Method for producing foamed particle, and foamed particle

Abstract

This invention relates to a method for manufacturing expanded beads with a bulk density of 10 to 240 kg / m³, produced by foaming resin particles made from a mixture of at least two linear low-density polyethylene resins as the base resin. The mixture comprises polyethylene A and polyethylene B, with a biomass of 50% or more and a melt flow rate (MFR) of 0.1 to 3 g / 10 min. The difference between the MFR of A and the MFR of B is 0 to 2 g / 10 min, the mass ratio of A to B is 5 / 95 to 95 / 5, the biomass of the mixture is 5% or more, and the mixture has a crystalline structure that exhibits the melting peak inherent to linear low-density polyethylene in a DSC curve and a high-temperature peak on the high-temperature side, with a heat of fusion of 10 to 50 J / g at the high-temperature peak.

Description

Technical Field

[0001] This invention relates to a method for manufacturing foamed particles and foamed particles. Prior Technology

[0002] Polyethylene resin foamed particle molded bodies, formed by in-mold molding of expanded polyethylene resin particles, exhibit excellent chemical resistance, cushioning properties, and recyclability. Therefore, these molded bodies are widely used as impact absorbers, thermal insulation materials, and various packaging materials, ranging from packaging / cushioning materials for electrical / electronic components and automotive parts to packaging materials for other precision parts and food products. In recent years, in response to concerns about the depletion of fossil resources such as oil and environmental issues such as the need to reduce carbon dioxide emissions, bioplastics have been developed and are being attempted to replace the resins derived from petroleum to date. For example, Patent Document 1 discloses polyethylene resin containing polyethylene resin with a plant content of 80% or more as measured by ASTM D 6866, and polyethylene resin foam particles with a plant content of 1% or more. [Previous Technical Documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2013-060514 Summary of the Invention

[0004] [The problem that the invention aims to solve]

[0005] However, the technology disclosed in Patent Document 1 results in low in-mold formability of the foamed particles, making it difficult to obtain good foamed particle molded bodies within a wide density range. The present invention relates to a method for manufacturing foamed particles that exhibit excellent in-mold formability and can produce high-quality polyethylene resin foamed particle molded bodies covering a wide density range. [Methods for solving problems]

[0006] After in-depth investigation, the inventors discovered that a method for manufacturing foamed particles, which involves foaming resin particles containing at least two specific linear low-density polyethylene resins as the base resin, solves the aforementioned problem. That is, one aspect of the present invention is the manufacturing method of foamed particles described in [1] to [7] below, and the foamed particles described in [8] and [9]. [1] A method for manufacturing foamed particles, comprising foaming resin particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less by foaming resin particles using a mixture of at least two linear low-density polyethylene resins as the base resin. The aforementioned mixed resin contains linear low-density polyethylene A and linear low-density polyethylene B with a biomass of 50% or more as measured according to ASTM D 6866. The melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A, measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. The difference between the melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A and the melt flow rate (MFR B) of the aforementioned linear low-density polyethylene B, measured at a temperature of 190°C and a load of 2.16 kg, |MFR A - MFR B|, is 0 g / 10 min or more and 2 g / 10 min or less. In the aforementioned mixed resin, the mass ratio (A / B) of the aforementioned linear low-density polyethylene A to the aforementioned linear low-density polyethylene B is 5 / 95 to 95 / 5. The biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, is 5% or higher. The aforementioned foamed particles exhibit a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, which displays the inherent melting peak (inherent peak) of linear low-density polyethylene, and one or more melting peaks (high-temperature peaks) located further up the temperature side than the inherent peak. The heat of fusion of the aforementioned high-temperature peak is above 10 J / g and below 50 J / g. [2] The method for manufacturing foamed particles as described in [1], wherein the biomass of the aforementioned linear low-density polyethylene B, as measured according to ASTM D 6866, is less than 20%. [3] The method for manufacturing foamed particles as described in [1] or [2], wherein the difference between the density ρB of the aforementioned linear low-density polyethylene B and the density ρA of the aforementioned linear low-density polyethylene A (ρB-ρA) is 3 kg / m3 or more, and the density of the aforementioned mixed resin is 910 kg / m3 or more and 928 kg / m3 or less. [4] The method for manufacturing foamed particles as described in any of [1] to [3], wherein the difference between the heat of fusion ΔHB of the aforementioned linear low-density polyethylene B and the heat of fusion ΔHA of the aforementioned linear low-density polyethylene A (ΔHB-ΔHA) is 3J / g or more, and the total heat of fusion of the aforementioned mixed resin is 70J / g or more and 120J / g or less. [5] The method for manufacturing foamed particles as described in any of [1] to [4], wherein the total heat of fusion of the aforementioned foamed particles is 70 J / g or more and 105 J / g or less, and the ratio of the heat of fusion of the aforementioned high-temperature peak of the aforementioned foamed particles to the total heat of fusion is 0.2 or more and 0.7 or less. [6] The method for manufacturing foamed particles as described in any of [1] to [5], wherein the melt flow rate of the aforementioned mixed resin, measured at a temperature of 190°C and a load of 2.16 kg, is 0.1 g / 10 min or more and 3 g / 10 min or less. [7] The method for manufacturing foamed particles as described in any of [1] to [6], wherein the aforementioned linear low-density polyethylene A contains butene and hexene as copolymerizing components. [8] A type of foamed particle, which is a foamed particle with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less, using at least two kinds of linear low-density polyethylene mixed resins as the base material. The density of the aforementioned mixed resin is above 910 kg / m³ and below 928 kg / m³. The biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, is above 5%. The melt flow rate of the aforementioned foamed particles, measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. The aforementioned foamed particles exhibit a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, which displays the inherent melting peak (inherent peak) of linear low-density polyethylene, and one or more melting peaks (high-temperature peaks) located further up the temperature side than the inherent peak. The heat of fusion of the aforementioned high-temperature peak is above 10 J / g and below 50 J / g. [9] The foamed particles described in [8] have a total heat of fusion of 70 J / g or more and 105 J / g or less, and the ratio of the heat of fusion of the aforementioned high-temperature peak of the aforementioned foamed particles to the total heat of fusion is 0.2 or more and 0.7 or less. [Effects of the Invention]

[0007] According to the present invention, a method for manufacturing foamed particles with excellent in-mold formability can be provided, which can produce high-quality polyethylene resin foamed particle molded bodies covering a wide density range. Implementation

[0008] [Manufacturing Method of Foamed Particles] The method for manufacturing foamed particles of the present invention involves foaming resin particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less by foaming resin particles using a mixture of at least two linear low-density polyethylene resins as the base resin. The aforementioned mixed resin contains linear low-density polyethylene A and linear low-density polyethylene B with a biomass of 50% or more as measured according to ASTM D 6866. The melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A, measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. The difference between the melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A and the melt flow rate (MFR B) of the aforementioned linear low-density polyethylene B, measured at a temperature of 190°C and a load of 2.16 kg, |MFR A - MFR B|, is 0 g / 10 min or more and 2 g / 10 min or less. In the aforementioned mixed resin, the mass ratio of the aforementioned linear low-density polyethylene A to the aforementioned linear low-density polyethylene B is 5 / 95 to 95 / 5. The biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, is 5% or higher. The aforementioned foamed particles exhibit a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, which displays the inherent melting peak (inherent peak) of linear low-density polyethylene, and one or more melting peaks (high-temperature peaks) located further up the temperature side than the inherent peak. The heat of fusion of the aforementioned high-temperature peak is above 10 J / g and below 50 J / g.

[0009] <Resin Particles> The method for manufacturing foamed particles according to the present invention involves foaming resin particles using a mixed resin of at least two types of linear low-density polyethylene as the base resin. The following description pertains to the aforementioned mixed resin and the aforementioned linear low-density polyethylene.

[0010] <Mixed Resins> The resin particles used in the manufacturing method of the foamed particles of the present invention are based on a mixture of at least two linear low-density polyethylene resins. In this specification, "based on a mixture of at least two linear low-density polyethylene resins" means that the resin particles are composed of resins with at least two linear low-density polyethylene resins as the main component.

[0011] Furthermore, the aforementioned mixed resin contains linear low-density polyethylene A and linear low-density polyethylene B with a biomass of 50% or more as measured according to ASTM D 6866. Furthermore, the melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A, measured at a temperature of 190°C and a load of 2.16 kg, is 0.1 g / 10 min or more and 3 g / 10 min or less; the difference between the melt flow rate (MFR A) of the aforementioned linear low-density polyethylene A and the melt flow rate (MFR B) of the aforementioned linear low-density polyethylene B, measured at a temperature of 190°C and a load of 2.16 kg, |MFR A - MFR B|, is 0 g / 10 min or more and 2 g / 10 min or less; the mass ratio (A / B) of the aforementioned linear low-density polyethylene A to the aforementioned linear low-density polyethylene B in the aforementioned mixed resin is 5 / 95 to 95 / 5; and the biomass of the aforementioned mixed resin, measured according to ASTM D 6866, is 5% or more. Furthermore, the aforementioned foamed particles exhibit a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / minute, which shows the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) that are closer to the high-temperature side than the inherent peaks. The heat of melting of the aforementioned high-temperature peaks is more than 10 J / g and less than 50 J / g. Next, the linear low-density polyethylene A and linear low-density polyethylene B contained in the aforementioned mixed resin will be explained.

[0012] (Linear low-density polyethylene A) The biomass of linear low-density polyethylene A, as measured according to ASTM D 6866, is 50% or higher. Furthermore, the melt flow rate (MFR) of A, measured at 190°C and a load of 2.16 kg, is 0.1 g / 10 min or higher and 3 g / 10 min or lower.

[0013] By ensuring that the biomass of the aforementioned linear low-density polyethylene A falls within the aforementioned range, the use of fossil resources can be suppressed during the manufacture of the molded body, and the amount of carbon dioxide emitted during the life cycle of the molded body can also be reduced. Considering the foregoing points, the biomass BCA of the aforementioned linear low-density polyethylene A, as measured according to ASTM D 6866, should be 50% or higher, preferably 60% or higher, more preferably 70% or higher, and even more preferably 80% or higher. Furthermore, there is no upper limit; if the biomass BCA of the aforementioned linear low-density polyethylene A, as measured according to ASTM D 6866, is below 100%, it is acceptable. Considering the need to improve the in-mold formability of the foamed particles, the biomass BCA of the aforementioned linear low-density polyethylene A, as measured according to ASTM D 6866, should preferably be below 95%, and more preferably below 90%. The aforementioned biomass, measured according to ASTM D 6866, refers to the proportion of naturally derived components contained in the linear low-density polyethylene A. Moreover, the aforementioned biomass is a value obtained by determining the concentration of radioactive carbon C14 in the linear low-density polyethylene.

[0014] The melt flow rate (MFR A) of linear low-density polyethylene A, measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. A melt flow rate (MFR A) of linear low-density polyethylene A within the aforementioned range can further improve the in-mold formability of the foamed particles. The melt flow rate (MFR) of linear low-density polyethylene (LDPE) A is preferably 0.3 g / 10 min or higher, more preferably 0.5 g / 10 min or higher, and even more preferably 0.7 g / 10 min or higher. Furthermore, the melt flow rate (MFR) of linear low-density polyethylene (LDPE) A is preferably 2.0 g / 10 min or lower, more preferably 1.8 g / 10 min or lower, even more preferably 1.5 g / 10 min or lower, and even more preferably 1.4 g / 10 min or lower. Furthermore, the melt flow rate (MFR A) of linear low-density polyethylene A was measured at a temperature of 190°C and a load of 2.16 kg. More specifically, it can be measured according to JIS K 7210-1:2014 using the method described in the examples.

[0015] The density ρA of the aforementioned linear low-density polyethylene A is preferably 910 kg / m³ or higher and 940 kg / m³ or lower. Considering the viewpoint that it is easy to obtain foamed particles with the desired physical properties, it is more preferably 910 kg / m³ or higher and 935 kg / m³ or lower, even more preferably 910 kg / m³ or higher and 928 kg / m³ or lower, even more preferably 912 kg / m³ or higher and 925 kg / m³ or lower, and especially preferably 914 kg / m³ or higher and 922 kg / m³ or lower. The density ρA of linear low-density polyethylene A was determined using Method A (water displacement method) as described in JIS K7112:1999.

[0016] From the viewpoint of improving the mechanical properties of the obtained molded article, the melting point Tm A of the aforementioned linear low-density polyethylene A is preferably 100°C or higher and 130°C or lower. More preferably, it is 110°C or higher, even more preferably 120°C or higher, and still more preferably 122°C or higher. On the other hand, from the viewpoint of improving the in-mold formability of the foamed particles under low molding pressure conditions, the melting point Tm A of the aforementioned linear low-density polyethylene A is preferably 128°C or lower, and more preferably 126°C or lower. The melting point Tm A of linear low-density polyethylene A was determined by preparing test pieces of linear low-density polyethylene and based on JIS K 7121:2012. Specifically, it can be determined using the method described in the examples.

[0017] Considering the viewpoint of easily obtaining foamed particles with desired physical properties, the heat of fusion ΔH A of the aforementioned linear low-density polyethylene A is preferably 60 J / g or higher, more preferably 70 J / g or higher, and even more preferably 75 J / g or higher. Furthermore, considering the same viewpoint, the heat of fusion ΔH A of the aforementioned linear low-density polyethylene A is preferably 120 J / g or lower, more preferably 110 J / g or lower, even more preferably 100 J / g or lower, and particularly preferably 90 J / g or lower. The heat of fusion ΔH A of the aforementioned linear low-density polyethylene A can be obtained by preparing a test piece of linear low-density polyethylene A and performing differential scanning calorimetry (DSC) according to JIS K 7122:2012. Specifically, the method described in the examples can be used for the determination.

