Method for producing foamable styrene-based resin particles

Abstract

To provide a method for producing foamable styrene-based resin particles that is capable of restraining increase in fluctuation of the particle size of the foamable resin particles, even when suspension polymerization is performed using a styrene-based solution containing recycled polystyrene.SOLUTION: A method for producing foamable styrene-based resin particles includes a charging step, a polymerization step, and a foaming agent impregnation step. In the charging step, an aqueous medium is charged into a styrene-based solution including recycled polystyrene dissolved in a styrene-based monomer, within a reaction vessel. In the polymerization step, the styrene-based solution is subjected to suspension polymerization while stirring the contents of the reaction vessel, to yield styrene-based resin particles. In the foaming agent impregnation step, the styrene-based resin particles are impregnated with a foaming agent. In the charging step, the viscosity ratio ηs / ηw of the viscosity ηs of the styrene-based solution to the viscosity ηw of the aqueous medium, charged into the reaction vessel, is 1 or more and 2000 or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] As a method for producing expandable styrene-based resin particles, a suspension polymerization method is known in which styrene-based monomers are polymerized in a state where droplets of styrene-based monomers are dispersed in an aqueous medium. In the suspension polymerization method for expandable styrene-based resin particles, in order to easily stabilize the dispersion state of the droplets of styrene-based monomers, first, a suspension in which droplets of styrene-based monomers are dispersed in an aqueous medium is prepared by adding and suspending the styrene-based monomers while stirring the aqueous medium. Next, the styrene-based monomers in the suspension are polymerized to form styrene-based resin particles. Then, in parallel with the polymerization of the styrene-based monomers, or after the polymerization is completed, a blowing agent is impregnated into the styrene-based resin particles to obtain expandable styrene-based resin particles.

[0003] In recent years, from the viewpoint of reducing the environmental load, reuse of used styrene-based products made of styrene-based polymers and defective products generated during the manufacturing process of styrene-based products as resources has been considered. For example, Patent Document 1 describes recycled expandable styrene-based resin particles, which are characterized in that an expandable styrene-based resin molded product and / or expandable particles of expandable styrene-based resin are dissolved in styrene monomer to prepare a styrene monomer solution, which is added to an aqueous medium and dispersed to cause suspension polymerization, and the resulting polymer particles are impregnated with a blowing agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-89728 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a styrene-based polymer derived from a used styrene-based product or a non-standard product generated during the manufacturing process is dissolved in a styrene monomer and the obtained styrene monomer solution is used to produce styrene-based resin particles by a suspension polymerization method, there is a problem that the particle size of the styrene-based resin particles tends to vary greatly.

[0006] The present invention has been made in view of the above background, and aims to provide a method for producing expandable styrene-based resin particles that can suppress an increase in the variation in particle size even when suspension polymerization is performed using a styrene-based solution containing recycled polystyrene. [Means for solving the problem]

[0007] One aspect of the present invention resides in a method for producing expandable styrene-based resin particles according to the following items [1] to [4].

[0008] [1] A step of introducing an aqueous medium into a styrene-based solution in which recycled polystyrene is dissolved in a styrene-based monomer in a reaction vessel; a polymerization step of obtaining styrene-based resin particles by performing suspension polymerization of the styrene-based solution while stirring the content of the reaction vessel; and a blowing agent impregnation step of impregnating the styrene-based resin particles with a blowing agent during and / or after completion of the polymerization step to obtain expandable styrene-based resin particles, The styrene-based solution is introduced into the reaction vessel in the introduction step at a temperature of 40° C. and a shear rate of 50 s -1 The viscosity ηs at the temperature of the aqueous medium is 40°C and the shear rate is 50s -1 The present invention relates to a method for producing expandable styrene-based resin particles, and a ratio ηs / ηw of the viscosity ηw at the time of the expansion to the viscosity ηw at the time of the expansion is 1 or more and 2000 or less.

[0009] [2] The method for producing expandable styrene-based resin particles described in [1], wherein the amount of the recycled polystyrene in the styrene-based solution is 1 part by mass or more and 35 parts by mass or less per 100 parts by mass of the styrene-based solution. [3] The method for producing expandable styrene-based resin particles according to [1] or [2], wherein the recycled polystyrene has a weight average molecular weight of 150,000 or more and 300,000 or less.

[0010] [4] The method for producing expandable styrene-based resin particles according to any one of [1] to [3], wherein the recycled polystyrene is a styrene-based polymer derived from one or more styrene-based articles selected from the group consisting of styrene-based resin particles, expandable styrene-based resin particles, expanded styrene-based resin particles, expanded styrene-based resin moldings, and scraps of expanded styrene-based resin moldings generated during the production process of expandable styrene-based resin particles. Effect of the Invention

[0011] According to the above aspect, it is possible to provide a method for producing expandable styrene-based resin particles (hereinafter referred to as "expandable resin particles") that can suppress an increase in particle size variation even when suspension polymerization is performed using a styrene-based solution containing recycled polystyrene. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Method of producing expandable styrene-based resin particles) Each step in the manufacturing method will now be described in detail.

[0013] [Feeding process] In the introduction step, an aqueous medium is introduced into a styrene-based solution containing a styrene-based monomer and recycled polystyrene dissolved in the styrene-based monomer in a reaction vessel. The styrene-based solution introduced into the reaction vessel in the introduction step has a temperature of 40° C. and a shear rate of 50 s -1 The viscosity ηs at the temperature of the aqueous medium is 40°C and the shear rate is 50s -1 The ratio ηs / ηw to the viscosity ηw at is 1 or more and 2000 or less.

[0014] Conventionally, when preparing styrene resin particles by suspension polymerization, a styrene solution containing a styrene monomer is prepared in a preparation vessel separate from a reaction vessel. The styrene solution in the preparation vessel is then transferred to a reaction vessel, and the styrene solution is poured into an aqueous medium while stirring the contents of the reaction vessel. However, when the styrene solution contains recycled polystyrene, there is a problem that the particle size variation of the expandable styrene resin particles increases.

[0015] In contrast, in the charging step of the above-mentioned production method, an aqueous medium is charged into the styrene-based solution in the reaction vessel. Therefore, more recycled polystyrene can be used in the production of expandable styrene-based resin particles, and suspension polymerization can proceed stably. Furthermore, by setting the ratio ηs / ηw of the viscosity ηs of the styrene-based solution used in the charging step to the viscosity ηw of the aqueous medium within the above-mentioned specific range, the variation in the size of droplets of the styrene-based solution when the contents of the reaction vessel are stirred can be reduced.

[0016] As a result of the above, even when suspension polymerization is carried out using a styrene-based solution containing recycled polystyrene, an increase in the variation in particle size of the expandable resin particles can be suppressed.

[0017] In the case where the styrene-based solution is introduced into the aqueous medium in the introduction step, as described above, the difference in viscosity between the styrene-based solution and the cleaning solution tends to increase the variation in droplet size of the styrene-based solution when the content of the reaction vessel is stirred, which tends to increase the variation in particle size of the expandable resin particles.

[0018] In addition, if the ratio ηs / ηw of the viscosity ηs of the styrene-based solution at the specific temperature and shear rate to the viscosity ηw of the aqueous medium at the specific temperature and shear rate used in the charging step is too high, the difference in viscosity between the aqueous medium and the styrene-based solution becomes excessively large, and the size of the droplets of the styrene-based solution tends to vary greatly when the contents of the reaction vessel are stirred. As a result, the particle size of the expandable resin particles tends to vary.

