Foamed polypropylene-based resin particle, foamed polypropylene-based resin molded article, and method for producing foamed polypropylene-based resin particle

Abstract

The present invention addresses the problem of providing novel foamed polypropylene-based resin particles that make it possible to produce a molded article having excellent compressive strength even when a polypropylene-based resin derived from a recycled raw material is used. Provided are foamed particles that comprise a base resin containing a polypropylene-based resin (A) and a polypropylene-based resin (B), have a melting point of 140.0-155.0°C and a bulk density of 10.0-200.0 g / L, and further satisfy prescribed conditions (conditions (1) to (8)).

Description

Polypropylene-based resin expanded particles, polypropylene-based resin expanded molded article, and method for producing polypropylene-based resin expanded particles

[0001] The present invention relates to polypropylene-based resin expanded particles, a polypropylene-based resin expanded molded article, and a method for producing polypropylene-based resin expanded particles.

[0002] Polypropylene-based resin expanded molded articles are used in various applications including automotive interior members, core materials for bumpers, heat insulating materials, cushioning packaging materials, and reusable containers. For example, Patent Document 1 describes polypropylene-based resin expanded particles including a base resin containing a propylene-based random copolymer and a propylene-based block copolymer.

[0003] International Publication WO2023 / 190441

[0004] The above-mentioned conventional technique is excellent when using a polypropylene-based resin derived from a virgin raw material, but when using a polypropylene-based resin derived from a recycled raw material, there is room for improvement from the viewpoint of the compressive strength of the obtained expanded molded article.

[0005] In the situation as described above, an aspect of the present invention is to provide polypropylene-based resin expanded particles that can provide an expanded molded article excellent in compressive strength even when a polypropylene-based resin derived from a recycled raw material is used.

[0006] As a result of intensive studies by the present inventors to solve the above problems, they have found that polypropylene-based resin expanded particles satisfying predetermined conditions can provide an expanded molded article excellent in compressive strength even when a polypropylene-based resin derived from a recycled raw material is used, and have completed the present invention.

[0007] In other words, a polypropylene resin foam particle according to one aspect of the present invention is a polypropylene resin foam particle comprising a base resin containing a polypropylene resin (A) and a polypropylene resin (B), and satisfying the following (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of the polypropylene resin (C) and 5% to 60% by weight of the polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0008] A method for producing polypropylene resin foam particles according to another aspect of the present invention is a method for producing polypropylene resin foam particles comprising the steps of: preparing a base resin by mixing a polypropylene resin (A) and a polypropylene resin (B); and preparing foam particles from the base resin, wherein the polypropylene resin foam particles satisfy the following conditions (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0009] According to one aspect of the present invention, a foamed molded article with excellent compressive strength can be provided even when using a polypropylene resin derived from recycled raw materials.

[0010] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference.

[0011] In this specification, a "constituent unit derived from an X monomer" contained in a polymer, copolymer, or resin may be referred to as an "X unit."

[0012] [1. Polypropylene Resin Foam Particles] Polypropylene resin foam particles according to one embodiment of the present invention (hereinafter sometimes simply referred to as "the foam particles") are polypropylene resin foam particles containing a base resin containing a polypropylene resin (A) and a polypropylene resin (B), and satisfy the following (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% by weight or more and 95% by weight or less of the polypropylene resin (A), and 5% by weight or more and 60% by weight or less of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0013] <Technical Concept of the Invention> Polypropylene resins are broadly classified into propylene homopolymers, which consist only of propylene units, and polypropylene copolymers, which consist of propylene units and constituent units derived from monomers other than propylene. Polypropylene copolymers are further broadly classified into polypropylene random copolymers, in which two or more constituent units constituting the resin are arranged randomly, and polypropylene block copolymers, in which two or more constituent units constituting the resin are arranged in a block-like manner.

[0014] Conventionally, the inventors have manufactured polypropylene resin foam particles (hereinafter sometimes simply referred to as "foam particles") using only polypropylene random copolymer as a raw material. This is because they had found that when a mixture of polypropylene random copolymer and polypropylene block copolymer is used as a raw material, the compressive strength of the resulting polypropylene resin foam molded article (hereinafter sometimes simply referred to as "foam molded article") formed by molding the foam particles decreases.

[0015] In recent years, there has been a growing demand for using polypropylene resins derived from recycled materials (recycled resins) as raw materials for foamed particles, from the perspective of reducing environmental impact. For example, a draft regulation published by the European Commission in July 2023 states that "25% of plastic products for automobiles should be made from recycled resins (post-consumer products), and of which 25% of such recycled resins should be derived from used plastic products for automobiles."

[0016] When using recycled resins, particularly those derived from post-consumer products (sometimes referred to as post-consumer recycled (PCR)) that are mostly polypropylene block copolymers, as raw materials, a problem arises in which the compressive strength of the resulting foamed molded product decreases. This problem becomes particularly pronounced when recycled resin is used at a high percentage, such as 25% or more.

[0017] In light of the above circumstances, the inventors diligently conducted research with the aim of providing foamed particles that can provide a foamed molded article with excellent compressive strength even when using recycled resin. As a result, they found that foamed particles obtained by mixing a polypropylene resin derived from virgin raw materials (polypropylene random copolymer) and a polypropylene resin containing a polypropylene resin derived from recycled raw materials (for example, polypropylene random copolymer and polypropylene block copolymer) such that the difference in melting points between the resin derived from virgin raw materials and the resin mixture derived from recycled raw materials is within a predetermined range, or more specifically, foamed particles that satisfy each of the above configurations, can provide a foamed molded article with excellent compressive strength even when using recycled resin (particularly polypropylene block copolymer derived from recycled raw materials), and thus completed the present invention.

[0018] As described above, these foamed particles make it possible to provide foamed molded articles with excellent compressive strength, even when using polypropylene resin derived from recycled materials (recycled resin). Furthermore, these foamed particles have the advantages of low shrinkage, easy control of the foaming ratio, and the ability to produce homogeneous foamed particles.

[0019] <Base Resin> These foamed particles contain a base resin that includes polypropylene resin (A) and polypropylene resin (B).

[0020] (Polypropylene resin (A)) The base resin of these foamed particles contains polypropylene resin (A). Polypropylene resin (A) is a polypropylene random copolymer (condition (1)) derived from virgin raw materials (condition (8)).

[0021] In this specification, "polypropylene resin" refers to a resin in which the content of propylene-derived constituent units (propylene units) is the highest among all constituent units of the resin. Preferably, the polypropylene resin contains 50 mol% or more of propylene units out of 100 mol% of all constituent units of the resin.

[0022] In this specification, "random copolymer" refers to a copolymer composed of constituent units derived from two or more monomers, wherein each constituent unit is arranged randomly. Furthermore, "block copolymer" refers to a copolymer composed of constituent units derived from two or more monomers, wherein each constituent unit is arranged continuously, forming a block structure.

[0023] In this specification, "resin derived from virgin raw materials" refers to a resin that has never been recycled, such as a resin newly polycondensed from monomers.

[0024] The polypropylene random copolymer, which is the polypropylene resin (A), is not particularly limited as long as the content of propylene-derived structural units is the largest among all structural units constituting the copolymer, and each structural unit is arranged randomly. Examples include ethylene-propylene random copolymer, ethylene-propylene-butene random copolymer, propylene-butene random copolymer, propylene-chlorinated vinyl random copolymer, and propylene-maleic anhydride random copolymer. One of these copolymers may be used alone as the polypropylene resin (A), or a mixture thereof may be used. Among these, ethylene-propylene random copolymer or ethylene-propylene-butene random copolymer or a mixture thereof is preferred as the polypropylene resin (A) because it is relatively inexpensive and readily available. In this specification, ethylene-propylene random copolymer is a random copolymer consisting of structural units derived from ethylene (ethylene units) and propylene units, and ethylene-propylene-butene random copolymer is a random copolymer consisting of ethylene units, propylene units and structural units derived from butene.

[0025] The ratio of each constituent unit in each random copolymer, which is the polypropylene resin (A), is not particularly limited and can be appropriately set by a person skilled in the art according to the desired application. Furthermore, when a mixture of multiple polypropylene random copolymers, for example, a mixture of ethylene-propylene random copolymer and ethylene-propylene-butene random copolymer, is used as the polypropylene resin (A), the mixing ratio is not particularly limited and can be appropriately set by a person skilled in the art according to the desired application.

[0026] The melting point of polypropylene resin (A) is not particularly limited, but is preferably 130°C or higher, more preferably 130°C to 160°C, more preferably 135°C to 155°C, and even more preferably 140°C to 150°C. The melting point of polypropylene resin (A) has the advantages of (i) being 130°C or higher, making it possible to provide a foamed molded article with excellent heat resistance, and (ii) being 160°C or lower, making it easier to increase the foaming ratio of the foamed particles in the production of these foamed particles. In this specification, the melting points of each polypropylene resin (including polypropylene resins (A) to (D)) are values ​​measured by differential scanning calorimetry (also referred to as the "DSC method"), and more specifically, values ​​measured by the procedure described in the examples.

