Polypropylene resin extruded foam particles and polypropylene resin foam molded articles

Abstract

To provide polypropylene resin extruded foam particles having excellent moldability and a polypropylene resin foam molded body having excellent break resistance. Polypropylene resin extruded foam particles obtained by foaming a base resin, the base resin including specific amounts of each of a polypropylene resin having a branched structure having a specific configuration, a thermoplastic elastomer, and an inorganic coloring agent.

Description

[Technical Field]

[0001] This invention relates to polypropylene resin extruded foam particles and polypropylene resin foam molded articles. [Background technology]

[0002] Polypropylene-based resin foam molded articles obtained using polypropylene-based resin foam particles possess the advantages of foam molded articles, such as arbitrariness of shape, cushioning properties, light weight, and heat insulation properties.

[0003] Methods for producing polypropylene resin foam particles include the batch foaming method, which is a discontinuous process, and the extrusion foaming method, which is a continuous process. The extrusion foaming method has many advantages in terms of efficiency and environmental impact.

[0004] Examples of techniques for obtaining polypropylene resin foam particles by extrusion foaming include the techniques described in Patent Documents 1 and 2.

[0005] Patent Document 1 discloses polypropylene resin pre-foamed particles, characterized in that they consist of a polypropylene resin in which the loss tangent and the melt-fracture take-up rate satisfy a specific relational expression.

[0006] Patent Document 2 discloses a method for producing a modified polypropylene resin, which includes a melt-kneading step to obtain a modified polypropylene resin by melt-kneading a mixture of (a) a random polypropylene resin having a specific composition, (b) a conjugated diene compound, and (c) a radical polymerization initiator having a specific composition. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Public Gazette WO2018 / 016399 [Patent Document 2] International Public Gazette WO2020 / 004429 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, the conventional technologies described above were insufficient in terms of the moldability of polypropylene resin extruded foam particles and the fracture resistance of polypropylene resin foam molded articles, leaving room for further improvement.

[0009] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide polypropylene resin extruded foam particles with excellent moldability and polypropylene resin foam molded articles with excellent fracture resistance. [Means for solving the problem]

[0010] In other words, the polypropylene resin extruded foam particles according to one embodiment of the present invention include a base resin containing a polypropylene resin having a branched structure, the melt tension of the polypropylene resin having a branched structure being 5 cN to 50 cN, and the base resin further contains a thermoplastic elastomer and an inorganic colorant. [Effects of the Invention]

[0011] According to one embodiment of the present invention, it is possible to provide polypropylene resin extruded foam particles with excellent moldability and polypropylene resin foam molded articles with excellent fracture resistance. [Modes for carrying out the invention]

[0012] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims. Further, embodiments or examples obtained by combining technical means respectively disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, by combining the technical means respectively disclosed in each embodiment, new technical features can be formed. All academic documents and patent documents described in this specification are hereby incorporated by reference as references in this specification. In addition, unless otherwise specified in this specification, "A~B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0013] In addition, unless otherwise specified in this specification, as a structural unit, X 1 a structural unit derived from a monomer, and X 2 a structural unit derived from a monomer, and ··· and X n a copolymer containing a monomer (n is an integer of 3 or more) is also referred to as "X 1 / X 2 / ··· / X n copolymer". X 1 / X 2 / ··· / X n Unless otherwise specified, the copolymerization mode of the copolymer is not particularly limited and may be a random copolymer, a block copolymer, or a graft copolymer.

[0014] 〔1. Technical idea of an embodiment of the present invention〕 When producing polypropylene resin extruded foam particles by the extrusion foaming method, it is necessary to foam a resin composition that is in a completely molten state. Therefore, when producing polypropylene resin extruded foam particles by the extrusion foaming method using a linear polypropylene resin that does not have a branched structure, the viscosity of the resin composition during foaming is low, and the resin composition cannot withstand the foaming force, so the cells may burst. Furthermore, because the open-cell ratio of the resulting extruded foam particles is high, they shrink during molding, and it may not be possible to obtain a good quality foamed molded product. As a technology to solve this problem, polypropylene resins with a cross-linked structure have been proposed, as described in Patent Documents 1 and 2.

[0015] However, the inventors have independently discovered that when extruded foam particles obtained using a polypropylene resin having a branched structure are foam-molded in a mold, the resulting foamed molded articles tend to crack with even slight deformation, such as when subjected to impact. The tendency for deformation-induced cracking in foamed molded articles obtained from extruded foam particles made by extruding polypropylene resin having a branched structure was particularly pronounced in low-compression foamed molded articles using low-compression extruded foam particles. Although the reasons for these are not clear, the inventors have inferred the following: There are many cross-linked portions (which can also be called "branching") in the molecular chains of the resin in the foamed molded article. When the foamed molded article is stretched, these cross-linked portions (branching) may intertwine, preventing the foamed molded article from stretching further. It is also possible that because the cross-linked portions (branching) intertwine and prevent stretching, the molecular chains have no choice but to break. In other words, the inventors inferred that the above reason is that the flexibility of the foamed molded article decreases, making it difficult to stretch, and specifically, the tensile elongation at break of the foamed molded article tends to decrease.

[0016] In other words, the technologies described in Patent Documents 1 and 2 above had room for further improvement in terms of the fracture resistance of the foamed molded article.

[0017] Therefore, the present inventors conducted intensive studies to provide extrusion foamed particles that can provide a foamed molded article excellent in fracture resistance. As a result, the present inventors surprisingly and independently found the following new findings: By using a polypropylene-based resin having a branched structure and a linear polypropylene-based resin having no branched structure in combination, extrusion foamed particles that can provide a foamed molded article excellent in fracture resistance can be provided.

[0018] Incidentally, depending on the intended use of the foamed molded article, there may be a suitable color (colored), to make the dirt on the surface of the foamed molded article less noticeable, and to impart light resistance to the foamed molded article, etc. In some cases, a colored foamed molded article is required. The present inventors tried to obtain colored extrusion foamed particles by using an inorganic colorant and using a polypropylene-based resin having a branched structure and a linear polypropylene-based resin having no branched structure in combination, and further to obtain a colored foamed molded article from the colored extrusion foamed particles. As a result, the present inventors surprisingly and independently found that (a) the colored extrusion foamed particles thus obtained have a significantly narrow molding width for obtaining good-quality foamed molded articles, and (b) the colored foamed molded article好不容易 obtained has extremely low fracture resistance.

[0019] Therefore, the present inventors conducted further intensive studies to provide both polypropylene-based resin extrusion foamed particles excellent in moldability and polypropylene-based resin foamed molded articles excellent in fracture resistance. As a result, the present inventors surprisingly and independently found the following new findings and completed the present invention: By using a polypropylene-based resin having a branched structure and a thermoplastic elastomer in combination, even when an inorganic colorant is used, (a) polypropylene-based resin extrusion foamed particles excellent in moldability and (b) polypropylene-based resin foamed molded articles excellent in fracture resistance can both be provided.

[0020] [2. Polypropylene-based resin extrusion foamed particles] The polypropylene-based resin extrusion foamed particles according to an embodiment of the present invention include a base resin containing a polypropylene-based resin having a branched structure, the melt tension of the polypropylene-based resin having the branched structure is 5 cN to 50 cN, and the base resin further contains a thermoplastic elastomer and an inorganic colorant.

[0021] The polypropylene-based resin extrusion foamed particles can be made into a polypropylene-based resin foamed molded body by molding (for example, in-mold foaming molding) the polypropylene-based resin extrusion foamed particles. In this specification, the "polypropylene-based resin extrusion foamed particles" may be referred to as "extrusion foamed particles", and the "polypropylene-based resin extrusion foamed particles according to an embodiment of the present invention" may be referred to as "the present extrusion foamed particles". The "polypropylene-based resin foamed molded body" may be referred to as "foamed molded body", and the "polypropylene-based resin foamed molded body according to an embodiment of the present invention" may be referred to as "the present foamed molded body".

[0022] Since the present extrusion foamed particles have the above-described configuration, they have the advantages that (a) they have excellent moldability and (b) they can provide a foamed molded body having excellent fracture resistance. In this specification, the moldability of the present extrusion foamed particles is evaluated by the molding width of the extrusion foamed particles. The molding width will be described later. Also, in this specification, the fracture resistance of the present foamed molded body is evaluated by the tensile fracture elongation rate of the foamed molded body. The tensile fracture elongation rate will be described later.

[0023] (2-1. Base resin) The base resin includes (a) a polypropylene-based resin having a branched structure, (b) a thermoplastic elastomer, and an inorganic colorant. The base resin may further optionally contain additives such as a bubble nucleating agent.

[0024] In this specification, "polypropylene resin having a branched structure" refers to (a) a polypropylene resin in which the molecules of a polypropylene resin without a branched structure are partially crosslinked intermolecularly, and (b) a polypropylene resin in which a diene compound other than (poly)propylene is introduced as a branched chain to a polypropylene resin without a branched structure. In this specification, "polypropylene resin without a branched structure" may be referred to as "linear polypropylene resin," and "polypropylene resin having a branched structure" may be referred to as "branched polypropylene resin," and "linear polypropylene resin" and "branched polypropylene resin" may be collectively referred to as "polypropylene resin." Linear polypropylene resin can also be considered a raw material for branched polypropylene resin.

