Polypropylene resin foam particles and polypropylene resin foam particle molded body

Abstract

The base resin constituting the foam particles includes a polypropylene resin A containing a biomass-derived monomer component and a fossil fuel-derived polypropylene resin B. Resin B is a propylene random copolymer containing 0.3-3.5 mass% of a comonomer component derived from one or more monomers selected from the group consisting of ethylene and butene. The flexural modulus MB of resin B is 1000 MPa or more. The mass ratio of resin A and resin B in the base resin is resin A:resin B=3:97-90:10 (where the total of resin A and resin B is 100 mass%.). The closed cell rate of the foamed particles is 80% or more.

Description

Expanded polypropylene resin beads and expanded polypropylene resin beads molded product

[0001] The present invention relates to expanded polypropylene resin beads and expanded polypropylene resin bead molded articles.

[0002] Polypropylene resin foam beads are excellent in strength and shock-absorbing properties and are therefore used in a variety of applications, such as packaging materials, automotive components, and building components.

[0003] Polypropylene resin foamed bead molded articles are produced, for example, by a method called in-mold molding, in which expanded polypropylene resin beads are filled into a mold and then heated by supplying a heating medium such as steam into the mold. In the in-mold molding method, when a heating medium is supplied into the mold, the expanded beads undergo secondary expansion and their surfaces melt. This causes the expanded beads in the mold to fuse together, resulting in a molded article having a shape corresponding to the shape of the mold cavity. Since the molded article is prone to expansion due to secondary expansion immediately after molding, it is cooled in the mold with water or the like for a predetermined time and then released from the mold.

[0004] In recent years, there has been growing awareness of environmental impacts such as an increase in the concentration of carbon dioxide in the atmosphere and the consumption of fossil fuel resources, and in order to reduce the environmental impact, the production of expanded resin beads using raw materials derived from biomass has been considered. For example, in the case of expanded polyethylene resin beads, a technology has been proposed in which a plant-derived polyethylene resin with a high plant content is used (for example, Patent Document 1).

[0005] JP 2013-60514 A

[0006] On the other hand, with regard to expanded polypropylene resin beads, no technology has been proposed for expanded beads using biomass-derived polypropylene resins. Therefore, there is a need for technology proposals for expanded polypropylene resin beads and expanded polypropylene resin bead moldings that use biomass-derived raw materials and can contribute to reducing environmental loads.

[0007] However, expanded beads containing biomass-derived polypropylene resin as a raw material sometimes have poor moldability in molds, and molded articles may not be obtained depending on the molding conditions in molds. Even when molded articles are obtained, the physical properties of the molded articles expected from the physical properties of the expanded beads may not be exhibited. Therefore, improvements in these respects have been strongly desired.

[0008] The present invention has been made in view of the above background, and aims to provide expanded polypropylene-based resin beads that contain a biomass-derived polypropylene-based resin, contribute to reducing the environmental load, have excellent in-mold moldability, and can easily produce an expanded polypropylene-based resin bead molding having desired physical properties by in-mold molding, and an expanded polypropylene-based resin bead molding made from the expanded polypropylene-based resin beads.

[0009] One aspect of the present invention resides in the expanded polypropylene resin particles according to the following items [1] to [5].

[0010] [1] Expanded polypropylene resin beads, wherein a base resin constituting the expanded beads comprises a polypropylene resin A containing a biomass-derived monomer component and a fossil fuel-derived polypropylene resin B, wherein the polypropylene resin B is a propylene random copolymer containing 0.3 mass % to 3.5 mass % of a comonomer component derived from one or more monomers selected from the group consisting of ethylene and butene, and the flexural modulus M of the polypropylene resin B is B a mass ratio of the polypropylene-based resin A to the polypropylene-based resin B in the base resin is such that the polypropylene-based resin A:the polypropylene-based resin B=3:97 to 90:10 (wherein the total of the polypropylene-based resin A and the polypropylene-based resin B is 100 mass %), and the expanded polypropylene-based resin particles have a closed cell rate of 80% or more.

[0011] [2] The expanded polypropylene resin beads according to [1], wherein the expanded beads have a biomass content of 1% or more and 50% or less as measured by ASTM D6866-21. [3] The melting point Tm of the polypropylene resin BB The melting point Tm of the polypropylene resin A is 145°C or higher and 160°C or lower. A and the melting point Tm of the polypropylene resin B B The difference Tm A -Tm B The expanded polypropylene resin particles according to [1] or [2], wherein the temperature is 5°C or higher and 20°C or lower.

[0012] [4] The flexural modulus M of the polypropylene resin A A The flexural modulus M of the polypropylene resin B B The ratio M B / M A [5] The expanded polypropylene resin beads according to any one of [1] to [3], wherein the bulk density of the expanded beads is 10 kg / m or more and less than 1.0. 3 More than 200kg / m 3 The expanded polypropylene resin particles according to any one of [1] to [4] below:

[0013] Another aspect of the present invention is an expanded polypropylene resin bead molding according to the following [6] to [7]. [6] An expanded polypropylene resin bead molding obtained by molding the expanded polypropylene resin beads according to any one of [1] to [5] in a mold. [7] The expanded polypropylene resin bead molding according to [6], wherein the expanded bead molding has a closed cell rate of 80% or more.

[0014] According to the above aspect, it is possible to provide expanded polypropylene-based resin beads that contain a biomass-derived polypropylene-based resin, contribute to reducing environmental impact, have excellent in-mold moldability, and can easily produce an expanded polypropylene-based resin bead molding having desired physical properties by in-mold molding, and a expanded polypropylene-based resin bead molding made from the expanded polypropylene-based resin beads.

[0015] FIG. 1 is an explanatory diagram showing a method for calculating the heat of fusion of the high-temperature peak.

[0016] (Polypropylene-based resin expanded beads) The polypropylene-based resin expanded beads (hereinafter also referred to as "expanded beads") are composed of a base resin containing a polypropylene-based resin A containing a biomass-derived monomer component in the molecular chain, and a polypropylene-based resin B composed of a fossil fuel-derived monomer component. In this specification, the "monomer component" refers to a structural unit that constitutes a polymer chain. The polypropylene-based resin B is the specific propylene-based random copolymer and has a flexural modulus M within the specific range. B The mass ratio of polypropylene resin A to polypropylene resin B in the base resin is 3:97 to 90:10, where the total of polypropylene resin A and polypropylene resin B is taken as 100 mass %. The foamed beads have a closed cell rate of 80% or more.

[0017] The expanded beads having such a configuration contain a biomass-derived polypropylene-based resin, which can contribute to reducing environmental impact. Furthermore, the expanded beads are composed of a base resin containing the polypropylene-based resin A and the polypropylene-based resin B in the specified mass ratio, and therefore have excellent moldability in a mold. Therefore, by molding the expanded beads in a mold, a polypropylene-based resin expanded bead molded article (hereinafter also referred to as an "expanded bead molded article" or "molded article") having desired physical properties can be easily obtained. The detailed configuration of the expanded beads is described below.

[0018] [Base Resin] The base resin constituting the expanded beads contains a polypropylene-based resin A and a polypropylene-based resin B. In this specification, the polypropylene-based resin refers to a propylene homopolymer and a propylene-based copolymer having a propylene component (i.e., a monomer component derived from propylene) content of 50 mass% or more.

[0019] Examples of propylene homopolymers include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Examples of propylene copolymers include copolymers of propylene with ethylene and / or an α-olefin having 4 to 8 carbon atoms, such as propylene-ethylene copolymer, propylene-butene copolymer, and propylene-ethylene-butene copolymer, as well as propylene-acrylic acid copolymer and propylene-maleic anhydride copolymer. The mode of copolymerization in the propylene copolymer is not particularly limited. For example, the propylene copolymer may be a block copolymer, a random copolymer, or a graft copolymer.

[0020] The polypropylene resin may be crosslinked or non-crosslinked. From the viewpoint of contributing to reducing the environmental load, the polypropylene resin is preferably non-crosslinked. The detailed structures of the polypropylene resin A and the polypropylene resin B will be described later.

[0021] Mass ratio of polypropylene resin A to polypropylene resin B The mass ratio of polypropylene resin A to polypropylene resin B in the base resin is polypropylene resin A:polypropylene resin B = 3:97 to 90:10. That is, the proportion of polypropylene resin A relative to 100% by mass of the total of polypropylene resin A and polypropylene resin B is 3% by mass or more and 90% by mass or less, and the proportion of polypropylene resin B is 10% by mass or more and 97% by mass or less. By setting the mass ratio of polypropylene resin A to polypropylene resin B in the base resin within the above-mentioned specific range, the expanded beads can improve in-mold moldability and contribute to reducing environmental impact.

[0022] If the content of polypropylene-based resin A in the base resin is too low, the ratio of biomass-derived monomer components in the base resin will be low, which may make it difficult to contribute to reducing the environmental load. From the viewpoint of increasing the ratio of biomass-derived monomer components in the base resin and further enhancing the effect of reducing the environmental load, the ratio of polypropylene-based resin A to the total 100% by mass of polypropylene-based resin A and polypropylene-based resin B is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, particularly preferably 15% by mass or more, and most preferably 20% by mass or more.

[0023] If the content of polypropylene-based resin A in the base resin is too high, the secondary expandability of the expanded beads will be low, resulting in a decrease in in-mold moldability, and it may become difficult to obtain a molded article having physical properties corresponding to those of the expanded beads. From the viewpoint of more easily avoiding such problems, the proportion of polypropylene-based resin A relative to 100% by mass of the total of polypropylene-based resin A and polypropylene-based resin B is preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, particularly preferably 45% by mass or less, and most preferably 40% by mass or less.

[0024] When determining a preferred range of the mass ratio of polypropylene-based resin A to polypropylene-based resin B in the base resin, any combination of the above-mentioned upper and lower limits of the ratio of polypropylene-based resin A can be used. For example, a preferred range of the mass ratio of polypropylene-based resin A to polypropylene-based resin B in the base resin may be polypropylene-based resin A:polypropylene-based resin B = 5:95 to 70:30, 7:93 to 60:40, 10:90 to 50:50, 15:85 to 45:55, or 20:80 to 40:60.

[0025] Other Polymers The base resin may contain, as necessary, other polymers different from these polypropylene-based resins, in addition to the polypropylene-based resin A and the polypropylene-based resin B. Examples of polymers other than the polypropylene-based resin A and the polypropylene-based resin B that may be contained in the base resin include polypropylene-based resins that do not fall under either the polypropylene-based resin A or the polypropylene-based resin B, thermoplastic resins other than polypropylene-based resins, such as polyethylene-based resins, polystyrene-based resins, polyamide-based resins, and polyester-based resins, and elastomers such as olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers.

