Method for manufacturing foamed particles

Abstract

To provide a method for producing foamed particles containing polypropylene (PP) resin and biomass-derived polyethylene (PE) resin, which exhibits excellent in-moldability. [Solution] Foamed particles are produced by foaming resin particles obtained by kneading PP resin and PE resin. PP resin A consists of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer, and has a density of 0.93 g / cm³. 3 The mixture contains a PE resin X with a biomass content of 30% or more, an MFR of 0.5 to 5 g / 10 min, and a mass ratio of PP resin A to PE resin X in the mixed resin of 50:50 to 95:5. The resin particles have a crystalline structure in which a melting peak (R2-1) originating from the PE resin and a melting peak (R2-2) originating from the PP resin located at a higher temperature appear in the second DSC curve, and are adjusted so that the difference in peak temperatures between (R2-2) and (R2-1) is between 10°C and 35°C.

Description

Technical Field

[0001] The present invention relates to a method for producing expanded particles by expanding resin particles composed of a mixed resin containing a polypropylene-based resin and a biomass-derived polyethylene-based resin to produce expanded particles.

Background Art

[0002] Expanded particle molded bodies formed by in-mold molding of polyolefin-based resin expanded particles are used in various applications such as impact absorbers, heat insulators, and cushioning materials.

[0003] For example, Patent Document ۱ discloses expanded particles produced using a base resin containing a polypropylene-based resin having a melt flow rate and a melting point within a predetermined range and a high-density polyethylene-based resin having a density and a melt flow rate within a predetermined range.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in recent years, efforts to reduce the environmental load have been active socially, and the provision of environmentally friendly products is desired in various fields. Such a demand is the same in the field of expanded particle molded bodies. As one method for producing an environmentally friendly expanded particle molded body, the use of a polyolefin-based resin using natural materials such as plants as a starting material instead of a polyolefin-based resin using a fossil fuel-derived raw material has been studied. Polyolefin resins derived from natural materials such as plants are known as polyethylene resins derived from natural materials such as plants. In the following, polyethylene resins derived from natural materials such as plants may be referred to as biomass-derived polyethylene resins.

[0006] The inventors attempted to produce foamed particles using polypropylene resin and biomass-derived polyethylene resin as raw materials, in order to provide an environmentally friendly foamed particle molded product while utilizing the properties of polypropylene resin. However, it was found that when foamed particles are produced using such a combination, the in-moldability of the foamed particles may decrease.

[0007] The present invention has been made in view of the above problems, and provides foamed particles comprising a polypropylene resin and a biomass-derived polyethylene resin, which have excellent in-moldability. [Means for solving the problem]

[0008] The present invention relates to a method for producing a foamed particle molded article, which involves foaming resin particles composed of a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin, wherein the polypropylene resin includes a polypropylene resin A consisting of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer, and the polyethylene resin has a density of 0.93 g / cm³. 3The mixture contains a polyethylene resin X which is less than 30%, the biomass content of the polyethylene resin X measured by ASTM D 6866-21 is 30% or more, the melt flow rate of the polyethylene resin X measured at a temperature of 190°C and a load of 2.16 kg is 0.5 g / 10 min or more and 5 g / 10 min or less, the mass ratio of polypropylene resin A to polyethylene resin X in the mixed resin is 50:50 to 95:5, and the resin particles are heated from 23°C to 200°C at a heating rate of 10°C / min by thermal flux differential scanning calorimetry, and then The material is characterized by having a crystal structure in which, in the DSC curve obtained by 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, a melting peak (R2-1) originating from the polyethylene resin and a melting peak (R2-2) originating from the polypropylene resin located at a higher temperature than the melting peak (R2-1) appear, and the difference between the peak temperature of the melting peak (R2-2) and the peak temperature of the melting peak (R2-1) is 10°C or more and 35°C or less. [Effects of the Invention]

[0009] According to the present invention, foamed particles containing a polypropylene resin and a biomass-derived polyethylene resin, exhibiting excellent in-moldability, can be produced. Therefore, by using foamed particles produced by the manufacturing method of the present invention, it is possible to provide an environmentally friendly foamed particle molded article while utilizing the properties of the polypropylene resin component. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the second DSC curve obtained using the resin particles of Example 1 of the present invention as the measurement sample, according to the method for measuring the transition temperature of plastics described in JIS K7121:2012. [Figure 2] This is a schematic diagram of the first DSC curve obtained using the foamed particles of Example 1 of the present invention as the measurement sample, according to the method for measuring the transition heat of plastics described in JIS K7122:2012. [Modes for carrying out the invention]

[0011] First, an overview of the method for producing foamed particle molded articles of the present invention (hereinafter sometimes simply referred to as the "method of production of the present invention") will be described. The method of production of the present invention relates to a method for producing foamed particles by foaming resin particles composed of a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin. The polypropylene resin in the present invention includes polypropylene resin A, which is composed of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer. On the other hand, the polyethylene resin in the present invention has a density of 0.93 g / cm³. 3 The product contains polyethylene resin X, which has a biomass content of 30% or more as measured by ASTM D 6866-21, and a melt flow rate of 0.5 g / 10 min to 5 g / 10 min as measured under conditions of a temperature of 190°C and a load of 2.16 kg. In the present invention, the mass ratio of polypropylene resin A to polyethylene resin X in the mixed resin is adjusted to 50:50 to 95:5. Resin particles composed of such a mixed resin have a crystalline structure in which, in the second DSC curve, a melting peak (R2-1) originating from the polyethylene resin and a melting peak (R2-2) originating from the polypropylene resin located at a higher temperature than the melting peak (R2-1) appear. In such a crystalline structure, in the present invention, the difference between the peak temperature of the melting peak (R2-2) and the peak temperature of the melting peak (R2-1) is 10°C or more and 35°C or less. The manufacturing method of the present invention, having the above configuration, can produce foamed particles with good in-moldability while promoting the recycling of carbon resources by blending a polypropylene resin with a biomass-derived polyethylene resin.

[0012] Furthermore, in relation to the present invention, the melting peak, the peak temperature of the melting peak, and the heat of fusion of the resin particles and foamed particles are determined from the DSC curve measured by differential scanning calorimetry based on the method for measuring the transition heat of plastics described in JIS K7121:2012 or JIS K7122:2012. In this invention, the "second DSC curve" of resin particles refers to the DSC curve obtained by heating resin particles from 23°C to 200°C at a heating rate of 10°C / min, then cooling them from 200°C to 23°C at a cooling rate of 10°C / min, and then heating them again from 23°C to 200°C at a heating rate of 10°C / min using differential scanning calorimetry. As illustrated in Figure 1, the two peaks observed in the second DSC curve of resin particles are sometimes referred to as the melting peak (R2-1) and the melting peak (R2-2) from the lower temperature side. The melting peak (R2-1) is a melting peak originating from polyethylene resin and refers to a melting peak that appears in the range of peak temperature between 100°C and 130°C. The melting peak (R2-2) is a melting peak originating from polypropylene resin and refers to a melting peak that appears in the range of peak temperature between 130°C and 160°C. Furthermore, if three or more peaks are observed in the second DSC curve of the resin particles, the peak with the highest peak height in the range of 100°C to less than 130°C, and the peak with the highest peak height in the range of 130°C to 160°C, should be recognized as the peak temperatures of the two peaks mentioned above. Note that peak height refers to the distance perpendicular to the horizontal axis of the DSC curve, from the baseline to the peak of the peak. In addition, since the peak temperature of each peak roughly corresponds to the melting point of the polyethylene-based resin and polypropylene-based resin used to manufacture the resin particles, they can also be recognized from the melting points of the polyethylene-based resin and polypropylene-based resin. Furthermore, in relation to the present invention, the "first DSC curve" of foamed particles refers to the DSC curve obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min using differential scanning calorimetry. As illustrated in Figure 2, when three peaks are observed in the first DSC of such foamed particles, these peaks may be referred to as melting peak (E1-1), melting peak (E1-2), and melting peak (E1-3) from the low-temperature side. Melting peak (E1-1) is a melting peak originating from the crystals normally present in polyethylene resin, melting peak (E1-2) is a melting peak originating from the crystals normally present in polypropylene resin, and melting peak (E1-3) is a melting peak originating from the secondary crystals of polypropylene resin. Furthermore, the melting peak (E1-1) appears near the melting point of the polyethylene resin used to manufacture the resin particles, and the melting peak (E1-2) appears near the melting point of the polypropylene resin used to manufacture the resin particles. Therefore, each peak can be identified from the melting points of the polypropylene resin and the polyethylene resin. In addition, as will be described later, the melting peak (E1-3) disappears in the second DSC curve, and can therefore be identified from the relationship between the first and second DSC curves. Furthermore, in relation to the present invention, the "second DSC curve" of foamed particles refers to the DSC curve obtained by heating the foamed particles from 23°C to 200°C at a heating rate of 10°C / min, then cooling them from 200°C to 23°C at a cooling rate of 10°C / min, and then heating them again from 23°C to 200°C at a heating rate of 10°C / min. When two peaks are observed in the second DSC of such foamed particles, these peaks may be referred to as the melting peak (E2-1) and the melting peak (E2-2) from the lower temperature side. The melting peak (E2-1) is a melting peak originating from polyethylene resin and refers to a melting peak that appears in the range of peak temperature between 100°C and 130°C. The melting peak (E2-2) is a melting peak originating from polypropylene resin and refers to a melting peak that appears in the range of peak temperature between 130°C and 160°C. Furthermore, if three or more peaks are observed in the second DSC curve of the foamed particles, the peak with the highest peak height in the range of 100°C to less than 130°C, and the peak with the highest peak height in the range of 130°C to 160°C, should be recognized as the peak temperatures of the two peaks mentioned above. Note that peak height refers to the distance perpendicular to the horizontal axis of the DSC curve, from the baseline to the peak of the peak. In addition, since the peak temperature of each peak roughly corresponds to the melting point of the polyethylene-based resin and polypropylene-based resin used to manufacture the resin particles, they can also be recognized from the melting points of the polyethylene-based resin and polypropylene-based resin. Further details of the present invention are described below.

