Polypropylene resin extruded foam particles, method for producing the same, and foamed molded articles

Abstract

The present invention provides: polypropylene resin extruded foam particles which enable the achievement of a polypropylene resin foam molded body that has excellent low-pressure moldability and excellent compressive strength; and the like. Polypropylene resin extruded foam particles according to the present invention contain a base material resin wherein the ratio of a low melting point polypropylene resin to a high melting point polypropylene resin is within a specific range.

Description

[Technical Field]

[0001] This invention relates to polypropylene resin extruded foam particles, a method for producing the same, and a foamed molded article. [Background technology]

[0002] Polypropylene-based foam molded articles obtained using polypropylene-based resin foam particles are characterized by their excellent flexibility in shape, cushioning properties, light weight, and heat insulation properties. These characteristics are also advantages of polypropylene-based foam molded articles. Furthermore, because the base material is polypropylene-based resin, polypropylene-based foam molded articles have excellent chemical resistance, heat resistance, compressive strength, and distortion recovery rate after compression. Due to these advantages, polypropylene-based foam molded articles are used in a variety of applications, mainly as automotive interior components and core materials for automotive bumpers, as well as heat insulation materials and cushioning packaging materials.

[0003] Polypropylene resin foam particles can generally be manufactured by a method called "pressure-relieving foaming," which involves dispersing polypropylene resin particles in water in a pressure vessel along with a volatile foaming agent. However, to obtain polypropylene resin particles for use in the pressure-relieving foaming method, it is necessary to pelletize the polypropylene resin to a size suitable for foaming using an extruder or the like beforehand. In other words, when obtaining polypropylene resin foam particles using the pressure-relieving foaming method with polypropylene resin as the raw material, two processes are required: a pelletizing process and a pressure-relieving foaming process. As a result, the pressure-relieving foaming method may have the following challenges: (a) it tends to require significant capital investment, and (b) it requires wastewater treatment facilities because it uses a dispersion medium such as water.

[0004] In recent years, in order to overcome these challenges, it has been proposed to obtain polypropylene resin extruded foam particles by an extrusion foaming method (for example, Patent Documents 1-3).

[0005] On the other hand, from the perspective of economy, there is a demand for the performance (low-pressure moldability) that polypropylene-based resin foamed particles can be molded using steam at a lower pressure. The low-pressure moldability can be achieved, for example, by a method of selecting a resin with a low melting point as the base resin constituting the polypropylene-based resin foamed particles (for example, Patent Document 4).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in conventional polypropylene-based resin extrusion foamed particles, the compatibility between the low-pressure moldability of the polypropylene-based resin extrusion foamed particles and the high compressive strength of the foamed molded body obtained from the polypropylene-based resin extrusion foamed particles has not been sufficient.

[0008] One embodiment of the present invention has been made in view of the above problems. The object is to provide polypropylene-based resin extrusion foamed particles having excellent low-pressure moldability and capable of providing a polypropylene-based resin foamed molded body having excellent compressive strength.

Means for Solving the Problems

[0009] That is, the polypropylene-based resin extrusion foamed particles according to one embodiment of the present invention have a melting point Tm 2AA polypropylene-based resin (A) having a branched structure with a melting point Tm of 130.0 °C or higher and less than 143.0 °C is more than 70% by weight and 98% by weight or less, 2B A polypropylene-based resin (B) having a branched structure with a melting point Tm of 150.0 °C or higher and less than 170.0 °C is 2% by weight or more and less than 30% by weight (the total of the polypropylene-based resin (A) and the polypropylene-based resin (B) is 100% by weight), and a base resin containing the same, wherein the melting point Tm1 in the first temperature rise of the polypropylene-based resin extrusion foam particles is 130.0 °C or higher and less than 155.0 °C.

Advantages of the Invention

[0010] According to one embodiment of the present invention, there is provided a polypropylene-based resin extrusion foam particle excellent in low-pressure moldability, and a polypropylene-based resin extrusion foam particle capable of providing a polypropylene-based resin foam molded body excellent in compressive strength.

Modes for Carrying Out the Invention

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

[0012] 〔1. Technical Concept of One Embodiment of the Present Invention〕 Similar to polypropylene resin foam particles obtained by the depressurization foaming method, when a resin with a low melting point is selected as the base resin constituting polypropylene resin extruded foam particles, the compressive strength of the molded article obtained by molding these polypropylene resin extruded foam particles tends to be low.

[0013] On the other hand, when a resin with a high melting point and excellent strength is blended with the base resin that constitutes polypropylene resin extruded foam particles, the melting point of the base resin approaches the melting point of the resin in question (high melting point), and as a result, the low-pressure moldability of the polypropylene resin extruded foam particles tends to be impaired.

[0014] However, after diligent research by the inventors, the following findings were discovered: (i) The melting point Tm1 of polypropylene resin extruded foam particles at the first heating stage, (ii) (Melting point Tm during the second heating step) 2A (Amount of polypropylene resin (A) which has a low temperature) (Melting point Tm at the second heating step) 2B The ratio (mixing ratio) of the amount of polypropylene resin (B) which is at high temperature, The relationship is not a simple proportional one. This is thought to be because the balance between the low-pressure moldability of the extruded foam particles and the compressive strength of the foamed molded product is achieved under a complex relationship between polypropylene resin (A) and polypropylene resin (B).

[0015] One embodiment of the present invention has been completed based on the aforementioned novel findings. The present embodiment of the present invention will be described in detail below.

[0016] [2. Polypropylene resin extruded foam particles] Polypropylene resin extruded foam particles according to one embodiment of the present invention have a melting point Tm 2A A polypropylene resin (A) having a branched structure with a melting point Tm is present in an amount of more than 70% by weight and 98% by weight or less, and the melting point Tm is 130.0°C or higher and less than 143.0°C. 2BThe polypropylene resin extruded foam particles contain a base resin containing a polypropylene resin (B) having a branched structure with a melting point of 150.0°C or higher and less than 170.0°C, in an amount of 2% by weight or more and less than 30% by weight (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight), wherein the melting point Tm1 of the polypropylene resin extruded foam particles at the first heating stage is 130.0°C or higher and less than 155.0°C.

[0017] Polypropylene resin extruded foam particles according to one embodiment of the present invention can be formed into a polypropylene resin foam molded article by in-mold foam molding of the polypropylene resin extruded foam particles. In this specification, "polypropylene resin having a branched structure" may be referred to as "branched polypropylene resin," and "polypropylene resin extruded foam particles" may be referred to as "extruded foam particles." Furthermore, in this specification, "polypropylene resin extruded foam particles according to one embodiment of the present invention" may be referred to as "the extruded foam particles," and "polypropylene resin foam molded article" may be referred to as "foam molded article." In addition, in this specification, "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as "the foam molded article."

[0018] Because these extruded foam particles have the aforementioned structure, they exhibit excellent low-pressure moldability. Furthermore, because these extruded foam particles have the aforementioned structure, they have the advantage of providing a foamed molded article with excellent compressive strength.

[0019] (1-1. Base resin) The base resin preferably comprises only branched polypropylene resins (e.g., branched polypropylene resins (A) and (B)). Alternatively, the base resin may contain a polypropylene resin having a branched structure (e.g., branched polypropylene resins (A) and (B)) and optionally include additives such as bubble nucleating agents. The base resin can also be said to be the resin component that substantially constitutes the extruded foam particles.

[0020] As described above, when the total of branched polypropylene resin (A) and branched polypropylene resin (B) is 100% by weight, the base resin preferably contains (i) more than 70% by weight and 98% by weight or less of branched polypropylene resin (A) and 2% by weight or more and less than 30% by weight of branched polypropylene resin (B); (ii) more than 75% by weight and 98% by weight or less of branched polypropylene resin (A) and 2% by weight or more and less than 25% by weight of branched polypropylene resin (B); (iii) more than 80% by weight and 98% by weight or less of branched polypropylene resin (A) and 2% by weight or more and less than 20% by weight of branched polypropylene resin (B); and (iv) more than 85% by weight and 95% by weight or less of branched polypropylene resin (A) and 5% by weight or more and 15% by weight or less of branched polypropylene resin (B). This configuration makes it possible to improve the low-pressure moldability of extruded foam particles.

[0021] In this specification, "branched polypropylene resin" 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 "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.

[0022] 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 also be referred to as "propylene units."

[0023] (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.

[0024] 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."

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Examples of styrene monomers include styrene, methylstyrene, dimethylstyrene, alpha-methylstyrene, para-methylstyrene, ethylstyrene, diethylstyrene, isopropylstyrene, t-butylstyrene, bromostyrene, dibromostyrene, tribromostyrene, chlorostyrene, dichlorostyrene, and trichlorostyrene.

[0029] The linear polypropylene resin preferably has structural units derived from α-olefins having 2 or 4 to 12 carbon atoms as comonomer units, more preferably structural units derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene and / or 1-decene, more preferably structural units derived from ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene and / or 4-methyl-1-pentene, even more preferably structural units derived from ethylene, 1-butene, isobutene and / or 1-pentene, and most preferably structural units derived from ethylene and / or 1-butene. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0030] The linear polypropylene resin is preferably a propylene homopolymer, a polypropylene block copolymer, and / or a polypropylene random copolymer, and more preferably a propylene homopolymer and / or a polypropylene random copolymer. This configuration has the advantages of (a) obtaining a branched polypropylene resin having high melt tension and low gel fraction, and (b) providing polypropylene resin extruded foam particles with excellent moldability from the obtained branched polypropylene resin.

[0031] The linear polypropylene resin preferably contains 90 mol% or more of propylene units, more preferably 93 mol% or more, even more preferably 94 mol% or more, and particularly preferably 95 mol% or more, of the total structural units contained in the linear polypropylene resin. This configuration has the advantage of yielding a branched polypropylene resin with high melt tension and low gel fraction.

[0032] The linear polypropylene-based resin used in the preparation of the branched polypropylene-based resin (A) is designated as the linear polypropylene-based resin (A'). The linear polypropylene-based resin (A') is, for example, (i) a linear polypropylene-based resin having a melting point Tm 3A of 130.0°C or higher and lower than 150.0°C, and (ii) preferably a linear polypropylene-based resin having a melting point Tm 3A of 132.0°C or higher and 147.0°C or lower, and (iii) more preferably a linear polypropylene-based resin having a melting point Tm 3A of 135.0°C or higher and 145.0°C or lower. If it is the said linear polypropylene-based resin (A'), it has the advantage that the desired branched polypropylene-based resin (A) can be efficiently prepared.

[0033] The linear polypropylene-based resin used in the preparation of the branched polypropylene-based resin (B) is designated as the linear polypropylene-based resin (B'). The linear polypropylene-based resin (B') is, for example, (i) a linear polypropylene-based resin having a melting point Tm 3B of 150.0°C or higher and lower than 170.0°C, and (ii) preferably a linear polypropylene-based resin having a melting point Tm 3B of 155.0°C or higher and 168.0°C or lower, and (iii) more preferably a linear polypropylene-based resin having a melting point Tm 3B of 160.0°C or higher and 165.0°C or lower. If it is the said linear polypropylene-based resin (B'), it has the advantage that the desired branched polypropylene-based resin (B) can be efficiently prepared.