[0019] From the viewpoint of more easily avoiding an increase in the variation in particle size of the expandable resin particles, the viscosity ratio ηs / ηw of the styrene solution and the aqueous medium is preferably 2000 or less, more preferably 1200 or less, even more preferably 800 or less, particularly preferably 400 or less, and most preferably 100 or less. From the viewpoint of suppressing an increase in the variation in particle size of the expandable resin particles, there is no lower limit to the viscosity ratio ηs / ηw of the styrene solution and the aqueous medium, but the viscosity ratio ηs / ηw of the styrene solution and the aqueous medium is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, particularly preferably 10 or more, and most preferably 20 or more.

[0020] The viscosity ratio ηs / ηw between the styrene-based solution and the aqueous medium can be adjusted, for example, by the amount of recycled polystyrene polymer in the styrene-based solution or the weight average molecular weight of the recycled polystyrene. More specifically, the viscosity ratio ηs / ηw between the styrene-based solution and the aqueous medium can be increased by increasing the amount of styrene-based polymer in the styrene-based solution. In addition, the viscosity ratio ηs / ηw between the styrene-based solution and the aqueous medium can be increased by preparing the styrene-based solution using a styrene-based polymer with a high weight average molecular weight.

[0021] The viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium may be measured based on JIS Z 8803:2011. A rotational rheometer having a temperature-adjustable coaxial double cylinder geometry may be used to measure the viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium. More specifically, the rotational rheometer may be, for example, a rheometer "Discovery HR-2" manufactured by TA Instruments. The geometry may be, for example, a coaxial double cylinder geometry ("HA Aluminum Recessed End Rotor" and "Stainless Steel Standard Concentric Cylinder Cup with Cap" manufactured by TA Instruments) equipped with a temperature adjustment device (Peltier coaxial cylinder temperature system "DHR Smart Swap Concentric Cylinder Peltier Jacket" manufactured by TA Instruments).

[0022] Specifically, the viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium can be measured as follows. First, the temperature of the measurement device geometry is set to 40°C, and the styrene-based solution or aqueous medium as a sample is placed in the geometry. Then, wait until the temperature of the sample reaches 40°C. After the temperature of the sample is stabilized at 40°C, the shear rate is reduced to 0.1 s -1 From 100s over 180 seconds -1 The viscosity of the sample is measured while increasing the shear rate to 10. At this time, the data acquisition interval in the measuring device is set so that 20 or more data points are acquired during an increase in shear rate of one order of magnitude.

[0023] The data thus obtained is plotted on a graph with the ordinate representing viscosity and the abscissa representing shear rate. -1 Data at shear rates lower than 50s -1 A linear regression equation is determined based on three or more data points, including data at shear rates above 50s. The linear regression equation is then interpolated based on the regression equation obtained in this way. -1The viscosity of the sample in is the viscosity ηs of the styrene-based solution or the viscosity ηw of the aqueous medium. The viscosity ηs of the styrene-based solution calculated above is divided by the viscosity ηw of the aqueous medium to obtain the viscosity ratio ηs / ηw of the styrene-based solution and the aqueous medium. For the above analysis, commercially available analysis software (for example, "TRIOS" manufactured by TA Instruments) can be used.

[0024] In the above-mentioned production method, the preparation of the styrene-based solution may be carried out in a reaction vessel. In addition, the styrene-based solution may be prepared in a preparation vessel other than the reaction vessel, and then the styrene-based solution may be transferred from the preparation vessel to the reaction vessel. From the viewpoint of further simplifying the production process of the expandable resin particles, it is preferable to prepare the styrene-based solution by dissolving recycled polystyrene in a styrene-based monomer in a reaction vessel, and then to add an aqueous medium into the styrene-based solution. In this way, by preparing the styrene-based solution in the reaction vessel, the work of transferring the styrene-based solution from the preparation vessel and the work of cleaning the preparation vessel, etc. are not required. As a result, the production process of the expandable resin particles can be further simplified and the productivity can be more easily improved.

[0025] The reaction vessel used in the introduction step may have an impeller for stirring the contents of the reaction vessel. In this case, from the viewpoint of preventing abnormal polymerization in which the suspension state of the suspension becomes unstable and the entire system solidifies during polymerization, the rotation speed of the impeller in the introduction step is preferably 50% or less, more preferably 20% or less, and even more preferably 10% or less of the rotation speed of the impeller in the polymerization step, and it is particularly preferable that the impeller is stopped.

[0026] Styrene solution temperature 40℃ and shear rate 50s -1The viscosity ηs at 40°C is preferably 1.0 mPa·s or more. In this case, the amount of water contained in the expandable styrene resin particles can be reduced, and the coarse bubbles in the styrene resin expanded particles obtained by expanding the expandable resin particles can be further reduced. From the viewpoint of more easily obtaining the effect of reducing the particle size variation of the expandable resin particles, the viscosity ηs at 40°C is preferably 1.0 mPa·s or more. -1 The viscosity ηs in is preferably 3000 mPa·s or less, more preferably 1200 mPa·s or less, further preferably 600 mPa·s or less, and particularly preferably 100 mPa·s or less.

[0027] The styrene-based solution used in the charging step contains a styrene-based monomer that becomes the styrene-based resin that constitutes the expandable resin particles after polymerization, and recycled polystyrene dissolved in the styrene-based monomer. The amount of recycled polystyrene in the styrene-based solution is preferably 1 part by mass or more and 35 parts by mass or less per 100 parts by mass of the styrene-based solution. In this case, the viscosity ratio ηs / ηw of the styrene-based solution and the aqueous medium can be more easily adjusted to within the specific range.

[0028] From the viewpoint of increasing the amount of recycled polystyrene blended in the styrene-based solution and promoting the reuse of recycled raw materials, the blending amount of recycled polystyrene in the styrene-based solution is more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 4 parts by mass or more, relative to 100 parts by mass of the styrene-based solution. On the other hand, from the viewpoint of more easily avoiding an excessive increase in the viscosity ηs of the styrene-based solution, the blending amount of recycled polystyrene in the styrene-based solution is more preferably 30 parts by mass or less, even more preferably 25 parts by mass or less, particularly preferably 20 parts by mass or less, and most preferably 15 parts by mass or less, relative to 100 parts by mass of the styrene-based solution.

[0029] In forming a preferred range of the amount of recycled polystyrene in the styrene-based solution, the upper and lower limits of the amount of recycled polystyrene described above can be combined arbitrarily. For example, the amount of recycled polystyrene in the styrene-based solution may be 2 parts by mass or more and 30 parts by mass or less, 3 parts by mass or more and 25 parts by mass or less, 4 parts by mass or more and 20 parts by mass or less, or 4 parts by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the styrene-based solution.

[0030] As the styrene monomer, one or more compounds selected from the group consisting of styrene and styrene derivatives can be used. Examples of the styrene derivatives include α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4-dichlorostyrene, pn-butylstyrene, pt-butylstyrene, pn-hexylstyrene, p-octylstyrene, styrenesulfonic acid, and sodium styrenesulfonate.

[0031] From the viewpoint of more reliably dissolving the recycled polystyrene in the styrene monomer and more reducing the variation in particle size of the expandable resin particles, it is preferable that the styrene monomer contains at least styrene. From the same viewpoint, the content of styrene in the styrene monomer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0032] From the viewpoint of more reliably dissolving the recycled polystyrene in the styrene monomer, the blending amount of the styrene monomer in the styrene solution is preferably 65 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 75 parts by mass or more, particularly preferably 80 parts by mass or more, and most preferably 85 parts by mass or more, relative to 100 parts by mass of the styrene solution. Also, from the viewpoint of more easily avoiding an excessive increase in the viscosity ηs of the styrene solution, the blending amount of the styrene monomer in the styrene solution is preferably 99 parts by mass or less, more preferably 98 parts by mass or less, even more preferably 97 parts by mass or less, and particularly preferably 96 parts by mass or less, relative to 100 parts by mass of the styrene solution.