[0027] The melt flow rate (MFR) of the polypropylene resin (A) is not particularly limited, but is preferably 3.0 g / 10 min to 30.0 g / 10 min, more preferably 4.0 g / 10 min to 20.0 g / 10 min, and even more preferably 5.0 g / 10 min to 18.0 g / 10 min. If the MFR of the polypropylene resin (A) is within the above range, it becomes easier to provide foamed particles with a high foaming ratio, and as a result, it becomes possible to provide a foamed molded article with a beautiful surface and low shrinkage rate. In this specification, the MFR of each polypropylene resin (including polypropylene resins (A) to (D)) is the value obtained using the melt mass flow rate measuring instrument described in JIS-K7210 under conditions of a temperature of 230°C and a load of 2160 g, and more specifically, the value obtained by the procedure described in the examples.

[0028] (Polypropylene resin (B)) The base resin of these foamed particles contains polypropylene resin (B). Polypropylene resin (B) is a resin containing polypropylene resin derived from recycled raw materials (condition (8)), containing 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D) (it is a mixture of polypropylene resin (C) and polypropylene resin (D)) (condition (5)), and having a melting point of less than 160.0°C (condition (2)). Polypropylene resin (C) is a polypropylene random copolymer (condition (6)), and the polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof (condition (7)).

[0029] As described above, the polypropylene resin (B) is a resin that includes a polypropylene resin derived from recycled raw materials. Therefore, at least one of its constituent polypropylene resins (C) and (D) is a polypropylene resin derived from recycled raw materials, and preferably, at least the polypropylene resin (C) is a polypropylene resin derived from recycled raw materials. In particular, from the viewpoint of reducing environmental impact, it is preferable that the polypropylene resin (B) consists only of resin derived from recycled raw materials, in other words, it is preferable that both the polypropylene resin (C) and the polypropylene resin (D) are polypropylene resins derived from recycled raw materials. That is, in one embodiment of the present invention, it is particularly preferable that the polypropylene resin (C) is a polypropylene random copolymer derived from recycled raw materials, and the polypropylene resin (D) is a polypropylene block copolymer derived from recycled raw materials. In this case, the polypropylene resin (B) can also be said to be a mixture of a polypropylene random copolymer derived from recycled raw materials and a polypropylene block copolymer derived from recycled raw materials.

[0030] In this specification, "resin derived from recycled materials" refers, for example, to resin obtained by recycling resin that has been processed once. "Recycled materials" include pre-consumer materials obtained by collecting and recycling resin products that have been discarded before shipment, such as scraps or substandard products generated in the production process, and post-consumer materials obtained by collecting and recycling resin products that have been shipped to the market and used by consumers. Note that "resin derived from recycled materials" can also be rephrased as "resin manufactured using recycled materials."

[0031] Polypropylene resin (B) may contain resins derived from either pre-consumer raw materials (sometimes referred to as post-industrial recycled raw materials or post-industrial recycled (PIR)) or post-consumer raw materials, or it may contain resins derived from a mixture of pre-consumer and post-consumer raw materials. In other words, polypropylene resin (C) and / or polypropylene resin (D) may contain resins derived from either pre-consumer and post-consumer raw materials, or they may contain resins derived from a mixture of pre-consumer and post-consumer raw materials. For example, polypropylene resin (C) may be a resin derived from pre-consumer raw materials, and polypropylene resin (D) may be a resin derived from post-consumer raw materials. In particular, given the high demand for recycling and the ability to meet advanced environmental standards, such as the draft regulations announced by the European Commission in July 2023, it is preferable that at least one of the polypropylene resin (C) or polypropylene resin (D), preferably both (i.e., the entire polypropylene resin (B)), is derived from post-consumer raw materials, preferably from post-consumer raw materials derived from automobiles (so-called ELV raw materials), and may also include raw materials derived from end-of-life automobiles (ASR materials). In conventional technology, recycling post-consumer raw materials derived from automobiles for molded product applications has been difficult from the viewpoint of compressive strength. However, with these foamed particles, it is possible to provide foamed molded products with excellent compressive strength even when using post-consumer raw materials derived from automobiles.

[0032] • Polypropylene resin (C) The polypropylene random copolymer, which is the polypropylene resin (C), is not particularly limited as long as the content of propylene-derived constituent units is the largest among all constituent units of the copolymer, and each constituent unit is arranged randomly. Examples include ethylene-propylene random copolymer, ethylene-propylene-butene random copolymer, propylene-butene random copolymer, propylene-chlorinated vinyl random copolymer, propylene-maleic anhydride random copolymer, etc. One of these copolymers may be used alone as the polypropylene resin (C), or a mixture thereof may be used. Among these, ethylene-propylene random copolymer or ethylene-propylene-butene random copolymer or a mixture thereof is preferred as the polypropylene resin (C) because it is relatively inexpensive and readily available.

[0033] The ratio of each constituent unit in the random copolymer, which is a polypropylene resin (C), is not particularly limited and can be appropriately set by a person skilled in the art according to the desired application. Furthermore, when a mixture of multiple polypropylene random copolymers, for example, a mixture of ethylene-propylene random copolymer and ethylene-propylene-butene random copolymer, is used as the polypropylene resin (C), the mixing ratio is also not particularly limited and can be appropriately set by a person skilled in the art according to the desired application.

[0034] The melting point of the polypropylene resin (C) is not particularly limited, but is preferably 135°C or higher, more preferably 135°C to 165°C, even more preferably 140°C to 160°C, and still more preferably 145°C to 155°C. If the melting point of the polypropylene resin (C) is within the above range, it becomes easier to adjust the difference in melting points between the polypropylene resin (A) and the polypropylene resin (B) to less than 10°C, which has the advantage of making it easier to provide a foamed molded article with excellent compressive strength.

[0035] The melt flow rate (MFR) of the polypropylene resin (C) is not particularly limited, but is preferably 3.0 g / 10 min to 30.0 g / 10 min, more preferably 4.0 g / 10 min to 20.0 g / 10 min, and even more preferably 5.0 g / 10 min to 18.0 g / 10 min. If the MFR of the polypropylene resin (C) is within the above range, the kneadability of the polypropylene resins (A) and (C) is improved, resulting in a more uniform cell structure of the resulting foamed particles, and making it possible to provide a foamed molded article with superior compressive strength.

[0036] The ash content of the polypropylene resin (C) (hereinafter sometimes referred to as "ash content") is not particularly limited, but is preferably 0 to 10,000 ppm, and more preferably 0 to 5,000 ppm. If the ash content of the polypropylene resin (C) is within the above range, the moldability of the foamed particles will be good, and the compressive strength of the resulting foamed molded article will tend to be high. The ash content of the polypropylene resin (C) is measured by the method described in the examples.

[0037] When the polypropylene resin (C) is derived from recycled materials, its carbon black concentration is not particularly limited, but is preferably 0 to 5% by weight, and more preferably 0 to 3% by weight. If the carbon black concentration of the polypropylene resin (C) is within the above range, the resulting foamed molded article tends to have good flame retardancy. The carbon black concentration of the polypropylene resin (C) is measured by the method described in the examples.

[0038] • Polypropylene resin (D) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof. The polypropylene block copolymer that is the polypropylene resin (D) is not particularly limited as long as the content of propylene-derived constituent units is the largest among all constituent units of the copolymer, and each constituent unit is arranged continuously to form a block structure. Examples include ethylene-propylene block copolymer, ethylene-propylene-butene block copolymer, propylene-butene block copolymer, propylene-chlorinated vinyl block copolymer, and propylene-maleic anhydride block copolymer. One of these copolymers may be used alone as the polypropylene resin (D), or a mixture thereof may be used. Among these, it is preferable to use an ethylene-propylene block copolymer or a propylene homopolymer, or a mixture thereof, as the polypropylene resin (D) because it is relatively inexpensive and readily available. In this specification, ethylene-propylene block copolymer is a block copolymer consisting of ethylene units and propylene units.

[0039] The ratio of each constituent unit in each block copolymer, which is the polypropylene resin (D), is not particularly limited. Furthermore, when a mixture of ethylene-propylene block copolymer and propylene homopolymer is used as the polypropylene resin (D), the mixing ratio is also not particularly limited.

[0040] The melting point of the polypropylene resin (D) is not particularly limited, but is preferably above 140°C, more preferably above 145°C, more preferably above 150°C, more preferably above 150°C, more preferably between 153°C and 175°C, more preferably between 155°C and 170°C, and even more preferably between 157°C and 167°C.

