Polypropylene resin foam particles, polypropylene resin foam molded articles, and methods for producing polypropylene resin foam particles

Abstract

The present invention addresses the problem of providing polypropylene-based foamed resin particles which contain a recycled polypropylene-based resin and with which it is possible to provide a polypropylene-based foamed resin molded body having excellent internal fusion properties. The polypropylene-based foamed resin particles contain a base material resin containing a non-recycled polypropylene-based resin and a specific amount of a recycled material that contains a recycled polypropylene-based resin. The crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene-based resin.

Description

[Technical Field]

[0001] The present invention relates to polypropylene resin foam particles, polypropylene resin foam molded articles, and a method for producing polypropylene resin foam particles. [Background technology]

[0002] Polypropylene-based foamed resin molded products are used in a variety of applications, including automotive interior components, core materials for automotive bumpers, as well as insulation materials, cushioning packaging materials, and reusable containers.

[0003] In recent years, in order to reduce environmental impact, there has been a demand for the use of recycled resins when manufacturing resin products, and the use of recycled resins has attracted attention (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-049877 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the conventional technologies described above, which use recycled polypropylene resin, are not sufficient from the standpoint of internal fusion properties of foamed molded products, and there is room for further improvement.

[0006] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide a novel polypropylene resin foam particle that contains recycled polypropylene resin and can provide a polypropylene resin foam molded article with excellent internal fusion properties. [Means for solving the problem]

[0007] As a result of diligent research to solve the aforementioned problems, the present inventors have independently discovered the following novel findings and completed the present invention: If polypropylene resin foam particles contain a non-recycled polypropylene resin and a specific amount of recycled material having a crystallization temperature higher than that of the non-recycled polypropylene resin, it is possible to provide a polypropylene resin foam molded article with excellent internal fusion properties.

[0008] In other words, the polypropylene resin foam particles according to one embodiment of the present invention are polypropylene resin foam particles containing a base resin, wherein the base resin contains a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin, the content of the recycled material in the base resin is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin.

[0009] Furthermore, a method for producing polypropylene resin foam particles according to one embodiment of the present invention comprises: a granulation step of melting and kneading a base resin containing a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin to obtain polypropylene resin particles; a dispersion step of dispersing the polypropylene resin particles, an aqueous dispersion medium, and a foaming agent in a container to obtain a dispersion liquid; a heating step of heating the temperature of the dispersion liquid to a temperature above the softening temperature of the polypropylene resin particles; a pressurizing step of increasing the pressure inside the container; and a release step of releasing the dispersion liquid inside the container into a region with a pressure lower than the pressure inside the container, wherein the amount of recycled material used is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin. [Effects of the Invention]

[0010] According to one embodiment of the present invention, there is provided an effect that novel polypropylene-based resin foam particles containing recycled polypropylene-based resin can provide a polypropylene-based resin foam molded body having excellent internal fusion properties.

Embodiments for Carrying Out the Invention

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

[0012] In this specification, when the "structural unit derived from the X monomer" contained in the polymer, copolymer or resin is referred to as "X unit".

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

[0014] In this specification, "polypropylene resin particles" may be referred to as "resin particles," "polypropylene resin foam particles" may be referred to as "foamed particles," "polypropylene resin foam particles according to one embodiment of the present invention" may be referred to as "the foamed particles," "polypropylene resin foam molded article" may be referred to as "foamed article," and "polypropylene resin foam molded article according to one embodiment of the present invention" may be referred to as "the foamed article." In this specification, "method for producing polypropylene resin foam particles" may be referred to as "manufacturing method," and "method for producing polypropylene resin foam particles according to one embodiment of the present invention" may be referred to as "the manufacturing method."

[0015] [1. Polypropylene resin foam particles] Polypropylene resin foam particles according to one embodiment of the present invention include a base resin, the base resin includes a non-recycled polypropylene resin and a recycled material including a recycled polypropylene resin, the content of the recycled material in the base resin is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin.

[0016] These foamed particles can be molded by known methods to provide a foamed molded article (this foamed molded article).

[0017] The expanded particles contain a recycled material containing a recycled polypropylene-based resin. Further, since the expanded particles have the above-described configuration, they have the advantage of being able to provide a polypropylene-based resin foam molded body excellent in internal fusion properties. A foam molded body formed by molding expanded particles containing a recycled material containing a recycled polypropylene-based resin also contains a recycled material containing a recycled polypropylene-based resin. That is, the expanded particles and the foam molded body contain a recycled material (recycled polypropylene-based resin) as described above. Therefore, it can be said that the expanded particles and the foam molded body have a small environmental load. In other words, in one embodiment of the present invention, a recycled material (recycled polypropylene-based resin) is used. Therefore, one embodiment of the present invention can not only reduce environmental pollution but also greatly reduce the amount of plastic waste generated and the amount of plastic used in manufacturing. Thereby, one embodiment of the present invention can contribute to the achievement of the Sustainable Development Goals (SDGs), for example, Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and use oceans and marine resources in a sustainable manner for sustainable development".

[0018] The polypropylene-based resin expanded particles according to a preferred embodiment of the present invention surprisingly also have the advantage that the molding cycle when manufacturing a foam molded body from the expanded particles is short.

[0019] The polypropylene-based resin expanded particles according to a preferred embodiment of the present invention can also be said to be polypropylene-based resin expanded particles obtained by expanding polypropylene-based resin particles containing a base resin.

[0020] <Component> (2-1. Base resin) In the present specification, the base resin is intended to be a resin component that substantially constitutes polypropylene-based resin expanded particles and a polypropylene-based resin foam molded body. The base resin contains a non-recycled polypropylene-based resin and a recycled material.

[0021] In this specification, “recycled material” means (a) a resin composition (or pellet) that has been repurposed from a resin product (e.g., foamed particles; foamed molded bodies; films; food trays; packaging containers such as bags and bottles; medical containers such as drip bags and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts; etc.) after it has been used and / or discarded, by any means (e.g., crushing, shredding, melting, and combinations thereof), and (b) a resin composition (or pellet) that has been repurposed from waste generated during the manufacturing process of resin products by any means (e.g., crushing, shredding, melting, and combinations thereof). In the recovery of resin products, resin products are often recovered according to their intended use and / or according to their raw materials. Therefore, recycled material may mainly consist of resins of the same or substantially the same composition (e.g., polypropylene resins and polyethylene resins). On the other hand, in the collection of resin products, the resin products intended for collection may be mixed with resin products for different uses and / or resin products made from different raw materials. Therefore, recycled materials may contain resins of other compositions in addition to the main resin they contain.

[0022] In this specification, the resin contained in recycled materials may be referred to as "recycled resin." For example, recycled materials obtained by (a) converting a resin product obtained using polypropylene resin as the main raw material back into a resin composition by any means, and / or (b) converting waste discharged during the manufacturing process of a resin product using polypropylene resin as the main raw material back into a resin composition by any means, include recycled polypropylene resin as the recycled resin. Recycled materials that mainly contain recycled polypropylene resin as the resin may also contain recycled polyethylene resin as the recycled resin in an amount less than the amount of recycled polypropylene resin.

[0023] Recycled materials may contain additives used in the manufacturing process of resin products (for example, foaming nucleating agents (e.g., talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium dioxide, zinc borate, etc.) and colorants, as described later in section (2-3. Additives)).

[0024] In this specification, the origin of recycled materials is not particularly limited. Recycled materials may be derived from foams such as foamed particles and foamed molded products. Recycled materials may also be derived from non-foams (e.g., films; food trays; packaging containers such as bags and bottles; medical containers such as drip bags and syringes; clothing cases; miscellaneous goods such as clear files; home appliances; automobile parts; fishing gear such as fishing nets, ropes, and floats).

[0025] In this specification, polypropylene resins that have never been in the form of a resin product are referred to as "non-recycled polypropylene resins."

[0026] (Polypropylene resin) For the purposes of this section only, unless otherwise specified, "polypropylene resin" refers to both non-recycled polypropylene resin and recycled polypropylene resin.

[0027] In this specification, "polypropylene resin" refers to a resin in which propylene units have the highest content among all constituent units. For example, a polypropylene resin contains 50 mol% or more of propylene units per 100 mol% of all structural units.

[0028] Polypropylene resins may be (i) homopolymers of propylene, (ii) block copolymers, alternating copolymers, random copolymers, or graft copolymers of propylene and monomers other than propylene, or (iii) mixtures of two or more of these. Block copolymers are sometimes called impact copolymers. Homopolymers of propylene, block copolymers, alternating copolymers, and random copolymers of propylene and monomers other than propylene are all linear polymers. Polypropylene resins are preferably linear polymers.

[0029] Polypropylene resins may contain one or more constituent units derived from monomers other than propylene monomers, in addition to propylene units, or may contain one or more of these units. The "monomers other than propylene monomers" used in the manufacture of polypropylene resins are sometimes referred to as "comonomers," and the "constituent units derived from monomers other than propylene monomers" contained in polypropylene resins are sometimes referred to as "comonomer units."

