Polypropylene resin foam particles and polypropylene resin foam molded article

Abstract

The present invention addresses the problem of providing polypropylene resin foam particles that (a) can provide a polypropylene resin foam molded article that exhibits almost no post-molding shrinkage or deformation, and (b) exhibit excellent foaming characteristics. The polypropylene resin foam particles contain prescribed amounts of: a polypropylene resin; a copolymer containing an acrylonitrile unit and a styrenic unit; and a hydrogenated styrenic copolymer.

Description

[Technical Field]

[0001] The present invention relates to expanded polypropylene resin beads and expanded molded polypropylene resin articles. [Background technology]

[0002] Polypropylene resin foam molded articles are used in a variety of applications, including automotive interior components, core materials for automotive bumpers, heat insulating materials, cushioning packaging materials, and returnable containers.

[0003] However, since polypropylene resin is a crystalline thermoplastic resin, polypropylene resin foam molded articles obtained by molding polypropylene resin foam beads shrink more after molding than amorphous thermoplastic resins such as polystyrene. Therefore, particularly when integrally molding other materials such as metal (insert molding), the polypropylene resin foam molded article shrinks after molding, which can cause deformation of the metal component. That is, with conventional technology, it has been difficult to control the dimensions and / or shape of the polypropylene resin foam molded article when integrally molding other materials such as metal.

[0004] As a method for controlling shrinkage of a polypropylene-based resin foam molded article after molding, a method in which an amorphous thermoplastic resin is mixed with a polypropylene-based resin is known.

[0005] For example, Patent Document 1 discloses a technique in which a polypropylene resin, an amorphous thermoplastic resin, and a compatibilizer are mixed and used.

[0006] Patent Document 2 discloses a technique in which a polypropylene resin is mixed with a polystyrene resin and a polymer mainly composed of a vinyl aromatic compound. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-302837 [Patent Document 2] Japanese Patent Publication No. Hei 6-100740 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, an object of one embodiment of the present invention is to provide (a) a polypropylene-based resin foam molded article that is substantially free from shrinkage and deformation after molding, and (b) a polypropylene-based resin foam particle that has excellent foaming properties. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0010] That is, the expanded polypropylene resin particles according to one embodiment of the present invention contain 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

[0011] Furthermore, a method for producing expanded polypropylene-based resin beads according to one embodiment of the present invention includes an expansion step of expanding polypropylene-based resin beads, and the polypropylene-based resin beads contain 100 parts by weight of a polypropylene-based resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units, and 3.0 to 30.0 parts by weight of a hydrogenated styrene-based copolymer. [Effects of the Invention]

[0012] According to one embodiment of the present invention, it is possible to provide (a) a polypropylene-based resin foam molded article that undergoes almost no shrinkage or deformation after molding, and (b) a polypropylene-based resin foam particle that has excellent foaming properties. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram of a foam molded article 100 used to evaluate the amount of deformation. DETAILED DESCRIPTION OF THE INVENTION

[0014] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0015] Unless otherwise specified in this specification, the structural unit is X 1 The structural units derived from the monomer and X 2 Structural units derived from monomers and X n A copolymer containing a monomer (n is an integer of 2 or more) is referred to as "X 1 / X 2 / ··· / X n Also called "copolymer". X 1 / X 2 / ··· / X n Unless otherwise specified, the copolymer is not particularly limited in terms of the polymerization mode, and may be a random copolymer, a block copolymer, or a graft copolymer.

[0016] In addition, in this specification, a constitutional unit derived from an X monomer contained in a polymer or copolymer may be referred to as an "X unit".

[0017] [1. Polypropylene resin foam particles] The expanded polypropylene resin particles according to one embodiment of the present invention contain 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

[0018] The expanded polypropylene resin beads according to one embodiment of the present invention can be molded by a known method to provide an expanded polypropylene resin molded article.

[0019] In this specification, "expanded polypropylene resin beads" may be referred to as "expanded beads," "expanded polypropylene resin beads according to one embodiment of the present invention" may be referred to as "the present expanded beads," and "expanded polypropylene resin molded body" may be referred to as "expanded molded body."

[0020] The expanded polypropylene resin beads according to one embodiment of the present invention have the above-described configuration, and therefore have the advantages of (a) being able to provide a polypropylene resin foam molded article that is almost free from shrinkage and deformation after molding, and (b) having excellent foamability. It can also be said that the expanded polypropylene resin beads according to one embodiment of the present invention can provide a polypropylene resin foam molded article that is reduced in shrinkage and deformation after molding compared to conventional products. In this specification, reduced shrinkage of a foam molded article after molding is also referred to as having excellent shrinkage.

[0021] In this specification, a polypropylene-based resin refers to a resin that contains 75 mol % or more of structural units derived from propylene monomers, based on 100 mol % of all structural units contained in the resin. In this specification, "structural units derived from propylene monomers" may also be referred to as "propylene units."

[0022] (Polypropylene resin) The polypropylene-based resin may be (a) a homopolymer of propylene, (b) a block copolymer, random copolymer, or graft copolymer of propylene and a monomer other than propylene, or (c) a mixture of two or more of these.

[0023] In addition to propylene units, polypropylene-based resins may have one or more structural units derived from monomers other than propylene monomers, and may have one or more types of structural units. A "monomer other than propylene monomer" used in the production of polypropylene-based resins may also be referred to as a "comonomer." A "structural unit derived from a monomer other than propylene monomer" contained in a polypropylene-based resin may also be referred to as a "comonomer unit."

[0024] Examples of the comonomer include α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene.

[0025] Specific examples of polypropylene-based resins include polypropylene homopolymers, ethylene / propylene random copolymers, 1-butene / propylene random copolymers, 1-butene / ethylene / propylene random copolymers, ethylene / propylene block copolymers, 1-butene / propylene block copolymers, propylene / chlorinated vinyl copolymers, propylene / maleic anhydride copolymers, and styrene-modified polypropylene-based resins. As polypropylene-based resins, these may be used alone or in combination of two or more. Among these, ethylene / propylene random copolymers and 1-butene / ethylene / propylene random copolymers are preferred because the resulting expanded beads have good expandability and the resulting molded articles have good moldability. Note that the term 1-butene is synonymous with butene-1.

[0026] Consider the case where an ethylene / propylene random copolymer or a 1-butene / ethylene / propylene random copolymer is used as the polypropylene-based resin (Case A). In Case A, the ethylene content of the ethylene / propylene random copolymer or the 1-butene / ethylene / propylene random copolymer is preferably 0.2 to 10.0% by weight based on 100% by weight of each copolymer. The ethylene content can also be referred to as the content of ethylene-derived structural units (ethylene units). When the ethylene / propylene random copolymer or the 1-butene / ethylene / propylene random copolymer has an ethylene unit content of (i) 0.2% by weight or more, the expandability of the expanded beads in the production of the expanded beads and / or the moldability of the resulting expanded beads tend to be good, and (ii) when it is 10.0% by weight or less, there is no risk of a decrease in the mechanical properties of the expanded molded articles obtained from the expanded beads.

[0027] In case A, the 1-butene content in the 1-butene / ethylene / propylene random copolymer is preferably 0.2 to 10.0% by weight based on 100% by weight of the copolymer. The 1-butene content can also be considered the content of structural units derived from 1-butene (1-butene units). When the 1-butene / ethylene / propylene random copolymer has a 1-butene content of (i) 0.2% by weight or more, the expandability of the expanded beads in the production of the expanded beads and / or the moldability of the resulting expanded beads tend to be good, and when the content is (ii) 10.0% by weight or less, there is no risk of a decrease in the mechanical properties of the expanded molded articles obtained from the expanded beads.

[0028] In case A, the total content of ethylene units and 1-butene units in the 1-butene / ethylene / propylene random copolymer is preferably 0.5 to 10.0% by weight, based on 100% by weight of the 1-butene / ethylene / propylene random copolymer. When the total content of ethylene units and 1-butene units in the 1-butene / ethylene / propylene random copolymer is (i) 0.5% by weight or more, the expandability of the expanded beads in the production of the expanded beads and / or the moldability of the resulting expanded beads tend to be good, and (ii) when it is 10.0% by weight or less, there is no risk of a decrease in the mechanical properties of the expanded molded article obtained from the expanded beads.

[0029] The melting point of the polypropylene resin is preferably 135.0° C. to 160.0° C., more preferably 138.0° C. to 158.0° C., more preferably 140.0° C. to 156.0° C., more preferably 143.0° C. to 154.0° C., even more preferably 145.0° C. to 152.0° C., and particularly preferably 148.0° C. to 150.0° C. When the polypropylene resin has a melting point of (i) 135.0° C. or higher, the foamed molded article obtained from the expanded beads has excellent heat resistance, and (ii) when the melting point is 160.0° C. or lower, it becomes easy to increase the expansion ratio of the expanded beads in the production of the expanded beads.

[0030] In this specification, the melting point of a polypropylene-based resin is a value determined by differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific procedure is as follows: (1) 5 mg to 6 mg of polypropylene-based resin is melted by increasing the temperature from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (2) The temperature of the molten polypropylene-based resin is then decreased from 220.0°C to 40.0°C at a heating rate of 10.0°C / min to crystallize the polypropylene-based resin; (3) The temperature of the crystallized polypropylene-based resin is then increased from 40.0°C to 220.0°C at a heating rate of 10°C / min. The melting point of the polypropylene-based resin can be determined by the peak temperature (melting peak) of the DSC curve obtained during the second heating (i.e., during (3)). In addition, when there are multiple peaks (melting peaks) in the DSC curve of the polypropylene-based resin obtained during the second temperature increase by the above-mentioned method, the temperature of the peak (melting peak) with the largest heat of fusion is taken as the melting point of the polypropylene-based resin. As the differential scanning calorimeter, for example, a DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0031] The melt flow rate (MFR) of the polypropylene resin is not particularly limited, but is preferably 3.0 g / 10 min to 30.0 g / 10 min, more preferably 4.0 g / 10 min to 20.0 g / 10 min, even more preferably 5.0 g / 10 min to 15.0 g / 10 min, and particularly preferably 6.0 g / 10 min to 13.0 g / 10 min. MFR is sometimes also referred to as "melt index (MI)."