[0013] [Polypropylene resin] In the present invention, the polypropylene resin refers to a polypropylene copolymer containing more than 50% by mass of a homopolymer of propylene monomers and constituent units derived from propylene. The polypropylene resin used in the production method of the present invention includes polypropylene resin A, which consists of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer. By blending a polypropylene resin containing such a specific random copolymer with a biomass-derived polyethylene resin, it is possible to produce foamed particles with good in-moldability. From the viewpoint of more stably improving in-moldability, it is preferable that the polypropylene resin contains a propylene-ethylene random copolymer, and more preferably that the polypropylene resin is a propylene-ethylene random copolymer. The propylene-ethylene random copolymer and / or propylene-ethylene-butene random copolymer used as polypropylene resin A may be one type or a combination of two or more types. The content of ethylene-derived components and / or butene-derived components in polypropylene resin A is preferably 0.1 mol% to 10 mol%, preferably 0.2 mol% to 8 mol%, and more preferably 0.5 mol% to 6 mol%.

[0014] From the viewpoint of producing foamed particles with better in-moldability, the proportion of polypropylene resin A in the polypropylene resin used in the manufacturing method of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Note that the proportion of polypropylene resin A in the polypropylene resin is the value with the total polypropylene resins as 100% by mass.

[0015] When the polypropylene-based resin A is composed of a combination of two or more resins, the physical properties of the polypropylene-based resin A described below are all measured using the polypropylene-based resin A, which is a mixed resin combined at a predetermined blending ratio, as a measurement sample. Such physical properties include, for example, melt flow rate, melting point, and heat of fusion. Regarding the polypropylene-based resin A, the melt flow rate is MFR PPA , the melting point is Tm PPA , and the heat of fusion is ΔH PPA may be abbreviated as such. In this specification, the melt flow rate may sometimes be abbreviated as MFR.

[0016] In addition, as the polypropylene-based resin used in the production method of the present invention, one or more polypropylene-based resins other than the polypropylene-based resin A may be included. Also, the polypropylene-based resin may be a biomass-derived polypropylene-based resin or a fossil fuel-derived polypropylene-based resin. However, from the perspective of high availability in the market and the ease of stably enhancing the in-mold formability of the foamed particles, it is preferable to use a fossil fuel-derived polypropylene-based resin. Also, from the perspective of further contributing to the reduction of environmental load, the above-mentioned polypropylene-based resin is preferably uncrosslinked. [

[0017] <Melt flow rate (MFR PPA )> The melt flow rate MFR of the polypropylene-based resin A PPA [ is preferably 3 g / 10 min or more and 10 g / 10 min or less, and more preferably 5 g / 10 min or more and 9 g / 10 min or less. MFR PPA is measured under the conditions of a temperature of 230 °C and a load of 2.16 kg based on JIS K7210-1:2014 using the polypropylene-based resin A as a measurement sample.

[0018] <Melting point (Tm PPA )> The melting point Tm of the polypropylene-based resin A PPAThe melting point is preferably between 130°C and 155°C, and more preferably between 132°C and 154°C. Having a melting point within this range makes it easier to achieve a wide molding range in in-mold molding, and also makes it easier to provide a foamed particle molded article with relatively high compressive strength, as the physical properties derived from the polypropylene resin component are fully expressed. Tm PPA The measurement is performed using polypropylene resin A as the sample, in accordance with JIS K7121:2012. Specifically, for conditioning the sample, "3.(2) When measuring the melting temperature after performing a certain heat treatment" is adopted. The sample is heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow of 30 mL / min, then maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (second DSC curve). Next, the peak temperature of the melting peak in the DSC curve is determined, and this value is taken as the melting point of polypropylene resin A. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest melting peak height relative to the baseline is adopted as the melting point.

[0019] <Heat of fusion (ΔH) PPA )> Heat of fusion ΔH of polypropylene resin A PPA The ΔH is preferably 50 J / g or more and 100 J / g or less, and more preferably 55 J / g or more and 90 J / g or less. PPA This is determined from the second DSC curve measured by differential scanning calorimetry (DSC) based on the method for measuring the transition heat of plastics described in JIS K7122:2012. Specifically, let α be the point on the second DSC curve at a temperature of 80°C, and β be the point on the DSC curve corresponding to the melting end temperature. The area enclosed by the DSC curve in the interval between points α and β and the line segment (α-β) is measured, and the heat of fusion of the foamed particles can be calculated from this area.

[0020] [Polyethylene resin] <Density (ρ)> In the present invention, polyethylene resin means an ethylene copolymer containing 50% by mass or more of ethylene homopolymers and constituent units derived from ethylene. The polyethylene resin used in the manufacturing method of the present invention has a density of 0.93 g / cm³. 3 It contains polyethylene resin X which is less than [amount missing]. The polyethylene resin used as polyethylene resin X may be one type or two or more types. When two or more types of polyethylene resins are mixed and used as polyethylene resin X, each polyethylene resin must have a density of 0.93 g / cm³. 3 It is less than 0.91 g / cm³. Furthermore, from the viewpoint of easily obtaining the foamed particles of the present invention stably, the density of polyethylene resin X is 0.91 g / cm³. 3 It is preferable that the above conditions are met. The density of polyethylene resins can be measured according to Method A (water displacement method) of JIS K7112:1999. From the viewpoint of producing foamed particles with better in-moldability, the proportion of polyethylene resin X in the polyethylene resin used in the manufacturing method of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Furthermore, the proportion of polyethylene resin X in the polyethylene resin is the proportion of polyethylene resin X when the total amount of polyethylene resin is set to 100% by mass.

[0021] Polyethylene resin X has a density of 0.93 g / cm³. 3 When two or more polyethylene resins with a density less than 0.93 g / cm³ are combined, all physical properties of the polyethylene resin X other than density are such that the density when combined in a predetermined mixing ratio is 0.93 g / cm³. 3 A mixed resin of multiple polyethylene-based resins, each having a property less than [amount missing], is used as the measurement sample. Such properties include, for example, biomass content, melt flow rate, melting point, and heat of fusion. Furthermore, regarding polyethylene resin X, the biomass content is D PEX Meltflow rate is MFR PEXThe melting point is Tm PEX The heat of fusion is ΔH PEX It is sometimes abbreviated as follows:

[0022] Polyethylene resin X has a density of 0.93 g / cm³. 3 A polyethylene resin is appropriately selected from those with a density less than [amount missing]. From the viewpoint of easily obtaining foamed particles with excellent in-moldability, the polyethylene resin X is preferably linear low-density polyethylene and / or low-density polyethylene, and more preferably linear low-density polyethylene. Here, linear low-density polyethylene refers to a copolymer of ethylene and α-olefin having a linear structure. Linear low-density polyethylene is indicated by the abbreviation "PE-LLD" in JIS K6899-1:2015 "Plastics - Symbols and abbreviations - Part 1: Basic polymers and their properties". Low-density polyethylene (LDL) refers to polyethylene with a long-chain branched structure. In JIS K6899-1:2015, "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties," LDL is abbreviated as "PE-LD." LDL can also be called branched LDL.