[0030] Examples of comonomers used in the production of polypropylene resins 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.

[0031] Specific examples of polypropylene 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, and styrene-modified polypropylene resins. These polypropylene resins may be used individually or in combination of two or more types.

[0032] Polypropylene resins can be obtained by known methods. There are no particular restrictions on the polymerization catalyst used when synthesizing polypropylene resins; Ziegler-Natta catalysts and metallocene catalysts can be used. From the viewpoint of availability, manufacturing cost, production stability, and the foaming properties of the resulting resin particles, it is preferable that polypropylene resins (i.e., non-recycled polypropylene resins and / or recycled polypropylene resins) are polymerized using a Ziegler-Natta catalyst. Resins polymerized using a Ziegler-Natta catalyst may contain the Ziegler-Natta catalyst. In other words, it is preferable that polypropylene resins contain a Ziegler-Natta catalyst. However, it is extremely difficult to determine whether a polypropylene resin is polymerized using a Ziegler-Natta catalyst or a metallocene catalyst by analyzing the polypropylene resin itself.

[0033] (Non-recycled polypropylene resin) The following section will describe non-recycled polypropylene resins.

[0034] From the viewpoint of moldability, it is preferable that the non-recycled polypropylene resin is (a) an alternating copolymer composed of propylene units and comonomer units (e.g., ethylene units and 1-butene units) in which both units are arranged alternately, and / or (b) a random copolymer composed of propylene units and comonomer units (e.g., ethylene units and 1-butene units) in which both units are arranged in a random order. It is more preferable that the non-recycled polypropylene resin contains 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, due to their availability.

[0035] From the viewpoint of moldability and availability, the non-recycled polypropylene resin preferably 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, more preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, in 100% by weight of the non-recycled polypropylene resin. The upper limit of the content of one or more selected from the above group in 100% by weight of the non-recycled polypropylene resin is not particularly limited, for example, 100% by weight. Most preferably, the non-recycled polypropylene resin consists only 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.

[0036] The crystallization temperature of the non-recycled polypropylene resin is not particularly limited. The crystallization temperature of the non-recycled polypropylene resin is preferably 95°C to 120°C, more preferably 98°C to 117°C, even more preferably 100°C to 115°C, even more preferably 103°C to 112°C, and particularly preferably 105°C to 110°C. This configuration has the advantage that the bubble diameter of the polypropylene resin foam particles is less likely to become fine. The method for measuring the crystallization temperature of the non-recycled polypropylene resin will be described in detail in the following examples.

[0037] The melt flow rate (sometimes referred to as "MFR") of non-recycled polypropylene resin at 230°C is not particularly limited. The MFR of non-recycled polypropylene resin at 230°C is preferably 1 g / 10 min or more, more preferably 2 g / 10 min or more, more preferably 3 g / 10 min or more, even more preferably 4 g / 10 min or more, and particularly preferably 5 g / 10 min or more. When the MFR of non-recycled polypropylene resin at 230°C is 1 g / 10 min or more, it tends to be easier to increase the foaming ratio of the foamed particles in the production of these foamed particles. The MFR of non-recycled polypropylene resin at 230°C is preferably 30 g / 10 min or less, more preferably 25 g / 10 min or less, even more preferably 20 g / 10 min or less, even more preferably 15 g / 10 min or less, and particularly preferably 10 g / 10 min or less. When the MFR of non-recycled polypropylene resin at 230°C is 30 g / 10 min or less, there is no risk of the bubbles in the resulting foamed particles becoming interconnected, and as a result, (i) the compressive strength of the foamed molded article obtained from these foamed particles tends to be good, (ii) the surface quality of the foamed molded article tends to be good, and / or (iii) the molding cycle of the foamed molded article tends to be shorter. Note that the "bubbles" of the foamed particles may also be referred to as "cells". In other words, in this specification, "bubbles" may be read as "cells", and "cells" may be read as "bubbles". The method for measuring the MFR of non-recycled polypropylene resin at 230°C will be described in detail in the following examples.

[0038] The melting point of the non-recycled polypropylene resin is not particularly limited. The melting point of the non-recycled polypropylene resin is preferably 160°C or lower, more preferably 158°C or lower, more preferably 155°C or lower, even more preferably 153°C or lower, and particularly preferably 152°C or lower. When the melting point of the non-recycled polypropylene resin is 160°C or lower, it becomes easier to increase the foaming ratio of the foam particles in the production of these foam particles. The melting point of the non-recycled polypropylene resin is preferably 125°C or higher, more preferably 127°C or higher, more preferably 130°C or higher, even more preferably 132°C or higher, and particularly preferably 135°C or higher. When the melting point of the non-recycled polypropylene resin is 125°C or higher, the foam molded article obtained from these foam particles has excellent heat resistance. The method for measuring the melting point of the non-recycled polypropylene resin will be described in detail in the following examples.

[0039] (2-2. Recycled Materials) In one embodiment of the present invention, the recycled material includes a recycled polypropylene resin. That is, the base resin includes at least a non-recycled polypropylene resin and a recycled polypropylene resin.

[0040] (Recycled polypropylene resin) The following section will explain recycled polypropylene resins.

[0041] From the viewpoint of moldability, it is preferable that the recycled polypropylene resin is (a) a block copolymer composed of propylene units and comonomer units (e.g., ethylene units and 1-butene units), and comprising a block structure consisting only of propylene units and a block structure consisting only of comonomer units; (b) an alternating copolymer composed of propylene units and comonomer units (e.g., ethylene units and 1-butene units), in which both units are arranged alternately; and / or (c) a random copolymer composed of propylene units and comonomer units (e.g., ethylene units and 1-butene units), in which both units are arranged in a random order. In the block copolymer, the arrangement order of the block structure consisting only of propylene units and the block structure consisting only of comonomer units is not particularly limited. Because they are readily available, recycled polypropylene resins more preferably contain one or more selected from the group consisting of ethylene / propylene block copolymer, ethylene / 1-butene / propylene block copolymer, ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer.

[0042] From the viewpoint of moldability and availability, recycled polypropylene resins contain ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer and ethylene / 1-Butene / It is preferable that the recycled polypropylene resin contains 60% by weight or more of one or more selected from the group consisting of propylene random copolymers, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. Most preferably, the recycled polypropylene resin consists of only one or more selected from the group consisting of ethylene / propylene block copolymer, ethylene / 1-butene / propylene block copolymer, ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer.

[0043] Because of their excellent recyclability and moldability, recycled materials preferably contain mainly recycled polypropylene resin as the recycled resin. Because of their excellent recyclability and moldability, recycled materials preferably contain 50 parts by weight or more of recycled polypropylene resin per 100 parts by weight, more preferably 60 parts by weight or more, even more preferably 70 parts by weight or more, and particularly preferably 80 parts by weight or more. There is no particular upper limit to the content of recycled polypropylene resin in recycled materials; for example, it may be 100 parts by weight per 100 parts by weight of recycled material, or it may be less than 100 parts by weight.

[0044] The base resin preferably contains a total of 60 to 100 parts by weight of non-recycled polypropylene resin and recycled polypropylene resin per 100 parts by weight of the base resin, more preferably 70 to 100 parts by weight, and even more preferably 80 to 100 parts by weight. This configuration has the advantage of minimizing the reduction in strength of the resulting foamed molded article.

[0045] (Recycled polyethylene resin) The recycled material may include recycled polyethylene resin. In other words, the base resin may contain recycled polyethylene resin in addition to non-recycled polypropylene resin and recycled polypropylene resin.

[0046] In this specification, "recycled polyethylene resin" refers to a recycled resin in which ethylene units have the highest content among all constituent units of the resin. For example, a recycled polyethylene resin contains 50 mol% or more of ethylene units per 100 mol% of all structural units.

[0047] In this specification, a resin in which the amounts of propylene units and ethylene units constituting the resin are equal is referred to as a "polypropylene resin."

[0048] Because of its excellent recyclability and moldability, it is preferable that the amount of recycled polyethylene resin in the recycled material be as small as possible. The recycled material preferably contains 20 parts by weight or less of recycled polyethylene resin per 100 parts by weight, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 1 part by weight or less. The amount of recycled polyethylene resin in the recycled material may be greater than 0 parts by weight, or 0 parts by weight. In other words, the recycled material may not contain recycled polyethylene resin at all.

[0049] The crystallization temperature of the recycled material is not particularly limited, as long as it is higher than the crystallization temperature of the non-recycled polypropylene resin. The crystallization temperature of the recycled material is preferably 100°C to 130°C, more preferably 103°C to 125°C, even more preferably 105°C to 120°C, even more preferably 107°C to 115°C, and particularly preferably 108°C to 113°C. This configuration has the advantage that the bubble diameter of the polypropylene resin foam particles does not tend to become fine. In addition, the crystallization temperature of the recycled material may change due to the influence of the ash content contained in the recycled material (residue that remains without burning when burned at 750°C for more than one hour). The method for measuring the crystallization temperature of the recycled material will be described in detail in the following examples.

