Styrenic seed resin particles for seed polymerization and their use

Abstract

To provide foamable polystyrene-based resin particles which have a small particle size and narrow particle size distribution and are excellent in foamability, and styrenic seed resin particles which improve productivity of polystyrene-based foamed particles excellent in appearance.SOLUTION: Styrenic seed resin particles for seed polymerization contain a base material resin containing a styrene unit as a constitutional unit, contain specific amounts of a plasticizer and a nucleating agent, have an average particle diameter of 0.20-0.50 mm, and UT indicating variations in particle size distribution of 2.15 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to styrene seed resin particles for seed polymerization to obtain expandable polystyrene seed resin particles, and to the use thereof. [Background technology]

[0002] Uniform polystyrene-based expanded beads are used for cushion beads, lightweight aggregates, and molded objects that require beauty. Uniform styrene-based seed resin particles are useful materials because they can be impregnated with styrene, polymerized, and then impregnated with a blowing agent to obtain uniform expandable polystyrene-based resin particles.

[0003] So far, various styrene-based seed resin particles have been developed. For example, Patent Document 1 discloses styrene-based seed resin particles obtained by separating polystyrene-based resin particles containing a nucleating agent and a plasticizer produced by suspension polymerization, and then separating particles having a particle size of 0.425 mm to 0.500 mm by sieving.

[0004] Patent Document 2 discloses styrene-based seed resin particles containing a nucleating agent and having an average particle size of 0.55 mm, which are produced by a droplet generating device. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2015-203042 [Patent Document 2] WO1998-029485 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the styrene-based seed resin particles described in Patent Document 1 are produced by a suspension polymerization method, the particle size distribution of the styrene-based seed resin particles is wide, and the expandable polystyrene-based resin particles produced using the styrene-based seed resin particles have a problem with the uniformity of particle size. Since the styrene-based seed resin particles described in Patent Document 2 do not contain a plasticizer, the expandable polystyrene-based resin particles obtained by seed polymerization using the styrene-based seed resin particles have low expandability, and the cells of the polystyrene-based expanded particles are coarse, so the aesthetics are insufficient, and there is room for further improvement.

[0007] One embodiment of the present invention has been made in consideration of the above problems, and its object is to provide styrene-based seed resin particles that enable good productivity of expandable polystyrene-based resin particles having a small particle size, a narrow particle size distribution, and excellent expandability, and polystyrene-based expanded beads having excellent aesthetic properties. [Means for solving the problem]

[0008] As a result of intensive research to solve the above-mentioned problems, the inventors discovered that by setting the amount of plasticizer and the amount of nucleating agent within specific ranges and by making the UT, which indicates the variation in particle size distribution, below a specified value, it is possible to obtain styrene-based seed resin particles that have a uniform particle size and excellent design properties and that allow for good productivity of polystyrene-based expanded beads, and thus completed the present invention.

[0009] That is, one embodiment of the present invention includes the following configuration. [1] A seed resin for seed polymerization comprising a base resin containing a styrene unit as a constituent unit, The composition contains 0.5 to 5.0 parts by weight of a plasticizer relative to 100 parts by weight of the base resin, The nucleating agent is contained in an amount of 0.03 to 0.30 parts by weight based on 100 parts by weight of the base resin, Styrene-based seed resin particles for seed polymerization, having an average particle size of 0.20 to 0.50 mm and a UT indicating the variation in particle size distribution of 2.15 or less. [2] The styrene-based seed resin particles for seed polymerization according to claim 1, wherein the base resin contains 90% or more of styrene units. [3] The styrene-based seed resin particles for seed polymerization according to [1] or [2], wherein the nucleating agent is an acrylic resin and the weight average molecular weight of the nucleating agent is 500,000 to 1,500,000. [4] Expandable polystyrene-based resin particles, characterized by being obtained by seed polymerization using the styrene-based seed resin particles according to any one of [1] to [3]. [5] Polystyrene-based expanded particles, characterized by being obtained by expanding the expandable polystyrene-based resin particles described in [4]. [6] A polystyrene foamed molded article, which is obtained by molding the polystyrene foamed beads according to [5] in a mold. Effect of the Invention

