Polyethylene resin foam sheet and method for producing same

Abstract

A method for producing a polyethylene resin foam sheet, said method comprising: co-extruding a foamable resin melt for forming a foam layer A, which is obtained by kneading a polyethylene resin A and a physical foaming agent, and a foamable resin melt for forming a foam layer B, which is obtained by kneading a polyethylene resin B and a physical foaming agent; the polyethylene resin A contains a polyethylene X comprising a low-density polyethylene or a mixture of a low-density polyethylene and a linear low-density polyethylene, and the polyethylene resin B contains a polyethylene Y comprising a low-density polyethylene or a mixture of a low-density polyethylene and a linear low-density polyethylene. The total Xb of the blending amount of the plant-derived polyethylene b-PEx in the polyethylene X is less than 25 mass% and contains 0, and the total Yb of the blending amount of the plant-derived polyethylene b-PEY in the polyethylene Y is greater than the total Xb of the blending amount of the plant-derived polyethylene b-PEx in the polyethylene X.

Description

Technical Field

[0001] The present invention relates to a polyethylene resin foam sheet and a method for producing the same. Background Art

[0002] Due to environmental concerns, the demand for carbon-neutral products is growing. This demand is driving the need to curb fossil fuel consumption. Against this backdrop, polyethylene resins have recently been produced using ethylene derived from natural sources, such as plants, instead of fossil fuels.

[0003] For example, Patent Document 1 discloses a polyethylene resin foam sheet containing low-density polyethylene derived from natural sources. Specifically, Patent Document 1 describes a polyethylene resin foam sheet having a foam layer composed of a polyethylene resin composition, wherein the polyethylene resin composition constituting the foam layer contains low-density polyethylene (PE-LD) containing ethylene derived from natural sources in its constituent units, the proportion of the low-density polyethylene (PE-LD) in the total resin contained is 3% by mass or more and 100% by mass or less, and the gel fraction is 4% or less, and the low-density polyethylene (PE-LD) satisfies all of the following four requirements: (1) a density of 910 kg / m 3 Above 929kg / m 3 below; (2) the mass average molecular weight (Mw) / number average molecular weight (Mn) is 2.5 or more and 7.0 or less; (3) the melt flow rate (MFR) is 0.1 g / 10 min or more and 1.0 g / 10 min or less; (4) the biomass content (biomass) measured according to ASTM D6866 (2004) is 3% or more.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-130796. Summary of the Invention

[0007] Among the polyethylene resin foam sheets described above, there is sometimes a need for foam sheets that can reduce environmental impact and have a low grammage. However, when natural polyethylene is used as the resin raw material for the foam layer to produce a foam sheet with a low grammage, as in Patent Document 1, the appearance of the resulting foam sheet tends to deteriorate.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a polyethylene resin foam sheet having a small environmental load, a low basis weight, and an excellent appearance, and a method for producing the same.

[0009] The present invention provides the following.

[0010] [1] A method for producing a polyethylene resin foam sheet having a gram weight of 100 g / m 2 A method for producing a polyethylene resin foam sheet having a biomass content of 5% or more as measured in accordance with ASTM D 6866, wherein the foam sheet is a multilayer foam sheet comprising a polyethylene resin foam layer A and a polyethylene resin foam layer B laminated and bonded together, the foam layer A and the foam layer B being formed by coextruding a foaming resin melt for forming the foam layer A obtained by kneading the polyethylene resin A with a physical foaming agent, and a foaming resin melt for forming the foam layer B obtained by kneading the polyethylene resin B with a physical foaming agent, the polyethylene resin A comprising polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene resin B comprising polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene, and the polyethylene X comprising plant-derived polyethylene b-PE. x The total amount Xb of the polyethylene Y is less than 25% by mass and contains 0, and the polyethylene b-PE derived from plants in the polyethylene Y is Y The total amount of Yb in the polyethylene X is greater than the plant-derived polyethylene b-PE x The total amount of compounding is Xb more.

[0011] [2] The method for producing a polyethylene resin foam sheet according to [1], wherein the plant-derived polyethylene b-PE measured according to ASTM D 6866 is x The biomass content of the plant-derived polyethylene b-PE is more than 80%, as determined by ASTM D 6866 Y The biomass content is more than 80%.

[0012] [3] The method for producing a polyethylene resin foam sheet according to [1] or [2], wherein the plant-derived polyethylene b-PE Y The total amount of Yb and the plant-derived polyethylene b-PE x The difference Yb-Xb between the total Xb of the blending amount is 20 mass % or more.

[0013] [4] The method for producing a polyethylene resin foam sheet according to any one of [1] to [3], wherein the ratio of the gram weight of the foam layer B to the gram weight of the foam layer A is 0.1 or more and 2 or less.

[0014] [5] The method for producing a polyethylene resin foam sheet according to any one of [1] to [4], wherein the foam sheet has a thickness of less than 2 mm.

[0015] [6] A polyethylene resin foam sheet having a gram weight of 100 g / m 2 A polyethylene resin foam sheet having a biomass content of 5% or more as measured in accordance with ASTM D 6866, wherein the foam sheet is a multilayer foam sheet comprising a polyethylene resin foam layer A and a polyethylene resin foam layer B laminated and bonded together, the polyethylene resin foam layer A comprising polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene resin foam layer B comprising polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene, wherein the polyethylene X comprises plant-derived polyethylene b-PE x The total amount Xb of the polyethylene Y is less than 25% by mass and contains 0, and the polyethylene b-PE derived from plants in the polyethylene Y is Y The total amount of Yb in the polyethylene X is greater than the plant-derived polyethylene b-PE x The total amount Xb of the blending amount is greater.

[0016] The present invention can provide a polyethylene resin foam sheet having a small environmental impact, a low basis weight, and an excellent appearance, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view of a polyethylene resin foam sheet according to an embodiment. DETAILED DESCRIPTION

[0018] The polyethylene resin foam sheet according to the present embodiment and a method for producing the same will be described below.

[0019] (1) Method for manufacturing foam sheet

[0020] The present invention relates to a method for manufacturing a 100g / m 2 The following method is used to prepare a polyethylene resin foam sheet (hereinafter referred to as a "foam sheet") having a biomass content of 5% or more as measured in accordance with ASTM D 6866.

[0021] The polyethylene resin foam sheet of the present invention is a multilayer foam sheet comprising a polyethylene resin foam layer A (hereinafter referred to as "foam layer A") and a polyethylene resin foam layer B (hereinafter referred to as "foam layer B") laminated and bonded together. The foam sheet of the present invention comprises at least one foam layer A and at least one foam layer B.

[0022] The foam layer A and the foam layer B are formed by co-extruding a foaming resin melt for forming the foam layer A (hereinafter also referred to as "foaming resin melt A") obtained by kneading a polyethylene resin A and a physical foaming agent, and a foaming resin melt for forming the foam layer B (hereinafter also referred to as "foaming resin melt B") obtained by kneading a polyethylene resin B and a physical foaming agent. The polyethylene resin A includes polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene. In addition, the polyethylene resin B includes polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene. The plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is less than 25 mass% (including 0), and the plant-derived polyethylene b-PE in the polyethylene Y Y The total amount of Yb is greater than the plant-derived polyethylene b-PE in polyethylene X. x The total amount of compounding is Xb.

[0023] In the method for producing a foam sheet of the present invention, as described above, the foamable resin melt A and the foamable resin melt B are co-extruded to produce a multilayer foam sheet having the foam layer A and the foam layer B.

[0024] In the method for producing a foam sheet of the present invention, a known extrusion device used in the field of extrusion foaming can be used. As an example, a multilayer foam sheet can be produced by using an extruder for forming a foam layer A configured to extrude a foamable resin melt A, an extruder for forming a foam layer B configured to extrude a foamable resin melt B, and a co-extrusion device configured to have a co-extrusion die downstream of these extruders capable of laminating the foamable resin melts A and B.

[0025] For example, by installing a coextrusion die downstream of the extruder for forming the foam layer A and connecting the downstream side of the extruder for forming the foam layer B and the coextrusion die, the foamable resin melts A and B can be stacked and coextruded.

[0026] When using extrusion device to carry out coextrusion, the foaming resin melt A formed with extruder using foaming layer A and the foaming resin melt B formed with extruder using foaming layer B are introduced into coextrusion die, and are extruded in layers from the discharge port of coextrusion die.As coextrusion die, for example, a flat die with a linear discharge port can be used, but from the viewpoint of easily and stably manufacturing a wide foam sheet, an annular die with an annular discharge port is preferably used. When using an annular die, after another foaming resin melt has been laminated with the outside side and / or the inner side of a foaming resin melt of cylindrical flow in the inside of mold, the laminate of these foaming resin melts A, B is extruded in a cylindrical shape from the discharge port of mold.When such laminate is extruded under the pressure environment lower than extruder inside (for example, in the atmosphere), foaming resin melt A, B foams and forms bubble, thereby forms stacked foam. Thereafter, the extruded cylindrical laminated foam is expanded in a cylindrical expander (eg, a mandrel) having a cooling mechanism, pulled along the expander, and cut in the extrusion direction, thereby producing a foam sheet.

[0027] <Foamable resin melt A>

[0028] The foamable resin melt A can be formed by melt-kneading the polyethylene resin A and the physical foaming agent. The foam layer A is formed by foaming the foamable resin melt A.

[0029] The polyethylene resin A in the present invention refers to a resin containing 50 mol% or more of structural units derived from ethylene. For example, the polyethylene resin A includes polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), or ethylene-vinyl acetate copolymer (EVA) containing 50 mol% or more of structural units derived from ethylene, or one or more combinations thereof.