[0050] The difference between the crystallization temperature of the recycled material and the crystallization temperature of the non-recycled polypropylene resin is not particularly limited. It is preferable that the difference between the crystallization temperature of the recycled material and the non-recycled polypropylene resin be 1°C or more, as this allows for the provision of a foamed molded article with superior internal fusion properties of the foamed particles. Through diligent research, the inventors have discovered a novel finding: when the difference between the crystallization temperature of the recycled material and the non-recycled polypropylene resin is 17°C or less, it has the advantage of making it less likely for the foamed polypropylene resin particles to have very fine bubbles. Therefore, it is preferable that the difference between the crystallization temperature of the recycled material and the non-recycled polypropylene resin be 17°C or less, and more preferably 15°C or less.

[0051] The MFR of the recycled material at 230°C is not particularly limited. Preferably, the MFR of the recycled material at 230°C is 1 g / 10 min to 30 g / 10 min, more preferably 1 g / 10 min to 25 g / 10 min, even more preferably 2 g / 10 min to 20 g / 10 min, and particularly preferably 3 g / 10 min to 18 g / 10 min. With this configuration, there is no risk of the bubbles in the resulting foam particles becoming interconnected, and as a result, (i) the compressive strength of the foam molded article obtained from these foam particles tends to be good, (ii) the surface quality of the foam molded article tends to be good, and / or (iii) the molding cycle of the foam molded article tends to be shorter. Furthermore, when the MFR of the recycled material at 230°C is within the above range, the compatibility between the non-recycled polypropylene resin and the recycled material tends to be good, and / or it tends to be easier to increase the foaming ratio of the foam particles in the production of these foam particles. The method for measuring the MFR of the recycled material at 230°C will be described in detail in the following examples.

[0052] The melting point of the recycled material is not particularly limited. The melting point of the recycled material is preferably 135°C to 170°C, more preferably 140°C to 165°C, even more preferably 143°C to 160°C, and particularly preferably 145°C to 158°C. This configuration offers the advantages of (i) making it easier to increase the foaming ratio of the foam particles in the production of the foam particles, (ii) providing excellent heat resistance to the foamed molded article obtained from the foam particles, and / or (iii) ensuring good compatibility between the non-recycled polypropylene resin and the recycled material. The method for measuring the melting point of the recycled material will be described in detail in the following examples.

[0053] The recycled material content in the base resin is 10 to 90 parts by weight per 100 parts by weight of the base resin, preferably 15 to 90 parts by weight, more preferably 20 to 90 parts by weight, even more preferably 23 to 90 parts by weight, and particularly preferably 25 to 87 parts by weight. This configuration has the advantage of further reducing the burden on the environment.

[0054] As mentioned above, recycled materials may include additives used in the manufacturing process of resin products. In this specification, even if recycled materials include additives that are not resin components, the amount of recycled material used is defined as the content of recycled material in the base resin of the resulting foamed particles.

[0055] (Other resins, etc.) The base resin may further contain resins other than non-recycled polypropylene resin and the recycled material described above (sometimes referred to as "other resins, etc.") to the extent that it does not impair the effects of the embodiment of the present invention. Examples of the other resins, etc. include (a) non-recycled polyethylene resin, (b) recycled material that does not contain recycled polypropylene resin, (c) styrene resins such as polystyrene, styrene / maleic anhydride copolymer and styrene / ethylene copolymer, (d) polyolefin waxes such as propylene-α-olefin wax, and (e) olefin rubbers such as ethylene / propylene rubber, ethylene / butene rubber, ethylene / hexene rubber and ethylene / octen rubber. The content of the 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 resin and the recycled material containing recycled polypropylene resin.

[0056] (2-3. Additives) These foamed particles may optionally contain additives in addition to a base resin containing a non-recycled polypropylene resin and recycled material containing a recycled polypropylene resin. These additives may include colorants, water-absorbing substances (e.g., (i) polyols such as glycerin and diglycerin, (ii) polyethers such as polyethylene glycol and polyethylene oxide, and (iii) metal borate salts such as borax and zinc borate), foaming nucleating agents (e.g., inorganic substances such as talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium dioxide, and zinc borate), and antistatic agents (e.g., glycerin monostearate, glycerin monostearate). • Distearates, etc.), flame retardants (e.g., hindered amine flame retardants, brominated flame retardants, phosphate ester flame retardants, melamine flame retardants, etc.), antioxidants (e.g., hindered phenol antioxidants, etc.), heat stabilizers (e.g., phosphorus heat stabilizers and sulfur heat stabilizers, etc.), light stabilizers (benzotriazole UV absorbers, triazine UV absorbers, HALS and / or hindered amine light stabilizers, etc.), nucleating agents, conductive agents (carbon, carbon nanotubes, metal fillers, etc.), lubricants, acids capture Examples of additives include anti-blocking agents, metal chelating agents (such as IRGANOX MD1024 and Adekastab CDA-1), lubricants, and antibacterial agents. Furthermore, these foamed particles may contain any one of these additives, or a combination of two or more, as additives for recycled materials.

[0057] (Coloring agent) Examples of colorants include chromatic pigments and carbon black. In this specification, "chromatic pigments" refers to pigments that can produce colors other than white, gray, and black. In this specification, "chromatic pigments" does not include carbon black. Examples of chromatic pigments include (i) blue pigments such as copper phthalocyanine blue, ultramarine, cobalt blue, and Prussian blue; (ii) red pigments such as perylene red, quinacridone red, and cadmium red; (iii) yellow pigments such as condensed azo yellow, cadmium yellow, and barium chromate; (iv) green pigments obtained by combining blue and yellow pigments; (v) orange pigments obtained by combining red and yellow pigments; and (vi) purple pigments such as cobalt violet and pigments obtained by combining blue and red pigments.

[0058] Since the color and / or stains derived from recycled materials become less noticeable, it is preferable that these foamed particles further contain carbon black in addition to the base resin, even if the recycled material contained in the base resin already contains carbon black.

[0059] (i) The amount of carbon black added separately from the base resin in the granulation process can be reduced, thereby increasing the proportion of recycled material in the base resin, and (ii) the color tone of the foamed particles tends to be more uniform, therefore, it is preferable that the recycled material contains carbon black.

[0060] In one embodiment of the present invention, the carbon black content in the polypropylene resin foam particles is not particularly limited. In this specification, "carbon black content in the polypropylene resin foam particles" refers to the total amount of carbon black contained in the recycled material in the base resin and the amount of carbon black included separately (blended) from the base resin. The carbon black content in these foam particles is preferably 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin. This configuration has the advantage that the color and / or stains derived from the recycled material are less noticeable.

[0061] Since the color and / or stains derived from recycled materials become less noticeable, it is preferable that these foamed particles further contain chromatic pigments separately from the base resin, even if the recycled materials contained in the base resin already contain chromatic pigments.

[0062] (i) The amount of chromatic pigment added separately from the base resin in the granulation process can be reduced, thereby increasing the proportion of recycled material in the base resin, and (ii) the color tone of the foamed particles tends to be more uniform, therefore it is preferable that the recycled material contains chromatic pigment.

[0063] <Physical properties> (DSC ratio of foamed particles) Preferably, these foamed particles have at least two melting peaks in the DSC curve obtained by differential scanning calorimetry, as described below. Of these melting peaks, the heat of fusion obtained from the higher temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the lower temperature melting peak is defined as the "low-temperature side heat of fusion." If there are three or more melting peaks, the heat of fusion obtained from the highest temperature melting peak is defined as the "high-temperature side heat of fusion," and the heat of fusion obtained from the other melting peaks is defined as the "low-temperature side heat of fusion."

[0064] The DSC ratio of the foamed particles is not particularly limited. Preferably, the DSC ratio of the foamed particles is 10.0% to 50.0%, more preferably 15.0% to 40.0%, even more preferably 18.0% to 30.0%, and particularly preferably 20.0% to 28.0%. When the DSC ratio of the foamed particles is 10.0% or higher, the foamed particles have the advantage of providing a foamed molded article with sufficient strength. On the other hand, when the DSC ratio of the foamed particles is 40% or lower, the foamed particles have the advantage of being able to be molded at a relatively low temperature (molding temperature) to provide a foamed molded article. The method for measuring the DSC ratio of the foamed particles will be described in detail in the following examples.

[0065] The DSC ratio of these foamed particles is also an indicator of the amount of high-melting-point crystals contained in the foamed particles. In other words, a DSC ratio of 10.0% to 50.0% indicates that the foamed particles contain a relatively large amount of high-melting-point crystals. Furthermore, the DSC ratio of the foamed particles greatly influences the viscoelasticity of the resin particles and the foamed particles during foaming and expansion. Specifically, when the DSC ratio of the foamed particles is 10.0% to 50.0%, the resin particles and the foamed particles can exhibit excellent foaming and expansion properties, respectively, during foaming and molding. As a result, the foamed particles have the advantage of producing foamed molded articles with excellent internal bonding properties at low molding pressure and excellent mechanical strength, such as compressive strength.

