Polystyrene-based seed resin particles for seed polymerization and their applications

Abstract

The present invention provides polystyrene-based seed resin particles for seed polymerization that have a fast maturation rate and a narrow particle size distribution, and can be used as seed resins for seed polymerization. [Solution] A polystyrene seed resin particle for seed polymerization containing a polystyrene resin and a composite containing an acrylic polymer, wherein the content of the composite is 0.03 to 0.50 parts by weight per 100 parts by weight of styrene units contained in the polystyrene resin, and the composite has a solubility of 13% or more in styrene monomers at 23°C.

Description

Technical Field

[0001] The present invention relates to polystyrene-based seed resin particles for seed polymerization and their use.

Background Art

[0002] Conventionally, polystyrene-based foamed particles have been used in cushion beads, lightweight aggregate applications, and molded bodies that require beauty. Polystyrene-based foamed particles are obtained by foaming polystyrene-based resin particles impregnated with a foaming agent. Further, the polystyrene-based resin particles can be produced by seed polymerization using polystyrene-based seed resin particles.

[0003] For example, Patent Document 1 discloses polystyrene-based seed resin particles for seed polymerization having an average particle diameter of 0.20 to 0.50 mm.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, conventional polystyrene-based resin particles have a slow aging rate, and the aging period until beautiful foamed particles are obtained may be long. On the other hand, when the addition amount of a nucleating agent is increased during the production of polystyrene-based seed resin particles used for seed polymerization, the aging rate of the polystyrene-based resin particles is improved, but the particle diameter of the polystyrene-based seed resin particles may become non-uniform and the particle size distribution (UT) may become wide.

[0006] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide polystyrene-based seed resin particles that can be used as seed resins for seed polymerization, which have a fast maturation rate and a narrow particle size distribution. [Means for solving the problem]

[0007] As a result of diligent research to solve the above problems, the present inventors have discovered that by dissolving a highly soluble nucleating agent in styrene monomer during seed resin production, not only is the maturation rate of the resin particles increased, but the nucleating agent can also be uniformly dispersed within the resin, thus completing the present invention.

[0008] In other words, one aspect of the present invention includes the following configuration. [1] Contains a polystyrene resin and a composite containing an acrylic polymer, The content of the composite is 0.03 to 0.50 parts by weight per 100 parts by weight of styrene units contained in the polystyrene resin. The composite has a solubility of 13% or more in styrene monomer at 23°C. Polystyrene-based seed resin particles for seed polymerization. [2] The composite is a polystyrene-based resin particle according to [1], wherein the specific viscosity of a solution obtained by dissolving 0.018 g of the composite in 30 mL of toluene is less than 0.10 at 23°C. Polystyrene resin particles, including polystyrene-based resin particles as described in [3][1] or [2]. Polystyrene foamed particles obtained by foaming the polystyrene resin particles described in [4][3]. A polystyrene foam molded article obtained by molding the polystyrene foam particles described in [5] and [4]. [6] A monomer polymerization step is included in which polystyrene-based resin particles are obtained from a mixture containing a styrene-based monomer and a composite containing an acrylic-containing polymer by droplet polymerization. The content of the composite in the mixed solution is 0.03 to 0.50 parts by weight per 100 parts by weight of the styrene monomer. The composite has a solubility of 13% or more in styrene monomer at 23°C. A method for producing polystyrene-based seed resin particles for seed polymerization. [7] The composite is a solution obtained by dissolving 0.018 g of the composite in 30 mL of toluene, the specific viscosity of which is less than 0.10 at 23°C, as described in [6], for producing polystyrene-based resin particles. [8] A method for producing polystyrene-based resin particles according to [6] or [7], wherein the specific viscosity of the mixed solution in the monomer polymerization step is 0.500 or less at 23°C. A method for producing polystyrene resin particles, comprising a seed resin polymerization step of seed polymerizing polystyrene-based seed resin particles obtained by the manufacturing method described in any one of [9], [6], to [8]. A method for producing polystyrene foam particles, comprising an impregnation step of impregnating polystyrene resin particles obtained by the manufacturing method described in

[10] [9] with a foaming agent, and a foaming step of foaming the polystyrene resin particles impregnated with the foaming agent. A method for producing a polystyrene foam molded article, comprising a molding step of molding polystyrene foam particles obtained by the manufacturing method described in

[11]

[10] . [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide polystyrene-based resin particles that have a fast maturation rate and a narrow particle size distribution, and that can be used as seed resins for seed polymerization. [Modes for carrying out the invention]

[0010] 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 appropriately 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)."

[0011] [1. Polystyrene-based resin particles] Polystyrene seed resin particles for seed polymerization according to one embodiment of the present invention contain a polystyrene resin and a composite containing an acrylic-containing polymer, wherein the content of the composite is 0.03 to 0.50 parts by weight per 100 parts by weight of styrene units contained in the polystyrene resin, and the solubility of the composite in styrene monomers is 13% or more at 23°C.

[0012] The polystyrene-based seed resin particles according to one embodiment of the present invention are for seed polymerization. That is, the polystyrene-based seed resin particles are used as seed resin particles when producing polystyrene-based resin particles by seed polymerization. In other words, polystyrene-based resin particles can be produced by seed polymerization using polystyrene-based seed resin particles. Furthermore, polystyrene-based foamed particles can be produced by impregnating the polystyrene-based resin particles with a foaming agent and then foaming them. In addition, a polystyrene-based foamed molded article can be produced by molding the polystyrene-based foamed particles.

[0013] In this specification, "polystyrene-based resin particles according to one embodiment of the present invention" may also be simply referred to as "polystyrene-based resin particles." That is, the term "polystyrene-based resin particles" refers to one embodiment of the polystyrene-based resin particles in the present invention. Similarly, "polystyrene-based resin particles," "polystyrene-based foamed particles," and "polystyrene-based foamed molded article" each refer to one embodiment of the respective particles and molded article.

[0014] The polystyrene-based seed resin particles preferably have an average particle diameter of 0.20 mm or more and 0.50 mm or less. If the average particle diameter is within the above range, styrene monomers can easily impregnate the polystyrene-based seed resin particles when they are produced by seed polymerization. As a result, polymerization can occur more uniformly inside and near the outer edge of the polystyrene-based resin particles, and the cell size tends to be more uniform when polystyrene-based foam particles are formed, resulting in a more aesthetically pleasing appearance of the individual polystyrene-based foam particles. In this specification, the average particle diameter is calculated from a distribution table showing the cumulative distribution of particle diameters measured on a volume basis. The average particle diameter is defined as the particle diameter at which the cumulative volume percentage is 50% (also called the median diameter).

