Composite resin particles, expandable particles, expanded particles, expanded molded article, and method for producing composite resin particles

Abstract

The purpose of the present invention is to provide: composite resin particles that can provide molded foam having excellent strength without undergoing an annealing step in production of the composite resin particles; and foamed particles that allow relatively fast escape of a foaming agent, and are capable of reducing the molding cycle of molded foam. The present invention pertains to the following polystyrene-based composite resin particles (C). The polystyrene-based composite resin particles (C) are for producing molded foam and contain a polyolefin-based resin and a polystyrene-based resin at a mass ratio of 10:90 to 50:50. In an image of the composite resin particles (C) obtained by the following method, (1) a bicontinuous structure of the polyolefin-based resin and the polystyrene-based resin is observed, (2) at least one polystyrene-based resin fine particle having a particle size of at least 1.0 μm is observed, and (3) the area proportion of the polystyrene-based resin fine particles having a particle size of at least 1.0 μm is 1-50%. Image-obtaining method: A thin film obtained by slicing the composite resin particles (C) through the centers of the particles is imaged by a transmission electron microscope to obtain an image in which a square portion thereof has a side of 10 μm and includes the centers of the particles.

Description

[Technical Field]

[0001] The present invention relates to seed particles, composite resin particles, expandable particles, expanded particles, 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 widely used as packaging and insulation materials because they have excellent cushioning and heat insulating properties and are easy to mold. However, due to insufficient impact resistance and flexibility, they are prone to cracking and chipping, making them unsuitable for packaging precision machinery products, for example. On the other hand, foam molded articles made from polyolefin-based resins have excellent impact resistance and flexibility, but require large-scale equipment for molding. Furthermore, due to the nature of the resin, they must be transported in the form of foamed beads from raw material manufacturers to molding manufacturers. This results in the problem of transporting bulky foamed beads, which increases manufacturing costs. Therefore, various polystyrene-based composite resin particles and foam molded articles made from them that combine the characteristics of the above two different resins have been proposed.

[0003] For example, Japanese Patent Laid-Open No. 2005-97555 (Patent Document 1) discloses polystyrene composite resin particles obtained by cutting a melt-kneaded mixture of a mixed resin of ethylene-vinyl acetate copolymer resin containing a specific amount of polystyrene resin, impregnating and polymerizing core resin particles in which polystyrene resin of a specific particle size is dispersed with styrene, subjecting the core resin particles to an annealing treatment step, and then further polymerizing the core resin particles. Patent Document 1 states that the composite resin particles have a specific area ratio of polystyrene components with a specific particle size in their surface layer, i.e., clumps of polystyrene components holding a blowing agent are present in the surface layer of the composite resin particles, thereby accelerating the escape of the blowing agent present in the surface layer.

[0004] Furthermore, Japanese Patent Application Laid-Open No. 2016-190991 (Patent Document 2) discloses that when polypropylene-based resin is fed into an extruder to produce polypropylene-based resin particles for seed polymerization, adding a polystyrene-based resin having specific resin properties, specifically a specific MFR or melt tension, can increase the rigidity of the styrene-modified polypropylene-based composite resin foam obtained thereafter, thereby satisfying the high quality required for industrial applications.

[0005] Japanese Patent Laid-Open Publication No. 2009-114432 (Patent Document 3) discloses styrene-modified polyethylene resin particles obtained by impregnating and polymerizing a polyethylene resin with a styrene monomer. The resin particles have a co-continuous structure of polyethylene resin and polystyrene resin with an average layer thickness of 0.3 to 1.0 μm at the center of the resin particle, and the expanded beads obtained from the resin particles contain 10 to 35 wt % of a xylene-insoluble gel component, and the expanded molded articles have excellent moldability and high crack resistance even after the blowing agent in the expanded beads has escaped.

[0006] JP 2011-42718 A (Patent Document 4) discloses expandable modified resin particles containing a physical blowing agent in a base resin in which a dispersed phase mainly composed of a styrene-based resin is dispersed in a continuous phase mainly composed of an olefin-based resin. The resin particles have a volume average diameter of the dispersed phase of 0.55 μm or more, and are excellent in retaining the blowing agent, and after foaming and molding in a mold, a foamed molded article can be obtained that exhibits the excellent tenacity (toughness) characteristic of olefin-based resins. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-97555 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-190991 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-114432 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-42718 Summary of the Invention [Problem to be solved by the invention]

[0008] The resin particles described in Patent Document 3 have a co-continuous structure at the particle center, which allows for excellent moldability even after the blowing agent has escaped from the expanded beads, resulting in a foam with high crack resistance, but the dispersed phase of polystyrene-based resin is hardly observed at the particle center. Furthermore, in the technology disclosed in Patent Document 1, if the amount of polystyrene-based resin increases on the particle surface of polystyrene-based composite resin particles, the expanded particles become less likely to fuse together during expansion molding, impairing chemical resistance and impact resistance. To prevent this, an annealing process is carried out for about two hours to soften the polyolefin-based resin and promote migration of the polystyrene-based resin from the surface.

[0009] The resin particles described in Patent Documents 2 and 4 have a dispersed phase of polystyrene resin in the particle center, which allows them to retain the blowing agent well, and after foaming and in-mold molding, they can produce foamed articles that exhibit the excellent toughness typical of olefin-based resins. However, the core of the particles is almost completely devoid of a co-continuous structure of polyethylene-based resin and polystyrene-based resin, and it takes a long time for the blowing agent retained by the foamed particles to dissipate. As a result, it takes a long time to adjust the blowing agent content of the foamed particles to an amount suitable for foam molding, and the time from production of the blowing agent to foam molding cannot be shortened, resulting in a long molding cycle.

[0010] Therefore, an object of the present invention is to solve the above problems and to provide polystyrene-based composite resin beads that can give foamed molded articles with excellent strength even without an annealing step and that can shorten the molding cycle, as well as a method for producing the same, foamed beads, and foamed molded articles. [Means for solving the problem]

[0011] In view of the above problems, the present inventors discovered that composite resin particles having a co-continuous structure of polyolefin-based resin and polystyrene-based resin in the center thereof, together with polystyrene-based resin microparticles having a particle diameter of 1.0 μm or more, can solve at least one of the above problems, and thus completed the present invention.

[0012] The present invention typically includes the following aspects. Section 1. Polystyrene-based composite resin particles (C) for producing a foamed molded article, containing a polyolefin-based resin and a polystyrene-based resin in a mass ratio of 10:90 to 50:50, The composite resin particles (C) are, in an image obtained by the following method, (1) A bicontinuous structure of polyolefin resin and polystyrene resin was observed. (2) One or more polystyrene resin microparticles with a particle size of 1.0 μm or more are observed, (3) The area ratio of polystyrene resin microparticles having a particle diameter of 1.0 μm or more is 1 to 50%. Composite resin particles (C). Image acquisition method: The composite resin particle (C) is sliced ​​so as to pass through the center of the particle, and the resulting thin film is photographed using a transmission electron microscope to obtain an image of a square portion with a side length of 10 μm that includes the center of the particle. Section 2. 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) that has been melt-kneaded at least once in an amount of 10 to 80 mass % of the seed particles (B); Item 1. The polystyrene composite resin particles (C) according to Item 1, wherein the seed particles (B) further contain a polyolefin resin in an amount of 20 to 90 mass % of the seed particles (B) in addition to the polyolefin resin contained in the seed polymerization composite resin (A). Section 3. Item 3. Expandable particles containing the composite resin particles (C) according to Item 1 or 2 and a blowing agent. Section 4. Item 3. Expanded particles of the expandable particles according to item 3. Section 5. Bulk density: 0.012 to 0.20 g / cm 3 Item 5. The expanded particles according to item 4, Section 6. Item 6. A foamed molded article of the foamed beads according to item 4 or 5. Section 7. A method for producing composite resin particles (C) containing a polyolefin resin and a polystyrene resin for use in producing a foamed molded article, comprising: a step of impregnating seed particles (B) with a styrene-based monomer and polymerizing the monomer to obtain the composite resin particles (C), The seed particles (B) contain a styrene-based monomer-polyolefin seed polymerization composite resin (A) that has been melt-kneaded at least once, The seed particles (B) contain a polyolefin-based resin in addition to the polyolefin-based resin contained in the seed polymer composite resin (A) in an amount of 20 to 90 mass % of the seed particles (B). A method for producing composite resin particles (C). Section 8. Item 8. The method for producing composite resin particles (C) according to Item 7, wherein the seed particles (B) contain 10 to 80 mass % of a seed polymerization composite resin (A) of a styrene-based monomer and polyolefin that has been melt-kneaded at least once. [Effects of the Invention]

