Polypropylene resin composition for extrusion foaming, extruded foam particles, and foamed molded articles

Abstract

The present invention addresses the problem of providing extrusion-blown particles of a polypropylene resin which have excellent moldability and a polypropylene resin composition for extrusion blowing capable of giving molded polypropylene resin foam which is excellent in terms of static compression strength and tensile elongation at break. The polypropylene resin composition for extrusion blowing comprises specific amounts of: a branched polypropylene resin (A) having a tensile modulus within a specific range; and a branched polypropylene resin (B) having a tensile modulus and a nominal tensile strain at break which are respectively within specific ranges.

Description

[Technical Field]

[0001] The present invention relates to a polypropylene resin composition for extrusion foaming, extruded foam particles, and foamed 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] One technique for obtaining polypropylene resin foam particles by extrusion foaming is the technique described in Patent Document 1. Patent Document 1 discloses polypropylene resin pre-foamed particles that are obtained by a specific method and are characterized in that the full width at half maximum of the melting point peak measured by differential scanning calorimeter is 20°C or higher. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-256460 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the conventional technologies described above were insufficient in terms of the moldability of polypropylene resin extruded foam particles, as well as the static compressive strength and tensile elongation at break of polypropylene resin foam molded articles, and there was room for further improvement.

[0007] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide a polypropylene resin composition for extrusion foaming that can obtain polypropylene resin extruded foam particles with excellent moldability, and polypropylene resin foam molded articles with excellent static compressive strength and tensile elongation at break. [Means for solving the problem]

[0008] In other words, the polypropylene resin composition for extrusion foaming according to one embodiment of the present invention comprises, in 100% by weight of the total resin components in the polypropylene resin composition for extrusion foaming, 65% by weight or more and 85% by weight or less of a branched polypropylene resin (A) having a tensile modulus of 1100 MPa or more as specified in JIS K7161, and 15% by weight or more and 35% by weight or less of a branched polypropylene resin (B) having a tensile modulus of 550 MPa or more and 950 MPa or less as specified in JIS K7161, and a tensile fracture nominal strain of 50% or more as specified in JIS K7161.

[0009] Furthermore, a foamed molded article according to one embodiment of the present invention is a polypropylene resin foamed molded article obtained by extruding foamed particles obtained by extruding foamed resin composition containing a branched polypropylene resin, wherein the open-cell ratio of the extruding foamed particles is 15% or less, the density of the foamed molded article is 60 g / L to 300 g / L, the tensile elongation at break of the foamed molded article satisfies formula 1, and the static compressive strength of the foamed molded article satisfies formula 2. Tensile elongation at break (%) ≥ -0.000002 × D 3 +0.0011 × D 2 -0.285×D+32.2 (Formula 1) Static compressive strength (kPa) ≥ 0.000049 × D 3 +0.0542×D 2 -0.265×D+146.9 (Formula 2) In formulas 1 and 2, D represents the density (g / L) of the foamed molded article. [Effects of the Invention]

[0010] According to one embodiment of the present invention, it is possible to provide a polypropylene resin composition for extrusion foaming that can obtain polypropylene resin extruded foam particles with excellent moldability, and polypropylene resin foam molded articles with excellent static compressive strength and tensile elongation at break. [Modes for carrying out the invention]

[0011] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)."

[0012] [1. Technical Concept of One Embodiment of an Embodiment] The inventors have found that foamed molded articles obtained from polypropylene resin foam particles obtained by extrusion foaming are inferior in static compressive strength and tensile elongation at break compared to foamed molded articles obtained from polypropylene resin foam particles obtained by depressurization foaming. In order to solve this problem, the inventors investigated and found that static compressive strength could be improved to some extent by using a branched polypropylene resin with a tensile modulus within a specific range, but the tensile elongation at break tended to be inferior. Furthermore, the tensile elongation at break could be improved to some extent by blending the branched polypropylene resin with various resins such as general-purpose linear polypropylene resin or elastomer, but in return, the static compressive strength tended to decrease. When a general-purpose linear polypropylene resin was blended with the branched polypropylene resin, there was also a tendency for the moldability to be inferior.

[0013] Therefore, as a result of further study, the present inventors have found that by using a polypropylene-based resin composition for extrusion foaming containing a specific amount of a branched polypropylene-based resin (A) having a tensile elastic modulus within a specific range and a branched polypropylene-based resin (B) having a tensile elastic modulus and a tensile fracture elongation within specific ranges, polypropylene-based resin extrusion foamed particles excellent in moldability and a polypropylene-based resin foamed molded article excellent in static compression strength and tensile elongation at break can be obtained.

[0014] [2. Polypropylene-based resin composition for extrusion foaming] The polypropylene-based resin composition for extrusion foaming according to one embodiment of the present invention contains, in 100% by weight in total of the resin components in the polypropylene-based resin composition for extrusion foaming, 65% by weight or more and 85% by weight or less of a polypropylene-based resin (A) having a branched structure and having a tensile elastic modulus defined in JIS K7161 of 1100 MPa or more, and 15% by weight or more and 35% by weight or less of a polypropylene-based resin (B) having a branched structure and having a tensile elastic modulus defined in JIS K7161 of 550 MPa or more and 950 MPa or less and a tensile fracture elongation defined in JIS K7161 of 50% or more.

[0015] By subjecting the polypropylene-based resin composition for extrusion foaming to extrusion foaming, polypropylene-based resin extrusion foamed particles can be obtained. Further, by molding the polypropylene-based resin extrusion foamed particles (for example, in-mold foaming molding), a polypropylene-based resin foamed molded article can be obtained. In this specification, the "polypropylene-based resin composition for extrusion foaming" may be referred to as the "resin composition", and the "polypropylene-based resin composition for extrusion foaming according to an embodiment of the present invention" may be referred to as the "present resin composition". Also, in this specification, the "polypropylene-based resin extrusion foamed particles" may be referred to as the "extrusion foamed particles", 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 article" may be referred to as the "foamed molded article", and the "polypropylene-based resin foamed molded article according to an embodiment of the present invention" may be referred to as the "present foamed molded article".

[0016] Since the present resin composition has the above-described configuration, it has the advantage of being able to provide extrusion foamed particles excellent in moldability and a foamed molded article excellent in static compression strength and tensile elongation at break. 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, the static compression strength and the tensile elongation at break will be described later.

[0017] Examples of the uses of the present resin composition include extrusion foamed particles, extrusion foamed sheets, and extrusion foamed boards. By subjecting the present resin composition to extrusion foaming, extrusion foamed particles, extrusion foamed sheets, or extrusion foamed boards can be obtained. The extrusion foamed particles, extrusion foamed sheets, and extrusion foamed boards can be separately produced by appropriately changing the shape of the die and the cutting method, etc.

[0018] <2-1. Polypropylene-based resin having a branched structure> 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.

[0019] 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."

[0020] This resin composition comprises a polypropylene resin (A) having a branched structure and a polypropylene resin (B) having a branched structure. In this specification, "polypropylene resin (A) having a branched structure" may be referred to as "branched polypropylene resin (A)," and polypropylene resin (B) having a branched structure may be referred to as "branched polypropylene resin (B)."

[0021] The branched polypropylene resin (A) has a tensile modulus of 1100 MPa or higher as specified in JIS K7161. JIS K7161 corresponds to ISO 527-1. By including the branched polypropylene resin (A) in this resin composition, a foamed molded article with excellent static compressive strength can be provided.

