Method for producing expanded polypropylene resin particles

Abstract

To provide a method for producing polypropylene-based resin foamed particles excellent in in-mold moldability while using a recycled polypropylene-based resin containing a biomass-derived polypropylene-based resin.SOLUTION: The recycled polypropylene resins contain biomass-derived polypropylene resins containing biomass-derived monomer components in molecular chains, and have a melt flow rate of 80g / 10 minutes or less, the weight ratio of the polypropylene resins to the recycled polypropylene resins in the polypropylene resins mixture is 5:95 to 95:5, and the melt flow rate of the polypropylene resins mixture is 1g / 10 minutes or more and 30g / 10 minutes or less. Provided is a method for producing polypropylene-based resin foamed particles having a biomass degree of 5% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing expanded polypropylene resin beads using recycled polypropylene resin including biomass-derived polypropylene resin. [Background technology]

[0002] Expanded polyolefin resin bead moldings obtained by molding expanded polyolefin resin beads in a mold are widely used as transport containers for food, etc., electrical and electronic components, precision components, shock-absorbing materials for vehicle components, building materials such as insulation for homes, and shock-absorbing materials for vehicle components, etc.

[0003] In recent years, awareness of environmental loads such as increasing carbon dioxide concentrations in the atmosphere and depletion of fossil fuel resources has increased, and environmentally friendly products are desired. As one method for producing environmentally friendly products, the use of polyolefin resins made from natural materials such as plants as starting materials has been considered, instead of polyolefin resins made from fossil fuel-derived raw materials.

[0004] For example, Patent Document 1 proposes a technology aimed at providing expanded polyethylene resin particles that can contribute to solving environmental problems and the depletion of fossil fuel resources. Specifically, Patent Document 1 discloses expanded polyethylene resin particles that contain a plant-derived polyethylene resin with a plant content of 80% or more and a plant content of 1% or more. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-60514 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, with regard to expanded polypropylene resin particles, it is desirable to use polypropylene resins made from natural materials such as plants as starting materials, instead of polypropylene resins made from raw materials derived from fossil fuels. In this specification, polypropylene resins made from natural materials such as plants as starting materials are sometimes referred to as biomass-derived polypropylene resins. In addition, in the recent trend toward a recycling-oriented society, it is desired to produce expanded polypropylene-based resin beads using recycled resin raw materials obtained by recycling molded articles using polypropylene-based resin. Examples of molded articles using polypropylene-based resin include expanded bead molded articles produced by molding expanded polypropylene-based resin beads in a mold and resin molded articles using polypropylene-based resin.

[0007] In view of the two social demands of using biomass-derived polypropylene resins and recycling molded articles using polypropylene resins, it is highly desirable to recycle polypropylene resin molded articles containing biomass-derived polypropylene resins. However, when expanded beads are produced using such recycled polypropylene resins, the moldability of the resulting expanded beads may be reduced in some cases, and this point has been left to be investigated.

[0008] The present invention has been made in view of the above-mentioned problems, and provides expanded polypropylene resin beads that are made from recycled polypropylene resins containing biomass-derived polypropylene resins and have excellent in-mold moldability. [Means for solving the problem]

[0009] The method for producing expanded polypropylene resin beads of the present invention is a method for producing expanded polypropylene resin beads by expanding polypropylene resin beads to obtain expanded beads, wherein the resin beads are made of a polypropylene resin mixture obtained by melt-kneading a virgin polypropylene resin and a recycled polypropylene resin, the recycled polypropylene resin comprising a biomass-derived polypropylene resin containing a biomass-derived monomer component in its molecular chain, a melt flow rate of the recycled polypropylene resin measured at 230°C under a load of 2.16 kg being 80 g / 10 min or less, a weight ratio of the virgin polypropylene resin to the recycled polypropylene resin in the polypropylene resin mixture being 5:95 to 95:5, a melt flow rate of the polypropylene resin mixture measured at 230°C under a load of 2.16 kg being 1 g / 10 min or more and 30 g / 10 min or less, and a biomass content of the resin beads measured according to ASTM D 6866-21 being 5% or more. [Effects of the Invention]

[0010] According to the present invention, expanded polypropylene resin beads having excellent in-mold moldability can be stably provided using recycled polypropylene resins containing biomass-derived polypropylene resins. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an example of a DSC curve obtained according to the method for measuring the heat of transition of plastics described in JIS K7122:2012 to obtain the high-temperature peak calorific value of the expanded polypropylene resin beads produced by the production method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] First, an outline of the method for producing an expanded bead molding of the present invention (hereinafter, sometimes simply referred to as the production method of the present invention) will be described. The manufacturing method of the present invention is a method for manufacturing expanded polypropylene-based resin beads, in which expanded beads are obtained by expanding polypropylene-based resin beads, and the polypropylene-based resin beads are made of a polypropylene-based resin mixture obtained by melt-kneading virgin polypropylene-based resin and recycled polypropylene-based resin. In the present invention, in order to fully satisfy social demands for the environment, a biomass-derived polypropylene-based resin containing a biomass-derived monomer component in the molecular chain is used as the recycled polypropylene-based resin. In addition, to improve the moldability of the expanded beads obtained by the present invention while incorporating a biomass-derived polypropylene resin, the present invention uses a recycled polypropylene resin having a melt flow rate measured at 230°C under a load of 2.16 kg within a specific range, and adjusts the weight ratio of virgin polypropylene resin to recycled polypropylene resin in the polypropylene resin mixture to virgin polypropylene resin:recycled polypropylene resin = 5:95 to 95:5. The melt flow rates of the recycled polypropylene resin and the polypropylene resin mixture measured at 230°C under a load of 2.16 kg and the biomass degree of the resin particles measured according to ASTM D 6866-21 are limited to specific ranges. According to the manufacturing method of the present invention having the above-mentioned configuration, it is possible to provide expanded beads having excellent in-mold moldability while using a resin raw material recycled from a molded article containing a biomass-derived polypropylene resin. The manufacturing method of the present invention will be described in detail below.

[0013] [Polypropylene resin] The virgin polypropylene resin and the recycled polypropylene resin used in the production method of the present invention are both polypropylene resins. The polypropylene resin contained in each of the virgin polypropylene resin and the recycled polypropylene resin refers to a propylene homopolymer or a polypropylene copolymer containing more than 50% by weight of structural units derived from propylene. Examples of the propylene homopolymer include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Examples of the polypropylene copolymer include copolymers of propylene with ethylene and / or an α-olefin having 4 or more carbon atoms, such as a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-ethylene-butene copolymer, as well as propylene-acrylic acid copolymers and propylene-maleic anhydride copolymers. These copolymers may be block copolymers, random copolymers, or graft copolymers. From the viewpoint of easily improving the moldability of the resulting expanded beads in a mold, it is preferable to use a polypropylene random copolymer as the virgin polypropylene resin. From the viewpoint of easily improving the moldability of the expanded beads in a mold, it is preferable that the virgin polypropylene resin contains, as a main component, one or more polypropylene resins selected from the group consisting of a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-ethylene-butene copolymer. Hereinafter, the one or more polypropylene resins selected from the group consisting of a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-ethylene-butene copolymer contained in the virgin polypropylene resin may be referred to as polypropylene resin A. More specifically, the proportion of polypropylene resin A in the virgin polypropylene resin is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. The polymers described above may be crosslinked, but are preferably non-crosslinked from the viewpoint of facilitating recycling of the resulting molded articles.

[0014] The virgin polypropylene-based resin and recycled polypropylene-based resin used in the present invention may each be composed of one type of polypropylene-based resin or a mixed resin of two or more types of polypropylene-based resins. When the virgin polypropylene-based resin is composed of a mixed resin of two or more types of polypropylene-based resins, the physical properties of the virgin polypropylene-based resin are measured using the mixed resin as a sample. Similarly, when the recycled polypropylene-based resin is composed of a mixed resin of two or more types of polypropylene-based resins, the physical properties of the recycled polypropylene-based resin are measured using the mixed resin as a sample.

[0015] Furthermore, the virgin polypropylene resin and the recycled polypropylene resin may each contain other polymers and additives in addition to the polypropylene resin, as long as the intended object of the present invention can be achieved.

[0016] Examples of the other polymers include thermoplastic resins other than polypropylene resins, such as polyethylene resins, polystyrene resins, polyamide resins, and polyester resins, and elastomers, such as olefin thermoplastic elastomers and styrene thermoplastic elastomers.

[0017] Examples of the additives include functional additives such as colorants, antioxidants, antistatic agents, surfactants, heat stabilizers, light stabilizers, ultraviolet absorbers, and flame retardants, and the like, which may be used alone or in combination of two or more.