[0013] According to the present invention, composite resin particles can be provided that can give foamed molded articles with excellent strength without undergoing an annealing step during the production of the composite resin particles. According to the present invention, it is possible to provide expanded beads from which the blowing agent dissipates relatively quickly, thereby shortening the molding cycle for foamed molded articles. According to the present invention, a composite resin derived from a foamed molded product of a styrene-based monomer-polyolefin composite resin produced through seed polymerization can be reused as the seed particles of the present invention. The seed particles of the present invention can provide a foamed molded article having excellent strength. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 1. [Figure 2] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 2. [Figure 3] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 3. [Figure 4] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 4. [Figure 5] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 5. [Figure 6] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Comparative Example 1. [Figure 7] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Comparative Example 2. [Figure 8] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Comparative Example 3. [Figure 9] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Comparative Example 4. [Figure 10] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 6. [Figure 11] 1 is a transmission electron microscope (TEM) image of the center portion of a composite resin particle of Example 7. [Figure 12] 11 is a diagram illustrating an example of determining whether or not the particle corresponds to a polystyrene-based resin microparticle having a particle diameter of 1.0 μm or more. Here, the original TEM image used is an image of the center of the composite resin particle of Example 7, i.e., the same image as in FIG. 11.

[0015] 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 a foamed molded article. Expanded composite resin beads are roughly divided into expanded beads obtained by melt-kneading a base resin (e.g., polyethylene and polystyrene) and then chopping it to obtain resin particles, and then incorporating a blowing agent into the resulting resin particles; and expanded beads obtained by impregnating resin (e.g., polyethylene) particles (seed particles) with a monomer of another resin (e.g., styrene), and then polymerizing the monomer to combine with the base resin, and then incorporating a blowing agent into composite resin particles (also called seed-polymerized composite resin particles).

[0016] In this specification, a composite resin (particle) obtained by impregnating a resin seed particle with a monomer and polymerizing the monomer is also referred to as a "seed-polymerized composite resin (particle)." In this specification, a composite resin (particle) obtained by impregnating and polymerizing a styrene-based monomer into a resin seed particle is also referred to as a "styrene-based monomer-seed particle seed polymerization composite resin (particle)." 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)."

[0017] As used herein, the phrase "comprising" is intended to encompass the phrases "consisting essentially of" and "consisting of."

[0018] (Polystyrene-based composite resin particles (C)) The present invention uses composite resin particles (C) which are polystyrene-based composite resin particles containing a polyolefin-based resin and a polystyrene-based resin, in which a bicontinuous structure of the polyolefin-based resin and the polystyrene-based resin and polystyrene-based resin fine particles having a particle diameter of 1.0 μm or more coexist in a specific ratio at the center of the composite resin particle. For example, polystyrene-based composite resin particles (C) for producing foamed molded articles, which contain a polyolefin-based resin and a polystyrene-based resin in a mass ratio of 10:90 to 50:50, The composite resin particles (C) are, in an image obtained by the following method, (1) A bicontinuous structure of polyolefin resin and polystyrene resin was observed. (2) One or more polystyrene resin microparticles with a particle size of 1.0 μm or more are observed, (3) The area ratio of polystyrene resin microparticles having a particle diameter of 1.0 μm or more is 1 to 50%. The composite resin particles (C) are Image acquisition method: The composite resin particle (C) is sliced ​​so as to pass through the center of the particle, and the resulting thin film is photographed using a transmission electron microscope to obtain an image (TEM image) of a square area with a side length of 10 μm that includes the center of the particle. In this specification, the term "TEM image" simply refers to an image obtained by this method.

[0019] According to analytical evaluations of TEM images and the like by the present inventors, the resin particles described in Patent Documents 1 to 4 do not satisfy any of the structures (1) to (3) above at their center portions.

[0020] (Structure of the particle core) In the present invention, a resin particle is sliced ​​along the center of the particle, and the resulting thin film is photographed using a transmission electron microscope to obtain an image of a square area with a side length of 10 μm that includes the center of the particle. Based on this TEM image, the distribution of the polyolefin resin component and the polystyrene resin component in the center of the particle can be determined. Therefore, the particle center refers to the area that can be confirmed in this image.

[0021] (Co-continuous structure of polyolefin resin and polystyrene resin) The composite resin particles (C) of the present invention may have a bicontinuous structure of polyolefin resin and polystyrene resin at the particle center. The presence of this structure can be confirmed by TEM images. If a structure is observed in a TEM image in which approximately circular and / or irregular granular polystyrene resin particles are connected to each other to form a continuous phase, and approximately circular and / or irregular granular polyolefin resin particles are encapsulated within the continuous phase, the presence of a "bicontinuous structure" can be confirmed.

[0022] (Polystyrene resin particles with a particle diameter of 1.0 μm or more) The composite resin particles (C) of the present invention may contain polystyrene-based resin fine particles having a particle diameter of 1.0 μm or more at the particle center. The particle diameter of the polystyrene-based resin fine particles can be confirmed by TEM images and is preferably 1.0 to 8.0 μm, more preferably 1.5 to 3.0 μm. The polystyrene-based resin fine particles are observed as approximately circular and / or irregularly shaped granules in TEM images.

[0023] (Percentage of polystyrene resin particles with a particle size of 1.0 μm or more) In the composite resin particles (C) of the present invention, the area ratio of polystyrene resin fine particles having a particle diameter of 1.0 μm or more at the particle center may be 1 to 50%, or 5 to 50%. This area ratio is preferably 10 to 20%, because it results in a co-continuous structure and an appropriate distribution state of polystyrene resin fine particles having a particle diameter of 1.0 μm or more, thereby improving the mechanical properties of the foamed molded article and the diffusion rate of the blowing agent in the foamed particles.

[0024] (Polystyrene resin (PS)) The polystyrene resin constituting the polystyrene composite resin particles (C) is not particularly limited as long as it is a resin containing a styrene monomer as the main component, and examples thereof include homopolymers and copolymers of styrene or styrene derivatives. Examples of styrene derivatives include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromostyrene, etc. These styrene-based monomers may be used alone or in combination.

[0025] The polystyrene-based resin may be one in which a vinyl-based monomer copolymerizable with a styrene-based monomer is used in combination. Examples of vinyl monomers include polyfunctional monomers such as divinylbenzenes (e.g., o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene), alkylene glycol di(meth)acrylates (e.g., ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate), (meth)acrylonitrile, methyl (meth)acrylate, and butyl (meth)acrylate. Among these, polyfunctional monomers are preferred, with ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylates having 4 to 16 ethylene units, and divinylbenzene being more preferred, and divinylbenzene and ethylene glycol di(meth)acrylate being particularly preferred. The monomers may be used alone or in combination. When a monomer is used in combination, the content is preferably set so that the styrene-based monomer is the main component (for example, 50% by mass or more). In the present invention, "(meth)acrylic" means "acrylic" or "methacrylic".

[0026] (Polyolefin resin (PO)) The polyolefin resin constituting the polystyrene composite resin particles (C) is not particularly limited, and resins obtained by known polymerization methods can be used. Furthermore, it is preferable to use a polyolefin resin that does not contain a benzene ring in its structure. Furthermore, the polyolefin resin may be crosslinked. Examples of polyolefin resins include polyethylene resins (PE) such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and crosslinked polymers thereof; and polypropylene resins (PP) such as propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene random copolymer, and ethylene-propylene-butene random copolymer. Furthermore, two or more of these can be used in combination. As the polyethylene resin, high density polyethylene, branched low density polyethylene, linear low density polyethylene, and ethylene-vinyl acetate copolymer are preferred, and branched low density polyethylene and ethylene-vinyl acetate copolymer are more preferred. As the polypropylene-based resin, an ethylene-propylene random copolymer, a propylene-1-butene random copolymer, or an ethylene-propylene-butene random copolymer is preferred. As the polyolefin resin, ethylene-vinyl acetate copolymer, branched low-density polyethylene, linear low-density polyethylene, linear low-density polyethylene, and ethylene-propylene random copolymer are preferred.