[0022] The tensile modulus of the branched polypropylene resin (A) is preferably 1200 MPa or higher, more preferably 1300 MPa or higher, even more preferably 1400 MPa or higher, and particularly preferably 1500 MPa or higher. The upper limit of the tensile modulus of the branched polypropylene resin (A) is not particularly limited, but may be, for example, 3000 MPa or less, or 2500 MPa or less.

[0023] The tensile fracture nominal strain of the branched polypropylene resin (A) is preferably less than 50%, and more preferably 45% or less. The lower limit of the tensile fracture nominal strain of the branched polypropylene resin (B) is not particularly limited, but may be, for example, 5% or more, or 10% or more.

[0024] The content of branched polypropylene resin (A) in this resin composition is preferably 65% ​​by weight or more and 85% by weight or less, and more preferably 70% by weight or more and 80% by weight or less, when the total amount of resin components in this resin composition is taken as 100% by weight. If the content of branched polypropylene resin (A) is 65% by weight or more, a foamed molded article with excellent static compressive strength can be provided. If the content of branched polypropylene resin (A) is 85% by weight or less, the decrease in tensile elongation at break can be suppressed. In this specification, "resin components" refers to a concept that encompasses branched polypropylene resin (A), branched polypropylene resin (B), and other resins described later that are included in this resin composition. This "resin components" can also be said to be a concept that excludes the stabilizers and additives described later.

[0025] The branched polypropylene resin (B) has a tensile modulus of 550 MPa to 950 MPa as specified in JIS K7161, and a tensile fracture strain of 50% or more as specified in JIS K7161. By including the branched polypropylene resin (B) in this resin composition, the open-cell ratio of the extruded foam particles can be reduced, and as a result, extruded foam particles with excellent moldability can be provided. Furthermore, by including the branched polypropylene resin (B) in this resin composition, a foamed molded article with excellent tensile elongation at break can be provided.

[0026] The tensile modulus of the branched polypropylene resin (B) is preferably 600 MPa or more and 900 MPa or less, more preferably 600 MPa or more and 850 MPa or less, and even more preferably 650 MPa or more and 850 MPa or less. The elastomer mentioned above has a tensile modulus of less than 550 MPa. The tensile fracture nominal strain of the branched polypropylene resin (B) is preferably 55% or more, more preferably 60% or more, even more preferably 80% or more, and particularly preferably 100% or more. The upper limit of the tensile fracture nominal strain of the branched polypropylene resin (B) is not particularly limited, but may be, for example, 500% or less, or 400% or less.

[0027] The content of branched polypropylene resin (B) in this resin composition is preferably 15% by weight or more and 35% by weight or less, and more preferably 20% by weight or more and 30% by weight or less, when the total amount of resin components in this resin composition is taken as 100% by weight. If the content of branched polypropylene resin (B) is 15% by weight or more, it is possible to provide extruded foam particles with excellent moldability and foam molded articles with excellent tensile elongation at break. If the content of branched polypropylene resin (B) is 35% by weight or less, the decrease in static compressive strength can be suppressed.

[0028] The melting point of branched polypropylene resin (A) is preferably 145°C or higher, more preferably 150°C or higher, and even more preferably 155°C or higher. The upper limit of the melting point of branched polypropylene resin (A) is not particularly limited, but may be, for example, 170°C or lower, or 165°C or lower. The melting point of branched polypropylene resin (B) is preferably less than 145°C, more preferably 143°C or lower, and even more preferably 140°C or lower. The lower limit of the melting point of branched polypropylene resin (B) is not particularly limited, but may be, for example, 120°C or higher, or 125°C or higher. By using branched polypropylene resin (A) and branched polypropylene resin (B) having these melting points in combination, a foamed molded article with an excellent balance between static compressive strength and tensile elongation at break can be provided.

[0029] In this specification, the melting point of branched 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: (a1) The branched polypropylene resin is melted by raising the temperature of 5 to 6 mg of branched polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min; (a2) The molten branched polypropylene resin is then crystallized by lowering the temperature of the branched polypropylene resin from 220°C to 40°C at a cooling rate of 10°C / min; (a3) ​​The crystallized branched polypropylene resin is then further heated 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 branched polypropylene resin obtained during the second heating (i.e., at (a3)) can be determined as the melting point of the branched polypropylene resin. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the branched 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 branched polypropylene resin. As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0030] The crystal content ΔH measured by differential scanning calorimetry is preferably 70 J / g or more, more preferably 75 J / g or more, and even more preferably 80 J / g or more for branched polypropylene resin (A). The upper limit of ΔH for branched polypropylene resin (A) is not particularly limited, but may be, for example, 150 J / g or less, or 120 J / g or less. Furthermore, the ΔH for branched polypropylene resin (B) is preferably 40 J / g or more and 65 J / g or less, more preferably 42 J / g or more and 63 J / g or less, and even more preferably 45 J / g or more and 60 J / g or less. By using branched polypropylene resin (A) and branched polypropylene resin (B) having these ΔH values ​​in combination, a foamed molded article with an excellent balance between static compressive strength and tensile elongation at break can be provided.

[0031] In this specification, the crystalline content ΔH of a branched polypropylene resin is a value calculated by performing the following (1) to (2) in order: (1) In the DSC curve of the branched polypropylene resin obtained during the second heating step measured by the DSC method (i.e., when (a3) ​​is described above), let A be the point at 80°C on the DSC curve and B be the melting end point. (2) Let ΔH be the amount of heat (J / g) calculated from the region enclosed by line segment AB and the DSC curve.

[0032] The melt flow rate (MFR) of the branched polypropylene resin is not particularly limited. The MFR of the branched polypropylene resin is preferably, for example, 0.3 g / 10 min to 20.0 g / 10 min, more preferably 0.5 g / 10 min to 15.0 g / 10 min, even more preferably 1.0 g / 10 min to 12.0 g / 10 min, and particularly preferably 1.5 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 tensile elongation at break. When the MFR of the branched polypropylene resin is (a) 0.3 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 having good foaming properties during extrusion foaming.

[0033] 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.

[0034] The melt tension of the branched polypropylene resin is preferably 5 cN to 20 cN, more preferably 7 cN to 17 cN, and even more preferably 9 cN to 15 cN. When the melt tension of the branched polypropylene is (a) 5 cN or higher, the extruded foam particles obtained from the branched polypropylene tend to have a low open-cell ratio, which has the advantage of providing a foamed molded article with good (beautiful) surface properties, and (b) when it is 20 cN or lower, it has the advantage of making it easier to increase the discharge amount during extrusion foaming, i.e., having excellent productivity.

[0035] 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-sensing 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.

[0036] Preferably, the melt flow rate of at least one of the branched polypropylene resin (A) and branched polypropylene resin (B), more preferably both branched polypropylene resin (A) and branched polypropylene resin (B), is 0.3 g / 10 min to 20.0 g / 10 min. Also preferably, the melt tension of at least one of the branched polypropylene resin (A) and branched polypropylene resin (B), more preferably both branched polypropylene resin (A) and branched polypropylene resin (B), is 5 cN to 20 cN.

