Expanded beads and expanded bead molded articles

Abstract

To provide foamed particles which are excellent in in-mold moldability, have a high biomass degree, and enable production of a polyethylene-based resin foamed particle molding in a wide density range, and a polyethylene-based resin foamed particle molding which has a high biomass degree and low apparent density.SOLUTION: Foamed particles contain linear low-density polyethylene as a base material resin, and have a bulk density of 10 kg / m3 or more and 240 kg / m3 or less, wherein the linear low-density polyethylene has a biomass degree measured by ASTM D 6866 of 40% or more, the foamed particles have such a crystal structure that a melting peak (inherent peak) inherent to the linear low-density polyethylene and one or more melting peaks (high temperature peaks) on the high-temperature side relative to the inherent peak appear, in a DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, a total melting heat quantity of the foamed particles is 70 J / g or more and 100 J / g or less, and a melting heat quantity of the high temperature peaks is 10 J / g or more and 50 J / g or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to expanded beads and expanded bead moldings. [Background technology]

[0002] Polyethylene resin foam bead moldings, obtained by molding polyethylene resin foam beads in a mold, have excellent chemical resistance, cushioning properties, etc., and are also highly recyclable. For these reasons, polyethylene resin foam bead moldings 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, in response to environmental concerns such as concerns about the depletion of fossil fuels such as petroleum and the need to reduce carbon dioxide emissions, biomass plastics have been developed and attempts are being made to replace petroleum-derived resins. For example, Patent Document 1 discloses expanded polyethylene resin particles containing a plant-derived polyethylene resin having a plant content of 80% or more as measured by ASTM D 6866, and having a plant content of 1% or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-060514 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it was difficult to obtain expanded beads having a low bulk density using biomass polyethylene with the technology disclosed in Patent Document 1. Furthermore, the technology disclosed in Patent Document 1 had poor moldability in the mold of the resulting expanded beads, making it difficult to obtain good expanded bead moldings over a wide range of densities. An object of the present invention is to provide expanded beads that have excellent in-mold moldability, a high biomass content, and can be used to produce expanded polyethylene resin bead moldings over a wide density range, and to provide expanded polyethylene resin bead moldings that have a high biomass content and a low apparent density. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that expanded beads that use a linear low-density polyethylene having a specific biomass content as a base resin and that satisfy a specific relationship in heat of fusion can solve the above-mentioned problems. That is, the present invention is a woven fabric having a bulk density of 10 kg / m and a base resin of linear low-density polyethylene. 3 More than 240kg / m 3 The expanded beads described below have a linear low-density polyethylene having a biomass content of 40% or more as measured according to ASTM D 6866, and a crystalline structure in which a melting peak (intrinsic peak) inherent to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear higher than the intrinsic peak in a DSC curve obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min, and the total heat of fusion of the expanded beads is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide expanded beads that have excellent in-mold moldability, a high biomass content, and can be used to produce expanded polyethylene resin bead moldings over a wide density range, as well as expanded polyethylene resin bead moldings that have a high biomass content and a low apparent density. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Foam particles] The expanded beads of the present invention are made of linear low-density polyethylene as a base resin and have a bulk density of 10 kg / m 3 More than 240kg / m 3The expanded beads described below have a linear low-density polyethylene having a biomass content of 40% or more as measured according to ASTM D 6866, and a crystalline structure in which a melting peak (intrinsic peak) inherent to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear higher than the intrinsic peak in a DSC curve obtained by heating the expanded beads from 23°C to 200°C at a heating rate of 10°C / min, and the total heat of fusion of the expanded beads is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less.

[0008] (linear low-density polyethylene) The expanded beads have linear low-density polyethylene as a base resin. In this specification, "linear low-density polyethylene as a base resin" means that the expanded beads are composed of a resin whose main component is linear low-density polyethylene. As will be described later, the expanded beads may contain polymers other than linear low-density polyethylene as long as the effects of the present invention are not impaired.