[0066] Methods for controlling the DSC ratio within a predetermined range in these foamed particles include adjusting the manufacturing conditions of the foamed particles (particularly the foaming temperature, foaming pressure, holding time, and the temperature of the region (space) where the dispersion is released). Because adjustments are easy, adjusting the foaming temperature, foaming pressure, and / or holding time is preferred as a method for controlling the DSC ratio within a predetermined range.

[0067] For example, increasing the foaming temperature tends to decrease the DSC ratio, while decreasing the foaming temperature tends to increase it. This is because the amount of unmelted crystals changes depending on the foaming temperature. Similarly, increasing the foaming pressure tends to decrease the DSC ratio, while decreasing the foaming pressure tends to increase it. This is because the degree of plasticization changes depending on the foaming pressure, which in turn changes the amount of unmelted crystals. Furthermore, increasing the holding time tends to increase the DSC ratio. This is because the amount of unmelted crystal growth changes depending on the holding time.

[0068] (Foaming ratio of foaming particles) The foaming ratio of these foam particles is not particularly limited. Preferably, the foaming ratio of these foam particles is greater than 1.0, more preferably 1.5 or greater, more preferably 2.0 or greater, and more preferably 2.5 or greater. A higher foaming ratio of the foam particles has the advantage of allowing for the production of lighter foamed molded articles with greater efficiency. Since lighter foamed molded articles can be produced with greater efficiency, the foaming ratio of these foam particles is more preferably 5.0 or greater, more preferably 10.0 or greater, even more preferably 13.0 or greater, and particularly preferably 15.0 or greater. Preferably, the foaming ratio of these foam particles is 50.0 or less. A lower foaming ratio of the foam particles has the advantage of yielding a foamed molded article with superior strength. Preferably, the foaming ratio of these foam particles is 45.0 or less, more preferably 40.0 or less, even more preferably 35.0 or less, and particularly preferably 30.0 or less. The method for calculating the foaming ratio of the foam particles will be explained in detail in the following examples.

[0069] (Average bubble diameter of foamed particles) The average bubble diameter of the foamed particles is not particularly limited. Preferably, the average bubble diameter of the foamed particles is 80 μm to 500 μm, more preferably 85 μm to 400 μm, even more preferably 90 μm to 300 μm, and particularly preferably 95 μm to 250 μm. (i) When the average bubble diameter of the foamed particles is 80 μm or more, the foamed particles can provide a polypropylene resin foamed molded article with excellent compressive strength, and (ii) when it is 500 μm or less, there is no risk of a longer molding cycle, resulting in the advantage of good productivity. The smaller the bubble diameter, the less likely there is to be a longer molding cycle, resulting in the advantage of good productivity. The method for measuring the average bubble diameter of the foamed particles, as well as the method for measuring and evaluating the molding cycle, will be described in detail in the following examples.

[0070] [2. Method for producing polypropylene resin foam particles] A method for producing polypropylene resin foam particles according to one embodiment of the present invention comprises: a granulation step of melting and kneading a base resin containing a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin to obtain polypropylene resin particles; a dispersion step of dispersing the polypropylene resin particles, an aqueous dispersion medium, and a foaming agent in a container to obtain a dispersion liquid; a heating step of heating the temperature of the dispersion liquid to a temperature above the softening temperature of the polypropylene resin particles; a pressurizing step of increasing the pressure inside the container; and a release step of releasing the dispersion liquid inside the container into a region with a pressure lower than the pressure inside the container, wherein the amount of recycled material used is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin.

[0071] Because this manufacturing method has the above-described structure, it has the advantage of being able to provide polypropylene resin foam particles that include recycled polypropylene resin and can provide polypropylene resin foam molded articles with excellent internal fusion properties. Furthermore, this manufacturing method uses recycled materials (recycled polypropylene resin). Therefore, this manufacturing method not only reduces environmental pollution but can also significantly reduce the amount of plastic waste generated and the amount of plastic used in manufacturing. As a result, this manufacturing method can contribute to achieving Sustainable Development Goals (SDGs), such as Goal 12, "Ensure sustainable consumption and production patterns," and Goal 14, "Conserve and sustainably use the oceans, seas and marine resources for sustainable development."

[0072] A preferred embodiment of the present invention provides a method for producing polypropylene resin foam particles, which surprisingly also has the advantage of being able to provide polypropylene resin foam particles that can provide a foamed molded article in a short molding cycle.

[0073] The following describes in detail each step and aspect of this manufacturing method. However, for matters not described in detail below, refer to the description in section [1. Polypropylene Resin Foamed Particles] above as appropriate.

[0074] (granulation process) In the granulation process, a mixture containing non-recycled polypropylene resin and recycled material containing recycled polypropylene resin is melt-kneaded. The non-recycled polypropylene resin and recycled material containing recycled polypropylene resin used in the granulation process constitute the base resin in the final polypropylene resin foam particles. Therefore, the granulation process can also be described as a process of melt-kneading a base resin containing non-recycled polypropylene resin and recycled material containing recycled polypropylene resin. Furthermore, the amount of non-recycled polypropylene resin used in the granulation process may correspond to the content of non-recycled polypropylene resin in the base resin of the final polypropylene resin foam particles. Furthermore, the amount of recycled material containing recycled polypropylene resin used in the granulation process may correspond to the content of recycled material containing recycled polypropylene resin in the base resin of the final polypropylene resin foam particles. In addition, the amount of recycled polypropylene resin in the recycled material used in the granulation process, in other words, the amount of recycled polypropylene resin used in the granulation process, may correspond to the content of recycled polypropylene resin in the base resin of the final polypropylene resin foam particles. The granulation process can also be described as a process for preparing polypropylene resin particles that include a base resin containing non-recycled polypropylene resin and recycled materials containing recycled polypropylene resin.

[0075] The apparatus used for melt-kneading the base resin (mixture) is not particularly limited, but for example, an extruder equipped with a die can be used. The extruder is not particularly limited, and a single-screw extruder or a twin-screw extruder can be suitably used.

[0076] In the granulation process, there are no particular limitations other than melting and kneading the base resin (mixture). For example, polypropylene resin particles can be prepared by performing the following steps (1) to (3) in order on the melted and kneaded base resin: (1) extrude the base resin from a die equipped with an extruder; (2) solidify the extruded base resin by cooling it by passing it through water, etc.; (3) then cut the solidified base resin with a cutter into desired shapes such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped, hollow cylindrical, polygonal prism, etc. Alternatively, the melted and kneaded base resin may be directly extruded into water from a die equipped with an extruder, the base resin may be cut into particle shapes immediately after extrusion, and the cut particles may be cooled and solidified.

[0077] In the granulation process, additional additives as described above (e.g., colorants and foaming nucleating agents) may be used. In other words, the granulation process may be a process of melting and kneading (i) a base resin containing a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin, and (ii) additives to obtain polypropylene resin particles. When additives are used in the granulation process, the final foamed particles may contain an amount of additive equal to the amount used.

[0078] In the granulation process of this manufacturing method, non-recycled polypropylene resin and recycled material are melt-kneaded together. Therefore, in the final foamed particles, the non-recycled polypropylene resin and recycled material are uniformly or nearly uniformly mixed together. In other words, these foamed particles do not need to have a core-sheath structure.

[0079] (Dispersion process) The container used in the dispersion process is not particularly limited. Examples of containers include pressure vessels and autoclave-type pressure vessels (pressure autoclaves). The container may be equipped with an agitator inside.

[0080] The aqueous dispersion medium is not particularly limited as long as it contains water. However, from the standpoint of enabling stable production of foamed particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis membrane method), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

[0081] Examples of blowing agents include (a) (a-1) inorganic gases such as nitrogen, carbon dioxide, and air (a mixture of oxygen, nitrogen, and carbon dioxide), and (a-2) water; and (b) organic blowing agents. From the viewpoint of reducing environmental impact and reducing combustion risk, inorganic blowing agents are preferred, inorganic gases and / or water are more preferred, and carbon dioxide and / or water are even more preferred. Water used as an aqueous dispersion medium can also be used as a blowing agent. In this case, both the aqueous dispersion medium and the blowing agent in the dispersion process can be water.

[0082] In this manufacturing method, it is preferable to use dispersants (e.g., inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay) and dispersion aids (e.g., sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium alkylsulfonate, sodium alkyldiphenyl ether disulfonate, sodium α-olefin sulfonate, etc.). This configuration reduces adhesion between resin particles (sometimes referred to as blocking) and improves the stability of the dispersion in the container. As a result, it has the advantage of being able to stably produce foamed particles.

[0083] (Heating process) In this specification, "softening temperature of polypropylene resin particles" means -10°C, which is the melting point of the resin with the highest melting point among the non-recycled polypropylene resin and the resin components contained in the base resin that constitutes the polypropylene resin particles.