[0018] The aforementioned linear low-density polyethylene A is a copolymer of ethylene and α-olefin with a density of 910 kg / m³ or more and 940 kg / m³ or less, and having a linear structure. The aforementioned α-olefins are preferably α-olefins with 3 to 20 carbon atoms, more preferably α-olefins with 3 to 10 carbon atoms, and even more preferably α-olefins with 3 to 6 carbon atoms. Specific examples of α-olefins 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, considering the viewpoint of stably obtaining foamed particles with excellent moldability, α-olefins should preferably include at least one from the group consisting of 1-butene, 1-hexene, and 4-methyl-1-pentene. Therefore, the aforementioned linear low-density polyethylene A is preferably linear low-density polyethylene A1 containing butene and hexene as copolymerizing components (comonomers) or linear low-density polyethylene A2 containing butene as copolymerizing component (comonomer), and linear low-density polyethylene A1 containing butene and hexene as copolymerizing components is more preferred. In addition, the asperene component in linear low-density polyethylene containing butene and hexene as copolymerizing components includes 1-hexene and 4-methyl-1-pentene.

[0019] From the perspective of being able to stably obtain foamed particles with excellent formability in the mold, when using linear low-density polyethylene A2 containing butene as the aforementioned linear low-density polyethylene A, the butene content in the linear low-density polyethylene A2 should preferably be 2 mol% or more and 7 mol% or less, and more preferably 3 mol% or more and 6 mol% or less. Furthermore, considering the same point, when using linear low-density polyethylene A1 containing butene and hexene as the aforementioned linear low-density polyethylene A, the butene content in the linear low-density polyethylene A1 should preferably be 0.5 mol% or more and 6 mol% or less, more preferably 1 mol% or more and 5 mol% or less, and even more preferably 2 mol% or more and 4 mol% or less. Also, when using linear low-density polyethylene A1 containing butene and hexene, the hexene content in the linear low-density polyethylene A1 should preferably be 0.2 mol% or more and 5 mol% or less, more preferably 0.5 mol% or more and 4 mol% or less, and even more preferably 0.8 mol% or more and 3 mol% or less. Furthermore, to the extent that the objectives of this invention are achieved without impairing its effects, the aforementioned linear low-density polyethylene A may also contain components derived from propylene as α-olefins (copolymer components, comonomers). When linear low-density polyethylene A contains components derived from propylene as copolymer components, although it has low density, it has a higher melting point and tends to become linear low-density polyethylene with a more moderate change in physical properties upon softening. This suppresses excessive shrinkage of the foamed particles immediately after foaming during resin particle foaming. Furthermore, it suppresses excessive sinking of the molded body immediately after molding during in-mold forming of the foamed particles. Thus, foamed particles with excellent in-mold formability can be obtained. When linear low-density polyethylene A contains components derived from propylene, the content of propylene-derived components in linear low-density polyethylene A should preferably be 0.3 mol% or more and 5 mol% or less, preferably 0.5 mol% or more and 4 mol% or less, even more preferably 0.8 mol% or more and 3 mol% or less, and especially preferably 1 mol% or more and 2 mol% or less. Furthermore, the above-mentioned content refers to the content when the total content of components from ethylene and components from α-olefins is 100% by mass. Also, the content of components from α-olefins in linear low-density polyethylene A is preferably 10 mol% or less, and more preferably 8 mol% or less. Furthermore, the content of components from α-olefins in linear low-density polyethylene A is preferably 0.5 mol% or more, and more preferably 1 mol% or more. The content of the components derived from each α-olefin in linear low-density polyethylene A can be determined by means of carbon-13 nuclear magnetic resonance (13C-NMR) as described in the examples.

[0020] Furthermore, considering the same point of view, when using linear low-density polyethylene A1 containing butene and hexene as the aforementioned linear low-density polyethylene A, the ratio of the content of hexene to the content of butene in the linear low-density polyethylene A1 [hexene content (mol%) / butene 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 linear low-density polyethylene A contains components 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 A [propylene content (mol%) / α-olefin 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.

[0021] (Linear low-density polyethylene B) The linear low-density polyethylene B refers to linear low-density polyethylene where the difference between the melt flow rate MFR A of the aforementioned linear low-density polyethylene A and the melt flow rate MFR B of the linear low-density polyethylene B measured at a temperature of 190°C and a load of 2.16 kg, |MFR A - MFR B| (absolute value), is 0 g / 10 min or more and 2 g / 10 min or less. When a mixed resin is formed by mixing linear low-density polyethylene A with linear low-density polyethylene B, which has different physical properties from linear low-density polyethylene A as described later, by using linear low-density polyethylene B, which has a small difference in melt flow rate from linear low-density polyethylene A, it is possible to obtain the effects of containing one type of linear low-density polyethylene in the mixed resin, while producing foam particles with excellent formability in the mold. The aforementioned |MFR A-MFR B| should ideally be below 1.8g / 10 minutes, preferably below 1.5g / 10 minutes, and even better below 1.4g / 10 minutes. There is no lower limit; it can also be 0g / 10 minutes.

[0022] The melt flow rate (MFR B) of linear low-density polyethylene (LDPE) B, measured at a temperature of 190°C and a load of 2.16 kg, should preferably be 0.1 g / 10 min or more and 2 g / 10 min or less. A melt flow rate (MFR B) within the aforementioned range for linear LDPE B can further improve the in-mold formability of the foamed particles. The melt flow rate (MFR) of linear low-density polyethylene (LDPE) B is preferably 0.3 g / 10 min or higher, even more preferably 0.5 g / 10 min or higher, and even more preferably 0.7 g / 10 min or higher. Furthermore, the melt flow rate (MFR) of linear LDPE B is preferably 1.8 g / 10 min or lower, even more preferably 1.5 g / 10 min or lower, and even more preferably 1.4 g / 10 min or lower. Furthermore, the melt flow rate (MFR) of linear low-density polyethylene B was measured at a temperature of 190°C and a load of 2.16 kg. More specifically, it can be measured according to JIS K 7210-1:2014 using the method described in the examples.

[0023] The density ρB of the aforementioned linear low-density polyethylene B is preferably 910 kg / m³ or higher and 940 kg / m³ or lower. Considering the viewpoint that it is easy to obtain foamed particles with the desired physical properties, it is more preferably 912 kg / m³ or higher and 935 kg / m³ or lower, even more preferably 914 kg / m³ or higher and 928 kg / m³ or lower, even more preferably 920 kg / m³ or higher and 928 kg / m³ or lower, and especially preferably 922 kg / m³ or higher and 928 kg / m³ or lower. The density ρB of linear low-density polyethylene B was determined using Method A (water displacement method) as described in JIS K7112:1999.

[0024] The absolute value of the difference between the density ρA of the aforementioned linear low-density polyethylene A and the density ρB of the aforementioned linear low-density polyethylene B, |ρA-ρB|, is preferably 3 kg / m³ or more. By using a mixed resin composed of linear low-density polyethylenes of different densities to form foamed particles, foamed particles with desired biomass can be produced. Furthermore, compared to, for example, using only one type of linear low-density polyethylene with a relatively low density to manufacture foamed particles, foamed particles with excellent moldability and compressive strength can be stably obtained. The aforementioned |ρA-ρB| is preferably 4 kg / m³ or more, more preferably 5 kg / m³ or more, and even more preferably 6 kg / m³ or more. There is no upper limit, but it is preferably 20 kg / m³ or less, and more preferably 15 kg / m³ or less. Furthermore, the density ρB of the aforementioned linear low-density polyethylene B should preferably be greater than the density ρA of the aforementioned linear low-density polyethylene A, and the difference between the density ρB of the aforementioned linear low-density polyethylene B and the density ρA of the aforementioned linear low-density polyethylene A (ρB-ρA) (relative value) should preferably be 3 kg / m³ or more. At this point, foamed particles with the desired biomass and excellent moldability can be stably obtained. The aforementioned (ρB-ρA) should preferably be 4 kg / m³ or more, preferably 5 kg / m³ or more, and even more preferably 6 kg / m³ or more. There is no upper limit, but it should preferably be 20 kg / m³ or less, and preferably 15 kg / m³ or less.

[0025] From the viewpoint of improving the mechanical properties of the obtained molded article, the melting point Tm B of the aforementioned linear low-density polyethylene B is preferably 100°C or higher and 130°C or lower. More preferably, it is 110°C or higher, even more preferably 116°C or higher, and even more preferably 120°C or higher. On the other hand, from the viewpoint of improving the in-mold formability of the foamed particles under low molding pressure conditions, the melting point Tm B of the aforementioned linear low-density polyethylene B is preferably 128°C or lower, even more preferably 126°C or lower, and even more preferably 124°C or lower. The melting point TmB of linear low-density polyethylene B was determined by preparing test pieces of linear low-density polyethylene based on JIS K 7121:2012. Specifically, it can be determined using the method described in the examples.

[0026] The difference between the melting point TmA of the aforementioned linear low-density polyethylene A and the melting point TmB of the aforementioned linear low-density polyethylene B, |TmA-TmB| (absolute value), should preferably be above 0°C and below 4°C. By using a mixed resin composed of linear low-density polyethylenes with small melting point differences to form foamed particles, foamed particles with the desired biomass and excellent in-mold formability can be stably obtained. The aforementioned |TmA-TmB| should preferably be below 3°C, and below 2°C is more preferred. There is no lower limit, and it can also be 0°C.

[0027] Considering the viewpoint that it is easy to obtain foamed particles with desired physical properties, the heat of fusion ΔH B of the aforementioned linear low-density polyethylene B should preferably be above 60 J / g and below 120 J / g. Furthermore, considering the possibility of producing foamed particles with desired biomass and improving the in-mold formability of the foamed particles, the heat of fusion ΔH B of linear low-density polyethylene B is preferably 70 J / g or higher, more preferably 80 J / g or higher, even more preferably 90 J / g or higher, even more preferably 100 J / g or higher, and especially preferably 105 J / g or higher. Also, considering the same point, the aforementioned heat of fusion ΔH B of linear low-density polyethylene B is preferably 118 J / g or lower, and more preferably 115 J / g or lower. The heat of fusion ΔH B of the aforementioned linear low-density polyethylene B can be obtained by preparing a test piece of linear low-density polyethylene B and performing differential scanning calorimetry (DSC) according to JIS K 7122:2012. Specifically, it can be measured using the method described in the examples.

[0028] Furthermore, the difference between the heat of melting ΔHB of the aforementioned linear low-density polyethylene B and the heat of melting ΔHA of the aforementioned linear low-density polyethylene A, |ΔHB - ΔHA| (absolute value), is preferably 3 J / g or more, more preferably 5 J / g or more, and even more preferably 10 J / g or more and 40 J / g or less. By using a mixed resin made by mixing linear low-density polyethylenes with different heats of melting to form foamed particles, foamed particles with the desired biomass can be produced. At the same time, compared with, for example, using only one type of linear low-density polyethylene with a relatively small heat of melting to manufacture foamed particles, foamed particles with excellent moldability and excellent compressive strength can be stably obtained. The aforementioned |ΔHB - ΔHA| is preferably 15 J / g or more, even more preferably 20 J / g or more, and particularly preferably 25 J / g or more. Furthermore, it is even better if the aforementioned |ΔH B-ΔH A| is below 38 J / g, and even better if it is below 35 J / g.

[0029] Furthermore, the heat of fusion ΔHB of the aforementioned linear low-density polyethylene B is preferably greater than the heat of fusion ΔHA of the aforementioned linear low-density polyethylene A. The difference between the heat of fusion ΔHB of the aforementioned linear low-density polyethylene B and the heat of fusion ΔHA of the aforementioned linear low-density polyethylene A (ΔHB - ΔHA) (relative value) is preferably 5 J / g or more, more preferably 10 J / g or more and less than 40 J / g. At this time, foamed particles with the desired biomass can be produced, and foamed particles with excellent formability and compressive strength in molds can be stably obtained. It is more preferably (ΔHB - ΔHA) is 15 J / g or more, more preferably 20 J / g or more, and especially preferably 25 J / g or more. Furthermore, it is more preferably (ΔHB - ΔHA) is 38 J / g or less, and more preferably 35 J / g or less.

[0030] The aforementioned linear low-density polyethylene B can be petroleum-derived linear low-density polyethylene or linear low-density polyethylene containing components derived from biomass. Therefore, there is no limitation on the biomass percentage (BCB) of the aforementioned linear low-density polyethylene B as measured according to ASTM D 6866. When the aforementioned linear low-density polyethylene B is linear low-density polyethylene containing components derived from biomass, the biomass percentage (BCB) can be 10% or more, 20% or more, 30% or more, 50% or more, or 70% or more. Furthermore, the upper limit for the biomass percentage (BCB) is 100%. Also, when the aforementioned linear low-density polyethylene B is petroleum-derived linear low-density polyethylene, the biomass percentage (BCB) of the aforementioned linear low-density polyethylene B as measured according to ASTM D 6866 can also be 0%. Considering the viewpoint of consistently improving the in-mold formability of foamed particles, the biomass of the aforementioned linear low-density polyethylene B (BCB) should preferably be 20% or less, and more preferably 10% or less. Furthermore, it is even more preferable that the aforementioned linear low-density polyethylene B is derived from petroleum.

[0031] The difference between the biomass BCA of linear low-density polyethylene A and the biomass BCB of linear low-density polyethylene B, as measured according to ASTM D 6866, |BCA - BCB| (absolute value), should preferably be 5% or more. At this point, foamed particles with the desired biomass can be produced, and foamed particles with excellent in-mold formability can be stably obtained. Furthermore, the biomass BCA of linear low-density polyethylene A should preferably be greater than the biomass BCB of linear low-density polyethylene B. Considering the viewpoint of more easily improving the in-mold formability of foamed particles, the aforementioned |BC A-BC B| should preferably be 10% or higher, preferably 20% or higher, even better 30% or higher, even better 50% or higher, and ideally 70% or higher. There is no upper limit; anything below 100% is acceptable. Considering the viewpoint of stably improving the in-mold formability of foamed particles, the aforementioned |BC A-BC B| should preferably be 95% or lower, preferably 90% or lower.