[0023] Examples of the α-olefin-derived components contained in linear low-density polyethylene include components derived from α-olefins having 3 to 20 carbon atoms. The linear low-density polyethylene preferably contains components derived from α-olefins having 4 to 10 carbon atoms, and more preferably contains components derived from α-olefins having 6 to 8 carbon atoms. Specific examples of the α-olefins mentioned above 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, and the like.

[0024] The polyethylene resin used in the manufacturing method of the present invention has a density of 0.93 g / cm³. 3As a polyethylene resin other than polyethylene resin X which is less than 0.93 g / cm³, a polyethylene resin with a density of 0.93 g / cm³ is used. 3 The above-mentioned polyethylene resin may be included in one or more types.

[0025] <Biomass content (D PEX )> In the present invention, the polyethylene resin X has a biomass degree D as measured by ASTM D 6866-21. PEX The percentage is 30% or more. Furthermore, when two or more polyethylene resins are mixed and used as polyethylene resin X, one or more of these two or more polyethylene resins must be biomass-derived polyethylene resins, and the biomass content of the mixed polyethylene resin X after blending in a predetermined ratio must be 30% or more. The biomass content of polyethylene resin X composed of a mixture of two or more polyethylene resins can be measured using the mixed polyethylene resin X as a measurement sample based on ASTM D 6866-21. In this invention, biomass content refers to the proportion of naturally derived components contained in the resin. Biomass content is measured by the radiocarbon content (C) of the resin. 14 This value is obtained by measuring the concentration of [the substance]. Alternatively, as an alternative to actual measurement, the biomass content of polyethylene resin X can be calculated from the blending ratio of the resins used as polyethylene resin X and the biomass content of each resin that has been previously confirmed.

[0026] From the perspective of providing foamed particles that are more environmentally conscious, the biomass content of polyethylene resin X is D PEX The biomass content of polyethylene resin X is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. PEX There is no particular upper limit; a guideline can be set at 100% or less, 99% or less, or 98% or less.

[0027] <Meltflow Rate (MFR PEX )> In the present invention, the melt flow rate (MFR) of polyethylene resin X PEX The MFR is between 0.5g / 10 mins and 5g / 10 mins. PEX This is measured according to JIS K7210-1:2014, under conditions of a temperature of 190°C and a load of 2.16 kg. MFR PEX If the temperature is too high, when in-mold molding is performed using the manufactured foam particles, heating until the foam particles are sufficiently fused together will cause the molded product to shrink after molding, making it prone to dents and other defects. Therefore, it may be difficult to obtain a good molded product, and it may be difficult to obtain foam particles with excellent in-moldability. From the perspective of stably obtaining foam particles that exhibit excellent in-moldability, MFR PEX However, it is preferable that the dose is 4g / 10 minutes or less, more preferably 3g / 10 minutes or less, and even more preferably less than 2g / 10 minutes. On the other hand, MFR PEX If the pressure is too low, when the manufactured foamed particles are used for in-mold molding, the foamed particles may not undergo secondary foaming easily, and the gaps between the foamed particles in the resulting molded product may not be filled properly. As a result, it may be difficult to obtain a good molded product and foamed particles with excellent in-moldability.

[0028] <Melting point (Tm PEX )> Melting point Tm of polyethylene resin X PEX The melting point is preferably between 100°C and 130°C, and more preferably between 110°C and 128°C. Having a melting point within this range allows for the stable production of foamed particles with good in-moldability while incorporating biomass-derived polyethylene resin. From the viewpoint of reducing shrinkage in the molded body even when molded under relatively high steam pressure conditions, and improving the in-moldability of the foamed particles, a melting point Tm is preferable. PEX The temperature is preferably 115°C or higher, and more preferably 120°C or higher. Tm PEXThe measurement is performed using polyethylene resin X as the sample, in accordance with JIS K7121:2012. Specifically, for conditioning the sample, "3.(2) When measuring the melting temperature after performing a certain heat treatment" is adopted. The sample is heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow of 30 mL / min, then maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a DSC curve (second DSC curve). Next, the peak temperature of the melting peak in the DSC curve is determined, and this value is taken as the melting point of polyethylene resin X. If multiple melting peaks appear in the DSC curve, the peak temperature of the melting peak with the highest melting peak height relative to the baseline is adopted as the melting point.

[0029] <Heat of fusion (ΔH) PEX )> Heat of fusion ΔH of polyethylene resin X PEX The heat of fusion is preferably 60 J / g or more and 120 J / g or less, more preferably 65 J / g or more and 110 J / g or less, and more preferably 70 J / g or more and 95 J / g or less. Having the heat of fusion within the above range allows for the stable production of foamed particles with good in-moldability while containing biomass-derived polyethylene resin. ΔH PEX This is determined from the second DSC curve measured by differential scanning calorimetry, based on the method for measuring the transition heat of plastics described in JIS K7122:2012.

[0030] [Other polymers and additives] The resin particles in the present invention may appropriately contain other polymers and additives other than the polypropylene resin and polyethylene resin described above, to the extent that the intended objectives of the present invention can be achieved. Other polymers include thermoplastic resins such as polystyrene resins, polyamide resins, and polyester resins, as well as elastomers such as olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers. Examples of the additives include colorants, antioxidants, antistatic agents, surfactants, heat stabilizers, light stabilizers, UV absorbers, and flame retardants.

[0031] [Relationship between polypropylene resin A and polyethylene resin X] <Mass ratio> In the present invention, the mass ratio of polypropylene resin A to polyethylene resin X in the mixed resin is polypropylene resin A:polyethylene resin X = 50:50 to 95:5. By satisfying this mass ratio, it is possible to produce foamed particles that contain biomass-derived polyethylene resin, are environmentally friendly, and exhibit sufficient physical properties derived from the propylene resin component, allowing for in-mold molding of foamed particle molded articles with good strength over a wide molding pressure range. As a guideline for the strength, for example, the compressive stress of the foamed particle molded article at 50% strain can be used as a guideline. From the viewpoint of obtaining a molded article with good compressive stress while increasing the biomass-derived polyethylene resin content, the mass ratio is preferably 55:45 to 90:10, and more preferably 60:40 to 85:15.

[0032] <Difference in Melt Flow Rate (MFR)> Melt flow rate (MFR) of polypropylene resin A PPA and polyethylene resin X MFR PEX The difference between the two is the MFR. PPA -MFR PEX The difference is preferably 3g / 10 min to 8g / 10 min, and more preferably 4g / 10 min to 7g / 10 min. By setting the difference within the above range, it is possible to stably produce foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin.

[0033] <Difference in melting points> From the perspective of stably obtaining foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin, the melting point Tm of polypropylene resin A is considered. PPAThe melting point Tm of the polypropylene resin A is between 130°C and 155°C. PPA and the melting point Tm of polyethylene resin X PEX The difference is Tm PPA -Tm PEX It is preferable that the temperature is between 10°C and 35°C. Furthermore, from the viewpoint of making it easier to improve the in-moldability of foamed particles, the difference (Tm PPA -Tm PEX It is more preferable that the temperature is between 15°C and 28°C.

[0034] <Difference in heat of fusion> From the perspective of stably obtaining foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin, the heat of fusion ΔH of polypropylene resin A is considered. PPA and the heat of fusion ΔH of polyethylene resin X PEX ΔH is the difference between the two. PPA -ΔH PEX Preferably, the value is between -40 J / g and 16 J / g. Furthermore, from the viewpoint of enabling in-mold molding even under low molding pressure conditions and enabling in-mold molding over a wide range of molding pressure conditions, the difference (ΔH PPA -ΔH PEX It is more preferable that the ) is between -25 J / g and 10 J / g, and even more preferable that it is between -20 J / g and 5 J / g.

[0035] [Resin particles] Next, the resin particles used in the manufacturing method of the present invention will be described. The resin particles are composed of a mixed resin obtained by kneading a polypropylene resin containing polypropylene resin A and a polyethylene resin containing polyethylene resin X. Preferably, the total content of polypropylene resin A and polyethylene resin X in the resin particles is 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0036] <Example of a method for producing resin particles> In the manufacturing method of the present invention, the production of resin particles can be carried out by known methods for producing resin particles, other than using the polypropylene resin and polyethylene resin described above. Specifically, for example, the following method can be used. First, the polypropylene resin and polyethylene resin described above are supplied to an extruder along with a foam regulator and other additives as needed, and melt-kneaded to obtain a molten mixture. Then, the molten mixture is extruded in strand form from a strand-forming die attached to the downstream side of the extruder, the extruded strands are water-cooled, and cut with a pelletizer or the like. In this way, pellet-shaped resin particles composed of a mixed resin of polypropylene resin and polyethylene resin can be obtained.