[0034] Here, the melting point Tm 3A of the linear polypropylene-based resin (A) and the melting point Tm 3B (In other words, the melting point Tm 3A and Tm 3BThe melting point Tm3 of the linear polypropylene resin can be determined by measuring it using differential scanning calorimetering (hereinafter referred to as the "DSC method"). The specific procedure is as follows: (1) The linear polypropylene resin is melted by raising the temperature of 5-6 mg of linear polypropylene resin from 40°C to 220°C at a heating rate of 10°C / min; (2) The molten linear polypropylene resin is then crystallized by lowering the temperature from 220°C to 40°C at a cooling rate of 10°C / min; (3) The crystallized linear 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 linear polypropylene resin obtained during the second heating (i.e., at (3)) can be determined as the melting point Tm3 of the linear polypropylene resin. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the linear polypropylene resin obtained during the second heating cycle using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) is defined as the melting point Tm3 of the linear polypropylene resin. As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0035] The MFR of the linear polypropylene resin is not particularly limited, but the MFR of the linear polypropylene resin may affect the MFR of the base resin. Therefore, the MFR of the linear polypropylene resin is preferably, for example, 0.5 g / 10 min to 22.0 g / 10 min, more preferably 1.0 g / 10 min to 20.0 g / 10 min, more preferably 2.0 g / 10 min to 15.0 g / 10 min, more preferably 2.0 g / 10 min to 12.0 g / 10 min, even more preferably 2.0 g / 10 min to 10.0 g / 10 min, and particularly preferably 3.0 g / 10 min to 9.0 g / 10 min. When the MFR of the linear polypropylene resin is within the above range, the resulting extruded foamed particles have the advantage of providing a foamed molded article with excellent low-pressure moldability and high compressive strength. When the MFR of the linear polypropylene resin is (a) 0.5 g / 10 min or more, the resulting branched polypropylene resin has the advantage of providing a foamed molded article with less deformation and good (beautiful) surface properties, and (b) when it is 22.0 g / 10 min or less, it has the advantage of providing good foaming properties of the composition during extrusion foaming.

[0036] In this specification, the MFR of linear polypropylene resin is a value obtained by measurement under the conditions of ISO 1133, with a temperature of 230°C and a load of 2.16 kg.

[0037] (Branched polypropylene resin) Branched polypropylene resins (for example, branched polypropylene resins (A) and (B)) can be obtained by introducing a branched structure into a linear polypropylene resin. For example, branched polypropylene resin (A) can be obtained by introducing a branched structure into linear polypropylene (A'), and branched polypropylene resin (B) can be obtained by introducing a branched structure into linear polypropylene (B'). For example, a branched polypropylene resin containing polypropylene resins (A) and (B) (in other words, a branched polypropylene resin containing polypropylene resin (A) and polypropylene resin (B) in a crosslinked state within a single molecule (single polymer)) can be obtained by introducing a branched structure into a mixture of linear polypropylene (A') and linear polypropylene (B').

[0038] In other words, a branched structure may be introduced independently into linear polypropylene (A') and (B'), or a branched structure may be introduced into a mixture of linear polypropylene (A') and (B').

[0039] The method for introducing a branched structure into a linear polypropylene resin is not particularly limited, but examples include (a1) irradiating the linear polypropylene resin with radiation, and (a2) melt-kneading a mixture containing the linear polypropylene resin, one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and a radical polymerization initiator.

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

[0041] A specific example of the method described in (a2) above is a method that includes a preparation step, which will be described later.

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

[0043] A polypropylene resin (A) having a branched structure, for example, has a melting point Tm 2A (ii) Preferably a polypropylene resin having a branched structure with a melting point Tm 2A (iii) is a polypropylene resin having a branched structure with a melting point Tm between 133.0°C and 142.0°C, and (iii) more preferably has a melting point Tm 2A This is a polypropylene resin having a branched structure with a temperature range of 135.0°C or higher and 141.0°C or lower. Extruded foam particles obtained using this polypropylene resin (A) have the advantage of providing a foamed molded article with excellent low-pressure moldability and compressive strength.

[0044] A polypropylene resin (B) having a branched structure is, for example, (i) melting point Tm 2B (ii) a polypropylene resin having a branched structure with a melting point of 150°C or higher and less than 170°C, and preferably with a melting point Tm 2B (iii) More preferably, a polypropylene resin having a branched structure with a melting point Tm 2B This is a polypropylene resin having a branched structure with a temperature range of 155.0°C or higher and 165.0°C or lower. The extruded foam particles obtained using this polypropylene resin (B) have the advantage of providing a polypropylene resin foam molded article that exhibits excellent low-pressure moldability and compressive strength.

[0045] In one embodiment of the present invention, the base resin may (i) contain polypropylene resin (A) and polypropylene resin (B) as independent molecules (in other words, contain a mixture of polypropylene resins (A) and (B)), or (ii) contain a branched polypropylene resin in which polypropylene resin (A) and polypropylene resin (B) are crosslinked within a single molecule (single polymer). In either of these embodiments, according to one embodiment of the present invention, it is possible to provide extruded foam particles that are excellent in low-pressure moldability and can provide a polypropylene resin foam molded article with excellent compressive strength.

[0046] Here, the melting point Tm of the branched polypropylene resin (A) 2A and the melting point Tm of (B) 2B (In other words, the melting point Tm in the second heating step) 2A and Tm 2B) is a value obtained by measurement using differential scanning calorimeter (also called the "DSC method"). The specific operating procedure is as follows: (1) Melt the polypropylene resin (A) or (B) by raising the temperature of 5-6 mg of polypropylene resin (A) or (B) from 40°C to 220°C at a heating rate of 10°C / min; (2) Then crystallize the polypropylene resin (A) or (B) by lowering the temperature of the molten polypropylene resin (A) or (B) from 220°C to 40°C at a cooling rate of 10°C / min; (3) Then further raise the temperature of the crystallized polypropylene resin (A) or (B) from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) in the DSC curve of the polypropylene resin (A) or (B) obtained during the second heating (i.e., when (3) is performed) can be determined as the melting point Tm2 of the polypropylene resin (A) or (B). If multiple peaks exist in the DSC curve obtained during the second heating using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) is taken as the melting point Tm2 of the polypropylene resin (A) or (B). As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0047] Here, we will describe a branched polypropylene resin (hereinafter referred to as branched polypropylene resin (X)) obtained by introducing a branched structure into a mixture of multiple types of linear polypropylene resins (for example, a mixture of linear polypropylene resin (A') and linear polypropylene resin (B')). As described above, branched polypropylene resin (X) has branched polypropylene resins in which a branched structure is introduced into each of the multiple types of linear polypropylene resins used as raw materials (for example, branched polypropylene resin (A) and branched polypropylene resin (B) in which a branched structure is introduced into each of linear polypropylene resins (A') and linear polypropylene resin (B'). In addition, branched polypropylene resin (X) may partially contain components in which linear polypropylene resin (A') and linear polypropylene resin (B') are crosslinked.

[0048] In the present invention, the branched polypropylene resin (A) and branched polypropylene resin (B) contained in the base resin used refer to the components obtained by the following methods. Note that components obtained by crosslinking linear polypropylene resin (A') and linear polypropylene resin (B') will be included in either (A) or (B) below, depending on their melting point.

[0049] (1) The base resin is separated at its melting point by the method described in Example 1 of Japanese Patent Publication No. 2014-055924 to obtain an elution chromatogram.

[0050] (2) In the obtained elution chromatogram, the component corresponding to the largest peak is defined as branched polypropylene resin (A), and the component corresponding to the next largest peak is defined as branched polypropylene resin (B).

[0051] Furthermore, the melting points Tm of the branched polypropylene resin (A) and branched polypropylene resin (B) obtained in this manner are as follows: 2A , Tm 2B This value is obtained by performing DSC measurements on the branched polypropylene resin (A) and branched polypropylene resin (B), which have been separated and partitioned by the method described above, using the method described above.

[0052] Furthermore, the ratio of branched polypropylene resin (A) and branched polypropylene resin (B) contained in branched polypropylene resin (X) is determined as the peak area ratio in the elution chromatogram.

[0053] In branched polypropylene resins obtained from linear polypropylene resins as raw materials, the structure of parts other than the crosslinked portion (in other words, the main chain) is derived from the structure of the linear polypropylene resin. For example, the main chain of branched polypropylene resin (A), the main chain of branched polypropylene resin (B), and / or the main chain of branched polypropylene resins (A) and (B) (i.e., branched polypropylene resin (X)) 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. With this configuration, the branched polypropylene resin has the advantages of (a) having high melt tension and low gel fraction, and (b) being able to provide polypropylene resin extruded foam particles with excellent moldability.

[0054] (Other resins or rubbers) The base resin 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 invention. 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 total content of other resins and rubbers in the base resin is not particularly limited. The total content of other resins and rubbers in the base resin is preferably 1 to 10 parts by weight, and more preferably 2 to 5 parts by weight, per 100 parts by weight of branched polypropylene resin.

[0055] (bubble nucleating agent) The base resin may contain a nucleating agent. In other words, a nucleating agent may be used in the production of these extruded foam particles. By using a nucleating agent, the number and shape of bubbles in the resulting polypropylene resin extruded foam particles can be controlled.

[0056] 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.

[0057] The content of the nucleating agent in the base resin, in other words, the amount of nucleating agent used in the production of extruded foam particles, is not particularly limited. The content of the nucleating agent is preferably 0.01 to 5.00 parts by weight, more preferably 0.01 to 3.50 parts by weight, even more preferably 0.01 to 1.00 parts by weight, and particularly preferably 0.01 to 0.50 parts by weight per 100 parts by weight of polypropylene resin. This configuration has the advantage that the average bubble diameter and bubble shape of the extruded foam particles become uniform, and as a result, the foaming properties during extrusion foaming tend to be more stable.

[0058] (Other ingredients) The base resin may further contain, as necessary, other components, (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, and / or (b) additives such as crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, colorants, and antistatic agents. These other components may be used individually or in combination of two or more. The total content of other components in the base resin is not particularly limited. The total content of other components in the base resin is preferably 0.01 to 50.00 parts by weight, and more preferably 0.05 to 30.00 parts by weight, per 100 parts by weight of branched polypropylene resin.

[0059] (Physical properties of the base resin) The physical properties of the base resin will be described below. The physical properties of the base resin contained in the extruded foam particles, or the base resin contained in the foamed molded body obtained from said extruded foam particles, that is, the base resin that substantially constitutes the extruded foam particles or the foamed molded body, do not substantially change even when the extruded foam particles or the foamed molded body are melted under reduced pressure and returned to a resin mass. Therefore, the physical properties of the resin mass obtained by melting the extruded foam particles or the foamed molded body obtained from said extruded foam particles under reduced pressure can be considered as the physical properties of the base resin contained in said extruded foam particles or the foamed molded body. In this specification, the process of melting the extruded foam particles or the foamed molded body obtained from said extruded foam particles under reduced pressure to obtain a resin mass may be referred to as "resin return," and the resin mass obtained by resin return may be referred to as "returned resin."

[0060] There are no particular limitations on the specific method of resin return, but for example, the following method can be performed in order: (a1) Place the extruded foam particles or foam molded body into a dryer adjusted to a temperature of 180°C; (a2) Then, using a vacuum pump, reduce the pressure inside the dryer to -0.05 MPa (cage pressure) to -0.10 MPa (cage pressure) over 5 to 10 minutes; (a3) ​​After that, leave the extruded foam particles in the dryer for 30 minutes to prepare a resin mass (returned resin); (a4) Then, after cooling the temperature inside the dryer to room temperature, return the pressure inside the dryer to atmospheric pressure; (a5) After that, remove the resin mass from the dryer.

[0061] (Melting elongation) The melt elongation of the base resin is 3.0 m / min to 30.0 m / min, preferably 4.0 m / min to 25.0 m / min, more preferably 5.0 m / min to 20.0 m / min, even more preferably 6.0 m / min to 18.0 m / min, and particularly preferably 7.0 m / min to 16.0 m / min. The melt elongation of the base resin may also be 3.0 m / min to 8.0 m / min, 4.0 m / min to 8.0 m / min, 5.0 m / min to 8.0 m / min, 6.0 m / min to 8.0 m / min, or 7.0 m / min to 8.0 m / min. When the melt elongation of the base resin is within the above range, the resulting extruded foam particles have the advantage of providing a foamed molded article with excellent low-pressure moldability and compressive strength.