[0032] The difference between the biomass BCA of linear low-density polyethylene A and the biomass BCB of the aforementioned linear low-density polyethylene B measured according to ASTM D 6866 (BCA-BCB) (relative value), considering the above points, should preferably be 5% or higher, ideally 10% or higher, better than 20%, even better than 30%, better than 50%, and exceptionally good than 70%. There is no upper limit; anything below 100% is acceptable. Considering the point of steadily improving the in-mold formability of the foamed particles, the aforementioned (BCA-BCB) should preferably be below 95%, and preferably below 90%.

[0033] The aforementioned linear low-density polyethylene B is a copolymer of ethylene and α-olefin with a density of 910 kg / m³ or higher and 940 kg / m³ or lower, and having a linear structure. The aforementioned α-olefins are preferably α-olefins with 3 to 20 carbon atoms, more preferably α-olefins with 3 to 10 carbon atoms, and even more preferably α-olefins with 3 to 6 carbon atoms. Specific examples of α-olefins 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, considering the viewpoint of stably obtaining foamed particles with excellent in-mold formability, α-olefins should preferably include at least one from the group consisting of 1-octene, 1-hexene, and 4-methyl-1-pentene. Therefore, the aforementioned linear low-density polyethylene B is preferably linear low-density polyethylene B1 containing octene as a copolymerizing component (comonomer) or linear low-density polyethylene B2 containing hexene as a copolymerizing component (comonomer), with linear low-density polyethylene B1 containing octene being more preferred. In addition, in linear low-density polyethylene containing octene as a copolymer, the octene-derived components include 1-octene, 2-methylheptene, 3-ethylhexene, etc., and 1-octene is preferred. Furthermore, in linear low-density polyethylene containing hexene, the hexene-derived components include 1-hexene and 4-methyl-1-pentene, and 4-methyl-1-pentene is preferred.

[0034] From the viewpoint of being able to stably obtain foamed particles with excellent formability in the mold, when using linear low-density polyethylene B2 containing hexene as the aforementioned linear low-density polyethylene B, the content of hexene in the linear low-density polyethylene B2 should preferably be 0.5 mol% or more and 5 mol% or less, and more preferably 1 mol% or more and 3 mol% or less. Furthermore, considering the same point of view, when using linear low-density polyethylene B1 containing octene as the aforementioned linear low-density polyethylene B, the octene content in the linear low-density polyethylene B1 should preferably be 0.5 mol% or more and 5 mol% or less, and preferably 1 mol% or more and 3 mol% or less. Furthermore, the above-mentioned content refers to the content when the total content of the components from ethylene and the components from α-olefins is 100% by mass. Also, the content of the components from α-olefins in linear low-density polyethylene B 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. Furthermore, the content of the components from α-olefins in linear low-density polyethylene B is preferably 0.5 mol% or more, more preferably 1 mol% or more. The content of the components derived from each α-olefin in linear low-density polyethylene B can be determined by means of carbon-13 nuclear magnetic resonance (13C-NMR) as described in the examples.

[0035] (Characteristics of mixed resins and foaming particles) The base resin of the resin particles is linear low-density polyethylene (LLDPE), which is a mixed resin containing at least two types of LLDPE, namely LLDPE A and LLDPE B. The mixed resin is, for example, prepared by mixing LLDPE A and LLDPE B. Considering the viewpoint of consistently obtaining foamed particles with excellent in-mold formability and a wide range of good product characteristics, LLDPE A is preferably LLDPE A1, and LLDPE B is preferably LLDPE B1. Furthermore, the mass ratio of linear low-density polyethylene A to linear low-density polyethylene B in the mixed resin is 5 / 95 to 95 / 5, the biomass of the aforementioned mixed resin measured according to ASTM D 6866 is 5% or more, and the mixed resin constituting the aforementioned foamed particles has a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, exhibiting the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) located on the higher temperature side than the inherent peak, wherein the heat of fusion of the aforementioned high-temperature peak is 10 J / g or more and 50 J / g or less.

[0036] In the mixed resin, the mass ratio of the aforementioned linear low-density polyethylene A to linear low-density polyethylene B is 5 / 95 to 95 / 5. When a linear low-density polyethylene A is mixed with a linear low-density polyethylene B, which has different physical properties from linear low-density polyethylene A as described above, to form a mixed resin, foamed particles can be formed by using a mixed resin made by mixing linear low-density polyethylene B, which has a small difference in melt flow rate from linear low-density polyethylene A, at a specific mass ratio. This demonstrates the effect of containing one type of linear low-density polyethylene in the mixed resin, and foamed particles with excellent in-mold formability can be produced. Considering the viewpoint of easily improving the biomass of foamed particles, the aforementioned mass ratio of linear low-density polyethylene A to linear low-density polyethylene B (A / B) is preferably 5 / 95 or higher (1 / 19 or lower), more preferably 10 / 90 or higher (1 / 9 or higher), more preferably 20 / 80 or higher (1 / 4 or higher), and even more preferably 30 / 70 or higher (3 / 7 or higher). Furthermore, considering the viewpoint of easily improving the in-mold formability of foamed particles, the aforementioned mass ratio of linear low-density polyethylene A to linear low-density polyethylene B (A / B) is preferably 95 / 5 or lower (19 or lower), more preferably 90 / 10 or lower (9 or lower), more preferably 80 / 20 or lower (4 or lower), even more preferably 70 / 30 or lower (7 / 3 or lower), and even more preferably 60 / 40 or lower (3 / 2 or lower). Furthermore, considering the view that in-mold molding can be performed under low molding pressure conditions, and that foamed particles with a wide molding range that can stably produce good products can be obtained, the aforementioned mass ratio of linear low-density polyethylene A to linear low-density polyethylene B (mass ratio of linear low-density polyethylene A to linear low-density polyethylene B) (A / B) should preferably be 25 / 75 or more (1 / 3 or more) and 90 / 10 or less (9 or less).

[0037] Furthermore, the mixed resin of the present invention may also contain polymers such as resins and elastomers other than the aforementioned linear low-density polyethylene, to a extent that does not impair the effects of the present invention. In this case, the content of polymers other than the aforementioned linear low-density polyethylene A and linear low-density polyethylene B in the aforementioned mixed resin is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, even more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less, relative to a total of 100 parts by weight of linear low-density polyethylene A or linear low-density polyethylene B in the mixed resin. Also, the content of polymers other than the aforementioned linear low-density polyethylene in the aforementioned mixed resin is preferably 80 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less, relative to a total of 100 parts by weight of linear low-density polyethylene (linear low-density polyethylene A or linear low-density polyethylene B) in the mixed resin.

[0038] The biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, is greater than 5%. By ensuring that the biomass of the aforementioned mixed resin falls within the aforementioned range, the use of fossil resources can be suppressed during the manufacture of the molded body, and the amount of carbon dioxide emitted during the life cycle of the molded body can also be reduced. Considering the foregoing points, the biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, should be 5% or higher, preferably 10% or higher, more preferably 20% or higher, even more preferably 30% or higher, and even more preferably 40% or higher. Furthermore, there is no upper limit; if the biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, is below 100%, it is acceptable. Considering the viewpoint of easily improving the in-mold formability of the foamed particles, the biomass of the aforementioned mixed resin, as measured according to ASTM D 6866, should preferably be below 90%, more preferably below 80%, even more preferably below 70%, and even more preferably below 60%. The aforementioned biomass, measured according to ASTM D 6866, refers to the proportion of naturally derived components contained in the mixed resin. Furthermore, the aforementioned biomass can be determined by measuring the concentration of radioactive carbon C14 in the resin particles or foam particles, or by the biomass of the resin used to manufacture the resin particles or foam particles and the proportion of the resin from the biomass in the resin particles or foam particles.

[0039] The aforementioned foamed particles (the mixed resin constituting the foamed particles) have a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / min, exhibiting the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) located on the higher temperature side than the inherent peaks. The heat of fusion of the aforementioned high-temperature peaks is 10 J / g or more and 50 J / g or less.

[0040] The aforementioned DSC curve was obtained using differential scanning calorimetry (DSC) according to JIS K7122:2012. Specifically, a differential scanning calorimeter can be used to obtain the aforementioned DSC curve by heating 1-3 mg of the aforementioned mixed resin (foaming particles) from 23°C to 200°C at a heating rate of 10°C / min. As mentioned earlier, the DSC curves before measuring the aforementioned foamed particles will show the inherent melting peak (inherent peak) of linear low-density polyethylene, and one or more melting peaks (high-temperature peaks) that are closer to the high-temperature side than the inherent peak.

[0041] Then I will explain in more detail. The aforementioned DSC curve refers to the DSC curve obtained by heating the foamed particles using the aforementioned measurement method (the DSC curve obtained by heating for the first time). Furthermore, the inherent melting peak of linear low-density polyethylene (inherent peak) refers to the melting peak exhibited due to the melting of crystals typically present in linear low-density polyethylene constituting the mixed resin. On the other hand, the melting peak (high-temperature peak) that is located at a higher temperature than the inherent peak refers to the melting peak that appears at a higher temperature than the aforementioned inherent peak in the DSC curve of the first heating. When this high-temperature peak is observed, it is inferred that secondary crystallization exists in the resin. In addition, the DSC curve obtained when the foamed particles are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C again at a heating rate of 10°C / min (second heating) (second heating) will only show the melting peak caused by the melting of crystals that are usually present in the linear low-density polyethylene constituting the mixed resin. This inherent peak will appear in both the first and second DSC curves. The temperature of the peak apex will differ slightly between the first and second heating cycles, typically by less than 5°C. This allows identification of which peak is the inherent peak. In addition, the aforementioned foamed particles should preferably be foamed particles that only exhibit the melting peak (inherent peak) inherent to linear low-density polyethylene in the DSC curve 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.

[0042] The total heat of fusion of the aforementioned foamed particles (mixed resin) is the sum of the heats of fusion of all melting peaks (endothermic peaks) shown in the DSC curve. The total heat of fusion of the aforementioned foamed particles should preferably be 70 J / g or higher and 120 J / g or lower, more preferably 70 J / g or higher and 105 J / g or lower. If the total heat of fusion of the foamed particles is within the aforementioned range, foamed particles with excellent two-stage foaming properties and in-mold formability can be obtained, and molded bodies with excellent strength can be obtained. The total heat of fusion of the aforementioned foamed particles, considering the improvement of the strength of the resulting molded body, is preferably 75 J / g or higher, more preferably 80 J / g or higher, even more preferably 85 J / g or higher, and especially preferably 90 J / g or higher. Furthermore, considering the improvement of the two-stage foaming properties and in-mold forming properties of the aforementioned foamed particles, the total heat of fusion of the aforementioned foamed particles is preferably 105 J / g or lower, more preferably 102 J / g or lower, even more preferably 100 J / g or lower, and even more preferably 98 J / g or lower. The total heat of fusion of the foamed particles can be obtained by preparing a test piece from the foamed particles and performing differential scanning calorimetry (DSC) according to JIS K 7122:2012. Specifically, firstly, regarding the conditioning of the test piece, the method of "(2) measuring the melting temperature after performing a certain heat treatment" is adopted. The test piece is heated from 23°C to 200°C at a heating rate of 10°C / min. After reaching 200°C, it is cooled from 200°C to 23°C at a heating rate of 10°C / min. Then, it is heated to 200°C twice at a heating rate of 10°C / min to obtain the DSC curve (the DSC curve at the second heating). The point at 80°C on the DSC curve at the second heating is defined as α, and the point on the DSC curve corresponding to the melting end temperature is defined as β. The area enclosed by the DSC curve and the line segment (α-β) in the interval between points α and β is measured, and the total heat of fusion of the mixed resin constituting the foamed particles can be calculated from this area.

[0043] The heat of fusion at the high-temperature peak of the aforementioned foamed particles is 10 J / g or more and 50 J / g or less. If the heat of fusion at the high-temperature peak of the foamed particles is within the aforementioned range, even when producing foamed particles with low bulk density, the in-mold formability of the foamed particles can be improved, and foamed particles with a wide range of molding pressures suitable for in-mold forming can be obtained. This allows for the acquisition of well-formed articles covering a broad density range. The heat of dissolution at the high-temperature peak of the aforementioned foamed particles, considering the viewpoint of suppressing shrinkage of the molded body immediately after molding and improving the moldability of the foamed particles in the mold, or the viewpoint of stably suppressing the shrinkage of the second-stage foamed particles during the second-stage foaming process, is preferably 15 J / g or higher, more preferably 20 J / g or higher, even more preferably 30 J / g or higher, and even more preferably 32 J / g or higher. Furthermore, the heat of dissolution at the high-temperature peak of the aforementioned foamed particles, considering the viewpoint of improving the weldability of the foamed particles under low molding pressure conditions and improving the moldability of the foamed particles in the mold, or the viewpoint of making it easier to obtain foamed particles with lower bulk density during the second-stage foaming process, is preferably 50 J / g or lower, preferably 45 J / g or lower, and even more preferably 40 J / g or lower. The heat of fusion at the high-temperature peak can be obtained by preparing test pieces from the foamed particles and measuring them using differential scanning calorimetry according to JIS K7122:2012. Specifically, it can be obtained from the DSC curve (DSC curve of the first heating) obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min. More specifically, it can be measured using the method described in the examples. In addition, foamed particles (the mixed resin constituting the foamed particles) having a crystalline structure that exhibits inherent peaks and high-temperature peaks in the aforementioned first DSC curve can be obtained, for example, by performing the following holding step on resin particles made by mixing the aforementioned linear low-density polyethylene A and linear low-density polyethylene B.

