Method for producing polyethylene-based resin foam particle, and polyethylene-based resin foam particle

Abstract

To provide a method for producing foam particles which can produce a polyethylene-based resin foam particle molding that is excellent in in-mold moldability, especially, has a small shrinkage factor, while enhancing a biomass degree.SOLUTION: A method for producing polyethylene-based resin particles (Expanded beads) is a method for foaming polyethylene-based resin particles and producing polyethylene-based resin foam particles, wherein the polyethylene-based resin particles are composed of a mixed resin of linear low density polyethylene and branched low density polyethylene, which is obtained by kneading the linear low density polyethylene and the branched low density polyethylene, a biomass degree of the branched low density polyethylene measured by ASTM D 6866 is 30% or more, heat of fusion of the branched low density polyethylene is 95 J / g or more, when the total of the linear low density polyethylene and the branched low density polyethylene is 100 mass%, a blending amount of the branched low density polyethylene in the mixed resin is 5 mass% or more and less than 40 mass%, heat of fusion of the polyethylene-based resin particles is 90 J / g or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing expanded polyethylene resin beads and expanded polyethylene resin beads. [Background technology]

[0002] Expanded polyethylene resin bead moldings, obtained by molding expanded polyethylene resin beads in a mold, are widely used as shock absorbers, heat insulators, and various packaging materials, including packaging and cushioning for electrical and electronic parts, packaging and cushioning for automotive parts, and a variety of other packaging materials for everything from precision parts to food. In recent years, due to environmental considerations, attempts have been made to obtain expanded polyethylene resin particles by using polyethylene resins produced from ethylene derived from natural materials such as plants as a starting material, instead of ethylene derived from fossil fuels. For example, Patent Document 1 discloses a method for producing expanded polyethylene resin beads, which is intended to obtain expanded polyethylene resin beads having a high biomass content, by expanding resin beads whose base resin is a mixed resin containing two specific types of linear low-density polyethylene. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-161416 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, when expanded beads are produced using naturally derived polyethylene resins made from natural materials such as plants as starting materials, the moldability of the expanded beads tends to be lower and the shrinkage rate of the resulting molded body tends to be higher than when expanded beads are produced using petroleum-derived polyethylene resins. An object of the present invention is to provide a method for producing expanded beads, which can produce expanded polyethylene resin bead moldings that have excellent in-mold moldability and particularly a small shrinkage rate while increasing the biomass content. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a method for producing expanded beads by expanding resin beads composed of a mixed resin of a specific linear low-density polyethylene and a specific branched low-density polyethylene. That is, one aspect of the present invention is the method for producing expanded beads described in the following [1] to [7], and the expanded beads described in [8] to

[10] . [1] A method for producing expanded polyethylene resin beads by expanding polyethylene resin particles, wherein the polyethylene resin particles are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene obtained by kneading linear low-density polyethylene and branched low-density polyethylene, wherein the branched low-density polyethylene has a biomass content of 30% or more as measured according to ASTM D6866, a heat of fusion of 95 J / g or more, an amount of the branched low-density polyethylene in the mixed resin of 5% by mass or more and less than 40% by mass, where the total of the linear low-density polyethylene and the branched low-density polyethylene is 100% by mass, and the total heat of fusion of the polyethylene resin particles is 90 J / g or more. [2] The heat of fusion of the linear low-density polyethylene (ΔH LL ) and the heat of fusion of the branched low-density polyethylene (ΔH LD ) and the difference (ΔH LL -ΔH LD ) is 0 J / g or more and 30 J / g or less. [3] The melting point of the polyethylene resin particles is 115°C or more and 130°C or less, and the melting point (Tm LL ) and the melting point (Tm LD) and the difference (Tm LL -Tm LD ) is 5°C or more and 15°C or less. [4] The method for producing expanded polyethylene resin beads according to any one of [1] to [3], wherein the branched low-density polyethylene has a melt flow rate of 0.1 g / 10 min or more and 3 g / 10 min or less, measured under conditions of a temperature of 190°C and a load of 2.16 kg. [5] The method for producing expanded polyethylene resin beads according to any one of [1] to [4], wherein the linear low-density polyethylene is a copolymer containing a component derived from octene. [6] The method for producing expanded polyethylene resin particles according to any one of [1] to [5], wherein the polyethylene resin particles have a biomass ratio of 5% or more as measured by ASTM D6866. [7] The method for producing expanded polyethylene resin beads according to any one of [1] to [6], wherein the mixed resin has a flexural modulus of 200 MPa or more. [8] Expanded polyethylene resin beads, the expanded beads being composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, the mixed resin having a flexural modulus of 200 MPa or more, a biomass content of the expanded beads measured according to ASTM D6866 of 5% or more, and a total heat of fusion of the expanded beads of 90 J / g or more. [9] Expanded polyethylene resin particles according to [8], wherein the amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass.

[10] The polyethylene resin expanded particles according to claim [8] or [9], wherein the melting point of the polyethylene resin expanded particles is 115°C or higher and 130°C or lower. [Effects of the Invention]

[0006] According to the present invention, there is provided a method for producing expanded beads, which can produce expanded polyethylene resin bead moldings that have excellent in-mold moldability and particularly a small shrinkage rate while increasing the biomass content. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Method of manufacturing polyethylene resin foam beads] The method for producing expanded polyethylene resin beads of the present invention is a method for producing expanded polyethylene resin beads by expanding polyethylene resin beads, comprising the steps of: the polyethylene-based resin particles are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene obtained by kneading linear low-density polyethylene and branched low-density polyethylene, the branched low-density polyethylene has a biomass content of 30% or more as measured by ASTM D6866; the branched low-density polyethylene has a heat of fusion of 95 J / g or more, the blending amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass, The method for producing expanded polyethylene resin beads has a total heat of fusion of the polyethylene resin beads of 90 J / g or more. In this specification, "expanded polyethylene resin particles" will also be referred to simply as "expanded particles," and "polyethylene resin particles" will also be referred to simply as "resin particles."

[0008] <Polyethylene resin particles> The method for producing expanded polyethylene resin beads of the present invention involves expanding resin beads composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene obtained by kneading the linear low-density polyethylene and the branched low-density polyethylene. The mixed resin of linear low-density polyethylene and branched low-density polyethylene is described below.

[0009] <Mixed resin> The polyethylene resin particles used in the method for producing expanded polyethylene resin particles of the present invention are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene obtained by kneading linear low-density polyethylene and branched low-density polyethylene.

[0010] The mixed resin is obtained by kneading a linear low-density polyethylene and a branched low-density polyethylene. Furthermore, the branched low-density polyethylene has a biomass degree of 30% or more as measured in accordance with ASTM D6866, a heat of fusion of 95 J / g or more, and an amount of the branched low-density polyethylene in the mixed resin of 5% by mass or more and less than 40% by mass, where the total of the linear low-density polyethylene and the branched low-density polyethylene is 100% by mass. Next, the linear low-density polyethylene before kneading (linear low-density polyethylene as a resin raw material) and the branched low-density polyethylene before kneading (branched low-density polyethylene as a resin raw material) used to form the mixed resin will be described.

[0011] (linear low-density polyethylene) Linear low-density polyethylene is a copolymer of ethylene and α-olefin with a linear structure, and its density is 910 kg / m 3 More than 940kg / m 3 It is preferable that the linear low-density polyethylene is represented by the abbreviation "PE-LLD" in JIS K 6899-1:2015 "Plastics - Symbols and abbreviations - Part 1: Basic polymers and their properties." The heat of fusion (ΔH LL ) is preferably 80 J / g or more and 140 J / g or less from the viewpoint of easily obtaining expanded beads having desired physical properties. In addition, from the viewpoint of improving the moldability of the expanded beads while obtaining expanded beads having a desired biomass content, the heat of fusion (ΔH LL) is preferably 90 J / g or more, more preferably 95 J / g or more, and even more preferably 100 J / g or more. From the same viewpoint, the heat of fusion (ΔH LL ) is preferably 130 J / g or less, more preferably 120 J / g or less. The heat of fusion of the linear low-density polyethylene (ΔH LL ) can be determined from a DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K 7122:2012 using a linear low-density polyethylene as a test piece. Specifically, it can be measured by the method described in the examples.

[0012] The melting point (Tm LL ) is preferably 100°C or higher and 130°C or lower from the viewpoint of improving the mechanical properties of the resulting molded article. LL ) is more preferably 110°C or higher, even more preferably 116°C or higher, and even more preferably 120°C or higher. On the other hand, the melting point (Tm LL ) is preferably 128°C or lower, more preferably 126°C or lower, and even more preferably 124°C or lower, from the viewpoint of improving the moldability of the expanded beads in a mold under low molding pressure conditions. Melting point (Tm) of linear low-density polyethylene LL ) is measured using a linear low-density polyethylene as a test piece in accordance with JIS K 7121:2012. Specifically, it can be measured by the method described in the examples.

[0013] The melt flow rate of the linear low-density polyethylene measured at a temperature of 190°C under a load of 2.16 kg is preferably 0.1 g / 10 min or more and 3 g / 10 min or less. When the melt flow rate of the linear low-density polyethylene is within this range, the in-mold moldability of the expanded beads can be further improved. The melt flow rate of the linear low-density polyethylene is more preferably 0.3 g / 10 min or more, even more preferably 0.5 g / 10 min or more, and even more preferably 0.7 g / 10 min or more, and more preferably 2 g / 10 min or less. The melt flow rate of the linear low-density polyethylene is a value measured under conditions of a temperature of 190°C and a load of 2.16 kg. More specifically, it can be measured in accordance with JIS K 7210-1:2014 by the method described in the examples.

[0014] The density of the linear low density polyethylene is preferably 910 kg / m 3 More than 940kg / m 3 From the viewpoint of easily obtaining expanded beads having desired physical properties, it is more preferably 915 kg / m or less. 3 More than 935kg / m 3 More preferably, it is 920 kg / m or less. 3 More than 930kg / m 3 and even more preferably 922 kg / m or less. 3 More than 928kg / m 3 The following is the result. The density of the linear low-density polyethylene is measured by Method A (water displacement method) described in JIS K 7112:1999.

[0015] The linear low-density polyethylene may be a petroleum-derived linear low-density polyethylene or a linear low-density polyethylene containing a biomass-derived component. Therefore, the biomass degree of the linear low-density polyethylene measured according to ASTM D6866 is not limited. However, when the linear low-density polyethylene is a linear low-density polyethylene containing a biomass-derived component, the biomass degree may be 10% or more, 20% or more, 30% or more, 50% or more, or 70% or more. The upper limit of the biomass degree is 100%. Furthermore, when the linear low-density polyethylene is a petroleum-derived linear low-density polyethylene, the biomass degree of the linear low-density polyethylene measured according to ASTM D6866 may be 0%. From the viewpoint of stably improving the moldability of the expanded beads in a mold, the biomass content of the linear low-density polyethylene is preferably 20% or less, more preferably 10% or less, and further preferably is petroleum-derived linear low-density polyethylene.