[0025] In this specification, polypropylene resin refers to a resin containing 50 mol% or more of structural units derived from propylene monomers out of 100 mol% of the total structural units contained in the resin. In this specification, "structural units derived from propylene monomers" may be referred to as "propylene units."

[0026] (Linear polypropylene resin) The linear polypropylene resin may be (a) a homopolymer of propylene, (b) a block copolymer or random copolymer of propylene and a monomer other than propylene, or (c) a mixture of two or more of these.

[0027] Linear polypropylene resins may contain one or more structural units derived from monomers other than propylene monomers, in addition to propylene units, or may contain one or more of these units. The "monomers other than propylene monomers" used in the manufacture of linear polypropylene resins are sometimes referred to as "comonomers," and the "structural units derived from monomers other than propylene monomers" contained in linear polypropylene resins are sometimes referred to as "comonomer units."

[0028] Examples of comonomers include the following monomers: (a) α-olefins having 2 or 4 to 12 carbon atoms, such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, and 1-decene; (b) cyclic olefins such as cyclopentene, norbornene, and tetracyclo[6,2,11,8,13,6]-4-dodecene; (c (d) Dienes such as 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, and (d) vinyl monomers such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, vinyl acetate, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic anhydride, styrene monomers, vinyltoluene, divinylbenzene, etc.

[0029] Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and glycidyl acrylate.

[0030] Examples of methacrylate esters include methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate.

[0031] Examples of styrene monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0032] The linear polypropylene resin preferably has structural units derived from α-olefins having 2 or 4 to 12 carbon atoms as comonomer units, more preferably structural units derived from 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 / or 1-decene, more preferably structural units derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene and / or 4-methyl-1-pentene, even more preferably structural units derived from ethylene, 1-butene, isobutene and / or 1-pentene, and most preferably structural units derived from ethylene and / or 1-butene. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0033] The linear polypropylene resin is preferably a propylene homopolymer, a polypropylene block copolymer, and / or a polypropylene random copolymer, and more preferably a propylene homopolymer and / or a polypropylene random copolymer. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0034] The linear polypropylene resin preferably contains 90 mol% or more of propylene units, more preferably 93 mol% or more, even more preferably 95 mol% or more, and particularly preferably 97 mol% or more, of the total structural units contained in the linear polypropylene resin. This configuration has the advantage of yielding a branched polypropylene resin with high melt tension and low gel fraction.

[0035] The melting point of the linear polypropylene resin is not particularly limited. The melting point of the linear polypropylene resin is preferably, for example, 130°C to 165°C, more preferably 135°C to 164°C, even more preferably 138°C to 163°C, and particularly preferably 140°C to 162°C. When the melting point of the linear polypropylene resin is within the above range, it has the advantages of (a) the obtained extruded foam particles having excellent moldability, and (b) the extruded foam particles being able to provide a foamed molded article with excellent fracture resistance. When the melting point of the linear polypropylene resin is (a) 130°C or higher, it has the advantages of not having a risk of reduced dimensional stability of the foamed molded article, not having a risk of insufficient heat resistance of the foamed molded article, and having a tendency for the compressive strength of the foamed molded article to be increased, and (b) 165°C or lower, it has the advantage that the extruded foam particles can be molded at a relatively low vapor pressure, and the extruded foam particles can be molded using a general-purpose molding machine for polypropylene resin foam particles.

[0036] In this specification, the melting point of linear polypropylene resin is a value obtained by measurement using differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific operating procedure (measurement method) is as follows: (1) Melt the linear polypropylene resin by raising the temperature of 5 to 6 mg of linear polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min; (2) Then, crystallize the linear polypropylene resin by lowering the temperature of the molten linear polypropylene resin from 220°C to 40°C at a cooling rate of 10°C / min; (3) Then, further raise the temperature of the crystallized linear polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve of the linear polypropylene resin obtained during the second heating (i.e., at (3)) can be determined as the melting point of the linear polypropylene resin. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the linear polypropylene resin obtained during the second heating cycle using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) is defined as the melting point of the linear polypropylene resin. As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0037] The melt flow rate (MFR) of the linear polypropylene resin is not particularly limited. The MFR of the linear polypropylene resin is preferably, for example, 0.5 g / 10 min to 20.0 g / 10 min, more preferably 1.0 g / 10 min to 15.0 g / 10 min, even more preferably 2.0 g / 10 min to 12.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 10.0 g / 10 min.

[0038] In this specification, the MFR of linear polypropylene resin is a value obtained by measurement under conditions of 230°C and 2.16 kg load, in accordance with ISO 1133.

[0039] (Polypropylene resin with a branched structure) A branched polypropylene resin can be obtained by introducing a branched structure into a linear polypropylene resin. The method for introducing a branched structure into a linear polypropylene resin is not particularly limited, but examples include (a1) irradiating the linear polypropylene resin with radiation, and (a2) melt-kneading a mixture containing the linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator. Preferably, the branched polypropylene resin is a resin obtained by the method in (a2), i.e., a branched polypropylene resin obtained by melt-kneading a mixture containing the linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator.

[0040] A specific example of the method described in (a1) above is the method described in Japanese Patent Publication No. 2002-542360.

[0041] The method described in (a2) above will be further explained. In the method described in (a2), for example, a branched polypropylene resin can be obtained by performing (i) to (iv) below in order: (i) a mixture containing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator is melt-kneaded in an apparatus equipped with a die; (ii) the resulting molten mixture is extruded from the die; (iii) the extruded molten mixture (also called a strand) is cooled; (iv) the strand is shredded simultaneously with and after the cooling of the strand. A specific example of the method described in (a2) above is the method described in WO2020 / 004429.

[0042] (i) A branched structure can be stably introduced into a linear polypropylene resin, and the introduction of the branched structure is highly reproducible, and / or (ii) a branched polypropylene resin can be obtained without requiring complex equipment and with high productivity, therefore, in one embodiment of the present invention, the branched polypropylene resin is preferably a branched polypropylene resin obtained by the method of (a2) described above.

[0043] (Melting tension of branched polypropylene resin) The melt tension of branched polypropylene resin can be higher than that of linear polypropylene resin. The melt tension of branched polypropylene resin is 5 cN to 50 cN, preferably 6 cN to 40 cN, more preferably 7 cN to 30 cN, even more preferably 8 cN to 25 cN, and particularly preferably 10 cN to 20 cN. When the melt tension of branched polypropylene resin is 5 cN or higher, when the composition containing the branched polypropylene resin and the foaming agent is completely melted and foamed, the tension of the composition becomes sufficiently high, preventing cell rupture in the resulting extruded foam particles. As a result, (a) the resulting extruded foam particles have the advantage of having excellent moldability, and (b) the extruded foam particles can provide a foamed molded article with excellent fracture resistance. When the melt tension of branched polypropylene resin is 50 cN or less, the resin pressure (the force with which the molten mixture pushes the pressure gauge installed in the manufacturing apparatus) does not become too high during the extrusion foaming process, and the discharge rate can be made relatively high. As a result, it has the advantage of being able to produce extruded foam particles with good productivity.

[0044] In this specification, the melt tension of branched polypropylene resins is measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd., Japan). Specifically, the procedure is as follows (1) to (5): (1) A sample resin for measurement (branched polypropylene resin) is filled into a 9.55 mm diameter barrel heated to the test temperature (200°C); (2) The sample resin is then heated for 10 minutes in the barrel heated to the test temperature (200°C); (3) The sample resin is then dispensed in a string-like form from a capillary die (1.0 mm diameter, 10 mm length) at a constant piston descent speed (10 mm / min), and this string-like material is passed through a tension-detecting pulley located 350 mm below the capillary die, after which winding using a winding roll is started; (4) After the winding of the string-like material stabilizes, the winding speed of the string-like material is increased at a constant rate from an initial speed of 1.0 m / min to a speed of 200 m / min in 4 minutes; (5) The load on the load cell pulley when the string-like material breaks is measured as the melt tension.

[0045] (MFR of branched polypropylene resin) The MFR of the branched polypropylene resin is not particularly limited. The MFR of the branched polypropylene resin is preferably, for example, 0.5 g / 10 min to 20.0 g / 10 min, more preferably 1.0 g / 10 min to 15.0 g / 10 min, even more preferably 2.0 g / 10 min to 12.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 10.0 g / 10 min. When the MFR of the branched polypropylene resin is within the above range, it has the advantages of (a) the obtained extruded foam particles having excellent moldability, and (b) the extruded foam particles being able to provide a foamed molded article with excellent fracture resistance. When the MFR of the branched polypropylene resin is (a) 0.5 g / 10 min or more, the extruded foam particles obtained from the branched polypropylene resin have the advantage of providing a foamed molded article with less deformation and good (beautiful) surface properties, and (b) when it is 20.0 g / 10 min or less, the composition containing the extruded foam particles obtained from the branched polypropylene resin has the advantage of good foaming properties during extrusion foaming.