[0037] It is preferable that a foam regulator is added to the resin particles. As the foam regulator, for example, one or more foam regulators selected from inorganic powders and organic powders can be used. Examples of inorganic powders include metal borate salts such as zinc borate and magnesium borate, and examples of organic powders include fluororesin powder such as polytetrafluoroethylene (PTFE). From the viewpoint of stably obtaining foamed particles that have the desired bulk density and have little variation in bubble diameter, the amount of bubble regulator added to the resin particles is preferably 0.005% by mass or more and 1% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, and even more preferably 0.02% by mass or more and 0.2% by mass or less. Furthermore, from the viewpoint of easily adjusting the average bubble diameter of the foamed particles to a desired range, it is preferable to use a metal borate salt as a bubble adjusting agent, and more preferably to use zinc borate.

[0038] <Meltflow Rate (MFR)> The MFR of the resin particles in this invention is not particularly limited, but it is preferably 3 g / 10 min to 7 g / 10 min, and more preferably 4 g / 10 min to 6 g / 10 min, when measured under conditions of a temperature of 230°C and a load of 2.16 kg. By adjusting the MFR of the resin particles to fall within the above range, it is possible to stably produce foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin. The MFR of resin particles is the same as that of polypropylene resin A described above, except that resin particles are used as the measurement sample. PPA It is measured using the same method as the measurement method for [another measurement]. Furthermore, the melt flow rate of the mixed resin constituting the resin particles generally corresponds to the melt flow rate of the mixed resin constituting the foamed particles formed by foaming the resin particles.

[0039] <Second DSC curve> The resin particles have a crystalline structure in which, in the second DSC curve, a melting peak (R2-1) originating from the polyethylene resin and a melting peak (R2-2) originating from the polypropylene resin located at a higher temperature than the melting peak (R2-1) appear. In this invention, the difference between the peak temperature of the melting peak (R2-2) and the peak temperature of the melting peak (R2-1) is adjusted to be in the range of 10°C to 35°C. If the difference, which is obtained by subtracting the peak temperature of the melting peak (R2-1) from the peak temperature of the melting peak (R2-2), is excessively small or excessively large, there is a risk that a sufficient range of moldable conditions for obtaining a good foamed particle molded body may not be secured during in-mold molding. From this viewpoint, the difference is preferably 12°C to 32°C, and more preferably 15°C to 30°C. Furthermore, from the viewpoint of being able to stably produce foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin, in the second DSC curve of the resin particles in the present invention, the ratio of the height of the melting peak (R2-1) to the height of the melting peak (R2-2) is preferably 0.5 or more and 4.0 or less, more preferably 0.8 or more and 3.0 or less, and even more preferably 1.0 or more and 2.0 or less.

[0040] <Heat of fusion> In this invention, the heat of fusion of the resin particles is preferably 60 J / g or more and 95 J / g or less, from the viewpoint of facilitating the production of foamed particles with excellent in-moldability. By setting the heat of fusion of the resin particles within the above range, good in-moldability is easily demonstrated and the molding range tends to be broadened. The heat of fusion of resin particles is determined from the second DSC curve measured by differential scanning calorimetry (DSC) based on the method for measuring the transition heat of plastics described in JIS K7122:2012. Specifically, let α be the point on the second DSC curve at a temperature of 80°C, and β be the point on the DSC curve corresponding to the melting end temperature of the resin particles. The area enclosed by the DSC curve in the interval between points α and β and the line segment (α-β) is measured, and the heat of fusion of the foamed particles can be calculated from this area. Furthermore, the heat of fusion of the mixed resin constituting the resin particles roughly corresponds to the heat of fusion of the mixed resin constituting the foamed particles formed by foaming the resin particles.

[0041] <Biomass content> Since this invention uses polyethylene resin X with a biomass content of 30% or more, the resin particles in this invention exhibit a biomass content. Furthermore, a biomass content of approximately the same degree as that observed in the resin particles is also observed in the foamed particles produced using these resin particles. Therefore, this invention can significantly contribute to the recycling of carbon resources. From the viewpoint of more significantly contributing to the recycling of carbon resources, the biomass content of the resin particles in this invention is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. On the other hand, from the viewpoint of easily improving the in-moldability of the foamed particles while incorporating biomass-derived polyethylene resin, the biomass content of the resin particles is preferably 50% or less, and more preferably 40% or less. The biomass content of resin particles and foamed particles can be measured according to ASTM D 6866-21, but it can also be calculated from the biomass content of the resin used in manufacturing and its blending ratio.

[0042] [Foaming particles] Next, the foamed particles produced by the manufacturing method of the present invention will be described. The foamed particles produced by the manufacturing method of the present invention may be referred to as "foamed particles of the present invention" as appropriate. The foamed particles of the present invention are manufactured by foaming the resin particles described above. Therefore, the characteristics of the resin particles are appropriately reflected in the foamed particles of the present invention. That is, the foamed particles of the present invention are foamed particles composed of a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin. Preferably, the total content of polypropylene resin A and polyethylene resin X in the foamed particles is 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The foamed particles of the present invention contain polypropylene resin A, which consists of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer, as the polypropylene resin, and the polyethylene resin has a density of 0.93 g / cm³. 3It contains polyethylene resin X, which is less than 5%. The biomass content of the foamed particles of the present invention, as measured by ASTM D 6866-21, is 5% or more. The foamed particles have a crystalline structure in which a melting peak (E2-1) and a melting peak (E2-2) located at a higher temperature than melting peak (E2-1) appear in the second DSC curve. Here, the difference between the peak temperature of melting peak (E2-2) and the peak temperature of melting peak (E2-1) should be between 10°C and 35°C. Furthermore, the MFR of the foamed particles measured under conditions of 230°C and a load of 2.16 kg should be between 3 g / 10 min and 7 g / 10 min. The composition of the foamed particles of the present invention can be appropriately described by referring to the above-mentioned descriptions of polypropylene resins, polyethylene resins, and resin particles.

[0043] The foamed particles of the present invention are manufactured by foaming the resin particles described above. Foamed particles can be obtained by impregnating resin particles, which are made from a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin, with a foaming agent, and then foaming the resin particles containing the foaming agent. Specifically, the foaming of the resin particles can be carried out as follows, for example. First, the resin particles are dispersed in a pressure vessel containing an aqueous dispersion medium such as water, an inorganic dispersant such as a poorly soluble inorganic salt or clay mineral, and a dispersion aid such as a surfactant (dispersion step). Next, a foaming agent is added to the pressure vessel to impregnate the resin particles with the foaming agent (foaming agent impregnation step). Then, the resin particles containing the foaming agent, along with the aqueous dispersion medium, are released from the pressure vessel into an atmosphere with a pressure lower than the pressure inside the pressure vessel, causing the resin particles to foam (foaming step). From the viewpoint of increasing the productivity of foamed particles, it is preferable to perform the impregnation of resin particles with a foaming agent and the foaming of the resin particles containing the foaming agent as a series of processes using a single sealed container, as described above.

[0044] Examples of blowing agents include inorganic physicoblasting agents such as air, nitrogen, carbon dioxide, argon, helium, oxygen, and neon; aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and n-hexane; alicyclic hydrocarbons such as cyclohexane and cyclopentane; 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; and organic physicoblasting agents such as dimethyl ether, diethyl ether, and methyl ethyl ether. Among these, from the viewpoint of having a low environmental impact and being economical, the blowing agent is preferably an inorganic physicoblasting agent, more preferably one or more selected from the group consisting of nitrogen, air, and carbon dioxide, and even more preferably carbon dioxide. These are used alone or in combination of two or more types. The amount of foaming agent to be added is determined by considering the desired bulk density of the foamed particles, the type of resin used, the type of foaming agent, etc. For example, when carbon dioxide is used, the amount to be added is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 15 parts by mass, per 100 parts by mass of resin particles.

[0045] Furthermore, the foamed particles obtained as described above can be further foamed in multiple stages to produce foamed particles with a higher foaming ratio. For example, by pressurizing the obtained foamed particles with air or the like to increase the pressure inside the bubbles, and then heating them with steam or the like to further foam them, a two-stage foaming process can be performed to produce foamed particles with a higher foaming ratio.

