Polypropylene resin foamed granules and polypropylene resin foamed molded bodies

Abstract

The objective is to (a) provide polypropylene resin foamed molded articles that exhibit almost no shrinkage or deformation after molding, and (b) provide polypropylene resin foamed granules with excellent foaming properties. A polypropylene resin foamed granule comprises specific amounts of polypropylene resin, a copolymer comprising acrylonitrile units and styrene units, and a hydrogenated styrene copolymer.

Description

Technical Field

[0001] This invention relates to polypropylene resin foamed granules and polypropylene resin foamed molded articles. Background Technology

[0002] Polypropylene resin foamed molded parts are used in a variety of applications, including automotive interior components, core materials for automotive bumpers, thermal insulation materials, cushioning packaging materials, and shipping containers.

[0003] However, because polypropylene resins are crystalline thermoplastic resins, compared to non-crystalline thermoplastic resins such as polystyrene, polypropylene resin foamed molded bodies obtained by molding polypropylene resin foam granules exhibit greater shrinkage after molding. Therefore, especially in cases where other raw materials such as metal are integrally molded (embedded molding), the metal component may deform after molding due to the shrinkage of the polypropylene resin foamed molded body. In other words, in the prior art, when other raw materials such as metal are integrally molded, it is difficult to control the size and / or shape of the polypropylene resin foamed molded body.

[0004] As a method for controlling the shrinkage of polypropylene resin foamed molded articles after molding, a method of mixing an amorphous thermoplastic resin into a polypropylene resin is known.

[0005] For example, Patent Document 1 discloses a technique for using a mixture of polypropylene resin, amorphous thermoplastic resin and compatibilizer.

[0006] Patent document 2 discloses a technique for mixing polystyrene resin and a polymer mainly composed of vinyl aromatic compounds into a polypropylene resin.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Publication No. 2001-302837

[0010] Patent Document 2: Japanese Patent Publication No. Hei 6-100740 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] In view of the above, an object of one embodiment of the present invention is to (a) provide polypropylene resin foamed molded articles that have almost no shrinkage and deformation after molding, and (b) provide polypropylene resin foamed particles with excellent foaming properties.

[0013] Solution for solving the problem

[0014] The inventors conducted in-depth research to solve the aforementioned problems, and as a result, completed this invention.

[0015] That is, the polypropylene resin foamed particles according to one embodiment of the present invention comprise: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of hydrogenated styrene copolymer.

[0016] In addition, one embodiment of the present invention describes a method for manufacturing polypropylene resin foamed particles, which includes a foaming step for foaming polypropylene resin particles. The aforementioned polypropylene resin particles comprise: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of hydrogenated styrene copolymer.

[0017] The effects of the invention

[0018] According to one embodiment of the present invention, it achieves the effects of (a) providing polypropylene resin foamed molded articles that have almost no shrinkage and deformation after molding, and (b) providing polypropylene resin foamed particles with excellent foaming properties. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a foamed molded body 100 used to evaluate the amount of deformation. Detailed Implementation

[0020] The following description describes one embodiment of the present invention, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications can be made within the scope shown in the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included within the technical scope of the present invention. Moreover, by combining the technical means disclosed in each embodiment, new technical features can be formed. It should be noted that all academic and patent documents described in this specification are incorporated herein by reference. Additionally, in this specification, unless otherwise specified, "A~B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

[0021] In addition, unless otherwise specified, this specification will also include information from X. 1 The structural unit of a single entity, originating from X 2 The structural unit of a single entity… and X n A copolymer in which monomers (n is an integer greater than or equal to 2) serve as structural units is called "X". 1 / X 2 / … / Xn "Copolymer". As X 1 / X 2 / … / X n Unless otherwise specified, copolymers are not particularly limited by polymerization method and can be random copolymers, block copolymers, or graft copolymers.

[0022] Additionally, in this specification, structural units derived from monomer X contained in polymers or copolymers are sometimes referred to as "unit X".

[0023] [1. Polypropylene resin foamed granules]

[0024] The polypropylene resin foamed particles according to one embodiment of the present invention comprise: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of hydrogenated styrene copolymer.

[0025] According to one embodiment of the present invention, polypropylene resin foamed particles can be molded using a known method to provide polypropylene resin foamed molded articles.

[0026] In this specification, "polypropylene resin foamed particles" are sometimes referred to as "foamed particles", "polypropylene resin foamed particles according to one embodiment of the present invention" are sometimes referred to as "the foamed particles", and "polypropylene resin foamed molded body" is sometimes referred to as "foamed molded body".

[0027] The polypropylene resin foamed granules according to one embodiment of the present invention have the following advantages due to the aforementioned structure: (a) they can provide polypropylene resin foamed molded articles that exhibit almost no shrinkage and deformation after molding; and (b) they have excellent foaming properties. It can also be said that the polypropylene resin foamed granules according to one embodiment of the present invention can provide polypropylene resin foamed molded articles with reduced shrinkage and deformation after molding compared to existing articles. In this specification, the reduced shrinkage of the molded foamed article is also referred to as excellent shrinkage properties.

[0028] In this specification, polypropylene resin refers to a resin in which at least 75 mol% of 100 mol% of all structural units contained in the resin are derived from propylene monomers. In this specification, "structural units derived from propylene monomers" are sometimes referred to as "propylene units".

[0029] (Polypropylene resin)

[0030] The polypropylene resin can be (a) a homopolymer of propylene, or (b) a block copolymer, random copolymer or graft copolymer of propylene and monomers other than propylene, or (c) a mixture of two or more of these.

[0031] Polypropylene resins can have one or more structural units derived from monomers other than propylene monomers, in addition to propylene units. They can also have one or more structural units derived from monomers other than propylene monomers. Sometimes, the monomers other than propylene monomers used to manufacture polypropylene resins are called "comonomers." Sometimes, the structural units derived from monomers other than propylene monomers contained in polypropylene resins are called "comonomer units."

[0032] Examples of comonomers include α-olefins with 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.

[0033] 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 / vinyl chloride copolymers, propylene / maleic anhydride copolymers, and styrene-modified polypropylene-based resins. One of these polypropylene-based resins can be used alone, or two or more can be used in combination. Among these, ethylene / propylene random copolymers and 1-butene / ethylene / propylene random copolymers are suitable from the viewpoints of good foaming properties of the resulting foamed particles and good moldability of the molded body. It should be noted that the terms 1-butene and butene-1 are synonymous.

[0034] As a polypropylene resin, the use of ethylene / propylene random copolymers or 1-butene / ethylene / propylene random copolymers is considered (denoted as Case A). In Case A, the ethylene content in the ethylene / propylene random copolymer or 1-butene / ethylene / propylene random copolymer is preferably 0.2% to 10.0% by weight per 100% of each copolymer. The ethylene content refers to the content of structural units (ethylene units) derived from ethylene. When the ethylene unit content in the ethylene / propylene random copolymer or 1-butene / ethylene / propylene random copolymer is (i) 0.2% by weight or more, there is a tendency for the foaming properties of the foamed particles and / or the moldability of the resulting foamed particles to become better when manufacturing the foamed particles, and (ii) 10.0% by weight or less, there is no concern about a decrease in the mechanical properties of the foamed molded articles obtained from the foamed particles.

[0035] Furthermore, in case A, the 1-butene content in the 1-butene / ethylene / propylene random copolymer is preferably 0.2% to 10.0% by weight in 100% by weight of the copolymer. The 1-butene content refers to the content of structural units derived from 1-butene (1-butene units). When the 1-butene unit content in the 1-butene / ethylene / propylene random copolymer is (i) 0.2% by weight or more, there is a tendency for the foaming properties of the foamed particles and / or the formability of the resulting foamed particles to become better when manufacturing the foamed particles, and (ii) 10.0% by weight or less, there is no concern about a decrease in the mechanical properties of the foamed molded articles obtained from the foamed particles.

[0036] Furthermore, 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 in 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, there is a tendency for the foaming properties of the foamed particles and / or the formability of the resulting foamed particles to become better when manufacturing the foamed particles, and (ii) 10.0% by weight or less, there is no concern about a decrease in the mechanical properties of the foamed molded articles obtained from the foamed particles.

[0037] The melting point of the polypropylene resin is preferably 135.0℃ to 160.0℃, more preferably 138.0℃ to 158.0℃, even more preferably 140.0℃ to 156.0℃, even more preferably 143.0℃ to 154.0℃, further preferably 145.0℃ to 152.0℃, and particularly preferably 148.0℃ to 150.0℃. When the melting point of the polypropylene resin is (i) 135.0℃ or higher, the foamed molded body obtained from the foamed granules has excellent heat resistance, and when it is (ii) 160.0℃ or lower, it is easy to increase the foaming ratio of the foamed granules during manufacturing.

[0038] In this specification, the melting point of the polypropylene resin is determined by differential scanning calorimetry (hereinafter referred to as "DSC method"). The specific operating steps are as follows: (1) The polypropylene resin is melted by heating 5 mg to 6 mg of the resin from 40.0 °C to 220.0 °C at a heating rate of 10.0 °C / min; (2) The melted polypropylene resin is then crystallized by cooling the temperature of the melted resin from 220.0 °C to 40.0 °C at a cooling rate of 10.0 °C / min; (3) The crystallized polypropylene resin is then further heated from 40.0 °C to 220.0 °C at a heating rate of 10 °C / min. The temperature of the peak (melting peak) of the DSC curve of the polypropylene resin obtained at the second heating (i.e., at (3)) can be used as the melting point of the polypropylene resin. It should be noted that when multiple peaks (melting peaks) appear in the DSC curve of the polypropylene resin obtained during the second heating using the above method, the temperature of the peak with the largest heat of fusion (melting peak) is taken as the melting point of the polypropylene resin. As a differential scanning calorimeter, a model such as the DSC6200 manufactured by Seiko Instruments Inc. can be used.