[0032] When the MFR of the polypropylene resin is 3 g / 10 min or more, it tends to be easier to increase the expansion ratio of the expanded beads during production of the expanded beads. When the MFR of the polypropylene resin is 30 g / 10 min or less, there is no risk of the cells in the resulting expanded beads becoming interconnected, and as a result, (i) the compressive strength of the expanded molded article obtained from the expanded beads tends to be good, or (ii) the surface properties of the expanded molded article tends to be good.

[0033] In this specification, the MFR value of a polypropylene-based resin is a value obtained by measurement using an MFR measuring device described in JIS K7210:1999 under the following conditions: orifice diameter 2.0959±0.005 mmφ, orifice length 8.000±0.025 mm, load 2.16 kgf, and temperature 230°C (230±0.2°C).

[0034] The polypropylene resin can be obtained by a known method. The polymerization catalyst used for synthesizing the polypropylene resin is not particularly limited, and for example, a Ziegler catalyst or a metallocene catalyst can be used.

[0035] (Copolymer containing acrylonitrile units and styrene-based units) The present expanded beads contain 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units per 100 parts by weight of polypropylene-based resin. The present expanded beads have the above-described structure, which has the advantage of providing expanded beads with excellent expandability and foamed molded articles with reduced shrinkage and deformation after molding compared to conventional products. In this specification, "a copolymer containing acrylonitrile units and styrene-based units" may be referred to as "AS copolymer." Note that AS copolymer is an amorphous resin.

[0036] In this specification, the term "AS copolymer" refers to a copolymer containing at least 50 mol % in total of structural units derived from acrylonitrile units or styrene-based units, based on 100 mol % of all structural units contained in the AS copolymer. The AS copolymer is not particularly limited as long as it contains 50 mol % or more of structural units containing at least acrylonitrile units and styrene-based units, and may be, for example, (a) a block copolymer, random copolymer, or graft copolymer, or (b) a mixture of two or more of these.

[0037] The styrene-based units contained in the AS copolymer are structural units derived from styrene-based monomers. Examples of such styrene-based monomers include (a) styrene and (b) styrene derivatives such as α-methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, 2,4-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, t-butylstyrene, and chlorostyrene. These styrene-based monomers may be used alone or in combination of two or more. That is, the styrene-based units contained in the AS copolymer may be one type or a combination of two or more types.

[0038] The styrene units contained in the AS copolymer preferably include α-methylstyrene units. The amount of α-methylstyrene units in the styrene units contained in the AS copolymer is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 100% by weight, based on 100% by weight of the styrene units contained in the AS copolymer. That is, the styrene units contained in the AS copolymer are most preferably α-methylstyrene units. The greater the amount of α-methylstyrene units in the styrene units contained in the AS copolymer, the more advantageously the resulting expanded beads will be (a) capable of providing a polypropylene resin expansion molded article that is almost free from shrinkage and deformation after molding, and (b) have excellent expandability.

[0039] The amount of styrene units contained in the AS copolymer (hereinafter sometimes referred to as "styrene content") is preferably 20 to 95% by weight, more preferably 50 to 90% by weight, even more preferably 55 to 85% by weight, even more preferably 60 to 80% by weight, and particularly preferably 65 to 75% by weight, based on 100% by weight of the AS copolymer. This configuration has the advantages of high productivity and of obtaining an AS copolymer with excellent heat resistance.

[0040] The amount of α-methylstyrene units as styrene-based units contained in the AS copolymer (hereinafter sometimes referred to as "α-methylstyrene content") is preferably 20 to 95% by weight, more preferably 50 to 90% by weight, even more preferably 55 to 85% by weight, even more preferably 60 to 80% by weight, and particularly preferably 65 to 75% by weight, based on 100% by weight of the AS copolymer. This configuration has the advantages of high productivity and of obtaining an AS copolymer with excellent heat resistance.

[0041] The AS copolymer may contain structural units other than acrylonitrile units and styrene-based units (hereinafter, sometimes referred to as "structural units other than AS"). Examples of structural units other than AS include vinyl esters such as vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate and ethyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; olefins such as ethylene and propylene; maleic anhydride; vinyl chloride; vinylidene chloride; and monomers other than the above-mentioned monomers copolymerizable with acrylonitrile units and / or styrene-based units. To improve the heat resistance of the AS copolymer, the amount of structural units other than AS contained in the AS copolymer is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 1 wt% or less, and particularly preferably 0 wt% based on 100 wt% of the AS copolymer. In other words, it is particularly preferred that the AS copolymer be a copolymer composed of acrylonitrile units and styrene-based units.

[0042] Specific examples of AS copolymers include acrylonitrile / styrene copolymer, acrylonitrile / α-methylstyrene copolymer, acrylonitrile / p-methylstyrene copolymer, acrylonitrile / m-methylstyrene copolymer, acrylonitrile / o-methylstyrene copolymer, acrylonitrile / 2,4-dimethylstyrene copolymer, acrylonitrile / p-ethylstyrene copolymer, acrylonitrile / m-ethylstyrene copolymer, acrylonitrile / o-ethylstyrene copolymer, acrylonitrile / t-butylstyrene copolymer, and acrylonitrile / chlorostyrene copolymer. Among the above-mentioned copolymers, acrylonitrile / α-methylstyrene copolymer is preferred because it has the advantage of producing expanded beads with excellent expandability. These AS copolymers may be used alone or in combination of two or more.

[0043] The glass transition temperature (sometimes referred to as "Tg") of the AS copolymer is not particularly limited, but is preferably 95°C to 140°C, more preferably 100°C to 135°C, even more preferably 103°C to 130°C, and particularly preferably 105°C to 125°C. When the Tg of the AS copolymer is (i) 95°C or higher, it is advantageous in that expanded beads and expanded molded articles having excellent heat resistance can be obtained, and (ii) when it is 140°C or lower, expanded beads with a low open cell ratio can be obtained.

[0044] In this specification, the Tg of an AS copolymer is a value obtained by measurement in accordance with JIS-K-7121 using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200 model). The specific operating procedure is as follows: (1) weigh out 5 mg of the AS copolymer; (2) increase the temperature of the AS copolymer from room temperature to 250°C at 10°C / min under a nitrogen atmosphere; (3) decrease the temperature of the increased AS copolymer from 250°C to room temperature at 10°C / min; (4) increase the temperature of the AS copolymer again from room temperature to 250°C at 10°C / min; (5) The temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained during the second temperature increase (i.e., during step (4)) is taken as the Tg of the AS copolymer.

[0045] The MFR of the AS copolymer is not particularly limited, but is preferably 2.0 g / 10 min to 15.0 g / 10 min, more preferably 3.0 g / 10 min to 12.0 g / 10 min, and even more preferably 4.0 g / 10 min to 10.0 g / 10 min. When the MFR of the AS copolymer is 2.0 g / 10 min to 15.0 g / min, the AS copolymer has excellent compatibility with polypropylene-based resins, and can reduce the formation of open cells when the resulting resin particles are expanded. As a result, expanded particles with a low open cell ratio can be obtained, which is an advantage.

[0046] In this specification, the MFR value of the AS copolymer is a value obtained by measurement using an MFR measuring device described in JIS K7210:1999 under the following conditions: orifice diameter: 2.0959±0.005 mmφ, orifice length: 8.000±0.025 mm, load: 2.16 kgf, and temperature: 230°C (230±0.2°C).

[0047] The content of the AS copolymer in the expanded beads is 5 to 60 parts by weight, more preferably 5 to 50 parts by weight, more preferably 8 to 50 parts by weight, more preferably 10 to 40 parts by weight, more preferably 13 to 40 parts by weight, even more preferably 15 to 35 parts by weight, and particularly preferably 20 to 30 parts by weight, per 100 parts by weight of the polypropylene resin. When the content of the AS copolymer is (a) 5 parts by weight or more per 100 parts by weight of the polypropylene resin, expanded beads with excellent expandability can be obtained, and expanded molded articles with reduced shrinkage and deformation after molding compared to conventional products can be obtained. When the content of the AS copolymer is (b) 60 parts by weight or less, expanded beads with a low open cell ratio and excellent expandability can be obtained.

[0048] (hydrogenated styrene copolymer) The expanded polypropylene resin beads according to one embodiment of the present invention contain 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer. In one embodiment of the present invention, the hydrogenated styrene copolymer has a compatibilizing effect between the polypropylene resin and the AS copolymer. In other words, the hydrogenated styrene copolymer can function as a compatibilizer. By including the hydrogenated styrene copolymer within the above-mentioned range, the expanded beads can be advantageously obtained with excellent expandability, and can also produce expanded molded articles with reduced shrinkage and deformation after molding compared to conventional products.

[0049] In this specification, the term "hydrogenated styrene copolymer" refers to a copolymer obtained by hydrogenating a block copolymer (hereinafter also referred to as copolymer X) containing a styrene block composed only of styrene units and a conjugated diene block composed only of conjugated diene units. In this specification, "hydrogenation" may also be referred to as "hydrogenation." More specifically, the term "hydrogenated styrene copolymer" refers to a copolymer obtained by hydrogenating copolymer X so that at least a portion of the carbon-carbon double bonds in the conjugated diene units of copolymer X are saturated.

[0050] Examples of the conjugated diene unit contained in copolymer X include, but are not limited to, a butadiene unit, an isoprene unit, a 1,3-pentadiene unit, a 2,3-dimethyl-1,3-butadiene unit, a 3-methyl-1,3-octadiene unit, or a 4-ethyl-1,3-hexadiene unit.

