Method for producing recycled foamable polystyrene resin particles, method for producing recycled polystyrene resin foam particles, and method for producing recycled polystyrene resin foam molded articles

Abstract

This invention provides a method for producing recycled foamed polystyrene resin particles with stable processing performance. [Solution] A manufacturing method comprising: (1) impregnating polystyrene resin particles obtained by polymerization of a predetermined seed resin and a styrene monomer with a foaming agent to produce regenerated foamable polystyrene resin particles; and (2) measuring the melt flow rate (MFR) of the heated volume reduction before polymerization, wherein (3) includes a step of determining polymerization conditions based on the MFR.

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled foamable polystyrene resin particles, a method for producing recycled polystyrene resin foam particles, and a method for producing recycled polystyrene resin foam molded articles. [Background technology]

[0002] Polystyrene foam molded products are lightweight and have excellent heat insulation and mechanical strength, making them widely used in various applications such as insulation materials, embankment materials, transport packaging materials, and cushioning materials.

[0003] In recent years, from the perspective of environmental considerations, a technology has been developed to recover discarded polystyrene foam molded articles and recycle them to obtain recycled foamable polystyrene resin particles (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-320406 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the conventional technologies described above were insufficient in terms of the processing performance (foaming performance) of recycled foamable polystyrene resin particles, and there was room for further improvement.

[0006] Therefore, the object of one embodiment of the present invention is to provide a novel method for producing recycled foamed polystyrene resin particles that can provide recycled foamed polystyrene resin particles having stable processing performance. [Means for solving the problem]

[0007] The inventors diligently investigated methods for producing recycled foamable polystyrene resin particles with stable processing performance. As a result, they found that recycled foamable polystyrene resin particles can be produced by a method that includes measuring the melt flow rate of the heated volume reduction product of a recovered foamed polystyrene resin molded product, and determining the polymerization conditions for polymerization between the seed resin and the styrene monomer based on the melt flow rate.

[0008] Furthermore, the inventors have also found that the recycled foamable polystyrene resin particles can be produced by a method that includes a control step of measuring the melt flow rate of the heated volume-reduced product and performing one or more of the following based on the melt flow rate: adjusting the blending ratio of the virgin polystyrene resin, selecting the melt flow rate of the virgin polystyrene resin, and selecting the weight-average molecular weight of the virgin polystyrene resin.

[0009] In other words, one embodiment of the present invention includes the following configuration.

[0010] (1) A step (1) in which a seed resin containing the heat-reduced volume of a recovered polystyrene foam molded product is polymerized with a styrene monomer, and the resulting polystyrene resin particles are impregnated with a foaming agent to produce recycled foamable polystyrene resin particles, Prior to the polymerization, a measurement step is taken to measure the melt flow rate of the heated volume-reduced product, Includes, The method for producing recycled foamable polystyrene resin particles, comprising the step (1) of determining the polymerization conditions for polymerizing the seed resin and the styrene monomer based on the melt flow rate obtained in the measurement step.

[0011] [2] A step (A) of mixing the heated volume reduction product of the recovered polystyrene foam molded product with virgin polystyrene resin, Step (B) involves impregnating the mixture obtained in step (A) with a foaming agent to produce recycled foamable polystyrene resin particles. Before obtaining the aforementioned mixture, a measurement step is taken to measure the melt flow rate of the heated volume reduction product, Includes, The method for producing recycled foamable polystyrene resin particles includes a control step in which one or more of the following are selected from the group consisting of (X), (Y), and (Z) based on the melt flow rate obtained in the measurement step: (X) Adjustment of the blending ratio of the virgin polystyrene resin to be mixed in step (A) above; (Y) Selection of the melt flow rate of the virgin polystyrene resin to be mixed in step (A); (Z) Selection of the weight-average molecular weight of the virgin polystyrene resin to be mixed in step (A) above.

[0012] [3] A method for producing recycled foamable polystyrene resin particles according to [1] or [2], comprising the step of confirming the concentration of environmentally hazardous substances regulated by the RoHS Directive in the heated volume-reduced product by fluorescent X-ray analysis.

[0013] [4] A method for producing recycled foamable polystyrene resin particles according to [1], further comprising a heating volume reduction step of heating and reducing the volume of the recovered polystyrene resin foam molded product prior to step (1).

[0014] [5] A method for producing recycled foamable polystyrene resin particles according to [2], comprising a heating volume reduction step of heating and reducing the volume of the recovered polystyrene resin foam molded product prior to step (A).

[0015] [6] A method for producing recycled foamable polystyrene resin particles according to [4] or [5], comprising a recovery step prior to the heating volume reduction step, wherein the foamed polystyrene resin molded body is recovered and used as the recovered product.

[0016] A method for producing recycled foamed polystyrene resin particles, comprising the step of foaming the recycled foamed polystyrene resin particles produced by the method for producing recycled foamed polystyrene resin particles described in [7], [1], or [2].

[0017] A method for manufacturing a recycled polystyrene-based resin foamed molded body, which includes a step of molding the recycled polystyrene-based resin foamed particles produced by the method for manufacturing recycled polystyrene-based resin foamed particles described in [8][7].

Advantages of the Invention

[0018] According to one embodiment of the present invention, there is an effect that a novel manufacturing method of recycled foaming polystyrene-based resin particles can be provided, which can provide recycled foaming polystyrene-based resin particles having stable processing performance.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing an example of a flow for manufacturing recycled foaming polystyrene-based resin particles in Embodiment 1 of the present invention, and further manufacturing recycled polystyrene-based resin foamed particles and a recycled polystyrene-based resin foamed molded body. [Figure 2] It is a diagram showing an example of a flow for manufacturing recycled foaming polystyrene-based resin particles in Embodiment 2 of the present invention, and further manufacturing recycled polystyrene-based resin foamed particles and a recycled polystyrene-based resin foamed molded body. [Figure 3] It is a diagram showing an example of a flow of Embodiment 1 including a step of checking the concentration of environmentally harmful substances.

Modes for Carrying Out the Invention

[0020] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the 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. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)." Furthermore, "mass" and "weight," "parts of mass" and "parts of weight," and "mass%" and "weight%" are treated as synonyms herein.

[0021] In this specification, "X unit" in a polymer, copolymer, or resin means "a constituent unit derived from an X monomer." For example, "styrene-based unit" means "a constituent unit derived from a styrene-based monomer."

[0022] In this specification, "X-type resin" and "X-type polymer" refer to the resin and polymer, respectively, in which the X-type unit content is the highest among all constituent units of the resin and polymer.

[0023] In this specification, "a method for producing recycled foamable polystyrene resin particles according to one embodiment of the present invention" may also be referred to as "this manufacturing method." Furthermore, "recycled foamable polystyrene resin particles" may also be referred to as "foamed resin particles," "recycled polystyrene resin foamed particles" may also be referred to as "foamed particles," and "recycled polystyrene resin foamed molded articles" may also be referred to as "foamed molded articles."

[0024] [Technical concept of one embodiment of the present invention] In recent years, the use of polystyrene foam molded products has increased. Consequently, the collection and processing of used polystyrene foam molded products has become a challenge. Conventional methods for reusing collected used polystyrene foam molded products can be broadly categorized into the following three methods: (1) to (3): (1) Method of reuse as a raw material for polystyrene resin (material recycling), (2) A method of grinding and reusing as a powder (material recycling), (3) A method of reuse as fuel (thermal recycling).

[0025] Among these methods, there is growing demand for the method described in (1) above, namely, the method of reusing waste from polystyrene foam molded products as raw materials for plastic components in products, from the perspective of resource recycling and reducing environmental impact.

[0026] For example, Patent Document 1 discloses a method for producing expandable polystyrene resin particles again using recovered polystyrene resin foam molded articles as raw materials.

[0027] However, conventional methods did not yield satisfactory recycled foamed polystyrene resin particles in terms of processing performance, such as foaming performance. For example, conventional methods sometimes yielded recycled foamed polystyrene resin particles with inferior processing performance, such as foaming performance. When using recycled foamed polystyrene resin particles with inferior processing performance to further manufacture polystyrene resin foam particles and polystyrene resin foam molded articles, there were concerns that this would lead to instability in the molding process. Furthermore, when using recycled foamed polystyrene resin particles with inferior processing performance to manufacture polystyrene resin foam molded articles, there were concerns that this would lead to instability in the quality (such as thermal insulation and cushioning performance) of the resulting polystyrene resin foam molded articles.

[0028] Polystyrene foam molded products are used in a variety of applications, including (i) molded products and block molded products made of expanded polystyrene, (ii) trays, (iii) foam sheets for bowl-shaped containers, (iv) packaging materials, (v) home appliances, and (vi) cushion beads. The required physical properties of polystyrene foam molded products differ depending on the application, and therefore, polystyrene resins with various physical properties can be used as raw materials depending on the application. Consequently, the resin obtained by heating and reducing the volume of recovered polystyrene foam molded products can also be polystyrene resins with various physical properties, and may even be an aggregate of polystyrene resins with various physical properties. Furthermore, the recovered polystyrene foam molded products themselves may have already been recycled multiple times, for example, through the material recycling described above. Therefore, the resin obtained by heating and reducing the volume of recovered polystyrene foam molded products may also be a resin that has already been recycled multiple times.

[0029] The inventors hypothesized that when the volume of recovered polystyrene foam molded products is reduced by heating, recycled foamable polystyrene resin particles may be obtained that have inferior processing performance, such as foaming performance, due to the fact that the resin obtained is a polystyrene resin with various physical properties and / or a resin that has already been recycled multiple times.

[0030] Therefore, the inventors conducted further intensive research with the aim of providing a novel method for producing recycled foamed polystyrene resin particles that can provide recycled foamed polystyrene resin particles with stable processing performance. As a result, the inventors independently discovered the following novel findings and completed the present invention: (1) Regarding the heated volume reduction product of recovered polystyrene foam molded articles, it has been discovered that, surprisingly, recycled foamable polystyrene resin particles with stable processing performance can be produced by a method that includes measuring at least the melt flow rate among various physical properties, and determining the polymerization conditions for polymerization between the seed resin and the styrene monomer based on the melt flow rate. (2) The discovery that, surprisingly, recycled foamable polystyrene resin particles with stable processing performance can be produced by a method that includes measuring the melt flow rate of the heated volume-reduced product among various physical properties, and performing one or more of the following steps selected from the group consisting of adjusting the blending ratio of virgin polystyrene resin, selecting the melt flow rate of the virgin polystyrene resin, and selecting the weight-average molecular weight of the virgin polystyrene resin, based on the melt flow rate.

[0031] [1] Embodiment 1 A method for producing recycled foamable polystyrene resin particles according to Embodiment 1 of the present invention includes a step (1) of polymerizing a seed resin containing heated volume reduction material of a recovered polystyrene resin foam molded product with a styrene monomer, impregnating the resulting polystyrene resin particles with a foaming agent to produce recycled foamable polystyrene resin particles, and a measurement step of measuring the melt flow rate of the heated volume reduction material before the polymerization, wherein step (1) includes a step of determining the polymerization conditions for polymerizing the seed resin and the styrene monomer based on the melt flow rate obtained in the measurement step.

[0032] According to this manufacturing method, recycled foamable polystyrene resin particles with stable processing performance can be obtained from recovered polystyrene resin foam molded products. Furthermore, by foaming and molding these recycled foamable polystyrene resin particles, recycled polystyrene resin foam molded products with stable quality can be obtained.

[0033] (1) Process (1) Step (1) of this manufacturing method will now be explained. Step (1) is a process in which a seed resin containing the heated volume reduction product of a recovered polystyrene foam molded product is polymerized with a styrene monomer, and the resulting polystyrene resin particles are impregnated with a foaming agent to produce recycled foamable polystyrene resin particles.

[0034] (1-1) Volume reduction due to heating of recovered polystyrene foam molded products A "polystyrene foam molded article" refers to a molded article obtained by filling a mold with polystyrene foam particles, which are formed by foaming polystyrene foam particles, and molding the polystyrene foam particles.