[0030] The polyethylene resin A used to form the foamable resin melt A comprises a low-density polyethylene LD x Polyethylene X or low density polyethylene LD x and linear low-density polyethylene LL x A mixture of polyethylene X.

[0031] From the viewpoint of improving the extrusion foamability of the foamable resin melt A, the polyethylene resin A preferably contains polyethylene X as a main component. Specifically, the proportion of polyethylene X in the polyethylene resin A is preferably 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 100% by mass, that is, the polyethylene resin A is polyethylene X.

[0032] [Low density polyethylene LD x ]

[0033] Low-density polyethylene (LD) used as polyethylene X x It has a long-chain branched structure and a density of 0.910 g / cm 3 Above and less than 0.930g / cm 3 Low-density polyethylene is represented by the abbreviation "PE-LD" in JIS K 6899-1:2015 "Plastics - Symbols and abbreviations - Part 1: Basic polymers and their properties". Low-density polyethylene LD x It can also be called high pressure low density polyethylene. x , for example, low-density polyethylene p-LD derived from petroleum x or plant-derived low-density polyethylene b-LD x Low-density polyethylene p-LD from petroleum x and plant-derived low-density polyethylene b-LD x The details are described later.

[0034] From the viewpoint of improving the extrusion foaming property of the foamable resin melt A and obtaining a foam sheet with good cushioning properties, the low-density polyethylene LD in the polyethylene X x The ratio of low density polyethylene LD x Compared with low density polyethylene LD x and linear low-density polyethylene LL x The ratio of the total 100 mass % is preferably 50 mass % or more, more preferably 60 mass % or more, and further preferably 70 mass % or more.

[0035] It should be noted that the low-density polyethylene LD in the polyethylene X x The range of the ratio includes: polyethylene X is low density polyethylene LD x The case (low density polyethylene LD in polyethylene X x The polyethylene X is a low-density polyethylene LD x and linear low-density polyethylene LL x In the case of a mixture of polyethylene X and low density polyethylene LD xand linear low-density polyethylene LL x Composition, low-density polyethylene LD in polyethylene X x The ratio of the linear low-density polyethylene LL is 50% or more by mass x The ratio is 50% by mass or less).

[0036] [Linear low-density polyethylene LL x ]

[0037] Linear low-density polyethylene LL used in polyethylene X x It is a linear ethylene copolymer of ethylene and α-olefin. Linear low-density polyethylene is represented by the abbreviation "PE-LLD" in JIS K 6899-1:2015 "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties". x The density is preferably 0.910 g / cm 3 Above and 0.935g / cm 3 Below, more preferably 0.910 g / cm 3 Above and less than 0.930g / cm 3 .

[0038] Examples of the α-olefin used in the ethylene-based copolymer include α-olefins having 4 to 10 carbon atoms. Examples of the α-olefins having 4 to 10 carbon atoms include butene (4 carbon atoms), hexene (6 carbon atoms), and octene (8 carbon atoms). From the perspective of easily increasing the rigidity of the foam sheet, it is preferred to use a linear low-density polyethylene LL which is a copolymer of ethylene and octene (8 carbon atoms). c8 Contains linear low-density polyethylene LL as a main component x It should be noted that octene includes isomers of octene such as 1-octene and isooctene.

[0039] Linear low-density polyethylene LL x Linear low-density polyethylene LL c8 The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0040] As linear low-density polyethylene LL x , linear low-density polyethylene from petroleum, linear low-density polyethylene from plants. It is also possible to combine two or more polyethylenes as linear low-density polyethylene LL xFrom the perspective of supply stability in the market, it is preferable to use linear low-density polyethylene derived from fossil fuel resources (linear low-density polyethylene derived from petroleum) produced using fossil fuels as raw materials as linear low-density polyethylene LL x .

[0041] Linear low-density polyethylene LL x The melting point of the polyethylene is preferably 116° C. or higher and 130° C. or lower, more preferably 118° C. or higher and 126° C. or lower. By using a linear low-density polyethylene LL having a melting point within the above range, x , it is easy to suppress the collapse of bubbles during extrusion foaming, so that a foam sheet with a high independent cell ratio can be easily and stably obtained.

[0042] Linear low-density polyethylene LL x The melt flow rate is preferably 0.1 g / 10 min or more and 15 g / 10 min or less, more preferably 0.2 g / 10 min or more and 12 g / 10 min or less. By using a linear low-density polyethylene LL having a melt flow rate within the above range x , it is easy to suppress the collapse of bubbles during extrusion foaming, so that a foam sheet with a high independent cell ratio can be easily and stably obtained.

[0043] The melting point and melt flow rate of the linear low-density polyethylene can be measured by the same methods as those for the melting point and melt flow rate of the polyethylene-based resin described below.

[0044] It should be noted that as a linear low-density polyethylene LL x The melting point or melt flow rate when using multiple linear low-density polyethylenes is determined as follows. First, the resins are melt-kneaded by an extruder or the like according to the mixing ratio of each linear low-density polyethylene used in the production of the foam layer to prepare a kneaded product for measurement. Then, various measurements are performed on the kneaded product for measurement, and the obtained melting point or melt flow rate is used as the linear low-density polyethylene LL. x Melting point or melt flow rate.

[0045] In the foamable resin melt A, a linear low-density polyethylene LL is added. x In the case of (as polyethylene X, low density polyethylene LD is used x and linear low-density polyethylene LL x In the case of a mixture of polyethylene X and polyethylene X, the linear low-density polyethylene LL x The amount of blending (linear low-density polyethylene LL x Compared with low density polyethylene LD x and linear low-density polyethylene LL xThe proportion of the total 100 mass % of the linear low-density polyethylene LL is preferably 5 mass % or more and 30 mass % or less, more preferably 10 mass % or more and 25 mass % or less. x The compounding amount XL is within the above-mentioned range, thereby easily improving the rigidity of the foam sheet, and even in the case of obtaining a foam sheet with a relatively thin thickness and a low gram weight, it is easy and stably to suppress the bursting of bubbles during extrusion foaming.

[0046] [Polyethylene b-PE from plants x ]

[0047] Polyethylene X can include polyethylene b-PE from plants x .

[0048] As polyethylene b-PE from plants x , low-density polyethylene or linear low-density polyethylene produced by polymerizing monomers containing bio-ethylene produced from plants such as sugar cane, corn, and sugar beets as raw materials can be used. x Examples of plant-derived low-density polyethylene or the linear low-density polyethylene LL x An example of a plant-derived linear low-density polyethylene is plant-derived polyethylene b-PE x It should be noted that the commercially available plant-derived low-density polyethylene b-LD x Examples of such polyethylenes include plant-derived low-density polyethylenes such as SEB853, SPB681, and STN7006 manufactured by Braskem SA.

[0049] Polyethylene X contains polyethylene b-PE from plants x In the case of the foam sheet, from the viewpoint of easily increasing the biomass content, polyethylene b-PE derived from plants x The biomass content measured according to ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0050] In the present invention, the biomass content measured according to ASTM D 6866 refers to the ratio of plant-derived components (naturally derived components) contained in the resin, and is determined by measuring the concentration of radioactive carbon C14 contained in the resin.

[0051] In plant-derived polyethylene (b-PE) x Contains plant-derived low-density polyethylene b-LD xIn the case of the above, polyethylene b-PE derived from plants is preferred because it is easy to obtain a foam sheet with a small environmental load and a good appearance. x Plant-derived low-density polyethylene b-LD x The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0052] Plant-derived low-density polyethylene b-LD x The melting point is preferably 100°C to 115°C, more preferably 102°C to 114°C, and even more preferably 104°C to 112°C. x When the melting point of the foamed layer is within the above range, a foamed layer A having a good cell structure can be stably obtained.

[0053] Plant-derived low-density polyethylene b-LD x The melting point of polyethylene resins such as can be measured in accordance with JIS K 7121-1987. Using a test piece conditioned according to the test piece conditioning (2) conditions (cooling rate 10°C / min) of JIS K 7121-1987, the temperature is raised at 10°C / min to obtain a melting peak, and the temperature at the top of the obtained melting peak is defined as the melting point. It should be noted that when two or more melting peaks appear, the temperature at the top of the melting peak with the largest area is defined as the melting point.

[0054] Plant-derived low-density polyethylene b-LD x The melt flow rate is preferably 0.1 g / 10 min or more and 15 g / 10 min or less, more preferably 0.2 g / 10 min or more and 12 g / 10 min or less, and further preferably 0.3 g / 10 min or more and 10 g / 10 min or less. x The melt flow rate is within the above range, thereby stably and easily producing a desired foamed sheet.

[0055] In addition, plant-derived low-density polyethylene b-LD x The melt flow rate can also exceed 1.0g / 10min. x When the melt flow rate is relatively high, it is difficult to obtain a foam sheet with a low gram weight and good appearance. On the other hand, in the present invention, when using a plant-derived low-density polyethylene b-LD having the above-mentioned melt flow rate, x Even in the case of , a foam sheet with good appearance can be stably produced.

[0056] Plant-derived low-density polyethylene b-LDx The melt flow rates of polyethylene resins are values ​​measured at a temperature of 190° C. and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0057] It should be noted that b-LD is a low-density polyethylene derived from plants. x The melting point or melt flow rate when using multiple plant-derived low-density polyethylenes is determined as follows. First, the resins are melt-kneaded using an extruder or the like at the same proportions as the plant-derived low-density polyethylenes used in the production of the foam layer to prepare a test mixture. Various measurements are then performed on the test mixture, and the obtained melting point or melt flow rate is used as the plant-derived low-density polyethylene b-LD. x Melting point or melt flow rate.