[0044] The ratio of the heat of fusion at the high-temperature peak of the aforementioned foamed particles to the total heat of fusion [heat of fusion at the high-temperature peak / total heat of fusion] is preferably 0.2 or higher and 0.7 or lower, and more preferably 0.25 or higher and 0.65 or lower. When the aforementioned heats of fusion are within the aforementioned ranges, and the aforementioned ratios are within the aforementioned ranges, foamed particles with excellent in-mold formability, covering a wide density range, and capable of in-mold forming under a wide molding pressure range can be obtained. Furthermore, foamed particles with good two-stage foaming properties can be obtained. The ratio of the heat of dissolution at the high-temperature peak of the aforementioned foamed particles to the total heat of dissolution, considering the viewpoint of suppressing shrinkage of the molded body immediately after molding and improving the moldability of the foamed particles in the mold, or the viewpoint of stably suppressing the shrinkage of the second-stage foamed particles during secondary foaming, is preferably 0.25 or higher, more preferably 0.28 or higher, and even more preferably 0.30 or higher. Furthermore, the ratio of the heat of dissolution at the high-temperature peak of the aforementioned foamed particles to the total heat of dissolution, considering the viewpoint of improving the weldability of the foamed particles under low molding pressure conditions and improving the moldability of the foamed particles in the mold, or the viewpoint of easily obtaining foamed particles with lower bulk density during secondary foaming, is preferably 0.65 or lower, more preferably 0.60 or lower, even more preferably 0.55 or lower, and especially preferably 0.50 or lower. Furthermore, the ratio of the heat of fusion at the high-temperature peak to the total heat of fusion can be obtained from the aforementioned total heat of fusion and the aforementioned heat of fusion at the high-temperature peak.

[0045] The melt flow rate of the aforementioned mixed resin, measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. A melt flow rate within the aforementioned range for the aforementioned mixed resin can further improve the in-mold formability of the foamed particles. The melt flow rate of the aforementioned mixed resin is preferably 0.3 g / 10 min or more, more preferably 0.5 g / 10 min or more, and even more preferably 0.7 g / 10 min or more. Furthermore, the melt flow rate of the aforementioned mixed resin is preferably 2.0 g / 10 min or less, 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. Furthermore, the melt flow rate of the aforementioned mixed resin was measured under conditions of 190°C and a load of 2.16 kg. More specifically, it can be measured according to JIS K 7210-1:2014 and using the method described in the examples.

[0046] The density of the aforementioned mixed resin should preferably be above 910 kg / m³ and below 940 kg / m³. Considering the ease of obtaining foamed particles with desired physical properties, a density of above 910 kg / m³ and below 928 kg / m³ is more preferred, above 912 kg / m³ and below 926 kg / m³ is even more preferred, above 914 kg / m³ and below 925 kg / m³ is still more preferred, and above 916 kg / m³ and below 924 kg / m³ is particularly preferred. The density of the aforementioned mixed resin was determined using Method A (water displacement method) as described in JIS K7112:1999.

[0047] (Manufacturing of resin particles) The aforementioned resin particles used in the method for manufacturing foamed particles of the present invention can be obtained by heating and mixing the aforementioned linear low-density polyethylene A, the aforementioned linear low-density polyethylene B, and bubble modifiers as needed in an extruder to form a mixed resin, i.e., a resin melt, and then extruding the resin melt from the extruder, while simultaneously granulating it using methods such as strand cutting, hot cutting, or underwater cutting.

[0048] The average mass of each of the aforementioned resin particles should preferably be adjusted to be 0.1-20 mg, more preferably 0.2-10 mg, even more preferably 0.3-5 mg, and still more preferably 0.4-2 mg. Furthermore, the shape of the aforementioned particles is not particularly limited if it is within the range that achieves the intended purpose of this invention, but it is preferably cylindrical. When the resin particles are cylindrical, the particle size (length in the extrusion direction) of the aforementioned resin particles is preferably 0.1~3.0 mm, and more preferably 0.3~1.5 mm. Furthermore, the ratio (length / diameter ratio) of the length of the aforementioned resin particles in the extrusion direction to the length in the direction perpendicular to the extrusion direction of the aforementioned resin particles is preferably 0.5~5.0, and more preferably 1.0~3.0.

[0049] In addition, when using the strand cutting method for granulation, 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 pulling speed, and the cutting machine speed when cutting the strands.

[0050] Furthermore, the resin particles may appropriately contain additives, to the extent that they do not impair the effects of the present invention. Examples of additives include: antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and bubble modifiers. These additives may be incorporated into the foamed particles, for example, by being added to the resin particles during the manufacturing process.

[0051] Bubble modifiers can be made from, for example, inorganic powders and organic powders. Examples of inorganic powders include borate metal salts such as zinc borate and magnesium borate, while examples of organic powders include fluoropolymer powders such as polytetrafluoroethylene (PTFE). Considering the viewpoint of being able to stably obtain foamed particles with the desired bulk density and minimal deviation in bubble diameter, the amount of bubble modifier in the resin particles should preferably be above 50 ppm by mass and below 5000 ppm by mass, preferably above 100 ppm by mass and below 2000 ppm by mass, and even more preferably above 150 ppm by mass and below 1500 ppm by mass. Furthermore, considering the ease with which the average bubble diameter of the foamed particles can be adjusted to the desired range, borate metal salts are preferred as bubble modifiers, with zinc borate being even better. Moreover, when using zinc borate, its arithmetic mean particle size, based on the number of particles, should preferably be 0.5 μm or more and 10 μm or less, and preferably 1 μm or more and 8 μm or less. The arithmetic mean particle size of zinc borate, based on the number of particles, can be obtained by taking a volume-based particle size distribution determined using laser diffraction scattering, assuming the particle shape is spherical, converting it to a number-based particle size distribution, and then arithmetically averaging the particle size based on this number-based distribution. Furthermore, the aforementioned particle size refers to the diameter of an imaginary sphere with the same volume as the particle.

[0052] <Manufacturing of Foamed Particles> The method for manufacturing foamed particles according to the present invention can be used to foam the aforementioned resin particles using a mixed resin as the base resin, and to produce foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less. The method for manufacturing foamed particles according to the present invention can also be, for example, a method of infiltrating a foaming agent into resin particles using a mixed resin of at least two types of linear low-density polyethylene as the base resin, and then foaming the resin particles containing the foaming agent. The foaming method for the resin particles can employ methods such as heating the resin particles containing the foaming agent using a heating medium such as steam, or opening the resin particles containing the foaming agent, which are maintained at a predetermined temperature and pressure environment, under a pressure environment lower than the aforementioned pressure environment. The following illustrates an example of an ideal manufacturing method.

[0053] The ideal manufacturing method of the foamed particles of the present invention is a method of manufacturing foamed particles by foaming the aforementioned resin particles. The method involves dispersing the aforementioned resin particles containing a foaming agent in an aqueous medium in a container, and releasing them together with the aforementioned aqueous medium from the aforementioned container to a pressure environment lower than the pressure inside the aforementioned container, so as to foam the aforementioned resin particles. More specifically, it includes the following steps: a dispersion step of dispersing resin particles, which are based on a mixture of at least two linear low-density polyethylene resins, in an aqueous medium within a container; a foaming agent infiltration step of infiltrating the aforementioned resin particles with a foaming agent within the container; and a foaming step of releasing the aforementioned resin particles containing the foaming agent and the aqueous medium together from the container to a pressure environment lower than the pressure inside the container to cause the resin particles to foam.

[0054] The ideal method for manufacturing foamed particles according to the present invention comprises the following steps: a dispersion step of dispersing the aforementioned resin particles in an aqueous medium within a container; a foaming agent impregnation step of impregnating the aforementioned resin particles with a foaming agent within the container; and a foaming step of releasing the aforementioned resin particles containing the foaming agent and the aqueous medium together from the container to a pressure environment lower than the pressure inside the container to foam the resin particles. These steps are preferably performed in this order, and it is more preferable that these steps are performed as a series of steps. Furthermore, the method of performing foaming using this series of steps is also called a dispersion medium release foaming method.

[0055] In the aforementioned dispersion step, an aqueous dispersion medium is preferably used as the dispersion medium for dispersing the resin particles obtained as described above in a closed container. This aqueous dispersion medium is one in which water is the 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, even more preferably 90% by mass or more, and can also be 100% by mass. Examples of dispersion media other than water in the aqueous dispersion medium include: ethylene glycol, glycerol, methanol, ethanol, etc.

[0056] In the dispersion medium release foaming method ideally applicable to this invention, a dispersant is preferably added to the dispersion medium to prevent the resin particles from fusing together after heating within the container. The dispersant can be any substance that prevents the resin particles from fusing together within the container; an inorganic dispersant is ideally suitable. Examples of inorganic dispersants include: natural or synthetic clay minerals such as kaolin, mica, and clay; alumina, titanium dioxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide; one or more of these can be used, or a combination of two or more can be used. Natural or synthetic clay minerals are preferred. The amount of the aforementioned dispersant added relative to 100 parts by weight of the aforementioned resin particles is preferably 0.001 to 5 parts by weight.

[0057] In addition, when using dispersants, it is advisable to use anionic surfactants such as sodium dodecylbenzenesulfonate, sodium alkyl sulfonate, and sodium oleic acid as dispersing aids. The aforementioned dispersing aids should be added at approximately 0.001 to 1 part by weight per 100 parts by weight of the aforementioned resin particles.

[0058] In the aforementioned foaming agent infiltration step, the foaming agent used to foam the aforementioned resin particles should preferably be a physical foaming agent. Examples of physical foaming agents include inorganic and organic physical foaming agents. Examples of inorganic physical foaming agents include carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical foaming 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. Furthermore, the aforementioned physical foaming agents can be used alone or in combination. Additionally, inorganic and organic physical foaming agents can also be used together. The foaming agent used in this manufacturing method is preferably an inorganic physical foaming agent, considering the ease of manufacturing the desired foamed particles; carbon dioxide is even better.

[0059] The amount of foaming agent added is determined by considering the desired bulk density of the foamed particles and the type of foaming agent. For example, when using a physical foaming agent, the amount of physical foaming agent added relative to 100 parts by weight of resin particles should be 0.1 to 30 parts by weight, and 0.5 to 15 parts by weight is even better.

[0060] In the foam particle manufacturing process, the method of incorporating the foaming agent into the resin particles can ideally be to disperse the resin particles in an aqueous dispersion medium in a closed container, while simultaneously pressing the foaming agent into the closed container, and heating and pressurizing the closed container and maintaining it, thereby incorporating the foaming agent into the resin particles.

[0061] In the aforementioned foaming step, the pressure (internal pressure) inside the sealed container during foaming should preferably be 0.5 MPa(G) or higher, and more preferably 0.8 MPa(G). Furthermore, the upper limit should preferably be 4 MPa(G) or lower, and more preferably 3 MPa(G). Within the above range, there are no concerns about damage or explosion of the sealed container, and the desired foamed particles can be safely manufactured. Additionally, the temperature should preferably be raised to 100-200°C, more preferably 130-160°C, and maintained at this temperature for approximately 5-30 minutes. Then, the resin particles containing the foaming agent are released from the sealed container to a pressure environment lower than the pressure inside the sealed container (e.g., one atmosphere) to allow them to foam.

[0062] Furthermore, foamed particles that exhibit a crystalline structure with inherent peaks and high-temperature peaks in the aforementioned first DSC curve can be manufactured, for example, by the following method. First, resin particles dispersed in a dispersion medium within a sealed container are heated from a temperature of 15°C (the melting point of the linear low-density polyethylene constituting the resin particles) to 10°C (the melting point of the linear low-density polyethylene constituting the resin particles), and held at this temperature for a sufficient time, preferably about 10 to 60 minutes (holding step). Then, by foaming the resin particles after this holding step, foamed particles exhibiting the aforementioned melting peaks can be obtained. In the manufacture of foamed particles, foamed particles can also be obtained by preparing resin particles that have undergone the aforementioned holding step in advance and then foaming the resin particles that have undergone the holding step. Alternatively, foamed particles can also be obtained by performing the aforementioned holding step on the resin particles in the form of a part of the aforementioned dispersion step or the aforementioned foaming agent infiltration step and then foaming the resin particles that have undergone the holding step. From the perspective of improving the productivity of foamed particles, it is advisable to perform the above-mentioned holding step by heating the resin particles dispersed in the dispersion medium in a closed container in the presence of a foaming agent, and then releasing the contents of the closed container to a pressure environment lower than the pressure inside the closed container, so that the resin particles that have undergone the above-mentioned holding step will foam to obtain foamed particles exhibiting the above-mentioned melting peak.

[0063] Furthermore, the foamed particles obtained as described above can be subjected to multi-stage foaming to obtain foamed particles with a higher expansion ratio (lower bulk density). For example, the foamed particles can be pressurized using air or the like to increase the pressure (internal pressure) within the bubbles, and then heated with steam or the like to further foam them (two-stage foaming), thus producing foamed particles with a higher expansion ratio (lower bulk density). Considering the viewpoint of obtaining molded bodies with low apparent density, two-stage foaming is preferable.

[0064] <Foamed particles manufactured using the aforementioned method> The foamed particles manufactured using the foamed particle manufacturing method of the present invention have a bulk density of 10 kg / m³ or more and 240 kg / m³ or less. The foamed particles manufactured using the foamed particle manufacturing method of the present invention are preferably the foamed particles described in the [foamed particles] section below, and more ideal foamed particles are also preferred. Furthermore, the foamed particles described in the above-mentioned (characteristics of mixed resin and foamed particles) section are preferred, and more ideal foamed particles are also preferred.