[0010] One embodiment of the present invention has been made in consideration of the above problems, and its object is to provide styrene-based seed resin particles that have a narrow particle size distribution and excellent expandability, and that improve the productivity of expandable polystyrene-based resin particles with excellent aesthetic properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. In addition, 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. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic documents and patent documents described in this specification are incorporated herein by reference. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and smaller than B)".

[0012] [1. Styrene-based seed resin particles] One embodiment of the present invention has been made in consideration of the above problems, and its object is to provide styrene-based seed resin particles that have a uniform particle size distribution and excellent expandability, and that can improve the productivity of expandable polystyrene-based resin particles with excellent aesthetic properties.

[0013] The present inventors have completed the present invention in order to achieve the object of improving the productivity of expandable polystyrene resin particles having a uniform particle size distribution and excellent expandability, and polystyrene expanded particles having excellent aesthetics. The following describes the embodiments of the present invention.

[0014] A styrene-based seed resin particle for seed polymerization according to one embodiment of the present invention is a styrene-based seed resin particle for seed polymerization composed of a base resin containing a styrene unit as a constituent unit, and contains 0.5 to 5.0 parts by weight of a plasticizer relative to 100 parts by weight of the base resin, and contains 0.03 to 0.30 parts by weight of a nucleating agent relative to 100 parts by weight of the base resin, has an average particle size of 0.20 to 0.50 mm, and has a UT indicating the variation in particle size distribution of 2.15 or less.

[0015] The styrene-based seed resin particles according to one embodiment of the present invention can provide expandable polystyrene-based resin particles by a known method using the styrene-based seed resin particles.Furthermore, the expandable polystyrene-based resin particles can provide polystyrene-based foamed molded articles by producing polystyrene-based expanded particles by a known method using the expandable polystyrene-based resin particles, and performing expansion molding by a known method using the polystyrene-based expanded particles.

[0016] In this specification, the "styrene-based seed resin particles according to one embodiment of the present invention" may be simply referred to as "styrene-based seed resin particles". In other words, the term "styrene-based seed resin particles" is intended to mean one embodiment of the styrene-based seed resin particles in the present invention.

[0017] The base resin contained in the styrene-based seed resin particles mainly contains styrene units as structural units. In this specification, "styrene units" are structural units derived from styrene monomers. Here, "mainly containing styrene units as structural units" means that the number of styrene units is 50% or more when the number of all structural units contained in the base resin is 100%. It is preferable that the base resin of the styrene-based resin seed particles in the present invention contains 90% or more of styrene units as structural units. If the styrene units are 90% or more, styrene monomers can be efficiently absorbed during seed polymerization.

[0018] The styrene resin seed particles in the present invention are generally known styrene resin granules, and examples of such particles include homopolymer particles of styrene monomers such as styrene derivatives such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene, and copolymer particles of acrylic acid and methacrylic acid esters such as methyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and cetyl methacrylate, or mixtures of acrylonitrile, dimethyl fumarate, ethyl fumarate, etc. Also, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate may be used in combination.

[0019] Generally known styrene-based resin seed particles can be obtained by (1) a conventional suspension polymerization method, or (2) a method in which a polymerizable monomer is dispersed in an aqueous medium as a group of droplets by passing it through a nozzle under regular vibration, and polymerized without causing coalescence or additional dispersion, etc. Uniform styrene-based resin seed particles having a UT of 2.15 or less as in the present invention can be obtained by method (2).