[0041] The melt flow rate (MFR) of the polypropylene resin (D) is not particularly limited, but is preferably 5.0 g / 10 min or more and 50.0 g / 10 min or less, more preferably 7.0 g / 10 min or more and 40.0 g / 10 min or less, still more preferably 8.0 g / 10 min or more and 35.0 g / 10 min or less, and even more preferably 10.0 g / 10 min or more and 30.0 g / 10 min or less. When the MFR of the polypropylene resin (D) is within the above range, the kneadability of the polypropylene resins (A) and (D) is improved, whereby the cell structure of the resulting expanded beads becomes uniform, and it becomes possible to provide an expanded molded article that is more excellent in compressive strength.

[0042] The ash content of the polypropylene resin (D) (hereinafter sometimes referred to as "ash content") is not particularly limited, but is preferably 0 or more and 100000 ppm or less, more preferably 0 or more and 70000 ppm or less, and even more preferably 0 or more and 50000 ppm or less. When the ash content of the polypropylene resin (D) is within the above range, the moldability of the expanded beads becomes favorable, and the compressive strength of the resulting expanded molded article tends to be high. The ash content of the polypropylene resin (D) is measured by the method described in the Examples.

[0043] When the polypropylene resin (D) is a resin derived from recycled raw material, the carbon black concentration is not particularly limited, but is preferably 0 or more and 5% by weight or less, and more preferably 0 or more and 3% by weight or less. When the carbon black concentration of the polypropylene resin (D) is within the above range, the flame retardancy of the resulting expanded molded article tends to be favorable. The carbon black concentration of the polypropylene resin (D) is measured by the method described in the Examples.

[0044] Polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D), based on a total amount of 100% by weight of polypropylene resin (C) and polypropylene resin (D). The content ratio of polypropylene resin (C) and polypropylene resin (D) in polypropylene resin (B) is not particularly limited as long as it is within the above range. For example, based on a total amount of 100% by weight, it may contain 50% to 85% by weight of polypropylene resin (C) and 15% to 50% by weight of polypropylene resin (D), or 55% to 80% by weight of polypropylene resin (C) and 20% to 45% by weight of polypropylene resin (D), or 60% to 75% by weight of polypropylene resin (C) and 25% to 40% by weight of polypropylene resin (D).

[0045] - Physical properties of polypropylene resin (B) The melting point of polypropylene resin (B) is less than 160.0°C. The melting point of polypropylene resin (B) is not particularly limited as long as it is less than 160.0°C, for example it may be 158.0°C or less, or 155°C or less. The lower limit is also not particularly limited, for example it may be 130.0°C or higher, 140.0°C or higher, or 150.0°C or higher. Note that the melting point of polypropylene resin (B) is the melting point of a mixture obtained by mixing polypropylene resin (C) and polypropylene resin (D) in the specified content ratio, and is the value measured by the DSC method described above for such a mixture.

[0046] The melt flow rate (MFR) of the polypropylene-based resin (B) is not particularly limited, but is preferably 4.0 g / 10 min or more and 35.0 g / 10 min or less, more preferably 5.0 g / 10 min or more and 25.0 g / 10 min or less, and even more preferably 6.0 g / 10 min or more and 22.0 g / 10 min or less. When the MFR of the polypropylene-based resin (B) falls within the above range, kneadability with the polypropylene-based resin (A) is improved, so that the resulting expanded beads have a uniform cell structure, and it becomes possible to provide an expanded molded article that is more excellent in compressive strength.

[0047] (Characteristics of base resin) ・Difference in melting point The difference between the melting point of the polypropylene-based resin (A) and the melting point of the polypropylene-based resin (B) contained in the base resin of the present expanded beads is less than 10.0°C (condition (3)). In other words, the polypropylene-based resin (A) and the polypropylene-based resin (B) contained in the base resin of the present expanded beads satisfy the following formula: −10.0 (°C) < (melting point of polypropylene-based resin (B) (°C)) − (melting point of polypropylene-based resin (A) (°C)) < 10.0 (°C).

[0048] As long as the difference between the melting point of the polypropylene-based resin (A) and the melting point of the polypropylene-based resin (B) contained in the base resin of the present expanded beads is less than 10.0°C (in other words, as long as the above inequality is satisfied), it is not particularly limited. For example, the difference may be 9.0°C or less, 8.0°C or less, 7.0°C or less, or 6.0°C or less. The lower limit of the difference is also not particularly limited, and may be 1°C or more, or 0°C.

[0049] - Composition of base resin The base resin of these foamed particles contains polypropylene resin (A) at a total amount of 100% by weight, with polypropylene resin (A) at 40% to 95% by weight and polypropylene resin (B) at 5% to 60% by weight. The content ratio of polypropylene resin (A) and polypropylene resin (B) in the base resin is not particularly limited as long as it is within the above range. For example, based on a total amount of 100% by weight, it may contain 45% to 90% by weight of polypropylene resin (A) and 10% to 55% by weight of polypropylene resin (B), or 50% to 85% by weight of polypropylene resin (A) and 15% to 50% by weight of polypropylene resin (B), or 55% to 80% by weight of polypropylene resin (A) and 20% to 45% by weight of polypropylene resin (B). Furthermore, from the perspective of meeting advanced environmental standards, as outlined in the draft regulations published by the European Commission in July 2023, the base resin of these foamed particles preferably contains polypropylene resin (B), which is a resin containing recycled materials, with a total amount of polypropylene resin (A) and polypropylene resin (B) of 100% by weight, such that the content of resin derived from recycled materials is 25% by weight or more. For example, if polypropylene resin (B) consists of resin derived from recycled materials (i.e., polypropylene resins (C) and (D) (When both are resins derived from recycled materials), it is preferable to contain 40% to 75% by weight of polypropylene resin (A) and 25% to 60% by weight of polypropylene resin (B), more preferably 45% to 70% by weight of polypropylene resin (A) and 30% to 55% by weight of polypropylene resin (B), and even more preferably 50% to 65% by weight of polypropylene resin (A) and 35% to 50% by weight of polypropylene resin (B).

[0050] These foamed particles may contain resins other than polypropylene resin (for example, polyethylene resin) that are derived from recycled materials or unintentionally mixed in during the recycling process of recycled materials.

[0051] (Additives) In addition to the base resin described above, these foamed particles may optionally contain additives. Such additives 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, and titanium dioxide), antistatic agents (e.g., glycerin monostearate, glycerin monodistearate), and flame retardants (e.g., Examples of additives include hindered amine flame retardants, bromine flame retardants, phosphate ester flame retardants, melamine flame retardants, etc.), antioxidants (e.g., hindered phenol antioxidants), heat stabilizers (e.g., phosphorus heat stabilizers and sulfur heat stabilizers), light stabilizers (e.g., benzotriazole UV absorbers, triazine UV absorbers, HALS and / or hindered amine light stabilizers), nucleating agents, conductive agents (carbon, carbon nanotubes, metal fillers, etc.), lubricants, acid scavengers, antiblocking agents, metal chelating agents (e.g., IRGANOX® MD1024, Adekastab® CDA-1), lubricants, antibacterial agents, etc. These additives can be used individually or in combination of two or more, depending on the purpose.

[0052] These foamed particles may contain additives that are intentionally mixed during the manufacturing process, as well as additives that are derived from recycled materials or unintentionally mixed during the recycling process of recycled materials.

[0053] <Physical Properties of the Foamed Particles> (Melting Point of the Foamed Particles) The melting point of the foamed particles is not particularly limited, but is preferably 140.0°C or higher and 155.0°C or lower. When the melting point of the foamed particles is within the above range, it has the advantage that it can be molded using a molding machine for ordinary polypropylene resin foamed particles and a molded article with superior compressive strength can be provided. The melting point of the foamed particles may be, for example, 141.0°C or higher and 154.0°C or lower, 142.0°C or higher and 153.0°C or lower, or 143.0°C or higher and 153.0°C or lower. The melting point of the foamed particles is a value measured by the DSC method described above, similar to polypropylene resin, and more specifically, a value measured by the procedure described in the examples.

[0054] (Bulk density of the foamed particles) The bulk density of the foamed particles is not particularly limited, but is preferably 10.0 g / L or more and 200.0 g / L or less. When the bulk density of the foamed particles is within the above range, it has the advantage of being applicable to foamed molded articles of various uses and shapes. The bulk density of the foamed particles may be, for example, 15.0 g / L or more and 150.0 g / L or less, or 20.0 g / L or more and 100.0 g / L or less. The bulk density of the foamed particles may be adjusted as appropriate within the above range according to its use and desired physical properties. For example, when applied to automotive component applications, a relatively low density is preferred from the viewpoint of reducing vehicle weight. Specifically, it is preferably 10.0 g / L or more and 40.0 g / L or less, more preferably 15.0 g / L or more and 35.0 g / L or less, and even more preferably 20.0 g / L or more and 33.0 g / L or less. On the other hand, when applied to energy absorbing members, a relatively high density is preferable, specifically, more preferably greater than 40 g / L and 200 g / L or less, more preferably 45.0 g / L or more and 150.0 g / L or less, and even more preferably 50.0 g / L or more and 100.0 g / L or less. The bulk density of these foamed particles is a value measured under atmospheric pressure, and more specifically, a value measured by the procedure described in the examples.