[0035] "Recovered polystyrene foam molded products" means recycled polystyrene foam molded products. The recycled products refer to (a) resin products that have been used and / or discarded after being in the form of resin products (e.g., food transport containers, casting scraps, food cushioning materials, etc.), and (b) waste generated during the manufacturing process of resin products. However, not all of the recovered products need to fall under (a) and / or (b), and may be a mixture of those falling under (a) and / or (b) and non-recovered (non-recycled) polystyrene foam molded products.

[0036] The resin component constituting the polystyrene-based resin foam molded article contains the most polystyrene-based resin among the resin components compared to other resins. The amount of polystyrene-based resin contained in the resin component constituting the polystyrene-based resin foam molded article is preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, more preferably 90% by weight or more, and particularly preferably 100% by weight, based on 100% by weight of the total amount of resin components. Furthermore, "polystyrene-based resin" refers to a resin in which the content of styrene-derived constituent units (styrene units) is the highest among all constituent units of the resin.

[0037] More specifically, polystyrene resins include (i) homopolymers of styrene monomers, and (ii) copolymers comprising a styrene monomer and another monomer polymerizable with the styrene monomer. Examples of (ii) include one or more resins selected from the group consisting of AS resin, ABS resin, and HIPS resin.

[0038] The styrene monomer may be a single type or a combination of two or more types. The styrene monomer is a monomer containing at least styrene, may contain a styrene derivative, or may consist only of styrene. Examples of styrene derivatives include one or more derivatives selected from the group consisting of α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene.

[0039] The styrene content relative to the total amount of the styrene monomer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0040] Here, examples of other monomers polymerizable with styrene monomers include polyfunctional monomers. The polyfunctional monomer may be used alone or in combination of two or more.

[0041] The ratio of polyfunctional monomers to styrene monomers is preferably 0.001% to 0.049% by mass, more preferably 0.003% to 0.040% by mass, and even more preferably 0.007% to 0.035% by mass, when the total mass of styrene monomers and polyfunctional monomers is taken as 100% by mass.

[0042] Specific examples of polyfunctional monomers include, for example, divinylbenzene (including various isomers); alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; (meth)acrylic acid ester compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and hexyl (meth)acrylate; maleic acid ester monomers such as dimethyl maleate; and fumarate ester monomers such as dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

[0043] Among the polyfunctional monomers, divinylbenzene is preferred because it can better exhibit the effects of the present invention.

[0044] The term "heat-reduced volume material" refers to the recovered material whose volume has been reduced by heating, crushing, and compressing. The heat-reduced volume material can be obtained, for example, by subjecting the recovered material to a volume reduction machine, crushing and compressing it, then heating and melting it, and extruding it to form an ingot. Alternatively, the heat-reduced volume material may be, for example, the recovered material, or a commercially available product in which a mixture of the recovered material and the non-recovered material has been preheated and reduced in volume.

[0045] The heated volume-reduced material may be pelletized. The method for pelletizing the heated volume-reduced material is not particularly limited. For example, methods include: crushing the ingot with a crusher, feeding the crushed material through an extruder to extrude it, and cutting the resulting strands; feeding the crushed material through an extruder to extrude it and cutting it in water at the same time; and feeding the crushed material through an extruder and cutting it immediately after the extruded material comes out of the extruder's die. As the crusher, for example, a crusher for plastics can be used, and a crusher for polystyrene is preferred.

[0046] The aforementioned heated volume-reduced material is preferably subjected to thermal melting in order to adjust its specific gravity. This thermal melting can be carried out, for example, by melting the heated volume-reduced material using an extruder or a hot roll.

[0047] In the thermal melting of the heated volume-reduced material, it is preferable to cool and solidify the molten resin so that no distortion occurs in the resulting resin, or if distortion occurs, it is very small. As for the thermal melting method, it is preferable to perform non-stretch melting using an extruder from the viewpoint of reducing the distortion remaining in the resulting resin. By reducing the distortion of the resin, it is possible to prevent flattening of the regenerated foamable polystyrene resin particles obtained at the end and make them easier to form into a spherical shape. Non-stretch melting can reduce the distortion remaining in the resin after cooling and solidification compared to thermal melting in a stretched state. If distortion remains in the resin obtained after thermal melting, the distortion of the resin can be alleviated (reduced) by curing (leaving) the resin at a temperature above the softening point of the resin for a certain period of time. When pelletizing the heated volume-reduced material, it is preferable to perform the thermal melting before preparing the pellets.

[0048] The aforementioned thermal melting adjusts the specific gravity of the heated volume-reduced material to preferably 0.6 or higher, and more preferably to 0.9 or higher. The fact that the specific gravity has been adjusted to the desired value can be confirmed by a pycnometer method applying Archimedes' principle.

[0049] The weight-average molecular weight of the heat-reduced volume is preferably 160,000 to 350,000, more preferably 180,000 to 300,000, and even more preferably 190,000 to 270,000. Having a weight-average molecular weight within this range allows for sufficient strength to be imparted to the recycled foamable polystyrene resin particles, facilitates the formation of spherical particles, and improves foamability.

[0050] The pellets obtained by pelletizing the heated volume-reduced material have an average particle diameter preferably of 0.2 mm to 2.0 mm, more preferably of 0.3 mm to 1.5 mm, even more preferably of 0.4 mm to 1.2 mm, and particularly preferably of 0.5 mm to 1.0 mm. The average particle diameter can be adjusted to these ranges, for example, by adjusting the cutting position when cutting the strands. The average particle diameter is the value measured as the particle size at 50% of the cumulative value from the particle size distribution obtained by the sieving test according to JIS Z 8815.

[0051] When the average particle size of the pellets is within the aforementioned range, the recycled foamed polystyrene resin particles can be easily formed into a spherical shape, and the particle size can be made to an appropriate size.

[0052] The ratio of the length of the long side to the length of the short side (L / D) of the pellet is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and even more preferably 1.0 to 2.5. Having an L / D within this range makes it easier to form the recycled foamed polystyrene resin particles into a spherical shape. The L / D can be adjusted to these ranges, for example, by adjusting the cutting position when cutting the strands.

[0053] The pellets may be further crushed to obtain a pulverized material. This pulverized material can be obtained, for example, by feeding the pellets into the pulverizer described above. The particle size of the pulverized material is not particularly limited.

[0054] (1-2) Polymerization process In step (1), polymerization is carried out between the seed resin containing the heat-reduced volume product and the styrene monomer (polymerization step). The polymerization operation in the polymerization step involves adding the styrene monomer and a polymerization initiator to the seed resin and polymerizing the seed resin and the styrene monomer for a predetermined time.

[0055] (1-2-1) Seed resin The seed resin includes the heat-reduced volume product. The seed resin may consist solely of the heat-reduced volume product. For example, one or more selected from the group consisting of the heat-reduced volume product, the pulverized heat-reduced volume product, the pellets of the heat-reduced volume product, and the pulverized pellets of the heat-reduced volume product may be used as the seed resin.

[0056] The polymerization in step (1) can also be described as a step in which a styrene monomer is polymerized onto the seed resin. Therefore, the polymerization step can also be called a seed polymerization step.

[0057] The aforementioned seed resin contains the heat-reduced volume product of recovered polystyrene-based resin foam molded products, and therefore contains polystyrene-based resin as a resin component. The polystyrene-based resin is as described in (1-1) above.

[0058] The amount of polystyrene resin contained in the resin component constituting the aforementioned type resin is preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, more preferably 90% by weight or more, and particularly preferably 100% by weight or more, based on 100% by weight of the total amount of resin component.

[0059] The content ratio of the seed resin to the total amount of the seed resin and the styrene monomer is preferably 15% to 85% by mass, more preferably 20% to 80% by mass, and even more preferably 25% to 75% by mass. By having the content ratio within the above range, the moldability of the recycled foamed polystyrene resin particles can be improved, and the recycling rate of the recovered product can be increased, thereby improving the contribution to the environment.

[0060] (1-2-2)Aqueous dispersion The polymerization method described above is not particularly limited as long as it can polymerize the seed resin and the styrene monomer. For example, one method involves dispersing the seed resin and any other component in water as a dispersion medium, raising the aqueous dispersion to a predetermined polymerization temperature, then dispersing the styrene monomer and a polymerization initiator in the aqueous dispersion, and reacting the seed resin and the styrene monomer.

[0061] The aqueous dispersion can be prepared by any method. For example, the seed resin and any other components can be dispersed in water using a device equipped with a stirring blade or a homomixer.

[0062] It is preferable to disperse the styrene monomer and polymerization initiator in the aqueous dispersion until the diameter of the oil droplets in the dispersion is less than or equal to the particle diameter of the seed resin. By keeping the oil droplet diameter less than or equal to the particle diameter of the seed resin, the incorporation of multiple polystyrene resin particles derived from the seed resin into the oil droplets of the dispersion containing the styrene monomer is inhibited. Therefore, adhesion, plasticization, and coalescence of the polystyrene resin particles can be avoided, and the generation of excessively large particles can be reduced.

[0063] As for the method of adding a styrene monomer to an aqueous dispersion containing the seed resin to impregnate the seed resin with the styrene monomer, any suitable method can be used as long as it does not impair the effects of the present invention. For example, such methods include partial addition or continuous addition. By using the above method, the weight-average molecular weight can be adjusted relatively easily to the desired level. Furthermore, the addition rate when adding the styrene monomer can be appropriately selected according to the capacity, shape, polymerization temperature, etc. of the polymerization apparatus. After adding the styrene monomer in this way, the polymerization reaction may be continued at any suitable temperature and time as needed.

[0064] The preparation of the aqueous dispersion is preferably carried out in the presence of a dispersant in order to sufficiently disperse the seed resin and any other components in water. Any suitable dispersant can be used as long as it is usable in suspension polymerization and does not impair the effects of the present invention. Examples of such dispersants include organic dispersants such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose; and sparingly soluble inorganic salts such as magnesium pyrophosphate and tricalcium phosphate. Among these, magnesium pyrophosphate is preferred as a dispersant in that it can better express the effects of the present invention.

[0065] From the viewpoint of ensuring smooth polymerization, the amount of dispersant used is preferably 0.1 to 2.0 parts by mass, more preferably 0.1 to 1.5 parts by mass, and even more preferably 0.1 to 1.0 parts by mass, when the mass of the seed resin is 100 parts by mass.

[0066] The preparation of the aqueous dispersion is preferably carried out in the presence of a surfactant in order to sufficiently disperse the seed resin and any other components in water. Any suitable surfactant can be used as long as it does not impair the effects of the present invention. Examples of such surfactants include one or more surfactants selected from the group consisting of calcium dodecylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyl ether disulfonate, and sodium α-olefin sulfonate. Among these, sodium dodecylbenzenesulfonate is preferred as the surfactant in that it can better express the effects of the present invention.

[0067] From the viewpoint of ensuring smooth polymerization, the amount of surfactant used is preferably 0.005 parts by mass to 0.1 parts by mass, more preferably 0.005 parts by mass to 0.08 parts by mass, and even more preferably 0.005 parts by mass to 0.06 parts by mass, when the mass of the seed resin is 100 parts by mass.

[0068] The aqueous dispersion may contain a foam regulator. Examples of foam regulators include fatty acid monoamides such as oleamide, stearamide, and hydroxystearamide; and fatty acid bisamides such as methylenebisstearamide and ethylenebisstearamide.

[0069] The polyfunctional monomer described in (1-1) above may be added to the aqueous dispersion separately from the styrene monomer, or it may be added together with the styrene monomer. When the polyfunctional monomer is added to the aqueous dispersant together with the styrene monomer, typically the polyfunctional monomer is dissolved in the styrene monomer and then added to the aqueous dispersant.

[0070] (1-2-3) Polymerization The polymerization described above is carried out in the presence of a polymerization initiator. Any suitable polymerization initiator can be used as the polymerization initiator, as long as it does not impair the effects of the present invention.

