Polypropylene resin foam particles, polypropylene resin foam molded body, and method for producing polypropylene resin foam particles

Abstract

The present invention addresses the problem of providing polypropylene resin foam particles which enable the achievement of a polypropylene resin foam molded body that contains a recycled resin and has excellent degree of blackness and excellent flame retardancy. The present invention provides polypropylene resin foam particles which contain carbon black and a base material resin that contains a predetermined amount of a recycled resin, wherein the ratio of the number of carbon black having a structure size per one structure of less than 1 × 104 nm2 to the total number of the carbon black is 10% to 50%.

Description

Polypropylene-based resin expanded beads, polypropylene-based resin expanded molded product, and method for producing polypropylene-based resin expanded beads

[0001] The present invention relates to expanded polypropylene resin beads, expanded molded polypropylene resin articles, and a method for producing expanded polypropylene resin beads.

[0002] BACKGROUND ART Polypropylene resin foam molded articles are used in a variety of applications, including automobile interior components, core materials for automobile bumpers, heat insulating materials, cushioning packaging materials, and returnable containers (see, for example, Patent Document 1).

[0003] In recent years, in order to reduce the environmental load, there has been a demand for using recycled resins when producing resin products, and the use of recycled resins has been attracting attention (for example, Patent Document 2).

[0004] Patent Document 1: WO2006 / 075491 Patent Document 2: JP2011-173273A

[0005] However, when a polypropylene-based resin foam molded article was produced using recycled polypropylene-based resin, the polypropylene-based resin foam molded article was not satisfactory in terms of blackness and flame retardancy, and there was room for further improvement.

[0006] One embodiment of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide expanded polypropylene-based resin particles that contain recycled resin and can provide expanded polypropylene-based resin molded articles that have excellent blackness and flame retardancy.

[0007] The expanded polypropylene resin beads according to one embodiment of the present invention are expanded polypropylene resin beads containing a base resin and carbon black, wherein the base resin contains a non-recycled polypropylene resin and a recycled polypropylene resin and / or a recycled polyethylene resin, the total content of the recycled polypropylene resin and the recycled polyethylene resin is 10 parts by weight to 60 parts by weight per 100 parts by weight of the base resin, and the carbon black has a structure size of 1 x 10 per structure relative to the total number of the carbon black. ４ nm２ The ratio of the number of carbon black particles that is less than 10% to 50%.

[0008] A method for producing expanded polypropylene resin beads according to one embodiment of the present invention comprises mixing a non-recycled polypropylene resin, a recycled material, and a polypropylene-based resin having an average structure size of 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ and carbon black A having an average structure size of less than 5.0 × 10 to obtain polypropylene-based resin particles; a dispersing step of dispersing the polypropylene-based resin particles, an aqueous dispersion medium, and a blowing agent in a container; a heating step of heating the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles; a pressurizing step of increasing the pressure in the container; and a discharging step of releasing one end of the container to discharge the dispersion in the container into a region having a pressure lower than the pressure in the container, wherein the recycled material is a recycled polypropylene-based resin and / or a recycled polyethylene-based resin and a polypropylene-based resin having an average structure size of less than 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ and carbon black B having an average molecular weight of less than 10 ...

[0009] An embodiment of the present invention includes the following features:

[0010] According to one embodiment of the present invention, it is possible to provide expanded polypropylene resin particles that contain recycled resin and can provide expanded polypropylene resin molded articles that are excellent in blackness and flame retardancy.

[0011] 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 the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0012] In this specification, a "structural unit derived from an X monomer" contained in a polymer, copolymer, or resin may be referred to as an "X unit."

[0013] Unless otherwise specified in this specification, the structural unit is X １ Units and X ２ Units, ... and X ｎ A copolymer containing units (n is an integer of 2 or more) is referred to as "X １ / X ２ / ・・・ / X ｎ Also referred to as "copolymer". X １ / X ２ / ・・・ / X ｎ Unless otherwise specified, the polymerization mode of the copolymer is not particularly limited, and the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

[0014] [1. Expanded Polypropylene Resin Beads] Expanded polypropylene resin beads according to one embodiment of the present invention are expanded polypropylene resin beads containing a base resin and carbon black, wherein the base resin contains a non-recycled polypropylene resin and a recycled polypropylene resin and / or a recycled polyethylene resin, the total content of the recycled polypropylene resin and the recycled polyethylene resin is 10 parts by weight to 60 parts by weight per 100 parts by weight of the base resin, and the carbon black has a structure size of 1 x 10 per structure relative to the total number of the carbon black. ４ nm ２ The ratio of the number of carbon black particles that is less than 10% to 50%.

[0015] The expanded polypropylene resin beads according to one embodiment of the present invention can be molded by a known method to provide an expanded polypropylene resin molded article.

[0016] In this specification, "expanded polypropylene resin beads" may be referred to as "expanded beads," "expanded polypropylene resin beads according to one embodiment of the present invention" may be referred to as "the present expanded beads," and "expanded polypropylene resin molded body" may be referred to as "expanded molded body."

[0017] The present expanded beads, having the above-described structure, have the advantage of being able to provide foamed molded articles with excellent blackness and flame retardancy. Furthermore, as described above, the present expanded beads contain recycled polypropylene-based resin and / or recycled polyethylene-based resin. Therefore, the present expanded beads can be said to have a low environmental impact. In other words, because one embodiment of the present invention uses recycled polypropylene-based resin and / or recycled polyethylene-based resin, one embodiment of the present invention not only reduces environmental pollution but also significantly reduces the amount of plastic waste generated and the amount of plastic used in manufacturing. As a result, one embodiment of the present invention can contribute to the achievement of, for example, Sustainable Development Goals (SDGs) Goal 12, "Ensure sustainable consumption and production patterns," and Goal 14, "Conserve and sustainably use the oceans and marine resources for sustainable development."

[0018] <Components> (2-1. Base Resin) In this specification, the base resin refers to the resin component that substantially constitutes the polypropylene-based resin particles, the expanded polypropylene-based resin particles, and the expanded polypropylene-based resin molded article. The base resin includes at least a non-recycled polypropylene-based resin, a recycled polypropylene-based resin, and / or a recycled polyethylene-based resin.

[0019] In this specification, the term "polypropylene resin" refers to a resin containing 50 mol % or more of propylene units out of 100 mol % of all structural units constituting the resin.

[0020] In this specification, a "structural unit derived from a propylene monomer" may also be referred to as a "propylene unit."

[0021] In this specification, the term "polyethylene resin" refers to a resin containing 50 mol % or more of ethylene units out of 100 mol % of all structural units constituting the resin.

[0022] In this specification, a "structural unit derived from an ethylene monomer" may also be referred to as an "ethylene unit."

[0023] In this specification, a resin in which 100 mol % of all structural units constituting the resin are composed of 50 mol % of propylene units and 50 mol % of ethylene units is referred to as a "polypropylene-based resin."

[0024] As used herein, "recycled polypropylene resin" refers to a polypropylene resin that has been in the form of a polypropylene resin product (e.g., expanded beads, expanded molded articles, films, packaging containers such as food trays, bags, and bottles, miscellaneous goods such as clothing cases and clear files) at least once, and then reverted to the form of a polypropylene resin (or polypropylene resin particles) by melting or other means. Also, as used herein, "recycled polyethylene resin" refers to a polyethylene resin that has been in the form of a polyethylene resin product (e.g., expanded beads, expanded molded articles, films, packaging containers such as food trays, bags, and bottles, miscellaneous goods such as clothing cases and clear files) at least once, and then reverted to the form of a polyethylene resin (or polyethylene resin particles) by melting or other means. In this specification, recycled polypropylene resin or recycled polyethylene resin may also be referred to as "recycled resin," and recycled polypropylene resin and recycled polyethylene resin may also be collectively referred to as "recycled resin." Also, as used herein, "non-recycled polypropylene resin" refers to a polypropylene resin that has never been in the form of a polypropylene resin product.

[0025] The method for producing recycled resins, in other words, the method for recycling polypropylene-based resin products and polyethylene-based resin products, is not particularly limited, and any known method can be used, such as a method of crushing and melting polypropylene-based resin products or polyethylene-based resin products, or a method of shredding these products.

[0026] (Structure of Polypropylene-Based Resin) In this section only, unless otherwise specified, the term "polypropylene-based resin" refers to both non-recycled polypropylene-based resin and recycled polypropylene-based resin. The structure of the polypropylene-based resin will be described below.

[0027] The polypropylene-based resin may be (i) a homopolymer of propylene, (ii) a block copolymer, alternating copolymer, random copolymer, or graft copolymer of propylene and a monomer other than propylene, or (iii) a mixture of two or more of these.

[0028] A polypropylene-based resin may have, in addition to a propylene unit, one or more units, or may have one or more types, of structural units derived from a monomer other than a propylene monomer. A "monomer other than a propylene monomer" used in the production of a polypropylene-based resin may also be referred to as a "comonomer." A "structural unit derived from a monomer other than a propylene monomer" contained in a polypropylene-based resin may also be referred to as a "comonomer unit."

[0029] Comonomers include 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.

[0030] Specific examples of polypropylene-based resins include polypropylene homopolymers, ethylene / propylene block copolymers, 1-butene / propylene block copolymers, ethylene / 1-butene / propylene block copolymers, ethylene / propylene alternating copolymers, 1-butene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, 1-butene / propylene random copolymers, ethylene / 1-butene / propylene random copolymers, propylene / chlorinated vinyl copolymers, propylene / maleic anhydride copolymers, styrene-modified polypropylene-based resins, etc. As the polypropylene-based resin, one of these may be used alone, or two or more may be used in combination.

[0031] From the viewpoint of moldability, the non-recycled polypropylene-based resin is preferably (a) an alternating copolymer composed of propylene units and comonomer units, the two units being arranged alternately, and / or (b) a random copolymer composed of propylene units and comonomer units, the two units being arranged in a random order. Because of easy availability, the non-recycled polypropylene-based resin more preferably contains one or more copolymers selected from the group consisting of ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers.

[0032] From the viewpoints of moldability and availability, the non-recycled polypropylene resin preferably contains at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, even more preferably at least 90 wt%, and particularly preferably at least 95 wt%, of one or more selected from the group consisting of ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers, based on 100 wt% of the non-recycled polypropylene resin. Most preferably, the non-recycled polypropylene resin is composed solely of at least one selected from the group consisting of ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers.

[0033] From the viewpoint of moldability, the recycled polypropylene-based resin is preferably (a) a block copolymer composed of propylene units and comonomer units, and composed of a block structure composed only of propylene units and a block structure composed only of comonomer units, (b) an alternating copolymer composed of propylene units and comonomer units, in which both units are arranged alternately, and / or (c) a random copolymer composed of propylene units and comonomer units, in which both units are arranged in a random order. In the block copolymer, the arrangement order of the block structure composed only of propylene units and the block structure composed only of comonomer units is not particularly limited. Because of easy availability, the recycled polypropylene-based resin more preferably contains one or more copolymers selected from the group consisting of ethylene / propylene block copolymers, ethylene / 1-butene / propylene block copolymers, ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers.

[0034] From the viewpoints of moldability and availability, the recycled polypropylene resin preferably contains at least 60 wt%, more preferably at least 70 wt%, more preferably at least 80 wt%, even more preferably at least 90 wt%, and particularly preferably at least 95 wt%, of one or more copolymers selected from the group consisting of ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / propylene random copolymers, based on 100 wt% of the recycled polypropylene resin. Most preferably, the recycled polypropylene resin is composed solely of at least one copolymer selected from the group consisting of ethylene / propylene block copolymers, ethylene / 1-butene / propylene block copolymers, ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers.

