Seed particles, composite resin particles, expanded particles, expanded molded article, and method for producing composite resin particles

Abstract

The purpose of the present invention is to provide: seed particles which generate a small amount of a polystyrene powder and enable easy escape of a foaming agent; composite resin particles; a method for producing the composite resin particles; and the like.　The present invention relates to: seed particles (B) for producing composite resin particles (C) for the production of foam particles that contain a polyolefin resin and a polystyrene resin; and the like. The composite resin particles (C) are seed polymerized composite resin particles of a styrene monomer and the seed particles (B); the seed particles (B) contain a seed polymerized composite resin (A) of a styrene monomer and a polyolefin in an amount of 20 to 100% by mass of the seed particles (B); the seed particles (B) contain a second polyolefin resin in an amount of 0 to 80% by mass of the seed particles (B) in addition to the polyolefin resin that is contained in the seed polymerized composite resin (A); the ratio of the mass of the polyolefin resin content to the mass of the polystyrene resin content in the seed particles (B) is 20:80 to 90:10; and the mass average molecular weight of the polystyrene resin in the seed particles (B) is 1.0 × 105 to 5.0 × 105.

Description

[Technical Field]

[0001] The present invention relates to seed particles, composite resin particles, expanded beads, expanded molded articles, a method for producing composite resin particles, and the like. [Background technology]

[0002] Foam molded articles made from polystyrene-based resins are known to have excellent rigidity, thermal insulation, light weight, water resistance, and foam moldability, but poor chemical resistance and impact resistance. To address this, composite foam molded articles obtained from composite resin particles of polystyrene-based resins and polyolefin-based resins are used. Composite resin particles are generally produced by shredding a base resin of a polyolefin-based resin, such as a polyethylene-based resin, to form seed particles (sometimes referred to as core particles), adding a styrene-based monomer to the seed particles, and then polymerizing them. This polymerization is also referred to as seed polymerization. The resulting composite resin particles contain a polyolefin resin and polystyrene. The resulting composite resin particles are also referred to as seed-polymerized composite resin particles, styrene-based monomer-polyolefin composite resin particles, etc. The composite resin particles are generally formed by blending a foaming gas to form expandable particles, which are then expanded (also referred to as pre-expanded) to form expanded particles (also referred to as pre-expanded particles). The expanded particles are then filled into a mold and heated to produce a composite foam molded article.

[0003] Such composite resin foam molded products are widely used as automotive components and transportation materials. In both applications, composite resin foam molded products require high strength and easy moldability. To increase the strength of composite resin foam molded products, attempts have been made to use high-density polyethylene (HDPE) as a polyolefin resin or to increase the polystyrene content. However, because high-density polyethylene is a crystalline resin, it is not compatible with polystyrene (PS). As a result, it is difficult to obtain molded products with the desired strength, shape, density, and other properties without increasing the steam pressure used in the foam molding or extending the steam heating time. Thus, the use of high-density polyethylene has not been found to be satisfactory for moldability. Furthermore, the use of high-pressure steam and long steam heating times increase the energy required for foam molding. For this reason, attempts have been made to improve compatibility with polystyrene by adding ethylene-vinyl acetate copolymer (EVA) to high-density polyethylene.

[0004] On the other hand, seed particles containing linear low-density polyethylene as a polyolefin resin and a polystyrene resin are also known (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-196444 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-190991 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the examples of Patent Documents 1 and 2, only linear low-density polyethylene is used as the polyolefin resin constituting the seed particles, and the seed particles are produced by melt-kneading linear low-density polyethylene and polystyrene. The present inventors noticed that when high-density polyethylene or polypropylene, etc., is used in the methods described in Patent Documents 1 and 2, due to poor compatibility with polystyrene, it is difficult for the seed particles to absorb the polystyrene during seed polymerization, and the unabsorbed styrene-based monomer polymerizes, resulting in the generation of a large amount of polystyrene powder. This powder adheres to the mold surface during foam molding, causing a problem of shortening the mold's lifespan. They also noticed that even when linear low-density polyethylene is used, if the amount of polystyrene-based resin is increased (if a large amount of styrene-based monomer is used during seed polymerization), a large amount of polystyrene powder is similarly generated.

[0007] Furthermore, the present inventors noticed that in the composite resin particles described in Patent Document 1, the polystyrene component is present in large amounts on the surface layer of the particles, which causes a long time to adjust the content of the blowing agent in the expanded beads (i.e., the dispersion of the blowing agent). That is, when the composite resin particles are made to contain a blowing agent to produce expanded beads, the blowing agent in the expanded beads is dispersed to adjust the content of the blowing agent to an amount suitable for the subsequent expansion molding. However, if the polystyrene component is present in large amounts on the surface layer of the particles, the dispersion of the blowing agent from the expanded beads is inhibited, and the time required for dispersion increases. If the time required for dispersion could be shortened, the molding cycle could be shortened.

[0008] An object of the present invention is to provide seed particles, composite resin particles, and methods for producing the same, which generate little polystyrene powder and facilitate the dispersion of a blowing agent.An object of the present invention is to provide composite resin foam particles that can be foam-molded at low vapor pressure and have excellent moldability.An object of the present invention is to provide a foam-molded product with excellent compressive strength. [Means for solving the problem]

[0009] In view of the above problems, the present inventors have discovered that at least one of the above problems can be solved by using particles having a base resin that is a styrene-based monomer-polyolefin seed polymerization composite resin (A) obtained by impregnating and polymerizing a polyolefin resin with a styrene-based monomer, as seed particles containing a polyolefin resin and a polystyrene-based resin, or by using particles having a base resin that is a mixed resin obtained by adding a second polyolefin resin to this seed polymerization composite resin (A); that various polyolefin resins can be easily used as the polyolefin resin; and that resins derived from styrene-based monomer-polyolefin composite resin foam moldings (for example, recycled resins from styrene-based monomer-polyolefin composite resin foam moldings) can be reused as the base resin for the seed polymerization composite resin (A), thereby completing the present invention.

[0010] The present invention typically includes the following aspects. Section 1. Seed particles (B) for producing composite resin particles (C) for producing expanded beads containing a polyolefin resin and a polystyrene resin, The composite resin particles (C) are seed-polymerized composite resin particles of a styrene-based monomer and a seed particle (B), the seed particles (B) contain a styrene-based monomer-polyolefin seed polymerization composite resin (A) in an amount of 20 to 100 mass % of the seed particles (B), the seed particles (B) contain, in addition to the polyolefin resin contained in the seed polymer composite resin (A), a second polyolefin resin in an amount of 0 to 80 mass % of the seed particles (B); the ratio of the mass content of the polyolefin-based resin to the mass content of the polystyrene-based resin in the seed particles (B) is 20:80 to 90:10; The mass average molecular weight of the polystyrene resin in the seed particles (B) is 1.0×10 5 ~5.0×10 5 That is, Seed particle (B). Section 2. Item 3. The seed particles (B) according to item 1, wherein the seed polymerization composite resin (A) has a gel fraction of 5 to 40 mass % as determined by the gel fraction measurement described below. Gel fraction measurement: Weigh out 1 g of seed-polymerized composite resin (A) and place it in a flask. Add 100 ml of toluene, then heat under reflux in a 130°C oil bath for 24 hours to dissolve it. After removing the flask from the oil bath, immediately filter the contents through an 80-mesh (φ0.12 mm) wire mesh. The wire mesh and the insoluble material remaining on it are placed in a 130°C oven for 1 hour, then placed under reduced pressure with a vacuum pump for 2 hours to remove the toluene. The weight of the solid material remaining on the wire mesh is measured. The gel fraction is calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100 Section 3. Item 1 or 2. The seed particles (B) according to Item 1 or 2, wherein the polyolefin resin contained in the seed polymerization composite resin (A) is at least one resin selected from the group consisting of an ethylene copolymer, a polyethylene resin, and a polypropylene resin, and the second polyolefin resin is at least one resin selected from the group consisting of an ethylene copolymer, a polyethylene resin, and a polypropylene resin. Section 4. Item 4. The seed particles (B) according to Item 3, wherein the ethylene-based copolymer is an ethylene-vinyl acetate copolymer, and the polyethylene-based resin is at least one resin selected from the group consisting of linear low-density polyethylene, high-density polyethylene, and low-density polyethylene. Section 5. Item 5. The seed particles (B) according to any one of Items 1 to 4, wherein the second polyolefin resin is a resin different from the polyolefin resin contained in the seed polymerization composite resin (A). Section 6. Item 6. The seed particles (B) according to any one of Items 1 to 5, wherein the seed polymerization composite resin (A) is derived from a foamed molded product of a styrene-based monomer-polyolefin composite resin. Section 7. Composite resin particles (C) for producing expanded beads, the composite resin particles (C) being seed-polymerized composite resin particles of a styrene-based monomer and seed particles (B), the seed particles (B) being the seed particles (B) according to any one of items 1 to 6. Section 8. Item 8. The composite resin particles (C) according to Item 7, wherein the content of the polystyrene resin composited with the seed particles (B) in the composite resin particles (C) is 100 to 500 parts by mass per 100 parts by mass of the seed particles (B). Section 9. Item 9. Expanded particles of the composite resin particles (C) according to Item 7 or 8. Section 10. Item 10. A foamed molded article of the foamed beads according to item 9. Section 11. Density: 20 to 200 kg / m 3 Item 11. The foam molded article according to Item 10, wherein Section 12. A method for producing composite resin particles (C) for producing expanded beads containing a polyolefin-based resin and a polystyrene-based resin, comprising: A step of shredding the base resin to obtain seed particles (B); a step of impregnating the seed particles (B) with a styrene-based monomer and polymerizing the monomer to obtain the composite resin particles (C), the base resin is a styrene-based monomer-polyolefin seed polymerization composite resin (A) obtained by a process of impregnating and polymerizing polyolefin-based resin particles with a styrene-based monomer, or a mixed resin of the seed polymerization composite resin (A) and a second polyolefin-based resin, and the seed particles (B) contain the seed polymerization composite resin (A) in an amount of 20 to 100% by mass of the seed particles (B), the seed particles (B) contain a second polyolefin resin in an amount of 0 to 80% by mass of the seed particles (B), the ratio of the mass content of the polyolefin-based resin to the mass content of the polystyrene-based resin in the seed particles (B) is 20:80 to 90:10; The mass average molecular weight of the polystyrene resin in the seed particles (B) is 1.0×10 5 ~5.0×10 5 That is, A method for producing composite resin particles (C). Section 13. Item 13. The method for producing composite resin particles (C) according to Item 12, wherein the seed-polymerized composite resin (A) has a gel fraction of 5 to 40% by mass as determined by the gel fraction measurement described below. Gel fraction measurement: Weigh out 1 g of seed-polymerized composite resin (A) and place it in a flask. Add 100 ml of toluene, then heat under reflux in a 130°C oil bath for 24 hours to dissolve it. After removing the flask from the oil bath, immediately filter the contents through an 80-mesh (φ0.12 mm) wire mesh. The wire mesh and the insoluble material remaining on it are placed in a 130°C oven for 1 hour, then placed under reduced pressure with a vacuum pump for 2 hours to remove the toluene. The weight of the solid material remaining on the wire mesh is measured. The gel fraction is calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100 Section 14. Item 12 or 13, wherein the polyolefin resin contained in the seed polymerization composite resin (A) is at least one resin selected from the group consisting of an ethylene copolymer, a polyethylene resin, and a polypropylene resin, and the second polyolefin resin is at least one resin selected from the group consisting of an ethylene copolymer, a polyethylene resin, and a polypropylene resin. Item 13, wherein the method for producing composite resin particles (C) is at least one resin selected from the group consisting of an ethylene copolymer, a polyethylene resin, and a polypropylene resin. Section 15. Item 15. The method for producing composite resin particles (C) according to Item 14, wherein the ethylene copolymer is an ethylene-vinyl acetate copolymer, and the polyethylene resin is at least one resin selected from the group consisting of linear low-density polyethylene, high-density polyethylene, and low-density polyethylene. Section 16. Item 16. The method for producing composite resin particles (C) according to any one of Items 12 to 15, wherein the second polyolefin resin is a resin different from the polyolefin resin contained in the seed-polymerized composite resin (A). Section 17. Item 17. The method for producing composite resin particles (C) according to any one of Items 12 to 16, wherein the seed-polymerized composite resin (A) is derived from a foamed molded product of a styrene-based monomer-polyolefin composite resin. Section 18. Item 18. The method for producing composite resin particles (C) according to any one of Items 12 to 17, wherein in the step of obtaining the composite resin particles (C), the amount of the styrene-based monomer used is 100 to 500 parts by mass per 100 parts by mass of the seed particles (B). [Effects of the Invention]