[0084] In this specification, the term "temperature above the softening temperature of polypropylene resin particles" may be referred to as the "foaming temperature." In other words, the heating process can be described as the process of heating the dispersion to the foaming temperature. The foaming temperature in the heating process is not particularly limited, as long as it is above the softening temperature of the polypropylene resin particles. There is no particular limit to how high the temperature of the dispersion is heated in the heating process, i.e., the upper limit of the foaming temperature. The foaming temperature is preferably 20.0°C or less above the softening temperature of the polypropylene resin particles, more preferably 17.0°C or less above the softening temperature of the polypropylene resin particles, and even more preferably 16.0°C or less above the softening temperature of the polypropylene resin particles. This configuration has the advantage that there is no risk of the polypropylene resin particles sticking together in the container.

[0085] (Pressurization process) In this specification, the pressure (a constant pressure) after the pressurization process may be referred to as the "foaming pressure." In other words, the pressurization process increases the pressure inside the container to the foaming pressure.

[0086] In the pressurization process, the pressure to which the container is pressurized, i.e., the foaming pressure, is not particularly limited. The foaming pressure in the pressurization process is preferably (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 foaming pressure is 1.0 MPa (gauge pressure) or higher, foamed particles with a suitable density can be obtained.

[0087] The heating process and the pressurizing process may be carried out sequentially in any order, or they may be carried out simultaneously.

[0088] (holding process) This manufacturing method may further include a holding step, after the heating and pressurizing steps and before the release step, in which the temperature inside the container is maintained at the foaming temperature and the pressure inside the container is maintained at the foaming pressure (or near the foaming pressure).

[0089] In the holding process, the time for which the temperature of the dispersion is maintained at the foaming temperature and the pressure inside the container is maintained at the foaming pressure (or near 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. When the holding time is 10 minutes or more, a sufficient amount of unmelted crystals (crystals of the base resin) are present, which has the advantage of reducing the shrinkage of the resulting foamed particles and / or the increase in the open-cell ratio. On the other hand, when the holding time is 60 minutes or less, there is no excessive amount of unmelted crystals, which has the advantage of allowing the foamed particles to be molded at a lower molding temperature.

[0090] (Release process) The release step can be performed (a) after the heating and pressurizing steps if the holding step is not performed, or (b) after the holding step if the holding step is performed. The release step can cause the resin particles to foam, resulting in foamed particles.

[0091] In the discharge process, the "region with a pressure lower than the pressure inside the container" refers to the "region under a pressure lower than the pressure inside the container" or the "space under a pressure lower than the pressure inside the container," and can also be described as "an atmosphere with a pressure lower than the pressure inside the container." The region with a pressure lower than the pressure inside the container can also be described as a region with a pressure lower than the foaming pressure, and may be, for example, a region under atmospheric pressure. The low-pressure region is, for example, the gas phase. Furthermore, for the purpose of improving foaming, the low-pressure region (space) may be filled with saturated water vapor.

[0092] In the discharge process, when discharging the dispersion into a region with a pressure lower than the pressure inside the container, the dispersion can also be discharged through an open orifice with a diameter of 1 mm to 5 mm for purposes such as adjusting the flow rate of the dispersion and reducing variations in the foaming ratio of the resulting foamed particles.

[0093] As described above, the process of producing foamed particles from resin particles is called the "first-stage foaming process," and the resulting foamed particles are called "first-stage foamed particles." To obtain foamed particles with a high foaming ratio, the first-stage foamed particles obtained in the first-stage foaming process may be foamed again. The process of increasing the foaming ratio of the first-stage foamed particles is called the "second-stage foaming process," and the polyolefin-based resin foamed particles obtained by the second-stage foaming process are called "second-stage foamed particles." The specific method for the second-stage foaming process is not particularly limited, and known methods can be used.

[0094] [3. Polypropylene-based resin foam molded product] One embodiment of the present invention also provides a polypropylene resin foam molded article obtained by molding the polypropylene resin foam particles described in the section [1. Polypropylene Resin Foam Particles] above. The polypropylene resin foam molded article according to one embodiment of the present invention can also be said to be a foam molded article containing the polypropylene resin foam particles described in the section [1. Polypropylene Resin Foam Particles].

[0095] Because the foamed molded article has the above-described structure, it has the advantage of excellent internal bonding properties. The foamed molded article has the advantage that the internal bonding rate, as measured by the measurement method described in detail in later examples, is, for example, 75% or more. The internal bonding rate of the foamed molded article is more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.

[0096] <Method for manufacturing foamed molded products> The method for manufacturing the foamed molded article is not particularly limited to any other aspect, as long as it involves molding the foamed particles (preferably by in-mold foaming) to obtain a foamed molded article, and known methods can be applied. As a method for manufacturing the foamed molded article, for example, the manufacturing method described in the section "Method for Manufacturing a Foamed Molded Article" of International Publication WO2022 / 149538 can be suitably adopted.

[0097] One embodiment of the present invention may have the following configuration.

[0098] [1] Polypropylene resin foam particles comprising a base resin, wherein the base resin comprises a non-recycled polypropylene resin and a recycled material comprising a recycled polypropylene resin, the content of the recycled material in the base resin is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin.

[0099] [2] The polypropylene resin foam particles according to [1], wherein the melt flow rate of the non-recycled polypropylene resin at 230°C is 5 g / 10 min or more.

[0100] [3] Polypropylene resin foam particles according to [1] or [2], wherein the melting point of the non-recycled polypropylene resin is 152°C or lower.

[0101] [4] Polypropylene resin foam particles according to any one of [1] to [3], wherein the crystallization temperature of the recycled material is 100°C to 130°C.

[0102] [5] The polypropylene resin foam particles according to any one of [1] to [4], wherein both the non-recycled polypropylene resin and the recycled polypropylene resin are resins polymerized using a Ziegler-Natta catalyst as the polymerization catalyst.

[0103] [6] The polypropylene resin foam particles according to any one of [1] to [5], wherein the polypropylene resin foam particles further contain carbon black in addition to the base resin.

[0104] [7] The polypropylene resin foam particles according to [6], wherein the carbon black content in the polypropylene resin foam particles is 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

[0105] [8] The polypropylene resin foam particles according to any one of [1] to [7], wherein the polypropylene resin foam particles further contain a colored pigment in addition to the base resin.

[0106] [9] The recycled material is polypropylene resin foam particles according to any one of [1] to [8], which contain a chromatic pigment.

[0107]

[10] Polypropylene resin foam particles according to any one of [1] to [9], wherein the recycled material is derived from foam.

[0108]

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

[10] , wherein the recycled material is derived from a non-foamed material.

[0109]

[12] The recycled material is polypropylene resin foam particles according to any one of [1] to

[11] , which contain carbon black.

[0110]

[13] The non-recycled polypropylene resin and the recycled polypropylene resin are polypropylene resin foam particles according to any one of [1] to

[12] , each containing a Ziegler-Natta catalyst.

[0111]

[14] The non-recycled polypropylene resin comprises 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, wherein the polypropylene resin foam particles are according to any one of [1] to

[13] .

[0112]

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

[14] , wherein the crystallization temperature of the non-recycled polypropylene resin is 95°C to 120°C.

[0113]

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

[15] , wherein the melt flow rate of the non-recycled polypropylene resin at 230°C is 30 g / 10 min or less.

[0114]

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

[16] , wherein the melting point of the non-recycled polypropylene resin is 125°C or higher.

[0115]

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

[17] , wherein the recycled polypropylene resin comprises one or more selected from the group consisting of ethylene / propylene block copolymer, ethylene / 1-butene / propylene block copolymer, ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer.

[0116]

[19] The recycled material is polypropylene resin foam particles according to any one of [1] to

[18] , wherein the recycled material contains more than 0 parts by weight and 20 parts by weight or less of recycled polyethylene resin in 100 parts by weight of the recycled material.

[0117]

[20] The recycled material is polypropylene resin foam particles according to any one of [1] to

[18] , which does not contain recycled polyethylene resin.

[0118]

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

[20] , wherein the difference between the crystallization temperature of the non-recycled polypropylene resin and the crystallization temperature of the recycled material is 1°C or more.

[0119]

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

[21] , wherein the difference between the crystallization temperature of the non-recycled polypropylene resin and the crystallization temperature of the recycled material is 17°C or less.

[0120]

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

[22] , wherein the melt flow rate of the recycled material at 230°C is 1 g / 10 min to 30 g / 10 min.

[0121]

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

[23] , wherein the melting point of the recycled material is 135°C to 170°C.

[0122]

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

[24] , wherein the DSC ratio of the polypropylene resin foam particles is 10.0% to 50.0%.

[0123]

[26] The polypropylene resin foam particles described in any one of [1] to

[25] , wherein the foaming ratio of the polypropylene resin foam particles is greater than 1.0 times.

[0124]

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

[26] , wherein the foaming ratio of the polypropylene resin foam particles is 50.0 times or less.

[0125]

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

[27] , wherein the average bubble diameter of the polypropylene resin foam particles is 80 μm to 500 μm.

[0126]

[29] The polypropylene resin foam particles described in any one of [1] to

[28] , wherein the polypropylene resin foam particles do not have a core-sheath structure.

[0127] A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles described in any one of

[30] , [1], to

[29] .