[0020] As the polymerization initiator for the above-mentioned monomer in the present invention, a radical-generating polymerization initiator generally used in the production of a thermoplastic polymer can be used, and representative examples thereof include organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, t-butyl perpivalate, t-butyl peroxy isopropyl carbonate, t-butyl peroxy acetate, 2,2-di-t-butyl peroxy butane, t-butyl peroxy-3,3,5-trimethylcyclohexanoate, di-t-butyl peroxy hexahydroterephthalate, and 1,1-di-t-butyl peroxy-3,3,5-trimethylcyclohexane, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination of two or more.

[0021] The aqueous dispersion medium used in the present invention is, for example, water.

[0022] The dispersant used in the present invention includes well-known water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyvinylpyrrolidone, polyacrylamide, and inorganic substances that are poorly soluble in water such as calcium triphosphate, hydroxyapatite, magnesium phosphate, and magnesium pyrophosphate. When using an inorganic substance that is poorly soluble in water, the dispersion stabilization effect is increased by using an anionic surfactant such as sodium dodecylbenzenesulfonate in combination. In addition, the combined use of a water-soluble polymer and an inorganic substance that is poorly soluble in water is also effective.

[0023] In the present invention, a nucleating agent capable of finely dispersing in a styrene-based resin matrix is ​​used. Examples of the nucleating agent include methacrylate polymers such as methacrylate-acrylate copolymers, methacrylate-acrylate copolymers, and methyl methacrylate-butadiene-styrene copolymers, styrene-butadiene copolymers, high impact polystyrene, styrene-butadiene-styrene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, styrene copolymers such as acrylonitrile-styrene copolymers, olefin waxes such as polyethylene wax and ethylene-vinyl acetate copolymer wax, glycerin monostearate, glycerin monobehenate, glycerin mono 12-hydroxystearate, glycerin monolaurate, and glycerin tri 12-hydroxystearate. and fatty acid esters such as hydrogenated castor oil, hydrogenated soybean oil, and hydrogenated rapeseed oil; amides such as fatty acid amides, fatty acid dicarboxylic acid diamides, aromatic bisamides, and aromatic dicarboxylic acid diamides; higher fatty acids such as stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, and lactic acid; fatty acid metal salts such as zinc stearate and calcium stearate; and surfactants such as polyethylene glycol monostearate, polyoxyethylene stearyl ether, and polyoxyethylene lauryl ether. In addition, since a nucleating agent insoluble in a monomer such as styrene, such as polystyrene wax, does not disperse uniformly in the droplet generation process or causes nozzle clogging, it is preferable to use a nucleating agent soluble in a monomer such as styrene. Examples of nucleating agents soluble in monomers such as styrene include acrylic resins such as methacrylic acid ester-acrylic acid ester copolymers. In addition, when an acrylic resin is used as a nucleating agent, it is preferable that the weight average molecular weight is 500,000 to 1,500,000 in view of the ease of dissolving in the monomer and the nucleating effect. When an acrylic resin is used as a nucleating agent, if the weight average molecular weight of the acrylic resin is 500,000 or more, an effective nucleating effect is easily obtained, and if it is 1,500,000 or less, it tends to be present in a state of being uniformly dispersed in the styrene seed resin particles.

[0024] These nucleating agents are used in an amount of 0.03 to 0.30 parts by weight, preferably 0.05 to 0.15 parts by weight, per 100 parts by weight of the styrene resin. If the amount used is less than 0.03 parts by weight, the cells obtained by expansion will be non-uniform and coarse, resulting in a decrease in the expandability of the expandable polystyrene resin particles and the beauty of the polystyrene expanded particles. If the amount used exceeds 0.30 parts by weight, the droplets will not be broken well in the droplet generation process by vibrating the styrene seed resin particles, resulting in coalesced particles and a deterioration in UT.