[0035] (Physical Properties of Non-Recycled Polypropylene Resin) The melting point of the non-recycled polypropylene resin according to one embodiment of the present invention is not particularly limited, but is preferably 135° C. to 160° C., more preferably 137° C. to 155° C., and even more preferably 139° C. to 153° C. When the melting point of the non-recycled polypropylene resin is (i) 135° C. or higher, the expanded molded article obtained from the present expanded beads has excellent heat resistance, and (ii) when it is 160° C. or lower, it becomes easy to increase the expansion ratio of the expanded beads in the production of the present expanded beads.

[0036] In this specification, the melting point of a non-recycled polypropylene resin is a value determined by differential scanning calorimetry (hereinafter referred to as "DSC"). Specific operating procedures are as follows: (1) 5 mg to 6 mg of non-recycled polypropylene resin are melted by increasing the temperature from 40°C to 220°C at a heating rate of 10°C / min; (2) The temperature of the molten non-recycled polypropylene resin is then decreased from 220°C to 40°C at a heating rate of 10°C / min to crystallize the non-recycled polypropylene resin; (3) The temperature of the crystallized non-recycled polypropylene resin is then increased 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 non-recycled polypropylene resin obtained during the second heating (i.e., during (3)) can be determined as the melting point of the non-recycled polypropylene resin. In addition, when there are multiple peaks (melting peaks) in the DSC curve of the non-recycled polypropylene-based resin obtained by the second temperature increase method described above, the temperature of the peak (melting peak) with the largest heat of fusion is taken as the melting point of the non-recycled polypropylene-based resin. As a differential scanning calorimeter, for example, a DSC7020 manufactured by Hitachi High-Tech Science Corporation can be used.

[0037] The MFR at 230°C of the non-recycled polypropylene resin used in one embodiment of the present invention is not particularly limited, but is preferably 1 g / 10 min to 40 g / 10 min, more preferably 2 g / 10 min to 35 g / 10 min, even more preferably 3 g / 10 min to 30 g / 10 min, and particularly preferably 3 g / 10 min to 10 g / 10 min. When the non-recycled polypropylene resin has an MFR at 230°C of 1 g / 10 min or more, it tends to be easier to increase the expansion ratio of the expanded beads in the production of the expanded beads. When the non-recycled polypropylene resin has an MFR at 230°C of 40 g / 10 min or less, there is no risk of the cells in the resulting expanded beads becoming interconnected. As a result, (i) the compressive strength of the expanded molded article obtained from the expanded beads tends to be good, or (ii) the surface properties of the expanded molded article tend to be good. Note that, in this specification, the "cells" of the expanded beads may also be referred to as "cells." That is, in this specification, "air bubbles" may be read as "cells", and "cells" may be read as "air bubbles".

[0038] Consider also the case where the MFR of the non-recycled polypropylene resin at 230°C is in the range of 1 g / 10 min to 40 g / 10 min. In this case, expanded polypropylene resin beads having a relatively high expansion ratio are easily obtained. Furthermore, in this case, the expanded molded articles obtained from the expanded beads have the advantages of excellent surface appearance and low dimensional shrinkage.

[0039] In this specification, the MFR value of a non-recycled polypropylene resin at 230°C is a value obtained by measurement using an MFR measuring device described in JIS K7210:1999 under the following conditions: orifice diameter: 2.0959±0.005 mmφ, orifice length: 8.000±0.025 mm, load: 2.16 kgf, and temperature: 230°C (230±0.2°C).

[0040] (Physical Properties of Recycled Polypropylene Resin) The melting point of the recycled polypropylene resin according to one embodiment of the present invention is not particularly limited, but is preferably 135° C. to 160° C., more preferably 137° C. to 155° C., and even more preferably 139° C. to 153° C. When the melting point of the recycled polypropylene resin is (i) 135° C. or higher, the foamed molded article obtained from the expanded beads has excellent heat resistance, and (ii) when the melting point is 160° C. or lower, it becomes easy to increase the expansion ratio of the expanded beads in the production of the expanded beads.

[0041] In this specification, the melting point of the recycled polypropylene-based resin is a value determined by measurement using the above-mentioned DSC method, in the same manner as the melting point of the non-recycled polypropylene-based resin, except that the recycled polypropylene-based resin is used instead of the non-recycled polypropylene-based resin.

[0042] The MFR at 230°C of the recycled polypropylene resin used in one embodiment of the present invention is not particularly limited, but is preferably 1 g / 10 min to 40 g / 10 min, more preferably 2 g / 10 min to 35 g / 10 min, even more preferably 3 g / 10 min to 30 g / 10 min, and particularly preferably 3 g / 10 min to 10 g / 10 min. When the recycled polypropylene resin has an MFR at 230°C of (a) 1.0 g / 10 min or more, it has the advantage of facilitating the increase in the expansion ratio of the expanded beads in the production of the expanded beads, and when it is (b) 40.0 g / 10 min or less, it has the advantage of preventing the cells in the resulting expanded beads from becoming interconnected.

[0043] In this specification, the MFR value at 230°C of the recycled polypropylene-based resin is a value obtained by measuring in the same manner as the MFR value at 230°C of the non-recycled polypropylene-based resin, except that the recycled polypropylene-based resin is used instead of the non-recycled polypropylene-based resin.

[0044] The non-recycled polypropylene resin can be obtained by a known method. The polymerization catalyst used for synthesizing the polypropylene resin is not particularly limited, and a Ziegler catalyst or the like can be used.

[0045] The base resin preferably contains 80 to 100 parts by weight, and more preferably 90 to 100 parts by weight, of polypropylene resin (non-recycled polypropylene resin and recycled polypropylene resin) per 100 parts by weight of the base resin. This configuration has the advantage of minimizing the decrease in strength of the resulting foamed molded article.

[0046] The base resin contains at least one of a recycled polypropylene resin and a recycled polyethylene resin. The base resin may further contain a non-recycled polyethylene resin. In this specification, the term "non-recycled polyethylene resin" refers to a polyethylene resin that has never been in the form of a polyethylene resin product.

[0047] (Structure of Polyethylene Resin) In this section only, unless otherwise specified, the term "polyethylene resin" refers to both non-recycled polyethylene resin and recycled polyethylene resin. The structure of the polyethylene resin will be described below.

[0048] The polyethylene resin may be (a) a homopolymer of ethylene, (b) a block copolymer, alternating copolymer, random copolymer, or graft copolymer of ethylene and a monomer other than ethylene, or (c) a mixture of two or more of these.

[0049] The polyethylene resin may have, in addition to the ethylene unit, one or more structural units derived from a monomer other than the ethylene monomer, or may have one or more types of structural units. The "structural units derived from a monomer other than the ethylene monomer" contained in the polyethylene resin may also be referred to as "comonomer units."

[0050] Examples of the comonomer include (a) α-olefins having 3 to 12 carbon atoms, such as propylene, 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, and (b) vinyl monomers, such as vinyl acetate.

[0051] Specific examples of polyethylene-based resins include (a) polyethylene homopolymers, (b) ethylene / α-olefin copolymers such as ethylene / propylene block copolymers, 1-butene / ethylene block copolymers, ethylene / 1-butene / propylene block copolymers, ethylene / propylene alternating copolymers, 1-butene / ethylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, 1-butene / ethylene random copolymers, and ethylene / 1-butene / propylene random copolymers, (c) ethylene / vinyl-based unit copolymers such as ethylene / chlorinated vinyl copolymers and ethylene / maleic anhydride copolymers, (d) styrene-modified polyethylene-based resins, and (e) chlorinated polyethylene. As the polyethylene-based resin, one of these may be used alone, or two or more may be used in combination.

[0052] From the viewpoint of differences in density, polyethylene resins also include high-density polyethylene (HDPE or PE-HD), medium-density polyethylene (MDPE or PE-MD), low-density polyethylene (LDPE or PE-LD), etc. Regarding HDPE, MDPE, and LDPE, JIS K 6760 defines the density ranges as follows: HDPE: 942 kg / m ３ Above, MDPE: 930kg / m ３ More than 942kg / m ３ Less than LPDE: 910 kg / m ３ More than 930kg / m ３ It is stipulated as less than.

[0053] Low-density polyethylene (LDPE) can be further classified into (a) low-density polyethylene produced by a high-pressure process and having long-chain branches in addition to short-chain branches such as ethyl groups (hereinafter also referred to as branched low-density polyethylene), and (b) low-density polyethylene produced using a transition metal catalyst at medium to low pressure and having short-chain branches (hereinafter also referred to as linear low-density polyethylene (LLDPE) or PE-LLD)). Branched low-density polyethylene is a polyethylene homopolymer. Linear low-density polyethylene is a copolymer obtained by linearly polymerizing ethylene and an α-olefin such as 1-butene, 1-hexene, and / or 4-methyl-1-pentene, and has short-chain branches derived from the side chains of the α-olefin. Therefore, linear low-density polyethylene can also be called an ethylene / α-olefin copolymer.

[0054] The recycled polyethylene resin may contain one or more selected from the group consisting of high-density polyethylene, medium-density polyethylene, and low-density polyethylene.

[0055] (Physical Properties of Recycled Polyethylene Resin) In one embodiment of the present invention, the melting point of the recycled polyethylene resin is not particularly limited, but is preferably 100° C. to 140° C., and more preferably 110° C. to 130° C. When the melting point of the recycled polyethylene resin is (a) 100° C. or higher, there is an advantage that the impact resistance of the foam molded article is less likely to decrease, and when it is (b) 140° C. or lower, there is an advantage that the surface elongation of the foam molded article is good.

[0056] In this specification, the melting point of the recycled polyethylene resin is a value determined by measurement using the above-mentioned DSC method, in the same manner as the melting point of the non-recycled polypropylene resin, except that a recycled polyethylene resin is used instead of a non-recycled polypropylene resin.

[0057] In one embodiment of the present invention, the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 10 to 60 parts by weight, preferably 10 to 60 parts by weight, more preferably 15 to 60 parts by weight, even more preferably 18 to 60 parts by weight, and particularly preferably 20 to 60 parts by weight, per 100 parts by weight of the base resin. This configuration has the advantage of further reducing the burden on the environment.

[0058] In one embodiment of the present invention, when the total content of the recycled polypropylene resin and the recycled polyethylene resin is taken as 100 parts by weight, (a) the recycled polypropylene resin is preferably 60 to 100 parts by weight and the recycled polyethylene resin is preferably 0 to 40 parts by weight, (b) the recycled polypropylene resin is more preferably 70 to 100 parts by weight and the recycled polyethylene resin is more preferably 0 to 30 parts by weight, (c) the recycled polypropylene resin is more preferably 80 to 100 parts by weight and the recycled polyethylene resin is more preferably 0 to 20 parts by weight, (d) the recycled polypropylene resin is even more preferably 90 to 100 parts by weight and the recycled polyethylene resin is more preferably 0 to 10 parts by weight, and (e) the recycled polypropylene resin is particularly preferably 95 to 100 parts by weight and the recycled polyethylene resin is more preferably 0 to 5 parts by weight. This configuration has the advantage of improving both the impact resistance and surface elongation of the foamed molded article.

[0059] The base resin preferably contains 80 to 100 parts by weight, more preferably 90 to 100 parts by weight, and even more preferably 95 to 100 parts by weight of polypropylene-based resin (non-recycled polypropylene-based resin and recycled polypropylene-based resin) and recycled polyethylene-based resin in total, per 100 parts by weight of the base resin. This configuration has the advantage of minimizing the decrease in strength of the resulting foamed molded article. The base resin may be composed solely of polypropylene-based resin (non-recycled polypropylene-based resin and recycled polypropylene-based resin) and recycled polyethylene-based resin.

[0060] (Other Resins, etc.) The base resin may further contain resins other than non-recycled polypropylene-based resins, recycled polypropylene-based resins, and recycled polyethylene-based resins (sometimes referred to as "other resins, etc.") to the extent that the effects of one embodiment of the present invention are not impaired. Examples of such other resins include (a) styrene-based resins such as polystyrene, styrene / maleic anhydride copolymers, and styrene / ethylene copolymers; (b) polyolefin-based waxes such as propylene-α-olefin-based waxes; and (c) olefin-based rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber, and ethylene / octene rubber. The content of such other resins is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of the total of the non-recycled polypropylene-based resin, recycled polypropylene-based resin, and recycled polyethylene-based resin.