[0015] When polystyrene-based resin particles are produced by the droplet polymerization method described later, in other words, the average particle size of the resulting polystyrene-based resin particles can be adjusted by changing the size of the droplets. The size of the droplets can be adjusted by changing the vibration frequency when the mixed liquid containing the styrene monomer and the composite is vibrated. When obtaining polystyrene-based resin particles with an average particle size of 0.20 mm or more, the vibration frequency when vibrating the mixed liquid in the droplet polymerization method becomes appropriate, and the size of the resulting droplets also becomes appropriate. As a result, there is no risk of a large amount of fine polystyrene-based resin particles being generated by the droplet polymerization method. This has the advantage of making it easier to obtain polystyrene-based resin particles with a narrow UT (for example, 2.50 or less).

[0016] Polystyrene-based seed resin particles have a narrow particle size distribution. In this specification, that the polystyrene-based seed resin particles "have a narrow particle size distribution" means that the particle size distribution of the polystyrene-based seed resin particles is 2.50 or less. The polystyrene-based seed resin particles preferably have a particle size distribution (also referred to as UT) of 2.50 or less, more preferably 2.45 or less, still more preferably 2.40 or less, still more preferably 2.35 or less, still more preferably 2.30 or less, still more preferably 2.25 or less, still more preferably 2.20 or less, still more preferably 2.15 or less, and particularly preferably 2.10 or less. If the particle size distribution of the polystyrene-based seed resin particles is 2.50 or less, the particle diameter of the obtained polystyrene-based expanded particles will also be uniform, and the appearance of the aggregate of the polystyrene-based expanded particles will tend to be beautiful. Also, if the particle size distribution of the polystyrene-based seed resin particles is 2.50 or less, seed polymerization can be carried out without adjusting the particle diameter of the seed resin particles to obtain polystyrene-based resin particles having a uniform or substantially uniform particle diameter.

[0017] In this specification, UT is calculated from a distribution table showing the particle diameter measured on a volume basis in a cumulative distribution. Specifically, when the particle diameters at which the cumulative volume percentages are 90%, 60%, 40%, and 10% are defined as D90, D60, D40, and D10, respectively, the numerical value obtained by the following formula is taken as the particle size distribution (UT). Particle size distribution (UT) = (D90 / D40) + (D60 / D10) Note that when all the particles have exactly the same particle diameter, UT becomes 2.00. Therefore, the particle size distribution UT of the polystyrene-based seed resin particles is 2.00 or more.

[0018] The polystyrene-based seed resin particles according to an embodiment of the present invention include a composite including an acrylic-containing polymer having a solubility of 13% or more with respect to a styrene monomer at 23°C, whereby polystyrene-based resin particles with a high aging rate can be provided. Since the aging rate of the polystyrene-based resin particles is high, it becomes possible to produce polystyrene-based foamed particles from the seed resin particles in a short period of time. Further, since the composite contained in the polystyrene-based seed resin particles has a solubility of 13% or more with respect to the styrene monomer at 23°C, it is uniformly dispersed within the polystyrene-based seed resin particles and can function as a nucleating agent. As a result, in the polystyrene-based foamed particles obtained by foaming the polystyrene-based resin particles obtained from the polystyrene-based seed resin particles, the cells do not become coarse and the resulting cell spots are reduced. Therefore, the appearance of the polystyrene-based foamed particles becomes beautiful. Hereinafter, the details of the polystyrene-based seed resin particles will be described.

[0019] (1-1. Styrene-based resin) The polystyrene-based seed resin particles include a styrene-based resin. The styrene-based resin is a resin mainly containing styrene-based units. In the present specification, the "styrene-based unit" is a structural unit derived from a styrene-based monomer. In one embodiment, the styrene-based monomer is styrene. Here, "mainly containing styrene-based units" is intended to mean that when the total number of all structural units contained in the styrene-based resin is 100%, the number of styrene-based units is contained at 50% or more. Preferably, the styrene-based resin contains 70% or more, more preferably 80% or more, and even more preferably 90% or more of styrene-based units as structural units. If the styrene-based units are contained at 50% or more, the polystyrene-based seed resin particles can efficiently absorb the styrene monomer during seed polymerization.

[0020] The styrene-based resin may be a homopolymer of styrene monomers. Specific examples of styrene monomers include (i) styrene and (ii) styrene derivatives such as α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. Alternatively, the styrene-based resin may be a copolymer of (i) a styrene monomer and (ii) a monomer other than a styrene monomer, such as an ester of acrylic acid (e.g., methyl acrylate, ethyl acrylate, butyl acrylate, cetyl acrylate, alkylene glycol diacrylate), an ester of methacrylic acid (e.g., methyl methacrylate, ethyl methacrylate, butyl methacrylate, cetyl methacrylate, alkylene glycol dimethacrylate), acrylonitrile, dimethyl fumarate, and ethyl fumarate. In one embodiment, the styrene-based resin may be a polymer of the above-mentioned styrene monomer and a difunctional monomer such as divinylbenzene or alkylene glycol dimethacrylate.

[0021] From the viewpoint of improving the foaming properties when polystyrene resin particles impregnated with a foaming agent foam, and making it easier to obtain foamed particles with a high foaming ratio, it is preferable that the styrene resin contains 50% or more styrene units as constituent units, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more.

[0022] The styrene resin contained in polystyrene-based resin particles is obtained by polymerization of styrene monomers. Therefore, the content of each component during the production of polystyrene-based resin particles may be based on the content of styrene monomers, while the content of each component in the polystyrene-based resin particles themselves may be based on 100 parts by weight of styrene units contained in the styrene resin. However, in the production of polystyrene-based resin particles, the weight of the styrene monomers used as raw materials is usually almost the same as the weight of styrene units contained in the styrene resin. Therefore, 100 parts by weight of styrene monomers during the production of polystyrene-based resin particles and 100 parts by weight of styrene units contained in the produced polystyrene-based resin particles can be said to represent substantially the same value.

[0023] (1-2. Composites containing acrylic polymers) The polystyrene-based resin particles contain a composite comprising an acrylic-containing polymer. The composite may be finely dispersible in the polystyrene-based resin and may function as a nucleating agent. In this specification, "acrylic-containing polymer" means a polymer containing at least acrylic units. In one embodiment, the acrylic units contained in the acrylic-containing polymer may be methacrylic units. However, the styrene-based resin described above is not included in the acrylic-containing polymer.