[0046] In this specification, the MFR of branched polypropylene resin is a value obtained by measurement under conditions of 230°C and 2.16 kg load, in accordance with ISO 1133.

[0047] (Melting point of branched polypropylene resin) The melting point of branched polypropylene resin is not particularly limited. Preferably, the melting point of branched polypropylene resin is 130°C to 165°C, and more preferably 135°C to 164°C. When the melting point of branched polypropylene resin falls within the above range, it has the advantages of (a) the resulting extruded foam particles having excellent moldability, and (b) the extruded foam particles providing a foamed molded article with excellent fracture resistance. The melting point of branched polypropylene resin is determined by measurement using the DSC method, similar to the melting point of linear polypropylene resin.

[0048] The base resin preferably contains 64.5% to 94.5% by weight of branched polypropylene resin, more preferably 64.5% to 90.0% by weight, and even more preferably 65.0% to 90.0% by weight, of 100% by weight of the base resin. This configuration has the advantages of (a) the resulting extruded foam particles having excellent moldability, and (b) the extruded foam particles providing a foamed molded article with excellent fracture resistance. The content of branched polypropylene resin in the base resin can also be said to be the amount of branched polypropylene resin used in the production of the extruded foam particles.

[0049] (Thermoplastic elastomer) In this specification, thermoplastic elastomers refer to those with a Shore A value of 20 to 95 as measured by ISO 868. Thermoplastic elastomers can also be described as resins having a thermoplastic resin as a hard segment and a rubber component as a soft segment.

[0050] Examples of thermoplastic elastomers include polyolefin elastomers, polyolefin plastomers, polystyrene elastomers, polyvinyl chloride elastomers, polyester elastomers, polyurethane elastomers, and polyamide elastomers. Examples of polyolefin elastomers include TAFMER®, MILASTOMER® (Mitsui Chemicals, Inc.), LUCENE® (LG Chem), VERSIFY® (Dow Inc.), ESPOLEX® (Sumitomo Chemical Co., Ltd.), MULTIUSE LEOSTOMER® (Riken Technos Co., Ltd.), and Vistamaxx® (Exxon Examples include Mobil. Examples of polyolefin plastomers include Excellen® FX, Toughselenium® (Sumitomo Chemical Co., Ltd.), AFFINITY® (Dow Inc.), and Queo® (Borealis). These thermoplastic elastomers may be used individually or in combination of two or more.

[0051] As a thermoplastic elastomer, it is preferable to use a polyolefin-based elastomer and / or a polyolefin-based plastomer, and more preferably a polyolefin-based elastomer, from the viewpoint of high elasticity and compatibility with polypropylene-based resins. As a thermoplastic elastomer, it is preferable to use a thermoplastic elastomer that has (a) a polyolefin such as polypropylene or polyethylene as a hard segment and (b) a rubber component such as ethylene / α-olefin rubber as a soft segment in one molecule. Thermoplastic elastomers having polypropylene or polyethylene as a hard segment have high compatibility with polypropylene-based resins. Furthermore, thermoplastic elastomers having one or more selected from the group consisting of ethylene / propylene rubber, ethylene / 1-butene rubber, ethylene / propylene / diene rubber, and ethylene / 1-octene rubber as a soft segment have even higher compatibility with polypropylene-based resins. Therefore, as thermoplastic elastomers, (a) thermoplastic elastomers having polypropylene or polyethylene as a hard segment, (b) thermoplastic elastomers having one or more selected from the group consisting of ethylene / propylene rubber, ethylene / 1-butene rubber, ethylene / propylene / diene rubber, and ethylene / 1-octene rubber as a soft segment, or (c) thermoplastic elastomers having (i) a polyolefin such as polypropylene or polyethylene as a hard segment in one molecule, and (ii) a rubber component such as ethylene-α-olefin rubber as a soft segment.

[0052] The tensile elongation at break of the thermoplastic elastomer is preferably 500% or more, more preferably 600% or more, even more preferably 650% or more, and particularly preferably 700% or more. The tensile elongation at break of the thermoplastic elastomer is preferably 10,000% or less, and more preferably 5,000% or less. This configuration has the advantage of improving the flexibility of the branched polypropylene resin, extruded foam particles, and foam molded articles, and making them less likely to break when deformed by applied force. In this specification, the tensile elongation at break of the thermoplastic elastomer is a value obtained by measuring the thermoplastic elastomer as a sample in accordance with ASTM D638.

[0053] The melting point of the thermoplastic elastomer is not particularly limited. The melting point of the thermoplastic elastomer is preferably, for example, 40°C to 110°C, more preferably 50°C to 90°C, and particularly preferably 60°C to 80°C. This configuration improves the flexibility of the extruded foam particles and the foamed molded article. As a result, when force is applied to the resulting foamed molded article and it deforms, it has the advantage of being less prone to breakage.

[0054] In this specification, the melting point of a thermoplastic elastomer is a value obtained by measurement using the DSC method. Specifically, the DSC curve of a thermoplastic elastomer can be obtained using the same method as for measuring the melting point of a linear polypropylene resin, except that the thermoplastic elastomer is used instead of the linear polypropylene resin. Similar to the melting point of a linear polypropylene resin, the melting point of a thermoplastic elastomer can be determined from its DSC curve.

[0055] The MFR of the thermoplastic elastomer is preferably 0.3 g / 10 min to 10.0 g / 10 min, more preferably 0.5 g / 10 min to 8.0 g / 10 min, more preferably 0.7 g / 10 min to 6.0 g / 10 min, and more preferably 1.0 g / 10 min to 5.0 g / 10 min. This configuration improves the compatibility between the thermoplastic elastomer and the branched polypropylene resin, and improves the flexibility of the resulting extruded foam particles and foam molded articles. As a result, the foam molded articles have the advantage of being less prone to breakage when force is applied and they deform.

[0056] In this specification, the MFR of thermoplastic elastomers is a value obtained by measurement under conditions of 230°C and 2.16 kg load, in accordance with ISO 1133.

[0057] The flexural modulus of the thermoplastic elastomer is preferably 10 MPa to 200 MPa, more preferably 15 MPa to 100 MPa, even more preferably 20 MPa to 80 MPa, and particularly preferably 25 MPa to 70 MPa. This configuration improves the flexibility of the extruded foam particles and the foamed molded article. As a result, when force is applied to the resulting foamed molded article and it deforms, it has the advantage of being less likely to break. In this specification, the flexural modulus of the thermoplastic elastomer is a value obtained by measuring the thermoplastic elastomer as a sample in accordance with ISO 178.

[0058] Commercially available thermoplastic elastomers can also be used. Examples of commercially available thermoplastic elastomers that can be suitably used in one embodiment of the present invention include LG Chem's "LUCENE LC180" and Dow Inc.'s "VERSIFY 2300," both of which are polyolefin-based elastomers.

[0059] The base resin preferably contains 5.0% to 35.0% by weight of thermoplastic elastomer, more preferably 6.0% to 30.0% by weight, more preferably 8.0% to 25.0% by weight, even more preferably 10.0% to 25.0% by weight, and particularly preferably 12.0% to 20.0% by weight of thermoplastic elastomer in 100% by weight of the base resin. This configuration has the advantages of (a) the resulting extruded foam particles having excellent moldability, and (b) the extruded foam particles being able to provide a foamed molded article with excellent fracture resistance. The content of thermoplastic elastomer in the base resin can also be said to be the amount of thermoplastic elastomer used in the production of the extruded foam particles.

[0060] (Inorganic colorants) Inorganic colorants may include black, red, green, blue, and yellow colorants, as well as white colorants. Examples of inorganic colorants include carbon black, red clay, yellow clay, green clay, titanium dioxide, cobalt blue, Prussian blue, and chromium oxide green. These inorganic colorants may be used individually or in combination of two or more. It is preferable that the inorganic colorants include one or more selected from the group consisting of carbon black, red clay, yellow clay, green clay, titanium dioxide, cobalt blue, Prussian blue, and chromium oxide green, and it is more preferable that they include one or more selected from this group. From the viewpoint of ultraviolet absorption performance, carbon black is particularly preferred as the inorganic colorant.

[0061] The base resin preferably contains 0.5% to 5.0% by weight of an inorganic colorant, more preferably 0.5% to 4.5% by weight, even more preferably 0.5% to 4.0% by weight, even more preferably 1.0% to 3.5% by weight, and particularly preferably 1.0% to 3.0% by weight of an inorganic colorant, based on 100% by weight of the base resin. This configuration has the advantage that the open-cell ratio of the extruded foam particles obtained by the extrusion foaming method tends to be low. The amount of inorganic colorant in the base resin can also be said to be the amount of inorganic colorant used in the production of the extruded foam particles.