[0071] Examples of polymerization initiators include organic peroxides such as t-butyl peroxy-2-ethylhexanoate, t-butyl peroxybenzoate, benzoyl peroxide, t-butyl peroxy-2-ethylhexyl carbonate, and t-butyl perbenzoate; and azo compounds such as azobisisobutyronitrile. The polymerization initiator may be used alone or in combination of two or more.

[0072] The amount of polymerization initiator used is preferably 0.1% to 1.0% by mass, and more preferably 0.1% to 0.8% by mass, when the total mass of the styrene monomer and the polymerization initiator is taken as 100% by mass.

[0073] The polymerization initiator is preferably added dissolved in a styrene monomer or a solvent. Examples of solvents include aromatic hydrocarbons such as ethylbenzene and toluene; and aliphatic hydrocarbons such as heptane and octane. When using a solvent, the solvent is usually used in an amount of 10% by mass or less, when the total mass of the styrene monomer and the solvent is 100% by mass.

[0074] The polymerization can be promoted by receiving radicals from the growing polymer chain and generating new radicals; therefore, it is preferable to carry out the polymerization in the presence of a chain transfer agent. As the chain transfer agent, one or more selected from the group consisting of octyl mercaptan, dodecyl mercaptan, and α-methylstyrene dimer can be used. The concentration of the chain transfer agent is appropriately determined based on the melt flow rate of the heated volume reduction product, as will be described later.

[0075] When adding the styrene monomer and polymerization initiator to the aqueous dispersion, the temperature of the aqueous dispersion is preferably 40°C to 118°C, more preferably 50°C to 117°C, and even more preferably 60°C to 115°C, in order to better exhibit the effects of the present invention.

[0076] By adjusting the temperature of the aqueous dispersion within these ranges, the styrene monomer can be polymerized onto the seed resin while maintaining the seed resin at an appropriate hardness. This allows the seed resin to be spheroidized well and the polymerization initiator to be sufficiently decomposed. As a result, the resulting recycled foamable styrene resin particles can be spheroidized well, and excellent moldability can be imparted to the recycled foamable styrene resin particles, while preventing the recycled foamable styrene resin particles from sticking together.

[0077] The polymerization conditions for polymerizing the aforementioned seed resin and the styrene monomer are determined based on the melt flow rate obtained in the measurement step described later.

[0078] (1-3) Impregnation process In step (1), the polystyrene resin particles obtained in the polymerization step are impregnated with a foaming agent to produce recycled foamable polystyrene resin particles (impregnation step). The impregnation step can also be described as a step in which foaming properties are impregnated into the polystyrene resin particles by impregnating them with a foaming agent, thereby obtaining recycled foamable polystyrene resin particles.

[0079] (1-3-1) Foaming agent Any suitable blowing agent can be used as the blowing agent, as long as it does not impair the effects of the present invention. Preferably, the blowing agent is an organic compound that has a boiling point below the softening point of the styrene resin and is gaseous or liquid at normal pressure. One blowing agent may be used, or two or more may be used in combination.

[0080] Examples of foaming agents include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane, neopentane), and n-hexane; alicyclic hydrocarbons such as cyclopentane and cyclopentadiene; ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol, and isopropyl alcohol; low-boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; and halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane. Inorganic gases such as carbon dioxide, nitrogen, and ammonia may also be used as foaming agents.

[0081] Among these, the foaming agent is preferably at least one selected from n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, and cyclopentadiene, and more preferably at least one selected from n-butane, isobutane, n-pentane, and isopentane, in order to better exhibit the effects of the present invention.

[0082] The amount of foaming agent impregnating the polystyrene resin particles can be appropriately set according to the purpose, as long as it is a sufficient amount to form recycled foamable polystyrene resin particles and recycled polystyrene resin foam molded articles. The amount of foaming agent is preferably 2 to 15 parts by mass, when the total amount of the heat-reduced volume product and the styrene monomer is 100 parts by mass.

[0083] In the impregnation process, an organic solvent may be used to adjust the foaming rate. Examples of organic solvents include cyclohexane and aromatic hydrocarbons (e.g., toluene, xylene, and ethylbenzene). Cyclohexane can also function as a foaming aid.

[0084] (1-3-2) Impregnation of polystyrene resin particles with foaming agent Recycled foamable polystyrene resin particles are obtained by impregnating the polystyrene resin particles obtained by the polymerization step described in (1-2) with a foaming agent. Examples of methods for impregnating the polystyrene resin particles with a foaming agent include the following methods (i) or (ii).

[0085] (i) A method of placing the polystyrene resin particles and a foaming agent into a reactor such as a pressure vessel and injecting the foaming agent into the polystyrene resin particles under pressure; (ii) A method in which the polystyrene resin particles are subjected to an extruder, melted and kneaded, and then a foaming agent is injected under pressure into the molten polystyrene resin particles.

[0086] However, in this specification, the mode of impregnation is not limited to the mode in which the foaming agent is soaked into the target while applying pressure (pressure infusion), as described in (i) and (ii) above, but may also be a mode in which the foaming agent is soaked into the target without applying pressure.

[0087] When the impregnation process is carried out by injection, it is preferable to inject the foaming agent while the polystyrene resin particles are heated, from the viewpoint of efficiently injecting the foaming agent. In this case, the temperature of the polystyrene resin particles after heating is preferably 40°C to 150°C, more preferably 40°C to 125°C, even more preferably 40°C to 105°C, particularly preferably 40°C to 90°C, and most preferably 40°C to 85°C.

[0088] When the temperature of the polystyrene resin particles after heating is within this range, the blowing agent is injected into the polystyrene resin particles at a relatively low temperature. By injecting the blowing agent at a relatively low temperature in this way and then raising the temperature, rapid impregnation of the blowing agent into the polystyrene resin particles is avoided, and uniform impregnation becomes possible. Therefore, for example, when recycled foamable polystyrene resin particles are molded into a recycled polystyrene resin foam molded body, air bubbles can be generated uniformly within the molded body, the areas of shrinkage on the surface of the molded body can be reduced, and uniform molding can be achieved.

[0089] Even when the impregnation process is carried out by allowing the foaming agent to permeate the target without applying pressure, it is preferable to impregnate the polystyrene resin particles with the foaming agent while the particles are heated. In this case, the temperature of the polystyrene resin particles after heating is preferably 93°C to 130°C, more preferably 94°C to 129°C, even more preferably 95°C to 128°C, particularly preferably 96°C to 127°C, and most preferably 97°C to 126°C.

[0090] When the temperature of the polystyrene resin particles after heating is within these ranges, rapid impregnation of the foaming agent into the polystyrene resin particles is avoided, and uniform impregnation becomes possible. Therefore, for example, when recycled foamable polystyrene resin particles are molded into a recycled polystyrene resin foam molded body, air bubbles can be uniformly generated within the molded body, the areas of shrinkage on the surface of the molded body can be reduced, and uniform molding can be achieved.

[0091] The time required to impregnate the polystyrene resin particles with the foaming agent can be any appropriate time, as long as it does not impair the effects of the present invention. The time is preferably 1 to 10 hours. For example, in the case of (i) above, it is preferable that the time from placing the polystyrene resin particles and the foaming agent into a reactor such as a pressure vessel until removing them is 1 to 10 hours.

[0092] In this way, by impregnating the polystyrene resin particles obtained in the polymerization step (1-2) with a foaming agent, regenerated foamable polystyrene resin particles can be obtained.

[0093] (1-3-3) Other components that may be contained in recycled foamed polystyrene resin particles The recycled foamable polystyrene resin particles may contain any other suitable components, such as one or more components selected from the group consisting of flame retardants, foam regulators, foaming aids, pigments, radiant heat transfer inhibitors, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antistatic agents, weathering agents, anti-aging agents, anti-fogging agents, and fragrances, as long as they do not impair the effects of the present invention.

[0094] These other components can be added, for example, when preparing the aqueous dispersion described in (1-2-2).

[0095] (1-3-4) Surface treatment of recycled foamed polystyrene resin particles The recycled foamable styrene resin particles may be surface-treated with at least one agent selected from the group consisting of silicone oil, antistatic agents, fatty acid metal salts, and fusion accelerators, to the extent that the effects of the present invention are not impaired. The method of surface treatment is not particularly limited, and conventionally known methods can be used.

[0096] (2) Measurement process The measurement step is to measure the melt flow rate of the heated volume-reduced product before polymerization. Step (1) includes determining the polymerization conditions for polymerization between the seed resin and the styrene monomer based on the melt flow rate obtained in the measurement step.

[0097] The melt flow rate of the heated volume-reduced material can be measured at a measurement temperature of 200°C and a test load of 5 kg by a method conforming to JIS K 7210, as shown in the examples described later. The measurement temperature is the temperature of the atmosphere in which the heated volume-reduced material being measured is placed.

[0098] The melt flow rate of the heated volume-reduced material is preferably measured using the pulverized material obtained by crushing the heated volume-reduced material, the pellets formed by extruding the pulverized material, or the pulverized material of the pellets.

[0099] The melt flow rate of the heated volume-reduced product is preferably 2.0 g / 10 min to 28 g / 10 min, more preferably 6.0 g / 10 min to 23 g / 10 min, and even more preferably 10 g / 10 min to 20 g / 10 min. "min" refers to a minute.

[0100] Because the melt flow rate is within these ranges, the fluidity of the heated volume reduction can be maintained appropriately, thereby (i) improving the processing performance and strength of the recycled foamable polystyrene resin particles, and (ii) improving the appearance of the polystyrene resin foam molded article.

[0101] The polymerization conditions are determined based on the melt flow rate of the heated volume reduction. When the melt flow rate of the heated volume reduction is 20 g / 10 min to 28 g / 10 min, the heated volume reduction is in a soft state with low strength due to (i) and / or (ii) below.

[0102] (i) Increased fluidity of the heat-reduced volume product due to the relatively low molecular weight of the polystyrene resin constituting the heat-reduced volume product; (ii) Increased fluidity of the heated volume reduction product due to the reduction in molecular weight of the polystyrene resin caused by the thermal history.

[0103] At this time, the weight-average molecular weight of the resin constituting the heated volume-reduced product decreases, and the heated volume-reduced product is in a state of low strength and softness. Considering this state, it is determined that the polymerization conditions should be such that they can improve the degree of polymerization of the resin in order to make the weight-average molecular weight of the resin a desirable weight-average molecular weight for imparting foaming properties to the resin. Based on this determination, the concentration of the polymerization initiator is set low to reduce the polymerization rate and increase the molecular weight of the resulting resin (polymer). Also, the concentration of the chain transfer agent is set low to reduce the polymerization rate and increase the molecular weight of the resulting resin. This makes it possible to set the concentrations of the polymerization initiator and the chain transfer agent to appropriate concentrations corresponding to the heated volume-reduced product which is in a state of low strength and softness. Here, the setting of the concentrations of the polymerization initiator and the chain transfer agent has been described, but the conditions to be set are not limited to these two. For example, the type of polymerization initiator, the type and amount of polyfunctional monomer, the type, amount, timing and rate of addition of various additives, etc., may be set appropriately based on the above determination.

[0104] At this time, if the polymerization temperature is too low, the decomposition of the polymerization initiator is inhibited, and polymerization does not proceed easily. On the other hand, if the polymerization temperature is too high, the decomposition rate of the polymerization initiator increases, so the polymerization rate increases, the molecular weight of the resulting resin becomes relatively low, and the seed resin becomes softer, so the adhesion of the seed resin increases. For this reason, based on the above determination, the polymerization temperature is set considering the balance with the polymerization time and polymerization rate. Then, by proceeding with polymerization, the melt flow rate of the recycled foamable polystyrene resin particles is adjusted to a range suitable for imparting foaminess (7g / 10min to 18g / 10min).

[0105] On the other hand, if the melt flow rate of the heated volume-reduced material is 2 g / 10 min to 10 g / 10 min, the heated volume-reduced material is in a hard state due to the following reasons (iii) and / or (iv).

[0106] (iii) A decrease in the fluidity of the heat-reduced volume product due to the relatively high molecular weight of the polystyrene resin constituting the heat-reduced volume product; (iv) The effect of thermal history is small, and the decrease in the fluidity of the heated volume reduction product is due to the inhibition of the reduction in molecular weight of the polystyrene resin.