[0024] The composite has a core-shell structure comprising a core portion and a shell portion. The core portion and shell portion of the composite are formed solely from an acrylic-containing polymer. In one embodiment, the composite is obtained by polymerizing another acrylic-containing polymer in a latex containing a pre-polymerized acrylic-containing polymer. In other words, in the composite, a portion of the pre-polymerized acrylic-containing polymer may be covered by the later-polymerized acrylic-containing polymer. Therefore, the composite may have the pre-polymerized acrylic-containing polymer as the core portion and the other acrylic-containing polymer as the shell portion. In the composite, the shell portion may cover the entire core portion.

[0025] The acrylic unit content of the composite is 25-60% by weight, preferably 30-55% by weight, more preferably 35-50% by weight, and even more preferably 40-45% by weight, when the total composite is considered to be 100% by weight. If the acrylic unit content of the composite is 60% by weight or less, the solubility in styrene monomer tends to improve.

[0026] The acrylic-containing polymer may be a homopolymer of the acrylic acid ester or methacrylic acid ester described above, or it may be a copolymer obtained by polymerizing multiple types of these monomers. Furthermore, the acrylic-containing polymer may be a copolymer having constituent units derived from monomers other than acrylic acid esters and methacrylic acid esters, i.e., constituent units other than acrylic units (e.g., styrene-based units). In one embodiment, the acrylic-containing polymer may be a mixture of a polymer containing acrylic units and / or a copolymer containing acrylic units.

[0027] Other monomers besides acrylic acid esters and methacrylic acid esters that can be used in the production of acrylic-containing polymers include styrene monomers (e.g., styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, chlorostyrene, etc.), acrylonitrile, dimethyl fumarate, ethyl fumarate, and divinylbenzene. Therefore, acrylic-containing polymers may contain styrene-based units.

[0028] If the composite contains styrene-based units, the content of styrene-based units is preferably 25 to 70% by weight, more preferably 30 to 60% by weight, even more preferably 35 to 55% by weight, and particularly preferably 35 to 50% by weight, when the total weight of the composite is 100% by weight. If the content of styrene-based units in the composite is 25% by weight or more, the solubility in styrene monomers tends to improve, and the uniformity of the composite within the seed resin particles increases. On the other hand, if it is 70% by weight or less, it becomes difficult to completely dissolve in styrene monomers, thus improving the nucleating effect.

[0029] In one embodiment, the styrene-based units contained in the composite may be styrene units. When the styrene-based units of the composite contain styrene units, the styrene unit content is preferably 25 to 70% by weight, more preferably 30 to 60% by weight, even more preferably 35 to 55% by weight, and particularly preferably 35 to 50% by weight, when the entire composite is considered to be 100% by weight. If the styrene unit content of the composite is 25% by weight or more, the solubility in styrene monomers tends to improve, and the uniformity of the composite within the seed resin particles increases. On the other hand, if it is 70% by weight or less, it becomes difficult to completely dissolve in styrene monomers, thus improving the nucleating effect.

[0030] If the composite contains acrylonitrile units, the acrylonitrile unit content is preferably 5 to 25% by weight, more preferably 8 to 20% by weight, and even more preferably 10 to 16% by weight, when the entire composite is considered to be 100% by weight. Preferably, the composite contains acrylonitrile units only in the core portion.

[0031] The acrylic-containing polymer may specifically be methyl methacrylate-butadiene-styrene copolymer, methyl methacrylate-styrene copolymer, methyl methacrylate-butyl acrylate-styrene copolymer, methyl methacrylate-butyl acrylate-acrylonitrile-styrene copolymer, methyl methacrylate-butyl acrylate copolymer, and mixtures thereof.

[0032] The composite has a solubility of 13% or more in styrene monomer at 23°C. Preferably, the solubility is 14% or more, and more preferably 15% or more. In one embodiment, the solubility may be 20% or less. If the solubility is 13% or more, when the composite is mixed with styrene monomer, the composite dissolves more uniformly, and when foamed particles are formed, the cells tend to be more uniform. In particular, since the composite is soluble in styrene monomer, when used as a nucleating agent, it disperses uniformly in the mixture and is less likely to cause nozzle clogging when droplets are generated from the mixture. The solubility of the composite in styrene monomer is measured by the method described in the examples below. Note that 23°C is the room temperature when the composite is dissolved in styrene monomer. In other words, it can be said that the temperature of the styrene monomer and the composite when measuring the solubility is 23°C.

[0033] The specific viscosity of the composite is preferably less than 0.100, more preferably 0.080 or less, even more preferably 0.070 or less, and particularly preferably 0.060 or less, of the solution obtained by dissolving 0.018 g of the composite in 30 mL of toluene at 23°C. In one embodiment, the specific viscosity of the composite may be 0.020 or more. If the specific viscosity of the composite in 30 mL of toluene is less than 0.100 at 23°C, it has the advantage that the viscosity of the mixed solution during droplet formation is low, making it easier to shear the mixed solution, and that the composite is uniformly dispersed in the droplet, resulting in more uniform cells when the resulting polystyrene-based resin particles are used as polystyrene-based foamed particles. The specific viscosity is measured by the method described in the examples below. Note that 23°C is the room temperature when measuring the specific viscosity. In other words, it can be said that the temperature of the toluene, composite, and solution when measuring the specific viscosity is 23°C.

[0034] The content of the composite in the polystyrene-based resin particles is 0.03 to 0.50 parts by weight, preferably 0.03 to 0.35 parts by weight, and more preferably 0.05 to 0.15 parts by weight, per 100 parts by weight of styrene-based units contained in the polystyrene-based resin. All of the composite used in the production of the polystyrene-based resin particles may be contained in the resulting polystyrene-based resin particles.

[0035] Therefore, the content of the composite in polystyrene-based resin particles can also be said to be the amount of the composite used in the method for producing polystyrene-based resin particles. If the content is 0.03 parts by weight or more, it has the advantages of (i) an improved foaming rate of foamed polystyrene-based resin particles produced using polystyrene-based resin particles, (ii) the advantage that the cells become uniform and less likely to become coarse in the polystyrene foam particles produced by foaming the foamed polystyrene-based resin particles, and (iii) the advantage that the appearance of the polystyrene foam particles becomes beautiful. To obtain polystyrene-based resin particles with a content of 0.50 parts by weight or less, the amount of the composite used in the production of polystyrene-based resin particles should be 0.50 parts by weight or less per 100 parts by weight of styrene monomer used. In the production of polystyrene seed resin particles, if the amount of the composite used is 0.50 parts by weight or less per 100 parts by weight of the styrene monomer used, the mixing properties of the mixture due to vibration become good, and uniform droplets are generated, which tends to narrow the UT of the seed resin particles.

