene resin particles having flame retardancy is improved, and therefore productivity can be improved. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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)."

[0010] In this 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.

[0011] The present inventors have found that conventional methods for producing expandable polystyrene-based resin particles by recycling styrene-based resins have room for improvement in terms of imparting flame retardancy to recycled expandable styrene-based resin particles. Specifically, in methods in which styrene-based resins are dissolved in styrene-based monomers and then subjected to suspension polymerization, it is difficult to control the average particle size of the styrene-based 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 flame-retardant styrene-based resin particles are produced by adding a flame retardant during suspension polymerization, it becomes more difficult to control the average particle size. Therefore, when flame-retardant styrene-based resin particles (recycled expandable styrene-based resin particles) are produced by adding a flame retardant during suspension polymerization of a styrene-based monomer in which a styrene-based resin has been dissolved, polymerization abnormalities or a broad particle size distribution occur, resulting in a significant decrease in productivity.

[0012] Therefore, the present inventors have conducted extensive research with the aim of providing a method for producing flame-retardant recycled expandable styrene-based resin particles, which can provide flame-retardant recycled expandable styrene-based resin particles with a narrow particle size distribution.

[0013] As a result, the present inventors discovered that recycled expandable styrene resin particles having a specific particle size can be obtained in good yield by adjusting the amount of expandable styrene resin particles dissolved in the styrene monomer, the amount of brominated flame retardant and flame retardant aid charged in the aqueous medium, and the timing of adding the dispersant during suspension polymerization, and thus completed the present invention.

[0014] A method for producing recycled expandable styrenic resin particles according to one embodiment of the present invention comprises the steps of: preparing a solution in which expandable styrenic resin particles are dissolved in a styrenic monomer; dispersing the solution in an aqueous medium prepared by adding a brominated flame retardant and a flame retardant aid to water to form a suspension and initiating polymerization; adding a dispersant when the polymer component ratio in the oil droplets of the suspension is between 30% and 50% by weight to obtain recycled styrenic resin particles; and impregnating the recycled styrenic resin particles with a blowing agent, wherein the blending amount of the expandable styrenic resin particles dissolved in the styrenic monomer is 15% by weight or less relative to the total amount of the styrenic monomer, the brominated flame retardant added to the aqueous medium is 0.7 parts by weight or more per 100 parts by weight of the recycled expandable styrenic resin particles, and the flame retardant aid added to the aqueous medium is 0.4 parts by weight or more per 100 parts by weight of the recycled expandable styrenic resin particles.

[0015] In one embodiment of the present invention, expandable styrene-based resin particles are dissolved in a styrene-based monomer. The expandable styrene-based resin particles are not expanded 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. Expanded particles and molded foams after being fed into a pre-expansion machine or molding machine are susceptible to contamination with expanded particles of different quality, and dissolution becomes difficult due to their large bulk. The expandable styrene-based resin particles to be dissolved in a styrene-based monomer are not particularly limited as long as they contain a blowing agent. However, it is preferable to use resin particles that are not suitable for use (non-standard particles). For example, in suspension polymerization, the resulting resin particles have a size distribution, so the produced expandable styrene-based resin particles are typically sieved into a particle size range suitable for use before being used as a final product. Resin particles that are determined to be unsuitable for use through this sieving process are called non-standard particles. When non-standard particles are used as expandable styrene-based resin particles that dissolve in a styrene-based monomer, there is an advantage that the composition of the raw material to be reused is easier to control compared to recovering foamed molded articles on the market. In this case, it is preferable that the expandable styrene-based resin particles to be dissolved do not contain external additives or coating agents. When expandable styrene-based resin particles that contain 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.

[0016] 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 soluble in the styrene-based monomer is 15% by weight or less, based on the total amount of the styrene-based monomer used in the suspension polymerization. If the amount of soluble expandable styrene-based resin particles exceeds 15% by weight, it takes a long time for the resin particles to dissolve in the monomer, and the viscosity of the monomer droplets at the initial stage of suspension polymerization becomes high, making it difficult to control the particle size of the expandable styrene-based resin particles. To balance particle size stability and recyclability of non-standard particles, the amount of expandable styrene-based resin particles soluble in the styrene-based monomer is preferably 1% by weight or more and 10% by weight or less, more preferably 2% by weight or more and 5% by weight or less.