[0027] The total content of the polyolefin resin and polystyrene resin in the composite resin particles (C) is, for example, 80 mass % or more, preferably 90 mass % or more, more preferably 95 mass % or more, based on the mass of the composite resin particles (C). The content of the polyolefin resin in the composite resin particles (C) can be, for example, 10 to 50 mass %, preferably 20 to 50 mass %, and more preferably 20 to 45 mass %, based on the mass of the composite resin particles (C). When the content of the polyolefin resin in the composite resin particles (C) is within the above range, it is advantageous in terms of impact resistance, flexibility, and chemical resistance of the foamed molded article. The content of the polystyrene resin in the composite resin particles (C) can be, for example, 50 to 90 mass %, preferably 50 to 80 mass %, and more preferably 55 to 80 mass %, based on the mass of the composite resin particles (C). When the content of the polystyrene resin in the composite resin particles (C) is within the above range, it is advantageous in terms of expandability, moldability, and compressive strength. The composite resin particles (C) contain a polyolefin resin and a polystyrene resin in a mass ratio of 10:90 to 50:50, preferably 20:80 to 50:50, and more preferably 20:80 to 45:55. A mass ratio of the polyolefin resin to the polystyrene resin within this range is advantageous in terms of expandability, moldability, strength, and flexibility.

[0028] (Styrene-based monomer-seed particle (B) seed polymerization composite resin particle) The composite resin particles (C) of the present invention may be seed-polymerized composite resin particles of a styrene-based monomer and a seed particle (B). The seed-polymerized composite resin particles of a styrene-based monomer and a seed particle (B) are composite resin particles obtained by so-called seed polymerization, in which a styrene-based monomer is impregnated into the seed particle (B) and polymerized. The seed polymerization can be carried out by a known method. For example, seed particles (B) can be impregnated with a styrene-based monomer in an aqueous medium, and then heated to the polymerization temperature of the monomer to obtain 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).

[0029] (Styrene-based monomer-polyolefin seed polymerization composite resin (A)) This seed polymerization composite resin (A) is obtained from composite resin particles obtained by so-called seed polymerization, in which seed particles of a polyolefin resin are impregnated with a styrene-based monomer and polymerized. Therefore, this seed polymerization composite resin (A) contains a polyolefin resin and a polystyrene-based resin. Seed polymerization can be carried out by a known method. For example, particles of the styrene-based monomer-polyolefin seed polymerization composite resin (A) can be obtained by impregnating a polyolefin with a styrene-based monomer in an aqueous medium and then heating the mixture to the polymerization temperature of the monomer. The use of the seed polymerization composite resin (A) for the seed particles (B) makes it easy to ensure that the particle center of the composite resin particle (C) has a co-continuous structure of polyolefin-based resin and polystyrene-based resin, polystyrene-based resin fine particles with a particle diameter of 1.0 μm or more, and the area ratio of the polystyrene-based resin fine particles with a particle diameter of 1.0 μm or more is 1 to 50%.

[0030] In the present invention, it is preferable to use a seed polymerization composite resin (A) in which particles of the seed polymerization composite resin (A) are melt-kneaded at least once (preferably once). The seed-polymerized composite resin (A) can typically be a composite resin particle obtained by seed-polymerizing a styrene-based monomer on a polyolefin seed particle, or an expandable particle, an expanded particle, or a foamed molded article of a polyolefin resin or a polystyrene resin produced from the composite resin particle. The present invention also has the advantage that these particles and foamed molded articles, whether used or unused, can be reused as the seed-polymerized composite resin (A). When a foamed molded article produced from composite resin particles obtained by seed polymerization of a styrene-based monomer on polyolefin seed particles is used as the seed-polymerized composite resin (A), for example, the foamed molded article can be pulverized and fed to an extruder to be melt-kneaded and granulated into pellets, making it easier to use the foamed molded article as the base resin for the seed particles.

[0031] The total content of the polyolefin-based resin and the polystyrene-based resin in the seed polymerization composite resin (A) is, for example, 80 mass% or more, preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 98 mass% or more, relative to the mass of the seed polymerization composite resin (A). The content of the polyolefin resin in the seed polymerization composite resin (A) can be, for example, 10 to 50 mass %, preferably 20 to 50 mass %, more preferably 20 to 45 mass %, based on the mass of the seed polymerization composite resin (A). When the content of the polyolefin resin in the seed polymerization composite resin (A) is within the above range, it is advantageous in terms of impact resistance, flexibility, and chemical resistance. The content of the polystyrene resin in the seed polymerization composite resin (A) can be, for example, 50 to 90 mass %, preferably 50 to 80 mass %, and more preferably 55 to 80 mass %, based on the mass of the seed polymerization composite resin (A). When the content of the polystyrene resin in the seed polymerization composite resin (A) is within the above range, it is advantageous in terms of foamability, moldability, or compressive strength. The ratio of the mass content of the polyolefin resin to the mass content of the polystyrene resin in the seed polymerization composite resin (A) can be, for example, 10:90 to 50:50, preferably 20:80 to 50:50, and more preferably 20:80 to 45:55. When the ratio of the mass content of the polyolefin resin to the mass content of the polystyrene resin in the seed polymerization composite resin (A) is within the above range, it is advantageous in terms of foamability, moldability, strength, or flexibility.

[0032] The content of the seed polymerization composite resin (A) in the seed particles (B) can be, for example, 10 to 80 mass %, 10 to 70 mass %, etc., preferably 10 to 60 mass %, and more preferably 10 to 55 mass %, based on the mass of the seed particles (B). When the content of the seed polymerization composite resin (A) in the seed particles (B) is within the above range, the co-continuous structure and the distribution state of the polystyrene resin fine particles of 1.0 μm or more become appropriate, which is advantageous because it improves the mechanical properties and the diffusion rate of the blowing agent.

[0033] The seed particles (B) can further contain a polyolefin resin in addition to the seed polymerization composite resin (A). The amount of polyolefin resin added to the seed polymerization composite resin (A) can be, for example, 20 to 90 mass%, 30 to 90 mass%, etc., relative to the mass of the seed particles (B), and is preferably 40 to 90 mass%, more preferably 45 to 90 mass%, from the viewpoint of strength or flexibility. The polyolefin resins exemplified above can be used as the polyolefin resin added to the seed polymerization composite resin (A).

[0034] The content of the polyolefin resin in the seed particles (B) can be, for example, 10 to 95 mass %, preferably 50 to 95 mass %, more preferably 60 to 95 mass %, and even more preferably 65 to 95 mass %, relative to the mass of the seed particles (B). If the content of the polyolefin resin in the seed particles (B) is within the above range, it is advantageous in terms of strength or flexibility. The content of the polystyrene resin in the seed particles (B) can be, for example, 5 to 90 mass %, preferably 5 to 50 mass %, more preferably 5 to 40 mass %, and even more preferably 5 to 35 mass %, relative to the mass of the seed particles (B). When the content of the polystyrene resin in the seed particles (B) is within the above range, the co-continuous structure and the distribution state of the polystyrene resin fine particles of 1.0 μm or more become appropriate, which is advantageous because it improves the mechanical properties and the diffusion rate of the blowing agent.

[0035] (Particle diameter of seed particles (B)) The shape of the seed particles (B) may be any known shape, but is preferably cylindrical, oval-spherical (egg-shaped), or spherical, and more preferably oval-spherical or spherical, from the viewpoint of good mold filling properties of the expanded beads obtained from the seed particles (B). The seed particles (B) preferably have an average particle size of 0.50 to 1.4 mm. When the average particle size of the seed particles (B) is within this range, it is advantageous in that the expandability is high and the packing properties of the expanded particles during molding are good.