[0009] The linear low-density polyethylene has a biomass degree of 40% or more as measured by ASTM D 6866. Having a biomass degree within this range makes it possible to suppress the use of fossil resources when producing a molded article, and also to reduce the amount of carbon dioxide emitted over the life cycle of the molded article. From the above viewpoint, the biomass degree of the linear low-density polyethylene measured by ASTM D 6866 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. There is no upper limit, and the biomass degree of the linear low-density polyethylene measured by ASTM D 6866 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 linear low-density polyethylene measured by ASTM D 6866 is preferably 95% or less, more preferably 90% or less. The biomass degree is measured by ASTM D 6866 and means the proportion of naturally occurring components contained in the linear low-density polyethylene. The biomass degree is also determined by radiocarbon C 14 When a mixed resin in which a plurality of linear low-density polyethylenes are mixed is used as the linear low-density polyethylene, the biomass degree of the linear low-density polyethylene may be calculated from the biomass degree of each linear low-density polyethylene used to form the mixed resin and the content of each linear low-density polyethylene in the mixed resin.

[0010] The linear low-density polyethylene has a density of 910 kg / m 3 More than 940kg / m 3 The linear low-density polyethylene may be a mixed resin obtained by mixing a plurality of copolymers of ethylene and α-olefins. The α-olefin is preferably an α-olefin having 3 to 20 carbon atoms, more preferably an α-olefin having 3 to 10 carbon atoms, and even more preferably an α-olefin having 3 to 6 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, 1-octene, 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-butene, 1-hexene, and 4-methyl-1-pentene. Therefore, the linear low-density polyethylene preferably comprises, as a main component, at least one linear low-density polyethylene selected from the group consisting of linear low-density polyethylene A containing butene and hexene as copolymerization components (comonomers) and linear low-density polyethylene B containing butene as copolymerization components (comonomers), and more preferably comprises, as a main component, linear low-density polyethylene A containing butene and hexene. In this case, the total proportion of linear low-density polyethylene A and linear low-density polyethylene B in the linear low-density polyethylene is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Furthermore, the total proportion of linear low-density polyethylene A and linear low-density polyethylene B in the linear low-density polyethylene is 100% by mass or less. From the viewpoint of further improving the moldability of the expanded beads in a mold, the proportion of the linear low-density polyethylene A in the linear low-density polyethylene is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, while the proportion of the linear low-density polyethylene A in the linear low-density polyethylene is 100% by mass or less. The components derived from hexene in the linear low-density polyethylene containing butene and hexene as copolymerization components include 1-hexene and 4-methyl-1-pentene.

[0011] From the viewpoint of stably obtaining expanded beads having excellent in-mold moldability, when a linear low-density polyethylene B containing a butene component is used as the linear low-density polyethylene, the content of the butene component in the linear low-density polyethylene B is preferably 2 mol % or more and 7 mol % or less, and more preferably 3 mol % or more and 6 mol % or less. From the same viewpoint, when a linear low-density polyethylene A containing butene and hexene components is used as the linear low-density polyethylene, the content of the butene components in the linear low-density polyethylene A is preferably from 0.5 mol% to 6 mol%, more preferably from 1 mol% to 5 mol%, and even more preferably from 2 mol% to 4 mol%. When a linear low-density polyethylene A containing butene and hexene components is used, the content of the hexene components in the linear low-density polyethylene A is preferably from 0.2 mol% to 5 mol%, more preferably from 0.5 mol% to 4 mol%, and even more preferably from 0.8 mol% to 3 mol%. Furthermore, the linear low-density polyethylene may contain a component derived from propylene as an α-olefin (copolymerization component, comonomer), provided that the objects of the present invention can be achieved and the effects of the present invention are not impaired. When the linear low-density polyethylene contains a component derived from propylene, the content of the component derived from propylene in the linear low-density polyethylene is preferably from 0.3 mol% to 5 mol%, more preferably from 0.5 mol% to 4 mol%, even more preferably from 0.8 mol% to 3 mol%, and particularly preferably from 1 mol% to 2 mol%. 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. 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.

[0012] From the same viewpoint, when a linear low-density polyethylene A containing a butene component and a hexene component is used as the linear low-density polyethylene, the ratio of the hexene component content to the butene component content in the linear low-density polyethylene A [hexene component content (mol%) / butene component content (mol%)] is preferably 0.1 or more and 2 or less, more preferably 0.2 or more and 1 or less, and even more preferably 0.3 or more and 0.8 or less. Furthermore, when the linear low-density polyethylene contains a component derived from propylene, the ratio of the content of components derived from propylene to the content of components derived from α-olefins other than propylene (e.g., butene and / or hexene) in the linear low-density polyethylene [propylene component content (mol%) / α-olefin component content other than propylene (mol%)] is preferably 0.1 or more and 2 or less, more preferably 0.2 or more and 1 or less, and even more preferably 0.3 or more and 0.7 or less.