[0046] Furthermore, the foamed particles may have a fusion layer on their surface to enhance the fusion properties between the foamed particles during in-mold molding. The fusion layer may be present over the entire surface of the foamed particles or only on a portion of the surface. Examples of resins that constitute the fusion layer include polyolefin resins. The method for forming a fusion layer on the surface of foamed particles is not particularly limited. Examples include a method of foaming resin particles having a fusion layer on their surface, or a method of obtaining foamed particles and then attaching a fusion layer to the surface of the foamed particles. When obtaining foamed particles by foaming resin particles having a fusion layer on their surface, it is preferable to employ a method of laminating a fusion layer on the surface of the resin particles by co-extruding a molten resin for forming the resin particle body and a molten resin for forming the fusion layer using an extruder capable of co-extrusion when manufacturing the resin particles. In the case of multilayer foamed particles consisting of a core layer and a fusion layer, the core layer may have the same configuration as the foamed particles described herein.

[0047] <Melting peak of foamed particles> The foamed particles produced by the manufacturing method of the present invention have a crystalline structure in which at least two melting peaks appear in the second DSC curve. Melting peak (E2-1) and melting peak (E2-2) generally correspond to melting peak (R2-1) and melting peak (R2-2), which are the melting peaks of the resin particles described above. Furthermore, the foamed particles produced by the manufacturing method of the present invention, in the first DSC curve, A crystal structure exhibiting three melting peaks, as illustrated in Figure 2, is preferred. The three melting peaks are referred to as melting peak (E1-1), melting peak (E1-2), and melting peak (E1-3), starting from the lowest temperature side. In particular, in the aforementioned crystalline structure, from the viewpoint of easily improving the in-moldability of the foamed particles while incorporating biomass-derived polyethylene resin, it is preferable that the peak temperature of the melting peak (E1-1) appears in the range of 100°C to 130°C, and the peak temperature of the melting peak (E1-3) appears in the range of 155°C to 170°C. Furthermore, in this case, it is more preferable that the difference between the peak temperature of the melting peak (E1-2) and the peak temperature of the melting peak (E1-1) is 3°C to 25°C, and the difference between the peak temperature of the melting peak (E1-3) and the peak temperature of the melting peak (E1-2) is 12°C or more.

[0048] From the viewpoint of stably obtaining foamed particles with good in-moldability, it is preferable that the ratio of the heat of fusion of the melting peak (E1-3) to the heat of fusion of the melting peak (E1-1) is 0.1 or more and 0.8 or less. In this case, it is more preferable that the ratio of the heat of fusion of the melting peak (E1-2) to the heat of fusion of the melting peak (E1-1) is 0.2 or more and 2 or less. Furthermore, it is preferable that the heat of fusion for the melting peak (E1-3) is 5 J / g or more and 20 J / g or less.

[0049] The melting peaks (E1-3) described above can be adjusted, for example, in the dispersion and / or foaming agent impregnation process described above, by controlling the rate at which the temperature inside the pressure vessel rises or by maintaining the temperature inside the pressure vessel at a predetermined temperature for a predetermined time. More specifically, for example, in the dispersion and / or foaming agent impregnation process described above, a holding process is performed in which the temperature inside the pressure vessel is maintained at a temperature of [melting point of resin particles - 20°C] or higher and below [melting end temperature of resin particles] for about 10 to 60 minutes. After that, the temperature inside the pressure vessel is adjusted to a temperature of [melting point of resin particles - 15°C] or higher and below [melting end temperature of resin particles]. At this time, if necessary, a second holding process may be performed in which the temperature is maintained at that temperature for another 10 to 60 minutes. After that, foaming can be performed to produce foamed particles having melting peaks (E1-3).

[0050] Furthermore, in the foamed particles produced by the manufacturing method of the present invention, it is preferable that in the second DSC curve, the peak corresponding to the melting peak (E1-3) disappears, while the melting peak (E2-1), which is a peak originating from the crystals normally present in polyethylene resins, and the melting peak (E2-2), which is a peak originating from the crystals normally present in polypropylene resins, are observed. Here, it is preferable that the difference between the peak temperature of the melting peak (E2-2) and the peak temperature of the melting peak (E2-1) is between 10°C and 35°C.

[0051] Using Figure 2, which shows the first DSC curve of the foamed particles of the present invention, the melting peak (E1-1), melting peak (E1-2), and melting peak (E1-3) will be explained. Figure 2 is a conceptual diagram of the first DSC curve obtained by using the foamed particles from Example 1 (described later) as the measurement sample and heating them at a heating rate of 10°C / min from 23°C to a temperature 30°C higher than the end of the melting peak of the measurement sample. The peak temperatures and heat of fusion of melting peaks (E1-1), (E1-2), and (E1-3) can be determined from the melting peaks observed in the first DSC curve of the foamed particles. Specifically, in the DSC curve shown in Figure 2, a straight line is drawn connecting point I, which corresponds to 80°C on the DSC curve, and point II, which corresponds to the melting end temperature of the foamed particles. The melting end temperature is the high-temperature endpoint of melting peak (E1-3), and is the intersection point of melting peak (E1-3) and the baseline on the higher temperature side of melting peak (E1-3) on the DSC curve. As shown in Figure 2, after drawing a straight line connecting point I and point II, let IV be the intersection of the line passing through the maximum point III, which lies between melting peaks (E1-1) and (E1-2), and the line connecting point I and point II. Also, let VI be the intersection of the line passing through the maximum point V, which lies between melting peaks (E1-2) and (E1-3), and the line connecting point I and point II. The area enclosed by the straight line connecting point I and point IV, the straight line connecting point III and point IV, and the DSC curve connecting point I and point III is defined as the area of ​​the melting peak (E1-1). Furthermore, the area enclosed by the straight line connecting point IV and point VI, the straight line connecting point III and point IV, the straight line connecting point V and point VI, and the DSC curve connecting point III and point V is defined as the area of ​​the melting peak (E1-2). Furthermore, the area enclosed by the straight line connecting point VI and point II, the straight line connecting point V and point VI, and the DSC curve connecting point V and point II is defined as the area of ​​the melting peak (E1-3). The value of the heat of fusion for each peak of the foamed particle is calculated from the area of ​​each peak obtained as described above. In addition, the peak temperature of each peak can be confirmed from the DSC curve. Furthermore, the temperature of the maximum point located between the melting peaks of the DSC curve corresponds to the temperature at which the differential curve (DDSC) of the DSC curve intersects the baseline of the differential curve; therefore, it can be determined, for example, from the differential curve of the DSC curve.

[0052] <Meltflow Rate (MFR)> The MFR of the mixed resin constituting the foamed particles, measured under conditions of a temperature of 230°C and a load of 2.16 kg, is preferably 3 g / 10 min to 7 g / 10 min, and more preferably 4 g / 10 min to 6 g / 10 min. By adjusting the MFR of the foamed particles to fall within the above range, it is possible to stably produce foamed particles with excellent in-moldability while containing biomass-derived polyethylene resin. The melt flow rate of the mixed resin constituting the foamed particles can be measured in accordance with JIS K7210-1:2014. For measurement, foamed particles that have undergone degassing treatment may be used as the measurement sample to measure the melt flow rate. Furthermore, since the melt flow rate of the mixed resin constituting the foamed particles generally corresponds to the melt flow rate of the mixed resin constituting the resin particles used to obtain the foamed particles, the melt flow rate of the resin particles can be considered as the melt flow rate of the mixed resin constituting the foamed particles.

[0053] <Biomass content> The biomass content of the foamed particles produced by the manufacturing method of the present invention is comparable to that of the resin particles used in the production of the foamed particles. Therefore, if the biomass content of the resin particles is known, it can be recognized as the biomass content of the foamed particles. Furthermore, when measuring the biomass content from the produced foamed particles, the foamed particles can be used as a measurement sample and measured according to ASTM D 6866-21.

[0054] <Bulk density> From the perspective of obtaining a molded product with an excellent balance between lightness and compressive stress, the bulk density of the foam particles should be 10 kg / m³. 3More than 200kg / m 3 Preferably, it is 12 kg / m 3 More than 100kg / m 3 It is more preferable that the following conditions are met: 15 kg / m 3 More than 60kg / m 3 The following is even more preferable. The bulk density of the foamed particles can be determined by the method described in the examples below.