[0062] (Other resins or rubbers) The base resin may further contain resins other than branched polypropylene resins and thermoplastic elastomers (sometimes referred to as "other resins") or rubber, to the extent that the effects of one embodiment of the present invention are not impaired. Examples of other resins other than branched polypropylene resins include (a) linear polypropylene resins such as ethylene / propylene random copolymers, ethylene / propylene block copolymers, and propylene homopolymers; (b) 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 copolymers, ethylene / acrylic acid copolymers, and ethylene / methacrylic acid copolymers; and (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymers, and styrene / ethylene copolymers. Examples of rubbers include olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. Preferably, the base resin contains 0% to 20% by weight of the other resins in a proportion of 100% by weight of the base resin.

[0063] (Bubble nucleating agent) The base resin may contain a nucleating agent. In other words, a nucleating agent may be used in the production of these extruded foam particles. By using a nucleating agent, the number and shape of bubbles in the resulting extruded foam particles can be controlled.

[0064] Examples of bubble nucleating agents include sodium bicarbonate-citric acid mixtures, monosodium citrate, talc, and calcium carbonate. These bubble nucleating agents may be used individually or in combination of two or more.

[0065] The content of the nucleating agent in the base resin, in other words, the amount of nucleating agent used in the production of extruded foam particles, is not particularly limited. The content of the nucleating agent is preferably 0.01 to 5.00 parts by weight, more preferably 0.01 to 3.50 parts by weight, even more preferably 0.01 to 1.00 parts by weight, and particularly preferably 0.01 to 0.50 parts by weight per 100 parts by weight of polypropylene resin. This configuration has the advantage that the cell size (average cell diameter) and cell shape of the extruded foam particles become uniform, and as a result, the foaming properties during extrusion foaming tend to be more stable. Note that "cell" refers to "bubble".

[0066] (Organic colorants) The base resin may contain an organic colorant to the extent that it does not impair the effects according to one embodiment of the present invention. Examples of organic colorants include perylene-based organic pigments, azo-based organic pigments, quinacridone-based organic pigments, phthalocyanine-based organic pigments, surene-based organic pigments, dioxazine-based organic pigments, isoindoline-based organic pigments, and the like. These organic colorants may be used individually or in combination of two or more. The content of the organic colorant in the base resin is not particularly limited.

[0067] (Other ingredients) The base resin may further contain, as necessary, other components, (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, and / or (b) additives such as lubricants, plasticizers, fillers, reinforcing agents, flame retardants, and antistatic agents. These other components may be used individually or in combination of two or more.

[0068] The types and amounts of branched polypropylene resins, thermoplastic elastomers, inorganic colorants, and other resins or rubbers contained in the base resin contained in the extruded foam particles or the base resin contained in the foamed molded article obtained from the extruded foam particles, i.e., the base resin that substantially constitutes the extruded foam particles or the foamed molded article, do not substantially change even when the extruded foam particles or the foamed molded article is melted under reduced pressure and returned to a resin mass. In this specification, the process of melting extruded foam particles or the foamed molded article obtained from the extruded foam particles under reduced pressure to obtain a resin mass may be referred to as "resin return," and the resin mass obtained by resin return may be referred to as "returned resin." In this specification, the types and amounts of branched polypropylene resins, thermoplastic elastomers, inorganic colorants, and other resins or rubbers contained in the returned resin can be considered as the types and amounts of branched polypropylene resins, thermoplastic elastomers, inorganic colorants, and other resins or rubbers contained in the base resin. The types and amounts of branched polypropylene resins, thermoplastic elastomers, inorganic colorants, and other resins or rubbers contained in the returned resin can be determined by analyzing the returned resin using any known method.

[0069] There are no particular limitations on the specific method of resin return, but for example, the following method can be performed in order: (b1) Place the extruded foam particles or foam molded body into a dryer adjusted to the melting point of the extruded foam particles or foam molded body + 10°C; (b2) Then, using a vacuum pump, reduce the pressure inside the dryer to -0.05 MPa (cage pressure) to -0.10 MPa (cage pressure) over 5 to 10 minutes; (b3) After that, leave the extruded foam particles or foam molded body in the dryer for 30 minutes to prepare a resin mass (returned resin); (b4) Then, after the temperature inside the dryer has cooled to room temperature, return the pressure inside the dryer to atmospheric pressure; (b5) After that, remove the resin mass from the dryer.

[0070] In this specification, the melting point of extruded foam particles or foamed molded articles is a value obtained by measurement using the DSC method. Specifically, the DSC curve of extruded foam particles or foamed molded articles can be obtained using the same method as for measuring the melting point of linear polypropylene resin, except that extruded foam particles or foamed molded articles are used instead of linear polypropylene resin. Similar to the melting point of linear polypropylene resin, the melting point of extruded foam particles or foamed molded articles can be determined from the DSC curve of the extruded foam particles or foamed molded articles.

[0071] (2-2. Method for producing polypropylene resin extruded foam particles) The method for producing the extruded foam particles is not particularly limited, and known extrusion foaming methods can be used. One embodiment of the method for producing the extruded foam particles is, for example, the following: a method for producing polypropylene resin extruded foam particles, comprising: a first step of producing an extruded foam by an extrusion foaming method using a branched polypropylene resin, a thermoplastic elastomer, an inorganic colorant, and a foaming agent; and a second step of producing extruded foam particles by cutting the extruded foam obtained in the first step into particle shapes.

[0072] (First step) The first step will now be explained in detail. A specific example of the first step is a process in which the following (c1) and (c2) are performed in order: (c1) A melt-kneading step in which a composition containing a resin mixture including a branched polypropylene resin, a thermoplastic elastomer, and an inorganic colorant, and a foaming agent is melt-kneaded in a device equipped with a die to obtain a melt-kneaded product; and (c2) An extrusion foaming step in which the obtained melt-kneaded product is extruded through a die into a region where the pressure is lower than the internal pressure of the device (low-pressure region) to obtain an extruded foam.

[0073] In the first step, particularly in (c1) above, if necessary, further nucleating agents, stabilizers (e.g., antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents) and additives (e.g., colorants, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, and antistatic agents) may be used.

[0074] The resin mixture in (c1) above can also be called a base resin. In (c1) above, the branched polypropylene resin, thermoplastic elastomer, inorganic colorant and blowing agent, and other optionally used resins, nucleating agents and other components may be mixed before being supplied to the apparatus or may be mixed within the apparatus. In other words, in (c1) above, the composition may be supplied to the apparatus or the composition may be prepared (completed) within the apparatus. In (c1) above, (i) the method and sequence of mixing the branched polypropylene resin, thermoplastic elastomer, inorganic colorant and blowing agent, and other optionally used resins, nucleating agents and other components, or (ii) the method and sequence of supplying the branched polypropylene resin, thermoplastic elastomer, inorganic colorant and blowing agent, and other optionally used resins, nucleating agents and other components to the apparatus is not particularly limited.

[0075] In (c1) above, the inorganic colorant may be incorporated (used) as a masterbatch. A masterbatch of an inorganic colorant can be obtained by mixing the inorganic colorant with any resin (e.g., a polypropylene-based resin) in any ratio. The concentration of the inorganic colorant in the masterbatch is not particularly limited; for example, a masterbatch may contain 40% by weight of the inorganic colorant in 100% by weight of the masterbatch.

[0076] In (c2) above, the molten mixture may be cooled before extruding it into the low-pressure region.

[0077] The blowing agent used in one embodiment of the present invention is not particularly limited, and known organic and inorganic blowing agents can be used. Examples of organic blowing agents include aliphatic hydrocarbons such as propane and fluorinated hydrocarbons such as difluoroethane. Examples of inorganic blowing agents include carbon dioxide, air, nitrogen and other inorganic gases, and water. The blowing agents described above may be used individually or in combination of two or more. The polypropylene resin extruded foam particles are preferably obtained using one or more selected from the group consisting of aliphatic hydrocarbons, fluorinated hydrocarbons, carbon dioxide, air, nitrogen and water as the blowing agent, more preferably using one or more selected from the group consisting of carbon dioxide, air, nitrogen and water, and even more preferably using carbon dioxide. The amount of blowing agent used in the first step may be appropriately adjusted according to the type of blowing agent and the target foaming ratio of the polypropylene resin extruded foam particles.

[0078] (Second step) The second step is to cut the extruded foam obtained in the first step into particle shapes to produce extruded foam particles. Cutting into particle shapes is also called shredding. The extruded foam particles obtained in the second step are polypropylene resin extruded foam particles.

[0079] In the second step, the shredding method, or cutting method, is preferably a cold cut method or a hot cut method. A cold cut method is the strand cut method. Hot cut methods include the underwater cut method and the watering cut method.

[0080] The extruded foam obtained in the first step may be fully foamed or still foaming before being cut into particles in the second step. In other words, in the second step, the fully foamed extruded foam may be cut into particles, or the extruded foam that is still foaming may be cut into particles. To put it another way, the extruded foam obtained in the first step includes not only the fully foamed extruded foam but also the extruded foam that is still foaming.

[0081] In the second step, the extruded foam may be cooled before cutting it into particles, simultaneously with cutting it, or after cutting it.