[0036] (Method for producing seed particles (B)) The seed particles (B) can be produced by melt-kneading a base resin and then shredding the melt-kneaded product. The melt-kneading temperature is preferably 120 to 300°C. Seed particles (B) can be produced by melt-kneading the base resins, polyolefin-based resin and polystyrene-based resin, and chopping the melt-kneaded mixture. Alternatively, seed particles (B) can be produced by melt-kneading the base resin, the seed polymer composite resin (A), with a polyolefin-based resin, and chopping the melt-kneaded mixture. For example, the base resin can be melt-kneaded in an extruder and extruded to obtain strands, and the resulting strands can be cut in air, water, or while heated to produce seed particles (B). The resin components may be mixed in a mixer before being added to the extruder.

[0037] (Other ingredients) The composite resin particles (C) 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, weathering stabilizers, anti-fogging agents, anti-blocking agents, slip agents, coating agents, neutron shielding agents, other resins, and inorganic foam control agents (talc, silica, calcium silicate, calcium carbonate, sodium borate, zinc borate, etc.). 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 mass of the composite resin.

[0038] (Particle diameter of composite resin particles (C)) The composite resin particles (C) preferably have an average particle size of 0.50 to 3.0 mm. When the average particle diameter of the composite resin particles (C) is within this range, it is advantageous in that the expandability is high and the packing properties of the expanded particles during molding are good. The average particle size of the composite resin particles (C) is more preferably 0.50 to 2.0 mm.

[0039] (Method for producing composite resin particles (C)) The composite resin particles (C) of the present invention can be obtained by impregnating the seed particles (B) with a desired amount of a styrene-based monomer and polymerizing the same. The method for producing the composite resin particles (C) of the present invention includes the steps of impregnating the seed particles (B) with a styrene-based monomer and polymerizing the same to obtain the composite resin particles (C). Here, the seed particles (B) may be produced by melt-kneading the seed-polymerized composite resin (A) with a polyolefin-based resin, and shredding the melt-kneaded mixture to obtain the seed particles (B). The step of impregnating seed particles (B) with a styrene-based monomer and polymerizing it to obtain the composite resin particles (C) can be carried out using so-called seed polymerization. Seed polymerization can be carried out by a known method. For example, seed particles (B) can be impregnated with a styrene-based monomer in an aqueous medium, and then heated to the polymerization temperature of the monomer to obtain particles of a seed-polymerized styrene-based monomer-polyolefin composite resin (A).

[0040] In the step of impregnating and polymerizing seed particles (B) with a styrene-based monomer to obtain the composite resin particles (C), the amount of styrene-based monomer used is an amount such that the ratio of the mass content of the polyolefin-based resin to the mass content of the polystyrene-based resin in the composite resin particles (C) is 10:90 to 50:50, preferably 20:80 to 50:50, and more preferably 20:80 to 45:55.

[0041] 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.

[0042] 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).

[0043] The amount of the polymerization initiator used is preferably 0.010 to 0.90 parts by mass, more preferably 0.10 to 0.50 parts by mass, relative to 100 parts by mass of the styrene-based monomer.

[0044] 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.

[0045] 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.

[0046] 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 and polymerization of the styrene-based monomer multiple times (preferably two times). By carrying out the polymerization multiple times, the shape of the resulting composite resin particles can be made spherical in the first polymerization of the styrene-based monomer, and the amount of polystyrene to be composited can be adjusted in the second and subsequent polymerizations of the styrene-based monomer. Furthermore, by carrying out the polymerization multiple times, 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 is impregnated.

[0047] (expandable particles) The expandable particles contain the composite resin particles (C) of the present invention and a blowing agent, and can be produced by impregnating the composite resin particles (C) with the blowing agent by a known method. For example, the expandable particles can be obtained by impregnating the composite resin particles (C) with the blowing agent during or after the completion of polymerization. The impregnation can be carried out by a known method. 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 containing the composite resin particles (C). The temperature at which the composite resin particles (C) are impregnated with the foaming agent is preferably 50 to 130° C., more preferably 60 to 100° C. An impregnation temperature within the above range is advantageous in that the impregnation time can be shortened and the occurrence of coalescence between the expandable particles is suppressed.

[0048] (foaming agent) The blowing agent can be any one that has been conventionally used for foaming polystyrene resins, without any particular limitation. Examples 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 blowing agent in the expandable particles is preferably 5 to 25% by mass relative to the mass of the composite resin particles (C). When the content of the blowing agent is within this range, sufficient expansion power can be obtained during expansion molding, which is advantageous in that the appearance of the expanded molded article becomes beautiful.

[0049] (foaming aid) The expandable particles may contain a foaming assistant together with the foaming agent. The foaming aid is not particularly limited as long as it is one that has conventionally been used for foaming polystyrene-based resins, and examples thereof include aromatic organic compounds such as styrene, toluene, ethylbenzene, and xylene; cyclic aliphatic hydrocarbons such as cyclohexane and methylcyclohexane; and solvents having a boiling point of 200°C or less at 1 atmospheric pressure, such as ethyl acetate and butyl acetate.

[0050] The content of the foaming aid in the expandable particles is usually in the range of 0.30 to 2.5 mass%, preferably 0.50 to 2.0 mass%. The content of the foaming aid within this range is advantageous in that the plasticizing effect of the polystyrene resin can be obtained and shrinkage and melting of the foamed molded article can be suppressed.

[0051] (foam particles) The expanded particles (generally also referred to as pre-expanded particles) are particles obtained by pre-expanding composite resin particles (C), and are obtained, for example, by expanding expandable particles impregnated with a blowing agent.

[0052] The bulk density of the expanded particles is 0.015 g / cm 3 ~0.20g / cm 3 is preferable, and 0.020 g / cm 3 ~0.15g / cm 3 is more preferable, and 0.020 g / cm 3 ~0.10g / cm 3 A bulk density within this range is advantageous in that the foamed molded article has high strength and is lightweight.

[0053] 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 1.2 mm to 6.6 mm.

[0054] Expanded beads can be obtained by expanding expandable beads to a desired bulk density using a known method. The expansion can be achieved by expanding the expandable beads using heated steam at a pressure of preferably 0.010 MPa to 0.20 MPa (gauge pressure), more preferably 0.010 MPa to 0.15 MPa. If the bulk density is within the above range, the foamed molded article can be made lightweight. The expansion can be carried out by batch-type expansion using steam introduction, continuous expansion, release expansion under pressure, or the like.

[0055] The expanded beads obtained by pre-expanding the expandable beads, in which a blowing agent is incorporated into the composite resin beads (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.

[0056] 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 contained in the expanded beads is sometimes allowed to dissipate to adjust the blowing agent content. However, if the time required for this adjustment is long, the time required to move on to expansion molding will be long. Therefore, from the perspective of the molding cycle, it is desirable to have a short time required for the blowing agent to dissipate. The expanded beads of the present invention have fast blowing agent dissipation, which allows for a shorter molding cycle.

[0057] (foam molded body) The foamed molded article is a foamed article composed of a fused body of foamed beads, and can be obtained, for example, by foam-molding the foamed beads in a mold. Because the foamed molded article uses the composite resin beads of the present invention as a raw material, it has excellent strength, fusion rate, and molding cycle.

[0058] The density of the foamed molded body is, for example, 0.015 g / cm 3 ~0.30g / cm 3 is preferable, and 0.020 g / cm 3 ~0.25g / cm 3 is more preferable, and 0.020 g / cm 3 ~0.20g / cm 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.

[0059] The 25% compressive strength of the foamed molded article can be, for example, 0.15 MPa or more, 0.15 MPa to 0.40 MPa, 0.20 MPa to 0.40 MPa, etc., and is preferably 0.25 MPa to 0.35 MPa. The 25% compressive strength is determined by the method described in the Examples.

[0060] 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.

[0061] The expanded beads of the present invention can be sufficiently expanded and fused even with steam at low pressure (e.g., a gauge pressure of 0.10 MPa or less), thereby reducing the energy required for expansion molding and simplifying the equipment required for expansion molding, thereby reducing the cost required for expansion molding (i.e., achieving excellent productivity).

[0062] According to the present invention, the molding cycle for a foamed molded article can be shortened. "Molding cycle" means the time from when automatic operation of the molding machine begins, when the mold begins to close, when foamed particles are filled into the mold, when heating and cooling are performed under specified conditions, when a specified surface pressure value is reached, when the mold opens, and when the foamed molded product is removed.