[0011] According to the present invention, the dispersion of the blowing agent can be facilitated, and the content of the blowing agent in the expanded beads can be reduced in a short time. In the present application, the dispersion of the blowing agent is evaluated in terms of the length of the molding cycle. According to the present invention, the amount of polymerized polystyrene powder (also referred to simply as "powder amount" in this specification) is reduced, which results in an extension of the mold life. According to the present invention, foam molding is possible even with a medium having a low vapor pressure (e.g., water vapor), which reduces the energy required for foam molding. As a result, the equipment required for foam molding can be simplified, the cost required for foam molding can be reduced, and the productivity of foam molded articles can be improved. According to the present invention, even if the amount of polystyrene resin is increased, various resins can be more easily used as the polyolefin resin. According to the present invention, a composite resin derived from a styrene-based monomer-polyolefin composite resin foam molded article produced via seed polymerization (e.g., recycled resin of a styrene-based monomer-polyolefin composite resin foam molded article) can be reused as the base resin for the seed particles of the present invention. The seed particles of the present invention can provide a foamed molded article having excellent compressive strength.

[0012] As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."

[0013] Generally, in expansion molding using expanded beads, a mold is filled with the expanded beads and heated to expand and fuse the expanded beads to produce an expanded molded article. Expanded beads of composite resins are roughly divided into expanded beads obtained by melt-kneading a base resin, then chopping the resulting resin particles, adding a blowing agent to the resulting resin particles, and pre-expanding them, and expanded beads obtained by impregnating resin particles (seed particles) with a monomer of another resin, polymerizing the monomer to form a composite, and then adding a blowing agent to the composite resin particles (also called seed-polymerized composite resin particles) and pre-expanding them.

[0014] In this specification, the composite resin (particles) obtained by impregnating and polymerizing seed particles with a styrene-based monomer is also referred to as "styrene-based monomer-seed particle seed-polymerized composite resin (particles)." In this specification, a composite resin (particle) obtained by impregnating and polymerizing seed particles of a polyolefin resin with a styrene monomer is also referred to as a "styrene monomer-polyolefin seed polymerization composite resin (particle)." In this specification, composite resin particles impregnated with a blowing agent are also referred to as “expandable particles.” In this specification, particles obtained by pre-expanding expandable particles are also referred to as “expanded particles” or “pre-expanded particles.”

[0015] The present invention is characterized mainly in that a styrene-based monomer-polyolefin seed polymerization composite resin (A) is used as seed particles (B) containing a polyolefin-based resin and a polystyrene-based resin for producing seed polymerization composite resin particles. On the other hand, the inventions described in Patent Documents 1 and 2 use particles of a melt-kneaded mixture of polystyrene and linear low-density polyethylene as seed particles containing a polyolefin-based resin and a polystyrene-based resin.

[0016] (Styrene-based monomer-polyolefin seed polymerization composite resin (A)) The styrene-based monomer-polyolefin seed polymerization composite resin (A) is a composite resin obtained by impregnating seed particles of a polyolefin resin with a styrene-based monomer and polymerizing the same. In the present invention, it is preferable to use the seed polymerization composite resin (A).

[0017] The seed polymerization composite resin (A) is typically a composite resin particle obtained by impregnating seed particles of a polyolefin resin with a styrene monomer and polymerizing the same, i.e., by seed polymerization. The seed polymerization composite resin (A) can also be used (recycled) as a seed polymerization composite foam molded product of a polyolefin resin and a polystyrene resin produced through the expanded particles. When the seed polymerization composite foam molded article is used as a base resin for the seed polymerization composite resin (A), for example, the foam molded article can be pulverized and then pelletized using an extruder or the like to produce a recycled resin, which can be easily used as a base resin for seed particles.

[0018] The seed polymerization composite resin (A) may have a total volatile organic compounds (TVOC) content of 1000 ppm or less, preferably 0 to 800 ppm. A TVOC content within the above range is advantageous in terms of stabilizing monomer absorption when used as seed particles. Here, TVOC does not include the blowing agent.

[0019] (TVOC content) The TVOC (total volatile organic compounds) content of a resin (for example, the seed-polymerized composite resin (A), the composite resin particles (C), etc.) is the sum of the measured values ​​of volatile organic compounds (VOCs) measured by the three measurement methods shown below. VOCs include chemical substances other than the 13 items established by the Ministry of Health, Labor and Welfare. However, among the measured values ​​obtained here, the measured value of the blowing agent contained in the sample resin is not included in the TVOC content.

[0020] VOC Measurement Method 1 (Measurement of hydrocarbons with carbon numbers of 5 or less) A predetermined amount of sample of composite resin particles is placed in a pyrolysis furnace at 180°C, and the volatilized hydrocarbons are measured by gas chromatography. Gas chromatography (GC): Shimadzu GC-14B Pyrolysis furnace: Shimadzu PYR-1A Column: Borapack Q 80 / 100 (3 mm diameter x 1.5 m) Column temperature: 100℃ Detector (FID) temperature: 120°C

[0021] VOC Measurement Method 2 (measurement of hydrocarbons with carbon numbers of 6 or more up to the styrene peak that appears on the gas chromatogram) A predetermined amount of composite resin particle sample is dissolved in dimethylformamide, and an internal standard solution (cyclopentanol) is added, followed by measurement by GC. However, any peaks that cannot be identified are quantified by converting them into the detected amount of toluene. GC: Shimadzu GC-14A Column: PEG-20M PT25% 60 / 80 (2.5 m) Column temperature: 105℃ Detector (FID) temperature: 220°C

[0022] VOC Measurement Method 3 (Measurement of hydrocarbons with carbon numbers from the peak next to styrene to 16 (n-hexadecane) on the gas chromatogram) A specified amount of composite resin particle sample is dissolved in chloroform and measured using a gas chromatograph mass spectrometer (GCMS). However, a blank test is conducted using only a solvent that does not dissolve the sample, and the amount of substance detected in the blank test is subtracted. Furthermore, any peaks that cannot be identified are converted into the amount of toluene detected and quantified. GCMS: Shimadzu QP5000 Column: J&W Scientific DB-1 (1μm×0.25mmφ×60m) Measurement conditions: Column temperature (After holding at 60°C for 1 minute, heat to 300°C at 10°C / min.) Split ratio: 10 Carrier gas: He (1 ml / min) Interface temperature: 260℃

[0023] (Polyolefin resin) The polyolefin resin is not particularly limited, and known resins can be used. The polyolefin resin may be crosslinked. Examples of the polyolefin resin include polyethylene resin and polypropylene resin.

[0024] (Polyethylene resin) The polyethylene resin is not particularly limited, and known resins can be used. The polyethylene resin may be crosslinked. Examples of polyethylene resins include ethylene copolymers, branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked polymers of these polymers. These polyethylene resins may be used alone or in combination. As polyethylene resins, low-density polyethylene and linear low-density polyethylene are preferred from the viewpoint of moldability (which in this specification may mainly mean the ease of foam molding at low vapor pressure or the high expansion ratio during foaming), high-density polyethylene is preferred from the viewpoint of strength, and ethylene copolymers, particularly ethylene-vinyl acetate copolymers, are preferred from the viewpoint of moldability.