[0058] Plant-derived low-density polyethylene b-LD x The biomass content measured according to ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0059] Plant-derived polyethylene b-PE in Polyethylene X x The total amount Xb of the blending amount is less than 25% by mass (including 0). By making the total amount Xb less than 25% by mass, the low-density polyethylene p-LD derived from petroleum, which is easy to improve the extrusion foaming property, can be blended into the foamable resin melt A. x In addition, by making the total amount Xb of the blending amount less than 25% by mass, the foaming resin melt A and the foaming resin melt B described later are co-extruded to produce a foam sheet with a multilayer structure, thereby being able to obtain a foam sheet with a small load on the environment, a low gram weight and a good appearance. In particular, by making the total amount Xb of the blending amount less than 25% by mass, even in the case of obtaining a foam sheet with a low gram weight, a thin thickness and a low density, a foam sheet with a good appearance can be obtained. From the above viewpoints, the polyethylene b-PE derived from plants in the polyethylene X x The total amount Xb of the compounding amount is more preferably 20 mass % or less (including 0).

[0060] From the viewpoint of easily increasing the biomass content of the foam sheet and reducing the environmental impact, the plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is preferably 2% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0061] [Polyethylene p-PE from petroleum x ]

[0062] Polyethylene X preferably comprises polyethylene p-PE derived from petroleum x As polyethylene p-PE from petroleum x , low-density polyethylene or linear low-density polyethylene derived from fossil fuel resources produced using fossil fuels such as naphtha as raw materials can be used. x Examples of petroleum-derived low-density polyethylene, or the linear low-density polyethylene LL x An example of a petroleum-derived linear low-density polyethylene is petroleum-derived polyethylene p-PE x It should be noted that p-LD, a low-density polyethylene derived from petroleum, x , low-density polyethylene derived from petroleum, which is used in the production of conventional polyethylene resin foams, can be used.

[0063] In polyethylene p-PE from petroleum x Contains low-density polyethylene p-LD derived from petroleum x In the case of the foamable resin melt A, polyethylene p-PE derived from petroleum is easy to improve the extrusion foaming property. x Low-density polyethylene (p-LD) from petroleum x The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0064] Low-density polyethylene p-LD from petroleum x The melting point is preferably 100°C to 115°C, more preferably 102°C to 114°C, and even more preferably 104°C to 112°C. By using a petroleum-derived low-density polyethylene p-LD having a melting point within the above range, x , thereby stably and easily forming a foaming layer A with a good bubble structure, and easily obtaining a foaming sheet with low gram weight and good appearance.

[0065] Low-density polyethylene p-LD from petroleum x The melt flow rate is preferably 0.1 g / 10 min or more and 12 g / 10 min or less, more preferably 0.2 g / 10 min or more and 10 g / 10 min or less. By using a petroleum-derived low-density polyethylene p-LD having a melt flow rate in the above range, x , thereby stably and easily producing the desired foamed sheet.

[0066] Low-density polyethylene p-LD from petroleum x The melting point and melt flow rate of plant-derived low-density polyethylene b-LD xSimilarly, it can be measured by the above-mentioned method for measuring the melting point and melt flow rate of polyethylene resins.

[0067] It should be noted that p-LD, a low-density polyethylene derived from petroleum, x The melting point or melt flow rate when using multiple petroleum-derived low-density polyethylenes is determined as follows. First, the resins are melt-kneaded using an extruder or the like at the same proportions as in the production of the foam layer to prepare a test mixture. Various measurements are then performed on the test mixture, and the obtained melting point or melt flow rate is used as the petroleum-derived low-density polyethylene p-LD. x Melting point or melt flow rate.

[0068] As polyethylene X, low-density polyethylene p-LD derived from petroleum is used x and plant-derived low-density polyethylene b-LD x In the case of the foamable resin melt A, the petroleum-derived low-density polyethylene p-LD x The amount of Xp-LD relative to the plant-derived low-density polyethylene b-LD x The ratio of the amount of Xb-LD to be blended (Xp-LD / Xb-LD) is preferably 2 or more and 5 or less, more preferably 3 or more and 4 or less. By setting the ratio (Xp-LD / Xb-LD) within the above range, a multilayer foam sheet having a reduced environmental load and good appearance in a wide density range can be stably and easily produced.

[0069] In addition, as polyethylene X, low-density polyethylene p-LD derived from petroleum is used. x and plant-derived low-density polyethylene b-LD x and linear low-density polyethylene LL x In the case of plant-derived low-density polyethylene b-LD x and petroleum-derived low-density polyethylene p-LD x The total amount of compounding (Xb-LD + Xp-LD) and the linear low-density polyethylene LL x The mass ratio of the amount of XL (Xb-LD + Xp-LD: XL) is preferably 1:0.05 to 1:0.4, and more preferably 1:0.1 to 1:0.3. By setting the mass ratio (Xb-LD + Xp-LD: XL) within the above range, the biomass content of the foam sheet is increased, and even when a foam sheet with a relatively thin thickness and a low grammage is obtained, it is easy to stably suppress the rupture of bubbles during the extrusion foaming process.

[0070] [Physical foaming agent]

[0071] As the physical foaming agent for forming the foamable resin melt A, an organic physical foaming agent or an inorganic physical foaming agent can be used.

[0072] As organic physical foaming agents, for example, aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, and isohexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; chlorinated hydrocarbons such as methyl chloride and ethyl chloride; fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane; ethers such as dimethyl ether and methyl ethyl ether; and alcohols such as methanol and ethanol can be used.

[0073] As the inorganic physical foaming agent, for example, oxygen, nitrogen, carbon dioxide, air, water, etc. can be used.

[0074] These physical foaming agents may be mixed and used in combination of two or more. Among these, organic physical foaming agents are preferred due to their excellent extrusion foamability and the stability of the multilayer foam sheet during collection, and butane is more preferred. As butane, n-butane, isobutane, or a mixture thereof can be used.

[0075] The amount of the physical foaming agent added can be adjusted according to the type of the physical foaming agent and the target density or grammage of the multilayer foam sheet. For example, when 30% by mass of isobutane and 70% by mass of n-butane are used as the physical foaming agent, the amount of the physical foaming agent added is preferably 3 parts by mass or more and 35 parts by mass or less, more preferably 5 parts by mass or more and 30 parts by mass or less, and even more preferably 6 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the polyethylene resin A.

[0076] [Other additives]

[0077] In addition to the polyethylene resin A and the physical foaming agent, various other additives may be added to the foamable resin melt A. Examples of these other additives include bubble regulators, shrinkage inhibitors, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, and colorants.

[0078] As bubble regulator, inorganic powder or chemical foaming agent can be used. As inorganic powder, talc, zeolite, silicon dioxide, calcium carbonate etc. are exemplified. As chemical foaming agent, azodicarbonamide, hydrazinodicarbonamide, azobisisobutyronitrile, sodium bicarbonate (heavy sodium) or a mixture of sodium bicarbonate and citric acid or citric acid-sodium citric acid monoalkali metal salts, i.e. sodium bicarbonate-citric acid system chemical foaming agent etc. are exemplified. The addition amount of bubble regulator is from the viewpoint of easily stably regulating the bubble diameter of the foaming layer to the desired range, relative to 100 mass parts of polyethylene resin A for forming the foamable resin melt A, preferably 0.01 mass parts or more and 3 mass parts or less, more preferably 0.2 mass parts or more to 2 mass parts.

[0079] Furthermore, other resins or elastomers other than the polyethylene resin A specified in the present invention may be blended as long as they are within a range that can achieve the intended effects of the present invention. When blending other resins or elastomers, the blending amount of the other resins or elastomers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the polyethylene resin A.

[0080] In the process of forming the foamable resin melt A, for example, the polyethylene resin A, the physical foaming agent, and additives as needed are supplied to an extruder for forming the foam layer A. These are then melt-kneaded in the extruder for forming the foam layer A to form the foamable resin melt A.

[0081] <Foamable resin melt B>

[0082] The foamable resin melt B can be formed by melt-kneading the polyethylene resin B and the physical foaming agent. The foamed layer B is formed by foaming the foamable resin melt B.

[0083] The polyethylene resin B in the present invention refers to a resin containing 50 mol% or more of structural units derived from ethylene, similar to the polyethylene resin A. For example, the polyethylene resin B includes polyethylenes such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE); or ethylene-vinyl acetate copolymers (EVA) containing 50 mol% or more of structural units derived from ethylene, or a combination of multiple types.

[0084] The polyethylene resin B used to form the foamable resin melt B comprises a low-density polyethylene LD Y Polyethylene Y, or low-density polyethylene LD Y and linear low-density polyethylene LL Y Polyethylene Y is composed of a mixture of polyethylene Y.

[0085] From the viewpoint of improving the extrusion foamability of the foamable resin melt B, the polyethylene resin B preferably contains polyethylene Y as a main component. Specifically, the proportion of polyethylene Y in the polyethylene resin B is preferably 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 100% by mass, that is, the polyethylene resin B is polyethylene Y.

[0086] [Low density polyethylene LD Y ]

[0087] Low-density polyethylene (LD) used as polyethylene YY It has a long-chain branched structure and a density of 0.910 g / cm 3 Above and less than 0.930g / cm 3 Low-density polyethylene is represented by the abbreviation "PE-LD" in JIS K 6899-1:2015 "Plastics - Symbols and abbreviations - Part 1: Basic polymers and their properties". Y It can also be called high pressure low density polyethylene. Y , examples include plant-derived low-density polyethylene b-LD Y Or low-density polyethylene from petroleum. Low-density polyethylene from plants b-LD Y The details will be described later.

[0088] From the viewpoint of improving the extrusion foaming property of the foamable resin melt B and obtaining a foam sheet with good cushioning properties, the low-density polyethylene LD in the polyethylene Y Y The ratio of low density polyethylene LD Y Compared with low density polyethylene LD Y and linear low-density polyethylene LL Y The ratio of the total 100 mass % is preferably 50 mass % or more, more preferably 60 mass % or more, and further preferably 70 mass % or more.