[0055] (Average cell diameter of the foamed particles) The average cell diameter of the foamed particles is not particularly limited and can be adjusted as appropriate according to its application and desired physical properties. For example, if the foamed particles are relatively low-density foamed particles having a bulk density of 10.0 g / L or more and 40.0 g / L or less, the average cell diameter is preferably 70 μm or more and 400 μm or less, more preferably 80 μm or more and 200 μm or less, and even more preferably 90 μm or more and 150 μm or less, in order to exhibit good moldability. On the other hand, if the foamed particles are relatively high-density foamed particles having a bulk density of more than 40.0 g / L and 200.0 g / L or less, their average cell diameter is preferably 40 μm to 400 μm, more preferably 50 μm to 400 μm, more preferably 60 μm to 400 μm, more preferably 70 μm to 400 μm, more preferably 70 μm to 300 μm, more preferably 80 μm to 200 μm, and even more preferably 90 μm to 150 μm, in order to exhibit good moldability. The average cell diameter of the foamed particles is the value measured by the procedure described in the examples.

[0056] (Shrinkage rate of the foamed particles) Because the foamed particles have the above-described structure (especially in order to satisfy conditions (1) to (8)), they have a low shrinkage rate, the foaming ratio can be easily controlled, and homogeneous foamed particles can be produced. The shrinkage rate of the foamed particles is affected by their bulk density and is therefore difficult to define in general terms. For example, if the foamed particles are relatively low-density foamed particles with a bulk density of 10.0 g / L or more and 40.0 g / L or less, the foamed particles can have a low shrinkage rate of 10.0% or less. If the foamed particles are relatively high-density foamed particles with a bulk density of more than 40.0 g / L and 200.0 g / L or less, the foamed particles can have a low shrinkage rate of 7.0% or less. In other words, in one embodiment of the present invention, the foamed particles may be foamed particles having a bulk density of 10 g / L or more and 40 g / L or less and a shrinkage rate of 10.0% or less, or a bulk density of more than 40 g / L and 200 g / L or less and a shrinkage rate of 7.0% or less.

[0057] From the viewpoint of making it easier to control the foaming ratio, a lower shrinkage rate of the foam particles is preferable. For example, if the foam particles have a bulk density of 10.0 g / L or more and 40.0 g / L or less, their shrinkage rate may be 9.0% or less, 8.0% or less, 7.0% or less, or 6.0% or less. Also, if the foam particles have a bulk density of more than 40.0 g / L and 200.0 g / L or less, their shrinkage rate may be 6.0% or less, 5.0% or less, 4.0% or less, or 3.0% or less. The lower limit of the shrinkage rate of the foam particles is not particularly limited and may be 1.0% or more, or 0%.

[0058] In this specification, the shrinkage rate of the foamed particles is intended to be the value calculated by the following formula (1): Shrinkage rate (%) = {(BD) - (VBD)} × 100 / (VBD) ... Formula (1) [where BD is the bulk density of the foamed particles measured under atmospheric pressure, and VBD is the reduced bulk density of the foamed particles measured under a pressure of -0.10 MPa·G or higher and -0.05 MPa·G or lower]. Note that "G" indicates that the pressure is gauge pressure.

[0059] The bulk density (BD) and bulk density under reduced pressure (VBD) values ​​of the foamed particles used in the calculation of formula (1) are values ​​measured by the procedure described in the examples.

[0060] (Open-cell ratio of the foamed particles) The open-cell ratio of the foamed particles is not particularly limited, but it is preferable to have a relatively low value in order to provide a molded article that exhibits good moldability and superior compressive strength. Specifically, when the foamed particles are relatively low-density foamed particles having a bulk density of 10 g / L or more and 40 g / L or less, it is preferable to have a ratio of 10.0% or less, more preferably 7.0% or less, and even more preferably 4.0% or less. On the other hand, when the foamed particles are relatively high-density foamed particles having a bulk density of more than 40.0 g / L and 200.0 g / L or less, it is preferable to have a ratio of 7.0% or less, more preferably 5.0% or less, and even more preferably 3.0% or less. The lower limit of the open-cell ratio of the foamed particles is not particularly limited and may be 1.0% or more, or 0%. Furthermore, the open-cell ratio of the foamed particles is a value measured by the procedure described in the examples.

[0061] [2. Method for Producing Polypropylene Resin Foamed Particles] The method for producing these foamed particles is not particularly limited, but a preferred method includes the steps of: preparing a base resin by mixing a polypropylene resin (A) and a polypropylene resin (B); and preparing foamed particles from the base resin. In other words, the present invention provides a method for producing polypropylene resin foam particles, comprising the steps of: preparing a base resin by mixing a polypropylene resin (A) and a polypropylene resin (B) in one embodiment of the present invention; and preparing foam particles from the base resin, wherein the method satisfies the following conditions (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0062] According to this manufacturing method, it is possible to provide novel polypropylene-based resin foam particles that can provide foam molded articles with excellent compressive strength, even when using recycled raw materials.

[0063] The specific aspects of this manufacturing method will be described in more detail below, but matters already explained in section [1. Polypropylene-based foamed particles] should be referred to in section [1. Polypropylene-based foamed particles], and will be omitted from this section.

[0064] <Step for preparing the base resin> This manufacturing method includes a step of preparing a base resin by mixing polypropylene resin (A) and polypropylene resin (B) (base resin preparation step). In the base resin preparation step, the method of mixing polypropylene resin (A) and polypropylene resin (B) is not particularly limited, and known methods such as dry blending and hand blending can be used.

[0065] The base resin preparation process can also be described as a process of mixing polypropylene resin (A), polypropylene resin (C), and polypropylene resin (D). In the base resin preparation process, polypropylene resin (C) and polypropylene resin (D) may be pre-mixed in a recycling process or the like, and then mixed with polypropylene resin (A) in the form of a mixed polypropylene resin (B) to form the base resin, or they may be mixed individually with polypropylene resin (A) to form the base resin.

[0066] In the base resin preparation process, when mixing polypropylene resin (A) and polypropylene resin (B), the various additives mentioned above may also be added.

[0067] (Granulation Process) The base resin preparation process related to this manufacturing method may further include a process (granulation process) for producing polypropylene resin particles (sometimes simply referred to as "resin particles") containing a base resin containing polypropylene resin (A) and polypropylene resin (B).

[0068] In the granulation process, there are no particular limitations on the method for producing resin particles, but one example is the use of an extruder. Specifically, for example, resin particles can be produced by the following methods (1) to (4): (1) A base resin containing polypropylene resin (A) and polypropylene resin (B) is put into an extruder and the base resin is melt-kneaded to prepare a polypropylene resin composition; (2) The obtained polypropylene resin composition is extruded from a die provided in the extruder; (3) The extruded polypropylene resin composition is solidified by cooling it by passing it through water, etc.; (4) The solidified polypropylene resin composition is then cut with a cutter into desired shapes such as cylindrical, elliptical, spherical, cubic, rectangular parallelepiped, hollow cylindrical, polygonal prism, etc. Alternatively, in (2), the melt-kneaded polypropylene resin composition may be directly extruded into water from a die provided in the extruder, and immediately after extrusion, the polypropylene resin composition may be cut into particle shapes, cooled, and solidified. In this way, by melt-kneading the base resin, more uniform resin particles can be obtained. Furthermore, in this manufacturing method, the resin particles containing the polypropylene resin (A) and the polypropylene resin (B) obtained in this operation can also be used as a base resin for foamed particles in the subsequent foamed particle preparation step.

[0069] The average weight per particle of the resin particles obtained as described above is preferably 0.5 mg / particle or more and 3.5 mg / particle or less, and more preferably 0.7 mg / particle or more and 2.0 mg / particle or less. By setting the average weight of the resin particles within the above range, it is possible to provide foamed particles with excellent filling properties during in-mold foam molding, which has the advantage of making it easier to manufacture foamed molded articles with complex shapes.

[0070] <Step for preparing foamed particles> This manufacturing method includes a step for preparing foamed particles (foamed particle preparation step) from a base resin (preferably resin particles) obtained in the base resin preparation step. In the foamed particle preparation step, the method for preparing foamed particles from the base resin is not particularly limited, but a method including a dispersion step and a foaming step including a heating-pressure step, a holding step and a release step can be preferably mentioned. That is, the foamed particle preparation step in this manufacturing method preferably includes a dispersion step and a foaming step.