[0025] The distinction between low-density polyethylene (LDPE), linear low-density polyethylene (L-LDPE), and high-density polyethylene (HDPE) is generally considered to be based on molecular structure: low-density polyethylene has short-chain branching and long-chain branching, linear low-density polyethylene has short-chain branching (and may have some long-chain branching) and is therefore somewhat linear, and high-density polyethylene has little branching and is therefore considered to be mostly linear. Low-density polyethylene and linear low-density polyethylene generally have relatively lower densities than high-density polyethylene.

[0026] Examples of ethylene copolymers include ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and ethylene-methyl methacrylate copolymer, with ethylene-vinyl acetate copolymer being preferred from the viewpoint of moldability. Ethylene-vinyl acetate copolymer is a copolymer of ethylene and vinyl acetate. Ethylene-vinyl acetate copolymer is superior to copolymers of ethylene and other ester monomers (e.g., alkyl acrylates, alkyl methacrylates, and vinyl aliphatic saturated monocarboxylates (excluding vinyl acetate)) in that it generates less powder during the production of foamed composite resin beads and has a smaller rate of dimensional change upon heating.

[0027] The proportion of vinyl acetate-derived components in the ethylene-vinyl acetate copolymer is preferably 1 to 20 mass %, more preferably 1 to 14 mass %, and even more preferably 1 to 10 mass %.

[0028] The melting point of the ethylene-vinyl acetate copolymer is not particularly limited, but can be, for example, 85 to 120°C, preferably 100 to 120°C, more preferably 100 to 115°C, and even more preferably 100 to 110°C. A melting point within the above range is advantageous in that the thermal dimensional change rate of the foamed molded product is small or that the compatibility with polyolefin resins is good, resulting in excellent fusion properties during foam molding. The melting point can be determined by the method described in the examples.

[0029] As the polyethylene resin, commercially available resins can be used, for example, those available from Tosoh Corporation, Japan Polyethylene Corporation, Prime Polymer Corporation, Asahi Kasei Corporation, etc. As the polyethylene resin, recycled products, for example, polyethylene resins used as packaging materials, etc., can be collected and recycled and used.

[0030] (Polypropylene resin) The polypropylene resin is not particularly limited, and known resins can be used. Examples of the polypropylene resin include homopolymers, random copolymers, and block copolymers, with random copolymers being preferred because of their high moldability (i.e., they can be foam-molded at low vapor pressure and tend to have a high expansion ratio during foaming). As the polypropylene-based resin, recycled products, for example, polypropylene-based resins used as packaging materials, etc., can be collected and recycled and used.

[0031] The copolymer may contain an olefin other than propylene (e.g., ethylene, butene, etc.). Examples of random copolymers include ethylene-propylene random copolymers, propylene-butene random copolymers, and ethylene-propylene-butene random copolymers. Examples of block copolymers include ethylene-propylene block copolymers, propylene-butene block copolymers, and ethylene-propylene-butene block copolymers. The proportion of components derived from olefins other than propylene in the copolymer can be, for example, 0.01 to 10 mass%, 0.01 to 8 mass%, 0.1 to 7 mass%, 0.1 to 6 mass%, etc., preferably 1 to 7 mass%, more preferably 2 to 6 mass%. As the polypropylene-based resin, commercially available resins can be used, for example, those available from Prime Polymer Co., Ltd., SunAllomer Co., Ltd., Sumitomo Chemical Co., Ltd., etc.

[0032] The content of the polyolefin resin in the seed polymerization composite resin (A) may be, for example, 10 to 50 mass%, 10 to 45 mass%, 10 to 40 mass%, 20 to 50 mass%, 20 to 45 mass%, 20 to 40 mass%, etc. of the seed polymerization composite resin (A).

[0033] (Polystyrene resin) In the seed polymerization composite resin (A), the polystyrene-based resin is preferably formed by seed polymerization of a styrene-based monomer with polyolefin-based resin particles. The content of the polystyrene-based resin in the seed polymerization composite resin (A) may be, for example, 50 to 90 mass%, 55 to 90 mass%, 60 to 90 mass%, 50 to 80 mass%, 55 to 80 mass%, or 60 to 80 mass% of the seed polymerization composite resin (A). The mass average molecular weight of the polystyrene-based resin is 1.0 × 10 5 ~5.0×10 5is preferable from the viewpoint of strength and moldability.

[0034] In the composite resin particles (C), the polystyrene-based resin can be divided into the polystyrene-based resin contained in the seed particles (B) and the polystyrene-based resin composited with the seed particles (B) by seed polymerization of a styrene monomer to the seed particles (B). The content of the latter polystyrene-based resin in the composite resin particles (C) may be, for example, 100 to 500 parts by mass per 100 parts by mass of the seed particles (B). A content of the latter polystyrene-based resin within the above range is preferred in terms of moldability, heat resistance, and impact resistance.

[0035] The content of the polystyrene-based resin in the seed-polymerized composite resin and the seed-polymerized composite resin particles may correspond to the amount of the styrene-based monomer used in the seed polymerization.

[0036] Examples of polystyrene-based resins include polymers derived from styrene-based monomers such as styrene, α-methylstyrene, p-methylstyrene, and 4-tert-butylstyrene. Furthermore, the polystyrene-based resin may be a polymer composed of a styrene-based monomer and another monomer copolymerizable with the styrene-based monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene and (meth)acrylic acid alkyl esters that do not contain a benzene ring in their structure, such as butyl (meth)acrylate. Components derived from these other monomers may be contained in the styrene-based polymer in an amount not exceeding 5% by mass.

[0037] The seed polymerization composite resin (A) may contain, in addition to the polyolefin resin and the polystyrene resin, an appropriate amount of conventional components that have been blended into the seed particles of styrene monomer-polyolefin seed polymerization composite resin particles.

[0038] (gel fraction) The seed polymerization composite resin (A) preferably has a gel fraction of 5 to 40% by mass, more preferably 10 to 30% by mass. A gel fraction within the above range is advantageous in that productivity is improved when the seed polymerization composite resin (A) is pelletized in an extruder to be reused as a foamed molded product of the styrene-based monomer-polyolefin seed polymerization composite resin. The gel fraction is measured as follows.

[0039] Weigh out 1 g of seed-polymerized composite resin (A) and place it in a flask. Add 100 ml of toluene, then heat under reflux in a 130°C oil bath for 24 hours to dissolve it. After removing the flask from the oil bath, immediately filter the contents through an 80-mesh (φ0.12 mm) wire mesh. The wire mesh and the insoluble material remaining on it are placed in a 130°C oven for 1 hour, then placed under reduced pressure with a vacuum pump for 2 hours to remove the toluene. The weight of the solid material remaining on the wire mesh is measured. The gel fraction is calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100

[0040] The content of the seed polymerization composite resin (A) in the seed particles (B) may be 20 to 100 mass%, 30 to 100 mass%, 40 to 100 mass%, 10 to 90 mass%, 10 to 80 mass%, 10 to 70 mass%, 20 to 90 mass%, 20 to 80 mass%, 20 to 70 mass%, etc. of the seed particles (B).

[0041] (Other resins contained in seed particles (B)) The seed particles (B) may contain only the seed polymerization composite resin (A) or may further contain other resins in addition to the seed particles (A). The content of the other resins in the seed particles (B) may be 0 to 80 mass%, 0 to 70 mass%, 0 to 60 mass%, 10 to 90 mass%, 20 to 90 mass%, 30 to 90 mass%, 10 to 80 mass%, 20 to 80 mass%, 30 to 80 mass%, etc., of the seed particles (B).

[0042] (Second polyolefin resin) Examples of the other resin include polyolefin resins (also referred to as "second polyolefin resins"), and these can be used alone or in combination of two or more. Examples of the second polyolefin resin include the polyolefin resins exemplified above, and ethylene copolymers, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and polypropylene are preferred, with ethylene copolymers, low-density polyethylene, linear low-density polyethylene, and high-density polyethylene being more preferred. As the second polyolefin resin, recycled products, for example, polyethylene resins used as packaging materials, etc. may be collected and recycled, and recycled resins may be used. The second polyolefin resin may be the same as or different from the polyolefin resin contained in the seed polymerization composite resin (A). Regarding other matters relating to the second polyolefin-based resin, the matters described above relating to polyolefin-based resins can be applied.

[0043] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is one or more resins selected from the group consisting of branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked products of these polymers, and the second polyolefin resin is an ethylene copolymer.

[0044] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is one or more resins selected from the group consisting of branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked polymers thereof, and the second polyolefin resin is one or more resins selected from the group consisting of branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked polymers thereof.

[0045] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is an ethylene copolymer, and the second polyolefin resin is one or more resins selected from the group consisting of branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and crosslinked products of these polymers.

[0046] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is a linear low-density polyethylene, and the second polyolefin resin is an ethylene copolymer.

[0047] In one embodiment, the polyolefin resin contained in the seed polymerization composite resin (A) is linear low-density polyethylene, and the second polyolefin resin is linear low-density polyethylene.

[0048] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is a high-density polyethylene, and the second polyolefin resin is an ethylene copolymer.

[0049] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is an ethylene copolymer, and the second polyolefin resin is a low-density polyethylene.

[0050] In one embodiment, the polyolefin resin contained in the seed polymerized composite resin (A) is a polypropylene resin (preferably a random copolymer), and the second polyolefin resin is a polypropylene resin (preferably a homopolymer).

[0051] (Inorganic component) The seed particles (B) may contain an inorganic component in addition to the polyolefin resin and the polystyrene resin, such as an inorganic bubble adjuster, such as talc, silica, calcium silicate, calcium carbonate, sodium borate, or zinc borate, and talc and silica are preferred in that they homogenize the bubble size. When the seed particles (B) contain an inorganic component, the content thereof can be, for example, 0.01 to 5 mass %, or 0.1 to 1 mass %, relative to the seed particles (B).