[0089] It should be noted that the low-density polyethylene LD in the polyethylene Y Y The range of the ratio includes: polyethylene Y is low-density polyethylene LD Y The situation (low density polyethylene LD in polyethylene Y Y The ratio of 100% by mass) is within the range, and the polyethylene Y is a low-density polyethylene LD Y and linear low-density polyethylene LL Y In the case of a mixture of (polyethylene Y is composed of low density polyethylene LD Y and linear low-density polyethylene LL Y Composition, low-density polyethylene LD in polyethylene Y Y The ratio of the linear low-density polyethylene LL is 50% or more by mass Y The ratio is 50% by mass or less).

[0090] [Linear low-density polyethylene LL Y ]

[0091] Linear low-density polyethylene LL used in polyethylene Y YIt is a linear ethylene copolymer that is a copolymer of ethylene and α-olefin. Linear low-density polyethylene is represented by the abbreviation "PE-LLD" in JIS K 6899-1:2015 "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties". Y The density is preferably 0.910 g / cm 3 Above and 0.935g / cm 3 Below, more preferably 0.910 g / cm 3 Above and less than 0.930g / cm 3 .

[0092] As linear low-density polyethylene LL Y The α-olefin used in the foaming process includes α-olefins having 4 to 10 carbon atoms. Examples of α-olefins having 4 to 10 carbon atoms include butene (4 carbon atoms), hexene (6 carbon atoms), and octene (8 carbon atoms). From the perspective of easily improving the rigidity of the foam sheet, it is preferred to use a linear low-density polyethylene LL which is a copolymer of ethylene and octene (8 carbon atoms). c8 Linear low-density polyethylene LL as the main component Y It should be noted that octene includes isomers of octene such as 1-octene and isooctene.

[0093] Linear low-density polyethylene LL Y Linear low-density polyethylene LL c8 The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0094] As linear low-density polyethylene LL Y , can use the linear low density polyethylene from plant or the linear low density polyethylene from oil.These polyethylene can be used in combination of two or more.From the viewpoint of supply stability in the market, can preferably use the linear low density polyethylene from fossil fuel resources (linear low density polyethylene from oil) manufactured using fossil fuel as raw material.

[0095] Linear low-density polyethylene LL Y The melting point of the polyethylene is preferably 116° C. or higher and 130° C. or lower, more preferably 118° C. or higher and 126° C. or lower. By using a linear low-density polyethylene LL having a melting point within the above range, Y , thereby easily suppressing the collapse of bubbles during extrusion foaming, and easily and stably obtaining a foam sheet with a high independent cell ratio.

[0096] Linear low-density polyethylene LL YThe melt flow rate of the linear low-density polyethylene LL is preferably 0.1 g / 10 min or more and 15 g / 10 min or less, more preferably 0.2 g / 10 min or more and 12 g / 10 min or less. Y , thereby easily suppressing the collapse of bubbles during extrusion foaming, and easily and stably obtaining a foam sheet with a high independent cell ratio.

[0097] The melting point and melt flow rate of the linear low-density polyethylene can be measured by the above-mentioned method for measuring the melting point and melt flow rate of polyethylene resins.

[0098] It should be noted that as a linear low-density polyethylene LL Y The melting point or melt flow rate when using multiple linear low-density polyethylenes is determined as follows. First, the linear low-density polyethylenes are melt-kneaded using an extruder or the like at the same proportions as those used in the production of the foam layer to prepare a kneaded product for measurement. Various measurements are then performed on the kneaded product for measurement, and the obtained melting point or melt flow rate is used as the linear low-density polyethylene LL. Y Melting point or melt flow rate.

[0099] In the foamable resin melt B, a linear low-density polyethylene LL is added. Y In the case of (as polyethylene Y, low density polyethylene LD is used Y and linear low-density polyethylene LL Y In the case of a mixture of polyethylene Y and polyethylene LL Y The amount of blending (linear low-density polyethylene LL Y Compared with low density polyethylene LD Y and linear low-density polyethylene LL Y The proportion of the total 100 mass % of the linear low-density polyethylene LL is preferably 5 mass % or more and 30 mass % or less, more preferably 10 mass % or more and 25 mass % or less. Y The compounding amount YL is set within the above-mentioned range, which makes it easy to improve the rigidity of the foam sheet, and even when a foam sheet with a relatively thin thickness and a low gram weight is obtained, it is easy to stably suppress the bursting of bubbles during extrusion foaming.

[0100] [Polyethylene b-PE from plants Y ]

[0101] As polyethylene b-PE from plants Y , and polyethylene b-PE from plants xSimilarly, low-density polyethylene or linear low-density polyethylene produced by polymerizing monomers containing bioethylene produced from plants such as sugar cane, corn, and sugar beets as raw materials can be used. Y Examples of plant-derived low-density polyethylene, or the linear low-density polyethylene LL Y An example of a plant-derived linear low-density polyethylene is plant-derived polyethylene b-PE Y .

[0102] From the perspective of easily increasing the biomass content of the foam sheet, plant-derived polyethylene b-PE Y The biomass content measured according to ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0103] From the perspective of low environmental impact and easy and stable production of foamed sheets with good appearance, plant-derived polyethylene b-PE Y Plant-derived low-density polyethylene b-LD Y The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0104] Plant-derived low-density polyethylene b-LD used as polyethylene Y Y The melting point is preferably 100°C to 115°C, more preferably 102°C to 114°C, and even more preferably 104°C to 112°C. By using plant-derived low-density polyethylene b-LD having a melting point within the above range, Y , so that it is easy to stably form a foam layer B with a good bubble structure, and it is easy to obtain a foam sheet with low gram weight and good appearance.

[0105] Plant-derived low-density polyethylene b-LD Y The melt flow rate is preferably 0.1 g / 10 min or more and 20 g / 10 min or less, more preferably 0.2 g / 10 min or more and 15 g / 10 min or less, further preferably 0.3 g / 10 min or more and 20 g / 12 min or less, and particularly preferably more than 1.0 g / 10 min and 10 g / 10 min or less. By using a plant-derived low-density polyethylene b-LD having a melt flow rate within the above range, Y , it is possible to make the foaming layer A and the foaming layer B well stacked during extrusion foaming, and it is easy to improve the appearance of the foam sheet. In addition, by using a low-density polyethylene b-LD having a melt flow rate in the above range from plant YThe foam layer B is well laminated during extrusion foaming, and the addition efficiency of the physical foaming agent blended into the foamable resin melt A can be improved. By improving the addition efficiency of the physical foaming agent blended into the foamable resin melt A, the foamable resin melt A can be foamed to a low density without excessive blending of the physical foaming agent, thereby suppressing the collapse of bubbles and stably producing a foamed sheet with a good appearance.

[0106] Plant-derived low-density polyethylene b-LD Y Melting point and melt flow rate of plant-derived low-density polyethylene b-LD x In this way, the melting point and melt flow rate of the polyethylene resin can be measured by the same method as above.

[0107] It should be noted that b-LD is a low-density polyethylene derived from plants. Y The melting point or melt flow rate when using multiple plant-derived low-density polyethylenes is determined as follows. First, the respective plant-derived low-density polyethylenes are melt-kneaded using an extruder or the like at the same proportions as used in the manufacture of the foam layer to prepare a test mixture. Various measurements are then performed on the test mixture, and the obtained melting point or melt flow rate is used as the plant-derived low-density polyethylene b-LD. Y Melting point or melt flow rate.

[0108] Plant-derived low-density polyethylene b-LD Y The biomass content measured according to ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0109] Plant-derived polyethylene b-PE in polyethylene Y Y The total amount of Yb in the polyethylene X is the plant-derived polyethylene b-PE x The foamable resin melt A and the foamable resin melt B are formed so that the total amount Xb of the blending amount is less than a specific value and the total amount Yb of the blending amount is greater than the total amount Xb of the blending amount, and a petroleum-derived low-density polyethylene p-LD polymer that is easy to improve extrusion foaming properties is added to the foamable resin melt A. xBy increasing the proportion of the biomass content of the foamed sheet and increasing the proportion of plant-derived polyethylene in the foamable resin melt B, and foaming the foamed sheet by coextrusion, the biomass content of the foamed sheet can be increased, thereby improving extrusion foamability. Thus, even when a foamed sheet with a relatively low grammage is obtained, a foamed sheet with a desired biomass content and a good appearance can be obtained. In particular, even when a foamed sheet with a low grammage, a thin thickness, and a low density is obtained, a foamed sheet with a good appearance can be obtained.

[0110] From the perspective of easily obtaining a foam sheet with a predetermined biomass content, a low basis weight, and a good appearance, polyethylene b-PE derived from plants is Y The total amount of Yb and plant-derived polyethylene b-PE x The difference Yb-Xb between the total amount Xb of the blended materials is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. Furthermore, from the perspective of easily increasing the biomass content of the foam sheet, the difference Yb-Xb between the total amount Yb of the blended materials and the total amount Xb of the blended materials may be 90% by mass or less, or 80% by mass or less.

[0111] Plant-derived polyethylene b-PE in polyethylene Y Y The total amount Yb of the compounding amount is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more, from the viewpoint of easily increasing the biomass content of the foam sheet.

[0112] [Physical foaming agent]

[0113] As the physical foaming agent for forming the foamable resin melt B, the physical foaming agent described as the physical foaming agent for forming the foamable resin melt A can be used.

[0114] From the viewpoint of excellent extrusion foamability and the collection stability of the multilayer foam sheet, it is preferred to use an organic physical foaming agent, and more preferably butane. As butane, n-butane, isobutane, or a mixture thereof can be used.

