Method for producing foamed polypropylene resin particles

Abstract

The present invention is a method for producing foamed polypropylene resin particles by foaming resin particles to obtain foamed particles, the method using resin particles comprising a mixture obtained by melt-kneading a primary polypropylene resin and a recovered polypropylene resin, the recovered polypropylene-based resin contains a biomass-derived polypropylene-based resin, the melt flow rate of the polypropylene-based resin is a specific value or less, the primary polypropylene-based resin and the recovered polypropylene-based resin in the resin mixture are in a specific weight ratio, and the melt flow rate of the resin mixture is within a specific range. The bio-based carbon content of the resin particles is equal to or greater than a specific value. According to the present invention, it is possible to provide foamed particles having excellent in-mold moldability while using a specific resin.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing polypropylene resin expanded particles using a recycled polypropylene resin containing a polypropylene resin derived from biomass. BACKGROUND

[0002] Polyolefin resin expanded particle molded bodies produced by in-mold molding of polyolefin resin expanded particles have been widely used as cushioning materials for food transport containers, electronic and electrical components, precision components, vehicle members, building components such as housing thermal insulation materials, impact absorbing materials for vehicle members, and the like.

[0003] However, in recent years, with the increasing awareness of environmental loads such as the increase in the concentration of carbon dioxide in the atmosphere or the depletion of fossil fuel resources, environmentally friendly products are expected. As one of the methods for producing environmentally friendly products, the use of polyolefin resins using natural materials such as plants as starting materials is being studied instead of polyolefin resins using raw materials derived from fossil fuels.

[0004] For example, Patent Literature 1 proposes a technology aimed at providing polyethylene resin expanded particles that contribute to solving environmental problems and depletion of fossil fuel resources. Specifically, Patent Literature 1 discloses polyethylene resin expanded particles containing a plant-derived polyethylene resin having a plant rate of 80% or more and having a plant rate of 1% or more.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2013-60514 SUMMARY

[0008] (1) PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] On the other hand, with respect to polypropylene resin expanded particles, it is also expected to use polypropylene resins using natural materials such as plants as starting materials instead of polypropylene resins using raw materials derived from fossil fuels. In addition, in this specification, polypropylene resins using natural materials such as plants as starting materials are sometimes referred to as polypropylene resins derived from biomass.

[0010] Further, in recent efforts toward a recycling-oriented society, it is expected to use recycled resin raw materials obtained by recycling molded bodies using polypropylene resins to produce polypropylene resin expanded particles. As the molded bodies using polypropylene resins, for example, expanded particle molded bodies produced by in-mold molding of polypropylene resin expanded particles or resin molded bodies using polypropylene resins can be cited.

[0011] In view of both the social needs for using biomass-derived polypropylene-based resin and recycling of molded bodies using polypropylene-based resin, it is highly desirable to recycle polypropylene-based resin molded bodies containing biomass-derived polypropylene-based resin. However, if such recycled polypropylene-based resin is used to produce expanded particles, the in-mold formability of the resulting expanded particles sometimes decreases, leaving room for improvement in this regard.

[0012] The present application was made in view of the above technical problem, and provides a polypropylene-based resin expanded particle that is excellent in in-mold formability while using recycled polypropylene-based resin containing biomass-derived polypropylene-based resin.

[0013] (II) Technical Solution

[0014] The method for producing a polypropylene-based resin expanded particle molded body of the present application is a method for producing a polypropylene-based resin expanded particle by foaming a polypropylene-based resin particle to obtain an expanded particle, characterized in that the resin particle is composed of a polypropylene-based resin mixture obtained by melt-kneading virgin polypropylene-based resin and recycled polypropylene-based resin, the recycled polypropylene-based resin containing biomass-derived polypropylene-based resin, the biomass-derived polypropylene-based resin containing a monomer component derived from biomass in a molecular chain, the recycled polypropylene-based resin having a melt flow rate of 80 g / 10 minutes or less as measured at a temperature of 230°C under a load of 2.16 kg, the weight ratio of the virgin polypropylene-based resin to the recycled polypropylene-based resin in the polypropylene-based resin mixture being virgin polypropylene-based resin:recycled polypropylene-based resin = 5:95 to 95:5, the polypropylene-based resin mixture having a melt flow rate of 1 g / 10 minutes or more and 30 g / 10 minutes or less as measured at a temperature of 230°C under a load of 2.16 kg, and the bio-based carbon content of the resin particle being 5% or more as measured based on ASTM D 6866-21.

[0015] (III) Advantageous Effects

[0016] According to the present application, a polypropylene-based resin expanded particle that is excellent in in-mold formability while using recycled polypropylene-based resin containing biomass-derived polypropylene-based resin can be stably provided. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is an example of a DSC curve obtained according to the transition heat measurement method for plastics described in JIS K7122:2012 for obtaining the high-temperature peak heat of the polypropylene-based resin expanded particle produced by the production method of the present application. DETAILED DESCRIPTION

[0018] First, a summary of the production method of the foamed particle molded body of the present application (hereinafter, sometimes referred to simply as the production method of the present application) will be described.

[0019] The production method of the present application is a production method of polypropylene resin foamed particles in which polypropylene resin particles are foamed to obtain foamed particles, and as the polypropylene resin particles, a substance composed of a polypropylene resin mixture obtained by melt-kneading virgin polypropylene resin and recycled polypropylene resin is used.

[0020] The present application uses, as the recycled polypropylene resin, a polypropylene resin derived from biomass that contains a monomer component derived from biomass in the molecular chain, in order to fully meet the social demand for the environment.

[0021] Further, in order to improve the in-mold formability of the foamed particles obtained in the present application while containing the polypropylene resin derived from biomass, in the present application, a recycled polypropylene resin having a melt flow rate in a specific range measured under the conditions of a temperature of 230°C and a load of 2.16 kg is used, and the weight ratio of the virgin polypropylene resin to the recycled polypropylene resin in the polypropylene resin mixture is adjusted to virgin polypropylene resin:recycled polypropylene resin = 5:95 to 95:5. Further, the melt flow rate of the recycled polypropylene resin and the polypropylene resin mixture measured under the conditions of a temperature of 230°C and a load of 2.16 kg and the biobased carbon content of the resin particles based on ASTM D 6866-21 are limited to a prescribed range.

[0022] According to the production method of the present application having this configuration, a foamed particle excellent in in-mold formability while using a resin raw material recycled from a molded body containing a polypropylene resin derived from biomass can be provided. Hereinafter, the details of the production method of the present application will be described.

[0023] In addition, in the present application, the "main component" refers to a component included in more than 50 mass% of the whole (100 mass%).

[0024] [Polypropylene resin]

[0025] The virgin polypropylene resin and the recycled polypropylene resin used in the production method of the present application are each a polypropylene resin.

[0026] The polypropylene resin included in each of the virgin polypropylene resin and the recycled polypropylene resin refers to a homopolymer of propylene or a polypropylene copolymer containing more than 50% by weight of a structural unit derived from propylene. As the homopolymer of propylene, for example, a homopolymer of propylene such as isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene can be exemplified.

[0027] Further, as the polypropylene-based copolymer, for example, a copolymer 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, a propylene-ethylene-butene copolymer, and the like; a propylene-acrylic acid copolymer, a propylene-maleic anhydride copolymer, and the like can be exemplified. In addition, these copolymers can be any one of a block copolymer, a random copolymer, a graft copolymer.

[0028] From the viewpoint of easily improving the moldability of the obtained expanded particles, as the virgin polypropylene-based resin, a polypropylene-based random copolymer is preferably used.

[0029] Further, from the viewpoint of easily improving the moldability of the expanded particles, the virgin polypropylene-based resin preferably contains one or more polypropylene-based resins selected from the group consisting of a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-ethylene-butene copolymer as a main component. In addition, hereinafter, one or more polypropylene-based resins contained in the virgin polypropylene-based resin and selected from the group consisting of a propylene-ethylene copolymer, a propylene-butene copolymer, and a propylene-ethylene-butene copolymer are sometimes referred to as a polypropylene-based resin A.

[0030] More specifically, the proportion of the polypropylene-based resin A in the virgin polypropylene-based resin is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, and more further preferably 90% by mass or more.

[0031] Further, the above-mentioned polymer can be a polymer crosslinked, but from the viewpoint of easily recycling the obtained molded body, a polymer not crosslinked is preferably used.

[0032] The virgin polypropylene-based resin and the recycled polypropylene-based resin used in the present application can each be composed of one polypropylene-based resin or a mixed resin of two or more polypropylene-based resins. When the virgin polypropylene-based resin is a mixed resin of two or more polypropylene-based resins, the measurement of the physical properties of the virgin polypropylene-based resin is performed by using the mixed resin as a sample. Similarly, when the recycled polypropylene-based resin is a mixed resin of two or more polypropylene-based resins, the measurement of the physical properties of the recycled polypropylene-based resin is performed by using the mixed resin as a sample.

[0033] Further, the virgin polypropylene-based resin and the recycled polypropylene-based resin can each contain a polymer other than a polypropylene-based resin or an additive within a range in which the desired object of the present application can be achieved.

[0034] As the other polymer, a thermoplastic resin other than the polypropylene-based resin, such as a polyethylene-based resin, a polystyrene-based resin, a polyamide-based resin, a polyester-based resin, or the like, or an elastomer such as an olefin-based thermoplastic elastomer, a styrene-based thermoplastic elastomer, or the like can be exemplified.

[0035] Further, as the additive, for example, any one or a combination of two or more of functional additives such as a colorant, an antioxidant, an antistatic agent, a surfactant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a flame retardant, or the like can be exemplified.

[0036] From the viewpoint of improving the moldability of the obtained foamed particles, the virgin polypropylene-based resin in the present application preferably contains a polypropylene-based resin derived from fossil fuels. More specifically, the proportion of the polypropylene-based resin derived from fossil fuels in the virgin polypropylene-based resin is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, and still further preferably 90% by mass or more. Note that when two or more polypropylene-based resins derived from fossil fuels are used, the proportion of the total amount of the polypropylene-based resins derived from fossil fuels in the virgin polypropylene-based resin is taken as the proportion of the polypropylene-based resins derived from fossil fuels in the virgin polypropylene-based resin.