[0033] In forming the preferred range of the amount of the styrene monomer in the styrene solution, the upper limit and the lower limit of the amount of the styrene monomer can be combined arbitrarily. For example, the amount of the styrene monomer in the styrene solution may be 65 parts by mass or more and 99 parts by mass or less, 70 parts by mass or more and 98 parts by mass or less, 75 parts by mass or more and 97 parts by mass or less, 80 parts by mass or more and 96 parts by mass or less, or 85 parts by mass or more and 96 parts by mass or less, relative to 100 parts by mass of the styrene solution.

[0034] In addition, a monomer copolymerizable with the styrene monomer can be added to the styrene solution. Examples of the monomer copolymerizable with the styrene monomer include acrylic acid esters and methacrylic acid esters. Examples of the acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Examples of the methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. These monomers may be used alone, or two or more types of monomers may be used in combination.

[0035] From the viewpoint of making it easier to obtain expandable resin particles having the desired characteristics, the proportion of styrene in all monomers contained in the styrene-based solution is, for example, preferably 50 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, and particularly preferably 100 mass%, i.e., the monomers in the styrene-based solution are composed only of styrene.

[0036] The recycled polystyrene used in the preparation of the styrene-based solution is composed of a styrene-based polymer. Examples of the recycled polystyrene include polystyrene (more specifically, GPPS) and styrene-based styrene-acrylic acid copolymers, styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, styrene-butyl acrylate copolymers, styrene-methacrylic acid copolymers, styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-butyl methacrylate copolymers, styrene-maleic anhydride copolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-methylstyrene copolymers, styrene-dimethylstyrene copolymers, styrene-ethylstyrene copolymers, and styrene-diethylstyrene copolymers. The recycled polystyrene may be composed of one type of styrene-based polymer selected from the group consisting of these styrene-based polymers, or may be composed of two or more types of styrene-based polymers.

[0037] From the viewpoint of more reliably dissolving the recycled polystyrene in the styrene monomer and more reducing the variation in particle size of the expandable resin particles, the proportion of the styrene polymer in the recycled polystyrene is preferably 75% by mass or more, more preferably 80% by mass or more, and particularly preferably 85% by mass or more, relative to 100% by mass of the recycled polystyrene. From the same viewpoint, the proportion of polystyrene in the recycled polystyrene is preferably 80% by mass or more, more preferably 85% by mass or more, and particularly preferably 90% by mass or more, relative to 100% by mass of the recycled polystyrene.

[0038] The weight average molecular weight of the recycled polystyrene is preferably 150,000 or more and 300,000 or less. In this case, the viscosity ratio ηs / ηw between the styrene-based solution and the aqueous medium can be more easily adjusted to within the specific range. From the viewpoint of more easily increasing the blending amount of recycled polystyrene while adjusting the viscosity ratio ηs / ηw between the styrene-based solution and the aqueous medium to within the specific range, the weight average molecular weight of the recycled polystyrene is preferably 170,000 or more and 300,000 or less, more preferably 180,000 or more and 300,000 or less, and even more preferably 200,000 or more and 290,000 or less.

[0039] The recycled polystyrene is preferably a styrene polymer derived from one or more styrene articles selected from the group consisting of styrene resin particles, expandable styrene resin particles, styrene resin expanded particles, styrene resin expanded bead moldings, and waste materials of styrene resin expanded bead moldings, which are generated during the manufacturing process of expandable styrene resin particles. In this way, by using a styrene polymer related to expandable styrene resin particles, styrene resin expanded particles, and styrene resin expanded bead moldings as the recycled polystyrene to be mixed in the styrene solution, it is possible to recycle these recycled polystyrenes as resources and to reduce the amount of styrene monomer used.

[0040] The recycled polystyrene may be the above-mentioned styrene-based product itself, or may be a styrene-based polymer obtained by subjecting a styrene-based product to processing such as compression or dissolution. For example, when using styrene-based resin particles or expandable styrene-based resin particles as recycled polystyrene, the recycled polystyrene is preferably resin particles or expandable resin particles having a particle size outside the desired particle size range, which are generated during the manufacturing process of expandable resin particles. In this case, non-standard products, etc., generated during the manufacturing process of expandable styrene-based resin particles can be reused as resources.

[0041] Furthermore, for example, when styrene-based resin foam particles are used as recycled polystyrene, the recycled polystyrene is preferably resin foam particles having a density outside the desired density range that are generated when expandable resin particles are expanded, resin foam particles that are unsuitable for use due to reasons such as non-uniform bubble state, or resin foam particles recovered from used styrene-based products, etc. In this case, non-standard products generated in the manufacturing process of resin foam particles, resin foam particles derived from used styrene-based products, etc. can be reused as resources.

[0042] Furthermore, for example, when a styrene-based resin expanded bead molding or its scrap material is used as recycled polystyrene, the recycled polystyrene is preferably a molding that is unsuitable for use because it does not meet the desired dimensional accuracy, has a large number of voids on the surface of the molding, or has insufficient fusion between the resin expanded particles, or scrap material generated during the manufacturing process of the molding, or a molding recovered from used styrene-based products, etc. In this case, non-standard products generated during the manufacturing process of the molding, or moldings derived from used styrene-based products, etc. can be reused as resources.

[0043] Recycled polystyrene may contain volatile organic components due to its type, deterioration during processing steps until it becomes recycled polystyrene, etc. According to the above-mentioned manufacturing method, even when recycled polystyrene contains a relatively large amount of volatile organic components, expandable resin particles can be stably manufactured, and the increase in the variation in the bubble diameter of the expandable resin particles can be suppressed. As a result, various polystyrene waste materials can be reused as resources. The amount of volatile organic components in recycled polystyrene may be, for example, 8% by mass or less relative to 100% by mass of recycled polystyrene. In this case, abnormal polymerization during polymerization can be more easily suppressed.

[0044] The content of volatile organic components in the recycled polystyrene can be determined by subtracting the water content from the total volatile content in the recycled polystyrene.

[0045] Specifically, first, approximately 1 g of recycled polystyrene is weighed out as a sample. Next, the sample is heated and dried in a dryer at 120°C for 4 hours. After heating and drying, the sample is transferred to a desiccator and allowed to cool for at least 30 minutes. The sample is then weighed. Using the mass W1 (unit: g) of the sample before drying and the mass W2 (unit: g) of the sample after drying obtained from the above, the total volatile content in the sample (unit: mass%) is calculated based on the following formula (1). Total volatile matter = 100 × (W1 - W2) / W1 (1)

[0046] In addition to the recycled polystyrene used in the measurement of the total volatile content, about 1 g of the recycled polystyrene is precisely weighed as a sample. This sample is placed in a moisture vaporizer (e.g., "CHK-501" manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the moisture vaporized in the moisture vaporizer is introduced into a Karl Fischer moisture meter (e.g., "MKC-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) to measure the moisture content (unit: mass%) in the sample.

[0047] The total volatile matter content (unit: mass%) in the sample thus obtained minus the moisture content (unit: mass%) is taken as the content of volatile organic components in the sample (unit: mass%). The above operation is carried out twice, and the arithmetic mean value of the contents of volatile organic components in the two measurements is taken as the content of volatile organic components in the recycled polystyrene.

[0048] In addition, the styrene-based solution may contain an unused styrene-based polymer as a component that becomes the styrene-based resin constituting the expandable resin particles, within a range that does not impair the above-mentioned effects. The unused styrene-based polymer may be, for example, a commercially available product. From the viewpoint of increasing the amount of recycled polystyrene and promoting the reuse of recycled raw materials, the amount of unused styrene-based polymer in the styrene-based solution is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, and particularly preferably 0 parts by mass, that is, no unused styrene-based resin is contained in the styrene-based solution, relative to 100 parts by mass of the total of the styrene-based monomer and the recycled polystyrene.