[0115] The amount of the physical foaming agent added is adjusted according to the type of the physical foaming agent and the target density or grammage of the multilayer foam sheet. For example, when 30% by mass of isobutane and 70% by mass of n-butane are used as the physical foaming agent, the amount of the physical foaming agent added is preferably 3 parts by mass or more and 35 parts by mass or less, more preferably 5 parts by mass or more and 30 parts by mass or less, and even more preferably 6 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the polyethylene resin B.

[0116] [Other additives]

[0117] In addition to the polyethylene resin B and the physical foaming agent, various other additives may be added to the foamable resin melt B. Examples of these other additives include bubble regulators, shrinkage inhibitors, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, and colorants.

[0118] As bubble regulator, inorganic powder or chemical foaming agent can be used. As inorganic powder, talc, zeolite, silicon dioxide, calcium carbonate etc. are exemplified. As chemical foaming agent, azodicarbonamide, hydrazinodicarbonamide, azobisisobutyronitrile, sodium bicarbonate (heavy sodium) or sodium bicarbonate-citric acid system chemical foaming agent etc. as a mixture of alkali metal salts of citric acid such as sodium bicarbonate and citric acid or monosodium citrate are exemplified. The addition amount of bubble regulator is from the viewpoint that the bubble diameter of foaming layer is stably adjusted to the desired range, relative to 100 mass parts of polyethylene resin B for forming foamable resin melt, preferably 0.01 mass parts or more and 3 mass parts or less, more preferably 0.2 mass parts or more to 2 mass parts.

[0119] As long as the intended effects of the present invention can be achieved, other resins or elastomers other than the polyethylene resin B specified in the present invention may be blended. When blending other resins or elastomers, the blending amount of the other resins or elastomers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the polyethylene resin B.

[0120] In the process of forming the foamable resin melt B, for example, the polyethylene resin B, the physical foaming agent, and, if necessary, additives are supplied to an extruder for forming the foam layer B. These are then melt-kneaded in the extruder for forming the foam layer B to form the foamable resin melt B.

[0121] [Melt flow rate ratio (b-LD Y / p-LD x )]

[0122] From the perspective of easily obtaining the desired foam sheet, plant-derived low-density polyethylene b-LD Y The melt flow rate of p-LD polyethylene is relatively low compared to that of petroleum-derived low-density polyethylene. x The ratio of the melt flow rate (b-LD Y / p-LD x ) is preferably 0.1 or more and 30 or less, more preferably 1 or more and 25 or less.

[0123] [Melting point difference (T_p-LD x -T_b-LD Y) ]

[0124] From the perspective of improving extrusion stability, petroleum-derived low-density polyethylene p-LD x Melting point T_p-LD x With plant-derived low-density polyethylene b-LD Y Melting point T_b-LD Y The difference (T_p-LD x -T_b-LD Y ) is preferably within 5°C, more preferably within 3°C.

[0125] The foam sheet having the desired gram weight can be obtained mainly by adjusting the collection speed of the foam sheet, the discharge amount of the foaming resin melt A and the foaming resin melt B, the blowing ratio (expansion ratio) of the foam sheet, etc. during the manufacture of the foam sheet.

[0126] Specifically, the blow-up ratio (Blow-up Ratio) of the tubular laminated foam extruded by an extruder is preferably set to more than 2.0 and less than 4.5, more preferably set to more than 2.1 and less than 4.0. It should be noted that blow-up ratio refers to the ratio (blow-up ratio: the lip diameter of the diameter / annular die of the diameter of the mandrel) of the diameter of annular die. In addition, the collection speed of the tubular laminated foam extruded by an extruder is preferably set to less than 120m / minutes of more than 10m / minutes, more preferably set to less than 100m / minutes of more than 20m / minutes.

[0127] The total discharge rate of the foamable resin melt A and the foamable resin melt B extruded by the extruder varies depending on the size of the extruder or the desired widthwise length of the foamed sheet, but is preferably 50 kg / hr to 300 kg / hr, more preferably 60 kg / hr to 260 kg / hr. Furthermore, the ratio of the discharge rate of the foamable resin melt B to the discharge rate of the foamable resin melt A is preferably 0.01 to 5, more preferably 0.1 to 2.

[0128] It should be noted that when the foamable resin melt A forms multiple layers, the total discharge amount of these foamable resin melts A is set as the discharge amount of the foamable resin melt A. When the foamable resin melt B forms multiple layers, the total discharge amount of these foamable resin melts B is set as the discharge amount of the foamable resin melt B.

[0129] It is preferable to co-extrude the foamable resin melt A and the foamable resin melt B so that the mass ratio of the foamable layer B to the foamable layer A (foamable layer B / foamable layer A) is 0.1 or more and 2 or less.

[0130] By satisfying the relationship between the above-mentioned foamable resin melt A and the above-mentioned foamable resin melt B, and co-extruding the above-mentioned foamable resin melt A and the above-mentioned foamable resin melt B with the above-mentioned mass ratio, the biomass content can be increased, and a foam sheet with a thin thickness, a small gram weight, and a good appearance can be stably manufactured. In addition, by satisfying the relationship between the above-mentioned foamable resin melt A and the above-mentioned foamable resin melt B, and co-extruding the above-mentioned foamable resin melt A and the above-mentioned foamable resin melt B with the above-mentioned mass ratio, in particular, by laminating the foaming layers of one on both sides of the foaming layer of the other, the addition efficiency of the physical foaming agent in the foamable resin melt used to form the foaming layer located in the center of the thickness direction can be further improved. As a result, a foam sheet with a low gram weight, a thin thickness, a low density, a high independent bubble rate, and an excellent appearance can be manufactured more stably.

[0131] From the perspective of imparting the desired biomass content and easily and stably producing a multi-layer foam sheet with a low grammage and excellent appearance, the mass ratio of the foam layer B to the foam layer A (foam layer B / foam layer A) is more preferably greater than 0.2 and less than 1, and further preferably greater than 0.3 and less than 0.8.

[0132] It should be noted that, when the foam layer A is formed into a plurality of layers, the total grammes of these foam layers A is taken as the gramme of the foam layer A, and when the foam layer B is formed into a plurality of layers, the total grammes of these foam layers B is taken as the gramme of the foam layer B. Therefore, the mass ratio of the foam layer B to the foam layer A can be calculated as, for example, the ratio of the total grammes of the foam layers B to the total grammes of the foam layers A.

[0133] The weight of each foaming layer [g / m 2 ] can be obtained by substituting the discharge amount X [g / hour] of each foaming layer during the manufacture of the foam sheet, the width W [m] of the obtained foam sheet, and the length L [m / hour] of the foam sheet extruded per unit time into the following formula (1). It should be noted that, when each foaming layer is formed into multiple layers, the total discharge amount of the corresponding foaming layers is taken as the discharge amount of each foaming layer, and the gram weight of each foaming layer is calculated.

[0134] The weight of each foaming layer [g / m 2 ]=〔X / (L×W)〕(1)

[0135] The weight of the foam layer A is preferably 5g / m 2 Above and 90g / m2 Below, more preferably 10g / m 2 Above and 60g / m 2 the following.

[0136] In addition, the weight of the foam layer B is preferably 5g / m 2 Above and 90g / m 2 Below, more preferably 10g / m 2 Above and 60g / m 2 the following.

[0137] According to the production method described above, it is possible to provide a foam sheet that has a small environmental impact, a small basis weight, and an excellent appearance.

[0138] Here, when foam sheet is manufactured by extrusion foaming, if it is desired to obtain a foam sheet with a low gram weight, it is difficult to manufacture the foam sheet. In particular, if it is desired to obtain a foam sheet with a low gram weight, a thin thickness and a low density, this trend is greater.

[0139] On the other hand, since polyethylene derived from plants has fewer types of resins to choose from than polyethylene derived from petroleum, there is a tendency for the manufacturing freedom of foam sheets to decrease. Therefore, in order to obtain a foam sheet having the desired physical properties such as gram weight and the desired biomass content, a single-layer foam sheet is sometimes manufactured by combining polyethylene derived from plants and polyethylene derived from petroleum. In this case, if you want to obtain a foam sheet with a high biomass content, it is sometimes difficult to manufacture the desired foam sheet. In particular, when obtaining a foam sheet with a low gram weight, a thin thickness and a low density, there is a tendency for the bubbles in the foam to burst easily during extrusion foaming. Therefore, even if the obtained foam sheet is maintained, the influence of shrinkage caused by the loss of the foaming agent cannot be eliminated, and sometimes the foam sheet will have residual wrinkles.

[0140] In contrast, in the manufacturing method of the present invention, a relatively large amount of polyethylene from petroleum is included, a specific foaming layer A is provided, and relative to the polyethylene from petroleum included in the foaming layer A, the amount of polyethylene from plants included in the foaming layer B is increased, and the foam sheet of the multilayer structure is co-extruded and manufactured. The foam sheet of the multilayer structure is formed by coextrusion, so that the extrusion conditions such as the extrusion temperature when each foamable resin melt is extruded and foamed become easy to stabilize, and the foam sheet can be easily and stably manufactured. On this basis, the biomass content in the foam sheet as a whole is ensured by the foaming layer B, and the foaming layer A with a high proportion of low-density polyethylene from petroleum, etc., which is easy to improve the extrusion foamability, is suppressed. The rupture of the bubbles of the foamed body during extrusion foaming is suppressed, and a foam sheet with a desired foamed state is easily formed. As a result, a foam sheet with a small load on the environment, a small gram weight, and a good appearance can be obtained.

