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

Abstract

The present invention addresses the problem of providing polypropylene resin extruded foam particles, etc., that can provide a polypropylene resin foam molded body having exceptional break resistance. Provided are polypropylene resin extruded foam particles that contain a polypropylene resin having a branched structure, the polypropylene resin extruded foam particles including a base resin that satisfies a specific melting point, melt elongation, and MFR.

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 steps are required: a pelletizing step and a pressure-relieving foaming step. As a result, the pressure-relieving foaming method may have the following challenges: (i) it tends to require significant capital investment, and (ii) 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] Furthermore, it has been proposed to use modified polypropylene resin, which is obtained by modifying polypropylene resin, in the production of polypropylene resin extruded foam particles (for example, Patent Document 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication H9-302131 [Patent Document 2] Japanese Patent Publication No. 2009-256460 [Patent Document 3] International Public Gazette 2018 / 016399 [Patent Document 4] International Public Gazette 2020 / 004429 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the conventional techniques described above were insufficient from the standpoint of providing a polypropylene resin foam molded article with excellent fracture resistance when manufacturing a foam molded article using extruded foam particles obtained by manufacturing with a modified polypropylene resin (for example, a polypropylene resin having a branched structure).

[0008] One embodiment of the present invention has been made in view of the above-mentioned problems, and its object is to provide polypropylene resin extruded foam particles and a method for producing the same, which can provide a polypropylene resin foam molded article with excellent fracture resistance, and a polypropylene resin foam molded article with excellent fracture resistance. [Means for solving the problem]

[0009] In other words, one embodiment of the present invention includes a base resin containing a polypropylene resin having a branched structure, wherein the base resin is a polypropylene resin extruded foam particle that satisfies all of the following conditions (i) to (iii): (i) The melting point Tm1 is 130.0 °C or higher and lower than 143.0 °C, where the melting point Tm1 is a value determined by measurement using differential scanning calorimetry; (ii) The melt elongation is 3.0 m / min to 30.0 m / min, where the melt elongation is a value determined by measurement of the melt tension at 230 °C; and (iii) The melt flow rate (MFR) is 1.0 g / 10 min to 20.0 g / 10 min, where the MFR is a value determined by measurement in accordance with ISO 1133 under the conditions of a temperature of 230 °C and a load of 2.16 kg.

[0010] Moreover, another embodiment of the present invention is a foamed molded article comprising extruded foam particles containing a base resin containing a polypropylene-based resin having a branched structure, wherein the closed cell ratio of the extruded foam particles is 15.0% or less, the density (X) of the foamed molded article is 60 g / L to 300 g / L, and the tensile elongation at break (Y) of the foamed molded article satisfies the following formula (1), which is a polypropylene-based resin foamed molded article: Y > 0.005 × X 2 -0.25 × X + 38 ··· (1).

Effects of the Invention

[0011] According to one embodiment of the present invention, there is an effect that (a) polypropylene-based resin extruded foam particles capable of providing a polypropylene-based resin foamed molded article excellent in fracture resistance, (b) a method for producing the same, and (c) a polypropylene-based resin foamed molded article excellent in fracture resistance can be provided.

Modes for Carrying Out the Invention

[0012] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims. 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~B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

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

[0014] [1. Technical idea of an embodiment of the present invention] In order to obtain pre-expanded particles with a low continuous cell ratio and capable of secondary molding by the extrusion foaming method, it is necessary to increase the poor melt tension of the polypropylene-based resin. For this purpose, a means using a modified polypropylene-based resin subjected to some modification treatment as a base material is used (for example, Patent Documents 1 and 2).

[0015] Incidentally, in foamed molded articles obtained by molding polypropylene foam particles, it is sometimes required that the fracture resistance of the foamed molded article be excellent (specifically, the amount of deformation at the time of sample fracture in a tensile test of the foamed molded article (tensile elongation at fracture)). The technology in Patent Document 3 provides extruded foam particles that exhibit good moldability by performing sufficient modification, using carbon dioxide as a foaming agent. However, the inventors have investigated and found that increasing the degree of modification of the extruded foam particles tends to worsen the fracture resistance of the foamed molded article obtained using those extruded foam particles. In other words, the inventors have independently discovered that when manufacturing a foamed molded article using extruded foam particles obtained by manufacturing with a modified polypropylene resin (for example, a polypropylene resin having a branched structure) (for example, the technology in Patent Document 3), there is a problem that the fracture resistance of the obtained foamed molded article may be insufficient.

[0016] One embodiment of the present invention has been made in view of the above-mentioned problems, and its object is to provide polypropylene resin extruded foam particles and a method for producing the same, which can provide a polypropylene resin foam molded article with excellent fracture resistance, and a polypropylene resin foam molded article with excellent fracture resistance.

[0017] [2. Polypropylene resin extruded foam particles] Polypropylene resin extruded foam particles according to one embodiment of the present invention include a base resin containing a polypropylene resin having a branched structure, wherein the base resin satisfies all of the following (i) to (iii): (i) The melting point Tm1 is 130.0°C or higher and less than 143.0°C. Here, the melting point Tm1 is a value obtained by differential scanning calorimetry; (ii) The melt elongation is 3.0 m / min to 30.0 m / min, Here, the melt elongation is a value determined by measuring the melt tension at 230°C; and (iii) The melt flow rate (MFR) is between 1.0 g / 10 min and 20.0 g / 10 min. Here, the MFR is a value obtained by measurement under conditions of 230°C and 2.16 kg load, in accordance with ISO 1133.

[0018] 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 extruded foam particles" may be referred to as "extruded foam particles," "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."

[0019] Because the extruded foam particles have the aforementioned structure, they have the advantage of providing a polypropylene resin foam molded article with excellent fracture resistance. Furthermore, because the extruded foam particles have the aforementioned structure, they also have the advantage of providing a polypropylene resin foam molded article with a low open-cell ratio. In this specification, the fracture resistance of the foam molded article is evaluated by the tensile elongation at fracture of the foam molded article. The method for measuring the tensile elongation at fracture will be described later.

[0020] (2-1. Base resin) The base resin includes a polypropylene-based resin having a branched structure, and may 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.

[0021] In this specification, "polypropylene resin having a branched structure" refers to (a) a polypropylene resin in which the molecules of a polypropylene resin without a branched structure are partially crosslinked intermolecularly, and (b) a polypropylene resin in which a diene compound other than (poly)propylene is introduced as a branched chain to a polypropylene resin without a branched structure. In this specification, "polypropylene resin without a branched structure" may be referred to as "linear polypropylene resin," and "polypropylene resin having a branched structure" may be referred to as "branched polypropylene resin," and "linear polypropylene resin" and "branched polypropylene resin" may be collectively referred to as "polypropylene resin." Linear polypropylene resin can also be considered a raw material for branched polypropylene resin.

[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, alternating 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 random copolymer in which propylene units are randomly bonded with one or more comonomer units selected from the group consisting of 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. This configuration has the advantage that a foamed molded article with a high tensile elongation at break can be obtained using the resulting extruded foamed particles.

[0031] 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.

[0032] 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.