[0025] Examples of the plasticizer used in the present invention include (a) fatty acid glycerides such as stearate triglyceride, palmitate triglyceride, laurate triglyceride, stearate diglyceride, stearate monoglyceride, etc., (b) vegetable oils such as coconut oil, palm oil, palm kernel oil, etc., (c) aliphatic esters such as dioctyl adipate, dibutyl sebacate, etc., and (d) organic hydrocarbons such as liquid paraffin, cyclohexane, etc. These plasticizers may be used alone or in combination of two or more kinds. These plasticizers are used in an amount of 0.50 to 5.0 parts by weight, preferably 1.0 to 3.0 parts by weight, per 100 parts by weight of the styrene resin. If the amount used is less than 0.5 parts by weight, the cells of the expandable polystyrene resin particles obtained by seed polymerization become nonuniform and coarse, resulting in a decrease in the expandability of the expandable polystyrene resin particles and the expandability during expansion of the expandable polystyrene resin particles, making it impossible to obtain a high expansion ratio. If the amount used exceeds 5.0 parts by weight, shrinkage during expansion becomes large, making it impossible to obtain a high expansion ratio.

[0026] The present expandable styrene-based seed resin particles may further contain a flame retardant, a flame retardant assistant, etc., within the range that does not impair the physical properties.

[0027] Flame retardants include (a) brominated polymers such as brominated polystyrene, brominated copolymers of 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).

[0028] Examples of the flame retardant auxiliary include high-temperature decomposition type organic substances having a high 10-hour half-life temperature, such as cumene peroxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane.

[0029] The styrene-based seed resin particles have an average particle diameter of 0.20 mm or more and 0.50 mm or less. If the average particle diameter is less than 0.20 mm, a large amount of fine particles is generated in the droplet generation process by vibrating the styrene-based seed resin particles, and it tends to be difficult to provide styrene-based seed expanded particles with a UT of 2.15 or less. If the average particle diameter is greater than 0.5 mm, the monomer is not impregnated well into the resin when the expandable polystyrene-based resin particles are produced by seed polymerization, resulting in resin particles with different physical properties in the resin interior and near the outer layer, and when the polystyrene-based resin particles are produced, the cells are not uniform and the beauty is poor. In this specification, the average particle diameter is calculated from a distribution table showing the particle diameter measured on a volume basis as a cumulative distribution. The particle diameter (also called the median diameter) at which the cumulative volume percentage is 50% is taken as the average particle diameter.

[0030] The styrene-based seed resin particles preferably have a particle size distribution (also referred to as UT) of 2.15 or less, more preferably 2.10 or less. When the particle size distribution is 2.5 or less, the particle diameter of the polystyrene-based expanded beads obtained by expanding the expandable polystyrene-based resin particles obtained by seed polymerization is uniform, resulting in polystyrene-based expanded beads with excellent designability.

[0031] In this specification, the particle size distribution (UT) is calculated from a distribution table showing the particle size measured on a volume basis as a cumulative distribution. Specifically, when the particle sizes at which the cumulative volume percentages are 90%, 60%, 40%, and 10% are D90, D60, D40, and D10, respectively, the value obtained by the following formula is defined as the particle size distribution (UT). Particle size distribution (UT)=D90 / D40+D60 / D10 If all particles had the same particle size, the particle size distribution (UT) would be 2.00. Therefore, the lower limit of the particle size distribution (UT) of the present expandable polystyrene resin particles is 2.00 or more.

[0032] [2. Expandable polystyrene resin particles] The expandable polystyrene-based resin particles according to one embodiment of the present invention can be obtained by a seed polymerization method using the present styrene-based seed resin particles described in the section [1. Styrene-based seed resin particles]. A known seed polymerization method can be used as a method for producing the present expandable polystyrene-based resin particles.

[0033] The seed polymerization method includes, for example, the following steps (1) to (4): (1) mixing water, styrene-based seed resin particles, a dispersant, a polymerization initiator, and optionally other additives (plasticizer, cell regulator, flame retardant, flame retardant auxiliary, etc.) to prepare an aqueous suspension; (2) then heating the aqueous suspension to a predetermined temperature; (3) then adding a monomer including a styrene monomer to the aqueous suspension over a predetermined time at the predetermined temperature, while simultaneously reacting the aqueous suspension to carry out a polymerization reaction, thereby obtaining a base resin (also referred to as a base resin composition) including additives; (4) during or after the above step (3), impregnating the base resin composition with a foaming agent.