[0026] The base resin may contain one or more types of polymers other than the polypropylene-based resin A and the polypropylene-based resin B. These polymers may be contained in the polypropylene-based resin A or in the polypropylene-based resin B. Furthermore, in the process of producing the expanded beads, polymers other than the polypropylene-based resin A and the polypropylene-based resin B may be added to the base resin as needed.

[0027] The content of polymers other than polypropylene-based resin A and polypropylene-based resin B in the base resin is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, still more preferably 3% by mass or less, particularly preferably 1% by mass or less, and most preferably 0% by mass, i.e., the base resin contains only polypropylene-based resin A and polypropylene-based resin B as polymers, relative to 100% by mass of the base resin.

[0028] Additives The base resin may contain additives such as colorants, antioxidants, antistatic agents, surfactants, light stabilizers, UV absorbers, and flame retardants, as needed. The base resin may contain one or more of these additives. These additives may be contained in either the polypropylene-based resin A or the polypropylene-based resin B. Furthermore, these additives may be added to the base resin as needed during the production process of the expanded beads.

[0029] The amount of additives blended in the base resin is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of the base resin.

[0030] [Polypropylene Resin A] Polypropylene resin A contains a biomass-derived monomer component in its molecular chain. In this specification, the biomass-derived monomer component refers to a structural unit derived from a monomer produced from a biomass raw material. The biomass-derived monomer component is incorporated into the molecular chain of polypropylene resin A by polymerization of a monomer produced from a biomass raw material (hereinafter also referred to as a "biomass-derived monomer"). In this specification, a polypropylene resin containing a biomass-derived monomer component may also be referred to as a biomass-derived polypropylene resin.

[0031] The polypropylene resin A may be composed solely of biomass-derived monomer components, or may be composed of biomass-derived monomer components and fossil fuel-derived monomer components (i.e., structural units derived from monomers produced from fossil fuels). The monomer produced from a biomass raw material may be, for example, propylene, or a comonomer copolymerizable with propylene, such as ethylene or an α-olefin having 4 to 8 carbon atoms.

[0032] As used herein, biomass refers to renewable organic resources derived from living organisms (excluding organic resources derived from fossil fuels such as petroleum and coal). More specifically, biomass includes, for example, agricultural and livestock products, forestry products, and algae. Furthermore, biomass raw materials refer to substances produced from biomass that serve as raw materials for monomers. Examples of biomass raw materials that can be used include monosaccharides, polysaccharides, vegetable oils and animal fats obtained from biomass. The method for producing monomers from biomass raw materials is not particularly limited and can take various forms. Examples of methods for producing biomass-derived monomers include a method of dehydrating alcohol produced from biomass raw materials and a method of cracking naphtha produced from biomass raw materials.

[0033] From the viewpoints of non-competition with food and contribution to a recycling-oriented society through the use of by-products and waste biomass, it is preferable to use, as the biomass raw material, bionaphtha produced from waste cooking oil, black liquor, tall oil, palm oil mill effluent, oils and fats contained in microalgae, etc. From the same viewpoint, it is preferable to use, as the biomass-derived monomer, biomass-derived propylene obtained by decomposition of bionaphtha.

[0034] As the polypropylene-based resin A, a propylene homopolymer containing a biomass-derived monomer component or a propylene-based copolymer containing a biomass-derived monomer component can be used. The propylene-based copolymer used as the polypropylene-based resin A may be a random copolymer, a block copolymer, or a graft copolymer. The base resin may contain one of these polypropylene-based resins as the polypropylene-based resin A, or two or more of these polypropylene-based resins.

[0035] From the viewpoint of further improving the moldability of the expanded beads in a mold, the polypropylene-based resin A is preferably a propylene homopolymer or a propylene-ethylene block copolymer, and more preferably a propylene homopolymer. By using such a polypropylene-based resin A, it is possible to more easily obtain a good molded article having physical properties matching those of the expanded beads.

[0036] Commercially available polypropylene resins derived from biomass can be used as the biomass-derived polypropylene resin A. Specific examples include Lyondellbasell's HP456J, HP640J, and EP348U products.

[0037] The biomass degree (biobased carbon content) of polypropylene-based resin A measured according to ASTM D6866-21 is preferably 1% or more. By producing expanded beads using polypropylene-based resin A having a biomass degree of 1% or more, the proportion of biomass-derived monomer components contained in the expanded beads can be further increased, and the effect of reducing the environmental load can be further enhanced. From this perspective, the biomass degree of polypropylene-based resin A is more preferably 10% or more, even more preferably 20% or more, and particularly preferably 30% or more. The upper limit of the biomass degree of polypropylene-based resin A is, by definition, 100%. A more specific method for measuring the biomass degree will be described in detail in the Examples.

[0038] From the viewpoint of further improving the moldability of the expanded beads in a mold, the biomass content of the polypropylene resin A is preferably 80% or less, more preferably 50% or less, and even more preferably 45% or less.

[0039] When determining a preferred range of the biomass degree of the polypropylene-based resin A, it is possible to arbitrarily combine the above-mentioned upper and lower limits of the biomass degree of the polypropylene-based resin A. For example, a preferred range of the biomass degree of the polypropylene-based resin A may be 1% or more and 100% or less, 10% or more and 80% or less, 20% or more and 50% or less, or 30% or more and 45% or less.

[0040] Melting point Tm of polypropylene resin A A is preferably in the range of 155° C. or higher and 170° C. or lower, more preferably in the range of 158° C. or higher and 168° C. or lower, and even more preferably in the range of 160° C. or higher and 165° C. In this case, the moldability of the expanded beads in the mold and the rigidity of the molded article can be improved in a better balance.

[0041] Melting point Tm of polypropylene resin A A is determined based on JIS K7121-1987. Specifically, first, a test piece made of polypropylene-based resin A is prepared, and the test piece is conditioned based on "(2) Measurement of melting temperature after a certain heat treatment" in "3. Conditioning of test piece" in JIS K7121-1987. The heating rate and cooling rate in the conditioning are both 10°C / min. The conditioned test piece is heated from 30°C to 200°C at a heating rate of 10°C / min to obtain a DSC curve, and the apex temperature of the melting peak that appears on the DSC curve is determined as the melting point Tm of polypropylene-based resin A. A The flow rate of nitrogen gas under the measurement environment is 30 mL per minute. When multiple melting peaks appear on the DSC curve, the apex temperature of the melting peak with the largest area is determined as the melting point Tm of the polypropylene resin A. A Let's say.

[0042] Crystallization temperature Tc of polypropylene resin A A From the viewpoint of further shortening the water cooling time during molding of the expanded beads, the temperature is preferably 110°C or higher and 130°C or lower, more preferably 113°C or higher and 128°C or lower, and even more preferably 115°C or higher and 123°C or lower.

[0043] Crystallization temperature Tc of polypropylene resin A A means the temperature at the apex of the crystallization peak determined by heat flux differential scanning calorimetry based on JIS K7121:2012. When two or more crystallization peaks appear, the temperature at the apex of the crystallization peak with the largest area is referred to as the crystallization temperature Tc A Let's say.

[0044] Melt mass flow rate MFR of polypropylene resin A at a temperature of 230°C and a load of 2.16 kg A In this case, the moldability of the expanded beads in a mold can be further improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained. From this viewpoint, the melt mass-flow rate MFR of the polypropylene-based resin A is A The melt mass-flow rate MFR of the polypropylene resin A is more preferably 1 g / 10 min or more and 8 g / 10 min or less, and further preferably 2 g / 10 min or more and 5 g / 10 min or less. A is a value measured based on JIS K7210-1:2014 under conditions of a test temperature of 230°C and a load of 2.16 kg.

[0045] Heat of fusion ΔH of polypropylene resin A A is preferably 75 J / g or more and 130 J / g or less, more preferably 85 J / g or more and 120 J / g or less, and even more preferably 95 J / g or more and 110 J / g or less. In this case, the moldability of the expanded beads in the mold can be further improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained.

[0046] Heat of fusion ΔH of polypropylene resin A Acan be determined based on a DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K7122-1987. Specifically, first, polypropylene resin A is used as a test piece, and the test piece is conditioned based on "(2) Measurement of melting temperature after a certain heat treatment" in "3. Conditioning of test piece" in JIS K7122-1987. The heating rate and cooling rate in the conditioning are both 10°C / min, and the temperature range is 23°C to 200°C. The conditioned test piece is then heated again from 23°C to 200°C at a rate of 10°C / min to obtain a DSC curve (DSC curve at the time of second heating). The flow rate of nitrogen gas in the measurement environment is 30 mL per minute. On this DSC curve, a straight line is drawn connecting the point corresponding to 80°C and the high-temperature end point of the melting peak with the highest apex temperature. The heat of fusion ΔH of polypropylene resin A is A can be calculated based on the area of ​​the region surrounded by the straight line thus determined and the melting peak of the DSC curve.

[0047] Flexural modulus M of polypropylene resin A A is preferably 1000 MPa or more and 2000 MPa or less, more preferably 1200 MPa or more and 1800 MPa or less, and even more preferably 1300 MPa or more and 1700 MPa or less. In this case, the moldability of the expanded beads in the mold can be further improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained.

[0048] Flexural modulus M of polypropylene resin A A can be determined based on JIS K7171:2008.

[0049] In the case where two or more kinds of polypropylene resins A are used in the production of expanded beads, a test piece is prepared from a molten mixture of polypropylene resins A obtained by melt-mixing the plurality of kinds of polypropylene resins A in the same ratio as the compounding ratio in the production process of expanded beads, and then the biomass ratio, melting point, crystallization temperature, melt mass-flow rate, heat of fusion, and flexural modulus measured by the above-mentioned methods using this test piece are respectively determined as the biomass ratio, melting point Tm A , crystallization temperature Tc A , Melt Mass Flow Rate MFR A , heat of fusion ΔH A , and the bending modulus M A Let's say.

[0050] Polypropylene Resin B The base resin of the expanded beads contains a fossil fuel-derived polypropylene resin B. In this specification, a fossil fuel-derived polypropylene resin refers to a polypropylene resin obtained by polymerizing fossil fuel-derived monomers and containing only fossil fuel-derived monomer components in the molecular chain. In other words, the polypropylene resin B is composed only of fossil fuel-derived monomer components. Therefore, the biomass content (biobased carbon content) of the polypropylene resin B measured in accordance with ASTM D6866-21 is 0%.