[0082] (2-3. Physical properties of polypropylene resin extruded foam particles, etc.) (Open cell ratio) The open-cell ratio of the extruded foam particles is preferably as low as possible. The open-cell ratio of the extruded foam particles is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 5% or less. The lower limit of the open-cell ratio of the polypropylene resin extruded foam particles is not particularly limited, and is, for example, 0.0% or more. This configuration has the advantages that (a) the extruded foam particles have excellent moldability because the cells hardly rupture and shrink during molding, and (b) the foamed molded article obtained using the extruded foam particles exhibits characteristics such as arbitrariness of shape, cushioning properties, lightness, compressive strength, and heat insulation properties to a greater extent.

[0083] In this specification, the open-cell ratio of polypropylene resin extruded foam particles is a value obtained by measuring using an air-comparable hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles is calculated by performing the following steps (1) to (3) in order: (1) Using an air-comparable hydrometer, the volume Vc (cm³) of the extruded foam particles 3 (1) Measure the volume of the extruded foam particles after measuring Vc; (2) Submerge the entire volume of extruded foam particles in ethanol in a graduated cylinder; (3) Then, from the rise in the position of the ethanol in the graduated cylinder, determine the apparent volume of the extruded foam particles Va (cm³). 3 (4) Determine the open-cell ratio of the extruded foam particles using the following formula: Open-cell ratio (%) = ((Va-Vc)×100) / Va. Note that the method for measuring the volume Va is also called the immersion method.

[0084] (Average cell diameter) The average cell diameter of the extruded foam particles is preferably 100 μm to 500 μm, more preferably 100 μm to 400 μm, even more preferably 120 μm to 350 μm, and particularly preferably 150 μm to 300 μm. With this configuration, the cells hardly rupture and shrink during molding of the extruded foam particles, which has the advantage of excellent moldability.

[0085] In this specification, the average cell diameter of polypropylene resin extruded foam particles is specifically calculated by performing the following steps (1) to (4) in order: (1) Cut the extruded foam particle with a razor blade so as to pass through the center of the extruded foam particle; (2) Observe the resulting cut surface with an optical microscope; (3) Draw a 2000 μm straight line on the cut surface and measure the number of cells present on the straight line. Measure the number of cells for 10 extruded foam particles and calculate their arithmetic mean cell number; (4) The value obtained by measurement using the following formula is defined as the average cell diameter of the extruded foam particle (i.e., it can also be called the area average diameter): Average cell diameter (μm) = 2000 / average number of cells.

[0086] (Bulk density) The bulk density of the extruded foam particles is preferably 60 g / L or more, more preferably 70 g / L or more, even more preferably 80 g / L or more, and particularly preferably 90 g / L or more. The upper limit of the bulk density of the extruded foam particles is not particularly limited, and is, for example, 300 g / L or less. As described above, the tendency for cracking due to deformation in a foamed molded article is such that the lower the material of the extruded foam particles used to make the foamed molded article, the lower the tensile elongation at break of the resulting foamed molded article tends to be. Because the extruded foam particles have the above-described structure, they have the advantage of being able to provide a foamed molded article with a high tensile elongation at break, i.e., excellent fracture resistance, even if the bulk density is as low as 60 g / L or more. Furthermore, when the bulk density of the extruded foam particles is within the above range, the polypropylene resin foamed molded article obtained using the extruded foam particles has the advantage of exhibiting more characteristics such as arbitrariness of shape, cushioning properties, lightness, and heat insulation properties. If the foaming ratio of the extruded foam particles obtained by manufacturing the extruded foam particles does not reach the aforementioned range, a method can also be used to increase the foaming ratio by pressurizing the extruded foam particles with an inert gas and then heating the extruded foam particles (for example, the method described in Japanese Patent Application Publication No. 10-237212).

[0087] In this specification, the bulk density of polypropylene resin extruded foam particles is calculated by following (1) to (3) in order: (1) Fill a container with a known volume V (L), such as a graduated cylinder, beaker, or bucket, with the extruded foam particles until it overflows; (2) Level off the top surface of the container and measure the weight W (g) of the extruded foam particles inside the container; (3) Calculate the bulk density of the extruded foam particles using the following formula: Bulk density (g / L) = Weight of extruded foam particles W (g) / Volume of container V (L).

[0088] (molding width) These extruded foam particles have the advantage of a wide molding width (e.g., greater than 0). In this specification, it is intended that the wider the molding width of the extruded foam particles, the better the moldability of the extruded foam particles. In this specification, "molding width of extruded foam particles" refers to the range of vapor pressure (gauge pressure) during in-mold foam molding that allows for the production of a foamed molded article satisfying the following conditions: (x1) sufficient fusion between the extruded foam particles (e.g., fusion rate of 80% or more), (x2) sufficient filling of gaps between the extruded foam particles, (x3) a smooth surface, (x4) no melting of the surface, and (x5) the shape of the mold used for in-mold foam molding is transferred without shrinking by more than 5% relative to the dimensions of the mold. Furthermore, if the foamed molded article sticks to the mold and cannot be removed, it is determined that a foamed molded article cannot be obtained. In this specification, for example, when extruded foam particles are foam-molded in a mold, a foamed molded article satisfying the above-described conditions (x1) to (x5) can be obtained. If the vapor pressure during in-mold foam molding is P1 to P2, the "value" obtained by P2 - P1 is defined as the "molding width of the extruded foam particles." In this specification, "P1 to P2" is also referred to as the "feasible vapor pressure range."

[0089] If the vapor pressure is too low relative to the extruded foam particles, the resulting foamed molded product may have (a) insufficient fusion between the extruded foam particles, (b) insufficient filling of gaps between the extruded foam particles, (c) poor surface appearance, and / or (d) shrinkage resulting in the shape of the mold used for in-mold foam molding not being transferred. If the vapor pressure is too high relative to the extruded foam particles, the resulting foamed molded product may have (a) a melted surface, and / or (b) insufficient compressive strength.

[0090] The feasible vapor pressure range for these extruded foam particles is not particularly limited. A wider molding width for these extruded foam particles is preferable. The molding width of these extruded foam particles is more preferably 0.02 MPa or more, more preferably 0.03 MPa or more, even more preferably 0.04 MPa or more, and particularly preferably 0.05 MPa or more.

[0091] (Crystal peak) Extruded foam particles obtained by the extrusion foaming method are characterized by having one crystal peak in the DSC curve obtained by DSC measurement. In other words, polypropylene foam particles with one crystal peak in the DSC curve obtained by DSC measurement are highly likely to have been obtained by the extrusion foaming method. These extruded foam particles may also have one crystal peak in the DSC curve obtained by DSC measurement.

[0092] In this specification, the DSC curve of extruded foam particles used to calculate crystal peaks is the curve obtained by DSC measurement while raising the temperature of 5-6 mg of extruded foam particles from 40°C to 220°C at a heating rate of 10°C / min.

[0093] [3. Polypropylene-based resin foam molded product] A polypropylene resin foam molded article according to one embodiment of the present invention is formed by molding extruded foam particles containing a base resin that contains 64.5% by weight or more of a polypropylene resin having a branched structure in 100% by weight of the base resin, the open-cell ratio of the extruded foam particles is 15% or less, the density of the foam molded article is 60 g / L to 300 g / L, and the tensile elongation at break of the foam molded article is 10% or more.

[0094] The following describes various aspects of this foamed molded product. However, for matters other than those described in detail below (for example, the base resin and the open-cell ratio), refer to the description in section [2. Polypropylene-based resin extruded foam particles] as appropriate.

[0095] The method for molding extruded foam particles is not particularly limited, but one example is in-mold foam molding using a mold equipped with a fixed mold that cannot be driven and a movable mold that can be driven. The in-mold foam molding method is not particularly limited, and known methods can be used.

[0096] (Density of foamed molded material) The density of this foamed molded article is 60 g / L to 300 g / L, preferably 70 g / L to 300 g / L, more preferably 80 g / L to 300 g / L, and even more preferably 90 g / L to 300 g / L. Regarding the tendency of cracking due to deformation in foamed molded articles, the lower the part ratio of the foamed molded article, the lower the tensile elongation at break tends to be. This foamed molded article has the advantage of having a density of 60 g / L or more and a tensile elongation at break of 10% or more, i.e., a low part ratio and excellent fracture resistance. Furthermore, when the density of the foamed molded article is within the above-mentioned range, it also has the advantage of exhibiting more characteristics such as arbitrariness of shape, cushioning properties, lightness, and heat insulation properties.

[0097] In this specification, the density of a polypropylene-based foam molded article is calculated by performing the following steps in order: (1) measure the weight W1 (g) of the polypropylene-based foam molded article; (2) measure the volume V1 (L) of the polypropylene-based foam molded article whose weight W1 has been measured; (3) divide W1 by V1 and define the obtained value as the density (g / L) of the polypropylene-based foam molded article.