[0049] The styrene-based solution contains a polymerization initiator for polymerizing the styrene-based monomer and the recycled polystyrene in addition to the styrene-based monomer and the recycled polystyrene. As the polymerization initiator, an initiator soluble in the styrene-based monomer can be used. Specific examples of the peroxyalkylene oxide include azo compounds such as azobisisobutyronitrile, cumene hydroperoxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl monocarbonate, 1,1-dimethylpropylperoxy-2-ethylhexyl monocarbonate, 1,1-dimethylbutylperoxy-2-ethylhexyl monocarbonate, pentylperoxy-2-ethylhexyl monocarbonate, hexylperoxy-2-ethylhexyl monocarbonate, lauroyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-di-t-butylperoxy-2-methylcyclohexane.

[0050] The amount of organic peroxide added is preferably 0.01 to 2 parts by mass per 100 parts by mass of the total of the styrene monomer, the recycled polystyrene, and other styrene polymers added as needed. In this case, it is possible to increase the polymerization rate and sufficiently increase productivity while suppressing the increase in production cost associated with the amount of organic peroxide used. From the same viewpoint, it is more preferable that the amount of organic peroxide added is 0.1 to 1 part by mass per 100 parts by mass of the total of the styrene monomer, the recycled polystyrene, and other styrene polymers added as needed.

[0051] The styrene-based solution may contain additives such as a plasticizer, a chain transfer agent, a cell regulator, an antistatic agent, an antioxidant, an ultraviolet absorber, and a light stabilizer in addition to the styrene-based monomer and the recycled polystyrene. Examples of the plasticizer that can be used include liquid paraffin, glycerin diacetomonolaurate, glycerin tristearate, di-2-ethylhexyl phthalate, and di-2-ethylhexyl adipate. From the viewpoint of further improving the moldability of the resin foamed particles, the amount of the plasticizer added is preferably 0.5 parts by mass or more and 5 parts by mass or less, more preferably 1 part by mass or more and 4 parts by mass or less, and even more preferably 2 parts by mass or more and 3 parts by mass or less, based on 100 parts by mass of the total of the styrene-based monomer, the recycled polystyrene, and other styrene-based polymers blended as necessary.

[0052] Examples of the chain transfer agent that can be used include octyl mercaptan, dodecyl mercaptan, and α-methylstyrene dimer. Examples of the cell regulator that can be used include methyl methacrylate copolymers, polyethylene wax, talc, silica, ethylene bisstearylamide, and silicone. Examples of the antistatic agent that can be used include alkyldiethanolamine, glycerin fatty acid ester, and sodium alkylsulfonate.

[0053] The antioxidant may be a phenol-based, phosphorus-based, or sulfur-based antioxidant. The ultraviolet absorber may be a benzotriazole-based, benzophenone-based, or other ultraviolet absorber. The light stabilizer may be a hindered amine-based light stabilizer.

[0054] As the aqueous medium used in the dispersion step, for example, deionized water can be used. From the viewpoint of more easily obtaining the effect of reducing the variation in particle size of the expandable resin particles, the aqueous medium is dispersed at a temperature of 40° C. and a shear rate of 50 s -1 In order to further reduce the amount of water contained in the expandable styrene resin particles and to further reduce the amount of coarse bubbles in the expanded styrene resin particles obtained by expanding the expandable resin particles, it is preferable that the viscosity ηw at the temperature of the aqueous medium is 40° C. and the shear rate is 50 s or more. -1 The viscosity ηw in is preferably 5 mPa·s or less, more preferably 4 mPa·s or less, and even more preferably 3 mPa·s or less.

[0055] The aqueous medium may contain a suspending agent and / or a surfactant, if necessary. Examples of the suspending agent include hydrophilic polymers such as polyvinyl alcohol, methyl cellulose, and polyvinylpyrrolidone, and water-insoluble inorganic salts such as calcium triphosphate, magnesium pyrophosphate, hydroxyapatite, aluminum oxide, talc, kaolin, and bentonite. Examples of the surfactant include anionic surfactants such as sodium alkylsulfonate, sodium dodecylbenzenesulfonate, sodium α-olefinsulfonate, and disodium alkylbiphenyldisulfonate.

[0056] The suspending agent contained in the aqueous medium is preferably a poorly water-soluble inorganic salt. In this case, the amount of water contained in the expandable styrene resin particles can be further reduced. In addition, by reducing the amount of water in the expandable resin particles, the generation of coarse bubbles in the expanded styrene resin particles can be further suppressed. From the same viewpoint, the surfactant contained in the aqueous medium is preferably an anionic surfactant. In addition, it is more preferable that the aqueous medium contains both a poorly water-soluble inorganic salt and an anionic surfactant.

[0057] The amount of the suspending agent used is preferably 0.01 to 5 parts by mass per 100 parts by mass of water in the aqueous medium. When a suspending agent made of a poorly water-soluble inorganic salt is used in combination with an anionic surfactant, it is preferable to use 0.05 to 3 parts by mass of the suspending agent and 1 to 1000 ppm by mass of the anionic surfactant per 100 parts by mass of water in the aqueous medium.

[0058] The aqueous medium and / or the styrene-based solution may contain a polymerization inhibitor to the extent that the polymerization of the styrene-based monomer, the recycled polystyrene, and other styrene-based polymers blended as necessary is not inhibited. In this case, the variation in the average particle size of the expandable resin particles can be further reduced. Examples of the polymerization inhibitor include oil-soluble polymerization inhibitors such as 4-t-butylcatechol (p-TBC), hydroquinone, p-benzoquinone, chloro-p-benzoquinone, 2,5-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone, methoxy-p-benzoquinone, tetrabromo-p-benzoquinone, tetrachloro-p-benzoquinone, dimethyl-p-benzoquinone, o-dinitrobenzene, m-dinitrobenzene, p-dinitrobenzene, 2,4-dinitrotoluene, 1,3,5-trinitrobenzene, 1,3,5-trinitroanisole, and 2,4,6-trinitrophenol; and water-soluble polymerization inhibitors such as sodium nitrite, potassium nitrate, ammonium nitrite, L-ascorbic acid, and citric acid.

[0059] The timing of adding the polymerization inhibitor is not particularly limited, but when an oil-soluble polymerization inhibitor is used, it is preferable to add an aqueous medium to the styrene-based solution after dissolving the polymerization initiator and the polymerization inhibitor in the styrene-based solution. The amount of the polymerization inhibitor added is preferably 0.0001 parts by mass or more and 0.01 parts by mass or less with respect to 100 parts by mass of the total of the styrene-based monomer and the styrene-based solution.

[0060] [Polymerization process] In the polymerization step, the contents of the reaction vessel, that is, the styrene-based solution and the aqueous medium, are stirred to disperse the styrene-based solution in the aqueous medium, and then the styrene-based solution is polymerized to produce resin particles. The stirring method and stirring conditions in the polymerization step are not particularly limited, and appropriate stirring methods and stirring conditions may be selected from known methods and known conditions so that the size of the droplets of the styrene-based solution in the stirred liquid falls within a desired range. For example, when the contents of the reaction vessel are stirred using a stirring blade, the droplets of the styrene-based solution can be made smaller by increasing the stirring power of the stirring blade and increasing the stirring blade speed.

[0061] In addition, the specific polymerization conditions in the polymerization step are not particularly limited, and appropriate polymerization conditions may be selected from the range of known polymerization conditions. For example, the polymerization step may include a first polymerization step in which the styrene monomer and recycled polystyrene are polymerized at a first polymerization temperature, and a second polymerization step in which the styrene monomer and recycled polystyrene are polymerized at a second polymerization temperature higher than that of the first polymerization step. The first polymerization step is a step in which most of the styrene monomer is polymerized at a relatively low temperature to form a styrene resin, and the second polymerization step is a step in which the remaining unreacted styrene monomer is polymerized. By carrying out the polymerization of the styrene monomer and recycled polystyrene in two stages in this way, styrene resin particles having desired properties and a low content of unreacted styrene monomer can be more easily obtained.