[0017] The styrene-based monomer used in this production method includes styrene and styrene derivatives such as α-methylstyrene, paramethylstyrene, t-butylstyrene, chlorostyrene, etc. These styrene-based monomers may be used alone or in combination of two or more.

[0018] In one embodiment of the present invention, a solution of expandable styrene-based resin particles dissolved in a styrene-based monomer is dispersed in an aqueous medium containing water and a brominated flame retardant and flame retardant aid, forming a suspension, thereby carrying out the polymerization reaction. An example of suspension polymerization is given below. An aqueous medium containing water, a dispersant, a brominated flame retardant and flame retardant aid, a polymerization initiator, and a plasticizer is stirred in an autoclave to produce a dispersion. A solution of expandable styrene-based resin particles dissolved in a styrene-based monomer is then introduced into the dispersion to produce a suspension in which the styrene-based monomer component is dispersed in the aqueous medium. 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 polymerization 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.

[0019] In one embodiment of the present invention, the amount of brominated flame retardant added to the aqueous medium is 0.7 parts by weight or more per 100 parts by weight of recycled expandable styrene-based resin particles. If the amount of brominated flame retardant is less than 0.7 parts by weight, sufficient flame retardancy tends to be insufficient. Although a large amount of flame retardant does not affect flame retardancy, if the amount is too large, the range of molding conditions becomes narrower and the resulting molded body becomes prone to yellowing. The amount of brominated flame retardant is preferably 0.75 to 1.5 parts by weight, more preferably 0.8 to 1.2 parts by weight.

[0020] Specific examples of brominated flame retardants 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-dibromopropyl ether. Examples of suitable flame retardants include brominated phenol derivatives such as glycidyl ethers, 2,2-bis[4'(2",3"-dibromoalkoxy)-3',5'-dibromophenyl]propane, 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. From an environmental perspective, polymeric brominated flame retardants are preferred, with brominated butadiene-vinyl aromatic hydrocarbon copolymers being particularly preferred.

[0021] In one embodiment of the present invention, the amount of the flame retardant synergist added to the aqueous medium is 0.4 parts by weight or more per 100 parts by weight of the recycled expandable styrene resin particles. The flame retardant synergist has the effect of supporting the effect of the brominated flame retardant during combustion, and the use of the flame retardant synergist can reduce the amount of brominated flame retardant used.

[0022] Specific examples of flame retardant synergists include peroxides with a one-hour half-life temperature of 120°C or higher, such as cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane. If the amount of flame retardant synergist is less than 0.4 parts by weight, sufficient flame retardancy tends to be insufficient. Although flame retardancy can sometimes be achieved by using a large amount of flame retardant even with a small amount of flame retardant synergist, this is undesirable as it may result in a deterioration in molded product quality. While a large amount of flame retardant synergist does not affect flame retardancy, too much may act as a plasticizer for the recycled expandable styrene resin particles, potentially affecting expandability and moldability. The preferred amount of flame retardant synergist is 0.45 to 0.9 parts by weight, more preferably 0.5 to 0.7 parts by weight, per 100 parts by weight of recycled expandable styrene resin particles.

[0023] The expandable styrene-based resin particles dissolved in the styrene-based monomer in the step of preparing the solution may be either expandable styrene-based resin particles containing a flame retardant or expandable styrene-based resin particles not containing a flame retardant, but since the flame retardancy of the recycled expandable styrene-based resin particles is easily obtained, it is preferable to contain a flame retardant. Furthermore, since expandable styrene-based resin particles containing a flame retardant tend to be easily thermally deteriorated, the method of dissolving in the styrene-based monomer as in the present production method is preferable from the viewpoint of recyclability, compared to a recycling method that involves thermal history, such as melt-kneading in an extruder.

[0024] The expandable styrene-based resin particles dissolved in the styrene-based monomer in the solution preparation step preferably contain 0.7 parts by weight or more of a brominated flame retardant per 100 parts by weight of the base resin component of the expandable styrene-based resin particles to be dissolved. If the brominated flame retardant is less than 0.7 parts by weight, the flame retardancy may be easily deteriorated, in which case it becomes necessary to increase the amount of flame retardant charged during suspension polymerization. It is more preferable that the resin particles to be dissolved contain 1 part by weight or more of a flame retardant.