[0063] 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]

[0064] 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.

[0065] (TEM image observation of the center of a composite resin particle) The composite resin particles are thinly sliced ​​so as to pass through the center of the particle, and the resulting slices are embedded in epoxy resin, after which ultrathin sections (70 nm thick) are prepared using an ultramicrotome (manufactured by Leica Microsystems, product name: LEICA ULTRACUT UCT). Next, the ultrathin sections are photographed using a transmission electron microscope (TEM, Hitachi High-Technologies Corporation, Model: H-7600) at a magnification of 3500x (5000x if necessary), and the dispersion state of the polyolefin resin and polystyrene-based resin is observed within a square area with sides of 10 μm, including the center of the particle. Ruthenium tetroxide is used as the staining agent.

[0066] Observe the distribution of polyolefin resin components and polystyrene resin components in the TEM image. Because the contrast of polystyrene resin components can change depending on the surrounding resins, distinguish not only the contrast due to the staining state but also the unique lamellar structure observed in polyolefin resins.

[0067] (Particle diameter of polystyrene-based particles at the center of composite resin particles) Based on the TEM image with the scale displayed, the longest and shortest diameters of the polystyrene resin microparticles, which may be roughly circular or irregularly shaped, dispersed in the polyolefin resin are measured, and the particle diameter is calculated according to the following formula. (Particle diameter of polystyrene resin microparticles) = (longest diameter + shortest diameter) / 2 (μm) The average particle size of any 20 of these polystyrene-based resin fine particles is taken as the average particle size (μm) of the polystyrene-based resin fine particles. In this case, particles of approximately circular and / or irregular shape that completely encompass a circle with a radius of 0.5 μm centered at the intersection of the longest and shortest diameters of the particles dispersed in the polyolefin resin are determined to be polystyrene resin microparticles. Furthermore, the fine continuous phase of the polystyrene component located in contact with the polystyrene resin microparticles is not considered to be polystyrene resin microparticles, but is considered to be part of the co-continuous structure, and is not used in the particle size calculation here.

[0068] An example of determining whether a particle corresponds to polystyrene-based resin microparticles with a particle diameter of 1.0 μm or more is shown in FIG. 12. The photograph in FIG. 12 is a transmission electron microscope (TEM) image of the center of a composite resin particle of Example 7, and is the same as the TEM image in FIG. 11. The black square indicates the observation range (10 μm × 10 μm) for determination. The perfect circle containing φ1 indicates a circle (reference circle) with a radius of 0.5 μm, centered at the intersection of the longest and shortest diameters of the particle. The two lines intersecting perpendicularly at the intersection indicate the longest and shortest diameters of the particle. Ellipses A to D indicate polystyrene-based resin microparticles with a particle diameter of 1.0 μm or more. E and F indicate cases where the particle does not completely encompass the reference circle and is therefore determined not to be polystyrene-based resin microparticles with a particle diameter of 1.0 μm or more.

[0069] (area ratio of polystyrene resin fine particles with particle diameter of 1.0 μm or more at the center of composite resin particles) The area ratio was calculated using the area of ​​polystyrene resin particles with a particle size of 1.0 μm or more calculated by the above method. Even if some polystyrene resin particles with a particle size of 1.0 μm or more are included on the boundary line of a 10 μm square, this will be included in the area calculated using the formula below. (area ratio of polystyrene resin particles) = (Total area of ​​polystyrene resin particles A) / (area B) × 100 (%) The total area of ​​the polystyrene resin particles A (μm 2 ) is the total area of ​​polystyrene resin fine particles (PS fine particles) with a particle diameter of 1.0 μm or more, and is calculated using the following formula. Σ [(particle diameter of PS fine particles of 1.0 μm or more / 2) 2 ×3.14](μm 2 ) Area B is the area of ​​a 10 μm square, that is, 10 × 10 (μm 2 )

[0070] (Gel fraction of seed particles and composite resin particles) 1 g of particles was precisely weighed using an electronic balance (Mettler) capable of measuring in grams to four decimal places, and placed in a 200 ml recovery flask together with 100 ml of toluene and approximately 0.4 g of zeolite. This was then connected to a condenser and placed in an oil bath at 130°C. An appropriate amount of water was then run through the condenser and the flask was heated for 24 hours. The flask is then removed from the oil bath and the contents are immediately filtered using an 80-mesh (φ0.12 mm) wire mesh. The insoluble matter in the boiling toluene and the zeolite remaining on the wire mesh are then placed in a 130°C oven for 1 hour to remove the toluene, followed by vacuum drying for another 2 hours. The remaining solid matter and zeolite are then removed from the oven and allowed to cool in a desiccator for approximately 1 hour. The total mass (Wt) of the remaining solid matter and zeolite, together with the wire mesh, is then measured. The mass of the solid matter, Ws (g), is calculated by subtracting the mass of the zeolite, Wz (g), and the mass of the wire mesh, Wm (g), which have been precisely weighed in advance, from the total mass, Wt (g), and the ratio of this mass to the composite resin particles, Wb (g), which have been precisely weighed in advance, is calculated as the gel fraction (mass%). Gel fraction (mass%) = (Wt - Wz - Wm) / Wb × 100

[0071] (Average particle size of composite resin particles) The particle diameter at 50% cumulative mass (median diameter: d50) in the cumulative mass distribution curve is defined as the average particle diameter of the composite resin particles. Specifically, using a low-tap sieve shaker (manufactured by Iida Seisakusho Co., Ltd.), approximately 50 g of sample was classified for 10 minutes using JIS standard sieves (JIS Z8801-1:2006) with mesh openings of 4.00 mm, 3.35 mm, 2.80 mm, 2.36 mm, 2.00 mm, 1.70 mm, 1.40 mm, 1.18 mm, 1.00 mm, 0.85 mm, 0.71 mm, 0.60 mm, 0.50 mm, 0.425 mm, 0.355 mm, 0.300 mm, 0.250 mm, 0.212 mm, and 0.180 mm, and the mass of the sample on the sieve was measured. A cumulative mass distribution curve was created from the results, and the particle diameter at which the cumulative mass reached 50% was taken as the average particle diameter (mm).

[0072] (Bulk density of expanded particles) Inner volume 100cm 3 Measure the mass B (g) of the measuring cylinder and measure the volume of 110-120 cm 3 The expanded beads are allowed to fall naturally through the funnel into the measuring cylinder. If the expanded beads are in clumps and stick to the funnel, they are broken up with a glass rod. Any expanded beads that have risen above the measuring cylinder are removed by running a straightedge along the edge of the cylinder, and the mass A (g) of the measuring cylinder containing the expanded beads is measured. The bulk density of the expanded beads is calculated using the following formula. Bulk density (g / cm 3 ) = [Mass A (g) - Mass B (g)] / Volume of measuring cylinder (100 cm 3 )

[0073] (Density of foamed molded product) The volume of the foamed product obtained after foam molding is Va (cm 3 ) and its mass W (g), and calculate the density of the foamed molded product using the formula below. Density of foamed molding (g / cm 3 ) = mass W (g) / volume Va (cm 3 )

[0074] (chemical resistance) Three flat rectangular plate-shaped test pieces measuring 100 mm long x 100 mm wide x 20 mm thick are cut out from the foam molded product and left to stand for 24 hours at 23±2°C and 50±5% humidity. The test pieces are cut out from the foam molded product so that the entire top surface of the test piece is formed from the surface of the foam molded product. Next, 1g of a different chemical (gasoline, kerosene, dibutyl phthalate (DBP)) is evenly applied to the top surface of each of the three test pieces, and they are left to stand for 60 minutes under conditions of 23±2°C and 50±5% humidity. After that, the chemicals are wiped off from the top surface of the test piece, and the top surface of the test piece is visually observed and evaluated based on the following criteria. 〇: Good, no change △: Slightly poor surface softening ×: Poor surface depression (shrinkage)

[0075] (Fusion rate of foam molded product) A rectangular foam molded article measuring 300 mm long x 400 mm wide x 50 mm high is cut 2 mm deep across the entire width of one surface (the 300 mm long x 400 mm wide surface) at the horizontal center, and then folded in the direction of the cut until the foam molded article breaks or until both ends abut. The fracture surface is then observed, and the number of foamed beads that have broken internally and those that have peeled off at the interface is visually counted. The ratio of foamed beads that have broken internally to the total number of foamed beads that have broken internally and those that have peeled off at the interface is then calculated, and this is expressed as a percentage to represent the fusion rate (%). Measurements are performed on an arbitrary range of 100 to 150 beads.