[0037] In the present specification, the polypropylene-based resin derived from fossil fuels refers to a polypropylene-based resin obtained by polymerization using only monomers derived from fossil fuels.

[0038] As the polypropylene-based resin derived from fossil fuels, conventionally known polypropylene-based resins can be exemplified. From the viewpoint of improving the moldability of the obtained foamed particles, the polypropylene-based resin derived from fossil fuels contained in the virgin polypropylene-based resin is preferably a polypropylene-based random copolymer. Further, the proportion of the polypropylene-based resin A in the polypropylene-based resin derived from fossil fuels is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 80% by mass or more, and still further preferably 90% by mass or more.

[0039] On the other hand, the recycled polypropylene-based resin in the present application contains a polypropylene-based resin derived from biomass, which contains a monomer component derived from biomass in the molecular chain. The recycled polypropylene-based resin can be composed of only the polypropylene-based resin derived from biomass, or can be composed of the polypropylene-based resin derived from biomass and a polypropylene-based resin derived from fossil fuels.

[0040] [Virgin polypropylene-based resin]

[0041] Regarding this invention, virgin polypropylene resin refers to a resin in which the polypropylene resin has not undergone the thermal process of molding or other processes used to form molded articles. Furthermore, from the perspective of differentiating it from resin obtained by regenerating recycled molded articles, the virgin polypropylene resin may also be referred to as non-recycled polypropylene resin. The resin may contain any additives, etc.

[0042] There are no particular limitations on the morphology of virgin polypropylene resins. From the perspective of improving the operability of manufacturing resin granules, for example, the morphology after granulation can be preferred.

[0043] <Mel flow rate (MFR)>

[0044] From the perspective of being able to stably obtain polypropylene resin mixtures with the MFR shown later, and easily further improving the in-mold moldability of the foamed particles, the MFR of the virgin polypropylene resin in this invention is preferably 1 g / 10 min or more and 50 g / 10 min or less, more preferably 2 g / 10 min or more and 20 g / 10 min or less, and even more preferably 3 g / 10 min or more and 10 g / 10 min or less. Furthermore, preferred numerical ranges for the MFR can be, for example, ranges with any one of 1 g / 10 min, 2 g / 10 min, or 3 g / 10 min as the lower limit and any one of 50 g / 10 min, 20 g / 10 min, or 10 g / 10 min as the upper limit.

[0045] In addition, the melt flow rate is sometimes abbreviated as MFR in this specification. Furthermore, the MFR described in this invention is based on JIS K7210-1:2014 and is measured at a temperature of 230°C and a load of 2.16 kg.

[0046] <Melting Point>

[0047] Even when virgin polypropylene resin is blended with recycled polypropylene resin containing biomass-derived polypropylene resin, from the perspective of easily obtaining foamed particles with good in-mold formability, the melting point of the virgin polypropylene resin in this invention is preferably 130°C or higher and 165°C or lower, more preferably 140°C or higher and 160°C or lower. Furthermore, preferred numerical ranges for the melting point can be, for example, ranges with either 130°C or 140°C as the lower limit and either 165°C or 160°C as the upper limit.

[0048] Furthermore, from the perspective of easily improving the in-mold moldability of foamed particles, it is preferable that the melting point of virgin polypropylene resin is lower than that of recycled polypropylene resin described later.

[0049] The melting point can be measured using virgin polypropylene-based resin as a measurement sample and calculated based on JIS K7121:2012. Details of the measurement method can be found in the measurement method of the melting point of polypropylene-based resin described later.

[0050] <Melting Heat>

[0051] From the viewpoint of easily and stably obtaining a foamed particle having excellent in-moldability while blending a recycled polypropylene-based resin containing a biomass-derived polypropylene-based resin, the melting heat of the virgin polypropylene-based resin is preferably 50 J / g or greater and 120 J / g or less, more preferably 60 J / g or greater and 110 J / g or less, and further preferably 70 J / g or greater and 100 J / g or less.

[0052] The melting heat is calculated based on the transition heat measurement method of plastics described in JIS K7122:2012 and obtained from a DSC curve obtained by performing heat flow type differential scanning calorimetry (DSC). More specifically, the melting heat is calculated 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 / minute, then cooling from 200°C to 23°C at a cooling rate of 10°C / minute, and then heating from 23°C to 200°C at a heating rate of 10°C / minute. That is, the melting heat is calculated from the DSC curve at the time of the second heating using the prescribed method. Details of the measurement method can be found in the measurement method of the melting heat of polypropylene-based resin described later.

[0053] Among the above, a plurality of preferable aspects of the virgin polypropylene-based resin are described. Among them, as the virgin polypropylene-based resin, it is more preferable to have two or more selected from the group consisting of a mode in which the melting point is 130°C or greater and 165°C or less, a mode in which the MFR is 1 g / 10 minutes or greater and 10 g / 10 minutes or less, a mode in which the melting heat is 60 J / g or greater and 120 J / g or less, and a mode in which a polypropylene-based resin containing polypropylene-based resin A as a main component is used, and it is further preferable to use a virgin polypropylene-based resin having all of the above modes.

[0054] [Recycled Polypropylene-Based Resin]

[0055] With respect to the present application, the recycled polypropylene-based resin refers to a resin in which a polypropylene-based resin contained in the recycled polypropylene-based resin has undergone a thermal history due to molding processing or the like for molding a molded product. The resin can contain any additive, an inclusion derived from a molded product as a raw material of the recycled polypropylene-based resin, or the like, within a range in which the desired object of the present application can be achieved.

[0056] The recycled polypropylene-based resin includes a polypropylene-based resin derived from a pre-consumer material, a polypropylene-based resin derived from a post-consumer material, or the like. In addition, in the present specification, the post-consumer material refers to "a material or product that has been discarded after use as a product" as collectively described in the certification standard book of "Plastic Products Version 2.13" issued by the NPO (Non-Profit Organization) Eco Mark Office, Japan Environmental Association. Further, in the present specification, the pre-consumer material refers to "a material or product that has been discarded from a manufacturing process, such as a material or product that is a byproduct or a defective product, and that has been subjected to a recycling process such as collection and sorting" as collectively described in the certification standard book of "Plastic Products Version 2.13" issued by the NPO (Non-Profit Organization) Eco Mark Office, Japan Environmental Association.

[0057] More specifically, the post-consumer material includes, for example, a post-consumer material derived from a member for an automobile, a post-consumer material derived from an electric home appliance, or the like. As the post-consumer material derived from a member for an automobile, for example, there can be mentioned an exterior material such as a bumper or the like removed from a used automobile, an interior material such as an instrument panel or the like, an automobile shredder residue (ASR; Automobile Shredder Residue) generated in a process of discarding an automobile, or the like. A polypropylene-based resin can be recycled from such a post-consumer material.

[0058] The form of the recycled polypropylene-based resin is not particularly limited, and, from the viewpoint of improving the operability in manufacturing the resin particles, for example, a pelletized resin form is preferred. The average weight of each of the recycled polypropylene-based resins after pelletization is generally preferably 1 mg or more and 30 mg or less, and more preferably 2 mg or more and 20 mg or less.

[0059] The recycled polypropylene-based resin in the present application includes a polypropylene-based resin derived from biomass and exhibits a significant biobased carbon content, the polypropylene-based resin derived from biomass containing a monomer component derived from biomass in a molecular chain. In addition, in the present specification, biomass refers to "a material other than a fossil resource among renewable organic resources derived from living organisms" as described in "Biomass・Japan Comprehensive Strategy" decided by the Cabinet of Japan on March 31, 2006. Further, in the present specification, the monomer component refers to a structural unit derived from a monomer in a polymer obtained by polymerizing a monomer such as propylene.

[0060] From the viewpoint of responding to the social needs of environmental protection, the bio-based carbon content of the recycled polypropylene-based resin is preferably 10% or more, more preferably 20% or more, and further preferably 30% or more. The production method of the present application can use a recycled polypropylene-based resin containing a polypropylene-based resin derived from biomass and having a bio-based carbon content of 10% or more to produce polypropylene-based resin foam particles having excellent in-mold formability. In addition, in in-mold molding, compared with foam particles in which a polypropylene-based resin derived from fossil fuels alone is used, polypropylene-based resin foam particles containing a polypropylene-based resin component derived from biomass have a tendency for the fusion of the foam particles to decrease. Therefore, there is a tendency for good foam particle molded bodies to be difficult to obtain as the amount of the polypropylene-based resin component derived from biomass in the foam particles increases. Furthermore, this tendency is also likely to occur when a polypropylene-based resin containing a polypropylene-based resin component derived from biomass is recycled and used. In contrast, the production method of the polypropylene-based resin foam particles of the present application can stably produce polypropylene-based resin foam particles having excellent in-mold formability while using a recycled polypropylene-based resin containing a polypropylene-based resin derived from biomass.

[0061] The upper limit of the bio-based carbon content of the recycled polypropylene-based resin can be within a range that enables the desired object of the present application to be achieved, and can be, for example, 100%, 90%, 80%, or 60%.

[0062] From the viewpoint of producing a recycled polypropylene-based resin having a bio-based carbon content within the above range, the proportion of the polypropylene-based resin derived from biomass in the recycled polypropylene-based resin is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 60% by mass or more, and more further preferably 70% by mass or more, and more further preferably 80% by mass or more. In addition, when two or more polypropylene-based resins derived from biomass are used, the proportion of the total amount of the polypropylene-based resins derived from biomass in the recycled polypropylene-based resin is taken as the proportion of the polypropylene-based resins derived from biomass in the recycled polypropylene-based resin.

[0063] In addition, the polypropylene-based resin derived from biomass can be a polypropylene-based resin produced by polymerization using only a monomer derived from biomass, or can be a polypropylene-based resin produced by polymerization using a monomer derived from biomass and a monomer derived from fossil fuels.

[0064] As the monomer component derived from biomass included in the molecular chain of the polypropylene-based resin derived from biomass, a component derived from propylene, ethylene, or an α-olefin having 4 or more and 8 or less carbon atoms, or the like produced from a biomass raw material can be exemplified. As the monomer component derived from biomass, a propylene component is preferably included, and as the monomer component derived from biomass, a propylene component is more preferably included as a main component.