[0051] In this specification, a fossil fuel-derived monomer component refers to a structural unit derived from a monomer produced from a fossil fuel. The monomer produced from a fossil fuel (hereinafter also referred to as a "fossil fuel-derived monomer") may be, for example, propylene, or a comonomer copolymerizable with propylene, such as ethylene or an α-olefin having from 4 to 8 carbon atoms. The method for producing a monomer from a fossil fuel is not particularly limited and can take various forms. An example of a method for producing a fossil fuel-derived monomer is a method of thermal cracking and fractional distillation of naphtha obtained in the process of petroleum refining.

[0052] The polypropylene-based resin B is a propylene-based random copolymer containing 0.3% by mass or more and 3.5% by mass or less of a comonomer component (hereinafter also referred to as a structural unit derived from a comonomer) derived from one or more monomers selected from the group consisting of ethylene and butene. When the polypropylene-based resin B contains both ethylene and butene, the total amount thereof is 0.3% by mass or more and 3.5% by mass or less. The flexural modulus M of the polypropylene-based resin B is B The base resin is a polypropylene-based resin B having a flexural modulus M within the above-mentioned specific range. B The expanded beads may contain one type of propylene-based copolymer or two or more types of propylene-based copolymers among the propylene-based copolymers containing the comonomer component, and may contain the specific polypropylene-based copolymer B. By using the specific polypropylene-based resin B together with the biomass-derived polypropylene-based resin A, the expanded beads contribute to reducing the environmental load, and also improve the secondary foaming property and in-mold moldability, making it easier to obtain a molded article having physical properties matching those of the expanded beads.

[0053] Flexural modulus M of polypropylene resin B B The flexural modulus M of the polypropylene resin B is 1000 MPa or more. B If the flexural modulus M of the polypropylene resin B is too low, the closed cell ratio of the expanded beads will decrease during molding in a mold, and it may not be possible to obtain a molded article having physical properties that match those of the expanded beads. B By making the flexural modulus M of the polypropylene resin B 1000 MPa or more, the above-mentioned problems can be easily avoided and a molded article having physical properties corresponding to those of the expanded beads can be easily obtained. B is preferably 1050 MPa or more, more preferably 1100 MPa or more, and even more preferably 1150 MPa or more.

[0054] On the other hand, from the viewpoint of further improving the moldability of the expanded beads in the mold, the flexural modulus M Bis preferably 1600 MPa or less, more preferably 1500 MPa or less, further preferably 1400 MPa or less, and particularly preferably 1300 MPa or less.

[0055] Flexural modulus M of polypropylene resin B B In determining the preferred range of the flexural modulus M of the polypropylene resin B, B For example, the flexural modulus M of the polypropylene resin B can be B The preferred range of the stress may be 1000 MPa or more and 1600 MPa or less, 1050 MPa or more and 1500 MPa or less, 1100 MPa or more and 1400 MPa or less, or 1150 MPa or more and 1300 MPa or less.

[0056] From the viewpoint of more easily avoiding a decrease in the closed cell ratio of the expanded beads during molding in a mold and more easily obtaining a molded article having physical properties corresponding to the physical properties of the expanded beads, it is preferable to set the flexural modulus M of the polypropylene-based resin A. A The bending modulus M of polypropylene resin B B The ratio M B / M A is preferably 0.70 or more and less than 1.0, more preferably 0.75 or more and less than 1.0, and even more preferably 0.75 or more and 0.90 or less. A and the flexural modulus M of polypropylene resin B B Difference with M A -M B is preferably 200 MPa or more and 500 MPa or less, and more preferably 250 MPa or more and 450 MPa or less.

[0057] Furthermore, polypropylene-based resin B is a propylene-based random copolymer containing 0.3% by mass or more and 3.5% by mass or less of the specific comonomer component. If polypropylene-based resin B does not contain the comonomer component, or if the content of the comonomer component is too low, the secondary foaming ability of the expanded beads may be insufficient, resulting in excessively poor in-mold moldability, and a satisfactory molded article may not be obtained. Even if a molded article is obtained, the closed-cell ratio of the molded article may be reduced, possibly due to excessive heat being applied to the expanded beads during in-mold molding, destroying the closed-cell structure, and a molded article having physical properties commensurate with those of the expanded beads may not be obtained. These problems can be easily avoided by setting the content of the comonomer component in polypropylene-based resin B to 0.3% by mass or more. To more reliably avoid the above-mentioned problems, polypropylene-based resin B preferably contains 0.5% by mass or more, more preferably 0.8% by mass or more, and even more preferably 1.0% by mass or more, of structural units derived from the specific comonomer.

[0058] On the other hand, by setting the content of the comonomer component in the polypropylene-based resin B to 3.5% by mass or less, sufficient strength is imparted to the cell membrane of the expanded beads, a decrease in the closed cell ratio of the expanded beads during in-mold molding can be easily avoided, and a molded article having physical properties commensurate with those of the expanded beads can be easily obtained. From the viewpoint of more reliably achieving this effect, the polypropylene-based resin B preferably contains 3.0% by mass or less of the comonomer component, more preferably 2.5% by mass or less, and even more preferably 1.8% by mass or less.

[0059] When determining a preferred range of the content of the comonomer component in the polypropylene-based resin B, any combination of the above-described upper and lower limits of the content of the comonomer component in the polypropylene-based resin B can be used. For example, a preferred range of the content of the comonomer component in the polypropylene-based resin B may be 0.5% by mass or more and 3.0% by mass or less, 0.8% by mass or more and 2.5% by mass or less, or 1.0% by mass or more and 1.8% by mass or less.

[0060] The content of the comonomer component in the polypropylene resin B can be determined, for example, based on an IR spectrum. The method for measuring the content of the comonomer component in the polypropylene resin B will be described in detail in the Examples.

[0061] Melting point Tm of polypropylene resin B B is 145°C or higher and 160°C or lower, and the melting point Tm A and the melting point Tm of polypropylene resin B B The difference Tm A -Tm B The melting point Tm of the polypropylene resin B is preferably 5° C. or higher and 20° C. or lower. In this case, the moldability of the expanded beads in the mold can be further improved. From this viewpoint, the melting point Tm B From the same viewpoint, the melting point Tm of the polypropylene resin A is more preferably 145°C or more and 155°C or less. A and the melting point Tm of polypropylene resin B B The difference Tm A -Tm B It is more preferable that the temperature is 8°C or higher and 15°C or lower.

[0062] Crystallization temperature Tc of polypropylene resin B B From the viewpoint of further improving the moldability of the expanded beads and maintaining the water cooling time within a favorable range, the temperature is preferably 100°C or higher and 118°C or lower, more preferably 102°C or higher and 115°C or lower, and even more preferably 105°C or higher and 112°C or lower.

[0063] Melt mass flow rate MFR of polypropylene resin B at a temperature of 230°C and a load of 2.16 kg B The viscosity is preferably 1 g / 10 min or more and 20 g / 10 min or less, more preferably 3 g / 10 min or more and 15 g / 10 min or less, even more preferably 4 g / 10 min or more and 12 g / 10 min or less, and particularly preferably 5 g / 10 min or more and 10 g / 10 min or less. In this case, the moldability of the expanded beads in the mold can be further improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained.

[0064] Heat of fusion ΔH of polypropylene resin B B is preferably 60 J / g or more and 110 J / g or less, more preferably 70 J / g or more and 105 J / g or less, even more preferably 80 J / g or more and 100 J / g or less, and particularly preferably 85 J / g or more and 98 J / g or less. In this case, the moldability of the expanded beads in the mold can be further improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained.

[0065] The biomass ratio and bending modulus M of the polypropylene resin B described above B , melting point Tm B , crystallization temperature Tc B , Melt Mass Flow Rate MFR B and heat of fusion ΔH B The measurement method of the biomass ratio and bending modulus M of the polypropylene resin A was the same as that of the polypropylene resin B except that the polypropylene resin A was replaced with the polypropylene resin B. A , melting point Tm A , crystallization temperature Tc A , Melt Mass Flow Rate MFR A and heat of fusion ΔH A The measurement method is the same as that of

[0066] In addition, when two or more kinds of polypropylene-based resins B are used in the production of expanded beads, a test piece made of a molten mixture of polypropylene-based resins B is prepared by melt-mixing the plural kinds of polypropylene-based resins B in the same ratio as the compounding ratio in the production process of expanded beads, and then the biomass ratio, melting point, crystallization temperature, melt mass-flow rate, heat of fusion, and flexural modulus measured by the above-mentioned method using this test piece are respectively determined as the biomass ratio, melting point Tm B , crystallization temperature Tc B , Melt Mass Flow Rate MFR B , heat of fusion ΔH B , and the bending modulus M B Let's say.

[0067] [Closed Cell Ratio of Expanded Beads] The closed cell ratio of the expanded beads is 80% or more. By setting the closed cell ratio of the expanded beads within the above-mentioned specific range, the moldability of the expanded beads in a mold can be improved, and the physical properties of the molded article obtained by molding the expanded beads in a mold can be improved. From the viewpoint of further improving the moldability of the expanded beads in a mold and the physical properties of the molded article, the closed cell ratio of the expanded beads is preferably 85% or more, more preferably 90% or more, and even more preferably 92% or more. The upper limit of the closed cell ratio of the expanded beads is not particularly limited, but may be, for example, 99%.

[0068] The closed cell ratio of the expanded beads is a value measured using an air comparison type hydrometer in accordance with procedure C of ASTM-D2856-70. The specific method for measuring the closed cell ratio of the expanded beads is as follows: Bulk volume after conditioning: about 20 cm 3 The expanded beads are used as a measurement sample, and the apparent volume Va of the measurement sample is measured from the rise in the liquid level when the measurement sample is submerged in a measuring cylinder containing ethanol. After measuring the apparent volume Va, the measurement sample is thoroughly dried, and then the true volume Vx of the measurement sample is measured using an air comparison hydrometer ("Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd.) in accordance with Procedure C described in ASTM-D2856-70. These volume values ​​Va and Vx are then used to calculate the closed cell ratio (unit: %) of the measurement sample based on the following formula (1). The above operation is performed five times using different measurement samples, and the arithmetic mean value (N=5) of the closed cell ratios of the five measurement samples is taken as the closed cell ratio (unit: %) of the expanded beads. Closed cell ratio = (Vx-W / ρ) x 100 / (Va-W / ρ)...(1)

[0069] The symbols in the above formula (1) have the following meanings: Vx: the true volume of the measurement sample measured by the above method, i.e., the sum of the volume of the resin constituting the expanded beads and the total volume of the cells in the closed cell portion within the expanded beads (unit: cm 3Va: Apparent volume of the measurement sample (unit: cm) measured from the rise in the liquid level when the measurement sample is submerged in a measuring cylinder containing ethanol. 3 ) W: Mass of the measurement sample (unit: g) ρ: Density of the resin constituting the expanded beads (unit: g / cm 3 )

[0070] [Biomass Degree of Expanded Beads] The biomass degree of the expanded beads, as measured by ASTM D6866-21, is preferably 1% to 50%, more preferably 2% to 40%, even more preferably 3% to 35%, and particularly preferably 5% to 30%. By setting the biomass degree of the expanded beads within the above-mentioned specific range, the effect of reducing the environmental load can be further enhanced, and the effect of improving the in-mold moldability of the expanded beads can be more reliably obtained.