[0051] In the production of a hydrogenated styrene copolymer, it is sufficient that at least a portion of the carbon-carbon double bonds in the conjugated diene units of copolymer X are saturated, and it is not necessary that all of them be saturated. In other words, the hydrogenated styrene copolymer may contain the conjugated diene units contained in copolymer X used in the production of the hydrogenated styrene copolymer. More specifically, when copolymer X contains butadiene units as conjugated diene units, the hydrogenated styrene copolymer obtained by hydrogenating copolymer X may contain (a) butadiene units to which no hydrogen has been added, (b-1) butylene units formed by 1,2-addition polymerization of hydrogen to the carbon-carbon double bonds of the butadiene units, or (b-2) ethylene units formed by 1,4-addition polymerization of hydrogen to the carbon-carbon double bonds of the butadiene units.

[0052] In the hydrogenated styrene copolymer, the proportion of conjugated diene units in which hydrogen has been added to carbon-carbon double bonds (hereinafter sometimes referred to as the "hydrogenation rate") in the total amount of conjugated diene units in copolymer X used in the production is preferably 50% or more, more preferably 70% to 100%, and even more preferably 80% to 100%. When the hydrogenation rate of the hydrogenated styrene copolymer is within the above range, the hydrogenated styrene copolymer is more likely to be present at the interface between the polypropylene resin and the AS copolymer, which tends to improve the compatibilizing effect of the hydrogenated styrene copolymer. The hydrogenation rate of the hydrogenated styrene copolymer may be 100%.

[0053] Specific examples of hydrogenated styrene copolymers include styrene / ethylene / butylene / styrene block copolymer (SEBS) and styrene / ethylene / propylene / styrene block copolymer (SEPS). SEBS is a copolymer obtained by hydrogenating a copolymer (copolymer X) consisting of (a) a styrene block consisting of only styrene units, (b) a butadiene block consisting of only butadiene units, and (c) a styrene block consisting of only styrene units, bonded in this order. More specifically, SEBS is a copolymer consisting of (a) a styrene block consisting of only styrene units, (b) a block in which (b-1) butylene units formed by hydrogenating 1,2-addition-polymerized butadiene units and (b-2) ethylene units formed by hydrogenating 1,4-addition-polymerized butadiene units are randomly bonded, and (c) the styrene block, bonded in this order. In SEBS, the block in which butylene units and ethylene units are randomly bonded may contain butadiene units. SEPS is a copolymer obtained by hydrogenating a copolymer (copolymer X) in which (a) a styrene block composed only of styrene units, (b) an isoprene block composed only of isoprene units, and (c) a styrene block composed only of styrene units are bonded in this order. More specifically, SEPS is a copolymer in which (a) a styrene block composed only of styrene units, (b) a block in which ethylene units and propylene units are bonded randomly, obtained by hydrogenating the isoprene units, and (c) the styrene block are bonded in this order. Among these, the hydrogenated styrene copolymer preferably contains SEBS, and SEBS is particularly preferred, because of its advantage of relatively high strength.

[0054] The styrene unit content of the hydrogenated styrene copolymer (hereinafter sometimes referred to as "styrene content") is preferably 5% to 90% by weight, more preferably 10% to 85% by weight, more preferably 15% to 80% by weight, and even more preferably 25% to 55% by weight, based on 100% by weight of the hydrogenated styrene copolymer. This configuration has the advantage of improving the compatibility between the polypropylene resin and the AS copolymer. In particular, when the styrene unit content of the hydrogenated styrene copolymer is 15% by weight or more based on 100% by weight of the hydrogenated styrene copolymer, a foamed molded article tends to be obtained that exhibits reduced shrinkage and deformation after molding compared to conventional products.

[0055] The content of the hydrogenated styrene copolymer in the expanded beads is 3.0 to 30.0 parts by weight, preferably 4.0 to 25.0 parts by weight, more preferably 5.0 to 20.0 parts by weight, even more preferably 5.0 to 15.0 parts by weight, and particularly preferably 5.0 to 10.0 parts by weight, per 100 parts by weight of the polypropylene resin. When the content of the hydrogenated styrene copolymer is 3.0 parts by weight or more per 100 parts by weight of the polypropylene resin, the hydrogenated styrene copolymer has the advantage of fully compatibilizing the polypropylene resin and the AS copolymer. When the content of the hydrogenated styrene copolymer is 30.0 parts by weight or less per 100 parts by weight of the polypropylene resin, the advantages are: (a) expanded beads with excellent expandability are obtained; (b) expanded molded articles obtained by molding the expanded beads have sufficient rigidity; and (c) expanded molded articles with reduced shrinkage and deformation after molding are obtained compared to conventional products.

[0056] (Other resins, etc.) The expanded beads may further contain resins other than polypropylene-based resins, AS copolymers, and hydrogenated styrene-based copolymers (sometimes referred to as "other resins") as resin components, provided that the effects of one embodiment of the present invention are not impaired. Examples of such other resins include: (a) ethylene-based resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear very-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; (b) styrene-based resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer; (c) polyphenylene ether-based resins such as polyphenylene ether and modified polyphenylene ether; (d) polyolefin-based waxes such as propylene / α-olefin-based wax; and (e) olefin-based rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. The styrene-based resins and polyphenylene ether-based resins are amorphous resins.

[0057] The content of other resins, etc. in the present expanded beads is preferably more than 0 parts by weight and not more than 50 parts by weight, more preferably more than 0 parts by weight and not more than 30 parts by weight, per 100 parts by weight of the polypropylene-based resin. The present expanded beads may not contain other resins, etc. In other words, the content of other resins, etc. in the present expanded beads may be 0 parts by weight.

[0058] (additives) The expanded beads of the present invention may contain, in addition to the resin components including the polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, optional additives. Examples of additives include colorants, water-absorbing substances, foam nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystal nucleating agents, conductive agents, and lubricants. In the production of the expanded beads of the present invention, such additives may be used during the production of the resin beads and incorporated into the resin beads, or may be added directly to the dispersion in the foaming step described below.

[0059] The water-absorbing substance is a substance used in the production of the expanded beads to increase the amount of water impregnated into the resin particles. By using the water-absorbing substance when producing the expanded beads, the resin particles can be imparted with expandability. The effect of the water-absorbing substance in imparting expandability to the resin particles is particularly pronounced when water is used as the blowing agent.

[0060] Examples of water-absorbing substances that can be used in one embodiment of the present invention include glycerin, diglycerin, polyethylene glycol, C12 to C18 aliphatic alcohols (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensate, zinc borate, etc. One of these water-absorbing substances may be used alone, or two or more may be used in combination. Furthermore, when two or more water-absorbing substances are used in combination, the mixing ratio may be adjusted appropriately depending on the purpose.

[0061] Glycerin and polyethylene glycol (a) do not promote the reduction of the average cell diameter of the expanded beads, and (b) have good affinity with polypropylene-based resins. Therefore, among the above-mentioned water-absorbing substances, glycerin and / or polyethylene glycol are preferred.

[0062] The amount of water-absorbing substance used in the production of the expanded beads, in other words, the content of the water-absorbing substance in the expanded beads, will be described below. The content of the water-absorbing substance in the expanded beads, relative to 100 parts by weight of the total amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, is preferably 0.01 to 1.00 parts by weight, more preferably 0.05 to 0.70 parts by weight, and even more preferably 0.10 to 0.60 parts by weight. When the content of the water-absorbing substance is (i) 0.01 part by weight or more, the foaming effect of the water-absorbing substance can be sufficiently obtained, and (ii) when it is 1.00 part by weight or less, there is no risk of shrinkage of the resulting expanded beads.

[0063] The foam nucleating agent is a substance that can be used in the production of the expanded beads and that can become a foam nucleus when the resin particles are expanded. It is preferable to use a foam nucleating agent in the production of the expanded beads, in other words, it is preferable that the expanded beads contain a foam nucleating agent.

[0064] Examples of foam nucleating agents that can be used in one embodiment of the present invention include silica (silicon dioxide), silicates, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar apatite, and barium sulfate. Examples of silicates include talc, magnesium silicate, kaolin, halloysite, dickite, aluminum silicate, and zeolite. These foam nucleating agents may be used alone or in combination of two or more. When two or more foam nucleating agents are used in combination, the mixing ratio may be adjusted appropriately depending on the purpose.

[0065] The amount of foam nucleating agent used in the production of the present expanded beads, in other words, the content of foam nucleating agent in the present expanded beads, is described below. From the viewpoint of uniformity of the average cell diameter, the content of foam nucleating agent in the present expanded beads is preferably 0.005 to 2,000 parts by weight, more preferably 0.010 to 1,000 parts by weight, and even more preferably 0.030 to 0.500 parts by weight, per 100 parts by weight of the total amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer.

[0066] The total amount of additives used in the production of the present expanded beads, in other words, the total content of each additive in the present expanded beads, is preferably more than 0 parts by weight and not more than 10 parts by weight, more preferably more than 0 parts by weight and not more than 5 parts by weight, per 100 parts by weight of the polypropylene-based resin. The present expanded beads may also be free of each additive. That is, the content of each additive in the present expanded beads may be 0 part by weight.

[0067] <Physical properties> The physical properties of the expanded beads will be described below.

[0068] (Expansion ratio of expanded beads) The expanded beads preferably have an expansion ratio of 15.0 to 50.0 times, more preferably 15.0 to 40.0 times, even more preferably 15.0 to 25.0 times, and particularly preferably 15.0 to 20.0 times. If the expansion ratio of the expanded beads is (i) 15.0 times or more, a lightweight expanded molded article can be obtained with high production efficiency, and (ii) if it is 50.0 times or less, there is no risk of the strength of the resulting expanded molded article being insufficient. In this specification, expanded beads "excellent in expandability" refer to expanded beads obtained by directly expanding resin beads (first-stage expanded beads, described below) having an expansion ratio of 15.0 times or more.