[0052] (Other ingredients) The seed particles (B) may contain other components in addition to the polyolefin resin and polystyrene resin. Examples of other components include colorants, nucleating agents, stabilizers, fillers (reinforcing materials), metal salts of higher fatty acids, antistatic agents, lubricants, natural or synthetic oils, waxes, UV absorbers, weather stabilizers, anti-fogging agents, anti-blocking agents, slip agents, coating agents, and neutron shielding agents. The content of other components may be 10% by mass or less, preferably 5% by mass or less, and particularly preferably 0% by mass (no other components) relative to the total mass of the seed particles (B).

[0053] (Method for producing seed particles (B)) The seed particles (B) can be obtained by a known method used for producing seed particles for forming foamed molded articles, except for using the seed polymerization composite resin (A). For example, the seed polymerization composite resin (A) as a base resin and the other resin (e.g., a second polyolefin resin) used as needed are melt-kneaded and extruded in an extruder to obtain strands, and the resulting strands are cut in air, water, or while heated to form granules. The resin components may be mixed in a mixer before being added to the extruder.

[0054] The seed particles may have any known shape, but are preferably cylindrical, oval-spherical (egg-shaped), or spherical, and more preferably oval-spherical or spherical, from the viewpoint of the ease with which the expanded beads obtained from the seed particles can be filled into a mold. The seed particles preferably have an average particle size of 0.5 to 1.4 mm.

[0055] (Composite resin particles (C)) The composite resin particles (C) are obtained by impregnating the seed particles (B) with a styrene-based monomer and polymerizing the same, i.e., the composite resin particles (C) are seed-polymerized composite resin particles of a styrene-based monomer and the seed particles (B).

[0056] The shape of the composite resin particles (C) may be any known shape, but cylindrical, approximately spherical, and spherical shapes are preferred, and approximately spherical or spherical shapes are more preferred in terms of the good mold-filling properties of the expanded composite resin beads formed from the composite resin particles (C).The average particle diameter of the composite resin particles is preferably 0.6 mm to 1.8 mm.

[0057] The composite resin particles (C) may have a total volatile organic compounds (TVOC) content of 1000 ppm or less, preferably 0 to 800 ppm. A TVOC content within this range is advantageous in terms of stabilizing monomer absorption when used as seed particles. Here, TVOC does not include the blowing agent. The TVOC measurement method is the same as above.

[0058] (Method for producing composite resin particles (C)) The method for producing the composite resin particles (C) is not particularly limited as long as it can impregnate and polymerize the seed particles (B) with a styrene-based monomer. For example, it may include a step of shredding a base resin to obtain seed particles (B), and a step of impregnating and polymerizing the seed particles (B) with a styrene-based monomer, i.e., seed-polymerizing the seed particles (B) with a styrene-based monomer, to obtain the composite resin particles (C).

[0059] In this seed polymerization, the amount of the styrene-based monomer used is not particularly limited, and may be an amount corresponding to the above-mentioned content of the polystyrene-based resin composited with the seed particles (B) by seed polymerization of the styrene-based monomer on the seed particles (B), for example, 100 to 500 parts by mass per 100 parts by mass of the seed particles (B).

[0060] An example of a method for producing the composite resin particles (C) using the seed polymerization method will be described below. First, the seed particles (B), the styrene-based monomer, and optionally a polymerization initiator are dispersed in an aqueous suspension. When a polymerization initiator is used, the styrene-based monomer and the polymerization initiator may be mixed in advance.

[0061] As the polymerization initiator, those generally used as initiators for suspension polymerization of styrene-based monomers can be suitably used. Examples include organic peroxides such as benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butyl-peroxy-2-ethylhexyl carbonate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination. Examples of aqueous media that constitute the aqueous suspension include water and mixed media of water and a water-soluble solvent (for example, an alcohol having 1 to 6 carbon atoms).

[0062] The amount of the polymerization initiator used is preferably 0.01 to 0.9 parts by mass, more preferably 0.1 to 0.5 parts by mass, based on 100 parts by mass of the styrene-based monomer.

[0063] A dispersant may be added to the aqueous suspension as needed. The dispersant is not particularly limited, and any known dispersant can be used. Specific examples include poorly soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate, and magnesium oxide. Furthermore, a surfactant such as sodium dodecylbenzenesulfonate may also be used.

[0064] Next, the obtained dispersion is heated to a temperature at which the styrene-based monomer does not substantially polymerize, and the styrene-based monomer is impregnated into the seed particles. The time for impregnating the seed particles with the styrene-based monomer is not particularly limited, but is preferably 20 minutes to 4 hours, and more preferably 30 minutes to 2 hours.

[0065] Next, the styrene-based monomer is polymerized. The polymerization temperature is not particularly limited, but it is preferable to carry out the polymerization at 115°C to 150°C, preferably 120°C to 145°C, for 1.5 to 5 hours. The polymerization is usually carried out in a pressurizable sealed container. It is preferable to carry out the impregnation of the styrene-based monomer and the polymerization in multiple steps. By carrying out the polymerization in multiple steps, the generation of polymer powder of the styrene-based resin can be minimized. Furthermore, taking into consideration the decomposition temperature of the polymerization initiator, the polymerization may be carried out while the styrene-based monomer is being impregnated into the seed particles, rather than initiating the polymerization after the styrene-based monomer has been impregnated.

[0066] (expandable particles) The expandable particles contain composite resin particles (C) and a foaming agent. Examples of the blowing agent that can be used include organic gases such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, and isohexane, and inorganic gases such as carbon dioxide, nitrogen, helium, argon, and air. These blowing agents can be used alone or in combination of two or more. Suitable organic gases are n-butane, isobutane, n-pentane, and isopentane, or a combination thereof. The content of the foaming agent is preferably 5 to 25 parts by mass relative to 100 parts by mass of the composite resin particles (C).

[0067] The expandable particles can be obtained, for example, by impregnating the composite resin particles (C) with a blowing agent during or after the completion of polymerization. The impregnation can be carried out by a method known per se. For example, impregnation during polymerization can be carried out by carrying out the polymerization reaction in a sealed container and injecting the blowing agent into the container under pressure. Impregnation after the completion of polymerization can be carried out, for example, by injecting the blowing agent under pressure into a sealed container into which the composite resin particles (C) have been placed.

[0068] (foam particles) Expanded beads are particles obtained by pre-expanding composite resin particles (C). For example, expanded beads can be obtained by expanding expandable beads impregnated with a blowing agent. By using composite resin particles (C) as a raw material, the expanded beads are fused together in a low vapor pressure medium (e.g., water vapor), which reduces the energy required for expansion molding and simplifies the equipment required for expansion molding, thereby reducing the cost required for expansion molding.

[0069] The bulk density of the foam particles is 15 kg / m 3 ~200kg / m 3 is preferable, and 20 kg / m 3 ~100kg / m 3 is more preferable, and 20 kg / m 3 ~50kg / m 3 A bulk density within this range is advantageous in that the foamed molded article has high strength and is lightweight.

[0070] The expanded beads preferably have a spherical or nearly spherical shape, and the average particle diameter is preferably 1.0 mm to 9.0 mm, more preferably 2.0 mm to 6.4 mm.

[0071] The expanded particles can be obtained by expanding the expandable particles to a desired bulk density by a known method, preferably using heated steam at a gauge pressure of 0.05 MPa to 0.20 MPa, more preferably 0.06 MPa to 0.15 MPa.

[0072] The expanded beads obtained by pre-expanding the expandable beads, in which a blowing agent is incorporated into the composite resin particles (C), generate little powder. Because powder shortens the life of a mold, the expanded beads of the present invention are useful for extending the life of a mold.

[0073] If the expanded beads contain too much blowing agent, the expanded molded product will expand during expansion molding, making it difficult to remove from the mold. For this reason, after the production of expanded beads, the blowing agent content may be adjusted by dissipating the blowing agent contained in the expanded beads. However, if the time required for this adjustment is long, the time required to proceed to expansion molding will be long. Therefore, from the viewpoint of the molding cycle, it is desirable to shorten the time required for the blowing agent to dissipate. The use of the expanded beads of the present invention has the advantage that the blowing agent can be dissipated in a shorter time than in expanded beads obtained using conventional particles of a melt-kneaded mixture of a polyolefin resin and a polystyrene resin as seed particles.

[0074] (foam molded body) The foamed molded article is a foamed article composed of a fused body of foamed beads, and is obtained, for example, by foam-molding the foamed beads. The foamed molded article uses the seed particles (B) and the composite resin particles (C) as raw materials, and therefore has excellent compressive strength and thermal dimensional change rate.

[0075] The density of the foamed molded body is, for example, 15 kg / m 3 ~200kg / m 3 , 20 kg / m 3 ~200kg / m 3 etc., 20kg / m 3 ~100kg / m 3 is preferable, and 20 kg / m 3 ~50kg / m 3 When the density is within the above range, the foamed molded article is excellent in both lightness and strength. The density of the foamed molded article is determined by the method described in the Examples.

[0076] The 25% compressive strength of the foamed molded article can be, for example, 0.15 MPa or more, 0.15 MPa to 0.30 MPa, 0.17 MPa to 0.30 MPa, etc., and is preferably 0.20 MPa to 0.30 MPa. The 25% compressive strength is determined by the method described in the Examples.

[0077] The thermal dimensional change rate of the foamed molded article can be, for example, 2.5% or less, 0.1 to 2.5%, etc., and is preferably 0.1 to 2.0%. The thermal dimensional change rate is determined by the method described in the Examples.

[0078] The foamed molded article can be obtained by filling the foamed beads into a mold of an expansion molding machine, heating the foamed beads to expand them, and heat-fusing the foamed beads together. Steam is preferably used as a heating medium.

[0079] When the expanded beads of the present invention do not contain a polypropylene-based resin, they can be sufficiently expanded and fused even with low-pressure steam (e.g., a gauge pressure of 0.10 MPa or less), which reduces the energy required for expansion molding and simplifies the equipment required for expansion molding, thereby reducing the cost required for expansion molding (i.e., achieving excellent productivity).Furthermore, even when the expanded beads of the present invention contain a polypropylene-based resin, they can be sufficiently expanded and fused with steam at a gauge pressure of 0.20 MPa or less.