[0141] (2) Foam sheet

[0142] The present invention comprises a polyethylene resin foam sheet having a gram weight of 100 g / m 2 A polyethylene resin foam sheet having a biomass content of 5% or more as measured in accordance with ASTM D 6866, the foam sheet comprising a polyethylene resin foam layer A and a polyethylene resin foam layer B, the polyethylene resin foam layer A comprising polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene resin foam layer B comprising polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene b-PE in the polyethylene X being a plant-derived polyethylene x The total amount Xb of the compounding amount is less than 25 mass% (including 0), and the plant-derived polyethylene b-PE in the polyethylene Y Y The total amount of Yb in the polyethylene X is the plant-derived polyethylene b-PE x The total amount of compounding is Xb more.

[0143] Such a foam sheet has a specific foam layer A, and the foam layer A and the foam layer B satisfy a specific relationship, thereby becoming a multilayer foam sheet with reduced environmental impact, a small basis weight, and a good appearance. Such a polyethylene resin foam sheet can be preferably produced by the above-mentioned production method.

[0144] In the foam sheet of the present invention, the foam layer A comprises at least one layer, and the foam layer B comprises at least one layer. A schematic diagram of a preferred laminated form of the foam sheet (a cross section in the thickness direction of the foam sheet of the present embodiment) is shown in FIG. Figure 1 . Figure 1 The foam sheet (a) has a configuration comprising a foam layer B and foam layers A laminated and bonded on both surfaces of the foam layer B (a configuration in which the foam layer B is sandwiched between two foam layers A). Figure 1 The foam sheet (b) has a configuration comprising a foam layer A and foam layers B laminated and bonded on both surfaces of the foam layer A (a configuration in which the foam layer A is sandwiched between two foam layers B). Figure 1 (c) is a structure having a foam layer A and a foam layer B laminated and bonded on one surface of the foam layer A.

[0145] From the viewpoint of easily obtaining a foam sheet with a low basis weight and good appearance, the foam sheet is preferably a multilayer foam sheet having a foam layer B and foam layers A laminated and bonded to both surfaces of the foam layer B.

[0146] It should be noted that, in the foam sheet of the present invention, as long as it is within the scope of the intended purpose of the present invention, layers other than the foam layer A and the foam layer B may be further laminated. For example, an antistatic foam sheet having an antistatic layer laminated on one or both sides of a multilayer foam sheet having one or more foam layers A and one or more foam layers B may be used. In this case, the antistatic layer can be composed of, for example, a polyethylene resin composition obtained by mixing the polyethylene resin described above with a known polymer antistatic agent used in the manufacture of an existing antistatic foam sheet having an antistatic layer.

[0147] <Foaming layer A>

[0148] The foam layer A comprises a low density polyethylene LD x Polyethylene X, or low-density polyethylene LD x and linear low-density polyethylene LL x Polyethylene X is a mixture of polyethylene X and low-density polyethylene LD used as polyethylene X. x And linear low-density polyethylene LL x , it is possible to appropriately refer to the description of the polyethylene X in the foamable resin melt A, or the low-density polyethylene LD used as the polyethylene X in the foamable resin melt A. x And linear low-density polyethylene LL x Description.

[0149] From the perspective of obtaining a foam sheet with a small basis weight and good cushioning properties, the low-density polyethylene LD in the foam layer A x The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0150] Plant-derived polyethylene b-PE in Polyethylene X x The total amount of Xb is less than 25% by mass (including 0). The foam sheet having such a foam layer A and a foam layer B described later has a small environmental impact, is thin and has a low grammage, and has a good appearance. From this point of view, the plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is more preferably 20 mass % or less (including 0).

[0151] From the viewpoint of easily obtaining a foam sheet with high cushioning properties, the foam layer A contains a petroleum-derived low-density polyethylene p-LD x , the petroleum-derived low-density polyethylene p-LD in the foam layer A x The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0152] From the viewpoint of easily increasing the biomass content of the foam sheet and reducing the environmental impact, the plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is preferably 2% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0153] It should be noted that for polyethylene p-PE derived from petroleum x or polyethylene b-PE from plants x , can appropriately refer to the petroleum-derived polyethylene p-PE in the foamable resin melt A x or polyethylene b-PE from plants x Description.

[0154] <Foaming layer B>

[0155] The foam layer B comprises a low density polyethylene LD Y Polyethylene Y or low-density polyethylene LD Y and linear low-density polyethylene LL Y Polyethylene Y composed of a mixture of polyethylene Y and low-density polyethylene LD used as polyethylene Y. Y And linear low-density polyethylene LL Y The polyethylene Y in the foamable resin melt B and the low-density polyethylene LD used as the polyethylene Y can be appropriately referred to. Y And linear low-density polyethylene LL Y Description.

[0156] From the perspective of obtaining a foam sheet with a small gram weight and good cushioning properties, the low-density polyethylene LD in the foam layer B Y The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0157] Plant-derived polyethylene b-PE in polyethylene Y Y The total amount of Yb in the polyethylene X is the plant-derived polyethylene b-PE x The total amount Xb of the compounding amount is large. The foam sheet having such foam layer B and foam layer A has a predetermined biomass content and a good appearance even when it is made into a foam sheet with a low basis weight.

[0158] From the perspective of easily obtaining a foamed sheet with a predetermined biomass content, a low basis weight, and a good appearance, plant-derived polyethylene b-PE Y The total amount of Yb and plant-derived polyethylene b-PE xThe difference Yb-Xb between the total amount Xb of the blended foam sheet is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and particularly preferably 50% by mass or more. Furthermore, from the perspective of easily increasing the biomass content of the foam sheet, the difference (Yb-Xb) between the total amount Yb of the blended foam sheet and the total amount Xb of the blended foam sheet may be 90% by mass or less, or 80% by mass or less.

[0159] From the viewpoint of easily increasing the biomass content of the foam sheet, the plant-derived polyethylene b-PE in the polyethylene Y Y The total amount of Yb blended is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0160] From the viewpoint of easily and stably obtaining a foam sheet having a small environmental impact and a good appearance, the plant-derived low-density polyethylene b-LD in the foam layer B Y The ratio is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0161] It should be noted that polyethylene p-PE from petroleum Y or polyethylene b-PE from plants Y , can appropriately refer to the petroleum-derived polyethylene p-PE in the foamable resin melt B Y or polyethylene b-PE from plants Y Description.

[0162] (3) Physical properties of foam sheets

[0163] <Weight>

[0164] The weight of the foam sheet is 100g / m 2 If the gram weight is within the above range, it becomes a low-gram weight foam sheet, which can be preferably used as a buffer material for logistics. From the perspective of making a lighter foam sheet, the gram weight of the foam sheet is more preferably 90g / m 2 Below, more preferably 80g / m 2 The following is required. It should be noted that the basis weight of the foam sheet can be determined by measuring the area (m2) of the foam sheet cut into a predetermined size (for example, 1000 mm × 250 mm). 2 ) and mass (g), divide the mass (g) by the area (m 2 ) and find out.

[0165] The mass ratio of the foam layer B to the foam layer A (foam layer B / foam layer A) is preferably greater than 0.1 and less than 2, more preferably greater than 0.2 and less than 1, and further preferably greater than 0.3 and less than 0.8, from the viewpoint of increasing the biomass content, achieving a thin thickness, a small gram weight, and a good appearance.

[0166] It should be noted that the grammage of each foam layer can be determined, for example, from the relationship between the discharge amount X of each foam layer during the manufacture of the foam sheet, the width W [m] of the resulting foam sheet, and the length L [m / hour] of the foam sheet extruded per unit time, as described above. Alternatively, for example, the grammage of each foam layer can be determined by multiplying the thickness of each foam layer by the density of the resin composition constituting each foam layer and performing unit conversion.

[0167] <Thickness>

[0168] The average thickness of the foam sheet is preferably from 0.05 mm to 5 mm. By setting the thickness of the foam sheet within this range, it can be preferably used in various cushioning applications, such as logistics cushioning materials. Furthermore, when used as a backing paper for plate-like objects, it can improve loading efficiency. The average thickness of the foam sheet is preferably less than 2 mm, and more preferably 1 mm or less.

[0169] The average thickness of the foam sheet can be obtained by measuring the total width of the foam sheet in the width direction orthogonal to the extrusion direction of the foam sheet at intervals of 1 cm and averaging the measured thicknesses. The thickness can be measured using an offline thickness measuring machine "TOF-4R" manufactured by Yamabun Electronics Co., Ltd. It should be noted that the foam sheet used in the measurement is a foam sheet that has been conditioned for more than 24 hours at a temperature of 23 ± 5 ° C and a relative humidity of 50%.

[0170] Density

[0171] The density of the foam sheet is preferably 300 kg / m 3 By setting the density of the foam sheet to the above range, a lightweight foam sheet with excellent cushioning properties can be obtained, which can be used more preferably as a buffer material for logistics. From the above viewpoints, the density of the foam sheet is preferably 10 kg / m 3 Above and 200kg / m 3 Below, more preferably 12kg / m 3 Above and 100kg / m 3 Below, more preferably 15kg / m 3 Above and 80kg / m 3 the following.

[0172] The density of the foam sheet can be calculated by the gram weight (g / m 2 ) divided by the average thickness of the foam sheet, further expressed as (kg / m 3 ) and convert the units to obtain the value.

[0173] Furthermore, when a foam sheet is formed having a foam layer A and foam layers B laminated and bonded on both surfaces of the foam layer A, the ratio of the density of the foam layer B to the density of the foam layer A can be set to 1 or more and 10 or less, or even 2 or more and 5 or less. In this case, the foam layer A, which is easily extruded and foamed, can be foamed at a relatively high ratio, while the foam layer B located on the surface side can be formed at a relatively low ratio. Therefore, the overall density of the foam sheet can be set to a low level, resulting in a multilayer foam sheet with excellent surface properties.