[0071] The biomass content of the expanded beads was measured using the expanded beads as a measurement sample, using the radiocarbon 14 It is possible to determine the biomass degree by measuring the concentration of C. When the biomass degree of the biomass-derived polypropylene resin A used to produce the expanded beads and the content of the biomass-derived polypropylene resin A in the expanded beads are known, the biomass degree of the expanded beads can also be calculated using these values.

[0072] [Bulk density of expanded beads] The bulk density of the expanded beads is 10 kg / m 3 More than 200kg / m 3 It is preferable that the viscosity is 15 kg / m or less. 3 More than 150kg / m 3 More preferably, it is 20 kg / m or less. 3 More than 120kg / m 3 More preferably, it is 25 kg / m or less. 3 More than 100kg / m 3 It is particularly preferable that the saturation is 30 kg / m or less. 3 More than 80kg / m 3By setting the bulk density of the expanded beads within the above-mentioned specific range, a molded article that is lightweight and has good physical properties can be more easily obtained.

[0073] The method for calculating the bulk density of expanded beads is as follows. First, the expanded beads are left to stand for 24 hours or more in an environment of 50% relative humidity, 23°C temperature, and 1 atm atmospheric pressure to condition the expanded beads. The condition-conditioned expanded beads are filled into a measuring cylinder, and the bottom of the measuring cylinder is lightly tapped against the floor several times to stabilize the filling height of the expanded beads in the measuring cylinder. The bulk volume (unit: L) of the expanded beads is read from the graduations on the measuring cylinder. Then, the mass (unit: g) of the expanded beads in the measuring cylinder is divided by the aforementioned bulk volume, and the bulk density (unit: kg / m) of the expanded beads is calculated by converting the units. 3 ) can be obtained.

[0074] [Fusing Layer] The expanded beads have a foam layer composed of a base resin containing the polypropylene-based resin A and the polypropylene-based resin B. The expanded beads may have a single-layer structure consisting of only the foam layer, or a multilayer structure comprising the foam layer and a fusing layer covering the foam layer. The fusing layer is provided to enhance the fusing between the expanded beads during in-mold molding. The fusing layer may be present on the entire surface of the expanded beads or on a portion of the surface. The fusing layer may be in a foamed or non-foamed state, but is preferably in a substantially non-foamed state. The aforementioned "non-foamed state" includes a state in which the fusing layer is not foamed and does not contain bubbles, and a state in which the bubbles have disappeared after foaming, meaning that there is almost no bubble structure in the fusing layer. When the expanded beads have a foam layer and a fusing layer, the foam layer covered by the fusing layer is sometimes referred to as the "foam core layer."

[0075] The method for producing expanded beads having a fusion layer is not particularly limited, and examples thereof include a method of foaming resin beads having a non-foamed core layer and a fusion layer covering the core layer, a method of foaming a non-foamed core layer to obtain an expanded core layer, and then attaching a fusion layer to the surface of the expanded core layer, etc. When foamed beads are obtained by foaming resin beads having a fusion layer on their surface, it is preferable to use a method in which, when producing the resin beads, a resin melt for forming the core layer and a resin melt for forming the fusion layer are co-extruded using an extrusion device capable of co-extrusion, thereby laminating the fusion layer on the surface of the core layer.

[0076] When the expanded beads have a fusion layer, the proportion of the fusion layer in the expanded beads is preferably approximately 0.5% by mass to 20% by mass, more preferably 1% by mass to 12% by mass.

[0077] Examples of the base resin constituting the fusion layer include a crystalline polyolefin resin having a melting point lower than that of the base resin constituting the foamed core layer, and an amorphous polyolefin resin having a softening point lower than that of the base resin constituting the foamed core layer. The base resin constituting the fusion layer is preferably a polypropylene resin and / or a polyethylene resin.

[0078] When the adhesive layer is made of a crystalline polyolefin resin having a melting point, the melting point of the crystalline polyolefin resin is preferably 110°C or higher and 150°C or lower, more preferably 120°C or higher and 145°C or lower, and even more preferably 125°C or higher and 142°C or lower.

[0079] Furthermore, the difference between the melting point of the base resin constituting the foamed core layer and the melting point of the crystalline polyolefin resin constituting the fusion layer (i.e., the value obtained by subtracting the melting point of the crystalline polyolefin resin constituting the fusion layer from the melting point of the base resin constituting the foamed core layer) is preferably approximately 1° C. or more and 40° C. or less, more preferably 2° C. or more and 35° C. or less, and even more preferably 5° C. or more and 30° C. or less. In this case, the in-mold moldability of the expanded beads can be improved even when the molding pressure is relatively low.

[0080] [Melting Point of Expanded Beads] The melting point of the expanded beads is preferably 135°C or higher and 170°C or lower, more preferably 140°C or higher and 168°C or lower, even more preferably 145°C or higher and 165°C or lower, and particularly preferably 150°C or higher and 162°C or lower. In this case, the moldability of the expanded beads in the mold can be more easily improved, and a molded article having physical properties corresponding to those of the expanded beads can be more easily obtained. The melting point of the expanded beads is measured by the melting point Tm of the polypropylene resin A described above, except that the expanded beads or the base resin constituting the expanded beads are used instead of the polypropylene resin A. A The measurement method is the same as that of

[0081] [High-Temperature Peak, Heat of Fusion of the High-Temperature Peak, and Total Heat of Fusion of Expanded Beads] The expanded beads preferably have a crystalline structure in which a DSC curve obtained when heated from 23°C to 200°C at a heating rate of 10°C / min exhibits a melting peak due to the melting of crystals inherent to the resin component contained in the expanded beads and one or more melting peaks located at a higher temperature than the melting peak. Expanded beads with such a crystalline structure exhibit excellent moldability in a mold. Furthermore, by molding such expanded beads in a mold, molded articles with excellent compression properties can be more easily obtained. Hereinafter, the melting peak due to the melting of crystals inherent to the resin component appearing in the DSC curve is referred to as the "resin-specific peak," and the melting peak appearing at a higher temperature than the resin-specific peak is referred to as the "high-temperature peak." The resin-specific peak appears due to the melting of crystals normally possessed by the resin component contained in the expanded beads. On the other hand, the high-temperature peak is presumed to appear due to the melting of secondary crystals formed in the resin component during the manufacturing process of the expanded beads. In other words, when a high-temperature peak appears in a DSC curve, it is presumed that secondary crystals are formed in the resin component.

[0082] Whether or not the expanded beads have the above-mentioned crystalline structure can be determined based on a DSC curve obtained by performing differential scanning calorimetry (DSC) under the above-mentioned conditions in accordance with JIS K7122-1987. Note that the flow rate of nitrogen gas in the measurement environment is 30 mL per minute. Furthermore, when performing DSC, 1 to 3 mg of the expanded beads can be used as a sample.

[0083] Specifically, the DSC curve obtained when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min (i.e., the first heating) as described above shows both a peak characteristic of the resin component contained in the expanded beads and a high-temperature peak. In contrast, the DSC curve obtained when the expanded beads are cooled from 200°C to 23°C at a cooling rate of 10°C / min after the first heating and then heated again from 23°C to 200°C at a heating rate of 10°C / min (i.e., the second heating) shows only a peak characteristic of the resin component contained in the expanded beads. Therefore, the resin peak and the high-temperature peak can be distinguished by comparing the DSC curves obtained during the first heating and the second heating.

[0084] From the viewpoint of further improving the in-mold moldability of the expanded beads and the compression properties of the molded article, the apex temperature of the high-temperature peak of the expanded beads is preferably from 160° C. to 175° C., more preferably from 162° C. to 172° C., and even more preferably from 165° C. to 170° C. From the same viewpoint, the heat of fusion of the high-temperature peak is preferably from 10 J / g to 50 J / g, more preferably from 12 J / g to 40 J / g, even more preferably from 15 J / g to 35 J / g, and particularly preferably from 20 J / g to 30 J / g.

[0085] The total heat of fusion of the expanded beads is preferably 60 J / g or more and 120 J / g or less, more preferably 70 J / g or more and 110 J / g or less, even more preferably 75 J / g or more and 105 J / g or less, and particularly preferably 85 J / g or more and 100 J / g or less. In this case, the moldability of the expanded beads in a mold can be more easily improved. Furthermore, by molding such expanded beads in a mold, a molded product having excellent compression properties can be more easily obtained.

[0086] From the viewpoint of further improving the moldability of the expanded beads in the mold and the compression properties of the molded body, the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads is preferably 0.15 or more and 0.35 or less, and more preferably 0.20 or more and 0.30 or less.

[0087] The methods for measuring the apex temperature of the high-temperature peak, the heat of fusion of the high-temperature peak, and the total heat of fusion are as follows. First, 1 to 3 mg of expanded beads are used as a sample, and a DSC curve is obtained by performing differential scanning calorimetry under conditions of heating from 23°C to 200°C at a heating rate of 10°C / min. An example of a DSC curve is shown in Figure 1. When the expanded beads have a high-temperature peak, the DSC curve will show a resin-specific peak ΔH1 and a high-temperature peak ΔH2, which has a peak higher than the peak of the resin-specific peak ΔH1, as shown in Figure 1. The temperature corresponding to the peak of this high-temperature peak ΔH2 is defined as the apex temperature of the high-temperature peak.

[0088] Next, a straight line L1 is drawn connecting point α corresponding to 80° C. on the DSC curve and point β corresponding to the melting end temperature T of the expanded beads. The melting end temperature T is the high-temperature end point of the high-temperature peak ΔH2, i.e., the intersection point of the high-temperature peak ΔH2 and the baseline on the higher temperature side of the high-temperature peak ΔH2 on the DSC curve.

[0089] After drawing the line L1, a line L2 is drawn that passes through the maximum point γ between the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2 and is parallel to the vertical axis of the graph. This line L2 separates the resin intrinsic peak ΔH1 from the high-temperature peak ΔH2. The heat of fusion of the high-temperature peak ΔH2 can be calculated based on the area of ​​the portion of the DSC curve that constitutes the high-temperature peak ΔH2 and the area surrounded by the lines L1 and L2. The total heat of fusion of the expanded beads can be calculated based on the area of ​​the portion of the DSC curve that constitutes the resin intrinsic peak ΔH1, the portion of the high-temperature peak ΔH2, and the line L1. In other words, the total heat of fusion of the expanded beads is the sum of the heat of fusion of the resin intrinsic peak ΔH1 and the heat of fusion of the high-temperature peak ΔH2.