[0062] The melt elongation of the base resin is determined by measuring the melt tension at 230°C. For example, the melt elongation of the base resin is determined by measuring the melt tension at 230°C using a sample of returned resin obtained by returning extruded foam particles or foam molded bodies to their original state. As the device used for melt tension measurement, a Capillograph 1D (manufactured by Toyo Seiki Seisakusho) can be used, which is equipped with a melt tension measuring attachment, has an orifice with a hole diameter (φ) of 1 mm and a length of 10 mm at its tip, and has a cylinder with a bore diameter (φ) of 10 mm. An example of a method for measuring the melt elongation of a base resin using the apparatus is as follows: (1) The returned resin obtained by returning extruded foam particles or foam molded bodies to the resin is filled into a cylinder of a capillograph, set to 230°C and fitted with an orifice with a diameter of 1 mm and a length of 10 mm at its tip; (2) The filled returned resin is left in the cylinder for 5 minutes to heat (preheat) the returned resin; (3) Then, the piston is lowered at a piston descent speed of 10 mm / min, and the returned resin is discharged from the orifice in a strand-like manner; (5) The discharged strand-shaped return resin is placed on a load cell-equipped pulley installed 350 mm below the orifice, and the return resin is withdrawn at a speed of 1 m / min; (6) After the return resin withdrawal stabilizes, the return resin withdrawal speed is increased at a constant rate from 1 m / min to 200 m / min in 4 minutes; (7) The withdrawal speed at which the strand-shaped return resin breaks is recorded; (8) The same operation is repeated four more times (a total of five times), and the arithmetic mean of the withdrawal speeds at n=5 is taken as the melt elongation.

[0063] (Melt Flow Rate (MFR)) The MFR of the base resin is 1.0 g / 10 min to 20.0 g / 10 min, more preferably 2.0 g / 10 min to 15.0 g / 10 min, more preferably 2.0 g / 10 min to 10.0 g / 10 min, even more preferably 2.0 g / 10 min to 8.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 6.0 g / 10 min. The MFR of the base resin may also be 1.0 g / 10 min to 4.4 g / 10 min, 2.0 g / 10 min to 4.4 g / 10 min, 3.0 g / 10 min to 4.4 g / 10 min, or 4.0 g / 10 min to 4.4 g / 10 min. When the MFR of the base resin is within the above range, the resulting extruded foam particles have the advantage of providing a foamed molded article with excellent low-pressure moldability and excellent compressive strength.

[0064] The MFR of the base resin is a value obtained by measurement in accordance with ISO 1133, under conditions of a temperature of 230°C and a load of 2.16 kg. The MFR of the base resin is a value obtained by measurement under the following conditions, for example: using a resin obtained by melting (returning resin) extruded foam particles or foam molded products as a sample, the measurement is performed in accordance with the provisions of Method B described in ISO 1133 (1997), using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho), under conditions of a temperature of 230°C and a load of 2.16 kg. Alternatively, the MFR of the base resin can be calculated by measuring the distance the piston of the melt indexer S-01 moves in a certain period of time, and 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. Note that the certain period of time should be 120 seconds if the melt flow rate exceeds 0.1 g / 10 min and is 1.0 g / 10 min or less. The aforementioned fixed time should be 60 seconds if the melt flow rate exceeds 1.0 g / 10 min and is 30.0 g / 10 min or less, and 30 seconds if it exceeds 3.5 g / 10 min and is 10 g / 10 min or less.

[0065] (1-2. Polypropylene resin extruded foam particles) (Physical properties of extruded foam particles) The physical properties of the extruded foam particles are described below. The manufacturing method for polypropylene resin extruded foam particles will be described in detail later.

[0066] (Melting point Tm1 of polypropylene resin extruded foam particles at the first heating stage) The melting point Tm1 of polypropylene resin extruded foam particles at the first heating stage is 130.0°C or higher and less than 155.0°C. From the viewpoint of lowering the minimum vapor pressure of the foamed molded article, it is preferable that the melting point Tm1 be 130.0°C or higher and less than 150.0°C, and more preferably 130.0°C or higher and less than 145.0°C. Furthermore, from the viewpoint of increasing the compressive strength of the foamed molded article, it is preferable that the melting point Tm1 be 142.0°C or higher and less than 155.0°C, and more preferably 150.0°C or higher and less than 155.0°C.

[0067] The melting point Tm1 of polypropylene resin extruded foam particles at the first heating stage is a value determined by differential scanning calorimetering (hereinafter referred to as the "DSC method"). As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0068] An example of a method for measuring the melting point Tm1 of polypropylene resin extruded foam particles during the first heating cycle using differential scanning calorimetering is as follows: The temperature of the polypropylene resin extruded foam particles is increased from 40°C to 220°C at a rate of 10°C / min. The temperature of the peak (melting peak) in the DSC curve of the extruded foam particles obtained in one heating cycle (first heating cycle) can be determined as the melting point Tm1 of the polypropylene resin extruded foam particles. If multiple peaks exist in the DSC curve obtained in one heating cycle (first heating cycle) using the above method, the temperature of the peak with the largest heat of fusion (melting peak) is taken as the melting point Tm1 of the polypropylene resin extruded foam particles.

[0069] (Bulk density) The extruded foam particles preferably have a bulk density of 30 g / L to 600 g / L, more preferably 45 g / L to 350 g / L, even more preferably 60 g / L to 200 g / L, and particularly preferably 60 g / L to 70 g / L. According to the above configuration, the polypropylene resin molded foam article obtained using the extruded foam particles has the advantage of exhibiting more characteristics such as arbitrary shape, cushioning properties, lightweight properties, and heat insulation properties. Furthermore, when the bulk density of the extruded foam particles is within the above range, the extruded foam particles have the advantage of providing a foamed article that is excellent in low-pressure moldability and compressive strength. If the foaming ratio of the extruded foam particles obtained by manufacturing the extruded foam particles does not reach the above range, a method of increasing the foaming ratio by pressurizing the inside of the extruded foam particles with an inert gas and then heating the extruded foam particles is also available (for example, the method described in Japanese Patent Publication No. 10-237212).

[0070] In this specification, the bulk density of polypropylene resin extruded foam particles is calculated by following (1) to (3) in order: (1) Fill a container with a known volume Vk (L), such as a graduated cylinder, beaker, or bucket, with the extruded foam particles until it overflows; (2) Level off the top surface of the container and measure the weight Wb (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 foamed particles Wb (g) / Volume of container Vk (L).

[0071] (Open cell ratio) The extruded foam particles are preferable as their open-cell ratio decreases. The extruded foam particles are preferably 10.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, more preferably 5.0% or less, more preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.4% or less, even more preferably 1.3% or less, and particularly preferably 1.2% or less. The lower limit of the open-cell ratio of the extruded foam particles is not particularly limited, and is, for example, 0.0% or more. According to the above configuration, (a) since cells hardly rupture and shrink during molding of the extruded foam particles, the extruded foam particles have the advantage of excellent moldability, and (b) the foamed molded article obtained using the extruded foam particles exhibits characteristics such as arbitrariness of shape, cushioning, lightness, compressive strength, and heat insulation. Furthermore, when the open-cell ratio of the extruded foam particles is within the above range, the extruded foam particles have the advantage of providing a foamed molded article that is excellent in low-pressure moldability and compressive strength.

[0072] In this specification, the open-cell ratio of polypropylene resin extruded foam particles is a value obtained by measuring using an air-comparison hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C (PROSEDURE C) of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles is calculated by performing the following (1) to (3) in order: (1) Using an air-comparison hydrometer, the volume Vc (cm³) of the extruded foam particles 3 (1) Measure the volume of the extruded foam particles after measuring Vc; (2) Submerge the entire volume of extruded foam particles in ethanol in a graduated cylinder; (3) Then, from the rise in the position of the ethanol in the graduated cylinder, determine the apparent volume of the extruded foam particles Va (cm³). 3 (4) Determine the open-cell ratio of the extruded foam particles using the following formula: Open-cell ratio (%) = ((Va-Vc)×100) / Va. Note that the method for measuring the volume Va is also called the immersion method.

[0073] Furthermore, these extruded foam particles exhibit excellent low-pressure moldability. In this specification, "excellent low-pressure moldability" means having a low minimum vapor pressure, as described later.

[0074] As described above, the extruded foam particles have the advantage of being able to provide a foamed molded article with excellent compressive strength (for example, the 50% compressive strength described later). In one embodiment of the present invention, for example, when a polypropylene resin foamed molded article with a density of 80 g / L to 90 g / L is produced using extruded foam particles, the 50% compressive strength of the foamed molded article is preferably 0.30 MPa or higher, more preferably 0.33 MPa or higher, more preferably 0.34 MPa or higher, more preferably 0.35 MPa or higher, and particularly preferably 0.36 MPa or higher. This configuration has the advantage that the resulting foamed molded article tends to exhibit good cushioning properties.

[0075] [3. Method for producing polypropylene resin extruded foam particles] A method for producing polypropylene resin extruded foam particles according to one embodiment of the present invention is a method for producing polypropylene resin extruded foam particles described in section [2. Polypropylene resin extruded foam particles], The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing a polypropylene resin (A) having a branched structure and a polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step comprises a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step, the polypropylene resin (A) and the polypropylene resin (B) are prepared separately. The extrusion foaming step includes a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin (A) and the polypropylene resin (B), and a foaming agent.

[0076] A method for producing polypropylene resin extruded foam particles according to one embodiment of the present invention is a method for producing polypropylene resin extruded foam particles described in section [2. Polypropylene resin extruded foam particles], The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing a polypropylene resin (A) having a branched structure and a polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step comprises a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step described above, (a) as a linear polypropylene resin, (a-1) melting point Tm 3A A linear polypropylene resin (A') having a melting point of 130.0℃ or higher and less than 150.0℃, and (a-2) melting point Tm 3B The polypropylene resin is prepared using a mixture with a linear polypropylene resin (B') whose temperature is 150.0°C or higher and less than 170.0°C. The extrusion foaming step includes a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin and a foaming agent.

[0077] In this specification, "a method for producing polypropylene resin extruded foam particles according to one embodiment of the present invention" may be referred to as "this manufacturing method." In this specification, "one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds" may be referred to as "conjugated dienes, etc."

[0078] Because this manufacturing method has the configuration described above, it has the advantage of being able to provide extruded foam particles that are excellent in low-pressure moldability and can provide foam molded articles with excellent compressive strength. Furthermore, because this manufacturing method has the configuration described above, it is possible to provide polypropylene resin extruded foam particles in which the melting point Tm1 at the first heating stage is 130°C or higher and less than 155°C.

[0079] (Linear polypropylene resin) As explained earlier, linear polypropylene resins are described in the section on (linear polypropylene resins) under [2. Extruded foamed polypropylene resins].

[0080] (Conjugated dienes, etc.) 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.

[0081] Examples of vinyl aromatic compounds include styrene; methylstyrene such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, and trimethylstyrene; chlorostyrene such as α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, and trichlorostyrene; bromostyrene such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene, and tribromostyrene; o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, and di Examples include fluorostyrenes such as fluorostyrene and trifluorostyrene; nitrostyrenes such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene, and trinitrostyrene; vinylphenols such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene, and trihydroxystyrene; divinylbenzenes such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene; and isopropenylstyrenes such as o-diisopropenylbenzene, m-diisopropenylbenzene, and p-diisopropenylbenzene. Among the vinyl aromatic compounds mentioned above, styrene and / or methylstyrene are preferred due to (a) their low cost and ease of handling, and (b) the fact that the reaction proceeds uniformly.

[0082] The amount of conjugated dienes, etc. used in the first melt-kneading step is preferably 0.01 to 5.00 parts by weight, more preferably 0.10 to 3.00 parts by weight, more preferably 0.10 to 2.00 parts by weight, more preferably 0.20 to 1.50 parts by weight, even more preferably 0.30 to 1.00 parts by weight, and particularly preferably 0.40 to 0.80 parts by weight, per 100 parts by weight of linear polypropylene resin. The more conjugated dienes, etc. used, the smaller the MFR of the resulting branched polypropylene resin tends to be, and the lower the melt elongation tends to be; that is, the MFR of the base resin also tends to be, and the lower the melt elongation tends to be. On the other hand, the less conjugated dienes, etc. used, the larger the MFR of the resulting branched polypropylene resin tends to be, and the higher the melt elongation tends to be; that is, the larger the MFR of the base resin also tends to be, and the higher the melt elongation tends to be.

[0083] In the first melt-kneading step, in addition to the random polypropylene resin, conjugated diene, etc., and radical polymerization initiator, monomers copolymerizable with the conjugated diene, etc. may be used in combination, to the extent that the effects according to one embodiment of the present invention are not impaired. In other words, the first mixture in this manufacturing method may further contain monomers copolymerizable with the conjugated diene, etc. Examples of monomers copolymerizable with the conjugated diene, etc. 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.