[0033] The melting point Tm2 of the linear polypropylene resin is not particularly limited, but the melting point Tm2 of the linear polypropylene resin may affect the melting point of the base resin. Therefore, the melting point Tm2 of the linear polypropylene resin is preferably, for example, 125.0°C to 148.0°C, more preferably 125.0°C to 145.0°C, more preferably 125.0°C to 143.0°C, more preferably 130.0°C to 143.0°C, more preferably 130.0°C or more and less than 143.0°C, more preferably 130.0°C to 142.0°C, more preferably 130.0°C to 140.0°C, even more preferably 131.0°C to 140.0°C, and particularly preferably 132.0°C to 138.0°C. When the melting point Tm2 of the linear polypropylene resin is within the range described above, the resulting extruded foam particles have the advantage of providing a polypropylene resin foam molded article with excellent fracture resistance. Furthermore, when the melting point Tm2 of the linear polypropylene resin is (a) 125.0°C or higher, there is no risk of reduced dimensional stability of the foam molded article, there is no risk of insufficient heat resistance of the foam molded article, and the compressive strength of the foam molded article tends to be increased. When it is (b) 148.0°C or lower, the extruded foam particles can be molded at a relatively low vapor pressure, which has the advantage of allowing the extruded foam particles to be molded using a general-purpose molding machine for polypropylene resin foam particles.

[0034] Here, the melting point Tm2 of the linear polypropylene resin is a value obtained by measurement using differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific operating 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 Tm2 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 Tm2 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 foam particles have the advantage of providing a polypropylene resin foam molded article with excellent fracture resistance. 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 can be obtained by introducing a branched structure into the linear polypropylene resin described above. 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.

[0038] A specific example of the method described in (a1) above is the method described in Japanese Patent Publication 2002-542360.

[0039] A specific example of the method described in (a2) above is a method that includes a preparation step, which will be described later.

[0040] (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. The branched polypropylene resin obtained by the method of (a2) described above contains constituent units derived from one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds. In other words, it is preferable that a polypropylene resin having a branched structure contains constituent units derived from one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds.

[0041] In branched polypropylene resins, the structure derived from the linear polypropylene resin used as the raw material is also referred to as the "main chain." The various aspects of the main chain of the branched polypropylene resin (for example, the constituent units included in the main chain and the content of propylene units in the main chain) are the same as those described in the section on linear polypropylene resins above, so we will refer to that description and omit further explanation here.

[0042] (Other resins and rubbers) The base resin may further contain resins other than branched polypropylene resins (sometimes referred to as "other resins") and / or rubber, to the extent that the effects of one embodiment of the present invention are not impaired. Other resins and rubbers may be collectively referred to as "other resins, etc." 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 in the base resin is not particularly limited. The total content of other resins 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. The total content of rubber in the base resin is not particularly limited. The total content of rubber in the base resin is preferably 5 to 30 parts by weight, and more preferably 10 to 25 parts by weight, per 100 parts by weight of branched polypropylene resin.

[0043] (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.

[0044] Examples of bubble nucleating agents include sodium bicarbonate-citric acid mixtures, monosodium citrate, talc, and calcium carbonate. These bubble nucleating agents may be used individually or in combination of two or more.

[0045] 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.

[0046] (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. Note that "other components" in the base resin refers to components other than (a) branched polypropylene resin, (b) other resins, etc., and (c) bubble nucleating agents in the base resin.

[0047] (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."

[0048] There are no particular limitations on the specific method of resin return, but for example, the following method can be performed in order: (b1) Place the extruded foam particles or foam molded body into a dryer adjusted to a temperature of 160°C; (b2) Then, using a vacuum pump, reduce the pressure inside the dryer to -0.05 MPa (cage pressure) to -0.10 MPa (cage pressure) over 5 to 10 minutes; (b3) After that, leave the extruded foam particles in the dryer for 30 minutes to prepare a resin mass (returned resin); (b4) Then, after cooling the temperature inside the dryer to room temperature, return the pressure inside the dryer to atmospheric pressure; (b5) After that, remove the resin mass from the dryer.

[0049] (Melting point Tm1 of the base resin) The melting point Tm1 of the base resin is 130.0°C or higher and less than 143.0°C, preferably 13.0°C to 142.0°C, more preferably 131.0°C to 141.0°C, even more preferably 132.0°C to 140.0°C, even more preferably 133.0°C to 139.0°C, and particularly preferably 133.0°C to 136.0°C. When the melting point Tm1 of the base resin is within the above range, the resulting extruded foam particles have the advantage of providing a polypropylene-based resin foam molded article with excellent fracture resistance. Furthermore, if the melting point Tm1 of the base resin is (a) 130.0°C or higher, there is no risk of reduced dimensional stability of the foamed molded article, no risk of insufficient heat resistance of the foamed molded article, and the compressive strength of the foamed molded article tends to be higher. If it is (b) below 143.0°C, it is possible to mold the extruded foamed particles at a relatively low vapor pressure, which has the advantage of allowing the extruded foamed particles to be molded using a general-purpose molding machine for polypropylene-based resin foamed particles.

[0050] The melting point Tm1 of the base resin is a value obtained by measurement using differential scanning calorimetry (hereinafter referred to as the "DSC method"). As a differential scanning calorimetry, for example, the DSC6200 model manufactured by Seiko Instruments Inc. can be used.

[0051] An example of a method for measuring the melting point Tm1 of a base resin using differential scanning calorimetering is as follows: (1) Melt the returned resin by heating 5 mg to 6 mg of the returned resin obtained by returning extruded foam particles or foam molded articles to resin from 40°C to 220°C at a heating rate of 10°C / min; (2) Then crystallize the returned resin by cooling it from 220°C to 40°C at a cooling rate of 10°C / min; (3) Then further heat the crystallized returned resin from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve of the returned resin obtained during the second heating (i.e., at (3)) can be determined as the melting point Tm1 of the base resin contained in the extruded foam particles or foam molded articles. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the returned resin obtained during the second heating process using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) shall be defined as the melting point Tm1 of the base resin.

[0052] The melting point Tm1 of the base resin may depend on the melting point of the branched polypropylene resin. The melting point of the branched polypropylene resin may depend on the melting point of the linear polypropylene resin that is the raw material for the branched polypropylene resin. In other words, the melting point Tm1 of the base resin can be adjusted by changing the melting point of the linear polypropylene resin.

[0053] In one embodiment of the present invention, when there are multiple melting peaks in the DSC curve of the return resin of extruded foamed particles, it is preferable that the melting heat of the peak with the largest melting heat is 75% or more, more preferably 80% or more, even more preferably 85% or more, and most preferably 90% or more of the total melting heat (100%) calculated from all melting peaks.

[0054] (Melting elongation) The melt elongation of the base resin is preferably 3.0 m / min to 30.0 m / min, more 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. When the melt elongation of the base resin is within the above range, the resulting extruded foam particles have the advantage of providing a polypropylene-based resin foam molded article with excellent fracture resistance. Furthermore, when the melt elongation of the base resin is (a) 3.0 m / min or more, the fusion properties between the extruded foam particles during molding are good, making it easier to obtain a foam molded article with a beautiful surface, and (b) when it is 30.0 m / min or less, there is a tendency to obtain extruded foam particles with a low open-cell ratio. Note that "min" is an abbreviation for "minute" and means "minute".

[0055] 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.