[0037] The branched polypropylene resin (A) and / or branched polypropylene resin (B) is preferably one or more selected from the group consisting of homopolypropylene resins having a branched structure, random polypropylene resins having a branched structure, and block polypropylene resins having a branched structure. Homopolypropylene resins having a branched structure mean propylene homopolymers into which a branched structure has been introduced. Similarly, random polypropylene resins having a branched structure and block polypropylene resins having a branched structure mean a polypropylene random copolymer and a polypropylene block copolymer and a branched structure, respectively.

[0038] <2-2. Method for producing polypropylene resin having a branched structure> A branched polypropylene resin (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 (b1) irradiating the linear polypropylene resin with radiation, and (b2) melt-kneading a mixture containing the linear polypropylene resin, a conjugated diene compound, and a radical polymerization initiator.

[0039] In addition, a branched polypropylene resin may be used as the raw material instead of a linear polypropylene resin in method (b1) or method (b2). This makes it possible to obtain a branched polypropylene resin with different physical properties from the branched polypropylene resin used as the raw material.

[0040] A specific example of the method described in (b1) above is the method described in Japanese Patent Publication No. 2002-542360.

[0041] The method described in (b2) above will be further explained. In the method described in (b2), 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. An example of a specific method of the method described in (b2) above is the method described in WO2020 / 004429.

[0042] (i) Because 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) because a branched polypropylene resin can be obtained without requiring complex equipment and with high productivity, in one embodiment of the present invention, the branched polypropylene resin is preferably a branched polypropylene resin obtained by the method of (b2) described above. In other words, preferably at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B), more preferably both the branched polypropylene resin (A) and the branched polypropylene resin (B) contain structural units derived from a conjugated diene compound.

[0043] One method for obtaining this resin composition is to separately introduce a branched structure into at least two types of linear polypropylene resins using the method described in (b2) to produce branched polypropylene resins (A) and (B), and then mix the branched polypropylene resins (A) and (B) to obtain this resin composition. In addition, two or more types of linear polypropylene resins may be used as raw materials in the production of branched polypropylene resin (A) or (B).

[0044] (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.

[0045] 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."

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Examples of styrene monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0050] 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 advantage that the resulting branched polypropylene resin can provide polypropylene resin extruded foam particles with excellent moldability.

[0051] 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 advantage that the resulting branched polypropylene resin can provide polypropylene resin extruded foam particles with excellent moldability.

[0052] The linear polypropylene resin preferably contains 90 mol% or more of propylene units out of 100 mol% of the total structural units contained in the linear polypropylene resin, more preferably 93 mol% or more, even more preferably 95 mol% or more, and particularly preferably 97 mol% or more.

[0053] 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.

[0054] In this specification, the melting point of linear polypropylene resin is a value determined by measurement using the DSC method. Specifically, it can be determined by the same method as the measurement method for the melting point of branched polypropylene resin described above, except that linear polypropylene resin is used instead of branched polypropylene resin.

[0055] The 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.

[0056] 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.

[0057] (Conjugated diene compounds) Examples of conjugated diene compounds include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene. These conjugated diene compounds may be used individually or in combination of two or more. Among these conjugated diene compounds, butadiene and isoprene are particularly preferred due to (a) their low cost and ease of handling, and (b) the fact that the reaction proceeds uniformly.

[0058] In the production of branched polypropylene resins, the amount of conjugated diene compound used is preferably 0.01 to 5.00 parts by weight, more preferably 0.10 to 3.00 parts by weight, and even more preferably 0.10 to 2.00 parts by weight, per 100 parts by weight of linear polypropylene resin. The more conjugated diene compound used, the lower the MFR of the resulting branched polypropylene resin tends to be, and the lower the tensile fracture nominal strain tends to be. On the other hand, the less conjugated diene compound used, the higher the MFR of the resulting branched polypropylene resin tends to be, and the higher the tensile fracture nominal strain tends to be.

[0059] In the production of branched polypropylene resins, in addition to linear polypropylene resins, conjugated diene compounds, and radical polymerization initiators, monomers copolymerizable with conjugated diene compounds may be used in combination, to the extent that the effects of one embodiment of the present invention are not impaired. Examples of monomers copolymerizable with conjugated diene compounds include (a) acrylic acid esters such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylate salts, metal methacrylate salts, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate, and (b) methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate.

[0060] (Radical polymerization initiator) The radical polymerization initiator is an organic peroxide that has the ability to abstract hydrogen from linear polypropylene resins and conjugated diene compounds. Examples of radical polymerization initiators that can be suitably used in one embodiment of the present invention include organic peroxides such as ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters.

[0061] As for organic peroxides, those with particularly high hydrogen abstraction ability are preferred. Examples of organic peroxides with high hydrogen abstraction ability include peroxyketals such as 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl4,4-bis(t-butylperoxy)valerate, and 2,2-bis(t-butylperoxy)butane; dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, t-butylcumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5- Suitable examples include dialkyl peroxides such as di(t-butylperoxy)-3-hexine; diacyl peroxides such as benzoyl peroxide; and peroxyesters such as t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, and di-t-butyl peroxyisophthalate. Among these, t-butyl peroxyisopropyl carbonate and / or t-butyl peroxybenzoate are preferred. These organic peroxides may be used individually or in combination of two or more.

[0062] The amount of radical polymerization initiator used in the production of branched polypropylene resin is not particularly limited, but is preferably 0.01 to 5.00 parts by weight, preferably 0.10 to 3.00 parts by weight, more preferably 0.10 to 2.00 parts by weight, and particularly preferably 0.10 to 1.00 parts by weight per 100 parts by weight of linear polypropylene resin. The more radical polymerization initiator used, the higher the MFR of the resulting branched polypropylene resin tends to be. On the other hand, the less radical polymerization initiator used, the lower the MFR of the resulting branched polypropylene resin tends to be.

[0063] <2-3. Other ingredients> The resin composition may further contain, as needed, (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 bubble nucleating agents, inorganic colorants, organic colorants, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, and antistatic agents. These components may be used individually or in combination of two or more.

[0064] This resin composition 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.

[0065] Examples of bubble nucleation agents include sodium bicarbonate-citric acid mixtures, monosodium citrate, talc, and calcium carbonate. These bubble nucleation agents may be used individually or in combination of two or more.

[0066] The content of the nucleating agent in this resin composition, in other words, the amount of nucleating agent used in the production of extruded foamed 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 the total resin components. This configuration has the advantage that the cell size (average cell diameter) and cell shape of the extruded foamed particles become uniform, and as a result, the foaming properties during extrusion foaming tend to be more stable. Note that "cell" refers to "bubble".

[0067] This resin composition may contain an inorganic colorant to the extent that it does not impair the effects of one embodiment of the present invention. The inorganic colorant 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. From the viewpoint of ultraviolet absorption performance, carbon black is particularly preferred as the inorganic colorant.

[0068] This resin composition preferably contains 0.5 to 5.0 parts by weight of inorganic colorant per 100 parts by weight of total resin components, more preferably 0.5 to 4.5 parts by weight, even more preferably 0.5 to 4.0 parts by weight, even more preferably 1.0 to 3.5 parts by weight, and particularly preferably 1.0 to 3.0 parts by weight. This configuration has the advantage that the open-cell ratio of extruded foam particles obtained by the extrusion foaming method tends to be low. The amount of inorganic colorant in this resin composition can also be said to be the amount of inorganic colorant used in the production of extruded foam particles.