[0016] The linear low-density polyethylene has a density of 910 kg / m 3 More than 940kg / m 3 or below, and is a copolymer of ethylene and an α-olefin having a linear structure. The linear low-density polyethylene may be a mixture of two or more types of linear low-density polyethylene. When a mixture of two or more types of linear low-density polyethylene is used as the linear low-density polyethylene, the various physical properties such as the heat of fusion and melting point measured for this mixture are used as the various physical properties such as the heat of fusion and melting point of the linear low-density polyethylene. When multiple types of linear low-density polyethylene are used in producing resin particles, a kneaded product for measurement is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each linear low-density polyethylene used in producing the resin particles, and the various physical properties measured for this kneaded product are used as the various physical properties of the linear low-density polyethylene. The α-olefin is preferably an α-olefin having 3 to 20 carbon atoms, more preferably an α-olefin having 4 to 10 carbon atoms, and even more preferably an α-olefin having 6 to 8 carbon atoms. Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-butene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 2-methylheptene, 3-ethylhexene, etc. Among these, from the viewpoint of stably obtaining expanded beads having excellent in-mold moldability, the α-olefin preferably includes at least one selected from the group consisting of 1-octene, 1-hexene, and 4-methyl-1-pentene. Therefore, the linear low-density polyethylene preferably contains, as a main component, linear low-density polyethylene 1, which is a copolymer containing, as a copolymerization component (comonomer), a component derived from octene in the molecular chain, or linear low-density polyethylene 2, which is a copolymer containing, as a copolymerization component (comonomer), a component derived from hexene in the molecular chain. From the viewpoint of being able to stably obtain expanded beads that have excellent in-mold moldability, the linear low-density polyethylene preferably contains linear low-density polyethylene 1 in an amount of 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Regarding linear low-density polyethylene 1 and linear low-density polyethylene 2, when they contain a component derived from octene and a component derived from hexene as copolymerization components, they are treated as linear low-density polyethylene 1 when they contain 50 mol% or more of the component derived from octene relative to 100 mol% in total of the component derived from octene and the component derived from hexene. In addition, the octene-derived components in the linear low-density polyethylene containing an octene-derived component as a copolymerization component include 1-octene, 2-methylheptene, 3-ethylhexene, etc., with 1-octene being preferred. In addition, the hexene-derived components in the linear low-density polyethylene containing a hexene-derived component include 1-hexene and 4-methyl-1-pentene, with 4-methyl-1-pentene being preferred.

[0017] From the viewpoint of being able to stably obtain expanded beads having excellent in-mold moldability, when the linear low-density polyethylene is linear low-density polyethylene 1 containing a component derived from octene, the content of the component derived from octene in the linear low-density polyethylene 1 is preferably 0.5 mol% or more and 5 mol% or less, and more preferably 1 mol% or more and 3 mol% or less. The above content is the content when the total of the ethylene-derived component and the α-olefin-derived component is taken as 100% by mass. The content of the α-olefin-derived component in the linear low-density polyethylene is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and even more preferably 3 mol% or less. The content of the α-olefin-derived component in the linear low-density polyethylene is preferably 0.5 mol% or more, more preferably 1 mol% or more. The content of components derived from each α-olefin in linear low-density polyethylene can be determined by carbon-13 nuclear magnetic resonance ( 13 It can be determined by measurement using C-NMR, etc.

[0018] (branched low-density polyethylene) Branched low-density polyethylene is a polyethylene with a long-chain branched structure, and has a density of 910 kg / m 3 More than 930kg / m 3 Preferably, the molecular weight is less than 1000. Branched low-density polyethylene is generally also called simply "low-density polyethylene" and is indicated by the abbreviation "PE-LD" in, for example, JIS K 6899-1:2015, "Plastics - Symbols and abbreviations - Part 1: Basic polymers and their properties." Branched low-density polyethylene can also generally be called high-pressure low-density polyethylene. The branched low-density polyethylene used to form the mixed resin has a biomass content of 30% or more as measured by ASTM D6866, and a heat of fusion of 95 J / g or more. By using a mixed resin obtained by kneading the above-mentioned linear low-density polyethylene with a branched low-density polyethylene having a high heat of fusion and high crystallinity, it is possible to obtain expanded beads that have excellent in-mold moldability, particularly while reducing the shrinkage rate of the molded product. The branched low-density polyethylene may be a mixture of two or more types of branched low-density polyethylene. When a mixture of two or more types of branched low-density polyethylene is used as the branched low-density polyethylene, the various physical properties measured for this mixture, such as the biomass degree and heat of fusion, are used as the various physical properties of the branched low-density polyethylene, such as the biomass degree and heat of fusion. When multiple types of branched low-density polyethylene are used in producing resin particles, a kneaded mixture for measurement is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each branched low-density polyethylene used in producing the resin particles, and the various physical properties measured for the kneaded mixture for measurement are used as the various physical properties of the branched low-density polyethylene.

[0019] Furthermore, when the biomass degree of the branched low-density polyethylene is within the above range, the use of fossil resources can be suppressed when producing a molded article, and the amount of carbon dioxide emitted in the life cycle of the molded article can also be reduced. From the above viewpoint, the biomass degree of the branched low-density polyethylene measured by ASTM D6866 is 30% or more, preferably 50% or more, more preferably 60% or more, and even more preferably 80% or more. There is no upper limit, and the biomass degree of the branched low-density polyethylene measured by ASTM D6866 may be 100% or less. However, from the viewpoint of improving the in-mold moldability of the expanded beads, the biomass degree of the branched low-density polyethylene measured by ASTM D6866 is preferably 99% or less, more preferably 97% or less. The biomass degree is measured by ASTM D6866 and means the proportion of naturally occurring components contained in the branched low-density polyethylene. The biomass degree is determined by radiocarbon dating of the branched low-density polyethylene. 14 This value is determined by measuring the concentration of C.

[0020] The biomass degree D of the branched low-density polyethylene measured by ASTM D6866 LD and the biomass degree D of the linear low-density polyethylene measured by ASTM D6866 LL The difference between (D LD -D LL ) is preferably 5% or more. In this case, expanded beads having a desired biomass degree and excellent moldability in a mold can be stably obtained. From the viewpoint of making it easier to improve the moldability of the expanded beads in a mold, the biomass degree D of the branched low-density polyethylene measured by ASTM D6866 is LD and the biomass degree D of the linear low-density polyethylene measured by ASTM D6866 LL The difference between (D LD -D LL ) is more preferably 10% or more, even more preferably 20% or more, even more preferably 30% or more, even more preferably 50% or more, and particularly preferably 70% or more. There is no upper limit to the biomass degree D of the branched low-density polyethylene as measured by ASTM D6866, provided that it is 100% or less. LD and the biomass degree D of the linear low-density polyethylene measured by ASTM D6866 LL The difference between (D LD -D LL ) may be 99% or less, or may be 98% or less.

[0021] The heat of fusion (ΔH LD ) is 95 J / g or more. From the viewpoint of obtaining expanded beads that can stably produce molded articles with a small shrinkage rate while improving the moldability of the expanded beads in a mold, the heat of fusion (ΔH LD ) is preferably 100 J / g or more, more preferably 102 J / g or more. In addition, the heat of fusion (ΔH LD) is preferably 120 J / g or less, more preferably 115 J / g or less. The heat of fusion (ΔH LD ) can be determined from a DSC curve obtained by performing differential scanning calorimetry (DSC) in accordance with JIS K 7122:2012 using a branched low-density polyethylene as a test piece. Specifically, it can be measured by the method described in the examples.

[0022] In addition, the heat of fusion (ΔH LL ) and the heat of fusion of the branched low-density polyethylene (ΔH LD ) and the difference (ΔH LL -ΔH LD ) is preferably 0 J / g or more and 30 J / g or less. The heat of fusion (ΔH LL ) and the heat of fusion of the branched low-density polyethylene (ΔH LD ) and the difference (ΔH LL -ΔH LD ) is more preferably 1 J / g or more, and even more preferably 2 J / g or more. LL -ΔH LD ) is more preferably 20 J / g or less, even more preferably 15 J / g or less, and even more preferably 8 J / g or less. In this case, expanded beads having a desired biomass degree, excellent in-mold moldability, and capable of being molded into a molded article with a small shrinkage rate can be stably obtained.

[0023] The branched low-density polyethylene preferably has a melt flow rate of 0.1 g / 10 min or more and 3 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg. When the branched low-density polyethylene has a melt flow rate within this range, the in-mold moldability of the expanded beads can be further improved. The branched low-density polyethylene preferably has a melt flow rate of 0.1 g / 10 min or more, more preferably 0.3 g / 10 min or more, and preferably 3 g / 10 min or less, more preferably 2 g / 10 min or less, and even more preferably 0.8 g / 10 min or less. The melt flow rate of the branched low-density polyethylene is a value measured under conditions of a temperature of 190°C and a load of 2.16 kg. More specifically, it can be measured in accordance with JIS K 7210-1:2014 by the method described in the examples.

[0024] The density of the branched low-density polyethylene is 910 kg / cm 3 More than 930kg / cm 3 From the viewpoint of easily obtaining expanded beads having desired physical properties, the compressive strength is preferably less than 915 kg / m 3 More than 929kg / m 3 More preferably, it is 920 kg / m or less. 3 More than 928kg / m 3 More preferably, it is 921 kg / m or less. 3 More than 927kg / m 3 and particularly preferably 922 kg / m 3 More than 926kg / m 3 The following is the result. The density of the branched low-density polyethylene is measured by Method A (water displacement method) described in JIS K7112:1999.

[0025] The difference (absolute value) between the density of the linear low-density polyethylene and the density of the branched low-density polyethylene is preferably 5 kg / m 3 More preferably, it is 4 kg / m or less. 3 More preferably, it is 3 kg / m or less. 3 There is no lower limit, but 0 kg / m 3 It may be more than 1 kg / m 3 It may be more than that.

[0026] The melting point (TmLD ) is preferably 100°C or higher, more preferably 105°C or higher, from the viewpoint of improving the mechanical properties of the resulting molded article. On the other hand, the melting point (Tm LD ) is preferably 120°C or lower, more preferably 118°C or lower, and even more preferably 116°C or lower, from the viewpoint of improving the moldability of the expanded beads in a mold under low molding pressure conditions. Melting point (Tm) of branched low density polyethylene LD ) is measured using a branched low-density polyethylene as a test piece in accordance with JIS K 7121:2012. Specifically, it can be measured by the method described in the examples.

[0027] The melting point (Tm LL ) and the melting point (Tm LD ) and the difference (Tm LL -Tm LD ) is preferably 5°C or more and 15°C or less. By forming the expanded beads from a mixed resin of linear low-density polyethylene and branched low-density polyethylene, the difference in melting point of which is within a specific range, it is possible to stably obtain expanded beads that have a desired biomass degree and excellent moldability in a mold. LL -Tm LD ) is more preferably 6°C or higher, and even more preferably 8°C or higher.

[0028] <Characteristics of mixed resin and polyethylene resin particles> The mixed resin constituting the resin particles is obtained by kneading the linear low-density polyethylene and the branched low-density polyethylene. From the viewpoint of stably obtaining expanded particles having excellent moldability in a mold and a wide molding range that can produce molded articles with a particularly small shrinkage ratio, it is preferable that the linear low-density polyethylene is the linear low-density polyethylene 1. The amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, where the total of the linear low-density polyethylene and the branched low-density polyethylene is 100% by mass, and the heat of fusion of the polyethylene resin particles is 90 J / g or more.