[0128]

[31] The polypropylene resin foam molded article according to

[30] , wherein the internal bonding rate is 75% or more.

[0129]

[32] A method for producing polypropylene resin foam particles, comprising: a granulation step of melting and kneading a base resin containing a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin to obtain polypropylene resin particles; a dispersion step of dispersing the polypropylene resin particles, an aqueous dispersion medium, and a foaming agent in a container to obtain a dispersion liquid; a heating step of heating the temperature of the dispersion liquid to a temperature above the softening temperature of the polypropylene resin particles; a pressurizing step of increasing the pressure inside the container; and a release step of releasing one end of the container to release the dispersion liquid inside the container into a region with a pressure lower than the pressure inside the container, wherein the amount of recycled material used is 10 to 90 parts by weight per 100 parts by weight of the base resin, and the crystallization temperature of the recycled material is higher than the crystallization temperature of the non-recycled polypropylene resin.

[0130]

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

[32] , wherein the melt flow rate of the non-recycled polypropylene resin at 230°C is 5 g / 10 min or more.

[0131]

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

[32] or

[33] , wherein the melting point of the non-recycled polypropylene resin is 152°C or lower.

[0132]

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

[32] to

[34] , wherein the crystallization temperature of the recycled material is 100°C to 130°C.

[0133]

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

[32] to

[35] , wherein both the non-recycled polypropylene resin and the recycled polypropylene resin are resins polymerized using a Ziegler-Natta catalyst as the polymerization catalyst.

[0134]

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

[32] to

[36] , wherein the polypropylene resin foam particles further contain carbon black in addition to the base resin.

[0135]

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

[37] , wherein the carbon black content in the polypropylene resin foam particles is 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

[0136]

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

[32] to

[38] , wherein the polypropylene resin foam particles further contain a colored pigment in addition to the base resin.

[0137]

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

[32] to

[39] , wherein the recycled material contains a colored pigment.

[0138]

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

[32] to

[40] , wherein the recycled material is derived from foam.

[0139]

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

[32] to

[41] , wherein the recycled material is derived from a non-foamed material.

[0140]

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

[32] to

[42] , wherein the recycled material contains carbon black.

[0141]

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

[32] to

[43] , wherein the non-recycled polypropylene resin and the recycled polypropylene resin both contain a Ziegler-Natta catalyst.

[0142]

[45] A method for producing foamed polypropylene resin particles according to any one of

[32] to

[44] , wherein the non-recycled polypropylene resin comprises 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.

[0143]

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

[32] to

[45] , wherein the crystallization temperature of the non-recycled polypropylene resin is 95°C to 120°C.

[0144]

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

[32] to

[46] , wherein the melt flow rate of the non-recycled polypropylene resin at 230°C is 30 g / 10 min or less.

[0145]

[48] ​​A method for producing polypropylene resin foam particles according to any one of

[32] to

[47] , wherein the melting point of the non-recycled polypropylene resin is 125°C or higher.

[0146]

[49] A method for producing foamed polypropylene resin particles according to any one of

[32] to

[48] , wherein the recycled polypropylene resin comprises one or more selected from the group consisting of ethylene / propylene block copolymer, ethylene / 1-butene / propylene block copolymer, ethylene / propylene alternating copolymer, ethylene / 1-butene / propylene alternating copolymer, ethylene / propylene random copolymer, and ethylene / 1-butene / propylene random copolymer.

[0147]

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

[32] to

[49] , wherein the recycled material contains more than 0 parts by weight and 20 parts by weight or less of recycled polyethylene resin in 100 parts by weight of the recycled material.

[0148]

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

[32] to

[49] , wherein the recycled material does not contain recycled polyethylene resin.

[0149]

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

[32] to

[51] , wherein the difference between the crystallization temperature of the non-recycled polypropylene resin and the crystallization temperature of the recycled material is 1°C or more.

[0150]

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

[32] to

[52] , wherein the difference between the crystallization temperature of the non-recycled polypropylene resin and the crystallization temperature of the recycled material is 17°C or less.

[0151]

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

[32] to

[53] , wherein the melt flow rate of the recycled material at 230°C is 1 g / 10 min to 30 g / 10 min.

[0152]

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

[32] to

[54] , wherein the melting point of the recycled material is 135°C to 170°C.

[0153]

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

[32] to

[55] , wherein the DSC ratio of the polypropylene resin foam particles is 10.0% to 50.0%.

[0154]

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

[32] to

[56] , wherein the foaming ratio of the polypropylene resin foam particles is greater than 1.0 times.

[0155]

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

[32] to

[57] , wherein the foaming ratio of the polypropylene resin foam particles is 50.0 times or less.

[0156]

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

[32] to

[58] , wherein the average bubble diameter of the polypropylene resin foam particles is 80 μm to 500 μm.

[0157]

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

[32] to

[59] , wherein the polypropylene resin foam particles do not have a core-sheath structure.

[0158] A method for producing a polypropylene resin foamed molded article, comprising the step of molding polypropylene resin foamed particles described in any one of

[61] , [1] to

[29] , or polypropylene resin foamed particles produced by a method for producing polypropylene resin foamed particles described in any one of

[32] to

[60] .

[0159]

[62] The method for producing a polypropylene-based resin foam molded article according to

[30] , wherein the internal bonding rate of the polypropylene-based resin foam molded article is 75% or more. [Examples]

[0160] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0161] <Material> The substances used in the examples and comparative examples are as follows, but were used without any special purification or other treatment.

[0162] (Non-recycled polypropylene resins and recycled materials) Table 1 shows the non-recycled polypropylene resins used, and Table 2 shows the recycled materials used. Non-recycled polypropylenes 1-4 are resins polymerized using a Ziegler-Natta catalyst. Since non-recycled polypropylene 5 is a mixture of non-recycled polypropylenes 3 and 4, it can also be said that non-recycled polypropylene 5 is a resin polymerized using a Ziegler-Natta catalyst. Furthermore, the recycled polypropylene resins contained in recycled materials 1-12 are resins polymerized using a Ziegler-Natta catalyst. In Table 2, recycled materials marked "-" in the "Carbon black content (weight %) in 100% recycled material" column are intended to contain no carbon black (0% weight). Similarly, in Table 2, recycled materials marked "-" in the "Polyethylene resin content (weight %) in 100% recycled material" column are intended to contain no polyethylene resin (0% weight). In Table 2, the content of recycled polypropylene resin in the recycled material is the amount obtained by subtracting the carbon black content, polyethylene resin content, and ash content from 100% by weight of the recycled material. [Table 1]

[0163] [Table 2] (Carbon Black) • Carbon Black Masterbatch A 40 parts by weight of carbon black and 60 parts by weight of non-recycled polypropylene resin [MFR = 7.5 g / 10 min at 230°C] were mixed to obtain the carbon black masterbatch A.

[0164] • Carbon Black Masterbatch B Three parts by weight of carbon black and 97 parts by weight of non-recycled polypropylene resin 2 listed in Table 1 were mixed to obtain the carbon black masterbatch B.

[0165] (Chromatic pigment masterbatch) • Green pigment masterbatch (containing a total of 25% by weight of copper phthalocyanine blue and condensed azo yellow) • Blue pigment masterbatch (containing a total of 21% by weight of phthalocyanine blue and ultramarine) • Red pigment masterbatch (containing 1% by weight of perylene-based red) (Foaming agent) • Talc [Manufactured by Hayashi Chemical Co., Ltd., Talc Powder PK-S] (water-absorbing substance) • Glycerin [Manufactured by Lion Corporation, refined glycerin D] • Polyethylene glycol [manufactured by Lion Corporation, PEG #300] (Flame retardant) • Hindered amine flame retardant [BASF, NOR116] <Method for measuring melting point and crystallization temperature> The melting point and crystallization temperature of non-recycled polypropylene resins and recycled materials were measured using a differential scanning calorimeter (DSC7020, Hitachi High-Tech Science Corporation). The specific operating procedure was as follows (1) to (3): (1) The temperature of 4.5 mg to 5.5 mg of the sample (non-recycled polypropylene resin or recycled material) was increased from 40°C to 220°C at a heating rate of 10°C / min to melt the sample; (2) The temperature of the melted sample was then decreased from 220°C to 40°C at a cooling rate of 10°C / min to crystallize the sample; (3) The temperature of the crystallized sample was then further increased from 40°C to 220°C at a heating rate of 10°C / min. The temperature of the peak (crystallization peak) of the DSC curve of the sample obtained during cooling (i.e., at (2)) was defined as the crystallization temperature of the sample. If multiple peaks (crystallization peaks) were obtained in the DSC curve of the sample during cooling, the highest-temperature peak was taken as the crystallization temperature of the sample. The temperature of the peak (melting peak) in the DSC curve of the sample obtained during the second heating (i.e., in (3)) was taken as the melting point of the sample. If multiple peaks (melting peaks) were obtained in the DSC curve of the sample during the second heating, the highest-temperature peak was taken as the melting point of the sample.