[0071] (Dispersion step) The foam particle preparation step preferably includes a dispersion step before the foaming step in which a base resin (resin particles), an aqueous dispersion medium, a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in a container. The dispersion step can also be described as a step of preparing a dispersion in which the base resin (resin particles), a foaming agent, and, if necessary, a dispersant and / or a dispersion aid are dispersed in an aqueous dispersion medium.

[0072] The container is not particularly limited, but it is preferable that it be able to withstand the foaming temperature and pressure described later. For example, a pressure-resistant container is preferable, and an autoclave-type pressure-resistant container is more preferable. The container may be equipped with an agitator.

[0073] The aqueous dispersion medium can be any medium capable of uniformly dispersing the base resin, foaming agent, etc., and is not particularly limited.

[0074] Examples of aqueous dispersion media include (a) dispersion media obtained by adding methanol, ethanol, ethylene glycol, and glycerin to water, (b) water such as ultrapure water, pure water, tap water, and industrial water, and (c) solutions (aqueous solutions) containing salts such as sodium chloride or sodium sulfate.

[0075] To enable stable production of foamed particles, it is preferable to use pure water and ultrapure water such as RO water (water purified by reverse osmosis), distilled water, and deionized water (water purified by ion exchange resin) as the aqueous dispersion medium.

[0076] 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) (b-1) saturated hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; (b-2) ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; and (b-3) halogenated hydrocarbons such as monocormethane, chloroethane, and hydrofluoroolefin.

[0077] As a blowing agent, at least one type selected from the group consisting of the inorganic and organic blowing agents described above can be used. When using a mixture of two or more blowing agents, the mixing ratio may be adjusted as appropriate depending on the purpose. From the viewpoint of environmental impact and blowing power, inorganic blowing agents are preferred among those described above. Furthermore, carbon dioxide is preferred among inorganic blowing agents because it has a moderately high plasticizing effect and easily improves the blowing properties of the foamed particles in the production of these foamed particles.

[0078] The aqueous dispersion medium and foaming agent described above may be used individually or in combination of two or more types.

[0079] In this manufacturing method, it is preferable to use dispersants (e.g., inorganic substances such as tricalcium phosphate, kaolin, and talc) and dispersion aids (e.g., anionic surfactants such as sodium alkanesulfonate and sodium dodecylbenzenesulfonate). 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.

[0080] (Foaming Process) The foaming particle preparation process preferably includes a foaming process, which follows the dispersion process, in which the base resin (resin particles) is foamed in the dispersion obtained in the dispersion process. The method for foaming the base resin (resin particles) in the foaming process is not particularly limited, but a method including (a) a heating-pressure-raising process in which the temperature inside the container of the dispersion is raised to a certain temperature and the pressure inside the container is raised to a certain pressure, (b) a holding process in which the temperature and pressure inside the container are maintained at a constant temperature and a constant pressure, and (c) a release process in which one end of the container is opened and the dispersion inside the container is released into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container). In other words, the foaming process according to this manufacturing method preferably includes a heating-pressure-raising process, a holding process, and a release process.

[0081] • Heating and Pressurizing Process: The heating and pressing process involves raising the internal temperature of a container filled with the dispersion liquid to a certain temperature and increasing the internal pressure to a certain pressure. The heating and pressing process can also be described as adjusting the internal temperature and internal pressure of the container filled with the dispersion liquid to a temperature suitable for depressurization and foaming of the base resin.

[0082] The internal temperature of the container holding the dispersion liquid (hereinafter also referred to as the foaming temperature), which is adjusted in the heating-pressure step, is not particularly limited as long as it is a temperature suitable for depressurizing and foaming the base resin. For example, it may be 145.0°C or higher and 165.0°C or lower, or 150.0°C or higher and 160.0°C or lower.

[0083] The internal pressure of the container holding the dispersion liquid, which is adjusted during the heating-pressure step (hereinafter also referred to as the foaming pressure), is not particularly limited as long as it is a pressure suitable for depressurizing and foaming the base resin. For example, it may be 1.0 MPa or more and 4.0 MPa or less in gauge pressure, and may also be 1.5 MPa or more and 3.5 MPa or less.

[0084] • Holding process: The holding process is a process of maintaining the foaming temperature and foaming pressure adjusted in the heating-pressure process for a certain period of time. The time for which the foaming temperature and foaming pressure are maintained in the holding process (holding time) is not particularly limited, but may be, for example, 10 minutes or more and 60 minutes or 15 minutes or more and 40 minutes or less.

[0085] • Release Process: The release process involves opening one end of the container that has undergone the heating-pressure and holding processes, and releasing the dispersion liquid inside the container into a region (space) with a pressure lower than the foaming pressure (i.e., the pressure inside the container). This operation (pressure release operation) allows the base resin to foam, and as a result, foamed particles can be obtained.

[0086] In the release process, the "region with a pressure lower than the foaming pressure" refers to the "region under a pressure lower than the foaming pressure" or the "space under a pressure lower than the foaming pressure," and can also be described as "an atmosphere under a pressure lower than the foaming pressure." The pressure in the region with a pressure lower than the foaming pressure is not particularly limited as long as it is lower than the foaming pressure; for example, it may be atmospheric pressure. In other words, the release process may be a process of releasing the dispersion under atmospheric pressure.

[0087] In the discharge process, when discharging the dispersion into a region with a pressure lower than the foaming pressure, the dispersion may be discharged through an open orifice with a diameter of 1 mm to 10 mm in order to adjust the flow rate of the dispersion and reduce variations in the foaming ratio of the resulting foamed particles. Furthermore, the low-pressure region (space) may be filled with saturated water vapor to improve foaming properties.

[0088] <Two-stage foaming process> This manufacturing method may include a two-stage foaming process in which the foamed particles obtained in the foamed particle preparation process are foamed again. By performing a two-stage foaming process, it is possible to obtain foamed particles with a higher foaming ratio. In this specification, foamed particles obtained through such a two-stage foaming process are referred to as two-stage foamed particles, and foamed particles obtained in a single foaming process (single-stage foaming process) (in other words, foamed particles made by foaming a base resin (resin particles) that have not undergone a two-stage foaming process) are referred to as single-stage foamed particles.

[0089] These foamed particles may be single-stage foamed particles or double-stage foamed particles. If these foamed particles are double-stage foamed particles, the physical properties (e.g., bulk density, average cell diameter, shrinkage rate, open-cell ratio, etc.) are intended to be values ​​measured for such double-stage foamed particles.

[0090] In the two-stage foaming process, the method for re-foaming the foamed particles (first-stage foamed particles) is not particularly limited, and known methods can be employed.

[0091] [3. Polypropylene Resin Foam Molded Article] In one embodiment of the present invention, a polypropylene resin foam molded article is provided, which is obtained by foam molding the foam particles. The polypropylene resin foam molded article according to one embodiment of the present invention (hereinafter also referred to as "the foam molded article") uses the foam particles as a raw material and, despite being a foam molded article manufactured using recycled materials, has excellent compressive strength.

[0092] <Physical Properties of the Foamed Molded Article> (Open Cell Ratio of the Foamed Molded Article) The open cell ratio of the foamed molded article is not particularly limited, but from the viewpoint of achieving good moldability and higher compressive strength, it is preferable that it be a relatively low value. Specifically, it is preferably 10.0% or less, more preferably 8.0% or less, and even more preferably 6.0% or less. The lower limit of the open cell ratio of the foamed molded article is not particularly limited and may be 1.0% or more, or 0%. Furthermore, the open cell ratio of the foamed molded article is a value measured by the procedure described in the examples.

[0093] (Compressive Strength of the Foamed Molded Article) The compressive strength of the foamed molded article can be evaluated by its compressive strength at 50% compression. Basically, the higher the compressive strength of the foamed molded article at 50% compression, the higher its compressive strength. The compressive strength of the foamed molded article is also affected by its density, so it is difficult to define the compressive strength of the foamed molded article at 50% compression in general terms. For example, if the density of the foamed molded article is 30 g / L, its compressive strength at 50% compression is preferably 0.235 MPa or higher, more preferably 0.240 MPa or higher, and even more preferably 0.245 MPa or higher. If the density of the foamed molded article is 20 g / L, its compressive strength at 50% compression is preferably 0.155 MPa or higher, more preferably 0.165 MPa or higher, and even more preferably 0.175 MPa or higher. When the density of the foamed molded article is 35 g / L, its compressive strength at 50% compression is preferably 0.240 MPa or higher, more preferably 0.245 MPa or higher, and even more preferably 0.250 MPa or higher. When the density of the foamed molded article is 45 g / L, its compressive strength at 50% compression is preferably 0.360 MPa or higher, more preferably 0.380 MPa or higher, and even more preferably 0.400 MPa or higher. If the foamed molded article satisfies the above relationship between density and compressive strength at 50% compression, it can be evaluated as a foamed molded article with excellent compressive strength. The compressive strength at 50% compression of the foamed molded article is a value measured by a compression test, and more specifically, it is a value measured by the method described in the examples.