[0076] (Appearance of foam molded product) The appearance of the foamed molded article is visually observed and evaluated according to the following criteria. In other words, the larger the value, the smaller the gaps between particles, and a score of 3 or more on a 5-point scale is considered to be acceptable. 5: No gaps between particles 4: There are gaps in some areas 3: There are some gaps here and there, but they are acceptable. 2: Gaps are noticeable 1: The gaps are noticeable and the product has no commercial value.

[0077] (Compressive strength of foam molded product) Measurements are made in accordance with JIS K7220:2006. The foamed molded body is cut into test pieces measuring 50 mm long x 50 mm wide x 25 mm thick, which are then compressed at a compression rate of 10 mm / min to measure the strength (MPa) at 25% compression.

[0078] (Flexural strength of foam molded product) The flexural strength (average maximum flexural strength) of the foam is measured in accordance with the method described in JIS K7221-2:2006. Five rectangular specimens measuring 25 mm long x 130 mm wide x 20 mm thick (one side skin down) were cut out from the foamed molded article and left for 24 hours at 23°C ± 2°C and 50 ± 5% humidity. The flexural strength (MPa) of these specimens was measured using a flexural strength measuring device (Orientec Co., Ltd., Model: UCT-10T) under the following conditions:

[0079] (Measurement conditions) Test speed: 10 mm / min Distance between supports: 100 mm Deflection: 50mm Pressure wedge: 5R Support stand: 5R

[0080] (molding cycle) The molding cycle is the time (in seconds) from when the foam molding machine starts automatic operation, when the mold begins to close, when the foam particles are filled into the mold, when heating and cooling are performed under specified conditions, until the mold opens at a specified surface pressure value and the foam molded product is removed, and is measured during the foam molding process. Foam molding machine: Sekisui Machinery Works, Ltd., Model: ACE-3SP Heating and cooling conditions: Steam at a pressure of 0.08 MPa was introduced under the following heating conditions: mold heating for 5 seconds, one-sided heating for 8 seconds, reverse one-sided heating for 2 seconds, and double-sided heating for 18 seconds to expand the foam particles, followed by water cooling for 10 seconds and then cooling in a vacuum. Surface pressure value: 0.02 MPa

[0081] Example 1 [Preparation of seed particles (B)] A foamed molded product obtained from 46 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and mixed with 54 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 35:65 (mass ratio)) for 5 minutes to obtain a resin mixture. The resulting resin mixture was then fed to a φ65mm-50mm tandem extruder (manufactured by Toshiba Machine Co., Ltd., model: SE-65) equipped with a four-thread notched screw, the cylinder temperature of which had been adjusted so that the resin temperature at the center of the resin flow path in the extruder head was 220°C, where it was melt-kneaded and granulated by an underwater cutting method to obtain seed particles (B) (average mass 0.38 mg / particle). At this time, the pressure in the head was 17 MPa, the resin temperature at the die inlet was 240°C, and the pressure at the resin flow path inlet of the die was 15 MPa.

[0082] [Preparation of composite resin particles (C)] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 19.8 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 8.5 kg of styrene, which had been prepared by dissolving 11.0 g of dicumyl peroxide as a polymerization initiator, was added quantitatively over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 4.2 kg of styrene, which had been prepared in advance by dissolving 43.9 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 3.3 g of t-butyl peroxybenzoate, 168 g of dicumyl peroxide, and 179 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 9.6 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 152 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0083] [Preparation of expandable granules] 2 kg (100 parts by mass) of the obtained composite resin particles (C), 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant) were placed in a 5-liter autoclave equipped with a stirrer, and the stirring power required was 0.20 kW / m. 3 While stirring at 40°C, 350 ml (200 g) of butane (isobutane: n-butane ratio 3:7) was poured in as a blowing agent. The temperature was then raised to 70°C, and stirring was continued for 4 hours. After cooling to room temperature, the contents were removed from the 5 L autoclave, dehydrated, and dried to obtain expandable granules.

[0084] [Preparation of foam particles] The obtained expandable granules were put into a pre-expander equipped with a stirrer and having an internal volume of 40 L, and the expandable granules were pre-expanded by stirring while introducing steam at a pressure of 0.02 MPa. At this time, the amount of the expandable granules put in was adjusted, and the granules were taken out of the pre-expander with a volume of 10 L, resulting in a bulk density of 0.05 g / cm. 3 As a result, foam particles of 100g were obtained.

[0085] [Production of foam molded products] After pre-expansion, the foamed beads were stored in a constant-temperature room at 23°C for 7 days and then filled into the mold of a foam molding machine (Sekisui Machinery Works, Ltd., Model: ACE-3SP). Steam at a pressure of 0.08 MPa was introduced under the following heating conditions: mold heating for 5 seconds, one-sided heating for 8 seconds, reverse one-sided heating for 2 seconds, and double-sided heating for 18 seconds to expand the foamed beads. After 10 seconds of water cooling, the foamed beads were allowed to cool under vacuum. When the contact pressure of the foamed molded product had dropped to 0.02 MPa, it was removed from the mold. At this point, automatic operation of the molding machine was initiated. During automatic operation, the mold began to close, the foamed beads were filled into the mold, and heating and cooling were performed under specified conditions. Once the contact pressure reached the specified value, the mold opened and the foamed molded product was removed. The time from the start of automatic operation to the removal of the foamed molded product was defined as the molding cycle (seconds). In this way, a density of 0.050 g / cm was obtained. 3 A foamed molded article having a rectangular parallelepiped shape with a length of 300 mm, a width of 400 mm and a thickness of 30 mm was obtained.

[0086] The physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 1.

[0087] Example 2 [Preparation of seed particles (B)] A foamed molded product obtained from 67 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and 33 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 35:65 (mass ratio)) was mixed for 5 minutes, and the resulting resin mixture was melt-kneaded and granulated using an underwater cutting method to obtain seed particles (B).

[0088] [Preparation of Composite Resin Particles (C)] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m.3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 16.6 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 7.2 kg of styrene, which had been prepared by dissolving 9.3 g of dicumyl peroxide as a polymerization initiator, was added thereto in a fixed amount over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 5.3 kg of styrene, which had been prepared in advance by dissolving 51.3 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 3.8 g of t-butyl peroxybenzoate, 142 g of dicumyl peroxide, and 285 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 8.7 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0089] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 2.

[0090] Example 3 [Preparation of seed particles (B)] A foamed molded product obtained from 76 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and mixed with 24 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 35:65 (mass ratio)) for 5 minutes, and the resulting resin mixture was melt-kneaded and granulated using an underwater cutting method to obtain seed particles (B).

[0091] [Preparation of composite resin particles (C)] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 15.8 kg to obtain a dispersion medium, to which 15.8 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 6.8 kg of styrene, which had been prepared by dissolving 8.8 g of dicumyl peroxide as a polymerization initiator, was added thereto in a fixed amount over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 5.5 kg of styrene, which had been prepared in advance by dissolving 53.3 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 4.0 g of t-butyl peroxybenzoate, 134.4 g of dicumyl peroxide, and 243 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 9.7 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0092] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles is shown in Figure 3.

[0093] Example 4 [Preparation of seed particles (B)] The amount of ethylene-vinyl acetate copolymer used was changed to 61 parts by mass, and the amount of seed polymerization composite resin (A) used was changed to 13 parts by mass. 26 parts by mass of recycled low-density polyethylene (LDPE) (Horng En Co., Ltd., product name "LDPE L2040") was further added to the seed polymerization composite resin (A). The resulting resin mixture was melt-kneaded and granulated by an underwater cutting method to obtain seed particles (B).