[0107] At this time, the weight-average molecular weight of the resin constituting the heated volume-reduced product is high, and the heated volume-reduced product is strong and hard. Considering these conditions, it is determined that the polymerization conditions should be such that the degree of polymerization of the resin is reduced in order to set the weight-average molecular weight of the resin to a weight-average molecular weight that is desirable for imparting foaming properties to the resin. Based on this determination, the concentration of the polymerization initiator is set high to increase the polymerization rate and reduce the increase in the molecular weight of the resulting resin. In addition, the concentration of the chain transfer agent is set high to increase the polymerization rate and reduce the increase in the molecular weight of the resulting resin. This makes it possible to set the concentrations of the polymerization initiator and the chain transfer agent to appropriate concentrations corresponding to the heated volume-reduced product, which is strong and hard. Here, the setting of the concentrations of the polymerization initiator and the chain transfer agent has been described, but the conditions to be set are not limited to these two. For example, the type of polymerization initiator, the type and amount of polyfunctional monomer, the type, amount, timing and rate of addition of various additives, etc., may be set as appropriate based on the above determination.

[0108] At this time, if the polymerization temperature is too low, the decomposition of the polymerization initiator is inhibited, and polymerization does not proceed easily. On the other hand, if the polymerization temperature is too high, the decomposition rate of the polymerization initiator increases, so the polymerization rate increases, the molecular weight of the resulting resin becomes relatively low, and the seed resin becomes softer, so the adhesion of the seed resin increases. For this reason, based on the above determination, the polymerization temperature is set considering the balance with the polymerization time and polymerization rate. Then, by proceeding with polymerization, the melt flow rate of the recycled foamable polystyrene resin particles is adjusted to a range suitable for imparting foaminess (7g / 10min to 18g / 10min).

[0109] If the melt flow rate of the heated volume-reduced material is less than 2 g / 10 min, the fluidity of the heated volume-reduced material is poor, and the processing performance of the foamed resin particles cannot be maintained. Furthermore, if the melt flow rate of the heated volume-reduced material exceeds 28 g / 10 min, the foamed particles obtained by foaming the foamed resin particles have reduced surface strength and cannot maintain independent bubbles.

[0110] In other words, the heat-reduced volume material having a melt flow rate of less than 2 g / 10 min or greater than 28 g / 10 min tends not to retain the processing performance of foamed resin particles, and is therefore judged to be unsuitable for use alone as a raw material for foamed resin particles. However, the heat-reduced volume material having a melt flow rate of less than 2 g / 10 min may be mixed with the heat-reduced volume material having a melt flow rate of 2 g / 10 min to 28 g / 10 min or greater than 28 g / 10 min to be used as a heat-reduced volume material or pellet having a melt flow rate of 2 g / 10 min to 28 g / 10 min. Alternatively, the heat-reduced volume material having a melt flow rate greater than 28 g / 10 min may be mixed with the heat-reduced volume material having a melt flow rate of 2 g / 10 min to 28 g / 10 min or less than 2 g / 10 min to be used as a heat-reduced volume material or pellet having a melt flow rate of 2 g / 10 min to 28 g / 10 min.

[0111] If the melt flow rate of the heated volume-reduced material is greater than 10 g / 10 min and less than 20 g / 10 min, the concentration of the polymerization initiator, the concentration of the chain transfer agent, and the polymerization temperature are appropriately adjusted so that the melt flow rate of the foaming resin particles is approximately the median of the range suitable for imparting foaming properties to the foaming resin particles (7 g / 10 min to 18 g / 10 min).

[0112] As described above, the polymerization conditions are determined based on the melt flow rate of the heated volume-reduced material. In other words, it is determined whether the conditions are such that they can improve or decrease the degree of polymerization of the resin obtained by polymerization. Based on the determined conditions, specific conditions such as the concentration of the polymerization initiator, the concentration of the chain transfer agent, and the polymerization temperature are set. This optimizes polymerization regardless of the state of the heated volume-reduced material, and the resulting high molecular weight material can have an appropriate molecular weight that imparts foaming properties. Therefore, it is possible to produce recycled foamable polystyrene resin particles with stable processing performance.

[0113] Figure 1 shows an example of a flow chart for producing recycled foamable polystyrene resin particles, and further producing recycled polystyrene resin foam particles and recycled polystyrene resin foam molded articles in Embodiment 1. Examples 1 and 2, described later, are carried out based on this flow chart.

[0114] First, discarded resin products are sorted and recovered (S1). This yields recovered polystyrene foam molded products. Next, these recovered products are crushed (S2). Subsequently, the crushed material is subjected to a volume reduction machine, where it is crushed and compressed, then heated, melted, and extruded to heat-reduce the volume of the recovered products and form them into ingots (S3). These ingots are the heated volume-reduced products.

[0115] Next, the ingot is crushed (S4), the resulting crushed material is put through an extruder and extruded, and the resulting strands are cut to form pellets (S5). The resulting pellets are the heated volume reduction material. Here, the pellets are taken (S6), and the melt flow rate of the pellets is measured in accordance with JIS K 7210 at a measurement temperature of 200°C and a test load of 5 kg (S7). S6 and S7 are the measurement steps.

[0116] Next, based on the measured melt flow rate, the level of decrease in the weight-average molecular weight of the resin constituting the heated volume reduction is determined, the level of increase in molecular weight due to polymerization is estimated, and the polymerization conditions are determined. Based on this determination, the concentration of the polymerization initiator, the concentration of the chain transfer agent, and the polymerization temperature are set (S8). S8 includes the step of determining the polymerization conditions of step 1.

[0117] Next, seed polymerization is performed under the determined polymerization conditions (S9), and the resulting polystyrene resin particles are impregnated with a foaming agent (S10) to obtain regenerated foamable polystyrene resin particles. S1-S5 and S8-S10 correspond to step (1).

[0118] Furthermore, recycled foamable polystyrene resin particles are foamed (S11) to obtain recycled polystyrene resin foam particles. Then, the recycled polystyrene resin foam particles are molded (S12) to obtain a recycled polystyrene resin foam molded article.

[0119] As described above, by determining the polymerization conditions when polymerizing the seed resin and the styrene monomer using the method according to Embodiment 1, polymerization can be optimized regardless of the state of the heated volume reduction product, and the resulting high molecular weight product can have an appropriate molecular weight that imparts foaming properties. Therefore, it is possible to produce recycled foamable polystyrene resin particles with stable processing performance.

[0120] [2] Embodiment 2 A method for producing recycled foamable polystyrene resin particles according to Embodiment 2 of the present invention includes the steps of: (A) mixing the heat-reduced volume of a recovered polystyrene foam molded product with virgin polystyrene resin; (B) impregnating the mixture obtained in step (A) with a foaming agent to produce recycled foamable polystyrene resin particles; and a measurement step of measuring the melt flow rate of the heat-reduced volume before obtaining the mixture, wherein step (A) includes a control step of performing one or more selected from the group consisting of (X), (Y), and (Z) below based on the melt flow rate obtained in the measurement step: (X) Adjustment of the blending ratio of the virgin polystyrene resin to be mixed in step (A) above; (Y) Selection of the melt flow rate of the virgin polystyrene resin to be mixed in step (A); (Z) Selection of the weight-average molecular weight of the virgin polystyrene resin to be mixed in step (A) above.

[0121] (1) Process (A) Step (A) of this manufacturing method will now be explained. Step (A) is a process of mixing the heated volume reduction product of the recovered polystyrene foam molded product with virgin polystyrene resin.

[0122] The "heat-reduced volume product of recovered polystyrene foam molded products" is as described in "(1-1) Heat-reduced volume product of recovered polystyrene foam molded products" of Embodiment 1, so the explanation is omitted here.

[0123] Virgin polystyrene resin is a polystyrene resin that does not use recycled materials. In other words, it is a polystyrene resin that has never been used as a material for resin products. Virgin polystyrene resin may be a commercially available product or may be newly produced by methods such as suspension polymerization. Virgin polystyrene resin usually has a water content of 0.5% or less, and if salt is used in the polymerization process, the water content becomes even lower due to the effect of osmosis, to less than 0.1%. The polystyrene resin is as described in "(1-1) Heat-reduced volume product of recovered polystyrene resin foam molded product" of Embodiment 1.

[0124] The method for mixing the heat-reduced volume product with the virgin polystyrene resin is not particularly limited. For example, the mixing can be performed by the following method (i) or (ii) to obtain the mixture.

[0125] (i) The heated volume-reduced material and virgin polystyrene resin are put into an extruder and melt-kneaded to obtain a molten material (mixture).

[0126] (ii) Pellet (mixture) is obtained by extruding the heated volume-reduced material and the crushed virgin polystyrene resin to form pellets.

[0127] Step (A) includes a control step that performs one or more actions selected from the group consisting of (X), (Y), and (Z) based on the melt flow rate obtained in the measurement step described later. This point will be described later.

[0128] (2) Process (B) Step (B) is a step in which a foaming agent is impregnated into the mixture obtained in step (A) to obtain recycled foamable polystyrene resin particles. Step (B) can also be described as a step in which foaming properties are impregnated into the mixture by impregnating it with a foaming agent to obtain recycled foamable polystyrene resin particles. The foaming agent is as described in "(1-3-1) Foaming Agent" of Embodiment 1. Furthermore, the method for impregnating the mixture with the foaming agent can also be the method described in "(1-3-2) Impregnation of Polystyrene Resin Particles with Foaming Agent" of Embodiment 1.

[0129] Examples of such methods include the method of injecting a foaming agent into the molten material as described in (i) of "(1) Step (A)" above; and the method of placing the pellets and foaming agent as described in (ii) of "(1) Step (A)" above into a reactor such as a pressure vessel and injecting the foaming agent into the polystyrene resin particles under pressure. In step (B) as well, the method of impregnating the mixture with the foaming agent is not limited to the method of injecting the foaming agent into the target while applying pressure, but may also be the method of injecting the foaming agent into the target without applying pressure. The other conditions can also be applied by replacing "polystyrene resin particles" in "(1-3-2) Impregnation of polystyrene resin particles with foaming agent" of Embodiment 1 with the "mixture".

[0130] (3) Measurement process and control process of process (A) The measurement step is to measure the melt flow rate of the heated volume-reduced product before obtaining the mixture. The method for measuring the melt flow rate, the object to be measured, and the preferred range are as described in "(2) Measurement Step" of Embodiment 1.

[0131] The method for producing recycled foamable polystyrene resin particles includes a control step in which one or more of the following are selected from the group consisting of (X), (Y), and (Z) based on the melt flow rate obtained in the measurement step: (X) Adjustment of the blending ratio of the virgin polystyrene resin to be mixed in step (A) above; (Y) Selection of the melt flow rate of the virgin polystyrene resin to be mixed in step (A); (Z) Selection of the weight-average molecular weight of the virgin polystyrene resin to be mixed in step (A) above.

[0132] As virgin polystyrene resins, virgin polystyrene resins having various melt flow rates are available. As virgin polystyrene resins, virgin polystyrene resins having various weight-average molecular weights are available. Therefore, it can be said that (Y) selects the virgin polystyrene resin to be mixed in step (A) from among various virgin polystyrene resins based on the melt flow rate of the virgin polystyrene resin. It can also be said that (Z) selects the virgin polystyrene resin to be mixed in step (A) from among various virgin polystyrene resins based on the weight-average molecular weight of the virgin polystyrene resin.

[0133] In other words, in the control step, the mixing conditions of the virgin polystyrene resin to be mixed with the heated volume-reduced material are adjusted based on the measurement results of the melt flow rate of the heated volume-reduced material.

[0134] When the melt flow rate of the heated volume-reduced material is 20 g / 10 min to 28 g / 10 min, the heated volume-reduced material is in a soft state with low strength due to (i) and / or (ii) below.

[0135] (i) Increased fluidity of the heat-reduced volume product due to the relatively low molecular weight of the polystyrene resin constituting the heat-reduced volume product; (ii) Increased fluidity of the heated volume reduction product due to the reduction in molecular weight of the polystyrene resin caused by the thermal history.