[0094] <Method for Manufacturing the Foamed Molded Article> One embodiment of the present invention provides a method for manufacturing a polypropylene resin foamed molded article, comprising the step of foam molding polypropylene resin foam particles according to one embodiment of the present invention described in section [1. Polypropylene Resin Foamed Particles] above, or polypropylene resin foam particles obtained by the method for manufacturing polypropylene resin foamed particles according to one embodiment of the present invention described in section [2. Method for Manufacturing Polypropylene Resin Foamed Particles] above.

[0095] The method for manufacturing this foamed molded article is not particularly limited, and known molding methods can be applied. Such known molding methods include, for example, a method that sequentially includes the following steps (b1) to (b3) (a so-called in-mold foaming method), but is not limited to this method: (b1) supplying foamed particles to be used as raw material into a mold having a molding space; (b2) heating the inside of the mold with steam at a predetermined pressure (molding pressure) to fuse the foamed particles together; (b3) water-cooling the inside of the mold and the surface of the foamed molded article, and then drying the foamed molded article.

[0096] (b1) In step (b), the foam particles may be supplied into the mold under conditions in which a predetermined internal pressure (foam particle internal pressure) is applied to the foam particles.

[0097] (b1) In step (b1), the internal pressure of the foamed particles is not particularly limited, but is preferably 0.10 MPa (absolute pressure) or more and 0.30 MPa (absolute pressure) or less, and preferably 0.15 MPa (absolute pressure) or more and 0.25 MPa (absolute pressure) or less. Methods for applying internal pressure to the foamed particles include pressurizing with air and impregnating with inorganic gas.

[0098] (b2) In step (b2), the pressure of the steam used to heat the mold (and the foam particles inside) is not particularly limited, but is preferably any pressure within the range of moldable pressure. In this specification, moldable pressure refers to the steam pressure at which a foamed molded article is obtained in which the intergranularity, surface appearance, fusion, and shrinkage rate all meet the acceptable standards when the foam particles are molded, and is more specifically measured by the method described in the Examples.

[0099] <Applications of this foamed molded product> This foamed molded product can be suitably used in various resin product applications. In particular, because this foamed molded product has excellent compressive strength despite being manufactured using recycled materials, it can be particularly suitably used in resin products with high recycling demand, such as automotive resin products like automotive interior components and core materials for automotive bumpers. That is, in one embodiment of the present invention, an automotive resin product including this foamed molded product is provided.

[0100] One aspect of the present invention may include the following configuration.

[0101] [1] Polypropylene resin foam particles containing a base resin containing polypropylene resin (A) and polypropylene resin (B), satisfying the following (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of the polypropylene resin (C) and 5% to 60% by weight of the polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0102] [2] Polypropylene resin foam particles as described in [1], wherein the melting point is 140.0°C or higher and 155.0°C or lower.

[0103] [3] Polypropylene resin foam particles as described in [1] or [2], having a bulk density of 10.0 g / L or more and 200.0 g / L or less.

[0104] [4] Polypropylene resin foam particles according to any one of [1] to [3], wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less, and the average cell diameter is 70 μm or more and 400 μm or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less, and the average cell diameter is 40 μm or more and 400 μm or less.

[0105] [5] Polypropylene resin foam particles described in any one of [1] to [4], wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less, and the shrinkage rate calculated by the following formula (1) is 10.0% or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less, and the shrinkage rate calculated by the following formula (1) is 7.0% or less: Shrinkage rate (%) = {(BD) - (VBD)} × 100 / (VBD) ... Formula (1) [wherein BD is the bulk density of the polypropylene resin foam particles measured under atmospheric pressure, and VBD is the reduced bulk density of the polypropylene resin foam particles measured under a pressure of -0.10 MPa·G or more and -0.05 MPa·G or less].

[0106] [6] Polypropylene resin foam particles according to any one of [1] to [5], wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less and the open-cell ratio is 10.0% or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less and the open-cell ratio is 7.0% or less.

[0107] [7] Polypropylene resin foam particles according to any one of [1] to [6], wherein the polypropylene resin (D) is derived from post-consumer raw materials derived from automobiles.

[0108] [8] The polypropylene resin foam particles according to any one of [1] to [7], wherein the melting point of the polypropylene resin (A) is 130°C or higher.

[0109] [9] The polypropylene resin foam particles according to any one of [1] to [8], wherein the melt flow rate of the polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0110]

[10] The polypropylene resin foam particle according to any one of [1] to [9], wherein the melting point of the polypropylene resin (C) is 135°C or higher.

[0111]

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

[10] , wherein the melt flow rate of the polypropylene resin (C) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0112]

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

[11] , wherein the melting point of the polypropylene resin (D) is greater than 140°C.

[0113]

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

[12] , wherein the melt flow rate of the polypropylene resin (D) is 5.0 g / 10 min or more and 50.0 g / 10 min or less.

[0114]

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

[13] , wherein the melting point of the polypropylene resin (A) is 160°C or lower.

[0115]

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

[14] , wherein the melting point of the polypropylene resin (B) is 158°C or lower.

[0116]

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

[15] , wherein the melting point of the polypropylene resin (C) is 165°C or lower.

[0117]

[17] The polypropylene resin foam particle according to any one of [1] to

[16] , wherein the melting point of the polypropylene resin (D) is 175°C or lower.

[0118] A polypropylene resin foam molded article obtained by foam molding polypropylene resin foam particles described in any one of [1] to

[17] .

[0119]

[19] A method for producing polypropylene resin foam particles, comprising the steps of: mixing a polypropylene resin (A) and a polypropylene resin (B) to prepare a base resin; and preparing foam particles from the base resin, wherein the following (1) to (8) are satisfied: (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% by weight or more and 95% by weight or less of the polypropylene resin (A), and 5% by weight or more and 60% by weight or less of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

[0120]

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

[19] , wherein the melting point of the polypropylene resin foam particles is 140.0°C or higher and 155.0°C or lower.

[0121]

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

[19] or

[20] , wherein the bulk density of the polypropylene resin foam particles is 10.0 g / L or more and 200.0 g / L or less.

[0122]

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

[19] to

[21] , wherein the bulk density of the polypropylene resin foam particles is 10.0 g / L or more and 40.0 g / L or less, and the average cell diameter of the polypropylene resin foam particles is 70 μm or more and 400 μm or less, or the bulk density of the polypropylene resin foam particles is greater than 40.0 g / L and 200.0 g / L or less, and the average cell diameter of the polypropylene resin foam particles is 40 μm or more and 400 μm or less.

[0123]

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

[19] to

[22] , wherein the bulk density of the polypropylene resin foam particles is 10.0 g / L or more and 40.0 g / L or less, and the shrinkage rate of the polypropylene resin foam particles calculated by the following formula (1) is 10.0% or less, or the bulk density of the polypropylene resin foam particles is greater than 40.0 g / L and 200.0 g / L or less, and the shrinkage rate of the polypropylene resin foam particles calculated by the following formula (1) is 7.0% or less: Shrinkage rate of polypropylene resin foam particles (%) = {(BD) - (VBD)} × 100 / (VBD) ... Formula (1) [Here, BD is the bulk density of the polypropylene resin foam particles measured under atmospheric pressure, and VBD is the bulk density of the polypropylene resin foam particles under reduced pressure measured at a pressure of -0.10 MPa·G or higher and -0.05 MPa·G or lower.]

[0124]

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

[19] to

[23] , wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less and the open-cell ratio is 10.0% or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less and the open-cell ratio is 7.0% or less.

[0125]

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

[19] to

[24] , wherein the polypropylene resin (D) is derived from post-consumer raw materials derived from automobiles.

[0126]

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

[19] to

[25] , wherein the melting point of the polypropylene resin (A) is 130°C or higher.

[0127]

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

[19] to

[26] , wherein the melt flow rate of the polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0128]

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

[19] to

[27] , wherein the melting point of the polypropylene resin (C) is 135°C or higher.

[0129]

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

[19] to

[28] , wherein the melt flow rate of the polypropylene resin (C) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

[0130]

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

[19] to

[29] , wherein the melting point of the polypropylene resin (D) is greater than 140°C.

[0131]

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

[19] to

[30] , wherein the melt flow rate of the polypropylene resin (D) is 5.0 g / 10 min or more and 50.0 g / 10 min or less.

[0132]

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

[19] to

[31] , wherein the melting point of the polypropylene resin (A) is 160°C or lower.

[0133]

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

[19] to

[32] , wherein the melting point of the polypropylene resin (B) is 158°C or lower.

[0134]

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

[19] to

[33] , wherein the melting point of the polypropylene resin (C) is 165°C or lower.

[0135]

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

[19] to

[34] , wherein the melting point of the polypropylene resin (D) is 175°C or lower.

[0136] A method for producing a polypropylene resin foamed molded article, comprising the step of foam molding polypropylene resin foamed particles described in any one of

[36] [1] to

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

[19] to

[35] .