[0166] <Method for measuring melt flow rate at 230°C> The melt flow rates of non-recycled polypropylene resins and recycled materials were measured using an MFR measuring instrument as described in JIS K7210-1:2014. The measurement conditions were as follows: orifice diameter of 2.0959±0.005 mmφ, orifice length of 8.000±0.025 mm, load of 2160 g, and temperature of 230±0.2 °C.

[0167] <Method for quantifying carbon black in recycled materials> The carbon black content in the recycled materials was measured using a differential thermogravimetric analyzer (STA200RV, manufactured by Hitachi High-Tech Science Corporation). The specific operating procedure was as follows (1) to (3): (1) 6 mg to 8 mg of recycled material was weighed into a platinum (Pt) measuring container to serve as the sample; (2) The sample temperature was raised to 600°C at a rate of 10°C / min under a nitrogen atmosphere, and then cooled to 400°C at a rate of 10°C / min; (3) After that, the atmosphere was changed to a simulated air (a mixture of oxygen:nitrogen = 21%:79%), and the sample temperature was raised to 800°C at a rate of 10°C / min and held at 800°C for 20 minutes; (4) In the TG weight loss rate curve obtained in the process of (3) above, the weight ratio of carbon black in the recycled material [weight %] was calculated from the difference between the weight loss rate [weight %] at 400°C during the heating process from 400°C to 800°C and the weight loss rate [weight %] after holding at 800°C for 20 minutes.

[0168] <Method for determining the amount of ash in recycled materials> The amount of ash in the recycled material was determined from the weight of the recycled material and the weight of the residue after burning the recycled material. The specific procedure was as follows (1) to (4): (1) The recycled material was heated at 150°C for 1 hour to completely remove moisture from the recycled material; (2) 1g to 2g of the recycled material was placed in a crucible and held at 300°C for 30 minutes or more using an electric furnace, and then burned at 750°C for 1 hour or more; (3) The crucible was removed from the electric furnace and cooled in a desiccator at 23°C for 1 hour; (4) The amount of ash in the recycled material was calculated using the following formula. W1: Crucible weight (g) W2: Weight of crucible before combustion + recycled material (g) W3: Weight of crucible after combustion + recycled material (g) Ash content (by weight %) in recycled material = {(W3-W1)*100} / (W2-W1).

[0169] <Measurement of DSC ratio of polypropylene resin foam particles> The DSC ratio of the foamed particles was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Co., Ltd.). The specific procedure was as follows (1) to (5): (1) 4.5 mg to 5.5 mg of polypropylene resin foamed particles were weighed out; (2) The temperature of the foamed particles was increased from 40°C to 220°C at a heating rate of 10°C / min to melt the foamed particles; (3) In the DSC curve of the foamed particles obtained in the process of (2) above (DSC curve of the foamed particles at the first heating stage), (a) a straight line was drawn connecting the maximum point between the highest temperature melting peak and the melting peak adjacent to that melting peak (on the lower temperature side) and the point at 100°C, and (b) the same maximum point and A straight line was drawn connecting the point representing the temperature after melting; (4) (a) (a-1) The heat quantity calculated from the region enclosed by the line segment connecting the maximum point and the point representing the temperature after melting, and (a-2) the DSC curve having the highest temperature melting peak, was defined as the high-temperature side melting heat quantity Qh; (b) (b-1) The heat quantity calculated from the region enclosed by 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 adjacent to the maximum point (low-temperature side), was defined as the low-temperature side melting heat quantity Ql; (5) The DSC ratio was calculated from the following formula. The obtained DSC ratio was rounded to the first decimal place by rounding to the second decimal place. DSC ratio (%)=(Qh / (Qh+Ql))×100.

[0170] <Foaming ratio of polypropylene resin foam particles> The method for measuring the expansion ratio of the foaming particles was as follows (1) to (4): (1) The weight w (g) of the foaming particles was measured; (2) Next, the foaming particles used for weight measurement were submerged in ethanol contained in a graduated cylinder, and the volume v (cm³) of the foaming particles was determined based on the rise in the liquid level of the graduated cylinder. 3 (3) The weight w (g) was measured to the volume v (cm³) 3(4) The density ρ1 of the foamed particles was calculated by dividing the density ρ2 of the polypropylene resin particles used in the production of the foamed particles by the density ρ1 of the foamed particles (ρ2 / ρ1), and the value obtained was taken as the foaming ratio of the foamed particles. The density ρ2 of the polypropylene resin particles was measured in the same manner using resin particles instead of foamed particles. In the examples and comparative examples shown below, the density ρ2 of the polypropylene resin particles was 0.9 g / cm³ in all cases. 3 That was the case.

[0171] <Average bubble diameter of polypropylene-based resin foam particles> The method for measuring the average bubble diameter of foamed particles was as follows (1) to (5): (1) While taking sufficient care not to destroy the bubble membrane (cell membrane) of the foamed particle, the foamed particle was cut using a razor (Feather High Stainless double-edged razor) so as to pass through the center of the foamed particle; (2) The cut surface of the obtained foamed particle was observed using a microscope [(Hyrox Co., Ltd., RH-2000)] and an image of the observed surface was obtained; (3) On the obtained image, a line segment corresponding to a length of 2000 μm was drawn in an arbitrary part of the foamed particle, excluding the surface layer; (4) The number of bubbles n that the line segment passes through was measured and the bubble diameter was calculated from the formula (bubble diameter = 2000 / n (μm)); (5) The same procedure was performed for 10 foamed particles, and the arithmetic mean of the calculated bubble diameters was taken as the average bubble diameter of the foamed particle.

[0172] <Internal fusion rate of polypropylene-based foamed molded articles> The method for measuring the internal bonding rate of the foamed molded body was as follows (1) to (4): (1) A cut 5 mm long was made perpendicular to one side of the foamed molded body with a cutter; (2) The foamed molded body was then broken by hand along the cut; (3) The area of ​​the resulting fracture surface excluding the cut portion was visually observed, and the number of foamed particles present in that area, and the number of foamed particles that fractured outside the particle interface in that area (i.e., foamed particles that fractured themselves) were measured; (4) The internal bonding rate was measured based on the following formula The fusion rate was calculated; Internal bonding rate (%) = (Number of foamed particles fractured outside the particle interface in the region / Total number of foamed particles present in the region) × 100.

[0173] <Molding cycle of polypropylene-based resin foam molded products> In the manufacturing of foamed molded products, the molding cycle for foamed molded products was defined as the period from the start of molding to the end of molding when the molded product is released from the mold. A detailed explanation follows. First, the molding process began when polypropylene resin foam particles were started to fill the mold. A mold capable of forming a molding space of 370mm (length) x 320mm (width) x 50mm (thickness) was used. Next, with the drain valve of the molding machine's drain line open, the foam particles were heated with 0.10 MPa (gauge pressure) steam for 3 seconds to expel air from the mold (preheating process). Then, steam was flowed from the fixed mold side to the movable mold side for 6 seconds (one-way heating process), and then steam was flowed from the movable mold side to the fixed mold side for 3 seconds (reverse one-way heating process) to expel air and heat the particles. Next, with the drain valve of the molding machine's drain line closed, steam at 0.30 MPa (gauge pressure) was sent into the mold for 9 seconds to heat the foam particles (double-sided heating process) and fuse them together to form a foamed molded product. Finally, the foamed molded product inside the mold was water-cooled. Next, the mold was opened and the foamed molded body was demolded when the surface pressure, measured by a surface pressure gauge attached to the surface of the plank mold, dropped to 0.01 MPa (gauge pressure). The molding process was considered complete when the foamed molded body had been demolded. The evaluation criteria for the molding cycle (productivity) are as follows. 3 (Excellent): Molding cycle is within 180 seconds. 2 (Excellent): The molding cycle is longer than 180 seconds and within 210 seconds. 1 (Inferior): Molding cycle is longer than 210 seconds.

[0174] The following describes the methods for producing polypropylene resin particles, polypropylene resin foam particles, and polypropylene resin molded foam articles in examples and comparative examples.

[0175] (Example 1) [Production of resin particles] (granulation process) 70 parts by weight of non-recycled polypropylene resin 2 (ethylene / 1-butene / propylene random copolymer), 30 parts by weight of recycled material 1, 0.20 parts by weight of talc, and 0.5 parts by weight of polyethylene glycol 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 melt-kneaded mixture was extruded in a strand shape from the die of the extruder. The extruded mixture (strand) was cooled in a 2m long water tank and solidified. After that, the solidified mixture was cut to produce polypropylene resin particles (1.2 mg / particle).

[0176] [Production of foamed particles] (Dispersion process) In a 10L pressure-resistant autoclave (autoclave-type pressure-resistant container), 100 parts by weight (2.4 kg) of polypropylene resin particles obtained as described above, 200 parts by weight of water as an aqueous dispersion medium, 0.3 parts by weight of kaolin [BASF, ASP170] as a dispersant, and 0.38 parts by weight of an aqueous solution of sodium dodecylbenzenesulfonate [Kao Corporation, Neoperex G-15, an aqueous solution of 16% by weight of sodium dodecylbenzenesulfonate] as a dispersion aid were charged. Stirring of the mixture was started. Thereafter, the mixture (dispersion) was continued to stir until the discharge process was completed. 4 parts by weight of carbon dioxide was added to the mixture as a blowing agent. Through this operation, the polypropylene resin particles, aqueous dispersion medium, blowing agent, dispersant and dispersion aid were dispersed in the container to obtain a dispersion.