[0056] (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, more preferably 2.0 g / 10 min to 8.0 g / 10 min, more preferably 2.0 g / 10 min to 6.0 g / 10 min, more preferably 2.0 g / 10 min to 5.0 g / 10 min, even more preferably 2.0 g / 10 min to 4.0 g / 10 min, and particularly preferably 2.0 g / 10 min to 3.0 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 polypropylene-based resin foam molded article with excellent fracture resistance. When the MFR of the base resin is (a) 1.0 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 20.0 g / 10 min or less, it has the advantage of providing good foaming properties of the composition during extrusion foaming.

[0057] 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. For example, the MFR of the base resin is obtained by using a resin obtained by melting (returning resin) extruded foam particles or foam molded products as a sample, and measuring it 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 within a certain 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. The aforementioned fixed 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, 60 seconds if it exceeds 1.0 g / 10 min and is 3.5 g / 10 min or less, and 30 seconds if it exceeds 3.5 g / 10 min and is 30.0 g / 10 min or less.

[0058] (2-2. 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.

[0059] (Bulk density of extruded foam particles) The extruded foam particles preferably have a bulk density of 45 g / L to 600 g / L, more preferably 50 g / L to 250 g / L, even more preferably 55 g / L to 200 g / L, and particularly preferably 60 g / L to 150 g / L. The above configuration has the advantage that the polypropylene resin molded foam articles obtained using the extruded foam particles exhibit characteristics such as arbitrary shape, cushioning, lightness, and heat insulation. If the foaming ratio of the extruded foam particles obtained by the production of 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. H10-237212).

[0060] 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).

[0061] (Open cell ratio) The extruded foam particles are preferable to have a low open-cell ratio. The extruded foam particles are preferably 10.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, more preferably 7.0% or less, even more preferably 6.0% or less, and particularly preferably 5.0% or less. The lower limit of the open-cell ratio of the polypropylene resin extruded foam particles is not particularly limited, and is, for example, 0.0% or more. 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 properties, lightness, compressive strength, and heat insulation properties to a greater extent.

[0062] In this specification, the open-cell ratio of polypropylene resin extruded foam particles is a value obtained by measuring using an air-comparable hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. Specifically, the open-cell ratio of extruded foam particles is calculated by performing the following steps (1) to (3) in order: (1) Using an air-comparable hydrometer, the volume Vc (cm³) of the extruded foam particles 3 (1) Measure the volume of the extruded foam particles after measuring Vc; (2) Submerge the entire volume of extruded foam particles in ethanol in a graduated cylinder; (3) Then, from the rise in the position of the ethanol in the graduated cylinder, determine the apparent volume of the extruded foam particles Va (cm³). 3 (4) Determine the open-cell ratio of the extruded foam particles using the following formula: Open-cell ratio (%) = ((Va-Vc)×100) / Va. Note that the method for measuring the volume Va is also called the immersion method.

[0063] (Crystal peak) Polypropylene resin extruded foam particles obtained by the extrusion foaming method are characterized by having one crystal peak in the DSC curve obtained by DSC measurement. In other words, polypropylene resin foam particles with one crystal peak in the DSC curve obtained by DSC measurement are highly likely to have been obtained by the extrusion foaming method. These polypropylene resin extruded foam particles may also have one crystal peak in the DSC curve obtained by DSC measurement.

[0064] The DSC curve of polypropylene resin extruded foam particles (or polypropylene resin foam particles) used to calculate the crystal peak is the curve obtained by DSC measurement while heating 5-6 mg of polypropylene resin extruded foam particles (or polypropylene resin foam particles) from 40°C to 220°C at a heating rate of 10°C / min. In this specification, the case in which multiple peaks are observed in the DSC curve of polypropylene resin extruded foam particles (or polypropylene resin foam particles) used to calculate the crystal peak will be explained. Unlike the depressurization foaming method, polypropylene resin extruded foam particles basically have a single peak, but multiple peaks may be observed when the comonomer unit content is high or when crystalline resins such as polyethylene are added. In this case, only the peak that shows the amount of heat that accounts for 15% or more of the total heat of fusion (100%) calculated from all peaks will be considered as the crystal peak of the polypropylene resin extruded foam particles (or polypropylene resin foam particles). In other words, peaks representing less than 15% of the total heat of fusion (100%) calculated from all peaks are not considered crystalline peaks of polypropylene resin extruded foam particles (or polypropylene resin foam particles).

[0065] [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 as described in section [2. Polypropylene Resin Extruded Foamed Particles], comprising: a preparation step for preparing a polypropylene resin having a branched structure; and an extrusion foaming step for preparing the polypropylene resin extruded foam particles, wherein 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 N selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator; and the extrusion foaming step comprises a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin having a branched structure and a foaming agent.

[0066] 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 N selected from the group consisting of conjugated dienes and vinyl aromatic compounds" may be referred to as "monomer N" or "conjugated dienes, etc."

[0067] Because this manufacturing method has the configuration described above, it has the advantage of being able to provide polypropylene resin extruded foam particles that can provide polypropylene resin foam molded articles with excellent fracture resistance. Furthermore, because this manufacturing method has the configuration described above, it is possible to provide polypropylene resin extruded foam particles containing a base resin having (i) a melting point Tm1 of 130.0°C or higher and less than 143.0°C, (ii) a melt elongation of 3.0 m / min to 30.0 m / min, and (iii) a melt flow rate (MFR) of 1.0 g / 10 min to 20.0 g / 10 min.

[0068] (Linear polypropylene resin) As explained earlier, linear polypropylene resins are described in the section on (linear polypropylene resins) under [2. Extruded foamed polypropylene resins].

[0069] (Monomer N (conjugated diene, 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.

[0070] 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.

[0071] Monomer N preferably contains one or more selected from the group consisting of butadiene, isoprene, styrene, and methylstyrene, more preferably contains one or more selected from the group consisting of butadiene and isoprene, and even more preferably contains isoprene. This configuration has the advantages of (a) monomer N being inexpensive and easy to handle, and (b) the reaction for introducing a branched structure (crosslinked structure) into the polypropylene resin proceeding uniformly. Monomer N may consist of only one or more selected from the group consisting of butadiene, isoprene, styrene, and methylstyrene, or it may consist of only butadiene and isoprene, or it may consist of only isoprene.

[0072] In the first melt-kneading step, the amount of monomer N (conjugated diene, etc.) used is preferably 0.01 to 5.00 parts by weight, more preferably 0.10 to 3.00 parts by weight, and even more preferably 0.10 to 2.00 parts by weight, per 100 parts by weight of linear polypropylene resin. The more monomer N (conjugated diene, 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 smaller the MFR of the base resin tends to be, and the lower the melt elongation tends to be. On the other hand, the less monomer N (conjugated diene, 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 tends to be, and the higher the melt elongation tends to be.

[0073] In the first melt-kneading step, in addition to the random polypropylene resin, monomer N (conjugated diene, etc.), and radical polymerization initiator, monomer copolymerizable with monomer N (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 resin mixture in this manufacturing method may further contain monomer copolymerizable with monomer N (conjugated diene, etc.). Examples of monomers copolymerizable with monomer N (such as conjugated dienes) include (a) vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylate salts, metal methacrylate salts, (b) acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and stearyl acrylate, and (c) methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate.

[0074] (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, peroxycarbonates, peroxydicarbonates, and peroxyesters.