[0137] The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to these examples.

[0138] [Materials] <Base Resin> (Polypropylene Resin) Table 1 shows the type, melting point, and MFR of each polypropylene resin used (polypropylene resins (A) to (D) and other polypropylene resins). For polypropylene resins derived from recycled materials, the main raw materials are also listed (those without a listed raw material are resins derived from virgin raw materials).

[0139] <Additives> ・Talc [Hayashi Chemical Co., Ltd., Talc Powder PK-S] ・Glycerin [Lion Corporation, Purified Glycerin D] [Measurement Method] The measurement and evaluation methods for various items performed in the examples and comparative examples are described below.

[0140] (MFR of polypropylene resin) The MFR of polypropylene resin was measured using an MFR measuring instrument described in JIS K7210-1:2014. The measurement conditions were an orifice diameter of 2.0959 ± 0.005 mmφ, an orifice length of 8.000 ± 0.025 mm, a load of 2160 g, and a temperature of 230 ± 0.2 °C.

[0141] (Melting point of polypropylene resin and foamed particles) The melting point of polypropylene resin and foamed particles was measured using a differential scanning calorimeter [Hitachi High-Tech Science Corporation, DSC7020]. The specific operating procedure was as follows (1) to (4): (1) The target material (polypropylene resin or foamed particles) was melted by raising the temperature of 5 mg to 6 mg of the material from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (2) The molten material was then crystallized by lowering the temperature from 220.0°C to 40.0°C at a cooling rate of 10.0°C / min; (3) The crystallized material was then heated from 40.0°C to 220.0°C at a heating rate of 10.0°C / min; (4) The temperature of the peak (melting peak) of the DSC curve of the material obtained during the second heating (i.e., at (3)) was taken as the melting point of the material. Furthermore, if multiple peaks (melting peaks) exist in the DSC curve of the object obtained during the second heating step using the method described above, the temperature of the peak with the largest heat of fusion (melting peak) was defined as the melting point of the object.

[0142] When measuring the melting point of polypropylene resin (B), resin particles prepared by the following procedure (1') to (3') were used as the object to be measured. (1') Polypropylene resin (C) and polypropylene resin (D) were mixed in the ratio used (the ratios listed in Tables 2 to 4) (for example, in Example 1, they were mixed in a ratio of C-1 / D-1 = 75 / 25 wt%); (2') The obtained mixture was melt-kneaded using a twin-screw extruder at a resin temperature of 220°C; (3') The obtained molten mixture was extruded from the extruder in the form of strands, and after water cooling the obtained strands, they were cut to obtain resin particles of polypropylene resin (B) for measurement.

[0143] <Carbon Black Concentration in Polypropylene Resins> The carbon black (CB) content in polypropylene resins 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) Weigh 6 mg to 8 mg of the sample to be measured into a Pt measuring container; (2) The temperature of the sample was raised to 600°C at a rate of 10°C / min under a nitrogen atmosphere, then cooled to 400°C at a rate of 10°C / min, and then raised to 800°C at a rate of 10°C / min under a simulated air atmosphere (a mixture of oxygen and nitrogen = 21%:79%); (3) In the TG weight loss rate curve obtained in the process of (2) above, the weight ratio (weight %) of carbon black was calculated from the difference between the weight loss rate (weight %) at 400°C and the weight loss rate (weight %) at 800°C during the process of raising the temperature from 400°C to 800°C.

[0144] <Ash Content of Polypropylene Resin> The amount of ash in polypropylene resin was determined from the weight of the polypropylene resin and the weight of the residue after combustion. The specific procedure was as follows (1) to (4): (1) The polypropylene resin was heated at 150°C for 1 hour to completely remove moisture from the polypropylene resin; (2) 1 g to 2 g of polypropylene resin 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 (ppm) in the polypropylene resin was calculated using the following formula. The results are shown in the "Ash Content (ppm)" column of Table 1. W1: Crucible weight (g) W2: Weight of crucible + polypropylene resin before combustion (g) W3: Weight of crucible + polypropylene resin after combustion (g) Ash content in polypropylene resin (ppm) = {(W3 - W1) × 1,000,000} / (W2 - W1).

[0145] (Bulk density, bulk density under reduced pressure, and shrinkage rate of foamed particles) The methods for measuring the bulk density, bulk density under reduced pressure, and shrinkage rate of foamed particles were as follows: The weight w (g) of the foamed particles was weighed, and its volume V1 (L) was measured using a graduated cylinder at atmospheric pressure at 23°C. The bulk density (BD) of the foamed particles was calculated as w / V1 (g / L). Next, the graduated cylinder was covered, and the pressure was reduced to between -0.10 MPa·G and -0.05 MPa·G. The volume V2 (L) of the foamed particles at this reduced pressure was measured, and the bulk density (VBD) of the foamed particles under reduced pressure was calculated as w / V2 (g / L). The shrinkage rate of the foamed particles was calculated from the bulk density (BD) and vacuum density (VBD) of the foamed particles measured above using the following formula (1): Shrinkage rate (%) = {(BD) - (VBD)} × 100 / (VBD) ... Formula (1).

[0146] (Open-cell ratio of foamed particles) The open-cell ratio of foamed particles was measured using an air-comparable hydrometer [Tokyo Science Co., Ltd., Model 1000] according to the method described in Procedure C of ASTM D2856-87. Specifically, it was calculated using the following steps (1) to (4): (1) Using an air-comparable hydrometer, the volume Vc (cm³) of the foamed particles was calculated. ３ (2) The amount of foaming particles after Vc measurement was measured; (3) The amount of rise in the liquid level of ethanol in the graduated cylinder after immersion of foaming particles was measured by the apparent volume Va (cm) of the foaming particles. ３ (4) The percentage of open cells in the foamed particles was calculated using the following formula: Percentage of open cells (%) = ((Va - Vc) × 100) / Va.

[0147] (Average cell diameter of foamed particles) The center of a foamed particle was cut in half with a razor blade, and the resulting cross-section was observed with an optical microscope. A 2000 μm straight line was drawn on the cross-section, and the number of cells present along that line was measured. The number of cells was measured for 10 foamed particles, the average number of cells was calculated, and the average cell diameter was measured using the following formula: Average cell diameter (μm) = 2000 / average number of cells.

[0148] (Moldable pressure for foamed molded articles) The moldable pressure was defined as the water vapor pressure at which a foamed molded article was obtained in which the intergranular spacing, surface appearance, fusion, and shrinkage rate described below all met the acceptable standards when foamed particles were molded by the method described in the examples.

[0149] - On the surface of the intergranular molded body, the spaces between foam particles were visually observed in a 100 mm x 100 mm area near the center of both sides (the surfaces perpendicular to the thickness direction), and the number of locations where gaps were found between foam particles was counted.

[0150] Products with 20 or fewer gaps between foam particles were deemed acceptable, while those with 21 or more gaps were deemed unacceptable.

[0151] For the surface-beautifying molded product, the longest edge was visually inspected, and the number of gaps between foam particles was counted.

[0152] Products with three or fewer gaps between foam particles were deemed acceptable, while those with four or more gaps were deemed unacceptable.

[0153] - At one corner of the fused foam molded body, a cut of about 5 mm in the thickness direction was made with a knife, extending from about 100 mm in the vertical direction to about 100 mm in the horizontal direction. The cut section was then bent to split the molded body in two. The fracture surface was observed, and if the total area of ​​the areas where the foam particles were destroyed and the cells were exposed was 60% or more of the total area of ​​the cross-section, it was considered acceptable; if it was less than 60%, it was considered unacceptable.

[0154] - Shrinkage Rate The length, width, and thickness dimensions of the foam molded body were measured. Using the obtained results, the shrinkage rate (%) for each of the length, width, and thickness dimensions of the foam molded body was evaluated using the following formula: Shrinkage Rate (%) = {(Dimensions of the molding space in the mold) - (Dimensions of the molded body)} × 100 / Dimensions of the molding space in the mold.

[0155] A product was deemed acceptable if the shrinkage rate in length, width, and thickness was all 3% or less. If any one of these values ​​was greater than 3%, the product was deemed unacceptable.

[0156] (Open-cell ratio of foamed molded material) The method for measuring the open-cell ratio of foamed molded material was as follows: A cube with length / width / thickness = 25 / 25 / 25 mm (without a full skin layer) was cut from the target foamed molded material. After leaving this cube undisturbed at 23°C for 24 hours or more, the open-cell ratio of the cube was measured as the open-cell ratio of the target foamed molded material, following the procedure described in the method for measuring the open-cell ratio of foamed particles above, except that the cube was used instead of the foamed particles as the target object.