[0018] From the viewpoint of improving the moldability of the resulting expanded beads in a mold, the virgin polypropylene resin in the present invention preferably contains a fossil fuel-derived polypropylene resin. More specifically, the proportion of the fossil fuel-derived polypropylene resin in the virgin polypropylene resin is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. When two or more fossil fuel-derived polypropylene resins are used, the proportion of the fossil fuel-derived polypropylene resin in the virgin polypropylene resin is defined as the proportion of the total amount of the fossil fuel-derived polypropylene resin in the virgin polypropylene resin. In this specification, the fossil fuel-derived polypropylene resin means a polypropylene resin polymerized using substantially only monomers derived from fossil fuels. Examples of fossil fuel-derived polypropylene resins include conventionally known polypropylene resins. From the viewpoint of easily improving the in-mold moldability of the resulting expanded beads, the fossil fuel-derived polypropylene resin contained in the virgin polypropylene resin is preferably a polypropylene random copolymer. Furthermore, the proportion of polypropylene resin A in the fossil fuel-derived polypropylene resin is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. On the other hand, the recycled polypropylene resin in the present invention includes a biomass-derived polypropylene resin containing a biomass-derived monomer component in the molecular chain. The recycled polypropylene resin may be composed essentially of only the biomass-derived polypropylene resin, or may be composed of the biomass-derived polypropylene resin and the fossil fuel-derived polypropylene resin.

[0019] [Virgin polypropylene resin] In the present invention, virgin polypropylene resin refers to a resin in which the polypropylene resin contained therein has not been subjected to thermal history such as molding processing for forming a molded article. The virgin polypropylene resin can also be considered a non-recycled polypropylene resin, as it differs from resins obtained by recycling recovered molded articles. The resin may contain any additives. The form of the virgin polypropylene resin is not particularly limited, but from the viewpoint of improving the handling properties when producing resin particles, it is preferable that the resin is in the form of pellets, for example.

[0020] <Melt flow rate (MFR)> The MFR of the virgin polypropylene resin in the present invention is preferably 1 g / 10 min to 50 g / 10 min, more preferably 2 g / 10 min to 20 g / 10 min, and even more preferably 3 g / 10 min to 10 g / 10 min, from the viewpoints of enabling a polypropylene resin mixture having an MFR as described below to be stably obtained and facilitating improved in-mold moldability of the expanded beads. A preferred numerical range for the MFR is, for example, a range having a lower limit of 1 g / 10 min, 2 g / 10 min, or 3 g / 10 min, and an upper limit of 50 g / 10 min, 20 g / 10 min, or 10 g / 10 min. In this specification, melt flow rate may be abbreviated as MFR, and the MFR in the present invention is measured in accordance with JIS K7210-1:2014 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0021] <Melting point> The melting point of the virgin polypropylene resin in the present invention is preferably 130° C. or higher and 165° C. or lower, and more preferably 140° C. or higher and 160° C. or lower, from the viewpoint that expanded beads with good in-mold moldability are easily obtained even when the virgin polypropylene resin is blended with a recycled polypropylene resin containing a biomass-derived polypropylene resin. A preferred numerical range of the melting point is, for example, a range having either 130° C. or 140° C. as the lower limit and either 165° C. or 160° C. as the upper limit. From the viewpoint of easily improving the moldability of the expanded beads in a mold, it is preferable that the melting point of the virgin polypropylene resin is lower than the melting point of the recycled polypropylene resin described below.

[0022] The melting point can be determined using a virgin polypropylene-based resin as a measurement sample in accordance with JIS K7121: 2012. For details of the measurement method, see the method for measuring the melting point of a polypropylene-based resin in the examples described below.

[0023] <Heat of fusion> From the viewpoint of easily and stably obtaining expanded beads with good moldability while blending recycled polypropylene resins including biomass-derived polypropylene resins, the heat of fusion of the virgin polypropylene resin is preferably 50 J / g or more and 120 J / g or less, more preferably 60 J / g or more and 110 J / g or less, and even more preferably 70 J / g or more and 100 J / g or less.

[0024] The heat of fusion is determined from a DSC curve obtained by heat flux differential scanning calorimetry (DSC) based on the method for measuring heat of transition of plastics described in JIS K7122:2012. More specifically, the heat of fusion is determined from a DSC curve obtained by heating a virgin polypropylene-based resin from 23°C to 200°C at a heating rate of 10°C / min, then cooling from 200°C to 23°C at a cooling rate of 10°C / min, and then heating from 23°C to 200°C at a heating rate of 10°C / min. That is, the heat of fusion is determined from a DSC curve obtained during the second heating performed by a predetermined method. For details of the measurement method, see the method for measuring the heat of fusion of a polypropylene-based resin in the examples described below.

[0025] In the above, several preferred embodiments of the virgin polypropylene-based resin have been described. Among them, it is more preferable that the virgin polypropylene-based resin has two or more embodiments selected from an embodiment having a melting point of 130°C or more and 165°C or less, an embodiment having an MFR of 1 g / 10 min or more and 10 g / 10 min or less, an embodiment having a heat of fusion of 60 J / g or more and 120 J / g or less, and an embodiment using a polypropylene-based resin containing polypropylene-based resin A as a main component, and it is even more preferable to use a virgin polypropylene-based resin that has all of these embodiments.

[0026] [Recycled polypropylene resin] In the present invention, the recycled polypropylene resin refers to a polypropylene resin contained in the recycled polypropylene resin that has been subjected to a thermal history during molding or other processes to form a molded article. The resin may contain any additives or impurities derived from the molded article that was the raw material for the recycled polypropylene resin, as long as the intended object of the present invention can be achieved. The recycled polypropylene resin includes polypropylene resin derived from pre-consumer materials and polypropylene resin derived from post-consumer materials. In this specification, post-consumer materials refer to "materials or products discarded after use as products" as described in the "Plastic Products Version 2.13" certification standard issued by the Eco Mark Office of the Japan Environmental Association, a public interest incorporated foundation. In this specification, pre-consumer materials refer to "materials such as scraps or defective products generated from the waste route in the manufacturing process of products, which have undergone recycling processes such as collection and sorting" as described in the "Plastic Products Version 2.13" certification standard issued by the Eco Mark Office of the Japan Environmental Association, a public interest incorporated foundation. More specifically, post-consumer materials include, for example, post-consumer materials derived from automotive parts and post-consumer materials derived from home appliances. Examples of post-consumer materials derived from automotive parts include exterior materials such as bumpers and interior materials such as instrument panels removed from used automobiles, and automobile shredder residue (ASR) generated during the automobile disposal process. Polypropylene resins are recovered from such post-consumer materials. The form of the recycled polypropylene resin is not particularly limited, but from the viewpoint of improving the handleability during the production of resin particles, for example, pelletized form is preferred. The average weight per pellet of the recycled polypropylene resin is preferably approximately 1 mg or more and 30 mg or less, more preferably 2 mg or more and 20 mg or less.

[0027] The recycled polypropylene resin of the present invention includes a biomass-derived polypropylene resin containing biomass-derived monomer components in the molecular chain and exhibits a significant biobased carbon content. In this specification, biomass refers to "renewable, biologically derived organic resources excluding fossil resources," as defined in the "Biomass Nippon Comprehensive Strategy" approved by the Cabinet on March 31, 2006. In this specification, the term "monomer component" refers to a monomer-derived structural unit in a polymer obtained by polymerizing a monomer such as propylene. From the viewpoint of fully responding to the social demand for environmental consideration, the biomass content of the recycled polypropylene resin is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. The production method of the present invention can produce expanded polypropylene resin beads with excellent in-mold moldability using a recycled polypropylene resin containing a biomass-derived polypropylene resin and having a biomass content of 10% or more. In in-mold molding, expanded polypropylene resin beads containing a biomass-derived polypropylene resin component tend to have lower inter-expanded particle fusion properties than expanded beads made solely from fossil fuel-derived polypropylene resin. Therefore, as the blending amount of the biomass-derived polypropylene resin component in the expanded beads increases, it tends to be more difficult to obtain a good expanded bead molding. This tendency also tends to occur when recycled polypropylene resin containing a biomass-derived polypropylene resin component is used. In contrast, the production method of the present invention can stably produce expanded polypropylene resin beads with excellent in-mold moldability using a recycled polypropylene resin containing a biomass-derived polypropylene resin. The upper limit of the biomass content of the recycled polypropylene resin may be within a range that allows the intended object of the present invention to be achieved, and may be, for example, 100%, 90%, 80%, or 60%.

[0028] From the viewpoint of obtaining a recycled polypropylene-based resin having a biomass degree within the above-mentioned range, the proportion of biomass-derived polypropylene-based resin in the recycled polypropylene-based resin is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 60% by weight or more, even more preferably 70% by weight or more, and even more preferably 80% by weight or more. When two or more types of biomass-derived polypropylene-based resins are used, the proportion of the total amount of biomass-derived polypropylene-based resins in the recycled polypropylene-based resin is defined as the proportion of biomass-derived polypropylene-based resin in the recycled polypropylene-based resin.

[0029] The biomass-derived polypropylene resin may be a polypropylene resin polymerized using only biomass-derived monomers, or may be a polypropylene resin polymerized using biomass-derived monomers and fossil fuel-derived monomers. Examples of biomass-derived monomer components contained in the molecular chain of the biomass-derived polypropylene resin include components derived from propylene, ethylene, or α-olefins having 4 to 8 carbon atoms, which are produced from biomass raw materials. The biomass-derived monomer components preferably contain a propylene component, and more preferably contain a propylene component as the main component of the biomass-derived monomer components.