[0090] (Method for producing expanded beads) The method for producing the expanded beads is not particularly limited, and for example, a conventional method for producing expanded polypropylene resin beads can be used as the method for producing the expanded beads. More specifically, examples of the method for producing the expanded beads include a method of producing resin beads composed of the base resin and then expanding the resin beads using a foaming agent, and a method of extruding a molten base resin while supplying a foaming agent to foam it, and then cutting the extrudate to a desired size.

[0091] The method for producing resin particles is not particularly limited. For example, when producing resin particles by the strand cutting method, the polypropylene resin A, the polypropylene resin B, and additives used as needed are fed into an extruder, and the resin raw materials are heated and kneaded in the extruder to obtain a molten mixture. This molten mixture is extruded in the form of a strand through a small hole in a die attached downstream of the extruder. This strand-shaped extrudate is taken up and cut to a desired length to obtain resin particles.

[0092] When foaming resin particles, for example, a method called a "direct foaming method" can be used, in which resin particles containing a foaming agent dispersed in an aqueous medium in a container are released together with the aqueous medium into an atmosphere whose pressure is lower than the pressure inside the container, or a method called an "impregnation foaming method" can be used, in which resin particles are impregnated with a foaming agent in a gas phase and then heated to foam the resin particles.

[0093] In the direct foaming method, resin particles are first dispersed in an aqueous medium in a container. The aqueous medium may be, for example, water. If necessary, a dispersant or a dispersing aid may be added to disperse the resin particles in the aqueous medium in the container.

[0094] As the dispersant, for example, inorganic fine particles such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, mica, etc. can be used. These inorganic fine particles may be used alone, or two or more types of inorganic fine particles may be used in combination. As the dispersing aid, for example, inorganic salts such as aluminum sulfate, and anionic surfactants such as sodium alkylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium alkanesulfonate can be used. These dispersing aids may be used alone, or two or more types of dispersing aids may be used in combination.

[0095] Next, a blowing agent is supplied into the container, and the pressure in the container is increased to impregnate the resin particles with the blowing agent. This allows resin particles containing the blowing agent to be obtained. At this time, the resin particles in the container are heated together with the aqueous medium to promote the impregnation of the resin particles with the blowing agent.

[0096] Examples of the blowing agent used in the foaming step include inorganic physical blowing agents such as carbon dioxide, air, nitrogen, helium, and argon; and organic physical blowing agents such as hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane; and halogenated hydrocarbons such as ethyl chloride, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, and trans-1-chloro-3,3,3-trifluoropropene. From the viewpoints of environmental load and ease of handling, carbon dioxide is preferably used as the blowing agent. The amount of the blowing agent added is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the resin particles.

[0097] The pressure in the container immediately before foaming is preferably 0.5 MPa (G) or more in gauge pressure. On the other hand, the pressure in the container is preferably 4.0 MPa (G) or less in gauge pressure. If the pressure is within the above range, expanded beads can be produced safely without risk of damage to the container or explosion.

[0098] After the resin particles are impregnated with the blowing agent, the contents of the container are released into an atmosphere with a lower pressure than the container, which causes the resin particles to expand and form a cellular structure, which is then cooled by the outside air (i.e., the atmosphere) to stabilize the cellular structure, thereby obtaining expanded particles.

[0099] In the above-described production method, a step of adjusting the crystalline structure of the resin component contained in the resin particles may be carried out between dispersing the resin particles in an aqueous medium and expanding the resin particles. By adjusting the crystalline structure of the resin component before expanding the resin particles, expanded beads having excellent in-mold moldability and excellent compressive strength can be easily obtained.

[0100] The method for adjusting the crystalline structure of the resin component is, for example, as follows. First, a holding step is performed in which the temperature of the resin particles is maintained within a temperature range of (the melting point of the base resin - 20°C) or more and (the melting end temperature of the base resin) or less for a sufficient time, preferably about 10 to 60 minutes. Thereafter, the temperature inside the pressure vessel is adjusted to a temperature of (the melting point of the base resin - 15°C) or more and less than (the melting end temperature of the base resin). Then, if necessary, a two-stage holding step is performed in which the temperature is maintained for an additional 10 to 60 minutes. By expanding the resin particles that have undergone this holding step, expanded beads having a crystalline structure that exhibits the aforementioned high-temperature peak in the DSC curve can be easily obtained.

[0101] In the above-mentioned production method, expanded beads may be obtained by preparing resin beads that have been subjected to the holding step in advance, impregnating the resin beads with a blowing agent, and expanding the resin beads. From the viewpoint of increasing productivity of expanded beads, it is preferable to carry out the above-mentioned holding step by heating resin beads dispersed in an aqueous medium in a container in the presence of a blowing agent, and then releasing the contents of the sealed container from the container into an atmosphere with a pressure lower than the pressure inside the container to expand the resin beads, thereby obtaining expanded beads having a crystalline structure that exhibits the above-mentioned high-temperature peak.

[0102] The reason why the in-mold moldability and compression properties of the expanded beads can be improved by heating and expanding under the above-mentioned conditions is thought to be the formation of secondary crystals of the polypropylene-based resin in the base resin constituting the expanded beads, etc. Whether or not secondary crystals of the polypropylene-based resin have formed in the base resin can be determined by the presence or absence of a high-temperature peak in the DSC curve.

[0103] In the manufacturing method, the resin particles may be expanded in one stage as described above, or in two or more stages. When expanding the resin particles in two stages, the resin particles are expanded by a direct expansion method or the like in the first expansion stage to obtain first-stage expanded particles. In the second expansion stage, the first-stage expanded particles may be pressurized with air or the like to increase the pressure (internal pressure) within the cells of the first-stage expanded particles, and then the first-stage expanded particles may be heated with steam or the like to further expand them. Expanding the resin particles in multiple stages in this manner makes it easy to obtain expanded beads with a higher expansion ratio (i.e., a lower bulk density).

[0104] (Polypropylene-based resin expanded bead molded article) After the expanded beads are filled into a mold, a heated medium such as steam is supplied into the mold to perform in-mold molding, thereby obtaining a molded article. The base resin of the expanded beads constituting the molded article contains a polypropylene-based resin A containing a biomass-derived monomer component and a polypropylene-based resin B derived from a fossil fuel. The polypropylene-based resin B is composed of the specific random copolymer and has a flexural modulus M within the specific range. B Therefore, the molded article contributes to reducing the environmental load and can easily exhibit good physical properties that match those of the expanded beads. Furthermore, the molded article can be suitably used for various applications such as packaging materials, automotive components, and building materials, just like conventional expanded bead molded articles made only of polypropylene-based resins derived from fossil fuels.

[0105] [Density of Molded Product] The density of the molded product is 10 kg / m 3 More than 200kg / m 3It is preferable that the viscosity is 15 kg / m or less. 3 More than 150kg / m 3 More preferably, it is 20 kg / m or less. 3 More than 120kg / m 3 More preferably, it is 30 kg / m or less. 3 More than 90kg / m 3 It is particularly preferable that the density is equal to or less than 1000 MPa. In this case, the balance between the light weight and physical properties of the molded body is better. The density of the molded body is calculated by dividing the mass (unit: g) of the molded body by the volume (unit: L) determined from the outer dimensions of the molded body, and converting the result into units.

[0106] [Closed Cell Ratio of Molded Article] The closed cell ratio of the molded article is preferably 75% or more, more preferably 78% or more, even more preferably 80% or more, and particularly preferably 85% or more, which allows the molded article to more easily exhibit desired physical properties.

[0107] The closed cell content of the molded body is measured in accordance with ASTM2865-70 Procedure C. Specifically, first, a test piece measuring 25 mm in length, 25 mm in width, and 30 mm in height is cut out from the center of the molded body, and the geometric volume Va (unit: cm 3 ), that is, the product of the vertical dimension (unit: cm), horizontal dimension (unit: cm), and height dimension (unit: cm) is calculated. Next, in accordance with procedure C described in ASTM-D2856-70, the true volume value Vx of the test specimen is measured using an air comparison hydrometer (specifically, a "Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd.). The true volume value Vx obtained by the air comparison hydrometer is the sum (unit: cm) of the volume of the resin constituting the measurement sample and the total volume of the air bubbles in the closed cell portion of the measurement sample. 3 )

[0108] The closed cell rate (unit: %) of the test specimen is calculated by multiplying the mass W (unit: g) of the test specimen by the density ρ (unit: g / cm) of the resin that constitutes the foamed particles. 3), and the geometric volume Va of the test specimen obtained by the above-mentioned method and the true volume Vx of the test specimen, the closed cell ratio is expressed by the following formula (2): Closed cell ratio=(Vx−W / ρ)×100 / (Va−W / ρ) (2)

[0109] The above procedure is carried out for five test specimens, and the closed cell ratio of each test specimen is calculated. The arithmetic mean value of the closed cell ratios of these five test specimens is then taken as the closed cell ratio of the molded article.

[0110] [Difference between Closed Cell Ratio of Expanded Beads and Closed Cell Ratio of Molded Article] The difference between the closed cell ratio of the expanded beads and the closed cell ratio of a molded article obtained by molding the expanded beads in a mold [closed cell ratio of expanded beads - closed cell ratio of molded article] is preferably 20% or less, more preferably 15% or less, even more preferably 12% or less, particularly preferably 10% or less, and most preferably less than 10%. In this case, the molded article can more easily exhibit physical properties that match those of the expanded beads. The lower limit of this difference [closed cell ratio of expanded beads - closed cell ratio of molded article] is not particularly limited, but may be, for example, 0% or more, 2% or more, or 3% or more.

[0111] Conventionally, expanded beads containing a biomass-derived polypropylene resin have had the problem that the closed cell structure is easily destroyed during molding in a mold, even when the closed cell content of the expanded beads is high, and the closed cell content of the molded article is easily reduced. As a result, the molded article sometimes fails to fully exhibit physical properties commensurate with those of the expanded beads. On the other hand, the base resin of the expanded beads is made of a random copolymer containing the specific comonomer component in the specific amount, and the flexural modulus M is within the specific range. B The expanded beads are made of a fossil fuel-derived polypropylene resin B having the above-mentioned properties. The fossil fuel-derived polypropylene resin B is contained in a proportion relative to the biomass-derived polypropylene resin A that falls within the above-mentioned specific range. By performing in-mold molding using expanded beads having such a configuration, a decrease in the closed cell rate during in-mold molding can be easily avoided. Furthermore, the molded article obtained by in-mold molding can fully exhibit physical properties that match the physical properties of the expanded beads.