[0029] The blending amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass. By using a mixed resin obtained by kneading the linear low-density polyethylene with the specific branched low-density polyethylene described above, it is possible to obtain expanded beads that are excellent in moldability while particularly reducing the shrinkage rate of the molded article. From the viewpoint of increasing the biomass content of the expanded beads and reducing the shrinkage rate of the molded article, the blending amount of the branched low-density polyethylene is 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on 100% by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene. Furthermore, from the viewpoint of easily improving the in-mold moldability of the expanded beads, the blending amount of the branched low-density polyethylene is less than 40% by mass, preferably 38% by mass or less, more preferably 35% by mass or less, even more preferably 32% by mass or less, and still more preferably 30% by mass or less, based on 100% by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene.

[0030] The mixed resin constituting the resin particles may contain polymers such as resins other than the linear low-density polyethylene and the branched low-density polyethylene, elastomers, etc., within the range that does not impair the effects of the present invention. In this case, the content of the polymers other than the linear low-density polyethylene and the branched low-density polyethylene in the mixed resin is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, relative to 100 parts by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene.

[0031] The biomass content of the resin particles as measured by ASTM D6866 is preferably 5% or more. When the biomass degree of the resin particles is within the above range, the use of fossil resources can be suppressed when producing the molded body, and the amount of carbon dioxide emitted during the life cycle of the molded body can also be reduced. From the above viewpoint, the biomass degree of the resin particles measured by ASTM D6866 is more preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. There is no upper limit, and the biomass degree of the resin particles measured by ASTM D6866 may be 100% or less. However, from the viewpoint of easily improving the in-mold moldability of the expanded beads, the biomass degree of the resin particles measured by ASTM D6866 is preferably 90% or less, more preferably 80% or less, even more preferably 50% or less, and even more preferably 40% or less. The biomass degree is measured by ASTM D6866 and means the proportion of naturally occurring components contained in the resin particles. The biomass degree is also determined by the radiocarbon content of the resin particles or expanded beads. 14 It can be calculated by measuring the concentration of C or from the biomass content of the biomass-derived resin used to produce the resin particles or expanded beads and the content of the biomass-derived resin in the resin particles or expanded beads.

[0032] The flexural modulus of the mixed resin constituting the resin particles is preferably 200 MPa or more from the viewpoint of obtaining a molded article that is resistant to excessive deformation due to stress. The flexural modulus of the mixed resin is more preferably 210 MPa or more, and even more preferably 220 MPa or more. The upper limit of the flexural modulus of the mixed resin is not particularly limited as long as it is within a range that can achieve the intended object of the present invention, but is preferably 300 MPa or less, and more preferably 280 MPa or less. By setting the flexural modulus of the mixed resin within the above range, the obtained expanded beads have excellent moldability, and a molded article that is resistant to excessive deformation due to stress can be obtained. The flexural modulus of the mixed resin can be determined by heat-pressing the resin particles to prepare a sheet-shaped test piece having a predetermined dimension, and measuring the flexural modulus of this test piece based on JIS K 7171:2016. In addition, since the flexural modulus of the mixed resin constituting the resin particles usually corresponds to the flexural modulus of the mixed resin constituting the expanded beads formed by expanding the resin particles, the flexural modulus of the mixed resin constituting the expanded beads described below may be adopted as the flexural modulus of the mixed resin constituting the resin particles.

[0033] The polyethylene-based resin particles made of the mixed resin used in the method for producing expanded beads of the present invention can be obtained by feeding the linear low-density polyethylene, the branched low-density polyethylene, and a cell control agent, etc., which are blended as needed, into an extruder, heating and kneading them to form a resin melt, and then extruding the resin melt from the extruder and pelletizing it by a strand cut method, a hot cut method, an underwater cut method, etc. That is, the mixed resin that makes up the resin particles can be obtained by kneading the linear low-density polyethylene and the branched low-density polyethylene.

[0034] The average mass per resin particle is preferably adjusted to 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and still more preferably 0.4 to 2 mg. The external shape of the particles is not particularly limited as long as it is within a range that allows the intended object of the present invention to be achieved, but is preferably cylindrical. When the resin particles have a cylindrical outer shape, the particle diameter (length in the extrusion direction) of the resin particles is preferably 0.1 to 3.0 mm, more preferably 0.3 to 1.5 mm. The ratio (length / diameter ratio) of the length of the resin particles in the extrusion direction to the length of the resin particles in the direction perpendicular to the extrusion direction (diameter of the resin particles) is preferably 0.5 to 5.0, more preferably 1.0 to 3.0.

[0035] When pelletizing by the strand cutting method, the particle size, length / diameter ratio, and average mass of the resin particles can be adjusted by appropriately changing the extrusion speed when extruding the resin melt, the strand take-up speed, and the cutter speed when cutting the strand.

[0036] The mixed resin constituting the resin particles may contain additives as appropriate within the range that does not impair the effects of the present invention. Examples of additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and cell regulators. These additives can be incorporated into the expanded beads by adding them to the resin particles during the process of producing the resin particles.

[0037] The cell regulator may be, for example, an inorganic powder or an organic powder. Examples of inorganic powders include metal borates such as zinc borate and magnesium borate, and examples of organic powders include fluororesin powders such as polytetrafluoroethylene (PTFE). From the viewpoint of stably obtaining expanded beads having a desired bulk density and little variation in cell diameter, the amount of the cell regulator in the resin beads is preferably 50 ppm by mass or more and 5000 ppm by mass or less, more preferably 100 ppm by mass or more and 2000 ppm by mass or less, and even more preferably 150 ppm by mass or more and 1500 ppm by mass or less. From the viewpoint of easily adjusting the average cell diameter of the expanded beads to a desired range, it is preferable to use a metal borate, more preferably zinc borate, as the cell adjusting agent. When zinc borate is used, the arithmetic mean particle diameter based on the number is preferably 0.5 μm to 10 μm, more preferably 1 μm to 8 μm. The number-based arithmetic mean particle diameter of zinc borate can be determined by converting the volume-based particle size distribution measured by laser diffraction scattering method into a number-based particle size distribution by assuming that the particles have a spherical shape, and then calculating the arithmetic mean of the particle diameters based on this number-based particle size distribution. Note that the particle diameter refers to the diameter of a hypothetical sphere having the same volume as the particle.

[0038] The polyethylene resin particles used in the method for producing expanded polyethylene resin particles of the present invention have a total heat of fusion of 90 J / g or more. The resin particles are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, and the total heat of fusion of the resin particles is within the above range, so that expanded beads can be obtained that have excellent in-mold moldability and can be used to mold molded articles with a small shrinkage rate. The total heat of fusion of the resin particles is preferably 100 J / g or more, more preferably 105 J / g or more, and even more preferably 110 J / g or more. Furthermore, the upper limit of the total heat of fusion of the resin particles is not particularly limited as long as it is within a range that can achieve the intended object of the present invention, but is preferably 140 J / g or less, and more preferably 130 J / g or less. The total heat of fusion of resin particles can be determined from a DSC curve obtained by performing differential scanning calorimetry (DSC) according to JIS K 7122:2012 on the resin particles as a test specimen. Specifically, the test specimen was first conditioned using "(2) Measurement of melting temperature after a certain heat treatment." The test specimen was heated from 23°C to 200°C at a heating rate of 10°C / min. After reaching 200°C, the temperature was lowered from 200°C to 23°C at a rate of 10°C / min. After that, the DSC curve (DSC curve during the second heating) was obtained by heating the test specimen for a second time at a rate of 10°C / min. The point at 80°C on the obtained DSC curve during the second heating was designated as α, and the point on the DSC curve corresponding to the end temperature of melting was designated as β. The area of ​​the portion enclosed by the DSC curve in the section between points α and β and the line segment (α-β) is measured, and the total heat of fusion of the resin particles can be calculated from this area. In addition, since the total heat of fusion of resin particles usually corresponds to the total heat of fusion of expanded beads obtained by expanding resin particles, the total heat of fusion of expanded beads described below may be used as the total heat of fusion of resin particles.

[0039] The melting point of the polyethylene resin particles used in the method for producing expanded polyethylene resin beads of the present invention is preferably 100°C or higher and 115°C or lower, from the viewpoints of improving the in-mold moldability of the expanded beads and easily improving the mechanical properties of the resulting molded article. The melting point of the resin particles is more preferably 116°C or higher, and even more preferably 118°C or higher. On the other hand, from the viewpoint of improving the in-mold moldability of the expanded beads under conditions of low molding pressure, the melting point of the resin particles is preferably 128°C or lower, and more preferably 125°C or lower. The melting point of the resin particles is measured using the resin particles as a test piece in accordance with JIS K 7121: 2012. Specifically, it can be measured by the method described in the examples. The melting point of the resin particles generally corresponds to the melting point of the expanded beads obtained by expanding the resin particles, and therefore the melting point of the expanded beads described below may be used as the melting point of the resin particles.

[0040] The melt flow rate of the mixed resin constituting the polyethylene resin particles, measured under conditions of a temperature of 190°C and a load of 2.16 kg, is preferably 0.1 g / 10 min or more and 3 g / 10 min or less. When the melt flow rate of the resin particles is within this range, the in-mold moldability of the resulting expanded beads can be further improved. The melt flow rate of the mixed resin is preferably 0.2 g / 10 min or more, more preferably 0.4 g / 10 min or more, and even more preferably 0.5 g / 10 min or more, and more preferably 2.0 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and even more preferably 1.2 g / 10 min or less. The melt flow rate of the mixed resin is a value measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K 7210-1: 2014. The melt flow rate of the mixed resin constituting the resin particles generally corresponds to the melt flow rate of the mixed resin constituting the expanded particles obtained by expanding the resin particles.

[0041] As described above, specific expanded beads obtained by kneading a branched low-density polyethylene having a specific heat of fusion with the linear low-density polyethylene in a specific blending ratio and expanding the resulting resin beads can be used to produce molded articles with a small shrinkage rate. The reason why a molded article having a small shrinkage rate can be produced in the present invention is not clear, but the following is thought to be the reason. The branched low-density polyethylene used in the present invention is believed to have a lower melting point and soften more easily than linear low-density polyethylene, while having a relatively high heat of fusion and high crystallinity. It is believed that expanded beads containing such branched low-density polyethylene have a moderate tendency for the mixed resin constituting the expanded beads to stretch during molding, while the crystalline components enhance resistance to shrinkage when the mixed resin cools and solidifies. These factors are believed to enable the production of molded articles with low shrinkage while maintaining the moldability of the expanded beads.

[0042] <Production of polyethylene resin foam beads> The method for producing expanded polyethylene resin beads of the present invention may be any method that involves expanding the above-mentioned resin particles composed of a mixed resin to produce expanded polyethylene resin beads. The method for producing expanded beads of the present invention is, for example, a method in which resin particles composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene are impregnated with a blowing agent to expand the resin particles containing the blowing agent. Examples of methods for expanding resin particles include heating resin particles containing a blowing agent with a heating medium such as steam, or releasing resin particles containing a blowing agent that have been held under a predetermined temperature and pressure atmosphere into a pressure atmosphere lower than the aforementioned pressure atmosphere. An example of a suitable production method is shown below.

[0043] A preferred method for producing the expanded beads of the present invention is a method for producing expanded beads by expanding the resin beads, in which the resin particles containing a blowing agent dispersed in an aqueous medium in a container are released from the container together with the aqueous medium into a pressure atmosphere lower than the pressure inside the container to expand the resin particles. More specifically, the process includes a dispersion step of dispersing resin particles composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene in an aqueous medium in a container, a foaming agent impregnation step of impregnating the resin particles with a foaming agent in the container, and an expansion step of releasing the resin particles containing the foaming agent together with the aqueous medium from the container into a pressure atmosphere lower than the pressure in the container, thereby expanding the resin particles.