[0061] (2-2. Carbon Black) The present expanded beads contain carbon black. More specifically, the present expanded beads have a structure size of 1×10 ４ nm ２ The carbon black contained in the expanded beads has a structure size of less than 1 x 10 per structure relative to the total number of the carbon black. ４ nm ２The proportion of carbon black particles having a size less than 10% is 10% to 50%. Through extensive research, the present inventors have independently and surprisingly found that expanded beads containing carbon black having the above-mentioned structure size within the above-mentioned range can provide a foamed molded article having excellent both blackness and flame retardancy. Through extensive research, the present inventors have independently and surprisingly found that expanded beads containing carbon black having the above-mentioned structure size within the above-mentioned range can provide a foamed molded article having excellent color unevenness.

[0062] The method for measuring the structure size of carbon black will be described in detail in the Examples below.

[0063] The carbon black is not particularly limited, and examples thereof include channel black, roller black, disc black, gas furnace black, oil furnace black, thermal black, acetylene black, etc. As the carbon black, one of these may be used alone, or two or more may be used in combination.

[0064] The shape of the carbon black is not particularly limited, and may be spherical, approximately spherical, or the like.

[0065] In the present expanded beads, the structure size per structure relative to the total number of carbon black particles is 1 x 10 ４ nm ２ The proportion of carbon black particles that are less than 10% is 10% to 50%, and preferably 15% to 30%. This configuration has the advantage that even when recycled resin is used, a foamed molded article that is excellent in color uniformity, blackness, and flame retardancy can be obtained.

[0066] In one embodiment of the present invention, in order to improve the blackness of the expanded beads and the expanded bead moldings, the average structure size is 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２In other words, the expanded beads contain carbon black A. The average structure size of carbon black A in the expanded beads is 0.2×10 ４ nm ２ Above 4.0 x 10 ４ nm ２ Preferably, it is less than 0.2 × 10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 0.5×10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 1.0 x 10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 1.5 x 10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 2.0 x 10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 2.5 x 10 ４ nm ２ 3.5 x 10 ４ nm ２ More preferably, less than 3.0 × 10 ４ nm ２ 3.5 x 10 ４ nm ２ According to this configuration, even when recycled resin is used, there is an advantage that a foamed molded article excellent in color unevenness, blackness, and flame retardancy can be obtained.

[0067] The expanded beads have an average structure size of 5.0 x 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ The carbon black B has an average structure size of less than 5.0 x 10 ４ nm ２ Above 9.0 x 10 ４ nm２ Preferably, it is less than 5.0 × 10 ４ nm ２ Above 8.0 x 10 ４ nm ２ More preferably, it is less than 5.0 × 10 ４ nm ２ 7.5 x 10 ４ nm ２ More preferably, less than 5.0 x 10 ４ nm ２ Above 7.0 x 10 ４ nm ２ More preferably, less than 5.0 x 10 ４ nm ２ 6.5 x 10 ４ nm ２ More preferably, less than 5.0 × 10 ４ nm ２ Above 6.0 x 10 ４ nm ２ According to this configuration, even when recycled resin is used, there is an advantage that a foamed molded article excellent in color unevenness, blackness, and flame retardancy can be obtained. As will be described later, the recycled material has an average structure size of 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ The carbon black may contain carbon black having a carbon content of less than 100%, i.e., carbon black B. Therefore, the carbon black B may be derived from a recycled material. Note that carbon black B may also be used separately from recycled materials.

[0068] In one embodiment of the present invention, the average structure size is 10x10 ４ nm ２ It is preferable that carbon black C having an average structure size of 10×10 or more is not used, or if used, the amount of carbon black C used is small. ４ nm ２ For example, the present expanded beads have an average structure size of 10×10 ４ nm ２Preferably, the composition does not contain carbon black C that is equal to or greater than 0 part by weight and less than 0.5 parts by weight per 100 parts by weight of the base resin. Surprisingly, during the course of extensive research, the present inventors independently obtained the novel finding that, with this configuration, a foamed molded article with improved flame retardancy can be obtained.

[0069] The content of carbon black A in the expanded beads is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 4.5 parts by weight, more preferably 0.5 to 4.3 parts by weight, even more preferably 1.0 to 4.0 parts by weight, even more preferably 1.5 to 3.5 parts by weight, still more preferably 2.0 to 3.5 parts by weight, and particularly preferably 2.5 to 3.0 parts by weight, relative to 100 parts by weight of the base resin. During the course of extensive research, the present inventors have surprisingly and independently obtained the novel finding that, according to this configuration, a foamed molded article having superior blackness can be obtained.

[0070] The content of carbon black B in the expanded beads is preferably 0.10 parts by weight to 2.00 parts by weight, more preferably 0.10 parts by weight to 1.80 parts by weight, and even more preferably 0.30 parts by weight to 1.80 parts by weight, per 100 parts by weight of the base resin. In the course of extensive research, the present inventors have surprisingly and independently obtained the novel finding that, with this configuration, a foamed molded article with improved color unevenness and flame retardancy can be obtained.

[0071] (2-3. Additives) The present expanded particles may further contain optional additives in addition to (a) non-recycled polypropylene resin, (b) recycled polypropylene resin and / or recycled polyethylene resin, and (c) carbon black A and B. Examples of additives include colorants other than carbon black, water-absorbing substances, foam nucleating agents, antistatic agents, flame retardants, antioxidants, light stabilizers, crystal nucleating agents, conductive agents, lubricants, etc. Such additives may be added directly to the blend or polypropylene resin composition described below in the production of polypropylene resin particles.

[0072] (Foam Nucleating Agent) A foam nucleating agent is a substance that can be used in the production of the present expanded beads and that can become a foam nucleus when the resin particles are expanded. It is preferable to use a foam nucleating agent in the production of the present expanded beads, in other words, it is preferable that the present expanded beads contain a foam nucleating agent. This configuration has the advantage of making the cell structure of the expanded beads uniform.

[0073] In this specification, the foam nucleating agent refers to an inorganic compound that remains as a residue when burned at 750°C for one hour or more, and is sometimes referred to as "ash" in this specification. Examples of the foam nucleating agent include silica (silicon dioxide), silicates, alumina, diatomaceous earth, calcium carbonate, magnesium carbonate, calcium phosphate, feldspar apatite, barium sulfate, and zinc borate. Examples of silicates include talc, magnesium silicate, kaolin, halloysite, dickite, aluminum silicate, and zeolite. These foam nucleating agents may be used alone or in combination of two or more. When two or more foam nucleating agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0074] In one embodiment of the present invention, the foam nucleating agent preferably contains talc, and is preferably talc, since this tends to make the cell structure of the foamed beads more uniform and reduce color unevenness of the foamed beads.

[0075] The amount of foam nucleating agent used in the production of the expanded beads, in other words, the content of the foam nucleating agent in the expanded beads, is described below. The content of the foam nucleating agent in the expanded beads refers to the total amount of foam nucleating agent in the expanded beads, including the content of foam nucleating agent in recycled materials. From the viewpoint of uniformity of the average cell diameter, the content of the foam nucleating agent in the expanded beads is preferably 0.001 to 2.00 parts by weight, more preferably 0.01 to 1.00 parts by weight, even more preferably 0.020 to 0.50 parts by weight, even more preferably 0.05 to 0.50 parts by weight, still more preferably 0.05 to 0.50 parts by weight, more preferably 0.10 to 0.50 parts by weight, even more preferably 0.20 to 0.50 parts by weight, and particularly preferably 0.20 to 0.45 parts by weight, per 100 parts by weight of the base resin. In conventional in-mold foamed articles made from expanded beads, if the talc content is 0.20 parts by weight or more, color unevenness tends to occur easily. However, in-mold foamed articles made from the present expanded beads, even if the talc content is 0.20 parts by weight or more, color unevenness does not occur and the blackness is good.

[0076] The method for identifying the type of foam nucleating agent is not particularly limited, and known qualitative analysis can be applied. Specific embodiments of the qualitative analysis of the foam nucleating agent may include, for example, a method of analyzing the ash content by infrared spectroscopy as described in detail in the Examples below, a method of performing solvent fractionation using chloroform and analyzing the chloroform insoluble matter by infrared spectroscopy, or a method of performing melt fractionation using heated xylene and analyzing the xylene insoluble matter by X-ray diffraction.

[0077] Examples of flame retardants that can be used in one embodiment of the present invention include intumescent flame retardants, hindered amine flame retardants, bromine-based flame retardants, phosphorus-based flame retardants, phosphate ester flame retardants, etc. By containing a hindered amine flame retardant, the expanded polyolefin resin particles of the present invention can achieve the desired flame retardancy with a small amount of flame retardant added.

[0078] The present expanded beads preferably contain a hindered amine flame retardant, which has the effect of achieving the desired flame retardancy with a small amount of flame retardant added.

[0079] In this specification, the term "hindered amine" refers to a hindered amine having an OR group (wherein R is a saturated or unsaturated monovalent hydrocarbon group) directly substituted on the N atom (hereinafter, this may be referred to as an N-substituted hindered amine). The hindered amine is not particularly limited as long as it is a hindered amine having an OR group directly substituted on the N atom, and known hindered amines can be used. As the hindered amine, one type of hindered amine may be used alone, or two or more types of hindered amines may be used in combination.

[0080] As the hindered amine, an N-substituted hindered amine containing a triazine component (hereinafter, sometimes referred to as a "triazine skeleton-containing hindered amine") is preferred because it can exhibit flame retardant effects over a wide temperature range. The triazine skeleton-containing hindered amine is not particularly limited, but examples thereof include (i) a compound having CAS number 191680-81-6 ((i-1) a reaction product of N,N'-bis(3-aminopropyl)ethylenediamine with a product obtained by reacting cyclohexane with a reaction product of peroxidized N-butyl-2,2,6,6-tetramethyl-4-piperidinamine and 2,4,6-trichloro-1,3,5-triazine, and (i-2) 2,4-bis((1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)butyl (i-3) N,N',N'''-tris{2,4-bis[(1-hydrocarbyloxy-2,2,6,6-tetramethylpiperidin-4-yl)alkylamino]-s-triazin-6-yl}-3,3'-ethylenediiminodipropylamine), and / or (ii) bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, which may be a reaction product of N,N'-bis(3-aminopropyl)ethylenediamine with N,N'-bis(3-aminopropyl)ethylenediamine, are preferred. Furthermore, isomers of the above-mentioned triazine skeleton-containing hindered amines and crosslinked derivatives of the above-mentioned triazine skeleton-containing hindered amines may also be used. More detailed information about triazine skeleton-containing hindered amines is disclosed in European Patent No. 0889085, page 2, line 32 to page 4, line 6.

[0081] Commercially available products of the triazine skeleton-containing hindered amine can also be suitably used. Examples of commercially available products of the triazine skeleton-containing hindered amine include FLAMSTAB (registered trademark) NOR116 (a compound having CAS number 191680-81-6) manufactured by BASF, HOSTAVIN (registered trademark) NOW XP manufactured by CLARIANT, and Adeka STAB LA-81 (bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate) manufactured by Adeka Corporation.

[0082] In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (iv):

[0083] In the above structural formula (iv), G １ and G ２ are independently １－８ an alkyl group, or pentamethylene; Z １ and Z ２ are each a methyl group, or Z １ and Z ２ together form a linking moiety, which may be additionally substituted with an ester group, an ether group, an amide group, an amino group, a carboxy group, or a urethane group; and E is C １－８ Alkoxy group, C ５－１２ Cycloalkoxy group C ７－１５ aralkoxy group, —O—C(O)—C １－１８ Alkyl group, or -OT-(OH) ｂ group; where T is (i) C １－１８ (ii) an alkylene chain; ５－１８ (iii) a cycloalkylene chain; ５－１８ a cycloalkenylene chain, or (iv) a phenyl group or C １－４ C substituted by alkyl-substituted phenyl groups １－４ an alkylene chain; b is 1 to 3 and is not greater than the number of carbon atoms in T, and when b is 2 or 3, each hydroxyl group is linked to a different carbon atom in T.