[0055] [Foam particle molded body] A molded foam particle body can be obtained by in-mold molding of foam particles produced by the manufacturing method of the present invention. In this specification, a molded foam particle body obtained by in-mold molding of foam particles produced by the manufacturing method of the present invention may be referred to as a molded foam particle body according to the present invention. The aforementioned in-mold molding broadly includes known in-mold molding methods using foamed particles. For example, foamed particles are filled into a mold having a cavity corresponding to the shape of a desired foamed particle molded body, and a predetermined molding pressure is applied to the foamed particles filled in the mold using a heating medium such as steam to heat them. The molding pressure can be adjusted, for example, in the range of 0.2 MPa(G) or more and 0.5 MPa(G) or less. In this specification, (G) refers to gauge pressure, that is, the pressure value relative to atmospheric pressure. By heating the foamed particles in the cavity in this way, the foamed particles are further foamed and fused to each other. Next, after heating with steam or the like is completed, the pressure in the cavity is released, and cooling of the mold and the molded body inside the mold is started immediately. When it is confirmed that the pressure (surface pressure) generated on the inner surface of the mold has decreased to below a predetermined value, cooling is stopped, and the foamed particle molded body is removed from the mold. The cooling method here is not particularly limited, but water cooling is one example. Through this series of molding steps, a foamed particle molded body corresponding to the shape of the cavity is obtained.

[0056] <Biomass content> The biomass content of the foamed particle molded body according to the present invention is approximately the same as that of the foamed particles used. When measuring the biomass content from the manufactured foamed particle molded body, a sample taken from the foamed particle molded body should be used and measured according to ASTM D 6866-21.

[0057] <Molded object density> The density of the foamed particle molded article according to the present invention is 10 kg / m³ 3 More than 200kg / m 3 Preferably, it is 12 kg / m 3 More than 100kg / m 3 It is more preferable that the following conditions are met: 15 kg / m 3 More than 60kg / m 3 The following is even more preferable: The density of the foamed particle molded body according to the present invention can be determined by dividing the mass of the foamed particle molded body by the volume calculated based on its external dimensions.

[0058] <Compressive stress at 50% strain> The compressive stress of the foamed particle molded article according to the present invention at 50% strain is preferably 100 kPa or more and 500 kPa or less, and more preferably 150 kPa or more and 400 kPa or less. The method for measuring the compressive stress of the foamed particle molded article at 50% strain can be found in the measurement method described in the examples below. Furthermore, the ratio of the compressive stress at 50% strain to the molded body density of the foamed particle molded article according to the present invention is 3 kPa / [kg / m²], from the viewpoint of providing a foamed particle molded article with a good balance between lightness and compressibility. 3 ] or more than 10kPa / [kg / m 3 It is preferable that it be 4 kPa / [kg / m²] or less. 3 ]9kPa / [kg / m 3 It is more preferable that the following conditions apply.

[0059] <Evaluation of in-moldability> The in-moldability of foamed particles is confirmed by evaluating the foamed particle molded product obtained by in-mold molding using the foamed particles. Examples of evaluation methods include fusion rate, peripheral shapeability, shape, and the number of moldable condition ranges. Details of these evaluation methods are described in the examples below. [Examples]

[0060] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In Examples 1 to 7 shown below, resin particles were prepared using the polypropylene resin A and polyethylene resin X described above. First, we will describe the polypropylene-based resin and polyethylene-based resin used as raw material resins in this example and comparative example.

[0061] Polypropylene resin: As raw material resins, we used resins PP1, PP2, and PP3, which are propylene-ethylene random copolymers (r-PP), and PP4, which is a propylene homopolymer (h-PP). Details of these resins are shown in Table 1. Resins PP1, PP2, and PP3 are polypropylene resin A. The density of these polypropylene resins is 0.9 g / cm³. 3 That was the case.

[0062] Polyethylene resin: As raw material resins, we used linear low-density polyethylene (PE-LLD) resins LLD1 and LLD2, low-density polyethylene (PE-LD) resins LD1, LD2, and LD3, and high-density polyethylene (PE-HD) resin HD1. Details of these resins are shown in Table 2. Resins LLD1, LLD2, and LD1 are polyethylene-based resins X.

[0063] (Example 1) <Preparation of resin particles> A manufacturing apparatus was prepared that included an extruder with an inner diameter of 50 mm and a strand-forming die attached to the downstream side of the extruder. The resins PP1 shown in Table 1 and LLD1 shown in Table 2, along with zinc borate as a foam regulator, were supplied to an extruder and melt-kneaded to obtain a molten mixture. The amount of zinc borate added was 0.1 parts by mass per 100 parts by mass of the total of resins PP1 and LLD1. The molten mixture was introduced into a strand-forming die and extruded into strands. The extruded strands were water-cooled and cut with a pelletizer to obtain resin particles composed of a mixed resin of resins PP1 and LLD1, with an average mass of 1 mg per strand.

[0064] <Production of foamed particles> As described above, 1 kg of the obtained resin particles was supplied to a pressurized pressure vessel with a capacity of 5 L along with 3 L of water, which is an aqueous dispersion medium. In addition, 0.3 parts by mass of kaolin as an inorganic dispersant and 0.04 parts by mass of a surfactant (product name: Neogen S-20F, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., active ingredient: sodium dodecylbenzenesulfonate) (as active ingredients) were added to the pressure vessel for every 100 parts by mass of the resin particles. Next, the pressure vessel was heated at a rate of 5°C / min while being stirred until it reached the foaming temperature of 150°C. Then, carbon dioxide was injected into the pressure vessel as a foaming agent, and the pressure was increased to 2.9 MPa(G). This was then maintained at the same temperature and pressure for 15 minutes. This adjusted the crystalline structure of the resulting foam particles so that a third melting peak, the melting peak (E1-3), would appear in the first DSC curve obtained by differential scanning calorimetry. Subsequently, the resin particles and water contained within the pressure vessel were released to atmospheric pressure, resulting in a bulk density of 36 kg / m³. 3 We obtained foamed particles. The various physical properties of the foamed particles, as described later, were measured using foamed particles that had been conditioned by standing for 24 hours under conditions of 50% RH, 23°C, and 1 atm.

[0065] <Manufacturing of foamed particle molded products> The obtained foamed particles were filled into a mold having a molding cavity capable of forming a plate-shaped foamed particle mold measuring 300 mm in length, 250 mm in width, and 60 mm in height, and heated using the following heating method. A metal mold was used as the molding die. The heating method involved preheating (exhaust process) by supplying steam to the mold with drain valves on both sides of the mold open. Then, steam was supplied from one side of the mold to heat it, and then from the other side to heat it further. Subsequently, steam was supplied from both sides of the mold to heat it at the molding pressure described later. After heating was complete, the pressure was released and water cooling was started immediately, and water cooling was continued until the pressure generated on the inner surface of the mold by the foaming force of the foamed particle molded body reached 0.04 MPa(G). After water cooling was complete, the foamed particle molded body was removed from the mold, and this was designated as Example 1. Furthermore, the various physical property measurements and evaluations of the foamed particle molded bodies described later were performed using molded bodies that had been cured by standing at 80°C and 1 atm for 12 hours after demolding, and then conditioned by standing at 50% RH, 23°C, and 1 atm for 24 hours.

[0066] (Examples 2-7, Comparative Examples 1-4) Except for the changes described in Tables 3 and 4, resin particles, foamed particles, and molded foamed particle articles were manufactured in the same manner as in Example 1 described above, and these were designated as Examples 2-7 and Comparative Examples 1-4. In addition, for the foamed particles of Examples 2-7 and Comparative Examples 1-4, in order to obtain the physical properties shown in Tables 3 and 4, the foaming temperature of the resin particles was adjusted in the range of 143°C to 166°C, and the pressure of the pressure vessel by carbon dioxide injection was adjusted in the range of 2.5 MPa(G) to 3.6 MPa(G) to produce the foamed particles.

[0067] The raw material resin used in this example, as well as the resin particles, foamed particles, and molded foamed particle products obtained in each example and comparative example, were used as measurement samples for the following measurements and evaluations. The measurement and evaluation results are shown in Table 1 for the raw material resin (polypropylene resin), in Table 2 for the raw material resin (polyethylene resin), and in Tables 3 and 4 for each example and comparative example.

[0068] <Raw material resin: Biomass content> The biomass content of the raw material resin is determined based on ASTM D 6866-21, and the radiocarbon content of the raw material resin is C 14This value was determined by measuring the concentration of [the substance]. Note that all polyethylene resins listed in Table 2 are manufactured by Braskem. Specifically, LLD1 is "SLH118", LLD2 is "SLH218", LD1 is "STN7006", HD1 is "SHE150", LD2 is "SBC818", and LD3 is "SBF0323HC". Furthermore, the polyethylene resins listed in Table 2 are polyethylenes that are included in the Japan Biomass Plastics Association's Positive List of Biomass Plastics.