[0065] The present application includes the above-described scheme of the bio-based carbon content of the virgin polypropylene-based resin, and from the viewpoint of easily improving the in-mold formability of the obtained expanded particles, the bio-based carbon content of the recycled polypropylene-based resin is preferably higher than that of the virgin polypropylene-based resin. With regard to the present application, the bio-based carbon content is determined based on ASTM D 6866-21. Details of the determination can be found in the determination method described in the Examples described later. In addition, when the bio-based carbon content of the polypropylene-based resin derived from biomass contained in the recycled polypropylene-based resin can be determined, the bio-based carbon content of the recycled polypropylene-based resin can be calculated from the relationship between the bio-based carbon content of the polypropylene-based resin derived from biomass contained in the recycled polypropylene-based resin and the blending amount thereof.

[0066] <Melting Flow Rate (MFR)>

[0067] The MFR of the recycled polypropylene-based resin in the present application is 80 g / 10 minutes or less. When the MFR of the recycled polypropylene-based resin containing the polypropylene-based resin derived from biomass is too high, even if the virgin polypropylene-based resin and the recycled polypropylene-based resin are blended in such a manner that the MFR of the polypropylene-based resin mixture is within the range described later and a mixture is formed, it is difficult to obtain expanded particles that exhibit good in-mold formability. In addition, there is a tendency that the MFR of the recycled polypropylene-based resin becomes high due to, for example, excessive thermal history during the recycling process.

[0068] From the viewpoint of further sufficiently improving the in-mold formability of the expanded particles, the MFR of the recycled polypropylene-based resin is preferably 1 g / 10 minutes or more and 60 g / 10 minutes or less, more preferably 3 g / 10 minutes or more and 40 g / 10 minutes or less, and further preferably 3 g / 10 minutes or more and 30 g / 10 minutes or less.

[0069] Further, the preferable numerical range of the MFR can be, for example, a range having either one of 1 g / 10 minutes or 3 g / 10 minutes as the lower limit value and either one of 60 g / 10 minutes, 40 g / 10 minutes, or 30 g / 10 minutes as the upper limit value.

[0070] <Ratio of Melt Flow Rates>

[0071] From the viewpoint of producing polypropylene-based resin expanded particles that exhibit better in-mold formability, the ratio of the MFR of the recycled polypropylene-based resin to the MFR of the virgin polypropylene-based resin is preferably 0.1 or more and 10 or less, and more preferably 0.2 or more and 5 or less.

[0072] <Melting Point>

[0073] From the perspective of easily and stably obtaining foamed granules with good in-mold formability, the melting point of the recycled polypropylene resin in this invention is preferably above 130°C and below 165°C, more preferably above 140°C and below 165°C, and even more preferably above 150°C and below 165°C.

[0074] In addition to using recycled polypropylene resin as the test sample, the melting point can be determined using the same method as for determining the melting point of virgin polypropylene resin, based on JIS K7121:2012. For details of the determination method, refer to the method for determining the melting point of polypropylene resin in the examples described later.

[0075] <Melting point difference>

[0076] From the perspective of easily and stably obtaining foamed granules with good in-mold formability, the melting point Tm of the recycled polypropylene resin is... r The melting point Tm of the virgin polypropylene resin v The difference Tm r -Tm v Preferably, the temperature is above -5°C and below 25°C, more preferably above 0°C and below 25°C, and even more preferably above 5°C and below 25°C.

[0077] <Heat of Melting>

[0078] From the perspective of easily and stably obtaining foamed granules with good in-mold formability, the heat of melting of the recycled polypropylene resin in this 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. Furthermore, the range of the heat of melting can be listed as having a lower limit of 60 J / g, 70 J / g, or 80 J / g or more, and an upper limit of 120 J / g, 115 J / g, or 110 J / g.

[0079] In addition to using recycled polypropylene resin as the test sample, the heat of melting can be determined using the same method as for determining the melting point of virgin polypropylene resin, based on the method for determining the heat of transformation of plastics described in JIS K7122:2012, and by performing differential scanning calorimetry (DSC) to obtain the DSC curve. For details of the determination method, please refer to the method for determining the heat of melting of polypropylene resin in the examples described later.

[0080] <Ratio of heat of fusion>

[0081] From the viewpoint of being able to stably produce resin foamed particles exhibiting good in-mold formability while blending a recycled polypropylene-based resin including a biomass-derived polypropylene-based resin, the ratio of the heat of fusion of the virgin polypropylene-based resin to the heat of fusion of the recycled polypropylene-based resin is preferably 0.5 or greater and 1.5 or less, more preferably 0.6 or greater and 1.4 or less, and further preferably 0.7 or greater and 1.3 or less. Furthermore, the preferable numerical range of the ratio of the heat of fusion can be exemplified by a range having any one of 0.5, 0.6, or 0.7 as a lower limit value and any one of 1.5, 1.4, or 1.3 as an upper limit value.

[0082] Among the above, as the recycled polypropylene-based resin, it is more preferable to have two or more of the modes selected from the group consisting of a mode in which the melting point is 130°C or greater and 165°C or less, a mode in which the MFR is 1 g / 10 minutes or greater and 60 g / 10 minutes or less, a mode in which the heat of fusion is 60 J / g or greater and 120 J / g or less, and a mode in which the biobased carbon content is 10% or greater, and it is further preferable to use a recycled polypropylene-based resin having all of the above modes.

[0083] Furthermore, it is preferable to select the virgin polypropylene-based resin and the recycled polypropylene-based resin used in the present application so that the ratio of the MFR is 0.1 or greater and 10 or less and the ratio of the heat of fusion is 0.5 or greater and 1.5 or less. The properties of the recycled polypropylene-based resin that has undergone a thermal history or the like have a tendency to easily fluctuate between batches of raw materials or the like compared to the properties of the virgin polypropylene-based resin. Therefore, in the production of polypropylene-based resin foamed particles, it can be difficult to stably exhibit good in-mold formability due to the use of a recycled polypropylene-based resin. In this regard, by using a virgin polypropylene-based resin and a recycled polypropylene-based resin that satisfy the ratio of the MFR in the above numerical range and the ratio of the heat of fusion in the above numerical range to form the resin particles, the effects of the present application can be more fully enjoyed.

[0084] [Polypropylene-based resin mixture]

[0085] The production method of the present application is a method of producing resin particles from a polypropylene-based resin mixture obtained by melt-kneading a virgin polypropylene-based resin and a recycled polypropylene-based resin.

[0086] The weight ratio of the virgin polypropylene-based resin to the recycled polypropylene-based resin in the polypropylene-based resin mixture is preferably virgin polypropylene-based resin:recycled polypropylene-based resin = 10:90 to 90:10, more preferably virgin polypropylene-based resin:recycled polypropylene-based resin = 15:85 to 85:15, and further preferably virgin polypropylene-based resin:recycled polypropylene-based resin = 20:80 to 80:20, from the viewpoint of stably producing the expanded particles having excellent in-moldability while increasing the content ratio of the recycled polypropylene-based resin containing the polypropylene-based resin derived from biomass.

[0087] In addition, in the polypropylene-based resin mixture, other polymers or additives other than the polypropylene-based resin can be contained within a range in which the desired object of the present application can be achieved.

[0088] "Melt flow rate"

[0089] The MFR of the polypropylene-based resin mixture is 1 g / 10 minutes or more and 30 g / 10 minutes or less. In forming the polypropylene-based resin mixture, it is preferable to determine the blending ratio of the virgin polypropylene-based resin and the recycled polypropylene-based resin so that the MFR of the polypropylene-based resin mixture is 1 g / 10 minutes or more and 30 g / 10 minutes or less, taking into account the MFR of the virgin polypropylene-based resin and the MFR of the recycled polypropylene-based resin.

[0090] [Polypropylene-based resin particles]

[0091] The polypropylene-based resin particles are composed of the polypropylene-based resin mixture described above. As a method for producing the polypropylene-based resin particles, for example, the following method can be used. First, the virgin polypropylene-based resin and the recycled polypropylene-based resin are supplied to an extruder together with a bubble modifier and the like as needed, and are melt-kneaded to obtain a resin melt of the polypropylene-based resin mixture. Then, the resin melt is extruded into a strand shape from a die for strand formation attached to the downstream side of the extruder, and then the extruded strand-like material is cooled with water and is cut by a granulator or the like. Thus, the polypropylene-based resin particles in the form of particles can be obtained.

[0092] It is preferable to add a bubble modifier to the polypropylene-based resin particles. As the bubble modifier, for example, one or more kinds of bubble modifiers selected from inorganic powder and organic powder can be used. As the inorganic powder, metal borate salts such as zinc borate or magnesium borate, and the like can be exemplified, and as the organic powder, fluororesin powder such as polytetrafluoroethylene (PTFE), and the like can be exemplified.

[0093] From the viewpoint of stably obtaining foamed particles having a desired bulk density with little variation in the diameter of the bubbles, the amount of the bubble regulator added to the resin particles is preferably 0.005% by mass or more and 1% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, and further preferably 0.02% by mass or more and 0.2% by mass or less.

[0094] Further, from the viewpoint of easily adjusting the average bubble diameter of the foamed particles to a desired range, as the bubble regulator, it is preferable to use a metal salt of boric acid, and more preferable to use zinc borate.

[0095] <Melting point>

[0096] From the viewpoint of improving the compression properties of the obtained foamed particle molded body while stably obtaining foamed particles having good in-mold moldability, the melting point of the polypropylene-based resin mixture constituting the polypropylene-based resin particles is preferably 130°C or higher and 165°C or lower, and preferably 140°C or higher and 160°C or lower. The melting point is measured in the same manner as the measurement of the melting point of the virgin polypropylene-based resin, based on JIS K7121:2012, except that the polypropylene-based resin particles or the polypropylene-based resin foamed particles are used as the measurement sample. The details of the measurement of the melting point can be found in the description of the Examples described later. In addition, with respect to the present application, the compression properties refer to the properties exhibited when the foamed particle molded body is compressed, and for example, as one example, the compression stress at 50% deformation measured in accordance with JIS K6767:1999 can be cited.