[0084] The compound represented by the structural formula (iv) is disclosed in more detail in EP 2225318, more specifically, from page 5, line 35 to page 25, line 48 of EP 2225318.

[0085] In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (v):

[0086] In the above structural formula (v), R is hydrogen or a methyl group, and R １ is C １－１８ Alkyl group, C ２－１８ Alkenyl group, C ２－１８ Alkynyl group, C ５－１２ Cycloalkyl group, C ５－８ Cycloalkenyl group, C ６－１０ Aryl group or C ７－９ It is an aralkyl group.

[0087] The compound represented by the above structural formula (v) is disclosed in more detail in European Patent No. 0309402, page 3, line 33 to page 8, line 58.

[0088] In one embodiment of the present invention, the hindered amine may be a compound represented by the following structural formula (vi):

[0089] In the structural formula (vi), E, ​​k, Y, W, and R １ ~R ７ and G １ ~G ４ is as defined in U.S. Pat. No. 8,598,369.

[0090] The compound represented by the above structural formula (vi) is disclosed in more detail in Examples 1 to 12 and Tables 1 to 5 of US Pat. No. 8,598,369.

[0091] The amount of flame retardant used in the production of the present expanded beads, in other words, the content of the flame retardant in the present expanded beads, will be described below. The content of the flame retardant in the present expanded beads is preferably 0.05 to 1.00 parts by weight, more preferably 0.05 to 0.20 parts by weight, and even more preferably 0.05 to 0.10 parts by weight, per 100 parts by weight of the base resin. When the content of the flame retardant is (i) 0.05 parts by weight or more, a sufficient flame retardant effect can be obtained, and (ii) when the content is 0.10 parts by weight or less, there is no risk of the cell diameter of the resulting expanded beads being non-uniform or fine.

[0092] <Physical Properties> The physical properties of the present expanded beads will be described below.

[0093] (DSC ratio of expanded beads) The expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry, which will be described later. Of the melting peaks, the heat of fusion determined from the melting peak on the higher temperature side is referred to as the "higher temperature side heat of fusion," and the heat of fusion determined from the melting peak on the lower temperature side is referred to as the "lower temperature side heat of fusion." When there are three or more melting peaks, the heat of fusion determined from the highest temperature melting peak is referred to as the "higher temperature side heat of fusion," and the heat of fusion determined from the other melting peaks is referred to as the "lower temperature side heat of fusion."

[0094] The DSC ratio of the expanded beads is not particularly limited, but is preferably 10.0% to 50.0%, more preferably 15.0% to 40.0%, and even more preferably 20.0% to 30.0%. When the DSC ratio of the expanded beads is 10.0% or more, the expanded beads have the advantage of being able to provide a foamed molded article with sufficient strength. On the other hand, when the DSC ratio of the expanded beads is 40% or less, the expanded beads have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article.

[0095] The method for measuring the DSC ratio of the expanded beads will be described in detail in the Examples below.

[0096] The DSC ratio of the expanded beads is also a measure of the amount of high-melting-point crystals contained in the expanded beads. That is, a DSC ratio of 10.0% to 50.0% indicates that the expanded beads contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the expanded beads is significantly related to the viscoelasticity of the resin beads and the expanded beads when they are foamed and expanded. That is, when the DSC ratio of the expanded beads is 10.0% to 50.0%, the resin beads and the expanded beads can exhibit excellent foamability and expansion properties, respectively, when they are foamed and when they are molded. As a result, the expanded beads have the advantage that they can produce foamed molded articles with excellent internal fusion properties and excellent mechanical strength, such as compressive strength, even at low molding pressures.

[0097] In the present expanded beads, examples of a method for controlling the DSC ratio within a predetermined range include a method for adjusting the conditions during production of the present expanded beads (particularly, the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) from which the dispersion is released, etc.) In terms of ease of adjustment, a method for controlling the DSC ratio within a predetermined range by adjusting the foaming temperature, foaming pressure, and / or holding time is preferred.

[0098] For example, increasing the foaming temperature tends to decrease the DSC ratio, while decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals varies depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio, while decreasing the foaming pressure also tends to increase the DSC ratio. This is because the degree of plasticization varies depending on the foaming pressure, thereby changing the amount of unmelted crystals. In addition, the DSC ratio tends to increase as the holding time increases. This is because the amount of growth of unmelted crystals varies depending on the holding time.

[0099] (Expansion Ratio of Expanded Beads) The expanded beads preferably have an expansion ratio of 10 to 50, more preferably 15 to 40, and even more preferably 15 to 30. If the expansion ratio of the expanded beads is (i) 10 or more, a lightweight expanded molded article can be obtained efficiently, and (ii) if it is 50 or less, there is no risk of the strength of the resulting expanded molded article being insufficient.

[0100] The method for calculating the expansion ratio of the expanded beads will be explained in detail in the examples below.

[0101] (Average Cell Diameter of Expanded Beads) The average cell diameter of the expanded beads is not particularly limited, but is preferably 100 μm to 500 μm, more preferably 120 μm to 400 μm, even more preferably 120 μm to 300 μm, and even more preferably 140 μm to 250 μm. When the average cell diameter of the expanded beads is (i) 100 μm or more, the expanded beads can provide polypropylene resin foam molded articles with no color unevenness, excellent colorability, and excellent compressive strength. (ii) When the average cell diameter of the expanded beads is 500 μm or less, there is no risk of the molding cycle of the in-mold foam molded article being extended, which has the advantage of improving productivity. Here, the molding cycle refers to the time from the start of in-mold foam molding to the end of molding, when the foam molded article is obtained by in-mold foam molding using the expanded beads, when the resulting molded article is released from the mold.

[0102] The method for measuring the average cell diameter of the expanded beads will be described in detail in the Examples below.

[0103] <Method for producing expanded polypropylene resin beads> A method for producing expanded polypropylene resin beads according to one embodiment of the present invention comprises mixing a non-recycled polypropylene resin, a recycled material, and a polypropylene-based resin having an average structure size of 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ In the method for producing expanded polypropylene-based resin beads according to one embodiment of the present invention, the recycled material comprises a granulation step of melt-kneading a mixture containing a recycled polypropylene-based resin and / or a recycled polyethylene-based resin and a mixture of carbon black A having an average structure size of 5.0 × 10 to obtain polypropylene-based resin particles, a dispersion step of dispersing the polypropylene-based resin particles, an aqueous dispersion medium, and a blowing agent in a container, a heating step of heating the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles, a pressurizing step of increasing the pressure in the container, and a discharging step of releasing one end of the container to discharge the dispersion in the container into a region having a pressure lower than the pressure in the container. ４ nm ２ Above 9.0 x 10 ４ nm ２and carbon black B having an average molecular weight of less than 10 ...

[0104] The present method for producing expanded beads has the above-mentioned features, and therefore has the advantage of being able to provide expanded polypropylene resin beads that can provide polypropylene resin foamed molded articles with excellent blackness and flame retardancy. Furthermore, as described above, the present method for producing expanded beads uses recycled polypropylene resin and / or recycled polyethylene resin. Therefore, the present method for producing expanded beads can be said to have a low environmental impact.

[0105] Recycled materials currently on the market (particularly recycled materials containing recycled polypropylene-based resins) may contain carbon black. This is because carbon black is added as a colorant to products before recycling, or because carbon black is added during the recycling process with the aim of neutralizing the appearance of the recycled material or the color of the product before recycling with carbon black, thereby improving the color of the recycled material. The present inventors measured the average structure size of carbon black contained in recycled polypropylene-based resins, which are an example of recycled materials, by the above-mentioned method, and found that the average structure size was, for example, 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ In this specification, the average structure size was less than 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ Carbon black having a carbon content of less than 1000 ppm is referred to as "carbon black B." In other words, the recycled material may contain carbon black B.

[0106] Furthermore, the present inventors have found that foamed molded articles obtained by molding foamed beads obtained using recycled materials (e.g., recycled polypropylene-based resins and / or recycled polyethylene-based resins) have poor blackness. Based on this finding, the present inventors have conducted extensive research to provide foamed molded articles having excellent blackness even when using foamed beads obtained using recycled materials.

[0107] The present inventors, in the course of intensive research, have found that carbon black having an average structure size (e.g., 0.2 × 10) smaller than that of carbon black contained in recycled materials can be obtained. ４ nm ２ Above 4.0 x 10 ４ nm ２ The present inventors have independently obtained a novel finding that, surprisingly, foamed molded articles having excellent blackness can be provided by further adding (using) carbon black having an average structure size of 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ Carbon black having a blackness of less than 100% is referred to as "carbon black A." In other words, the present inventors have independently obtained the novel finding that expanded beads obtained by using (adding) carbon black A in addition to recycled materials can provide expanded molded articles having excellent blackness.

[0108] The inventors measured the average structure size of the carbon black in the expanded beads by the above-mentioned method using expanded beads obtained by using (adding) carbon black A in addition to recycled materials. As a result, it was found that in at least some of the expanded beads, the structure size per structure relative to the total number of carbon black in the expanded beads was 1×10 ４ nm ２ The ratio of the number of carbon black particles having a particle size of less than 10% to 50% was 10% to 50%. That is, this production method can provide expanded beads according to one embodiment of the present invention. Note that, in the expanded beads, the structure size per structure is 1×10 ４ nm ２The carbon black having a content of less than 100% may come from carbon black B in the recycled material and may also come from carbon black A that has been additionally used (added).

[0109] Furthermore, the inventors have found that by appropriately adjusting the average structure size and amount of carbon black used in addition to recycled materials, the structure size per structure relative to the total number of carbon black particles in the expanded beads can be reduced to 1 x 10 ４ nm ２ The present inventors have independently obtained a novel finding that, by making the expanded beads so that the ratio of the number of carbon black particles less than 10% to 50%, it is possible to provide expanded polypropylene resin particles that contain recycled resin and that can provide polypropylene resin foamed molded articles that are excellent in blackness and flame retardancy.

[0110] One embodiment of the method for producing the expanded beads of the present invention will be described in detail below, but the description in the above section [2. Expanded Polypropylene Resin Beads] will be used for matters other than those described below, as appropriate. However, the method for producing the expanded beads of the present invention is not limited to the following method.

[0111] (Granulation Step) The granulation step can also be considered a step of preparing polypropylene-based resin particles containing (a) a base resin containing a non-recycled polypropylene-based resin and a recycled polypropylene-based resin and / or a recycled polyethylene-based resin, and (b) carbon black. The amount of recycled material used in this production method (e.g., the granulation step) is an amount such that the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin in the resulting polypropylene-based resin particles is 10 to 60 parts by weight per 100 parts by weight of the base resin contained in the polypropylene-based resin particles. In this specification, "polypropylene-based resin particles" may also be referred to as "resin particles."

[0112] The polypropylene-based resin particles produced by the present production method contain a base resin. It can also be said that the polypropylene-based resin particles obtained through the granulation step contain a base resin.

[0113] It is preferable to further use a foam nucleating agent in the granulation step. In other words, it is preferable that the polypropylene-based resin particles in the present production method contain a foam nucleating agent. Specific examples of the foam nucleating agent are the same as those explained in the above section (Foam Nucleating Agent), so that this description is incorporated herein by reference and further explanation is omitted here. The amount of foam nucleating agent used in the present production method (e.g., the granulation step) is preferably such that the content of foam nucleating agent in the obtained polypropylene-based resin particles is the amount explained in the above section (Foam Nucleating Agent) per 100 parts by weight of the base resin in the polypropylene-based resin particles.