[0069] In this specification, the expansion ratio of expanded beads is calculated by the following methods (1) to (6): (1) The weight Gi of a certain amount of expanded beads is measured accurately to the nearest 0.001 g (rounded off to the fourth decimal point); (2) Next, the entire amount of expanded beads used to measure the weight Gi is immersed in 100 mL of ethanol at 23°C contained in a measuring cylinder; (3) The volume yi (cm) of the expanded beads is calculated based on the rise in the liquid level in the measuring cylinder. 3 (4) The weight Gi (g) of the expanded beads is calculated based on the volume yi (cm 3 ) and convert it to g / L to calculate the apparent density di (g / L) of the expanded beads; (5) By carrying out the same operations as in (1) to (4) but using the resin particles used in the production of the expanded beads instead of the expanded beads, the density ds (g / L) of the resin particles is calculated; (6) The expansion ratio of the expanded beads is calculated using the following formula: Expansion ratio Ki=ds / di.

[0070] (DSC ratio of expanded particles) The expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry (DSC) as described below. The heat of fusion determined from the higher-temperature melting peak is referred to as the "higher-temperature heat of fusion," and the heat of fusion determined from the lower-temperature melting peak is referred to as the "lower-temperature heat of fusion." When there are three or more melting peaks, the heat of fusion determined from the highest-temperature melting peak is referred to as the "higher-temperature heat of fusion," and the heats of fusion determined from the remaining melting peaks are referred to as the "lower-temperature heat of fusion."

[0071] The DSC ratio of the expanded beads is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 20.0% to 40.0%, and even more preferably 22.0% to 30.0%. When the DSC ratio of the expanded beads is 10.0% or more, there is an advantage that the expanded molded article obtained by molding the expanded beads has sufficient strength. On the other hand, when the DSC ratio of the expanded beads is 40% or less, there is an advantage that the expanded beads can be molded at a relatively low molding temperature.

[0072] In this specification, the DSC ratio refers to the ratio of the heat of fusion on the higher temperature side to the total heat of fusion calculated from the DSC curve of the expanded beads. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., DSC6200 manufactured by Seiko Instruments Inc.). More specifically, in this specification, the method for measuring (calculating) the DSC ratio of the expanded beads using a differential scanning calorimeter (e.g., DSC6200 manufactured by Seiko Instruments Inc.) is as follows: (1) weigh out 5 mg to 6 mg of expanded beads; (2) raise the temperature of the expanded beads from 40°C to 220°C at a heating rate of 10°C / min to melt the expanded beads; (3) in the DSC curve of the expanded beads obtained in the process (2), (a) connect the maximum point between the highest temperature melting peak and the melting peak adjacent thereto (on the lower temperature side) with a straight line, and the point representing the temperature before the onset of melting; (b) A straight line is drawn between the maximum point and the point representing the temperature after the end of melting; (4) (a) (a-1) The heat quantity calculated from the high-temperature region surrounded by the line segment connecting the maximum point and the point representing the temperature after the end of melting, (a-2) the DSC curve, is defined as the high-temperature side heat of fusion; (b) (b-1) The heat quantity calculated from the low-temperature region surrounded by the line segment connecting the maximum point and the point representing the temperature before the start of melting, (b-2) the DSC curve, is defined as the low-temperature side heat of fusion; (c) The sum of the high-temperature side heat of fusion and the low-temperature side heat of fusion is defined as the total heat of fusion (= high-temperature side heat of fusion + low-temperature side heat of fusion); (5) The DSC ratio is calculated using the following formula: DSC ratio (%) = (high temperature heat of fusion / total heat of fusion) × 100.

[0073] The DSC ratio of the expanded beads is also a measure of the amount of high-melting-point crystals contained in the expanded beads. That is, a DSC ratio of 10.0% to 50.0% indicates that the expanded beads contain a relatively large amount of high-melting-point crystals. The DSC ratio of the expanded beads also plays a significant role in the viscoelasticity of the resin beads and the expanded beads during foaming and expansion. That is, when the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads can exhibit excellent foamability and expansion properties during foaming and molding, respectively. As a result, the expanded beads have the advantage of being able to produce foamed molded articles with excellent internal fusion and mechanical strength, such as compressive strength, even at low molding pressures.

[0074] In the present expanded beads, the DSC ratio can be controlled within a predetermined range by adjusting the conditions during production of the present expanded beads (particularly, the expansion temperature, expansion pressure, holding time, and the temperature of the region (space) where the dispersion is released, etc.) In terms of ease of adjustment, the method of controlling the DSC ratio within a predetermined range by adjusting the expansion temperature, expansion pressure, and / or holding time is preferred.

[0075] For example, increasing the foaming temperature tends to decrease the DSC ratio of the resulting expanded beads, while decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals contained in the expanded beads varies depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio of the resulting expanded beads, while decreasing the foaming pressure tends to increase the DSC ratio. This is because the degree of plasticization varies with the foaming pressure, thereby changing the amount of unmelted crystals contained in the expanded beads. Furthermore, the longer the holding time, the higher the DSC ratio of the resulting expanded beads. This is because the amount of growth of unmelted crystals contained in the expanded beads varies depending on the holding time.

[0076] (Open cell ratio) The lower the open cell ratio of the expanded beads, the better. The open cell ratio of the expanded beads is preferably 15.0% or less, more preferably 10.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, more preferably 7.0% or less, more preferably 6.0% or less, more preferably 5.0% or less, even more preferably 4.0% or less, and particularly preferably 3.0% or less. The lower limit of the open cell ratio of the expanded beads is not particularly limited, and may be, for example, 0.0% or more. This configuration offers the advantages of (a) excellent moldability due to almost no cell rupture or shrinkage during molding, and (b) molded foams obtained using the expanded beads exhibit features such as flexible shape, cushioning, light weight, compressive strength, and thermal insulation. The open cell ratio of the expanded beads can be controlled, for example, by the amount of AS copolymer used.

[0077] In this specification, the open cell ratio of expanded beads is a value determined by measurement using an air-comparison type hydrometer (Tokyo Science Co., Ltd., Model 1000) in accordance with the method described in Procedure C of ASTM D2856-87. Specifically, the open cell ratio of expanded beads is calculated by carrying out the following steps (1) to (4) in order: (1) Using an air-comparison type hydrometer, the volume Vc (cm) of the expanded beads is measured. 3 (2) Next, the entire volume of the foamed particles after measuring Vc is submerged in the ethanol contained in the measuring cylinder; (3) After that, the apparent volume Va (cm 3 ) of the foamed particles is calculated from the amount of rise in the position of the ethanol in the measuring cylinder. 3 (4) The open cell ratio of the expanded beads is calculated using the following formula: Open cell ratio (%) = ((Va - Vc) × 100) / Va. The method for measuring the volume Va as described above is also called the submersion method.

[0078] <Method of manufacturing expanded polypropylene resin beads> The method for producing the expanded beads is not particularly limited, and known production methods can be used as appropriate. The method for producing the expanded beads preferably includes an expansion step of expanding polypropylene-based resin particles, the polypropylene-based resin particles comprising 100 parts by weight of a polypropylene-based resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units, and 3 to 30 parts by weight of a hydrogenated styrene-based copolymer. One embodiment of the method for producing the expanded beads is described in detail below, but the above descriptions (e.g., the description in the <Components> section) are incorporated by reference as appropriate for matters other than those described below. The method for producing the expanded beads is not limited to the following production method.

[0079] (granulation process) When producing the expanded beads, a step of producing polypropylene-based resin particles (granulation step) may be carried out first. In this specification, "polypropylene-based resin particles" may also be referred to as "resin particles." The granulation step can also be said to be a step of producing resin particles containing 100 parts by weight of a polypropylene-based resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units, and 3 to 30 parts by weight of a hydrogenated styrene-based copolymer.

[0080] Examples of methods for producing resin particles include methods using an extruder. Specifically, resin particles can be produced by, for example, the following methods (1) to (5): (1) blending a polypropylene resin, an AS copolymer, a hydrogenated styrene copolymer, and, if necessary, one or more selected from the group consisting of other resins and additives to produce a blend; (2) feeding the blend into an extruder and melt-kneading the blend to prepare a polypropylene resin composition; (3) extruding the polypropylene resin composition through a die provided in the extruder; (4) solidifying the extruded polypropylene resin composition by cooling it, for example, by passing it through water; (5) subsequently cutting the solidified polypropylene resin composition into a desired shape, such as a cylindrical, elliptical, spherical, cubic, or rectangular parallelepiped, using a cutter. Alternatively, the melt-kneaded polypropylene resin composition in (3) may be directly extruded through a die provided in the extruder into water, and immediately after extrusion, the polypropylene resin composition may be cut into particles, cooled, and solidified. By melt-kneading the blend in this manner, more uniform resin particles can be obtained.

[0081] The weight per particle of the resin particles obtained as described above is preferably 0.5 mg / particle to 3.0 mg / particle, more preferably 0.7 mg / particle to 2.5 mg / particle. When the weight per particle of the resin particles is 0.5 mg / particle or more, the handleability of the resin particles tends to be improved, and when it is 3.0 mg / particle or less, the mold filling property in the in-mold foam molding step tends to be improved.

[0082] The amounts of polypropylene resin, AS copolymer, hydrogenated styrene copolymer, and other resins and additives subjected to the granulation step (blended and melt-kneaded) will be the contents of each of the above components in the produced resin particles. Therefore, the granulation step preferably includes a step of blending at least 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene units, and 3 to 30 parts by weight of a hydrogenated styrene copolymer, and melt-kneading the blend.

[0083] (Foaming process) The form of the expansion step in the method for producing expanded beads of the present invention is not particularly limited as long as it can expand the resin beads. (a) a dispersing step of dispersing resin particles, an aqueous dispersion medium, a foaming agent, and optionally a dispersant and / or a dispersion aid in a container; (b) a temperature-pressure increasing step of increasing the temperature inside the container to a constant temperature and increasing the pressure inside the container to a constant pressure; (c) maintaining the temperature and pressure in the container at a constant temperature and constant pressure; (d) a discharging step of opening one end of the container and discharging the dispersion liquid in the container into a region (space) having a pressure lower than the foaming pressure (i.e., the pressure inside the container).

[0084] This process of producing expanded beads from resin beads is called the "first-stage expansion process," and the resulting expanded beads are called "first-stage expanded beads."