[0030] The present invention encompasses embodiments in which the biomass degree of the virgin polypropylene-based resin described above is significant. However, from the viewpoint of easily improving the moldability of the resulting expanded beads in a mold, it is preferable that the biomass degree of the recycled polypropylene-based resin be higher than that of the virgin polypropylene-based resin. In the present invention, the biomass degree is measured in accordance with ASTM D 6866-21. For details of the measurement, see the measurement method described in the Examples below. When the biomass degree of the biomass-derived polypropylene-based resin contained in the recycled polypropylene-based resin can be measured, the biomass degree of the recycled polypropylene-based resin may be calculated from the relationship between the biomass degree of the biomass-derived polypropylene-based resin contained in the recycled polypropylene-based resin and its blending amount.

[0031] <Melt flow rate (MFR)> The MFR of the recycled polypropylene resin in the present invention is 80 g / 10 min or less. If the MFR of the recycled polypropylene resin containing biomass-derived polypropylene resin is too high, it becomes difficult to obtain expanded beads that exhibit good in-mold moldability, even if the recycled polypropylene resin is blended with virgin polypropylene resin to form a mixture so that the MFR of the polypropylene resin mixture falls within the range described below. Note that recycled polypropylene resins tend to have a high MFR due to excessive heat history during the recycling process. From the viewpoint of more sufficiently improving the moldability of the expanded beads in a mold, the MFR of the recycled polypropylene resin is preferably 1 g / 10 min or more and 60 g / 10 min or less, more preferably 3 g / 10 min or more and 40 g / 10 min or less, and even more preferably 3 g / 10 min or more and 30 g / 10 min or less. Furthermore, preferred numerical ranges for the MFR include, for example, a range having a lower limit of either 1 g / 10 min or 3 g / 10 min and an upper limit of either 60 g / 10 min, 40 g / 10 min, or 30 g / 10 min.

[0032] <Melt flow rate ratio> From the viewpoint of producing expanded polypropylene resin beads exhibiting better moldability in a mold, the ratio of the MFR of the recycled polypropylene resin to the MFR of the virgin polypropylene resin is preferably 0.1 or more and 10 or less, and more preferably 0.2 or more and 5 or less.

[0033] <Melting point> The melting point of the recycled polypropylene resin in the present invention is preferably 130°C or higher and 165°C or lower, more preferably 140°C or higher and 165°C or lower, and even more preferably 150°C or higher and 165°C or lower, from the viewpoint of easily and stably obtaining expanded beads with good moldability in a mold.

[0034] The melting point can be determined in accordance with JIS K7121:2012 in the same manner as in the measurement of the melting point of a virgin polypropylene resin, except that a recycled polypropylene resin is used as a measurement sample. For details of the measurement method, see the method for measuring the melting point of a polypropylene resin in the examples described below.

[0035] <Melting point difference> From the viewpoint of easily and stably obtaining expanded beads with good moldability in a mold, the melting point Tm of the recycled polypropylene resin is r and the melting point Tm of the virgin polypropylene resin v Difference from Tm r -Tm v The temperature is preferably -5°C or higher and 25°C or lower, more preferably 0°C or higher and 25°C or lower, and even more preferably 5°C or higher and 25°C or lower.

[0036] <Heat of fusion> From the viewpoint of stably obtaining expanded beads with good moldability in a mold, the heat of fusion of the recycled polypropylene resin in the present invention is preferably 60 J / g or more and 120 J / g or less, more preferably 70 J / g or more and 115 J / g or less, and even more preferably 80 J / g or more and 110 J / g or less. The numerical range of the heat of fusion can be any one of 60 J / g, 70 J / g, and 80 J / g or more as the lower limit and any one of 120 J / g, 115 J / g, and 110 J / g as the upper limit.

[0037] The heat of fusion is determined from a DSC curve obtained by heat flux differential scanning calorimetry (DSC) based on the method for measuring the heat of transition of plastics described in JIS K7122: 2012, in the same manner as in measuring the melting point of a virgin polypropylene resin, except that a recycled polypropylene resin is used as a measurement sample. For details of the measurement method, see the method for measuring the heat of fusion of a polypropylene resin in the examples described below.

[0038] <Ratio of heat of fusion> From the viewpoint of being able to stably produce expanded resin beads that exhibit good moldability while blending a recycled polypropylene resin containing a biomass-derived polypropylene resin, the ratio of the heat of fusion of the virgin polypropylene resin to the heat of fusion of the recycled polypropylene resin is preferably 0.5 to 1.5, more preferably 0.6 to 1.4, and even more preferably 0.7 to 1.3. A preferred numerical range for the ratio of heats of fusion is, for example, a range having a lower limit of 0.5, 0.6, or 0.7, and an upper limit of 1.5, 1.4, or 1.3.

[0039] In the above, several preferred embodiments of the recycled polypropylene-based resin have been described. Among them, the recycled polypropylene-based resin preferably has two or more embodiments selected from the following: a melting point of 130°C or more and 165°C or less, an MFR of 1g / 10 min or more and 60g / 10 min or less, a heat of fusion of 60 J / g or more and 120 J / g or less, and a biomass degree of 10% or more. It is even more preferable to use a recycled polypropylene-based resin that has all of these embodiments.

[0040] Furthermore, the virgin polypropylene-based resin and recycled polypropylene-based resin used in the present invention are preferably selected so that the MFR ratio is 0.1 to 10 and the heat of fusion ratio is 0.5 to 1.5. The physical properties of recycled polypropylene-based resins that have been subjected to thermal history tend to vary more easily between raw material lots than those of virgin polypropylene-based resins, so the use of recycled polypropylene-based resins may make it difficult to consistently achieve good in-mold moldability. In contrast, the effects of the present invention can be more fully achieved by forming resin particles using virgin polypropylene-based resins and recycled polypropylene-based resins that satisfy the above-mentioned ranges of MFR ratio and heat of fusion ratio.

[0041] [Polypropylene resin mixture] In the production method of the present invention, resin particles are produced from a polypropylene resin mixture obtained by melt-kneading the above-mentioned virgin polypropylene resin and recycled polypropylene resin. As described above, the weight ratio of the virgin polypropylene resin to the recycled polypropylene resin is virgin polypropylene resin:recycled polypropylene resin=5:95 to 95:5. From the viewpoint of stably producing expanded beads having excellent in-mold moldability while increasing the content of recycled polypropylene resin containing biomass-derived polypropylene resin, the weight ratio of the virgin polypropylene resin to the recycled polypropylene resin in the polypropylene resin mixture is preferably virgin polypropylene resin:recycled polypropylene resin=10:90 to 90:10, more preferably virgin polypropylene resin:recycled polypropylene resin=15:85 to 85:15, and even more preferably virgin polypropylene resin:recycled polypropylene resin=20:80 to 80:20. The polypropylene resin mixture may contain other polymers and additives in addition to the polypropylene resin, as long as the intended object of the present invention can be achieved.

[0042] <Melt flow rate> The polypropylene resin mixture has an MFR of 1 g / 10 min or more and 30 g / 10 min or less. When forming the polypropylene resin mixture, it is preferable to determine the blending ratio of these resins while taking into consideration the MFR of the virgin polypropylene resin and the MFR of the recycled polypropylene resin so that the MFR is 1 g / 10 min or more and 30 g / 10 min or less.

[0043] [Polypropylene resin particles] The polypropylene-based resin particles are formed from the polypropylene-based resin mixture described above. Examples of methods for producing polypropylene-based resin particles include the following: First, virgin polypropylene-based resin and recycled polypropylene-based resin are fed into an extruder together with optional cell control agents and the like, and melt-kneaded to obtain a resin melt of the polypropylene-based resin mixture. The resin melt is then extruded into strands from a strand-forming die attached downstream of the extruder, after which the extruded strands are water-cooled and cut with a pelletizer or the like. In this way, pellet-shaped polypropylene-based resin particles can be obtained.

[0044] It is preferable that a cell control agent be added to the polypropylene-based resin particles. As the cell control agent, for example, one or more types of cell control agents selected from inorganic powders and organic powders can be used. Examples of inorganic powders include metal borate salts such as zinc borate and magnesium borate, and examples of organic powders include fluororesin powders such as polytetrafluoroethylene (PTFE). From the viewpoint of consistently obtaining expanded beads having the desired bulk density and little variation in bubble diameter, the amount of bubble control agent added to the resin beads is preferably 0.005% by weight or more and 1% by weight or less, more preferably 0.01% by weight or more and 0.5% by weight or less, and even more preferably 0.02% by weight or more and 0.2% by weight or less. From the viewpoint of easily adjusting the average cell diameter of the expanded beads to a desired range, it is preferable to use a metal borate, and more preferably zinc borate, as the cell adjusting agent.