[0034] The amount of polystyrene-based resin seed particles in the seed polymerization method is preferably 5 to 60% by weight when the amount of the finally obtained expandable polystyrene-based resin particles is taken as 100% by weight. When the amount of polystyrene-based resin seed particles is (a) 5% by weight or more, the proportion of monomers that are not polymerized alone but are polymerized within the polystyrene-based resin seed particles tends to increase in the monomers added to the aqueous suspension, and (b) 60% by weight or less makes it possible to polymerize more monomers in one production run, which is economically advantageous.

[0035] Examples of the dispersant 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, methyl cellulose, polyacrylamide, and polyvinylpyrrolidone.

[0036] Examples of the polymerization initiator include organic peroxides and azo compounds. Examples of the organic peroxide include benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxy isopropyl carbonate, di-t-butyl peroxy hexahydroterephthalate, 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-butylperoxy-2-ethylhexyl carbonate. Examples of the azo compound include azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination of two or more. t-Butylperoxy-2-ethylhexyl carbonate is also called t-butylperoxy-2-ethylhexyl monocarbonate.

[0037] In the method for producing the expandable polystyrene resin particles, a chain transfer agent and a polymerization regulator may be further used. 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 generally used in the polymerization of acrylonitrile-styrene resins.

[0038] In this specification, the blowing agent refers to a compound that is easily volatile and only slightly swells polystyrene resin particles. The blowing agent contained in the expandable polystyrene resin particles includes, but is not limited to, (a) aliphatic hydrocarbons such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentanecyclohexane, and (b) fluorohydrocarbons with zero ozone depletion potential such as difluoroethane and tetrafluoroethane. The above-mentioned blowing agents may be used alone or in combination of two or more.

[0039] The present expandable polystyrene-based resin particles may be configured to further contain a plasticizer, a bubble regulator, a flame retardant, a flame retardant assistant, etc., by mixing these with each other during the production process, specifically, in step (1) of the above-mentioned seed polymerization method, within the limits that do not impair the physical properties.

[0040] [3. Polystyrene foam particles] The polystyrene-based expanded particles according to one embodiment of the present invention are obtained by expanding the present expandable polystyrene-based resin particles described in the section [2. Expandable polystyrene-based resin particles]. Since the polystyrene-based expanded particles according to one embodiment of the present invention have the above-mentioned constitution, they have a uniform particle size and excellent aesthetics.

[0041] The method for expanding the expandable polystyrene resin particles, i.e., the method for producing the expanded particles, is not particularly limited, and known methods can be used. For example, the expansion method includes a method in which the following (1) to (3) are carried out in sequence: (1) expandable polystyrene resin particles are placed in a container equipped with a stirrer, (2) the expandable polystyrene resin particles are heated with a heat source such as steam, and (3) expansion is carried out until a desired expansion ratio is reached, thereby obtaining polystyrene expanded particles. Note that the polystyrene expanded particles may also be referred to as polystyrene resin pre-expanded particles, and therefore the expansion method for obtaining the polystyrene resin pre-expanded particles may also be referred to as a pre-expanding method.

[0042] [4. Polystyrene foam molding] The polystyrene foamed molded article according to one embodiment of the present invention is produced by molding the foamed beads described in the section [3. Polystyrene foamed beads] in a mold. The polystyrene foamed molded article according to one embodiment of the present invention has the above-mentioned constitution, and therefore has the advantage of excellent surface beauty.

[0043] In this specification, the "polystyrene foam molded article according to one embodiment of the present invention" may be simply referred to as the "present foam molded article." In other words, the term "present foam molded article" is intended to mean one embodiment of the polystyrene foam molded article of the present invention.