[0085] The amounts of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer contained in the resin particles subjected to the expansion step will be the amounts of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer in the resulting expanded beads. Therefore, the expansion step in the present method for producing expanded beads is preferably a step of expanding resin particles containing 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene units, and 3 to 30 parts by weight of a hydrogenated styrene copolymer.

[0086] (Dispersion process) The dispersion step can also be said to be a step of preparing a dispersion in which resin particles, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium.

[0087] The container used in the dispersion step is not particularly limited, but is preferably a container that can withstand the foaming temperature and foaming pressure described below. For example, the container is preferably a pressure-resistant container, and more preferably an autoclave-type pressure-resistant container.

[0088] The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse resin particles, a blowing agent, etc. Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerin, etc. to water, and (b) water such as tap water and industrial water. In order to enable stable production of expanded particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis membrane), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

[0089] The amount of the aqueous dispersion medium used is not particularly limited, but is preferably 100 to 400 parts by weight per 100 parts by weight of the resin particles. When the amount of the aqueous dispersion medium used is (a) 100 parts by weight or more, there is no risk of the stability of the dispersion liquid decreasing (in other words, the dispersion of the resin particles becomes good), and when it is (b) 400 parts by weight or less, there is no risk of the productivity of the expanded beads decreasing.

[0090] Examples of blowing agents include (a) (a-1) inorganic blowing agents such as inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents such as (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and (b-3) halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane. The blowing agent may be at least one selected from the group consisting of the inorganic and organic blowing agents described above. When two or more blowing agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose. From the viewpoints of environmental impact and foaming power, inorganic blowing agents are preferred among the above-mentioned blowing agents. Furthermore, carbon dioxide is preferred among the inorganic blowing agents because it has a moderately high plasticizing effect and is easy to improve the expandability of the expanded beads in the production of the present expanded beads.

[0091] The amount of foaming agent used is not particularly limited and may be appropriately determined depending on (a) the type of foaming agent and / or (b) the desired expansion ratio of the expanded beads. The amount of foaming agent used is, for example, preferably 1 to 10,000 parts by weight, more preferably 1 to 5,000 parts by weight, and even more preferably 1 to 1,000 parts by weight, per 100 parts by weight of resin particles. When the amount of foaming agent used is 1 part by weight or more per 100 parts by weight of resin particles, expanded beads with a suitable density can be obtained. On the other hand, when the amount of foaming agent used is 10,000 parts by weight or less per 100 parts by weight of resin particles, the effect corresponding to the amount of foaming agent used is obtained, and therefore economic waste is not generated. The amount of foaming agent used may be, for example, 1 to 100 parts by weight, or 1 to 10 parts by weight, per 100 parts by weight of resin particles.

[0092] When water is used as a blowing agent, the water in the dispersion in the container can be used as the blowing agent. Specifically, when water in the dispersion is used as the blowing agent, it is preferable to incorporate a water-absorbing material into the resin particles in advance. This makes it easier for the resin particles to absorb the water in the dispersion in the container, and as a result, it becomes easier to use water as a blowing agent.

[0093] In the present method for producing expanded beads, it is preferable to use a dispersant. The use of a dispersant has the advantage of reducing adhesion between resin particles (sometimes referred to as blocking) and enabling stable production of expanded beads. Examples of dispersants include inorganic substances such as tribasic calcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, aluminum oxide, titanium oxide, and aluminum hydroxide. One of these dispersants may be used alone, or two or more may be used in combination. When two or more dispersants are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0094] The amount of dispersant used in the dispersion liquid in one embodiment of the present invention is preferably 0.01 to 3.00 parts by weight, more preferably 0.05 to 2.00 parts by weight, and even more preferably 0.10 to 1.00 parts by weight, relative to 100 parts by weight of resin particles. When the amount of dispersant used is (a) 0.01 part by weight or more, there is no risk of insufficient dispersion of the resin particles, and (b) when it is 3.00 parts by weight or less, there is no risk of insufficient fusion of the expanded particles with each other during in-mold expansion molding using the resulting expanded particles.

[0095] In the present method for producing expanded beads, it is preferable to use a dispersing aid (a) to improve the effect of reducing adhesion between resin particles and / or (b) to increase the stability of the dispersion in the container. Examples of dispersing aids include anionic surfactants. Examples of anionic surfactants include sodium alkylbenzenesulfonates such as sodium dodecylbenzenesulfonate, sodium alkanesulfonates, sodium alkylsulfonates, sodium alkyldiphenyletherdisulfonates, and sodium α-olefinsulfonates. One of these dispersing aids may be used alone, or two or more may be used in combination. When two or more dispersing aids are used in combination, the mixing ratio may be adjusted appropriately depending on the purpose.

[0096] The amount of the dispersing aid used in the dispersion liquid used in one embodiment of the present invention is preferably 0.001 to 0.500 parts by weight, more preferably 0.001 to 0.200 parts by weight, and even more preferably 0.010 to 0.200 parts by weight, relative to 100 parts by weight of the resin particles. When the amount of the dispersing aid used is within the above range, there is no risk of poor dispersion of the resin particles.

[0097] If the stability of the dispersion liquid decreases, multiple resin particles may coalesce or form clumps in the container, which may result in (i) coalesced expanded beads, (ii) clumps of resin particles remaining in the container, making it impossible to produce expanded beads, or (iii) a decrease in productivity of expanded beads.

[0098] (Temperature-pressure increase process and holding process) The temperature-pressure increasing step is preferably carried out after the dispersion step, and the holding step is preferably carried out after the temperature-pressure increasing step. In this specification, the (a) constant temperature in the temperature-pressure increasing step and the holding step may be referred to as the foaming temperature, and the (b) constant pressure in the foaming step may be referred to as the foaming pressure.

[0099] The foaming temperature cannot be generally defined because it varies depending on the types of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, the type of blowing agent, the desired apparent density of the foamed particles, etc. The foaming temperature is preferably (i) from −20.0°C to +10.0°C of the melting point of (a) a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) a polypropylene resin composition, or (c) resin particles, more preferably (ii) from −15.0°C to +8.0°C of the melting point of (a) a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) a polypropylene resin composition, or (c) resin particles, and even more preferably (iii) from −10.0°C to +6.0°C of the melting point of (a) a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) a polypropylene resin composition, or (c) resin particles.

[0100] The expansion pressure is preferably 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and more preferably 2.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). When the expansion pressure is 1.0 MPa (gauge pressure) or more, expanded particles with a suitable density can be obtained.

[0101] In the holding step, the time (holding time) for holding the dispersion in the container at near the foaming temperature and foaming pressure is not particularly limited. The holding time is preferably 10 to 60 minutes, more preferably 12 to 55 minutes, and even more preferably 15 to 50 minutes. A holding time of 10 minutes or longer has the advantage that a sufficient amount of unmelted crystals (crystals of the polypropylene resin) are present, thereby reducing shrinkage and / or an increase in the open cell ratio of the resulting expanded beads. On the other hand, a holding time of 60 minutes or less has the advantage that an excessive amount of unmelted crystals are not present, allowing the expanded beads to be molded at a low molding temperature.

[0102] (Release process) The releasing step is preferably carried out after the temperature-pressure increasing step (a) when the holding step is not carried out, or after the holding step (b) when the holding step is carried out. The releasing step allows the resin particles to expand, resulting in expanded particles.

[0103] In the releasing step, the "region under a pressure lower than the foaming pressure" refers to a "region under a pressure lower than the foaming pressure" or a "space under a pressure lower than the foaming pressure", and can also be referred to as "an atmosphere under a pressure lower than the foaming pressure". The region under a pressure lower than the foaming pressure is not particularly limited as long as it is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure.

[0104] In the discharging step, when the dispersion is discharged into a region with a pressure lower than the expansion pressure, the dispersion can be discharged through an orifice with a diameter of 1 mm to 5 mm for the purposes of adjusting the flow rate of the dispersion, reducing variations in the expansion ratio of the resulting expanded beads, etc. Furthermore, for the purpose of improving the expandability, the low-pressure region (space) can be filled with saturated water vapor.

[0105] (2-stage foaming process) Incidentally, in order to obtain expanded beads with a high expansion ratio, there is a method (hereinafter referred to as Method 1) in which a large amount of inorganic blowing agent is used in the first-stage expansion step. Furthermore, as a method other than Method 1, a method (hereinafter referred to as Method 2) can also be employed in which expanded beads (first-stage expanded beads) with a relatively low expansion ratio (expansion ratio of about 2.0 to 35.0 times) are obtained in the first-stage expansion step, and then the obtained first-stage expanded beads are expanded again to increase the expansion ratio.

[0106] Method 2 includes, for example, the following steps (a1) to (a3), in order: (a1) producing first-stage expanded beads having an expansion ratio of 2.0 to 35.0 in a first-stage expansion step; (a2) placing the first-stage expanded beads in a pressure-resistant vessel and pressurizing them with nitrogen, air, carbon dioxide, or the like at 0.2 to 0.6 MPa (gauge pressure) to increase the pressure inside the first-stage expanded beads (hereinafter sometimes referred to as "internal pressure") above atmospheric pressure; (a3) ​​subsequently heating the first-stage expanded beads with increased internal pressure using steam or the like to further expand them. The step of increasing the expansion ratio of the first-stage expanded beads, as in Method 2, is called the "second-stage expansion step," and the polypropylene resin expanded beads obtained by Method 2 are called "second-stage expanded beads."

[0107] In the second-stage expansion step (a3), the pressure of the steam used to heat the first-stage expanded beads is preferably adjusted to 0.03 MPa (gauge pressure) to 0.20 MPa (gauge pressure), taking into consideration the expansion ratio of the second-stage expanded beads. If the steam pressure in the second-stage expansion step is 0.03 MPa (gauge pressure) or higher, the expansion ratio tends to increase, while if it is 0.20 MPa (gauge pressure) or lower, the resulting second-stage expanded beads are less likely to coalesce. If the second-stage expanded beads coalesce, the resulting second-stage expanded beads may not be able to be used in the subsequent in-mold expansion molding.