[0075] Organic peroxides 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-di(t-butylperoxy)hexane. Dialkyl peroxides such as t-peroxy)-3-hexine; diacyl peroxides such as benzoyl peroxide; peroxyesters such as t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy3,5,5-trimethylhexanoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, and di-t-butyl peroxyisophthalate; peroxycarbonates such as t-butyl peroxyisopropyl carbonate; etc. are preferred. Among these, t-butyl peroxyisopropyl carbonate and / or t-butyl peroxybenzoate are preferred. In other words, (c) the radical polymerization initiator preferably contains at least one of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate. These organic peroxides may be used individually or in combination of two or more.

[0076] The amount of radical polymerization initiator used in the first melt-mixing step is not particularly limited, but is preferably 0.01 to 5.00 parts by weight, preferably 0.10 to 3.00 parts by weight, preferably 0.30 to 2.50 parts by weight, more preferably 0.50 to 2.00 parts by weight, even more preferably 0.50 to 1.50 parts by weight, even more preferably 0.50 to 1.00 parts by weight, and particularly preferably 0.55 to 1.00 parts by weight, per 100 parts by weight of linear polypropylene resin.

[0077] The following describes, with some speculation, the effects of monomer N (such as a conjugated diene) and radical polymerization initiators on the melt elongation and MFR of the base resin of the resulting branched polypropylene resin and extruded foam particles in this manufacturing method. It should be noted that the embodiment of this invention is not limited in any way to the following description.

[0078] 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.

[0079] In this manufacturing method, (a) a linear polypropylene resin is subjected to a combination of (c) a radical polymerization initiator and (b) monomer N (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) monomer N (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) monomer N (conjugated diene, etc.) to the linear polypropylene resin molecules that have undergone a hydrogen abstraction reaction proceeds, forming a branched structure by monomer N (conjugated diene, etc.) in the linear polypropylene resin. Furthermore, in this manufacturing method, a dimerization reaction proceeds between the molecules of multiple linear polypropylene resins in which branched structures by monomer N (conjugated diene, etc.) have been formed, and a crosslinked structure is generated between the molecules of the linear polypropylene resin as this reaction progresses. It is believed that a branched polypropylene resin is obtained by this manufacturing method through the progress of this series of reactions. Furthermore, the molecular chain severing reaction of the linear polypropylene resin described above can also proceed in parallel with the series of reactions described above. Therefore, in this manufacturing method, by appropriately adjusting (a) the amount of monomer N (conjugated diene, etc.) and (c) the amount of 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.

[0080] Radical polymerization initiators can be said to be components that determine the degree of progress of the molecular chain severing reaction of the linear polypropylene resin described above, as well as the reaction of branching and / or crosslinking structures by monomer N (conjugated diene, etc.) of the linear polypropylene resin. Increasing the amount of radical polymerization initiator added has the effect of increasing the degree of progress of both of the above reactions. Therefore, in this manufacturing method, it is preferable to use an amount of radical polymerization initiator necessary to cause branching and / or crosslinking structure formation reactions to a sufficient extent. It should be noted that as the branching and / or crosslinking structure formation reactions increase, the melt elongation of the base resin of the resulting branched polypropylene resin and extruded foam particles tends to decrease, and the MFR tends to decrease. Furthermore, the balance between the progress of the molecular chain severing reaction and the branching and / or crosslinking structure formation reaction can be adjusted by changing the ratio of the amount of monomer N (conjugated diene, etc.) used (parts by weight) to the amount of radical polymerization initiator used (parts by weight) (amount of monomer N (conjugated diene, etc.) used / amount of radical polymerization initiator used).

[0081] At a given amount of radical polymerization initiator used, the higher the ratio (amount of monomer N (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 monomer N (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.

[0082] The ratio (amount of monomer N (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, more preferably 0.25 to 1.00, more preferably 0.26 to 0.80, even more preferably 0.27 or more and less than 0.60, even more preferably 0.28 to 0.50, and particularly preferably 0.28 to 0.45. With this configuration, it is possible to obtain extruded foam particles containing a base resin having melt elongation and MFR within the above range, and as a result, a foam molded article with excellent fracture resistance can be obtained.

[0083] As described above, by appropriately adjusting the amounts of (a) linear polypropylene resin, (b) monomer N (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 within the range of the present invention. Furthermore, by adjusting the melt elongation and MFR of the base resin of the extruded foam particles within the range of the present invention, it is possible to obtain extruded foam particles with a low open-cell ratio and extruded foam particles that can provide a foam molded article with excellent fracture resistance.

[0084] (Other ingredients) The resin mixture may further contain, as optional, other components, (a) stabilizers such as antioxidants, metal deactivators, phosphorus-based processing stabilizers, UV absorbers, UV 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.

[0085] (3-1. Preparation process) The preparation process can also be described as a process of preparing a branched polypropylene resin (branched polypropylene resin) using one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds.

[0086] (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) a linear polypropylene resin, (b) monomer N (such as a conjugated diene), and (c) a radical polymerization initiator.

[0087] Apparatus that can be used in the first melt-mixing step 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) equipped with rolls, cone kneaders, Banbury mixers, brabenders, single-screw extruders, and multi-screw extruders equipped with multiple screws (e.g., twin-screw extruders equipped with twin screws), (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, it is preferable to use a kneader as the melt-mixing apparatus because it can continuously mix the first mixture and is easy to scale up, 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. In other words, it is preferable that the first melt-mixing step is a step of melt-mixing the first mixture using a twin-screw extruder.

[0088] 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.

[0089] The molten compound of the first mixture obtained in the first molten compounding step is a branched polypropylene resin.

[0090] (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 (a) linear polypropylene resin, (b) monomer N (conjugated diene, etc.), and (c) radical polymerization initiator to obtain the first mixture are not particularly limited, and examples include the following methods (m1) to (m4): (m1) A method for preparing a first mixture by simultaneously or in any order mixing an unmelted linear polypropylene resin, monomer N (such as a conjugated diene), and a radical polymerization initiator; (m2) A method for preparing a first mixture by introducing unmelted linear polypropylene resin into an apparatus and melting and kneading the linear polypropylene resin. Then, monomer N (such as a conjugated diene) and a radical polymerization initiator are added simultaneously or separately to the partially or completely melted and kneaded linear polypropylene resin; (m3) 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 monomer N (conjugated diene, etc.) to the partially or completely melt-kneaded linear polypropylene resin and radical polymerization initiator; and (m4) A method for preparing a first mixture by simultaneously or separately introducing unmelted linear polypropylene resin and monomer N (conjugated diene, etc.) into an apparatus and melt-kneading the linear polypropylene resin and monomer N (conjugated diene, etc.). Subsequently, a radical polymerization initiator is added to the partially or completely melt-kneaded polypropylene resin and monomer N (conjugated diene, etc.) to prepare the first mixture.

[0091] Methods (m2) to (m4) 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 (m2) to (m4) 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, monomer N (conjugated diene, etc.) is highly volatile, so it is desirable to add it in a state that does not release. For this reason, the melt-kneading process is more preferably (m3) 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 monomer N (such as a conjugated diene) to a linear polypropylene resin and a radical polymerization initiator that have been partially or completely melt-kneaded.

[0092] (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.