[0045] <Melting point> The melting point of the polypropylene resin mixture constituting the polypropylene resin beads is preferably 130°C to 165°C, more preferably 140°C to 160°C, from the viewpoint of improving the compression properties of the resulting expanded bead molding while stably obtaining expanded beads with good in-mold moldability. The melting point is measured in accordance with JIS K7121:2012, similar to the measurement of the melting point of virgin polypropylene resin, except that polypropylene resin beads or expanded polypropylene resin beads are used as the measurement sample. For details on the measurement of the melting point, see the Examples below. In the present invention, the compression properties refer to the properties exhibited when the expanded bead molding is compressed, and one example is the compressive stress at 50% strain measured in accordance with JIS K6767:1999.

[0046] <Biomass ratio> The biomass degree of polypropylene-based resin particles is adjusted by the biomass degree and blending ratio of the virgin polypropylene-based resin and recycled polypropylene-based resin blended. The biomass degree of polypropylene-based resin particles is 5% or more, more preferably 8% or more, and even more preferably 10% or more. In order to increase the biomass degree of polypropylene-based resin particles, it is necessary to increase the blending amount of biomass-derived polypropylene-based resin components in the resin particles. However, as mentioned above, this has traditionally tended to reduce the moldability of expanded beads in a mold. The production method of the present invention can stably produce expanded beads with good moldability in a mold using polypropylene-based resin particles exhibiting the above-mentioned significant biomass degree. The upper limit of the biomass degree of polypropylene-based resin particles may be within a range that achieves the intended object of the present invention, and may be, for example, 100%, 90%, 80%, or 60%.

[0047] The biomass degree is measured based on ASTM D 6866-21. For details of the measurement method, see the description in the Examples below. The biomass degree of polypropylene-based resin particles and the biomass degree of expanded polypropylene-based resin beads produced from the resin particles usually correspond to each other. Therefore, the biomass degree of the resin particles can be interpreted as the biomass degree of expanded beads.

[0048] [Polypropylene resin foam particles] In the manufacturing method of the present invention, expanded polypropylene resin particles are manufactured by expanding the polypropylene resin particles described above. When expanding the polypropylene resin particles, resin particles containing a blowing agent are expanded to obtain expanded particles. Specifically, for example, the method can be carried out as follows. First, polypropylene resin particles are dispersed in a pressure vessel containing an aqueous dispersion medium such as water, a dispersant such as a sparingly soluble inorganic salt, a dispersion aid such as a surfactant, etc. Next, a blowing agent is added to the pressure vessel, and the resin particles are impregnated with the blowing agent. Next, the resin particles containing the blowing agent in the pressure vessel are released from the pressure vessel together with the aqueous dispersion medium into a pressure atmosphere lower than the pressure inside the pressure vessel, and the resin particles are expanded. From the viewpoint of increasing the productivity of expanded beads, it is preferable to carry out the impregnation of resin beads with a blowing agent and the expansion of resin beads containing the blowing agent as a series of steps using a single sealed container, as described above.

[0049] Examples of blowing agents include inorganic physical blowing agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen, and neon; aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and normal hexane; alicyclic hydrocarbons such as cyclohexane and cyclopentane; halogenated hydrocarbons such as ethyl chloride, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene; and organic physical blowing agents such as dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. Among these, from the viewpoints of environmental friendliness and economic efficiency, inorganic physical blowing agents are preferred, more preferably one or more selected from the group consisting of nitrogen, air, and carbon dioxide, and even more preferably carbon dioxide. These blowing agents can be used alone or in combination of two or more. The amount of foaming agent to be added is determined taking into consideration the desired bulk density of the expanded polypropylene resin particles, the type of polypropylene resin, the type of foaming agent, etc. For example, when carbon dioxide is used, the amount to be added is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 15 parts by weight, per 100 parts by weight of the polypropylene resin particles.

[0050] The expanded polypropylene resin beads produced by the production method of the present invention preferably have a crystalline structure in which a DSC curve shows an intrinsic peak and a high-temperature peak located higher than the intrinsic peak. The DSC curve here refers to a DSC curve obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min by heat flux differential scanning calorimetry, and more specifically, refers to a DSC curve in the first heating. The intrinsic peak refers to a melting peak resulting from the melting of inherent crystals of the polypropylene resin constituting the expanded beads. On the other hand, the high-temperature peak refers to a melting peak present at a higher temperature than the intrinsic peak confirmed in the first DSC curve. When this high-temperature peak appears, it is presumed that secondary crystals exist in the resin constituting the expanded beads. In particular, in the crystalline structure, it is preferable that the peak temperature of the intrinsic peak is 130°C or higher, and the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak is 20°C or higher and 30°C or lower. From the viewpoints of improving the secondary expandability of the expanded beads during in-mold molding, easily obtaining an expanded bead molding in which the occurrence of localized depressions after molding is suppressed, and easily expanding the moldable range of the expanded beads, it is preferable that the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak be relatively large, as described above. On the other hand, when expanded beads are produced using only recycled polypropylene-based resin, or when expanded beads are produced using recycled polypropylene-based resin with an excessively high MFR and virgin polypropylene-based resin, the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak is small. In contrast, in the expanded beads obtained by the production method of the present invention, the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak can be increased while using recycled polypropylene-based resin. Therefore, it is easy to obtain expanded polypropylene resin beads having a crystalline structure that exhibits a "difference in peak temperature" within the above-mentioned preferred range, and as a result, it is easy to exhibit good in-mold moldability while exhibiting a significant biomass content.

[0051] The high-temperature peak can be adjusted, for example, by controlling the rate of temperature rise in the pressure vessel during the dispersion step and / or the blowing agent impregnation step, or by maintaining the temperature in the pressure vessel at a predetermined temperature for a predetermined period of time. More specifically, during the dispersion step and / or the blowing agent impregnation step, a first-stage holding step is performed in which the temperature in the pressure vessel is maintained at a temperature between the melting point of the resin particles minus 20°C and the end temperature of melting of the resin particles for approximately 10 to 60 minutes. The temperature in the pressure vessel is then adjusted to a temperature between the melting point of the resin particles minus 15°C and the end temperature of melting of the resin particles. If necessary, a second-stage holding step may be performed in which the temperature is maintained for an additional 10 to 60 minutes. Expanded beads having a high-temperature peak can then be produced by performing the expansion step.

[0052] The DSC curve obtained during the second heating is the second DSC curve obtained when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating). It is preferable that only the intrinsic peak appears in the second DSC curve. In this case, the intrinsic peak and the high-temperature peak can be distinguished by comparing the shapes and peak positions of the first and second DSC curves.

[0053] The heat of fusion of the high-temperature peak, the apex temperature of the high-temperature peak, and the apex temperature of the intrinsic peak of the expanded beads can be determined from a DSC curve measured by heat flux differential scanning calorimetry based on the method for measuring the heat of transition of plastics described in JIS K7122: 2012. Specifically, 1 to 3 mg of expanded beads are used as a measurement sample, and the measurement sample is heated at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the temperature at which the melting peak of the measurement sample ends, and the above-mentioned physical properties can be determined from the DSC curve (see Figure 1) obtained during the first heating. More specifically, a straight line is drawn connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the melting end temperature of the expanded beads, on the DSC curve shown in Fig. 1. The melting end temperature is the high-temperature end point of high-temperature peak b, and is the intersection point of high-temperature peak b and the baseline on the higher temperature side of high-temperature peak b on the DSC curve. As shown in Figure 1, after drawing a line connecting points I and II, the intersection point of the line passing through the maximum point III between the intrinsic peak a and the high-temperature peak b and the line parallel to the vertical axis of the graph is designated as IV. The area enclosed by the line connecting points I and IV, the line connecting points III and IV, and the DSC curve connecting points I and III is defined as the area of ​​intrinsic peak a. The area enclosed by the line connecting points IV and II, the line connecting points III and IV, and the DSC curve connecting points III and II (shaded area) is defined as the area of ​​high-temperature peak b. The value of the heat of fusion of the high-temperature peak of the expanded beads is calculated from the area of ​​high-temperature peak b obtained as described above. The top temperature of the high-temperature peak and the top temperature of the intrinsic peak can also be confirmed from the DSC curve.

[0054] The heat of fusion of the expanded beads can be determined from a DSC curve measured by heat flux differential scanning calorimetry based on the method for measuring the heat of transition of plastics described in JIS K7122:2012. Specifically, 1–3 mg of expanded beads were used as the measurement sample. The sample conditioning method employed was "(2) Measurement of melting temperature after a certain heat treatment." The sample was heated from 23°C to 200°C at a heating rate of 10°C / min. After reaching 200°C, the temperature was lowered from 200°C to 23°C at a rate of 10°C / min. The sample was then heated again at a rate of 10°C / min from 23°C to 200°C to obtain a DSC curve (the DSC curve obtained during the second heating). The point at 80°C on the DSC curve obtained during the second heating was designated as α, and the point on the DSC curve corresponding to the melting end temperature was designated as β. The area enclosed by the DSC curve between points α and β and the line segment (α–β) was measured, and the heat of fusion of the expanded beads was calculated from this area. The heat of fusion measured as described above can also be interpreted as the heat of fusion of the polypropylene-based resin mixture constituting the expanded beads, and can also be interpreted as the heat of fusion of the polypropylene-based resin mixture constituting the resin particles.