[0044] A preferred method for producing expanded beads of the present invention includes a dispersion step of dispersing the resin particles in an aqueous medium in a container, a foaming agent impregnation step of impregnating the resin particles with a foaming agent in the container, and an expansion step of releasing the resin particles containing the foaming agent together with the aqueous medium from the container into a pressure atmosphere lower than the pressure inside the container to expand the resin particles. These steps are preferably performed in this order, and more preferably, these steps are performed as a series of steps. Note that a method of foaming by this series of steps is also called a dispersion medium release foaming method.

[0045] In the dispersion step, an aqueous dispersion medium is preferably used as a dispersion medium for dispersing the resin particles obtained as described above in a sealed container. The aqueous dispersion medium is a dispersion medium containing water as a main component. The proportion of water in the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include ethylene glycol, glycerin, methanol, and ethanol.

[0046] In the dispersion medium release foaming method suitably used in the present invention, a dispersant is preferably added to the dispersion medium to prevent resin particles heated in a container from fusing together within the container. Any dispersant can be used as long as it prevents the resin particles from fusing together within the container, but inorganic dispersants are preferably used. Examples of inorganic dispersants include natural or synthetic clay minerals such as kaolin, mica, and clay, as well as aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. One or more of these may be used alone or in combination. Of these, natural or synthetic clay minerals are preferred. The amount of the dispersant added is preferably 0.001 to 5 parts by mass per 100 parts by mass of the resin particles.

[0047] When a dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylsulfonate, or sodium oleate as a dispersing aid in combination. The dispersing aid is preferably added in an amount of about 0.001 to 1 part by mass per 100 parts by mass of the resin particles.

[0048] In the blowing agent impregnation step, a physical blowing agent is preferably used as the blowing agent for expanding the resin particles. Examples of the physical blowing agent include inorganic and organic physical blowing agents. Examples of inorganic physical blowing agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane; cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; 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. The physical blowing agents may be used alone or in combination. Alternatively, inorganic and organic physical blowing agents may be used in combination. From the viewpoint of facilitating the production of desired expanded particles, the blowing agent used in this production method is preferably an inorganic physical blowing agent, and more preferably carbon dioxide.

[0049] The amount of foaming agent to be added is determined taking into consideration the desired bulk density of the expanded beads, the type of foaming agent, etc. For example, when a physical foaming agent is used, the amount of physical foaming agent to be added per 100 parts by mass of resin particles is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass.

[0050] In the expanded bead production process, a preferred method for impregnating the resin particles with the blowing agent is, for example, to disperse the resin particles in an aqueous dispersion medium in a sealed container, and simultaneously inject the blowing agent into the sealed container, and then heat and pressurize the sealed container and hold it therein, thereby impregnating the resin particles with the blowing agent.

[0051] In the expansion step, the pressure (internal pressure) inside the sealed container during expansion is preferably 0.5 MPa (G) or more, more preferably 0.8 MPa (G) or more, even more preferably 1.0 MPa (G) or more, still more preferably 2.0 MPa (G) or more, and even more preferably 3.0 MPa (G) or more. The upper limit is preferably 5.0 MPa (G) or less, more preferably 4.5 MPa (G) or less. Within the above range, the desired expanded beads can be safely produced without risk of damage or explosion of the sealed container. Preferably, the temperature is raised to 100 to 200°C, more preferably 110 to 140°C, and the resin beads containing the blowing agent are then preferably expanded by releasing them from the sealed container into an atmosphere with a pressure lower than the pressure inside the sealed container (e.g., atmospheric pressure).

[0052] Further, expanded beads having a crystalline structure in which an intrinsic peak and a high-temperature peak appear in the first DSC curve can be produced, for example, as follows. First, resin particles dispersed in a dispersion medium in a sealed container are heated to a temperature between (the melting point of the mixed resins constituting the resin particles -15°C) and (the melting point of the mixed resins constituting the resin particles +10°C) and maintained at this temperature for a sufficient time, preferably for about 10 to 60 minutes (maintenance step). Next, the resin particles that have undergone this maintenance step are expanded to obtain expanded particles that exhibit the above-mentioned melting peak. In the production of expanded beads, resin particles that have undergone the holding step may be prepared in advance, and the resin particles that have undergone the holding step may be expanded to obtain expanded beads. Alternatively, for example, the resin particles may be subjected to the holding step as part of the dispersion step or the blowing agent impregnation step, and the resin particles that have undergone the holding step may be expanded to obtain expanded beads. From the viewpoint of increasing the productivity of expanded beads, it is preferable to carry out the above-mentioned holding step by heating resin particles dispersed in a dispersion medium in a sealed container in the presence of a blowing agent, and then release the contents of the sealed container from the sealed container into an atmosphere of pressure lower than the pressure inside the sealed container, thereby expanding the resin particles that have undergone the above-mentioned holding step, thereby obtaining expanded beads that exhibit the above-mentioned melting peak.

[0053] The expanded beads obtained as described above can be expanded in multiple stages to obtain expanded beads with a higher expansion ratio (lower bulk density). For example, the expanded beads can be pressurized with air or the like to increase the pressure (internal pressure) within the cells of the expanded beads, and then heated with steam or the like to further expand (two-stage expansion) to obtain expanded beads with a higher expansion ratio (lower bulk density). From the viewpoint of obtaining a molded product with a low density, two-stage expansion is preferred.

[0054] <Polyethylene-based resin expanded particles produced by the above production method> The expanded polyethylene resin particles produced by the method for producing expanded polyethylene resin particles of the present invention are preferably the expanded polyethylene resin particles described in the section [Expanded Polyethylene Resin Particles] below, and the same applies to more preferred expanded polyethylene resin particles.

[0055] The biomass content of the expanded polyethylene resin beads measured according to ASTM D6866 is 5% or more. When the biomass degree of the expanded beads is within the above range, the use of fossil resources can be suppressed in the production of the molded article, and the amount of carbon dioxide emitted in the life cycle of the molded article can also be reduced. From the above viewpoint, the biomass degree of the expanded beads measured by ASTM D6866 is 10% or more, more preferably 15% or more, and even more preferably 20% or more. There is no upper limit, and the biomass degree of the expanded beads measured by ASTM D6866 may be 100% or less. However, from the viewpoint of easily improving the in-mold moldability of the expanded beads, the biomass degree of the expanded beads measured by ASTM D6866 is preferably 90% or less, more preferably 80% or less, even more preferably 50% or less, and even more preferably 30% or less. The biomass degree is measured by ASTM D6866 and means the proportion of naturally occurring components contained in the expanded beads. The biomass degree is determined by radiocarbon dating of linear low-density polyethylene. 14It can be calculated by measuring the concentration of C or from the biomass content of the biomass-derived resin used to produce the expanded beads and the content of the biomass-derived resin in the expanded beads.

[0056] [Polyethylene resin foam particles] The expanded polyethylene resin beads of the present invention are polyethylene resin expanded beads, which are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, and in which the mixed resin has a flexural modulus of 200 MPa or more, a biomass degree of the expanded beads measured according to ASTM D6866 of 5% or more, and a total heat of fusion of the expanded beads of 90 J / g or more. The expanded polyethylene resin beads of the present invention are preferably those produced by the above-mentioned method for producing expanded polyethylene resin beads, and the method for producing expanded polyethylene resin beads of the present invention is preferably the above-mentioned method for producing expanded polyethylene resin beads, and the same is true for more preferred methods. The expanded beads described in the section [Expanded Polyethylene Resin Beads] of the present invention are preferably expanded beads produced by the above-mentioned [Method for Producing Expanded Polyethylene Resin Beads], and the same is true for more preferred expanded beads.

[0057] (mixed resin) The polyethylene-based resin foam particles are made of a mixed resin of linear low-density polyethylene and branched low-density polyethylene.

[0058] The mixed resin of linear low-density polyethylene and branched low-density polyethylene constituting the expanded polyethylene resin beads of the present invention is preferably the mixed resin described in the section <Mixed Resin> of the "Method for producing expanded polyethylene resin beads" explained in the above-mentioned method for producing expanded beads. Therefore, the mixed resin is preferably a mixed resin obtained by kneading linear low-density polyethylene and branched low-density polyethylene. Therefore, the mixed resin preferably contains a branched low-density polyethylene and a linear low-density polyethylene, the branched low-density polyethylene having a biomass degree of 30% or more as measured according to ASTM D6866 and a heat of fusion of 95 J / g or more, and the amount of the branched low-density polyethylene blended is preferably 5% by mass or more and less than 40% by mass, where the total of the linear low-density polyethylene and the branched low-density polyethylene is 100% by mass. Furthermore, from the viewpoint of being able to stably obtain expanded beads that have excellent in-mold moldability and a wide molding range in which good molded articles can be obtained, it is preferable that the linear low-density polyethylene is a linear low-density polyethylene that contains an octene component as a copolymerization component (comonomer).

[0059] The flexural modulus of the mixed resin constituting the expanded beads is preferably 200 MPa or more, from the viewpoint of obtaining a molded article that is resistant to excessive deformation due to stress. The flexural modulus of the mixed resin is more preferably 210 MPa or more, and even more preferably 220 MPa or more. The upper limit of the flexural modulus of the mixed resin is not particularly limited as long as it is within a range in which the intended object of the present invention can be achieved, but is preferably 300 MPa or less, and more preferably 280 MPa or less. By setting the flexural modulus of the mixed resin within the above range, the resulting expanded beads have excellent moldability, and a molded article that is resistant to excessive deformation due to stress can be obtained. The flexural modulus of the mixed resin can be determined by heat-pressing the foamed beads to prepare a sheet-shaped test piece having a predetermined dimension, and measuring the flexural modulus of this test piece based on JIS K 7171:2016.

[0060] The expanded polyethylene resin particles are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, and the amount of the branched low-density polyethylene in the mixed resin is preferably 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass. By using a mixed resin obtained by kneading the above-mentioned linear low-density polyethylene with a branched low-density polyethylene that has a high heat of fusion and is highly crystalline, it is possible to obtain expanded beads that have excellent in-mold moldability, particularly while reducing the shrinkage rate of the molded product. From the viewpoint of increasing the biomass content of the expanded beads and reducing the shrinkage rate of the molded article, the blending amount of the branched low-density polyethylene is preferably 5% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and still more preferably 20% by mass or more, based on 100% by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene. Furthermore, from the viewpoint of easily improving the in-mold moldability of the expanded beads, the blending amount of the branched low-density polyethylene is preferably less than 40% by mass, more preferably 38% by mass or less, even more preferably 35% by mass or less, still more preferably 32% by mass or less, and still more preferably 30% by mass or less, based on 100% by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene.