[0044] The in-mold molding method of polystyrene-based expanded beads, that is, the manufacturing method of the present expanded molded product, is not particularly limited, and a known method can be used. As an example of the in-mold molding method, there is a method in which the expanded beads are filled into a mold that can be closed but cannot be sealed, and the expanded beads are heated and fused with steam to form an expanded molded product. As an example of the in-mold molding method, there is a method in which the expanded beads are filled into a closed mold having a desired shape and having a large number of small holes drilled in the wall surface, and a heating medium such as steam is ejected from the mold small holes to heat the expanded beads to a temperature above the softening point of the expanded beads, and the expanded beads are fused to each other, and then the expanded beads are removed from the mold through a cooling process to produce a polystyrene-based expanded molded product of a desired shape. EXAMPLES

[0045] (Average particle size and particle size distribution (UT) of styrene-based seed resin particles, and evaluation of the design (uniformity) of polystyrene-based expanded particles) The particle size of the styrene-based seed resin particles was measured on a volume basis using an image processing type Millitrac JPA particle size analyzer. The results were displayed as a cumulative distribution, and a particle size distribution table was created. Using the distribution table obtained, the average particle size and particle size distribution (UT) of the styrene-based seed resin particles were calculated according to the above-mentioned definitions. Using the obtained UT, the design (uniformity) of the polystyrene-based expanded beads was evaluated based on the following index: ⊚ when the UT of the styrene-based seed resin particles was 2.10 or less; △ when it was 2.15 or less; × when it exceeded 2.15.

[0046] (Method for evaluating expandability of expandable polystyrene resin particles) The expandable polystyrene resin particles were placed in a steamer at 100°C and heated for 7 minutes to obtain polystyrene expanded particles. 10 g of the obtained polystyrene expanded particles were placed in a 1000 cm 3 The volume of the polystyrene foam particles (cm 3 The bulk density (g / cm3) was measured using the following formula: 3 ) was calculated as follows: Bulk density (g / cm 3 ) = 10g / volume of polystyrene foam particles (cm 3 )

[0047] Using the obtained bulk density, the expandability of the expandable polystyrene resin particles was evaluated based on the following index: 3 If it is less than 0.0250g / cm, it is 0.0250g / cm 3 If it exceeds, it is invalid.

[0048] (Method for evaluating the design (beauty) of polystyrene foam particles) The average chord length of the cells of the polystyrene foam beads was measured in accordance with ASTM-D-2842-97 by counting the number of cells that were aligned on a straight line on a cut surface of a photograph projected onto the cut surface of the polystyrene foam beads. The design (beauty) of the styrene-based seed resin particles was evaluated based on the obtained average chord length in accordance with the following indices: ⊚ when the average chord length was 85 μm or less; ◯ when it was 115 μm; × when it exceeded 115 μm.

[0049] Example 1 <Production of styrene-based seed resin particles> Into a 6-liter reactor equipped with a flat stirring blade and an inlet for the droplet generator at the bottom, 1.5 liters of an aqueous dispersion medium containing 11,000 ppm of calcium phosphate and 110 ppm of sodium dodecylbenzenesulfonate was added, and stirring was started.