[0080] The foamed molded article can be used for cushioning materials, packaging materials, building materials, shoe components, and sporting goods. Specifically, it can be used for midsole components, insole components, or outsole components of shoes; core materials for hitting implements such as rackets and bats; protective gear for sporting goods such as pads and protectors; medical, nursing care, welfare, or health care products such as pads and protectors; tire core materials for bicycles and wheelchairs; interior materials, seat core materials, shock absorbing materials, vibration absorbing materials, and the like for transportation equipment such as automobiles, railway vehicles, and airplanes; fenders; floats; toys; underfloor materials; wall materials; beds; cushions; electronic components, various industrial materials, and transport containers for food, etc. The material is preferably used as an interior material for an automobile, a shock absorbing material, a vibration absorbing material, or a packaging material for parts. [Example]

[0081] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these. The methods for determining various physical properties in the examples are as follows.

[0082] (Density of polyolefin resin) The density of the polyolefin resin is measured by the density gradient tube method in accordance with JIS K6922-1:1998.

[0083] (Melt flow rate (MFR) of polyolefin resin) The MFR was measured at 190°C under a load of 2.16 kg in accordance with JIS K6922-1:1998.

[0084] (Melting point of polyolefin resin) The melting point was measured according to the method described in JIS K7122:1987 "Method for measuring heat of transition of plastics." Specifically, a differential scanning calorimeter RDC220 (Seiko Electronics Industries, Inc.) was used. 7 mg of sample was filled into the measurement container, and the temperature was increased, decreased, and increased again from room temperature to 220°C at a rate of 10°C / L under a nitrogen gas flow rate of 30 mL / min. The melting peak temperature on the DSC curve during the second temperature increase was taken as the melting point. When there were two or more melting peaks, the lower peak temperature was taken as the melting point.

[0085] (Softening temperature of polyolefin resin (Vicat softening point)) The softening temperature was measured by the method described in JIS 7196:1991 "Test method for softening temperature by thermomechanical analysis of thermoplastic plastic films and sheets." That is, the resin particles were hot-pressed and crushed to a thickness of 2 mm, and then a flat rectangular film test piece measuring 10 mm long x 20 mm wide x 2 mm thick was prepared. The test piece was then subjected to a thermal stress and strain measurement in a needle insertion test mode (needle tip area 1 mm) using a thermal stress and strain measurement device (Seiko Instruments Inc., product name "TMA / SS6200"). 2 ), a load of 50 g was applied, and a needle was placed on the film-like test piece, and the temperature was raised at a rate of 5°C / min. The temperature at which the film-like test piece began to distort was taken as the softening temperature (Vicat softening point) of the resin particles.

[0086] (Mass average molecular weight of polystyrene resin) The mass average molecular weight was measured using a gel permeation chromatography (GPC) apparatus (manufactured by Tosoh Corporation, model: HLC-8121GPC / HT) and a column (manufactured by Tosoh Corporation, model: TSKgel GMHhr-H(20)HT). The measurement conditions were as follows: the column temperature was set to 140°C, and 1,2,4-trichlorobenzene was used as the eluent. The measurement sample was adjusted to a concentration of 1.0 mg / mL, and the injection volume into the GPC apparatus was 0.3 mL. The calibration curve for each molecular weight was calibrated using polystyrene samples with known molecular weights, and the mass average molecular weight (Mw) was calculated as a polystyrene equivalent value.

[0087] (gel fraction) One gram of seed-polymerized composite resin (A) or extrusion-kneaded composite resin of polyolefin-based resin and polyolefin-based resin was weighed and placed in a flask. 100 ml of toluene was added, and the mixture was heated to reflux in a 130°C oil bath for 24 hours to dissolve the resin. After removing the flask from the oil bath, the contents were immediately filtered through an 80-mesh (0.12 mm diameter) wire mesh. The wire mesh and the insoluble material remaining on it were placed in an oven at 130°C for one hour, then placed under reduced pressure with a vacuum pump for two hours to remove the toluene. The weight of the solid material remaining on the wire mesh was then measured. The gel fraction was calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100

[0088] (Bulk density of expanded particles) Put 500cm of foam particles into a measuring cylinder. 3 However, the measuring cylinder was visually inspected from the horizontal direction to ensure that even one composite resin foam particle did not exceed the 500 cm mark. 3 When the scale reached the mark, the filling was completed. Next, the mass of the expanded composite resin beads filled in the measuring cylinder was weighed to two decimal places, and this mass was designated as W (g). The bulk density of the expanded composite resin beads was calculated using the following formula. Bulk density (kg / m 3 )=(W / 500)×1000

[0089] (Measurement of the amount of polymerized polystyrene powder) To 2 L of slurry containing composite resin particles (this slurry was the autoclave contents cooled to below 30°C after the second polymerization in the production of composite resin particles (C)), 100 ml of 20% hydrochloric acid was added and the mixture was filtered through a 0.3 mm mesh to separate the composite resin particles from the suspension. 1 L of pure water was added to the filtered composite resin particles to make a slurry again, which was then filtered through a 0.3 mm mesh filter. This procedure was repeated five times, and the resulting 6 L of filtrate was subjected to suction filtration using a Buchner funnel (glass fiber filter paper GA-200). The powder on the filter paper obtained by suction filtration and the composite resin particles were each dried and weighed. The amount of polymerized powder (%) was calculated using the following formula. Polymerized powder amount (%) = Powder weight (g) / Composite resin particle weight (g)

[0090] (Density of foamed molded product) The mass (a) and volume (b) of a test piece (75 mm x 300 mm x 35 mm) cut out from a foamed molded product (dried at 50°C for at least 4 hours after molding) were measured to three or more significant figures, and the density (kg / m) of the foamed molded product was calculated using the formula (a) / (b). 3 ) was sought.

[0091] (25% compression strength of foamed molded body) The compressive strength was measured according to the method described in JIS K7220:2006, "Rigid foam plastics - Determination of compression properties." Specifically, using a Tensilon universal testing machine (manufactured by Orientec Co., Ltd., UCT-10T), the compressive strength of a 50 mm × 50 mm × 25 mm test specimen (with upper surface skin) was measured at a compression rate of 10 mm / min at 25% compression (10 mm displacement).

[0092] (Dimensional change rate of foam molded body due to heating) The thermal dimensional change of the foamed molded article was measured using Method B described in JIS K 6767:1999 "Foamed Plastics - Polyethylene - Test Methods." Test specimens measuring 150 mm long x 150 mm wide x 20 mm high were cut from the foamed molded article. Three 50 mm long lines parallel to each other were drawn on the surface of the test specimen at 50 mm intervals, and three 50 mm long lines parallel to each other were drawn on the surface of the test specimen at 50 mm intervals. The test specimen was then placed in a hot air circulation dryer at 80°C for 168 hours, then removed and placed under standard conditions (20±2°C, 65±5% humidity) for 1 hour. The lengths of the six lines drawn on the surface of the test specimen were then measured, and the arithmetic mean value L1 of the six line lengths was calculated. The degree of change S was calculated using the following formula, and the absolute value of the degree of change S was taken as the thermal dimensional change (%). S=100×(L1-50) / 50

[0093] (Moldability of foamed molded products; minimum water vapor pressure to achieve a fusion rate of 90% or more) The composite resin foam beads were filled into a 300mm x 400mm x 30mm mold in a foam molding machine and heated with steam to expand the composite resin foam beads while thermally fusing the foam beads together. The steam pressure during the steam heating (50 seconds) was varied in 0.01 MPa increments from 0.08 MPa to 0.25 MPa, and the fusion rate of the resulting foamed molded body was determined for each pressure. Moldability was evaluated using the lowest steam pressure (minimum steam pressure) at which a fusion rate of 90% or greater was achieved. Obtaining well-fused foamed molded bodies at low steam pressures allows for simplified molding equipment and reduced manufacturing energy, resulting in lower manufacturing costs and improved productivity.

[0094] (Foaming evaluation) A 5-liter autoclave equipped with a stirrer was charged with 2 kg (100 parts by weight) of composite resin particles, 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant). Furthermore, butane (normal butane:isobutane = 7:3 (volume ratio)) was added as a blowing agent (15 parts by weight per 100 parts by weight of composite resin particles). The mixture was then heated to 70°C and stirred for 4 hours to incorporate the blowing agent into the composite resin particles. The mixture was then cooled to below 30°C. After cooling was complete, the autoclave was depressurized, and the surfactant was immediately washed away with distilled water. The mixture was then dehydrated and dried to obtain expandable particles. The mass (a) of approximately 2 g of expandable particles was weighed to two decimal places. The weighed expandable particles were placed in a container, and after confirming that the temperature inside the expansion tank was below 80°C, the container containing the expandable particles was placed in the expansion tank, and steam (steam temperature: 99°C) at a gauge pressure of 0.04 MPa was introduced. Once the temperature inside the expansion tank reached 90°C, the expandable particles were heated at 90-100°C for 1 minute to expand. The expansion ratio was measured immediately after removal from the expansion tank. The expansion ratio was determined by placing approximately 2 g (a) of the expanded particles in a measuring cylinder, measuring the volume, and dividing the volume by (a) to determine the bulk ratio of the expanded particles. Based on the obtained bulk ratio, evaluation was performed according to the following criteria. Bulking factor 30 times or more: 〇 (good) Bulk ratio: 20 times or more but less than 30 times: △ (Acceptable) Bulking ratio less than 20 times or blocking occurs: × (bad)

[0095] (Polyethylene resin) The polyethylene resins used in the examples are as follows: The physical properties of the polyethylene resins are shown in Table 1. NF444A: Linear low-density polyethylene (manufactured by Japan Polyethylene Co., Ltd., product number NF444A) 2500: High-density polyethylene (Tosoh Corporation, product number 2500) M1703: Low-density polyethylene (Asahi Kasei Corporation, product number M1703) EF0505: Ethylene-vinyl acetate copolymer (manufactured by Asahi Kasei Corporation, vinyl acetate content 4.7% by mass) LV115: Ethylene-vinyl acetate copolymer (manufactured by Japan Polyethylene Co., Ltd., product number LV115, vinyl acetate content 4% by mass)

[0096] [Table 1]

[0097] (Polypropylene resin) The polypropylene-based resins (PP) used in the examples are as follows: The physical properties of the polypropylene-based resins are shown in Table 2. F744NP: Random copolymer of PP (Prime Polymer, ethylene content 7% by mass) PL500A: PP homopolymer (manufactured by SunAllomer Co., Ltd.)