[0108] The internal pressure of the first-stage expanded beads obtained by impregnating the first-stage expanded beads with nitrogen, air, carbon dioxide, or the like is desirably adjusted in consideration of the expansion ratio of the second-stage expanded beads and the steam pressure during the second-stage expansion process. The internal pressure of the first-stage expanded beads is preferably 0.15 MPa (absolute pressure) to 0.60 MPa (absolute pressure), more preferably 0.20 MPa (absolute pressure) to 0.60 MPa (absolute pressure), and even more preferably 0.30 MPa (absolute pressure) to 0.60 MPa (absolute pressure). When the internal pressure of the first-stage expanded beads is 0.15 MPa (absolute pressure) or higher, high-pressure steam is not required to increase the expansion ratio, reducing the likelihood of the second-stage expanded beads coalescing. When the internal pressure of the first-stage expanded beads is 0.60 MPa (absolute pressure) or lower, the second-stage expanded beads are less likely to form open cells. As a result, the rigidity, such as the compressive strength, of the final in-mold foamed article is less likely to decrease. Note that "open cell formation" can also be referred to as "interconnection of cells."

[0109] [2. Polypropylene resin foam molding] A polypropylene-based resin foam molded article according to one embodiment of the present invention is a foam molded article obtained by molding the expanded polypropylene-based resin beads described in the section [1. Expanded Polypropylene-Based Resin Beads]. It can also be said that the expanded polypropylene-based resin foam molded article according to one embodiment of the present invention contains the expanded polypropylene-based resin beads described in the section [1. Expanded Polypropylene-Based Resin Beads]. The expanded molded article can also be said to be a foam molded article obtained by molding the expanded polypropylene-based resin beads obtained by the expanded bead manufacturing method (for example, the manufacturing method described in the section <Manufacturing Method of Expanded Polypropylene-Based Resin Beads>), or a foam molded article containing the expanded polypropylene-based resin beads obtained by the expanded bead manufacturing method. The expanded molded article can also be said to be a foam molded article obtained by molding the expanded beads described in the section [1. Expanded Polypropylene-Based Resin Beads], or a foam molded article containing the expanded beads.

[0110] In this specification, the "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as the "present foam molded article."

[0111] The foamed molded article has the above-mentioned structure and therefore has the advantage of being almost free from shrinkage and deformation after molding.

[0112] (shrinkage rate) In this specification, the phrase "almost no shrinkage after molding" in relation to a foam molded article means that the shrinkage rate is small as determined by the following methods (1) to (3): (1) Using a mold with known dimensions (e.g., 369 mm in the longitudinal direction × 319 mm in the lateral direction × 50 mm in the thickness direction), the foam beads are foam-molded in-mold. Here, the longitudinal length of the mold is designated as L0; (2) The longitudinal length of the resulting foam molded article, L1, is measured; and (3) The shrinkage rate (%) is calculated according to the following formula: Shrinkage rate (%) = ((L1-L0) x 100) / L0.

[0113] The present foamed molded article preferably has a shrinkage rate of 1.2% or less, more preferably 1.0% or less, even more preferably 0.8% or less, and particularly preferably 0.6% or less. A foamed molded article with a shrinkage rate of 1.2% or less is said to have good dimensional stability, meaning that the foamed molded article obtained by production is less likely to have dimensional variation. The foamed beads capable of providing a foamed molded article with good dimensional stability, and the foamed molded article, have the advantage that they can be suitably used in the field of insert molding, in which the foamed molded article is integrally molded with other materials such as metal.

[0114] (deformation amount) The deformation amount of this foam molded article will be described below with reference to FIG. 1. FIG. 1 is a schematic diagram of a foam molded article 100 used to evaluate the deformation amount. The foam molded article 100 was produced using a mold (longitudinal direction 350 mm × lateral direction 320 mm × thickness direction (driving direction of the movable mold) 180 mm) with a partition plate in the center of the mold. In FIG. 1, the X direction can be referred to as the thickness direction of the foam molded article 100 or the driving direction of the movable mold. The Y direction can be referred to as the longitudinal direction of the foam molded article 100 and is a direction perpendicular to the X direction. The Z direction can be referred to as the lateral direction of the foam molded article 100 and is a direction perpendicular to both the X direction and the Y direction. As shown in FIG. 1, the Z direction dimensions (lengths) of the two longitudinal end portions of the foam molded article 100 are designated K1 and K2, respectively, and the Z direction dimension of the longitudinal center portion is designated K3.

[0115] In this specification, the phrase "almost no deformation" in relation to a foam molded product means that the amount of deformation is small as determined by measurements using the following methods (1) to (3): (1) foaming the foamed beads in a mold having dimensions (lengths) of 350 mm in the longitudinal direction (Y direction), 320 mm in the transverse direction (Z direction), and 180 mm in the thickness direction (X direction) and having a partition plate in the center of the mold; (2) measuring the Z-direction dimensions (mm) (K1, K2) of the two longitudinal end portions of the obtained foam molded product (foam molded product 100) and the Z-direction dimension (mm) (K3) of the longitudinal center portion; (3) calculating the amount of deformation according to the following formula: Deformation (mm) = {(K1 + K2) / 2} - K3.

[0116] The amount of deformation of the foamed molded article is preferably 14.0 mm or less, more preferably 13.0 mm or less, more preferably 12.0 mm or less, more preferably 11.0 mm or less, more preferably 10.0 mm or less, more preferably 9.0 mm or less, more preferably 8.0 mm or less, more preferably 7.0 mm or less, even more preferably 6.0 mm or less, and particularly preferably 5.0 mm or less. A foamed molded article having an amount of deformation of 14.0 mm or less is said to have good dimensional stability, which is intended to reduce dimensional variation in the foamed molded article obtained by production.

[0117] <Method of manufacturing foam molded article> The method for producing the present foamed molded article is not particularly limited, and known methods can be applied. The method for producing the present foamed molded article preferably includes a step of in-mold foaming of the present foamed beads described in the above section [1. Expanded Polypropylene Resin Beads] or the expanded beads obtained by the production method described in the above section <Production Method of Expanded Polypropylene Resin Beads>. Specific embodiments of the method for producing the present foamed molded article include, for example, a production method (in-mold foaming method) that includes the following steps (b1) to (b6) in order, but is not limited to such a production method: (b1) A mold consisting of a fixed mold that cannot be driven and a movable mold that can be driven is mounted on an in-mold foam molding machine. Here, the fixed mold and the movable mold can be formed inside the fixed mold and the movable mold by driving the movable mold toward the fixed mold (this operation may be referred to as "mold closing"); (b2) The movable mold is driven toward the fixed mold so that a small gap (also called cracking) is formed between the fixed mold and the movable mold so that they are not completely closed; (b3) Filling the molding space formed inside the fixed mold and the movable mold with foam particles, for example, through a filling machine; (b4) driving the movable mold so that the fixed mold and the movable mold are completely closed (i.e., completely closing the molds); (b5) After preheating the mold with steam, the mold is heated on one side and on the other side with steam, and then heated on both sides with steam to perform in-mold foam molding; (b6) The in-mold foamed product is removed from the mold and dried (for example, at 75°C) to obtain a foamed molded product.

[0118] In the above (b3), the following methods (b3-1) to (b3-4) can be mentioned as methods for filling the molded space with the expanded beads: (b3-1) A method in which expanded beads (including the above-mentioned two-stage expanded beads, the same applies hereinafter) are pressurized with an inorganic gas in a container to impregnate the expanded beads with the inorganic gas, and then a predetermined internal pressure is applied to the expanded beads, and the expanded beads are then filled into a molding space; (b3-2) A method in which the foamed particles are filled into a molding space and then compressed to reduce the volume within the mold by 10% to 75%; (b3-3) A method of compressing foam particles with gas pressure to fill the molding space; (b3-4) A method of filling foamed particles into a molding space without any special pretreatment.

[0119] In the method (b3-1) for producing a foamed molded article, the inorganic gas that can be used is at least one selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc. Among these inorganic gases, air and / or carbon dioxide are preferred.

[0120] Among the methods for producing the foamed molded article, the internal pressure of the foamed particles in the (b3-1) method is preferably 0.10 MPa (absolute pressure) to 0.30 MPa (absolute pressure), and more preferably 0.11 MPa (absolute pressure) to 0.25 MPa (absolute pressure).

[0121] In the method (b3-1) for producing a foamed molded article, the temperature inside the vessel when the inorganic gas is impregnated into the foamed particles is preferably 10 to 90°C, more preferably 40 to 90°C.

[0122] In the above methods (b3-2) and (b3-3), in the subsequent step (b5), the recovery force of the expanded beads compressed by gas pressure is utilized to fuse the expanded beads.

[0123] An embodiment of the present invention may have the following configuration.

[0124] [1] Expanded polypropylene resin particles comprising 100 parts by weight of a polypropylene resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

[0125] [2] The expanded polypropylene resin particles according to [1], wherein the styrene unit is an α-methylstyrene unit.

[0126] [3] The expanded polypropylene resin particles according to [1] or [2], wherein the hydrogenated styrene copolymer is a styrene / ethylene / butylene / styrene copolymer (SEBS).

[0127] [4] The expanded polypropylene resin particles according to any one of [1] to [3], wherein the styrene unit content of the hydrogenated styrene copolymer is 15% by weight to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

[0128] [5] The expanded polypropylene resin particles according to any one of [1] to [4], wherein the copolymer containing acrylonitrile units and styrene units has a glass transition temperature of 95°C to 140°C.

[0129] [6] A polypropylene resin foam molded article obtained by molding the expanded polypropylene resin beads according to any one of [1] to [5].

[0130] [7] A method for producing expanded polypropylene-based resin particles, comprising an expansion step of expanding polypropylene-based resin particles, wherein the polypropylene-based resin particles contain 100 parts by weight of a polypropylene-based resin, 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units, and 3.0 to 30.0 parts by weight of a hydrogenated styrene-based copolymer.