[0025] 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 the styrene-based monomer is preferably 100 ppm or less, more preferably 20 ppm or less. If peroxide remains, it affects the polymerization rate during suspension polymerization, making it difficult to control the particle size and molecular weight. The amount of peroxide in the 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 using iodine titration using potassium iodide and sodium thiosulfate, for example.

[0026] 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.

[0027] 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 the polymeric nonionic surfactant is preferably used at a concentration of 15 ppm to 30 ppm in water. The use of a polymeric nonionic surfactant sharpens the particle size distribution and improves product yield. The polymeric nonionic surfactant is preferably a polyoxyethylene polyoxypropylene glycol-based surfactant. If the polymeric nonionic surfactant is used at a concentration of less than 15 ppm in water, the effect of sharpening the particle size distribution is difficult to achieve, while if the polymeric nonionic surfactant is used at a concentration of more than 30 ppm in water, polymerization stability tends to decrease. The concentration of the polymeric nonionic surfactant in water is more preferably 15 ppm to 25 ppm.

[0028] In one embodiment of 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. Among these, it is preferable to add the polymerization initiator to an aqueous medium to form a suspension. Radical-generating polymerization initiators commonly used in the production of thermoplastic polymers can be used as the polymerization initiator. Representative examples of polymerization initiators 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.

[0029] 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.

[0030] In the method for producing recycled expandable styrene-based resin particles according to one embodiment of the present invention, other additives such as plasticizers, solvent components, dispersants, etc. may be added to the aqueous medium to form a suspension, as necessary, in order to adjust the average particle size, particle size distribution, and expandability and moldability. 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, it tends 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. The amount of plasticizer used is preferably 0.4 to 1.0 parts by weight per 100 parts by weight of the base resin component of the recycled expandable styrene-based resin particles, and the amount of solvent used is preferably 0.3 to 1.3 parts by weight per 100 parts by weight of the base resin component of the recycled expandable styrene-based resin particles. Using less than 0.4 parts by weight of plasticizer makes it difficult to achieve a high expansion ratio, while using more than 1.0 part by weight tends to narrow the range of molding conditions. If the amount of solvent used is less than 0.3 parts by weight, it becomes difficult to achieve a high expansion ratio, and if it exceeds 1.3 parts by weight, the flame retardancy tends to deteriorate.

[0031] 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.

[0032] 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 in an aqueous medium containing a brominated flame retardant and a flame retardant aid in water to form a suspension, followed by adding a dispersant to the suspension at least once during the polymerization to control particle size and stabilize the polymerization. This process allows for the production of recycled styrene-based resin particles. The dispersant should be added during the 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. 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.

[0033] In one embodiment of the present invention, a method for producing recycled expandable styrene-based resin particles includes a step of impregnating recycled styrene-based resin particles obtained by adding a dispersant during polymerization with a blowing agent. The blowing agent impregnation step involves introducing a blowing agent and a blowing aid, raising the temperature above the glass transition point of the styrene-based resin particles, and maintaining the temperature for a certain period of time. The blowing agent impregnation temperature (temperature to which the temperature is raised) and time (time for which the temperature is maintained after the temperature is raised) depend on the glass transition point and particle size of the styrene-based resin particles, but are typically carried out at a temperature of 105°C to 120°C for approximately 3 to 10 hours. This allows for the production of recycled expandable styrene-based resin particles.

[0034] The usable blowing agent is not particularly limited as long as it is a blowing agent commonly used in producing expandable styrene-based resin particles, but examples thereof 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 because of its good foaming power, and it is more preferred to use one in which the ratio of normal butane to isobutane is 50 / 50 to 80 / 20.

[0035] The amount of foaming agent used 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, based on 100% by weight of recycled expandable styrene-based resin particles. 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 processing tends to be long, which tends to reduce energy efficiency.

[0036] In one embodiment of the present invention, the recycled expandable styrene resin particles preferably contain less than 0.03% by weight of a monomer component, which tends to volatilize from the foamed molded article obtained by expanding the recycled expandable styrene resin particles. If the content of the monomer component is 0.03% by weight or more, the resin is not suitable for use in building interiors.