[0065] The aforementioned foamed particles are foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less. From the viewpoint of improving the mechanical properties of the resulting molded article, the bulk density of the aforementioned foamed particles is 10 kg / m³ or more, preferably 13 kg / m³ or more, and more preferably 15 kg / m³ or more. On the other hand, from the viewpoint of obtaining a molded article with low apparent density, the bulk density of the aforementioned foamed particles is 240 kg / m³ or less, preferably 200 kg / m³ or less, more preferably 100 kg / m³ or less, even more preferably 80 kg / m³ or less, and still more preferably 60 kg / m³ or less. As described below, in this invention, the obtained foamed particles can be subjected to pressure treatment, followed by heating with steam or the like to perform a second-stage foaming process, resulting in foamed particles with a higher expansion ratio (lower bulk density). Considering the viewpoint of obtaining a molded body with low apparent density, it is advisable to perform a second-stage foaming process. For the two-stage foaming process, the bulk density of the foamed particles after the first stage of foaming (before the second stage) should ideally be 60 kg / m³ or higher, preferably 70 kg / m³ or higher, and even better if it is 80 kg / m³ or higher, considering the goal of consistently obtaining foamed particles with the desired bubble structure. On the other hand, for the two-stage foaming process, the bulk density of the foamed particles after the first stage of foaming (before the second stage) should ideally be 240 kg / m³ or lower, preferably 200 kg / m³ or lower, even better if it is 180 kg / m³ or lower, and even better if it is 160 kg / m³ or lower, considering the goal of consistently obtaining foamed particles with low apparent density. In addition, the bulk density can be determined using the method described in the examples.

[0066] [Foaming particles] The foamed particles of the present invention are foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less, using at least two kinds of mixed resins of linear low-density polyethylene as the base material, and the density of the aforementioned mixed resins is 910 kg / m³ or more and 928 kg / m³ or less. The biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, is 5% or more, and the melt flow rate of the aforementioned foamed particles is 0.1 g / 10 min or more and 3 g / 10 min or less. The aforementioned foamed particles 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, the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) located on the higher temperature side than the inherent peak, and the heat of melting of the aforementioned high-temperature peaks is 10 J / g or more and 50 J / g or less. The foamed particles of the present invention are preferably manufactured using the above-described method for manufacturing foamed particles. The method for manufacturing the foamed particles of the present invention is preferably the above-described method for manufacturing foamed particles.

[0067] (Mixed resin) The aforementioned foamed particles use a mixture of at least two linear low-density polyethylene resins as the base resin. In this specification, "using a mixture of at least two linear low-density polyethylene resins as the base resin" means that the foamed particles are composed of resins with at least two linear low-density polyethylene resins as the main component.

[0068] The base resin of the foamed particles of the present invention is a mixture of at least two linear low-density polyethylene resins, preferably the mixture of resins described in the aforementioned section on <linear low-density polyethylene (mixed resin)> as explained in the method for manufacturing the foamed particles. Therefore, the aforementioned mixture of resins is preferably a mixture of at least two linear low-density polyethylenes, namely linear low-density polyethylene A and linear low-density polyethylene B, which have a biomass of 50% or more as measured according to ASTM D 6866. Furthermore, considering the viewpoint that foamed particles with excellent in-mold formability and a wide range of forming capabilities can be stably obtained to produce good products, the aforementioned at least two types of linear low-density polyethylene are preferably linear low-density polyethylene A1 containing butene and hexene as copolymerizing components (comonomers) and linear low-density polyethylene B1 containing octene as copolymerizing component (comonomer).

[0069] The density of the aforementioned mixed resin is preferably 910 kg / m³ or higher and 928 kg / m³ or lower. Considering the ease of obtaining foamed particles with desired physical properties, a density of 912 kg / m³ or higher and 926 kg / m³ or lower is more preferred, 914 kg / m³ or higher and 925 kg / m³ or lower is even more preferred, and 916 kg / m³ or higher and 924 kg / m³ or lower is still more preferred. Furthermore, considering the possibility of in-mold molding under lower molding pressure conditions, the density of the aforementioned mixed resin is preferably 917 kg / m³ or higher and 923 kg / m³ or lower. The density of the aforementioned mixed resin was determined using Method A (water displacement method) as described in JIS K7112:1999. Alternatively, when determining the density of the mixed resin from foamed particles, the density can be determined by using defoamed foamed particles as a sample and performing the aforementioned density measurement. Specifically, the method described in the examples can be used for the determination.

[0070] <Characteristics / Composition of Foamed Particles> As described above, the foamed particles of this invention are foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less, using at least two kinds of mixed resins of linear low-density polyethylene as the base material, and the density of the mixed resins being 910 kg / m³ or more and 928 kg / m³ or less. The biomass of the foamed particles, as measured according to ASTM D 6866, is 5% or more, and the melt flow rate of the foamed particles is 0.1 g / 10 min or more and 3 g / 10 min or less. The foamed particles 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, the inherent melting peak (inherent peak) of linear low-density polyethylene and at least one melting peak (high-temperature peak) located on the higher temperature side than the inherent peak, and the heat of melting of the aforementioned high-temperature peak is 10 J / g or more and 50 J / g or less. The foamed particles preferably have the following characteristics.

[0071] The aforementioned foamed particles have a bulk density of 10 kg / m³ or higher and 240 kg / m³ or lower. From the viewpoint of improving the mechanical properties of the resulting molded article, the bulk density of the aforementioned foamed particles is preferably 10 kg / m³ or higher, more preferably 13 kg / m³ or higher, and even more preferably 15 kg / m³ or higher. On the other hand, from the viewpoint of obtaining a molded article with low apparent density, the bulk density of the aforementioned foamed particles is preferably 240 kg / m³ or lower, more preferably 200 kg / m³ or lower, even more preferably 100 kg / m³ or lower, even more preferably 80 kg / m³ or lower, and even more preferably 60 kg / m³ or lower. As described below, in this invention, the obtained foamed particles can be subjected to pressure treatment, followed by heating with steam or the like to perform a second-stage foaming process, resulting in foamed particles with a higher expansion ratio (lower bulk density). Considering the viewpoint of obtaining a molded body with low apparent density, it is advisable to perform a second-stage foaming process. For the two-stage foaming process, the bulk density of the foamed particles after the first stage of foaming (before the second stage) should ideally be 60 kg / m³ or higher, preferably 70 kg / m³ or higher, and even better if it is 80 kg / m³ or higher, considering the goal of consistently obtaining foamed particles with the desired bubble structure. On the other hand, for the two-stage foaming process, the bulk density of the foamed particles after the first stage of foaming (before the second stage) should ideally be 240 kg / m³ or lower, preferably 200 kg / m³ or lower, even better if it is 180 kg / m³ or lower, and even better if it is 160 kg / m³ or lower, considering the goal of consistently obtaining foamed particles with low apparent density. In addition, the bulk density can be determined using the method described in the examples.

[0072] The biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, is above 5%. By ensuring that the biomass of the aforementioned foamed particles falls within the aforementioned range, the use of fossil resources can be suppressed during the manufacture of the molded body, and the amount of carbon dioxide emitted during the life cycle of the molded body can also be reduced. Considering the foregoing points, the biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, should be 5% or higher, preferably 10% or higher, more preferably 20% or higher, even better if 30% or higher, and still better if 40% or higher. Furthermore, there is no upper limit; if the biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, is below 100%, it is acceptable. Considering the viewpoint of easily improving the in-mold formability of the foamed particles, the biomass of the aforementioned foamed particles, as measured according to ASTM D 6866, should preferably be below 90%, more preferably below 80%, even better if below 70%, and still better if below 60%. The aforementioned biomass, measured according to ASTM D 6866, refers to the proportion of naturally derived components contained in the foamed particles. Furthermore, the aforementioned biomass can be determined by measuring the concentration of radioactive carbon C14 in linear low-density polyethylene, or by the biomass of the resin derived from the biomass used to manufacture the foamed particles and the proportion of the resin derived from the biomass in the foamed particles.

[0073] The melt flow rate of the aforementioned foamed particles (the mixed resin constituting the foamed particles), measured at a temperature of 190°C and a load of 2.16 kg, was 0.1 g / 10 min or more and 3 g / 10 min or less. Having a melt flow rate within the aforementioned range further improves the in-mold formability of the foamed particles. The melt flow rate of the aforementioned foamed particles is preferably 0.3 g / 10 min or more, more preferably 0.5 g / 10 min or more, and even more preferably 0.7 g / 10 min or more. Furthermore, the melt flow rate of the aforementioned foamed particles is preferably 2.0 g / 10 min or less, 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. Furthermore, the melt flow rate of the aforementioned foamed particles was measured under conditions of 190°C and a load of 2.16 kg. More specifically, it can be measured according to JIS K 7210-1:2014 and using the method described in the examples. Alternatively, the above-mentioned melt flow rate measurement can be performed using foamed particles that have undergone defoaming treatment as the test sample.

[0074] The foamed particles of the present invention exhibit a crystalline structure in the DSC curve obtained by heating from 23°C to 200°C at a heating rate of 10°C / minute, which shows the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) that are closer to the high-temperature side than the inherent peak. The heat of melting of the aforementioned high-temperature peak is more than 10 J / g and less than 50 J / g.

[0075] The aforementioned DSC curve was obtained using differential scanning calorimetry (DSC) according to JIS K7122:2012. Specifically, a differential scanning calorimeter can be used to obtain the aforementioned DSC curve by heating 1-3 mg of the foaming particles of the present invention from 23°C to 200°C at a heating rate of 10°C / min. As described above, the foamed particles of the present invention exhibit, in the aforementioned DSC curve before the foamed particles are measured, the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) that are closer to the high-temperature side than the inherent peak. The foamed particles described in the [foamed particles] item of this invention should preferably have a range of total heat of fusion, a range of heat of fusion at the high temperature peak, and a range of the ratio of heat of fusion at the high temperature peak to total heat of fusion of the foamed particles manufactured using the aforementioned foamed particle manufacturing method. More ideally, the foamed particles should also have the same characteristics.

[0076] From the perspective of improving the mechanical properties of the resulting molded article, the melting point of the aforementioned foamed particles should preferably be 100°C or higher and 130°C or lower. A melting point of 110°C or higher is more preferable, 115°C or higher is even more preferable, and 118°C or higher is still more preferable. On the other hand, from the perspective of improving the moldability of the foamed particles under low molding pressure conditions, a melting point of 128°C or lower, and 126°C or lower is more preferable. The melting point of the foamed particles was determined by preparing test pieces of the foamed particles and measuring them according to JIS K 7121:2012. Specifically, the method described in the examples can be used for the determination.

[0077] The independent bubble rate of the foamed particles of the present invention is preferably 80% or higher. A higher independent bubble rate within the aforementioned range further improves the in-mold forming properties of the foamed particles. The independent bubble rate of the foamed particles of the present invention is preferably 85% or higher, more preferably 88% or higher, and even more preferably 90% or higher. Furthermore, there is no upper limit to the independent bubble rate of the foamed particles of the present invention; it is preferably 99% or lower, more preferably 98% or lower, and even more preferably 97% or lower. In addition, the independent bubble rate can be determined using the method described in the examples.

[0078] The average bubble diameter of the foamed particles of the present invention is preferably 60 μm or more and 200 μm or less. Having an average bubble diameter within the aforementioned range can stably improve the in-mold formability of the foamed particles. The average bubble diameter of the foamed particles 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 bubble diameter of the foamed particles of the present invention is preferably 180 μm or less, more preferably 160 μm or less, and even more preferably 140 μm or less. Furthermore, when implementing two-stage foaming, the average bubble diameter of the foamed particles after the first stage of foaming (before the second stage of foaming) should preferably be 50 μm or more, preferably 60 μm or more, and even more preferably 70 μm or more. Also, when implementing two-stage foaming, the average bubble diameter of the foamed particles after the first stage of foaming (before the second stage of foaming) should preferably be 120 μm or less, preferably 110 μm or less, and even more preferably 100 μm or less. Furthermore, the average bubble diameter can be determined by drawing multiple line segments from the outermost surface of the foamed particle through the center to the outermost surface on the opposite side in a magnified photograph of a cross-section of the halved foamed particle, and dividing the total length of the line segments by the number of bubbles intersecting each line segment. Specifically, the method described in the examples can be used for measurement. The average bubble diameter of the foamed particles can be controlled within the desired range by adjusting the type and amount of bubble conditioner added to the resin particles, or by adjusting the foaming temperature of the resin particles during foaming, the pressure inside the pressure vessel, etc.

[0079] Furthermore, the foamed particles should preferably be non-crosslinked. Because they are non-crosslinked, the foamed particles are easy to regenerate and their environmental impact is easily reduced. In this specification, "non-crosslinked" refers to the proportion of insoluble components in the foamed particles obtained by hot xylene extraction being less than 5% by mass. Considering that foamed particles are easier to regenerate, the proportion of insoluble components obtained by hot xylene extraction should preferably be less than 3% by mass, with 0% by mass being optimal. The xylene-insoluble fraction obtained from the hot xylene extraction of foamed particles can be determined as follows: First, approximately 1 g of precisely weighed foamed particles (let its correct mass be M(g)) is placed in a 150 mL round-bottom flask, and 100 mL of xylene is added. The mixture is heated using a mantle heater and refluxed for 6 hours. Afterward, the dissolved residue (insoluble fraction) is filtered through a 100-mesh metal mesh and dried in a vacuum desiccator at 80 °C for at least 8 hours. The mass m(g) of the dried product obtained after drying the residue is measured, and the ratio of m to M is expressed as a percentage. This allows the determination of the proportion of xylene-insoluble fraction in the foamed particles.

[0080] The average mass of each foaming particle of the present invention (the arithmetic mean of the masses of 100 randomly selected particles) is preferably 0.1~20 mg, more preferably 0.2~10 mg, even more preferably 0.3~5 mg, and still more preferably 0.4~2 mg. The average mass of each foaming particle can be obtained by measuring the mass of 100 randomly selected foaming particles separately and then taking the arithmetic mean of these masses.

[0081] Furthermore, the foamed particles of the present invention may appropriately contain additives, to the extent that they do not impair the effects of the present invention. Examples of additives include: antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, and bubble modifiers. These additives can be incorporated into the foamed particles, for example, by adding them during the manufacturing process of the resin particles. The additives contained in the foamed particles of the present invention are the same as those contained in the resin particles described in the aforementioned <Manufacturing of Foamed Particles>.