[0039] 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. It should be noted that MFR is sometimes also referred to as "melt index (MI)".

[0040] When the MFR of the polypropylene resin is 3 g / 10 min or higher, there is a tendency to easily increase the expansion ratio of the foamed granules during manufacturing. When the MFR of the polypropylene resin is 30 g / 10 min or lower, there is no concern about the air bubbles in the resulting foamed granules becoming interconnected. As a result, there is a tendency for (i) the compressive strength of the foamed molded body obtained from the foamed granules to become better, or (ii) the surface properties of the foamed molded body to become better.

[0041] In this specification, the MFR value of the polypropylene resin is the value measured using the MFR measuring instrument described in JIS K7210:1999 under the following conditions: orifice diameter of 2.0959±0.005mmφ, orifice length of 8.000±0.025mm, load of 2.16kgf, and temperature of 230℃ (230±0.2℃).

[0042] Polypropylene resins can be obtained using known methods. There are no particular limitations on the polymerization catalyst used in the synthesis of polypropylene resins; for example, Ziegler catalysts and metallocene catalysts can be used.

[0043] (A copolymer containing acrylonitrile units and styrene-based units)

[0044] This foamed granule contains 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units relative to 100 parts by weight of polypropylene resin. This foamed granule, by having the above-described structure, possesses the following advantages: it can produce foamed granules with excellent foaming properties, and it can produce foamed molded articles with further reduced shrinkage and deformation after molding compared to existing articles. In this specification, "copolymer comprising acrylonitrile units and styrene units" is sometimes referred to as "AS copolymer." It should be noted that AS copolymer is an amorphous resin.

[0045] In this specification, an AS copolymer refers to a copolymer in which at least 50 mol% of 100 mol% of all structural units contained in the AS copolymer are derived from acrylonitrile units or styrene units. There is no particular limitation as long as the AS copolymer contains at least 50 mol% of structural units comprising both acrylonitrile and styrene units; for example, it can be (a) a block copolymer, a random copolymer, or a graft copolymer, or (b) a mixture of two or more of these.

[0046] 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, tert-butylstyrene, and chlorostyrene. One or more of these styrene-based monomers may be used. That is, the styrene-based units contained in the AS copolymer may be one type or a combination of two or more.

[0047] The styrene-based units contained in the AS copolymer preferably include α-methylstyrene units. The amount of α-methylstyrene units in the styrene-based units of the AS copolymer is preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 100% by weight, out of 100% by weight of the styrene-based units contained in the AS copolymer. That is, the styrene-based units contained in the AS copolymer are most preferably α-methylstyrene units. A high amount of α-methylstyrene units in the styrene-based units of the AS copolymer has the following advantages: the resulting foamed particles (a) can provide polypropylene resin foamed molded articles that exhibit almost no shrinkage or deformation after molding, and (b) have excellent foaming properties.

[0048] The amount of styrene-based 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, further preferably 55% to 85% by weight, even more preferably 60% to 80% by weight, and particularly preferably 65% ​​to 75% by weight in 100% by weight of the AS copolymer. According to this composition, it has the advantage of being able to obtain an AS copolymer with good productivity and excellent heat resistance.

[0049] The amount of α-methylstyrene units (hereinafter sometimes referred to as "α-methylstyrene content") contained in the AS copolymer as styrene-based units is preferably 20% to 95% by weight, more preferably 50% to 90% by weight, further preferably 55% to 85% by weight, even more preferably 60% to 80% by weight, and particularly preferably 65% ​​to 75% by weight in 100% by weight of the AS copolymer. According to this configuration, it has the advantage of being able to obtain AS copolymers with good productivity and excellent heat resistance.

[0050] AS copolymers can have 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; acrylates such as methyl acrylate and ethyl acrylate; methacrylates such as methyl methacrylate and ethyl methacrylate; olefins such as ethylene and propylene; maleic anhydride; vinyl chloride; vinylidene chloride; and monomers other than those mentioned above that can copolymerize with acrylonitrile units and / or styrene-based units. From the perspective of improving the heat resistance of AS copolymers, the amount of structural units other than AS contained in the AS copolymer is preferably 10% by weight or less, more preferably 5% by weight or less, further preferably 1% by weight or less, and particularly preferably 0% by weight in 100% by weight of the AS copolymer. That is, AS copolymers are particularly preferred to be copolymers composed of acrylonitrile units and styrene-based units.

[0051] Specific examples of AS copolymers include acrylonitrile / styrene copolymers, acrylonitrile / α-methylstyrene copolymers, acrylonitrile / p-methylstyrene copolymers, acrylonitrile / m-methylstyrene copolymers, acrylonitrile / o-methylstyrene copolymers, acrylonitrile / 2,4-dimethylstyrene copolymers, acrylonitrile / p-ethylstyrene copolymers, acrylonitrile / m-ethylstyrene copolymers, acrylonitrile / o-ethylstyrene copolymers, acrylonitrile / tert-butylstyrene copolymers, and acrylonitrile / chlorostyrene copolymers. Among these copolymers, acrylonitrile / α-methylstyrene copolymers are preferred due to their ability to produce foamed particles with excellent foaming properties. Only one type of these AS copolymers may be used, or two or more may be used in combination.

[0052] 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, further 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 has the advantage of being able to obtain foamed particles and foamed molded articles with excellent heat resistance, and when it is (ii) 140°C or lower, it is possible to obtain foamed particles with a low continuous bubble rate.

[0053] In this specification, the Tg of the AS copolymer is the value measured using a differential scanning calorimeter [Seiko Instruments Inc., DSC6200 type] according to JIS-K-7121. The specific operating steps are as follows (1) to (5): (1) Measure 5 mg of the AS copolymer; (2) Under a nitrogen atmosphere, raise the temperature of the AS copolymer from room temperature to 250°C at a rate of 10°C / min; (3) Cool the heated AS copolymer from 250°C to room temperature at a rate of 10°C / min; (4) Raise the temperature of the AS copolymer from room temperature to 250°C again at a rate of 10°C / min; (5) Take the temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained at the second heating (i.e., at (4)) as the Tg of the AS copolymer.

[0054] The mean flow rate (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 exhibits excellent compatibility with the polypropylene resin, reducing the tendency for bubbles to connect during foaming of the resulting resin particles. As a result, it has the advantage of obtaining foamed particles with a low continuous bubble rate.

[0055] In this specification, the MFR value of the AS copolymer is the value measured using the MFR measuring instrument described in JIS K7210:1999 under the following conditions: orifice diameter of 2.0959±0.005mmφ, orifice length of 8.000±0.025mm, load of 2.16kgf, and temperature of 230℃ (230±0.2℃).

[0056] The content of the AS copolymer in these foamed granules is 5 to 60 parts by weight relative to 100 parts by weight of the polypropylene resin, more preferably 5 to 50 parts by weight, even more preferably 8 to 50 parts by weight, even more preferably 10 to 40 parts by weight, even more preferably 13 to 40 parts by weight, further preferably 15 to 35 parts by weight, and particularly preferably 20 to 30 parts by weight. When the content of the AS copolymer relative to 100 parts by weight of the polypropylene resin is (a) 5 parts or more, it has the advantage of being able to obtain foamed granules with excellent foaming properties and foamed molded articles with further reduced shrinkage and deformation after molding compared with existing articles. When it is (b) 60 parts by weight or less, it has the advantage of being able to obtain foamed granules with low continuous bubble rate and excellent foaming properties.

[0057] (Hydrogenated styrene copolymer)

[0058] The polypropylene resin foamed granules of one embodiment of the present invention comprise 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. The foamed granules, by comprising the hydrogenated styrene copolymer within the above-mentioned range, have the following advantages: foamed granules with excellent foaming properties can be obtained, and foamed molded articles with further reduced shrinkage and deformation after molding compared to existing articles can be obtained.

[0059] In this specification, "hydrogenated styrene copolymer" refers to a copolymer obtained by hydrogenating a block copolymer (hereinafter also referred to as copolymer X) comprising styrene blocks consisting only of styrene units and conjugated diene blocks consisting only of conjugated diene units. In this specification, "hydrogenation" is sometimes referred to as "hydrogenation". More specifically, "hydrogenated styrene copolymer" refers to a copolymer obtained by hydrogenating copolymer X in such a manner that at least a portion of the carbon-carbon double bonds in the conjugated diene units of copolymer X are saturated.

[0060] Examples of conjugated diene units included in copolymer X include butadiene units, isoprene units, 1,3-pentadiene units, 2,3-dimethyl-1,3-butadiene units, 3-methyl-1,3-octadiene units, or 4-ethyl-1,3-hexadiene units, etc., without particular limitation.

[0061] In the manufacture of hydrogenated styrene copolymers, it is sufficient that at least a portion of the carbon-carbon double bonds in the conjugated diene units of copolymer X are saturated; complete saturation is not necessary. In other words, hydrogenated styrene copolymers can include the conjugated diene units contained in copolymer X used in the manufacture of hydrogenated styrene copolymers. More specifically, when copolymer X contains butadiene units as conjugated diene units, the hydrogenated styrene copolymer obtained by hydrogenating copolymer X can contain (a) unhydrogenated butadiene units, (b-1) butene units formed by hydrogen 1,2-addition polymerization of carbon-carbon double bonds in butadiene units, and (b-2) ethylene units formed by hydrogen 1,4-addition polymerization of carbon-carbon double bonds in butadiene units.

[0062] For hydrogenated styrene copolymers, the proportion of conjugated diene units with hydrogenated carbon-carbon double bonds (hereinafter sometimes referred to as "hydrogenation rate") in the total amount of conjugated diene units of copolymer X used in manufacturing 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, there is a tendency for the hydrogenated styrene copolymer to easily exist at the interface between the polypropylene resin and the AS copolymer, thus improving the compatibility of the hydrogenated styrene copolymer. The hydrogenation rate of the hydrogenated styrene copolymer can be 100%.