[0131] [8] The method for producing expanded polypropylene resin beads according to [7], wherein the styrene unit is an α-methylstyrene unit.

[0132] [9] The method for producing expanded polypropylene resin beads according to [7] or [8], wherein the hydrogenated styrene copolymer is a styrene / ethylene / butylene / styrene copolymer (SEBS).

[0133]

[10] The method for producing expanded polypropylene resin particles according to any one of [7] to [9], wherein the styrene unit content of the hydrogenated styrene copolymer is 15% by weight to 80% by weight based on 100% by weight of the hydrogenated styrene copolymer.

[0134]

[11] The method for producing expanded polypropylene resin beads according to any one of [7] to

[10] , wherein the copolymer containing acrylonitrile units and styrene units has a glass transition temperature of 95°C to 140°C.

[0135]

[12] A method for producing a polypropylene resin foam molded article, comprising a step of molding the expanded polypropylene resin beads according to any one of [1] to [5] or the expanded polypropylene resin beads obtained by the method according to any one of [7] to

[11] . [Example]

[0136] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0137] 〔material〕 The materials used in the examples and comparative examples will be described below.

[0138] <Resin component> (Polypropylene resin) Polypropylene resin: 1-butene / ethylene / propylene random copolymer [melting point 149°C, 1-butene content 3.8% by weight, ethylene content 0.5% by weight, MFR = 10g / 10min] (AS copolymer) AS copolymer 1: acrylonitrile / α-methylstyrene copolymer [Tg 121°C, α-methylstyrene content 70% by weight (styrene content 70% by weight), MFR = 4.9 g / 10 min] AS copolymer 2: acrylonitrile / styrene copolymer [Tg 108°C, styrene content 75% by weight (styrene content 75% by weight), MFR = 6.1 g / 10 min] AS copolymer 3: acrylonitrile / styrene copolymer [Tg 115°C, styrene content 50% by weight (styrene content 50% by weight), MFR = 8.1 g / 10 min] (hydrogenated styrene copolymer) Hydrogenated styrene copolymer 1: SEBS (styrene / ethylene / butylene / styrene copolymer, JSR Dynaron 9901P) [styrene content 53%] Hydrogenated styrene copolymer 2: SEBS (styrene / ethylene / butylene / styrene copolymer, JSR Dynaron 8300P) [styrene content 9%] (Other resins) (amorphous resin) Amorphous resin 1: Polystyrene [Tg 101°C, MFR = 7.0] Amorphous resin 2: A mixture of polyphenylene ether and polystyrene [Tg 120°C, MFR = 1.8 g / 10 min] (Compatibilizer) Compatibilizer: Polypropylene / (acrylonitrile / styrene) graft copolymer [main chain: polypropylene, side chain: acrylonitrile / styrene copolymer, polypropylene: acrylonitrile / styrene copolymer = 70 (mol%): 30 (mol%)] (NOF Corporation, Modiper A3400) <Additives> (water-absorbing substance) Glycerin (Lion Corporation, refined glycerin D) (foam nucleating agent) Talc (Talc Powder (registered trademark) PK-S, manufactured by Hayashi Kasei Co., Ltd.) [Measurement method] Measurement and evaluation of various items were carried out as follows.

[0139] (Melting point of polypropylene resin) The melting point of the polypropylene resin was determined by measurement using a DSC method using a differential scanning calorimeter (manufactured by Seiko Instruments Inc., DSC6200 model). The specific operating procedures were as follows (1) to (4): (1) The temperature of 5 mg to 6 mg of polypropylene resin was raised from 40.0°C to 220.0°C at a heating rate of 10.0°C / min to melt the polypropylene resin; (2) The temperature of the molten polypropylene resin was then lowered from 220.0°C to 40.0°C at a heating rate of 10.0°C / min to crystallize the polypropylene resin; (3) The temperature of the crystallized polypropylene resin was then raised from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (4) The temperature of the peak (melting peak) of the DSC curve of the polypropylene resin obtained during the second heating (i.e., during (3)) was determined as the melting point of the polypropylene resin. In addition, when there are multiple peaks (melting peaks) in the DSC curve of the polypropylene-based resin obtained during the second heating by the above-mentioned method, the temperature of the peak (melting peak) with the largest heat of fusion was taken as the melting point of the polypropylene-based resin.

[0140] (Glass transition temperature (Tg) of AS copolymer) The glass transition temperature (Tg) of the AS copolymer was measured using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200) in accordance with JIS-K-7121 by the following methods (1) to (5): (1) 5 mg of the AS copolymer was weighed out; (2) Under a nitrogen atmosphere, the temperature of the AS copolymer was increased from room temperature to 250°C at 10°C / min; (3) The temperature of the increased AS copolymer was decreased from 250°C to room temperature at 10°C / min; (4) The temperature of the AS copolymer was again increased from room temperature to 250°C at 10°C / min; (5) The temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained during the second temperature increase (i.e., during (4)) was determined as the Tg of the AS copolymer.

[0141] (MFR of polypropylene resin and AS copolymer) The MFR of the polypropylene resin or AS copolymer was measured using an MFR measuring device specified in JIS K7210:1999 under the following conditions: orifice diameter 2.0959±0.005 mmφ, orifice length 8.000±0.025 mm, load 2.16 kgf, and temperature 230°C (230±0.2°C).

[0142] (Expansion ratio of expanded beads (first-stage expanded beads, second-stage expanded beads)) The expansion ratio of the expanded beads was measured as follows (1) to (6): (1) The weight Gi of a certain amount of expanded beads (first-stage expanded beads or second-stage expanded beads) was measured accurately to the nearest 0.001 g (rounded to the fourth decimal point); (2) Next, the entire amount of expanded beads used for measuring the weight Gi was immersed in 100 mL of water at 23°C contained in a measuring cylinder; (3) The volume yi (cm) of the expanded beads was calculated based on the rise in the liquid level of the measuring cylinder. 3 (4) The weight Gi (g) of the expanded beads was calculated based on the volume yi (cm 3) and converted to g / L to calculate the apparent density di (g / L) of the expanded beads; (5) The density ds (g / L) of the resin beads was calculated by carrying out the same procedures as in (1) to (4) except that the resin beads used in the production of the expanded beads were used instead of the expanded beads; (6) The expansion ratio of the expanded beads was calculated by the following formula: Expansion ratio Ki=ds / di.

[0143] (foaming) The expandability of the expanded beads was evaluated based on the expansion ratio of the first-stage expanded beads obtained by performing the first-stage expansion process under the same conditions. The evaluation criteria were as follows: ◯ (Good): The expansion ratio of the first-stage expanded particles is 15.0 times or more. × (bad): The expansion ratio of the first-stage expanded beads is less than 15.0 times.

[0144] The expansion ratio of expanded beads is affected by the DSC ratio of the expanded beads. For example, when expanded beads are produced by adjusting the expansion temperature, etc. so that the DSC ratio of the expanded beads is low, expanded beads with a high expansion ratio tend to be obtained. Therefore, when comparing the expansion ratios of different expanded beads, it is necessary to compare the expansion ratios while taking into account the influence of the DSC ratio of the expanded beads. In other words, when comparing the expansion ratios of different expanded beads, the expansion ratios of the expanded beads can be compared relatively accurately by producing expanded beads so that the DSC ratios are similar.

[0145] (DSC ratio of expanded particles) A differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.) was used to measure (calculate) the DSC ratio of the expanded beads. The method for measuring (calculating) the DSC ratio of the expanded beads using the differential scanning calorimeter was as follows (1) to (5): (1) 5 mg to 6 mg of expanded beads were weighed; (2) the temperature of the expanded beads was increased from 40°C to 220°C at a heating rate of 10°C / min to melt the expanded beads; (3) in the DSC curve of the expanded beads obtained in the process (2), (a) a line was drawn connecting the maximum point between the highest melting peak and the melting peak adjacent to that (on the lower temperature side) and the point representing the temperature before the start of melting, and (b) a line was drawn connecting the maximum point and the point representing the temperature after the end of melting. and (4) (a) (a-1) the line segment connecting the maximum point and the point representing the temperature after the end of melting, (a-2) the DSC curve, and the calorific value calculated from the high-temperature region surrounded by (a-1) the line segment connecting the maximum point and the point representing the temperature before the start of melting, (b-2) the DSC curve, and the calorific value calculated from the low-temperature region surrounded by (b ... DSC ratio (%) = (high temperature heat of fusion / total heat of fusion) × 100.

[0146] (Open cell ratio of expanded beads) The open cell ratio of the expanded polypropylene resin beads was measured using an air-comparison type hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. More specifically, the open cell ratio of the expanded beads was calculated by carrying out the following steps (1) to (4) in order: (1) Using the air-comparison type hydrometer, the volume Vc (cm) of the expanded beads was measured. 3 (2) Then, the entire volume of the expanded particles after measuring Vc was submerged in ethanol contained in a measuring cylinder; (3) After that, the apparent volume Va (cm 3 ) of the expanded particles was calculated from the amount of rise in the position of the ethanol in the measuring cylinder. 3 (4) The open cell ratio of the expanded beads was calculated using the following formula: Open cell rate (%) = ((Va - Vc) × 100) / Va.

[0147] (Shrinkage rate of foam molded product) The shrinkage rate of the foamed molded article was measured as follows (1) to (3): (1) Using a mold with known dimensions (for example, 369 mm in the longitudinal direction × 319 mm in the transverse direction × 50 mm in the thickness direction), the foamed beads were foam-molded in the mold. The longitudinal length of the mold was designated as L0; (2) The longitudinal length L1 of the resulting foamed molded article was measured; (3) The shrinkage rate (%) was calculated according to the following formula: Shrinkage rate (%) = ((L1-L0) x 100) / L0 The mold used to measure the shrinkage rate may be referred to as a mold for evaluating the shrinkage rate.