[0098] In (2), the method for measuring the volume of the foamed molded body is not particularly limited. For example, the volume V1 can be determined by submerging the foamed molded body in a container filled with water and measuring the amount of water that overflows. If the foamed molded body is in the shape of a plate, the length, width, and thickness of the foamed molded body can be measured, and the volume V1 can be calculated from these lengths. Furthermore, for density measurement, a foamed molded body that has been thoroughly dried after molding and left for 24 hours or more at room temperature of 23°C and 50% humidity may be used.

[0099] (Tensile elongation at fracture) This foamed molded article has the advantage of having a high tensile elongation at break. In this specification, it is intended that the higher the tensile elongation at break of the foamed molded article, the better the fracture resistance of the said foamed molded article.

[0100] The tensile elongation at break of the foamed molded article is preferably 10% or more, more preferably 12% or more, even more preferably 13% or more, and particularly preferably 15% or more.

[0101] In this specification, the tensile elongation at break of a polypropylene resin foam molded article is a value obtained by performing a tensile elongation test in accordance with ISO 1798. Specifically, the tensile elongation at break of a foam molded article is calculated by performing the following steps in order: (1) Prepare a dumbbell-shaped foam molded article as specified in ISO 1798, and use the obtained foam molded article as a test piece; (2) Fix both ends of the test piece; (3) Pull one side of the test piece until the test piece breaks; (4) The elongation of the test piece at the time of breakage is taken as the tensile elongation at break of the foam molded article.

[0102] A polypropylene resin foam molded article according to another embodiment of the present invention may have the following configuration: A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles as described in section [2. Polypropylene Resin Extruded Foam Particles].

[0103] One embodiment of the present invention may have the following configuration: [1] Polypropylene resin extruded foam particles comprising a base resin containing a polypropylene resin having a branched structure, wherein the melt tension of the polypropylene resin having a branched structure is 5 cN to 50 cN, and the base resin further contains a thermoplastic elastomer and an inorganic colorant. [2] The base resin is the polypropylene resin extruded foam particle according to [1], wherein the base resin contains 64.5% to 94.5% by weight of the polypropylene resin having the branched structure in 100% by weight of the base resin. [3] The base resin is a polypropylene resin extruded foam particle according to [1] or [2], wherein the base resin contains 5.0% to 35.0% by weight of the thermoplastic elastomer in 100% by weight of the base resin. [4] The base resin is a polypropylene resin extruded foam particle according to any one of [1] to [3], wherein the base resin contains 0.5% to 5.0% by weight of the inorganic colorant in 100% by weight of the base resin. [5] The polypropylene resin extruded foam particles according to any one of [1] to [4], wherein the inorganic coloring agent is one or more selected from the group consisting of carbon black, red clay, yellow clay, green clay, titanium dioxide, cobalt blue, Prussian blue, and chromium oxide green. [6] The thermoplastic elastomer is a polyolefin-based elastomer, the polypropylene resin extruded foam particle according to any one of [1] to [5]. [7] Polypropylene resin extruded foam particles according to any one of [1] to [6], wherein the tensile elongation at break of the thermoplastic elastomer is 500% to 1000%. [8] Polypropylene resin extruded foam particles according to any one of [1] to [7], wherein the melting point of the thermoplastic elastomer is 40°C to 110°C. [9] Polypropylene resin extruded foam particles according to any one of [1] to [8], wherein the melt flow rate of the thermoplastic elastomer is 0.3 g / 10 min to 10.0 g / 10 min.

[10] The polypropylene resin extruded foam particles according to any one of [1] to [9], wherein the melting point of the polypropylene resin having the branched structure is 130°C to 165°C.

[11] The polypropylene resin having a branched structure is a polypropylene resin having a branched structure obtained by melt-kneading a mixture containing a linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator, as described in any one of [1] to

[10] .

[12] The polypropylene resin extruded foam particles according to any one of [1] to

[11] , wherein the polypropylene resin extruded foam particles are obtained using one or more selected from the group consisting of aliphatic hydrocarbons and fluorinated hydrocarbons, carbon dioxide, air, nitrogen, and water as a foaming agent.

[13] Polypropylene resin extruded foam particles as described in any one of [1] to

[12] , wherein the open-cell ratio is 15% or less.

[14] Polypropylene resin extruded foam particles as described in any one of [1] to

[13] , with an average cell diameter of 100 μm to 500 μm.

[15] Polypropylene resin extruded foam particles as described in any one of [1] to

[14] , having a bulk density of 60 g / L or more.

[16] Polypropylene resin extruded foam particles as described in

[15] , wherein the bulk density is 300 g / L or less.

[17] When extruded foamed particles are foamed in a mold, a foamed molded article satisfying the following can be obtained, wherein the molding width, which is the upper and lower range of the vapor pressure during the in-mold foaming, is 0.02 MPa or more, according to any one of [1] to

[16] . (1) The fusion rate between extruded foam particles is 80% or higher; (2) The gaps between the extruded foam particles are sufficiently filled; (3) The surface is beautiful; (4) The surface is not melted; and (5) A foamed molded body in which the shape of the mold used for in-mold foam molding is transferred without shrinking by more than 5% relative to the dimensions of the mold.

[18] The polypropylene resin extruded foam particles according to any one of [1] to

[17] , wherein the melt flow rate of the polypropylene resin having the branched structure is 0.5 g / 10 min to 20.0 g / 10 min.

[19] Polypropylene resin extruded foam particles according to any one of [1] to

[18] , wherein the flexural modulus of the thermoplastic elastomer is 10 MPa to 200 MPa.

[20] A foamed molded article, Extruded foam particles containing a base resin, wherein the base resin contains 64.5% by weight or more of a polypropylene-based resin having a branched structure, in a total of 100% by weight of the base resin, are molded. The open-cell ratio of the extruded foam particles is 15% or less. The density of the foamed molded article is 60 g / L to 300 g / L, and A polypropylene resin foam molded article having a tensile elongation at break of 10% or more. A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles described in any one of items

[21] , [1], to

[19] . [Examples]

[0104] One embodiment of the present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to the following examples.

[0105] (Measurement and evaluation methods) <Melting tension of polypropylene resin with a branched structure> The melt tension of the branched polypropylene resins used in the examples and comparative examples was measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd., Japan). Specifically, the procedure was as follows (1) to (5): (1) A 9.55 mm diameter barrel heated to 200°C was filled with the branched polypropylene resin used in the examples and comparative examples; (2) The branched polypropylene resin was then heated for 10 minutes in the barrel heated to 200°C; (3) The branched polypropylene resin was then dispensed in a string-like form from a capillary die (1.0 mm diameter, 10 mm length) at a constant piston descent speed (10 mm / min), and this string-like material was passed through a tension-sensing pulley located 350 mm below the capillary die, after which winding using a winding roll was started; (4) After the winding of the string-like material stabilized, the winding speed of the string-like material was increased at a constant rate from an initial speed of 1.0 m / min to a speed of 200 m / min in 4 minutes; (5) The load on the load cell pulley when the string-like material broke was measured as the melt tension.

[0106] <Open cell ratio> The open-cell ratio of extruded foam particles was measured using an air-comparison hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles was calculated by performing the following steps (1) to (3) in order: (1) Using an air-comparison hydrometer, the volume Vc (cm³) of the extruded foam particles was measured. 3(1) The volume of the extruded foam particles after measuring Vc was measured; (2) Then, the entire volume of the extruded foam particles was submerged in ethanol in a graduated cylinder; (3) After that, the apparent volume of the extruded foam particles Va (cm³) was determined from the rise in the position of the ethanol in the graduated cylinder. 3 (4) The open-cell ratio of the extruded foamed particles was calculated using the following formula: Open cell percentage (%) = ((Va - Vc) × 100) / Va. The obtained values ​​are listed in Tables 1 to 3.

[0107] <Average cell diameter> The average cell diameter of the extruded foam particles was calculated by following steps (1) to (4) in order: (1) The extruded foam particles were cut with a razor blade so as to pass through the center of the particle; (2) The resulting cut surface was observed with an optical microscope; (3) A 2000 μm straight line was drawn on the cut surface, and the number of cells present on the straight line was measured. The number of cells was measured for 10 extruded foam particles, and their arithmetic mean cell count was calculated; (4) The value obtained by measurement using the following formula was taken as the average cell diameter (area average diameter) of the extruded foam particles: Average cell diameter (μm) = 2000 / average number of cells.

[0108] <Bulk density> The bulk density of the extruded foam particles was calculated by following steps (1) to (3) in order: (1) The extruded foam particles were placed in a container of known volume V (L), such as a graduated cylinder, beaker, or bucket, until it overflowed; (2) The weight W (g) of the extruded foam particles in the container was measured by leveling the powder surface (top edge); (3) The bulk density of the extruded foam particles was calculated using the following formula: Bulk density (g / L) = Weight W (g) of extruded foam particles / Volume V (L) of container. The obtained values ​​are listed in Tables 1 to 3.