[0094] [Preparation of Composite Resin Particles (C)] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 14.6 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m3 The temperature was adjusted to 130°C, and 6.3 kg of styrene, which had been prepared by dissolving 8.2 g of dicumyl peroxide as a polymerization initiator, was added quantitatively over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 5.8 kg of styrene, which had been prepared in advance by dissolving 56.2 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 4.2 g of t-butyl peroxybenzoate, 124.0 g of dicumyl peroxide, and 264 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 11.1 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0095] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 4.

[0096] Example 5 [Preparation of seed particles (B)] A foamed molded product obtained from 49 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrasene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and 51 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 40:60 (mass ratio)) was mixed for 5 minutes, and the resulting resin mixture was melt-kneaded and granulated using an underwater cutting method to obtain seed particles (B).

[0097] [Preparation of Composite Resin Particles (C)] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 11.1 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 4.8 kg of styrene, which had been prepared by dissolving 6.2 g of dicumyl peroxide as a polymerization initiator, was added thereto in a fixed amount over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 6.7 kg of styrene, which had been prepared in advance by dissolving 64.5 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 4.8 g of t-butyl peroxybenzoate, 94.6 g of dicumyl peroxide, and 285 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 15.2 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0098] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 5.

[0099] Comparative Example 1 [Seed particle production] Without using the seed polymerization composite resin (A), only ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, trade name "Ultrathene 20K51A") was used as the polyolefin resin, which was granulated by the underwater cutting method to obtain seed particles.

[0100] [Preparation of composite resin particles] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 13.3 kg of seed particles were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3The temperature was adjusted to 130°C, and 5.7 kg of styrene, which had been prepared by dissolving 7.4 g of dicumyl peroxide as a polymerization initiator, was added quantitatively over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 6.1 kg of styrene, which had been prepared in advance by dissolving 59.3 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 4.4 g of t-butyl peroxybenzoate, 113.1 g of dicumyl peroxide, and 285 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 12.6 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles.

[0101] The obtained composite resin particles were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles, composite resin particles, and foamed molded article were measured and evaluated. The results are shown in Table 2. A TEM image of the composite resin particles is shown in Figure 6.

[0102] Comparative Example 2 [Preparation of seed particles] Without using the seed polymerization composite resin (A), only ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, trade name "Ultrathene 20K51A") was used as the polyolefin resin, which was granulated by the underwater cutting method to obtain seed particles.

[0103] [Preparation of composite resin particles] In a 100-liter autoclave equipped with a stirrer, 38 kg of water, 321 g of magnesium pyrophosphate as a dispersant, and 2.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 11.4 kg of seed particles were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 4.9 kg of styrene, which had been prepared in advance by dissolving 6.4 g of dicumyl peroxide as a polymerization initiator, was added quantitatively over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 120°C at a temperature decrease rate of 0.5°C / min. Next, 11.4 g of sodium dodecylbenzenesulfonate was added to the dispersion as a surfactant, and 10 minutes later, 6.6 kg of styrene, which had been prepared in advance by dissolving 114.0 g of dicumyl peroxide and 285 g of butyl acrylate as a polymerization initiator, was added quantitatively over 1.5 hours. Next, 14.8 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 16.9 g of magnesium pyrophosphate, 1.0 g of sodium dodecylbenzenesulfonate, and 114 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles.

[0104] Using the obtained composite resin particles, composite resin particles and foamed molded articles having a polyolefin resin to polystyrene resin mass ratio of 30:70 were produced in the same manner as in Example 1. Various physical properties of the obtained seed particles, composite resin particles, and foamed molded articles were measured and evaluated. The results are shown in Table 2. A TEM image of the composite resin particles is shown in Figure 7.

[0105] Comparative Example 3 [Preparation of seed particles] Seed particles were obtained in the same manner as in Example 1, except that 90 parts by mass of an ethylene-vinyl acetate copolymer (manufactured by Japan Polyethylene Co., Ltd., product name "Novatec EVA LV-115") and 10 parts by mass of a polystyrene resin (manufactured by Toyo Styrene Co., Ltd., product name "Toyo Styrol GP HRM-26") were mixed for 5 minutes to obtain a resin mixture.

[0106] [Preparation of composite resin particles] In a 100-liter autoclave equipped with a stirrer, 40 kg of water, 356 g of magnesium pyrophosphate as a dispersant, and 7.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 8.8 kg of seed particles were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 100°C, and 3.8 kg of styrene, which had been prepared in advance by dissolving 4.6 g of dicumyl peroxide as a polymerization initiator, was added in a fixed amount over 30 minutes. 3The temperature of the dispersion was adjusted to 60°C, and the seed particles were impregnated with styrene by stirring for 1 hour while maintaining the temperature at 60°C. The dispersion was then heated at a temperature increase rate of 0.78°C / min and held at 130°C for 2 hours. The temperature was then increased to 140°C at 0.5°C / min and annealed for 2 hours, after which the dispersion was cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 11.5 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and after 10 minutes, 8.9 kg of styrene, which had been prepared in advance by dissolving 67 g of benzoyl peroxide (75% pure content) as a polymerization initiator, 6.2 g of t-butyl peroxybenzoate, 64 g of dicumyl peroxide, and 200 g of butyl acrylate, was added quantitatively over 3 hours. Next, 17.9 kg of styrene, which had been prepared in advance by dissolving 400 g of butyl acrylate and 200 g of ethylenebisstearic acid amide, was added quantitatively to the dispersion over a period of 3 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated using a centrifuge and the moisture adhering to the surface was removed using an airflow dryer, yielding composite resin particles with a polyolefin resin and polystyrene resin content ratio of 20:80 by mass.

[0107] The obtained composite resin particles were used to produce expandable particles, expanded particles, and foamed molded articles in the same manner as in Example 1. Various physical properties of the obtained seed particles, composite resin particles, and foamed molded articles were measured and evaluated. The results are shown in Table 2. A TEM image of the composite resin particles is shown in Figure 8.

[0108] Comparative Example 4 [Preparation of seed particles] Seed particles were obtained in the same manner as in Example 1, except that 90 parts by mass of an ethylene-vinyl acetate copolymer (manufactured by Japan Polyethylene Co., Ltd., product name "Novatec EVA LV-115") and 10 parts by mass of a polystyrene resin (manufactured by Toyo Styrene Co., Ltd., product name "Toyo Styrol GP HRM-26") were mixed for 5 minutes to obtain a resin mixture.

[0109] [Preparation of composite resin particles] In a 100-liter autoclave equipped with a stirrer, 40 kg of water, 356 g of magnesium pyrophosphate as a dispersant, and 7.0 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 The mixture was stirred at 100°C to obtain a dispersion medium, to which 13.3 kg of seed particles were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 60°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 50°C, and 5.7 kg of styrene, which had been prepared in advance by dissolving 6.2 g of dicumyl peroxide as a polymerization initiator, was added in a fixed amount over 30 minutes. 3 The temperature of the dispersion was adjusted to 60°C, and the dispersion was stirred for 1 hour while maintaining the temperature at 60°C, thereby impregnating the seed particles with styrene. The dispersion was then heated at a temperature increase rate of 0.78°C / min and held at 130°C for 2 hours. The temperature was then increased to 140°C at a rate of 0.5°C / min, and the dispersion was cooled to 90°C at a rate of 0.5°C / min. Next, 11.5 g of sodium dodecylbenzenesulfonate was added to the dispersion as a surfactant, and 10 minutes later, 6.1 kg of styrene, which had been prepared in advance by dissolving 60 g of benzoyl peroxide (75% pure content) as a polymerization initiator, 5.6 g of t-butyl peroxybenzoate, 107 g of dicumyl peroxide, and 200 g of butyl acrylate, was added quantitatively over 2 hours. Next, 14.3 kg of styrene, which had been prepared in advance by dissolving 400 g of butyl acrylate and 200 g of ethylenebisstearic acid amide, was added quantitatively to the dispersion over 2 hours. The dispersion was then maintained at 90°C for 1 hour, heated to 143°C at a rate of 0.66°C / min, and maintained at this temperature for 2 hours. Thereafter, the dispersion was cooled to 30°C at a rate of 0.94°C / min. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 400 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated using a centrifuge and the moisture adhering to the surface was removed using an airflow dryer, yielding composite resin particles with a polyolefin resin and polystyrene resin content ratio of 30:70 by mass.