[0082] The foamed particles of this invention may also contain polymers such as resins and elastomers other than the aforementioned linear low-density polyethylene, without impairing the effects of this invention. In this case, the content of polymers other than the aforementioned linear low-density polyethylene A and linear low-density polyethylene B in the foamed particles is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, even more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less, relative to a total of 100 parts by weight of linear low-density polyethylene A or linear low-density polyethylene B in the mixed resin. Furthermore, the content of polymers other than the aforementioned linear low-density polyethylene in the foamed particles is preferably 80 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, and particularly preferably 10 parts by weight or less, relative to a total of 100 parts by weight of linear low-density polyethylene (linear low-density polyethylene A or linear low-density polyethylene B) in the mixed resin.

[0083] The foamed particles of this invention may have a weld layer on their surface to improve the weldability between the foamed particles during molding. The weld layer may be present on the entire surface of the foamed particles or on a portion of the surface. Examples of resin systems constituting the weld layer include: crystalline polyolefin resins having a melting point lower than that of the mixed resin constituting the foamed particles, and amorphous polyolefin resins having a softening point lower than that of the mixed resin constituting the foamed particles. There are no particular limitations on the method for forming a weld layer on the surface of foamed particles. Examples include: foaming resin particles with a weld layer on their surface, and attaching the weld layer to the surface of the foamed particles after obtaining them. When obtaining foamed particles by foaming resin particles with a weld layer on their surface, the following method is preferable: during the manufacture of resin particles, an extrusion apparatus capable of co-extrusion is used, and the resin melt used to form the resin particle body and the resin melt used to form the weld layer are co-extruded, thereby laminating a weld layer on the surface of the resin particles.

[0084] As described above, the foaming particles of the present invention can be ideally used as foaming particles for in-mold forming. Furthermore, the foaming particles of the present invention, by conforming to a specific heat of melting relationship, become foaming particles with excellent foaming properties in two-stage foaming, and are therefore also ideal foaming particles for two-stage foaming. On the other hand, the foamed particles of the present invention, by conforming to a specific heat of melting, become foamed particles with appropriate softness and resilience. Therefore, the foamed particles of the present invention can also be ideally used, for example, as filler beads for cushioning materials. Filler beads are granular fillers that are filled into the bag body and used to form cushioning materials, and the foamed particles of the present invention are particularly ideally used as filler beads for beaded cushioning pads.

[0085] [Polyethylene Resin Foamed Particle Molding Material] Polyethylene resin foamed particle molded bodies can be obtained by in-mold molding of the foamed particles of the present invention or the foamed particles obtained by the manufacturing method of the foamed particles of the present invention. That is, the polyethylene resin foamed particle molded body (hereinafter referred to as foamed particle molded body) is formed by molding the aforementioned foamed particles in a mold.

[0086] The aforementioned foamed particle molded body can be formed by filling the foamed particles into a molding mold and heating them using a heating medium such as steam. Specifically, after filling the foamed particles into the molding mold, a heating medium such as steam is introduced into the molding mold to heat and expand the foamed particles (secondary foaming), while simultaneously fusing them together to obtain a foamed particle molded body with a shape endowed with a molding space. Furthermore, the in-mold forming in this invention can also be performed using the following method: the foamed particles are pre-pressurized using a pressurized gas such as air to increase the pressure inside the bubbles of the foamed particles; after adjusting the pressure inside the foamed particles to a pressure 0.01 to 0.3 MPa higher than atmospheric pressure, the foamed particles are filled into the molding mold under atmospheric pressure or depressurization, and then a heating medium such as steam is supplied into the mold to heat and fuse the foamed particles (e.g., Japanese Patent Publication No. 51-22951). Alternatively, molding can be performed using the following method: After filling a molding die pressurized to above atmospheric pressure with compressed gas, a heating medium such as steam is supplied to the mold cavity to heat and fuse the foam particles – a compression filling molding method (Japanese Patent Publication No. 4-46217). Other molding methods include: filling a molding die cavity with high secondary foaming power obtained under special conditions under atmospheric pressure or reduced pressure, then supplying a heating medium such as steam to heat and fuse the foam particles – an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795), or a combination of the above methods (Japanese Patent Publication No. 6-22919), etc.

[0087] From the perspective of improving mechanical properties, the density of the aforementioned foamed particle molded body should preferably be 10 kg / m³ or higher, more preferably 13 kg / m³ or higher, and even more preferably 15 kg / m³ or higher. Furthermore, from the perspective of making it a lightweight molded body, the density of the foamed particle molded body should preferably be 240 kg / m³ or lower, more preferably 200 kg / m³ or lower, even more preferably 100 kg / m³ or lower, even more preferably 80 kg / m³ or lower, and especially preferably 60 kg / m³ or lower. In addition, the density of the foamed particle molded body is calculated by dividing the mass of the foamed particle molded body by the volume obtained based on the size of the foamed particle molded body, and can be measured using the method described in the examples.

[0088] From the perspective of creating a molded body that exhibits good strength and flexibility, the ratio of the compressive stress at 50% strain of the foamed particle molded body to the density of the aforementioned foamed particle molded body should preferably be 4 kPa / [kg / m 3] or more and 12 kPa / [kg / m 3] or less, and more preferably 5 kPa / [kg / m 3] or more and 10 kPa / [kg / m 3] or less. Furthermore, the ratio of the compressive stress at 50% strain to the density of the foamed particle molded body is obtained by dividing the stress at 50% strain, which is measured by compressing the aforementioned foamed particle molded body into a test piece with a length of 5cm, a width of 5cm, and a height of 2.5cm at a compression speed of 10mm / min, by the aforementioned density. This ratio can be measured and obtained using the method described in the examples.

[0089] The aforementioned polyethylene resin foamed particle molded body is lightweight and has excellent mechanical properties, so it can be used in the form of impact absorbers, heat insulation materials and various packaging materials for food handling containers, packaging / cushioning materials for electrical / electronic parts, vehicle components such as car bumpers, building components such as residential heat insulation materials, and general merchandise. [Example]

[0090] The invention will then be described in more detail with reference to examples, but the invention is not limited by these examples.

[0091] [Measurement and Evaluation] The following measurements and evaluations were performed on the resins, foamed particles, and foamed particle molded articles used in the examples and comparative examples. Tables 3 and 4, which show the results of the aforementioned measurements and evaluations and the manufacturing conditions, are respectively divided into Tables 3-1, 3-2, 4-1, and 4-2. In addition, the evaluation of the foamed particles or foamed particle molded articles was carried out after they were placed under conditions of 50% relative humidity, 23°C, and 1 atm for 2 days for condition conditioning.

[0092] <Biological quality of polyethylene, biological quality of foamed particles (mixed resin)> The biomass of the polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) used in the examples and comparative examples was determined based on the concentration of radioactive carbon C14 as measured by ASTM D 6866. Furthermore, the biomass of the foamed particles (mixed resin) was determined from the biomass of the resin derived from the biomass used to manufacture the foamed particles and the proportion of the resin derived from the biomass in the foamed particles. In addition, in Table 1, LL1 is "SLH118" manufactured by Braskem, LL2 is "SLL118" manufactured by Braskem, and LL3 is "SLH218" manufactured by Braskem. Furthermore, LL1 to LL3 are polyethylenes listed in the positive list of bioplastics of the Japan Bioplastics Association. In this positive list, LL1 and LL3 are described as linear low-density polyethylene containing butene and hexene as copolymers, represented by the chemical formula [(C2H4)n(C4H8)m(C6H12)o]. LL2 is described as linear low-density polyethylene containing butene as a copolymer, represented by the chemical formula [(C2H4)n(C4H8)m].

[0093] <Density of polyethylene, density of mixed resins> The densities of the polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) and the mixed resins used in the examples and comparative examples were determined based on Method A (water displacement method) of JIS K 7112:1999. In addition, in the determination of the density of the mixed resin, firstly, the foamed particles were defoamed by hot pressing them for 3 minutes using a heated pressing pan with the temperature adjusted to 160°C, thus obtaining a resin sheet composed of the mixed resin that constitutes the foamed particles. The density was then measured using granular samples obtained by cutting the resin sheet.

[0094] <Content of α-olefins in linear low-density polyethylene> The content of each α-olefin component in linear low-density polyethylene was determined using carbon-13 nuclear magnetic resonance (13C-NMR). First, linear low-density polyethylene was dissolved in a mixed solvent of o-dichlorobenzene-d4 (ODCB):benzene-d6 (C6D6) = 4:1 (130°C) to prepare a 10 wt / vol% analytical solution. NMR (13C-NMR) spectra of the analytical solution were measured using a NEC-400S instrument manufactured by NJEOL Ltd., with 13C as the analyte. Based on the chemical shift information in the obtained NMR spectrum, the α-olefin components in the linear low-density polyethylene were identified, and their content (mol%) was determined.

[0095] Melt Flow Rate (MFR) of Polyethylene and Foamed Particles (Mixed Resins) According to JIS K7210-1:2014, the melt flow rate (MFR) of the polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) used in the examples and comparative examples, and the melt flow rate (MFR) of the foamed particles (mixed resin) of the examples and comparative examples were determined under conditions of 190°C and 2.16 kg. In the determination of the melt flow rate of the foamed particles, firstly, the foamed particles were defoamed by hot-pressing them for 3 minutes using a heated pressing pan with the temperature adjusted to 160°C, resulting in a resin sheet composed of the mixed resin constituting the foamed particles. The melt flow rate was then measured using pellet-shaped samples obtained by cutting the resin sheet.

[0096] Melting point of polyethylene, melting point of foamed particles (mixed resin) The melting points of polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) and foamed particles used in the examples and comparative examples were determined by differential scanning calorimetry (DSC) according to JIS K7121:2012. A high-sensitivity differential scanning calorimeter "EXSTAR DSC7020" (manufactured by SII NanoTechnology) was used for the determination. Regarding the conditioning of the test pieces, the following method was adopted: "(2) After performing a certain heat treatment, the melting temperature was measured". Approximately 2 mg of polyethylene or approximately 2 mg of foamed particles were prepared into test pieces and collected. The test pieces were heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow rate of 30 mL / min. After holding at that temperature for 10 minutes, the temperature was cooled to 23°C at a cooling rate of 10°C / min. The temperature was then heated again to 200°C at a heating rate of 10°C / min to obtain the DSC curve (DSC curve during the second heating). Find the peak temperature of the melting peak in the DSC curve and set this value as the melting point. Furthermore, when the DSC curve exhibits multiple melting peaks, the vertex temperature of the melting peak with the largest area is used as the melting point. In this case, the melting peaks can be distinguished by using the valley temperatures of the DSC curves located between the vertex temperatures of each melting peak as boundaries, and by comparing the areas (heat of fusion) of each melting peak to determine the melting peak with the largest area. The valley temperatures of the DSC curve correspond to the temperature at which the vertical axis of the differential curve (DDSC) of the DSC curve is 0, so this can also be determined from the differential curve of the DSC.

[0097] <Heat of melting of polyethylene and total heat of melting of foamed particles (mixed resin)> The heat of fusion of polyethylene (linear low-density polyethylene, low-density polyethylene or high-density polyethylene) and the total heat of fusion of foamed particles (mixed resin) used in the examples and comparative examples were determined in accordance with JIS K7122:2012. First, test pieces of polyethylene or foamed particles are prepared, and DSC curves for the second heating are obtained using the same method as for determining the melting point of polyethylene. Let the point on the DSC curve at 80°C during the second heating be α, and let the point on the DSC curve corresponding to the melting point be β. The area enclosed by the DSC curve and the line segment (α-β) in the interval between points α and β is measured, and the heat of fusion of polyethylene or the total heat of fusion of the foamed particles is obtained from this area.

[0098] <Heat of melting at the high-temperature peak of foamed particles> The heat of fusion of the high-temperature peak of the foamed particles was determined using differential scanning calorimetry (DSC) according to JIS K7122:2012. Specifically, approximately 2 mg of foamed particles were prepared into test pieces and collected. Using a differential scanning calorimeter (EXSTAR DSC7020), the particles were heated from 23°C to 200°C at a heating rate of 10°C / min to obtain DSC curves with two or more melting peaks (DSC curves from the first heating). Let the inherent peak of polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) described below be A, and let the high-temperature peak exhibited on the higher temperature side than the inherent peak be B. Draw a straight line (α-β) connecting point α on the DSC curve corresponding to 80°C and point β on the DSC curve corresponding to the melting point T of the test piece. The melting point T refers to the endpoint of the high-temperature side of the high-temperature peak B, which is the intersection of the high-temperature peak and the high-temperature side baseline. Then, from point γ on the DSC curve corresponding to the valley between the inherent peak A and the high-temperature peak B, draw a straight line parallel to the vertical axis of the graph, and let δ be the point where this line intersects the aforementioned straight line (α-β). Calculate the area enclosed by the curve, line segment (δ-β), and line segment (γ-δ) of the high-temperature peak B portion in the DSC curve, and obtain the heat of fusion for each high-temperature peak from this area. Perform the above-mentioned heat of fusion measurement on three different test pieces, and take the arithmetic mean of the obtained values ​​as the heat of fusion of the high-temperature peak of the foamed particles.

[0099] <Bulk density of foamed particles> Fill a graduated cylinder with approximately 500 cm³ of foamed particles, and tap the bottom of the cylinder on the floor several times to stabilize the filling height. Record the total volume of the foamed particles as indicated on the graduated cylinder scale and denote it as V1 (L). Then, measure the mass of the foamed particles and denote it as W1 [g]. The bulk density of the foamed particles is obtained by dividing the mass W1[g] of the foamed particles by the volume V1 (W1 / V1) and converting the unit to [kg / m 3].