[0061] <Characteristics and composition of polyethylene resin foam beads> As described above, the expanded beads of the present invention are polyethylene-based resin expanded beads that are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, the mixed resin having a flexural modulus of 200 MPa or more, the expanded beads having a biomass content of 5% or more as measured according to ASTM D6866, and the expanded beads having a heat of fusion of 90 J / g or more, and preferably have the following properties:

[0062] The expanded beads have a biomass content of 5% or more as measured by ASTM D6866. When the biomass degree of the expanded beads is within the above range, the use of fossil resources can be suppressed in the production of the molded article, and the amount of carbon dioxide emitted in the life cycle of the molded article can also be reduced. From the above viewpoint, the biomass degree of the expanded beads measured by ASTM D6866 is 10% or more, more preferably 15% or more, and even more preferably 20% or more. There is no upper limit, and the biomass degree of the expanded beads measured by ASTM D6866 may be 100% or less. However, from the viewpoint of easily improving the in-mold moldability of the expanded beads, the biomass degree of the expanded beads measured by ASTM D6866 is preferably 90% or less, more preferably 80% or less, even more preferably 50% or less, and even more preferably 30% or less. The biomass degree is measured by ASTM D6866 and means the proportion of naturally occurring components contained in the expanded beads. The biomass degree is determined by the radiocarbon content of the expanded beads. 14 It can be calculated by measuring the concentration of C or from the biomass content of the biomass-derived resin used to produce the expanded beads and the content of the biomass-derived resin in the expanded beads.

[0063] The expanded polyethylene resin beads of the present invention have a total heat of fusion of 90 J / g or more. When the expanded beads are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene and the total heat of fusion of the expanded beads is within the above range, expanded beads that have excellent in-mold moldability and can be used to form molded articles with a small shrinkage rate can be obtained. The total heat of fusion of the expanded beads is preferably 100 J / g or more, more preferably 105 J / g or more, and even more preferably 110 J / g or more. The upper limit of the total heat of fusion of the expanded beads is not particularly limited as long as the intended object of the present invention can be achieved, but is preferably 140 J / g or less, more preferably 130 J / g or less. The total heat of fusion of the expanded beads can be determined from a DSC curve obtained by performing differential scanning calorimetry (DSC) according to JIS K 7122:2012 using the expanded beads as a test specimen. Specifically, the test specimen was first conditioned using "(2) Measurement of melting temperature after a certain heat treatment." The test specimen was heated from 23°C to 200°C at a heating rate of 10°C / min. After reaching 200°C, the temperature was lowered from 200°C to 23°C at a rate of 10°C / min. After heating for a second time, the temperature was lowered from 23°C to 200°C at a rate of 10°C / min. The DSC curve (DSC curve for the second heating) was obtained by heating the DSC curve obtained for the second heating at a temperature of 80°C as α, and the point on the DSC curve corresponding to the end temperature of melting as β. The area of ​​the portion enclosed by the DSC curve in the section between points α and β and the line segment (α-β) is measured, and the total heat of fusion of the expanded beads can be calculated from this area.

[0064] The expanded polyethylene resin particles preferably have a crystalline structure in which, in a DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, a melting peak (intrinsic peak) inherent to the mixed resin and one or more melting peaks (high-temperature peaks) appear at temperatures higher than the intrinsic peak.

[0065] The DSC curve is a DSC curve obtained by differential scanning calorimetry (DSC) in accordance with JIS K 7122: 2012. Specifically, the DSC curve can be obtained by heating 1 to 3 mg of the expanded beads from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter. As described above, the DSC curve measured for the expanded beads shows a melting peak (intrinsic peak) inherent to the mixed resin and one or more melting peaks (high-temperature peaks) at temperatures higher than the inherent peak.

[0066] This will be explained in more detail below. The DSC curve refers to a DSC curve obtained by heating the expanded beads by the measurement method (DSC curve in the first heating). The melting peak (intrinsic peak) inherent to the mixed resin refers to a melting peak that appears due to melting of crystals that are normally present in the mixed resin of the linear low-density polyethylene and the branched low-density polyethylene. On the other hand, the melting peak (high-temperature peak) on the higher temperature side than the intrinsic peak is a melting peak that appears on the higher temperature side than the intrinsic peak in the DSC curve in the first heating. The appearance of this high-temperature peak is presumed to indicate the presence of secondary crystals in the resin. In addition, when expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating), the DSC curve (DSC curve in the second heating) obtained shows only the melting peak due to the melting of the crystals normally present in the mixed resin. This makes it possible to identify which peak is the intrinsic peak. The expanded beads are preferably those in which only a melting peak (intrinsic peak) specific to the mixed resin appears in the DSC curve obtained during the second heating, which is obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, then cooling from 200°C to 23°C at a cooling rate of 10°C / min, and then heating from 23°C to 200°C at a heating rate of 10°C / min.

[0067] The heat of fusion of the expanded beads at the high-temperature peak is preferably 10 J / g or more and 50 J / g or less. When the heat of fusion of the expanded beads at the high-temperature peak is within this range, the expandable beads can be molded in a mold even when the expanded beads have a low bulk density, and expanded beads can be molded in a mold over a wide range of molding pressures. This allows for the production of good molded products over a wide range of densities. The heat of fusion of the expanded beads at their high-temperature peak is preferably 15 J / g or more, more preferably 20 J / g or more, from the viewpoints of suppressing sink marks in a molded article immediately after molding, improving the in-mold moldability of the expanded beads, and stably suppressing shrinkage of the second-stage expanded beads when the expanded beads are subjected to two-stage expansion. The heat of fusion of the expanded beads at their high-temperature peak is preferably 45 J / g or less, more preferably 40 J / g or less, and even more preferably 35 J / g or less, from the viewpoints of improving the fusibility of the expanded beads under low molding pressure conditions, improving the in-mold moldability of the expanded beads, and making it easier to obtain expanded beads with a lower bulk density when the expanded beads are subjected to two-stage expansion. The heat of fusion of the high-temperature peak can be determined by heat flux differential scanning calorimetry using the expanded beads as a test piece in accordance with JIS K 7122: 2012. Specifically, it can be determined from a DSC curve (DSC curve in the first heating) obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min, and more specifically, it can be measured by the method described in the Examples. In addition, expanded beads having a crystalline structure in which an intrinsic peak and a high-temperature peak appear in the first DSC curve can be obtained, for example, by expanding resin beads that have undergone the above-mentioned holding step.

[0068] The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads [heat of fusion of the high-temperature peak / total heat of fusion] is preferably 0.1 or more and 0.4 or less, more preferably 0.15 or more and 0.35 or less, even more preferably 0.18 or more and 0.30 or less, and even more preferably 0.20 or more and 0.28 or less. When the heats of fusion are within the above ranges and the ratios are within the above ranges, expanded beads can be obtained that have excellent moldability and can be molded in a wide range of densities and a wide molding pressure range. Furthermore, expanded beads that can be molded into molded articles with a small shrinkage rate can be stably obtained. The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion can be calculated from the total heat of fusion and the heat of fusion of the high-temperature peak.

[0069] The bulk density of the expanded beads is 10 kg / m from the viewpoint of improving the mechanical properties of the resulting molded article. 3 or more, preferably 13 kg / m 3 More preferably, it is 15 kg / m or more. 3 On the other hand, from the viewpoint of obtaining a low-density molded product, the bulk density of the expanded beads is 300 kg / m 3 or less, preferably 200 kg / m 3 More preferably, it is 100 kg / m or less. 3 More preferably, it is 80 kg / m or less. 3 and even more preferably 60 kg / m or less. 3 or less, and particularly preferably 30 kg / m 3 The following is the result. As described above, in the present invention, the obtained expanded beads are subjected to a pressure treatment, and then to a second-stage expansion in which they are further expanded by heating with steam or the like, thereby obtaining expanded beads with a higher expansion ratio (lower bulk density). From the viewpoint of obtaining a molded product with a low density, it is preferable to perform the second-stage expansion. In the case of two-stage expansion, the bulk density of the expanded beads after the first stage expansion (before the second stage expansion) is preferably 60 kg / m from the viewpoint of stably obtaining expanded beads having a desired cell structure. 3 More preferably, it is 70 kg / m or more. 3 More preferably, it is 80 kg / m or more. 3 On the other hand, in the case of two-stage expansion, the bulk density of the expanded beads after the first stage expansion (before the second stage expansion) is preferably 240 kg / m from the viewpoint of stably obtaining a low-density molded product. 3 or less, preferably 200 kg / m 3 More preferably, it is 150 kg / m or less. 3 More preferably, it is 120 kg / m or less. 3 The following is the result. The bulk density can be measured by the method described in the examples.

[0070] The melt flow rate of the resin mixture constituting the expanded beads, measured at a temperature of 190°C under a load of 2.16 kg, is preferably 0.1 g / 10 min or more and 3 g / 10 min or less. When the melt flow rate of the resin mixture is in this range, the moldability of the expanded beads in a mold can be further improved. The melt flow rate of the mixed resin is preferably 0.2 g / 10 min or more, more preferably 0.4 g / 10 min or more, and even more preferably 0.5 g / 10 min or more, and more preferably 2.0 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and even more preferably 1.2 g / 10 min or less. The melt flow rate of the mixed resin constituting the expanded beads is a value measured under conditions of a temperature of 190°C and a load of 2.16 kg. More specifically, it can be measured in accordance with JIS K 7210-1:2014 by the method described in the examples. The melt flow rate may be measured using expanded beads that have been subjected to a degassing treatment as a measurement sample.

[0071] The melting point of the expanded beads is preferably 115° C. or higher and 130° C. or lower, from the viewpoint of improving the in-mold moldability of the expanded beads while easily improving the mechanical properties of the resulting molded article. The melting point of the expanded beads is more preferably 116° C. or higher, and even more preferably 118° C. or higher. On the other hand, the melting point of the expanded beads is more preferably 128° C. or lower, and even more preferably 125° C. or lower, from the viewpoint of improving the in-mold moldability of the expanded beads under conditions of low molding pressure. The melting point of the expanded beads is measured using the expanded beads as a test piece in accordance with JIS K 7121: 2012. Specifically, it can be measured by the method described in the examples.

[0072] The closed cell ratio of the expanded beads of the present invention is preferably 80% or more. When the closed cell ratio of the expanded beads is within the above range, the in-mold moldability of the expanded beads can be further improved. The closed cell ratio of the expanded beads of the present invention is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. There is no upper limit to the closed cell ratio of the expanded beads of the present invention as long as the intended object of the present invention can be achieved, but it may be 99% or less, 98% or less, or 96% or less. The closed cell ratio can be measured by the method described in the examples.

[0073] The average cell diameter of the expanded beads of the present invention is preferably 150 μm or more and 300 μm or less. When the average cell diameter of the expanded beads is within this range, the in-mold moldability of the expanded beads can be stably improved. The average cell diameter of the expanded beads of the present invention is preferably 200 μm or more, more preferably 210 μm or more, even more preferably 230 μm or more, and even more preferably 250 μm or more. In particular, when the average cell diameter of the expanded beads is 200 μm or more, the cell membrane constituting the expanded beads becomes relatively thick, making the molded article less likely to shrink immediately after molding, and thus, it becomes easier to stably obtain expanded beads that can be molded into molded articles with a small shrinkage rate. Furthermore, by producing expanded beads using a linear low-density polyethylene and a specific branched low-density polyethylene as in the production method of the present invention, it becomes easier to obtain expanded beads with an average cell diameter of 200 μm or more. Furthermore, in the past, when expanded beads were produced using a copolymer containing an octene-derived component as a copolymerization component (comonomer) as a linear low-density polyethylene, the expanded beads tended to have a relatively small cell diameter. However, by adopting the production method of the present invention, expanded beads with a large cell diameter can be stably produced using a copolymer containing an octene-derived component. The average cell diameter of the expanded beads of the present invention is not particularly limited as long as it is within a range that allows the intended object of the present invention to be achieved, but is preferably 400 μm or less, more preferably 350 μm or less, and even more preferably 300 μm or less. The average cell diameter can be measured by drawing multiple lines from the outermost surface of an expanded bead through the center to the outermost surface on the opposite side in an enlarged photograph of the cross section of the expanded bead divided into two, and then dividing the number of cells intersecting each line by the total length of the lines. Specifically, it can be measured by the method described in the Examples. The average cell diameter of the expanded beads can be adjusted to a desired range by adjusting the type and amount of a cell-regulating agent added to the resin beads, or by adjusting the foaming temperature or the pressure inside the pressure-resistant vessel during foaming of the resin beads.