[0110] The obtained composite resin particles were used to produce a foamed molded article in the same manner as in Comparative Example 3, except that the annealing step was not carried out. Various physical properties of the obtained seed particles, composite resin particles, and foamed molded article were measured and evaluated. The results are shown in Table 2. A TEM image of the composite resin particles is shown in Figure 9.

[0111] Example 6 [Preparation of seed particles (B)] A foamed molded product obtained from 63 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and mixed with 37 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 30:70 (mass ratio)) for 5 minutes, and the resulting resin mixture was melt-kneaded and granulated using an underwater cutting method to obtain seed particles (B).

[0112] [Preparation of composite resin particles (C)] In a 100-liter autoclave equipped with a stirrer, 39 kg of water, 373 g of magnesium pyrophosphate as a dispersant, and 6.3 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3The mixture was stirred at 100°C to obtain a dispersion medium, to which 24.9 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 65°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 4.2 kg of styrene, which had been prepared by dissolving 5.5 g of dicumyl peroxide as a polymerization initiator, was added thereto in a fixed amount over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 47.1 g of sodium dodecylbenzenesulfonate was added to the dispersion as a surfactant, and 10 minutes later, 2.7 kg of styrene, which had been prepared in advance by dissolving 26.5 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 2.5 g of t-butyl peroxybenzoate, 249 g of dicumyl peroxide, and 732 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 4.7 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 45.5 g of magnesium pyrophosphate, 8.0 g of sodium dodecylbenzenesulfonate, and 146 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 500 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0113] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 10.

[0114] Example 7 [Preparation of seed particles (B)] A foamed molded product obtained from 22 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene 20K51A") and styrene-based monomer-polyolefin seed polymerization composite resin particles was crushed, melt-kneaded, and mixed with 78 parts by mass of pelletized styrene-based monomer-polyolefin seed polymerization composite resin (A) (polyolefin-based resin:polystyrene-based resin = 38:62 (mass ratio)) for 5 minutes, and the resulting resin mixture was melt-kneaded and granulated using an underwater cutting method to obtain seed particles (B).

[0115] [Preparation of Composite Resin Particles (C)] In a 100-liter autoclave equipped with a stirrer, 39 kg of water, 373 g of magnesium pyrophosphate as a dispersant, and 6.3 g of sodium dodecylbenzenesulfonate as a surfactant were added, and the stirring power required was 0.20 kw / m. 3 7.1 kg of seed particles (B) were added and dispersed to obtain a suspension (dispersion liquid). Next, the temperature of this dispersion was adjusted to 65°C, and the stirring power was adjusted to 0.22 kw / m 3 The temperature was adjusted to 130°C, and 3.0 kg of styrene, which had been prepared by dissolving 3.9 g of dicumyl peroxide as a polymerization initiator, was added thereto in a fixed amount over 30 minutes. The dispersion was then heated at a temperature increase rate of 1.0°C / min, held at 130°C for 1.5 hours, and then cooled to 90°C at a temperature decrease rate of 0.5°C / min. Next, 47.1 g of sodium dodecylbenzenesulfonate was added as a surfactant to the dispersion, and 10 minutes later, 6.7 kg of styrene, which had been prepared in advance by dissolving 63.0 g (75% pure content) of benzoyl peroxide as a polymerization initiator, 5.9 g of t-butyl peroxybenzoate, 71 g of dicumyl peroxide, and 732 g of butyl acrylate, was added quantitatively over 1.5 hours. Next, 19 kg of styrene was added to the dispersion liquid at a constant rate over 1.5 hours. Next, a solution previously prepared by dissolving 45.5 g of magnesium pyrophosphate, 8.0 g of sodium dodecylbenzenesulfonate, and 146 g of ethylenebisstearamide in 2.5 kg of water was added quantitatively to the dispersion over 0.5 hours. The autoclave was then heated to 143°C at a rate of 1.0°C / min and maintained at that temperature for 2.5 hours. The dispersion was then cooled to 30°C at a rate of 0.94°C / min. The contents were removed from the autoclave, and 500 ml of 20% hydrochloric acid was added to decompose the magnesium pyrophosphate adhering to the surface of the resin particles. After washing, the contents were dehydrated in a centrifuge and the moisture adhering to the surface was removed using an airflow dryer to obtain composite resin particles (C).

[0116] The obtained composite resin particles (C) were used to produce a foamed molded article in the same manner as in Example 1. Various physical properties of the obtained seed particles (B), composite resin particles (C), and foamed molded article were measured and evaluated. The results are shown in Table 1. A TEM image of the composite resin particles (C) is shown in Figure 11.

[0117] [Table 1]

[0118] [Table 2]

[0119] TEM images (Figs. 1-5, 10, and 11) of the center of the composite resin particles of Examples 1-7 showed a co-continuous structure of polyethylene resin and polystyrene resin, and one or more polystyrene resin microparticles with a particle diameter of 1.0 μm or more. The area percentages of polystyrene resin microparticles with a particle diameter of 1.0 μm or more were 43.9%, 15.4%, 7.9%, 15.7%, 19.4%, 11.5%, and 6.2%, respectively. The foamed molded articles of Examples 1-7 showed excellent results in chemical resistance, molding cycle, fusion rate, appearance, 25% compressive strength, flexural strength, and flexural modulus.

[0120] In the composite resin particles of Comparative Examples 1 to 4, the presence of polystyrene resin fine particles having a particle diameter of 1.0 μm or more could not be confirmed in the particle center (FIGS. 6 to 9). The foam molded article of Comparative Example 1 had a molding cycle 27% longer than that of the foam molded article of Example 1. The presence of a co-continuous structure of the polyethylene resin and the polystyrene resin could not be confirmed in the composite resin particles of Comparative Example 2. The foam molded article of Comparative Example 2 clearly had low strength. In Comparative Example 3, an annealing step was carried out, but the foam molded article had a low flexural modulus. The foam molded article of Comparative Example 4 had poor appearance and low flexural strength and flexural modulus.

Claims

1. Polystyrene-based composite resin particles (C) for producing a foamed molded article, comprising a polyolefin-based resin and a polystyrene-based resin in a mass ratio of 10:90 to 50:50, The composite resin particles (C) are, in an image obtained by the following method, (1) A co-continuous structure of polyolefin resin and polystyrene resin is observed, (2) One or more polystyrene-based resin microparticles having a particle diameter of 1.0 μm or more are observed, (3) The area ratio of polystyrene-based resin fine particles having a particle diameter of 1.0 μm or more is 1 to 50%. Composite resin particles (C). Image acquisition method: The composite resin particle (C) is sliced ​​so as to pass through the center of the particle, and the resulting thin film is photographed with a transmission electron microscope to obtain an image of a square portion having a side length of 10 μm and including the center of the particle.

2. 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) that has been melt-kneaded at least once in an amount of 10 to 80 mass % of the seed particles (B); The polystyrene-based composite resin particles (C) according to claim 1, wherein the seed particles (B) further contain a polyolefin-based resin in an amount of 20 to 90 mass % of the seed particles (B) in addition to the polyolefin-based resin contained in the seed polymerization composite resin (A).

3. Expandable particles comprising the composite resin particles (C) according to claim 1 or 2 and a blowing agent.

4. Expanded particles of the expandable particles according to claim 3.

5. Bulk density of 0.012 to 0.20 g / cm ３ The expanded particles according to claim 4, wherein

6. A foamed molded article made from the foamed beads according to claim 4.

7. A method for producing composite resin particles (C) containing a polyolefin-based resin and a polystyrene-based resin for use in producing a foamed molded article, comprising: a step of impregnating seed particles (B) with a styrene-based monomer and polymerizing the monomer to obtain the composite resin particles (C), the seed particles (B) contain a styrene-based monomer-polyolefin seed polymerization composite resin (A) that has been melt-kneaded at least once, the seed particles (B) contain, in addition to the polyolefin-based resin contained in the seed polymer composite resin (A), a polyolefin-based resin in an amount of 20 to 90 mass % of the seed particles (B); A method for producing composite resin particles (C).

8. The method for producing composite resin particles (C) according to claim 7, wherein the seed particles (B) contain 10 to 80 mass % of a seed polymerization composite resin (A) of a styrene-based monomer-polyolefin that has been melt-kneaded at least once.

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