[0063] Specific examples of hydrogenated styrene-based copolymers include styrene / ethylene / butene / styrene block copolymers (SEBS) and styrene / ethylene / propylene / styrene block copolymers (SEPS). SEBS is a copolymer obtained by hydrogenating a copolymer (copolymer X), which is formed by sequentially bonding (a) styrene blocks consisting only of styrene units, (b) butadiene blocks consisting only of butadiene units, and (c) styrene blocks consisting only of styrene units. More specifically, SEBS is a copolymer formed by sequentially bonding (a) styrene blocks consisting only of styrene units, (b) blocks randomly bonded with (b-1) butene units formed by hydrogenation of butadiene units obtained through 1,2-addition polymerization and (b-2) ethylene units formed by hydrogenation of butadiene units obtained through 1,4-addition polymerization, and (c) the aforementioned styrene blocks. The blocks in SEBS randomly bonded with butene and ethylene units may contain butadiene units. SEPS is a copolymer obtained by hydrogenation of a copolymer (polymer X) consisting of (a) styrene blocks composed solely of styrene units, (b) isoprene blocks composed solely of isoprene units, and (c) styrene blocks composed solely of styrene units. More specifically, SEPS is a copolymer consisting of (a) styrene blocks composed solely of styrene units, (b) blocks randomly bonded with ethylene and propylene units (obtained by hydrogenating isoprene units), and (c) the aforementioned styrene blocks. Among these, hydrogenated styrene copolymers preferably contain SEBS, and particularly preferably SEBS, due to their higher strength.

[0064] The styrene unit content (hereinafter sometimes referred to as "styrene content") of the hydrogenated styrene copolymer 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, in 100% by weight of the hydrogenated styrene copolymer. According to this composition, it has the advantage of improving the compatibility between polypropylene resins and AS copolymers. In particular, when the styrene unit content of the hydrogenated styrene copolymer is 15% by weight or more in 100% by weight of the hydrogenated styrene copolymer, there is a tendency to obtain foamed molded articles with further reduced shrinkage and deformation after molding compared to existing articles.

[0065] The content of the hydrogenated styrene copolymer in these foamed granules is 3.0 to 30.0 parts by weight relative to 100 parts by weight of the polypropylene resin, 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. When the content of the hydrogenated styrene copolymer is 3.0 parts by weight or more relative to 100 parts by weight of the polypropylene resin, it has the advantage of fully utilizing the compatibility effect between the polypropylene resin and the AS copolymer by utilizing the hydrogenated styrene copolymer. When the content of the hydrogenated styrene copolymer is 30.0 parts by weight or less relative to 100 parts by weight of the polypropylene resin, it has the following advantages: (a) foamed granules with excellent foaming properties can be obtained, (b) the rigidity of the foamed molded body formed from the foamed granules is sufficiently improved, and (c) a foamed molded body with further reduced shrinkage and deformation after molding compared to existing products can be obtained.

[0066] (Other resins, etc.)

[0067] In this foamed granule, without impairing the effects described in one embodiment of the present invention, the resin component may further include resins other than polypropylene resins, AS copolymers, and hydrogenated styrene copolymers (sometimes referred to as other resins, etc.). Examples of the aforementioned other resins include (a) ethylene resins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, and ethylene / methacrylic acid copolymer; (b) styrene resins such as polystyrene, styrene / maleic anhydride copolymer, and styrene / ethylene copolymer; (c) polyphenylene ether resins such as polyphenylene ether and modified polyphenylene ether; (d) polyolefin waxes such as propylene / α-olefin waxes; and (e) olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. It should be noted that styrene resins and polyphenylene ether resins are amorphous resins.

[0068] The content of other resins, etc., in this foamed granule is preferably more than 0 parts by weight and less than 50 parts by weight relative to 100 parts by weight of polypropylene resin, more preferably more than 0 parts by weight and less than 30 parts by weight. Furthermore, this foamed granule may not contain any other resins, etc. That is, the content of other resins, etc., in this foamed granule may be 0 parts by weight.

[0069] (additive)

[0070] In addition to resin components comprising polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, these foamed granules may optionally contain additives. Examples of additives include colorants, water-absorbing substances, foaming nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystallizing nucleating agents, conductive agents, and lubricants. These additives can be incorporated into the resin granules during the manufacturing process or added directly to the dispersion during the foaming step described later.

[0071] The water-absorbing substance is used in the manufacture of these foamed granules to increase the amount of water impregnated in the resin granules. By using the water-absorbing substance in the manufacture of these foamed granules, the resin granules are given foaming properties. When water is used as the foaming agent, the effect of using the water-absorbing substance to give the resin granules foaming properties becomes particularly significant.

[0072] Examples of absorbent materials that can be used in one embodiment of the present invention include glycerol, diglycerol, polyethylene glycol, C12-C18 aliphatic alcohols (e.g., pentaerythritol, cetyl alcohol, stearyl alcohol), melamine, isocyanuric acid, melamine-isocyanuric acid condensate, zinc borate, etc. These absorbent materials can be used alone or in combination of two or more. Furthermore, when using two or more absorbent materials in combination, the mixing ratio can be adjusted appropriately according to the intended purpose.

[0073] Glycerin and polyethylene glycol (a) do not promote the miniaturization of the average bubble diameter of the foamed particles, and (b) have good affinity with polypropylene resins. Therefore, among the above-mentioned water-absorbing materials, glycerin and / or polyethylene glycol are preferred.

[0074] The amount of water-absorbing material used in the manufacture of these foamed granules, in other words, the content of water-absorbing material in these foamed granules, will be explained. The content of water-absorbing material in these foamed granules 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, relative to 100 parts by weight of the total amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer. When the aforementioned content of the water-absorbing material is (i) 0.01 parts by weight or more, the effect of imparting foaming properties using the water-absorbing material can be sufficiently obtained; when (ii) 1.00 parts by weight or less, there is no concern about shrinkage of the resulting foamed granules.

[0075] A foaming nucleating agent is a substance that can be used in the manufacture of these foamed granules and can form foam nuclei during the foaming of resin granules. In the manufacture of these foamed granules, it is preferable to use a foaming nucleating agent; in other words, these foamed granules preferably contain a foaming nucleating agent.

[0076] Examples of foaming nucleating agents that can be used in one embodiment of the present invention include, for example, silicon dioxide, silicates, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar apatite, and barium sulfate. Examples of silicates include, for example, talc, magnesium silicate, kaolin, hydrous kaolin, dickite, aluminum silicate, and zeolite. It should be noted that these foaming nucleating agents can be used individually or in combination of two or more. Furthermore, when using two or more foaming nucleating agents in combination, the mixing ratio can be adjusted appropriately according to the intended purpose.

[0077] The amount of foaming nucleating agent used in the manufacture of these foamed granules, in other words, the content of the foaming nucleating agent in these foamed granules, will be explained. From the viewpoint of uniformity of average bubble diameter, the content of the foaming nucleating agent in these foamed granules is preferably 0.005 parts by weight to 2.000 parts by weight relative to 100 parts by weight of the total amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, more preferably 0.010 parts by weight to 1.000 parts by weight, and even more preferably 0.030 parts by weight to 0.500 parts by weight.

[0078] The total amount of additives used in the manufacture of this foamed granule, in other words, the total content of each additive in this foamed granule, is preferably more than 0 parts by weight and less than 10 parts by weight relative to 100 parts by weight of polypropylene resin, more preferably more than 0 parts by weight and less than 5 parts by weight. Alternatively, this foamed granule may not contain any additives. That is, the content of each additive in this foamed granule may be 0 parts by weight.

[0079] <Physical properties>

[0080] The following describes the physical properties of these foamed granules.

[0081] (Expansion ratio of foamed granules)

[0082] The foaming ratio of the foamed granules is preferably 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 foaming ratio of the foamed granules is (i) 15.0 times or more, lightweight foamed molded articles can be obtained with good production efficiency; if it is (ii) 50.0 times or less, there is no need to worry about insufficient strength of the obtained foamed molded articles. In this specification, "foamed granules with excellent foaming properties" refers to foamed granules (hereinafter referred to as foamed granules) formed by directly foaming resin granules, with a foaming ratio of 15.0 times or more.

[0083] In this specification, the expansion ratio of the foamed particles is calculated by the following methods (1) to (6): (1) The weight Gi of the specified amount of foamed particles is accurately measured to a unit of 0.001 g (rounding to the fourth decimal place); (2) Then, the foamed particles used to measure the weight Gi are completely immersed in 100 mL of ethanol at 23°C contained in a graduated cylinder; (3) The volume yi (cm³) of the foamed particles is measured according to the rise in the liquid level of the graduated cylinder. 3 (4) Divide the weight Gi (g) of the foamed particle by the volume yi (cm³) of the foamed particle. 3 (5) Using resin particles used to manufacture the foamed particles instead of the foamed particles, the density ds (g / L) of the resin particles is calculated by performing the same operations as (1) to (4); (6) The expansion ratio of the foamed particles is calculated by the following formula:

[0084] Foaming ratio Ki = ds / di.

[0085] (DSC ratio of foamed granules)

[0086] The foamed particles preferably have at least two melting peaks in the DSC curve obtained by differential scanning calorimetry (DSC) as described later. Among these melting peaks, the heat of fusion determined from the high-temperature melting peak is denoted as "high-temperature melting heat," and the heat of fusion determined from the low-temperature melting peak is denoted as "low-temperature melting heat." Furthermore, if there are three or more melting peaks, the heat of fusion determined from the highest-temperature melting peak is denoted as "high-temperature melting heat," and the heat of fusion determined from the other melting peaks is denoted as "low-temperature melting heat."