[0097] <Bio-based carbon content>

[0098] The bio-based carbon content of the polypropylene-based resin particles can be adjusted depending on the bio-based carbon contents of the virgin polypropylene-based resin and the recycled polypropylene-based resin and the blending ratio. The bio-based carbon content of the polypropylene-based resin particles is 5% or more, more preferably 8% or more, and further preferably 10% or more. In addition, in order to increase the bio-based carbon content of the polypropylene-based resin particles, it is necessary to increase the amount of the polypropylene-based resin component derived from biomass blended in the resin particles, but at this time, as described above, there has been a tendency for the in-mold moldability of the foamed particles to decrease. The production method of the present application can stably produce foamed particles having good in-mold moldability using the polypropylene-based resin particles described above that exhibit a significant bio-based carbon content. In addition, the upper limit of the bio-based carbon content of the polypropylene-based resin particles can be in a range that enables the desired object of the present application to be achieved, and for example, can be 100%, can be 90%, can be 80%, or can be 60%.

[0099] The bio-based carbon content can be determined based on ASTM D 6866-21. Details of the determination method can be found in the description of the Examples described later. In addition, the bio-based carbon content of the polypropylene resin particles generally corresponds to the bio-based carbon content of the polypropylene resin expanded particles produced from the resin particles. Therefore, the bio-based carbon content of the resin particles can be expressed as the bio-based carbon content of the expanded particles.

[0100] [Polypropylene resin expanded particles]

[0101] In the production method of the present application, the polypropylene resin expanded particles can be produced by expanding the polypropylene resin particles as described above. When the polypropylene resin particles are expanded, the expanded particles can be obtained by expanding the resin particles containing a blowing agent. Specifically, for example, the expansion can be performed as described below.

[0102] First, the polypropylene resin particles are dispersed in a pressure vessel to which an aqueous dispersion medium such as water and a dispersant such as a water-insoluble inorganic salt, a dispersion aid such as a surfactant, and the like are added. This process is sometimes referred to as a dispersion process. Next, a blowing agent is added to the pressure vessel, and the blowing agent is impregnated in the resin particles. This process is sometimes referred to as a blowing agent impregnation process. Next, the resin particles containing the blowing agent in the pressure vessel are released from the pressure vessel to an atmosphere having a lower pressure than the pressure in the pressure vessel together with the aqueous dispersion medium, and the resin particles are expanded. This process is sometimes referred to as an expansion process.

[0103] From the viewpoint of improving the productivity of the expanded particles, as described above, it is preferable to use a single closed container to perform the impregnation of the blowing agent in the resin particles and the expansion of the resin particles containing the blowing agent in a series of processes.

[0104] As the blowing agent, for example, inorganic physical blowing agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen, neon, and the like; aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, and the like; alicyclic hydrocarbons such as cyclohexane, cyclopentane, and the like; halogenated hydrocarbons such as chloroethane, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, trans-1-chloro-3,3,3-trifluoropropene, and the like; organic physical blowing agents such as dimethyl ether, diethyl ether, methyl ethyl ether, and the like; and the like can be exemplified. Among them, from the viewpoint of less load on the environment and economy, the blowing agent is preferably an inorganic physical blowing agent, more preferably one or more selected from the group consisting of nitrogen, air, and carbon dioxide, and further preferably carbon dioxide. These blowing agents can be used alone or in combination with two or more.

[0105] The amount of the foaming agent to be added can be determined in consideration of the desired bulk density of the polypropylene-based resin expanded particles, the kind of the polypropylene-based resin, the kind of the foaming agent, and the like. For example, in the case of using carbon dioxide, the amount of the foaming agent to be added is preferably 0.1 parts by weight to 30 parts by weight, more preferably 0.5 parts by weight to 15 parts by weight, relative to 100 parts by weight of the polypropylene-based resin particles.

[0106] The polypropylene-based resin expanded particles produced by the production method of the present application can have a crystal structure in which an inherent peak and a high-temperature peak, which is located on the high-temperature side compared to the inherent peak, appear in a DSC curve. Here, the DSC curve refers to a DSC curve obtained by heat flow-type differential scanning calorimetry in which the expanded particles are heated from 23°C to 200°C at a heating rate of 10°C / minute, and more specifically, refers to a DSC curve at the time of the first heating.

[0107] The inherent peak refers to a melting peak generated by the inherent crystalline melting of the polypropylene-based resin constituting the expanded particles. On the other hand, the high-temperature peak refers to a melting peak that is present on the high-temperature side compared to the inherent peak, which is confirmed in the first DSC curve. When the high-temperature peak appears, it can be inferred that secondary crystallization is present in the resin constituting the expanded particles.

[0108] In particular, in the crystal structure, it is preferable that the peak temperature of the inherent peak be 130°C or higher, and the difference between the peak temperature of the high-temperature peak and the peak temperature of the inherent peak be 20°C or higher and 30°C or lower. When in-mold foaming, it is easy to obtain an expanded particle molded body in which the generation of local depressions after molding is suppressed, and it is easy to widen the angle of the moldable range of the expanded particles, from the viewpoint of improving the secondary expandability of the expanded particles, and as described above, it is preferable that the difference between the peak temperature of the high-temperature peak and the peak temperature of the inherent peak be large. On the other hand, when the expanded particles are produced using only recycled polypropylene-based resin, or using recycled polypropylene-based resin having 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 inherent peak becomes small. In this regard, in the expanded particles obtained by the production method of the present application, it is possible to make the difference between the peak temperature of the high-temperature peak and the peak temperature of the inherent peak large while using recycled polypropylene-based resin. Therefore, the present application makes it easy to obtain polypropylene-based resin expanded particles having a crystal structure that exhibits the "difference between the peak temperatures" in the above-described preferable range, and as a result, the expanded particles produced by the production method of the present application make it easy to exhibit good in-mold foaming properties while exhibiting a significant bio-based carbon content.

[0109] The aforementioned high-temperature peak can be adjusted, for example, in the dispersion process and / or the foaming agent impregnation process, by controlling the rate of temperature rise within the pressure vessel and maintaining the temperature within the pressure vessel at a specified temperature for a specified time. More specifically, for example, in the dispersion process and / or the foaming agent impregnation process, a holding process is performed to maintain the temperature within the pressure vessel at a temperature above [the melting point of the resin particles - 20°C] and below [the melting point of the resin particles] for approximately 10 to 60 minutes. Then, the temperature within the pressure vessel is adjusted to a temperature above [the melting point of the resin particles - 15°C] and below [the melting point of the resin particles]. At this time, a second holding process can be performed as needed, maintaining this temperature for approximately 10 to 60 minutes. Then, by performing a foaming process, foamed particles with a high-temperature peak can be manufactured.

[0110] Furthermore, the DSC curve in the second heating refers to the second DSC curve obtained when the foamed particles 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). Preferably, only the inherent peaks appear in the second DSC curve. Moreover, by comparing the shape and peak position of the first and second DSC curves, the inherent peaks and high-temperature peaks can be identified.

[0111] The heat of fusion, peak temperature of the high-temperature peak, and peak temperature of the intrinsic peak of the foamed granules can be determined by DSC curves obtained through differential scanning calorimetry (DSC) based on the method for determining the heat of transformation of plastics described in JIS K7122:2012. Specifically, 1 mg to 3 mg of foamed granules can be used as the test sample, heated from 23 °C to a temperature 30 °C higher than the end of the melting peak of the test sample at a heating rate of 10 °C / min. The DSC curve obtained from the first heating (refer to...) Figure 1 Determine the above-mentioned physical properties.

[0112] More specifically, in Figure 1 In the DSC curve shown, draw a straight line connecting point I, which corresponds to 80°C, and point II, which corresponds to the melting end temperature of the foamed particles. Furthermore, the melting end temperature is the endpoint of the high-temperature side of high-temperature peak b, which is the intersection of high-temperature peak b in the DSC curve and the baseline located on the high-temperature side compared to high-temperature peak b.

[0113] like Figure 1 As shown, after drawing the straight line connecting point I and point II, the intersection of the straight line passing through the maximum point III between the inherent peak a and the high-temperature peak b and parallel to the vertical axis of the graph with the straight line connecting point I and point II is taken as IV.

[0114] Then, the area of the portion surrounded by the straight line connecting point I and point IV, the straight line connecting point III and point IV, and the DSC curve connecting point I and point III is taken as the area of the intrinsic peak a. Further, the area of the portion (hatched portion) surrounded 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 is taken as the area of the high-temperature peak b. The value of the heat of fusion of the high-temperature peak of the foamed particles is calculated from the area of the high-temperature peak b calculated as described above. Further, the vertex temperature of the high-temperature peak and the vertex temperature of the intrinsic peak can be confirmed from the DSC curve.

[0115] The heat of fusion of the foamed particles can be calculated based on the DSC curve measured by heat flow type differential scanning calorimetry according to the method for measuring the heat of transition of plastics described in JIS K7122:2012.

[0116] Specifically, 1 mg to 3 mg of the foamed particles is used as the measurement sample, and the measurement sample is adjusted in state, and "(2) after a certain heat treatment, the melting temperature is measured" is adopted, the measurement sample is heated from 23°C to 200°C at a heating rate of 10°C / minute, after reaching 200°C, the temperature is decreased from 200°C to 23°C at a rate of 10°C / minute, and then the temperature is again increased from 23°C to 200°C at a rate of 10°C / minute for the second time, thereby obtaining the DSC curve (DSC curve at the second time of heating). A point at a temperature of 80°C on the obtained DSC curve at the second time of heating is taken as a, and a point on the DSC curve corresponding to the end temperature of melting is taken as β. The area of the portion surrounded by the DSC curve of the interval from point a to point β and the line segment (a-β) is measured, and the heat of fusion of the foamed particles is calculated from the area.

[0117] In addition, the heat of fusion measured as described above can be alternatively expressed as the heat of fusion of the polypropylene-based resin mixture constituting the foamed particles, and further alternatively expressed as the heat of fusion of the polypropylene-based resin mixture constituting the resin particles.