[0174] Furthermore, when a foam sheet is prepared having a foam layer B and a foam layer A laminated and bonded on both surfaces of the foam layer B, the ratio of the density of the foam layer B to the density of the foam layer A can be set to be greater than 1 and less than 10. In this case, the foam layer A, which is easily extruded and foamed, can be foamed at a relatively high ratio and positioned on the surface side, thereby obtaining a multilayer foam sheet having a low overall density and a relatively soft surface portion.

[0175] Furthermore, when a foam sheet is formed having a foam layer B and a foam layer A laminated and bonded onto both surfaces of the foam layer B, the density of the foam layer B can be set lower than the density of the foam layer A. In this case, the foam layer B can be foamed at a relatively high ratio, and the foam layer A, which is easily extruded and foamed, can be positioned on the surface side, thereby obtaining a multilayer foam sheet having a low overall density and excellent surface properties.

[0176] Biomass content

[0177] The biomass content of the foam sheet, as measured according to ASTM D 6866, is 5% or greater. From the perspective of further reducing the environmental impact, the biomass content of the foam sheet is preferably 10% or greater, more preferably 15% or greater, even more preferably 20% or greater, and particularly preferably 25% or greater. Alternatively, the biomass content of the foam sheet may be 60% or less, 50% or less, 45% or less, or even 40% or less.

[0178] Biomass content D of foam layer A measured according to ASTM D 6866 A It is preferably less than 25% (including 0), and more preferably 20% or less. In addition, the biomass content D of the foamed layer B measured according to ASTM D 6866 is B It is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more.

[0179] Biomass content D of foam layer B B and the biomass content D of the foaming layer A A The difference (D B -D A ) is preferably 20% or more, more preferably 25% or more, and further preferably 30% or more. B -D A ) is within the above-mentioned range, thereby easily obtaining a foam sheet with increased biomass content, low gram weight, and good appearance.

[0180] The biomass content of the foam sheet or each foam layer can be determined by measuring the concentration of radioactive carbon in the foam sheet or each foam layer according to ASTM D 6866. Alternatively, the biomass content can be determined based on the plant-derived low-density polyethylene (b-LDPE) used in the production of the foam sheet. x , b-LD Y ) and the biomass content measured according to ASTM D 6866 and the blending ratio of the plant-derived low-density polyethylene in each foaming layer.

[0181] <Gel ratio of foam sheet>

[0182] The foam sheet of the present invention is preferably non-crosslinked.

[0183] It should be noted that when a low-weight and non-crosslinked polyethylene resin foam sheet is produced by using polyethylene from plants instead of a crosslinking agent, the foam tends to shrink during the production of the foam, making it difficult to obtain a polyethylene resin foam sheet with a good appearance. On the other hand, in the present invention, the foam sheet is produced by the above-mentioned production method as a multilayer foam sheet in which the foam layer A and the foam layer B are laminated and bonded, thereby being able to produce a polyethylene resin foam sheet having a specified biomass content, a low weight, and further an excellent appearance.

[0184] From this perspective, the gel fraction of the foam sheet is preferably 5% or less (including 0), more preferably 3% or less (including 0), even more preferably 2% or less (including 0), even more preferably 1% or less (including 0), and particularly preferably 0. When the gel fraction of the foam sheet satisfies the above range, the sheet becomes a non-crosslinked foam sheet that does not substantially form a crosslinked structure, resulting in a foam sheet with excellent recyclability. The gel fraction can be measured by the following method.

[0185] First, approximately 50 mg of the foam sheet was immersed in 25 mL of xylene at 130°C for 3 hours, then filtered through a 200-mesh stainless steel mesh and washed with acetone. The insoluble matter remaining on the mesh was then vacuum-dried. The mass of the insoluble matter was then precisely weighed, and the gel fraction was calculated as a percentage using the following formula (2).

[0186] Gel fraction (%) = {mass of insoluble components (mg) / weighed mass of foam (mg)} × 100 (2)

[0187] <Independent bubble ratio>

[0188] The closed cell fraction of the foam sheet is preferably 40% by mass or greater, more preferably 50% or greater, and even more preferably 60% or greater. A closed cell fraction within the above range makes it easier to obtain a foam sheet with excellent appearance. Furthermore, the foam sheet can be given appropriate rigidity, making it less prone to sagging.

[0189] Regarding the independent bubble rate, a slice sample randomly cut into 25mm×25mm×sheet thickness (thickness of the foam sheet) from the foam sheet is prepared. Multiple slice samples are overlapped in such a way that the total sheet thickness is closest to 20mm as a test piece. Then, according to step C of ASTM-D2856-70, an air comparison type densitometer 930 type of Toshiba Beckman Co., Ltd. is used to measure the true volume Vx of the test piece, and the independent bubble rate S (%) is calculated by the following formula (3). The above measurement is carried out using 5 test pieces, and the arithmetic average thereof is taken as the independent bubble rate of the foam sheet.

[0190] S(%)=(Vx-W / ρ)×100 / (Va-W / ρ) (3)

[0191] Vx: The actual volume of the test piece measured using the above method (cm 3 ), which is equivalent to the sum of the volume of the resin constituting the foam sheet and the total volume of the bubbles in the independent bubble part in the test piece.

[0192] Va: Apparent volume of the test piece calculated from the external dimensions of the test piece used for measurement (cm 3 ).

[0193] W: total mass of the slice sample used in the measurement (g).

[0194] ρ: Density of the resin composition constituting the foam sheet (g / cm 3 ).

[0195] [Example]

[0196] The present invention will be described in more detail below with reference to the following examples, but the present invention is not limited to these examples.

[0197] The following apparatuses were used in Examples and Comparative Examples.

[0198] In the manufacture of the foam sheet of embodiment, first, as the extruder used for foaming layer A formation, the first extruder of barrel internal diameter 90mm is prepared.On the downstream side of this extruder, coextrusion annular die is installed, and the mandrel (cooling tube) of diameter 380mm is configured on the downstream side of annular die.In addition, as the extruder used for foaming layer B formation, the second extruder of barrel internal diameter 65mm is prepared, and the downstream side and the coextrusion annular die of the second extruder are connected.The extrusion device prepared in this way is used for the manufacture of foam sheet.

[0199] In the manufacture of the foam sheet of the comparative example, a first extruder with a barrel inner diameter of 90 mm was prepared as an extruder for forming the foam layer. An annular die was installed on the downstream side of the extruder, and a mandrel (cooling tube) with a diameter of 380 mm was configured on the downstream side of the annular die. The extruder thus prepared was used for the manufacture of the foam sheet.

[0200] Table 1 shows the details of the polyethylene resins used in the Examples and Comparative Examples. The biomass content is measured according to ASTM D 6866. The melt flow rate is measured according to JIS K7210-1:2014 at 190°C and a load of 2.16 kg. The melting point is measured according to JIS K7121-1987.

[0201] [Table 1]

[0202]

[0203] Table 2 shows the raw material blends involved in the production of the foamed sheets of Examples and Comparative Examples, and the physical properties of the foamed sheets obtained in each of the Examples and Comparative Examples.

[0204]

[0205] The foamed sheets of Examples were produced as follows using the above-mentioned extruder.

[0206] To form the foam layer A, 100 parts by mass of the polyethylene resin A shown in Table 2 and 1 part by mass of talc (HI-FILLER #12, manufactured by Matsumura Sangyo Co., Ltd.) as a cell control agent were fed to a first extruder, heated, melted, and kneaded to produce a resin melt. Next, a physical foaming agent (isobutane) was press-fed into the resin melt to produce the foam layer A of the desired density, followed by further kneading. The temperature was then adjusted to approximately 200°C to produce a foamable resin melt A. The amount of the physical foaming agent in the foamable resin melt A was adjusted to a range of 10% to 16% by mass.

[0207] Next, the temperature of the foamable resin melt A was adjusted to approximately 112°C on the downstream side of the extruder.

[0208] Separately, to form the foamed layer B, the polyethylene resin B listed in Table 2 and 1 part by mass of talc (HI-FILLER #12, manufactured by Matsumura Sangyo Co., Ltd.) as a cell control agent were fed to a second extruder, heated, melted, and kneaded to produce a resin melt. Next, a physical foaming agent (isobutane) was pressurized into this resin melt to form the foamed layer B of the desired density. After further kneading, the temperature was adjusted to approximately 200°C to produce a foamed resin melt B. The amount of the physical foaming agent in the foamed resin melt B was adjusted within a range of 10% to 16% by mass.

[0209] Next, the temperature of the foamable resin melt B was adjusted to about 112°C on the downstream side of the extruder.

[0210] The foamable resin melt A and the foamable resin melt B are stacked in a coextrusion annular die and extruded from the coextrusion annular die into the atmosphere to foam the foamable resin melt A and the foamable resin melt B, thereby forming a multilayer foam.

[0211] The multi-layer foam is expanded using a tubular expansion device (mandrel) and collected using a puller to a specified thickness, grammage, and density. The multi-layer foam is further cut along the extrusion direction to produce a foam sheet of the embodiment shown in Table 2 with a width of approximately 1.3 m.

[0212] In Examples 1 to 3, a laminated structure was formed in which foamable resin melt A was laminated on both sides of foamable resin melt B (hereinafter referred to as "foamable resin melt A / foamable resin melt B / foamable resin melt A"). Specifically, the total discharge rate of foamable resin melt A and foamable resin melt B was set to 120 kg / hr, the discharge rate ratio of foamable resin melt B to foamable resin melt A was set to 0.50 (foamable resin melt A: foamable resin melt B: foamable resin melt A = 1:1:1), and the collection speed was set to 51 m / min to produce a foam sheet, thereby obtaining a multilayer foam sheet having foam layer A on both sides of foam layer B ( Figure 1 (a) stacked morphology).