[0098] [Table 2]

[0099] The polystyrene resins used in the comparative examples are as follows: HRM26: Polystyrene resin (manufactured by Toyo Styrene Co., Ltd., product name: Toyo Styrol GP, product type: HRM26)

[0100] Example 1 [Preparation of styrene monomer-polyolefin seed polymerization composite resin (A)] NF444A was fed to an extruder as a polyethylene resin, melted and kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by an underwater cutting method to obtain polyethylene resin particles (average mass 0.6 mg). A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to obtain a dispersion medium. 600 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution, which had been cooled to 115°C, over 10 minutes. Next, a solution of 5 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1100 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene monomer and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30° C. or less, and the particles of the styrene-based monomer-polyolefin seed-polymerized composite resin (A) were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the particles of the obtained seed-polymerized composite resin (A) was measured and found to be 2.5 × 10 5 It was.

[0101] [Preparation of seed particles (B)] The obtained particles of seed-polymerized composite resin (A) and LV115 (second polyolefin resin) as an ethylene-vinyl acetate copolymer were charged in a mass ratio of 20:80 into a tumbler mixer and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded material was then cut into oval (egg) spheres using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene monomer-polyolefin seed polymerization composite resin (A) and an ethylene-vinyl acetate copolymer.

[0102] [Preparation of composite resin particles (C) by seed polymerization of styrene-based monomer-seed particles (B)] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to obtain a dispersion medium. 700 g of seed particles (B) were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.6 g of dicumyl peroxide (polymerization initiator) in 350 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise over 10 minutes to the reaction solution cooled to 115°C. Next, a solution of 3 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 950 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles (B). After the dropwise addition, the temperature was maintained at 115°C for 1 hour, thereby impregnating the seed particles (B) with the styrene monomer. After the impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization). Then, the mixture was cooled to 30° C. or less, and the composite resin particles (C) were taken out from the autoclave.

[0103] [Preparation of expandable granules] 2 kg (100 parts by mass) of composite resin particles (C), 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant) were added to a 5-liter autoclave equipped with a stirrer. Furthermore, butane (normal butane: isobutane = 7:3 (volume ratio)) was added as a blowing agent at a ratio of 15 parts by mass per 100 parts by mass of composite resin particles (C). The mixture was then heated to 70°C and stirred for 4 hours to produce expandable particles. The mixture was then cooled to below 30°C. After cooling was complete, the autoclave was depressurized, and the surfactant was immediately washed with distilled water. The expandable particles were then obtained by dehydrating and drying.

[0104] [Preparation of foam particles] The obtained expandable granules were placed in a 50 L cylindrical pre-expander equipped with a stirrer, and pre-expanded by heating with steam at 0.02 MPa while stirring, to a bulk density of 29 kg / m 3 The foamed particles were prepared.

[0105] [Production of foam molded products] The resulting expanded beads were left at 23°C for 1 day and then packed into a molding die (length 400 mm × width 300 mm × thickness 30 mm) of an automatic expanded bead molding machine (DABO Japan, DPM-7454). Steam at 0.07 MPa was introduced into the die for 50 seconds to heat and expand the expanded beads, and the expanded molded product was then cooled until the maximum surface pressure of the expanded molded product decreased to 0.01 MPa, resulting in a density of 29 kg / m. 3 A foamed molded article of this size was obtained. The results of the various tests are shown in Table 3.

[0106] Example 2 Seed particles (B), composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 1, except that the mass ratio of the styrene monomer-polyolefin composite resin (A) particles to LV115 was 70:30 and the steam pressure used for foam molding was 0.06 MPa. The results of various tests are shown in Table 3.

[0107] Example 3 [Preparation of foamed molded composite resins from seed polymerization of styrene-based monomers and polyolefins] In the same manner as in Example 1, particles of a seed-polymerized composite resin of a styrene-based monomer and polyolefin were obtained. 2 kg (100 parts by weight) of seed polymerization composite resin particles, 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant) were added to a 5-liter autoclave equipped with a stirrer. Furthermore, butane (normal butane: isobutane = 7:3 (volume ratio)) was added as a blowing agent at a ratio of 15 parts by weight per 100 parts by weight of seed polymerization composite resin particles. The mixture was then heated to 70°C and stirred for 4 hours to produce expandable particles. The mixture was then cooled to below 30°C. After cooling was complete, the autoclave was depressurized, and the surfactant was immediately washed with distilled water. The expandable particles were then dehydrated and dried to obtain expandable particles. The obtained expandable granules were placed in a 50 L cylindrical pre-expander equipped with a stirrer, and pre-expanded by heating with steam at 0.02 MPa while stirring, to a bulk density of 29 kg / m 3 The foamed particles were prepared. The resulting expanded beads were left at 23°C for 1 day and then packed into a molding die (length 400 mm × width 300 mm × thickness 30 mm) of an automatic expanded bead molding machine (DABO Japan, DPM-7454). Steam at 0.07 MPa was introduced into the die for 50 seconds to heat and expand the expanded beads, and the expanded molded product was then cooled until the maximum surface pressure of the expanded molded product decreased to 0.01 MPa, resulting in a density of 29 kg / m. 3 A foamed molded article of this size was obtained.

[0108] [Preparation of seed particles (B) (reuse of foamed molded products)] The obtained foamed molded body was pulverized using a Mitsui Mining Co., Ltd. CUM300 centrifugal mill (grinding track method, 1.0 mm perforation) to produce pulverized resin particles. The pulverized resin particles obtained were fed into an extruder and melt-kneaded at a temperature of 230-250°C. The kneaded product was then cut into cylindrical pellets using a strand cut method to obtain pellets with an average mass of 6 mg. The obtained pellets (styrene-based monomer-polyolefin seed polymerization composite resin (A) derived from foamed molded products) and NF444A (second polyolefin-based resin) as linear low-density polyethylene were placed in a tumbler mixer in a mass ratio of 50:50 and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded material was then cut into oval (egg) spheres using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene monomer-polyolefin seed polymerization composite resin (A) and linear low-density polyethylene.

[0109] Except for using the obtained seed particles (B), composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 1. The results of various tests are shown in Table 3.

[0110] Example 4 [Preparation of foamed molded composite resins from seed polymerization of styrene-based monomers and polyolefins] 2500 polyethylene resin was fed to an extruder and melt-kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by underwater cutting to obtain polyethylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 800 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.8 g of dicumyl peroxide (polymerization initiator) in 400 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution, which had been cooled to 120°C, over 10 minutes. Next, a solution of 4 g of dicumyl peroxide (polymerization initiator) dissolved in 800 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 120°C for 1 hour, allowing the styrene monomer to be impregnated into the polyethylene resin particles. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 120°C for 1 hour, allowing the styrene monomer and cell bubble control agent to be impregnated into the seed particles. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30°C or less, and the styrene monomer-polyolefin seed polymerization composite resin particles were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the obtained seed polymerization composite resin particles was measured and found to be 4.2 × 10 5 It was. Next, a sintered product having a density of 29 kg / m was prepared in the same manner as in Example 3, except that the sintered product particles of the sintered product polymerized in the seed polymerization of a ... 3 A foamed molded article of this size was obtained.

[0111] [Preparation of seed particles (B) (reuse of foamed molded products)] The obtained foamed molded article was treated in the same manner as in Example 3 to obtain pellets with an average mass of 6 mg. The obtained pellets (styrene-based monomer-polyolefin seed polymerization composite resin (A) derived from the foamed molded article) and EF0505 as an ethylene-vinyl acetate copolymer were charged into a tumbler mixer in a mass ratio of 40:60 and mixed for 10 minutes. The obtained resin mixture was treated in the same manner as in Example 3 to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene-based monomer-polyolefin seed polymerization composite resin (A) and an ethylene-vinyl acetate copolymer.

[0112] [Preparation of composite resin particles (C) by seed polymerization of styrene-based monomer-seed particles (B)] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to prepare a dispersion medium. 600 g of seed particles (B) were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to prepare a suspension. While maintaining the suspension at 60°C, a solution containing 0.5 g of dicumyl peroxide (polymerization initiator) dissolved in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C and polymerization (first polymerization) was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise over 10 minutes to the reaction solution, which had been cooled to 115°C. Next, a solution prepared by dissolving 5 g of t-butyl peroxybenzoate (polymerization initiator) in 1,100 g of styrene monomer was added dropwise at a rate corresponding to 0.05 parts by mass / second relative to 100 parts by mass of seed particles (B). After the dropwise addition, the temperature was maintained at 115°C for 1 hour, thereby impregnating the seed particles (B) with the styrene monomer. After impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization). Next, the mixture was cooled to 30°C or below, and composite resin particles (C) were removed from the autoclave.

[0113] Except for using the obtained composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 1. Table 3 shows the results of various tests.

[0114] Example 5 [Preparation of foamed molded composite resins from seed polymerization of styrene-based monomers and polyolefins] EF0505 was fed to an extruder as a polyethylene resin, melted and kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by an underwater cutting method to obtain polyethylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 800 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.8 g of dicumyl peroxide (polymerization initiator) in 400 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 122°C over 10 minutes. Next, a solution of 4 g of dicumyl peroxide (polymerization initiator) dissolved in 800 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 122°C for 1 hour, thereby impregnating the polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 122°C for 1 hour, thereby impregnating the seed particles with the styrene monomer and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30°C or less, and the styrene-based monomer-polyolefin seed polymerization composite resin particles were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the obtained seed polymerization composite resin particles was measured and found to be 3.8 × 10 5 It was. Next, a sintered product having a density of 29 kg / m was prepared in the same manner as in Example 3, except that the sintered product particles of the sintered product polymerized in the seed polymerization of a ... 3 A foamed molded article of this size was obtained.