[0118] <Heat of fusion>

[0119] From the viewpoint of stably obtaining foamed particles having good in-mold formability by the production method of the present application, the heat of fusion of the foamed particles of the present application is preferably 60 J / g or more and 120 J / g or less, more preferably 65 J / g or more and 110 J / g or less, preferably 70 J / g or more and 100 J / g or less, more preferably 75 J / g or more and 95 J / g or less. Further, the heat of fusion can be, for example, a range having any one of 60 J / g, 65 J / g, 70 J / g, or 75 J / g or more as a lower limit value and any one of 120 J / g, 110 J / g, 100 J / g, or 95 J / g as an upper limit value.

[0120] <High temperature peak melting heat>

[0121] From the viewpoint of stably obtaining the foamed particles having good in-mold formability by the production method of the present application, the high temperature peak melting heat is preferably 5 J / g or greater and 50 J / g or less, more preferably 10 J / g or greater and 40 J / g or less, further preferably 15 J / g or greater and 35 J / g or less. In addition, the high temperature peak melting heat can be exemplified by a range having any one of 5 J / g, 10 J / g, or 15 J / g or greater as a lower limit value and any one of 50 J / g, 40 J / g, or 35 J / g or less as an upper limit value.

[0122] <Ratio of high temperature peak melting heat to melting heat>

[0123] From the viewpoint of stably obtaining the foamed particles having good in-mold formability by the production method of the present application, the ratio of the high temperature peak melting heat to the melting heat is preferably 0.10 or greater and 0.40 or less, more preferably 0.12 or greater and 0.35 or less. In addition, the ratio can be exemplified by a range having any one of 0.10 or 0.12 or greater as a lower limit value and any one of 0.40 or 0.35 or less as an upper limit value.

[0124] <Native peak top temperature>

[0125] From the viewpoint of stably obtaining the foamed particles having good in-mold formability by the production method of the present application, the native peak top temperature is preferably 135°C or greater and 160°C or less, more preferably 140°C or greater and 158°C or less. In addition, the native peak top temperature can be exemplified by a range having any one of 135°C or 140°C or greater as a lower limit value and any one of 160°C or 158°C or less as an upper limit value.

[0126] <Stacking density of foamed particles>

[0127] From the viewpoint of obtaining a molded body having a good balance between lightness and compression properties, the stacking density of the foamed particles is preferably 10 kg / m 3 or greater and 200 kg / m 3 or less, more preferably 12 kg / m 3 or greater and 100 kg / m 3 or less, further preferably 15 kg / m 3 or greater and 60 kg / m 3 or less. In addition, the stacking density can be exemplified by a range having any one of 10 kg / m 3 , 12 kg / m 3 , or 15 kg / m 3 or greater as a lower limit value and 200 kg / m 3, 100 kg / m 3 or 60 kg / m 3 Any one of the ranges of the upper limit value. The bulk density of the foamed particles can be obtained using the method described in the examples described later.

[0128] Furthermore, the foamed particles can have a fusion layer on the surface thereof for improving the fusion of the foamed particles with each other at the time of in-mold molding. The fusion layer can be present on the entire surface of the foamed particles or on a part of the surface. As the resin constituting the fusion layer, for example, a polyolefin-based resin can be exemplified.

[0129] The method of forming the fusion layer on the surface of the foamed particles is not particularly limited, and for example, a method of foaming resin particles having a fusion layer on the surface, a method of adhering a fusion layer to the surface of the foamed particles after obtaining the foamed particles, and the like can be exemplified. When the foamed particles are obtained by foaming resin particles having a fusion layer on the surface, it is preferable to use the following method at the time of manufacturing the resin particles: using an extrusion device that can be co-extruded, co-extruding a molten mixture for forming the main body of the resin particles and a resin melt for forming the fusion layer, and thereby laminating the fusion layer on the surface of the resin particles.

[0130] The polypropylene-based resin foamed particles manufactured by the manufacturing method of the present application described above are composed of a polypropylene-based resin mixture obtained by melt-kneading virgin polypropylene-based resin and recycled polypropylene-based resin. The polypropylene-based resin mixture contains a polypropylene-based resin derived from biomass, the polypropylene-based resin derived from biomass containing a monomer component derived from biomass in a molecular chain, the melt flow rate of the polypropylene-based resin mixture determined under the conditions of a temperature of 230°C and a load of 2.16 kg is 1 g / 10 minutes or more and 30 g / 10 minutes or less, and the bio-based carbon content of the foamed particles determined based on ASTM D 6866-21 is 5% or more.

[0131] The polypropylene-based resin foamed particles preferably have a crystal structure in which an inherent peak and a high-temperature peak located on the high-temperature side of the inherent peak appear in a DSC curve obtained by heat flow type differential scanning calorimetry and heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / minute, and more preferably the peak temperature of the inherent peak is 130°C or more and the difference between the peak temperature of the high-temperature peak and the peak temperature of the inherent peak is 20°C or more and 30°C or less.

[0132] By producing the polypropylene-based resin foamed particles satisfying the above constitution, polypropylene-based resin foamed particles excellent in in-mold moldability can be obtained while using a recycled polypropylene-based resin containing a polypropylene-based resin derived from biomass.

[0133] [Polypropylene-based resin foamed particle molded body]

[0134] By in-mold molding the polypropylene resin foamed particles produced by the production method of the present application, a polypropylene resin foamed particle molded body can be obtained. In the present specification, the polypropylene resin foamed particle molded body obtained by in-mold molding the polypropylene resin foamed particles produced by the production method of the present application is sometimes referred to as a foamed particle molded body of the present application.

[0135] The in-mold molding broadly includes a known in-mold molding method using foamed particles. For example, the in-mold molding using the foamed particles obtained by the present application can be carried out as follows. First, the foamed particles are filled in a molding die having a cavity corresponding to the shape of the desired foamed particle molded body, and the foamed particles filled in the molding die are subjected to a prescribed molding pressure and heating by a heating medium such as steam. The molding pressure can be adjusted, for example, in the range of 0.2 MPa (G) or more and 0.5 MPa (G) or less. In the present specification, (G) indicates a value of pressure based on atmospheric pressure, i.e., gauge pressure. The foamed particles in the cavity are thereby heated to further foam them, and at the same time, to fuse the foamed particles with each other. Subsequently, after the heating based on the steam or the like is completed, the pressure in the cavity is released, and at the same time, the cooling of the molding die and the molded body in the molding die is rapidly started. The cooling is ended after the pressure (surface pressure) generated on the inner face of the molding die is confirmed to be 0.04 MPa (G), and the foamed particle molded body is taken out of the molding die. The cooling method is not particularly limited here, and for example, water cooling or the like can be mentioned. By this series of molding procedures, a foamed particle molded body corresponding to the shape of the cavity is obtained.

[0136] <Density>

[0137] The density of the foamed particle molded body of the present application is preferably 10 kg / m 3 or more and 200 kg / m 3 or less. More preferably, it is 12 kg / m 3 or more and 100 kg / m 3 or less. Further preferably, it is 15 kg / m 3 or more and 60 kg / m 3 or less. The density can be obtained by dividing the weight of the polypropylene resin foamed particle molded body by the volume of the molded body. Specifically, it can be obtained by the method described in the Examples described later.

[0138] <Ratio of compressive stress at 50% deformation to density>

[0139] From the viewpoint of providing a foamed particle molded body having a good balance between lightness and compression property, the ratio of the compressive stress at 50% deformation to the density of the foamed particle molded body of the present application is preferably 6 kPa / [kg / m3 ]above and 14 kPa / [kg / m 3 ]below, more preferably 7 kPa / [kg / m 3 ]above and 14 kPa / [kg / m 3 ]below, further preferably 8 kPa / [kg / m 3 ]above and 14 kPa / [kg / m 3 ]below.

[0140] Examples

[0141] Hereinafter, the present application will be described in more detail using examples, but the present application is not limited thereto. First, virgin polypropylene resins and recycled polypropylene resins used as raw materials of resins for the present examples and comparative examples will be described.

[0142] (Preparation of virgin polypropylene resins)

[0143] As the virgin polypropylene resins used in the present examples, pellet-shaped virgin polypropylene resins V1 to V3 shown in Table 1 were prepared. Virgin polypropylene resins V1 and V2 were both propylene-ethylene random copolymers. In addition, virgin polypropylene resin V3 was "NOVATEC PP MG05ES" manufactured by Japan Polypropylene Corporation.

[0144] Sometimes, the virgin polypropylene resins V1 to V3 are simply referred to as resin V1 to resin V3. In addition, sometimes, the recycled polypropylene resins R1 to R6 described later are simply referred to as resin R1 to resin R6.

[0145] In addition, the recycled polypropylene resins R1 to R6 were prepared assuming that they were recycled polypropylene resins derived from post-consumer materials.

[0146] (Preparation of recycled polypropylene resins)

[0147] <Recycled polypropylene resin R1 (resin R1)>

[0148] The recycled polypropylene resin was prepared by recycling a fusion body of foamed particles prepared using polypropylene resins as raw materials of resins.

[0149] Specifically, first, a manufacturing apparatus equipped with an extruder having an inner diameter of 50 mm and a wire harness forming die attached to the downstream side of the extruder was prepared. After a propylene homopolymer (manufactured by Lyondell basell, grade HP456J, bio-based carbon content 42%) as a polypropylene resin and zinc borate (0.1 parts by weight with respect to 100 parts by weight of the polypropylene resin) as a bubble regulator were supplied to the extruder to be melt-kneaded, the extruder was extruded into a wire harness shape, and by performing granulation, a polypropylene resin granule was obtained.

[0150] 1 kg of the obtained resin granule was supplied to a pressurizable pressure container having a content of 5 L together with 3 L of water as an aqueous dispersion medium. In addition, 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 DKS Co. Ltd., sodium dodecylbenzenesulfonate) were added to the pressure container with respect to 100 parts by weight of the polypropylene resin granule, respectively.