[0084] (Radical polymerization initiator) The radical polymerization initiator is an organic peroxide that has the ability to abstract hydrogen from 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.

[0085] 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.

[0086] The amount of radical polymerization initiator used in the first melt-kneading step is not particularly limited, but is preferably 0.01 to 5.00 parts by weight, more preferably 0.10 to 3.00 parts by weight, more preferably 0.10 to 2.50 parts by weight, more preferably 0.10 to 2.00 parts by weight, more preferably 0.30 to 2.00 parts by weight, more preferably 0.50 to 1.90 parts by weight, even more preferably 0.80 to 1.90 parts by weight, and particularly preferably 1.0 to 1.70 parts by weight per 100 parts by weight of linear polypropylene resin.

[0087] The following describes, with some speculation, the effects of conjugated dienes and radical polymerization initiators on the melt elongation and MFR of the base resin of the resulting branched polypropylene resin and extruded foamed particles in this manufacturing method. However, the embodiment of this invention is not limited in any way to the following description.

[0088] In this manufacturing method, the radical polymerization initiator is a component that initiates the reaction by abstracting hydrogen from the main chain of (a) linear polypropylene resin. Generally, when (a) linear polypropylene resin and (c) radical polymerization initiator are melt-kneaded, a chain reaction of molecular chain severance occurs in (a) linear polypropylene resin following the hydrogen abstraction reaction, so the MFR of the base resin increases significantly.

[0089] In this manufacturing method, (a) a linear polypropylene resin is used in combination with (c) a radical polymerization initiator and (b) a conjugated diene, etc. As a result, in this manufacturing method, the molecular chain severance reaction of the linear polypropylene resin described above can be suppressed by the addition of (b) a conjugated diene, etc. to the linear polypropylene resin molecules that have undergone a hydrogen abstraction reaction. Furthermore, in this manufacturing method, the addition reaction of (b) a conjugated diene, etc. to the linear polypropylene resin molecules that have undergone a hydrogen abstraction reaction proceeds, forming a branched structure in the linear polypropylene resin due to the conjugated diene, etc. Furthermore, in this manufacturing method, a dimerization reaction proceeds between multiple linear polypropylene resin molecules in which a branched structure due to the conjugated diene, etc. has been formed, and a crosslinked structure is generated as this proceeds. It is believed that a branched polypropylene resin can be obtained by this manufacturing method through the progress of this series of reactions. In addition, the molecular chain severance reaction of the linear polypropylene resin described above may also proceed in parallel with the series of reactions described above. Therefore, in this manufacturing method, by appropriately adjusting (a) the amount of (b) conjugated diene and (c) radical polymerization initiator added to the linear polypropylene resin, it is possible to adjust the melt elongation and MFR of the base resin of the resulting branched polypropylene resin and extruded foam particles.

[0090] Radical polymerization initiators can be said to be components that determine the degree of progress of the molecular chain severance reaction of the linear polypropylene resin described above, as well as the reaction of branching and / or crosslinking of the linear polypropylene resin by conjugated dienes, etc. Here, the balance between the degree of progress of the molecular chain severance reaction and the reaction of branching and / or crosslinking can be adjusted by changing the ratio of the amount of conjugated dienes, etc. used (parts by weight) to the amount of radical polymerization initiator used (parts by weight) (amount of conjugated dienes, etc. used / amount of radical polymerization initiator used).

[0091] The higher the ratio (amount of conjugated diene, etc. used / amount of radical polymerization initiator used), the more the reaction for forming the branched structure and / or crosslinked structure becomes more favorable than the molecular chain severance reaction. As a result, the higher the ratio, the lower the melt elongation of the base resin of the resulting branched polypropylene resin and extruded foam particles tends to be, and the MFR tends to be smaller. The lower the ratio (amount of conjugated diene, etc. used / amount of radical polymerization initiator used), the more the molecular chain severance reaction becomes more favorable than the reaction for forming the branched structure and / or crosslinked structure. As a result, the lower the ratio, the higher the melt elongation of the base resin of the resulting branched polypropylene resin and extruded foam particles tends to be, and the MFR tends to be larger.

[0092] The ratio (amount of conjugated diene, etc. used / amount of radical polymerization initiator used) is not particularly limited, but is preferably 0.05 to 5.00, more preferably 0.10 to 3.00, even more preferably 0.20 to 2.00, even more preferably 0.25 to 1.00, and particularly preferably 0.30 to 0.70. With this configuration, extruded foamed particles containing a base resin having melt elongation and MFR within the above range can be obtained. As a result, the obtained extruded foamed particles have the advantage of providing a foamed molded article with excellent low-pressure moldability and excellent compressive strength.

[0093] As described above, by appropriately adjusting the amounts of (a) linear polypropylene resin, (b) conjugated diene, etc., and (c) radical polymerization initiator used, the melt elongation and MFR of the base resin of the resulting branched polypropylene resin and extruded foam particles can be adjusted to within the range described above. Furthermore, by adjusting the melt elongation and MFR of the base resin of the extruded foam particles to within the range described above, extruded foam particles with a low open-cell ratio can be obtained. As a result, the resulting extruded foam particles have the advantage of providing a foamed molded article with excellent low-pressure moldability and excellent compressive strength.

[0094] (Other ingredients) The first mixture may further contain, as optional, other components, (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, ultraviolet absorbers, ultraviolet stabilizers, fluorescent whitening agents, metal soaps, and antacid adsorbents, and / or (b) additives such as foam regulators, colorants, crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, flame retardants, and antistatic agents. These other components may be used individually or in combination of two or more.

[0095] (2-1. Preparation process) The preparation step can also be described as a step of preparing a branched polypropylene resin using one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds. In the preparation step, (i) polypropylene resin (A) and polypropylene resin (B) may be prepared as separate molecules, or (ii) a branched polypropylene resin may be prepared in which polypropylene resin (A) and polypropylene resin (B) are crosslinked within a single molecule (single polymer).

[0096] (First melting and mixing process) The first melt-kneading step can also be described as a step of preparing a melt-kneaded product of a first mixture containing a linear polypropylene resin, a conjugated diene, and a radical polymerization initiator. Alternatively, the first melt-kneading step can also be described as a step of reacting a linear polypropylene resin with a conjugated diene compound and a radical polymerization initiator to either (i) separately prepare (obtain) (i-1) a branched polypropylene resin (A) and (i-2) a branched polypropylene resin (B), or (ii) prepare (obtain) a branched polypropylene resin containing polypropylene resin (A) and polypropylene resin (B) in a crosslinked state within a single molecule (single polymer).

[0097] Apparatus that can be used in the first melt-mixing process includes a melt-mixing apparatus for melt-mixing the first mixture. Such melt-mixing apparatuses include (a) kneaders such as rolls, cone kneaders, Banbury mixers, brabenders, single-screw extruders, and multi-screw extruders (e.g., twin-screw extruders), (b) horizontal agitators such as multi-screw surface resurfacing machines and multi-screw multi-disc devices, and (c) vertical agitators such as double helical ribbon agitators. Of these, kneaders are preferred as melt-mixing apparatuses because they allow for continuous mixing of the first mixture and are easy to scale up. Among kneaders, extruders are more preferred in terms of productivity, multi-screw extruders are even more preferred, and twin-screw extruders are particularly preferred.

[0098] The apparatus that may be used in the first melt-kneading step (e.g., a melt-kneading apparatus) is preferably equipped with a die at the end of the apparatus in the extrusion direction. The die is equipped with at least one hole (sometimes referred to as an extrusion hole) for discharging the melt-kneaded first mixture. The number and diameter of the holes in the die, as well as the thickness of the die (length of the holes in the extrusion direction), are not particularly limited.

[0099] The molten compound of the first mixture obtained in the first molten compounding step is a branched polypropylene resin.

[0100] The following describes the case in which polypropylene resin (A) and polypropylene resin (B) are prepared separately in the first melt-mixing step. In this case, (i) a melt-mixed product of branched polypropylene resin (A) is prepared using linear polypropylene resin (A') having a melting point Tm2 of 130.0°C or higher and less than 150.0°C, and separately, (ii) a melt-mixed product of branched polypropylene resin (B) is prepared using linear polypropylene resin (B') having a melting point Tm2 of 150.0°C or higher and less than 170.0°C. In this case, more specifically, (i) a first mixture containing (a) a linear polypropylene resin (A') having a melting point Tm2 of 130.0°C or higher and less than 150.0°C, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator is melt-kneaded, and separately, (ii) a first mixture containing (a) a linear polypropylene resin (B') having a melting point Tm2 of 150°C or higher and less than 170.0°C, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator is melt-kneaded. Then, the separately obtained melt-kneaded product of branched polypropylene resin (A) and the melt-kneaded product of branched polypropylene resin (B) are separately subjected to a discharge process to produce separate resin particles, and the obtained resin particles of branched polypropylene resin (A) and resin particles of branched polypropylene resin (B) are mixed to be used as a second mixture.

[0101] The following describes the preparation of a branched polypropylene resin containing a crosslinked polypropylene resin (A) and a polypropylene resin (B) within a single molecule (single polymer) during the first melt-kneading step. In this case, the linear polypropylene resin can be a mixture of (i) a linear polypropylene resin (A') having a melting point Tm2 of 130.0°C or higher and less than 150.0°C, and (ii) a linear polypropylene resin (B') having a melting point Tm2 of 150.0°C or higher and less than 170.0°C. In this case, more specifically, a first mixture comprising (a) a linear polypropylene resin (A') having a melting point Tm2 of 130.0°C or higher and less than 150.0°C, (a-2) a linear polypropylene resin (B') having a melting point Tm2 of 150.0°C or higher and less than 170.0°C, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator may be melt-kneaded. In this case, the mixture containing linear polypropylene resin (A') and linear polypropylene resin (B') preferably contains, when the total of linear polypropylene resin (A') and linear polypropylene resin (B') is 100% by weight, (i) more than 70% by weight and 98% by weight or less of linear polypropylene resin (A') and 2% by weight or more and less than 30% by weight of linear polypropylene resin (B'), and (ii) more than 75% by weight and 98% by weight or less of linear polypropylene resin (A') and linear It is more preferable to contain (iii) a polypropylene resin (B') in an amount of 2% or more and less than 25% by weight, (iii) a linear polypropylene resin (A') in an amount of more than 80% or less and 98% by weight or less, and a linear polypropylene resin (B') in an amount of 2% or more and less than 20% by weight, and (iv) a linear polypropylene resin (A') in an amount of 85% or more and 95% by weight or less, and a linear polypropylene resin (B') in an amount of 5% or more and 15% by weight or less. With this configuration, the low-pressure moldability of the extruded foam particles can be improved. After melt-kneading the first mixture, the resulting melt-kneaded branched polypropylene resin can be subjected to a discharge process to produce resin particles.The resin particles of the branched polypropylene resin obtained in this way contain polypropylene resin (A) and polypropylene resin (B) in a crosslinked state within a single molecule (single polymer).

[0102] (First mixture preparation step) The preparation step may include a first mixture preparation step to obtain a first mixture before the melt-kneading step. In the first mixture preparation step, the order and method of mixing linear polypropylene resin, conjugated diene, etc., and radical polymerization initiator to obtain the first mixture are not particularly limited, and examples include the following methods (a) to (d): (a) A method for preparing a first mixture by simultaneously or in any order mixing an unmelted linear polypropylene resin, a conjugated diene, and a radical polymerization initiator; (b) A method of preparing a first mixture by introducing unmelted linear polypropylene resin into an apparatus and melting and kneading the linear polypropylene resin, and then simultaneously or separately adding a conjugated diene and a radical polymerization initiator to the partially or completely melted and kneaded linear polypropylene resin; (c) A method of preparing a first mixture by simultaneously or separately introducing unmelted linear polypropylene resin and radical polymerization initiator into an apparatus and melt-kneading the linear polypropylene resin and radical polymerization initiator. Then, adding a conjugated diene or the like to the partially or completely melt-kneaded linear polypropylene resin and radical polymerization initiator; and (d) A method of preparing a first mixture by simultaneously or separately introducing unmelted linear polypropylene resin and conjugated diene into an apparatus and melt-kneading the linear polypropylene resin and conjugated diene. Subsequently, a radical polymerization initiator is added to the partially or completely melt-kneaded polypropylene resin and conjugated diene to prepare a first mixture.