[0112] Examples of the expanded beads are described below.

[0113] (Polypropylene Resin A) Table 1 shows the properties of two types of biomass-derived polypropylene resin A used in the production of expanded beads. The polypropylene resins A used in this example (Table 1, PP-A1 and PP-A2) are both propylene homopolymers containing a biomass-derived monomer component. Specifically, PP-A1 is "HP456J" manufactured by Lyondellbasell, and PP-A2 is "HP640J" manufactured by Lyondellbasell. In Table 1, the propylene homopolymer is referred to as "h-PP."

[0114]

[0115] The physical properties of the polypropylene resin A shown in Table 1 were measured as follows.

[0116] [Biomass Degree] The biomass degree of polypropylene-based resin A was measured in accordance with ASTM D6866-21. More specifically, polypropylene-based resin A was first combusted to generate combustion gas containing carbon dioxide (CO2). This combustion gas was introduced into a vacuum line, and the carbon dioxide (CO2) was purified in the vacuum line. Graphite (C) was produced by reducing this carbon dioxide using hydrogen. Iron was used as a catalyst for the reduction of carbon dioxide.

[0117] Next, graphite, background samples, and standard samples were measured using an accelerator mass spectrometer (AMS), and the 14 the number of C atoms, 12 When the number of C atoms is used as a reference 13 The concentration of C atoms ( 13 C / 12 C) and 12 When the number of C atoms is used as a reference 14 The concentration of C atoms ( 14 C / 12 C) was calculated. The isotope ratio was measured using a tandem accelerator based on NEC Corporation. 14A dedicated C-AMS device was used. For the measurement, graphite was packed into a cathode with an inner diameter of 1 mm using a hand press, and then it was fitted into a wheel. 14 The instrument was installed in a dedicated C-AMS instrument. Oxalic acid (HOxII) provided by the National Institute of Standards (NIST) was used as the standard sample.

[0118] Based on these measurement results, the modern 14 in graphite versus concentration of C atoms 14 The deviation in the concentration of C atoms is expressed in parts per thousand (‰). 14 C and the modern obtained based on the measurement results of the standard sample 13 in graphite versus concentration of C atoms 13 The deviation in the concentration of C atoms is expressed in parts per thousand (‰). 13 C was calculated. 13 In order to correct for the isotope effect due to C, the δ 14 C, δ 13 The value of C was used for correction. 14 The value of C (Δ 14 The percent modern carbon (pMC) value was obtained based on the results of the HPLC method. Then, the biomass degree was calculated by performing atmospheric correction on this pMC value.

[0119] The atmospheric correction factor used for atmospheric correction was the atmospheric correction factor for 2019-2021 described in ASTM D6866-21 (100.0 pMC). More specifically, the atmospheric correction factor for the year in which the polypropylene resin was produced was used to determine the biomass content.

[0120] [Melting point Tm A Melting point Tm of polypropylene resin A based on JIS K7121-1987 Awas measured. Specifically, first, the condition of a test piece made of polypropylene-based resin A was adjusted based on "(2) Measurement of melting temperature after a certain heat treatment" in "3. Conditioning of test piece" described in JIS K7121-1987. In the condition adjustment, the heating rate and cooling rate were set to 10°C / min. The test piece after the condition adjustment was heated from 23°C to 200°C at a heating rate of 10°C / min to obtain a DSC curve. The flow rate of nitrogen gas in the measurement environment was set to 30 mL per minute. The apex temperature of the melting peak that appeared on the DSC curve was determined as the melting point Tm of polypropylene-based resin A. A The measurement device used was a heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Inc., model number: DSC7020). When multiple melting peaks appear in the DSC curve, the apex temperature of the melting peak with the largest area was determined as the melting point Tm of the polypropylene-based resin A. A It was decided.

[0121] [Crystallization temperature Tc A ] The crystallization temperature Tc of polypropylene resin A based on JIS K7121-1987 A was measured. Specifically, a heat flux differential scanning calorimeter (manufactured by SII Nanotechnology Inc., model number: DSC7020) was used to obtain a DSC curve by heating a test piece made of polypropylene resin A from 23°C to 200°C at a heating rate of 10°C / min, and then cooling from 200°C to 30°C at a cooling rate of 10°C / min. The peak temperature of the crystallization peak in this DSC curve was taken as the crystallization temperature. The flow rate of nitrogen gas in the measurement environment was 30 mL per minute. When multiple crystallization peaks appeared in the DSC curve, the peak temperature of the crystallization peak with the largest area was taken as the crystallization temperature Tc of polypropylene resin A. A It was decided.

[0122] [Heat of fusion ΔH A From the DSC curve obtained by differential scanning calorimetry in accordance with JIS K7122-1987, the heat of fusion ΔH of polypropylene resin A was determined. Awas determined. Specifically, first, polypropylene resin A was used as a test specimen, and the condition of the test specimen was adjusted based on "(2) Measurement of melting temperature after a certain heat treatment" in "3. Conditioning of test specimen" in JIS K7122-1987. In the conditioning, the heating rate and cooling rate were 10°C / min. Thereafter, the conditioned test specimen was again heated from 23°C to 200°C at a rate of 10°C / min to obtain a DSC curve (DSC curve at the time of the second heating). The flow rate of nitrogen gas in the measurement environment was 30 mL per minute.

[0123] On the DSC curve thus obtained, a straight line was drawn connecting the point corresponding to 80°C on the DSC curve and the high-temperature end point of the melting peak with the highest peak temperature. Then, the heat of fusion ΔH of polypropylene resin A was calculated based on the area enclosed by the straight line thus determined and the melting peak of the DSC curve. A was calculated.

[0124] [Melt mass flow rate MFR A ] Melt mass flow rate (MFR) of polypropylene resin A under conditions of a temperature of 230°C and a load of 2.16 kg in accordance with JIS K7210-1:2014 A was measured.

[0125] [Flexural modulus M A Polypropylene resin A was heat-pressed at 180°C to prepare a sheet having a thickness of 4 mm, and a test piece having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm was cut out from this sheet. The flexural modulus of the test piece determined in accordance with JIS K7171:2008 was used as the flexural modulus M of polypropylene resin A. A The radius R1 of the indenter and the radius R2 of the support base were both 5 mm, the distance between the supports was 64 mm, and the test speed was 2 mm / min.

[0126] (Polypropylene Resin B) Table 2 shows the properties of four types of fossil fuel-derived polypropylene resins B used in the production of expanded beads. Of the four types of polypropylene resins B used in this example, PP-B1 to PP-B3 are all propylene-ethylene random copolymers made from fossil fuel-derived monomer components. Of the four types of polypropylene resins B, PP-B4 is a propylene homopolymer made from fossil fuel-derived monomer components. In Table 2, the random copolymers are referred to as "r-PP" and the propylene homopolymers are referred to as "h-PP."

[0127]

[0128] The methods for measuring the physical properties shown in Table 2 are the same as the methods for measuring the corresponding physical properties of the polypropylene resin A. The "ethylene component content" and "butene component content" of the polypropylene resin B in Table 2 are calculated as follows.

[0129] The contents of ethylene and butene in polypropylene resin B were determined by a known method based on IR spectroscopy. Specifically, the contents were determined by the method described in Polymer Analysis Handbook (edited by the Polymer Analysis Research Forum of the Japan Society for Analytical Chemistry, published in January 1995, published by Kinokuniya Shoten, page numbers and item names: 615-616 "II.2.3 2.3.4 Propylene / ethylene copolymer", 618-619 "II.2.3 2.3.5 Propylene / butene copolymer"), that is, by a method of quantifying the absorbance of ethylene and butene based on the relationship between the value corrected by a predetermined coefficient and the thickness of a film-like test piece, etc.

[0130] More specifically, first, polypropylene resin B was heat-pressed in an environment of 180°C to form a film, and a plurality of test pieces with different thicknesses of 0.1 to 0.3 mm were prepared. Next, the IR spectrum of each test piece was measured to find that the 722 cm -1 and 733 cm -1 The absorbance (A 722 , A 733 ) and butene-derived 766 cm -1The absorbance (A 766 ) was read. Next, for each test piece, the ethylene component content (unit: mass%) in polypropylene-based resin B was calculated using the following formulas (3) to (5). The ethylene component contents obtained for each test piece were arithmetically averaged to obtain the ethylene component content (unit: mass%) in polypropylene-based resin B.

[0131] (K' 733 ) c = 1 / 0.96 {(K' 733 ) a -0.268 (K' 722 ) a} ... (3) (K' 722 ) c = 1 / 0.96 {(K' 722 ) a -0.150 (K' 733 ) a} (4) Ethylene component content = 0.575 {(K' 722 ) c + (K' 733 ) c} ... (5)

[0132] However, K' in equations (3) to (5) a is the apparent absorption coefficient (K') at each wave number a = A / ρt), and K' c is the corrected extinction coefficient, A is the absorbance, and ρ is the density of the resin (unit: g / cm 3 ) and t is the thickness of the film-like test piece (unit: cm). The above formulas (3) to (5) can be applied to random copolymers.

[0133] Further, for each test piece, the butene component content (unit: mass%) in the polypropylene-based resin was calculated using the following formula (6). The arithmetic mean of the butene component contents obtained for each test piece was taken as the butene component content (unit: mass%) in the polypropylene-based resin. Butene component content = 12.3 (A 766 / L) (6) where A in formula (6) is absorbance, and L is the thickness (unit: mm) of the film-like test piece.

[0134] Next, the structure and manufacturing method of the expanded beads of this example will be described.

[0135] Example 1 PP-A1 as polypropylene resin A, PP-B1 as polypropylene resin B, and a cell control agent were charged into an extruder, and a molten mixture of these resins was formed in the extruder. The mass ratios of PP-A1 and PP-B1 were as shown in Table 3. Zinc borate was used as the cell control agent. The amount of zinc borate added was 0.1% by mass relative to 100% by mass of the total of PP-A1 and PP-B1. In Tables 3 and 4, polypropylene resin A is abbreviated as "PP(A)" and polypropylene resin B is abbreviated as "PP(B)."

[0136] The molten mixture was then extruded in the form of a strand through a small hole in a die provided downstream of the extruder. The strand-like extrudate was taken up, cooled, and then cut into an appropriate length using a pelletizer to obtain resin particles. The average mass of each resin particle was approximately 1.0 mg.

[0137] The resin particles thus obtained were expanded by a direct foaming method. Specifically, 1 kg of resin particles was first placed in a 5 L container together with 3 L of water as an aqueous medium. Next, 0.3 parts by mass of dispersant and 0.004 parts by mass of dispersion aid were added to the container per 100 parts by mass of resin particles, and the resin particles were dispersed in the aqueous medium. Kaolin was used as the dispersant. Sodium dodecylbenzenesulfonate was also used as the dispersion aid. The amount of dispersion aid added above refers to the amount of active ingredient in the dispersion aid.