[0037] The amount of the monomer component contained in the recycled expandable styrene-based resin particles in one embodiment of the present invention can be controlled by a combination of the amount of polymerization initiator used and the polymerization temperature when producing the recycled styrene-based resin particles. For example, the amount of the monomer component contained can be reduced by increasing the amount of polymerization initiator used or the polymerization temperature.

[0038] The weight-average molecular weight Mw of the recycled expandable styrene-based resin particles in one embodiment of the present invention is preferably 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 be low, but the surface of the molded article will tend to melt easily, impairing the appearance, while if it is 320,000 or more, the foaming ability will be low and the moldability will tend to deteriorate.

[0039] 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.

[0040] 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").

[0041] The average particle diameter of the recycled expandable styrene resin particles produced by the production method 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. When the average particle diameter of the expandable polystyrene 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, when 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 of the recycled expandable styrene resin particles produced by the production method of the present invention is preferably a particle size distribution index (UT) of 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.

[0042] A nucleating agent can be added to the aqueous medium to control the bubble diameter when the recycled expandable styrene-based resin particles are pre-expanded. Examples of nucleating agents used in the present invention 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.

[0043] The cell diameter of the pre-expanded particles obtained by pre-expanding the expandable styrene-based resin particles obtained by the production method of the present invention is preferably such that the average chord length of the cells in the cross section of the expanded molded article obtained from the 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.

[0044] 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.

[0045] As an additive that can be applied to the surface of the expandable resin particles of the present invention, an external additive may be used within a range that does not impair the effects of the present invention. As the external additive used in the present invention, known and commonly used ones can be used.

[0046] Specific examples of external additives include fatty acid triglycerides such as lauric acid triglyceride, stearate triglyceride, and linoleic acid triglyceride, fatty acid diglycerides such as lauric acid diglyceride, stearate diglyceride, and linoleic acid diglyceride, fatty acid monoglycerides such as lauric acid monoglyceride, stearate monoglyceride, and linoleic acid monoglyceride, fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, and calcium laurate, nonionic surfactants such as polyoxyethylene cetyl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene laurate, polyoxyethylene palmitate, polyoxyethylene stearate, and polyoxyethylene oleate, silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane, castor wax, and vegetable oils such as castor oil and olive oil. These external additives may be used alone or in combination of two or more.

[0047] 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 wash and dehydrate the expandable styrene-based resin particle-containing slurry obtained in the suspension polymerization and foaming agent impregnation steps, dry the particles, and then sieve them into particle sizes appropriate for the intended use before coating them in a mixer. The amounts of external additives used are preferably 0.10 to 0.20 parts by weight of zinc stearate as an antiblocking 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 antiblocking agent is less than 0.10 parts by weight, blocking (expanded particles bonding together) 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 the fusion promoter is less than 0.03 parts by weight, fusion tends to deteriorate when the heating conditions during molding are low, while if it exceeds 0.10 parts by weight, blocking tends to increase. Furthermore, it is preferable to apply 0.05 to 0.15 parts by weight of a fatty acid triglyceride as a molding cycle shortener. If the amount of the molding cycle shortener is less than 0.05 parts by weight, a sufficient molding cycle shortening effect cannot be obtained, while if it exceeds 0.15 parts by weight, the foaming speed during pre-foaming tends to decrease.

[0048] Pre-expanded particles can be obtained by expanding the recycled expandable styrene-based resin particles obtained by the production method according to one embodiment of the present invention. The pre-expanded particles can be obtained by expanding (pre-expanding) the recycled expandable styrene-based resin particles obtained by the production method according to one embodiment of the present invention by a known method.

[0049] 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.

[0050] 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.

[0051] A foamed molded article can be obtained by molding the pre-expanded particles obtained by expanding the recycled expandable styrene-based resin particles according to one embodiment of the present invention in a mold. The foamed molded article can be obtained by performing expansion molding using the pre-expanded particles by a known method.

[0052] The pre-expanded particles can be expanded by a conventional method such as in-mold expansion molding, in which the pre-expanded particles are filled into a mold, and then steam or the like is blown in and heated to obtain an expanded molded article. The steam pressure during in-mold expansion is typically about 0.03 to 0.09 MPa, and the mold temperature is preferably 105°C to 130°C. The expanded molded article can be suitably used in fields where styrene resin foams are used. For example, it can be suitably used in fields such as heat insulating materials for building components, civil engineering materials, and automotive components. [Example]

[0053] 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.