[0151] Next, while stirring the inside of the pressure container, the temperature was raised to a predetermined foaming temperature. Carbon dioxide was pressurized into the pressure container as a foaming agent, and after a predetermined time was maintained, the contents (polypropylene resin granule and water) of the pressure container were released at atmospheric pressure to obtain a polypropylene resin foamed granule having a bulk density of 50 kg / m 3

[0152] The obtained polypropylene resin foamed granule was filled in a molding die having a molding cavity that could be molded into a fused body in a plate shape, and the foamed granule was fused to each other by heating with steam. In this way, a fused body of foamed granules was manufactured.

[0153] The manufactured fused body of foamed granules was crushed to reduce the volume to obtain a crushed product of a size that could be supplied to an extruder. The above crushed product and an antioxidant (Irganox 1010 manufactured by BASF, a hindered phenol-based antioxidant; 0.2 parts by weight with respect to 100 parts by weight of the crushed product) were supplied to the extruder, and melt-kneaded at 210°C to obtain a resin melt. The resin melt was introduced into a wire harness forming die and extruded into a wire harness. The extruded wire harness was cooled with water, and cut off with a granulator to obtain a granular recycled polypropylene resin R1 having an average weight of 10 mg per 1.

[0154] <Recycled polypropylene resin R2 (Resin R2)>

[0155] ​Instead of the propylene homopolymer as the grade HP456J, virgin polypropylene-based resin VI was supplied to the extruder at a ratio of resin VI : HP456J = 50 : 50 together with the propylene homopolymer of the grade HP456J, and polypropylene-based resin particles were produced, and otherwise, a fused body of foamed particles was produced in the same manner as the recycled polypropylene-based resin Rl.

[0156] The produced fused body of foamed particles was granulated in the same manner as the recycled polypropylene-based resin Rl, and a granulated recycled polypropylene-based resin R2 was obtained.

[0157] < Recycled polypropylene-based resin R3 (Resin R3) >

[0158] Instead of the propylene homopolymer as the grade HP456J, virgin polypropylene-based resin VI was supplied to the extruder at a ratio of resin VI : HP456J = 50 : 50 together with the propylene homopolymer of the grade HP456J, and polypropylene-based resin particles were produced, and otherwise, a fused body of foamed particles was produced in the same manner as the recycled polypropylene-based resin Rl.

[0159] The produced fused body of foamed particles was granulated in the same manner as the recycled polypropylene-based resin Rl, and a granulated recycled polypropylene-based resin R2 was obtained.

[0160] < Recycled polypropylene-based resin R4 (Resin R4) >

[0161] The temperature of the melt kneading of the extruder at the time of granulating the crushed product of the fused body of foamed particles was changed to 240°C, and otherwise, particles were produced in the same manner as the recycled polypropylene-based resin Rl, and a recycled polypropylene-based resin R4 was obtained.

[0162] < Recycled polypropylene-based resin R5 (Resin R5) >

[0163] The temperature of the melt kneading of the extruder at the time of granulating the crushed product of the fused body of foamed particles was changed to 240°C, and otherwise, particles were produced in the same manner as the recycled polypropylene-based resin Rl, and a recycled polypropylene-based resin R4 was obtained.

[0164] < Recycled polypropylene-based resin R6 (Resin R6) >

[0165] The temperature of melt-kneading of the extruder at the time of granulating the broken pieces of the fused body of the foamed particles was changed to 300°C, and otherwise, granules were produced in the same manner as the recycled polypropylene-based resin R1. The obtained granules were again supplied to the extruder, and melt-kneading was performed at 300°C to obtain a resin melt. The resin melt was introduced into a wire harness forming die and an extruded wire harness was obtained. The extruded wire harness was cooled with water, cut with a granulator, and granules were again produced (second granulation). This operation was further repeated three times, and a total of five granulation operations were performed. In this way, a granulated recycled polypropylene-based resin R6 was obtained.

[0166] (Measurement of properties of polypropylene-based resin)

[0167] The MFR, melting point, and heat of fusion of the resins V1 to V3 as virgin polypropylene-based resins and the resins R1 to R6 as recycled polypropylene-based resins were measured by the methods described later. In addition, the bio-based carbon content of the resins R1 to R6 can be calculated from the bio-based carbon content of the biomass-derived polypropylene-based resin (HP456J) used for producing the recycled polypropylene-based resin, which was measured by the method described later, 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 addition, the MFR r ratio of the MFR of the virgin polypropylene-based resin v ratio of the melting point Tm of the recycled polypropylene-based resin r from the melting point Tm of the virgin polypropylene-based resin v value obtained by subtracting the melting point Tm of the virgin polypropylene-based resin v ratio of the heat of fusion AH of the recycled polypropylene-based resin r to the heat of fusion AH of the virgin polypropylene-based resin. In addition, the densities of the resins V1 to V3 and the resins R1 to R6 were 0.90 g / cm 3 .

[0168] <Heat of fusion>

[0169] The heat of fusion of the polypropylene-based resin was measured by heat flow type differential scanning calorimetry based on the method for measuring the heat of transition of plastics described in JIS K7122:2012.

[0170] As the measuring device, a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation.) was used. As the state adjustment of the measurement sample, "(2) Measurement of the melting temperature after a certain heat treatment" was adopted. About 2 mg of the polypropylene-based resin was taken as the measurement sample, and the measurement sample was heated from 23°C to 200°C at a heating rate of 10°C / min under the condition that the nitrogen gas flow rate was 30 mL / min, and then, after keeping at that temperature for 10 minutes, it was cooled to 23°C at a cooling rate of 10°C / min, and then, it was heated to 200°C at a heating rate of 10°C / min again, to obtain the DSC curve (DSC curve at the second heating).

[0171] The point of 80°C on the DSC curve at the second heating obtained was taken as α, and the point on the DSC curve corresponding to the end temperature of the dissolution was taken as β. The area of the portion enclosed by the DSC curve of the interval from the point α to the point β and the line segment (α-β) was measured, and the heat of fusion of the polypropylene-based resin was calculated from the area.

[0172] < Melting point >

[0173] The melting point of the polypropylene-based resin was measured based on JIS K7121:2012 and by a heat flow type differential scanning calorimetry. As the measuring device, a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation.) was used. As the state adjustment of the measurement sample, "(2) Measurement of the melting temperature after a certain heat treatment" was adopted. About 2 mg of the polypropylene-based resin was taken as the measurement sample, and the measurement sample was heated from 23°C to 200°C at a heating rate of 10°C / min under the condition that the nitrogen gas flow rate was 30 mL / min, and then, after keeping at that temperature for 10 minutes, it was cooled to 23°C at a cooling rate of 10°C / min, and then, it was heated to 200°C at a heating rate of 10°C / min again, to obtain the DSC curve (DSC curve at the second heating). The peak temperature of the dissolution peak in the DSC curve was calculated, and the value was taken as the melting point.

[0174] In addition, when a plurality of dissolution peaks appeared in the DSC curve, the peak temperature of the dissolution peak having the largest area was used as the melting point. At this time, the dissolution peaks were distinguished with the temperature of the peak valley of the DSC curve between the peak temperatures of the respective dissolution peaks as the boundary, and the areas (heat of fusion) of the respective dissolution peaks were compared, whereby the dissolution peak having the largest area could be judged. Since the temperature of the peak valley of the DSC curve corresponds to the temperature at which the value of the ordinate of the differential curve (DDSC) of the DSC curve is 0, the judgment could also be made from the differential curve of the DSC.

[0175] <Mel flow rate>

[0176] Based on JIS K7210-1:2014, the melt flow rate of polypropylene resin was determined at a temperature of 230℃ and a load of 2.16 kg.

[0177] <Bio-based carbon content>

[0178] Based on ASTM D6866-21, the bio-based carbon content of polypropylene resins was determined as follows.

[0179] Specifically, biomass-derived polypropylene resin from recycled polypropylene resins is used in the test sample. This test sample is subjected to analysis and combustion, generating carbon dioxide (CO2), which is then purified via a vacuum route. The purified carbon dioxide is reduced with hydrogen using iron as a catalyst, thereby producing graphite (C). The graphite is then manually loaded into a 1mm inner diameter cathode, embedded in a wheel, and mounted on a tandem accelerator based on a device manufactured by NEC Corporation. 14 A dedicated C-AMS device is used for measurement. Measurements are performed using this device. 14 The number of Cs 13 C concentration ( 13 C / 12 C) 14 C concentration ( 14 C / 12 C) Determination. In this determination, oxalic acid (HOxII) provided by the National Institute of Standards and Technology (NIST) was used as the standard sample. The determination of this standard sample and the background sample were performed simultaneously.

[0180] The carbon content obtained from the measured sample was calculated based on the obtained measurement results. 14 The ratio of C to modern carbon in the standard sample, followed by comparison with the standard sample. 13 The deviation of C concentration is corrected to obtain the corrected pMC (percent Modern Carbon) value.

[0181] The bio-based carbon content was calculated using the corrected pMC value. The atmospheric correction factor was the value (100.0 pMC) for 2019-2021 as described in ASTM D6866-21. In the determination of the bio-based carbon content of the polypropylene resin of the present invention, the atmospheric correction factor as described in ASTM D6866 for the year the polypropylene resin was manufactured was used to determine the bio-based carbon content.

[0182] In this embodiment, the properties of the biomass-derived polypropylene-based resin contained in the recycled polypropylene-based resin were clarified. Therefore, based on the bio-based carbon content of the biomass-derived polypropylene-based resin determined as described above and the blending amount of the biomass-derived polypropylene-based resin, the bio-based carbon content of the recycled polypropylene-based resin, the resin particles, and the expanded particles was calculated.

[0183] In addition, the recycled polypropylene-based resin, the resin particles, and the expanded particles themselves were used as the determination sample, and the determination of the bio-based carbon content described above was performed, whereby the bio-based carbon content of the recycled polypropylene-based resin, the resin particles, and the expanded particles could also be directly determined.

[0184] (Example 1)

[0185] <Production of polypropylene-based resin particles>

[0186] A manufacturing device having an extruder with an inner diameter of 50 mm and a strand forming die attached to the downstream side of the extruder was prepared.