[0100] <Independent bubble ratio of foaming particles> The independent bubble rate of foamed particles is determined as follows. A group of foamed particles with a total volume of approximately 20 cm³ was immersed in ethanol, and the apparent volume Va of the foamed particle group was determined. Then, after the foamed particle group was thoroughly dried after the apparent volume Va was measured, the true volume Vx (the sum of the volume of the resin constituting the foamed particle and the total volume of the individual air bubbles within the foamed particle) of the foamed particle group was determined according to procedure C as described in ASTM-D2856-70. The true volume Vx was determined using an air comparison hydrometer "930" manufactured by TOSHIBA-BECKMAN. Then, the percentage of individual air bubbles was obtained using the following formula (1), and the arithmetic mean of the results of 5 measurements using different foamed particle groups was calculated. Independent bubble rate (%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ･･･(1) Vx: The true volume (cm³) of the foamed particle swarm measured using the above method. Va: Apparent volume of the foamed particle group (cm³) measured from the rise in water level when the foamed particle group is submerged in ethanol in a graduated cylinder. W: Mass of the foamed particle cluster (g) ρ: Density of the resin that makes up the foamed particles (g / cm³)

[0101] <Average bubble diameter of foaming particles> The average bubble diameter of the foamed particles is determined as follows. Randomly select 30 foamed particles from the group of foamed particles. Cut the foamed particles in half in a way that passes through their central parts, and take magnified photos of one of the cross-sections respectively. In each cross-section photo, from the outermost surface of the foamed particle through the central part to the outermost surface on the opposite side, draw 4 line segments in such a way that the angles formed by adjacent 2 line segments are equal. Measure the number of bubbles intersecting with each line segment respectively, and divide the total length of the 4 line segments by the total number of bubbles intersecting with the line segments, thereby obtaining the average bubble diameter of each foamed particle, and by performing arithmetic mean on these values, obtain the average bubble diameter of the foamed particles.

[0102] <Ratio of the volume density of the first-stage foamed particles to the volume density of the second-stage foamed particles> Using the above method for measuring the volume density, measure the volume density of the first-stage foamed particles and the volume density of the second-stage foamed particles. By dividing the volume density of the first-stage foamed particles by the volume density of the second-stage foamed particles, obtain the ratio of the volume density of the first-stage foamed particles to the volume density of the second-stage foamed particles (volume density of the first-stage foamed / volume density of the second-stage foamed). In addition, the larger the value of this ratio, the lower the volume density of the second-stage foamed particles that can be obtained, so it indicates excellent secondary foaming property.

[0103] <State of the second-stage foamed particles> Visually observe the surface state of the second-stage foamed particles. When there are no clear wrinkles on the foamed particles and almost no shrinkage of the foamed particles is observed, it is evaluated as "〇 (good)". When clear wrinkles are observed on the foamed particles and a lot of shrinkage of the foamed particles is observed, it is evaluated as "× (bad)". In addition, when the above evaluation is "〇 (good)", the deviation of the density between the obtained second-stage foamed particles is small, it is easy to control the density of the foamed particles when manufacturing the desired shaped body, and at the same time, it becomes foamed particles that can stably exhibit good in-mold formability.

[0104] <Forming pressure range for forming good products> Using the method described below <Manufacture of foamed particle shaped body>, form the foamed particle shaped body by gradually changing the forming pressure (forming steam pressure) between 0.10 and 0.20 MPa (G) at intervals of 0.01 MPa, and evaluate the in-mold formability for the items of the weldability, surface appearance (gap = porosity), and recovery property (recovery of expansion or shrinkage after in-mold forming) of the obtained shaped body. Those meeting the following criteria are evaluated as qualified, and the steam pressure at which all items are qualified is the steam pressure for forming. In addition, the pressure marked with (G) is the gauge pressure, that is, the pressure value based on one atmospheric pressure. The wider the range between the lower and upper limits of the vapor pressure that can be formed, the wider the range of forms that can be formed, and the more ideal it is. Furthermore, if it can still be formed under low vapor pressure conditions, the amount of vapor required for forming can be reduced, resulting in excellent productivity, and therefore it is more ideal. (Weldability) The foamed particle molded body is bent and broken, and the number of foamed particles present on the fracture surface (C1) and the number of broken foamed particles (C2) are determined. The ratio of the number of broken foamed particles to the total number of foamed particles (C2 / C1×100) is taken as the material failure rate. The above test is performed 5 times using different test pieces, and the material failure rate is calculated for each test piece. A material failure rate of 80% or higher after arithmetic averaging is considered acceptable, and a failure rate of less than 80% is considered unacceptable. (Surface appearance) Draw a 100mm × 100mm square in the center of the foamed particle molded body. Draw a line from one corner of the square along the diagonal and count the number of gaps (voids) larger than 1mm × 1mm along the line. If the number of gaps is less than 5 and the surface is smooth, it is considered acceptable; otherwise, it is considered unacceptable. (Responsive) Measure the thickness of the four corners (within 10mm from the corners towards the center) and the center (the intersection of the lines dividing the molded body into two equal parts in the longitudinal and transverse directions) of a flat, 250mm long, 200mm wide, and 50mm thick sheet formed using in-mold molding. Then, calculate the ratio (%) of the center thickness to the thickness of the thickest point among the four corners. A ratio of 95% or higher is considered acceptable; a ratio below 95% is considered unacceptable.

[0105] <Density of foamed particle molded body> The foamed particle molded body was placed under conditions of 50% relative humidity, 23°C, and 1 atm for 2 days. Then, its mass was measured and set as W[g]. Then, based on the dimensions of the foamed particle molded body, the volume V [cm 3] of the foamed particle molded body is measured. The density of the foamed particle molded body is obtained by dividing the mass W[g] of the foamed particle molded body by the volume V (W / V) and converting the unit to [kg / m 3].

[0106] <Compressive Stress at 50% Strain in Foamed Particle Moldings> Test pieces measuring 5 cm in length, 5 cm in width, and 2.5 cm in height were collected from the molded bodies obtained in the examples and comparative examples. These test pieces were compressed at a compression rate of 10 mm / min, and the stress at 50% strain was measured. Higher stress indicates better strength of the foamed particle molded body. Furthermore, the aforementioned test pieces were collected from molded bodies formed at the lower limit of the formable vapor pressure. Divide the compressive stress at 50% strain obtained earlier by the aforementioned density to obtain the ratio of the compressive stress at 50% strain to the density of the foamed particle molded body. A ratio of 4 kPa / [kg / m³] or higher and 12 kPa / [kg / m³] or lower is ideal. Furthermore, a ratio of 5 kPa / [kg / m³] or higher and 10 kPa / [kg / m³] or lower indicates a better balance between strength and flexibility, which is even more ideal.

[0107] Polyethylene The polyethylene (linear low-density polyethylene, low-density polyethylene, or high-density polyethylene) used in the examples and comparative examples are shown in Tables 1 and 2.

[0108] [Table 1] Resin code LL1 LL2 LL3 LL4 LL5 LL6 Types of resins linear low-density polyethylene linear low-density polyethylene linear low-density polyethylene linear low-density polyethylene linear low-density polyethylene linear low-density polyethylene Main types of comonomers in LLDPE C6 / C4 C4 C6 / C4 C8 iC6 C4 Comonomer content (α-olefin content) (mol%) C3 (propylene) 1.6 1.6 1.6 - - - C4(1-Butene) 3.1 4.6 3.1 - - 2.4 C6(1-hexene) 1.4 - 1.4 - - - C8(1-octene) - - - 1.8 - - iC6(4-methyl-pentene) - - - - 1.9 - Quality [%] 84 87 84 0 0 0 Density (ρ) [kg / m³] 916 916 916 926 927 925 MFR [g / 10min] 1.0 1.0 2.3 1.0 2.3 8.0 Melting point (Tm) [℃] 124 123 123 121 123 124 Heat of fusion (ΔH) [J / g] 83 80 80 113 104 110

[0109] [Table 2] Resin code LD1 HD1 HD2 HD3 HD4 HD5 HD6 Types of resins Low-density polyethylene High-density polyethylene High-density polyethylene High-density polyethylene High-density polyethylene High-density polyethylene High-density polyethylene Quality [%] 95 0 94 0 94 94 0 Density (ρ) [kg / m³] 924 956 948 955 955 954 950 MFR [g / 10min] 0.6 0.4 1.0 7.9 7.2 4.5 5.0 Melting point (Tm) [℃] 111 132 133 133 133 133 133 Heat of fusion (ΔH) [J / g] 105 227 179 230 200 230 190

[0110] [Manufacturing of foamed particles and molded foamed particle bodies] (Example 1) <Manufacturing of Foamed Particles> An extruder with an inner diameter of 26 mm is prepared to be equipped with a die for forming strands attached to the export side. LL1, LL4, and zinc borate (arithmetic mean particle size based on number: 7 μm) as a bubble modifier are supplied to an extruder and melt-blended to form a resin melt composed of mixed resins. Furthermore, LL1 and LL4 are supplied in the proportions shown in Table 3, and zinc borate is supplied in such a manner that the content of zinc borate in the foamed particles is 500 ppm by mass. The obtained resin melt is extruded from the strand forming die to form strands, and the extruded strands are water-cooled and then cut using a granulator. In this way, resin particles with an average mass of 1.5 mg, a particle size of 1.9 mm, and a length / diameter ratio of 1.9 are obtained, using a mixture of two linear low-density polyethylene resins as the base resin.

[0111] 500g of the aforementioned resin particles, 3.5L of water as a dispersion medium, 3g of kaolin as a dispersant, and 0.2g of sodium dodecylbenzenesulfonate (trade name: NOIGEN, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) as a surfactant were fed into a 5L sealed container. Then, carbon dioxide, used as a foaming agent, was pressurized into a sealed container and pressurized to the equilibrium vapor pressure shown in Table 3. The contents of the sealed container were then stirred while heating at a rate of 2°C / min to the foaming temperature shown in Table 3. This temperature was then maintained for 15 minutes (holding step). The heat of fusion at the high-temperature peak was adjusted using this holding step (obtained from the endothermic curve measured using DSC). Subsequently, the contents of the sealed container were released at one atmosphere to obtain foamed particles (a single-stage foamed particle). The foamed particles obtained as described above were placed in an environment with an air temperature of 23°C, a relative humidity of 50%, and a humidity of 1 atm for 24 hours to cure. Then, the cured foamed particles were filled into a pressurized, sealed container, and the pressure inside the container was increased from atmospheric pressure to pressurize the foamed particles. This pressurized state was maintained for 24 hours, allowing air to permeate into the air bubbles within the foamed particles. Subsequently, the foamed particles were removed from the sealed container, yielding foamed particles with an internal pressure of 0.5 MPa (G) within the air bubbles. These foamed particles were then fed into a two-stage foaming apparatus. Steam was supplied to this apparatus to induce two-stage foaming of the particles, resulting in two-stage foamed particles. The two-stage foamed particles were then used in the aforementioned measurements and the manufacture of foamed particle molded articles.

[0112] <Manufacturing of Foamed Particle Moldings> After applying an internal pressure of 0.25 MPa (G) to the foamed particles with air, the foamed particles are filled into a mold that can form a flat plate with a length of 250 mm × width of 200 mm × thickness of 50 mm, and then heated using the following heating method. First, steam is supplied to the mold with the vent valves on both sides open for preheating (venting step). Then, steam is supplied from one side of the mold for heating, followed by steam from the other side. Next, steam is supplied from both sides of the mold at a predetermined forming heating steam pressure for heating (formal heating). After formal heating is completed, the pressure is released and the mold is water-cooled until the pressure on the forming surface reaches 0.04 MPa(G). The mold is then opened and the foamed particle molded body is removed. The resulting molded body was cured in an oven at 80°C for 12 hours to obtain a foamed particle molded body. Furthermore, in the aforementioned evaluation of the <molding pressure range for producing good products>, the molding process was carried out by changing the molding pressure. The results of the measurement of the physical properties of the obtained foamed particles and the evaluation results of the foamed particle molded bodies are shown in Table 3. Furthermore, each foamed particle is a non-crosslinked foamed particle.

[0113] (Examples 2-8 and 11) The polyethylene and its proportions, foaming temperature, and equilibrium vapor pressure in Example 1 were changed to the conditions shown in Table 3. Otherwise, the process was the same as in Example 1 to obtain foamed particles and foamed particle molded articles. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the foamed particle molded articles are shown in Table 3.

[0114] (Examples 9 and 10) The foaming temperature and equilibrium vapor pressure in Example 1 were changed to the conditions shown in Table 3. A section of the obtained foamed particles was used for in-mold molding. Otherwise, the process was the same as in Example 1 to obtain foamed particles and foamed particle molded bodies. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the foamed particle molded bodies are shown in Table 3.

[0115] (Comparative Examples 1-8) The polyethylene and its proportions, foaming temperature, and equilibrium vapor pressure in Example 1 were changed to the conditions shown in Table 4. Otherwise, the process was the same as in Example 1 to obtain foamed particles and foamed particle molded articles. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the foamed particle molded articles are shown in Table 4.

[0116] (Compare Examples 9 and 10) The polyethylene and its proportions, as well as the foaming temperature in Example 1, were changed to the conditions shown in Table 4. A section of the obtained foamed particles was then used for in-mold molding. Otherwise, the process was the same as in Example 1 to obtain foamed particles and foamed particle molded bodies. The measurement results of the physical properties of the obtained foamed particles and the evaluation results of the foamed particle molded bodies are shown in Table 4.