[0093] (3-2. 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.

[0094] (Second melting and mixing process) The second melt-mixing step can also be described as a step in 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 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. Specific examples of the second melt-mixing step include, for example, the following methods (n1) to (n3): (n1) A method of preparing a composition by mixing or blending a branched polypropylene resin, a foaming agent, and optionally other resins, bubble nucleating agents, and other components, and then melt-kneading the composition; (n2) 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; (n3)(n3-1) 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; (n3-2) A method of preparing a composition by adding a blowing agent to the obtained second mixture and further melt-kneading the composition.

[0095] In any of the methods (n1) to (n3) 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.

[0096] The second melt-kneading step may further include, for example, a step of melt-kneading the composition using the methods (n1) to (n3) described above, and then lowering the temperature of the melt-kneaded composition within a temperature range in which the melt-kneaded composition does not solidify.

[0097] 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.

[0098] The apparatus that may be used in the second 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 has already been described in the section on the first melt-kneading step.

[0099] 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 melt-mixing device. 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.

[0100] (Foaming agent) The blowing agents that can be used in this manufacturing method are not particularly limited as long as they are blowing agents commonly used in extrusion foaming. Examples of such blowing agents include physical blowing agents such as (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) water; and chemical blowing agents including thermal decomposition type blowing agents such as sodium bicarbonate, azodicarbonamide, and dinitrosopentamethylenetetramine.

[0101] 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. In other words, it is preferable that the blowing agent contains carbon dioxide. Furthermore, due to the lower production costs and environmental impact, it is preferable to use only carbon dioxide as the blowing agent and to substantially not contain any other 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 parts by weight or less, and particularly preferably 0 parts by weight, per 100 parts by weight of the composition.

[0102] The amount of blowing agent used in the second melt-kneading step is preferably 0.5 to 7.0 parts by weight, more preferably 0.5 to 6.0 parts by weight, even 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. Furthermore, if the bulk density of the target extruded foam particles is in the range of 100 g / L to 600 g / L, the amount of blowing agent used in the second melt-kneading step is preferably 0.5 to 3.0 parts by weight, more preferably 1.0 to 3.0 parts by weight, even more preferably 1.5 to 2.5 parts by weight, and even more preferably 1.5 to 2.0 parts by weight, per 100.0 parts by weight of the second mixture. Furthermore, when the bulk density of the target extruded foam particles is in the range of 45 g / L to 100 g / L, the amount of foaming agent used in the second melt-kneading step is preferably 3.0 to 7.0 parts by weight, more preferably 4.0 to 6.0 parts by weight, and even more preferably 5.0 to 6.0 parts by weight, per 100.0 parts by weight of the second mixture.

[0103] (Extrusion process) The foaming process may further include an extrusion process 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 process, the molten and kneaded composition may be extruded into the gas phase or into the liquid phase.

[0104] (Shredding process) The foaming step may further include a shredding step for shredding the composition extruded in the extrusion step. In the extrusion step, the composition extruded through a die provided in the apparatus, for example, into a region where the pressure is lower than the pressure inside the apparatus, immediately begins to foam. In the shredding step, 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 step can also be described as a step of shredding the composition into parts to prepare polypropylene resin extruded foam particles.

[0105] 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.

[0106] [4. Polypropylene-based foamed molded articles] A polypropylene resin foam molded article according to one embodiment of the present invention is a foam molded article comprising extruded foam particles containing a base resin having a branched structure, wherein the open-cell ratio of the extruded foam particles is 15.0% or less, the density (X) of the foam molded article is 60 g / L to 300 g / L, and the tensile elongation at break (Y) of the foam molded article satisfies the following formula (1): Y > 0.005 × X 2 -0.25 × X + 38 (1).

[0107] In this specification, "a polypropylene-based resin foamed molded article according to one embodiment of the present invention" may be referred to as "the foamed molded article."

[0108] The following describes various aspects of this foamed molded product. However, for matters other than those described in detail below (for example, the base resin and the open-cell ratio), refer to the descriptions in sections [2. Polypropylene-based resin extruded foam particles] and [3. Method for producing polypropylene-based resin extruded foam particles] as appropriate.

[0109] A polypropylene-based resin foam molded article according to one embodiment of the present invention has the above-described structure and has the advantage of excellent fracture resistance in a specific density range.

[0110] The method for producing a polypropylene-based resin foamed molded article according to one embodiment of the present invention, that is, the method for molding extruded foam particles, is not particularly limited, and for example, a known in-mold foaming method can be employed.

[0111] (Density of the foamed molded product (X)) The density (X) of the foamed molded article is 60 g / L to 300 g / L, preferably 65 g / L to 300 g / L, more preferably 70 g / L to 300 g / L, even more preferably 75 g / L to 250 g / L, and particularly preferably 75 g / L to 200 g / L. According to the above configuration, the foamed molded article has the advantage of being superior in characteristics such as arbitrariness of shape, cushioning properties, lightness, and heat insulation.

[0112] In this specification, the density (X) of a polypropylene resin foam molded article is calculated by performing the following steps in order: (1) measuring the weight Ws (g) of the foam molded article; (2) measuring the length, width, and thickness of the foam molded article with calipers, and the volume Vs (cm³) of the foam molded article. 3 (3) Calculate the density of the foamed molded body using the following formula: The density of a foamed molded product (X) (g / L) = Ws / Vs × 1000.

[0113] (Tensile elongation at break (Y)) A higher tensile elongation at break (Y) (%) of the foamed molded article is preferable. A higher tensile elongation at break (Y) (%) of the foamed molded article indicates superior fracture resistance.

[0114] In this specification, the tensile elongation at break (Y) (%) of a polypropylene resin foam molded article shall be the value obtained from the results of a tensile test conducted on the foam molded article as a sample in accordance with ISO 1798. Specifically, in a tensile test using a foam molded article, the value of the tensile elongation at the time the foam molded article breaks is measured and defined as the tensile elongation at break (Y) (%) of the foam molded article.

[0115] A polypropylene resin foamed molded article according to another embodiment of the present invention may have the following configuration: A foamed molded article obtained by molding polypropylene resin extruded foamed particles described in section [2. Polypropylene Resin Extruded Foamed Particles] or polypropylene resin extruded foamed particles obtained by the manufacturing method described in section [3. Method for Manufacturing Polypropylene Resin Extruded Foamed Particles], wherein the open-cell ratio of the polypropylene resin extruded foamed particles is 15.0% or less, the density (X) of the foamed molded article is 60 g / L to 300 g / L, and the tensile elongation at break (Y) of the foamed molded article satisfies the following formula (1): Y > 0.005 × X 2 -0.25 × X + 38 (1).

[0116] [1] Polypropylene resin extruded foam particles containing a base resin having a branched structure, wherein the base resin satisfies all of the following conditions (i) to (iii): (i) The melting point Tm1 is 130.0°C or higher and less than 143.0°C. Here, the melting point Tm1 is a value obtained by differential scanning calorimetry; (ii) The melt elongation is 3.0 m / min to 30.0 m / min, Here, the melt elongation is a value determined by measuring the melt tension at 230°C; and (iii) The melt flow rate (MFR) is between 1.0 g / 10 min and 20.0 g / 10 min. Here, the MFR is a value obtained by measurement under conditions of 230°C and 2.16 kg load, in accordance with ISO 1133.