[0187] The resin V1 shown in Table 1 and the resin R1 shown in Table 2 and zinc borate as a bubble regulator (0.1 parts by weight with respect to 100 parts by weight of the total amount of the polypropylene-based resin) were supplied to the extruder, and melt-kneading was performed to obtain a resin melt. In addition, the ratio (wt%) of virgin PP to recycled PP shown in Table 3 means the ratio (wt%) of each when the total of the blending amounts of both is set to 100 wt%. The resin melt was introduced into the strand forming die and extruded into a strand. The extruded strand was cooled with water, and cut with a pelletizer so that the average weight of each 1 was 1 mg. Thus, polypropylene-based resin particles composed of a polypropylene-based resin mixture as a mixed resin of a virgin polypropylene-based resin and a recycled polypropylene-based resin were obtained.

[0188] <Production of polypropylene-based resin expanded particles>

[0189] 1 kg of the polypropylene-based resin particles obtained as described above and 3 L of water as an aqueous dispersion medium were supplied together into a pressurizable pressure container with a content of 5 L. In addition, with respect to 100 parts by weight of the polypropylene-based resin particles, 0.3 parts by weight of kaolin as an inorganic dispersant, 0.2 parts by weight (as an active ingredient) of a surfactant (trade name: NEOGEN, manufactured by DKS Co. Ltd., sodium dodecylbenzenesulfonate) were added to the pressure container, respectively.

[0190] Next, while stirring the pressure vessel, the temperature was raised to the foaming temperature at a temperature increase rate of 5°C / min, and then carbon dioxide as a foaming agent was pressurized into the pressure vessel to 2.1 MPa (G), and the temperature and the pressure were maintained for 15 minutes. Thus, the crystal structure of the obtained foamed particles was adjusted, and the DSC curve obtained by heat flow type differential scanning calorimetry was adjusted so that a high temperature peak appeared.

[0191] Then, the contents of the pressure vessel (the polypropylene-based resin particles and water) were released at atmospheric pressure to obtain polypropylene-based resin foamed particles having a bulk density of 54 kg / m 3

[0192] In addition, in the examples and comparative examples, the foaming temperature was adjusted in the range of 161°C to 169°C in such a manner that foamed particles having a prescribed bulk density were obtained, and the resin particles were foamed.

[0193] The physical properties of the foamed particles described later were measured using foamed particles whose state was adjusted by being left to stand for 24 hours under conditions of 50% RH, 23°C, and 1 atm.

[0194] <Manufacture of polypropylene-based resin foamed particle molded body>

[0195] The obtained polypropylene-based resin foamed particles were filled in a molding cavity of a molding die having a plate shape with a moldable length of 250 mm x width of 200 mm x height of 20 mm, and heating was performed using the following heating method. As the molding die, a metal die was used.

[0196] The heating method was to supply steam to the molding die while releasing the discharge valves provided on both sides of the molding die, and perform preheating (degassing step). Then, steam was supplied from one side of the molding die, and heating was performed, and further, steam was supplied from the other side of the molding die, and heating was performed. Next, steam was supplied from both sides of the molding die and heating was performed at the lower limit molding pressure (0.30 MPa (G) ) described later. After the heating was completed, pressure release was performed, and at the same time, cooling with water was rapidly started, and the cooling with water was performed until the foaming force of the foamed particle molded body reached a position where the pressure generated on the inner surface of the molding die was 0.04 MPa (G). After the cooling with water was completed, the foamed particle molded body was taken out of the molding die, and was used as Example 1.

[0197] In addition, the physical property measurement and evaluation of the foamed particle molded body described later were performed using a molded body whose state was adjusted by leaving the molded body after demolding to stand for 12 hours under conditions of 50% RH, 80°C, and 1 atm.

[0198] (Examples 2 to 9, Comparative Examples 1 to 3)

[0199] ​The polypropylene resin particles, the polypropylene resin foamed particles, and the polypropylene resin foamed particle molded bodies were produced in the same manner as in Example 1 except that the contents described in Table 3 were changed, and were used as Examples 2 to 9 and Comparative Examples 1 to 3.

[0200] With respect to each of the examples and comparative examples obtained as described above, the following measurements were performed on the polypropylene resin particles, the polypropylene resin foamed particles, and the polypropylene resin foamed particle molded bodies. The measurement results of the polypropylene resin particles and the polypropylene resin foamed particles are shown in Table 4, and the measurement results of the polypropylene resin foamed particle molded bodies are shown in Table 5.

[0201] [Measurement of polypropylene resin foamed particles]

[0202] <Melting point>

[0203] The MFR of the polypropylene resin mixture constituting the polypropylene resin particles was measured based on JIS K7210-1:2014 at a temperature of 230°C and a load of 2.16 kg, using the polypropylene resin particles as a measurement sample.

[0204] <Melting point>

[0205] The melting point of the polypropylene resin mixture constituting the polypropylene resin particles was measured by heat flow type differential scanning calorimetry based on JIS K7121:2012 in the same manner as in the measurement of the melting point of the polypropylene resin except that the polypropylene resin particles were used as a measurement sample.

[0206] [Measurement of polypropylene resin foamed particles]

[0207] <Heat of fusion>

[0208] The heat of fusion of the foamed particles was measured in the same manner as in the heat of fusion of the polypropylene resin except that the polypropylene resin foamed particles were used as a measurement sample.

[0209] <Heat of fusion of high-temperature peak>

[0210] The heat of fusion of the high-temperature peak of the foamed particles was determined by heat flow type differential scanning calorimetry based on the transition heat measurement method for plastics described in JIS K7122:2012. As the measurement apparatus, a high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Corporation.) was used. About 3 mg of the foamed particles was used as the measurement sample, and the DSC curve in which the inherent peak and the high-temperature peak appeared (DSC curve in the first heating) was obtained by heating from 23°C to 200°C at a heating rate of 10°C / minute. In addition, the measurement was performed under the condition that the nitrogen flow rate was 30 mL / minute.

[0211] As described in the above, the use of the foamed particles Figure 1 In the DSC curve obtained using each of the foamed particles, a straight line connecting a point I corresponding to 80°C and a point II corresponding to the melting end temperature of the foamed particles in the DSC curve was drawn. With reference to Figure 1 As shown in the above, after the straight line connecting the point I and the point II was drawn, the intersection of the straight line passing through the maximum point III present between the inherent peak a and the high-temperature peak b and parallel to the ordinate of the graph and the straight line connecting the point I and the point II was taken as IV.

[0212] Then, the area of the portion (diagonal portion) surrounded by the straight line connecting the point IV and the point II, the straight line connecting the point III and the point IV, and the DSC curve connecting the point III and the point II was taken as the area of the high-temperature peak b. The value of the heat of fusion (J / g) of the high-temperature peak b of the foamed particles was calculated from the area of the high-temperature peak b obtained as described above. The determination of the heat of fusion of the high-temperature peak was performed on three different measurement samples, and the arithmetic mean of the values obtained was taken as the heat of fusion of the high-temperature peak of the foamed particles.

[0213] <Apex temperature of high-temperature peak, apex temperature of inherent peak>

[0214] In the three DSC curves obtained in order to determine the heat of fusion of the high-temperature peak, the apex temperature of the high-temperature peak and the apex temperature of the inherent peak were each read. The arithmetic mean of the values obtained was taken as the apex temperature of the high-temperature peak and the apex temperature of the inherent peak.

[0215] <Bulk density>

[0216] A group of foamed particles having a weight W (g) was filled in a graduated cylinder, and the filling height of the group of foamed particles in the graduated cylinder was stabilized by tapping the bottom surface of the graduated cylinder several times to make the level. The bulk volume V (L) of the group of foamed particles indicated by the scale of the graduated cylinder was read, and the bulk volume V of the group of foamed particles was divided by the weight W of the group of foamed particles (W / V). The value obtained was converted into kg / m 3 The bulk density of the foamed particles (kg / m3 ).

[0217] In addition, the ratio of the heat of fusion of the high-temperature peak to the heat of fusion determined as described above is shown in Table 4, and furthermore, the value obtained by subtracting the peak temperature of the inherent peak from the peak temperature of the high-temperature peak is shown.

[0218] [Measurement of polypropylene resin foamed particle molded body]

[0219] <Density of molded body>

[0220] The density of the polypropylene resin foamed particle molded body is obtained by dividing the weight of the polypropylene resin foamed particle molded body by the volume calculated based on the outer dimensions.

[0221] <Lower limit molding pressure>

[0222] The in-mold molding of the foamed particles was performed by changing the molding pressure (molding steam pressure) in the range of 0.20 MPa (G) to 0.40 MPa (G) at an interval of 0.01 MPa (G) using the heating method in the above-mentioned <Manufacture of polypropylene resin foamed particle molded body>.

[0223] With respect to the obtained molded body, the following fusion rate, periphery portion compactibility, and shape were evaluated. In addition, the evaluation of the shape refers to the evaluation of the occurrence of sink marks in the central portion of the foamed particle molded body. Here, the sink mark refers to the depression of the molded body. Then, the lowest molding pressure at which the foamed particle molded body that passed all of the above-mentioned evaluations was obtained was taken as the lower limit molding pressure.

[0224] Fusion rate:

[0225] A test piece (length 100 mm x width 100 mm x thickness: thickness of the foamed particle molded body) was cut out from the central portion of the foamed particle molded body, and after a cut of about 5 mm was made in the thickness direction of each test piece with an art knife, the test piece was broken from the cut portion. Next, the number of foamed particles (n) present on the fractured surface of the foamed particle molded body and the number of foamed particles broken (b) were measured. Then, the number of foamed particles broken (b) was taken as the fusion rate (%) expressed in percentage with respect to the total number of foamed particles (n), and the fusion rate was taken as passing when it was 80% or more and as failing when it was less than 80%.

[0226] Periphery portion compactibility:

[0227] In the periphery portion of the foamed particle molded body, a sample in which the gaps between the foamed particles were not apparent and the shape of the molding metal mold was sufficiently compacted was taken as passing, and a sample in which the gaps between the foamed particles were apparent and the shape of the molding metal mold was not sufficiently compacted was taken as failing.