[0087] The DSC ratio of the foamed granules 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 foamed granules is 10.0% or more, it has the advantage that the foamed molded body obtained by molding the foamed granules has sufficient strength. On the other hand, when the DSC ratio of the foamed granules is 40% or less, it has the advantage that the foamed granules can be molded at a lower molding temperature.

[0088] In this specification, the DSC ratio refers to the ratio of the high-temperature side heat of fusion calculated from the DSC curve of the foamed particles to the total heat of fusion. In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., a Seiko Instruments Inc. DSC6200 model). More specifically, in this specification, a differential scanning calorimeter (e.g., a Seiko Instruments...) is used. The method for determining (calculating) the DSC ratio of foamed particles using a DSC6200 (manufactured by Inc.) is as follows (1) to (5): (1) Measure 5 mg to 6 mg of foamed particles; (2) Heat the foamed particles from 40 °C to 220 °C at a heating rate of 10 °C / min to melt the foamed particles; (3) In the DSC curve of the foamed particles obtained in the process described above (2), (a) connect the maximum point between the highest melting peak and the adjacent (lower temperature side) melting peak of the highest melting peak with a straight line to the point representing the temperature before the start of melting, and (b) connect the aforementioned maximum point with the point representing the temperature after the end of melting with a straight line. (4) (a) The heat calculated from the line segment obtained by connecting the aforementioned maximum point (a-1) with the point representing the temperature after melting ends and the high-temperature side region enclosed by the DSC curve (a-2) is set as the high-temperature side melting heat; (b) The heat calculated from the line segment obtained by connecting the aforementioned maximum point (b-1) with the point representing the temperature before melting begins and the low-temperature side region enclosed by the DSC curve (b-2) is set as the low-temperature side melting heat; (c) The sum of the high-temperature side melting heat and the low-temperature side melting heat is set as the total melting heat (= high-temperature side melting heat + low-temperature side melting heat); (5) The DSC ratio is calculated according to the following formula:

[0089] DSC ratio (%) = (Heat of melting on the high-temperature side / Total heat of melting) × 100.

[0090] The DSC ratio of these foamed particles can serve as a benchmark value for the amount of high-melting-point crystals contained within the foamed particles. That is, a DSC ratio of 10.0% to 50.0% indicates that the foamed particles contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the foamed particles is significantly related to the viscoelasticity of both the resin particles during foaming and the foamed particles during expansion. In other words, when the DSC ratio of the foamed particles is between 10.0% and 50.0%, both the resin particles and the foamed particles exhibit excellent foaming and expansion properties, respectively, during both foaming and molding. As a result, it offers the advantage of obtaining foamed molded bodies with excellent internal cohesion under low molding pressure and excellent mechanical strength, such as compressive strength.

[0091] In this foamed granule, methods for controlling the DSC ratio within a specified range include adjusting the conditions during the manufacture of the foamed granule (especially foaming temperature, foaming pressure, holding time, and the temperature of the area (space) where the dispersion is released). From the viewpoint of ease of adjustment, adjusting the foaming temperature, foaming pressure, and / or holding time is preferred as a method for controlling the DSC ratio within a specified range.

[0092] For example, increasing the foaming temperature tends to decrease the DSC ratio of the resulting foamed particles, while decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals in the foamed particles changes with the foaming temperature. Furthermore, increasing the foaming pressure tends to decrease the DSC ratio of the resulting foamed particles, while decreasing the foaming pressure tends to increase the DSC ratio. This is because the degree of plasticization changes with the foaming pressure, thus changing the amount of unmelted crystals in the foamed particles. Additionally, there is a tendency for a longer holding time to result in a larger DSC ratio in the resulting foamed particles. This is because the amount of unmelted crystal growth in the foamed particles changes with the holding time.

[0093] (Continuous bubble rate)

[0094] The lower the continuous bubble rate of the foamed granules, the better. The continuous bubble rate of the foamed granules 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, further preferably 4.0% or less, and particularly preferably 3.0% or less. The lower limit of the continuous bubble rate of the foamed granules is not particularly limited, for example, it is 0.0% or more. According to this configuration, it has the following advantages: (a) during the molding of the foamed granules, the cells hardly break and shrink, therefore, the moldability of the foamed granules is excellent; and (b) in the foamed molded body obtained using the foamed granules, characteristics such as shape arbitrariness, cushioning, lightweight, compressive strength, and thermal insulation are further exhibited. The continuous bubble rate of the foamed granules can be controlled, for example, by the amount of AS copolymer used.

[0095] In this specification, the continuous bubble rate of the foamed particles is a value obtained by measuring using an air comparative hydrometer [Tokyo Scientific Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. Specifically, the continuous bubble rate of the foamed particles is calculated by performing the following steps (1) to (4) in sequence: (1) Measuring the volume Vc (cm³) of the foamed particles using an air comparative hydrometer. 3(2) Next, the total amount of foamed particles after Vc measurement is submerged in the ethanol contained in the graduated cylinder; (3) Subsequently, based on the rise of the ethanol level in the graduated cylinder, the apparent volume Va (cm³) of the foamed particles is calculated. 3 (4) The continuous bubble rate of the foamed particles is calculated using the following formula: Continuous bubble rate (%) = ((Va-Vc)×100) / Va. It should be noted that the above method for determining the volume Va is also known as the water immersion method.

[0096] <Manufacturing Method of Polypropylene Resin Foamed Granules>

[0097] There are no particular limitations on the manufacturing method of this foamed granule, and any known manufacturing method may be appropriately used. Preferably, the manufacturing method includes a foaming step that foams polypropylene resin particles, wherein the polypropylene resin particles comprise: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3 to 30 parts by weight of a hydrogenated styrene copolymer. Hereinafter, one embodiment of the manufacturing method of this foamed granule will be described in detail, and except as detailed below, the above descriptions (e.g., the description in the <Composition> section) will be appropriately referenced. It should be noted that the manufacturing method of this foamed granule is not limited to the following manufacturing method.

[0098] (Granulation process)

[0099] In manufacturing these foamed granules, the first step is to manufacture polypropylene resin granules (granulation process). In this specification, "polypropylene resin granules" is sometimes referred to as "resin granules". The granulation process can also be described as the process of manufacturing resin granules comprising 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3 to 30 parts by weight of a hydrogenated styrene copolymer.

[0100] As a method for manufacturing resin granules, an extruder can be used. Specifically, resin granules can be produced by, for example, the following methods (1) to (5): (1) a blend is prepared by blending a polypropylene resin, an AS copolymer, a hydrogenated styrene copolymer, and one or more of the group consisting of other resins and additives as needed; (2) the blend is fed into an extruder and melt-blended to prepare a polypropylene resin composition; (3) the polypropylene resin composition is extruded from a die provided by the extruder; (4) the extruded polypropylene resin composition is cooled by passing it through water or the like, thereby curing it; (5) thereafter, the cured polypropylene resin composition is finely cut into desired shapes such as cylinders, ellipses, spheres, cubes, cuboids, etc. using a cutting machine. Alternatively, in (3), the melt-blended polypropylene resin composition can be directly extruded from a die provided by the extruder into water, and the polypropylene resin composition can be cut into granular shapes immediately after extrusion, cooled, and cured. In this way, by melt-blending the blends, it is possible to obtain more uniform resin particles.

[0101] The weight of each resin particle obtained by the above operation 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 of each resin particle is 0.5 mg / particle or more, there is a tendency to improve the workability of the resin particles, and when it is 3.0 mg / particle or less, there is a tendency to improve the mold filling performance in the in-mold foaming molding process.

[0102] The amounts of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, as well as other resins and additives supplied to the granulation process (through blending and melt mixing) constitute the content of the aforementioned components in the manufactured resin granules. Therefore, the granulation process preferably includes: blending at least 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of the copolymer comprising acrylonitrile units and styrene units, and 3 to 30 parts by weight of the hydrogenated styrene copolymer, and then melt-mixing the blend.

[0103] (Foaming process)

[0104] The foaming process in this method of manufacturing foamed granules is not particularly limited as long as it enables the resin granules to foam. In one embodiment of the present invention, the foaming process preferably includes:

[0105] (a) A dispersion process that disperses resin particles, an aqueous dispersion medium, a foaming agent, and, as needed, a dispersant and / or a dispersing aid in a container.

[0106] (b) A heating-pressurization process that raises the temperature inside the container to a specified temperature and pressurizes the pressure inside the container to a specified pressure;

[0107] (c) A holding process that maintains the temperature and pressure inside the container at a specified temperature and pressure; and

[0108] (d) A release process in which the dispersion inside the container is released into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container) by opening one end of the container.

[0109] It should be noted that, in this case, the process of manufacturing foamed granules from resin particles is called "single-stage foaming process", and the resulting foamed granules are called "single-stage foamed granules".

[0110] The amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer contained in the resin particles supplied to the foaming process is the amount of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer in the resulting foamed particles. Therefore, the foaming process in this method of manufacturing foamed particles is preferably a process of foaming 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 hydrogenated styrene copolymer.

[0111] (Distributed processes)

[0112] The dispersion process can also be described as the process of preparing a dispersion, for example, in an aqueous dispersion medium containing resin particles, a foaming agent, and, as needed, a dispersant and / or dispersing aid.

[0113] The container used in the dispersion process is not particularly limited, but it is preferably a container that can withstand the foaming temperature and foaming pressure described later. As a container, a pressure-resistant container is preferred, and a pressure-resistant container of the autoclave type is more preferred.

[0114] As an aqueous dispersion medium, any medium that can uniformly disperse resin particles, foaming agents, etc., is acceptable; there are no particular limitations. Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerol, etc. to water; and (b) tap water and industrial water, etc. From the viewpoint of stable production of foaming particles, it is preferable to use pure water and ultrapure water such as RO water (water purified using reverse osmosis membrane method), distilled water, deionized water (water purified using ion exchange resin), etc., as an aqueous dispersion medium.