[0036] (1-3. Other ingredients) Polystyrene-based resin particles may contain plasticizers. Examples of plasticizers include (a) fatty acid glycers such as triglyceride stearate, triglyceride palmitate, triglyceride laurate, diglyceride stearate, and monoglyceride stearate; (b) vegetable oils such as coconut oil, palm oil, and palm kernel oil; (c) aliphatic esters such as dioctyl adipate and dibutyl sebacate; and (d) organic hydrocarbons such as liquid paraffin and cyclohexane. These plasticizers may be used individually or in combination of two or more.

[0037] The content of these plasticizers is preferably 0.25 to 5.0 parts by weight, and more preferably 0.50 to 3.0 parts by weight, per 100 parts by weight of styrene-based units. If the content is 0.25 parts by weight or more, the cells of the foamed particles obtained by foaming polystyrene-based resin particles obtained by seed polymerization become uniform and less likely to become coarse. Therefore, the foaming ability when polystyrene-based resin particles impregnated with the foaming agent foam is improved, and it becomes easier to obtain foamed particles with a high foaming ratio. Also, if the content is 5.0 parts by weight or less, shrinkage during foaming is reduced, making it easier to obtain foamed particles with a high foaming ratio.

[0038] The polystyrene-based resin particles may further contain flame retardants, flame retardant enhancers, etc., to the extent that their physical properties are not impaired.

[0039] Examples of flame retardants include (a) brominated polymers such as brominated polystyrene, copolymers of brominated butadiene and vinyl aromatics, brominated novolac resin allyl ethers, brominated poly(1,3-cycloalkadiene) and brominated poly(4-vinylphenol allyl ether), and (b) low molecular weight compounds such as polyglycerin dibromopropyl ether, tetrabromobisphenol A and tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl ether).

[0040] Examples of flame retardant additives include high-temperature decomposition type organic substances with high 10-hour half-life temperatures, such as cumene peroxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane.

[0041] [2. Polystyrene resin particles] Polystyrene resin particles according to one embodiment of the present invention include the polystyrene seed resin particles described above. In one embodiment, the polystyrene resin particles are obtained by seed polymerization of the polystyrene seed resin particles described above. In other words, a method for producing polystyrene resin particles according to one embodiment of the present invention includes a seed resin polymerization step of seed polymerization of the polystyrene seed resin particles described above.

[0042] In one embodiment, the seed resin polymerization step may include, for example, the following steps (1) to (3): (1) Mix polystyrene seed resin particles, a dispersant, a polymerization initiator, and optionally other additives (plasticizer, foam regulator, flame retardant, and flame retardant aid, etc.) with water to prepare an aqueous suspension. (2) Heat the aqueous suspension to a predetermined temperature. (3) At the predetermined temperature, add a monomer solution containing styrene monomers to the aqueous suspension over a predetermined period of time, and carry out a polymerization reaction by reacting the aqueous suspension. This yields polystyrene resin particles. The seed resin polymerization step may further include (4) a step of impregnating the polystyrene resin particles with a foaming agent during or after step (3) to make foamable polystyrene resin particles. If the seed resin polymerization step includes (4), the end of the seed resin polymerization step is defined as the point at which both (3) and (4) are completed. In this specification, polystyrene resin particles impregnated with a foaming agent are referred to as foamed polystyrene resin particles. That is, when the seed resin polymerization step includes (4), foamed polystyrene resin particles can be obtained by the method for producing polystyrene resin particles.

[0043] Polystyrene resin particles and foamed polystyrene resin particles are obtained by seed polymerization of the polystyrene seed resin particles described above, and therefore have a fast maturation rate. In this specification, "fast maturation rate" means that, one day after the completion of the seed resin polymerization process, foamed particles with uniform cell size can be obtained from the resin particles obtained by the seed resin polymerization process, or from the foamed resin particles used as foamed particles. In this specification, "uniform cell size" means that when the cells within the foamed particles are observed by the method described in the examples below, the average chord length of each cell is 30 to 80 μm. Furthermore, if the average chord length is within the above range, the cells can also be said to be fine.

[0044] The amount of polystyrene-based seed resin particles in the seed resin polymerization process is preferably 5 to 60% by weight, when the amount of polystyrene-based resin particles obtained is taken as 100% by weight. If the final product is foamed polystyrene-based resin particles, the weight excluding the foaming agent is taken as 100% by weight. When the amount of polystyrene-based seed resin particles is 5% by weight or more, the proportion of styrene-based monomers added to the aqueous suspension that polymerize independently decreases, while the proportion of monomers that polymerize into seed resin particles to form styrene-based resin particles tends to increase. Furthermore, when the amount of polystyrene-based seed resin particles is 60% by weight or less, it becomes economically advantageous because it is possible to polymerize more monomers per seed resin particle in a single production cycle to produce resin particles.

[0045] Examples of the above-mentioned dispersants include (a) poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin, and (b) water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone.

[0046] Examples of polymerization initiators include organic peroxides and azo compounds. Examples of organic peroxides include benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl carbonate. Examples of azo compounds include azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used individually or in combination of two or more. Note that t-butyl peroxy-2-ethylhexyl carbonate is also called t-butyl peroxy-2-ethylhexyl monocarbonate.

[0047] Polystyrene resin particles may further be produced by seed polymerization using a chain transfer agent and a polymerization regulator. Examples of the chain transfer agent include mercaptan compounds such as n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan. Examples of the polymerization regulator include α-methylstyrene dimer, which is commonly used in the polymerization of acrylonitrile-styrene resins.

[0048] In this specification, a blowing agent refers to a readily volatile compound that slightly swells polystyrene resin particles. Examples of blowing agents include, but are not limited to, (a) aliphatic hydrocarbons such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentanecyclohexane, and (b) fluorinated hydrocarbons with zero ozone depletion potential such as difluoroethane and tetrafluoroethane. The blowing agents described above may be used alone or in combination of two or more. Among the blowing agents described above, it is preferable to use a combination of 7.7 parts by weight of n-butane and 2.0 parts by weight of cyclohexane.

[0049] The polystyrene resin particles may further contain plasticizers, foam regulators, flame retardants, flame retardant aids, etc., to the extent that their physical properties are not impaired. These components can be added in step (1) of the seed resin polymerization process described above.