[0050] Next, a monomer mixture was added to a container having a supply line to a droplet generator, in which 5,000 g of styrene monomer was dissolved with 9.7 g of 1,1-di(tert-butylperoxy)cyclohexane, 85 g of tert-butylperoxy-2-ethylhexanoate, 50 g of liquid paraffin as a plasticizer, and 3.5 g of methyl methacrylate-butyl acrylate copolymer (Kane Ace PA-20 manufactured by Kanegafuchi Chemical Industry Co., Ltd.) as a nucleating agent in the amount shown in Table 1. This was supplied to a droplet generator having one plate with 45 holes of 0.17 mmφ at a rate of 90 cc / min, and mechanical vibration of 800 Hz was applied to generate monomer droplets in the aqueous dispersion medium, which were then transferred to the above-mentioned 6-liter reactor. In addition, an aqueous dispersant prepared by dissolving 530 g of 3% polyvinyl alcohol and 20 g of sodium nitrite in 5,000 g of pure water was added to a container having a supply line to a droplet generating device separate from the monomer mixture liquid, and the aqueous dispersant was transferred to the droplet generating device at a rate of 80 cc / min. After 1500 g of the monomer solution was introduced into a 6-liter reactor, droplet generation was stopped, and the dispersion in the reactor was heated to 90° C. and polymerized for 3 hours. The dispersion was further heated to 120° C. and held for 1 hour to complete the polymerization. The slurry in the reactor was cooled, dehydrated, and dried to obtain polymer particles. The obtained particles are referred to as styrene-based seed particles. Here, the average particle size and particle size distribution (UT) of the styrene-based seed resin particles were measured, and the design properties (uniformity) were evaluated. The results are shown in Table 1.

[0051] <Production of Expandable Polystyrene-Based Resin Particles> In a 6L autoclave equipped with a stirrer, 92 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 parts 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 then stirring was started. Next, the temperature inside the autoclave was raised to 90°C, and polymerization was carried out while adding 0.064 parts by weight of (a) dibenzoyl peroxide as a polymerization initiator over 4 hours and 50 minutes, and 80 parts by weight of (b) styrene monomer over 5 hours and 30 minutes into the autoclave. In addition, 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 after the start of polymerization. Thereafter, the inside of the autoclave was kept at 90°C for 30 minutes, and then 6.5 parts by weight of butane (normal-rich butane (normal butane / isobutane=70 / 30)) and 1.0 part by weight of cyclohexane were charged, and the mixture was further kept at 120°C for 3 hours, thereby impregnating the base resin composition with the blowing agent. Thereafter, the inside of the autoclave was cooled to room temperature, and the expandable polystyrene-based resin particles were taken out of the autoclave. The taken-out expandable polystyrene-based resin particles were washed, dehydrated, and dried. Here, the expandability of the expandable styrene-based resin particles was evaluated, and the results are shown in Table 1.

[0052] <Production of polystyrene foam particles> The obtained expandable polystyrene resin particles were put into a rotary agitation type expansion device, and then the expandable polystyrene resin particles were expanded in water vapor at about 100°C until the bulk density reached an expansion ratio of 50 times, to obtain polystyrene expanded particles. Here, the design (beauty) of the polystyrene foam particles was evaluated. The results are shown in Table 1.

[0053] Example 2 As shown in Table 1, the same procedure as in Example 1 was carried out except that the amount of liquid paraffin was changed to 0.7 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated. The evaluation results are shown in Table 1.

[0054] Example 3 As shown in Table 1, the same procedure as in Example 1 was carried out except that the amount of liquid paraffin was changed to 4.5 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated. The evaluation results are shown in Table 1.

[0055] Example 4 As shown in Table 1, the same procedure as in Example 1 was carried out except that the nucleating agent PA-20 was changed to 0.03 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated. The evaluation results are shown in Table 1.

[0056] Example 5 As shown in Table 1, the same procedure as in Example 1 was carried out except that the nucleating agent PA-20 was changed to 0.25 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated. The evaluation results are shown in Table 1.

[0057] Example 6 As shown in Table 1, in the production process of styrene-based seed resin particles, the monomer mixture was supplied at a rate of 90 cc / min to a droplet generator having one plate with 148 holes of 0.10 mmφ, and mechanical vibration was changed to 1200 Hz, but the same operations as in Example 1 were performed and evaluation was performed in the same manner as for expandable polystyrene-based resin particles and polystyrene-based expanded particles. The evaluation results are shown in Table 1.