[0069] This resin composition may contain organic colorants to the extent that they do not impair the effects of 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 organic colorants in this resin composition is not particularly limited.

[0070] The present resin composition may further contain resins other than branched polypropylene resins (sometimes referred to as "other resins") or rubber, to the extent that it does not impair the effects of the present embodiment. 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. The present resin composition may contain 0% to 20% by weight of the other resins when the total amount of resin components in the present resin composition is 100% by weight.

[0071] [3. Polypropylene resin extruded foam particles] Polypropylene resin extruded foam particles according to one embodiment of the present invention are obtained by extruding foam the resin composition. The extruded foam particles can also be said to contain the resin composition. The extruded foam particles can also be said to contain the resin composition as a base resin. The base resin can also be said to be a resin component that substantially constitutes the extruded foam particles.

[0072] (Average cell diameter) The average cell diameter of the extruded foam particles is preferably 100 μm to 400 μm, more preferably 120 μm to 350 μm, and even more 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 the extruded foam particles having excellent moldability.

[0073] 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 obtained cut surface with an optical microscope; (3) Measure the number of cells present on a 2000 μm straight line of the cut surface. 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.

[0074] (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 extruded foam particles is not particularly limited, and is, for example, 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.

[0075] In this specification, the open-cell ratio of 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 (4) in order: (1) Using an air-comparable hydrometer, measure 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.

[0076] (Bulk density) The bulk density of the extruded foam particles is preferably 40 g / L or more, preferably 50 g / L or more, more preferably 60 g / L or more, even more preferably 70 g / L or more, and particularly preferably 80 g / L or more. The upper limit of the bulk density of the extruded foam particles is not particularly limited, for example, 300 g / L or less. The lower the material ratio of the extruded foam particles used as the material for 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 excellent tensile elongation at break even if the material ratio is as low as having a bulk density of 40 g / L or more. Furthermore, when the bulk density of the extruded foam particles is within the above range, the foamed molded article obtained using these extruded foam particles has the advantage of exhibiting more characteristics such as arbitrariness of shape, cushioning properties, lightness, and heat insulation properties.

[0077] In this specification, the bulk density of 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 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).

[0078] (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 extruded foam particles (e.g., fusion rate of 80% or more), (x2) sufficient filling of gaps between 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."

[0079] 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.

[0080] 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.

[0081] (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.

[0082] 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.

[0083] [4. 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. For example, the method for producing the extruded foam particles includes a first step of melting and kneading the resin composition and a foaming agent in a manufacturing apparatus, and a second step of extruding the molten mixture obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the manufacturing apparatus.

[0084] (First step) The first step will now be explained in detail. A specific example of the first step is the process of melting the resin composition in a manufacturing apparatus and dissolving a foaming agent into the resin composition. The first step can also be described as the process of preparing a molten mixture containing the resin composition and the foaming agent.

[0085] The blowing agent 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 amount of blowing agent used in the first step should be appropriately adjusted according to the type of blowing agent and the target foaming ratio of the polypropylene resin extruded foam particles.

[0086] In the first step, stabilizers (e.g., antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, etc.) and additives (e.g., bubble nucleating agents, inorganic colorants, organic colorants, crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, pigments, dyes, flame retardants, and antistatic agents, etc.) may be used as needed.

[0087] Inorganic colorants may be formulated (used) as a masterbatch. An inorganic colorant masterbatch can be obtained by mixing the inorganic colorant with any resin (e.g., a polypropylene resin) in any ratio. The concentration of the inorganic colorant in the masterbatch is not particularly limited; for example, a masterbatch may contain 5 to 50% by weight of the inorganic colorant in a 100% by weight masterbatch.

[0088] In the first step, the resin composition and the blowing agent, as well as any other components that may be used, may be mixed before being supplied to the manufacturing apparatus, or they may be mixed within the manufacturing apparatus. In other words, in the first step, the resin composition may be supplied to the manufacturing apparatus, or the resin composition may be prepared (completed) within the manufacturing apparatus. In the first step, (i) the method and sequence of mixing the resin composition and the blowing agent, as well as any other components that may be used, or (ii) the method and sequence of supplying the resin composition and the blowing agent, as well as any other components that may be used, to the manufacturing apparatus is not particularly limited.

[0089] The molten mixture obtained in the first step may be cooled before being extruded into the low-pressure region.

[0090] (Second step) The second step involves extruding the molten mixture obtained in the first step through a die into a region with a pressure lower than the internal pressure of the manufacturing equipment, and then shredding the extruded molten mixture. This second step yields extruded foam particles. Therefore, the second step can also be described as a granulation step for granulating polypropylene resin extruded foam particles.

[0091] In the second step, the region in which the molten mixture obtained in the first step is extruded is not particularly limited, as long as the pressure is lower than the internal pressure of the manufacturing apparatus. For example, in the second step, the molten mixture obtained in the first step may be extruded into the gas phase or into the liquid phase.

[0092] In the second step, the molten mixture extruded into a region with a pressure lower than the internal pressure of the manufacturing apparatus immediately begins to foam. In the second step, the molten mixture may be shredded while foaming, or it may be shredded after foaming has finished. If the molten mixture is shredded while foaming, the shredded mixture may complete foaming in the region to which it was extruded.

[0093] Depending on the region in which the molten mixture obtained in the first step is extruded and the method of shredding the extruded molten mixture, the second step (granulation step) can be broadly classified into two types: the cold cut method and the die face cut method. An example of the cold cut method is a method in which the molten mixture containing a foaming agent extruded from the die is foamed, and the strand-shaped foam is taken up while being cooled through a water tank and then shredded (strand cut method). The die face cut method is a method in which the molten mixture extruded from the holes in the die is cut by a cutter that rotates while in contact with the surface of the die or while maintaining a small gap.

[0094] The die face cutting method can be further divided into the following three types based on differences in cooling methods: the underwater cut (sometimes referred to as UWC), the watering cut (sometimes referred to as WRC), and the hot cut (sometimes referred to as HC). The UWC method involves filling a chamber attached to the tip of the die with cooling water adjusted to a predetermined pressure so that it is in contact with the resin discharge surface of the die, and cutting the molten mixture extruded from the die hole underwater. The WRC method involves placing a cooling drum downstream of the die through which cooling water flows along the inner circumference of the cooling drum connected to the die, and cooling the molten mixture cut by the cutter in the air while foaming, or after foaming, in the cooling water. The HC method involves cutting the molten mixture in the air with a cutter, and then cooling the cut molten mixture in the air while foaming, or after foaming. The HC method may also include the mist cut method, which further includes a step of spraying a mixed mist of water and air. In the second step, it is preferable that the method for shredding the molten mixture discharged is one or more selected from the group consisting of the HC method, the WRC method, and the UWC method.

[0095] [5. Polypropylene-based foamed molded articles] A polypropylene resin foam molded article according to one embodiment of the present invention is obtained by in-mold foam molding of extruded foam particles described in section [3. Polypropylene Resin Extruded Foam Particles] or extruded foam particles obtained by the manufacturing method described in section [4. Method for Manufacturing Polypropylene Resin Extruded Foam Particles]. 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 the foamed molded article is preferably 60 g / L to 300 g / L, more preferably 70 g / L to 300 g / L, even more preferably 80 g / L to 300 g / L, and particularly preferably 90 g / L to 300 g / L. According to the above configuration, the foamed molded article has the advantage of being superior in characteristics such as arbitrariness of shape, cushioning properties, lightness, and heat insulation.