[0055] <Heat of fusion> From the viewpoint of stably obtaining expanded beads with good moldability by the production method of the present invention, the heat of fusion of the expanded beads of the present invention is preferably 60 J / g to 120 J / g, more preferably 65 J / g to 110 J / g, preferably 70 J / g to 100 J / g, and more preferably 75 J / g to 95 J / g. The heat of fusion can be, for example, within a range having a lower limit of any one of 60 J / g, 65 J / g, 70 J / g, or 75 J / g or more and an upper limit of any one of 120 J / g, 110 J / g, 100 J / g, or 95 J / g.

[0056] <Heat of fusion at high temperature peak> From the viewpoint of stably obtaining expanded beads having good moldability in a mold by the production method of the present invention, the heat of fusion of the high-temperature peak is preferably 5 J / g or more and 50 J / g or less, more preferably 10 J / g or more and 40 J / g or less, and even more preferably 15 J / g or more and 35 J / g or less. The heat of fusion of the high-temperature peak can be, for example, within a range having a lower limit of 5 J / g, 10 J / g, or 15 J / g or more and an upper limit of 50 J / g, 40 J / g, or 35 J / g.

[0057] <Ratio of the heat of fusion of the high-temperature peak to the heat of fusion> From the viewpoint of stably obtaining expanded beads with good moldability in a mold by the production method of the present invention, the ratio of the heat of fusion of the high-temperature peak to the heat of fusion is preferably 0.10 to 0.40, more preferably 0.12 to 0.35. The ratio can be, for example, within a range having a lower limit of either 0.10 or 0.12 and an upper limit of either 0.40 or 0.35.

[0058] <Temperature at the peak of the characteristic peak> From the viewpoint of stably obtaining expanded beads with good moldability in a mold by the production method of the present invention, the apex temperature of the intrinsic peak is preferably 135° C. or higher and 160° C. or lower, and more preferably 140° C. or higher and 158° C. or lower. The apex temperature of the intrinsic peak can be, for example, within a range having either 135° C. or 140° C. as the lower limit and either 160° C. or 158° C. as the upper limit.

[0059] <Bulk density of expanded particles> From the viewpoint of obtaining a molded product having a good balance between light weight and compressibility, the bulk density of the expanded particles is 10 kg / m 3 More than 200kg / m 3 It is preferable that the saturation is 12 kg / m or less. 3 More than 100kg / m 3 More preferably, it is 15 kg / m or less. 3 More than 60kg / m 3 It is more preferable that the bulk density is, for example, 10 kg / m or less. 3 , 12 kg / m 3 or 15 kg / m 3 The lower limit is 200 kg / m 3 , 100 kg / m 3 or 60 kg / m 3 The range may have any one of the values ​​as the upper limit. The bulk density of the expanded beads can be determined by the method described in the examples below.

[0060] The expanded beads may have a fusion layer on their surface to enhance fusion between the expanded beads during molding. The fusion layer may be present on the entire surface of the expanded beads or on a part of the surface. Examples of resins constituting the fusion layer include polyolefin resins. The method for forming a fusion layer on the surface of expanded beads is not particularly limited, and examples thereof include a method of expanding resin beads having a fusion layer on their surface, a method of obtaining expanded beads and then attaching a fusion layer to the surface of the expanded beads, etc. When expanding resin beads having a fusion layer on their surface to obtain expanded beads, it is preferable to employ a method in which, when producing the resin beads, a molten mixture for forming the resin bead body and a resin melt for forming the fusion layer are co-extruded using an extrusion device capable of co-extrusion, thereby laminating a fusion layer on the surface of the resin beads.

[0061] The expanded polypropylene resin beads produced by the production method of the present invention described above are composed of a polypropylene resin mixture obtained by melt-kneading a virgin polypropylene resin and a recycled polypropylene resin. The polypropylene resin mixture contains a biomass-derived polypropylene resin containing a biomass-derived monomer component in its molecular chain, and has a melt flow rate of 1 g / 10 min to 30 g / 10 min measured at 230°C under a load of 2.16 kg, and a biomass content of 5% or more measured according to ASTM D 6866-21. The expanded polypropylene resin beads preferably have a crystalline structure in which an intrinsic peak and a high-temperature peak located higher than the intrinsic peak appear in a DSC curve obtained by heat flux differential scanning calorimetry, in which the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min. It is more preferable that the peak temperature of the intrinsic peak is 130°C or higher, and the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak is 20°C or higher and 30°C or lower. By making the expanded polypropylene resin beads satisfying the above-mentioned configuration, it is possible to obtain expanded polypropylene resin beads that have excellent in-mold moldability while using recycled polypropylene resin including biomass-derived polypropylene resin.

[0062] [Polypropylene resin foam bead molding] The expanded polypropylene resin beads produced by the production method of the present invention can be molded in a mold to obtain an expanded polypropylene resin bead molding. In this specification, the expanded polypropylene resin bead molding produced by the production method of the present invention in a mold may be referred to as the expanded bead molding of the present invention. The in-mold molding broadly encompasses known in-mold molding methods using expanded beads. For example, in-mold molding using the expanded beads obtained by the present invention can be carried out as follows. First, the expanded beads are filled into a mold having a cavity corresponding to the desired shape of the expanded bead molded article. The expanded beads filled in the mold are then heated by applying a predetermined molding pressure using a heating medium such as steam. The molding pressure can be adjusted, for example, within a range of 0.2 MPa (G) to 0.5 MPa (G). Note that, in this specification, "(G)" refers to gauge pressure, i.e., a pressure value relative to atmospheric pressure. By heating the expanded beads in the cavity in this manner, they are further expanded and fused together. Next, after heating with steam or the like is completed, the pressure in the cavity is released, and cooling of the mold and the molded article in the mold is promptly initiated. When it is confirmed that the pressure (surface pressure) generated on the inner surface of the mold has reached 0.04 MPa (G), cooling is stopped, and the expanded bead molded article is removed from the mold. The cooling method here is not particularly limited, but examples include water cooling. Through this series of molding steps, a foamed bead molding corresponding to the shape of the cavity is obtained.

[0063] <density> The density of the foamed bead molding of the present invention is 10 kg / m 3 More than 200kg / m 3 It is preferable that the saturation is 12 kg / m or less. 3 More than 100kg / m 3 More preferably, it is 15 kg / m or less. 3 More than 60kg / m 3The density can be determined by dividing the weight of the expanded polypropylene resin bead molding by the volume of the molding. Specifically, it can be determined by the method described in the examples below.

[0064] <Ratio of compressive stress at 50% strain to density> The ratio of the compressive stress at 50% strain to the density of the expanded bead molding of the present invention is 6 kPa / [kg / m] from the viewpoint of providing an expanded bead molding having a good balance between light weight and compressive properties. 3 ] or more than 15kPa / [kg / m 3 ] or less, and 7kPa / [kg / m 3 ] or more than 14kPa / [kg / m 3 ] or less, and more preferably 8kPa / [kg / m 3 ] or more than 13kPa / [kg / m 3 ] or less is even more preferable. [Example]

[0065] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. First, virgin polypropylene-based resins and recycled polypropylene-based resins used as resin raw materials in the examples and comparative examples will be described.

[0066] (Preparation of virgin polypropylene resin) As the virgin polypropylene-based resins used in this example, virgin polypropylene-based resins V1 to V3 in pellet form shown in Table 1 were prepared. Virgin polypropylene-based resins V1 and V2 are both propylene-ethylene random copolymers. Virgin polypropylene-based resin V3 is "Novatec PP MG05ES" manufactured by Japan Polypropylene Corporation. Virgin polypropylene resins V1 to V3 may be abbreviated as resins V1 to V3, and recycled polypropylene resins R1 to R6, which will be described later, may be abbreviated as resins R1 to R6. The recycled polypropylene resins R1 to R6 were produced assuming that they were recycled polypropylene resins derived from post-consumer materials.