[0058] Comparative Example 1 In a reactor equipped with a stirrer, 100 parts by weight of pure water, 0.4 parts by weight of tricalcium phosphate, 0.01 parts by weight of sodium dodecylbenzenesulfonate, 0.5 parts by weight of sodium chloride, 0.5 parts by weight of coconut oil as a plasticizer, and 0.07 parts by weight of polyethylene wax as a nucleating agent were added and stirred to form a water suspension, and then 100 parts by weight of styrene monomer were dissolved in 0.2 parts by weight of benzoyl peroxide and 0.2 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as a polymerization initiator, added to the reactor, heated to 98°C, and polymerized for 4.5 hours. Next, the temperature was raised to 110°C, held for 1 hour, cooled, and the contents were taken out, dehydrated, dried, and sieved to obtain polystyrene-based resin seed particles with a particle diameter of 0.425 to 0.500 mm. Except for this, the same operation as in Example 1 was performed, and the expandable polystyrene-based resin particles and polystyrene-based expanded particles were evaluated in the same manner. The evaluation results are shown in Table 1.

[0059] Comparative Example 2 As shown in Table 1, the same procedure as in Example 1 was carried out except that the amount of liquid paraffin was changed to 0 part by weight in the production process of the styrene-based seed resin particles, and the expandable polystyrene-based resin particles and the polystyrene-based expanded particles were evaluated. The evaluation results are shown in Table 1.

[0060] Comparative Example 3 As shown in Table 1, the same procedure as in Example 1 was carried out except that the amount of liquid paraffin was changed to 6.0 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated in the same manner. The evaluation results are shown in Table 1.

[0061] Comparative Example 4 As shown in Table 1, the same procedure as in Example 1 was carried out except that the nucleating agent PA-20 was changed to 0.35 parts by weight in the production process of the styrene seed resin particles, and the expandable polystyrene resin particles and the polystyrene expanded particles were evaluated. The evaluation results are shown in Table 1.

[0062] Comparative Example 5 As shown in Table 1, the same procedure as in Example 1 was carried out except that the nucleating agent PA-20 was changed to 0 parts by weight in the production process of the styrene-based seed resin particles, and the expandable polystyrene-based resin particles and the polystyrene-based expanded particles were evaluated. The evaluation results are shown in Table 1.

[0063] In Table 1, the parts by weight of the plasticizer and nucleating agent are the contents relative to 100 parts by weight of the total of the styrene monomer used in the production process of the styrene seed resin particles.

[0064] [Table 1] [Industrial Applicability]

[0065] The present invention provides styrene-based seed resin particles that have a uniform particle size distribution and are excellent in expandability, and that can be used to produce polystyrene-based expanded particles with excellent aesthetics. Therefore, the present invention can be suitably used for producing cushion beads, foamed moldings for building materials, and lightweight concrete.

Claims

1. A styrene-based seed resin particle for seed polymerization, comprising a base resin containing a styrene unit as a constituent unit, The composition contains 0.5 to 5.0 parts by weight of a plasticizer relative to 100 parts by weight of the base resin, The nucleating agent is contained in an amount of 0.03 to 0.30 parts by weight based on 100 parts by weight of the base resin, The average particle size is 0.20 to 0.50 mm, and UT, which indicates the variation in particle size distribution, is 2.15 or less. The plasticizer is liquid paraffin, The nucleating agent is a methyl methacrylate-butyl acrylate copolymer. Styrene-based seed resin particles for seed polymerization.

2. 2. The styrene-based seed resin particles for seed polymerization according to claim 1, wherein the base resin contains 90% or more of styrene units as constituent units.

3. Styrenic seed resin particles for seed polymerization described in claim 1 or 2, wherein the weight average molecular weight of the nucleating agent is 500,000 to 1,500,000.

4. 4. Expandable polystyrene-based resin particles obtained by seed polymerization using the styrene-based seed resin particles according to claim 1.

5. 5. A polystyrene-based expanded bead obtained by expanding the expandable polystyrene-based resin bead according to claim 4.

6. A polystyrene foamed molded article obtained by molding the polystyrene foamed beads according to claim 5 in a mold.

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