[0117] [Table 3-1] Example 1 Example 2 Example 3 Example 4 Example 5 Raw material characteristics LLDPE A type - LL1 LL1 LL2 LL3 LL1 MFR A g / 10 min 1.0 1.0 1.0 2.3 1.0 Quality % 84 84 87 84 84 Proportion % 60 60 60 60 60 LLDPE B type - LL4 LL4 LL4 LL4 LL5 MFR B g / 10 min 1.0 1.0 1.0 1.0 2.3 Proportion(%) % 40 40 40 40 40 [MFR A]‐[MFR B] g / 10 min 0 0 0 1.3 -1.3 [Tm A]‐[Tm B] ℃ 3 3 2 2 1 [ρ A]‐[ρ B] kg / m 3 -10 -10 -10 -10 -11 [ΔH B]‐[ΔH A] J / g 30 30 33 33 twenty one foaming temperature ℃ 123.1 122.5 122.5 123.1 123.9 CO2 equilibrium vapor pressure MPa(G) 4.0 4.0 4.0 4.0 4.0 Foamed particles (mixed resin) (A) Total heat of fusion J / g 96 96 90 96 93 (B) Heat of fusion at the high-temperature peak J / g 30 40 30 30 30 (B) / (A) - 0.31 0.42 0.33 0.31 0.32 Quality % 50 50 52 50 50 MFR (190℃, 2.16kg) g / 10min 1.0 1.0 1.0 1.7 1.5 Melting point ℃ 122 122 122 122 123 Density of mixed resins kg / m 3 920 920 920 920 920 Bulk density of foamed particles kg / m 3 131 184 135 108 123 Independent bubble rate of foaming particles % 97 98 94 94 94 Average bubble diameter of a section of foaming particles μm 100 90 110 110 90 Two-stage foaming particle volume density kg / m 3 twenty one 37 twenty four 20 twenty four Independent bubble rate of two-stage foaming particles % 93 90 92 90 90 Average bubble diameter of particles in the second stage of foaming μm 155 145 160 150 110 Bulk density stage 1 foaming / Bulk density stage 2 foaming - 6.3 5.0 5.6 5.3 5.1 The state of the two-stage foamed particles - 〇 〇 〇 〇 〇 Foamed Particle Molding Density of molded body kg / m 3 26 45 30 25 30 The range of molding conditions within which good products can be obtained (lower vapor pressure limit - upper vapor pressure limit) MPa(G) 0.13- 0.16 0.13- 0.17 0.13- 0.14 0.13- 0.14 0.13- 0.14 Compressive stress at 50% strain kPa 143 231 158 139 158 Compressive stress / density at 50% strain kPa / [kg / m³] 5.5 5.1 5.3 5.6 5.3

[0118] [Table 3-2] Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Raw material characteristics LLDPE A type - LL1 LL1 LL1 LL1 LL1 LL1 MFR A g / 10 min 1.0 1.0 1.0 1.0 1.0 1.0 Quality % 84 84 84 84 84 84 Ratio % 30 20 90 60 60 60 LLDPE B Type - LL4 LL4 LL4 LL4 LL4 LL3 MFR B g / 10 min 1.0 1.0 1.0 1.0 1.0 2.3 Ratio(%) % 70 80 10 <00010*24> 40 40 <00010*26> 40 [MFR A]‐[MFR B] <* g / 10 min *0 *0 *0 *0 *0 -1.3 [Tm A]‐[Tm B] ℃ 3 3 3 3 * 1 [ρ A]‐[ρ B] kg / m 3 -10 -10 -10 -10 Note: There seem to be some asterisks in the original text where numbers might be expected. I've left them as they are in the translation for consistency with the original. If these are errors in the original, they should be corrected before relying on this translation for accurate interpretation. -10 0 [ΔH B]‐[ΔH A] J / g 30 30 30 30 30 3 foaming temperature ℃ 122.6 122.7 123.5 123.1 124.7 124.2 CO2 equilibrium vapor pressure MPa(G) 4.0 4.0 4.0 4.0 3.5 4.0 Foamed particles (mixed resin) (A) Total heat of fusion J / g 100 99 85 96 96 83 (B) Heat of fusion at the high-temperature peak J / g 30 30 30 30 15 35 (B) / (A) - 0.30 0.30 0.35 0.31 0.16 0.42 Quality % 25 17 76 50 50 84 MFR (190℃, 2.16kg) g / 10min 1.0 1.0 1.0 1.0 1.0 1.4 Melting point ℃ 122 121 123 122 122 122 Density of mixed resins kg / m 3 923 924 917 920 920 916 Bulk density of foamed particles kg / m 3 123 115 153 131 131 100 Independent bubble rate of foaming particles % 98 97 96 97 91 95 Average bubble diameter of a section of foaming particles μm 90 85 110 100 120 83 Two-stage foaming particle volume density kg / m 3 twenty four 20 twenty three - - twenty two Independent bubble rate of two-stage foaming particles % 93 91 93 90 Average bubble diameter of particles in the second stage of foaming μm 135 140 155 120 Bulk density stage 1 foaming / Bulk density stage 2 foaming - 5.1 5.8 6.7 4.5 The state of the two-stage foamed particles - 〇 〇 〇 〇 Foamed Particle Molding Density of molded body kg / m 3 30 25 28 161 160 28 The range of molding conditions within which good products can be obtained (lower vapor pressure limit - upper vapor pressure limit) MPa(G) 0.13- 0.15 0.14- 0.17 0.13- 0.15 0.13- 0.17 0.13- 0.14 0.14- 0.16 Compressive stress at 50% strain kPa 151 129 154 1277 1270 125 Compressive stress / density at 50% strain kPa / [kg / m³] 5.0 5.1 5.5 7.9 7.9 4.5

[0119] [Table 4-1] Comparative example 1 Comparative example 2 Comparative example 3 Comparative example 4 Comparative example 5 Raw material characteristics LLDPE A type - LL1 LL1 HD2 LL3 HD4 MFR A g / 10 min 1.0 1.0 1.0 2.3 7.2 Quality % 84 84 94 84 94 Ratio % 60 60 60 34.5 32 LLDPE B Type - HD1 LD1 LL4 HD3 HD1 MFR B g / 10 min 0.4 1.0 1.0 7.9 0.4 Ratio (%) % 40 40 40 65.5 68 [MFR A]−[MFR B] g / 10 min <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​144 twenty two 66 150 27 foaming temperature ℃ 128.5 119.2 130.5 131.6 133.4 CO2 equilibrium vapor pressure MPa(G) 4.0 4.0 4.0 4.0 4.0 Foamed particles (mixed resin) (A) Total heat of fusion J / g 95 62 110 151 190 (B) Heat of fusion at the high-temperature peak J / g 30 30 30 30 30 (B) / (A) - 0.32 0.48 0.27 0.20 0.16 Quality % 50 88 56 29 30 MFR (190℃, 2.16kg) g / 10min 0.8 1.0 1.0 6.0 2.6 Melting point ℃ 127 116 128 127 132 Density of mixed resins kg / m 3 932 919 939 942 956 Bulk density of foamed particles kg / m 3 263 92 230 240 240 Independent bubble rate of foaming particles % 96 90 85 90 95 Average bubble diameter of a section of foaming particles μm 80 120 95 80 80 Two-stage foaming particle volume density kg / m 3 92 twenty three 224 240 240 Independent bubble rate of two-stage foaming particles % 90 90 89 95 95 Average bubble diameter of particles in the second stage of foaming μm 110 150 95 95 95 Bulk density stage 1 foaming / Bulk density stage 2 foaming - 2.9 4.0 1.0 1.0 1.0 The state of the two-stage foamed particles - 〇 × 〇 〇 〇 Foamed Particle Molding Density of molded body kg / m 3 113 28 275 294 294 The range of molding conditions within which good products can be obtained (lower vapor pressure limit - upper vapor pressure limit) MPa(G) none none 0.18 0.18 0.18 Compressive stress at 50% strain kPa - - 4500 4700 4800 Compressive stress / density at 50% strain kPa / [kg / m³] - - 16 16 16

[0120] [Table 4-2] Comparative example 6 Comparative example 7 Comparative example 8 Comparative example 9 Comparative example 10 Raw material characteristics LLDPE A type - HD5 LL1 LL1 HD2 LL3 MFR A g / 10 min 4.5 1.0 1.0 1.0 2.3 Quality % 94 84 84 94 84 Proportion % 60 60 60 60 34.5 LLDPE B type - HD6 LL6 LL4 LL4 HD3 MFR B g / 10 min 5.0 8.0 1.0 1.0 7.9 Proportion(%) % 40 40 40 40 65.5 [MFR A]‐[MFR B] g / 10 min -0.5 -7.0 0 0 -5.6 [Tm A]‐[Tm B] ℃ 0 0 3 12 -10 [ρ A]‐[ρ B] kg / m 3 4 -9 -10 twenty two -39 [ΔH B]‐[ΔH A] J / g -40 27 30 66 150 foaming temperature ℃ 133.3 124.5 125.0 130.5 131.6 CO2 equilibrium vapor pressure MPa(G) 4.0 4.0 3.0 4.0 4.0 Foaming particles (mixed resins) (A) Total heat of fusion J / g 180 80 96 110 151 (B) Heat of fusion at the high-temperature peak J / g 30 30 5 30 30 (B) / (A) - 0.17 0.38 0.05 0.27 0.20 Quality % 56 50 50 56 29 MFR (190℃, 2.16kg) g / 10min 4.7 3.8 1.0 1.0 6.0 Melting point ℃ 133 124 124 128 125 Density of mixed resins kg / m 3 952 920 920 939 942 Bulk density of foamed particles kg / m 3 240 131 131 230 240 Independent bubble rate of foaming particles % 95 90 85 85 90 Average bubble diameter of a section of foaming particles μm 80 120 125 95 80 Two-stage foaming particle volume density kg / m 3 245 twenty three 12 - - Independent bubble rate of two-stage foaming particles % 95 85 75 Average bubble diameter of particles in the second stage of foaming μm 95 150 190 Bulk density stage 1 foaming / Bulk density stage 2 foaming - 0.98 5.7 11 The state of the two-stage foamed particles - 〇 × × Foamed Particle Molding Density of molded body kg / m 3 300 28 15 275 294 The range of molding conditions within which good products can be obtained (lower vapor pressure limit - upper vapor pressure limit) MPa(G) 0.18 none none 0.18 0.18 Compressive stress at 50% strain kPa 4800 - - 4500 4700 Compressive stress / density at 50% strain kPa / [kg / m³] 16 - - 16 16

[0121] As shown in Table 3, the foamed particles of the examples exhibit high biomass and excellent in-mold formability. Furthermore, the foamed particles of the examples can be molded under low molding pressure conditions, while achieving a wide range of good-quality products. It is also evident that by using the foamed particles of the examples, polyethylene-based resin foamed particle molded articles with low apparent density can be obtained effectively. Moreover, the polyethylene-based resin foamed particle molded articles manufactured using the foamed particles of the examples, despite their low apparent density, exhibit high compressive stress and a good balance between strength and flexibility.

Claims

1. A method for manufacturing foamed particles, comprising foaming resin particles using a mixture of at least two linear low-density polyethylene (LDPE) resins as base resins to produce foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less, wherein the mixture of resins contains linear low-density polyethylene A and linear low-density polyethylene B with a biomass of 50% or more as measured according to ASTM D 6866, wherein the melt flow rate (MFRA) of the linear low-density polyethylene A, measured at 190°C and under a load of 2.16 kg, is 0.1 g / 10 min or more and 3 g / 10 min or less, and the difference between the melt flow rate (MFRA) of the linear low-density polyethylene A and the melt flow rate (MFRB) of the linear low-density polyethylene B, measured at 190°C and under a load of 2.16 kg, |MFRA-MFRB|, is 0 g / 10 min or more and 2 g / 10 min or less. The mass ratio (A / B) of the linear low-density polyethylene A to the linear low-density polyethylene B in the mixed resin is 5 / 95 to 95 / 5. The biomass of the mixed resin, as measured by ASTM D 6866, is 5% or more. The foamed particles 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, the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) located on the higher temperature side than the inherent peak, the heat of fusion of the high-temperature peak is 10 J / g or more and 50 J / g or less.

2. The method for manufacturing foamed particles as described in claim 1, wherein, The biomass of this linear low-density polyethylene B, as measured by ASTM D 6866, is less than 20%.

3. A method for manufacturing foamed particles as described in claim 1 or 2, wherein, The difference (ρB-ρA) between the density ρB of the linear low-density polyethylene B and the density ρA of the linear low-density polyethylene A is 3 kg / m3 or more, and the density of the mixed resin is 910 kg / m3 or more and 928 kg / m3 or less.

4. A method for manufacturing foamed particles as described in claim 1 or 2, wherein, The difference between the heat of fusion ΔHB of the linear low-density polyethylene B and the heat of fusion ΔHA of the linear low-density polyethylene A (ΔHB-ΔHA) is 3 J / g or more, and the total heat of fusion of the mixed resin is 70 J / g or more and 120 J / g or less.

5. A method for manufacturing foamed particles as described in claim 1 or 2, wherein, The total heat of fusion of the foamed particle is above 70 J / g and below 105 J / g, and the ratio of the heat of fusion of the high-temperature peak of the foamed particle to the total heat of fusion is above 0.2 and below 0.

7.

6. A method for manufacturing foamed particles as described in claim 1 or 2, wherein, The melt flow rate of the mixed resin, measured at a temperature of 190°C and a load of 2.16 kg, was ≥0.1 g / 10 min and ≤3 g / 10 min.

7. A method for manufacturing foamed particles as described in claim 1 or 2, wherein, This linear low-density polyethylene A contains butene and hexene as copolymer components.

8. A type of foamed particle, comprising foamed particles with a bulk density of 10 kg / m³ or more and 240 kg / m³ or less, wherein the bulk density of the mixed resin is 910 kg / m³ or more and 928 kg / m³ or less, the biomass of the foamed particle as measured according to ASTM D 6866 is 5% or more, and the melt flow rate of the foamed particle as measured under conditions of 190°C and 2.16 kg load is 0.1 g / 10 min or more and 3 g / 10 min or less, wherein the foamed particle has 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, the inherent melting peak (inherent peak) of linear low-density polyethylene and one or more melting peaks (high-temperature peaks) located on the higher temperature side than the inherent peak, the inherent melting peak (inherent peak) of linear low-density polyethylene. The heat of fusion at this high-temperature peak is above 10 J / g and below 50 J / g.

9. As in request item 8, the foaming particles, wherein, The total heat of fusion of the foamed particle is above 70 J / g and below 105 J / g, and the ratio of the heat of fusion of the high-temperature peak of the foamed particle to the total heat of fusion is above 0.2 and below 0.7.