[0067] (Production of recycled polypropylene resin) <Recycled Polypropylene Resin R1 (Resin R1)> A recycled polypropylene resin was produced by recycling a fused foam made from polypropylene resin as a resin raw material. Specifically, a manufacturing apparatus was prepared, which included an extruder with an inner diameter of 50 mm and a strand-forming die attached downstream of the extruder. A propylene homopolymer (manufactured by Lyondellbasell, grade HP456J, biomass content 42%) as a polypropylene-based resin and zinc borate (0.1 parts by mass per 100 parts by mass of polypropylene-based resin) as a cell control agent were fed into the extruder and melt-kneaded, then extruded from the extruder in the form of strands and pelletized to obtain polypropylene-based resin particles. 1 kg of the obtained resin particles was supplied to a 5 L pressure vessel capable of being pressurized together with 3 L of water as an aqueous dispersion medium. Furthermore, 0.3 parts by weight of kaolin as an inorganic dispersant and 0.2 parts by weight (as an active ingredient) of a surfactant (trade name: NEOGEN, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were added to the pressure vessel per 100 parts by weight of the polypropylene-based resin particles. Next, the pressure vessel was heated to a predetermined foaming temperature while stirring. Carbon dioxide was injected into the pressure vessel as a foaming agent, and after maintaining the pressure vessel for a predetermined time, the contents of the pressure vessel (polypropylene resin particles and water) were released under atmospheric pressure to form a foam with a bulk density of 50 kg / m. 3 As a result, expanded polypropylene resin particles of the above formula were obtained. The resulting expanded polypropylene resin beads were filled into a mold having a molding cavity capable of forming a plate-shaped fused body, and the expanded beads were heated with steam to fuse together, thereby producing a fused body of expanded beads. The fused foam beads produced were crushed to reduce their volume, obtaining crushed material of a size suitable for feeding into an extruder. The crushed material and an antioxidant (Irganox 1010, manufactured by BASF, a hindered phenol-based antioxidant; 0.2 parts by weight per 100 parts by weight of crushed material) were fed into the extruder and melt-kneaded at 210°C to obtain a resin melt. The resin melt was introduced into a strand-forming die and extruded into strands. The extruded strands were water-cooled and cut with a pelletizer to obtain recycled polypropylene resin R1 in the form of pellets with an average weight of 10 mg per pellet. <Recycled Polypropylene Resin R2 (Resin R2)> A fused foamed particle body was produced in the same manner as in the recycled polypropylene resin R1, except that virgin polypropylene resin V1 and the propylene homopolymer of grade HP456J were supplied to the extruder in a ratio of resin V1:HP456J = 50:50 instead of the propylene homopolymer of grade HP456J to produce polypropylene resin particles. The fused foam beads thus produced were pelletized in the same manner as in the case of the recycled polypropylene resin R1, to obtain a pellet-shaped recycled polypropylene resin R2. <Recycled Polypropylene Resin R3 (Resin R3)> A fused foamed particle body was produced in the same manner as in the recycled polypropylene resin R1, except that virgin polypropylene resin V1 and propylene homopolymer of grade HP456J were supplied to the extruder in a ratio of resin V1:HP456J = 10:90 instead of the propylene homopolymer of grade HP456J to produce polypropylene resin particles. The fused foam beads thus produced were pelletized in the same manner as in the case of the recycled polypropylene resin R1, to obtain a pellet-shaped recycled polypropylene resin R3. <Recycled polypropylene resin R4 (resin R4)> Pellets were prepared in the same manner as for recycled polypropylene resin R1, except that the temperature of the melt-kneading in the extruder when pelletizing the crushed material of the fused foam beads was changed to 240°C, thereby obtaining recycled polypropylene resin R4. <Recycled polypropylene resin R5 (resin R5)> Pellets were prepared in the same manner as for recycled polypropylene resin R1, except that no antioxidant was used when pelletizing the crushed material of the fused foam beads and the temperature of the melt-kneading in the extruder was changed to 240°C, thereby obtaining recycled polypropylene resin R5. <Recycled polypropylene resin R6 (resin R6)> Pellets were prepared in the same manner as for recycled polypropylene resin R1, except that the temperature of melt kneading in the extruder when pelletizing the crushed material of the fused foam beads was changed to 300°C. The obtained pellets were fed back into the extruder and melt kneaded at 300°C to obtain a resin melt. The resin melt was introduced into a strand-forming die to extrude strands. The extruded strands were water-cooled and cut with a pelletizer, and pellets were prepared again (second pelletization). This operation was repeated three more times, for a total of five pelletization operations. In this way, pelletized recycled polypropylene resin R6 was obtained.

[0068] (Measurement of physical properties of polypropylene resin) The MFR, melting point, and heat of fusion of Resins V1 to V3, which are virgin polypropylene-based resins, and Resins R1 to R6, which are recycled polypropylene-based resins, were measured using the methods described below. The biomass degree of Resins R1 to R6 was calculated by measuring the biomass degree of the biomass-derived polypropylene resin (HP456J) used to prepare the recycled polypropylene-based resin using the method described below, and then calculating the biomass degree of the measured biomass-derived polypropylene-based resin and the blending ratio of the biomass-derived polypropylene-based resin in the recycled polypropylene-based resin. The measurement results are shown in Tables 1 to 3. In Table 3, the MFR of the virgin polypropylene-based resins is v MFR of recycled polypropylene resinr The ratio of the melting point Tm of recycled polypropylene resin r From the melting point Tm of virgin polypropylene resin v The value obtained by subtracting ΔH and the heat of fusion of recycled polypropylene resin r Heat of fusion of virgin polypropylene resin ΔH v The density of resins V1 to V3 and resins R1 to R6 was 0.90 g / cm 3 It was.

[0069] <Heat of fusion> The heat of fusion of the polypropylene-based resin was measured by heat flux differential scanning calorimetry based on the method for measuring the heat of transition of plastics described in JIS K7122:2012. The measurement device used was a high-sensitivity differential scanning calorimeter, "EXSTAR DSC7020" (Hitachi High-Tech Science Corporation). The sample conditioning method used was "(2) Measurement of melting temperature after a certain heat treatment." Approximately 2 mg of polypropylene resin was collected as the sample. The sample was heated from 23 to 200 °C at a heating rate of 10 °C / min under conditions of a nitrogen inflow rate of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23 °C at a cooling rate of 10 °C / min, and then heated again to 200 °C at a heating rate of 10 °C / min to obtain a DSC curve (DSC curve for the second heating). The point at 80°C on the DSC curve obtained during the second heating was designated as α, and the point on the DSC curve corresponding to the melting end temperature was designated as β. The area of ​​the portion enclosed by the DSC curve in the section between points α and β and the line segment (α-β) was measured, and the heat of fusion of the polypropylene-based resin was calculated from this area.

[0070] <Melting point> The melting point of the polypropylene resin was measured by heat flux differential scanning calorimetry in accordance with JIS K7121:2012. The measurement device used was a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation). The sample conditioning method used was "(2) Measuring the melting temperature after a certain heat treatment." Approximately 2 mg of polypropylene resin was collected as a measurement sample. The sample was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow rate of 30 mL / min, then held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve at the second heating). The apex temperature of the melting peak in the DSC curve was determined, and this value was taken as the melting point. If multiple melting peaks appear on a DSC curve, the apex temperature of the melting peak with the largest area is used as the melting point. The melting peak with the largest area can be determined by distinguishing each melting peak using the valley temperature of the DSC curve located between the peak temperatures of the melting peaks as a boundary and comparing the areas (heat of fusion) of each melting peak. The valley temperature of the DSC curve corresponds to the temperature at which the vertical axis of the differential DSC curve (DDSC) becomes 0, so it can also be determined from the DSC differential curve.

[0071] <Melt flow rate> The melt flow rate of the polypropylene resin was measured at a temperature of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0072] <Biomass ratio> The biomass content of the polypropylene resin was measured as follows based on ASTM D6866-21. Specifically, biomass-derived polypropylene resin contained in recycled polypropylene resin was used as the measurement sample. The measurement sample was subjected to measurement and burned to generate carbon dioxide (CO2), which was then purified in a vacuum line. The purified carbon dioxide was reduced with hydrogen using iron as a catalyst, thereby producing graphite (C). The graphite was then packed into a cathode with an inner diameter of 1 mm using a hand press, which was then fitted into a wheel and used in a tandem accelerator based on NEC Corporation. 14 The measurement was carried out using the C-AMS dedicated device. 14 The number of C's, 13 C concentration ( 13 C / 12 C). 14 C concentration ( 14 C / 12 C) was measured. For the measurements, oxalic acid (HOxII) provided by the National Institute of Standards (NIST) was used as the standard sample. Measurements of this standard sample and a background sample were also carried out simultaneously. From the measurement results, the carbon obtained from the measurement sample relative to the modern carbon of the standard sample was 14 Calculate the C percentage, then calculate the C percentage from the standard sample. 13 Corrected pMC (percent modern carbon) values ​​were obtained by correcting for deviations in C concentration. The biomass degree was calculated using the corrected pMC value. The atmospheric correction factor used was the value for 2019-2021 described in ASTM D6866-21 (100.0 pMC). To measure the biomass degree of the polypropylene-based resin of the present invention, the atmospheric correction factor described in ASTM D6866 for the year the polypropylene-based resin was manufactured was used to determine the biomass degree. In this example, the properties of the biomass-derived polypropylene resin contained in the recycled polypropylene resin were known, and therefore the biomass degrees of the recycled polypropylene resin, resin particles, and expanded particles were calculated based on the biomass degree of the biomass-derived polypropylene resin measured as described above and the blending amount of the biomass-derived polypropylene resin. The biomass degree of the recycled polypropylene-based resin, resin particles, and expanded beads can also be measured directly by using the recycled polypropylene-based resin, resin particles, and expanded beads themselves as measurement samples and measuring the biomass degree.