[0136] At this time, the weight-average molecular weight of the resin constituting the heated volume-reduced product decreases, and the heated volume-reduced product is in a state of low strength and softness. Considering this state, it is determined that in order to make the weight-average molecular weight of the resin a weight-average molecular weight that is desirable for imparting foaming properties to the resin, it is preferable to perform control that can improve the degree of polymerization of the resin. Based on this determination, one or more measures selected from the group consisting of (X), (Y), and (Z) below are taken.

[0137] (X) The virgin polystyrene resin mixed in step (A) above shall be blended in a ratio of 50% by mass or more, when the sum of the mass of the heat-reduced volume product and the mass of the virgin polystyrene resin is 100% by mass.

[0138] (Y) Select a virgin polystyrene resin to be mixed in step (A) above, having a melt flow rate of 2 g / 10 min to 8 g / 10 min.

[0139] (Z) As the virgin polystyrene resin to be mixed in step (A) above, a virgin polystyrene resin having a weight-average molecular weight of more than 250,000 and less than or equal to 350,000 is selected.

[0140] On the other hand, if the melt flow rate of the heated volume-reduced material is 2 g / 10 min to 10 g / 10 min, the heated volume-reduced material is in a hard state due to the following reasons (iii) and / or (iv).

[0141] (iii) A decrease in the fluidity of the heat-reduced volume product due to the relatively high molecular weight of the polystyrene resin constituting the heat-reduced volume product; (iv) The effect of thermal history is small, and the reduction in molecular weight of the polystyrene resin is inhibited, resulting in a decrease in the fluidity of the heated volume reduction product. At this time, the weight-average molecular weight of the resin constituting the heated volume-reduced product is high, and the heated volume-reduced product is strong and hard. Considering these conditions, it is determined that in order to make the weight-average molecular weight of the resin a weight-average molecular weight that is desirable for imparting foaming properties to the resin, it is preferable to control the degree of polymerization of the resin. Based on this determination, one or more measures selected from the group consisting of (X), (Y), and (Z) below are taken.

[0142] (X) The virgin polystyrene resin mixed in step (A) above is blended in a ratio of less than 50% by mass when the sum of the mass of the heat-reduced volume product and the mass of the virgin polystyrene resin is 100% by mass.

[0143] (Y) Select a virgin polystyrene resin to be mixed in step (A) above, having a melt flow rate of more than 8 g / 10 min and 23 g / 10 min.

[0144] (Z) As the virgin polystyrene resin to be mixed in step (A) above, a virgin polystyrene resin with a weight-average molecular weight of 180,000 or more and 250,000 or less is selected.

[0145] In Embodiment 2, one or more measures selected from the group consisting of (X), (Y), and (Z) are taken depending on the state of the heated volume-reduced material, and then the heated volume-reduced material is mixed with the virgin polystyrene resin. Therefore, one or more of the factors selected from the group consisting of the blending ratio of the virgin polystyrene resin, the melt flow rate, and the weight-average molecular weight are appropriately adjusted according to the state of the heated volume-reduced material. In other words, by controlling the conditions when mixing the heated volume-reduced material and the virgin polystyrene resin, the blending of the heated volume-reduced material and the virgin polystyrene resin can be optimized according to the state of the heated volume-reduced material. Therefore, the melt flow rate of the recycled foamable polystyrene resin particles can be set to a range suitable for imparting foaming properties (7g / 10min to 18g / 10min).

[0146] One or more measures selected from the group consisting of (X), (Y), and (Z) may be (X), (Y), or (Z), but the more conditions that can be combined, the more suitable the selection of virgin polystyrene resins becomes for the state of the heated volume reduction product. For this reason, it is more preferable to select two or more from the group consisting of (X), (Y), and (Z), and even more preferable to select (X), (Y), and (Z).

[0147] If the melt flow rate of the heated volume-reduced material is less than 2 g / 10 min, the fluidity of the heated volume-reduced material is poor, and the processing performance of the foamed resin particles cannot be maintained. Furthermore, if the melt flow rate of the heated volume-reduced material exceeds 28 g / 10 min, the foamed particles obtained by foaming the foamed resin particles have reduced surface strength and cannot maintain independent bubbles.

[0148] In other words, the heat-reduced volume material having a melt flow rate of less than 2 g / 10 min or greater than 28 g / 10 min tends not to retain the processing performance of foamed resin particles, and is therefore judged to be unsuitable for use alone as a raw material for foamed resin particles. However, the heat-reduced volume material having a melt flow rate of less than 2 g / 10 min may be mixed with the heat-reduced volume material having a melt flow rate of 2 g / 10 min to 28 g / 10 min or greater than 28 g / 10 min to be used as a heat-reduced volume material or pellet having a melt flow rate of 2 g / 10 min to 28 g / 10 min. Alternatively, the heat-reduced volume material having a melt flow rate greater than 28 g / 10 min may be mixed with the heat-reduced volume material having a melt flow rate of 2 g / 10 min to 28 g / 10 min or less than 2 g / 10 min to be used as a heat-reduced volume material or pellet having a melt flow rate of 2 g / 10 min to 28 g / 10 min.

[0149] If the melt flow rate of the heated volume-reduced material is greater than 10 g / 10 min and less than 20 g / 10 min, one or more measures selected from the group consisting of (X), (Y), and (Z) are appropriately taken so that the melt flow rate of the foaming resin particles is approximately the median of the range suitable for imparting foaming properties to the foaming resin particles (7 g / 10 min to 18 g / 10 min).

[0150] The resulting recycled foamable polystyrene resin particles may contain any other suitable components, such as one or more components selected from the group consisting of flame retardants, foam regulators, foaming aids, pigments, radiant heat transfer inhibitors, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antistatic agents, weathering agents, anti-aging agents, anti-fogging agents, and fragrances, as long as they do not impair the effects of the present invention.

[0151] These other components can be mixed together, for example, in step (A), when the heated volume reduction product of the recovered polystyrene foam molded product is mixed with virgin polystyrene resin.

[0152] Furthermore, the obtained recycled foamable polystyrene resin particles may be surface-treated with at least one agent selected from the group consisting of silicone oil, antistatic agents, fatty acid metal salts, and fusion accelerators, to the extent that the effects of the present invention are not impaired. The method of surface treatment is not particularly limited, and conventionally known methods can be used.

[0153] Figure 2 shows an example of a flow chart for producing recycled foamable polystyrene resin particles, and further producing recycled polystyrene resin foam particles and recycled polystyrene resin foam molded articles in Embodiment 2. Examples 3 to 5, described later, are carried out based on this flow chart.

[0154] Steps S1 to S7 are the same as those described in Figure 1, so their explanation is omitted. Steps S6 and S7 correspond to the measurement steps of Embodiment 2. Next, based on the measured melt flow rate in S7, and considering the strength and hardness of the heated volume reduction product, it is determined whether to control the degree of polymerization of the resin constituting the heated volume reduction product to improve or to control it to improve the degree of polymerization of the resin in order to make the weight-average molecular weight of the resin a weight-average molecular weight that is favorable for imparting foaming properties to the resin. As a result of the determination, one or more measures selected from the group consisting of (X), (Y), and (Z) described above are taken. Specifically, in order to make the weight-average molecular weight of the resin a molecular weight necessary to impart foaming properties to the resin, the type of virgin polystyrene resin used for mixing in step (A) is determined based on the melt flow rate and / or weight-average molecular weight, and the blending ratio is determined (S16). Subsequently, based on the blending ratio determined in S16, the heated volume reduction product and the virgin polystyrene resin are mixed (S17). S16 and S17 correspond to step (A) of Embodiment 2, and S16 corresponds to the control step of step (A).

[0155] The resulting mixture is subjected to an extruder and extruded, and the resulting strands are cut and pelletized (S18). The pellets (polystyrene resin particles) obtained in S18 are impregnated with a foaming agent (S19) to obtain recycled foamable polystyrene resin particles.

[0156] Furthermore, recycled foamable polystyrene resin particles are foamed (S20) to obtain recycled polystyrene resin foam particles. Then, the recycled polystyrene resin foam particles are molded (S21) to obtain a recycled polystyrene resin foam molded article.

[0157] By controlling the conditions for mixing the heated volume-reduced material and the virgin polystyrene resin according to the method of Embodiment 2, the blending ratio of the heated volume-reduced material and the virgin polystyrene resin can be optimized according to the state of the heated volume-reduced material. As a result, recycled foamable polystyrene resin particles with stable processing performance can be produced.

[0158] [3] Recycled foamed polystyrene resin particles The recycled foamed polystyrene resin particles obtained by this manufacturing method have a particle shape as a whole. The average particle diameter of the recycled foamed styrene resin particles is preferably 0.4 mm to 2.0 mm, and more preferably 0.6 mm to 1.8 mm. The average particle diameter is measured as the particle size representing 50% of the cumulative value from the particle size distribution obtained by the sieving test according to JIS Z 8815.

[0159] The shape of the recycled foamed polystyrene resin particles can be any suitable shape, as long as it does not impair the effects of the present invention. Examples of such shapes include spherical, substantially spherical, and ellipsoidal (egg-shaped). Among these, the spherical shape is preferred because it is easier to exhibit the effect of the present invention, which is to provide recycled foamed polystyrene resin particles with good processing performance.

[0160] The weight-average molecular weight of the recycled foamable polystyrene resin particles can be any appropriate weight-average molecular weight within a range that does not impair the effects of the present invention. Such a weight-average molecular weight is preferably 160,000 to 400,000, more preferably 170,000 to 350,000, even more preferably 180,000 to 300,000, and particularly preferably 190,000 to 240,000.

[0161] The aforementioned weight-average molecular weight can be achieved by performing operations such as determining the polymerization conditions in step (1) of Embodiment 1, and controlling the mixing conditions between the heated volume-reduced product and the virgin polystyrene resin in step (A) of Embodiment 2.

[0162] [4] Heating volume reduction process The present manufacturing method may include a heating and volume reduction step prior to step (1) in which the recovered polystyrene foam molded product is heated and reduced in volume. Alternatively, the present manufacturing method may include a heating and volume reduction step prior to step (A) in which the recovered polystyrene foam molded product is heated and reduced in volume.

[0163] "Heating volume reduction" refers to reducing the volume of the recovered material by heating, crushing, and compressing. As an example of a method for performing the heating volume reduction process, as described in (1-1) of Embodiment 1, the recovered material is subjected to a volume reduction machine, crushed and compressed, then heated and melted, and extruded to form an ingot.

[0164] Since the heating volume reduction step is performed prior to step (1) or step (A), it is performed before the measurement step included in step (1) and the control step included in step (A).

[0165] [5] Recovery process The present manufacturing method may include a recovery step prior to the heating and volume reduction step, in which the polystyrene-based resin foam molded body is recovered and used as the recovered product. Such a step may include, for example, the operation of selecting and recovering the polystyrene-based resin foam molded body from various types of waste. The recovered product is as described in (1-1) of Embodiment 1.

[0166] [6] Confirmation of the concentration of environmentally harmful substances Recycled polystyrene foam molded products may contain environmentally harmful substances such as heavy metals. In recent years, an increasing number of countries and states have been regulating the content of environmentally harmful substances in these products.

[0167] Therefore, in both Embodiments 1 and 2, this manufacturing method may include a step of confirming the concentration of environmentally hazardous substances regulated by the RoHS Directive in the heated volume-reduced product by fluorescent X-ray analysis.

[0168] The RoHS (Restriction of Hazardous Substances) Directive is an EU law concerning the restriction of the use of certain hazardous substances, and is also known as the "Directive on the Restriction of Hazardous Substances."

[0169] The RoHS Directive's inspections target cadmium (Cd), lead (Pb), mercury (Hg), hexavalent chromium (Cr), polybrominated biphenyls and polybrominated diphenyl ethers (hereinafter referred to as specific bromines (Br)), and di-2-ethylhexyl phthalate, dibutyl phthalate, benzyl butyl phthalate, and diisobutyl phthalate (hereinafter referred to as phthalate esters), and measure and investigate their content. The permissible limit concentrations for the above-mentioned substances are set at 100 ppm for cadmium and 1,000 ppm for all others.