[0103] Methods (b) to (d) are preferred because, at the start of the melt-kneading process, the polypropylene resin in the first mixture is partially or completely melted. The apparatus used in methods (b) to (d) may be the same as the apparatus used in the subsequent first melt-kneading process. Performing the first mixture preparation process and the melt-kneading process consecutively in the same apparatus offers advantages in terms of efficiency and environmental impact. Generally, conjugated dienes and the like are highly volatile, so it is desirable to add them in a state where they do not evaporate. For this reason, the melt-kneading process is more preferably (c) because the reaction proceeds more uniformly, and the following method is even more preferable: Unmelted linear polypropylene resin is introduced into the apparatus and the linear polypropylene resin is melt-kneaded. Then, a radical polymerization initiator is introduced into the partially or completely melt-kneaded linear polypropylene resin and the linear polypropylene resin and radical polymerization initiator are melt-kneaded. A method for preparing a first mixture by adding a conjugated diene or the like to a linear polypropylene resin and a radical polymerization initiator that have been partially or completely melt-kneaded.

[0104] (Discharge process) The preparation step may further include a discharge step in which the molten mixture of the first mixture obtained in the first melt-kneading step, i.e., the branched polypropylene resin, is discharged through a die provided in the apparatus. In the discharge step, the branched polypropylene resin is discharged from the die in strand form at a temperature at which it can be discharged from the holes of the die. By cooling and shredding the discharged strand-shaped branched polypropylene resin (also simply referred to as "strands"), branched polypropylene resin of a desired shape and size can be obtained. The method of cooling the strands is not particularly limited, and examples include water cooling using water. The strands may be shredded after cooling, or cooling and shredding may be performed simultaneously.

[0105] (2-2. Extrusion and Foaming Process) The extrusion foaming process can also be described as a process of foaming a second mixture containing a branched polypropylene resin.

[0106] (Second melting and mixing process) The second melt-mixing step can also be described as the step of preparing a melt-mixed product (hereinafter sometimes referred to as the melt-mixed composition) of a composition containing a second mixture containing a branched polypropylene resin and a blowing agent. In other words, the second melt-mixing step can also be described as (i) the step of preparing a melt-mixed product of a composition containing a second mixture containing a branched polypropylene resin (A) and a branched polypropylene resin (B), and a blowing agent, or (ii) the step of preparing a melt-mixed product of a composition containing a second mixture containing a branched polypropylene resin, in which polypropylene resin (A) and polypropylene resin (B) are crosslinked within a single molecule (single polymer), and a blowing agent. That is, in the second melt-mixing step, it is sufficient that the composition containing the second mixture containing the branched polypropylene resin and the blowing agent is ultimately melt-mixed.

[0107] The following describes the process of preparing a molten mixture of a composition containing a branched polypropylene resin (A) and a second mixture containing a branched polypropylene resin (B), and a blowing agent, in the second molten mixture step. In this case, when the total of branched polypropylene resin (A) and branched polypropylene resin (B) is 100% by weight, it is preferable that (i) the branched polypropylene resin (A) is greater than 70% by weight and 98% by weight or less, and branched polypropylene resin (B) is greater than 2% by weight and less than 30% by weight; (ii) the branched polypropylene resin (A) is greater than 75% by weight and 98% by weight or less, and branched polypropylene resin (B) is greater than 2% by weight and less than 25% by weight; (iii) the branched polypropylene resin (A) is greater than 80% by weight and 98% by weight or less, and branched polypropylene resin (B) is greater than 2% by weight and less than 20% by weight; and (iv) the branched polypropylene resin (A) is greater than 85% by weight and 95% by weight or less, and branched polypropylene resin (B) is greater than 5% by weight and less than 15% by weight. This configuration makes it possible to improve the low-pressure moldability of extruded foam particles.

[0108] Specific examples of the second melt-mixing process include, for example, the following methods (a) to (c): (a) A method of preparing a composition by mixing or blending a branched polypropylene resin, a foaming agent, and, if necessary, other resins, bubble nucleating agents, and other components, and then melt-kneading the composition; (b) A method of mixing or blending a branched polypropylene resin with a foaming agent, melt-kneading the resulting composition, and then adding other resins, bubble nucleating agents and other components as needed to the composition, and further melt-kneading the resulting composition; (c)(c-1) A method of preparing a second mixture by mixing or blending a branched polypropylene resin with other resins, bubble nucleating agents and other components as needed, and melt-kneading the second mixture; (c-2) A method of preparing a composition by adding a blowing agent to the obtained second mixture and further melt-kneading the composition.

[0109] In any of the methods (a) to (c) described above, the method and order of adding other resins, bubble nucleating agents, and other components used as needed are not particularly limited. Other resins, bubble nucleating agents, and other components used as needed may be added simultaneously, separately, and in any order.

[0110] The second melt-kneading step may further include, for example, a step of melt-kneading the composition using the methods described in (a) to (c) above, and then lowering the temperature of the melt-kneaded composition within a temperature range in which the melt-kneaded composition does not solidify.

[0111] An example of equipment used in the second melt-mixing process is a melt-mixing apparatus for melt-mixing the second mixture. An example of a melt-mixing apparatus used in the second melt-mixing process is the melt-mixing apparatus exemplified in the first melt-mixing process. Similar to the first melt-mixing process, it is preferable to use a kneader as the melt-mixing apparatus for the second melt-mixing process, and among kneaders, it is more preferable to use an extruder from the viewpoint of productivity, even more preferable to use a multi-screw extruder, and particularly preferable to use a twin-screw extruder. When an extruder is used as the melt-mixing apparatus in the second melt-mixing process, the extruder has a screw configuration, which has the advantage that the injected foaming agent does not flow back upstream of the apparatus.

[0112] The apparatus that may be used in the second melt-mixing step (e.g., a melt-mixing apparatus) is preferably equipped with a die at the end of the apparatus in the extrusion direction. The die has already been described in the section on the first melt-mixing step.

[0113] The apparatus that may be used in the second melt-mixing step may further include a cooling device between the melt-mixing device and the die to lower the temperature of the melt-mixed composition. Examples of such cooling devices include a single-screw extruder, a static mixer, and a melt cooler, which are installed after the mixer. One type of cooling device may be used alone, or two or more types may be used in combination. The apparatus that may be used in the second melt-mixing step may further include a gear pump between the melt-mixing device and the die (for example, between the melt-mixing device and the cooling device and / or between the cooling device and the die) to improve the discharge stability of the composition. The apparatus that may be used in the second melt-mixing step may further include a diverter valve between the melt-mixing device and the die.

[0114] (Foaming agent) The blowing agents that can be used in this manufacturing method are not particularly limited as long as they are blowing agents that are commonly used in extrusion foaming. Examples of such blowing agents include (a) (a-1) aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane; (a-2) alicyclic hydrocarbons such as cyclopentane and cyclobutane; (a-3) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; (a-4) alcohols such as methanol and ethanol; (a-5) inorganic gases such as air, nitrogen, and carbon dioxide; and (a-6) physical blowing agents such as water; and (b) chemical blowing agents including thermal decomposition type blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine.

[0115] In this manufacturing method, inorganic gases are preferred as blowing agents, and carbon dioxide is more preferred, due to the low production costs and environmental impact. Furthermore, due to the even lower production costs and environmental impact, it is preferable to use only carbon dioxide as the blowing agent, and to substantially not contain any blowing agents other than carbon dioxide, as mentioned above. Specifically, the content of substances other than carbon dioxide that can function as blowing agents in the composition is preferably 0.01 parts by weight or less, more preferably 0.001 parts by weight or less, even more preferably 0.0001 parts by weight or less, and particularly preferably 0 parts by weight, per 100 parts by weight of the composition.

[0116] The amount of blowing agent used is 0.5 to 7.0 parts by weight, preferably 0.5 to 6.0 parts by weight, more preferably 0.5 to 5.0 parts by weight, even more preferably 0.5 to 4.0 parts by weight, and particularly preferably 0.5 to 3.0 parts by weight, per 100.0 parts by weight of the second mixture. When the blowing agent consists only of carbon dioxide, the "amount of blowing agent used" can also be said to be the "amount of carbon dioxide used" or the "content of the blowing agent (carbon dioxide) in the second mixture."

[0117] (Extrusion process) The extrusion foaming process may further include an extrusion step in which the molten and kneaded composition is extruded, for example, through a die provided in the apparatus, into a region where the pressure is lower than the pressure inside the apparatus. In the extrusion step, the molten and kneaded composition may be extruded into the gas phase or into the liquid phase.

[0118] (Shredding process) The extrusion foaming process may further include a shredding process for shredding the composition extruded in the extrusion process. In the extrusion process, the extruded composition immediately begins to foam, for example, by passing through a die provided in the apparatus, into a region where the pressure is lower than the pressure inside the apparatus. In the shredding process, the composition may be shredded while it is foaming, or the composition may have finished foaming. When the composition is shredded while it is foaming, the shredded composition may complete foaming in the region to which it was extruded. The shredding process can also be described as a process for shredding the composition into parts to prepare polypropylene resin extruded foam particles.

[0119] The method for shredding the extruded composition is not particularly limited. For example, the composition may be shredded by a cutter placed after the die along the extrusion direction. The number of blades of the cutter is also not particularly limited.

[0120] Here, the extrusion and shredding steps can also be described as a series of steps for granulating polypropylene resin extruded foam particles from the composition obtained in the second melt-kneading step. Therefore, the extrusion and shredding steps (the series of steps from the extrusion to the shredding step) can also be described as a "granulation step." In other words, the extrusion foaming step of the method for producing polypropylene resin extruded foam particles according to one embodiment of the present invention may further include a granulation step in addition to the second melt-kneading step.

[0121] Depending on the region in which the composition obtained in the second melt-kneading step is extruded and the method of shredding the composition, the granulation step can be broadly classified into two types: the cold-cut method and the die-face-cut method. In other words, the granulation step can be one selected from the group consisting of the hot-cut method, the water-ring-cut method, and the underwater-cut method. An example of the cold-cut method is a method (strand-cut method) in which the composition 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. The die-face-cut method is a method in which the composition extruded from the hole 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.

[0122] The die face cutting method can be further divided into the following three types based on differences in cooling methods: the underwater cut (UWC) method, the water ring cut (WRC) method, and the hot cut (HC) method. 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 composition extruded from the hole in the die 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 composition cut by the cutter in the air while foaming or after foaming in the cooling water. The HC method involves cutting the composition in the air with a cutter, and cooling the cut composition 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.

[0123] [4. Polypropylene-based foamed molded articles] A polypropylene resin foam molded article according to one embodiment of the present invention is made by molding polypropylene resin extruded foam particles described in section [2. Polypropylene resin extruded foam particles] or polypropylene resin extruded foam particles obtained by the manufacturing method described in section [3. Method for manufacturing polypropylene resin extruded foam particles].

[0124] The method for producing a polypropylene-based resin foam molded article according to one embodiment of the present invention, that is, the method for molding the extruded foam particles, is not particularly limited, and for example, a known in-mold foam molding method can be employed.

[0125] As a method for molding a polypropylene resin foamed molded article from polypropylene resin extruded foamed particles of the present invention, for example, (A) a method in which foamed particles are pressurized with an inorganic gas to impregnate them with the inorganic gas and apply a predetermined internal pressure to the foamed particles, and then the foamed particles are filled into a mold and heated and fused together with steam or the like (for example, Japanese Patent Publication No. 51-22951), (B) a method in which foamed particles are compressed with gas pressure and filled into a mold, and the foamed particles are heated and fused together with steam or the like by utilizing the recovery force of the particles (for example, Japanese Patent Publication No. 53-33996), (C) a method in which foamed particles are filled into a mold with a widened gap, the mold is closed to a predetermined gap to compress the filled foamed particles, and the foamed particles are heated and fused together with steam or the like. By using the above methods, a foamed molded article with high compressive strength can be obtained at a low molding pressure. Of course, the present invention is not limited to these methods.