[0069] <Raw resin: Density> The density of the raw material resin was measured according to Method A (water displacement method) of JIS K7112:1999.

[0070] <Raw material resin: Melt Flow Rate (MFR)> The MFR of each polypropylene resin used as a raw material was measured according to JIS K7210-1:2014 under conditions of 230°C and 2.16 kg load. The MFR of each polyethylene resin used as a raw material was measured according to JIS K7210-1:2014 under conditions of 190°C and 2.16 kg load.

[0071] <Raw material resin: Melting point> The melting point of the raw resin was measured by differential scanning calorimetry (DSC) in accordance with JIS K7121:2012. A high-sensitivity differential scanning calorimetry instrument, "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Co., Ltd.), was used. For sample conditioning, "3.(2) When measuring the melting temperature after performing a certain heat treatment" was adopted. Approximately 2 mg of the raw resin was taken as the sample. The sample was heated from 23°C to 200°C at a heating rate of 10°C / min under a nitrogen inflow of 30 mL / min. It was then maintained at this temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain a second DSC curve. The peak temperature of the melting peak in this second DSC curve was determined. This measurement was performed on three different samples, and the average of the obtained peak temperatures was taken as the melting point of the raw resin. Furthermore, if multiple melting peaks appear in the second DSC curve, the peak temperature of the melting peak with the highest melting peak height relative to the baseline will be adopted as the melting point of the raw resin.

[0072] <Raw material resin: Heat of fusion> The heat of fusion of the raw resin was measured by differential scanning calorimetry based on the method for measuring the transition heat of plastics described in JIS K7122:2012. A high-sensitivity differential scanning calorimeter, "EXSTAR DSC7020" (manufactured by Hitachi High-Tech Science Co., Ltd.), was used as the measuring device. For preparing the sample, "3.(2) When measuring the heat of fusion after performing a certain heat treatment" was adopted. Approximately 2 mg of the raw resin was taken as the sample, and the sample was heated from 23°C to 200°C at a heating rate of 10°C / min under conditions of a nitrogen inflow of 30 mL / min. Then, it was maintained at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and then heated again to 200°C at a heating rate of 10°C / min to obtain the second DSC curve. The point at 80°C on the second obtained DSC curve was designated as α, and the point on the DSC curve corresponding to the melting end temperature was designated as β. The area of ​​the region enclosed by the DSC curve between points α and β and the line segment (α-β) was measured, and the heat of fusion of the raw resin was calculated from this area.

[0073] <Resin particles: 2nd DSC curve / peak temperature, melting peak height, heat of fusion> Except for using resin particles as the measurement sample, the second DSC curve was obtained by differential scanning calorimetry (DSC) based on JIS K7121:2012 and JIS K7122:2012, under the same conditions as the method for measuring the melting point of the raw resin described above. The two peaks identified in the second DSC curve were designated as melting peak (R2-1) and melting peak (R2-2) from the low-temperature side, and the peak temperature, melting peak height, and heat of fusion of each melting peak were read. This measurement was performed on three different measurement samples, and the arithmetic mean values ​​of the obtained peak temperature, melting peak height, and heat of fusion were calculated and used as the peak temperature, melting peak height, and heat of fusion of the resin particles. Furthermore, the peak temperature difference was calculated by subtracting the peak temperature of melting peak (R2-1) from the peak temperature of melting peak (R2-2) of the resin particles obtained as described above. Furthermore, as described above, the ratio of the melting peak height of melting peak (R2-1) to the melting peak height of melting peak (R2-2) of the obtained resin particles was determined.

[0074] <Foamed Particles: First DSC Curve / Peak Temperature and Heat of Fusion> Based on JIS K7121:2012 and JIS K7122:2012, differential scanning calorimetry (DSC) was performed using approximately 1 mg of foamed particles as the sample. The first DSC curve was obtained by heating the sample from 23°C to 200°C at a heating rate of 10°C / min. The three peaks observed in this first DSC were designated as the melting peak (E1-1), melting peak (E1-2), and melting peak (E1-3) from the lowest temperature side, and the peak temperature and heat of fusion of each melting peak were read. This measurement was performed on three different samples, and the arithmetic mean of the obtained peak temperatures and heats of fusion was calculated for each sample. These were then defined as the peak temperature and heat of fusion of each melting peak of the foamed particles. Furthermore, as described above, the ratio of the heat of fusion of melting peak (E1-3) to the heat of fusion of melting peak (E1-1), and the ratio of the heat of fusion of melting peak (E1-2) to the heat of fusion of melting peak (E1-1) were determined.

[0075] <Resin particles: Biomass content> The biomass content of the resin particles was calculated based on the biomass content of each raw resin and the blending ratio of each raw resin in the resin particles.

[0076] <Resin particles: Meltflow rate> Using resin particles as the measurement sample, the MFR of the resin particles was determined under the conditions of 230°C and a load of 2.16 kg, in accordance with JIS K7210-1:2014. Since the resin particles in each example and comparative example were composed of a mixed resin mainly consisting of polypropylene resin, 230°C was adopted as the measurement temperature for the MFR of the resin particles.

[0077] <Foaming particles: Bulk density> A group of foamed particles weighing W (g) was filled into a graduated cylinder, and the filling height of the foamed particles inside the cylinder was stabilized by lightly tapping the horizontal surface of the bottom of the graduated cylinder several times. The bulk volume V (L) of the foamed particles indicated by the scale on the graduated cylinder was read, and the weight W of the foamed particles was divided by the bulk volume V (W / V). The value obtained from this was calculated in kg / m 3 By converting the units, the bulk density of the foamed particles (kg / m³) can be calculated. 3 ) was obtained.

[0078] <Foam particle molded body: molded body density> The density of the foamed particle molded body was determined by dividing its mass by its volume, which was calculated based on its external dimensions.

[0079] <Foam particle molded body: Minimum molding pressure for obtaining good quality products> In the heating method described above for the production of foamed particle molded articles, the molding pressure (molding steam pressure) was increased in increments of 0.02 MPa (G) from 0.18 MPa (G), and in-mold molding of foamed particles was performed under each molding condition. The resulting foam particle molded articles were evaluated for their fusion rate, peripheral shapeability, and form, as described below. The lowest molding pressure at which a foam particle molded article that passed all of these evaluations was obtained was defined as the minimum molding pressure at which a good product could be produced.

[0080] Fusion rate: A test specimen (100mm long x 100mm wide x thickness: thickness of the foam particle molded body) was cut from the center of the foam particle molded body. An incision of approximately 5mm in the thickness direction of each test specimen was made with a utility knife, and then the test specimen was fractured along the incision. Next, the number of foam particles present on the fracture surface of the foam particle molded body (n) and the number of foam particles that were destroyed (b) were measured. The number of destroyed foam particles (b) relative to the total number of foam particles (n) was expressed as a percentage to determine the fusion rate (%). A fusion rate of 80% or higher was considered a pass, and a fusion rate of less than 80% was considered a fail.

[0081] Peripheral shaping: In the periphery of the foamed particle molded body, those with inconspicuous gaps between foamed particles and a sufficiently defined mold shape were deemed acceptable, while those with noticeable gaps between foamed particles and a poorly defined mold shape were deemed unacceptable.

[0082] shape: The presence or absence of sink marks (indentations) in the central part of the foam particle molded body was evaluated. Specifically, the thickness t1 near both ends in the longitudinal direction of the molded body and the thickness t2 in the central part of the molded body were measured for a flat foam particle molded body. Next, the ratio (%) of the thickness t2 in the central part of the molded body to the larger of the two thicknesses t1 near the ends was calculated. If this ratio was 95% or higher, it was judged that no excessive sink marks had occurred in the central part of the molded body, and it was deemed acceptable. If this ratio was less than 95%, it was judged that sink marks had occurred in the central part of the molded body, and it was deemed unacceptable. Specifically, the thickness t1 refers to the thickness at the intersection of a point 10 mm inward from the end towards the center in the longitudinal direction of the molded body and a point that divides the molded body in half horizontally. Furthermore, the thickness t2 refers to the thickness at the intersection of a point that divides the molded body in half vertically and a point that divides it in half horizontally.

[0083] <Foam particle molded body: Moldable condition range> In the in-mold molding of the foamed particles described above, the molding pressure during in-mold molding was increased by 0.02 MPa(G) increments from the lower limit molding pressure to confirm the range of moldable conditions in which good products could be obtained. For example, if the minimum molding pressure was 0.22 MPa(G) and good products could be obtained up to 0.26 MPa(G), the moldable condition range was counted as 3 points of moldability and evaluated as follows. ◎: 3-point molding possible 〇: 2-point molding possible △: 1 point molding possible ×: Non-defective product cannot be formed

[0084] Furthermore, since the molding temperature is controlled by the molding pressure, a larger number of molding pressures capable of producing good products, and a wider range from the lower limit to the upper limit, indicates a wider range of moldable heating temperatures. In addition, products that can be molded even under low molding pressure conditions are preferable because they allow for a reduction in the amount of steam required for molding, resulting in superior productivity.