[0115] The amount of aqueous dispersion medium is not particularly limited, but is preferably 100 to 400 parts by weight relative to 100 parts by weight of resin particles. When the amount of aqueous dispersion medium is (a) 100 parts by weight or more, there is no concern about a decrease in the stability of the dispersion (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 concern about a decrease in the productivity of the foamed particles.

[0116] Examples of blowing agents include: (a) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a) inorganic blowing agents such as water; and (b) organic blowing agents such as saturated hydrocarbons with 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; (b) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and (b) halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane. At least one blowing agent selected from the group consisting of the above-mentioned inorganic and organic blowing agents can be used. When two or more blowing agents are used in combination, the mixing ratio can be adjusted appropriately according to the purpose. From the viewpoint of environmental impact and foaming power, inorganic blowing agents are preferred among the above-mentioned blowing agents. Furthermore, from the viewpoint of moderately improving the plasticizing effect and easily improving the foaming properties of the foamed particles during manufacturing, carbon dioxide is preferred among inorganic foaming agents.

[0117] The amount of foaming agent used is not particularly limited, as long as it is used appropriately according to (a) the type of foaming agent and / or (b) the desired foaming ratio of the foamed particles. The amount of foaming agent used relative to, for example, 1 part to 10,000 parts by weight of resin particles is preferably 1 part to 5,000 parts by weight, and even more preferably 1 part to 1,000 parts by weight. When the amount of foaming agent used is 1 part or more relative to 100 parts by weight of resin particles, foamed particles with suitable density can be obtained. On the other hand, when the amount of foaming agent used is less than 10,000 parts by weight relative to 100 parts by weight of resin particles, an effect consistent with the amount of foaming agent can be obtained, thus avoiding economic waste. The amount of foaming agent used relative to, for example, 100 parts by weight of resin particles can be 1 part to 100 parts by weight, or 1 part to 10 parts by weight.

[0118] When using water as a foaming agent, the water in the dispersion in the container can be used as the foaming agent. Specifically, when using water in the dispersion as a foaming agent, it is preferable to pre-contain a water-absorbing substance in the resin particles. This allows the resin particles to easily absorb the water in the dispersion in the container, thus facilitating the use of water as a foaming agent.

[0119] In this method for manufacturing foamed granules, a dispersant is preferably used. Using a dispersant provides the following advantages: it reduces the adhesion (sometimes called sticking) between resin particles, enabling the stable production of foamed granules. Examples of dispersants include inorganic substances such as calcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, alumina, titanium dioxide, and aluminum hydroxide. These dispersants can be used individually or in combination of two or more. Furthermore, when using two or more dispersants in combination, the mixing ratio can be adjusted appropriately according to the desired effect.

[0120] In one embodiment of the present invention, the amount of dispersant in the dispersion is preferably 0.01 to 3.00 parts by weight relative to 100 parts by weight of resin particles, more preferably 0.05 to 2.00 parts by weight, and even more preferably 0.10 to 1.00 parts by weight. When the amount of dispersant is (a) 0.01 parts by weight or more, there is no concern about poor dispersion of the resin particles; and when it is (b) 3.00 parts by weight or less, there is no concern about poor fusion of the foamed particles when using the obtained foamed particles for in-mold foaming.

[0121] In this method for manufacturing foamed granules, (a) to improve the effect of reducing the adhesion between resin particles and / or (b) to improve the stability of the dispersion in the container, a dispersing agent is preferably used. Examples of dispersing agents include, for instance, anionic surfactants. Examples of anionic surfactants include sodium dodecylbenzene sulfonate and other alkylbenzene sulfonates; sodium alkane sulfonate, sodium alkyl sulfonate, sodium alkyl diphenyl ether disulfonate, sodium α-olefin sulfonate, etc. These dispersing agents can be used individually or in combination of two or more. Furthermore, when using two or more dispersing agents in combination, the mixing ratio can be appropriately adjusted according to the purpose.

[0122] In one embodiment of the present invention, the amount of dispersing agent in the dispersion 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 resin particles. When the amount of dispersing agent is within the aforementioned range, there is no concern about causing poor dispersion of resin particles.

[0123] If the stability of the dispersion decreases, multiple resin particles in the container may adhere to each other or clump together. As a result, sometimes (i) adhered foamed particles are obtained; or (ii) clumps of resin particles remain in the container, making it impossible to produce foamed particles; or (iii) the production rate of foamed particles decreases.

[0124] (Heating-pressurization process and holding process)

[0125] The heating-pressurization process is preferably performed after the dispersion process, and the holding process is preferably performed after the heating-pressurization process. In this specification, the specified temperature (a) in the heating-pressurization process and the holding process is sometimes referred to as the foaming temperature, and the specified pressure (b) is sometimes referred to as the foaming pressure.

[0126] The foaming temperature varies depending on the type of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, the type of foaming agent, and the desired apparent density of the foamed particles, and therefore cannot be generalized. Preferably, the foaming temperature is (i) the melting point of a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) the polypropylene resin composition, or (c) the resin particles, ranging from -20.0°C to +10.0°C; more preferably, it is (ii) the melting point of a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) the polypropylene resin composition, or (c) the resin particles, ranging from -15.0°C to +8.0°C; and even more preferably, it is (iii) the melting point of a mixture of polypropylene resin, AS copolymer, and hydrogenated styrene copolymer, (b) the polypropylene resin composition, or (c) the resin particles, ranging from -10.0°C to +6.0°C.

[0127] The foaming 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 even more preferably 2.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). If the foaming pressure is 1.0 MPa (gauge pressure) or higher, foamed particles with suitable density can be obtained.

[0128] In the holding process, the holding time (holding time) for maintaining 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. When the holding time is 10 minutes or more, a sufficient amount of unmelted crystals (polypropylene resin crystals) are present, resulting in the advantage of reducing the shrinkage of the resulting foamed particles and / or the increase in the continuous bubble rate. On the other hand, when the holding time is 60 minutes or less, there is no excessive amount of unmelted crystals, thus providing the advantage of being able to mold the foamed particles at a low molding temperature.

[0129] (Release process)

[0130] Regarding the release process, it is preferred to perform it after the heating-pressurization process when (a) the holding process is not performed, and after the holding process when (b) the holding process is performed. The release process enables the resin particles to foam, resulting in foamed particles.

[0131] In the release process, "the region with pressure lower than the foaming pressure" refers to "the region under pressure lower than the foaming pressure" or "the space under pressure lower than the foaming pressure," or it can be described as "the atmosphere under pressure lower than the foaming pressure." The region with pressure lower than the foaming pressure is not specifically limited as long as the pressure is lower than the foaming pressure; for example, it can be a region under atmospheric pressure.

[0132] During the release process, when releasing the dispersion into a region with a pressure lower than the foaming pressure, the dispersion can be released through an opening with a diameter of 1 mm to 5 mm for purposes such as adjusting the flow rate of the dispersion and reducing the deviation in the foaming ratio of the resulting foamed particles. Alternatively, to improve foaming properties, the aforementioned low-pressure region (space) can be filled with saturated water vapor.

[0133] (Two-stage foaming process)

[0134] However, in order to obtain foamed granules with a high expansion ratio, there is a method of increasing the amount of inorganic foaming agent in a single foaming process (hereinafter referred to as Method 1). Furthermore, as a method other than Method 1, the following method can also be used: after obtaining foamed granules (single foamed granules) with a low expansion ratio (approximately 2.0 to 35.0 times) in a single foaming process, the obtained single foamed granules are foamed again, thereby increasing the expansion ratio (hereinafter referred to as Method 2).

[0135] As for the aforementioned Method 2, examples include the following steps (a1) to (a3): (a1) manufacturing a single-stage foaming granule with a foaming ratio of 2.0 to 35.0 times in a single-stage foaming process; (a2) placing the single-stage foaming granule into a pressure-resistant container and pressurizing it at 0.2 MPa (gauge pressure) to 0.6 MPa (gauge pressure) using nitrogen, air, carbon dioxide, etc., thereby increasing the pressure inside the single-stage foaming granule (hereinafter sometimes referred to as "internal pressure") to higher than atmospheric pressure; (a3) ​​subsequently heating the single-stage foaming granule with increased internal pressure using steam, etc., and then foaming it. The process of increasing the foaming ratio of the single-stage foaming granule as in Method 2 is called the "two-stage foaming process," and the polypropylene resin foaming granules obtained by the method of Method 2 are called "two-stage foaming granules."

[0136] In the aforementioned (a3) ​​of the two-stage foaming process, the pressure of the steam used to heat the first-stage foaming particles is preferably adjusted to 0.03 MPa (gauge pressure) to 0.20 MPa (gauge pressure) taking into account the expansion ratio of the second-stage foaming particles. When the steam pressure in the second-stage foaming process is 0.03 MPa (gauge pressure) or higher, there is a tendency to easily increase the expansion ratio; when it is below 0.20 MPa (gauge pressure), the possibility of the resulting second-stage foaming particles sticking together decreases. It should be noted that when the second-stage foaming particles stick together, it is sometimes impossible to supply the resulting second-stage foaming particles for subsequent in-mold foaming molding.

[0137] The internal pressure of the first-stage foamed granules, obtained by impregnating them with nitrogen, air, carbon dioxide, etc., should be appropriately varied considering the expansion ratio of the second-stage foamed granules and the steam pressure of the second-stage foaming process. The internal pressure of the first-stage foamed granules 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 foamed granules is 0.15 MPa (absolute pressure) or higher, high-pressure steam is not required to increase the expansion ratio; therefore, the possibility of adhesion between the second-stage foamed granules is reduced. When the internal pressure of the first-stage foamed granules is 0.60 MPa (absolute pressure) or lower, the possibility of cell interconnection between the second-stage foamed granules is reduced. As a result, the possibility of a decrease in the compressive strength and other rigidities of the final in-mold foamed molded body is reduced. It should be noted that "bubble connectivity" can also be called "bubble connectivity".