[0013] The melting point of the linear low-density polyethylene is preferably 110° C. or higher, more preferably 120° C. or higher, and even more preferably 122° C. or higher, from the viewpoint of improving the mechanical properties of the resulting molded article. On the other hand, the melting point of the linear low-density polyethylene is preferably 135° C. or lower, more preferably 130° C. or lower, and even more preferably 126° 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 linear low-density polyethylene is measured using the 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.

[0014] 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 2.0 g / 10 min or less. When the melt flow rate of the linear low-density polyethylene is in 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 still more preferably 0.7 g / 10 min or more. The melt flow rate of the linear low-density polyethylene is more preferably 1.8 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and still more preferably 1.4 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.

[0015] The density of the linear low-density polyethylene is 910 kg / m 3 More than 940kg / m 3 From the viewpoint of easily obtaining expanded beads having desired physical properties, it is preferably 910 kg / m or less. 3 More than 935kg / m 3 More preferably, it is 912 kg / m or less.3 More than 930kg / m 3 More preferably, it is 914 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, for example, by Method A (water displacement method) described in JIS K7112:1999.

[0016] From the viewpoint of facilitating the production of expanded beads having desired physical properties, the heat of fusion of the linear low-density polyethylene is preferably 60 J / g or more, more preferably 70 J / g or more, and even more preferably 75 J / g or more. From the same viewpoint, the heat of fusion of the linear low-density polyethylene is preferably 120 J / g or less, more preferably 110 J / g or less, even more preferably 100 J / g or less, and particularly preferably 90 J / g or less. The heat of fusion of the linear low-density polyethylene 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.

[0017] <Characteristics and composition of foamed beads> As described above, the expanded beads of the present invention have as their base resin a linear low-density polyethylene having a biomass content of 40% or more as measured by ASTM D 6866, and preferably have the following properties:

[0018] The expanded beads of the present invention have a bulk density of 10 kg / m 3 More than 240kg / m 3 The expanded beads have a bulk density of 10 kg / m or less 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, the bulk density of the expanded beads is 240 kg / m from the viewpoint of obtaining a molded product with a low apparent density. 3or 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 The following is the result. As will be described later, in the present invention, the expanded beads obtained 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 article with a low apparent 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 expanded beads having a low apparent density. 3 or less, preferably 200 kg / m 3 More preferably, it is 180 kg / m or less. 3 More preferably, it is 160 kg / m or less. 3 The following is the result. The bulk density can be measured by the method described in the examples.

[0019] 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, but it is preferably 99% or less, more preferably 98% or less, and even more preferably 97% or less. The closed cell ratio can be measured by the method described in the examples.

[0020] The average cell diameter of the expanded beads of the present invention is preferably 60 μm or more and 200 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 70 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more. Furthermore, the average cell diameter of the expanded beads of the present invention is preferably 180 μm or less, more preferably 160 μm or less, and even more preferably 140 μm or less. In the case of two-stage expansion, the average cell diameter of the expanded beads after the first stage expansion (before the second stage expansion) is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. In the case of two-stage expansion, the average cell diameter of the expanded beads after the first stage expansion (before the second stage expansion) is preferably 120 μm or less, more preferably 110 μm or less, and even more preferably 100 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.

[0021] The expanded beads of the present invention 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 linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear higher than the intrinsic peak, and the total heat of fusion of the expanded beads is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less.

[0022] The DSC curve is a DSC curve obtained by differential scanning calorimetry (DSC) in accordance with JIS K7122: 2012. Specifically, the DSC curve can be obtained by heating 1 to 3 mg of the expanded beads of the present invention from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter. As described above, in the DSC curve measured for the expanded beads of the present invention, a melting peak (intrinsic peak) inherent to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear at temperatures higher than the intrinsic peak.

[0023] 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 linear low-density polyethylene is a melting peak that appears due to melting of crystals that the linear low-density polyethylene constituting the expanded beads normally has. 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 obtained 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, in the DSC curve obtained when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating), only the melting peak due to the melting of crystals typically found in the linear low-density polyethylene that constitutes the expanded beads appears. This intrinsic peak appears in both the DSC curves obtained in the first heating and the second heating. The peak apex temperatures may differ slightly between the first and second heatings, but the difference is usually less than 5°C. This allows identification of the intrinsic peak. The expanded beads of the present invention are preferably expanded beads in which only a melting peak (intrinsic peak) inherent to linear low-density polyethylene appears in a DSC curve obtained during the second heating cycle when the expanded beads are heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min.