[0054] <Polymer ratio when adding dispersant during the production of expandable styrene resin particles> During suspension polymerization in the process of producing 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.

[0055] 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 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.).

[0056] 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).

[0057] 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.

[0058] Particle size distribution index UT=U90 / U40+U60 / U10 <Production of foam molded product> The expandable styrene resin particles obtained by the <Production of Recycled Expandable Styrenic Resin Particles> described below were sieved to 0.6 mm to 1.6 mm. For 100 parts by weight of the resulting 0.6 mm to 1.6 mm expandable styrene resin particles, 0.17 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corporation), 0.06 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.) as a molding cycle improver were mixed and stirred with the expandable styrene resin particles, and coated. The particles were placed in a pre-expander [Daika 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. 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] and molded under an initial pressure of 0.5 MPa and a steam injection pressure of 0.07 MPa to obtain a molded foam plate. The heating and cooling timer conditions were as follows: mold heating 2 seconds, one-sided heating 6 seconds, reverse one-sided heating 4 seconds, double-sided heating 8 seconds, heat retention 5 seconds, water cooling 3 seconds, air cooling 5 seconds, and vacuum cooling 150 seconds.

[0059] <Minimum Oxygen Index (LOI) of foamed molded products> To evaluate flame retardancy, the minimum oxygen index of the foamed molded article was measured. The foamed molded article was left standing at 60°C for 48 hours, and then at 23°C for 24 hours, and the minimum oxygen index was measured according to JIS K7201. A value of 26 or higher was considered acceptable.

[0060] <Self-extinguishing properties of foam molded products> To evaluate the flame retardancy, the self-extinguishing property of the foam molded article was measured. The foam molded article was left standing at 60°C for 48 hours, and then at 23°C for 24 hours, and the evaluation was performed in accordance with JIS A9511 (Foamed Plastic Heat Insulation Material) Measurement Method A.

[0061] A fire extinguishing time of 3 seconds or less was considered a pass, and the following criteria were used: ◎: Extinguishing time is within 1 second 〇: Fire extinguishing time is within 2 seconds △: Fire extinguishing time is within 3 seconds ×: Fire extinguishing time exceeds 3 seconds <Preparation of Expandable Styrenic Resin Particles Dissolving in Styrene Monomers> (Method for producing expandable styrene resin particles A) A 6 L 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, 0.08 parts by weight of benzoyl peroxide and 0.38 parts by weight of t-butylperoxy-2-ethylhexyl carbonate as initiators, 0.06 parts by weight of polyethylene wax as a nucleating agent, 1.1 parts by weight of brominated butadiene-vinyl aromatic hydrocarbon copolymer (EMERALD 3000, LANXESS) as a brominated flame retardant, 0.6 parts by weight of dicumyl peroxide as a flame retardant aid, and 0.9 parts by weight of coconut oil as a plasticizer. Subsequently, 100 parts by weight of styrene monomer was added while stirring at 250 rpm. The autoclave was then purged with nitrogen (a process of pressurizing with nitrogen to 0.1 MPa and purging was repeated three times). Thereafter, the temperature was raised to 98°C and maintained at 98°C for 2.25 hours, after which 0.10 parts by weight of calcium phosphate was added and the mixture was maintained for a further 2.5 hours to obtain styrene-based resin particles.

[0062] Next, 0.6 parts by weight of cyclohexane as a solvent and 7.0 parts by weight of butane as a blowing agent were pressure-charged into the autoclave and heated to 116°C. After maintaining the temperature at 116°C for 4 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, as well as the 1-minute half-life temperature, 1-hour half-life temperature, and 10-hour half-life temperature of the peroxide, and the activation energy, and was found to be less than 20 ppm.

[0063] (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.

[0064] 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, 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 B of 0.6 mm or less. The amount of peroxide in expandable styrene-based resin particles B was calculated from the polymerization and blowing agent impregnation temperature and the half-life temperature of the peroxide, and was found to be less than 30 ppm.