[0109] <Molding width> A mold with dimensions of length / width / thickness = 381 / 381 / 60 mm was given a cracking of 18 mm, and the mold was filled with extruded foam particles. While changing the vapor pressure of the in-mold foam molding in increments of 0.02 MPa (gauge pressure), the extruded foam particles were foam-molded within a certain range of vapor pressure to obtain a polypropylene resin foam molded article. At this time, the range of vapor pressure (gauge pressure) during in-mold foam molding that can be obtained satisfying the following conditions was determined: (x1) The extruded foam particles are sufficiently fused together (internal fusion rate of 80% or more), (x2) The gaps between the extruded foam particles are sufficiently filled, (x3) The surface is beautiful, (x4) The surface is not melted, and (x5) The shape of the mold used for in-mold foam molding is transferred without shrinking by more than 5% relative to the dimensions of the mold. For the above evaluation, foamed molded articles were used that were dried in a 75-80°C dryer for 12-24 hours after molding, and then left to stand for more than 24 hours in an environment of 23°C and 50% humidity.

[0110] When the vapor pressure range obtained by the method described above is denoted as P1 to P2, "P1 to P2" is defined as the "feasible vapor pressure range," and the "value" obtained by P2-P1 is defined as the "molding width of the extruded foam particles." The "feasible vapor pressure range" and the "molding width of the polypropylene resin extruded foam particles" are listed in the "vapor pressure range" and "molding width" columns of Tables 1 to 3, respectively.

[0111] <Internal fusion rate> The measurement of the internal fusion rate of a polypropylene foam molded article with respect to the molding width was performed as follows (1) to (4): (1) A cut was made perpendicular to any one surface of the polypropylene foam molded article with a cutter, to a depth of 1 / 20 to 1 / 5 of the thickness of the part having that surface; (2) The polypropylene foam molded article was then broken by hand along the cut. If it could not be broken by hand, the polypropylene foam molded article was struck near the cut with a hammer or the like to break it along the cut; (3) Of the resulting fracture surface, the cut portion was excluded, and a certain range including the center in the thickness direction was visually observed, and the number of all extruded foam particles present in that range, and the number of extruded foam particles that were broken outside the particle interface in that range (i.e., extruded foam particles in which the extruded foam particles themselves were broken) was measured; (4) The internal fusion rate was calculated based on the following formula (4); Internal bonding rate (%) = (Number of extruded foam particles that have fractured outside the particle interface within the range / Total number of extruded foam particles present within the range) × 100 ... (4).

[0112] <Density of foamed molded material> The density of the foamed molded body was calculated by following the steps (1) to (3) below: (1) The weight W1 (g) of the foamed molded body was measured; (2) The length, width, and thickness of the foamed molded body to which weight W1 was measured were measured, and the volume V1 (L) of the foamed molded body was calculated from these lengths; (3) W1 was divided by V1, and the resulting value was taken as the density (g / L) of the foamed molded body. For density measurement, a foamed molded body that had been thoroughly dried after molding and left for 24 hours or more in an environment of room temperature 23°C and 50% humidity was used.

[0113] <Tensile elongation at breaking> Tensile elongation tests were conducted in accordance with ISO 1798 to measure the tensile elongation at break of the foamed molded articles. Specifically, the tensile elongation at break of the foamed molded articles was calculated by following the steps (1) to (4) below in order: (1) A dumbbell-shaped foamed molded article as specified in ISO 1798 was prepared and used as a test specimen; (2) Both ends of the test specimen were fixed; (3) One side of the test specimen was pulled until the specimen broke; (4) The elongation of the test specimen at the time of breakage was taken as the tensile elongation at break of the foamed molded article. The obtained values ​​are listed in Tables 1 to 3.

[0114] <Density measurement of test specimens used in tensile elongation testing> The volume Ld of the test specimen (dumbbell-shaped foamed molded body) used in the tensile elongation test was determined. Next, the weight Wd (g) of the test specimen was measured using an electronic balance. Then, the density of the test specimen used in the tensile elongation test was determined by dividing Wd by Ld. The obtained values ​​are recorded in the "Density of Test Specimen" column of Tables 1 to 3.

[0115] <Overall Rating> The overall evaluation based on the following criteria is shown in Tables 1 to 3. ○ (Good): The molding width is 0.04 MPa or more, and the tensile elongation at break is 10% or more. △ (Standard): The molding width is 0.02 MPa or more and less than 0.04 MPa, but the tensile elongation at break is 10% or more, or the molding width is 0.04 MPa or more, but the tensile elongation at break is less than 10%. × (Defective): The molding width is less than 0.02 MPa and the tensile elongation at break is less than 10%.

[0116] (material) The following materials were used in the examples and comparative examples.

[0117] <Polypropylene resin with a branched structure> As a polypropylene resin having a branched structure, we used Borealis' "WB140HMS" (measured melt tension of 14 cN and melting point of 161°C), which has a melt tension of 10 cN or more and 50 cN or less.

[0118] The melt tension of the branched polypropylene resin was measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd., Japan). Specifically, the procedure was as follows (1) to (5): (1) A sample resin (branched polypropylene resin) for measurement was filled into a 9.55 mm diameter barrel heated to the test temperature (200°C); (2) The sample resin was then heated for 10 minutes in the barrel heated to the test temperature (200°C); (3) The sample resin was then dispensed in a string-like form from a capillary die (1.0 mm diameter, 10 mm length) at a constant piston descent speed (10 mm / min), and this string-like material was passed through a tension-detecting pulley located 350 mm below the capillary die, after which winding using a winding roll was started; (4) After the winding of the string-like material stabilized, the winding speed of the string-like material was increased at a constant rate from an initial speed of 1.0 m / min to a speed of 200 m / min in 4 minutes; (5) The load on the load cell pulley when the string-like material broke was measured as the melt tension. Furthermore, the melting point of the branched polypropylene resin was determined by DSC (Digital Spectroscopy) in the same way as the melting point of the linear polypropylene resin, except that a thermoplastic elastomer was used instead of the linear polypropylene resin.

[0119] <Thermoplastic elastomer> As thermoplastic elastomers, polyolefin-based elastomer resin (LG Chem, "LUCENE LC180", abbreviation E1) or polyolefin-based elastomer resin (Dow Inc, "VERSIFY 2300", abbreviation E2) were used. E1 had a tensile elongation at break of 850%, a melting point of 73°C, and a MFR of 2.3 g / 10 min. E2 had a tensile elongation at break of 730%, a melting point of 66°C, and a MFR of 2.0 g / 10 min. The tensile elongations at break of E1 and E2 were determined by measuring E1 and E2 as samples in accordance with ASTM D638. The melting points of E1 and E2 were determined by DSC method, similar to the melting point of the linear polypropylene resin described above, except that thermoplastic elastomers were used instead of linear polypropylene resins. The MFRs for E1 and E2 were determined by measuring them in accordance with ISO 1133 under conditions of 230°C and 2.16 kg load, similar to the MFRs for linear polypropylene resins.

[0120] <Other resins> As another resin, ethylene / propylene random copolymer (Prime Polymer Co., Ltd., "F-724NPC") was used.

[0121] <Inorganic colorants> Carbon black was used as the inorganic coloring agent. The carbon black was used as a carbon black masterbatch with a carbon black concentration of 40%. The carbon black masterbatch was prepared as follows: Carbon black was added to the branched polypropylene resin to a concentration of 40%, the mixture was melt-kneaded in an extruder, and the resulting molten mixture was extruded into water and cut. In Tables 1 to 3, the "Inorganic Coloring Agent" column shows both the number outside the parentheses and the number inside the parentheses. The number outside the parentheses indicates the amount of carbon black masterbatch added, and the number inside the parentheses indicates the actual amount of carbon black added.

[0122] <Bubble nucleation agent> Talc (Luzenac 20MO, manufactured by Imerys) was used as the bubble nucleating agent.

[0123] Examples and comparative examples are described below. In the examples and comparative examples, the apparatus used for manufacturing extruded foam particles consisted of a twin-screw extruder with a shaft diameter of φ26 mm, a melt cooler, a diverter valve, and a die connected in series.

[0124] (Examples 1-9, Comparative Example 1, and Reference Examples 1-4) A resin mixture was prepared by mixing (a) a polypropylene resin having a branched structure, (b) a thermoplastic elastomer and / or ethylene propylene random copolymer shown in Tables 1 to 3, (c) an inorganic colorant (a carbon black masterbatch with a carbon black concentration of 40%), and (d) a bubble nucleating agent in the amounts shown in Tables 1 to 3. The resin mixture was then supplied to a twin-screw extruder and melt-kneaded at a cylinder temperature of 210°C. Furthermore, carbon dioxide, a foaming agent, was supplied from a press-in section installed in the middle of the extruder at a rate of 3 parts by weight per 100 parts by weight of polypropylene resin using a metering pump, and the resulting composition was further melt-kneaded.

[0125] The obtained molten mixture was cooled by passing it through a melt cooler connected to the tip of a twin-screw extruder and set to 185°C. Then, the molten mixture was extruded through a die attached to the tip of the melt cooler into a region filled with water at a pressure lower than the internal pressure of the apparatus, causing foaming. Within the water-filled region, a rotary cutter attached to the tip of the die shredded the composition immediately after it passed through the die, yielding polypropylene resin extruded foam particles. The temperature of the molten mixture (composition) immediately before entering the die was 205°C. The temperature of the molten mixture immediately before entering the die was measured using a thermometer placed near the outlet of the diverter valve, specifically 10 mm upstream from the die inlet in the extrusion direction, in contact with the composition.