[0074] In addition, the expanded beads are preferably non-crosslinked, which makes it easier to recycle the expanded beads and reduces the environmental load. In this specification, "non-crosslinked" means that the proportion of insoluble matter in the expanded beads as determined by hot xylene extraction is 5% by mass or less. From the viewpoint of facilitating recycling of the expanded beads, the proportion of insoluble matter in the expanded beads as determined by hot xylene extraction is preferably 3% by mass or less, and most preferably 0% by mass. The xylene-insoluble content of expanded beads can be measured using the hot xylene extraction method as follows. First, approximately 1 g of precisely weighed expanded beads (the exact mass is referred to as M (g)) is placed in a 150 mL round-bottom flask, 100 mL of xylene is added, and the mixture is heated to reflux in a mantle heater for 6 hours. The undissolved residue (insoluble content) is then separated by filtration through a 100-mesh wire screen and dried in a vacuum oven at 80°C for at least 8 hours. The mass m (g) of the dried material obtained by drying the residue is measured, and the ratio of m to M is expressed as a percentage, allowing the proportion of xylene-insoluble content in the expanded beads to be determined.

[0075] The average mass per expanded bead of the present invention (the arithmetic mean value per bead obtained by measuring the masses of 100 randomly selected expanded beads) is preferably 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and still more preferably 0.4 to 2 mg. The average mass per expanded bead can be calculated by measuring the masses of 100 randomly selected expanded beads and arithmetically averaging these masses.

[0076] The mixed resin constituting the expanded beads of the present invention may contain additives as appropriate, provided that the effects of the present invention are not impaired. Examples of additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and cell regulators. These additives can be incorporated into the expanded beads, for example, by adding them during the process of producing the resin beads. The additives contained in the expanded beads of the present invention are the same as the additives contained in the resin beads described above in <Production of Expanded Polyethylene Resin Beads>.

[0077] The mixed resin constituting the expanded beads of the present invention may contain polymers such as resins other than the linear low-density polyethylene and the branched low-density polyethylene, elastomers, etc., within the range that does not impair the effects of the present invention. In this case, the content of the polymers other than the linear low-density polyethylene and the branched low-density polyethylene in the expanded beads is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the total of the linear low-density polyethylene and the branched low-density polyethylene.

[0078] The expanded beads of the present invention may have a fusion layer on their surface to enhance fusion between the expanded beads during molding in a mold. The fusion layer may be present on the entire surface of the expanded beads or on a part of the surface. Examples of resins constituting the fusion layer include crystalline polyolefin resins having a melting point lower than that of the mixed resins constituting the expanded beads, and amorphous polyolefin resins having a softening point lower than that of the mixed resins constituting the expanded beads. The method for forming a fusion layer on the surface of expanded beads is not particularly limited, and examples thereof include a method of expanding resin beads having a fusion layer on their surface, a method of obtaining expanded beads and then attaching a fusion layer to the surface of the expanded beads, etc. When expanding resin beads having a fusion layer on their surface to obtain expanded beads, it is preferable to employ a method in which, when producing the resin beads, a resin melt for forming the resin bead body and a resin melt for forming the fusion layer are co-extruded using an extrusion device capable of co-extrusion, thereby laminating a fusion layer on the surface of the resin beads.

[0079] <Polyethylene resin foam bead molding> The expanded beads of the present invention or the expanded beads obtained by the method for producing expanded beads of the present invention can be molded in a mold to obtain a polyethylene resin expanded bead molded article. That is, the polyethylene resin foamed bead molded article (hereinafter also simply referred to as foamed bead molded article) is obtained by molding the foamed beads in a mold.

[0080] The foamed bead molded article can be produced by filling a mold with the foamed beads and heat-molding them using a heating medium such as steam. Specifically, after filling the mold with the foamed beads, a heating medium such as steam is introduced into the mold to heat and expand (secondary foaming) the foamed beads and fuse them together, thereby obtaining a foamed bead molded article having the shape of the molding space. The in-mold molding of the present invention can also be carried out by a pressure molding method (e.g., JP-B-51-22951), in which the foamed beads are pre-pressurized with a pressurized gas such as air to increase the pressure within the cells of the foamed beads and adjust the pressure within the foamed beads to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, and then the foamed beads are filled into the mold under atmospheric or reduced pressure, and a heating medium such as steam is then supplied into the mold to heat-fuse the foamed beads (e.g., JP-B-51-22951). Alternatively, molding can be performed by a compression filling molding method (Japanese Patent Publication No. 4-46217), in which a mold pressurized to atmospheric pressure or higher by a compressed gas is filled with expanded beads pressurized to atmospheric pressure or higher, and then a heating medium such as steam is supplied into the cavity to heat and fuse the expanded beads. Alternatively, molding can be performed by a normal pressure filling molding method (Japanese Patent Publication No. 6-49795), in which expanded beads with high secondary expansion power obtained under special conditions are filled into the cavity of a mold under atmospheric or reduced pressure, and then a heating medium such as steam is supplied to heat and fuse the expanded beads, or a combination of the above methods (Japanese Patent Publication No. 6-22919).

[0081] From the viewpoint of improving mechanical properties, the density of the expanded bead molding is preferably 10 kg / m 3 More preferably, it is 13 kg / m or more. 3 More preferably, it is 15 kg / m or more. 3 In order to obtain a lightweight molded article, the density of the expanded bead molded article is preferably 240 kg / m 3 More preferably, it is 200 kg / m or less. 3 More preferably, it is 100 kg / m or less. 3 and even more preferably 80 kg / m or less. 3 and even more preferably 60 kg / m or less. 3or less, and particularly preferably 30 kg / m 3 The following is the result. The density of the expanded bead molding is calculated by dividing the mass of the expanded bead molding by the volume calculated based on the dimensions of the expanded bead molding, and can be measured by the method described in the examples.

[0082] The volumetric shrinkage of an expanded bead molded article obtained by in-mold molding of the expanded beads is preferably less than 8.0%. The volumetric shrinkage (unit: %) is determined by dividing the volume of the molded article, which is removed from the mold after in-mold molding and cured at atmospheric pressure (1 atm) and 80°C for 12 hours, by the volume of the mold (molding space) used to mold the article. In in-mold molding of expanded beads, the expanded beads are heated in a mold to fuse the expanded beads together, and then the resulting molded body is cooled. During this process, the molded body typically undergoes molding shrinkage (volume shrinkage). However, expanded beads prone to excessive molding shrinkage may experience unintended deformation when molding a complex molded body. Furthermore, such expanded beads may be prone to fluctuations in the dimensions of the molded body when molding conditions change, potentially making mold design difficult. From this perspective, a small volume shrinkage rate for the expanded bead molded body is preferred. In the present invention, as described above, by using specific expanded beads composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, it is possible to produce a molded article with a small volume shrinkage rate. From this viewpoint, the volume shrinkage rate of the expanded beads molded article obtained by molding the expanded beads in a mold is more preferably 7.5% or less, and even more preferably 7.0% or less. The volume of the molded body can be determined, for example, by a method of calculation from the outer dimensions of the molded body, or by a method of calculation from the increase in volume when the molded body is submerged in water (submersion method).

[0083] Furthermore, from the viewpoint of making it easier to obtain a molded body that fully reflects the shape of the molding space when obtaining a relatively thin molded body, such as a plate-shaped molded body, or a molded body having a shape that is longer in one direction than in other directions, the shrinkage rate of the expanded bead molded body in the maximum Feret diameter direction in a planar view when viewing the expanded bead molded body from the direction in which the projected area of ​​the expanded bead molded body is greatest is preferably less than 3.0%, more preferably 2.8% or less, and even more preferably 2.6%. The shrinkage rate in the maximum Feret diameter direction means the shrinkage rate (unit: %) obtained by dividing the maximum Feret diameter of the expanded bead molding in a planar view when the expanded bead molding is viewed from the direction in which the projected area of ​​the expanded bead molding is maximized by the length of the corresponding position of the molding die (molding space) used to mold the molding.

[0084] From the viewpoint of obtaining a molded article that is resistant to excessive deformation under stress and exhibits good strength and flexibility, the ratio of the compressive stress at 50% strain of the expanded bead molding to the density of the expanded bead molding is 4.0 kPa / [kg / m 3 ] or more than 12kPa / [kg / m 3 ] or less, and 5.0 kPa / [kg / m 3 ] or more than 10kPa / [kg / m 3 ] or less is more preferable. The ratio of the compressive stress at 50% strain of the expanded bead molding to the density of the expanded bead molding is calculated by compressing the expanded bead molding into a test piece of 5 cm length x 5 cm width x 2.5 cm height at a compression speed of 10 mm / min and dividing the stress at 50% strain measured by the density, and can be measured and calculated using the method described in the examples.

[0085] The polyethylene resin foam bead molded article is lightweight and has excellent mechanical properties, and therefore can be used as an impact absorbing material, a heat insulating material, various packaging materials, etc., for example, food transport containers, packaging and cushioning materials for electric and electronic parts, vehicle parts such as automobile bumpers, building parts such as residential heat insulating materials, miscellaneous goods, etc. [Example]

[0086] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples in any way.

[0087] [Measurement and Evaluation] The resins, expanded beads, and expanded bead molded articles used in the examples and comparative examples were subjected to the following measurements and evaluations. The expanded beads and expanded bead molded articles were evaluated after being left to condition for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm.

[0088] <Biomass content of polyethylene resin, resin particles and foam particles (mixed resin)> The biomass content (%) of the polyethylene resin (linear low-density polyethylene or branched low-density polyethylene) used in the examples and comparative examples was determined by radiocarbon dating in accordance with ASTM D6866. 14 The value was determined by measuring the concentration of C. The biomass content (%) of the resin particles and expanded particles (mixed resin) was calculated from the biomass content of the biomass-derived resin used to produce the expanded particles and the content of the biomass-derived resin in the expanded particles. In Table 1, LL3 is "SLH118" manufactured by Braskem, LD1 is "STN7006" manufactured by Braskem, and LD2 is "LD3020F" manufactured by LyondellBasell. LL3 and LD1 are polyethylenes listed on the positive list of biomass plastics of the Japan Biomass Plastics Association. In the positive list, LL3 is a polyethylene containing [(C2H4) n (C4H8) m (C6H 12 ) o It is described as a linear low-density polyethylene having the chemical structural formula:

[0089] <Polyethylene density, mixed resin density> The density of the polyethylene (linear low-density polyethylene or branched low-density polyethylene) and the density of the mixed resin used in the examples and comparative examples were measured based on Method A (water displacement method) of JIS K 7112:1999. In measuring the density of the mixed resin, the expanded beads were first degassed by hot pressing them for 3 minutes using a heating press platen adjusted to a temperature of 160°C to produce a resin sheet made of the mixed resin that constitutes the expanded beads. The density was measured using pellet-shaped samples obtained by cutting this resin sheet.