[0170] The X-ray fluorescence analyzer used in the aforementioned X-ray fluorescence analysis analyzes the elemental content of a substance by irradiating it with X-rays and measuring the fluorescent X-rays emitted from the substance.

[0171] The procedure for quantifying the concentration of elements contained in a sample is generally known. First, the measurement time for X-ray fluorescence is set, and the measurement is started. After the set time has elapsed, the concentration of the contained elements is calculated based on the measurement results, and the results are displayed.

[0172] Figure 3 shows an example of the flow of Embodiment 1, which includes a step to confirm the concentration of the environmentally hazardous substances. In Figure 3, steps S1 to S12 are the same as the steps described in Figure 1. Step S13 is the step of subjecting the pellets collected in S6 (corresponding to the heated volume reduction) to fluorescent X-ray analysis.

[0173] The measurement results of the X-ray fluorescence analysis are determined (S14), and if the concentration of any one or more of the target substances significantly exceeds the permissible limit, the heated volume-reduced material is not used as a raw material for recycled polystyrene foam particles, and measures such as disposal and incineration are taken (S15).

[0174] On the other hand, if the measurement result for any one or more of the target substances is in the boundary region of the permissible limit concentration, recycled polystyrene foam particles with a concentration of the target substance below the permissible limit concentration are obtained by the following measures.

[0175] (i) In Embodiment 1, the target substance is diluted by polymerization in step (1) to adjust the concentration of the target substance to less than the permissible limit concentration.

[0176] (ii) In Embodiment 2, the target substance is diluted by mixing with a virgin polystyrene resin in step (A) to adjust the concentration of the target substance to below the permissible limit concentration.

[0177] If the concentration of any of the aforementioned target substances is below the permissible limit concentration, the heat-reduced volume product can be used as is as a raw material for recycled polystyrene foam particles.

[0178] By including the above-mentioned process, the concentration of the target substance contained in the recycled polystyrene foam particles can be reliably kept below the permissible limit concentration. Therefore, recycled polystyrene foam molded products can be safely recycled, and recycled foamable polystyrene particles that do not harm people or the environment can be produced.

[0179] [7] Method for producing foamed particles of recycled polystyrene resin A method for producing recycled polystyrene foam particles according to one embodiment of the present invention (hereinafter sometimes referred to as the method for producing these foam particles) includes a step of foaming the recycled foamable polystyrene resin particles produced by the method.

[0180] As mentioned above, the recycled foamable polystyrene resin particles produced by this manufacturing method have excellent processing performance. Therefore, this method for producing foamed particles can provide foamed particles with stable quality.

[0181] The method for foaming the recycled foamable polystyrene resin particles produced by this manufacturing method is not particularly limited, and known foaming methods can be used. For example, such a foaming method may be one in which the following (1) to (3) are performed sequentially: (1) the recycled foamable polystyrene resin particles are placed in a container equipped with a stirrer, (2) the recycled foamable polystyrene resin particles are heated by a heat source such as steam, and (3) foaming is performed until a desired bulk expansion ratio is reached to obtain recycled foamed polystyrene resin particles.

[0182] The bulk expansion ratio is preferably 2 to 150 times, more preferably 2 times or more but less than 100 times, more preferably 5 to 90 times, even more preferably 10 to 85 times, and particularly preferably 15 to 83 times. The reciprocal of the bulk expansion ratio is the bulk density.

[0183] By having the aforementioned bulk expansion ratio within these ranges, blocking during foaming and molding can be better prevented. Furthermore, while reducing static charge during foaming and molding, it is possible to produce recycled polystyrene-based resin foam molded articles that exhibit better fusion properties and surface properties, resulting in less static electricity.

[0184] The foamed particles have an average bubble diameter of preferably 0.01 mm to 1.10 mm, more preferably 0.01 mm to 1.00 mm, even more preferably 0.01 mm to 0.90 mm, particularly preferably 0.01 mm to 0.80 mm, and most preferably 0.01 mm to 0.70 mm.

[0185] By having the average bubble diameter within these ranges, blocking during foaming and molding, as well as surface shrinkage due to surface dissolution during molding, can be further prevented. Furthermore, it is possible to produce foamed molded articles with lower static electricity by exhibiting better fusion properties and surface properties while further reducing electrostatic charge during foaming and molding.

[0186] The average bubble diameter can be determined as follows. First, the foam particle is divided into two halves, passing through the center of the foam particle. Next, the area of ​​the bubble cross-section of each bubble present in the cut surface is measured, and the diameter of a virtual circle having the same area is taken as the bubble diameter of each bubble. Then, the average bubble diameter of the entire foam particle is obtained by taking the arithmetic mean of the obtained bubble diameters of each bubble. The average bubble diameter (for example, the area of ​​each bubble cross-section) can be measured by subjecting the cross-sectional image obtained by cross-sectional observation to image processing or other methods.

[0187] As described later, the foamed particles can be used in the manufacture of foamed molded articles, but they can also be used as cushioning material, heat insulating material, concrete aggregate, etc. Furthermore, the foamed particles are preferably used as a filler in which a large number of the foamed particles are filled into a bag or the like. An example of such a filler is a cushion in which the foamed particles are filled as a core material.

[0188] [8] Method for producing a recycled polystyrene foam molded product A method for producing a recycled polystyrene-based resin foamed molded article according to one embodiment of the present invention (hereinafter sometimes referred to as the method for producing this foamed molded article) includes a step of molding recycled polystyrene-based resin foamed particles (foamed particles) produced by the method for producing this foamed particle.

[0189] A recycled polystyrene-based foamed molded article (foamed molded article) is composed of multiple foamed particles that are fused together. The foamed molded article is manufactured by placing the foamed particles into a mold having a shape appropriate to the purpose and performing in-mold foam molding. In-mold foam molding includes, for example, the following steps (i) and (ii).

[0190] (i) Filling a closed mold having numerous small holes with the foamed particles; (ii) Heating and foaming the foam particles with a heat transfer medium (for example, pressurized steam, etc.) to fill the gaps between the foam particles and fuse them together to form a single unit.

[0191] More specifically, examples of in-mold foam molding include a method in which foam particles are filled into a mold that can be closed but cannot be airtight, and the particles are heated and fused together with steam to form a foamed molded body; and a method in which foam particles are filled into a closed mold having a desired shape and numerous small holes drilled in its walls, a heating medium such as steam is ejected from the mold holes to heat the particles to a temperature above their softening point, causing them to fuse together, and then removed from the mold after a cooling process.

[0192] The density of the foamed molded article can be appropriately set depending on the purpose. This density can be adjusted, for example, by pre-adjusting the bulk expansion ratio of the foamed particles to be filled into the mold, or by adjusting the amount of foamed particles to be filled into the mold.

[0193] The temperature of the foamed particles during heating and foaming is preferably 90°C to 150°C, and more preferably 110°C to 130°C. The time required for heating and foaming is preferably 5 seconds to 50 seconds, and more preferably 10 seconds to 50 seconds. The molding vapor pressure (gauge pressure of the heat transfer medium) during heating and foaming is preferably 0.04 MPa to 0.1 MPa, and more preferably 0.06 MPa to 0.08 MPa.

[0194] Furthermore, the foaming ratio of the foam particles in the foamed molded body is preferably 2 times or more and less than 110 times, more preferably 5 times to 90 times, even more preferably 10 times to 85 times, and particularly preferably 15 times to 80 times.

[0195] When the density, temperature of the foam particles, time required for heating and foaming, molding vapor pressure during heating and foaming, and foaming ratio are met, the foam particles can be well fused to each other, thereby obtaining a foamed molded article of stable quality.

[0196] The method for manufacturing the foamed molded article may include a step of maturing the foamed particles before the step of molding the foamed particles. For example, a method for maturing the foamed particles may involve placing the foamed particles in a constant temperature bath and leaving them at a temperature of 20°C to 60°C for 12 to 48 hours. This further prevents the dissipation of the foaming agent in the foamed particles, thereby improving moldability.

[0197] The foamed molded article obtained by this method can exhibit an average maximum bending strength equivalent to that of the foamed molded article made of virgin polystyrene resin. The foamed molded article has a density of 0.0167 g / cm³. 3 The average maximum bending strength is preferably 0.33 MPa or higher, more preferably 0.34 MPa or higher, even more preferably 0.35 MPa or higher, and particularly preferably 0.36 MPa or higher. The higher the upper limit of the average maximum bending strength, the better. For example, in the example described later, an average maximum bending strength of up to 0.38 MPa was obtained.

[0198] Because the foamed molded body is manufactured from foamed particles with excellent processing properties, it has stable quality, is lightweight, and has excellent heat insulation and mechanical strength. For this reason, the foamed molded body is suitably used as insulation material for walls, floors, roofs, automobiles, hot water tanks, pipes, solar systems, water heaters, containers for food and industrial products (e.g., food containers such as fish boxes, returnable containers), cushioning materials, floats, blocks, packaging materials for fish and agricultural products, molded bodies for embankments, core materials for tatami mats, core materials for cushions, aggregates for concrete, etc.

[0199] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0200] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, comparative examples and tables, "parts" and "%" refer to weight-based amounts (parts by weight and weight %) unless otherwise specified.

[0201] [Measurement and evaluation methods] The measurement and evaluation of each physical property in the examples were performed using the following methods.

[0202] (1) Expansion ratio of foamed particles The bulk expansion ratio of the foamed particles was calculated by placing the foamed particles in a graduated cylinder to a volume of 1,000 cc, measuring the weight, and using the following formula (1). Bulk expansion ratio (cc / g) = 1,000cc / [weight of foamed particles (g)] ... (1) (2) Density of the foamed molded product The density of the foamed molded product was calculated according to the following formula (2), in accordance with JIS K 7222. Density of foamed molded material (kg / m³) 3 ) = Weight of foamed molded body (kg) / Volume of foamed molded body (m³)3 )...(2) (3) Measurement of melt flow rate (MFR) The melt flow rates of various particles were measured in accordance with JIS K 7210, at a measurement temperature of 200°C and a test load of 5 kg.

[0203] (4) Average maximum bending strength of foamed molded articles A test specimen measuring 300 mm (length) x 75 mm (width) x 30 mm (thickness) was cut from the foamed molded body. Bending tests were performed on this specimen in accordance with JIS A 9511, and the average value for n=3 was calculated to determine the average maximum bending strength. Based on the measurement results, evaluation was performed according to the following criteria. Good: Average maximum bending strength of 0.36 MPa or higher. Acceptable: Average maximum bending strength of 0.33 MPa or more and less than 0.36 MPa Not suitable: Average maximum bending strength less than 0.33 MPa (5) Appearance of the foamed molded product The surface of the foamed molded product was visually inspected and evaluated according to the following criteria. Good: There are no gaps between foam particles, no molten foam particles on the surface, and it is smooth and looks good. Defective: There are many gaps between foam particles, or many molten foam particles are present on the surface, resulting in an uneven surface and poor appearance.

[0204] (6) Weight average molecular weight A sample was prepared by weighing 0.02 g of the substance to be measured and dissolving it in 20 ml of tetrahydrofuran. This sample was subjected to gel permeation chromatography (measuring instrument: HLC-8020, manufactured by Tosoh Corporation; column: TSKgel Super HZM-H; column temperature: 40°C; flow rate: 0.35 ml / min). The weight-average molecular weight (g / mol) of the substance to be measured was calculated by comparing the obtained data with a calibration curve for standard polystyrene.

[0205] [Example 1] (1) Heating volume reduction step and measurement step of the manufacturing method according to Embodiment 1 A polystyrene foamed resin container (A), which had been used as a reusable container (shipper), was crushed and compressed using a volume reduction machine (Eco-Ac Packer; EAP-800S, manufactured by Sigma Kiki Co., Ltd.). The compressed container was then heated and melted at approximately 200°C in the machine, and the molten material was extruded. As a result, strips (ingots) approximately 250 mm wide and 1,000 mm long were obtained. These ingots were placed on a plastic pallet in a 5x35 arrangement.