[0114] The melt-kneading of the mixture is not particularly limited, but for example, an extruder is used. In the granulation step, other modes than melt-kneading the mixture are not particularly limited. For example, polypropylene resin particles can be prepared by sequentially performing the following steps (1) to (3) on the melt-kneaded mixture: (1) extruding the mixture through a die provided in an extruder; (2) solidifying the extruded mixture by cooling, for example, by passing it through water; and (3) subsequently cutting the solidified mixture with a cutter into a desired shape such as a cylindrical, elliptical, spherical, cubic, rectangular, hollow cylinder, polygonal prism, etc. Alternatively, the melt-kneaded mixture may be directly extruded through a die provided in an extruder into water, and immediately after extrusion, the mixture may be cut into particles, cooled, and solidified.

[0115] In the granulation step, a mixture containing a non-recycled polypropylene resin, a recycled material, and carbon black A is melt-kneaded. Carbon black A may be used as is, or may be used in the form of a masterbatch in which it has been previously kneaded with a polypropylene resin. In the granulation step, carbon black B and carbon black C may be further used in addition to carbon black A. The amounts of carbon black A, B, and C used in the granulation step may be the respective contents of carbon black A, B, and C in the resulting expanded beads. Therefore, with regard to the amounts of carbon black A, B, and C used in this production method (e.g., the granulation step), it is preferable that the amounts of carbon black A, B, and C used in the resulting polypropylene resin particles be the amounts described above in (2-2. Carbon Black) per 100 parts by weight of the base resin in the polypropylene resin particles. The average structures of carbon blacks A, B, and C used in the granulation step are the same as those described above for the average structures of carbon blacks A, B, and C, and therefore will be incorporated herein by reference and will not be described further. The amount of carbon black B used in this production method (e.g., in the granulation step) refers to the total amount of carbon black B contained in the recycled material used and the amount of carbon black B used separately and arbitrarily, rather than as a recycled material.

[0116] The total amount of the non-recycled polypropylene-based resin and the recycled material used in this production method (e.g., the granulation step) is preferably such that the total content of the non-recycled polypropylene-based resin, the recycled polypropylene-based resin, and the recycled polyethylene-based resin in the polypropylene-based resin particles is the amount described above in (2-1. Base resin).

[0117] (Dispersion Step) The dispersion step can be said to be, for example, a step of preparing a dispersion in which resin particles, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium.

[0118] The container used in the dispersion step is not particularly limited, but it is preferable that the container be able to withstand the foaming temperature and foaming pressure described below.

[0119] Examples of the vessel include a pressure vessel and an autoclave-type pressure vessel. The vessel may be equipped with a stirrer therein.

[0120] The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse the resin particles, the foaming agent, etc.

[0121] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, glycerin, or the like to water, (b) water such as tap water and industrial water, and (c) solutions (aqueous solutions) containing salts such as sodium chloride or sodium sulfate. In terms of enabling stable production of expanded beads, it is preferable to use, as the aqueous dispersion medium, pure water such as RO water (water purified by a reverse osmosis membrane method), distilled water, deionized water (water purified by an ion exchange resin), or ultrapure water.

[0122] Examples of the blowing agent include (a) (a-1) inorganic blowing agents such as nitrogen, carbon dioxide, air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents such as (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane, (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether, and (b-3) halogenated hydrocarbons such as monochloromethane, chloroethane, and hydrofluoroolefins.

[0123] As the blowing agent, halogenated hydrocarbons such as dichloromethane and dichlorodifluoroethane can also be used.

[0124] In the present method for producing expanded beads, it is preferable to use a dispersant (e.g., an inorganic substance such as tricalcium phosphate or kaolin) and a dispersing aid (e.g., an anionic surfactant such as sodium dodecylbenzenesulfonate). This configuration can reduce adhesion of resin particles (sometimes called blocking) and improve the stability of the dispersion in the container. As a result, it has the advantage of enabling stable production of expanded beads.

[0125] The aqueous dispersion medium and the blowing agent may each be used alone or in combination of two or more.

[0126] This production method includes, between the dispersing step and the releasing step, a heating step of heating the temperature inside the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles, and a pressurizing step of increasing the pressure inside the container, for example, to a constant pressure. The heating step and the pressurizing step may be performed in any order, or may be performed simultaneously. Furthermore, this production method may further include, after the heating step and the pressurizing step, a maintaining step of maintaining the temperature inside the container at a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles and maintaining the pressure inside the container at a constant pressure.

[0127] (Heating Step, Pressurizing Step, and Holding Step) In this specification, (a) "a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles" in the heating step, pressurizing step, and holding step may be referred to as the "expansion temperature," and (b) the constant pressure may be referred to as the "expansion pressure." In this specification, "a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles" means a temperature 10°C lower than the melting point of the polypropylene-based resin constituting the polypropylene-based resin particles, and when two or more polypropylene-based resins are used, means a temperature 10°C lower than the melting point of the polypropylene-based resin with the highest melting point.

[0128] The foaming temperature in the heating step varies depending on the type of non-recycled polypropylene resin and recycled material, the type of blowing agent, the desired apparent density of the expanded particles, and so cannot be generally defined. In the heating step, the temperature inside the container is not particularly limited, as long as it is heated to a temperature above the softening temperature of the polypropylene resin particles. In one embodiment of the present invention, the heating step is preferably a step of heating the container to a temperature (i) above the softening temperature of the polypropylene resin particles and not higher than 10.0°C above the softening temperature of the polypropylene resin particles, more preferably a step of heating to a temperature above the softening temperature of the polypropylene resin particles and not higher than 8.0°C above the softening temperature of the polypropylene resin particles, and even more preferably a step of heating to a temperature above the softening temperature of the polypropylene resin particles and not higher than 6.0°C above the softening temperature of the polypropylene resin particles. This configuration has the advantage of preventing adhesion of the polypropylene resin particles to each other inside the container.

[0129] In the pressurizing step, the pressure inside the container is not particularly limited. The pressurizing step in one embodiment of the present invention is preferably a step of increasing the pressure inside the container to (i) 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably (ii) 1.5 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and even more preferably (iii) 1.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). When the pressurizing step is a step of increasing the pressure inside the container to 1.0 MPa (gauge pressure) or more, expanded beads having a suitable density can be obtained.

[0130] In the holding step, the time (holding time) for holding the temperature inside the container (temperature of the dispersion) at the foaming temperature and the pressure inside the container at around the foaming pressure is not particularly limited. The holding time is preferably 10 to 60 minutes, more preferably 12 to 55 minutes, and even more preferably 15 to 50 minutes. A holding time of 10 minutes or longer has the advantage that a sufficient amount of unmelted crystals (crystals of the base resin) are present, thereby reducing shrinkage and / or an increase in the open cell ratio of the resulting expanded beads. On the other hand, a holding time of 60 minutes or shorter has the advantage that an excessive amount of unmelted crystals are not present, allowing the expanded beads to be molded at a low molding temperature.

[0131] (Releasing Step) The releasing step can be carried out after the heating step and the pressurizing step (a) when the holding step is not carried out, or after the holding step (b) when the holding step is carried out. The releasing step can expand the resin particles, resulting in expanded particles.

[0132] In the releasing step, the "region having a lower pressure than the pressure inside the container" refers to a "region under a pressure lower than the pressure inside the container" or a "space under a pressure lower than the pressure inside the container", and can also be referred to as "an atmosphere under a lower pressure than the pressure inside the container". The region having a lower pressure than the pressure inside the container can also be referred to as a region having a pressure lower than the foaming pressure, and may be, for example, a region under atmospheric pressure.

[0133] In the discharging step, when the dispersion is discharged into a region having a pressure lower than the pressure inside the container, the dispersion can also be discharged through an orifice having a diameter of 1 mm to 5 mm for the purposes of adjusting the flow rate of the dispersion and reducing variation in the expansion ratio of the resulting expanded beads.

[0134] The low-pressure region is, for example, a gas phase. In addition, for the purpose of improving foaming properties, the low-pressure region (space) may be filled with saturated water vapor.

[0135] As described above, the process for producing expanded beads from resin beads is called the "first-stage expansion process," and the resulting expanded beads are called "first-stage expanded beads."

[0136] (Second-stage expansion process) In order to obtain expanded beads with a high expansion ratio, the first-stage expanded beads obtained in the first-stage expansion process may be expanded again. The process of increasing the expansion ratio of the first-stage expanded beads is called the "second-stage expansion process", and the expanded polyolefin resin beads obtained by the second-stage expansion process are called "second-stage expanded beads". The specific method for the second-stage expansion process is not particularly limited, and known methods can be used.

[0137] [3. Polypropylene-based resin foam molded article] One embodiment of the present invention also provides a polypropylene-based resin foam molded article obtained by molding the expanded polypropylene-based resin beads described in the above section [2. Expanded polypropylene-based resin beads]. The polypropylene-based resin foam molded article according to one embodiment of the present invention can also be said to be a foam molded article containing the expanded polypropylene-based resin beads described in the section [2. Expanded polypropylene-based resin beads].

[0138] In this specification, the "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as the "present foam molded article."

[0139] Because of the above-described configuration, the present foamed molded article has the advantage of excellent blackness and flame retardancy (self-extinguishing properties). Specifically, a foamed molded article with excellent blackness, with an L value of less than 28 as measured with a spectrophotometer, can be obtained. The present foamed molded article also has the advantage of excellent color unevenness and surface properties. Specifically, a foamed molded article with reduced color unevenness, with a standard deviation of the L value as measured with a spectrophotometer of less than 2, can be obtained. Methods for measuring and evaluating the blackness, color unevenness, flame retardancy, and surface properties of the foamed molded article are described in detail in the examples below.

[0140] The density of the foamed molded article is not particularly limited. The density is preferably 20 g / L to 90 g / L, and more preferably 20 g / L to 60 g / L. This configuration has the advantage of achieving both excellent lightness and excellent impact resistance of the molded article. The method for measuring the density of the foamed molded article will be described in detail in the Examples below.

[0141] <Method for producing foamed molded article> The method for producing the foamed molded article is not particularly limited as long as it is possible to produce a foamed molded article by molding the foamed beads (preferably in-mold foam molding), and any known method can be used. As a method for producing the foamed molded article, for example, the method described in the section <Method for producing foamed molded article> of International Publication WO2022 / 149538 can be suitably used.

[0142] An embodiment of the present invention may have the following configuration.

[0143] [1] Polypropylene-based resin expanded beads containing a base resin and carbon black, wherein the base resin contains a non-recycled polypropylene-based resin and a recycled polypropylene-based resin and / or a recycled polyethylene-based resin, the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 10 parts by weight to 60 parts by weight per 100 parts by weight of the base resin, and the carbon black has a structure size of 1 x 10 per structure relative to the total number of the carbon black. ４ nm ２ The expanded polypropylene resin particles have a ratio of the number of carbon black particles that is less than 10% to 50%.

[0144] [2] Average structure size is 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ Carbon black A having an average structure size of less than 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２ and carbon black B having a molecular weight of less than 10 ...

[0145] [3] The expanded polypropylene resin particles according to [1] or [2], further comprising a foaming nucleating agent.

[0146] [4] The expanded polypropylene resin particles according to [3], wherein the content of the foaming nucleating agent is 0.05 to 0.50 parts by weight per 100 parts by weight of the base resin.

[0147] [5] The expanded polypropylene resin particles according to [3], wherein the content of the foaming nucleating agent is 0.20 to 0.50 parts by weight per 100 parts by weight of the base resin.

[0148] [6] The expanded polypropylene resin particles according to any one of [3] to [5], wherein the foaming nucleating agent is talc.

[0149] [7] The expanded polypropylene resin particles according to any one of [1] to [6], further comprising a hindered amine flame retardant.

[0150] [8] The expanded polypropylene resin particles according to [2], wherein the content of the carbon black A is 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

[0151] [9] The expanded polypropylene resin particles according to [2], wherein the content of the carbon black B is 0.10 to 2.00 parts by weight per 100 parts by weight of the base resin.