[0062] The polymerization temperature in the first polymerization step is preferably 110°C or less, more preferably 105°C or less. In this case, the weight average molecular weight of the styrene resin constituting the expandable resin particles can be appropriately increased. The expandable resin particles composed of such a styrene resin are expanded to prepare resin expanded particles, and then the resin expanded particles are molded in a mold, so that a molded body having excellent mechanical strength can be more easily obtained. On the other hand, from the viewpoint of polymerization efficiency, the lower limit of the polymerization temperature in the first polymerization step is about 70°C. In addition, the polymerization time in the first polymerization step may be, for example, 3 hours or more, and is preferably 4 hours or more. From the viewpoint of increasing productivity, the polymerization time in the first polymerization step is preferably 10 hours or less, more preferably 8 hours or less.

[0063] The polymerization temperature in the latter polymerization step is preferably more than 115°C and not more than 135°C, and more preferably 118°C or more and 130°C or less. In this case, the amount of unreacted styrene-based monomer can be further reduced. The amount of unreacted styrene-based monomer in the latter polymerization step can be controlled by the holding time of the final polymerization temperature. The polymerization time in the latter polymerization step may be, for example, 1 hour or more, and is preferably 2 hours or more. In addition, from the viewpoint of increasing productivity, the polymerization time in the latter polymerization step is preferably 8 hours or less, and more preferably 6 hours or less.

[0064] [Foaming agent impregnation step] In the manufacturing method, a foaming agent impregnation step is performed during the polymerization step and / or after the polymerization step is completed, in which the resin particles are impregnated with a foaming agent, to prepare expandable resin particles containing a foaming agent. The foaming agent impregnation step may be performed at any timing as long as the resin particles can be impregnated with the foaming agent. For example, in the manufacturing method, the foaming agent impregnation step may be started simultaneously with the polymerization step or during the polymerization step, and the resin particles in the middle of the polymerization may be impregnated with the foaming agent. In addition, the foaming agent impregnation step may be started after the polymerization step is completed, and the resin particles after the polymerization is completed may be impregnated with the foaming agent. The foaming agent impregnation step may be performed once or twice or more.

[0065] In carrying out the foaming agent impregnation step, for example, the foaming agent can be added to a reaction vessel to impregnate the styrene-based resin particles with the foaming agent. The amount of foaming agent added in the foaming agent impregnation step may be, for example, an amount such that the foaming agent content in the expandable resin particles is about 2 to 20 mass %.

[0066] Examples of the blowing agent that can be used include aliphatic chain hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, normal hexane, etc. These blowing agents may be used alone or in combination of two or more kinds.

[0067] (Expandable styrene resin particles) According to the above-mentioned manufacturing method, it is possible to obtain expandable resin particles that contain components derived from recycled polystyrene, have a desired particle size, and have little variation in particle size. The upper limit of the median size based on the volumetric particle size distribution of the expandable resin particles is not particularly limited, but may be, for example, 2.0 mm. The median size based on the volumetric particle size distribution of the expandable resin particles can be adjusted by changing the amount of the suspending agent contained in the aqueous medium or by changing the rotation speed of the stirring blade in the polymerization process.

[0068] Conventionally, when resin particles are produced by suspension polymerization using a styrene-based solution containing recycled polystyrene, there is a problem that the smaller the particle diameter of the resin particles, the greater the variation in particle diameter. In contrast, in the above-mentioned production method, a styrene-based solution and an aqueous medium having the viscosity ratio ηs / ηw within the above-mentioned specific range are used, and the aqueous medium is added to the styrene-based solution in the charging step, thereby reducing the variation in particle diameter of the resin particles. Therefore, according to the above-mentioned production method, the increase in the variation in particle diameter of the expandable resin particles can be suppressed.

[0069] A particle size distribution measuring device can be used to measure the median diameter (i.e., d50), cumulative 90% particle diameter (i.e., d90), and cumulative 10% particle diameter (i.e., d10) in the volume-based particle size distribution of the expandable resin particles.

[0070] The specific method for measuring the median diameter, cumulative 90% particle diameter, and cumulative 10% particle diameter of expandable resin particles is as follows. First, a particle size distribution measuring device ("Militrack JPA" manufactured by Nikkiso Co., Ltd.) is used to measure the particle size distribution of expandable resin particles on a volume basis. Specifically, 30 g of expandable resin particles are allowed to fall freely from the sample supply feeder of the measuring device, and the projected image is captured by a CCD camera. Next, calculation and combination processing are sequentially performed on the captured image information, and the particle size distribution is measured under the conditions of an image analysis method that outputs the particle size distribution and shape index results. Based on this particle size distribution, the cumulative 10% particle diameter, median diameter, and cumulative 90% particle diameter can be calculated.

[0071] In addition, the difference between the cumulative 90% particle size and the cumulative 10% particle size is divided by the median size (i.e., (d90-d10) / d50), and the magnitude of the variation in particle size can be compared. A smaller value of (d90-d10) / d50 means a smaller variation in particle size.

[0072] From the viewpoint of using the expandable styrene-based resin particles for various applications, the number average molecular weight Mn of the expandable resin particles is preferably 50,000 or more and 150,000 or less. From the same viewpoint, the weight average molecular weight Mw of the expandable resin particles is preferably 150,000 or more and 300,000 or less, and the z average molecular weight Mz is preferably 300,000 or more and 800,000 or less.

[0073] The number average molecular weight Mn, weight average molecular weight Mw and z average molecular weight Mz of the expandable styrene resin particles can be measured by gel permeation chromatography (GPC) using polystyrene as a standard substance. Specifically, the expandable styrene resin particles are first dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1% by mass. Then, the recycled polystyrene in the sample solution is separated according to the difference in molecular weight under separation conditions of eluent: tetrahydrofuran (THF) and THF flow rate: 0.6 ml / min using a column consisting of one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H connected in series to obtain a chromatogram. Then, the retention time in the chromatogram is converted to molecular weight using a calibration curve created using standard polystyrene to obtain a differential molecular weight distribution curve. The number average molecular weight Mn, weight average molecular weight Mw and z average molecular weight Mz of the measurement sample can be calculated based on this differential molecular weight distribution curve.

[0074] The internal moisture content of the expandable resin particles is preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.0% or less. By expanding such expandable resin particles, resin expanded particles with fewer coarse bubbles can be easily obtained. For measuring the internal moisture content of the expandable resin particles, a moisture vaporizer (e.g., "CHK-501" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and a Karl Fischer moisture meter (e.g., "MKC-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) can be used in combination as a measuring device. For the measurement, 0.28 g of expandable resin particles can be used as a measurement sample.

[0075] The expandable resin particles are heated with a heating medium such as steam to expand the expandable resin particles, thereby obtaining expanded styrene resin particles. The use of the expanded styrene resin particles is not particularly limited. For example, the expanded styrene resin particles are used as a cushion filler. In addition, for example, the expanded styrene resin particles are filled in a mold and molded in the mold to obtain a styrene resin expanded bead molded article having a desired shape. The molded article thus obtained is used for various purposes such as automobile interior parts, shock absorbing materials, building materials, and packaging boxes. EXAMPLES

[0076] An example of the method for producing the expandable styrene-based resin particles will now be described.