[0050] [3. Polystyrene foam particles] Polystyrene foam particles according to one embodiment of the present invention are obtained by foaming the polystyrene resin particles described above. Polystyrene foam particles according to one embodiment of the present invention can also be said to include the polystyrene resin particles described above. In other words, the method for producing polystyrene foam particles according to one embodiment of the present invention includes an impregnation step of impregnating the polystyrene resin particles described above with a foaming agent, and a foaming step of foaming the polystyrene resin particles impregnated with the foaming agent. Foamable polystyrene resin particles may be used instead of polystyrene resin particles. When producing polystyrene foam particles using foamable polystyrene resin particles, the impregnation step may be omitted. Due to the above configuration, polystyrene foam particles have a uniform particle size and few cell irregularities, resulting in a beautiful appearance.

[0051] The method for foaming polystyrene resin particles, that is, the method for carrying out the foaming process described above, is not particularly limited, and known methods can be used. An example of a foaming method is to sequentially perform the following steps (1) to (3): (1) Place the foaming polystyrene resin particles in a container equipped with a stirrer. (2) Heat the foaming polystyrene resin particles with a heat source such as steam. (3) Continue foaming until a desired foaming ratio is reached to obtain polystyrene foamed particles. Note that polystyrene foamed particles may be referred to as polystyrene resin pre-foamed particles. Therefore, the foaming method for obtaining polystyrene resin pre-foamed particles may be referred to as a pre-foaming method.

[0052] [4. Polystyrene foam molded articles] A polystyrene foam molded article according to one embodiment of the present invention is obtained by molding (for example, in-mold molding) the polystyrene foam particles described above. In other words, a method for manufacturing a polystyrene foam molded article according to one embodiment of the present invention includes a molding step of molding (for example, in-mold molding) the polystyrene foam particles described above. Because the polystyrene foam molded article according to one embodiment of the present invention has the above-described structure, it has the advantage of having excellent surface aesthetics.

[0053] The method for molding polystyrene foam particles, that is, the method for manufacturing polystyrene foam molded articles, is not particularly limited, and known methods can be used. One example of a molding method is an in-mold molding method in which foam particles are filled into a mold that can be closed but is not airtight, and the foam particles are heated and fused together with steam to form a foam molded article. Another in-mold molding method is to fill foam particles into a closed mold having a desired shape and numerous small holes drilled in its walls, and then heat the foam particles to a temperature above their softening point by spraying a heating medium such as steam from the mold holes, causing them to fuse together, and then cool them to produce a polystyrene foam molded article of the desired shape.

[0054] [5. Method for producing polystyrene-based resin particles] A method for producing polystyrene-based seed resin particles according to one embodiment of the present invention includes a monomer polymerization step of obtaining polystyrene-based seed resin particles by droplet polymerization from a mixed solution containing a styrene monomer and the composite, wherein the content of the composite in the mixed solution is 0.03 to 0.50 parts by weight per 100 parts by weight of the styrene monomer, and the composite has a solubility of 13% or more in the styrene monomer at 23°C.

[0055] Matters already described in sections [1. Polystyrene-based resin particles] to [4. Polystyrene-based foamed molded articles] are omitted.

[0056] The aforementioned droplet polymerization method is intended to be a method of polymerizing monomers by dispersing them as droplets in an aqueous medium by passing them through a nozzle under regular vibration, without causing droplet adhesion or additional dispersion (or with significantly reduced occurrence of adhesion and additional dispersion). Examples of aqueous mediums used in the droplet polymerization method include water.

[0057] A droplet polymerization method for obtaining a seed resin has, for example, the following configuration: (1) A dispersion step in which a mixture containing at least a styrene monomer, the composite and a polymerization initiator, and optionally other additives is passed through a droplet generation nozzle under regular vibration to disperse the mixture as droplets in an aqueous medium containing water and optionally a dispersant, etc., to prepare an aqueous suspension; (2) Next, a heating step in which the aqueous suspension is heated to a predetermined polymerization temperature; (3) Next, a seed resin polymerization step in which the aqueous suspension is reacted at the predetermined polymerization temperature for a predetermined polymerization time to carry out a polymerization reaction and obtain a copolymer. Steps (1) to (3) are usually carried out under gentle stirring (for example, 200 rpm or less).

[0058] In droplet polymerization, droplet groups are dispersed in an aqueous medium by passing them through a droplet generation nozzle under regular vibrations, making it unlikely or impossible for droplets to adhere to each other or to undergo additional dispersion. Therefore, seed resin particles produced by droplet polymerization tend to have a narrow particle size distribution and excellent uniformity of particle size.

[0059] As polymerization initiators, radical-generating polymerization initiators commonly used in the production of thermoplastic resins can be used. Examples of radical-generating polymerization initiators include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-di-t-butyl peroxybutane, t-butyl peroxy-3,3,5-trimethylcyclohexanoate, di-t-butyl peroxyhexahydroterephthalate, and 1,1-di-t-butyl peroxy-3,3,5-trimethylcyclohexane, as well as azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used individually or in combination of two or more.

[0060] Additives included in the aforementioned mixture include dispersants. Commonly known dispersants include water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyvinylpyrrolidone, and polyacrylamide, as well as water-insoluble inorganic substances such as tricalcium phosphate, hydroxyapatite, magnesium phosphate, and magnesium pyrophosphate. When a water-insoluble inorganic substance is selected as the dispersant, the dispersion stability of droplets in the aqueous medium is improved by using an anionic surfactant such as sodium dodecylbenzenesulfonate in combination. Similarly, when a water-soluble polymer and a water-insoluble inorganic substance are used together as dispersants, the dispersion stability of droplets is also improved.

[0061] In the monomer polymerization step, the specific viscosity of the mixture is preferably 0.500 or less, more preferably 0.450 or less, even more preferably 0.400 or less, and particularly preferably 0.350 or less at 23°C. The specific viscosity of the mixture may also be, for example, 0.100 or more. If the specific viscosity of the mixture is within the above range, the UT of the resulting droplet will be narrower. The specific viscosity of the mixture is measured by the method described in the examples below. Note that 23°C is the room temperature when measuring the specific viscosity of the mixture. In other words, it can be said that the temperature of the mixture when measuring the specific viscosity is 23°C.