[0126] (Physical properties of polypropylene-based foamed molded products) The following describes the physical properties of the foamed molded product.

[0127] (minimum vapor pressure) The minimum vapor pressure of the foamed molded article is not limited, but a lower value is preferable. The minimum vapor pressure of the foamed molded article is preferably 0.30 MPa or less, more preferably less than 0.30 MPa, more preferably less than 0.30 MPa, more preferably 0.28 MPa or less, more preferably 0.25 MPa or less, even more preferably 0.23 MPa or less, and particularly preferably 0.20 MPa or less. The lower limit of the minimum vapor pressure of the foamed molded article is not limited and may be, for example, 0.01 MPa, 0.05 MPa, or 0.10 MPa.

[0128] In this specification, the minimum vapor pressure of a polypropylene resin foam molded article is measured as follows (1) to (3): (1) The water vapor pressure is changed in increments of 0.01 MPa between 0.14 MPa (gauge pressure) and 0.42 MPa (gauge pressure), and foam particles are foamed in a mold at each water vapor pressure to obtain a foam molded article; (2) The internal bonding rate is measured for each foam molded article; (3) The lowest water vapor pressure at which a foam molded article with an internal bonding rate of 60% or more is obtained is defined as the minimum vapor pressure.

[0129] However, in this specification, the internal bonding rate is a value measured by the following methods (1) to (4): (1) Make a 5 mm cut perpendicular to any one surface of the foamed molded body with a cutter, perpendicular to the portion having that surface; (2) Then, break the foamed molded body by hand along the cut; (3) Visually observe the area of ​​the resulting fracture surface excluding the cut portion, and measure the number of foamed particles present in that area, and the number of foamed particles that have broken outside the particle interface in that area (i.e., foamed particles that have broken themselves); (4) Calculate the internal bonding rate based on the following formula; Internal bonding rate (%) = (Number of foamed particles fractured outside the particle interface in the region / Total number of foamed particles present in the region) × 100.

[0130] (Maximum vapor pressure) The maximum vapor pressure of this foamed molded product is not particularly limited. It may be 0.35 MPa or less, 0.30 MPa or less, or 0.25 MPa or less. The lower limit of the maximum vapor pressure of this foamed molded product is not limited and may be, for example, 0.01 MPa, 0.05 MPa, or 0.10 MPa.

[0131] In this specification, the measurement of the maximum vapor pressure of a polypropylene resin foam molded article is as follows (1) to (3): (1) The water vapor pressure is changed in increments of 0.01 MPa between 0.14 MPa (gauge pressure) and 0.42 MPa (gauge pressure), and foam particles are foamed in a mold at each water vapor pressure to obtain a foam molded article; (2) The surface of each foam molded article is visually inspected for the presence or absence of "melt," "shrinkage (wrinkling)," and "sink marks" caused by the melting of the base resin, and the surface properties of the foam molded article are evaluated according to the following criteria. ○ (Pass): No melting, shrinkage (wrinkling), or sink marks are observed on any surface of the foamed molded product. × (Failure): At least one of the following is observed on any surface of the foamed molded product: melting, shrinkage (wrinkling), or sink marks. (3) The highest water vapor pressure among those obtained when a foamed molded article with a surface quality evaluation of "○ (passing)" is obtained shall be defined as the maximum vapor pressure.

[0132] (Molded object density) The density of the foamed molded article is not limited, but is preferably 30 g / L to 600 g / L, more preferably 45 g / L to 200 g / L, even more preferably 60 g / L to 200 g / L, and particularly preferably 80 g / L to 90 g / L. When the density of the molded article is within the above range, it has the advantage of easily exhibiting good buffering properties.

[0133] In this specification, the density of a polypropylene resin foam molded article is measured according to the following method. The weight Ws (g) of the obtained foam molded article was measured. The length, width, and thickness of the foam molded article were measured using calipers, and the volume Vs (cm³) of the foam molded article was measured. 3 The density (g / L) of the foamed molded product was calculated according to the following formula: The density of a foamed molded product (g / L) = Ws / Vs × 1000.

[0134] (Compressive strength) The compressive strength of this foamed molded article is not limited, but a higher value is preferable. The compressive strength of this foamed molded article also varies depending on the density of the foamed molded article, but for example, in a foamed molded article with a density in the range of 80 g / L to 90 g / L, it is preferably 0.30 MPa or higher, more preferably 0.33 MPa or higher, more preferably 0.34 MPa or higher, more preferably 0.35 MPa or higher, and particularly preferably 0.36 MPa or higher. When the compressive strength is within the above range, it has the advantage of easily exhibiting good cushioning properties.

[0135] In this specification, the compressive strength of a polypropylene foam molded article is measured by taking a test piece measuring 50 mm (length) x 50 mm (width) x 25 mm (thickness) cut from the polypropylene foam molded article as a sample, and compressing it at a speed of 10 mm / min in accordance with NDZ-Z0504, and measuring the compressive stress (MPa) at 50% compression. As described above, the compressive strength of the foam molded article is measured as the compressive stress (MPa) at 50% compression. Therefore, in this specification, the compressive strength of the foam molded article may be referred to as the "50% compressive strength".

[0136] [5. Method for manufacturing polypropylene resin foam molded articles] A method for producing a polypropylene resin foam molded article according to one embodiment of the present invention includes a step of molding polypropylene resin extruded foam particles obtained by the manufacturing method described in section 3. Method for producing polypropylene resin extruded foam particles.

[0137] The method for manufacturing the foamed molded article, that is, the method for molding the extruded foamed particles, is not particularly limited, and for example, a known in-mold foaming method using a mold can be employed.

[0138] Methods for molding polypropylene resin foam molded articles from these extruded foam particles include, for example, (A) pressurizing the extruded foam particles with an inorganic gas to impregnate them with the inorganic gas and apply a predetermined internal pressure, then filling the extruded foam particles into a mold and heating and fusing the extruded foam particles together with steam or the like (for example, Japanese Patent Publication No. 51-22951), (B) compressing the extruded foam particles with gas pressure and filling them into a mold, then using the recovery force of the extruded foam particles to heat and fusing the extruded foam particles together with steam or the like (for example, Japanese Patent Publication No. 53-33996), and (C) filling a mold with widened gaps (cracking), then closing the mold to a predetermined gap (cracking) to compress the filled extruded foam particles, and heating and fusing the extruded foam particles together with steam or the like. By using such methods, foam molded articles with high compressive strength can be obtained at low molding pressure. Of course, the present invention is not limited to these methods.

[0139] One embodiment of the present invention may have the following configuration: [1] Polypropylene resin extruded foam particles, The aforementioned polypropylene resin extruded foam particles have a melting point Tm 2A A polypropylene resin (A) having a branched structure with a melting point Tm is present in an amount of more than 70% by weight and 98% by weight or less, and the melting point Tm is 130.0°C or higher and less than 143.0°C. 2B The material contains a base resin containing a branched polypropylene resin (B) having a temperature of 150.0°C or higher and less than 170.0°C, in an amount of 2% by weight or more and less than 30% by weight (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight), Polypropylene resin extruded foam particles having a melting point Tm1 of 130.0°C or higher and less than 155.0°C at the first heating stage. [2] The polypropylene resin extruded foam particles according to [1], wherein the base resin comprises more than 80% by weight and 98% by weight or less of the polypropylene resin (A), and 2% by weight or more and less than 20% by weight of the polypropylene resin (B) (the sum of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight). [3] The polypropylene resin extruded foam particles according to [1] or [2], wherein the melt elongation of the base resin is 3.0 m / min to 30.0 m / min. [4] The polypropylene resin extruded foam particles according to any one of [1] to [3], wherein the melt flow rate of the base resin is 1.0 g / 10 min to 20.0 g / 10 min. [5] The polypropylene resin extruded foam particles according to any one of [1] to [4], wherein the bulk density of the polypropylene resin extruded foam particles is 30 g / L to 600 g / L. [6] The polypropylene resin extruded foam particles according to any one of [1] to [5], wherein the open-cell ratio of the polypropylene resin extruded foam particles is 10.0% or less. [7] The polypropylene resin extruded foam particle according to any one of [1] to [6], wherein the main chain of the polypropylene resin (A), the main chain of the polypropylene resin (B), and / or the main chains of the polypropylene resins (A) and (B) are a propylene homopolymer, a polypropylene block copolymer, and / or a polypropylene random copolymer. [8] Polypropylene resin extruded foam particles according to any one of [1] to [7], wherein when a polypropylene resin foam molded article with a density of 80 g / L to 90 g / L is produced, the 50% compressive strength of the polypropylene resin foam molded article is 0.30 MPa or more. A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles described in any one of [9], [1], to [8].

[10] The polypropylene-based resin foam molded article according to [9], wherein the density of the polypropylene-based resin foam molded article is 80 g / L to 90 g / L and the 50% compressive strength is 0.30 MPa or more. A method for producing polypropylene resin extruded foam particles according to any one of

[11] , [1] to [8], The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step comprises a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step, the polypropylene resin (A) and the polypropylene resin (B) are prepared separately. A method for producing polypropylene resin extruded foam particles, wherein the extrusion foaming step comprises a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin (A) and the polypropylene resin (B), and a foaming agent. A method for producing polypropylene resin extruded foam particles according to any one of

[12] [1] to [8], The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step comprises a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step described above, (a) as a linear polypropylene resin, (a-1) melting point Tm 3A A linear polypropylene resin (A') having a melting point of 130.0℃ or higher and less than 150.0℃, and (a-2) melting point Tm 3BUsing a mixture with a linear polypropylene resin (B') having a temperature of 150.0°C or higher and less than 170.0°C, a polypropylene resin having a branched structure is prepared, containing the polypropylene resin (A) and the polypropylene resin (B) in a crosslinked state within a single molecule. A method for producing polypropylene resin extruded foam particles, comprising a second melt-kneading step of melt-kneading a composition comprising a second mixture containing a polypropylene resin having the branched structure and a foaming agent, wherein the extrusion foaming step is a second melt-kneading step.

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

[11] or

[12] , wherein one or more monomers selected from the group consisting of the conjugated diene and vinyl aromatic compound in the first melt-kneading step are one or more selected from the group consisting of isoprene, butadiene, 1,3-heptadiene, 2,3-dimethylbutadiene, and 2,5-dimethyl-2,4-hexadiene.

[14] The method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[13] , wherein the amount of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds used in the first melt-kneading step is 0.01 parts by weight to 5.00 parts by weight per 100 parts by weight of the linear polypropylene resin.

[15] A method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[14] , wherein the radical polymerization initiator in the first melt-kneading step is one or more selected from the group consisting of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate.

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

[11] to

[15] , wherein the amount of radical polymerization initiator used in the first melt-kneading step is 0.01 parts by weight to 5.00 parts by weight per 100 parts by weight of the linear polypropylene resin.

[17] A method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[16] , wherein the ratio of the amount (parts by weight) of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds to the amount (parts by weight) of the radical polymerization initiator used is 0.05 to 5.00.

[18] The method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[17] , wherein the foaming agent is carbon dioxide.

[19] A method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[18] , wherein the amount of the foaming agent used is 0.5 to 7.0 parts by weight per 100.0 parts by weight of the second mixture.

[20] The extrusion foaming process further comprises a granulation process, The granulation process includes an extrusion process in which the molten and kneaded composition is extruded into a region where the pressure is lower than the internal pressure of the apparatus, and a shredding process in which the composition extruded in the extrusion process is shredded. The method for producing polypropylene resin extruded foam particles according to any one of

[11] to

[19] , wherein the granulation step is one selected from the group consisting of the hot cut method, the water ring cut method, and the underwater cut method. A method for producing a polypropylene resin foamed molded article, comprising a molding step of molding polypropylene resin extruded foam particles produced by the method for producing polypropylene resin extruded foam particles described in any one of

[21] ,

[11] , to

[20] .

[22] The method for producing a polypropylene resin foamed molded article according to

[21] , wherein in the molding step, the polypropylene resin extruded foam particles are heated at a vapor pressure of 0.30 MPa or less. [Examples]

[0140] 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.