[0138] [2. Polypropylene resin foamed molded body]

[0139] The polypropylene resin foamed molding body described in one embodiment of the present invention is a foamed molding body formed by molding the polypropylene resin foamed particles described in item [1. Polypropylene Resin Foamed Particles]. The polypropylene resin foamed molding body described in one embodiment of the present invention can also be said to include the polypropylene resin foamed particles described in item [1. Polypropylene Resin Foamed Particles]. Furthermore, this foamed molding body can also be said to be a foamed molding body formed by molding polypropylene resin foamed particles obtained by the manufacturing method of these foamed particles (for example, the manufacturing method described in the aforementioned item <Manufacturing Method of Polypropylene Resin Foamed Particles>), or it can be said to be a foamed molding body containing polypropylene resin foamed particles obtained by the manufacturing method of these foamed particles. Furthermore, this foamed molding body can also be said to be a foamed molding body formed by molding the foamed particles described in the aforementioned item [1. Polypropylene Resin Foamed Particles], or it can be said to be a foamed molding body containing these foamed particles.

[0140] In this specification, the term "polypropylene resin foamed molded article according to one embodiment of the present invention" is sometimes referred to as "the foamed molded article".

[0141] This foamed molded body has the advantage of almost no shrinkage and deformation after molding due to the above-mentioned structure.

[0142] (Shrinkage rate)

[0143] In this specification, regarding the foamed molded body, "almost no shrinkage after molding" 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 length direction × 319 mm in width direction × 50 mm in thickness direction), the foamed particles are in-mold foamed. Here, the length of the mold in the length direction is set as L0; (2) The length L1 of the resulting foamed molded body in the length direction is measured; (3) The shrinkage rate (%) is calculated according to the following formula:

[0144] Shrinkage rate (%) = ((L1-L0)×100) / L0.

[0145] The shrinkage rate of this foamed molded body is preferably 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 body with a shrinkage rate of 1.2% or less means that the foamed molded body obtained through manufacturing is unlikely to exhibit dimensional deviations, and can be said to have good dimensional stability. The foamed particles that provide a foamed molded body with good dimensional stability and the foamed molded body itself have the advantage of being suitable for use in the field of insert molding, where it is integrally formed with other raw materials such as metals.

[0146] (Deformation)

[0147] The following is for reference Figure 1 The deformation amount of this foamed molded body is explained. Figure 1 This is a schematic diagram of a foamed molded body 100 used for evaluating deformation. The foamed molded body 100 is manufactured using a mold (350mm in length direction × 320mm in width direction × 180mm in thickness direction (driving direction for moving types)) with a baffle at the center of the mold. Figure 1 In this context, the X direction can be considered the thickness direction of the foamed molded body 100, and also the driving direction for movement. The Y direction can be considered the length direction of the foamed molded body 100, and is a direction perpendicular to the X direction. The Z direction can be considered the width direction of the foamed molded body 100, and is a direction perpendicular to both the X and Y directions. For example... Figure 1As shown, in the foamed molded body 100, the Z-direction dimensions (lengths) of the two end portions in the length direction are set as K1 and K2 respectively, and the Z-direction dimension of the central portion in the length direction is set as K3.

[0148] In this specification, "almost no deformation" for foamed molded bodies means that the amount of deformation is small as determined by the following methods (1) to (3): (1) Foamed particles are in-mold foamed using a mold with dimensions (length) of 350 mm in the length direction (Y direction), 320 mm in the width direction (Z direction), and 180 mm in the thickness direction (X direction) and a baffle in the center of the mold; (2) The Z-direction dimensions (mm) (K1, K2) of the two ends of the length direction of the resulting foamed molded body (foamed molded body 100) and the Z-direction dimensions (mm) (K3) of the center of the length direction are measured; (3) The amount of deformation is calculated according to the following formula:

[0149] Deformation (mm) = {(K1+K2) / 2}-K3.

[0150] The deformation of this foamed molded body 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 body with a deformation of 14.0 mm or less means that the foamed molded body obtained by manufacturing is not prone to dimensional deviations, and can be said to have good dimensional stability.

[0151] <Manufacturing Method of Foamed Molded Body>

[0152] The manufacturing method of this foamed molded body is not particularly limited, and known methods can be used. Preferably, the manufacturing method includes an in-mold foaming process of the foamed particles described in item [1. Polypropylene Resin Foamed Particles] or foamed particles obtained by the manufacturing method described in item [Method for Manufacturing Polypropylene Resin Foamed Particles] above. Specific examples of the manufacturing method of this foamed molded body include, for example, the following manufacturing methods (in-mold foaming method) sequentially comprising (b1) to (b6), but are not limited to this method:

[0153] (b1) A mold consisting of a stationary, non-driveable type and a movable, driveable type is mounted on an in-mold foaming molding machine. Here, the stationary and movable types are formed by driving the movable type toward the stationary type (sometimes referred to as "mold closing").

[0154] (b2) The moving type is driven toward the fixed type in such a way that the fixed type and the moving type are not fully closed, so as to form a slight gap (also known as a crack);

[0155] (b3) Foamed particles are filled into the molding space formed inside the fixed and movable types by means of, for example, a filling machine;

[0156] (b4) Drive the mobile type in a manner that allows the fixed and mobile types to fully close the mold (i.e., fully close the mold);

[0157] (b5) After preheating the mold with steam, the mold is heated on one side and the other side with steam, and then heated on both sides with steam to achieve in-mold foaming molding.

[0158] (b6) Remove the in-mold foamed material from the mold and dry it (e.g., at 75°C) to obtain the foamed body.

[0159] As mentioned above (b3), the following methods (b3-1) to (b3-4) can be listed as methods for filling foamed particles into the molding space:

[0160] (b3-1) A method of pressurizing foamed particles (including the above two-stage foamed particles, the same below) in a container using inorganic gas, so that the inorganic gas permeates into the foamed particles, and then filling the foamed particles into the molding space after applying a specified internal pressure to the foamed particles.

[0161] (b3-2) A method of compressing foamed granules into the molding space by reducing the volume of the mold by 10% to 75%;

[0162] (b3-3) A method of compressing foamed particles using gas pressure and filling them into the molding space;

[0163] (b3-4) A method of filling foamed particles into the molding space without special pretreatment.

[0164] In this method for manufacturing the foamed molded article, the inorganic gas used in the aforementioned method (b3-1) can be 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.

[0165] In the manufacturing method of this foamed molded body, the internal pressure of the foamed particles in the aforementioned (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).

[0166] In this method for manufacturing a foamed molded body, the temperature inside the container when the inorganic gas in method (b3-1) is impregnated into the foamed particles is preferably 10°C to 90°C, and more preferably 40°C to 90°C.

[0167] In the methods described above (b3-2) and (b3-3), in the subsequent step (b5), the restoring force of the foamed particles compressed by gas pressure is utilized in order to fuse the foamed particles.

[0168] One embodiment of the present invention may be configured as follows.

[0169] [1] A polypropylene resin foamed granule, comprising: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of hydrogenated styrene copolymer.

[0170] [2] The polypropylene resin foamed particles according to [1], wherein the aforementioned styrene unit is an α-methylstyrene unit.

[0171] [3] Polypropylene resin foamed particles according to [1] or [2], wherein the aforementioned hydrogenated styrene copolymer is styrene / ethylene / butene / styrene copolymer (SEBS).

[0172] [4] Polypropylene resin foamed particles according to any one of [1] to [3], wherein the styrene unit content of the aforementioned hydrogenated styrene copolymer is 15% to 80% by weight in 100% by weight of the hydrogenated styrene copolymer.

[0173] [5] Polypropylene resin foamed particles according to any one of [1] to [4], wherein the glass transition temperature of the aforementioned copolymer comprising acrylonitrile units and styrene units is 95°C to 140°C.

[0174] [6] A polypropylene resin foamed molded body, which is formed by molding polypropylene resin foamed particles as described in any one of [1] to [5].

[0175] [7] A method for manufacturing polypropylene resin foamed granules, comprising a foaming step of foaming polypropylene resin granules, wherein the aforementioned polypropylene resin granules comprise: 100 parts by weight of polypropylene resin, 5 to 60 parts by weight of a copolymer comprising acrylonitrile units and styrene units, and 3.0 to 30.0 parts by weight of hydrogenated styrene copolymer.

[0176] [8] The method for manufacturing polypropylene resin foamed particles according to [7], wherein the aforementioned styrene unit is an α-methylstyrene unit.

[0177] [9] The method for manufacturing polypropylene resin foamed particles according to [7] or [8], wherein the aforementioned hydrogenated styrene copolymer is a styrene / ethylene / butene / styrene copolymer (SEBS).

[0178]

[10] A method for manufacturing polypropylene resin foamed particles according to any one of [7] to [9], wherein the styrene unit content of the aforementioned hydrogenated styrene copolymer is 15% to 80% by weight in 100% by weight of the hydrogenated styrene copolymer.

[0179]

[11] A method for manufacturing polypropylene resin foamed particles according to any one of [7] to

[10] , wherein the glass transition temperature of the aforementioned copolymer comprising acrylonitrile units and styrene units is 95°C to 140°C.

[0180]

[12] A method for manufacturing a polypropylene resin foamed molded body, comprising: a step of molding polypropylene resin foamed particles as described in any one of [1] to [5], or polypropylene resin foamed particles obtained by any one of [7] to

[11] .