[0097] In this specification, the density of a foamed molded body is calculated by following (1) to (3) in order: (1) Measure the weight W1 (g) of the foamed molded body. (2) Measure the volume V1 (L) of the foamed molded body. For example, 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 volume V1 may be calculated from the length, width, and thickness. (3) Calculate the density using W1 / V1. For measurement, a foamed molded body that has been thoroughly dried after molding and left at room temperature of 23°C and humidity of 50% for 24 hours or more should be used.

[0098] (Static compressive strength) The static compressive strength of the foamed molded article preferably satisfies Equation 2. Static compressive strength (kPa) ≥ 0.000049 × D 3 +0.0542×D 2 -0.265×D+146.9 (Formula 2) In Equation 2, D represents the density (g / L) of the foamed molded product.

[0099] In this specification, the static compressive strength of a foamed molded article is measured by the following method. First, a test piece with a length / width / thickness of 50 / 50 / 50 mm is cut from the foamed molded article. Here, only one side of the surface perpendicular to the thickness direction of the foamed molded article is cut. That is, the uncut side of the surface perpendicular to the thickness direction of the foamed molded article is the surface that was in contact with the mold during in-mold foaming (also called the skin layer). For this test piece, in accordance with ISO 844, the value of the compressive stress at 50% compression is measured when compressed at a speed of 10% of the thickness (approximately 5 mm / min) using a tensile-compression testing machine (for example, MinebeaMitsumi TG-50kN). The obtained value is taken as the static compressive strength of the foamed molded article.

[0100] (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.

[0101] The tensile break elongation rate of the foam molded body preferably satisfies Formula 1. Tensile break elongation rate (%) ≥ -0.000002 × D 3 +0.0011 × D 2 -0.285 × D + 32.2 (Formula 1) D in Formula 1 represents the density (g / L) of the foam molded body.

[0102] In this specification, the tensile break elongation rate (%) of the foam molded body is taken as the value obtained from the result of a tensile test performed based on ISO 1798 using the foam molded body as a sample. Specifically, in the tensile test using the foam molded body, the value of the tensile elongation rate when the foam molded body breaks is measured and taken as the tensile break elongation rate (%) of the foam molded body. Preferably, the tensile break elongation rate of the foam molded body satisfies Formula 1, and the static compression strength of the foam molded body satisfies Formula 2.

[0103] Also, the foam molded body according to an embodiment of the present invention is formed by molding extrusion foam particles obtained by extrusion foaming a resin composition containing a polypropylene-based resin having a branched structure. The closed cell ratio of the extrusion foam particles is 15% or less, the density of the foam molded body is 60 g / L to 300 g / L, the tensile break elongation rate of the foam molded body satisfies Formula 1, and the static compression strength of the foam molded body satisfies Formula 2. A polypropylene-based resin foam molded body is also included: Tensile break elongation rate (%) ≥ -0.000002 × D 3 +0.0011 × D 2 -0.285 × D + 32.2 (Formula 1) Static compression strength (kPa) ≥ 0.000049 × D 3 +0.0542 × D 2 -0.265 × D + 146.9 (Formula 2) D in Formula 1 and Formula 2 represents the density (g / L) of the foam molded body. The resin composition may be the above-described main resin composition, and the extrusion foam particles may be the above-described main extrusion foam particles.

[0104] An embodiment of the present invention may have the following configuration. [1] A polypropylene resin composition for extrusion foaming, comprising, in 100% by weight of the total resin components in the polypropylene resin composition for extrusion foaming, 65% by weight or more and 85% by weight or less of a branched polypropylene resin (A) having a tensile modulus of 1100 MPa or more and 3000 MPa or less as specified in JIS K7161, and 15% by weight or more and 35% by weight or less of a branched polypropylene resin (B) having a tensile modulus of 550 MPa or more and 950 MPa or less as specified in JIS K7161, and a tensile fracture nominal strain of 50% or more and 500% or less as specified in JIS K7161. [2] The polypropylene resin composition for extrusion foaming according to [1], wherein the branched polypropylene resin (A) has a melting point of 145°C or more and 170°C or less, and the branched polypropylene resin (B) has a melting point of 120°C or more and less than 145°C. [3] The polypropylene resin composition for extrusion foaming according to [1] or [2], wherein the amount of crystals ΔH measured by differential scanning calorimetry is 70 J / g or more and 150 J / g or less for the polypropylene resin (A) having a branched structure, and 40 J / g or more and 65 J / g or less for the polypropylene resin (B) having a branched structure. [4] A polypropylene resin composition for extrusion foaming according to any one of [1] to [3], wherein the tensile fracture nominal strain of the branched polypropylene resin (A) as specified in JIS K7161 is 5% or more and less than 50%. [5] The polypropylene resin composition for extrusion foaming according to any one of [1] to [4], wherein the melt tension of at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) is 5 cN to 20 cN. [6] A polypropylene resin composition for extrusion foaming according to any one of [1] to [5], wherein at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) contains structural units derived from a conjugated diene compound. [7] The polypropylene resin composition for extrusion foaming according to any one of [1] to [6], wherein the melt flow rate of at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) is 0.3 g / 10 min to 20.0 g / 10 min. [8] The polypropylene resin composition for extrusion foaming according to any one of [1] to [7], wherein the polypropylene resin having a branched structure (A) and / or the polypropylene resin having a branched structure (B) is one or more selected from the group consisting of homopolypropylene resin having a branched structure, random polypropylene resin having a branched structure, and block polypropylene resin having a branched structure. Polypropylene resin extruded foam particles obtained by extruding a polypropylene resin composition for extrusion foaming described in any one of [9], [1], to [8].

[10] Polypropylene resin extruded foam particles as described in [9], wherein the average cell diameter is 100 μm or more and 400 μm or less.

[11] Polypropylene resin extruded foam particles as described in [9] or

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

[12] Polypropylene resin extruded foam particles as described in any one of [9] to

[11] , having a bulk density of 40 g / L or more and 300 g / L or less.

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

[12] , wherein the DSC curve of the extruded foam particles obtained by DSC measurement has one crystal peak. A first step of melting and kneading a polypropylene resin composition for extrusion foaming described in any one of [1] to [8] and a foaming agent in a manufacturing apparatus, A method for producing polypropylene resin extruded foam particles, comprising a second step of discharging the molten mixture obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the manufacturing apparatus.

[15] The method for producing polypropylene resin extruded foam particles according to

[14] , wherein the foaming agent is one or more selected from the group consisting of aliphatic hydrocarbons, fluorinated hydrocarbons, carbon dioxide, air, nitrogen, and water.

[16] A method for producing polypropylene resin extruded foam particles according to

[14] or

[15] , wherein the method for shredding the molten mixture discharged in the second step is one or more selected from the group consisting of a hot cut method, a watering cut method, and an underwater cut method. A polypropylene resin foamed molded article obtained by in-mold foam molding of polypropylene resin extruded foam particles described in any one of

[17] , [9], to

[13] .