[0228] Shape:

[0229] The thickness t1 of the vicinity of both ends in the longitudinal direction of the molded body of the foamed particle molded body in a flat shape and the thickness t2 of the center portion of the molded body are measured, respectively. Then, the ratio (%) of the thickness t2 of the center portion of the molded body to the thickness t1 of the larger one of the thicknesses t1 of the vicinity of both ends is calculated. When the ratio is 95% or more, it is judged that no excessive sink marks are generated in the center portion of the molded body, and is recorded as pass. Further, when the ratio is less than 95%, it is judged that sink marks are generated in the center portion of the molded body, and is recorded as fail.

[0230] Further, specifically, the thickness t1 refers to the thickness of the intersection portion of the position within 10 mm from the end toward the center in the longitudinal direction of the molded body and the position bisecting the molded body in the lateral direction. Further, specifically, the thickness t2 refers to the thickness of the intersection portion of the position bisecting the molded body in the longitudinal direction and the position bisecting the molded body in the lateral direction.

[0231] <Number of moldable condition ranges>

[0232] As described above, the number of moldable condition ranges in which good products can be obtained is confirmed by increasing the molding pressure at the time of molding in the mold by 0.01 MPa (G) at a time from the lower limit molding pressure. For example, when the lower limit molding pressure is 0.30 MPa (G) and good products can be obtained until 0.34 MPa (G) is reached, the number of moldable condition ranges is counted as 5. Here, the good product refers to a foamed particle molded body in which the fusion rate, the periphery portion moldability, and the shape evaluation are all pass.

[0233] Further, since the molding temperature can be adjusted by the molding pressure, the number of points of the moldable molding pressure is larger, the width from the lower limit value to the upper limit value is wider, and the range of the moldable molding heating temperature is wider. Further, the molded body that can be molded even under a condition in which the vapor pressure is low is suitable because the amount of steam required for molding can be reduced, and the productivity is excellent.

[0234] <Compression stress at 50% deformation>

[0235] A test piece of 50 mm x 50 mm x 15 mm having no skin layer is cut out from the vicinity of the center portion of the foamed particle molded body, and using the test piece, a compression test is performed as follows. Specifically, based on JIS K6767:1999, the compression test is performed at a compression rate of 10 mm / minute, and thereby the compression stress (kPa) at 50% deformation of the foamed particle molded body is found.

[0236] Further, the ratio of the compression stress at 50% deformation to the density of the test piece is shown.

[0237] [Table 1]

[0238]

[0239] [Table 2]

[0240]

[0241] [Table 3]

[0242]

[0243] [Table 4]

[0244]

[0245] [Table 5]

[0246]

[0247] In the foamed particles of Comparative Example 1, the foamed particles are not sufficiently fused with each other by in-mold foaming, and there is no molding condition in which a good molded body can be obtained. Further, in the foamed particles of Comparative Examples 2 and 3, if heated to such a degree that the foamed particles are sufficiently fused with each other by in-mold foaming, sink marks are generated in the molded body, and there is no molding condition in which a good molded body can be obtained.

[0248] On the other hand, according to the production method of the foamed particles of the present application, it is possible to obtain foamed particles of a polypropylene-based resin which are excellent in in-mold foaming property while using a recycled polypropylene-based resin containing a polypropylene-based resin derived from biomass. Specifically, according to the foamed particles of the present application, in-mold foaming at a low molding pressure is possible, and the range of molding pressure in which molding is possible is wide.

[0249] The present application described above includes the following technical ideas.

[0250] (1) A production method of foamed particles of a polypropylene-based resin, which is a production method of foamed particles of a polypropylene-based resin in which particles of a polypropylene-based resin are foamed to obtain foamed particles, in which

[0251] the resin particles are composed of a polypropylene-based resin mixture in which virgin polypropylene-based resin and recycled polypropylene-based resin are melt-kneaded,

[0252] the recycled polypropylene-based resin contains a polypropylene-based resin derived from biomass, the polypropylene-based resin derived from biomass containing a monomer component derived from biomass in a molecular chain,

[0253] the recycled polypropylene-based resin has a melt flow rate of 80 g / 10 minutes or less as measured at a temperature of 230°C under a load of 2.16 kg,

[0254] The weight ratio of the virgin polypropylene-based resin to the recycled polypropylene-based resin in the polypropylene-based resin mixture is virgin polypropylene-based resin:recycled polypropylene-based resin = 5:95 to 95:5,

[0255] The polypropylene-based resin mixture has a melt flow rate of 1 g / 10 min or more and 30 g / 10 min or less, measured at a temperature of 230°C under a load of 2.16 kg,

[0256] The bio-based carbon content of the resin particles is 5% or more, measured based on ASTM D 6866-21.

[0257] (2) The method for producing polypropylene-based resin foamed particles according to the above (1), wherein the ratio of the melt flow rate of the recycled polypropylene-based resin to the melt flow rate of the virgin polypropylene-based resin is 0.1 or more and 10 or less.

[0258] (3) The method for producing polypropylene-based resin foamed particles according to the above (1) or (2), wherein the melting point of the virgin polypropylene-based resin is 130°C or more and 165°C or less.

[0259] (4) The method for producing polypropylene-based resin foamed particles according to any one of the above (1) to (3), wherein the difference Tm r -Tm v of the melting point Tm r -Tm v of the recycled polypropylene-based resin to the melting point Tm

[0260] (5) The method for producing polypropylene-based resin foamed particles according to any one of the above (1) to (4), wherein the heat of fusion of the virgin polypropylene-based resin is 50 J / g or more and 120 J / g or less.

[0261] (6) The method for producing polypropylene-based resin foamed particles according to any one of the above (1) to (5), wherein the ratio of the heat of fusion of the virgin polypropylene-based resin to the heat of fusion of the recycled polypropylene-based resin is 0.5 or more and 1.5 or less.

[0262] (7) The method for producing polypropylene-based resin foamed particles according to any one of the above (1) to (6), wherein the bio-based carbon content of the recycled polypropylene-based resin is 10% or more, measured based on ASTM D 6866-21.

[0263] (8) The method for producing polypropylene-based resin expanded particles according to any one of (1) to (7), wherein the polypropylene-based resin expanded particles have a crystal structure in which an inherent peak and a high-temperature peak located on a high-temperature side than the inherent peak appear in a DSC curve obtained by heating the expanded particles from 23°C to 200°C at a heating rate of 10°C / minute using a heat flow type differential scanning calorimetry measurement,

[0264] the peak temperature of the inherent peak is 130°C or higher,

[0265]

[0266] (9) Polypropylene-based resin expanded particles, the expanded particles being composed of a polypropylene-based resin mixture obtained by melt-kneading virgin polypropylene-based resin and recycled polypropylene-based resin,

[0267] the polypropylene-based resin mixture contains biomass-derived polypropylene-based resin containing a biomass-derived monomer component in a molecular chain,

[0268] the melt flow rate of the polypropylene-based resin mixture determined under conditions of a temperature of 230°C and a load of 2.16 kg is 1 g / 10 minutes or higher and 30 g / 10 minutes or lower,

[0269] the bio-based carbon content of the expanded particles determined based on ASTM D 6866-21 is 5% or higher,

[0270] the expanded particles have a crystal structure in which an inherent peak and a high-temperature peak located on a high-temperature side than the inherent peak appear in a DSC curve obtained by heating the expanded particles from 23°C to 200°C at a heating rate of 10°C / minute using a heat flow type differential scanning calorimetry measurement,

[0271] the peak temperature of the inherent peak is 130°C or higher,

[0272] the difference between the peak temperature of the high-temperature peak and the peak temperature of the inherent peak is 20°C or higher and 30°C or lower.

[0273] (10) A polypropylene-based resin expanded particle molded body obtained by in-mold molding the polypropylene-based resin expanded particles according to (9).​

Claims

1. A method for producing polypropylene-based resin expanded particles, which is a method for producing polypropylene-based resin expanded particles by expanding polypropylene-based resin particles to obtain expanded particles, wherein the resin particles are composed of a polypropylene-based resin mixture obtained by melt-kneading virgin polypropylene-based resin and recycled polypropylene-based resin, the recycled polypropylene-based resin contains a biomass-derived polypropylene-based resin containing a biomass-derived monomer component in a molecular chain, a melt flow rate of the recycled polypropylene-based resin measured at a temperature of 230°C under a load of 2.16 kg is 80 g / 10 min or less, a weight ratio of the virgin polypropylene-based resin to the recycled polypropylene-based resin in the polypropylene-based resin mixture is virgin polypropylene-based resin:recycled polypropylene-based resin = 5:95 to 95:5, a melt flow rate of the polypropylene-based resin mixture measured at a temperature of 230°C under a load of 2.16 kg is 1 g / 10 min or more and 30 g / 10 min or less, a bio-based carbon content of the resin particles measured based on ASTM D 6866-21 is 5% or more. a ratio of the melt flow rate of the recycled polypropylene-based resin to the melt flow rate of the virgin polypropylene-based resin is 0.1 or more and 10 or less.

2. The method for producing polypropylene-based resin expanded particles according to claim 1, wherein, a melting point of the virgin polypropylene-based resin is 130°C or more and 165°C or less.

3. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a heat of fusion of the virgin polypropylene-based resin is 50 J / g or more and 120 J / g or less.

4. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, The melting point Tm of the recycled polypropylene resin r The melting point Tm of the virgin polypropylene resin v The difference Tm r -Tm v It is between -5℃ and 25℃.

5. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a ratio of the heat of fusion of the virgin polypropylene-based resin to the heat of fusion of the recycled polypropylene-based resin is 0.5 or more and 1.5 or less.

6. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a bio-based carbon content of the recycled polypropylene-based resin measured based on ASTM D 6866-21 is 10% or more.

7. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, the polypropylene-based resin expanded particles have a crystal structure in which an inherent peak and a high-temperature peak located on a high-temperature side of the inherent peak appear in a DSC curve obtained by heating the expanded particles from 23°C to 200°C at a heating rate of 10°C / min by heat flow type differential scanning calorimetry, 8. The method for producing polypropylene-based resin expanded particles according to claim 1 or 2, wherein, a peak top temperature of the inherent peak is 130°C or more, a difference between a peak top temperature of the high-temperature peak and the peak top temperature of the inherent peak is 20°C or more and 30°C or less. ​

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