[0206] The aforementioned expanded polystyrene resin container (A) is a recovered product of a polystyrene resin foam molded body. The aforementioned ingot is a product of volume reduction due to heating.

[0207] Next, the ingot was crushed and then fed into a φ30 mm twin-screw extruder, where it was melted and kneaded at 230°C and extruded in strand form through a mold (hole diameter 0.6 mm, 8 holes). After cooling and solidifying the strand with cooling water at 20°C, it was cut into pellets with an average diameter of 0.75 mm and an average length of 0.9 mm, obtaining cylindrical pellets. The MFR of these pellets was measured according to the method in accordance with JIS K 7210, at a measurement temperature of 200°C and a test load of 5 kg (measurement process). The result was 15 g / 10 min.

[0208] (2) Polymerization, step (1) of the manufacturing method according to Embodiment 1, step (1) for determining polymerization conditions and impregnation of foaming agent A 5L pressure-resistant container equipped with a stirrer was filled with 2,000g of deionized water as a dispersion medium, 0.3g of calcium dodecylbenzenesulfonate as a surfactant, 5g of magnesium pyrophosphate as a dispersant, and 1,500g of the pellets obtained in (1) above. The mixture was heated to 75°C while stirring to prepare a suspension. The pellets correspond to both the seed resin and the heat-reduced volume product.

[0209] Next, an emulsion was prepared by dissolving 1.2 g of t-butylperoxy-2-ethylhexanoate and 0.4 g of t-butylperoxybenzoate as polymerization initiators, and 0.06 g of divinylbenzene as a polyfunctional monomer, in 400 g of styrene monomer. This emulsion was supplied to the suspension at 75°C while stirring. 60 minutes after supply, the temperature was raised to 108°C over 150 minutes for 3 hours of polymerization, then heated to 120°C and held for 2 hours to continue polymerization. After that, the mixture was cooled and dehydrated to obtain polystyrene resin particles.

[0210] The MFR of the aforementioned pellets, 15 g / 10 min, corresponds to the case where the MFR of the heated volume-reduced product is greater than 10 g / 10 min but less than 20 g / 10 min. Therefore, it was determined that the polymerization conditions should be such that the weight-average molecular weight of the resin constituting the pellets is increased by polymerization so that the MFR of the foamable resin particles is approximately the median of the range suitable for imparting foaminess to the foamable resin particles (7 g / 10 min to 18 g / 10 min). Based on the results of this determination, the type and amount of polymerization initiator, the type and amount of polyfunctional monomer, the polymerization temperature, and the polymerization time were set.

[0211] Next, 2,200 g of water, 1,800 g of the polystyrene resin particles, 0.4 g of calcium dodecylbenzenesulfonate as a surfactant, and 6 g of magnesium pyrophosphate as a dispersant were supplied to another 5 L pressure vessel equipped with a stirrer, and the temperature was raised to 70°C while stirring. Subsequently, 16 g of cyclohexane as a foaming aid and 13 g of diisobutyl adipate as a plasticizer were supplied to the pressure vessel, which was then sealed and the temperature was raised to 100°C.

[0212] Next, 140 g of n-butane, used as a foaming agent, was injected under pressure into the pressure-resistant container containing the polystyrene resin particles. After holding it for 3 hours, it was cooled to below 30°C. This impregnated the polystyrene resin particles with the foaming agent. Subsequently, the cooled material was removed from the pressure-resistant container and dried to obtain recycled foamable polystyrene resin particles.

[0213] Polyethylene glycol as an antistatic agent was applied to the surface of the foamed resin particles, followed by the application of zinc stearate as a surface treatment agent and hydroxystearate triglyceride as a fusion accelerator. The mixture was then left in a constant temperature room at 12°C for 60 hours to obtain recycled foamed polystyrene resin particles 1.

[0214] The obtained recycled foamed polystyrene resin particles 1 were pressed into a sheet with a thickness of approximately 0.2 mm to 1 mm using a heated press machine with the temperature controlled to 200°C, and pellet-shaped or rod-shaped samples were cut from the sheet. Using these samples, the MFR was measured according to the method in accordance with JIS K 7210, at a measurement temperature of 200°C and a test load of 5 kg. The result was 12.5 g / 10 min.

[0215] In this example, the MFR of the pellets obtained by crushing the ingot in (1) above was 15 g / 10 min. Therefore, the polymerization conditions were determined as described above. The MFR of a resin depends on (corresponds with) the molecular weight of the resin. Specifically, the weight-average molecular weight of recycled foamable polystyrene resin particles 1 was designed to be 223,000, which is the molecular weight at which the MFR of recycled foamable polystyrene resin particles 1 is 12.5 g / 10 min. To obtain this molecular weight, the type and amount of polymerization initiator, the type and amount of polyfunctional monomer, the polymerization temperature, and the polymerization time were set as described above.

[0216] (3) Production of recycled polystyrene foam particles Recycled foamable polystyrene resin particles 1 are placed in a cylindrical batch-type pressure foaming machine and heated with steam for 2 minutes, resulting in a bulk density of 0.0167 g / cm³. 3 The material was foamed to obtain foamed particles. These foamed particles were aged for 24 hours at a temperature of 23°C to obtain recycled polystyrene-based foamed particles 1.

[0217] (4) Manufacturing of recycled polystyrene foam molded products After leaving the recycled polystyrene foam particles 1 in a room temperature atmosphere for 24 hours, the recycled polystyrene foam particles 1 were filled into the cavity of a foam bead molding machine equipped with a pair of molds having a rectangular parallelepiped cavity with internal dimensions of 400 mm × 300 mm × 30 mm.

[0218] Next, recycled polystyrene foam particles 1 were subjected to heat molding for 15 seconds using steam at a gauge pressure of 0.04 MPa (low-pressure molding conditions) and 0.09 MPa (high-pressure molding conditions) to obtain a recycled polystyrene foam molded body.

[0219] Next, the foamed molded body in the cavity was water-cooled for 5 seconds, and then allowed to cool under reduced pressure to obtain a recycled polystyrene-based foamed molded body 1. The recycled polystyrene-based foamed molded body 1 was aged in a drying chamber at 50°C for 12 hours, and its density was measured to be 0.0167 g / cm³. 3 The recycled polystyrene foam molded body 1, which was formed using recycled polystyrene foam particles 1, showed no deformation due to shrinkage and had a good appearance. The average maximum bending strength of the recycled polystyrene foam molded body 1 was 0.37 MPa.

[0220] [Example 2] (1) Heating volume reduction step and measurement step of the manufacturing method according to Embodiment 1 Cylindrical pellets were obtained using the same method as in Example 1, except that a polystyrene foamed resin container previously used as a vegetable box was used. The MFR of these pellets was measured using the same method as in Example 1 (measurement step). The result was 17 g / 10 min.

[0221] (2) Polymerization, step (1) of the manufacturing method according to Embodiment 1, step (1) for determining polymerization conditions and impregnation of foaming agent A 5L pressure-resistant container equipped with a stirrer was filled with 2,000g of deionized water as a dispersion medium, 0.3g of calcium dodecylbenzenesulfonate as a surfactant, 5g of magnesium pyrophosphate as a dispersant, and 1,500g of the pellets obtained in (1) above. The mixture was heated to 75°C while stirring to prepare a suspension. The pellets correspond to both the seed resin and the heat-reduced volume product.

[0222] Next, an emulsion was prepared by dissolving 1.0 g of t-butylperoxy-2-ethylhexanoate and 0.3 g of t-butylperoxybenzoate as polymerization initiators, and 0.06 g of divinylbenzene as a polyfunctional monomer, in 800 g of styrene monomer. This emulsion was supplied to the suspension at 75°C while stirring. 60 minutes after supply, the temperature was raised to 108°C over 150 minutes for 3 hours of polymerization, then heated to 120°C and held for 2 hours to continue polymerization. After that, the mixture was cooled, dehydrated, and dried to obtain regenerated foamable polystyrene resin particles.

[0223] The aforementioned pellet's MFR of 17g / 10min corresponds to the case where the MFR of the heated volume-reduced product is greater than 10g / 10min but less than 20g / 10min. Therefore, it was determined that the polymerization conditions should preferably be as follows, so that the MFR of the foamed resin particles is approximately the median value within the range suitable for imparting foaminess to the foamed resin particles (7g / 10min to 18g / 10min). Compared to Example 1, the amount of polymerization initiator was reduced and the amount of styrene monomer was increased, resulting in conditions that further increased the weight-average molecular weight of the resin constituting the pellets through polymerization.

[0224] Based on the results of this determination, the type and amount of polymerization initiator, the type and amount of polyfunctional monomer, the polymerization temperature, and the polymerization time were set.

[0225] Next, in another 5L pressure vessel equipped with a stirrer, 2,200g of water, 1,800g of the polystyrene resin particles, 0.4g of calcium dodecylbenzenesulfonate as a surfactant, and 6g of magnesium pyrophosphate as a dispersant were supplied, as in Example 1, and the temperature was raised to 70°C while stirring. Subsequently, 16g of cyclohexane as a foaming aid and 13g of diisobutyl adipate as a plasticizer were supplied to the pressure vessel, which was then sealed and the temperature was raised to 100°C.

[0226] Next, using another pressure-resistant container with a capacity of 5 L equipped with a stirrer, the recycled foamable polystyrene resin particles were impregnated with n-butane as a foaming agent in the same manner as in Example 1. The same procedure as in Example 1 was performed on the resulting cooled material to obtain recycled foamable polystyrene resin particles 2.

[0227] Similar to Example 1, the MFR of the obtained recycled foamed polystyrene resin particles 2 was measured. The result was 12.5 g / 10 min.

[0228] In this example, the MFR of the pellets obtained by crushing the ingot in (1) above was 17 g / 10 min. Therefore, the polymerization conditions were determined as described above. The MFR of the resin depends on (corresponds to) the molecular weight of the resin. Specifically, the weight-average molecular weight of the recycled foamable polystyrene resin particles 2 was designed to be 223,000, which is the molecular weight at which the MFR of the recycled foamable polystyrene resin particles 2 is 12.5 g / 10 min. To obtain this molecular weight, the type and amount of polymerization initiator, the type and amount of polyfunctional monomer, the polymerization temperature, and the polymerization time were set as described above.

[0229] (3) Production of recycled polystyrene foam particles The recycled foamable polystyrene resin particles 2 were subjected to the same method as in Example 1 to obtain recycled polystyrene resin foam particles 2.

[0230] (4) Manufacturing of recycled polystyrene foam molded products The recycled polystyrene foam particles 2 were subjected to the same method as in Example 1 to obtain a recycled polystyrene foam molded body 2. The recycled polystyrene foam molded body 2 was aged in a drying chamber at 50°C for 12 hours, and its density was measured to be 0.0167 g / cm³. 3 The recycled polystyrene foam molded article, formed using recycled polystyrene foam particles 2, showed no deformation due to shrinkage and had a good appearance. The average maximum bending strength of the recycled polystyrene foam molded article 2 was 0.38 MPa.

[0231] [Example 3] (1) Step (A) and measurement step of the manufacturing method according to Embodiment 2 Cylindrical pellets were obtained using the same method as in Example 1, except that a polystyrene foamed resin container (B) that had been used as a reusable container (shipper) was used. The MFR of the pellets was measured using the same method as in Example 1 and was found to be 18 g / 10 min.

[0232] The aforementioned MFR (18g / 10min) corresponds to the case where the MFR of the heated volume-reduced product is greater than 10g / 10min but less than 20g / 10min. Therefore, the virgin polystyrene resin to be mixed with the pellets was selected so that the MFR of the recycled foamable polystyrene resin particles 3, described later, would be approximately the median value within the range (7g / 10min to 18g / 10min) suitable for imparting foaming properties to the recycled foamable polystyrene resin particles 3.

[0233] Specifically, PS680 manufactured by PSJ, exhibiting an MFR of 6.6 g / 10 min, was selected as the virgin polystyrene resin, and the mixing ratio of PS680 to the aforementioned pellets was adjusted to a weight ratio of 50:50.