[0062] In one embodiment, the method for producing polystyrene-based resin particles also includes the method for producing a composite containing an acrylic-containing polymer. The method for producing the composite has, for example, the following configuration: (1) a core-forming step in which a monomer mixture containing at least an ester of acrylic acid or an ester of methacrylic acid is placed in water to which semi-cured potassium tallow fatty acid, disodium ethylenediaminetetraacetate, and ferrous sulfate are added, and the monomers are polymerized to form a core portion which is an acrylic-containing polymer; (2) a shell-forming step in which a mixture containing at least methyl methacrylate is continuously added to the latex containing the formed core portion and polymerized. [Examples]

[0063] One embodiment of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0064] (Method of manufacturing complex A) 1.0 part by weight of semi-hardened potassium tallow fatty acid, 0.0050 parts by weight of ethylenediaminetetraacetate disodium salt, and 0.0025 parts by weight of ferrous sulfate, pre-dissolved in water, were placed in a reactor equipped with a stirrer, and water was added until the total volume of the mixed solution reached 200 parts by weight. The gas in the reactor was replaced with nitrogen to remove oxygen contained in the solution and the space inside the reactor. The mixture was then stirred. During stirring, 0.4 parts by weight of sodium formaldehyde sulfoxylate was added to the reactor, and after raising the temperature of the contents to 75°C, a mixture of 12.6 parts by weight of acrylonitrile, 43.4 parts by weight of styrene, 6.0 parts by weight of butyl acrylate, 18.0 parts by weight of methyl methacrylate, 1.6 parts by weight of t-dodecyl mercaptan, and 1.6 parts by weight of t-butyl hydroperoxide was continuously added over 200 minutes to start the polymerization of the core. At 50 minutes and 100 minutes after the start of continuous addition, 0.3 parts by weight of semi-cured potassium tallow fatty acid was added, respectively. Also, at 100 minutes after the start of continuous addition, 0.15 parts by weight of sodium formaldehyde sulfoxylate was added. 200 minutes after the end of continuous addition, after the polymerization of the methyl methacrylate-butyl acrylate-acrylonitrile-styrene copolymer, which forms the core, was completed, a mixture of 2 parts by weight of butyl acrylate, 18 parts by weight of methyl methacrylate, and 0.3 parts by weight of t-butyl hydroperoxide was continuously added over 50 minutes to start the polymerization of the shell portion of the composite. After the completion of continuous addition, an additional 0.2 parts by weight of sodium formaldehyde sulfoxylate was added. After the addition of the polymerization components for the shell portion was completed, the contents of the reactor were kept at 75°C and stirred for more than 1 hour to complete the polymerization of the methyl methacrylate-butyl acrylate copolymer, which forms the shell portion. Subsequently, the contents of the reactor were cooled to obtain the latex of complex A. Four parts by weight of calcium chloride diluted to 1% at 25°C were added to the obtained complex A latex to allow it to coagulate. After that, heat treatment, dehydration, washing, and drying were performed to obtain the powder of complex A. The specific viscosity of a solution prepared by dissolving 0.018 g of complex A in 30 mL of toluene was 0.054 at 23°C. The solubility of complex A in styrene monomer was 15% at 23°C.

[0065] (Method for manufacturing complex B) 0.5 parts by weight of sodium dioctyl succinate, 0.0008 parts by weight of ferrous sulfate (FeSO4·7H2O), 0.0032 parts by weight of disodium ethylenediaminetetraacetate, and 0.06 parts by weight of sodium formaldehyde sulfoxylate, all pre-dissolved in water, were placed in a reactor equipped with a stirrer, and water was added to bring the total volume of the mixed solution to 200 parts by weight. The gas in the reactor was replaced with nitrogen to remove oxygen contained in the solution and the space inside the reactor. The mixture was then stirred. While the contents were heated to 60°C during stirring, a mixture of 80 parts by weight of methyl methacrylate and 0.05 parts by weight of t-butyl hydroperoxide was continuously added over 170 minutes to initiate polymerization of the core. 0.2 parts by weight of sodium dodecylbenzenesulfonate were added at 60 minutes and 120 minutes after the start of the continuous addition. 200 minutes after the completion of continuous addition, and after the polymerization of the methyl methacrylate homopolymer, which is an acrylic-containing polymer forming the core, was completed, a mixture of 8 parts by weight of methyl methacrylate, 12 parts by weight of butyl acrylate, and 0.05 parts by weight of t-butyl hydroperoxide was continuously added over 50 minutes to start the polymerization of the shell portion of the composite. After the addition of the polymer components for the shell portion was completed, the contents of the reactor were kept at 60°C and stirred for more than 1 hour to complete the polymerization of the methyl methacrylate-butyl acrylate copolymer, which is an acrylic-containing polymer forming the shell portion. Subsequently, the contents of the reactor were cooled to obtain the latex of composite B. 4 parts by weight of calcium chloride diluted to 1% at 25°C was added to the obtained composite B latex to solidify it, and then heat treatment, dehydration, washing, and drying were performed to obtain the powder of composite B. The specific viscosity of a solution prepared by dissolving 0.018 g of composite B in 30 mL of toluene was 0.102 at 23°C. Furthermore, the solubility of complex B in styrene monomer was 12% at 23°C.

[0066] (Method for producing polymer C) In a 6L autoclave equipped with a stirrer, 150 parts by weight of water, 0.46 parts by weight of tricalcium phosphate as the first poorly water-soluble inorganic salt, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide and 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as polymerization initiators, 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, 0.240 parts by weight of n-dodecyl mercaptan as a chain transfer agent, and 0.03 parts by weight of "Sumisorb 200" (registered trademark, manufactured by Sumika Chemtex Co., Ltd.) as a light stabilizer were added to prepare a mixture containing the first poorly water-soluble inorganic salt. Subsequently, 96.5 parts by weight of methyl methacrylate and 3.5 parts by weight of butyl acrylate as a monomer mixture, and 1.0 part by weight of toluene as a solvent were added to the mixture to prepare an aqueous suspension. Next, the temperature of this aqueous suspension was raised to 80°C to initiate polymerization. After 1 hour and 45 minutes from the start of polymerization, the polymerization conversion rate was measured to be 40% to 50%. After 1 hour and 45 minutes from the start of polymerization, 0.12 parts by weight of tricalcium phosphate was added to the aqueous suspension as a second poorly water-soluble inorganic salt. After the polymerization was completed, the aqueous suspension was cooled. After cooling the aqueous suspension, the obtained product was washed, dehydrated, and dried to obtain polymer C, a methyl methacrylate-butyl acrylate copolymer containing a base resin containing methyl methacrylate units and butyl acrylate units, which are acrylic acid esters, as constituent units. The specific viscosity of a solution prepared by dissolving 0.018 g of polymer C in 30 mL of toluene was 0.271 at 23°C. The solubility of polymer C in styrene monomer was 0% at 23°C.