[0024] The total heat of fusion of the expanded beads of the present invention is the sum of the heats of fusion of all melting peaks (endothermic peaks) appearing in a DSC curve. The total heat of fusion of the expanded beads of the present invention is 70 J / g or more and 100 J / g or less. When the total heat of fusion of the expanded beads is within this range, expanded beads having excellent two-stage expandability and in-mold moldability can be obtained, and a molded product having excellent strength can be obtained. The total heat of fusion of the expanded beads of the present invention is preferably 72 J / g or more, more preferably 75 J / g or more, and even more preferably 78 J / g or more, from the viewpoint of improving the strength of the resulting molded article. Also, the total heat of fusion of the expanded beads of the present invention is preferably 95 J / g or less, more preferably 90 J / g or less, and even more preferably 85 J / g or less, from the viewpoint of improving the two-stage expandability and in-mold moldability of the expanded beads. 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 again at a rate of 10°C / min from 23°C to 200°C, a DSC curve (DSC curve during the second heating) was obtained. 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 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 heat of fusion of the expanded beads can be calculated from this area.

[0025] The expanded beads of the present invention have a heat of fusion of 10 J / g or more and 50 J / g or less at their high-temperature peak. When the heat of fusion of the expanded beads at their high-temperature peak is within this range, the expandable beads can be molded in a mold even when they have a low bulk density, and the expanded beads can be molded in a mold over a wide range of molding pressures. This allows for the production of good molded articles over a wide range of densities. The heat of fusion of the expanded beads of the present invention at the high-temperature peak is preferably 15 J / g or more, more preferably 20 J / g or more, even more preferably 30 J / g or more, and still more preferably 32 J / g, from the viewpoints of suppressing sink marks in the 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 of the present invention at the high-temperature peak is 50 J / g or less, preferably 45 J / g or less, and more preferably 40 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 K7122: 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.

[0026] The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads of the present invention [heat of fusion of the high-temperature peak / total heat of fusion] is preferably 0.2 or more and 0.7 or less, more preferably 0.3 or more and 0.7 or less. When the heats of fusion described above are within the above ranges and the ratio is within the above ranges, expanded beads having excellent moldability and a wide molding pressure range that allows moldability in a wide density range can be obtained. In addition, expanded beads with excellent two-stage expandability can be obtained. The ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads of the present invention is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.45 or more, from the viewpoints of suppressing sink marks in the molded body 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. Furthermore, the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads of the present invention is preferably 0.6 or less, more preferably 0.55 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 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.

[0027] The expanded beads of the present invention preferably have a biomass ratio of 40% or more as measured by ASTM D 6866. Having a biomass ratio within this range makes it possible to suppress the use of fossil resources in the production of molded articles and also to reduce the amount of carbon dioxide emitted over the life cycle of the molded articles. From the above viewpoint, the biomass degree of the expanded beads of the present invention measured by ASTM D 6866 is more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. There is no upper limit, and the biomass degree of the expanded beads of the present invention measured by ASTM D 6866 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 of the present invention measured by ASTM D 6866 is preferably 95% or less, more preferably 90% or less. The biomass degree is measured by ASTM D 6866 and means the proportion of naturally occurring components contained in the expanded beads of the present invention. The biomass degree is also determined by the radioactive carbon C 14 or can be calculated 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.

[0028] The expanded beads preferably have a melt flow rate of 0.1 g / 10 min or more and 2.0 g / 10 min or less, measured at a temperature of 190° C. and a load of 2.16 kg. When the expanded beads have a melt flow rate within this range, the in-mold moldability of the expanded beads can be further improved. The expanded beads have a melt flow rate of 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 1.8 g / 10 min or less, even more preferably 1.5 g / 10 min or less, and even more preferably 1.4 g / 10 min or less. The melt flow rate of 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. In the measurement, expanded beads may be degassed, as necessary, by a heat press or the like, to the extent that the physical properties of the resin are not significantly impaired, and the measurement sample may be used.

[0029] 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. 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.

[0030] 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.