[0077] Example 1 A 3-L autoclave equipped with a stirring blade was used as a reaction vessel. 600.3 g of styrene as a styrene monomer and recycled polystyrene (weight-average molecular weight 23 × 10) derived from expandable polystyrene resin particles and containing butane as a volatile organic component were added to the autoclave. 4 66.7g of styrene, 0.67g of bubble regulator, 13.3g of plasticizer, and polymerization initiator were added. The contents of the autoclave were heated to a temperature of 40°C, and the contents were stirred for 30 minutes by rotating the stirring blade at a rotation speed of 400 rpm, and the recycled polystyrene was dissolved in the styrene to prepare a styrene-based solution. The blending ratio of styrene and recycled polystyrene in the styrene-based solution is as shown in Table 1. In addition, polyethylene wax (Polywax1000-80M manufactured by Baker Petrolite) was used as the bubble regulator. As the polymerization initiator, 2.4g of benzoyl peroxide ("Niper (registered trademark) BW" manufactured by NOF Corporation) and 1.3g of t-butylperoxy 2-ethylhexyl monocarbonate ("Perbutyl (registered trademark) E" manufactured by NOF Corporation) were used in combination. Cyclohexane was used as the plasticizer.

[0078] In addition, apart from the preparation of the styrene-based solution, an aqueous medium was prepared by dissolving 13.0 g of tribasic calcium phosphate slurry (tribasic calcium phosphate content: 20.5% by mass), 0.033 g of sodium α-olefin sulfonate ("Lipolan (registered trademark) LB-440" manufactured by Lion Corporation), 1.25 g of sodium acetate, and 6.25 g of an aqueous solution of sodium hydrogen sulfite (concentration: 0.1% by mass) in 823 g of deionized water. The aqueous medium thus prepared was poured into the styrene-based solution in the autoclave (feeding step). Note that the stirring blade of the autoclave was kept stationary while the aqueous medium was being fed into the styrene-based solution.

[0079] After the aqueous medium was added, the rotation speed of the stirring blade was changed to 200 rpm, and the mixture was stirred for 5 minutes, and the inside of the autoclave was replaced with nitrogen. Then, the rotation speed of the stirring blade was changed to 400 rpm, and the styrene-based solution was suspended in the aqueous medium to prepare a suspension (stirring step). Then, the styrene-based solution in the suspension was polymerized in two steps, a first-stage polymerization step and a second-stage polymerization step (polymerization step). In the first-stage polymerization step, the temperature inside the autoclave was first raised from 40°C to 90°C over 75 minutes. After the temperature inside the autoclave reached 90°C, the temperature inside the autoclave was further raised to 100°C over 5 hours, and the first-stage polymerization step was completed.

[0080] After the first polymerization step was completed, the second polymerization step was carried out successively. In the second polymerization step, the temperature in the autoclave was raised to 120°C over 2 hours. The temperature of 120°C was then maintained for 5 hours to complete the second polymerization step. After the second polymerization step was completed, the temperature in the autoclave was cooled to 25°C over 4 hours.

[0081] In this example, the blowing agent impregnation step was performed halfway through the first polymerization step. More specifically, while the temperature inside the autoclave was being raised from 90°C to 100°C, more specifically, when 4.5 hours had elapsed since the temperature inside the autoclave reached 90°C, the blowing agent was started to be supplied into the autoclave, and the blowing agent was supplied over 30 minutes. As the blowing agent, 25.3 g of pentane (a mixture of 80% normal pentane and 20% isopentane) and 33.4 g of butane (a mixture of about 70% by mass of normal butane and about 30% by mass of isobutane) were used in combination. After the addition of the blowing agent was completed, the rotation speed of the stirring blade was changed from 400 rpm to 300 rpm.

[0082] In this manner, the expandable resin particles of Example 1 were obtained.

[0083] Example 2 The method for producing expandable resin particles in Example 2 was the same as that for producing expandable resin particles in Example 1, except that the blending ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 1.

[0084] Example 3 The method for producing expandable resin particles in Example 3 is the same as that for producing expandable resin particles in Example 1, except that the blending ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 1, and the amount of sodium α-olefin sulfonate added was changed to 0.050 g.

[0085] Comparative Example 1 In Comparative Example 1, a styrene-based solution containing recycled polystyrene was prepared in a preparation vessel, and then the styrene-based solution transferred from the preparation vessel was added to the aqueous medium in the reaction vessel to prepare a suspension. Specifically, 500.3 g of styrene as a styrene-based monomer, 66.7 g of recycled polystyrene, 0.67 g of a bubble adjuster, 13.3 g of a plasticizer, and a polymerization initiator were first placed in the preparation vessel. The contents of the preparation vessel were then stirred for 30 minutes to dissolve the recycled polystyrene in the styrene, thereby preparing a styrene-based solution. The recycled polystyrene, bubble adjuster, polymerization initiator, and plasticizer used in this example were the same as those in Example 1.

[0086] In addition, in parallel with the preparation of the styrene-based solution, an aqueous medium was prepared in an autoclave as a reaction vessel by the same method as in Example 1. Thereafter, the stirring blade of the autoclave was rotated at a rotation speed of 400 rpm, and the styrene-based solution in the preparation vessel was poured into the aqueous medium while stirring the aqueous medium. After the pouring of the styrene-based solution into the aqueous medium was completed, 100 g of styrene was poured into the preparation vessel, and the preparation vessel and the transfer path from the preparation vessel to the reaction vessel were washed. Then, the washing liquid thus obtained was poured into the aqueous medium in the autoclave, to prepare a suspension in the autoclave. The rest is the same as in the method for producing expandable resin particles in Example 1. The blending amount of styrene described in Comparative Example 1 in Table 1 is the sum of the blending amount of styrene used in the preparation of the styrene-based solution and the amount of styrene used for washing. In addition, in the "Feeding Order" column in Table 1, the method of pouring the aqueous medium into the styrene-based solution was described as "Step A", and the method of pouring the styrene-based solution and the washing liquid into the aqueous medium was described as "Step B".

[0087] Comparative Example 2 The method for producing expandable resin particles in Comparative Example 2 is the same as that for producing expandable resin particles in Comparative Example 1, except that the amount of styrene used in preparing the styrene-based solution was changed to 533.7 g, and the amount of recycled polystyrene was changed to 33.3 g.

[0088] Comparative Example 3 The method for producing expandable resin particles in Comparative Example 3 was the same as that in Example 1, except that the blending ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 1.

[0089] Example 4 An autoclave with an internal volume of 3 L equipped with an agitator was used as a reaction vessel, and 532.0 g of styrene as a styrene monomer, 228 g of recycled polystyrene, 0.38 g of a cell regulator, a plasticizer, and a polymerization initiator were placed in the autoclave. The contents of the autoclave were heated to a temperature of 40° C., and the stirring blade was rotated at a rotation speed of 400 rpm to stir for 30 minutes, and the recycled polystyrene was dissolved in the styrene to prepare a styrene-based solution. The blending ratio of styrene and recycled polystyrene in the styrene-based solution is as shown in Table 2. Note that polyethylene wax (Polywax1000-80M manufactured by Baker Petrolite) was used as the cell regulator. As the polymerization initiator, 1.64 g of benzoyl peroxide ("Niper BW" manufactured by NOF Corporation) and 0.66 g of t-butylperoxy 2-ethylhexyl monocarbonate ("Perbutyl E" manufactured by NOF Corporation) were used in combination. As a plasticizer, 6.1 g of liquid paraffin ("RCM-S" manufactured by Sanko Chemical Industry Co., Ltd.) and 11.4 g of cyclohexane were used in combination.

[0090] Separately from the preparation of the styrene-based solution, an aqueous medium was prepared by dissolving 13.0 g of a slurry of tribasic calcium phosphate (tribasic calcium phosphate content: 20.5% by mass), 0.0285 g of sodium α-olefin sulfonate ("Lipolan LB-440" manufactured by Lion Corporation), 0.0095 g of disodium alkylbiphenyl disulfonate ("Pelex SSH" manufactured by Kao Corporation) and 1.14 g of sodium acetate in 823 g of deionized water. The aqueous medium thus prepared was poured into the styrene-based solution in the autoclave (feeding step). Note that the stirring blade of the autoclave was kept stationary while the aqueous medium was being fed into the styrene-based solution.