[0067] (Measurement of average particle size and UT of polystyrene-based resin particles) The particle size of polystyrene-based resin particles was measured on a volume basis using an image processing type Millitrack JPA particle size analyzer. The measurement results of the volume-based particle size were displayed as a cumulative distribution, and a particle size distribution table was created. Using the obtained distribution table, the average particle size [mm] and particle size distribution (UT) of polystyrene-based resin particles were calculated according to the definition described above.

[0068] (Method for evaluating the maturation rate of polystyrene resin particles) After the seed resin polymerization process was completed, the resulting foamed polystyrene resin particles were placed in a 100°C steamer one day and two days after the completion of the polymerization process, and heated for 5 minutes to induce foaming, thereby obtaining foamed polystyrene particles. The obtained foamed polystyrene particles were cut in half, and the internal cell structure was observed using a JCM-7000NeoScope® desktop scanning electron microscope. The observation of the foamed particles was performed in low vacuum mode at a magnification of 35x. The maturation rate was evaluated according to the following criteria. If foamed particles with a uniform cell size and an average chord length of 30-80 μm were obtained from both resin particles one day and two days after the completion of the seed resin polymerization process, it was classified as A; if foamed particles with a uniform cell size and an average chord length of 30-80 μm were obtained only from resin particles two days after the completion of the seed resin polymerization process, it was classified as B; and if, regardless of which resin particles were used, only foamed particles with an average chord length of 30-80 μm and an uneven cell size were obtained, it was classified as C.

[0069] (Method for evaluating the nucleation effect of composites in polystyrene foam particles) A foamed molded body was obtained from polystyrene foam particles, and the molded body was sliced ​​thinly to about 0.1 mm using a bread slicer to obtain cell samples. The appearance of the obtained cell samples was observed visually, and the nucleation effect was evaluated based on the following indicators. The fewer the cell spots, the better the nucleation effect. Case A: Almost no cell spots and a beautiful surface; Case B: Slightly visible cell spots; Case C: Many cell spots.

[0070] (Method for measuring the solubility of the complex) At 23°C, 10 g of styrene was used as 100 parts by weight, and the composite was added 1 part by weight at a time while stirring. The state was checked after 2 hours. If the composite was completely dissolved, another 1 part by weight of the composite was added and stirred again. This process was repeated. If it was not dissolved after 2 hours, the solubility was calculated as (total weight of composites up to the last added part, relative to 100 parts by weight of styrene / 100) × 100 [%].

[0071] (Method for measuring specific viscosity) Complexes A and B, and polymer C were dissolved in 30 mL of toluene, and the specific viscosity of each was measured at 23°C using an automatic viscometer (capillary type). The specific viscosity of the monomer mixtures in each example and comparative example was also measured using an automatic viscometer (model SS-180-L1, Shibayama Scientific Instruments Co., Ltd.). Complexes A and B dissolved in styrene by stirring alone, but polymer C did not dissolve in styrene by stirring alone, so it was dissolved by ultrasonic vibration.

[0072] (Example 1) <Manufacturing of polystyrene-based resin particles> In a 6-liter reactor with a flat plate and stirring blades, which had an inlet at the bottom for a droplet generation device, 1.5 liters of aqueous dispersion medium, prepared in pure water to contain 11,000 ppm tricalcium phosphate and 110 ppm sodium dodecylbenzenesulfonate, were added and stirring was started.

[0073] Next, a monomer mixture was placed in a container having a supply line to a droplet generator. This mixture contained 5000 g of styrene monomer, 9.7 g of 1,1-di(tert-butylperoxy)cyclohexane, 25 g of tert-butylperoxy-2-ethylhexanoate, 50 g of liquid paraffin as a plasticizer, and 3.5 g of the above-mentioned complex A in the amount shown in Table 1 as a nucleating agent. The mixture was supplied to the droplet generator at a rate of 90 cc / min through a plate having 45 holes of 0.17 mmφ, and mechanical vibration at 800 Hz was applied to generate droplets of the mixture in an aqueous dispersion medium. The generated droplets were then transferred to the 6-liter reactor described above.

[0074] Furthermore, a solution of 530 g of 3% polyvinyl alcohol and 20 g of sodium nitrite dissolved in 5000 g of pure water was added to a container having a separate supply line to the droplet generation device from the monomer mixture, and this aqueous dispersion medium was supplied to the droplet generation device at a rate of 80 cc / min without passing through the plate.

[0075] After introducing droplets of 1500 g of monomer mixture into a 6-liter reactor, droplet formation was stopped. The dispersion in the reactor was heated to 90°C and polymerized for 3 hours. Polymerization was then completed by further heating the dispersion to 120°C and holding it for 1 hour. The slurry in the reactor was cooled and dehydrated to obtain polystyrene-based resin particles. The average particle size [mm] and particle size distribution (UT) of the obtained polystyrene-based resin particles were measured. The results are shown in Table 1.

[0076] <Manufacturing of expanded polystyrene resin particles> In a 6L autoclave equipped with a stirrer, 89.1 parts by weight of pure water, 0.38 parts by weight of tricalcium phosphate, 0.0104 parts by weight of sodium α-olefin sulfonate, 0.1 part by weight of sodium chloride, and 20 parts by weight of polystyrene resin seed particles with an average particle size of 0.43 mm were charged, and stirring was started. After raising the temperature inside the autoclave to 90°C, polymerization was carried out while adding (a) 0.223 parts by weight of dibenzoyl peroxide over 4 hours and 50 minutes, and (b) 80 parts by weight of styrene monomer over 5 hours and 30 minutes, as polymerization initiators. Furthermore, 0.064 parts by weight of 1,1-di(tert-butylperoxy)cyclohexane was added 4 hours and 45 minutes after the start of polymerization, and 0.012 parts by weight of divinylbenzene was added 5 hours and 23 minutes later, and the temperature inside the autoclave was maintained at 90°C for 30 minutes. Subsequently, 7.7 parts by weight of butane (n-rich butane (n-butane / isobutane = 70 / 30)) and 2.0 parts by weight of cyclohexane were added, and the mixture was maintained at 120°C for a further 3 hours to impregnate the polystyrene resin particles in the autoclave with the foaming agent. The autoclave was then cooled to room temperature, and the foamed polystyrene resin particles were removed from the autoclave. The removed foamed polystyrene resin particles were washed, dehydrated, and dried.