[0152]

[10] The expanded polypropylene resin particles according to any one of [1] to [9], wherein the base resin contains the recycled polyethylene resin, and the recycled polyethylene resin contains a recycled high-density polyethylene resin.

[0153]

[11] The expanded polypropylene resin particles according to any one of [1] to

[10] , wherein the recycled polypropylene resin is 60 to 100 parts by weight and the recycled polyethylene resin is 0 to 40 parts by weight, when the total content of the recycled polypropylene resin and the recycled polyethylene resin is 100 parts by weight.

[0154]

[12] Average structure size is 10.0 × 10 ４ nm ２

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

[11] , which do not contain carbon black C of the above or contain less than 0.5 parts by weight of carbon black C per 100 parts by weight of the base resin.

[0155]

[13] The expanded polypropylene resin particles according to any one of [1] to

[12] , wherein the non-recycled polypropylene resin contains 60% by weight or more of one or more selected from the group consisting of ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer, based on 100% by weight of the non-recycled polypropylene resin.

[0156]

[14] The expanded polypropylene resin beads according to any one of [1] to

[13] , wherein the base resin contains the recycled polypropylene resin, and the recycled polypropylene resin contains one or more selected from the group consisting of an ethylene / propylene alternating copolymer, an ethylene / 1-butene / propylene alternating copolymer, an ethylene / propylene random copolymer, and an ethylene / propylene random copolymer.

[0157]

[15] The expanded polypropylene-based resin particles according to any one of [1] to

[14] , wherein the base resin contains 80 to 100 parts by weight of the non-recycled polypropylene-based resin, the recycled polypropylene-based resin, and the recycled polyethylene-based resin in total, per 100 parts by weight of the base resin.

[0158]

[16] The expanded polypropylene resin beads according to any one of [1] to

[15] , wherein the DSC ratio of the expanded polypropylene resin beads is 10.0% to 50.0%.

[0159]

[17] The expanded polypropylene resin beads according to any one of [1] to

[16] , wherein the expansion ratio of the expanded polypropylene resin beads is 10 to 50 times.

[0160]

[18] The expanded polypropylene resin beads according to any one of [1] to

[17] , wherein the expanded polypropylene resin beads have an average cell diameter of 100 μm to 500 μm.

[0161]

[19] A polypropylene resin foam molded article obtained by molding the expanded polypropylene resin beads according to any one of [1] to

[18] .

[0162]

[20] The polypropylene-based resin foam molded article according to

[19] , wherein the molded article density of the polypropylene-based resin foam molded article is 20 g / L to 90 g / L.

[0163]

[21] The polypropylene resin foam molded article according to

[19] or

[20] , which has self-extinguishing properties.

[0164]

[22] The polypropylene-based resin foam molded article according to any one of

[19] to

[21] , wherein the L value of the polypropylene-based resin foam molded article measured by a spectrophotometer is less than 28.

[0165]

[23] The polypropylene-based resin foam molded article according to any one of

[19] to

[22] , wherein the standard deviation of the L value of the polypropylene-based resin foam molded article measured by a spectrophotometer is less than 2.

[0166]

[24] A non-recycled polypropylene resin, a recycled material, and an average structure size of 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ and carbon black A having an average structure size of less than 5.0 × 10 to obtain polypropylene-based resin particles; a dispersing step of dispersing the polypropylene-based resin particles, an aqueous dispersion medium, and a blowing agent in a container; a heating step of heating the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles; a pressurizing step of increasing the pressure in the container; and a discharging step of releasing one end of the container to discharge the dispersion in the container into a region having a pressure lower than the pressure in the container, wherein the recycled material is a recycled polypropylene-based resin and / or a recycled polyethylene-based resin and a polypropylene-based resin having an average structure size of less than 5.0 × 10 ４ nm ２ Above 9.0 x 10 ４ nm ２and carbon black B, wherein the recycled material is used in an amount such that the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 10 to 60 parts by weight per 100 parts by weight of a base resin containing the non-recycled polypropylene-based resin and the recycled polypropylene-based resin and / or the recycled polyethylene-based resin.

[0167]

[25] The method for producing expanded polypropylene-based resin beads described in

[24] , wherein the heating step is a step of heating the temperature inside the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles and equal to or lower than the softening temperature of the polypropylene-based resin particles + 10.0°C.

[0168]

[26] The method for producing expanded polypropylene resin beads according to

[24] or

[25] , wherein the pressurizing step is a step of increasing the pressure inside the container to a pressure of 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure).

[0169]

[27] The method for producing expanded polypropylene resin particles according to any one of

[24] to

[26] , wherein the polypropylene resin particles further contain a foaming nucleating agent.

[0170]

[28] The method for producing expanded polypropylene-based resin particles according to

[27] , wherein the content of the foaming nucleating agent in the polypropylene-based resin particles is 0.05 to 0.50 parts by weight per 100 parts by weight of the base resin.

[0171]

[29] The method for producing expanded polypropylene-based resin particles according to

[27] , wherein the content of the foaming nucleating agent in the polypropylene-based resin particles is 0.20 parts by weight to 0.50 parts by weight per 100 parts by weight of the base resin.

[0172]

[30] The method for producing expanded polypropylene resin beads according to any one of

[27] to

[29] , wherein the foaming nucleating agent is talc.

[0173]

[31] The method for producing expanded polypropylene resin particles according to any one of

[24] to

[30] , wherein the polypropylene resin particles further contain a hindered amine flame retardant.

[0174]

[32] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[31] , wherein the amount of carbon black A used is an amount such that the content of carbon black A is 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

[0175]

[33] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[32] , wherein the amount of carbon black B used is an amount such that the content of carbon black B is 0.10 parts by weight to 2.00 parts by weight per 100 parts by weight of the base resin.

[0176]

[34] The method for producing expanded polypropylene-based resin beads according to any one of

[24] to

[33] , wherein the recycled material contains the recycled polyethylene-based resin, and the recycled polyethylene-based resin contains a recycled high-density polyethylene-based resin.

[0177]

[35] The method for producing expanded polypropylene-based resin beads according to any one of

[24] to

[34] , wherein, in the recycled material, when the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 100 parts by weight, the recycled polypropylene-based resin is 60 parts by weight to 100 parts by weight, and the recycled polyethylene-based resin is 0 parts by weight to 40 parts by weight.

[0178]

[36] Average structure size is 10.0 × 10 ４ nm ２

[36] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[35] , wherein carbon black C having a content of 100 parts by weight or more is not used, or the carbon black C is used in an amount such that the content of the carbon black C is less than 0.5 parts by weight per 100 parts by weight of the base resin.

[0179]

[37] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[36] , wherein the non-recycled polypropylene resin contains 60% by weight or more of one or more selected from the group consisting of ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer, based on 100% by weight of the non-recycled polypropylene resin.

[0180]

[38] The method for producing expanded polypropylene-based resin beads according to any one of

[24] to

[37] , wherein the recycled material contains the recycled polypropylene-based resin, and the recycled polypropylene-based resin contains one or more selected from the group consisting of an ethylene / propylene alternating copolymer, an ethylene / 1-butene / propylene alternating copolymer, an ethylene / propylene random copolymer, and an ethylene / propylene random copolymer.

[0181]

[39] The method for producing expanded polypropylene-based resin beads according to any one of

[24] to

[38] , wherein the total amount of the non-recycled polypropylene-based resin and recycled material used is such that the total content of the non-recycled polypropylene-based resin, the recycled polypropylene-based resin, and the recycled polyethylene-based resin in the polypropylene-based resin particles is 80 to 100 parts by weight per 100 parts by weight of the base resin in the polypropylene-based resin particles.

[0182]

[40] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[39] , wherein the DSC ratio of the expanded polypropylene resin beads is 10.0% to 50.0%.

[0183]

[41] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[40] , wherein the expansion ratio of the expanded polypropylene resin beads is 10 to 50 times.

[0184]

[42] The method for producing expanded polypropylene resin beads according to any one of

[24] to

[41] , wherein the expanded polypropylene resin beads have an average cell diameter of 100 μm to 500 μm.

[0185]

[43] A method for producing a polypropylene-based resin foamed molded article, comprising a step of molding the expanded polypropylene-based resin beads according to any one of [1] to

[18] or the expanded polypropylene-based resin beads obtained by the method for producing expanded polypropylene-based resin beads according to any one of

[24] to

[42] .

[0186]

[44] The method for producing a polypropylene resin foam molded article according to

[43] , wherein the molded article density of the polypropylene resin foam molded article is 20 g / L to 90 g / L.

[0187]

[45] The method for producing a polypropylene resin foam molded article according to

[43] or

[44] , wherein the polypropylene resin foam molded article has self-extinguishing properties.

[0188]

[46] The L value of the polypropylene-based resin foam molded article measured by a spectrophotometer is less than 28.

[43] -

[45] The method for producing a polypropylene-based resin foam molded article according to any one of

[43] to

[45] .

[0189]

[47] The method for producing a polypropylene-based resin foam molded article according to any one of

[43] to

[46] , wherein the standard deviation of the L value of the polypropylene-based resin foam molded article measured by a spectrophotometer is less than 2.

[0190] Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The substances used in the examples and comparative examples are as follows, but they were used without any particular purification or the like.

[0191] <Materials> (Non-recycled polypropylene resin) Ethylene / 1-butene / propylene random copolymer [ethylene content 1.0% by weight, 1-butene content 4 parts by weight, melting point 148°C] (Recycled materials) Recycled material-1: A mixture consisting of 96.2 parts by weight of ethylene / propylene random copolymer [ethylene content 9.0% by weight and melting point 151°C], 3 parts by weight of carbon black B, and 0.8 parts by weight of talc. The average structure size of the carbon black B in Recycled material-1 was measured by the following method and was found to be 5.8 x 10 ４ nm ２ The content of carbon black B in recycled material-1 was measured by the following method and found to be 0.8 parts by weight. The ash content in recycled material-1 was measured by the following method and found to be 0.8 parts by weight. The ash content was qualitatively analyzed by the following method and found to be talc. - Recycled material-2: High density polyethylene [melting point 126°C] (carbon black) - Carbon black A [average structure size: 3.2 x 10 ４ nm ２ (Minimum structure value: 0.01 x 10 ４ nm ２ , Maximum structure value: 5.0 x 10 ４ nm ２ ) ] Carbon black B (carbon black contained in recycled material-1) [average structure size: 5.8 × 10 ４ nm ２ (Structure minimum value 1.0 x 10 ４ nm ２ , maximum value 9.9 × 10 ４ nm ２) )] (foam nucleating agent) Talc [Talc Powder PK-S, manufactured by Hayashi Kasei Co., Ltd.] (water-absorbing substance) Glycerin [Purified Glycerin D, manufactured by Lion Corporation] (flame retardant) Hindered amine flame retardant [NOR116, manufactured by BASF] <Method for measuring melting point> The melting points of the non-recycled polypropylene-based resin, recycled polypropylene-based resin, and recycled polyethylene-based resin were values ​​determined by measurement by the DSC method using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation). The specific operating procedures were as follows (1) to (3): (1) 5 to 6 mg of a sample (non-recycled polypropylene-based resin, recycled polypropylene-based resin, or recycled polyethylene-based resin) was melted by increasing the temperature from 40°C to 220°C at a heating rate of 10°C / min; (2) the temperature of the melted sample was then decreased from 220°C to 40°C at a heating rate of 10°C / min to crystallize the sample; (3) the temperature of the crystallized sample was then increased from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (melting peak) of the DSC curve of the sample obtained during the second heating (i.e., during (3)) was taken as the melting point of the sample.