[0091] After the aqueous medium was added, the rotation speed of the stirring blade was changed to 200 rpm, and the mixture was stirred for 5 minutes, and the inside of the autoclave was replaced with nitrogen. Then, the rotation speed of the stirring blade was changed to 400 rpm, and the styrene-based solution was suspended in the aqueous medium to prepare a suspension (stirring step). Next, the styrene-based solution in the suspension was polymerized in two steps, a first-stage polymerization step and a second-stage polymerization step (polymerization step). In the first-stage polymerization step, the temperature inside the autoclave was first raised from 40°C to 90°C over 75 minutes. At this time, when the temperature inside the autoclave reached 60°C, 38g of an aqueous potassium persulfate solution (concentration 0.01% by mass) was added to the autoclave by a pump. After the temperature inside the autoclave reached 90°C, the temperature inside the autoclave was further raised to 100°C over 5 hours, and the first-stage polymerization step was completed.

[0092] After the first polymerization step was completed, the second polymerization step was carried out successively. In the second polymerization step, the temperature in the autoclave was raised to 120°C over 2 hours. The temperature of 120°C was then maintained for 4 hours to complete the second polymerization step. After the second polymerization step was completed, the temperature in the autoclave was cooled to 25°C over 4 hours.

[0093] In this example, the blowing agent impregnation step was performed halfway through the first-stage polymerization step. More specifically, while the temperature inside the autoclave was being raised from 90°C to 100°C, more specifically, when 3 hours had elapsed since the temperature inside the autoclave reached 90°C, the blowing agent was started to be supplied into the autoclave, and the blowing agent was supplied over 30 minutes. As the blowing agent, 64.6 g of butane (a mixture of about 70% by mass of normal butane and about 30% by mass of isobutane) was used. After the addition of the blowing agent was completed, the rotation speed of the stirring blade was changed from 400 rpm to 300 rpm.

[0094] In this manner, the expandable resin particles of Example 4 were obtained.

[0095] (Examples 5 to 6) The manufacturing method of the expandable resin particles in these examples is generally the same as that of Example 4, except that the mixing ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 2, and the amount of polymerization initiator added and the timing of adding the blowing agent were adjusted.

[0096] Example 7 The method for producing the expandable resin particles in Example 7 was generally similar to that for producing the expandable resin particles in Example 4, except that recycled polystyrene having the weight average molecular weight shown in Table 2 was used, the blending ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 2, and 5.0 g of brominated styrene-butadiene block copolymer (LANXESS's "Emerald 3000") as a flame retardant and 2.5 g of dicumyl peroxide (NOF Corporation's "Percumyl (registered trademark) D") as a flame retardant assistant were added.

[0097] Example 8 The method for producing the expandable resin particles in Example 8 was generally the same as that for producing the expandable resin particles in Example 6, except that recycled polystyrene having the weight average molecular weight shown in Table 2 was used.

[0098] Example 9 The method for producing the expandable resin particles in Example 9 was to use recycled polystyrene (weight average molecular weight: 23×10 4 The method for producing expandable resin particles is generally the same as in Example 6, except that a styrene-based solution containing styrene and recycled polystyrene was used, and the blending ratio of styrene to recycled polystyrene in the styrene-based solution was changed as shown in Table 2.

[0099] Comparative Example 4 In Comparative Example 4, a styrene-based solution containing recycled polystyrene was prepared in a preparation vessel, and then the styrene-based solution transferred from the preparation vessel was added to the aqueous medium in the reaction vessel to prepare a suspension. Specifically, 418.0 g of styrene as a styrene-based monomer, 228 g of recycled polystyrene, 0.38 g of a bubble adjuster, a plasticizer, and a polymerization initiator were first placed in the preparation vessel. The contents of the preparation vessel were then stirred for 30 minutes to dissolve the recycled polystyrene in the styrene, thereby preparing a styrene-based solution. The recycled polystyrene, bubble adjuster, polymerization initiator, and plasticizer used in this example were the same as those in Example 4.

[0100] In addition, in parallel with the preparation of the styrene-based solution, an aqueous medium was prepared in an autoclave as a reaction vessel by the same method as in Example 4. Then, the stirring blade of the autoclave was rotated at a rotation speed of 400 rpm, and the styrene-based solution in the preparation vessel was poured into the aqueous medium while stirring the aqueous medium. After the pouring of the styrene-based solution into the aqueous medium was completed, 114 g of styrene was poured into the preparation vessel, and the preparation vessel and the transfer path from the preparation vessel to the reaction vessel were washed. Then, the washing liquid thus obtained was poured into the aqueous medium in the autoclave, thereby preparing a suspension in the autoclave. The rest is the same as the manufacturing method of the expandable resin particles in Example 4. The amount of styrene described in Comparative Example 4 in Table 2 is the sum of the amount of styrene used in the preparation of the styrene-based solution and the amount of styrene used for washing.

[0101] Comparative Example 5 The method for producing expandable resin particles in Comparative Example 5 was the same as that in Example 4, except that the blending ratio of styrene and recycled polystyrene in the styrene-based solution was changed as shown in Table 2.

[0102] The properties of the styrene-based solution, the aqueous medium, and the expandable styrene-based resin particles obtained as above are shown in Tables 1 and 2. The properties shown in Tables 1 and 2 were evaluated according to the following methods.

[0103] (Viscosity of styrene-based solution ηs and viscosity of aqueous medium ηw) A rotational rheometer (TA Instruments' "Discovery HR-2") was used to measure the viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium. The measurement geometry used was a coaxial double cylinder geometry (TA Instruments' "HA Aluminum Recessed End Rotor" and "Stainless Steel Standard Concentric Cylinder Cup with Cap") equipped with a Peltier coaxial cylinder temperature system (TA Instruments' "DHR Smart Swap Concentric Cylinder Peltier Jacket").

[0104] The viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium were measured based on JIS Z 8803: 2011. The specific measurement method is as follows.

[0105] First, the temperature of the geometry of the measurement device was set to 40 °C, and 9 mL of a styrene-based solution or aqueous medium as a sample was placed in the geometry. After that, it was waited for 60 seconds until the temperature of the sample reached 40 °C. After the temperature of the sample stabilized at 40 °C, the measurement mode: Flow Ramp mode was selected, and the shear rate was set to 0.1 s -1 From 100s over 180 seconds -1 The viscosity of the sample was measured while increasing the shear rate to 100. The data acquisition interval of the measuring device was set so that 20 or more data points were acquired during an increase in shear rate of one order of magnitude.

[0106] The data thus obtained was input into analysis software ("TRIOS" manufactured by TA Instruments) and analyzed for 50 s. -1 Data at shear rates lower than 50s -1 A straight line analysis was performed based on three or more data points, including both data at shear rates of 50 s and higher, and a linear regression equation was determined. -1The viscosity of the sample at was defined as the viscosity ηs of the styrene-based solution or the viscosity ηw of the aqueous medium. Tables 1 and 2 also show the viscosity ηs of the styrene-based solution and the viscosity ηw of the aqueous medium, as well as the ratio ηs / ηw.

[0107] (Molecular weight of recycled polystyrene) The weight-average molecular weight Mw of the recycled polystyrene was measured by gel permeation chromatography (GPC) using polystyrene as a standard substance. Specifically, the recycled polystyrene was dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1% by mass. The recycled polystyrene in the sample solution was separated according to the difference in molecular weight under separation conditions of eluent: tetrahydrofuran (THF) and THF flow rate: 0.6 ml / min using a column consisting of one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H connected in series, and a chromatogram was obtained. Then, the retention time in the chromatogram was converted to molecular weight using a calibration curve created using standard polystyrene, and a differential molecular weight distribution curve was obtained. The weight-average molecular weight Mw of the measurement sample was calculated from this differential molecular weight distribution curve. The chromatogram was obtained using HLC-8320GPC EcoSEC manufactured by Tosoh Corporation.