[0031] The expanded beads of the present invention 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, for example, during the process of producing resin beads.

[0032] 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.

[0033] The expanded beads of the present invention may contain polymers such as resins and elastomers other than the linear low-density polyethylene, as long as the effects of the present invention are not impaired. In this case, the content of the polymers other than the linear 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 linear low-density polyethylene.

[0034] 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 linear low-density polyethylene constituting the expanded beads, and amorphous polyolefin resins having a softening point lower than that of the linear low-density polyethylene 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.

[0035] As described above, the expanded beads of the present invention can be suitably used as expanded beads for in-mold molding. Furthermore, since the expanded beads of the present invention satisfy the specific relationship of heat of fusion, they have excellent expandability during second-stage expansion, and are therefore suitable as expanded beads for second-stage expansion. On the other hand, the expanded beads of the present invention satisfy a specific relationship of heat of fusion, thereby becoming expanded beads having appropriate flexibility and recovery. Therefore, the expanded beads of the present invention can be suitably used, for example, as filler beads for cushioning. Filler beads are particulate fillers that are filled into a bag to form cushioning, and the expanded beads of the present invention can be suitably used, in particular, as filler beads for bead cushions.

[0036] <Method of manufacturing expanded beads> As described above, the expanded beads of the present invention are made of linear low-density polyethylene as a base resin and have a bulk density of 10 kg / m 3 More than 240kg / m 3The method for producing the expanded beads is not particularly limited, as long as the linear low-density polyethylene has a biomass content of 40% or more as measured according to ASTM D 6866, the expanded beads 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 specific to linear low-density polyethylene (intrinsic peak) and one or more melting peaks (high-temperature peaks) appear higher than the intrinsic peak, the total heat of fusion of the expanded beads is 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less. The expanded beads can be produced, for example, by impregnating resin particles having linear low-density polyethylene as a base resin with a blowing agent and then expanding the resin particles containing the blowing agent. An example of a suitable production method is shown below.

[0037] A preferred method for producing the expanded beads of the present invention includes a dispersing step of dispersing resin particles having a linear low-density polyethylene as a base resin in an aqueous medium in a container, a blowing agent impregnation step of impregnating the resin particles with a blowing agent in the container, and an expansion step of releasing the resin particles containing the blowing 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.

[0038] (Production of resin particles using linear low-density polyethylene as the base resin) The resin particles used in the production of the expanded beads of the present invention can be obtained by supplying the linear low-density polyethylene, a cell control agent, etc., which is optionally blended, 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 cutting method, a hot cutting method, an underwater cutting method, or the like.

[0039] 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.

[0040] 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.

[0041] (Production of expanded beads) 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.

[0042] 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.

[0043] 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 amsnite, 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. Among 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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. The upper limit is preferably 4 MPa (G) or less, more preferably 3 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 preferably 100 to 200°C, more preferably 130 to 160°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 (for example, atmospheric pressure).

[0049] The expanded beads of the present invention 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 (-15°C of the melting point of the linear low-density polyethylene constituting the resin particles) and (+10°C of the melting point of the linear low-density polyethylene constituting the resin particles) and maintained at this temperature for a sufficient time, preferably 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. The maintenance step can be performed, for example, as part of the dispersion step or the blowing agent impregnation step. 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 under a pressure lower than the pressure inside the sealed container to expand the resin particles, thereby obtaining expanded beads that exhibit the above-mentioned melting peak.

[0050] 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 apparent density, two-stage expansion is preferred.

[0051] [Polyethylene resin foam bead molding] The foamed polyethylene resin bead molded article of the present invention (hereinafter also simply referred to as foamed bead molded article) is obtained by molding the foamed beads in a mold. Specifically, linear low-density polyethylene is used as the base resin, and the bulk density is 10 kg / m 3 More than 240kg / m 3 or less, wherein the linear low-density polyethylene has a biomass degree as measured in accordance with ASTM D 6866 of 40% or more, and the expanded beads have a crystalline structure in which a melting peak (intrinsic peak) inherent to linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear higher than the intrinsic peak in a DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, and the expanded beads have a total heat of fusion of 70 J / g or more and 100 J / g or less, and the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less, and are molded in a mold.