[0192] <Measurement of Carbon Black Structure Size> The structure size of carbon black in expanded beads was determined by the following method: (1) polypropylene-based resin expanded beads were cut approximately in half using a microtome; (2) the cross section of the cell membrane of the obtained polypropylene-based resin expanded beads was photographed at 40,000 times magnification using a transmission electron microscope to obtain a cross-sectional photograph; (3) 30 carbon black structures were randomly extracted from the obtained cross-sectional photograph taken using the transmission electron microscope, and the area of ​​each carbon black structure was measured. Specifically, a line was drawn along the outline of the carbon black structure, and the area of ​​the portion surrounded by the line was measured using the area measurement function of PDF file editing software [Adobe, Adobe Acrobat DC].

[0193] The structure size of the carbon black in the recycled material was measured by the same method as above in (3) above, except that an image obtained by photographing the recycled material with a transmission electron microscope at a magnification of 40,000 times was used. Furthermore, the structure size of separately added (used) carbon black A or B was measured by the same method as above in (3) above, except that an image obtained by photographing carbon black A or B with a transmission electron microscope at a magnification of 40,000 times was used.

[0194] <Measurement of Carbon Black Content in Recycled Material> The carbon black content in the recycled material was measured using a thermogravimetric and differential thermal analyzer [STA200RV, manufactured by Hitachi High-Tech Science Corp.]. The specific operating procedures were as follows (1) to (3): (1) 6 to 8 mg of recycled material was weighed into a Pt measuring vessel; (2) The temperature of the sample was increased to 600°C at 10°C / min in a nitrogen atmosphere, then cooled to 400°C at 10°C / min, and then the sample was changed to a simulated air (oxygen:nitrogen=21%:79%) atmosphere and heated to 800°C at 10°C / min; (3) In the TG weight loss curve obtained in step (2), the weight loss rate [wt%] at 400°C during the temperature increase from 400°C to 800°C was calculated from the difference between the weight loss rate [wt%] at 400°C and the weight loss rate [wt%] at 800°C.

[0195] <Measurement of Ash Content in Recycled Material> The ash content in the recycled material was determined from the weight of the recycled material and the weight of the recycled material after combustion. The specific operating procedures were as follows (1) to (4): (1) The recycled material was heated at 150°C for 1 hour to completely remove moisture; (2) 1 to 2 g of recycled material was placed in a crucible with a weight of W1, and the weight of the crucible containing the recycled material was measured and designated as W2; (3) Using an electric furnace, the crucible containing the recycled material was held at 300°C for 30 minutes or more, and then held at 750°C for 1 hour or more to combust the recycled material; (4) The crucible was removed from the electric furnace and cooled in a desiccator at 23°C for 1 hour; (5) The weight of the crucible after cooling was measured and designated as W3; (6) The ash content A was calculated using the following formula: W1: Weight of crucible W2: Weight of crucible + recycled material before combustion W3: Weight of crucible + recycled material after combustion A = (W3 - W1) x 100 / (W2 - W1).

[0196] <Qualitative Analysis of Ash> The ash in the recycled material was identified as talc using infrared spectroscopy. The specific operating procedures were as follows (1) and (2): (1) The ash obtained above was pressed onto the crystal part of a total reflection measurement device [Spectrum Two, manufactured by PerkinElmer Japan Co., Ltd.] and measured with a resolution of 4 cm. －１ Total reflection measurement was performed with 16 integration times. －１ ~4000cm －１ (2) The spectrum obtained includes a spectrum at 3700 cm －１ Near 1020 cm －１ Near 670 cm －１ Around 550 cm －１ Four peaks were observed around 3700 cm －１ Near 1020 cm －１ Near 670 cm －１ Around 550 cm －１ The spectrum shape, with peaks observed in four nearby locations, is characteristic of talc, and so the ash contained in the recycled material was identified as talc.

[0197] <Measurement of DSC Ratio of Expanded Polypropylene Resin Beads> The DSC ratio of the expanded beads was measured using a differential scanning calorimeter [DSC7020, manufactured by Hitachi High-Tech Science Corporation]. The specific operating procedures were as follows (1) to (5): (1) 5 to 6 mg of expanded polypropylene resin beads were weighed; (2) The temperature of the expanded beads was increased from 40°C to 220°C at a heating rate of 10°C / min to melt the expanded beads; (3) In the DSC curve of the expanded beads obtained in the process (2) (the DSC curve during the first heating of the expanded beads), (a) a line was drawn connecting the maximum point between the highest melting peak and the melting peak adjacent to the highest melting peak (on the low-temperature side) and the point representing the temperature before the start of melting, and (b) a line was drawn connecting the maximum point and the temperature after the completion of melting. (4) (a) The amount of heat calculated from the area surrounded by (a-1) the line segment connecting the maximum point and the point representing the temperature after the end of melting, and (a-2) the DSC curve having the highest temperature melting peak, was designated as the high-temperature side heat of fusion Qh, (b) the amount of heat calculated from the area surrounded by (b-1) the line segment connecting the maximum point and the point representing the temperature before the start of melting, and (b-2) the DSC curve having the melting peak next to the maximum point (on the low-temperature side), was designated as the low-temperature side heat of fusion Ql, and (c) the high-temperature side heat of fusion Qh; (5) The DSC ratio was calculated from the following formula: DSC ratio (%) = Qh / (Qh + Ql) × 100.

[0198] <Expansion Ratio of Expanded Polypropylene Resin Beads> The expansion ratio of expanded beads was measured by the following methods (1) to (4): (1) The weight w (g) of the expanded beads was measured; (2) Next, the expanded beads used for the weight measurement were submerged in ethanol contained in a measuring cylinder, and the volume v (cm) of the expanded beads was calculated based on the rise in the liquid level in the measuring cylinder. ３ (3) The weight w (g) was measured, and the volume v (cm ３ ) and the density of the foamed particles ρ １ (4) The density ρ of the polypropylene resin particles used in the production of the expanded beads was calculated. ２ is the density of the foam particles ρ １ Divide by (ρ ２ / ρ １ The value obtained was taken as the expansion ratio of the expanded beads.

[0199] <Average Cell Diameter of Expanded Beads> The average cell diameter of expanded beads was measured by the following methods (1) to (5): (1) Using a razor (high-stainless steel double-edged blade manufactured by Feather Co., Ltd.), the expanded beads were cut so as to pass through the center of the expanded beads, while being careful not to destroy the cell membranes (cell membranes) of the expanded beads; (2) The cut surface of the expanded beads obtained was observed using a microscope [manufactured by Hirox Co., Ltd., RH-2000], and an image of the observed surface was taken; (3) On the obtained image, a line segment corresponding to a length of 2000 μm was drawn at any part of the expanded beads except for the surface layer part; (4) The number n of cells through which the line segment passed was measured, and the cell diameter was calculated from the formula (cell diameter=2000 / n (μm)); (5) The same procedure was performed on 10 expanded beads, and the arithmetic mean value of the calculated cell diameters was taken as the average cell diameter of the expanded beads.

[0200] <Density of foamed molded article> The weight (g) (referred to as W) of the obtained foamed molded article was measured. Then, the length, width and thickness of the foamed molded article were measured with a vernier caliper to determine the volume (unit: 1000 cm ３ , that is, L) (referred to as V) was calculated. Subsequently, the density (g / L) of the foamed molded article was calculated using the formula (density of foamed molded article=W / V).

[0201] <Measurement of Blackness and Color Unevenness of Foam Molded Articles> Using a spectrophotometer [CM-26dG, manufactured by Konica Minolta Japan, Inc.], the L value was measured at 50 random points on the surface of the foam molded article, and the average value was taken as the blackness. Note that only diffusely reflected light was used as reflected light during the measurement. The standard deviation of the measured L values ​​was taken as the color unevenness. The blackness and color unevenness were evaluated according to the following criteria. The larger the value, the better the blackness and color unevenness.

[0202] (Blackness) 1 (Excellent): The average measured L value is less than 28. 0 (Poor): The average measured L value is 28 or more. (Color Unevenness) 1 (Excellent): The standard deviation of the measured L value is less than 2. 0 (Poor): The standard deviation of the measured L value is 2 or more. <Flame Retardancy Evaluation of Polypropylene Resin In-Mold Foam Molded Articles> Flame retardancy test samples measuring 350 mm in length, 100 mm in width, and 12 mm in thickness were cut from the resulting foam molded articles. An A marking was made 38 mm from one end of the sample in the longitudinal direction, and a B marking was made 292 mm from the other end. Flame retardancy was evaluated according to the combustion test method specified in FMVSS 302. Using an FMVSS flammability tester (manufactured by Suga Test Instruments Co., Ltd.), a flame from a burner adjusted to a height of 38 mm was applied to the end of the sample in the longitudinal direction for 15 seconds, with the end of the sample positioned at the center of the flame. Flame retardancy was evaluated based on the combustion state at that time according to the following criteria. The higher the number, the better the flame retardancy. 1 (Excellent): The flame is extinguished before it reaches the A-marked line, or within 60 seconds or 50 mm after passing the A-marked line. This is said to have "self-extinguishing properties." 0 (Poor): The burning rate is 100 mm / min or less when the flame burns beyond the A-marked line (38 mm from the end of the sample where the flame hits) and continues to burn until it reaches the B-marked line (292 mm from the end of the sample where the flame hits), or when it burns beyond the A-marked line and is extinguished more than 60 seconds or more than 50 mm after passing the A-marked line. This is said to be "slow-fire". -1 (Very Poor): This is not judged to be either self-extinguishing or slow-fire. This is said to be "easily flammable."

[0203] <Evaluation of Surface Properties of In-Mold Polypropylene Resin Foam Molded Articles> The surface of the obtained in-mold foam molded article was visually observed, and the surface properties were judged according to the following criteria. Interparticle gaps (gaps between expanded polypropylene resin particles), which are one of the evaluation indices for surface properties, were judged by visually counting the number of gaps present in a 50 mm square area at the center of the surface of the molded article. A higher value indicates better surface properties. 2 (Good): There are 0 to 1 interparticle gap (gaps between expanded polypropylene resin particles), and the surface is clean and wrinkle-free. 1 (Fair): There are 2 to 3 interparticle gaps, and no wrinkles. 0 (Poor): There are 4 or more interparticle gaps, and wrinkles are visible.

[0204] The methods for producing polypropylene resin particles, expanded polypropylene resin particles, and in-mold foamed polypropylene resin articles in Examples and Comparative Examples will be described below.

[0205] Example 1 [Preparation of Resin Particles] (a) 75 parts by weight of non-recycled polypropylene resin (ethylene / 1-butene / propylene random copolymer), (b) 25 parts by weight of recycled material-1, (c) 3 parts by weight of carbon black A, (d) 0.2 parts by weight of glycerin, (e) 0.05 parts by weight of talc, and (f) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The obtained mixture was melt-kneaded at a resin temperature of 220°C using a twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX], and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle).

[0206] [Preparation of Expanded Beads and Expanded Molded Articles] A 10 L pressure-resistant autoclave was charged with 100 parts by weight (2.4 kg) of the polypropylene resin particles obtained as described above, 200 parts by weight of water, 0.3 parts by weight of kaolin (manufactured by BASF, ASP170) as a dispersant, and 0.038 parts by weight of an aqueous solution of sodium dodecylbenzenesulfonate (manufactured by Kao Corporation, Neopelex G-15, a 16% aqueous solution of sodium dodecylbenzenesulfonate) as a dispersing aid, and then 4 parts by weight of carbon dioxide as a blowing agent was added under stirring. The contents of the autoclave were heated to a foaming temperature of 155.5°C and maintained for 10 minutes. After that, carbon dioxide was additionally injected to increase the internal pressure of the autoclave to a foaming pressure of 2.2 MPa. After maintaining the foaming temperature and foaming pressure for 20 minutes, the valve at the bottom of the autoclave was opened, and the foam was released through an orifice with a diameter of 3.6 mm to atmospheric pressure, yielding expanded polypropylene resin beads with an expansion ratio of 17. During this release, carbon dioxide was injected to maintain the pressure in the container so as not to decrease the pressure.