[0077] The obtained foamable polystyrene resin particles were placed into a rotary stirring foaming apparatus. The foamable polystyrene resin particles were then foamed in steam at approximately 100°C until the foaming ratio reached 60 times, obtaining polystyrene foam particles. The cells of the polystyrene foam particles were then observed to evaluate the maturation rate of the polystyrene resin particles. Next, the obtained polystyrene foam particles were molded using a KR-57 molding machine under the conditions of a blown steam pressure adjustment of 80 kPa, a steam input heating time of 18 seconds, and a water cooling time of 3 seconds, to obtain a polystyrene foam molded body (450 × 300 × 25 mm). Cell samples obtained from the polystyrene foam molded body were then observed to evaluate the nucleation effect.

[0078] (Example 2) As shown in Table 1, polystyrene resin particles, foamed polystyrene resin particles, polystyrene foam particles, and polystyrene foam molded articles were produced using the same procedure as in Example 1, except that the amount of composite A, which is a nucleating agent, was changed to 7.0 g in the manufacturing process of polystyrene-based seed resin particles. These were then evaluated in the same manner as in Example 1.

[0079] (Example 3) As shown in Table 1, polystyrene resin particles, foamed polystyrene resin particles, polystyrene foam particles, and polystyrene foam molded articles were produced using the same procedure as in Example 1, except that the amount of composite A, which is a nucleating agent, was changed to 17.5 g in the manufacturing process of polystyrene-based seed resin particles. These were then evaluated in the same manner as in Example 1.

[0080] (Comparative Example 1) As shown in Table 1, polystyrene resin particles, foamed polystyrene resin particles, polystyrene foam particles, and polystyrene foam molded articles were produced using the same procedure as in Example 1, except that the nucleating agent, composite A, was changed to composite B in the manufacturing process of polystyrene-based seed resin particles. These were then evaluated in the same manner as in Example 1.

[0081] (Comparative Example 2) As shown in Table 1, the same procedure as in Example 1 was followed, except that the nucleating agent complex A was changed to complex B and the amount was changed to 7.0 g in the manufacturing process of polystyrene-based seed resin particles. Polystyrene-based resin particles, foamed polystyrene-based resin particles, polystyrene-based foamed particles, and polystyrene-based foamed molded articles were produced and evaluated in the same manner as in Example 1.

[0082] (Comparative Example 3) As shown in Table 1, polystyrene resin particles, foamed polystyrene resin particles, polystyrene foam particles, and polystyrene foam molded articles were produced using the same procedure as in Example 1, except that the nucleating agent, composite A, was changed to composite B and the amount was changed to 17.5 g in the manufacturing process of polystyrene-based seed resin particles. These were then evaluated in the same manner as in Example 1.

[0083] (Comparative Example 4) As shown in Table 1, polystyrene resin particles, foamed polystyrene resin particles, polystyrene foam particles, and polystyrene foam molded articles were produced using the same procedure as in Example 1, except that composite A, which is a nucleating agent, was replaced with polymer C in the manufacturing process of polystyrene-based seed resin particles. These were then evaluated in the same manner as in Example 1.

[0084] In Table 1, the nucleating agent content is shown as parts by weight per 100 parts by weight of the total styrene monomers used in the production of polystyrene-based seed resin particles.

[0085] [Table 1]

[0086] Table 1 shows that Examples 1-2, which used composite A, having a solubility of 13% or more in styrene monomer at 23°C, exhibited a faster maturation rate compared to Comparative Examples 1-2. Furthermore, Comparative Examples 1-3, using composite B, all showed higher UT compared to Examples 1-3, which used the same amount of composite A. Comparative Example 4, using polymer C, was inferior to Examples 1-3 in both maturation rate and nucleating effect. Therefore, according to one embodiment of the present invention, it is possible to provide polystyrene-based resin particles with a fast maturation rate and a narrow particle size distribution, which can be used as seed resins for seed polymerization. [Industrial applicability]

[0087] According to one aspect of the present invention, it is possible to provide polystyrene-based resin particles having a fast maturation rate and a narrow particle size distribution, which can be used as seed resin for seed polymerization. Therefore, seed resin particles according to one embodiment of the present invention can be suitably used in the manufacture of cushion beads, foamed molded articles for building materials, and lightweight concrete, etc.

Claims

1. It contains a polystyrene resin and a composite containing an acrylic polymer. The content of the composite is 0.03 to 0.50 parts by weight per 100 parts by weight of styrene units contained in the polystyrene resin. The composite has a solubility of 13% or more in styrene monomer at 23°C. Polystyrene-based seed resin particles for seed polymerization.

2. The composite is a polystyrene-based resin particle according to claim 1, wherein the specific viscosity of a solution obtained by dissolving 0.018 g of the composite in 30 mL of toluene is less than 0.10 at 23°C.

3. Polystyrene resin particles comprising polystyrene-based species resin particles according to claim 1 or 2.

4. Polystyrene foamed particles obtained by foaming the polystyrene resin particles described in claim 3.

5. A polystyrene foam molded article obtained by molding polystyrene foam particles as described in claim 4.

6. The process includes a monomer polymerization step in which polystyrene-based resin particles are obtained from a mixture containing a styrene-based monomer and a composite containing an acrylic-containing polymer by droplet polymerization. The content of the composite in the mixed solution is 0.03 to 0.50 parts by weight per 100 parts by weight of the styrene monomer. The composite has a solubility of 13% or more in styrene monomer at 23°C. A method for producing polystyrene-based seed resin particles for seed polymerization.

7. The method for producing polystyrene-based resin particles according to claim 6, wherein the composite is a solution obtained by dissolving 0.018 g of the composite in 30 mL of toluene, and the specific viscosity of the solution is less than 0.10 at 23°C.

8. The method for producing polystyrene-based resin particles according to claim 6, wherein the specific viscosity of the mixed solution in the monomer polymerization step is 0.500 or less at 23°C.

9. A method for producing polystyrene resin particles, comprising a seed resin polymerization step of seed polymerizing polystyrene-based seed resin particles obtained by the manufacturing method described in any one of claims 6 to 8.

10. A method for producing polystyrene foam particles, comprising an impregnation step of impregnating polystyrene resin particles obtained by the manufacturing method described in claim 9 with a foaming agent, and a foaming step of foaming the polystyrene resin particles impregnated with the foaming agent.

11. A method for producing a polystyrene foam molded article, comprising a molding step of molding polystyrene foam particles obtained by the manufacturing method described in claim 10.

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