[0141] (Test method) The test methods used to measure and evaluate various physical properties in the examples and comparative examples are as follows:

[0142] The extruded foam particles obtained in each example and comparative example were returned to the resin using the following method, and the returned resin was used as a sample to measure the melt elongation and MFR using the following method. The resulting values ​​were defined as the melt elongation and MFR of the base resin, respectively.

[0143] (Resin return) The following steps (a1) to (a5) were performed in order to return the resin: (a1) The extruded foam particles obtained in each example and comparative example were placed in a dryer with the temperature adjusted to 180°C; (a2) Then, using a vacuum pump, the pressure inside the dryer was reduced to -0.05 MPa (cage pressure) to -0.10 MPa (cage pressure) over a period of 5 to 10 minutes; (a3) ​​After that, the extruded foam particles were left in the dryer for 30 minutes to prepare a resin mass (returned resin); (a4) Then, after the temperature inside the dryer was cooled to room temperature, the pressure inside the dryer was returned to atmospheric pressure; (a5) After that, the resin mass (returned resin) was removed from the dryer. The returned resin obtained as described above was used as is, or finely shredded with scissors as needed, and the resulting resin was used as a sample for measuring each physical property.

[0144] [Melting elongation in melt tension measurement] The melt elongation of the base resin was determined by measuring the melt tension at 230°C using the returned resin as a sample. The apparatus used for melt tension measurement was a capillary graph (manufactured by Toyo Seiki Seisakusho) equipped with a melt tension measuring attachment, which had an orifice with a hole diameter (φ) of 1 mm and a length of 10 mm at its tip, and a cylinder with a bore diameter (φ) of 10 mm. The method for measuring the melt elongation of the base resin using the apparatus was as follows: (1) The sample (return resin) was filled into a cylinder of the capillograph set to 230°C; (2) The filled sample was left in the cylinder for 5 minutes to heat (preheat) the sample; (3) Then, the piston was lowered at a piston descent speed of 10 mm / min, and the sample was discharged in strand form from the orifice; (4) The discharged strand-shaped sample was placed on a load cell pulley installed 350 mm below the orifice, and the sample was taken up at a speed of 1 m / min; (5) After the sample take-up stabilized, the sample take-up speed was increased at a constant rate from 1 m / min to a speed of 200 m / min in 4 minutes; (6) The take-up speed when the strand-shaped sample (return resin) broke was recorded; (7) The same operation was repeated four more times (a total of 5 times), and the average value of the take-up speed for n=5 was taken as the melt elongation of the base resin.

[0145] [MFR] The MFR of the base resin was determined by measuring the return resin as a sample using a melt indexer S-01 (manufactured by Toyo Seiki Seisakusho) 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 of the base resin was calculated by measuring the distance the piston of the melt indexer S-01 traveled within a certain time, and converting the obtained distance and the density of the sample (return resin) at the measurement temperature into the weight of the sample extruded from the orifice in 10 minutes. The certain 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.

[0146] [Melting points Tm2 and Tm3 of polypropylene resins] The melting points Tm2 and Tm3 of branched and linear polypropylene resins were determined by differential scanning calorimetry. A Seiko Instruments DSC6200 differential scanning calorimeter was used. The method for measuring the melting points Tm2 and Tm3 by differential scanning calorimetry was as follows: (1) The sample (polypropylene resin) was melted by raising the temperature of 5-6 mg from 40°C to 220°C at a heating rate of 10°C / min; (2) The resulting sample was then crystallized by lowering the temperature from 220°C to 40°C at a cooling rate of 10°C / min; (3) The crystallized sample was then further heated from 40°C to 220°C at a heating rate of 10°C / min. The temperatures of the peaks (melting peaks) in the DSC curve of the sample (polypropylene resin) obtained during the second heating (i.e., when (3) occurred) were defined as the melting points Tm2 and Tm3.

[0147] [Bulk density] The bulk density of polypropylene resin extruded foam particles was calculated by following steps (1) to (3) in order: (1) Fill a measuring cup of approximately 1 L with polypropylene resin extruded foam particles until it overflows, after accurately measuring the internal volume Vk (L) in advance; (2) Level off the top surface of the container and measure the weight Wb (g) of the polypropylene resin extruded foam particles inside the container; (3) Calculate the bulk density of the polypropylene resin extruded foam particles using the following formula: Bulk density (g / L) = Weight of foam particles Wb (g) / Volume of container Vk (L).

[0148] [Open cell ratio] The open-cell ratio of polypropylene resin extruded foam particles was determined by measuring it using an air-comparison hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in procedure C (PROSEDURE C) of ASTM D2856-87. More 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.

[0149] [Melting point Tm1 of polypropylene resin extruded foam particles] The melting point Tm1 of polypropylene resin extruded foam particles at the first heating stage is a value determined by differential scanning calorimetering (hereinafter referred to as the "DSC method"). As a differential scanning calorimeter, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0150] The method for measuring the melting point Tm1 of polypropylene resin extruded foam particles during the first heating stage using differential scanning calorimetering was as follows: The temperature of the polypropylene resin extruded foam particles was increased from 40°C to 220°C at a rate of 10°C / min. The peak (melting peak) of the DSC curve obtained during heating of the polypropylene resin extruded foam particles was observed, and the temperature of the melting peak was determined as the melting point Tm1 of the polypropylene resin extruded foam particles.

[0151] [Density of foamed molded material] The weight Ws (g) of the obtained foamed molded body was measured. The length, width, and thickness of the foamed molded body were also measured using calipers, and the volume Vs (cm³) of the foamed molded body was measured. 3 The density (g / L) of the foamed molded product was calculated according to the following formula: The density of a foamed molded product (g / L) = Ws / Vs × 1000.

[0152] [Minimum vapor pressure, maximum vapor pressure] The minimum and maximum vapor pressures of polypropylene resin foam molded articles were measured according to the following methods (1) to (5).

[0153] (1) For each example and comparative example, the polypropylene extruded foam particles obtained were filled into a block-shaped mold (400 mm long x 300 mm wide x variable thickness) with a thickness of 52 mm (cracking rate of 30%) using a molding machine (KD345) manufactured by Daisen Co., Ltd., and then compressed to a mold thickness of 40 mm. Next, the air in the mold was expelled with steam at 0.1 MPa (gauge pressure), and then heated and molded for 10 seconds using steam with a vapor pressure of 0.14 MPa (gauge pressure) to obtain a polypropylene foam molded body. Furthermore, polypropylene foam molded bodies were obtained using steam up to a vapor pressure of 0.42 MPa using the same procedure except that the steam pressure was changed in increments of 0.01 MPa. (2) The obtained polypropylene resin foam molded articles were cured in a 75°C curing chamber for 24 hours, and then left at room temperature for 4 hours. The internal fusion rate of each polypropylene resin foam molded article was measured. (3) The lowest water vapor pressure among those obtained when a foam molded article with an internal fusion rate of 60% or more was obtained was defined as the minimum vapor pressure. (4) Similarly, for the obtained polypropylene resin foam molded articles, the surface of each foam molded article was visually inspected for the presence or absence of "melt," "shrinkage (wrinkling)," and "sink marks" caused by the melting of the base resin, and the surface properties of the foam molded articles were evaluated according to the following criteria. (5) The highest water vapor pressure among those obtained when a foam molded article with a surface property evaluation of "○ (pass)" was obtained was defined as the maximum vapor pressure.

[0154] <Criteria for evaluating surface properties> ○ (Pass): No melting, shrinkage (wrinkling), or sink marks are observed on any surface of the foamed molded product. × (Failure): At least one of the following is observed on any surface of the foamed molded product: melting, shrinkage (wrinkling), or sink marks.

[0155] The internal bonding rate is a value measured by the following methods (1) to (4): (1) Make a 5 mm cut perpendicular to any one surface of the foamed molded body with a cutter, perpendicular to the part of the surface in question; (2) Then, break the foamed molded body by hand along the cut; (3) Visually observe the area of ​​the resulting fracture surface excluding the cut portion, and measure the number of foamed particles present in that area, and the number of foamed particles that have broken outside the particle interface in that area (i.e., foamed particles that have broken themselves); (4) Calculate the internal bonding rate based on the following formula; Internal bonding rate (%) = (Number of foamed particles fractured outside the particle interface in the region / Total number of foamed particles present in the region) × 100.

[0156] [Compressive strength of polypropylene foam molded articles] The compressive strength of the polypropylene resin foam molded article was measured according to the following (1) and (2). (1) A polypropylene resin foam molded article, which was molded using water vapor at the minimum vapor pressure + 0.02 MPa obtained in the measurement of the minimum and maximum vapor pressures, was used as a sample, and a test piece measuring 50 mm in length, 50 mm in width, and 25 mm in thickness was cut out from the foam molded article. (2) Using the cut-out test piece as a sample, the compressive stress (MPa) at 50% compression when compressed at a speed of 10 mm / min was measured in accordance with NDZ-Z0504, and the obtained compressive stress value was defined as the compressive strength.

[0157] (material) The following materials were used in the examples and comparative examples.

[0158] (Linear polypropylene resin) • F227D; Prime Polymer Random Polypropylene (F227D) (Melting point 139.8°C, MFR=7) J-700GP; Prime Polymer homopolypropylene (J-700GP) (melting point 164.2℃, MFR=7), • F113G; Prime Polymer Homopolypropylene (F113G) (Melting point 161.5℃, MFR=3) (Conjugated dienes, etc.) • IP; Isoprene (manufactured by Kuraray) (Radical polymerization initiator) PBI; t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I), PBZ; t-butyl peroxybenzoate (manufactured by NOF Corporation, Perbutyl Z), (Branched polypropylene resin) • MPL-1; a resin modified with a composition of F227D / PBI / IP = 100 / 1.4 / 0.5 (parts by weight) (melting point 139.7℃, MFR = 2.1, melt elongation 5.9 m / min), • MPH-1; J-700GP / PBI / IP = 100 / 1.4 / 0.7 (parts by weight) modified resin (melting point 157.9℃, MFR = 2.7, melt elongation 6.1 m / min) • MPH-2: A resin modified with a composition of F113G / PBI / IP=100 / 1.75 / 0.7 (parts by weight) (melting point 155.8℃, MFR=2.9, melt elongation 6.5 m / min), • MPH-3: A resin modified with a composition of J-700GP / PBZ / IP=100 / 0.25 / 0.5 (parts by weight) (melting point 161.0℃, MFR=0.4, melt elongation 3.9 m / min), • MPB-1; a resin modified with a composition of F227D / J-700GP / PBI / IP=85 / 15 / 1.4 / 0.6 (parts by weight) (MFR=3.0, melt elongation 6.3 m / min). However, MPB-1 is a resin containing branched polypropylene resin (A) and branched polypropylene resin (B).

[0159] The preparation methods for each branched polypropylene resin are described in the sections on Examples and Comparative Examples below.

[0160] (Example 1) (a) As a linear polypropylene resin, random polypropylene (F-227D) manufactured by Prime Polymer, with a melting point Tm measured by the method described above. 3AA mixture of (a) 100 parts by weight of (139.8℃) and 1.4 parts by weight of t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I) as a radical polymerization initiator was supplied from the hopper at a rate of 70 kg / hour to a 45 mmφ twin-screw extruder (L / D=40). The mixture was melt-kneaded at a cylinder temperature of 200℃ and a rotation speed of 150 rpm, and (b) isoprene, which is a conjugated diene as a monomer, was supplied using a metering pump from a press-fit section installed in the middle of the extruder in a ratio of 0.5 parts by weight per 100 parts by weight of (a) linear polypropylene resin, and after further melt-kneading, it was extruded from the die in a strand shape, water-cooled and shredded to obtain pellets of branched polypropylene resin (A) (first melt-kneading step of polypropylene resin (A)).