[0181] Example

[0182] The following examples and comparative examples illustrate one embodiment of the present invention in more detail, but the present invention is not limited to the examples described.

[0183] 〔Material〕

[0184] The materials used in the embodiments and comparative examples will be described below.

[0185] <Resin Composition>

[0186] (Polypropylene resin)

[0187] Polypropylene resin: 1-Butene / Ethylene / Propylene random copolymer [melting point 149℃, 1-butene content 3.8 wt%, ethylene content 0.5 wt%, MFR = 10 g / 10 min]

[0188] (AS copolymer)

[0189] AS copolymer 1: Acrylonitrile / α-methylstyrene copolymer [Tg: 121℃, α-methylstyrene content: 70% by weight (styrene content: 70% by weight), MFR: 4.9 g / 10 min]

[0190] AS copolymer 2: Acrylonitrile / styrene copolymer [Tg: 108℃, styrene content: 75% by weight (styrene-based content: 75% by weight), MFR: 6.1 g / 10 min]

[0191] AS copolymer 3: Acrylonitrile / styrene copolymer [Tg: 115℃, styrene content: 50% by weight (styrene-based content: 50% by weight), MFR: 8.1 g / 10 min]

[0192] (Hydrogenated styrene copolymer)

[0193] Hydrogenated styrene copolymer 1: SEBS (styrene / ethylene / butene / styrene copolymer, Dynaron 9901P manufactured by JSR) [styrene content 53%]

[0194] Hydrogenated styrene copolymer 2: SEBS (styrene / ethylene / butene / styrene copolymer, Dynaron 8300P manufactured by JSR) [styrene content 9%]

[0195] (Other resins)

[0196] (Amorphous resin)

[0197] Amorphous resin 1: Polystyrene [Tg = 101℃, MFR = 7.0]

[0198] Amorphous resin 2: A mixture of polyphenylene ether and polystyrene [Tg = 120℃, MFR = 1.8 g / 10 min]

[0199] (Compatibilizer)

[0200] Compatibilizer: Polypropylene / (Acrylonitrile / Styrene) graft copolymer [Main chain: Polypropylene, Side chain: Acrylonitrile / Styrene copolymer, Polypropylene: Acrylonitrile / Styrene copolymer = 70 (mol%): 30 (mol%)] (Modiper A3400 manufactured by Nippon Oil Company)

[0201] <Additives>

[0202] (Water-absorbing material)

[0203] Glycerin (Lion Corporation, Refined Glycerin D)

[0204] (Foaming nucleating agent)

[0205] Talc (manufactured by Lin Huacheng Company, talc powder (registered trademark) PK-S)

[0206] [Measurement Method]

[0207] The measurement and evaluation of various items are carried out as follows.

[0208] (Melting point of polypropylene resin)

[0209] The melting point of the polypropylene resin was determined by DSC using a differential scanning calorimeter (DSC6200, manufactured by Seiko Instruments Inc.). The specific operating steps are as follows (1) to (4): (1) The polypropylene resin was melted by heating 5 mg to 6 mg of the resin from 40.0 °C to 220.0 °C at a heating rate of 10.0 °C / min; (2) The melted polypropylene resin was then crystallized by cooling the resin from 220.0 °C to 40.0 °C at a cooling rate of 10.0 °C / min; (3) The crystallized polypropylene resin was then further heated 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 at the second heating (i.e., at (3)) was taken as the melting point of the polypropylene resin. It should be noted that when multiple peaks (melting peaks) are present in the DSC curve of the polypropylene resin obtained during the second heating using the above method, the temperature of the peak with the largest heat of fusion (melting peak) shall be taken as the melting point of the polypropylene resin.

[0210] (Glass transition temperature (Tg) of AS copolymer)

[0211] The glass transition temperature (Tg) of the AS copolymer was determined by using a differential scanning calorimeter [Seiko Instruments Inc., DSC6200] according to JIS-K-7121 and by the following methods (1) to (5): (1) 5 mg of the AS copolymer was measured; (2) the temperature of the AS copolymer was increased from room temperature to 250°C at 10°C / min under a nitrogen atmosphere; (3) the temperature of the heated AS copolymer was decreased from 250°C to room temperature at 10°C / min; (4) the temperature of the AS copolymer was increased from room temperature to 250°C again at 10°C / min; (5) the temperature of the peak (melting peak) of the DSC curve of the AS copolymer obtained at the second heating (i.e., at (4)) was taken as the Tg of the AS copolymer.

[0212] (MFR of polypropylene resin and AS copolymer)

[0213] The MFR of polypropylene resin or AS copolymer is set as the value measured using the MFR measuring instrument described in JIS K7210:1999 under the following conditions: orifice diameter of 2.0959±0.005 mmφ, orifice length of 8.000±0.025 mm, load of 2.16 kgf, and temperature of 230℃ (230±0.2℃).

[0214] (Expansion ratio of foamed granules (single-stage foamed granules, two-stage foamed granules))

[0215] The method for determining the expansion ratio of foamed particles is as follows (1) to (6): (1) Accurately measure the weight Gi of a specified amount of foamed particles (single-stage or two-stage foamed particles) to a unit of 0.001g (rounding to the fourth decimal place); (2) Next, immerse all the foamed particles used to measure the weight Gi in 100mL of water at 23°C contained in a graduated cylinder; (3) Measure the volume yi (cm³) of the foamed particles according to the rise in the liquid level of the graduated cylinder. 3 (4) Divide the weight Gi (g) of the foamed particle by the volume yi (cm³) of the foamed particle. 3 (5) Using resin particles used to manufacture the foamed particles instead of the foamed particles, the density ds (g / L) of the resin particles is calculated by performing the same operations as (1) to (4); (6) The expansion ratio of the foamed particles is calculated by the following formula:

[0216] Foaming ratio Ki = ds / di.

[0217] (Foaming)

[0218] The foaming properties of foamed particles are evaluated based on the expansion ratio of a single foaming process obtained under the same conditions. The evaluation criteria are as follows.

[0219] 〇 (Good): The foaming ratio of the first-stage foamed granules is 15.0 times or more.

[0220] × (Defective): The foaming ratio of the foamed granules is less than 15.0 times.

[0221] Here, the expansion ratio of foamed granules is affected by the DSC ratio of the foamed granules. For example, when manufacturing foamed granules by adjusting the foaming temperature to lower the DSC ratio of the foamed granules, there is a tendency to obtain foamed granules with a high expansion ratio. Therefore, when comparing the expansion ratios of different foamed granules, the influence of the DSC ratio of the foamed granules needs to be considered. That is, when comparing the expansion ratios between different foamed granules, by manufacturing foamed granules with similar DSC ratios, the expansion ratios of the foamed granules can be compared more accurately.

[0222] (DSC ratio of foamed granules)

[0223] In the determination (calculation) of the DSC ratio of the foamed particles, a differential scanning calorimeter (Seiko Instruments Inc., DSC6200 model) was used. The method for determining (calculating) the DSC ratio of the foamed particles using a differential scanning calorimeter is as follows (1) to (5): (1) 5 mg to 6 mg of foamed particles were measured; (2) the temperature of the foamed particles was increased from 40 °C to 220 °C at a heating rate of 10 °C / min to melt the foamed particles; (3) in the DSC curve of the foamed particles obtained in the process of (2) above, (a) a straight line was used to connect the maximum point between the melting peak at the highest temperature and the adjacent (lower temperature side) melting peak of the melting peak to the point representing the temperature before the start of melting, and (b) a straight line was used to connect the aforementioned maximum point to the point representing the temperature after the end of melting. (4)(a) The heat calculated from the line segment obtained by connecting the aforementioned maximum point (a-1) with the point representing the temperature after melting ends and the high-temperature side region enclosed by the DSC curve (a-2) is set as the high-temperature side melting heat; (b) The heat calculated from the line segment obtained by connecting the aforementioned maximum point (b-1) with the point representing the temperature before melting begins and the low-temperature side region enclosed by the DSC curve (b-2) is set as the low-temperature side melting heat; (c) The sum of the high-temperature side melting heat and the low-temperature side melting heat is set as the total melting heat (= high-temperature side melting heat + low-temperature side melting heat); (5) The DSC ratio is calculated according to the following formula:

[0224] DSC ratio (%) = (Heat of melting on the high-temperature side / Total heat of melting) × 100.

[0225] (Continuous bubble rate of foamed particles)

[0226] The continuous bubble rate of polypropylene resin foamed particles was determined by measuring it using an air comparative hydrometer [Tokyo Scientific Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. More specifically, the continuous bubble rate of the foamed particles was calculated by performing the following steps (1) to (4) in sequence: (1) The volume Vc (cm³) of the foamed particles was measured using an air comparative hydrometer. 3 (2) Next, the total amount of foamed particles after Vc measurement is submerged in the ethanol contained in the graduated cylinder; (3) Subsequently, based on the rise of the ethanol level in the graduated cylinder, the apparent volume Va (cm³) of the foamed particles is calculated. 3 (4) The continuous bubble rate of the foamed particles is calculated using the following formula:

[0227] Continuous bubble rate (%) = ((Va-Vc)×100) / Va.

[0228] (Shrinkage rate of foamed molded parts)

[0229] The method for determining the shrinkage rate of the foamed molded body is as follows (1) to (3): (1) In-mold foaming of the foamed particles is performed using a mold with known dimensions (e.g., 369 mm in length direction × 319 mm in width direction × 50 mm in thickness direction). Here, the length of the mold in the length direction is set as L0; (2) The length L1 of the resulting foamed molded body in the length direction is measured; (3) The shrinkage rate (%) is calculated according to the following formula:

[0230] Shrinkage rate (%) = ((L1-L0)×100) / L0

[0231] It should be noted that the mold used to measure shrinkage is sometimes called a shrinkage evaluation mold.