[0085] <Foam particle molded body: Compressive stress at 50% strain> For each example of foam particle molded body obtained at the minimum molding pressure that yields a good product, a 50mm x 50mm x 25mm test piece without a skin layer was cut from near the center of the foam particle molded body, and a compression test was performed using the test piece as follows. Specifically, the compressive stress (kPa) at 50% strain of the foam particle molded body was determined by performing a compression test at a compression speed of 10mm / min in accordance with JIS K6767:1999. Furthermore, the ratio of the compressive stress at 50% strain to the density of the molded body of the test specimen was calculated.

[0086] In Comparative Examples 1 and 4, the foamed particles did not fuse well with each other during in-mold molding, resulting in no molding conditions that could produce a good molded product. In Comparative Example 2, heating the foamed particles until they fused sufficiently during in-mold molding caused shrinkage in the molded product, resulting in no molding conditions that could produce a good molded product. In Comparative Example 3, the foamed particles had low secondary foaming properties, making it difficult to fill the gaps between the foamed particles in the resulting molded product. Consequently, no molding conditions were found that could produce a molded product with small gaps between foamed particles and no shrinkage. On the other hand, according to the method for producing foamed particles of the present invention, it was possible to obtain foamed particles containing a polypropylene resin and a biomass-derived polyethylene resin, which exhibit excellent in-moldability. Specifically, according to the foamed particles of the present invention, it was possible to obtain a molded article that has a wide range of moldable molding pressures, contains a predetermined amount of biomass, and exhibits good compressibility due to the polypropylene resin component.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

[0091] The present invention described above encompasses the following technical concepts. (1) A method for producing foamed particles by foaming resin particles composed of a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin, The polypropylene resin comprises a polypropylene resin A consisting of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer. The aforementioned polyethylene resin has a density of 0.93 g / cm³. 3 It contains polyethylene resin X which is less than The biomass content of the polyethylene resin X, as measured by ASTM D 6866-21, is 30% or more. The melt flow rate of the polyethylene resin X measured under the conditions of a temperature of 190°C and a load of 2.16 kg is 0.5 g / 10 min or more and 5 g / 10 min or less. The mass ratio of polypropylene resin A to polyethylene resin X in the mixed resin is 50:50 to 95:5. The resin particles have a crystalline structure in which, as determined by differential scanning calorimetry, the resin particles are heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min, and in the DSC curve obtained, a melting peak (R1-1) originating from the polyethylene resin and a melting peak (R2-2) originating from the polypropylene resin located at a higher temperature than the melting peak (R2-1) appear. A method for producing foamed particles, wherein the difference between the peak temperature of the melting peak (R2-2) and the peak temperature of the melting peak (R2-1) is 10°C or more and 35°C or less. (2) The melt flow rate of the resin particles measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 3 g / 10 min or more and 7 g / 10 min or less, and the method for producing foamed particles according to (1) above. (3) The melt flow rate MFR of the polypropylene-based resin A measured under the conditions of a temperature of 230°C and a load of 2.16 kg PPA and the melt flow rate MFR of the polyethylene-based resin X PEX and the difference MFR PPA -MFR PEX is 3 g / 10 min or more and 8 g / 10 min or less, and the method for producing foamed particles according to (1) or (2) above. (4) The melting point Tm of the polypropylene-based resin A PPA is 130°C or more and 155°C or less, the melting point Tm of the polypropylene-based resin A PPA and the difference Tm PEX between the melting point Tm of the polypropylene-based resin A and the melting point Tm of the polyethylene-based resin X PPA -Tm PEX is 10°C or more and 35°C or less, and the method for producing foamed particles according to any one of (1) to (3) above. (5) The heat of fusion of the resin particles is 60 J / g or more and 95 J / g or less, and the method for producing foamed particles according to any one of (1) to (4) above. (6) The polyethylene-based resin X is linear low-density polyethylene and / or low-density polyethylene, and the method for producing foamed particles according to any one of (1) to (5) above. (7) The biomass content of the resin particles measured by ASTM D 6866-21 is 5% or more, and the method for producing foamed particles according to any one of (1) to (6) above. (8) Foamed particles composed of a mixed resin obtained by kneading a polypropylene-based resin and a polyethylene-based resin, where the polypropylene-based resin includes a polypropylene-based resin A composed of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer, and the polyethylene-based resin includes a polyethylene-based resin X having a density less than 0.93 g / cm 3 and the method for producing foamed particles according to any one of (1) to (7) above. The foamed particles are The biomass content measured by ASTM D 6866-21 is 5% or more. Differential scanning calorimetry (DSC) measurements revealed that the foam particles, when heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated again from 23°C to 200°C at a heating rate of 10°C / min, exhibited a crystalline structure in which a melting peak (E2-1) originating from the polyethylene resin and a melting peak (E2-2) originating from the polypropylene resin located at a higher temperature than melting peak (E2-1) appeared. The difference between the peak temperature of the melting peak (E2-2) and the peak temperature of the melting peak (E2-1) is 10°C or more and 35°C or less. Foamed particles in which the melt flow rate of the mixed resin constituting the foamed particles, measured under conditions of a temperature of 230°C and a load of 2.16 kg, is 3 g / 10 min or more and 7 g / 10 min or less.

Claims

1. A method for producing foamed particles by foaming resin particles composed of a mixed resin obtained by kneading a polypropylene resin and a polyethylene resin, The polypropylene resin comprises a polypropylene resin A consisting of a propylene-ethylene random copolymer and / or a propylene-ethylene-butene random copolymer. The aforementioned polyethylene resin has a density of 0.93 g / cm³. ３ It contains polyethylene resin X which is less than The biomass content of the polyethylene resin X, as measured by ASTM D 6866-21, is 30% or more. The melt flow rate of the polyethylene resin X, measured under conditions of a temperature of 190°C and a load of 2.16 kg, is 0.5 g / 10 min or more and 5 g / 10 min or less. The mass ratio of polypropylene resin A to polyethylene resin X in the mixed resin is 50:50 to 95:

5. The resin particles have a crystalline structure in which, as determined by differential scanning calorimetry, the resin particles are heated from 23°C to 200°C at a heating rate of 10°C / min, then cooled from 200°C to 23°C at a cooling rate of 10°C / min, and then heated from 23°C to 200°C at a heating rate of 10°C / min, and in the DSC curve obtained, a melting peak (R2-1) originating from the polyethylene resin and a melting peak (R2-2) originating from the polypropylene resin located at a higher temperature than the melting peak (R2-1) appear. A method for producing foamed particles, wherein the difference between the peak temperature of the melting peak (R2-2) and the peak temperature of the melting peak (R2-1) is 10°C or more and 35°C or less.

2. A method for producing foamed particles according to claim 1, wherein the melt flow rate of the resin particles measured under the conditions of a temperature of 230°C and a load of 2.16 kg is 3 g / 10 min or more and 7 g / 10 min or less.

3. The melt flow rate (MFR) of the polypropylene resin A is measured under the conditions of a temperature of 230°C and a load of 2.16 kg. ＰＰＡ and the melt flow rate MFR of the polyethylene resin X ＰＥＸ The difference between MFR ＰＰＡ - MFR ＰＥＸ A method for producing foamed particles according to claim 1 or 2, wherein the amount is 3 g / 10 min or more and 8 g / 10 min or less.

4. Melting point Tm of the polypropylene resin A ＰＰA The temperature is between 130°C and 155°C. The melting point Tm of the polypropylene-based resin A ＰＰA and the melting point Tm of the polyethylene-based resin X ＰEＸ The difference Tm ＰＰＡ - Tm ＰＥＸ is 10°C or higher and 35°C or lower. The method for producing expanded particles according to claim 1 or 2

5. A method for producing foamed particles according to claim 1 or 2, wherein the heat of fusion of the resin particles is 60 J / g or more and 95 J / g or less.

6. The method for producing foamed particles according to claim 1 or 2, wherein the polyethylene resin X is linear low-density polyethylene and / or low-density polyethylene.

7. A method for producing foamed particles according to claim 1 or 2, wherein the biomass content of the resin particles, as measured by ASTM D 6866-21, is 5% or more.

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