[18] The polypropylene resin foam molded article according to

[17] , wherein the tensile elongation at break of the foam molded article satisfies formula 1, and the static compressive strength of the foam molded article satisfies formula 2: Tensile elongation at break (%) ≥ -0.000002 × D 3 +0.0011 × D 2 -0.285×D+32.2 (Formula 1) Static compressive strength (kPa) ≥ 0.000049 × D 3 +0.0542×D 2 -0.265×D+146.9 (Formula 2) In formulas 1 and 2, D represents the density (g / L) of the foamed molded article.

[19] A foamed molded article comprising extruded foamed particles obtained by extruding a resin composition containing a polypropylene resin having a branched structure, wherein the open-cell ratio of the extruded foamed particles is 15% or less, the density of the foamed molded article is 60 g / L to 300 g / L, the tensile elongation at break of the foamed molded article satisfies formula 1, and the static compressive strength of the foamed molded article satisfies formula 2: Tensile elongation at break (%) ≥ -0.000002 × D 3 +0.0011 × D 2 -0.285×D+32.2 (Formula 1) Static compressive strength (kPa) ≥ 0.000049 × D 3 +0.0542×D 2 -0.265×D+146.9 (Formula 2) In formulas 1 and 2, D represents the density (g / L) of the foamed molded article. [Examples]

[0105] One embodiment of the present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0106] [Measurement and evaluation methods] <mfr> The MFR of the branched polypropylene resins used in the examples and comparative examples was determined by measuring the resin as a sample using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with Method B described in ISO 1133 (1997), under conditions of a temperature of 230°C and a load of 2.16 kg. The MFR was calculated by measuring the distance the piston of the melt indexer S-01 traveled in a certain period of time, and then converting the obtained distance and the density of the sample at the measurement temperature into the weight of the sample extruded from the orifice in 10 minutes. The certain period of time was defined as 120 seconds if the melt flow rate was greater than 0.1 g / 10 min and 1.0 g / 10 min or less, 60 seconds if it was greater than 1.0 g / 10 min and 3.5 g / 10 min or less, and 30 seconds if it was greater than 3.5 g / 10 min and 30.0 g / 10 min or less.

[0107] <Melting point> The melting points of the branched polypropylene resins used in the examples and comparative examples were determined by measuring the branched polypropylene resin as a sample using differential scanning calorimetry. A Seiko Instruments DSC6200 differential scanning calorimeter was used. The method for measuring the melting point using differential scanning calorimetry was as follows: (a1) The sample was melted by raising its temperature from 40°C to 220°C at a heating rate of 10°C / min; (a2) The sample was then crystallized by lowering its temperature from 220°C to 40°C at a cooling rate of 10°C / min; (a3) ​​The crystallized sample was then further heated 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 sample obtained during the second heating (i.e., at (a3)) was defined as the melting point.

[0108] <Tensile modulus and tensile fracture specified strain> The tensile modulus and tensile fracture strain of the branched polypropylene resins used in the examples and comparative examples were measured in accordance with JIS K7161.

[0109] <Melt Tension> 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.

[0110] <Crystal amount ΔH> The crystalline content ΔH of the branched polypropylene resin used in the examples and comparative examples was calculated by performing the following steps in order: (1) In the DSC curve of the branched polypropylene resin obtained during the second heating step measured by the DSC method (i.e., when (a3) ​​is described above), point A was set to 80°C and point B was set to the melting end point. (2) The amount of heat (J / g) calculated from the region enclosed by line segment AB and the DSC curve was set to ΔH.

[0111] <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 of extruded foam particles W (g) / Volume of container V (L).

[0112] <Average cell diameter> The following steps (1) to (4) were performed in order to calculate the values: (1) The extruded foam particles were cut with a razor blade so as to pass through the center of the extruded foam particles; (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 that line was measured. The number of cells was measured for 10 extruded foam particles, and their arithmetic mean number of cells was calculated; (4) The average cell diameter of the extruded foam particles used in the test was calculated using the following formula: Average cell diameter (μm) = 2000 / average number of cells.

[0113] <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 after measuring Vc 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 amount of 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.

[0114] <Molding width> A mold with dimensions of length / width / thickness = 400 / 300 / 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 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. The above evaluation was performed using molded products that had been dried in a 75-80°C dryer for 12-24 hours after molding, and then left to stand for at least 24 hours in an environment of 23°C and 50% humidity.

[0115] 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 2 to 4, respectively.

[0116] <Density of foamed molded material> The density of the foamed molded articles obtained in the examples and comparative examples was calculated by following (1) to (3) in order: (1) the weight W1 (g) of the foamed molded article was measured; (2) the length, width, and thickness of the foamed molded article were measured and the volume V1 (L) was calculated; (3) the density was calculated using W1 / V1.

[0117] <Static compressive strength> Test specimens with a length / width / thickness of 50 / 50 / 50 mm were cut from the foamed molded articles obtained in the examples and comparative examples. Here, only one side of the surface perpendicular to the thickness direction of the foamed molded article was cut. That is, the uncut surface of the surface perpendicular to the thickness direction of the foamed molded article is the surface that was in contact with the mold during in-mold foam molding (also called the skin layer). For these test specimens, the compressive stress value at 50% compression was measured using a tensile-compression testing machine (e.g., MinebeaMitsumi TG-50kN) in accordance with ISO 844, when compressed at a speed of 10% of the thickness (approximately 5 mm / min). The obtained value was defined as the static compressive strength of the foamed molded article.

[0118] <Tensile elongation at breaking> The tensile elongation at break (%) of the foamed molded articles obtained in the examples and comparative examples was determined from the results of tensile tests conducted on the foamed molded articles in accordance with ISO 1798. Specifically, the value of the tensile elongation at break when the sample fractured was measured in the tensile test using the sample, and this was defined as the tensile elongation at break (%) of the foamed molded article.

[0119] 〔material〕 The following materials were used in the examples and comparative examples. <Raw material resin> • F-724NPC (manufactured by Prime Polymer, linear polypropylene resin (polypropylene random copolymer), melting point: 150℃, MFR: 7g / 10min) • F113G (manufactured by Prime Polymer, linear polypropylene resin (propylene homopolymer), melting point: 162°C, MFR: 3g / 10min) • WB140HMS (Borealis, branched polypropylene resin, melting point 162°C, MFR: 2g / 10min, melt tension 14.4cN) • F227D (manufactured by Prime Polymer, linear polypropylene resin (polypropylene random copolymer), melting point: 140℃, MFR: 7g / 10min) • F-744NP (manufactured by Prime Polymer, linear polypropylene resin (polypropylene random copolymer), melting point 134°C, MFR: 7g / 10min) • E228 (manufactured by Prime Polymer, linear polypropylene resin (polypropylene random copolymer), melting point 146°C, MFR: 8g / 10min) • RD208CF (manufactured by Borealis, linear polypropylene resin (polypropylene random copolymer), melting point 140°C, MFR: 8g / 10min) <Conjugated diene compounds> • Isoprene: Manufactured by Kuraray Co., Ltd., isoprene monomer <Radical polymerization initiator> • t-Butyl peroxyisopropyl carbonate: Manufactured by NOF Corporation, Perbutyl (registered trademark) I <Additives> • Talc: Imerys brand, Luzenac 20MO • Carbon Black Furthermore, 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 a mixture of branched polypropylene resins used in the examples and comparative examples to a concentration of 40%, the mixture was melt-kneaded in an extruder, and the resulting molten mixture was extruded into water and cut. For example, in Example 8, carbon black was added to a mixture containing 80% by weight of resin A and 20% by weight of resin D. In the "Inorganic Colorants" column of Tables 2 to 4, the numbers outside the parentheses and the numbers inside the parentheses are indicated. The numbers outside the parentheses indicate the amount of carbon black masterbatch added, and the numbers inside the parentheses indicate the actual amount of carbon black added.