[0115] [Preparation of seed particles (B) (reuse of foamed molded products)] The obtained foamed molded article was treated in the same manner as in Example 3 to obtain pellets with an average mass of 6 mg. The obtained pellets (styrene-based monomer-polyolefin seed polymerization composite resin (A) derived from the foamed molded article) and M1703 as low-density polyethylene were charged into a tumbler mixer in a mass ratio of 50:50 and mixed for 10 minutes. The resulting resin mixture was treated in the same manner as in Example 3 to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene monomer-polyolefin seed polymerization composite resin (A) and low-density polyethylene.

[0116] [Preparation of composite resin particles (C) by seed polymerization of styrene-based monomer-seed particles (B)] A 5-liter autoclave equipped with a stirrer was charged with 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to obtain a dispersion medium. 400 g of seed particles (B) were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 200 g of styrene monomer and 0.3 g of dicumyl peroxide (polymerization initiator) was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 115°C over 10 minutes. Next, a solution of 8 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1,400 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles (B). After the dropwise addition, the temperature was maintained at 115°C for 1 hour, thereby impregnating the seed particles (B) with the styrene monomer. After impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization). The mixture was then cooled to 30°C or below, and the composite resin particles (C) were removed from the autoclave.

[0117] Except for using the obtained composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 1. Table 3 shows the results of various tests.

[0118] Example 6 [Preparation of styrene monomer-polyolefin seed polymerization composite resin (A)] NF444A was fed to an extruder as a polyethylene resin, melted and kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by an underwater cutting method to obtain polyethylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 1,400 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution, which had been cooled to 115°C, over 10 minutes. Next, a solution of 2 g of t-butyl peroxybenzoate (polymerization initiator) and 3 g of dicumyl peroxide dissolved in 300 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, allowing the styrene monomer to be impregnated into the polyethylene resin particles. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, allowing the styrene monomer and cell bubble control agent to be impregnated into the seed particles. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30° C. or less, and the particles of the styrene-based monomer-polyolefin seed-polymerized composite resin (A) were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the particles of the obtained seed-polymerized composite resin (A) was measured and found to be 2.7 × 10 5 It was.

[0119] [Preparation of seed particles (B)] The obtained particles of seed polymerization composite resin (A) were fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded product was then cut into oval (egg) shapes using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of styrene-based monomer-polyolefin seed polymerization composite resin (A).

[0120] [Preparation of composite resin particles (C) by seed polymerization of styrene-based monomer-seed particles (B)] A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 600 g of seed particles (B) were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.5 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise over 10 minutes to the reaction solution cooled to 115°C. Next, a solution of 4 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1100 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles (B). After the dropwise addition, the temperature was maintained at 115°C for 1 hour, thereby impregnating the seed particles (B) with the styrene monomer. After the impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization). Then, the mixture was cooled to 30° C. or less, and the composite resin particles (C) were taken out from the autoclave.

[0121] Except for using the obtained composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 1. Table 3 shows the results of various tests.

[0122] Comparative Example 1 [Preparation of extrusion-mixed composite resins of polyethylene-based resin and polystyrene-based resin] A polyethylene resin, 2500, and a polystyrene resin, HRM26, were charged into a tumbler mixer in a mass ratio of 40:60 and mixed for 10 minutes. The resulting resin mixture was fed to an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded product was cut into oval spherical (egg-shaped) particles using an underwater cutting method to obtain extrusion-kneaded composite resin particles. The mass-average molecular weight of the polystyrene resin was measured to be 3.2 × 10 5 It was. [Preparation of seed particles (B)] The obtained extrusion-kneaded composite resin particles and EF0505 (second polyolefin resin) as an ethylene-vinyl acetate copolymer were charged into a tumbler mixer in a mass ratio of 40:60 and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded material was then cut into oval (egg) spheres using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene monomer-polyolefin seed polymerization composite resin (A) and an ethylene-vinyl acetate copolymer.

[0123] Except for using the obtained seed particles (B), composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 4. The results of various tests are shown in Table 3.

[0124] Comparative Example 2 [Preparation of styrene monomer-polyolefin seed polymerization composite resin (A)] NF444A was fed to an extruder as a polyethylene resin, melted and kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by an underwater cutting method to obtain polyethylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 100 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.1 g of dicumyl peroxide (polymerization initiator) in 50 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 115°C over 10 minutes. Next, a solution of 10 g of t-butyl peroxybenzoate (polymerization initiator) dissolved in 1850 g of styrene monomer was added dropwise at a rate of 0.03 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 115°C for 1 hour, thereby impregnating the seed particles with the styrene monomer and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30° C. or less, and the particles of the styrene-based monomer-polyolefin seed-polymerized composite resin (A) were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the particles of the obtained seed-polymerized composite resin (A) was measured and found to be 2.2 × 10 5 It was.

[0125] [Preparation of seed particles (B)] The obtained particles of seed-polymerized composite resin (A) and LV115 as an ethylene-vinyl acetate copolymer were charged into a tumbler mixer in a mass ratio of 90:10 and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded product was then cut into oval (egg) spheres using an underwater cutting method to obtain seed particles (B) (seed particles, average mass 0.6 mg) consisting of a styrene monomer-polyolefin seed polymerization composite resin (A) and an ethylene-vinyl acetate copolymer.

[0126] Except for using the seed particles (B) obtained and changing the pressure of the steam used in the expansion molding to 0.05 MPa, composite resin particles (C), expandable particles, expanded particles, and expansion molded articles were obtained in the same manner as in Example 1. The results of various tests are shown in Table 3.

[0127] Comparative Example 3 [Preparation of styrene monomer-polyolefin seed polymerization composite resin (A)] LV115 was fed to an extruder as a polyethylene resin, melted and kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) using an underwater cutting method to obtain polyethylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 600 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.1 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction solution cooled to 90°C over 10 minutes. Next, a solution of 3.5 g of dicumyl peroxide, 5.2 g of benzoyl peroxide, and 0.2 g of t-butyl peroxide (polymerization initiator) dissolved in 1100 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 90°C for 1 hour to impregnate the polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 90°C for 1 hour to impregnate the seed particles with the styrene monomer and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30° C. or less, and the seed-polymerized composite resin particles of styrene-based monomer and polyolefin were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the particles of the obtained seed-polymerized composite resin (A) was measured and found to be 9.1 × 10 4 It was.

[0128] [Preparation of seed particles (B)] The resulting particles of seed polymerization composite resin (A) and EF0505 (ethylene-vinyl acetate copolymer) were placed in a tumbler mixer in a mass ratio of 20:80 and mixed for 10 minutes. The resulting resin mixture was fed into an extruder and melt-kneaded at a temperature of 230-250°C. The kneaded product was then cut into oval (egg-shaped) shapes using an underwater cutting method, yielding seed particles (B) (average mass 0.6 mg / particle) consisting of styrene monomer-polyolefin seed polymerization composite resin (A) and ethylene-vinyl acetate copolymer.

[0129] Except for using the seed particles (B) obtained and changing the pressure of the steam used in the expansion molding to 0.05 MPa, composite resin particles (C), expandable particles, expanded particles, and expansion molded articles were obtained in the same manner as in Example 1. The results of various tests are shown in Table 3.

[0130] Example 7 [Preparation of styrene monomer-polyolefin seed polymerization composite resin (A)] PL500A was supplied to an extruder as a polypropylene resin, melt-kneaded at a temperature of 230 to 250°C, and the kneaded product was cut into oval spheres (egg shapes) by an underwater cutting method to obtain polypropylene resin particles (average mass 0.6 mg). A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 400 g of seed particles were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.5 g of dicumyl peroxide (polymerization initiator) in 200 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with the styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise over 10 minutes to the reaction solution, which had been cooled to 122°C. Next, a solution of 5 g of dicumyl peroxide (polymerization initiator) dissolved in 1,400 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles. After the dropwise addition, the mixture was maintained at 122°C for 1 hour, thereby impregnating the polyethylene resin particles with the styrene monomer. A dispersion medium prepared by dispersing 3 g of ethylenebisstearamide (cell bubble control agent) in 100 g of pure water was then added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 122°C for 1 hour, thereby impregnating the seed particles with the styrene monomer and cell bubble control agent. After the impregnation, the mixture was heated to 140°C and maintained at this temperature for 3 hours to allow polymerization. Then, the autoclave was cooled to 30° C. or less, and the particles of the styrene-based monomer-polyolefin seed-polymerized composite resin (A) were taken out from the autoclave. The mass average molecular weight of the polystyrene resin constituting the particles of the obtained seed-polymerized composite resin (A) was measured and found to be 4.5 × 10 5 It was.

[0131] [Preparation of seed particles (B)] The obtained particles of seed-polymerized composite resin (A) and F744NP as a polypropylene resin were charged into a tumbler mixer in a mass ratio of 30:70 and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C. The kneaded product was then cut into oval (egg) spheres using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a styrene-based monomer-polyolefin seed polymerization composite resin (A) and a polypropylene-based resin.

[0132] [Preparation of composite resin particles (C) by seed polymerization of styrene-based monomer-seed particles (B)] A dispersion medium was prepared by adding 40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water to a 5-liter autoclave equipped with a stirrer. 600 g of seed particles (B) were dispersed in the dispersion medium at 30°C and held for 10 minutes. The temperature was then raised to 60°C to obtain a suspension. While holding the suspension at 60°C, a solution of 0.5 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and the suspension was then held for 30 minutes to impregnate the seed particles with styrene monomer. After impregnation, the temperature was raised to 140°C, and polymerization (first polymerization) was carried out at this temperature for 2 hours. Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise over 10 minutes to the reaction solution cooled to 122°C. Next, a solution of 4 g of dicumyl peroxide (polymerization initiator) dissolved in 1,100 g of styrene monomer was added dropwise at a rate of 0.05 parts by mass / second per 100 parts by mass of seed particles (B). After the dropwise addition, the temperature was maintained at 122°C for 1 hour, thereby impregnating the seed particles (B) with the styrene monomer. After the impregnation, the temperature was raised to 140°C and maintained at this temperature for 3 hours to allow polymerization (second polymerization). Then, the mixture was cooled to 30° C. or less, and the composite resin particles (C) were taken out from the autoclave.