[0234] Next, the mixture was supplied to a twin-screw extruder with a 40 mm bore and co-meshing design (first extruder).

[0235] Next, the cylinder temperature after the raw material feed section of the twin-screw extruder was set to 200°C, and the feed material was melted and kneaded to obtain a molten and kneaded product.

[0236] (2) Step (B) of the manufacturing method according to Embodiment 2 Next, 6.0 parts by weight of mixed pentane (a mixture of 80% by weight n-pentane and 20% by weight isopentane (manufactured by SK Industries Co., Ltd.)) as an easily volatile foaming agent was injected under pressure into the middle section of the cylinder after the raw material feed section of the twin-screw extruder, relative to 100 parts by weight of the molten mixture, and the mixture was further melted and kneaded to obtain a thermoplastic resin molten product.

[0237] Next, the thermoplastic resin molten material was supplied to a 90 mm diameter single-screw extruder (second extruder) through a continuation pipe set to 225°C. A gear pump set to 180°C and a diverter valve were connected to the tip of the single-screw extruder, and a die set to 250°C was connected downstream of the diverter valve, having 60 small holes with a diameter of 0.65 mm and a land length of 5.0 mm. After kneading the thermoplastic resin molten material with the cylinder temperature of the single-screw extruder set to 180°C, the molten mixture was extruded (discharged) at a rate of 60 kg / hr into pressurized water at a temperature of 80°C and a water pressure of 1.2 MPa from the die connected to the tip of the single-screw extruder.

[0238] Immediately thereafter, a rotary cutter with blades was used to cut the molten mixture extruded into water, thereby pulverizing it. This produced recycled foamed polystyrene resin particles 3 for in-mold molding. The average particle weight of these recycled foamed polystyrene resin particles 3 was 0.8 mg.

[0239] Similar to Example 1, the MFR of the obtained recycled foamed polystyrene resin particles 3 was measured. The result was 12.5 g / 10 min.

[0240] In this example, the MFR of the pellets obtained by crushing the ingot in (1) above was 18 g / 10 min. Therefore, the mixing conditions (type of virgin polystyrene resin and blending ratio) of the pellets and the virgin polystyrene resin were controlled as described in (1) above. Specifically, the weight-average molecular weight of the recycled foamable polystyrene resin particles 3 was designed to be 223,000, which is the molecular weight at which the MFR of the recycled foamable polystyrene resin particles 3 is 12.5 g / 10 min. To obtain this molecular weight, the selection of the virgin polystyrene resin and the blending ratio of the resin to the pellets were set as described in (1) above.

[0241] (3) Production of recycled polystyrene foam particles The recycled foamable polystyrene resin particles 3 obtained in (2) above were placed in a pre-foaming machine, and foaming was carried out by introducing 0.1 MPa of steam. This formed the recycled polystyrene resin foam particles 3. The bulk density of the recycled polystyrene resin foam particles 3 was 0.0167 g / cm³. 3 That was the case.

[0242] (4) Manufacturing of recycled polystyrene foam molded products The recycled polystyrene foam particles 3 obtained in (3) above were filled into a mold (in-mold molding mold) attached to a polystyrene foam molding machine, and in-mold foaming was performed by introducing 0.12 MPa of steam. After that, the mold was cooled with water until the pressure of the foamed resin molded body pressing against the mold was 0.015 MPa (gauge pressure), thereby obtaining the recycled polystyrene foam molded body 3.

[0243] After aging the recycled polystyrene foam molded body 3 in a 50°C drying chamber for 12 hours, its density was measured and found to be 0.016 g / cm³. 3 The recycled polystyrene foam molded body 3, formed using recycled polystyrene foam particles 3, showed no deformation due to shrinkage and had a good appearance. The average maximum bending strength of the recycled polystyrene foam molded body 3 was 0.35 MPa.

[0244] [Example 4] Cylindrical pellets were obtained using the same method as in Example 1, except that a polystyrene foam resin container (C) that had been used as a reusable container (shipper) was used. The MFR of the pellets was measured using the same method as in Example 1 and was found to be 22 g / 10 min.

[0245] Based on the aforementioned MFR (22g / 10min), the mixing conditions between the pellets and the virgin polystyrene resin were controlled so that the MFR of the recycled foamable polystyrene resin particles 4, described later, would be approximately the median value within the range suitable for imparting foamability (7g / 10min to 18g / 10min). The aforementioned mixing conditions refer to the type and blending ratio of the virgin polystyrene resin. Specifically, the determination was made based on "when the melt flow rate of the heated volume reduction is 20g / 10min to 28g / 10min" in "(3) Measurement process and control process of process (A)" of Embodiment 2. As a result, PSJ's G9401 (MFR 2.5g / 10min), which exhibits an MFR of 2.5g / 10min, was selected, and the pellets and G9401 were mixed in a weight ratio of 50:50.

[0246] Next, recycled foamable polystyrene resin particles 4 for in-mold molding were produced in the same manner as in Example 3, except that the mixture was supplied to a 40 mm diameter co-meshing twin-screw extruder (first extruder). Subsequently, recycled foamed polystyrene resin particles 4 were produced from the recycled foamable polystyrene resin particles 4 in the same manner as in Example 3, and a recycled foamed polystyrene resin molded body 4 was produced from these recycled foamed polystyrene resin particles 4.

[0247] Similar to Example 1, the MFR of the obtained recycled foamed polystyrene resin particles 4 was measured. The result was 13.5 g / 10 min.

[0248] In this example, the MFR of the pellets obtained by pulverizing the ingot in the same manner as in Example 1 was 22 g / 10 min. Therefore, the mixing conditions (type and blending ratio of virgin polystyrene resin) of the pellets and the virgin polystyrene resin were controlled as described above. That is, the type of the virgin polystyrene resin mixed in Example 3 was changed to a virgin polystyrene resin having a lower MFR value, and the blending ratio was determined.

[0249] After the recycled polystyrene resin foam molded body 4 was aged in a drying chamber at 50 °C for 12 hours, its density was measured. As a result, it was 0.0167 g / cm 3 The recycled polystyrene resin foam molded body 4 formed by molding using the recycled polystyrene resin foam particles 4 had no deformation due to shrinkage and had a good appearance. The average maximum flexural strength of the recycled polystyrene resin foam molded body 4 was 0.38 MPa.

[0250] [Example 5] The columnar pellets produced in (1) of Example 1 were subjected to a fluorescence X-ray analyzer (XL3t-700-ss manufactured by Thermo Fisher Scientific Inc.) to measure and confirm the content (concentration) of the substances subject to the RoHS Directive in the pellets. As a result, it was confirmed that the pellets were below the allowable limit concentration for the 10 substances subject to the RoHS Directive regulations. The pellets correspond to the heat shrinkage material.

[0251] [Reference Example 1] As the virgin polystyrene resin, PS680 (MFR 6.6 g / 10 min) manufactured by PSJ and PS679 (MFR 18.0 g / 10 min) manufactured by PSJ were selected, and the blending ratio was adjusted to a weight ratio of 50:50 to obtain a melt-kneaded product. Except for this point, reference foaming polystyrene resin particles were produced in the same manner as in Example 3. The MFR of the obtained reference foaming polystyrene resin particles was measured. As a result, it was 12.5 g / 10 min.

[0252] Subsequently, in the same manner as in Example 3, reference polystyrene-based resin foamed particles were produced from reference foaming polystyrene-based resin particles, and a reference polystyrene-based resin foamed molded body was produced from the reference polystyrene-based resin foamed particles.

[0253] The reference polystyrene-based resin foamed molded body was aged in a drying chamber at 50°C for 12 hours, and then its density was measured. As a result, it was 0.0167 g / cm 3 . The reference polystyrene-based resin foamed molded body formed by molding using the reference polystyrene-based resin foamed particles had no deformation due to shrinkage and had a good appearance. The average maximum bending strength of the reference polystyrene-based resin foamed molded body was 0.38 MPa.

[0254] As described above, the polystyrene-based resin foamed molded bodies 1 to 5 produced using the recycled polystyrene-based resin foamed particles 1 to 5 produced by the present manufacturing method all had no deformation due to shrinkage and had a good appearance. Also, the average maximum bending strength of the recycled polystyrene-based resin foamed molded bodies 1 to 5 was 0.34 MPa to 0.38 MPa, showing an average maximum bending strength equivalent to that of a foamed molded body made of virgin polystyrene-based resin.

[0255] Furthermore, the MFR of the recycled foaming polystyrene-based resin particles 1 to 5 of Examples 1 to 5 was 12.5 g / 10 min to 15.5 g / 10 min. This was significantly lower than the MFR of the comparative foaming polystyrene-based resin particles constituting the comparative recycled polystyrene-based resin foamed molded bodies 1 and 2, and was within the range of 7 g / 10 min to 18 g / 10 min, which is a range suitable for imparting foaming properties, that is, a range having stable processing performance.

[0256] Therefore, it can be understood that according to the present manufacturing method, recycled foaming polystyrene-based resin particles having stable processing performance can be provided.

Industrial Applicability

[0257] The present invention is suitably used in fields such as: transport packaging materials (reusable containers) for fish boxes, vegetable boxes, and food containers; residential insulation materials for walls, floors, roofs, etc.; insulation materials used in automobiles, etc.; building material insulation materials used for water heaters, hot water tanks, piping, solar systems, etc.; cushioning materials, floats, embankment materials, tatami core materials, cushion core materials, and concrete aggregates.

Claims

1. Step (1) involves polymerizing a seed resin containing the heat-reduced volume of a recovered polystyrene foam molded product with a styrene monomer, and impregnating the resulting polystyrene resin particles with a foaming agent to produce recycled foamable polystyrene resin particles. Prior to the polymerization, a measurement step is taken to measure the melt flow rate of the heated volume-reduced product, Includes, The method for producing recycled foamable polystyrene resin particles, comprising the step (1) of determining the polymerization conditions for polymerizing the seed resin and the styrene monomer based on the melt flow rate obtained in the measurement step.

2. Step (A) involves mixing the heated volume reduction product of a recovered polystyrene foam molded product with virgin polystyrene resin, Step (B) involves impregnating the mixture obtained in step (A) with a foaming agent to produce recycled foamable polystyrene resin particles. Before obtaining the aforementioned mixture, a measurement step is taken to measure the melt flow rate of the heated volume reduction product, Includes, The method for producing recycled foamable polystyrene resin particles includes a control step in which one or more of the following are selected from the group consisting of (X), (Y), and (Z) based on the melt flow rate obtained in the measurement step: (X) Adjustment of the blending ratio of the virgin polystyrene resin to be mixed in step (A); (Y) Selection of the melt flow rate of the virgin polystyrene resin to be mixed in step (A); (Z) Selection of the weight-average molecular weight of the virgin polystyrene resin to be mixed in step (A).

3. A method for producing recycled foamable polystyrene resin particles according to claim 1 or 2, comprising the step of confirming the concentration of environmentally hazardous substances regulated by the RoHS Directive in the heated volume-reduced product by fluorescent X-ray analysis.

4. A method for producing recycled foamable polystyrene resin particles according to claim 1, comprising a heating and volume reduction step of heating and reducing the volume of the recovered polystyrene resin foam molded product prior to step (1) above.

5. A method for producing recycled foamable polystyrene resin particles according to claim 2, comprising a heating and volume reduction step of heating and reducing the volume of the recovered polystyrene resin foam molded product prior to step (A) above.

6. A method for producing recycled foamable polystyrene resin particles according to claim 4 or 5, comprising a recovery step prior to the heating volume reduction step, wherein the foamed polystyrene resin molded body is recovered and used as the recovered product.

7. A method for producing recycled foamed polystyrene resin particles, comprising the step of foaming the recycled foamed polystyrene resin particles produced by the method for producing recycled foamed polystyrene resin particles according to claim 1 or 2.

8. A method for producing a recycled polystyrene foam molded article, comprising the step of molding the recycled polystyrene foam particles produced by the method for producing recycled polystyrene foam particles described in claim 7.

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