Polyethylene-based resin foamed sheet and method for manufacturing the same

Abstract

To provide a polyethylene-based resin foamed sheet having small load to the environment, low basis weight, and moreover, having excellent external appearance, and a method for manufacturing the same.SOLUTION: There is provided a method for manufacturing a polyethylene-based resin foamed sheet which is obtained by coextrusion of : a foamable resin molten material for forming a foamed layer A prepared by kneading a polyethylene-based resin A and a physical blowing agent; and a foamable resin molten material for forming a foamed layer B prepared by kneading a polyethylene-based resin B and a physical blowing agent, wherein the polyethylene-based resin A includes a polyethylene X comprising a low-density polyethylene or a blend of a low-density polyethylene and a linear low-density polyethylene, the polyethylene-based resin B includes a polyethylene Y comprising a low-density polyethylene or a blend of a low-density polyethylene and a linear low-density polyethylene, a blend amount of a plant-derived polyethylene in the polyethylene X is less than 25 mass% (including 0), and a blend amount of a plant-derived polyethylene in the polyethylene Y is higher than the blend amount of the plant-derived polyethylene in the polyethylene X.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Due to environmental considerations, there is a growing demand for carbon-neutral product manufacturing and a need to reduce fossil fuel consumption. Against this background, in recent years, polyethylene resins have been produced from ethylene derived from natural materials such as plants, instead of ethylene derived from fossil fuels.

[0003] For example, Patent Document 1 discloses a polyethylene-based resin foam sheet containing naturally-derived low-density polyethylene. Specifically, Patent Document 1 discloses a polyethylene-based resin foam sheet having a foam layer made of a polyethylene-based resin composition, wherein the polyethylene-based resin composition constituting the foam layer contains low-density polyethylene (PE-LD) containing naturally-derived ethylene as a structural unit, the proportion of the low-density polyethylene (PE-LD) in all resins 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) has: (1) a density of 910 kg / m 3 More than 929kg / m 3 The following describes a polyethylene resin foam sheet that satisfies all four requirements: (2) a mass average molecular weight (Mw) / number average molecular weight (Mn) ratio of 2.5 to 7.0, (3) a melt mass-flow rate (MFR) of 0.1 g / 10 min to 1.0 g / 10 min, and (4) a biomass content of 3% or more as measured by ASTM D 6866 (2004). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-130796 Summary of the Invention [Problem to be solved by the invention]

[0005] In the polyethylene-based resin foam sheet described above, there is a demand for a foam sheet with a low basis weight that can reduce the burden on the environment. However, when a foam sheet with a low basis weight is produced using naturally occurring polyethylene as the resin raw material for the foam layer as in Patent Document 1, the appearance of the resulting foam sheet tends to be poor. The present invention has been made in view of the above problems, and an object of the present invention is to provide a polyethylene-based resin foamed sheet that has a small environmental impact, a small basis weight, and an excellent appearance, and a method for producing the same. [Means for solving the problem]

[0006] [1] Basis weight: 100 g / m 2 a method for producing a polyethylene-based resin foam sheet having a biomass content of 5% or more as measured by ASTM D 6866, the foam sheet being a multilayer foam sheet in which a polyethylene-based resin foam layer A and a polyethylene-based resin foam layer B are laminated and bonded together, the foam layer A and the foam layer B being formed by co-extruding a foamable resin melt for forming foam layer A, which is obtained by kneading a polyethylene-based resin A with a physical foaming agent, and a foamable resin melt for forming foam layer B, which is kneaded with a polyethylene-based resin B with a physical foaming agent, the polyethylene-based resin A comprising polyethylene X consisting of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene-based resin B comprising polyethylene Y consisting of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the plant-derived polyethylene b-PE in the polyethylene X X The total amount Xb of the blended polyethylene Y is less than 25% by mass (including 0), and the plant-derived polyethylene b-PE Y The total amount Yb of the plant-derived polyethylene b-PE in the polyethylene X is X The method for producing a polyethylene resin foam sheet, wherein the blending amount of the above is greater than the total blending amount Xb.

[0007] [2] The plant-derived polyethylene b-PE measured according to ASTM D 6866 X The biomass content of the plant-derived polyethylene b-PE is 80% or more, as measured by ASTM D 6866. Y The method for producing a polyethylene resin foam sheet according to [1], wherein the biomass content is 80% or more.

[0008] [3] The plant-derived polyethylene b-PE Y The total amount of Yb and the plant-derived polyethylene b-PE X and the difference Yb-Xb from the total amount Xb of the blended amount of the polyethylene resin foam sheet is 20 mass % or more.

[0009] [4] The method for producing a polyethylene resin foam sheet according to any one of [1] to [3], wherein the ratio of the basis weight of the foam layer B to the basis weight of the foam layer A is 0.1 or more and 2 or less.