[0073] Example 1 <Preparation of polypropylene resin particles> A production apparatus was prepared, which was equipped with an extruder having an inner diameter of 50 mm and a strand-forming die attached to the downstream side of the extruder. Resin V1 shown in Table 1, Resin R1 shown in Table 2, and zinc borate as a cell regulator (0.1 part by weight per 100 parts by weight of the total polypropylene resin) were fed into an extruder and melt-kneaded to obtain a resin melt. The resin melt was introduced into a strand-forming die to extrude strands. The extruded strands were water-cooled and cut with a pelletizer to an average weight of 1 mg per piece. This resulted in polypropylene resin particles composed of a polypropylene resin mixture, which is a mixed resin of virgin polypropylene resin and recycled polypropylene resin.

[0074] <Preparation of expanded polypropylene resin beads> 1 kg of the polypropylene resin particles obtained as described above was supplied to a 5 L pressure vessel capable of being pressurized together with 3 L of water as an aqueous dispersion medium. Furthermore, 0.3 parts by weight of kaolin as an inorganic dispersant and 0.2 parts by weight (as an active ingredient) of a surfactant (trade name: NEOGEN, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were added to the pressure vessel per 100 parts by weight of the polypropylene resin particles. Next, the pressure vessel was heated at a rate of 5°C / min while stirring until the foaming temperature was reached, after which carbon dioxide was injected as a foaming agent into the pressure vessel, the pressure was increased to 2.1 MPa (G), and the same temperature and pressure were maintained for 15 minutes. This adjusted the crystalline structure of the resulting foamed beads, and adjusted so that a high-temperature peak appeared in the DSC curve obtained by heat flux differential scanning calorimetry. The contents of the pressure vessel (polypropylene resin particles and water) were then released under atmospheric pressure to a bulk density of 54 kg / m 3 As a result, expanded polypropylene resin particles of the above formula were obtained. In the examples and comparative examples, the resin particles were expanded at an expansion temperature adjusted within the range of 161 to 169° C. so as to obtain expanded particles having a predetermined bulk density. The physical properties of the expanded beads described below were measured using expanded beads that had been conditioned by being left to stand for 24 hours under conditions of 50% RH, 23°C and 1 atm.

[0075] <Production of expanded polypropylene resin bead molded body> The resulting expanded polypropylene resin beads were filled into a mold having a cavity capable of forming a plate-shaped expanded bead molding measuring 250 mm long x 200 mm wide x 20 mm high, and heated by the following heating method: A metal mold was used as the mold. The heating method involved supplying steam to the mold with drain valves on both sides open to perform preheating (exhaust process). Then, steam was supplied from one side of the mold to heat it, and then steam was supplied from the other side to heat it again. Next, steam was supplied from both sides of the mold to heat it at a lower limit molding pressure (0.30 MPa (G)) described below. After heating was completed, the pressure was released and water cooling was quickly initiated. Water cooling was continued until the pressure generated on the inner surface of the mold due to the expansion force of the expanded bead molding reached 0.04 MPa (G). After water cooling was completed, the expanded bead molding was removed from the mold and designated Example 1. The measurement and evaluation of the physical properties of the expanded bead moldings described below were carried out using molded articles that had been conditioned by leaving the expanded bead moldings after demolding at 50% RH, 80°C, and 1 atm for 12 hours.

[0076] (Examples 2 to 9, Comparative Examples 1 to 3) Polypropylene-based resin particles, expanded polypropylene-based resin particles, and expanded polypropylene-based resin particle moldings were produced in the same manner as in Example 1 described above, except for the changes made to the contents shown in Table 3, and these were designated Examples 2 to 9 and Comparative Examples 1 to 3.

[0077] For each of the Examples and Comparative Examples obtained as described above, the polypropylene resin particles, expanded polypropylene resin particles, and expanded polypropylene resin particle moldings were subjected to the following measurements. The measurement results for the polypropylene resin particles and expanded polypropylene resin particles are shown in Table 4, and the measurement results for the expanded polypropylene resin particle moldings are shown in Table 5.

[0078] [Measurement of polypropylene resin particles] <Melt flow rate (MFR)> Using polypropylene resin particles as a measurement sample, the MFR of the polypropylene resin mixture constituting the polypropylene resin particles was determined under conditions of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0079] <Melting point> The melting point of the polypropylene-based resin mixture constituting the polypropylene-based resin particles was measured by heat flux differential scanning calorimetry based on JIS K7121:2012 in the same manner as in the measurement of the melting point of the polypropylene-based resin described above, except that polypropylene-based resin particles were used as the measurement sample.

[0080] [Measurement of polypropylene resin foam particles] <Heat of fusion> The heat of fusion of the expanded polypropylene resin beads was measured in the same manner as in the above-described method for measuring the heat of fusion of the polypropylene resin, except that expanded polypropylene resin beads were used as the measurement sample. <Heat of fusion at high temperature peak> The heat of fusion of the high-temperature peak of the expanded beads was measured by heat flux differential scanning calorimetry based on the method for measuring the heat of transition of plastics described in JIS K7122:2012. The measurement device used was a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation). Approximately 3 mg of expanded beads were used as a measurement sample, and the sample was heated from 23°C to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve from the first heating) showing an intrinsic peak and a high-temperature peak. The measurement was performed under conditions of a nitrogen inflow rate of 30 mL / min. As explained above with reference to Figure 1, a line was drawn on the DSC curve obtained using each expanded bead, connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the end-of-melting temperature of the expanded bead. As shown in Figure 1, after drawing the line connecting points I and II, point IV was determined as the intersection of the line connecting points I and II and the line passing through maximum point III between intrinsic peak a and high-temperature peak b, which is parallel to the vertical axis of the graph. The area of ​​the portion (shaded area) enclosed by the straight line connecting point IV and point II, the straight line connecting point III and point IV, and the DSC curve connecting point III and point II was defined as the area of ​​high-temperature peak b. The value of the heat of fusion (J / g) of high-temperature peak b of the expanded beads was calculated from the area of ​​high-temperature peak b determined as described above. The heat of fusion of the above-mentioned high-temperature peak was measured for three different measurement samples, and the arithmetic mean value of the obtained values ​​was defined as the heat of fusion of the high-temperature peak of the expanded beads.

[0081] <Top temperature of high-temperature peak, top temperature of intrinsic peak> The apex temperatures of the high-temperature peak and the intrinsic peak were read from the three DSC curves obtained for measuring the heat of fusion of the high-temperature peak, and the arithmetic mean values ​​obtained were used as the apex temperatures of the high-temperature peak and the intrinsic peak.

[0082] <Bulk density> A measuring cylinder was filled with expanded particles of weight W (g), and the bottom of the measuring cylinder was lightly tapped several times on a horizontal surface to stabilize the filling height of the expanded particles in the measuring cylinder. The bulk volume V (L) of the expanded particles indicated on the measuring cylinder was read, and the weight W of the expanded particles was divided by the bulk volume V of the expanded particles (W / V). The value obtained in this way was expressed in kg / m 3 The bulk density of the expanded particles (kg / m 3 ) was obtained.

[0083] Table 4 shows the ratio of the heat of fusion of the high-temperature peak to the heat of fusion measured as described above, and also shows the value obtained by subtracting the apex temperature of the intrinsic peak from the apex temperature of the high-temperature peak.

[0084] [Measurement of polypropylene resin foam beads] <Molded object density> The density of the expanded polypropylene resin bead molding was determined by dividing the weight of the expanded polypropylene resin bead molding by the volume calculated based on the outer dimensions.

[0085] <Lower limit molding pressure> Using the heating method described above in <Production of expanded polypropylene resin bead moldings>, the molding pressure (molding steam pressure) was changed in increments of 0.01 MPa (G) within the range of 0.20 to 0.40 MPa (G) to mold the expanded beads in the mold. The obtained molded articles were evaluated for the fusion rate, peripheral shapeability, and shape (sink mark (depression) in the center of the molded article) as described below. The minimum molding pressure at which an expanded bead molded article that passed all of these evaluations could be obtained was defined as the lower limit molding pressure.

[0086] Fusion rate: Test pieces (100 mm long x 100 mm wide x thickness: the thickness of the foamed bead molding) were cut from the center of the foamed bead molding. A 5 mm incision was made in each test piece in the thickness direction with a utility knife, and the test piece was broken at the incision. The number of foamed beads (n) present on the fracture surface of the foamed bead molding and the number of foamed beads that had broken (b) were then measured. The number of foamed beads that had broken (b) relative to the total number of foamed beads (n) was expressed as a percentage to determine the fusion rate (%). A fusion rate of 80% or more was considered a pass, and a fusion rate of less than 80% was considered a fail.

[0087] Peripheral Shape: The foamed bead moldings were evaluated as passing if the gaps between the foamed beads were not noticeable at the periphery and the shape of the molding die was sufficiently formed, while those with noticeable gaps between the foamed beads and the shape of the molding die was not sufficiently formed were evaluated as failing.

[0088] shape: For a flat-plate-shaped expanded bead molding, the thickness t1 near both ends in the longitudinal direction of the molding and the thickness t2 at the center of the molding were measured. Next, the ratio (%) of the thickness t2 at the center of the molding to the larger of the thicknesses t1 near both ends was calculated. If this ratio was 95% or more, it was determined that no excessive sink marks had occurred in the center of the molding and the molding was passed. On the other hand, if this ratio was less than 95%, it was determined that sink marks had occurred in the center of the molding and the molding was rejected. The thickness t1 specifically refers to the thickness at the intersection of a position 10 mm inward from the end toward the center in the longitudinal direction of the molded body and a position that divides the molded body in half in the transverse direction of the molded body. The thickness t2 specifically refers to the thickness at the intersection of a position that divides the molded body in half in the longitudinal direction and a position that divides the molded body in half in the transverse direction.