[0138] The container was then heated at a rate of 2°C / min while stirring, and the temperature inside the container was raised to the foaming temperature shown in Table 3. After the temperature inside the container reached the foaming temperature, carbon dioxide was supplied as a foaming agent into the container, and the pressure inside the container was raised to the foaming pressure shown in Table 3. This temperature and pressure were maintained for 15 minutes, thereby impregnating the resin particles with the foaming agent and adjusting the crystalline structure of the base resin that constitutes the resin particles. The container was then opened, and the contents were released into an atmospheric pressure atmosphere, thereby foaming the resin particles. In this way, the expanded beads of Example 1 were obtained.

[0139] (Examples 2 to 3) The expanded beads of Examples 2 to 3 have the same structure as the expanded beads of Example 1, except that the mass ratio between PP-A1 and PP-B1 was changed as shown in Table 3. The manufacturing method of the expanded beads of Examples 2 to 3 is generally the same as the manufacturing method of the expanded beads of Example 1, except that the mass ratio between PP-A1 and PP-B1 was changed as shown in Table 3.

[0140] Example 4 The expanded beads of Example 4 have the same structure as the expanded beads of Example 1, except that PP-B2 was used instead of PP-B1 as the polypropylene-based resin B. The manufacturing method of the expanded beads of Example 4 is generally the same as the manufacturing method of the expanded beads of Example 1, except that the polypropylene-based resin B was changed as described above.

[0141] Example 5 The expanded beads of Example 5 have the same structure as the expanded beads of Example 1, except that PP-A2 was used instead of PP-A1 as the polypropylene-based resin A. The manufacturing method of the expanded beads of Example 5 is generally the same as the manufacturing method of the expanded beads of Example 1, except that the polypropylene-based resin A was changed as described above.

[0142] (Comparative Example 1) The expanded beads of Comparative Example 1 have the same structure as the expanded beads of Example 1, except that they do not contain polypropylene-based resin B and are composed of polypropylene-based resin A, as shown in Table 4. The manufacturing method of the expanded beads of Comparative Example 1 is generally the same as the manufacturing method of the expanded beads of Example 1, except that polypropylene-based resin B is not blended.

[0143] (Comparative Examples 2 to 3) As shown in Table 4, the expanded beads of Comparative Examples 2 to 3 have the same structure as the expanded beads of Example 1, except that PP-B3 or PP-B4 was used instead of PP-B1 as the polypropylene-based resin B. The manufacturing method of the expanded beads of Comparative Examples 2 to 3 is generally the same as the manufacturing method of the expanded beads of Example 1, except that the polypropylene-based resin B was changed as described above.

[0144] (Reference Example 1) The expanded beads of Reference Example 1 have the same structure as the expanded beads of Comparative Example 2, except that they do not contain polypropylene-based resin A and are composed of PP-B3 as polypropylene-based resin B. The manufacturing method of the expanded beads of Reference Example 1 is generally the same as the manufacturing method of Comparative Example 2, except that polypropylene-based resin A was not blended and the expansion temperature was set to 151.0°C.

[0145] Tables 3 and 4 show the physical properties of the expanded beads of Examples 1 to 5 and Comparative Examples 1 to 3 and the molded articles obtained using these expanded beads. The methods for measuring and evaluating the physical properties shown in Tables 3 and 4 are as follows.

[0146] (Biomass Degree of Expanded Beads) The biomass degree of expanded beads was calculated from the biomass degree of polypropylene resin A used to produce the expanded beads and the content of polypropylene resin A in the expanded beads.

[0147] (Bulk Density of Expanded Beads) The expanded beads were left to stand for one day in an environment of 50% relative humidity, 23°C temperature, and 1 atm atmospheric pressure to condition the expanded beads. The expanded beads after the condition conditioning were filled into a measuring cylinder, and the bottom of the measuring cylinder was lightly tapped against the floor several times to stabilize the filling height of the expanded beads in the measuring cylinder. Next, the bulk volume (unit: L) of the expanded beads was read from the scale of the measuring cylinder. Thereafter, the mass (unit: g) of the expanded beads in the measuring cylinder was divided by the aforementioned bulk volume and converted into a unit to determine the bulk density (unit: kg / m) of the expanded beads. 3 ) was calculated.

[0148] (Closed Cell Ratio of Expanded Beads) Based on ASTM-D2856-70 Procedure C, the closed cell ratio of expanded beads was measured using an air comparison type hydrometer. Specifically, first, the expanded beads were left to stand for one day in an environment of 50% relative humidity, 23°C temperature, and 1 atm atmospheric pressure to condition the expanded beads. After the condition condition, the bulk volume was about 20 cm. 3 The expanded beads were used as a measurement sample, and the apparent volume Va of the measurement sample was measured from the rise in the liquid level when the measurement sample was submerged in a measuring cylinder containing ethanol. After measuring the apparent volume Va, the measurement sample was thoroughly dried, and then the true volume Vx of the measurement sample was measured using an air comparison hydrometer ("Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd.) in accordance with Procedure C described in ASTM-D2856-70. These volume values ​​Va and Vx were then used to calculate the closed cell ratio (unit: %) of the measurement sample according to the following formula (1). This procedure was repeated five times using different measurement samples, and the arithmetic mean value (N = 5) of the closed cell ratios of the five measurement samples was taken as the closed cell ratio (unit: %) of the expanded beads. Closed cell ratio = (Vx-W / ρ) x 100 / (Va-W / ρ)...(1)

[0149] The symbols in the above formula (1) have the following meanings: Vx: the true volume of the measurement sample measured by the above method, i.e., the sum of the volume of the resin constituting the expanded beads and the total volume of the cells in the closed cell portion within the expanded beads (unit: cm 3 Va: Apparent volume of the measurement sample (unit: cm) measured from the rise in the liquid level when the measurement sample is submerged in a measuring cylinder containing ethanol. 3 ) W: Mass of the measurement sample (unit: g) ρ: Density of the resin constituting the expanded beads (unit: g / cm 3 )

[0150] (Melting Point of Expanded Beads) The melting point of the expanded beads was measured in the same manner as the melting point Tm of the polypropylene-based resin A, except that expanded beads were used instead of the polypropylene-based resin A. A The measurement method is the same as that of

[0151] (Apex temperature of high-temperature peak, heat of fusion of high-temperature peak, and total heat of fusion of expanded beads) A DSC curve was obtained by performing differential scanning calorimetry using approximately 3 mg of expanded beads as a sample, heating from 23°C to 200°C at a heating rate of 10°C / min. The flow rate of nitrogen gas in the measurement environment was 30 mL / min. Based on this DSC curve, the apex temperature of the high-temperature peak ΔH2 was determined.

[0152] Next, a line L1 (see FIG. 1 ) was drawn connecting point α corresponding to 80° C. on the DSC curve and point β corresponding to the melting end temperature T of the expanded beads. Furthermore, a line L2 was drawn parallel to the vertical axis of the graph, passing through the maximum point γ existing between the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2, and the resin intrinsic peak ΔH1 and the high-temperature peak ΔH2 were separated by the line L2.

[0153] The heat of fusion of the high-temperature peak ΔH2 of the sample was calculated based on the area of ​​the portion of the DSC curve surrounded by the line L1 and the line L2 and the portion of the DSC curve consisting of the resin-specific peak ΔH1, the portion of the high-temperature peak ΔH2, and the line L1. The total heat of fusion of the sample was calculated based on the area of ​​the portion of the DSC curve surrounded by the line L1 and the portion of the DSC curve consisting of the resin-specific peak ΔH1, the

[0154] The above procedure was carried out three times using different samples, and the arithmetic mean value of the heat of fusion of the high-temperature peak ΔH2 obtained in each measurement was taken as the heat of fusion of the high-temperature peak ΔH2 of the expanded beads. In addition, the arithmetic mean value of the total heat of fusion obtained in each measurement was taken as the total heat of fusion of the expanded beads.

[0155] (Moldable range) In evaluating the moldable range, molded bodies were produced by in-mold molding while changing the molding pressure during main heating from 0.26 MPa (G) to 0.44 MPa (G) in increments of 0.02 MPa, and the lower limit molding pressure and moldable range were determined based on the surface properties, fusion properties, and recovery properties of the obtained molded bodies.

[0156] The manufacturing method of the molded articles using the expanded beads of Example 1, Examples 3 to 5, and Comparative Examples 1 and 3 is as follows. First, the expanded beads that had been thoroughly dried were filled into a mold by the cracking filling method. In this example, a mold was used having a cavity capable of molding a flat-plate-shaped molded article having a length of 250 mm, a width of 200 mm, and a thickness of 20 mm. In the cracking filling method, the expanded beads were filled into the mold with a cracking gap of 4 mm in the thickness direction of the molded article (i.e., a cracking amount of 20%), and then the mold was completely closed to mechanically compress the expanded beads in the mold.

[0157] Next, steam was supplied into the mold to perform in-mold molding. In the in-mold molding, first, steam was supplied into the mold for 5 seconds with the drain valve of the mold open to perform preheating. Next, the drain valve was closed, and steam was supplied from one side of the mold until a pressure 0.08 MPa (G) lower than the molding pressure during main heating was reached, performing a first one-way heating. Next, steam was supplied from the other side of the mold until a pressure 0.04 MPa (G) lower than the molding pressure during main heating was reached, performing a second one-way heating. Thereafter, steam was supplied from both sides of the mold until the molding pressure during main heating was reached, performing main heating. After main heating was completed, the pressure inside the mold was released, and the molded body in the mold was cooled with water until the surface pressure generated on the inner surface of the mold due to the foaming force of the molded body reached 0.04 MPa (G).

[0158] Thereafter, the molded body was removed from the mold and allowed to stand in an oven at 80° C. for 12 hours for a curing step. After the curing step, the molded body was allowed to stand for 24 hours under conditions of a relative humidity of 50%, 23° C., and 1 atm, for conditioning the condition of the molded body.

[0159] The manufacturing methods for molded articles using the expanded beads of Example 2 and Comparative Example 2 were the same as those for molded articles using the expanded beads of Example 1, except that the expanded beads were impregnated with air before being filled into the mold, and an internal pressure of 0.12 MPa (G) was applied to the air bubbles.