[0148] (Deformation amount of foam molded body) The deformation amount of the foam molded article was measured by the following methods (1) to (3): (1) The foam beads were foam-molded in a mold having dimensions (lengths) of 350 mm in the longitudinal direction (Y direction), 320 mm in the transverse direction (Z direction), and 180 mm in the thickness direction (X direction), and having a partition plate in the center of the mold; (2) The Z-direction dimensions (mm) (K1, K2) of the two longitudinal end portions of the obtained foam molded article (foam molded article 100) and the Z-direction dimension (mm) (K3) of the longitudinal center portion were measured; (3) The deformation amount was calculated according to the following formula: Deformation (mm) = {(K1 + K2) / 2} - K3. The mold used to measure the amount of deformation may be referred to as a mold for evaluating the amount of deformation.

[0149] Example 1 (Preparation of polypropylene resin particles) 100 parts by weight (10 kg) of polypropylene resin, 12 parts by weight (1.2 kg) of AS copolymer 1, 7.0 parts by weight (700 g) of hydrogenated styrene copolymer 1, 0.050 parts by weight (5 g) of talc as a foam nucleating agent, and 0.2 parts by weight (20 g) of glycerin as a water-absorbing material were dry-blended.

[0150] The resulting blend was placed in a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26-SX) and melt-kneaded at a resin temperature of 250°C. The melt-kneaded polypropylene resin composition was extruded into strands through a die with circular holes attached to the tip of the extruder. The extruded polypropylene resin composition was cooled with water and then cut with a cutter to obtain cylindrical resin particles (1.2 mg / particle).

[0151] (Preparation of polypropylene resin expanded beads (first-stage expanded beads)) 100 parts by weight of the resulting resin particles, 200 parts by weight of pure water, 0.2 parts by weight of kaolin (ASP-170 manufactured by Engelhard) as a water-insoluble inorganic compound, and 0.03 parts by weight of sodium dodecylbenzenesulfonate as a surfactant were placed in a pressure-resistant sealed container. Then, while stirring the ingredients in the pressure-resistant sealed container, 6.7 parts by weight of carbon dioxide as a blowing agent was introduced into the pressure-resistant sealed container to prepare a dispersion. The temperature inside the pressure-resistant sealed container was then heated to a foaming temperature of 151.0°C. Additional carbon dioxide was then injected into the pressure-resistant sealed container, and the pressure inside the pressure-resistant sealed container was increased to a foaming pressure of 3.2 MPa (gauge pressure) (temperature-pressure increase step). The pressure-resistant sealed container was then maintained at the foaming temperature and foaming pressure for 30 minutes (holding step), after which the valve at the bottom of the sealed container was opened, and the dispersion was released into an expansion tube at atmospheric pressure through a 3.6 mm orifice to obtain expanded particles (first-stage expanded particles). During this process, to prevent the pressure in the pressure-resistant sealed container from dropping below the foaming pressure while the dispersion was being released, additional carbon dioxide was injected into the pressure-resistant sealed container to maintain the pressure in the container at 3.2 MPa (gauge pressure). The expansion ratio, expandability, DSC ratio, and open cell ratio of the resulting expanded beads were measured, and the results are shown in Table 1.

[0152] (Production of polypropylene resin expanded beads (two-stage expanded beads)) The obtained first-stage expanded beads were dried at 60°C for 6 hours and then placed in a pressure-resistant sealed container. Air was introduced into the pressure-resistant sealed container, and the first-stage expanded beads in the pressure-resistant sealed container were impregnated with pressurized air, applying an internal pressure (absolute pressure) of 0.24 MPa (absolute pressure) to the first-stage expanded beads. Approximately 20 L of the air-impregnated first-stage expanded beads (to which internal pressure was applied) were placed in an expansion machine. Next, the first-stage expanded beads in the expansion machine were heated with steam at 0.06 MPa (gauge pressure) for 30 seconds, thereby further expanding the first-stage expanded beads (second-stage expansion), and expanded beads (second-stage expanded beads) were obtained.

[0153] (Production of polypropylene resin foam molded body) The resulting foamed beads (second-stage foamed beads) were placed in a pressure-resistant sealed container. Air was introduced into the pressure-resistant sealed container, impregnating the second-stage foamed beads in the container with pressurized air, applying an internal pressure (absolute pressure) of 0.20 MPa (absolute pressure) to the second-stage foamed beads. The air-impregnated second-stage foamed beads were heated and molded with steam at 0.30 MPa (gauge pressure) using a molding machine (a polypropylene in-mold foam molding machine manufactured by Daisen Co., Ltd.) and a mold for evaluating shrinkage and deformation to obtain foamed molded articles. Each foamed molded article was left at room temperature for 1 hour, then cured and dried in a constant-temperature chamber at 75°C for 12 hours, and then left at room temperature for another 4 hours. The shrinkage and deformation of the resulting foamed molded articles were then evaluated using the methods described above. The results are shown in Table 1.

[0154] (Examples 2 to 7, Comparative Examples 1 to 9) Expanded beads and foamed molded articles were obtained in the same manner as in Example 1, except that the type and amount of each material and / or the production conditions were changed as shown in Table 1. The physical properties of the resulting expanded beads and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0155] [Table 1] There is no significant difference in the DSC ratios of the expanded beads between Examples and Comparative Examples, so the expansion ratios of the expanded beads can be compared relatively accurately between Examples and Comparative Examples.

[0156] 〔summary〕 From Table 1, it is clear that: (1) A comparison of Examples 1 to 7 with Comparative Example 1 reveals that when only a polypropylene-based resin is used alone, the amount of deformation of the foam-molded article is large, and the reduction in shrinkage of the foam-molded article is insufficient.

[0157] (2) A comparison of Examples 1 to 7 with Comparative Example 2 reveals that when polystyrene, an amorphous resin, is used instead of AS copolymer, the expandability of the expanded beads is low.

[0158] (3) A comparison of Examples 1 to 7 with Comparative Example 3 reveals that when a mixture of polyphenylene ether and polystyrene was used as the amorphous resin instead of AS copolymer, the expandability of the expanded beads was low and the shrinkage of the resulting foamed molded article was insufficient.

[0159] (4) Comparison of Examples 1 to 7 with Comparative Example 4 reveals that when the amount of AS copolymer used is greater than the range of the present invention, the expandability and open cell ratio of the expanded beads become poor (low).

[0160] (5) A comparison of Examples 1 to 7 with Comparative Example 5 reveals that when no hydrogenated styrene copolymer was used, the shrinkage of the resulting foamed molded article was insufficiently reduced.

[0161] (6) A comparison of Examples 1 to 7 with Comparative Example 6 reveals that when the amount of hydrogenated styrene copolymer used is greater than the range of the present application, the expandability of the expanded beads is low and the reduction in shrinkage of the resulting foamed molded article is insufficient.

[0162] (7) A comparison of Examples 1 to 7 with Comparative Example 7 reveals that when a non-hydrogenated styrene copolymer is used instead of a hydrogenated styrene copolymer, the shrinkage of the resulting foamed molded article is not sufficiently reduced.

[0163] (8) Comparison of Examples 1 to 7 with Comparative Example 8 reveals that when the amount of AS copolymer used is less than the range of the present invention, the shrinkage of the resulting foamed molded article is insufficiently reduced.

[0164] (9) Comparison of Examples 1 to 7 with Comparative Example 9 reveals that when the amount of hydrogenated styrene copolymer used is less than the range of the present invention, the shrinkage of the resulting foamed molded article is insufficiently reduced. [Industrial Applicability]

[0165] The expanded polypropylene resin particles according to one embodiment of the present invention can provide a polypropylene resin foamed molded article that has excellent expandability and is almost free from shrinkage and deformation after molding. The expanded polypropylene resin foamed molded article can be suitably used for various applications such as cushioning packaging materials, logistics materials, heat insulating materials, civil engineering and construction materials, and automotive parts.

Claims

1. 100 parts by weight of polypropylene resin; 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units; and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer.

2. The expanded polypropylene resin particles according to claim 1, wherein the styrene unit is an α-methylstyrene unit.

3. The expanded polypropylene resin particles according to claim 1 or 2, wherein the hydrogenated styrene copolymer is a styrene / ethylene / butylene / styrene copolymer (SEBS).

4. The expanded polypropylene resin particles according to any one of claims 1 to 3, wherein the styrene unit content of the hydrogenated styrene copolymer is 15% by weight to 80% by weight, based on 100% by weight of the hydrogenated styrene copolymer.

5. The expanded polypropylene resin particles according to any one of claims 1 to 4, wherein the copolymer containing acrylonitrile units and styrene units has a glass transition temperature of 95°C to 140°C.

6. A polypropylene resin foam molded article obtained by molding the expanded polypropylene resin beads according to any one of claims 1 to 5.

7. The method includes a foaming step of foaming polypropylene-based resin particles, The polypropylene resin particles are 100 parts by weight of polypropylene resin; 5 to 60 parts by weight of a copolymer containing acrylonitrile units and styrene-based units; and 3 to 30 parts by weight of a hydrogenated styrene copolymer.

8. The method for producing expanded polypropylene resin beads according to claim 7, wherein the styrene unit is an α-methylstyrene unit.

9. 9. The method for producing expanded polypropylene resin beads according to claim 7, wherein the hydrogenated styrene copolymer is a styrene / ethylene / butylene / styrene copolymer (SEBS).

10. The method for producing expanded polypropylene resin beads according to any one of claims 7 to 9, wherein the styrene unit content of the hydrogenated styrene copolymer is 15% by weight to 80% by weight, based on 100% by weight of the hydrogenated styrene copolymer.

11. The method for producing expanded polypropylene resin beads according to any one of claims 7 to 10, wherein the copolymer containing acrylonitrile units and styrene units has a glass transition temperature of 95°C to 140°C.

12. A method for producing a polypropylene-based resin foamed article, comprising a step of in-mold foaming of the expanded polypropylene-based resin beads according to any one of claims 1 to 5 or the expanded polypropylene-based resin beads obtained by the method for producing expanded polypropylene-based resin beads according to any one of claims 7 to 11.

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