[0177] (Heating process, pressurizing process, holding process) The temperature of the dispersion was raised (heated) to the foaming temperature of 153.3°C, and the temperature of the dispersion was maintained at this foaming temperature for 10 minutes. Then, carbon dioxide was added to the container under pressure to increase the internal pressure of the autoclave to the foaming pressure of 2.0 MPa (gauge pressure). The temperature of the dispersion was maintained at the foaming temperature and the internal pressure of the autoclave was maintained at the foaming pressure for 20 minutes.

[0178] (Release process) Subsequently, the valve at the bottom of the autoclave was opened, and the dispersion was released under atmospheric pressure through a 3.6 mm diameter open orifice to obtain polypropylene resin foam particles with a foaming ratio of 15.7 times. During this process, carbon dioxide was injected to maintain the pressure inside the container and prevent a drop in pressure.

[0179] [Production of foamed molded products] The obtained foamed particles were dried at 80°C. Then, the foamed particles were placed in a pressure vessel, and pressurized air was injected into them to adjust the internal pressure to 0.20 MPa (absolute pressure). Next, the pressurized foamed particles were filled into a mold measuring 370 mm (length) x 320 mm (width) x 50 mm (thickness). The mold chamber was then heated with steam at 0.30 MPa (gauge pressure) (molding pressure) to fuse the foamed particles together. After water-cooling the inside of the mold and the surface of the molded body, the molded body was released from the mold to obtain a polypropylene-based foamed molded body. The obtained foamed molded body was left to stand at 23°C for 2 hours, and then cured at 75°C for 16 hours.

[0180] (Example 2) The foamed particles obtained in Example 1 were dried at 80°C. Then, the foamed particles were placed in a pressure vessel, and pressurized air was impregnated into the foamed particles to adjust the internal pressure to 0.30 MPa (absolute pressure). Next, the foamed particles with the applied internal pressure were brought into contact with 0.07 MPa (gauge pressure) water vapor to induce two-stage foaming, obtaining two-stage foamed particles. The foaming ratio of the obtained two-stage foamed particles was 26.2 times. Subsequently, a polypropylene resin foamed molded article was produced using the same procedure as described in the [Preparation of Foamed Molded Article] section of Example 1.

[0181] (Examples 3-11, 13-18, and Comparative Examples 1-3) Polypropylene resin particles, polypropylene resin foam particles, and polypropylene resin foam molded articles were produced by the same procedures as described in the sections on "Preparation of Resin Particles," "Preparation of Foam Particles," and "Preparation of Foam Molded Articles" of Example 1, except that the formulation was changed as shown in Table 3 or 4 in the "Preparation of Resin Particles" section, and the foaming conditions were changed as shown in Table 3 or 4 in the "Preparation of Foam Particles" section.

[0182] (Example 12) In the [Preparation of Resin Particles], the formulation was changed as shown in Table 4 to obtain polypropylene resin particles.

[0183] [Production of foamed particles] (Dispersion process) In a 10L pressure-resistant autoclave (autoclave-type pressure-resistant container), 100 parts by weight (2.4 kg) of the obtained polypropylene resin particles, 200 parts by weight of water as an aqueous dispersion medium, 0.46 parts by weight of tricalcium phosphate [manufactured by Taihei Chemical Industry Co., Ltd.] as a dispersant, and 0.04 parts by weight of sodium alkyl sulfonate [manufactured by Kao Corporation, Latemul PS] as a dispersion aid were charged. Stirring of the mixture was started. Thereafter, the mixture (dispersion) was continued to stir until the discharge process was completed. Through this operation, the polypropylene resin particles, aqueous dispersion medium, dispersant and dispersion aid were dispersed in the container to obtain a dispersion.

[0184] (Heating process, pressurizing process, holding process) The temperature of the dispersion was raised (heated) to the foaming temperature of 154.2°C. Compressed air was also injected into the container to increase the autoclave pressure to the foaming pressure of 2.3 MPa (gauge pressure). The dispersion temperature was maintained at the foaming temperature, and the autoclave pressure at the foaming pressure, for 20 minutes.

[0185] (Release process) Subsequently, the valve at the bottom of the autoclave was opened, and the dispersion was released under atmospheric pressure through a 4.4 mm diameter open orifice to obtain polypropylene resin foam particles with a foaming ratio of 2.9 times. During this process, air was injected to maintain the pressure inside the container and prevent a drop in pressure.

[0186] [Production of foamed molded products] The obtained foam particles were dried at 80°C. Next, the foam particles were filled into a mold measuring 370 mm (length) x 320 mm (width) x 50 mm (thickness). Then, the mold chamber was heated with steam at 0.30 MPa (gauge pressure) (molding pressure) to fuse the foam particles together. After water-cooling the inside of the mold and the surface of the molded body, the molded body was released from the mold to obtain a polypropylene resin foam molded body. The obtained foam molded body was left to stand at 23°C for 2 hours, and then cured at 75°C for 16 hours.

[0187] (Examples 19-26) Polypropylene resin particles and polypropylene resin foam particles were prepared using the same procedures as described in the "Preparation of Resin Particles" and "Preparation of Foamed Particles" sections of Example 1, except that the formulation was changed as shown in Table 5 in the "Preparation of Resin Particles" section and the foaming conditions were changed as shown in Table 4 in the "Preparation of Foamed Particles" section.

[0188] [Production of foamed molded products] The obtained foamed particles were placed in a pressure vessel and compressed by air pressure. Next, the compressed foamed particles were filled into a mold measuring 370 mm (length) x 320 mm (width) x 50 mm (thickness). Then, the mold chamber was heated with steam at 0.30 MPa (gauge pressure) (molding pressure) to fuse the foamed particles together. After water cooling the inside of the mold and the surface of the molded body, the molded body was released from the mold to obtain a polypropylene resin foamed molded body. The obtained foamed molded body was left to stand at 23°C for 2 hours, and then cured at 75°C for 16 hours.

[0189] Various measurements and evaluations were performed on the polypropylene resin foam particles and polypropylene resin molded foam articles obtained in each example and comparative example. The results are shown in Tables 3 to 5. [Table 3] [Table 4] [Table 5] [Industrial applicability]

[0190] One embodiment of the present invention has the advantage of providing a polypropylene resin foam molded article with excellent internal fusion properties and providing polypropylene resin foam particles containing recycled polypropylene resin. Therefore, one embodiment of the present invention can be suitably used in a variety of applications such as cushioning packaging materials, logistics materials, heat insulation materials, civil engineering and construction components, and automotive components.

Claims

1. Polypropylene resin foam particles containing a base resin, The aforementioned base resin includes a non-recycled polypropylene resin and a recycled material containing a recycled polypropylene resin. The content of the recycled material in the base resin is 10 to 90 parts by weight per 100 parts by weight of the base resin. The crystallization temperature of the recycled material is higher than that of the non-recycled polypropylene resin. The aforementioned non-recycled polypropylene resin is a random copolymer. The recycled polypropylene resin is a random copolymer. The recycled material contains, in 100 parts by weight, 0 to 20 parts by weight of recycled polyethylene resin. The recycled material has a crystallization temperature of 100°C to 115°C, and is composed of polypropylene resin foam particles.

2. The polypropylene resin foam particles according to claim 1, wherein the melting point of the recycled material is 135°C to 151°C.

3. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the non-recycled polypropylene resin at 230°C is 5 g / 10 min or more.

4. The polypropylene resin foam particles according to claim 1, wherein the melting point of the non-recycled polypropylene resin is 152°C or lower.

5. The polypropylene resin foam particles according to claim 1, wherein both the non-recycled polypropylene resin and the recycled polypropylene resin are resins polymerized using a Ziegler-Natta catalyst as the polymerization catalyst.

6. The polypropylene resin foam particles according to claim 1, wherein the polypropylene resin foam particles further contain carbon black in addition to the base resin.

7. The polypropylene resin foam particles according to claim 6, wherein the carbon black content in the polypropylene resin foam particles is 0.1 to 5.0 parts by weight per 100 parts by weight of the base resin.

8. The polypropylene resin foam particles according to claim 1, wherein the polypropylene resin foam particles further contain a colored pigment in addition to the base resin.

9. The polypropylene resin foam particles according to claim 1, wherein the recycled material contains a chromatic pigment.

10. The polypropylene resin foam particles according to claim 1, wherein the recycled material is derived from foam.

11. The polypropylene resin foam particles according to claim 1, wherein the recycled material is derived from a non-foamed material.

12. The recycled material comprises carbon black, and the polypropylene resin foam particles are as described in claim 1.

13. A polypropylene resin foam molded article obtained by molding polypropylene resin foam particles as described in claim 1.

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