[0090] <Melt flow rate (MFR) of polyethylene, melt flow rate (MFR) of mixed resin> The melt flow rate (MFR) of the polyethylene (linear low density polyethylene or branched low density polyethylene) used in the examples and comparative examples LL or MFR LD The melt flow rates (MFR) of the mixed resins constituting the expanded beads of the Examples and Comparative Examples were measured in accordance with JIS K 7210-1:2014 at a temperature of 190°C and a load of 2.16 kg. To measure the melt flow rates of the mixed resins constituting the expanded beads, the expanded beads were first degassed by hot pressing them for 3 minutes using a heating press platen adjusted to a temperature of 160°C, to produce a resin sheet made of the mixed resins constituting the expanded beads. The melt flow rates were measured using pellet-shaped samples obtained by cutting this resin sheet.

[0091] <Melting point of polyethylene, resin particles and foam particles> The melting point (Tm LL or Tm LDThe melting points of the polyethylene resin and the expanded particles were measured by heat flux differential scanning calorimetry in accordance with JIS K 7121:2012. A high-sensitivity differential scanning calorimeter, "EXSTAR DSC7020" (manufactured by SII NanoTechnology Inc.), was used as the measuring device. The specimen conditioning method employed was "(2) Measurement of melting temperature after a certain heat treatment." Approximately 2 mg of polyethylene resin or approximately 2 mg of expanded particles was collected as a test specimen. The specimen was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow rate of 30 mL / min, then held at that temperature for 10 minutes. It was then cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (DSC curve for the second heating). The apex temperature of the melting peak in the DSC curve was determined, and this value was taken as the melting point. The melting point of the expanded beads and the melting point of the resin beads were assumed to be the same. If multiple melting peaks appear on a DSC curve, the apex temperature of the melting peak with the largest area is used as the melting point. The melting peak with the largest area can be determined by distinguishing each melting peak using the valley temperature of the DSC curve located between the peak temperatures of the melting peaks as a boundary and comparing the areas (heat of fusion) of each melting peak. The valley temperature of the DSC curve corresponds to the temperature at which the vertical axis of the differential DSC curve (DDSC) becomes 0, so it can also be determined from the DSC differential curve.

[0092] <Heat of fusion of polyethylene, total heat of fusion of resin particles and foamed particles> The heat of fusion (ΔH LL or ΔH LD The total heat of fusion of the foam particles (mixed resin) and the expanded particles (mixed resin) was measured in accordance with JIS K 7122:2012. First, a DSC curve was obtained for the second heating using polyethylene or expanded beads as a test specimen, using the same method as for measuring the melting point of low-density polyethylene described above. The point at 80°C on the obtained DSC curve for the second heating was designated α, and the point on the DSC curve corresponding to the melting end temperature was designated β. The area enclosed by the DSC curve in the section between points α and β and the line segment (α-β) was measured, and the heat of fusion of the polyethylene or the total heat of fusion of the expanded beads was calculated from this area. Note that the total heat of fusion of the expanded beads and the total heat of fusion of the resin beads were assumed to be the same.

[0093] <Heat of fusion of the high-temperature peak of foamed beads> The heat of fusion of the high-temperature peak of the expanded beads was measured by heat flux differential scanning calorimetry in accordance with JIS K 7122:2012. Specifically, approximately 2 mg of expanded beads was collected as a test piece and heated from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter (EXSTAR DSC7020). A DSC curve with two or more melting peaks (DSC curve from the first heating) was obtained. The measurement was performed under conditions of a nitrogen inflow rate of 30 mL / min. In the obtained DSC curve, the peak specific to the mixed resin constituting the expanded beads was designated A, and the high-temperature peak appearing above that was designated B. A straight line (α-β) was drawn connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting end temperature T of the test piece. The melting end temperature T is the high-temperature end point of high-temperature peak B, and refers to the intersection point between the high-temperature peak and the high-temperature-side baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve corresponding to the valley between the intrinsic peak A and high-temperature peak B, and the point where it intersected with the straight line (α-β) was designated δ. The area enclosed by the curve of the high-temperature peak B in the DSC curve, the line segment (δ-β), and the line segment (γ-δ) was determined, and the heat of fusion of each high-temperature peak was calculated from this area. The heat of fusion of the high-temperature peak was measured for three different test pieces, and the arithmetic mean value of the obtained values ​​was taken as the heat of fusion of the high-temperature peak of the expanded beads.

[0094] <Flexural modulus> The flexural modulus of polyethylene (linear low-density polyethylene or branched low-density polyethylene) was measured as follows. First, polyethylene resin was heat-pressed at 160°C to produce 4 mm sheets, and test pieces measuring 80 mm in length, 10 mm in width, and 4 mm in thickness were cut from these sheets. The flexural modulus of these test pieces was measured in accordance with JIS K 7171:2016. The radius R1 of the indenter and the radius R2 of the support table were both 5 mm, the distance between supports was 64 mm, and the test speed was 2 mm / min. The flexural modulus of the mixed resin was measured as follows. The expanded beads were heat-pressed at 160°C to produce a 4 mm thick sheet, and a test piece measuring 80 mm long, 10 mm wide, and 4 mm thick was cut from this sheet. The flexural modulus of this test piece was measured in accordance with JIS K7171:2016. The radius R1 of the indenter and the radius R2 of the support table were both 5 mm, the distance between supports was 64 mm, and the test speed was 2 mm / min. The flexural modulus of the mixed resin constituting the expanded beads was assumed to be the same as the flexural modulus of the mixed resin constituting the resin beads.

[0095] <Bulk density of expanded particles> Approximately 500cm 3 The expanded particles were filled into a measuring cylinder, and the bottom of the measuring cylinder was lightly tapped on the floor several times to stabilize the filling height of the expanded particles in the measuring cylinder. The bulk volume of the expanded particles indicated on the measuring cylinder was read and defined as V1 (L). Next, the mass of the expanded particles was measured and defined as W1 [g]. The mass W1 [g] of the foam particles is divided by the volume V1 (W1 / V1) and the unit is [kg / m 3 The bulk density of the expanded beads was calculated by converting the value into the value of the particle diameter.

[0096] <Closed cell ratio of expanded beads> The closed cell ratio of the expanded beads was measured as follows. Bulk volume approximately 20cm 3The expanded beads were immersed in ethanol to measure the apparent volume Va of the expanded beads. Next, the expanded beads whose apparent volume Va had been measured were thoroughly dried, and the true volume Vx of the expanded beads (the sum of the volume of the resin constituting the expanded beads and the total volume of the closed-cell portion within the expanded beads) was measured according to procedure C described in ASTM D2856-70. To measure this true volume Vx, an air comparison hydrometer "930" manufactured by Toshiba Beckman Corporation was used. The closed-cell ratio was then calculated using the following formula (1), and the arithmetic average of five measurements using different expanded beads was calculated. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) (1) Vx: The true volume (cm) of the foam particles measured by the above method 3 ) Va: The apparent volume (cm) of the foam particles measured from the rise in water level when the foam particles are submerged in ethanol in a measuring cylinder. 3 ) W: Mass of foam particles (g) ρ: Density of the resin that makes up the foamed particles (g / cm 3 )

[0097] <Average cell diameter of expanded beads> The average cell diameter of the expanded beads was measured as follows. Thirty expanded beads were randomly selected from the group of expanded beads. Each expanded bead was cut through the center and divided into two, and an enlarged photograph of one cross section was taken. In each cross-sectional photograph, four lines were drawn from the outermost surface of the expanded bead through the center to the outermost surface on the opposite side, so that the angles between any two adjacent lines were equal. The number of cells intersecting each line was counted, and the average cell diameter for each expanded bead was calculated by dividing the total length of the four line segments by the total number of cells intersecting the lines. These values ​​were then arithmetically averaged to determine the average cell diameter for the expanded beads.

[0098] <Ratio of bulk density of first-stage expanded beads to bulk density of second-stage expanded beads> The bulk density of the first-stage expanded beads and the bulk density of the second-stage expanded beads were measured by the above-mentioned bulk density measurement method. The bulk density of the first-stage expanded beads was divided by the bulk density of the second-stage expanded beads to obtain the ratio of the bulk density of the first-stage expanded beads to the bulk density of the second-stage expanded beads (bulk density 1段発泡 / bulk density 2段発泡 The larger the value of this ratio, the lower the bulk density of second-stage expanded particles that can be obtained, which means that the second-stage expandability is excellent.

[0099] <Density of foamed bead molding> The expanded bead molding was left to stand for 2 days under conditions of 50% relative humidity, 23°C, and 1 atm, and then its mass was measured and defined as W [g]. Next, based on the dimensions of the foamed bead molding, the volume V [cm 3 ] was measured. The mass W [g] of the foamed bead molding is divided by the volume V (W / V), and the unit is [kg / m 3 The density of the expanded bead molding was calculated by converting the calculated value into the value of the density of the expanded bead molding.

[0100] <Molding pressure range> Using the method described below in "Manufacturing Expanded Bead Molded Articles," expanded bead molded articles were molded at molding pressures (molding steam pressures) varying in 0.01 MPa increments between 0.10 and 0.16 MPa (G), and the moldability of the resulting molded articles was evaluated in terms of fusion, surface irregularities, and shape (sink marks (dents) in the center of the molded article). A sample that met the criteria listed below was deemed to have passed, and the steam pressure that met all criteria was defined as the molding pressure range. Note that pressures marked with (G) are gauge pressures, i.e., pressure values ​​relative to atmospheric pressure. The wider the range from the lower limit to the upper limit of the molding pressure range, the wider the moldable range and the more preferable it is. Also, those that can be molded under low steam pressure conditions are preferable because they can reduce the amount of steam required for molding and are excellent in productivity. (Fusing ability) The foamed bead molding was bent and broken, and the number of foamed beads present on the fracture surface (C1) and the number of broken foamed beads (C2) were determined. The ratio of the number of broken foamed beads to the total number of foamed beads (C2 / C1 × 100) was calculated as the material failure rate. The above measurement was performed five times using different test pieces, and the material failure rate was calculated for each. An arithmetic average of the material failure rates of 80% or more was considered to be pass, and an arithmetic average of the material failure rates of less than 80% was considered to be fail. (Surface unevenness) The foamed bead molding was evaluated as passing if the shape of the molding die was sufficiently formed at the periphery and the unevenness caused by adjacent foamed beads was not noticeable, while the foamed bead molding was evaluated as failing if the shape of the molding die was not sufficiently formed and the unevenness caused by adjacent foamed beads was noticeable. (shape) The thickness of the flat-plate-shaped expanded bead molding obtained by in-mold molding was measured near both longitudinal ends (the intersection of a position 10 mm inward from the end toward the center in the longitudinal direction of the molding and the position dividing the molding in half in the transverse direction) and at the center (the intersection of the position dividing the molding in half in the longitudinal direction and the position dividing the molding in half in the transverse direction). Next, the ratio (%) of the thickness at the center to the thickness of the thickest point near both ends was calculated. A ratio of 95% or more was considered pass (no excessive sink marks in the center of the molding), and a ratio of less than 95% was considered fail (sink marks in the center of the molding).