[0232] (Deformation of the foamed molded body)

[0233] The method for determining the deformation of the foamed molded body is as follows (1) to (3): (1) Using a mold with dimensions (length) of 350 mm in the length direction (Y direction), 320 mm in the width direction (Z direction), and 180 mm in the thickness direction (X direction) and a baffle in the center of the mold, the foamed particles are foamed in-mold; (2) The Z-direction dimensions (mm) (K1, K2) of the two ends of the length direction of the resulting foamed molded body (foamed molded body 100) and the Z-direction dimensions (mm) (K3) of the center of the length direction are measured; (3) The deformation is calculated according to the following formula:

[0234] Deformation (mm) = {(K1+K2) / 2}-K3.

[0235] It should be noted that the mold used to measure the amount of deformation is sometimes called the mold for evaluating the amount of deformation.

[0236] [Example 1]

[0237] (Preparation of polypropylene resin granules)

[0238] 100 parts by weight (10 kg) of polypropylene resin, 12 parts by weight (1.2 kg) of AS copolymer, 7.0 parts by weight (700 g) of hydrogenated styrene copolymer, 0.050 parts by weight (5 g) of talc as a foaming nucleating agent, and 0.2 parts by weight (20 g) of glycerol as a water-absorbing substance were dry-mixed.

[0239] The resulting blend was fed into a twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX] and melt-blended at a resin temperature of 250°C. The melt-blended polypropylene resin composition was extruded into a filament through a die with a circular orifice mounted at the front of the extruder. The extruded polypropylene resin composition was water-cooled and then cut using a cutter to obtain cylindrical resin particles (1.2 mg / particle).

[0240] (Production of polypropylene resin foamed granules (single-stage foamed granules))

[0241] 100 parts by weight of the obtained resin particles, 200 parts by weight of pure water, 0.2 parts by weight of kaolin (Engelhard, ASP-170), a poorly water-soluble inorganic compound, and 0.03 parts by weight of sodium dodecylbenzenesulfonate, a surfactant, were added to a pressure-resistant sealed container. Then, while stirring the raw materials in the pressure-resistant sealed container, 6.7 parts by weight of carbon dioxide, a foaming agent, were introduced into the aforementioned pressure-resistant sealed container to prepare a dispersion. Next, the temperature inside the pressure-resistant sealed container was heated to a foaming temperature of 151.0°C. Subsequently, carbon dioxide was added pressurized into the pressure-resistant sealed container, increasing the pressure inside to a foaming pressure of 3.2 MPa (gauge pressure) (heating-pressurization process). Next, after maintaining the pressure-resistant sealed container at the aforementioned foaming temperature and pressure for 30 minutes (holding process), the valve at the bottom of the sealed container is opened, and the dispersion is released through a 3.6 mm orifice into the foaming cylinder under atmospheric pressure, resulting in foamed particles (single-stage foamed particles). During the release of the dispersion, carbon dioxide is added to the pressure-resistant sealed container to prevent the pressure inside from decreasing compared to the foaming pressure, maintaining the pressure inside the pressure-resistant sealed container at 3.2 MPa (gauge pressure). The foaming ratio, foaming properties, DSC ratio, and continuous bubble rate of the obtained foamed particles are measured, and the results are shown in Table 1.

[0242] (Preparation of polypropylene resin foamed granules (two-stage foamed granules))

[0243] After drying the resulting foamed granules at 60°C for 6 hours, they were placed into a pressure-resistant sealed container. Air was introduced into the pressure-resistant sealed container, impregnating the foamed granules with pressurized air, applying an internal pressure of 0.24 MPa (absolute pressure) to the foamed granules. Approximately 20 L of the air-impregnated foamed granules (with the applied internal pressure) was then fed into a foaming machine. Next, the foamed granules in the foaming machine were heated for 30 seconds using water vapor at 0.06 MPa (gauge pressure), thereby further foaming the foamed granules (secondary foaming) to obtain foamed granules (secondary foamed granules).

[0244] (Preparation of polypropylene resin foamed molded articles)

[0245] The obtained foamed granules (two-stage foamed granules) were placed into a pressure-resistant sealed container. Air was introduced into the pressure-resistant sealed container, impregnating the two-stage foamed granules with pressurized air, applying an internal pressure (absolute pressure) of 0.20 MPa to the two-stage foamed granules. Using a molding machine (DAISEN polypropylene in-mold foaming molding machine) and molds for evaluating shrinkage and deformation, the air-impregnated two-stage foamed granules were heated and molded with steam at 0.30 MPa (gauge pressure) to obtain foamed molded bodies. After being placed at room temperature for 1 hour, each foamed molded body was cured and dried in a constant temperature chamber at 75°C for 12 hours, and then placed at room temperature again for 4 hours. Subsequently, the shrinkage and deformation of the obtained foamed molded bodies were evaluated using the above method. The results are shown in Table 1.

[0246] (Examples 2-7, Comparative Examples 1-9)

[0247] The types and amounts of materials and / or manufacturing conditions were varied as described in Table 1, except that the foamed particles and foamed molded articles were obtained using the same method as in Example 1. The physical properties of the obtained foamed particles and foamed molded articles were measured and evaluated. The results are shown in Table 1.

[0248] [Table 1]

[0249]

[0250] According to the examples and comparative examples, there was no significant difference in the DSC ratio of the foamed particles. Therefore, according to the examples and comparative examples, the foaming ratio of the foamed particles can be compared relatively accurately.

[0251] 〔Summarize〕

[0252] Based on Table 1, the following information is clearly available:

[0253] (1) According to the comparison between Examples 1 to 7 and Comparative Example 1, when polypropylene resin is used alone, the deformation of the foamed molded body is large and the shrinkage of the foamed molded body is not sufficiently reduced.

[0254] (2) According to the comparison between Examples 1 to 7 and Comparative Example 2, when polystyrene, as an amorphous resin, is used instead of AS copolymer, the foaming properties of the foamed particles are low.

[0255] (3) According to the comparison between Examples 1 to 7 and Comparative Example 3, when a mixture of polyphenylene ether and polystyrene is used instead of AS copolymer as an amorphous resin, the foaming properties of the foam particles are low and the shrinkage of the resulting foamed molded body is not sufficiently reduced.

[0256] (4) According to the comparison between Examples 1 to 7 and Comparative Example 4, when the amount of AS copolymer exceeds the range of this application, the foaming properties and continuous bubble rate of the foamed particles become poor (lower).

[0257] (5) Based on the comparison between Examples 1 to 7 and Comparative Example 5, it can be seen that when hydrogenated styrene copolymer is not used, the shrinkage of the foamed molded body is not sufficiently reduced.

[0258] (6) According to the comparison between Examples 1 to 7 and Comparative Example 6, when the amount of hydrogenated styrene copolymer exceeds the range of this application, the foaming properties of the foamed particles are low and the shrinkage of the resulting foamed molded body is not sufficiently reduced.

[0259] (7) According to the comparison between Examples 1 to 7 and Comparative Example 7, 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.

[0260] (8) According to the comparison between Examples 1 to 7 and Comparative Example 8, when the amount of AS copolymer is less than the range of this application, the shrinkage of the obtained foamed molded article is not sufficiently reduced.

[0261] (9) According to the comparison between Examples 1 to 7 and Comparative Example 9, when the amount of hydrogenated styrene copolymer is less than the range of this application, the shrinkage of the resulting foamed molded article is not sufficiently reduced.

[0262] Industrial availability

[0263] The polypropylene resin foaming granules described in one embodiment of the present invention provide polypropylene resin foamed molded articles with excellent foaming properties and almost no shrinkage or deformation after molding. Polypropylene resin foamed molded articles are suitable for various applications such as cushioning packaging materials, logistics materials, thermal insulation materials, civil engineering components, and automotive components.

Claims

1. A polypropylene resin expanded particle comprising: 100 parts by weight of a polypropylene resin; 5 to 60 parts by weight of a copolymer containing an acrylonitrile unit and a styrene unit; and 3.0 to 30.0 parts by weight of a hydrogenated styrene copolymer, the styrene unit is an α-methylstyrene unit.

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

3. The polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a content of a styrene unit in the hydrogenated styrene copolymer is 15 to 80% by weight in 100% by weight of the hydrogenated styrene copolymer.

4. The polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a glass transition temperature of the copolymer containing an acrylonitrile unit and a styrene unit is 95 to 140°C.

5. A polypropylene resin expanded molded body obtained by molding the polypropylene resin expanded particle according to any one of claims 1 to 4.

6. A method for producing a polypropylene resin expanded particle, comprising a foaming step of foaming a polypropylene resin particle, the polypropylene resin particle comprising: 100 parts by weight of a polypropylene resin; 5 to 60 parts by weight of a copolymer containing an acrylonitrile unit and a styrene unit; and 3 to 30 parts by weight of a hydrogenated styrene copolymer, the styrene unit is an α-methylstyrene unit.

7. The method for producing polypropylene-based resin expanded particles according to claim 6, wherein the hydrogenated styrene copolymer is a styrene / ethylene / butylene / styrene copolymer (SEBS).

8. The method for producing polypropylene-based resin expanded particles according to claim 6 or 7, wherein, a content of a styrene unit in the hydrogenated styrene copolymer is 15 to 80% by weight in 100% by weight of the hydrogenated styrene copolymer.

9. The method for producing polypropylene-based resin expanded particles according to claim 6 or 7, wherein, a glass transition temperature of the copolymer containing an acrylonitrile unit and a styrene unit is 95 to 140°C.

10. A method for producing a polypropylene resin foamed molded body, comprising: a step of in-mold foaming the polypropylene resin expanded particle according to any one of claims 1 to 4 or the polypropylene resin expanded particle obtained by the method for producing a polypropylene resin expanded particle according to any one of claims 6 to 9.

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