[0117] [2] The polypropylene resin extruded foam particles described in [1] satisfy the following conditions (iv) and (v): (iv) The bulk density is 45 g / L to 600 g / L; and (v) The open-cell ratio is 10.0% or less.

[0118] [3] The polypropylene resin having the branched structure comprises a constituent unit derived from one or more monomers N selected from the group consisting of conjugated dienes and vinyl aromatic compounds, as described in [1] or [2].

[0119] A method for producing polypropylene resin extruded foam particles according to any one of [4] [1] to [3], comprising: a preparation step for preparing a polypropylene resin having a branched structure; and an extrusion foaming step for preparing the polypropylene resin extruded foam particles, wherein 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 N selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator; and the extrusion foaming step comprises a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin having a branched structure and a foaming agent.

[0120] [5] The method for producing polypropylene resin extruded foam particles according to [4], wherein the melting point Tm2 of the linear polypropylene resin (a) is 125.0°C to 148.0°C.

[0121] [6] The method for producing polypropylene resin extruded foam particles according to [4] or [5], wherein the linear polypropylene resin (a) is a random copolymer formed by randomly bonding propylene units with one or more comonomer units selected from the group consisting of 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.

[0122] [7] A method for producing polypropylene resin extruded foam particles according to any one of [4] to [6], wherein the MFR of the linear polypropylene resin in (a) is 0.5 g / 10 min to 22.0 g / 10 min.

[0123] [8] The method for producing polypropylene resin extruded foam particles according to any one of [4] to [7], wherein the monomer N in (b) contains isoprene.

[0124] [9] The method for producing polypropylene resin extruded foam particles according to any one of [4] to [8], wherein the amount of monomer N (b) 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 (a).

[0125]

[10] The method for producing polypropylene resin extruded foam particles according to any one of [4] to [9], wherein the (c) radical polymerization initiator comprises at least one of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate.

[0126]

[11] The method for producing polypropylene resin extruded foam particles according to any one of [4] to

[10] , wherein the amount of the (c) 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 (a) linear polypropylene resin.

[0127]

[12] A method for producing polypropylene resin extruded foam particles according to any one of [4] to

[11] , wherein in the first melt-kneading step, the ratio of the amount of monomer N used to the amount of radical polymerization initiator used (c) (amount of monomer N used / amount of radical polymerization initiator used) is 0.05 to 5.00.

[0128]

[13] The foaming agent contains carbon dioxide, The method for producing polypropylene resin extruded foam particles according to any one of [4] to

[12] , wherein the amount of the foaming agent used in the second melt-kneading step is 0.5 to 7.0 parts by weight per 100.0 parts by weight of the second mixture.

[0129]

[14] A method for producing polypropylene resin extruded foam particles according to any one of [4] to

[13] , wherein the first melt-kneading step is a step of melt-kneading the first mixture using a twin-screw extruder.

[0130] A foamed molded article made by molding polypropylene resin extruded foam particles described in any one of [1] to [3], or polypropylene resin extruded foam particles obtained by a method for producing polypropylene resin extruded foam particles described in any one of [4] to

[14] , wherein the open-cell ratio of the polypropylene resin extruded foam particles is 15.0% or less, the density (X) of the foamed molded article is 60 g / L to 300 g / L, and the tensile elongation at break (Y) of the foamed molded article satisfies the following formula (1): Y > 0.005 × X 2 -0.25 × X + 38 (1).

[0131]

[16] A foamed molded article comprising extruded foamed particles containing a base resin having a branched structure, wherein the open-cell ratio of the extruded foamed particles is 15.0% or less, the density (X) of the foamed molded article is 60 g / L to 300 g / L, and the tensile elongation at break (Y) of the foamed molded article satisfies the following formula (1): Y > 0.005 × X 2 -0.25 × X + 38 (1). [Examples]

[0132] 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.

[0133] (Test method) The test methods used to measure and evaluate various physical properties in the examples and comparative examples are as follows:

[0134] The extruded foam particles obtained in each example and comparative example were returned to the resin using the following method, and the melting point, melt elongation, and MFR were measured using the following method. The resulting values ​​were defined as the melting point Tm1, melt elongation, and MFR of the base resin, respectively.

[0135] (Resin return) The following steps (b1) to (b5) were performed in order to return the resin: (b1) The extruded foam particles obtained in each example and comparative example were placed in a dryer with the temperature adjusted to 160°C; (b2) 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 5 to 10 minutes; (b3) After that, the extruded foam particles were left in the dryer for 30 minutes to prepare a resin mass (returned resin); (b4) Then, after the temperature inside the dryer was cooled to room temperature, the pressure inside the dryer was returned to atmospheric pressure; (b5) 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.

[0136] [Melting point of the base resin (Tm1)] The melting point Tm1 of the base resin was determined by differential scanning calorimetry using the returned resin as a sample. A Seiko Instruments DSC6200 differential scanning calorimetry instrument was used. The method for measuring the melting point Tm1 of the base resin by differential scanning calorimetry was as follows: (1) The sample (returned resin) was melted by raising its temperature from 40°C to 220°C at a heating rate of 10°C / min; (2) The resulting sample was then crystallized by lowering its 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 temperature of the peak (melting peak) of the DSC curve of the sample (returned resin) obtained during the second heating (i.e., at step (3)) was taken as the melting point Tm1 of the base resin. The results are shown in Tables 1 and 2.

[0137] [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 at which the strand-shaped sample (return resin) broke was recorded; (7) The same operation was repeated four more times (a total of five times), and the arithmetic mean of the take-up speeds for n=5 was taken as the melt elongation of the base resin.

[0138] [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.

[0139] [DSC curve of extruded foamed particles] Using a differential scanning calorimeter (Seiko Instruments Inc., DSC6200 model), 5-6 mg of polypropylene resin extruded foam particles were heated from 40°C to 220°C at a heating rate of 10°C / min. The DSC curve obtained during this heating process was defined as the DSC curve for the polypropylene resin extruded foam particles.

[0140] [Bulk density of extruded foam particles] The bulk density of the polypropylene resin extruded foam particles was calculated by following steps (1) to (3) in order: (1) The polypropylene resin extruded foam particles were placed into a measuring cup of approximately 1 L, whose internal volume Vk (L) had been accurately measured in advance, until it overflowed; (2) The powder surface (top edge) of the container was leveled, and the weight Wb (g) of the polypropylene resin extruded foam particles inside the container was measured; (3) The bulk density of the polypropylene resin extruded foam particles was calculated using the following formula: Bulk density (g / L) = Weight of foamed particles Wb (g) / Volume of container Vk (L).

[0141] [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 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.

[0142] [Density of foamed molded material (X)] The density (X) of the obtained polypropylene resin foam molded article was calculated by performing the following steps in order: (1) the weight Ws (g) of the foam molded article was measured; (2) the length, width, and thickness of the foam molded article were measured with calipers, and the volume Vs (cm³) of the foam molded article was measured. 3 (3) The density of the foamed molded product was calculated using the following formula: The density of a foamed molded product (X) (g / L) = Ws / Vs × 1000.