[0120] [Manufacturing of branched polypropylene resin] Resin A was manufactured as a branched polypropylene resin as follows. First, the raw material resin F-724NPC was supplied to a twin-screw extruder, and then 1.0 part by weight of a radical polymerization initiator was supplied to the twin-screw extruder for every 100 parts by weight of the raw material resin. Subsequently, 0.45 parts by weight of a conjugated diene compound was supplied to the twin-screw extruder containing the melt-kneaded raw material resin and radical polymerization initiator for every 100 parts by weight of the raw material resin, and the resin mixture was prepared in the twin-screw extruder. The supply rate of the resin mixture to the twin-screw extruder was 70 kg / h. Note that the supply rate of the resin mixture refers to the amount of resin mixture prepared per unit time in the twin-screw extruder at the time the conjugated diene compound is supplied to the twin-screw extruder.

[0121] The prepared resin mixture was melt-kneaded in a twin-screw extruder at a cylinder temperature of 200°C and a screw rotation speed of 230 rpm to obtain a branched polypropylene resin. The obtained branched polypropylene resin was extruded from the die in strand form at a discharge rate of 70 kg / h. The extruded branched polypropylene resin (strands) was (a) water-cooled and then (b) shredded into pellet form (cylindrical form). Resins B, D to H were obtained in the same manner as above, except that the type of raw material resin, the amount of radical polymerization initiator added, and / or the amount of conjugated diene compound added were changed as shown in Table 1.

[0122] As resin C, we used WB140HMS, a branched polypropylene resin. As resin J, we used RD208CF. In other words, these resins C and J were used without any separate reaction with the conjugated diene compound as described above.

[0123] [Examples 1-8, Comparative Examples 1-14] For the production of extruded foam particles, a twin-screw extruder with a shaft diameter of φ26 mm, a melt cooler, a diverter valve, and a die were connected in series. The types of resins and additives shown in Tables 2-4 were blended in the amounts shown in Tables 2-4 to prepare a polypropylene resin composition for extrusion foaming. Next, the resin composition was supplied to the twin-screw extruder and melted and kneaded at the cylinder temperature (extruder temperature) shown in Tables 2-4. Furthermore, carbon dioxide, a foaming agent, was supplied from a pressure injection section installed in the middle of the extruder in the amount shown in Tables 2-4 using a metering pump, and the resulting composition was further melted and kneaded.

[0124] 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 the temperatures shown in Tables 2-4. Then, the molten mixture was extruded through a die attached to the tip of the melt cooler into air at a pressure lower than the internal pressure of the apparatus (HC method), or into a region filled with water at a pressure lower than the internal pressure of the apparatus (UWC method), causing it to foam. A rotary cutter attached to the tip of the die shredded the composition immediately after passing through the die to obtain extruded foam particles. The temperature of the molten mixture immediately before entering the die (resin temperature at the die) was as shown in Tables 2-4. 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 molten mixture. The bulk density, average cell diameter, and open-cell ratio of the obtained extruded foam particles were measured, and the results are shown in Tables 2-4. Furthermore, 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 2-4.

[0125] The obtained extruded foam particles were used with a Daisen Co., Ltd. molding machine (KD345) to fill a block-shaped mold (400 mm long x 300 mm wide x variable thickness) with a thickness of 78 mm (cracking rate 30%). The extruded foam particles were then compressed into the mold to a thickness of 60 mm. Next, the air in the mold was expelled with steam at 0.10 MPa (gauge pressure), and then the foam molded body was heated and molded for 10 seconds using steam with a vapor pressure of 0.20 MPa (gauge pressure) to obtain a foam molded body. The density, static compressive strength, and tensile elongation at break of the obtained foam molded body were measured, and the results are shown in Tables 2 to 4.

[0126] [Evaluation Results] The physical properties of resins A-H and J are shown in Table 1. Resins A-C correspond to branched polypropylene resins (A). Resins D-F correspond to branched polypropylene resins (B). Resins G and H correspond to other branched polypropylene resins (referred to as branched polypropylene resins (C) for convenience). Resin J is a linear polypropylene resin.

[0127] [Table 1]

[0128] Tables 2 to 4 show the composition of the extruded foam particles, manufacturing conditions, moldability of the extruded foam particles, and physical properties of the foamed molded articles for Examples 1 to 8 and Comparative Examples 1 to 14.

[0129] [Table 2]

[0130] [Table 3]

[0131] [Table 4]

[0132] In Tables 2-4, branched polypropylene resin (A), branched polypropylene resin (B), branched polypropylene resin (C), and linear polypropylene resin are simply referred to as (A), (B), (C), and linear, respectively. For resins A, B, and D-H, the resins listed in parentheses in Tables 2-4 are the raw materials used in the production of each resin. For resins C and J, the resins listed in parentheses in Tables 2-4 are resins C and J themselves. The resin formulations in Tables 2-4 indicate the proportion of each resin in 100% by weight of the total resin components (a mixture of resins A-H and J). The amounts of additives and foaming agents in Tables 2-4 indicate the amount added relative to 100 parts by weight of the total resin components.

[0133] Examples 1 to 8 each contain a specific amount of any of resins A to C corresponding to branched polypropylene resin (A) with a tensile modulus of 1100 MPa or more, and any of resins D to F corresponding to branched polypropylene resin (B) with a tensile modulus of 550 MPa or more and a tensile fracture nominal strain of 50% or more. Examples 1 to 8 show that polypropylene resin extruded foam particles with excellent moldability, as well as polypropylene resin foam molded articles with excellent static compressive strength and tensile fracture elongation, can be obtained.

[0134] The evaluation results will be explained in more detail below. It is necessary to compare the evaluation results between the example and the comparative example, where the type of main resin component, granulation method, and density of the foamed molded product are the same. In the following, "the comparative example is inferior in tensile elongation at break" means that the tensile elongation at break decreases at a rate exceeding the rate of change in static compressive strength compared to the example. Similarly, "the comparative example is inferior in static compressive strength" means that the static compressive strength decreases at a rate exceeding the rate of change in tensile elongation at break compared to the example.

[0135] First, we compare Examples 1-5 and Comparative Examples 1-9, where the granulation method is HC and the density of the foamed molded article is 70 g / L (when measuring static compressive strength) or 65 g / L (when measuring tensile elongation at break). Comparative Examples 1 and 2, where the amount of resin A equivalent to branched polypropylene resin (A) used exceeds 85% by weight, have inferior tensile elongation at break compared to Examples 1-5, where the amount of resin A used is 85% by weight or less. Furthermore, Comparative Example 3, where the amount of resin A used is less than 65% by weight, has inferior static compressive strength compared to Examples 1-5, where the amount of resin A used is 65% by weight or more.