[0101] <Molding pressure range and minimum shrinkage rate that allows molding of molded products with a volume shrinkage rate of less than 8.0%> The volume of the molded body molded within the above <molding pressure range> was measured. The volume of this molded body was divided by the volume of the molding die (molding space) used to mold the molded body to calculate the volumetric shrinkage rate (unit: %). The molding pressure range within which molded bodies with a volumetric shrinkage rate of less than 8.0% could be obtained is shown in the table as the molding pressure range within which molded bodies with a volumetric shrinkage rate of less than 8.0% can be molded. Note that, since the molded bodies molded within the above <molding pressure range> fully reflected the shape of the molding space, the length of the molded body in the longitudinal direction, lateral direction, and thickness direction were measured, and the volume of the molded body was calculated by multiplying these values. The volumetric shrinkage rate of the compact that exhibited the lowest volumetric shrinkage rate among the compacts obtained within this molding pressure range is also shown in the table. Furthermore, for the molded bodies obtained in this molding pressure range, the length of the molded body in the longitudinal direction (the direction corresponding to 200 mm), which is the maximum Feret diameter direction of the expanded bead molded body in a plan view of the molded body when viewed from the direction in which the projected area of ​​the molded body is maximized (in the molded bodies in the examples, the plan view when viewed from the mold clamping direction of the mold), was measured. The longitudinal length of this molded body was divided by the length in the corresponding direction in the molding mold (molding space) used to mold the molded body, to calculate the longitudinal shrinkage rate (shrinkage rate in the maximum Feret diameter direction of the expanded bead molded body, unit:%). Then, among the molded bodies obtained in this molding pressure range, the value of the shrinkage rate of the molded body showing the lowest longitudinal shrinkage rate was determined. In the examples, molded bodies with a longitudinal shrinkage rate of less than 3.0% were obtained over the entire molding pressure range in which molded bodies with a volume shrinkage rate of less than 8.0% could be molded.

[0102] <Compressive stress at 50% strain of expanded bead molding and ratio of compressive stress at 50% strain of expanded bead molding to the density of expanded bead molding> Test pieces measuring 5 cm long x 5 cm wide x 2.5 cm high were taken from the molded articles obtained in the Examples and Comparative Examples, and the stress at 50% strain was measured by compressing the test pieces at a compression rate of 10 mm / min. The higher the stress, the better the strength of the expanded bead molded article. The test pieces were taken from molded articles molded at the lowest possible steam pressure. The obtained compressive stress at 50% strain was divided by the density to calculate the ratio of the compressive stress at 50% strain of the expanded bead molding to the density of the expanded bead molding. 3 ] or more, the molded body is less likely to deform excessively due to compressive stress, which is preferable.

[0103] [polyethylene] The polyethylenes (linear low-density polyethylene (PE-LLD) or branched low-density polyethylene (PE-LD)) used in the examples and comparative examples are shown in Table 1. LL1 is a linear low-density polyethylene containing 1.8 mol% of a component derived from 1-octene as a copolymerization component (comonomer). LL2 is a linear low-density polyethylene containing 1.9 mol% of a component derived from 4-methyl-1-pentene as a copolymerization component (comonomer). LD3 is "LF244E" manufactured by Japan Polyethylene Corporation.

[0104] [Table 1]

[0105] [Production of Expanded Beads and Expanded Bead Molded Articles] Example 1 <Production of expanded beads> An extruder having an inner diameter of 26 mm and equipped with a strand-forming die on the downstream side was prepared. Linear low-density polyethylene LL1, branched low-density polyethylene LD1, and zinc borate as a cell control agent were fed into an extruder and melt-kneaded to form a resin melt consisting of the mixed resins. LL1 and LD1 were fed in the ratios shown in Table 2, and zinc borate was fed so that the content of zinc borate in the expanded beads was 500 ppm by mass. The resulting molten resin was extruded as strands through a strand-forming die, and the extruded strands were water-cooled and then cut with a pelletizer to obtain resin particles composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, each having an average mass of 1.5 mg, a particle diameter of 1.9 mm, and a length / diameter ratio of 1.9.

[0106] In a 5 L sealed container were placed 500 g of the resin particles, 3.5 L of water as a dispersion medium, 3 g of kaolin as a dispersant, and 0.2 g of sodium dodecylbenzenesulfonate (trade name: Neogen, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a surfactant. Next, carbon dioxide as a blowing agent was injected into the sealed container and pressurized until the equilibrium vapor pressure reached 4.0 MPa (G). Next, the contents of the sealed container were heated to the foaming temperature shown in Table 2 at a temperature increase rate of 2°C / min while stirring. The temperature was then maintained for 15 minutes (holding step). This holding step adjusted the heat of fusion of the high-temperature peak (obtained from the endothermic curve in DSC measurement). The contents of the sealed container were then released under atmospheric pressure to obtain expanded particles (first-stage expanded particles). The expanded beads obtained as described above were left to cure for 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. Next, the cured expanded beads were filled into a pressurizable sealed container, and the pressure inside the sealed container was increased from normal pressure to pressurize the expanded beads. The pressurized state of the expanded beads was maintained for 24 hours to allow air to penetrate into the cells of the expanded beads. The expanded beads were then removed from the sealed container, and expanded beads with an internal cell pressure of 0.5 MPa (G) were obtained. These expanded beads were then fed into a two-stage expansion device. Steam was supplied into the device to cause two-stage expansion of the expanded beads, yielding expanded beads (two-stage expanded beads). The expanded beads after two-stage expansion were used for the measurements described above and for producing expanded bead moldings.

[0107] <Production of foamed bead molded body> The expanded beads were filled into a mold capable of forming a flat plate of 200 mm length x 65 mm width x 45 mm thickness, and heated by the following heating method. First, with the drain valves on both sides of the mold open, steam was supplied to the mold to perform preheating (exhaust process). Then, steam was supplied from one side of the mold to heat it, and then steam was supplied from the other side to heat it again. Next, steam was supplied from both sides of the mold at a predetermined molding heating steam pressure to heat it (main heating). After main heating was completed, the pressure was released, and the mold was water-cooled until the pressure generated on the molding surface of the mold was 0.04 MPa (G), after which the mold was opened and the foamed bead molding was removed. The obtained molded body was cured for 12 hours in an oven at 80°C under atmospheric pressure (1 atm) to obtain an expanded bead molded body. In the evaluation of the above-mentioned <molding pressure range>, molding was performed by changing the molding pressure. The measurement results of the physical properties of the obtained expanded beads and the evaluation results of the expanded bead moldings are shown in Table 2. The expanded beads were non-crosslinked. Furthermore, among the moldings obtained within the <molding pressure range>, the molding that showed the lowest shrinkage rate in the longitudinal direction was 2.5%.

[0108] Examples 2 to 4 Expanded beads and expanded bead molded articles were obtained in the same manner as in Example 1, except that the types and ratios of the linear low-density polyethylene and the branched low-density polyethylene and the expansion temperature were changed as shown in Table 2. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the expanded bead molded articles are shown in Table 2. Note that each expanded bead was non-crosslinked. Furthermore, among the molded articles obtained within the <molding pressure range>, the values ​​of the shrinkage percentages of the molded articles showing the lowest shrinkage percentages in the longitudinal direction were 2.8% for Example 2, 2.5% for Example 3, and 2.9% for Example 4.

[0109] (Comparative Examples 1 to 6) Expanded beads and expanded bead molded articles were obtained in the same manner as in Example 1, except that the types and ratios of the linear low-density polyethylene and the branched low-density polyethylene, and the expansion temperature were changed as shown in Table 3. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the expanded bead molded articles are shown in Table 3. Note that each expanded bead was uncrosslinked. Furthermore, among the molded articles obtained within the <molding pressure range>, the values ​​of the shrinkage percentages of the molded articles showing the lowest shrinkage percentages in the longitudinal direction were 3.2% for Comparative Example 1, 3.1% for Comparative Example 2, 3.1% for Comparative Example 3, 2.9% for Comparative Example 4, and 3.3% for Comparative Example 6.

[0110] [Table 2]

[0111] [Table 3]

[0112] The results shown in Table 2 indicate that the expanded beads of the Examples have a biomass content equal to or greater than a specific value and are excellent in-mold moldability. Furthermore, the expanded beads of the Examples can be molded in-mold under low molding pressure conditions, and a wide molding range allows for the production of molded articles with particularly low shrinkage rates. Furthermore, the polyethylene resin expanded bead molded articles produced using the expanded beads of the Examples have high compressive stress even though they have low density.

Claims

1. A method for producing expanded polyethylene resin particles by expanding polyethylene resin particles, comprising: the polyethylene-based resin particles are composed of a mixed resin of linear low-density polyethylene and branched low-density polyethylene obtained by kneading linear low-density polyethylene and branched low-density polyethylene, the branched low-density polyethylene has a biomass content of 30% or more as measured by ASTM D6866; the branched low-density polyethylene has a heat of fusion of 95 J / g or more, the blending amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass, The method for producing expanded polyethylene resin beads, wherein the total heat of fusion of the polyethylene resin beads is 90 J / g or more.

2. The heat of fusion of the linear low-density polyethylene (ΔH ＬＬ ) and the heat of fusion of the branched low-density polyethylene (ΔH ＬＤ ) and the difference (ΔH ＬＬ -ΔH ＬＤ 2. The method for producing expanded polyethylene resin beads according to claim 1, wherein the elongation coefficient (E / E) is 0 J / g or more and 30 J / g or less.

3. The polyethylene resin particles have a melting point of 115°C or higher and 130°C or lower, The melting point (Tm ＬＬ ) and the melting point (Tm ＬＤ ) and the difference (Tm ＬＬ -Tm ＬＤ 3. The method for producing expanded polyethylene resin beads according to claim 1, wherein the temperature is 5°C or higher and 15°C or lower.

4. 3. The method for producing expanded polyethylene resin beads according to claim 1, wherein the branched low-density polyethylene has a melt flow rate of 0.1 g / 10 min or more and 3 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg.

5. 3. The method for producing expanded polyethylene resin beads according to claim 1, wherein the linear low-density polyethylene is a copolymer containing a component derived from octene.

6. 3. The method for producing expanded polyethylene resin beads according to claim 1, wherein the polyethylene resin beads have a biomass content of 5% or more as measured by ASTM D6866.

7. The method for producing expanded polyethylene resin beads according to claim 1 or 2, wherein the mixed resin has a flexural modulus of 200 MPa or more.

8. Polyethylene-based resin foam particles, the expanded beads are made of a mixed resin of linear low-density polyethylene and branched low-density polyethylene, The flexural modulus of the mixed resin is 200 MPa or more, The expanded beads have a biomass content of 5% or more as measured by ASTM D6866; The expanded polyethylene resin beads have a total heat of fusion of 90 J / g or more.

9. 9. The expanded polyethylene resin particles according to claim 8, wherein the amount of the branched low-density polyethylene in the mixed resin is 5% by mass or more and less than 40% by mass, with the total of the linear low-density polyethylene and the branched low-density polyethylene being 100% by mass.

10. The expanded polyethylene resin beads according to claim 8 or 9, wherein the melting point of the expanded polyethylene resin beads is 115°C or higher and 130°C or lower.

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