[0143] [Tensile elongation at break (Y)] The tensile elongation at break (Y) (%) of the obtained polypropylene resin foam molded article was determined from the results of tensile tests conducted on the foam molded article as a sample, in accordance with ISO 1798. Specifically, the tensile elongation value at which the sample broke was measured in the tensile test using the sample, and this was defined as the tensile elongation at break (Y) (%) of the foam molded article. The results are shown in Tables 1 and 2.

[0144] [Fracture resistance evaluation] Based on the tensile elongation at break obtained by the measurement method described above, the fracture resistance of each foamed molded article was evaluated according to the following criteria. The results are shown in Tables 1 and 2. ○ (Good): Let X be the density of the foamed molded material (g / L) and Y be the tensile elongation at break of the foamed molded material (%), where Y > 0.0005 × X 2 The equation -0.25 × X + 38 is satisfied. × (Defective): Let X be the density of the foamed molded material (g / L) and Y be the tensile elongation at break of the foamed molded material (%), where Y > 0.0005 × X 2 -0.25 × X + 38 is not satisfied.

[0145] (material) The following materials were used in the examples and comparative examples.

[0146] (Linear polypropylene resin) PP-1; Prime Polymer Random Polypropylene (F-744NP) (Melting point 133.8°C, MFR 7.0°C) PP-2; Prime Polymer Random Polypropylene (E237J) (Melting Point 140.3°C, MFR 7.0°C) PP-3; Prime Polymer Random Polypropylene (F227D) (Melting Point 139.8°C, MFR 7.0°C) PP-4; Prime Polymer Random Polypropylene (F-724NPC) (Melting point 148.8°C, MFR 7.0°C) PP-5; Prime Polymer Random Polypropylene (E309M) (Melting Point 148.5°C, MFR 9.0°C) PP-6; Prime Polymer Random Polypropylene (E228) (Melting Point 144.3°C, MFR 9.0°C) PP-7; Prime Polymer Random Polypropylene (B241) (Melting Point 140.5°C, MFR 0.5°C) (Monomer N (conjugated diene, etc.)) Isoprene (Radical polymerization initiator) t-Butyl peroxyisopropyl carbonate (manufactured by NOF Corporation, Perbutyl I) (Bubble nucleation regulator) Talc (manufactured by Hayashi Chemical Co., Ltd., PK-S).

[0147] (Example 1) (Preparation process) (a) 100 parts by weight of PP-1 (Prime Polymer Random Polypropylene (F-744NP, melting point Tm2: 133.8℃ as measured by the method described above)) as a linear polypropylene resin, and (c) 1.0 part by weight of t-butyl peroxyisopropyl carbonate (NOF Corporation, Perbutyl I) as a radical polymerization initiator, were mixed and supplied from the hopper to a 45 mmφ twin-screw extruder (L / D=40) at a rate of 70 kg / hour. Next, the raw materials in the extruder were 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 from a press-in section installed in the middle of the extruder using a metering pump at a ratio of 0.3 parts by weight per 100 parts by weight of (a) linear polypropylene resin, thereby preparing (completing) the first mixture in the extruder (first mixture preparation step). Next, the first mixture in the extruder was further melt-kneaded to obtain a melt-kneaded product of the first mixture, i.e., a branched polypropylene resin (first melt-kneading step). Subsequently, the branched polypropylene resin was extruded in strand form through a die provided in the apparatus. Next, the extruded strand-shaped branched polypropylene resin was water-cooled and shredded to obtain pellets of branched polypropylene resin (extrusion step).

[0148] (Extrusion foaming process) Next, a mixture (second mixture) obtained by mixing 100 parts by weight of the obtained branched polypropylene resin with 0.2 parts by weight of talc (PK-S manufactured by Hayashi Chemical Co., Ltd.) was supplied from the hopper to a 15 mmφ twin-screw extruder (L / D=30) at a rate of 1.0 kg / hour. Then, the second mixture in the extruder was melt-kneaded at a cylinder temperature of 200°C and a rotation speed of 100 rpm, and carbon dioxide gas, 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, thereby preparing (completing) the composition in the extruder. Next, the composition in the extruder was further melt-kneaded to obtain a melt-kneaded product of the composition (second melt-kneading step).

[0149] Furthermore, the molten mixture of the composition was cooled by passing it through a static mixer connected to the tip of a twin-screw extruder and set to 155°C. Subsequently, the molten mixture of the composition was extruded under atmospheric pressure and foamed (extrusion process) through a die with two 0.7 mm diameter holes attached to the tip of the static mixer, and then cut by a rotary cutter attached to the tip of the die (shredding process). Through this series of operations, polypropylene resin extruded foam particles were obtained.

[0150] Using the obtained extruded foam particles, the melting point Tm1, melt elongation, and MFR of the base resin were measured using the method described above. The results are shown in Table 1. In addition, the bulk density and open-cell ratio of the obtained extruded foam particles were evaluated using the method described above. The results are shown in Table 1.

[0151] Furthermore, using a Daisen Corporation molding machine (KD345), the obtained extruded foam particles 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%), 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 the mold was heated and molded for 10 seconds using steam with a vapor pressure of 0.20 MPa (gauge pressure) to obtain a foamed polypropylene resin molded body.

[0152] The obtained foamed molded bodies were cured in a 75°C curing chamber for 24 hours, and then left at room temperature for 4 hours. The density (X) and tensile elongation at break (Y) of the foamed molded bodies were measured using the method described above to evaluate their fracture resistance. The results are shown in Table 1.

[0153] (Examples 2-5 and Comparative Examples 1-8) In Example 1, branched polypropylene resin pellets were obtained in the same manner as in Example 1, except that (a) the linear polypropylene resin used was one of the resins shown in Table 1 or 2, and (c) the amounts of the radical polymerization initiator and (b) the conjugated diene monomer (isoprene) were changed as described in Table 1 or 2.

[0154] 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 replaced with the branched polypropylene resin obtained in each example and comparative example. In Comparative Examples 6 and 8, the molten mixture extruded from the die did not foam sufficiently, so no further evaluation was performed.

[0155] (Example 6) Polypropylene resin extruded foam particles were obtained in the same manner as in Example 1, except that the amount of carbon dioxide used as a foaming agent was changed to 1.0 part by weight per 100 parts by weight of polypropylene resin.

[0156] (Comparative Example 9) 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 replaced with the branched polypropylene resin obtained in Comparative Example 1, and the amount of carbon dioxide used as a foaming agent was changed to 1.0 part by weight per 100 parts by weight of polypropylene resin.

[0157] (Comparative Example 10) 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 replaced with the branched polypropylene resin obtained in Comparative Example 3, and the amount of carbon dioxide used as a foaming agent was changed to 1.0 part by weight per 100 parts by weight of polypropylene resin.

[0158] In Examples 2-6 and Comparative Examples 1-10, the melting point Tm1, melt elongation, and MFR of the base resin were measured using the obtained extruded foam particles in the same manner as in Example 1, by the method described above. The results are shown in Table 1 or 2. In addition, the bulk density and open-cell ratio of the obtained extruded foam particles were evaluated using the same method as in Example 1, by the method described above. The results are shown in Table 1 or 2.