[0089] <Number of molding condition ranges> As mentioned above, the molding pressure during molding in the mold was increased in increments of 0.01 MPa (G) from the lower limit molding pressure, and the number of moldable condition ranges in which good products could be obtained was confirmed. For example, if the lower limit molding pressure is 0.30 MPa (G) and good products could be obtained up to 0.34 MPa (G), the number of moldable condition ranges would be counted as 5. Since the molding temperature is adjusted by the molding pressure, the greater the number of molding pressures that can be molded and the wider the range from the lower limit to the upper limit, the wider the range of molding heating temperatures that can be molded. Also, those that can be molded under low steam pressure conditions are preferable because they can reduce the amount of steam required for molding and are excellent in productivity.

[0090] <Compressive stress at 50% strain> A 50 mm × 50 mm × 15 mm test piece without a skin layer was cut out from near the center of the expanded bead molding, and a compression test was carried out using the test piece as follows: Specifically, the compression test was carried out at a compression rate of 10 mm / min based on JIS K6767:1999, and the compressive stress (kPa) of the expanded bead molding at 50% strain was determined. The ratio of compressive stress at 50% strain to the density of the test specimen was also shown.

[0091] [Table 1]

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] [Table 5]

[0096] In the case of the expanded beads of Comparative Example 1, the expanded beads were not sufficiently fused together during in-mold molding, and there were no molding conditions under which a good molded article could be obtained. In addition, in the case of the expanded beads of Comparative Examples 2 and 3, when heated until the expanded beads were sufficiently fused together during in-mold molding, sink marks occurred in the molded article, and there were no molding conditions under which a good molded article could be obtained. On the other hand, according to the method for producing expanded beads of the present invention, expanded polypropylene resin beads having excellent moldability can be obtained using recycled polypropylene resin containing biomass-derived polypropylene resin. Specifically, the expanded beads of the present invention can be molded in a mold at a low molding pressure and over a wide range of molding pressures.

[0097] The present invention described above encompasses the following technical ideas. (1) A method for producing expanded polypropylene resin beads by expanding polypropylene resin beads to obtain expanded beads, the resin particles are made of a polypropylene-based resin mixture obtained by melt-kneading a virgin polypropylene-based resin and a recycled polypropylene-based resin, the recycled polypropylene-based resin includes a biomass-derived polypropylene-based resin containing a biomass-derived monomer component in its molecular chain, The recycled polypropylene resin has a melt flow rate of 80 g / 10 min or less, measured under conditions of a temperature of 230°C and a load of 2.16 kg, a weight ratio of virgin polypropylene resin to recycled polypropylene resin in the polypropylene resin mixture is virgin polypropylene resin:recycled polypropylene resin=5:95 to 95:5; the melt flow rate of the polypropylene resin mixture measured under conditions of a temperature of 230°C and a load of 2.16 kg is 1 g / 10 min or more and 30 g / 10 min or less, A method for producing expanded polypropylene resin beads, wherein the resin beads have a biomass content of 5% or more as measured in accordance with ASTM D 6866-21. (2) The method for producing expanded polypropylene resin beads according to (1) above, wherein the ratio of the melt flow rate of the recycled polypropylene resin to the melt flow rate of the virgin polypropylene resin is 0.1 or more and 10 or less. (3) The method for producing expanded polypropylene resin beads according to (1) or (2) above, wherein the melting point of the virgin polypropylene resin is 130°C or higher and 165°C or lower. (4) Melting point Tm of the recycled polypropylene resin r and the melting point Tm of the virgin polypropylene resin v Difference from Tm r -Tm v The method for producing expanded polypropylene resin beads according to any one of (1) to (3) above, wherein the temperature is −5° C. or higher and 25° C. or lower. (5) The method for producing expanded polypropylene resin beads according to any one of (1) to (4) above, wherein the virgin polypropylene resin has a heat of fusion of 50 J / g or more and 120 J / g or less. (6) The method for producing expanded polypropylene resin beads according to any one of (1) to (5), wherein the ratio of the heat of fusion of the virgin polypropylene resin to the heat of fusion of the recycled polypropylene resin is 0.5 or more and 1.5 or less. (7) The method for producing expanded polypropylene resin beads according to any one of (1) to (6), wherein the recycled polypropylene resin has a biomass content of 10% or more as measured in accordance with ASTM D 6866-21. (8) The expanded polypropylene resin beads have a crystalline structure in which an intrinsic peak and a high-temperature peak located at a higher temperature than the intrinsic peak appear in a DSC curve obtained by heat flux differential scanning calorimetry (DSC) measurement by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min, The peak temperature of the characteristic peak is 130°C or higher, The method for producing expanded polypropylene resin beads according to any one of (1) to (7), wherein the difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak is 20°C or more and 30°C or less. (9) Polypropylene-based resin foam particles, the expanded beads are made of a polypropylene-based resin mixture obtained by melt-kneading a virgin polypropylene-based resin and a recycled polypropylene-based resin, the polypropylene-based resin mixture contains a biomass-derived polypropylene-based resin containing a biomass-derived monomer component in its molecular chain, the melt flow rate of the polypropylene resin mixture measured under conditions of a temperature of 230°C and a load of 2.16 kg is 1 g / 10 min or more and 30 g / 10 min or less, The expanded beads have a biomass content of 5% or more as measured in accordance with ASTM D 6866-21; The expanded beads have a crystalline structure in which an intrinsic peak and a high-temperature peak located at a higher temperature than the intrinsic peak appear in a DSC curve obtained by heat flux differential scanning calorimetry, the DSC curve being obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min; The peak temperature of the characteristic peak is 130°C or higher, The expanded polypropylene resin particles have a difference between the peak temperature of the high-temperature peak and the peak temperature of the intrinsic peak of 20°C or more and 30°C or less. (10) A polypropylene resin expanded bead molded article obtained by molding the polypropylene resin expanded bead described in (9) above in a mold.

Claims

1. A method for producing expanded polypropylene resin beads by expanding polypropylene resin beads to obtain expanded beads, comprising: the resin particles are made of a polypropylene-based resin mixture obtained by melt-kneading a virgin polypropylene-based resin and a recycled polypropylene-based resin, the recycled polypropylene-based resin includes a biomass-derived polypropylene-based resin containing a biomass-derived monomer component in its molecular chain, The recycled polypropylene resin has a melt flow rate of 80 g / 10 min or less, as measured under conditions of a temperature of 230° C. and a load of 2.16 kg, a weight ratio of virgin polypropylene resin to recycled polypropylene resin in the polypropylene resin mixture is virgin polypropylene resin:recycled polypropylene resin=5:95 to 95:5; the melt flow rate of the polypropylene resin mixture measured under conditions of a temperature of 230°C and a load of 2.16 kg is 1 g / 10 min or more and 30 g / 10 min or less, A method for producing expanded polypropylene resin beads, wherein the resin beads have a biomass content of 5% or more as measured in accordance with ASTM D 6866-21.

2. 2. The method for producing expanded polypropylene resin beads according to claim 1, wherein the ratio of the melt flow rate of the recycled polypropylene resin to the melt flow rate of the virgin polypropylene resin is 0.1 or more and 10 or less.

3. 3. The method for producing expanded polypropylene resin beads according to claim 1, wherein the melting point of the virgin polypropylene resin is 130°C or higher and 165°C or lower.

4. The melting point Tm of the recycled polypropylene resin ｒ and the melting point Tm of the virgin polypropylene resin ｖ The difference Tm ｒ -Tm ｖ The method for producing expanded polypropylene resin beads according to claim 1 or 2, wherein the temperature is −5° C. or higher and 25° C. or lower.

5. 3. The method for producing expanded polypropylene resin beads according to claim 1, wherein the virgin polypropylene resin has a heat of fusion of 50 J / g or more and 120 J / g or less.

6. 3. The method for producing expanded polypropylene resin beads according to claim 1, wherein the ratio of the heat of fusion of the virgin polypropylene resin to the heat of fusion of the recycled polypropylene resin is 0.5 or more and 1.5 or less.

7. 3. The method for producing expanded polypropylene resin beads according to claim 1, wherein the recycled polypropylene resin has a biomass content of 10% or more as measured in accordance with ASTM D 6866-21.

8. the expanded polypropylene resin beads have a crystalline structure in which an intrinsic peak and a high-temperature peak located at a higher temperature than the intrinsic peak appear in a DSC curve obtained by heat flux differential scanning calorimetry, the DSC curve being obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min; The peak temperature of the characteristic peak is 130°C or higher, 3. The method for producing expanded polypropylene resin beads according to claim 1, wherein a difference between the apex temperature of the high-temperature peak and the apex temperature of the intrinsic peak is 20°C or more and 30°C or less.

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