[0108] (Content of volatile organic compounds in recycled polystyrene) First, about 1 g of recycled polystyrene was weighed as a sample. The sample was heated and dried using a dryer at 120°C for 4 hours, then transferred to a desiccator and allowed to cool for 30 minutes or more. The sample was then weighed. The total volatile content in the sample was calculated based on the following formula (1) using the mass W1 (unit: g) of the sample before drying and the mass W2 (unit: g) of the sample after drying obtained above. Total volatile matter = 100 × (W1 - W2) / W1 (1)

[0109] In addition to the recycled polystyrene used in the measurement of the total volatile content, about 1 g of the recycled polystyrene was precisely weighed as a sample. This sample was placed in a moisture vaporizer (e.g., "CHK-501" manufactured by Kyoto Electronics Manufacturing Co., Ltd.), and the moisture vaporized in the moisture vaporizer was introduced into a Karl Fischer moisture meter (e.g., "MKC-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) to measure the moisture content (unit: mass%) in the sample.

[0110] The total volatile matter content (unit: mass%) in the sample thus obtained minus the moisture content (unit: mass%) was taken as the content of volatile organic components in the sample (unit: mass%). The above operation was carried out twice, and the arithmetic average value of the contents of volatile organic components in the two measurements was taken as the content of volatile organic components in the recycled polystyrene.

[0111] (Particle diameter of expandable resin particles) Using a particle size distribution measuring device ("Militrack JPA" manufactured by Nikkiso Co., Ltd.), the particle size distribution of the expandable resin particles on a volume basis was measured. Specifically, 30 g of expandable resin particles were allowed to fall freely from the sample supply feeder of the measuring device, and the projected image was captured by a CCD camera. Next, calculation and combination processing was performed sequentially on the captured image information, and the particle size distribution was measured under the conditions of an image analysis method that outputs the particle size distribution and shape index results. Based on this particle size distribution, the cumulative 10% particle size (i.e., d10), median size (i.e., d50), and cumulative 90% particle size (i.e., d90) were calculated. In addition, Tables 1 and 2 show the value obtained by dividing the difference between the cumulative 90% particle size and the cumulative 10% particle size by the median size (i.e., (d90-d10) / d50). The value of (d90-d10) / d50 indicates the degree of variation in particle size, and a smaller value of (d90-d10) / d50 means a smaller variation in particle size.

[0112] ·Internal moisture content The amount of moisture contained inside the expandable styrene resin particles was measured using a Karl Fischer moisture meter. Specifically, after removing the water adhering to the surface of the expandable styrene resin particles, about 0.28 g of the expandable styrene resin particles was precisely weighed to prepare a sample. The moisture in the sample was vaporized by heating the sample at a temperature of 160° C. using a moisture vaporizer (Kyoto Electronics Manufacturing Co., Ltd.'s "CHK-501"), and the vaporized moisture was introduced into a Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd.'s "MKC-610") to measure the amount of moisture contained inside the expandable resin particles. The amount of moisture was measured by coulometric titration.

[0113] (Molecular weight of expandable resin particles) The number average molecular weight Mn, weight average molecular weight Mw, and z-average molecular weight Mz of the styrene resin constituting the expandable resin particles were measured by gel permeation chromatography (GPC) using polystyrene as the standard substance. The method for measuring the molecular weight of the styrene resin was the same as the method for measuring the molecular weight of the recycled polystyrene described above, except that expandable resin particles were used instead of recycled polystyrene.

[0114] [Table 1]

[0115] [Table 2]

[0116] As shown in Table 1, in the manufacturing method of the expandable resin particles of Examples 1 to 3, an aqueous medium is introduced into the styrene-based solution in the introducing step. In addition, the viscosity ratio ηs / ηw of the styrene-based solution and the aqueous medium used in the introducing step is within the above-mentioned specific range. Therefore, the expandable resin particles obtained by these manufacturing methods could suppress the increase in the variation in particle size.

[0117] On the other hand, in the manufacturing methods of expandable resin particles in Comparative Examples 1 and 2, the styrene-based solution was added to the aqueous medium in the adding step, so that the particle size of the expandable resin particles varied widely.

[0118] In the manufacturing method of expandable resin particles of Comparative Example 3, the viscosity ratio ηs / ηw of the styrene solution and the aqueous medium used in the adding step was larger than the specific range, so the particle size variation of the expandable resin particles increased. In addition, it was difficult to control the particle size by the amount of the suspending agent added, and expandable resin particles having the desired particle size could not be obtained.

[0119] Moreover, as shown in Table 2, the expandable resin particles of Examples 4 to 8 have a larger median diameter than the expandable resin particles of Examples 1 to 3. However, in the manufacturing methods of expandable resin particles of Examples 4 to 8, an aqueous medium is introduced into the styrene-based solution in the introducing step, as in Examples 1 to 3. In addition, the viscosity ratio ηs / ηw of the styrene-based solution and the aqueous medium used in the introducing step is within the above-mentioned specific range. Therefore, the manufacturing methods of expandable resin particles of Examples 4 to 8 were able to suppress an increase in the variation in particle diameter of the expandable resin particles, as in Examples 1 to 3.

[0120] On the other hand, in the manufacturing method of expandable resin particles in Comparative Example 4, the styrene-based solution was introduced into the aqueous medium in the introducing step, so that the particle size of the expandable resin particles varied widely.

[0121] In the manufacturing method of expandable resin particles of Comparative Example 5, the viscosity ratio ηs / ηw of the styrene-based solution and the aqueous medium used in the adding step was larger than the specific range, so the particle size variation of the expandable resin particles increased. In addition, it was difficult to control the particle size by the amount of the suspending agent added, and expandable resin particles having the desired particle size could not be obtained.

[0122] The above describes the aspects of the method for producing expandable styrene-based resin particles according to the present invention based on the examples. However, the specific aspects of the method for producing expandable styrene-based resin particles according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not depart from the spirit of the present invention.

Claims

1. A step of introducing an aqueous medium into a styrene-based solution in which recycled polystyrene is dissolved in a styrene-based monomer in a reaction vessel; a polymerization step of obtaining styrene-based resin particles by performing suspension polymerization of the styrene-based solution while stirring the content of the reaction vessel; and a blowing agent impregnation step of impregnating the styrene-based resin particles with a blowing agent during and / or after completion of the polymerization step to obtain expandable styrene-based resin particles, The styrene-based solution is introduced into the reaction vessel in the introduction step at a temperature of 40° C. and a shear rate of 50 s -1 The viscosity ηs of the aqueous medium at a temperature of 40° C. and a shear rate of 50 s -1 a ratio ηs / ηw of the viscosity ηw to the viscosity ηs at 1 or more and 2,000 or less.

2. 2. The method for producing expandable styrene-based resin particles according to claim 1, wherein the amount of the recycled polystyrene in the styrene-based solution is 1 part by mass or more and 35 parts by mass or less per 100 parts by mass of the total of the styrene-based monomer and the recycled polystyrene.

3. The method for producing expandable styrene-based resin particles according to claim 1 or 2, wherein the recycled polystyrene has a weight average molecular weight of 150,000 or more and 300,000 or less.

4. 3. The method for producing expandable styrene-based resin particles according to claim 1 or 2, wherein the recycled polystyrene is a styrene-based polymer derived from one or more styrene-based articles selected from the group consisting of styrene-based resin particles, expandable styrene-based resin particles, styrene-based resin expanded particles, styrene-based resin expanded bead moldings, and scraps of styrene-based resin expanded bead moldings generated during the production process of expandable styrene-based resin particles.

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