[0052] The foamed bead molded article of the present invention can be produced by filling a mold with foamed beads and heat-molding them using a heating medium such as steam. Specifically, after filling the mold with foamed beads, a heating medium such as steam is introduced into the mold to heat and expand the foamed beads (secondary expansion), and the foamed beads are fused together to produce 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).

[0053] From the viewpoint of improving mechanical properties, the density of the expanded bead molding of the present invention 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 particularly preferably 60 kg / m 3The 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.

[0054] The polyethylene resin foam bead molded article of the present invention 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]

[0055] 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.

[0056] [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.

[0057] <Biomass content of polyethylene and foam beads> The biomass content of the polyethylene (linear low-density polyethylene or high-density polyethylene) used in the examples and comparative examples was determined by radiocarbon C in accordance with ASTM D 6866. 14 The biomass degree of the expanded beads was calculated from the biomass degree of the biomass-derived resin used to produce the expanded beads and the content of the biomass-derived resin in the expanded beads. In Table 1, LL1 to LL3 and HD1 are polyethylenes listed in the positive list of biomass plastics of the Japan Biomass Plastics Association. In the positive list, LL1 and LL3 are polyethylenes listed in the positive list of biomass plastics of the Japan Biomass Plastics Association. n (C4H8) m (C6H12 ) o LL2 is described as a linear low-density polyethylene containing butene and hexene as copolymer components, represented by the chemical structural formula [(C2H4) n (C4H8) m It is described as a linear low-density polyethylene containing a butene component as a copolymer component, represented by the chemical structural formula:

[0058] <Polyethylene density> The density of the polyethylene (linear low-density polyethylene or high-density polyethylene) used in the examples and comparative examples was measured based on Method A (water displacement method) of JIS K 7112:1999.

[0059] <Content of components derived from α-olefins in linear low-density polyethylene> The content of components derived from each α-olefin in linear low-density polyethylene was determined by the following carbon-13 nuclear magnetic resonance ( 13 C-NMR). First, linear low-density polyethylene was dissolved in a mixed solvent (130°C) of o-dichlorobenzene-d4 (ODCB):benzene-d6 (C6D6) = 4:1 to prepare a 10 wt / vol% solution for measurement. A JEOL ECZ-400S nuclear magnetic resonance spectrometer was used. 13 NMR of the measurement solution using C as the measurement nucleus ( 13 Based on the chemical shift information in the obtained NMR spectrum, the components derived from α-olefins contained in the linear low-density polyethylene were identified, and their contents (mol%) were calculated.

[0060] <Melt flow rate (MFR) of polyethylene and foam particles> The melt flow rates (MFR) of the polyethylene (linear low-density polyethylene or high-density polyethylene) used in the Examples and Comparative Examples and the melt flow rates (MFR) of the expanded beads in the Examples and Comparative Examples were measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1: 2014. In measuring the melt flow rates of the expanded beads, expanded beads that had been degassed to a degree that did not significantly impair the physical properties of the resin were used as measurement samples.

[0061] <Polyethylene melting point> The melting points of the polyethylenes (linear low-density polyethylene or high-density polyethylene) used in the examples and comparative examples were measured by heat flux differential scanning calorimetry in accordance with JIS K7121:2012. A high-sensitivity differential scanning calorimeter, "EXSTAR DSC7020" (manufactured by SII NanoTechnology Inc.), was used as the measuring device. The specimen was conditioned using "(2) Measurement of melting temperature after a fixed heat treatment." 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, 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. 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.

[0062] <Heat of fusion of polyethylene and total heat of fusion of foamed beads> The heat of fusion of the polyethylene (linear low-density polyethylene or high-density polyethylene) used in the examples and comparative examples and the total heat of fusion of the expanded beads were measured in accordance with JIS K7121:2012. First, a DSC curve was obtained for the second heating of polyethylene or expanded beads as a test specimen using the same method as for measuring the melting point of 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.

[0063] <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 K7122:2012. Specifically, approximately 2 mg of expanded beads was sampled and heated from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter (EXSTAR DSC7020), obtaining a DSC curve (DSC curve from the first heating) with two or more melting peaks. In the following explanation, the peak characteristic of polyethylene (linear low-density polyethylene or high-density polyethylene) is designated A, and the high-temperature peak appearing above that is designated B. A straight line (α-β) was drawn connecting point α on the DSC curve, which corresponds to 80°C, and point β on the DSC curve, which corresponds to the melting end temperature T of the expanded beads. 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 baseline. Next, a straight line parallel to the vertical axis of the graph was drawn from point γ on the DSC curve, which corresponds to the valley between the intrinsic peak A and high-temperature peak B, and the point where this line intersected with the straight line (α-β) was designated δ. The area surrounded by the curve of the high-temperature peak B portion of the DSC curve, the line segment (δ-β), and the line segment (γ-δ) was determined, and the heat of fusion of the high-temperature peak was calculated from this area.