[0161] Similarly, (a) as a linear polypropylene resin, Prime Polymer homopolypropylene (J-700GP, with a melting point Tm measured by the method described above) 3B A mixture of (a) 100 parts by weight of (164.2℃) and (c) 1.4 parts by weight of t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I) as a radical polymerization initiator was supplied from the hopper at 70 kg / hour to a 45 mmφ twin-screw extruder (L / D=40), and melt-kneaded at a cylinder temperature of 200℃ and a rotation speed of 150 rpm. At the same time, (b) isoprene, which is a conjugated diene as a monomer, was supplied using a metering pump from a press-fit section installed in the middle of the extruder in a ratio of 0.7 parts by weight per 100 parts by weight of (a) linear polypropylene resin, and melt-kneaded further. After that, it was extruded from the die in a strand shape, water-cooled and shredded to obtain pellets of branched polypropylene resin (B) (first melt-kneading step of polypropylene resin (B)).

[0162] Next, the mixture obtained by mixing 85% by weight of branched polypropylene resin (A) and 15% by weight of branched polypropylene resin (B) was supplied from the hopper at a rate of 1.0 kg / hour to a 15 mmφ twin-screw extruder (L / D=30), where it was melt-kneaded at a cylinder temperature of 200°C and a rotation speed of 100 rpm. At the same time, carbon dioxide, a foaming agent, was supplied from a press-in section installed in the middle of the extruder using a metering pump at a ratio of 1.7 parts by weight per 100 parts by weight of polypropylene resin, and the mixture was further melt-kneaded (second melt-kneading step).

[0163] Furthermore, the molten mixture was cooled by passing it through a melt cooler connected to the tip of a twin-screw extruder and set to 155°C. Then, it was extruded under atmospheric pressure through a die with two 0.7 mm diameter holes attached to the tip of the melt cooler to induce foaming, and simultaneously cut by a rotary cutter attached to the tip of the die to obtain polypropylene resin extruded foam particles.

[0164] Using the obtained polypropylene resin extruded foam particles, the melt elongation and MFR of the base resin were measured by the method described above. Furthermore, the melting point Tm1, bulk density, and open-cell ratio of the obtained polypropylene resin extruded foam particles were measured by the method described above. The results are shown in Table 1.

[0165] Furthermore, the minimum vapor pressure, maximum vapor pressure, molded article density, and compressive strength were measured using the obtained polypropylene resin extruded foam particles by the method described above. The results are shown in Table 1.

[0166] (Example 7) (a) As the linear polypropylene resin (A'), random polypropylene (F-227D) manufactured by Prime Polymer, with a melting point Tm measured by the method described above. 3A 85 parts by weight (139.8℃) and as a linear polypropylene resin (B'), Prime Polymer homopolypropylene (J-700GP, with a melting point Tm measured by the method described above). 3BA mixture of (a) 15 parts by weight (at 164.2°C) and 1.4 parts by weight of t-butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I) as a radical polymerization initiator was supplied from the hopper at a rate of 70 kg / hour to a 45 mmφ twin-screw extruder (L / D=40). The mixture was melt-kneaded at a cylinder temperature of 200°C and a rotation speed of 150 rpm, and (b) isoprene, which is a conjugated diene as a monomer, was supplied using a metering pump from a press-fit section installed in the middle of the extruder in a ratio of 0.6 parts by weight per 100 parts by weight of the sum of (a) linear polypropylene resins (A') and (B'). After further melt-kneading, the mixture was extruded from the die in a strand shape, water-cooled, and shredded. This yielded branched polypropylene resin pellets containing polypropylene resin (A) and polypropylene resin (B) in a crosslinked state within a single molecule (single polymer) (first melt-kneading step).

[0167] Next, the obtained branched polypropylene resin was supplied from the hopper at a rate of 1.0 kg / hour to a 15 mmφ twin-screw extruder (L / D=30), where it was melted and kneaded at a cylinder temperature of 200°C and a rotation speed of 100 rpm. At the same time, carbon dioxide, a foaming agent, was supplied from a pressure injection section installed in the middle of the extruder using a metering pump at a ratio of 1.7 parts by weight per 100 parts by weight of polypropylene resin, and the mixture was further melted and kneaded (second melting and kneading step).

[0168] Furthermore, the molten mixture was cooled by passing it through a melt cooler connected to the tip of a twin-screw extruder and set to 155°C. Then, it was extruded under atmospheric pressure through a die with two 0.7 mm diameter holes attached to the tip of the melt cooler to induce foaming, and simultaneously cut by a rotary cutter attached to the tip of the die to obtain polypropylene resin extruded foam particles.

[0169] Using the obtained polypropylene resin extruded foam particles, the melt elongation and MFR of the base resin were measured using the method described above. Furthermore, the melting points and weight ratios of branched polypropylene resin (A) and branched polypropylene resin (B) in the base resin were measured as follows: As described above, the base resin was separated by melting point to obtain an elution chromatogram. Subsequently, in the obtained elution chromatogram, the component corresponding to the largest peak was identified as branched polypropylene resin (A), and the component corresponding to the next largest peak was identified as branched polypropylene resin (B). For the branched polypropylene resin (A) and branched polypropylene resin (B) obtained in this way, their respective melting points Tm 2A , Tm 2B The above method was used to measure the values. Furthermore, the weight ratio of branched polypropylene resin (A) and branched polypropylene resin (B) contained in MPB-1 was calculated from the peak area ratio in the elution chromatogram of MPB-1.

[0170] As a result, the melting point Tm of branched polypropylene resin (A) 2A The melting point Tm of branched polypropylene resin (B) is 140.1℃. 2B The temperature was 156.2°C, and the weight ratio of resin (A) to resin (B) was A / B = 86 / 14.

[0171] Furthermore, the melting point Tm1, bulk density, and open-cell ratio of the obtained polypropylene resin extruded foam particles were measured. The results are shown in Table 2.

[0172] Furthermore, the minimum vapor pressure, maximum vapor pressure, molded article density, and compressive strength were measured using the obtained polypropylene resin extruded foam particles by the method described above. The results are shown in Table 2.

[0173] (Examples 2-6, Comparative Examples 1-3) Regarding Example 1, pellets of branched polypropylene resin were obtained in the same manner as in Example 1, except that the modifications were made as described in (for branched polypropylene resin).

[0174] Next, polypropylene resin extruded foam particles were obtained in the same manner as in Example 1, except that the branched polypropylene resin used in Example 1 was changed to the mixing ratio of branched polypropylene resins shown in Tables 1 and 2.

[0175] Using the obtained polypropylene resin extruded foam particles, the melt elongation and MFR of the base resin were measured using the method described above, in the same manner as in Example 1. Also, the melting point Tm1, bulk density, and open-cell ratio of the obtained polypropylene resin extruded foam particles were measured using the method described above, in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0176] Furthermore, a polypropylene resin foam molded article was obtained in the same manner as in Example 1, and after curing and leaving it at room temperature in the same manner as in Example 1, the minimum vapor pressure, maximum vapor pressure, molded article density, and compressive strength were measured. The results are shown in Tables 1 and 2.

[0177] [Table 1]

[0178] [Table 2]

[0179] As shown in Tables 1 and 2, the extruded foam particles according to one embodiment of the present invention exhibited excellent low-pressure moldability. Furthermore, the foamed molded articles obtained from the extruded foam particles according to one embodiment of the present invention exhibited excellent compressive strength. In contrast, as shown in Comparative Examples 1 to 3, (i) extruded foam particles outside the scope of the present invention exhibited poor low-pressure moldability, or (ii) foamed molded articles obtained from extruded foam particles outside the scope of the present invention exhibited poor compressive strength. [Industrial applicability]

[0180] According to one embodiment of the present invention, polypropylene resin extruded foam particles that exhibit excellent low-pressure moldability and can provide polypropylene resin foam molded articles with excellent compressive strength can be provided. Therefore, one embodiment of the present invention can be suitably used in fields such as automotive interior components, cushioning materials, packaging materials, and heat insulating materials.

Claims

1. Polypropylene resin extruded foam particles, The aforementioned polypropylene resin extruded foam particles have a melting point Tm ２Ａ A polypropylene resin (A) having a branched structure with a melting point Tm is present in an amount of more than 70% by weight and less than 98% by weight, and the melting point Tm is present in an amount of more than 70% by weight and less than 98% by weight. ２Ｂ The material contains a base resin containing a branched polypropylene resin (B) having a temperature of 150.0°C or higher and less than 170.0°C, in an amount of 2% by weight or more and less than 30% by weight (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight), The melting point Tm of the polypropylene resin extruded foam particles at the first heating stage. １ The temperature is between 130.0°C and 155.0°C. Polypropylene resin extruded foam particles, wherein the melt elongation of the base resin is 7.0 m / min to 8.0 m / min.

2. Polypropylene resin extruded foam particles, The polypropylene resin extruded foam particles contain a base resin comprising: more than 70% by weight and 98% by weight or less of a branched polypropylene resin (A) having a melting point Tm 2A of 130.0°C or higher and less than 143.0°C; and 2% by weight and less than 30% by weight of a branched polypropylene resin (B) having a melting point Tm 2B of 150.0°C or higher and less than 170.0°C (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight). The melting point Tm1 of the polypropylene resin extruded foam particles in the first heating stage is 130.0°C or higher and less than 155.0°C. The polypropylene resin extruded foam particles have a bulk density of 66 g / L to 69 g / L.

3. The polypropylene resin extruded foam particle according to claim 1 or 2, wherein the base resin comprises more than 80% by weight and 98% by weight or less of the polypropylene resin (A), and 2% by weight or more and less than 20% by weight of the polypropylene resin (B) (the sum of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight).

4. The polypropylene resin extruded foam particles according to claim 2, wherein the melt elongation of the base resin is 3.0 m / min to 30.0 m / min.

5. The polypropylene resin extruded foam particles according to any one of claims 1 to 4, wherein the melt flow rate of the base resin is 1.0 g / 10 min to 20.0 g / 10 min.

6. The polypropylene resin extruded foam particles according to claim 1, wherein the bulk density of the polypropylene resin extruded foam particles is 30 g / L to 600 g / L.

7. The polypropylene resin extruded foam particles according to any one of claims 1 to 6, wherein the open-cell ratio of the polypropylene resin extruded foam particles is 10.0% or less.

8. A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles according to any one of claims 1 to 7.

9. A method for producing polypropylene resin extruded foam particles according to any one of claims 1 to 7, The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step includes a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step, the polypropylene resin (A) and the polypropylene resin (B) are prepared separately. A method for producing extruded polypropylene resin foam particles, wherein the extrusion foaming step comprises a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin (A) and the polypropylene resin (B), and a foaming agent.

10. A method for producing polypropylene resin extruded foam particles according to any one of claims 1 to 7, The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step includes a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-kneading step, (a) as a linear polypropylene resin, (a-1) melting point Tm ３Ａ A linear polypropylene resin (A') having a melting point of 130.0°C or higher and less than 150.0°C, and (a-2) melting point Tm ３Ｂ Using a mixture with a linear polypropylene resin (B') having a temperature of 150.0°C or higher and less than 170.0°C, a polypropylene resin having a branched structure is prepared, containing the polypropylene resin (A) and the polypropylene resin (B) in a crosslinked state within a single molecule. A method for producing polypropylene resin extruded foam particles, comprising a second melt-kneading step of melt-kneading a composition comprising a second mixture containing a polypropylene resin having the branched structure and a foaming agent, wherein the extrusion foaming step is a second melt-kneading step.

11. The method for producing polypropylene resin extruded foam particles according to claim 9 or 10, wherein one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds in the first melt-kneading step are isoprene and / or butadiene.

12. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 11, wherein the amount of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds used in the first melt-kneading step is 0.01 parts by weight to 5.00 parts by weight per 100 parts by weight of the linear polypropylene resin.

13. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 12, wherein the radical polymerization initiator in the first melt-kneading step is one or more selected from the group consisting of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate.

14. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 13, wherein the ratio of the amount (parts by weight) of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds to the amount (parts by weight) of the radical polymerization initiator used is 0.05 to 5.

00.

15. A method for producing a polypropylene resin foamed molded article, comprising a molding step of molding polypropylene resin extruded foam particles produced by the method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 14.

16. The method for producing a polypropylene resin foamed molded article according to claim 15, wherein in the molding step, the polypropylene resin extruded foam particles are heated at a vapor pressure of 0.30 MPa or less.

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