[0160] The surface roughness, fusion property, and recovery property of the molded body thus obtained were evaluated. The range of molding pressures that passed all items according to the evaluation criteria described below (i.e., the molding pressures at which acceptable products could be obtained) was defined as the moldable range, and the lowest molding pressure within the moldable range was defined as the lower limit molding pressure. If an acceptable product could not be obtained at any molding pressure, it was judged to be "unmoldable." The "Water cooling time at lower limit molding pressure" column in Tables 3 and 4 lists the time required from the start of cooling until the surface pressure reached 0.04 MPa (G) when in-mold molding was performed at the lower limit molding pressure. The evaluation methods for surface roughness, fusion property, and recovery property in the moldable range evaluation are as follows.

[0161] [Surface Properties (Secondary Foaming)] A 100 mm x 100 mm square was drawn in the center of one skin surface in the thickness direction of the molded article, i.e., the surface that was in contact with the inner surface of the mold during in-mold molding, and a diagonal line was then drawn from one corner of the square. The number of voids present on the diagonal line, i.e., gaps formed between the expanded beads, and gaps measuring 1 mm x 1 mm or more were counted. A sample with two or fewer voids was judged to be acceptable, and a sample with three or more voids was judged to be unacceptable.

[0162] [Fusing Property] A test piece measuring 100 mm in length, 100 mm in width, and 20 mm in thickness was cut from the center of the molded article. A 5 mm deep incision was made on one surface of the test piece in the thickness direction, roughly dividing the test piece into two equal parts, and the test piece was then bent to break along the incision. One hundred or more randomly selected expanded beads exposed on the fracture surface were visually observed to determine whether they had broken internally (i.e., expanded beads with material fracture) or at the interface between the expanded beads. The ratio of the number of expanded beads with internal fracture to the total number of observed expanded beads was calculated as a percentage (i.e., material fracture rate), and this value was taken as the fusion rate. A fusion rate of 80% or more was judged to be acceptable, and a fusion rate of less than 80% was judged to be unacceptable.

[0163] [Recovery] In a plan view of the molded body from the thickness direction, the thickness of the corners of the molded body at four positions 10 mm inward from each vertex of a surface bounded by a 250 mm vertical side and a 200 mm horizontal side toward the center of the surface was measured, and the thickness of the molded body at the center of the surface was also measured. Next, the ratio (unit: %) of the thickness of the center to the thickness of the thickest corner among the four corners was calculated. If the thickness ratio obtained in this way was 90% or more, it was judged to be acceptable, and if it was less than 90%, it was judged to be unacceptable.

[0164] (Density of Molded Article) In the above-described method for producing a molded article, a molded article was obtained by molding in a mold at a lower limit molding pressure. The mass (unit: g) of this molded article was divided by the volume (unit: L) calculated from the outer dimensions of the molded article, and the density (unit: kg / m) of the molded article was calculated by converting the unit. 3 ) was calculated.

[0165] (Closed Cell Content of Molded Article) The closed cell content of the molded article was measured in accordance with ASTM2865-70 Procedure C. Specifically, first, a molded article was obtained by molding in a mold at the lower limit molding pressure in the above-mentioned molded article manufacturing method. Two small pieces measuring 25 mm length x 25 mm width x 15 mm height were cut out from the center of this molded article so as not to include the skin surface, and these small pieces were stacked to prepare a test specimen measuring 25 mm length x 25 mm width x 30 mm height. The geometric volume Va (unit: cm) of the test specimen was 3 ), that is, the product of the vertical dimension (unit: cm), horizontal dimension (unit: cm), and height dimension (unit: cm) was calculated. Next, in accordance with procedure C described in ASTM-D2856-70, the true volume value Vx of the test specimen was measured using an air comparison hydrometer (specifically, a "Beckman Model 1000 Air Comparison Pycnometer" manufactured by Tokyo Science Co., Ltd.). The true volume value Vx obtained by the air comparison hydrometer is the sum (unit: cm) of the volume of the resin constituting the measurement sample and the total volume of the air bubbles in the closed cell portion of the measurement sample. 3 )

[0166] The mass W (unit: g) of the specimen obtained above and the density ρ (unit: g / cm3 ), and the geometric volume Va of the specimen and the true volume Vx of the specimen obtained by the above-mentioned method were used to calculate the closed cell ratio (unit: %) of the specimen according to the following formula (2): Closed cell ratio = (Vx - W / ρ) × 100 / (Va - W / ρ) (2)

[0167] The above procedure was carried out for five test specimens, and the closed cell ratio of each test specimen was calculated. The arithmetic mean value of the closed cell ratios of these five test specimens was taken as the closed cell ratio of the molded article.

[0168] (Compression stress at 50% strain) In the method for producing a molded body described above, a molded body was obtained by performing in-mold molding at the lower limit molding pressure. Two rectangular parallelepiped pieces measuring 50 mm in length, 50 mm in width, and 12.5 mm in thickness were taken from the center of this molded body so as not to include the skin surface, and these pieces were stacked to prepare a test piece measuring 50 mm in length, 50 mm in width, and 25 mm in thickness. Then, a compression test was performed on the above test piece at a compression rate of 10 mm / min based on the method specified in JIS K7220:2006, and a stress-strain curve was obtained. The compression test was performed in a laboratory at 23 ° C. The compressive stress at 50% strain in this stress-strain curve was taken as the compressive stress at 50% strain of the molded body.

[0169]

[0170]

[0171] As shown in Table 3, the base resin constituting the expanded beads of Examples 1 to 5 contains the biomass-derived polypropylene resin A and the fossil fuel-derived polypropylene resin B in the specific mass ratios described above. The polypropylene resin B is the specific random copolymer described above, and the flexural modulus M of the polypropylene resin B is B is within the specified range. Therefore, the expanded beads of Examples 1 to 5 have excellent moldability in a mold, the decrease in the closed cell ratio of the expanded beads during mold molding is small, and molded articles having the physical properties expected from the physical properties of the expanded beads can be easily obtained. Furthermore, since these expanded beads contain a biomass-derived monomer component in the base resin, they can contribute to reducing the environmental load.

[0172] In contrast, as shown in Table 4, the base resin constituting the expanded beads of Comparative Example 1 did not contain polypropylene-based resin B. Therefore, the expanded beads of Comparative Example 1 had excessively low secondary expandability and poor in-mold moldability, and a molded article with acceptable surface properties could not be obtained at any molding pressure. When the expanded beads of Comparative Example 1 were used for in-mold molding at a molding pressure of 0.45 MPa (G), a molded article with acceptable fusion properties and recovery properties but unacceptable surface properties was obtained. The closed cell content of this molded article was 66%.

[0173] The polypropylene resin B used in the expanded beads of Comparative Example 2 has a flexural modulus M lower than the specific range. B Therefore, when the expanded beads of Comparative Example 2 are molded in a mold, the closed cell ratio of the molded product is lower than that of the expanded beads, making it difficult to obtain a molded product having physical properties that match those of the expanded beads. The molded product of Comparative Example 2 had a lower compressive stress than the molded products of the Examples.

[0174] The expanded beads of Comparative Example 3 used a polypropylene-based resin B different from the specific random copolymer. Therefore, the expanded beads of Comparative Example 3 had poor moldability in a mold, and no good molded articles were obtained at any molding pressure.

[0175] The expanded beads of Reference Example 1, which did not contain biomass-derived polypropylene resin A and were composed only of fossil fuel-derived polypropylene resin B, had a closed cell ratio of 95%. Furthermore, the lower limit molding pressure of the expanded beads of Reference Example 1 was evaluated by the method described above, and a molded body was produced by in-mold molding at the lower limit molding pressure. The closed cell ratio of the molded body was 88%. From these results, it can be seen that, for the expanded beads composed of fossil fuel-derived polypropylene resin B, the closed cell ratio of the expanded beads and the closed cell ratio of the molded body were relatively close values, and there was almost no decrease in the closed cell ratio during in-mold molding. On the other hand, for the expanded beads of Comparative Example 1, which did not contain fossil fuel-derived polypropylene resin B and was composed only of biomass-derived polypropylene resin A, as described above, the closed cell ratio of the expanded beads (specifically, 91%) and the closed cell ratio of the molded body (specifically, 66%) were significantly different, and the closed cell ratio significantly decreased during in-mold molding.

[0176] Therefore, from a comparison between Reference Example 1 and Comparative Example 1, it can be said that the decrease in the closed cell ratio of the expanded beads during in-mold molding is a problem specific to expanded beads containing biomass-derived polypropylene-based resin A. As shown in the examples, the base resin constituting the expanded beads of Examples 1 to 5 contains, in addition to biomass-derived polypropylene-based resin A, fossil fuel-derived polypropylene-based resin B having the specific composition, and therefore the above problem is solved.

[0177] The above describes the embodiments of the expanded polypropylene-based resin beads and expanded polypropylene-based resin bead moldings according to the present invention based on the examples. However, the specific embodiments of the expanded polypropylene-based resin beads and expanded polypropylene-based resin bead moldings according to the present invention are not limited to those in the examples, and the configurations can be changed as appropriate within the scope of the present invention.

Claims

1. Expanded polypropylene resin beads, wherein the base resin constituting the expanded beads comprises a polypropylene resin A containing a biomass-derived monomer component and a fossil fuel-derived polypropylene resin B, wherein the polypropylene resin B is a propylene random copolymer containing 0.3% by mass or more and 3.5% by mass or less of a comonomer component derived from one or more monomers selected from the group consisting of ethylene and butene, and the flexural modulus M of the polypropylene resin B is B a mass ratio of the polypropylene-based resin A to the polypropylene-based resin B in the base resin is such that the polypropylene-based resin A:the polypropylene-based resin B=3:97 to 90:10 (wherein the total of the polypropylene-based resin A and the polypropylene-based resin B is 100 mass %), and the expanded polypropylene-based resin particles have a closed cell rate of 80% or more.

2. The expanded polypropylene resin beads according to claim 1, wherein the expanded beads have a biomass content of 1% or more and 50% or less as measured by ASTM D6866-21.

3. Melting point Tm of the polypropylene resin B B The melting point Tm of the polypropylene resin A is 145°C or higher and 160°C or lower. A and the melting point Tm of the polypropylene resin B B Difference Tm A -Tm B The expanded polypropylene resin particles according to claim 1 or 2, wherein the temperature is 5°C or higher and 20°C or lower.

4. The flexural modulus M of the polypropylene resin A A The flexural modulus M of the polypropylene resin B B The ratio M B / M A The expanded polypropylene resin particles according to claim 1 or 2, wherein the ρ is 0.75 or more and less than 1.

0.

5. The bulk density of the expanded particles is 10 kg / m 3 More than 200kg / m 3 The expanded polypropylene resin particles according to claim 1 or 2, wherein:

6. A polypropylene resin expanded bead molding obtained by molding the polypropylene resin expanded bead according to claim 1 or 2 in a mold.

7. The expanded polypropylene resin bead molding according to claim 6, wherein the closed cell rate of said molding is 80% or more.

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