[0157] (Compressive Strength of Foamed Molded Body) The method for measuring the compressive strength of the foamed molded body was as follows: A rectangular parallelepiped with length / width / height = 50 / 50 / 25 mm (without a full skin layer) was cut from the foamed molded body to serve as a test specimen. After leaving the test specimen undisturbed for more than 24 hours in an environment of 23°C and 50% humidity, its weight and dimensions were measured and the density of the test specimen was calculated. Subsequently, the test specimen was compressed at a compression speed of 10 mm / min using a tensile-compression testing machine (MinebeaMitsumi, TG-20kN), and the value of the compressive stress at 50% strain was measured to determine the compressive strength of the foamed molded body.

[0158] [Examples 1 to 15, Comparative Examples 1 to 8, and Reference Examples 1 to 8] <Preparation Process for Base Resin (Resin Particles)> The types and amounts of polypropylene resins and additives listed in Tables 2 to 4 were hand-blended and melt-kneaded at a resin temperature of 220°C using a twin-screw extruder. The resulting melt-kneaded material was then extruded from the extruder in the form of strands, and the resulting strands were water-cooled and cut to obtain resin particles containing base resin with an average weight of 1.2 mg.

[0159] <Preparation of Foamed Particles> 100 parts by weight (2.4 kg) of resin particles obtained by the method described above, 200 parts by weight of water, 0.3 parts by weight of kaolin [BASF ASP170] as a dispersant, and 0.030 parts by weight of aqueous solution of sodium dodecylbenzenesulfonate [Kao Corporation Neoperex G-15] as a dispersion aid were charged into a 10 L container (pressure-resistant autoclave). Then, while stirring the charged raw materials, 5 parts by weight of carbon dioxide was added to the autoclave as a foaming agent to prepare a dispersion (dispersion step). Next, the contents of the autoclave were heated to the foaming temperatures listed in Tables 2 to 4, held for 10 minutes, and then carbon dioxide was added under pressure to increase the internal pressure of the autoclave to the foaming pressure listed in Tables 2 to 4 (heating-pressure step). After holding the foam at the aforementioned foaming temperature and pressure for 20 minutes (holding step), the valve at the bottom of the autoclave was opened, and the foam was released through a 3.6 mm diameter open orifice to atmospheric pressure to obtain foamed particles (release step). During this process, carbon dioxide was injected to maintain the pressure inside the autoclave and prevent a drop in pressure. The obtained foamed particles were dried at 75°C and cured at 23°C for 24 hours or more. The measurement or evaluation results of the physical properties of these foamed particles are shown in Tables 2 to 4.

[0160] <Two-stage foaming of foamed particles> In some examples and reference cases, two-stage foaming was performed on the foamed particles obtained above. The foamed particles were placed in a pressure vessel and pressurized with air to adjust the internal pressure (absolute pressure) to the level shown in Table 2 or 4. The foamed particles with internal pressure were placed in the pressure vessel and heated for 30 seconds at the vapor pressure shown in Table 2 or 4, and then released to atmospheric pressure to obtain two-stage foamed particles. The obtained two-stage foamed particles were dried at 75°C and cured at 23°C for 24 hours or more. The measurement or evaluation results of each physical property of these two-stage foamed particles are shown in Tables 2 to 4.

[0161] <Preparation of Foamed Molded Body> The foamed particles obtained above (or double-stage foamed particles if double-stage foaming was performed) were placed in a pressure vessel and pressurized with air to adjust the internal pressure (absolute pressure) to the levels shown in Tables 2 to 4. The foamed particles with internal pressure were then filled into a mold having a molding space of 370 mm (length) x 320 mm (width) x 50 mm (thickness). The inside of the mold was then heated with steam at the molding pressure (gauge pressure) shown in Tables 2 to 4 to fuse the foamed particles together and obtain a foamed molded body. After water cooling the inside of the mold and the surface of the foamed molded body, the foamed molded body was removed. The obtained foamed molded body was left to stand at 23°C for 1 hour, dried at 75°C for 16 hours, and cured at 23°C for 24 hours, after which its various physical properties were measured or evaluated. The results are shown in Tables 2 to 4.

[0162] A comparison of the foamed molded articles of Examples 1, 5 to 9, and 12 to 14, which have similar densities, with the foamed molded articles of Comparative Examples 1, 3 to 7, a comparison of the foamed molded articles of Examples 3 and 11 with the foamed molded article of Comparative Example 2, and a comparison of the foamed molded article of Example 15 with the foamed molded article of Comparative Example 8 shows that, using the foamed particles that satisfy conditions (1) to (8), it is possible to provide foamed molded articles with superior compressive strength even while using recycled materials. Furthermore, a comparison of the foamed molded articles of the Examples with the foamed molded article of the Reference Example manufactured using only polypropylene resin derived from virgin raw materials shows that the foamed molded articles made by molding the foamed particles that satisfy conditions (1) to (8) have excellent compressive strength comparable to that of the foamed molded article of the Reference Example manufactured using only polypropylene resin derived from virgin raw materials, despite being manufactured using recycled materials.

[0163] According to one embodiment of the present invention, it is possible to provide novel polypropylene-based resin foam particles that can provide a foam molded article with excellent compressive strength, even when using recycled materials. A foam molded article formed by molding such polypropylene-based resin foam particles can be suitably used for various resin products, particularly for automotive resin products such as automotive interior components and core materials for automotive bumpers, where there is a high demand for recycling.

Claims

1. Polypropylene resin foam particles comprising a base resin containing polypropylene resin (A) and polypropylene resin (B), wherein the polypropylene resin foam particles satisfy the following conditions (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of the polypropylene resin (C) and 5% to 60% by weight of the polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

2. Polypropylene resin foam particles according to claim 1, wherein the melting point is 140.0°C or higher and 155.0°C or lower.

3. Polypropylene resin foam particles according to claim 1, wherein the bulk density is 10.0 g / L or more and 200.0 g / L or less.

4. Polypropylene resin foam particles according to claim 1, wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less, and the average cell diameter is 70 μm or more and 400 μm or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less, and the average cell diameter is 40 μm or more and 400 μm or less.

5. Polypropylene resin foam particles according to claim 1, wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less, and the shrinkage rate calculated by the following formula (1) is 10.0% or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less, and the shrinkage rate calculated by the following formula (1) is 7.0% or less: Shrinkage rate (%) = {(BD) - (VBD)} × 100 / (VBD) ... Formula (1) [wherein BD is the bulk density of the polypropylene resin foam particles measured under atmospheric pressure, and VBD is the reduced bulk density of the polypropylene resin foam particles measured under a pressure of -0.10 MPa·G or more and -0.05 MPa·G or less].

6. Polypropylene resin foam particles according to claim 1, wherein the bulk density is 10.0 g / L or more and 40.0 g / L or less and the open-cell ratio is 10.0% or less, or the bulk density is greater than 40.0 g / L and 200.0 g / L or less and the open-cell ratio is 7.0% or less.

7. The polypropylene resin foam particles according to claim 1, wherein the polypropylene resin (D) is derived from post-consumer raw materials derived from automobiles.

8. The polypropylene resin foam particles according to claim 1, wherein the melting point of the polypropylene resin (A) is 130°C or higher.

9. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the polypropylene resin (A) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

10. The polypropylene resin foam particles according to claim 1, wherein the melting point of the polypropylene resin (C) is 135°C or higher.

11. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the polypropylene resin (C) is 3.0 g / 10 min or more and 30.0 g / 10 min or less.

12. The polypropylene resin foam particles according to claim 1, wherein the melting point of the polypropylene resin (D) is greater than 140°C.

13. The polypropylene resin foam particles according to claim 1, wherein the melt flow rate of the polypropylene resin (D) is 5.0 g / 10 min or more and 50.0 g / 10 min or less.

14. A polypropylene resin foam molded article obtained by foam molding polypropylene resin foam particles according to any one of claims 1 to 13.

15. A method for producing polypropylene resin foam particles, comprising the steps of: preparing a base resin by mixing a polypropylene resin (A) and a polypropylene resin (B); and preparing foam particles from the base resin, wherein the polypropylene resin foam particles satisfy the following conditions (1) to (8): (1) The polypropylene resin (A) is a polypropylene random copolymer; (2) The polypropylene resin (B) has a melting point of less than 160.0°C; (3) The difference between the melting point of the polypropylene resin (A) and the melting point of the polypropylene resin (B) is less than 10.0°C; (4) The base resin contains 40% to 95% by weight of the polypropylene resin (A) and 5% to 60% by weight of the polypropylene resin (B); (5) The polypropylene resin (B) contains 40% to 95% by weight of polypropylene resin (C) and 5% to 60% by weight of polypropylene resin (D); (6) The polypropylene resin (C) is a polypropylene random copolymer; (7) The polypropylene resin (D) is a polypropylene block copolymer or a propylene homopolymer, or a mixture thereof; (8) The polypropylene resin (A) is derived from virgin raw materials, and the polypropylene resin (B) is derived from recycled raw materials.

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