[0133] Except for using the obtained composite resin particles (C) and changing the pressure of the steam used in the expansion molding to 0.18 MPa, expandable particles, expanded particles, and expansion molded articles were obtained in the same manner as in Example 1. The results of various tests are shown in Table 4.

[0134] Comparative Example 4 [Preparation of composite resin particles (seed particles (B)) by extrusion kneading of polypropylene resin and ethylene copolymer polystyrene resin] F744NP as a polypropylene-based resin and EF0505 as an ethylene-vinyl acetate copolymer were charged into a tumbler mixer in a mass ratio of 80:20 and mixed for 10 minutes. The obtained resin mixture was fed into an extruder and melt-kneaded at a temperature of 230 to 250°C, and the kneaded material was cut into oval (egg) spherical shapes using an underwater cutting method to obtain seed particles (B) (average mass 0.6 mg / particle) consisting of a polypropylene-based resin-modified ethylene-vinyl acetate copolymer.

[0135] Composite resin particles (C), expandable particles, expanded particles, and foamed molded articles were obtained in the same manner as in Example 7, except that the obtained seed particles (B) were used and the steam pressure used in the expansion molding was set to 0.18 MPa. The results of various tests are shown in Table 4.

[0136] [Table 3]

[0137] [Table 4]

[0138] In Examples 1 to 7, the amount of powder was small, molding was possible at low vapor pressure (excellent productivity), the molding cycle was short (fast dissipation of the foaming agent), 25% compressive strength was high, and the rate of dimensional change upon heating was small (excellent heat resistance), and overall, the effects were superior to those of the comparative examples. In Comparative Example 1, the same polyolefin resin, the same amount of polyolefin resin, and the same amount of polystyrene resin were used as in Example 4, but the seed particles (B) did not contain the styrene monomer-polyolefin seed polymerization composite resin (A). In Comparative Example 1, a large amount of polymerization powder was generated and the molding cycle was long. Comparison with Example 4 reveals that excellent effects can be obtained by including the styrene monomer-polyolefin seed polymerization composite resin (A) in the seed particles (B). In Comparative Example 2, the mass ratio of the polyolefin resin to the polystyrene resin in the seed particles (B) was 15:85, which was outside the range of 20:80 to 90:10. In Comparative Example 3, the mass average molecular weight of the polystyrene resin in the seed polymerized composite resin (A) was 9.1 × 10 4 is 1.0 × 10 5 ~5.0×10 5 In Comparative Examples 2 and 3, the molding cycle was long, and blocking occurred in the foaming evaluation. Due to the characteristics of polypropylene-based resins, the molding cycle tends to be long (Comparative Example 4), but the molding cycle was shortened by containing the seed particles (B) with the styrene-based monomer-polyolefin seed polymerization composite resin (A). Furthermore, due to the characteristics of polypropylene-based resins, the vapor pressure during molding tends to be higher than that of polyolefin-based resins, but in Example 7 molding was possible with a vapor pressure that was low for a polypropylene-based resin.

Claims

1. Seed particles (B) for producing composite resin particles (C) for producing expanded beads containing a polyolefin resin and a polystyrene resin, The composite resin particles (C) are seed-polymerized composite resin particles of a styrene-based monomer and a seed particle (B), the seed particles (B) contain a styrene-based monomer-polyolefin seed polymerization composite resin (A) in an amount of 20 to 100% by mass of the seed particles (B), the seed particles (B) contain, in addition to the polyolefin-based resin contained in the seed polymer composite resin (A), a second polyolefin-based resin in an amount of 0 to 80% by mass of the seed particles (B); the ratio of the mass content of the polyolefin-based resin to the mass content of the polystyrene-based resin in the seed particles (B) is 20:80 to 90:10; The mass average molecular weight of the polystyrene resin in the seed particles (B) is 1.0×10 ５ ~5.0 x 10 ５ That is, Seed particle (B).

2. The seed particles (B) according to claim 1, wherein the seed polymerization composite resin (A) has a gel fraction of 5 to 40 mass % as determined by the gel fraction measurement described below. Gel fraction measurement: One gram of seed-polymerized composite resin (A) was weighed and placed in a flask. 100 ml of toluene was added, and the mixture was heated to reflux in a 130°C oil bath for 24 hours to dissolve the resin. The flask was then removed from the oil bath and the contents were immediately filtered through an 80-mesh (0.12 mm diameter) wire mesh. The wire mesh and the insoluble material remaining on it were then placed in a 130°C oven for one hour, and then the mixture was placed under reduced pressure with a vacuum pump for two hours to remove the toluene. The weight of the solid material remaining on the wire mesh was then measured. The gel fraction was calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100

3. 3. The seed particles (B) according to claim 1 or 2, wherein the polyolefin-based resin contained in the seed polymer composite resin (A) is at least one resin selected from the group consisting of an ethylene-based copolymer, a polyethylene-based resin, and a polypropylene-based resin, and the second polyolefin-based resin is at least one resin selected from the group consisting of an ethylene-based copolymer, a polyethylene-based resin, and a polypropylene-based resin.

4. The seed particles (B) according to claim 3, wherein the ethylene-based copolymer is an ethylene-vinyl acetate copolymer, and the polyethylene-based resin is at least one resin selected from the group consisting of linear low-density polyethylene, high-density polyethylene, and low-density polyethylene.

5. The seed particles (B) according to claim 1 or 2, wherein the second polyolefin resin is a resin different from the polyolefin resin contained in the seed polymer composite resin (A).

6. The seed particles (B) according to claim 1 or 2, wherein the seed polymerization composite resin (A) is derived from a foamed molded product of a styrene-based monomer-polyolefin composite resin.

7. A composite resin particle (C) for producing expanded beads, the composite resin particle (C) being a seed-polymerized composite resin particle of a styrene-based monomer and a seed particle (B), the seed particle (B) being the seed particle (B) according to claim 1 or 2.

8. The composite resin particles (C) according to claim 7, wherein the content of the polystyrene-based resin composited with the seed particles (B) in the composite resin particles (C) is 100 to 500 parts by mass per 100 parts by mass of the seed particles (B).

9. Expanded particles of the composite resin particles (C) according to claim 7.

10. A foamed molded article made from the foamed beads according to claim 9.

11. Density: 20 to 200 kg / m ３ The foamed molded article according to claim 10,

12. A method for producing composite resin particles (C) for producing expanded beads, which contains a polyolefin-based resin and a polystyrene-based resin, comprising: A step of shredding the base resin to obtain seed particles (B); a step of impregnating the seed particles (B) with a styrene-based monomer and polymerizing the monomer to obtain the composite resin particles (C), the base resin is a styrene-based monomer-polyolefin seed polymerization composite resin (A) obtained by a process of impregnating and polymerizing polyolefin-based resin particles with a styrene-based monomer, or a mixed resin of the seed polymerization composite resin (A) and a second polyolefin-based resin, and the seed particles (B) contain the seed polymerization composite resin (A) in an amount of 20 to 100% by mass of the seed particles (B), the seed particles (B) contain a second polyolefin-based resin in an amount of 0 to 80% by mass of the seed particles (B), the ratio of the mass content of the polyolefin-based resin to the mass content of the polystyrene-based resin in the seed particles (B) is 20:80 to 90:10; The mass average molecular weight of the polystyrene resin in the seed particles (B) is 1.0×10 ５ ~5.0 x 10 ５ That is, A method for producing composite resin particles (C).

13. The method for producing composite resin particles (C) according to claim 12, wherein the seed-polymerized composite resin (A) has a gel fraction of 5 to 40 mass % as determined by the gel fraction measurement described below. Gel fraction measurement: One gram of seed-polymerized composite resin (A) was weighed and placed in a flask. 100 ml of toluene was added, and the mixture was heated to reflux in a 130°C oil bath for 24 hours to dissolve the resin. The flask was then removed from the oil bath and the contents were immediately filtered through an 80-mesh (0.12 mm diameter) wire mesh. The wire mesh and the insoluble material remaining on it were then placed in a 130°C oven for one hour, and then the mixture was placed under reduced pressure with a vacuum pump for two hours to remove the toluene. The weight of the solid material remaining on the wire mesh was then measured. The gel fraction was calculated using the following formula: Gel fraction (%) = weight of remaining solid (g) / sample weight (g) × 100

14. 14. The method for producing composite resin particles (C) according to claim 12 or 13, wherein the polyolefin-based resin contained in the seed polymerization composite resin (A) is at least one resin selected from the group consisting of an ethylene-based copolymer, a polyethylene-based resin, and a polypropylene-based resin, and the second polyolefin-based resin is at least one resin selected from the group consisting of an ethylene-based copolymer, a polyethylene-based resin, and a polypropylene-based resin.

15. The method for producing composite resin particles (C) according to claim 14, wherein the ethylene-based copolymer is an ethylene-vinyl acetate copolymer, and the polyethylene-based resin is at least one resin selected from the group consisting of linear low-density polyethylene, high-density polyethylene, and low-density polyethylene.

16. The method for producing composite resin particles (C) according to claim 12 or 13, wherein the second polyolefin resin is a resin different from the polyolefin resin contained in the seed-polymerized composite resin (A).

17. The method for producing composite resin particles (C) according to claim 12 or 13, wherein the seed-polymerized composite resin (A) is derived from a foamed molded product of a styrene-based monomer-polyolefin composite resin.

18. The method for producing composite resin particles (C) according to claim 12 or 13, wherein in the step of obtaining the composite resin particles (C), the amount of the styrene-based monomer used is 100 to 500 parts by mass per 100 parts by mass of the seed particles (B).

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