[0064] <Bulk density of expanded particles> Approximately 500cm 3The 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.

[0065] <Closed cell ratio of expanded beads> The closed cell ratio of the expanded beads was measured as follows. Bulk volume approximately 20cm 3 The apparent volume Va of the expanded beads was measured by immersing the expanded beads in ethanol. 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 that makes up 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. This true volume Vx was measured using a Toshiba Beckman 930 air comparison hydrometer. The closed-cell ratio was then calculated using the following formula (1), and the arithmetic mean 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 )

[0066] <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.

[0067] <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.

[0068] <State of second-stage expanded particles> The surface condition of the second-stage expanded beads was visually observed. When there were no obvious wrinkles on the expanded beads and there was almost no shrinkage of the expanded beads, the result was evaluated as "Good." When there were obvious wrinkles on the expanded beads and there was a lot of shrinkage of the expanded beads, the result was evaluated as "Poor." In addition, if the above evaluation is "Good", there is little variation in density among the obtained second-stage expanded beads, making it easy to control the density of the expanded beads when producing the desired molded body, and the expanded beads will stably exhibit good in-mold moldability.

[0069] <Molding pressure range that can mold good products> 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 0.20 MPa (G). The resulting molded articles were evaluated for in-mold moldability in terms of fusion, surface appearance (degree of voids), and recoverability (recovery from expansion or shrinkage after in-mold molding). Products meeting the criteria listed below were deemed to pass, and the steam pressure at which all items passed was deemed to be the steam pressure at which molding was possible. Note that pressures marked with (G) are gauge pressures, i.e., pressure values ​​relative to atmospheric pressure. The wider the range between the lower limit and the upper limit of the steam pressure at which molding is possible, the wider the molding range is, and therefore more preferable. (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 appearance) A 100 mm × 100 mm square was drawn in the center of the expanded bead molding, a line was drawn diagonally from one corner of the square, and the number of voids (gaps) of 1 mm × 1 mm or larger along the line was counted. A sample with fewer than 5 voids and no surface irregularities was deemed to pass, while any other sample was deemed to fail. (Recoverability) The thickness of a flat expanded bead molding obtained by in-mold molding, measuring 250 mm in length, 200 mm in width, and 50 mm in thickness, was measured near each of the four corners (10 mm inward from the corner toward the center) and at the center (the intersection of the line dividing the molding in half vertically and the line dividing the molding in half horizontally). The ratio (%) of the thickness at the center to the thickness at the thickest point near each of the four corners was then calculated. A ratio of 95% or more was considered acceptable, and a ratio of less than 95% was considered unacceptable.

[0070] <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.

[0071] <Compressive stress at 50% strain of foamed bead moldings> 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.

[0072] [polyethylene] Table 1 shows the polyethylene (linear low-density polyethylene or high-density polyethylene) used in the examples and comparative examples.

[0073] [Table 1]

[0074] [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 outlet side was prepared. LL1 and zinc borate (arithmetic mean particle size based on number: 7 μm) as a cell control agent were fed into the extruder and melt-kneaded to form a resin melt. The zinc borate content in the expanded beads was fed to 500 ppm by mass. The resulting resin melt was extruded as a strand from a strand-forming die. The extruded strand was cooled with water and then cut using a pelletizer to obtain resin particles with a base resin of linear 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.

[0075] A 5 L sealed container was charged with 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 shown in Table 2 was reached. Next, the contents of the sealed container were heated to the foaming temperature (124°C) at a 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 temperature, 50% relative humidity, and 1 atm. Next, the cured expanded beads were filled into a pressurizable airtight container, and the pressure inside the airtight container was increased from normal pressure to pressurize the expanded beads. The pressurized state of the expanded beads was maintained for 24 hours, allowing air to be impregnated into the cells of the expanded beads. The expanded beads were then removed from the airtight container, and expanded beads with an internal 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, resulting in a bulk density of 22 kg / m 3 The expanded beads after the second expansion were used for the above-mentioned measurements and for producing expanded bead moldings.