[0136] Comparative Example 4, in which the amount of resin D equivalent to branched polypropylene resin (B) exceeds 35% by weight, exhibits inferior static compressive strength compared to Examples 1 and 2, in which the amount of resin D used is 35% by weight or less. Comparative Example 5, in which the amount of resin E equivalent to branched polypropylene resin (B) exceeds 35% by weight, exhibits inferior static compressive strength compared to Example 3, in which the amount of resin E used is 35% by weight or less. Comparative Example 6, in which the amount of resin F equivalent to branched polypropylene resin (B) exceeds 35% by weight, exhibits inferior static compressive strength compared to Examples 4 and 5, in which the amount of resin F used is 35% by weight or less.

[0137] Comparative Examples 7 and 9, which did not use a resin equivalent to either branched polypropylene resin (A) or branched polypropylene resin (B), and Comparative Example 8, which used branched polypropylene resin (C) instead of branched polypropylene resin (A) and branched polypropylene resin (B), exhibited inferior static compressive strength compared to Examples 1 to 5.

[0138] Next, we compare Examples 6-8 and Comparative Examples 10-14, where the granulation method is UWC and the density of the foamed molded body is 140 g / L (when measuring static compressive strength) or 130 g / L (when measuring tensile elongation at break). Comparative Example 10, in which the amount of resin A equivalent to branched polypropylene resin (A) used exceeds 85% by weight, shows inferior tensile elongation at break compared to Example 6, in which the amount of resin A used is 85% by weight or less. Furthermore, Comparative Example 11, in which the amount of resin B equivalent to branched polypropylene resin (A) used exceeds 85% by weight, shows inferior tensile elongation at break compared to Example 7, in which the amount of resin B used is 85% by weight or less. Furthermore, Comparative Example 12, in which the amount of resin C equivalent to branched polypropylene resin (A) used exceeds 85% by weight, shows inferior tensile elongation at break compared to Example 8, in which the amount of resin C used is 85% by weight or less.

[0139] Comparative Example 13, in which the amount of resin D, equivalent to branched polypropylene resin (B), exceeds 35% by weight, exhibits inferior static compressive strength compared to Examples 6-8, in which the amount of resin D used is 35% by weight or less. Furthermore, Comparative Example 14, which uses linear polypropylene resin J instead of a resin equivalent to branched polypropylene resin (B), had a high open-cell ratio, making it impossible to measure the molded width.

[0140] Example 1 contains 80% by weight of resin A and 20% by weight of resin D. When resin A is 100% by weight, the static compressive strength is 480 kPa and the tensile elongation at break is 16%, as in Comparative Example 1. When resin D is 100% by weight, the static compressive strength is 350 kPa and the tensile elongation at break is 25%, as in Comparative Example 4. From the results of Comparative Examples 1 and 4, the static compressive strength of Example 1, calculated proportionally based on the proportions of resins A and D, is 480 kPa × 0.80 + 350 kPa × 0.20 = 454 kPa, and the tensile elongation at break, calculated proportionally based on the proportions of resins A and D, is 16% × 0.80 + 25% × 0.20 = 17.8%. However, in reality, the static compressive strength of Example 1 was 470 kPa and the tensile elongation at break was 19%, indicating that both the static compressive strength and tensile elongation at break were higher than the calculated values.

[0141] A comparison between Examples 1 and 2 and Comparative Examples 1 and 4, between Example 3 and Comparative Examples 1 and 5, between Examples 4 and 5 and Comparative Examples 1 and 6, between Example 6 and Comparative Examples 10 and 13, between Example 7 and Comparative Examples 11 and 13, and between Example 8 and Comparative Examples 12 and 13 revealed that in all examples, the static compressive strength and tensile elongation at fracture were equivalent to or higher than the calculated values. [Industrial applicability]

[0142] 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 having excellent static compressive strength and tensile elongation at break. 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.< / mfr>

Claims

1. A polypropylene resin composition for extrusion foaming, In the polypropylene resin composition for extrusion foaming, the total of 100% by weight of the resin components is: A polypropylene resin (A) having a branched structure and a tensile modulus of 1100 MPa or more as specified in JIS K7161, in an amount of 65% to 85% by weight, A polypropylene resin composition for extrusion foaming, comprising 15% to 35% by weight of a branched polypropylene resin (B) having a tensile modulus of 550 MPa or more and a tensile fracture nominal strain of 50% or more as specified in JIS K7161.

2. The polypropylene resin composition for extrusion foaming according to claim 1, wherein the branched polypropylene resin (A) has a melting point of 145°C or higher, and the branched polypropylene resin (B) has a melting point of less than 145°C.

3. The polypropylene resin composition for extrusion foaming according to claim 1 or 2, wherein the amount of crystals ΔH measured by differential scanning calorimetry is 70 J / g or more for the branched polypropylene resin (A) and 40 J / g or more and 65 J / g or less for the branched polypropylene resin (B).

4. A polypropylene resin composition for extrusion foaming according to any one of claims 1 to 3, wherein the tensile fracture nominal strain of the branched polypropylene resin (A) as defined in JIS K7161 is less than 50%.

5. The polypropylene resin composition for extrusion foaming according to any one of claims 1 to 4, wherein the melt tension of at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) is 5 cN to 20 cN.

6. The polypropylene resin composition for extrusion foaming according to any one of claims 1 to 5, wherein at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) contains structural units derived from a conjugated diene compound.

7. The polypropylene resin composition for extrusion foaming according to any one of claims 1 to 6, wherein the melt flow rate of at least one of the branched polypropylene resin (A) and the branched polypropylene resin (B) is 0.3 g / 10 min to 20.0 g / 10 min.

8. Polypropylene resin extruded foam particles obtained by extruding a polypropylene resin composition for extrusion foaming according to any one of claims 1 to 7.

9. Polypropylene resin extruded foam particles according to claim 8, wherein the average cell diameter is 100 μm or more and 400 μm or less.

10. Polypropylene resin extruded foam particles according to claim 8 or 9, wherein the open-cell ratio is 15% or less.

11. Polypropylene resin extruded foam particles according to any one of claims 8 to 10, wherein the bulk density is 40 g / L or more.

12. A first step of melt-kneading the polypropylene resin composition for extrusion foaming according to any one of claims 1 to 7 and a foaming agent in a manufacturing apparatus, A method for producing polypropylene resin extruded foam particles, comprising a second step of discharging the molten mixture obtained in the first step through a die into a region where the pressure is lower than the internal pressure of the manufacturing apparatus.

13. The method for producing polypropylene resin extruded foam particles according to claim 12, wherein the foaming agent is one or more selected from the group consisting of aliphatic hydrocarbons, fluorinated hydrocarbons, carbon dioxide, air, nitrogen, and water.

14. A polypropylene resin foamed molded article obtained by in-mold foam molding of polypropylene resin extruded foamed particles according to any one of claims 8 to 11.

15. A polypropylene resin foam molded article according to claim 14, The open-cell ratio of the polypropylene resin extruded foam particles is 15% or less. The density of the polypropylene-based resin foam molded article is 60 g / L to 300 g / L. The tensile elongation at break of the polypropylene resin foam molded article satisfies formula 1, and The polypropylene-based foamed molded material having a static compressive strength satisfying formula 2: Tensile elongation at break (%) ≥ -0.000002 × D ３ +0.0011 × D ２ -0.285×D+32.2 (Formula 1) Static compressive strength (kPa) ≥ 0.000049 × D ３ +0.0542 × D ２ -0.265×D+146.9 (Formula 2) In formulas 1 and 2, D represents the density (g / L) of the polypropylene-based resin foam molded article.