[0207] The resulting expanded beads were dried at 80°C, and then impregnated with pressurized air in a pressure vessel until the internal pressure reached 0.3 MPa (absolute pressure), followed by contact with water vapor at 0.07 MPa (gauge pressure) to cause second-stage expansion. The resulting second-stage expanded beads had an expansion ratio of 25 times.

[0208] The resulting two-stage expanded beads were placed in a pressure-resistant container and impregnated with pressurized air. The expanded polypropylene resin beads, previously adjusted to an internal pressure of 0.20 MPa (absolute pressure), were then filled into a mold measuring 370 mm long, 320 mm wide, and 50 mm thick. The mold chamber was then heated with steam at 0.30 MPa to fuse the expanded beads together. The mold interior and the surface of the molded article were then water-cooled, after which the molded article was removed to obtain a polypropylene resin in-mold foamed article. The resulting in-mold foamed article was left to stand at 23°C for 2 hours and then aged at 75°C for 16 hours.

[0209] (Examples 2 and 3) Polypropylene-based resin particles, expanded polypropylene-based resin particles, and in-mold polypropylene-based resin foamed molded articles were prepared by the same procedures as in Example 1, except that in [Preparation of resin particles] the formulation was changed as shown in Table 1 or Table 2, and in [Preparation of expanded particles and foamed molded articles] the foaming conditions were changed as shown in Table 1 or Table 2.

[0210] (Examples 4 and 5) (a) Non-recycled polypropylene resin in the amount shown in Table 1, (b) Recycled Material-1 and Recycled Material-2 in the amounts shown in Table 1, (c) 3 parts by weight of carbon black A, (d) 0.2 parts by weight of glycerin, (e) 0.05 parts by weight of talc, and (f) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The resulting mixture was melt-kneaded at a resin temperature of 220°C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle). Polypropylene resin expanded beads and polypropylene resin in-mold foamed molded articles were produced using the same procedures as in Example 1, except that the foaming conditions in [Preparation of Expanded Beads and Expanded Molded Articles] were changed as shown in Table 1.

[0211] Comparative Example 1 (a) Non-recycled polypropylene resin in the amount shown in Table 1, (b) recycled material-1 and recycled material-2 in the amounts shown in Table 1, (c) 0.2 parts by weight of glycerin, (d) 0.05 parts by weight of talc, and (e) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The resulting mixture was melt-kneaded at a resin temperature of 220°C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle). In the [Preparation of Expanded Beads and Expanded Molded Articles] section, the same procedures as in Example 1 were used to prepare expanded polypropylene resin beads and polypropylene resin in-mold expanded molded articles, except that the expansion conditions were changed as shown in Table 2.

[0212] Comparative Example 2: (a) Recycled Material-1 in the amount shown in Table 1, (b) 3 parts by weight of Carbon Black A, (c) 0.2 parts by weight of glycerin, (d) 0.05 parts by weight of talc, and (e) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The resulting mixture was melt-kneaded at a resin temperature of 220°C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene-based resin particles (1.2 mg / particle). In the [Preparation of Expanded Beads and Expanded Molded Articles] section, polypropylene-based resin expanded beads and polypropylene-based resin in-mold expanded molded articles were prepared using the same procedures as in Example 1, except that the expansion conditions were changed as shown in Table 2.

[0213] Comparative Example 3: (a) Recycled Material-1 and Recycled Material-2 in the amounts shown in Table 1, (b) 3 parts by weight of carbon black A, (c) 0.2 parts by weight of glycerin, (d) 0.05 parts by weight of talc, and (e) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The resulting mixture was melt-kneaded at a resin temperature of 220°C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene-based resin particles (1.2 mg / particle). Polypropylene-based resin expanded beads and polypropylene-based resin in-mold foamed molded articles were produced using the same procedures as in Example 1, except that the foaming conditions in [Preparation of Expanded Beads and Expanded Molded Articles] were changed as shown in Table 2.

[0214] Reference Example 1 (a) 100 parts by weight of non-recycled polypropylene resin, (b) 3 parts by weight of carbon black A, (c) 0.2 parts by weight of glycerin, (d) 0.05 parts by weight of talc, and (e) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The obtained mixture was melt-kneaded at a resin temperature of 220°C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2-m-long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle). [Preparation of Expanded Beads and Expanded Molded Articles] Polypropylene resin expanded beads and polypropylene resin in-mold expanded molded articles were prepared using the same procedures as in Example 1, except that the expansion conditions were changed as shown in Table 2. The evaluation results of the obtained polypropylene resin expanded beads and polypropylene resin in-mold expanded molded articles are shown in Table 2.

[0215] (Reference Example 2) (a) 100 parts by weight of non-recycled polypropylene resin, (b) 3 parts by weight of carbon black A, (c) 0.2 parts by weight of glycerin, (d) 0.25 parts by weight of talc, and (e) 0.10 parts by weight of a hindered amine flame retardant were dry-blended using a blender to obtain a mixture. The obtained mixture was melt-kneaded at a resin temperature of 220 ° C using the same twin-screw extruder as in Example 1, and the extruded strand was water-cooled in a 2 m long water tank and then cut to produce polypropylene resin particles (1.2 mg / particle). [Preparation of expanded particles and expanded molded products] Polypropylene resin expanded particles and polypropylene resin in-mold expanded molded products were prepared using the same procedures as in Example 1, except that the expansion conditions were changed as shown in Table 2.

[0216] The formulations of the polypropylene resin particles during production in each of the Examples, Comparative Examples, and Reference Examples are shown in Table 1 or Table 2. In Table 1 or Table 2, (i) the amount of carbon black B is the total amount of the carbon black B derived from recycled materials and the amount of carbon black B added separately, and (ii) the amount of talc is the total amount of the talc derived from recycled materials and the amount of talc added separately.

[0217] The expanded polypropylene resin particles and in-mold foamed polypropylene resin articles obtained in each of the Examples, Comparative Examples, and Reference Examples were subjected to various measurements and evaluations. The results are shown in Table 1 or Table 2.

[0218] Reference Examples 1 and 2 show the evaluation results of conventional expanded beads that do not contain recycled materials. As can be seen from a comparison of Reference Examples 1 and 2, it has been confirmed that increasing the amount of talc contained in resin beads from 0.05 parts by weight to 0.25 parts by weight conventionally reduces the average cell diameter and worsens color unevenness. Examples 1 to 5 show the evaluation results of expanded polypropylene resin beads and in-mold foamed polypropylene resin articles according to one embodiment of the present invention. As can be seen from Examples 1 to 5, in-mold foamed articles made of expanded polypropylene resin beads obtained by this production method are free of color unevenness, have excellent blackness and surface appearance, and exhibit good flame retardancy, even when containing 0.25 parts by weight or more of talc. As in Comparative Examples 1 to 3, when the structure size is 1.0 x 10 ４ nm ２ When the ratio of carbon black is reduced below this level, there is room for improvement in blackness and flame retardancy.

[0219] The polypropylene-based expanded beads according to one embodiment of the present invention have the advantage of being able to improve the blackness and flame retardancy of the molded product. The polypropylene-based expanded molded article can be suitably used for various applications such as cushioning packaging materials, logistics materials, heat insulating materials, civil engineering and construction materials, and automotive components.

Claims

1. A polypropylene-based resin expanded particle containing a base resin and carbon black, The base resin includes a non-recycled polypropylene-based resin, a recycled polypropylene-based resin and / or a recycled polyethylene-based resin, The total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 10 parts by weight to 60 parts by weight per 100 parts by weight of the base resin, The carbon black has a structure size of 1×10 per structure relative to the total number of the carbon black. ４ nm ２ The proportion of the number of carbon black particles that is less than 10% to 50%.

2. Average structure size is 0.2 x 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ Carbon black A having an average structure size of less than 5.0×10 ４ nm ２ Above 9.0 x 10 ４ nm ２ and carbon black B, which is less than 1.

0.

3. The polypropylene resin expanded particles according to claim 1 , further comprising a foam nucleating agent.

4. 4. The polypropylene resin expanded particles according to claim 3, wherein the content of the foaming nucleating agent is 0.05 to 0.50 parts by weight based on 100 parts by weight of the base resin.

5. 4. The polypropylene resin expanded particles according to claim 3, wherein the content of the foaming nucleating agent is 0.20 parts by weight to 0.50 parts by weight based on 100 parts by weight of the base resin.

6. The polypropylene resin expanded particles according to claim 3, wherein the foam nucleating agent is talc.

7. The expanded polypropylene resin particles according to claim 1 , further comprising a hindered amine flame retardant.

8. 3. The expanded polypropylene resin particles according to claim 2, wherein the content of the carbon black A is 0.1 to 5.0 parts by weight based on 100 parts by weight of the base resin.

9. 3. The expanded polypropylene resin particles according to claim 2, wherein the content of the carbon black B is 0.10 parts by weight to 2.00 parts by weight based on 100 parts by weight of the base resin.

10. The expanded polypropylene resin particles according to claim 1 , wherein the base resin comprises the recycled polyethylene resin, and the recycled polyethylene resin comprises a recycled high-density polyethylene resin.

11. 2. The polypropylene-based resin expanded particles according to claim 1, wherein the recycled polypropylene-based resin is 60 parts by weight to 100 parts by weight, and the recycled polyethylene-based resin is 0 parts by weight to 40 parts by weight, when the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 100 parts by weight.

12. Average structure size is 10.0 x 10 ４ nm ２ 2. The expanded polypropylene resin particles according to claim 1, wherein the expanded polypropylene resin particles contain no carbon black C having a molecular weight of 100 or more, or contain less than 0.5 parts by weight of carbon black C per 100 parts by weight of the base resin.

13. The polypropylene-based resin expanded particles according to claim 1, wherein the non-recycled polypropylene-based resin contains 60% by weight or more of one or more selected from the group consisting of ethylene / propylene alternating copolymers, ethylene / 1-butene / propylene alternating copolymers, ethylene / propylene random copolymers, and ethylene / 1-butene / propylene random copolymers, based on 100% by weight of the non-recycled polypropylene-based resin.

14. The expanded polypropylene resin particles according to claim 1, wherein the base resin comprises the recycled polypropylene resin, and the recycled polypropylene resin comprises at least one selected from the group consisting of an ethylene / propylene alternating copolymer, an ethylene / 1-butene / propylene alternating copolymer, an ethylene / propylene random copolymer, and an ethylene / 1-butene / propylene random copolymer.

15. The polypropylene-based resin expanded particles according to claim 1, wherein the base resin contains 80 to 100 parts by weight of the non-recycled polypropylene-based resin, the recycled polypropylene-based resin, and the recycled polyethylene-based resin in total, per 100 parts by weight of the base resin.

16. A polypropylene resin foamed molded article obtained by molding the expanded polypropylene resin beads according to any one of claims 1 to 15.

17. Non-recycled polypropylene resin, recycled material, and an average structure size of 0.2 × 10 ４ nm ２ Above 4.0 x 10 ４ nm ２ and a granulation step of melt-kneading a mixture containing carbon black A having a molecular weight of less than 1000 to obtain polypropylene-based resin particles. a dispersing step of dispersing the polypropylene-based resin particles, an aqueous dispersion medium, and a blowing agent in a container; a heating step of heating the temperature inside the container to a temperature equal to or higher than the softening temperature of the polypropylene-based resin particles; a pressurizing step of increasing the pressure inside the container; and releasing the dispersion liquid in the container into a region having a pressure lower than the pressure in the container. The recycled material is a recycled polypropylene-based resin and / or a recycled polyethylene-based resin, and a cellulose ether having an average structure size of 5.0×10 ４ nm ２ Above 9.0 x 10 ４ nm ２ and carbon black B, The method for producing expanded polypropylene-based resin particles, wherein the amount of the recycled material used is an amount such that the total content of the recycled polypropylene-based resin and the recycled polyethylene-based resin is 10 parts by weight to 60 parts by weight per 100 parts by weight of a base resin containing the non-recycled polypropylene-based resin and the recycled polypropylene-based resin and / or the recycled polyethylene-based resin.