[0159] In Examples 2-6 and Comparative Examples 1-10, polypropylene resin foam molded articles were obtained in the same manner as in Example 1, except that the molding pressure was changed as shown in Table 1 or 2, using the obtained extruded foam particles. Next, the density (X) and tensile elongation at break (Y) of the foam molded articles, which had been cured and left at room temperature in the same manner as in Example 1, were measured in the same manner as in Example 1, and the fracture resistance was evaluated. The results are shown in Table 1 or 2. In Comparative Examples 5 and 7, the obtained extruded foam particles did not expand sufficiently, and satisfactory foam molded articles could not be obtained, so further evaluation was not performed.

[0160] Furthermore, in all of the extruded foam particles of Examples 1 to 6, there was only one melting peak in the DSC curve of the return resin of the extruded foam particles. That is, in the DSC curves of the return resin of the extruded foam particles of Examples 1 to 6, the heat of fusion at the peak with the largest heat of fusion was equal to the total heat of fusion.

[0161] Furthermore, in all of the extruded foamed particles of Examples 1 to 6, the DSC curve of the extruded foamed particles showed only one peak representing the amount of heat accounting for 15% or more of the total heat of fusion (100%), meaning there was only one crystal peak. [Table 1]

[0162] [Table 2] The results shown in Table 1 show that, as demonstrated in the examples, (a) extruded foam particles, which have a specific Tm2 as a linear polypropylene resin and whose melting point Tm1, melt elongation, and MFR of the base resin (A) are within the range of the embodiment of the present invention due to the formulation of the initiator and isoprene used during modification, have a low open-cell ratio, and the foam molded articles formed from them exhibit better fracture resistance.

[0163] In contrast, Comparative Examples 1-4 and 4, in which the melting point Tm1 falls outside the range of the embodiment of the present invention, 9 ~10 In this case, it is evident that the foamed molded product has poor fracture resistance.

[0164] Furthermore, in Comparative Example 5, where the amount of initiator used during modification was small and the degree of modification was insufficient, the open-cell ratio of the extruded foamed particles was high, indicating that good molding could not be achieved.

[0165] Furthermore, in Comparative Example 6, where the MFR of the modified polypropylene resin is low and falls outside the range of the embodiment of the present invention, it is clear that good extruded foam particles themselves cannot be obtained.

[0166] Furthermore, in Comparative Example 7, where the MFR and melt elongation of the modified polypropylene resin fall outside the range of the embodiment of the present invention, the open-cell ratio of the extruded foamed particles is high, and good molding cannot be achieved.

[0167] Furthermore, in Comparative Example 8, where the MFR and melt elongation of the modified polypropylene resin fall outside the range of the embodiment of the present invention, it is clear that good extruded foam particles themselves cannot be obtained. [Industrial applicability]

[0168] According to one embodiment of the present invention, polypropylene resin extruded foam particles can be provided that can provide a polypropylene resin foam molded article with excellent fracture resistance. Therefore, one embodiment of the present invention can be suitably used in fields such as automotive interior components, cushioning materials, packaging materials, and heat insulating materials.

Claims

1. The base resin contains a polypropylene resin having a branched structure, The polypropylene resin having the branched structure includes a structure derived from a linear polypropylene resin and constituent units derived from a conjugated diene. The content of the constituent units derived from the conjugated diene in the polypropylene resin having the branched structure is 0.3 to 0.6 parts by weight per 100 parts by weight of the structure derived from the linear polypropylene resin. The aforementioned base resin is polypropylene resin extruded foam particles that satisfy all of the following conditions (i) to (iii): (i) Melting point Tm １ The temperature is between 130.0°C and 142.5°C. Here, the melting point Tm １ This is a value obtained by differential scanning calorimetry; (ii) The melt elongation is 3.0 m / min to 30.0 m / min, Here, the melt elongation is a value determined by measuring the melt tension at 230°C; and (iii) The melt flow rate (MFR) is between 1.0 g / 10 min and 20.0 g / 10 min. Here, the MFR is a value obtained by measurement under conditions of a temperature of 230°C and a load of 2.16 kg, in accordance with ISO 1133.

2. The polypropylene resin extruded foam particles described above satisfy the following (iv) and (v): (iv) The bulk density is 45 g / L to 600 g / L; and (v) The open cell ratio is 10.0% or less.

3. A method for producing polypropylene resin extruded foam particles, The process comprises a preparation step for preparing a polypropylene resin having a branched structure, and an extrusion foaming step for preparing extruded foam particles of the polypropylene resin. The preparation step includes a first melt-kneading step of melt-kneading a first mixture containing (a) a linear polypropylene resin, (b) a conjugated diene, and (c) a radical polymerization initiator. The extrusion foaming step includes a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin having the branched structure and a foaming agent, The melting point Tm2 of the linear polypropylene resin (a) is 125.0°C to 143.0°C. A method for producing polypropylene resin extruded foam particles, wherein the amount of (b) conjugated diene used in the first melt-kneading step is 0.3 to 0.6 parts by weight per 100 parts by weight of the (a) linear polypropylene resin: Here, the polypropylene resin extruded foam particles include a base resin containing a polypropylene resin having a branched structure. The aforementioned base resin satisfies all of the following conditions (i) to (iii): (i) The melting point Tm 1 is 130.0°C or higher and 142.5°C or lower. Here, the melting point Tm 1 is a value obtained by differential scanning calorimetry; (ii) The melt elongation is 3.0 m / min to 30.0 m / min, Here, the melt elongation is a value determined by measuring the melt tension at 230°C; and (iii) The melt flow rate (MFR) is between 1.0 g / 10 min and 20.0 g / 10 min. Here, the MFR is a value obtained by measurement under conditions of a temperature of 230°C and a load of 2.16 kg, in accordance with ISO 1133.

4. The method for producing polypropylene resin extruded foam particles according to claim 3, wherein the linear polypropylene resin (a) is a random copolymer formed by randomly bonding propylene units with one or more comonomer units selected from the group consisting of 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.

5. The method for producing polypropylene resin extruded foam particles according to claim 3 or 4, wherein the MFR of the linear polypropylene resin (a) is 0.5 g / 10 min to 22.0 g / 10 min.

6. The method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 5, wherein the conjugated diene (b) contains isoprene.

7. The method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 6, wherein the (c) radical polymerization initiator comprises at least one of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate.

8. A method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 7, wherein the amount of the radical polymerization initiator (c) 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 (a).

9. A method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 8, wherein in the first melt-kneading step, the ratio of the amount of (b) conjugated diene used to the amount of (c) radical polymerization initiator used (amount of (b) conjugated diene used / amount of (c) radical polymerization initiator used) is 0.05 to 5.

00.

10. The foaming agent contains carbon dioxide, The method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 9, wherein the amount of the foaming agent used in the second melt-kneading step is 0.5 to 7.0 parts by weight per 100.0 parts by weight of the second mixture.

11. The method for producing polypropylene resin extruded foam particles according to any one of claims 3 to 10, wherein the first melt-kneading step is a step of melt-kneading the first mixture using a twin-screw extruder.

12. A foamed molded article obtained by molding polypropylene resin extruded foam particles according to claim 1 or 2, The open-cell ratio of the polypropylene resin extruded foam particles is 15.0% or less. The density (X) of the foamed molded body is 60 g / L to 300 g / L, and The tensile elongation at break (Y) of the foamed molded article satisfies the following equation (1): Y>0.0005×X ２ -0.25×X+38・・・(1)。

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