[0065] (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 1.6 mm or less were collected, and 100 parts by weight of the collected expandable styrene-based resin particles were coated with 0.17 parts by weight of zinc stearate (Zinc Stearate GF-200, manufactured by NOF Corporation), 0.06 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.), to obtain expandable styrene-based resin particles C.

[0066] (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. 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.

[0067] <Production of recycled expandable styrene resin particles> Example 1 Five parts by weight of the expandable styrene resin particles A were dissolved in 95 parts by weight of a styrene monomer to prepare a solution in which the expandable styrene resin particles were dissolved.

[0068] A 6 L 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, 20 ppm of polyoxyethylene polyoxypropylene glycol (ADEKA Pluronic® L-44, ADEKA) as a polymer surfactant, and 7 ppm of xanthan gum (KELZAN S Plus, Sansho) as a thickener. Additionally, 0.08 parts by weight of benzoyl peroxide and 0.38 parts by weight of t-butylperoxy-2-ethylhexyl carbonate as initiators, 0.06 parts by weight of polyethylene wax as a nucleating agent, 1.1 parts by weight of brominated butadiene-vinyl aromatic hydrocarbon copolymer (EMERALD 3000, LANXESS) as a brominated flame retardant, 0.6 parts by weight of dicumyl peroxide as a flame retardant aid, and 0.9 parts by weight of coconut oil as a plasticizer. Next, while stirring at 250 rpm, 100 parts by weight of the above solution was added, and the autoclave was then 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 after holding at 98°C for 2.25 hours, 0.10 parts by weight of calcium phosphate was added (sometimes referred to as "dispersant addition" in this example), and the mixture was held for another 2.5 hours to obtain styrene-based resin particles. Sampling was also performed at the time of dispersant addition, and the polymer ratio at the time of dispersant addition was measured.

[0069] Next, 0.6 parts by weight of cyclohexane as a solvent and 7.0 parts by weight of butane as a blowing agent were pressure-fed into the autoclave, and the temperature was again raised to 116°C. After maintaining the temperature at 116°C for 4 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 recycled expandable styrene-based resin particles.

[0070] The recycled expandable styrene resin particles were evaluated for average particle size and particle size distribution index. Furthermore, the recycled expandable styrene resin particles were used to produce expanded molded articles as described in the above section "Preparation of Expanded Molded Articles," and the minimum oxygen index and self-extinguishing ability were evaluated. The evaluation results are shown in Table 1.

[0071] (Examples 2 to 13, 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 or foamed molded articles, the number of parts of styrene monomer used in suspension polymerization, the number of parts of brominated flame retardant and flame retardant aid, the timing of addition of additional dispersant, the number of parts of thickener, and the number of parts of polymer surfactant were changed as shown in Table 1 or Table 2, respectively, to obtain recycled expandable styrene-based resin particles, pre-expanded particles, and foamed molded articles. The evaluation results are shown in Tables 1 and 2.

[0072] [Table 1]

[0073] [Table 2]

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; a step of dispersing the solution in an aqueous medium prepared by adding a brominated flame retardant and a flame retardant aid to water 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 is 15% by weight or less based on the total amount of the expandable styrene-based resin particles and the styrene-based monomer; the brominated flame retardant added to the aqueous medium is 0.7 parts by weight or more relative to 100 parts by weight of the recycled expandable styrene-based resin particles; The method for producing recycled expandable styrene resin particles, wherein the amount of the flame retardant auxiliary added to the aqueous medium is 0.4 parts by weight or more based on 100 parts by weight of the recycled expandable styrene resin particles.

2. The expandable styrene-based resin particles to be dissolved in the styrene-based monomer contain 0.7 parts by weight or more of a bromine-based flame retardant per 100 parts by weight of a base resin of the expandable styrene-based resin particles. A method for producing the recycled expandable styrene resin particles according to claim 1.

3. The aqueous medium contains a thickener, The concentration of the thickener in water is 4 ppm or more and 9 ppm or less. A method for producing the recycled expandable styrene resin particles according to claim 1 or 2.

4. the aqueous medium contains a polymeric nonionic surfactant, The concentration of the polymeric nonionic surfactant in water is 15 ppm or more and 30 ppm or less. A method for producing the recycled expandable styrene resin particles according to claim 1 or 2.

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

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