[0126] In the water-filled region, the water pressure relative to the composition was 0.35 MPa (gauge pressure) for Examples 1-7 and Comparative Example 1, and 0.40 MPa (gauge pressure) for Reference Examples 1-4.

[0127] The open-cell ratio, average cell diameter, and bulk density of the obtained extruded foam particles were measured, and the results are shown in Tables 1-3. In addition, the molding width was evaluated using the obtained extruded foam particles, and the results are recorded in the "Vapor Pressure Width" and "Molding Width" columns of Tables 1-3.

[0128] The obtained extruded foam particles were used in a molding machine (KD345) manufactured by Daisen Co., Ltd. A block-shaped mold (400 mm long x 300 mm wide x variable thickness) was set to a thickness of 52 mm (cracking rate 30%), and the extruded foam particles were filled into the mold. After that, the mold was compressed to a thickness of 40 mm. Next, the air in the mold was expelled with steam at 0.10 MPa (gauge pressure), and then the foam molded body was obtained by heating and molding for 10 seconds with steam at a vapor pressure of 0.20 MPa (gauge pressure). The density of the foam molded body, the density of the test specimen, and the tensile elongation at break of the obtained foam molded body were measured, and the results are shown in Tables 1 to 3. In addition, a comprehensive evaluation was performed based on the evaluation criteria described above, and the results are shown in Tables 1 to 3.

[0129] (Reference examples 5 and 6) In Examples 1-9, Comparative Example 1, and Reference Examples 1-4, polypropylene resin extruded foam particles were produced by extrusion foaming. On the other hand, in Reference Examples 5 and 6 below, polypropylene resin foam particles were produced by depressurization foaming. The methods for producing the polypropylene resin foam particles in Reference Examples 5 and 6 will be described below.

[0130] [Preparation of polypropylene resin particles] A resin mixture was prepared by mixing the ethylene / propylene random copolymer (Prime Polymer Co., Ltd., "F-724NPC") described in the section on "Other Resins" above, a nucleating agent, and optionally an inorganic colorant (carbon black masterbatch with a carbon black concentration of 40%) in the amounts shown in Table 3. The resin mixture was then supplied to a twin-screw extruder [Shibaura Machinery Co., Ltd., TEM26] and melt-kneaded at a resin temperature of 215°C to 225°C. Subsequently, the resulting molten mixture was extruded from the die in the form of strands. The extruded strands were then water-cooled in a water bath. The water-cooled strands were then cut to produce polypropylene resin particles (1.80 mg / particle).

[0131] [Preparation of polypropylene resin foam particles] A 10L pressure-resistant container was filled with 100 parts by weight of the obtained polypropylene resin particles, 200 parts by weight of water, 1.0 part by weight of powdered basic tricalcium phosphate as a dispersant, 0.06 parts by weight of sodium n-paraffin sulfonate as a dispersion aid, and 4 parts by weight of carbon dioxide as a foaming agent. The container was heated to 156°C while stirring the raw materials (aqueous dispersion). After the container temperature reached 156°C, it was maintained at 156°C for 10 minutes, at which point carbon dioxide was added to the container to adjust the internal pressure to 2.2 MPa (gauge pressure). The container temperature was then raised to 158°C. After the container temperature reached 158°C, it was maintained at 158°C and 2.2 MPa (gauge pressure) for 20 minutes.

[0132] Subsequently, the valve at the bottom of the container was opened, and the aqueous dispersion was released through an orifice plate with a pore diameter of 4.0 mmφ under atmospheric pressure. This procedure yielded polypropylene resin foam particles. The obtained polypropylene resin foam particles were washed with a 1% hydrochloric acid solution, thoroughly rinsed with water, and then dried.

[0133] The open-cell ratio, average cell diameter, and bulk density of the polypropylene resin foam particles obtained in this manner were measured, and the results are shown in Table 3. In addition, the molding width was evaluated using the obtained polypropylene resin foam particles, and the results are recorded in the "Vapor Pressure Width" and "Molding Width" columns of Table 3.

[0134] Using the obtained polypropylene-based foam particles, polypropylene-based foam molded articles were prepared in the same manner as described above. The density of the obtained polypropylene-based foam molded articles, the density of the test specimens, and the tensile elongation at break were measured, and the results are shown in Table 3. In addition, an overall evaluation was performed based on the evaluation criteria described above, and the results are shown in Table 3.

[0135] [Table 1]

[0136] [Table 2]

[0137] [Table 3]

[0138] Table 3, Reference Example 1 shows that the tensile elongation at break of a foamed molded article using extruded foamed particles containing a branched polypropylene resin is 7%, indicating poor fracture resistance. As shown in Reference Examples 2-4, the tensile elongation at break can be improved to 10% or more by using a thermoplastic elastomer. As shown in Comparative Example 1, when a branched polypropylene resin and carbon black are used but a thermoplastic elastomer is not used, the tensile elongation at break is 6%, the molding width is 0 MPa, and both fracture resistance and moldability are poor.

[0139] Examples 1 to 9 show that when a thermoplastic elastomer is used in addition to a branched polypropylene resin and carbon black, each within the scope of one embodiment of the present invention, the tensile elongation at break becomes 10% or more, the molded width becomes 0.04 MPa or more, and the fracture resistance and moldability are good.

[0140] In Reference Examples 5 and 6, where polypropylene resin foam particles were produced by depressurization foaming, it was found that the moldability of the polypropylene resin foam particles was good, and the fracture resistance of the polypropylene resin foam molded articles was also good. In other words, it was found that, regardless of whether or not inorganic colorants were included, there was no risk of the molding width required to obtain good quality polypropylene resin foam molded articles being significantly narrowed, nor was there any risk of the fracture resistance of the polypropylene resin foam molded articles being significantly reduced. [Industrial applicability]

[0141] According to one embodiment of the present invention, extruded foam particles with excellent moldability can be provided. Therefore, one embodiment of the present invention can be suitably used to obtain a foamed molded article with excellent fracture resistance. Therefore, one embodiment of the present invention can be suitably used in fields such as automotive interior components, cushioning materials, packaging materials, and heat insulating materials.

Claims

1. The base resin contains a polypropylene resin having a branched structure, The melt tension of the polypropylene resin having the branched structure is 5 cN to 50 cN. The aforementioned base resin further contains a thermoplastic elastomer and an inorganic colorant. The base resin contains 64.5% to 94.5% by weight of the polypropylene resin having the branched structure in 100% by weight of the base resin. The base resin contains 5.0% to 35.0% by weight of the thermoplastic elastomer in 100% by weight of the base resin. The base resin is polypropylene resin extruded foam particles, containing 0.5% to 5.0% by weight of the inorganic colorant in 100% by weight of the base resin.

2. The polypropylene resin extruded foam particles according to claim 1, wherein the inorganic coloring agent is one or more selected from the group consisting of carbon black, red clay, yellow clay, green clay, titanium dioxide, cobalt blue, Prussian blue, and chromium oxide green.

3. The polypropylene resin extruded foam particles according to claim 1 or 2, wherein the thermoplastic elastomer is a polyolefin-based elastomer.

4. Polypropylene resin extruded foam particles according to any one of claims 1 to 3, wherein the tensile elongation at break of the thermoplastic elastomer is 500% to 1000%.

5. The polypropylene resin extruded foam particles according to any one of claims 1 to 4, wherein the melting point of the thermoplastic elastomer is 40°C to 110°C.

6. The polypropylene resin extruded foam particles according to any one of claims 1 to 5, wherein the melt flow rate of the thermoplastic elastomer is 0.3 g / 10 min to 10.0 g / 10 min.

7. Polypropylene resin extruded foam particles according to any one of claims 1 to 6, wherein the open-cell ratio is 15% or less.

8. Polypropylene resin extruded foam particles according to any one of claims 1 to 7, wherein the average cell diameter is 100 μm to 500 μm.

9. Polypropylene resin extruded foam particles according to any one of claims 1 to 8, wherein the bulk density is 60 g / L or more.

10. A foamed molded body, Extruded foam particles containing a base resin are formed, wherein the base resin contains 64.5% to 94.5% by weight of a polypropylene-based resin having a branched structure in a quantity of 100% by weight of the base resin. The open-cell ratio of the extruded foam particles is 15% or less. The density of the foamed molded body is 60 g / L to 300 g / L, and The tensile elongation at break of the foamed molded article is 10% or more. The aforementioned base resin contains 5.0% to 35.0% by weight of thermoplastic elastomer in 100% by weight of the base resin. The aforementioned base resin is a polypropylene resin foam molded article containing 0.5% to 5.0% by weight of an inorganic colorant in 100% by weight of the base resin.

11. A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles according to any one of claims 1 to 9.

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