[0213] In Example 4, a laminated structure of foamable resin melt A / foamable resin melt B / foamable resin melt A was formed, the total discharge rate of foamable resin melt A and foamable resin melt B was set to 120 kg / hr, the discharge rate ratio of foamable resin melt B to foamable resin melt A was set to 1.0 (foamable resin melt A:foamable resin melt B:foamable resin melt A=1:2:1), and the take-up speed was set to 38 m / min to produce a foam sheet, thereby obtaining a multilayer foam sheet having foam layer A on both sides of foam layer B ( Figure 1 (a) stacked morphology).

[0214] In Example 5, a laminated structure of foamable resin melt A / foamable resin melt B / foamable resin melt A was obtained. Specifically, the total discharge rate of foamable resin melt A and foamable resin melt B was set to 120 kg / hr, the discharge rate ratio of foamable resin melt B to foamable resin melt A was set to 1.5 (foamable resin melt A:foamable resin melt B:foamable resin melt A=1:3:1), and the take-up speed was set to 31 m / min to produce a foam sheet, thereby obtaining a multilayer foam sheet having foam layer A on both sides of foam layer B ( Figure 1 (a) stacked morphology).

[0215] In Example 6, a laminated structure was formed in which foamable resin melt B was laminated on both sides of foamable resin melt A (hereinafter referred to as "foamable resin melt B / foamable resin melt A / foamable resin melt B"). Specifically, the total discharge rate of foamable resin melt A and foamable resin melt B was set to 120 kg / hr, the discharge rate ratio of foamable resin melt B to foamable resin melt A was set to 0.67 (foamable resin melt B:foamable resin melt A:foamable resin melt B=1:3:1), and the collection speed was set to 31 m / min to produce a foam sheet, thereby obtaining a multilayer foam sheet having foam layers B on both sides of foam layer A ( Figure 1 (b) stacked morphology).

[0216] In Example 7, a laminated structure was formed in which the foamable resin melt B was laminated on one side of the foamable resin melt A (hereinafter referred to as "foamable resin melt A / foamable resin melt B"), the total discharge rate of the foamable resin melt A and the foamable resin melt B was set to 120 kg / hr, the discharge rate ratio of the foamable resin melt B to the foamable resin melt A was set to 0.83 (foamable resin melt A:foamable resin melt B=1:0.83), and the take-up speed was set to 70 m / min to produce a foam sheet, thereby obtaining a multilayer foam sheet having the foam layer B on one side of the foam layer A ( Figure 1 (c) stacked morphology).

[0217] A single-layer foam sheet of the comparative example was produced in the same manner as in Example 1 except that the foaming resin melt A having the raw material composition shown in Table 2 was extruded using the above-mentioned extruder to form only a single foam layer.

[0218] For the multilayer foam sheets obtained in each example and the single-layer foam sheets obtained in the comparative examples, the average thickness, gram weight, density, independent cell ratio, and biomass content were calculated. It should be noted that the foam sheets obtained in the examples and comparative examples were non-crosslinked foam sheets.

[0219] <Average thickness>

[0220] The average thickness of the foam sheet is determined by measuring the total width of the foam sheet in the width direction perpendicular to the extrusion direction at 1 cm intervals and taking the arithmetic average of the measured thicknesses. The thickness is measured using an off-line thickness gauge, such as the "TOF-4R," manufactured by Yamamoto Electric Co., Ltd. The foam sheet used in the measurement was conditioned at a temperature of 23±5°C and a relative humidity of 50% for at least 24 hours.

[0221] <Weight>

[0222] The basis weight of the entire foam sheet was measured by measuring the area (m2) of the foam sheet cut out to a predetermined size (1000 mm × 250 mm). 2 ) and mass (g), divide the mass (g) by the area (m 2 ) and calculate the gram weight (g / m 2 ).

[0223] Regarding the grammage of each foaming layer, the grammage of the entire foaming sheet is calculated from the relationship between the discharge amount X [g / hour] of each foaming layer during the manufacture of the foaming sheet, the width W [m] of the obtained foaming sheet, and the length L [m / hour] of the foaming sheet extruded per unit time using the following formula (1), and is calculated from the relationship between the grammage of the entire foaming sheet and the discharge amount of each foaming layer.

[0224] The total weight of the resin layer [g / m 2 ]=〔X / (L×W)〕(1)

[0225] Density

[0226] Regarding the density of the foam sheet, the gram weight of the foam sheet (g / m 2 ) divided by the average thickness of the foam sheet, further expressed as (kg / m 3 ) and convert the units.

[0227] <Independent bubble ratio>

[0228] The independent bubble rate of the foam sheet is measured as follows. First, prepare a slice sample randomly cut from the foam sheet into 25 mm × 25 mm × sheet thickness (thickness of the foam sheet). Overlap multiple slice samples in such a way that the total sheet thickness is closest to 20 mm as a test piece. Then, according to step C of ASTM-D2856-70, use an air comparison type densitometer 930 type of Toshiba Beckman Co., Ltd. to measure the true volume Vx of the test piece, and calculate the independent bubble rate S (%) by the following formula (3). The above measurement is performed using 5 test pieces, and the arithmetic average thereof is taken as the independent bubble rate of the foam sheet.

[0229] S(%)=(Vx-W / ρ)×100 / (Va-W / ρ) (3)

[0230] Vx: The actual volume of the test piece measured using the above method (cm 3 ), which is equivalent to the sum of the volume of the resin constituting the foam sheet and the total volume of the bubbles in the independent bubble part in the test piece.

[0231] Va: Apparent volume of the test piece calculated from the external dimensions of the test piece used for measurement (cm 3 ).

[0232] W: total mass of the slice sample used in the measurement (g).

[0233] ρ: Density of the resin constituting the foam sheet (g / cm 3 ).

[0234] Biomass content

[0235] The biomass content is calculated from the biomass content measured according to ASTM D6866 of the plant-derived polyethylene used in producing the foam sheet and the blending ratio of the plant-derived polyethylene in each foam layer.

[0236] The appearance of the foamed sheets of Examples and Comparative Examples was evaluated as follows. The results are shown in Table 2.

[0237] <Appearance>

[0238] As an evaluation of the appearance of the obtained foamed sheet, the occurrence of wrinkles in the surface layer portion of each surface of the foamed sheet was evaluated from the following viewpoints.

[0239] A: Almost no wrinkles were observed on the foam sheet on each side, and the foam sheet had a good appearance.

[0240] B: Many wrinkles were observed on at least one surface of the foam sheet.

[0241] Note that "A" in the above evaluation indicates a good appearance. Furthermore, wrinkles appearing in "B" are believed to be caused by the rupture of foam cells during extrusion. It is believed that even with curing of the foam, the effects of shrinkage associated with loss of the blowing agent cannot be eliminated due to the rupture of the foam cells, resulting in the remaining wrinkles.

[0242] The comparative example, which is a single-layer foam sheet, has a poor appearance. Furthermore, the closed cell ratio of the foam sheet is lower than that of the multilayer foam sheet of the example. In contrast, the foam sheet of the example has a good appearance. Furthermore, the foam sheet of the example has a higher closed cell ratio than that of the comparative example.

Claims

1. A method for producing a polyethylene resin foam sheet having a gram weight of 100 g / m 2 The following method is used to prepare a polyethylene resin foam sheet having a biomass content of 5% or more as measured according to ASTM D6866, wherein: The foam sheet is a multi-layer foam sheet in which a polyethylene resin foam layer A and a polyethylene resin foam layer B are laminated and bonded. The foam layer A and the foam layer B are formed by co-extruding a foaming resin melt for forming the foam layer A obtained by kneading a polyethylene resin A and a physical foaming agent, and a foaming resin melt for forming the foam layer B obtained by kneading a polyethylene resin B and a physical foaming agent. The polyethylene resin A comprises polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene, The polyethylene resin B comprises polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene, Plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is less than 25 mass % and includes 0, The polyethylene b-PE in the polyethylene Y is derived from plants Y The total amount of Yb in the polyethylene X is greater than the plant-derived polyethylene b-PE x The total amount of compounding is Xb more.

2. The method for producing a polyethylene resin foam sheet according to claim 1, wherein The polyethylene b-PE of plant origin is determined according to ASTM D 6866 x The biomass content is more than 80%, The polyethylene b-PE of plant origin is determined according to ASTM D 6866 Y The biomass content is more than 80%.

3. The method for producing a polyethylene resin foam sheet according to claim 1 or 2, wherein: The plant-derived polyethylene b-PE Y The total amount of Yb and the plant-derived polyethylene b-PE x The difference Yb-Xb between the total Xb of the blending amount is 20 mass % or more.

4. The method for producing a polyethylene resin foam sheet according to claim 1 or 2, wherein: The ratio of the gram weight of the foam layer B to the gram weight of the foam layer A is 0.1 or more and 2 or less.

5. The method for producing a polyethylene resin foam sheet according to claim 1 or 2, wherein: The thickness of the foam sheet is less than 2 mm.

6. A polyethylene resin foam sheet having a gram weight of 100 g / m 2 The following polyethylene resin foam sheet having a biomass content of 5% or more as measured according to ASTM D6866, wherein: The foam sheet is a multi-layer foam sheet in which a polyethylene resin foam layer A and a polyethylene resin foam layer B are laminated and bonded together. The polyethylene resin foam layer A comprises polyethylene X composed of low-density polyethylene or polyethylene X composed of a mixture of low-density polyethylene and linear low-density polyethylene. The polyethylene resin foam layer B comprises polyethylene Y composed of low-density polyethylene or polyethylene Y composed of a mixture of low-density polyethylene and linear low-density polyethylene. Plant-derived polyethylene b-PE in the polyethylene X x The total amount Xb of the compounding amount is less than 25 mass % and includes 0, The polyethylene b-PE in the polyethylene Y is derived from plants Y The total amount of Yb in the polyethylene X is greater than the plant-derived polyethylene b-PE x The total amount of compounding is Xb more.

Images