[0076] <Production of foamed bead molded body> After applying an internal pressure of 0.25 MPa (G) to the expanded beads with air, the expanded beads were filled into a mold capable of forming a flat plate measuring 250 mm in length, 200 mm in width, and 50 mm in thickness, and heated using 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 in an oven at 80°C for 12 hours to obtain an expanded bead molded body (expanded polyethylene resin bead molded body). In addition, in the evaluation of the above-mentioned <molding pressure range capable of molding a non-defective product>, 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 molded bodies are shown in Table 2. The biomass degree of the expanded beads was the same as the biomass degree of the polyethylene constituting each expanded bead. Furthermore, each expanded bead was non-crosslinked.

[0077] Examples 2 to 8 Expanded beads and polyethylene resin expanded bead molded articles were obtained in the same manner as in Example 1, except that the polyethylene, foaming temperature, and equilibrium vapor pressure were changed to the conditions shown in Table 2. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the molded articles are shown in Table 2.

[0078] Example 9 Expanded beads and polyethylene resin expanded bead molded articles were obtained in the same manner as in Example 1, except that the expansion temperature and equilibrium vapor pressure in Example 1 were changed to the conditions shown in Table 2 and in-mold molding was performed using the obtained first-stage expanded beads. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the molded articles are shown in Table 2.

[0079] Example 10 Expanded beads and polyethylene resin expanded bead molded articles were obtained in the same manner as in Example 1, except that the expansion temperature and equilibrium vapor pressure in Example 1 were changed to the conditions shown in Table 2, and in-mold molding was performed using the obtained first-stage expanded beads. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the molded articles are shown in Table 2.

[0080] (Comparative Examples 1 to 6) Expanded beads and polyethylene resin expanded bead molded articles were obtained in the same manner as in Example 1, except that the polyethylene and the expansion temperature in Example 1 were changed to the conditions shown in Table 3. Measurement results of the physical properties of the obtained expanded beads and evaluation results of the molded articles are shown in Table 3.

[0081] [Table 2]

[0082] [Table 3]

[0083] The results shown in Table 2 indicate that the expanded beads of the Examples have a high biomass content and excellent moldability. It is also clear that expanded polyethylene resin bead moldings with low apparent density can be obtained. Furthermore, it is clear that the expanded polyethylene resin bead moldings produced using the expanded beads of the Examples have high compressive stress and excellent strength, despite their low apparent density.

Claims

1. Linear low-density polyethylene is used as the base resin, and the bulk density is 10 kg / m 3 More than 240kg / m 3 The following expanded particles: The linear low-density polyethylene has a biomass content of 40% or more as measured by ASTM D 6866; the expanded beads 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 linear low-density polyethylene and one or more melting peaks (high-temperature peaks) appear on the higher temperature side of the intrinsic peak; the total heat of fusion of the expanded beads is 70 J / g or more and 100 J / g or less, The expanded particles have a heat of fusion of the high-temperature peak of 10 J / g or more and 50 J / g or less.

2. The expanded beads according to claim 1, wherein the heat of fusion of the high-temperature peak is 30 J / g or more and 50 J / g or less.

3. 3. The expanded beads according to claim 1, wherein the ratio of the heat of fusion of the high-temperature peak to the total heat of fusion of the expanded beads is 0.3 or more and 0.7 or less.

4. The expanded beads according to any one of claims 1 to 3, wherein the expanded beads have a melt flow rate of 0.1 g / 10 min or more and 2.0 g / 10 min or less, measured at a temperature of 190°C and a load of 2.16 kg.

5. The expanded beads according to any one of claims 1 to 4, wherein the linear low-density polyethylene comprises a linear low-density polyethylene A containing a butene component and a hexene component as copolymerization components.

6. The expanded beads according to any one of claims 1 to 5, wherein the linear low-density polyethylene has a biomass content of 70% or more as measured in accordance with ASTM D 6866.

7. The expanded beads according to any one of claims 1 to 6, wherein the expanded beads have a closed cell rate of 80% or more.

8. The expanded beads according to any one of claims 1 to 7, wherein the expanded beads have an average cell diameter of 60 µm or more and 200 µm or less.

9. A foamed bead molding obtained by molding the foamed beads according to any one of claims 1 to 8 in a mold.

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