[0010] [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.

[0011] [6] Basis weight: 100 g / m 2 and a biomass ratio of 5% or more as measured by ASTM D 6866, 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 contains polyethylene X which is made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene resin foam layer B contains polyethylene Y which is made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the polyethylene X contains plant-derived polyethylene b-PE. X The total amount Xb of the blended polyethylene Y is less than 25% by mass (including 0), and the plant-derived polyethylene b-PE YThe total amount Yb of the plant-derived polyethylene b-PE in the polyethylene X is X A polyethylene resin foam sheet in which the blending amount is greater than the total blending amount Xb. [Effects of the Invention]

[0012] The present invention can provide a polyethylene resin foamed sheet that has a small environmental impact, a small basis weight, and an excellent appearance, and a method for producing the same. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view of a polyethylene-based resin foam sheet according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The polyethylene resin foam sheet according to the present embodiment and the method for producing the same will be described below.

[0015] (1) Manufacturing method of foam sheet The present invention uses a material having a basis weight of 100 g / m 2 The present invention relates to a method for producing a polyethylene resin foamed sheet (hereinafter also referred to as "foamed sheet") having a biomass content of 5% or more as measured in accordance with ASTM D 6866, which is as follows: The polyethylene-based resin foam sheet of the present invention is a multilayer foam sheet in which a polyethylene-based resin foam layer A (hereinafter also referred to as "foam layer A") and a polyethylene-based resin foam layer B (hereinafter also referred to as "foam layer B") are laminated and bonded together. The foam sheet of the present invention includes at least one foam layer A and at least one foam layer B.

[0016] The foam layers A and B are formed by co-extruding a foamable resin melt for forming foam layer A (hereinafter also referred to as "foamable resin melt A"), which is obtained by kneading a polyethylene resin A with a physical foaming agent, and a foamable resin melt for forming foam layer B (hereinafter also referred to as "foamable resin melt B"), which is obtained by kneading a polyethylene resin B with a physical foaming agent. The polyethylene resin A contains polyethylene X, which is made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene. The polyethylene resin B contains polyethylene Y, which is made of low-density polyethylene or 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 of the plant-derived polyethylene b-PE in polyethylene Y is less than 25% by mass (including 0). Y The total amount of Yb in polyethylene X is the plant-derived polyethylene b-PE X is greater than the total compounding amount Xb.

[0017] In the method for producing a foamed 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 multi-layer foamed sheet having a foamed layer A and a foamed layer B.

[0018] The method for producing a foamed sheet according to the present invention can use a known extrusion device used in the field of extrusion foaming. As an example, a multilayer foamed sheet can be produced by using a co-extrusion device equipped with an extruder for forming a foamed layer A configured to be able to extrude a foamable resin melt A, an extruder for forming a foamed layer B configured to be able to extrude a foamable resin melt B, and a co-extrusion die configured downstream of these extruders to be able to laminate the foamable resin melt A and the foamable resin melt B. For example, by attaching a co-extrusion die to the downstream side of the extruder for forming foam layer A and connecting the downstream side of the extruder for forming foam layer B to the co-extrusion die, it is possible to stack these foamable resin melts and co-extrude them.

[0019] In co-extrusion using an extrusion device, a foamable resin melt A formed in an extruder for forming foam layer A and a foamable resin melt B formed in an extruder for forming foam layer B are introduced into a co-extrusion die and extruded in layers from the outlet of the co-extrusion die. As the co-extrusion die, for example, a flat die equipped with a linear outlet may be used. However, from the viewpoint of easily and stably producing a wide foamed sheet, an annular die equipped with a circular outlet is preferably used. When an annular die is used, one foamable resin melt flowing cylindrically inside the die is laminated on the outer and / or inner surface of the other foamable resin melt, and then a laminate of these foamable resin melts is extruded cylindrically from the outlet of the die. When such a laminate is extruded under a pressure atmosphere (e.g., atmospheric air) lower than that inside the extruder, the foamable resin melt foams to form bubbles, forming a laminated foam. The extruded tubular laminated foam is then expanded by a tubular widening device (e.g., a mandrel) equipped with a cooling mechanism, pulled along the widening device, and cut open along the extrusion direction to produce a foamed sheet.

[0020] <Foamable resin melt A> The foamable resin melt A can be formed by melt-kneading a polyethylene resin A and a physical foaming agent. The foamable resin melt A is foamed to form a foam layer A.

[0021] The polyethylene resin A in the present invention refers to a resin containing 50 mol % or more of structural units derived from ethylene. Examples of the polyethylene resin A include one or a combination of two or more of polyethylenes such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and ethylene copolymers containing 50 mol % or more of structural units derived from ethylene, such as ethylene-vinyl acetate copolymer (EVA).

[0022] The polyethylene resin A used to form the foamable resin melt A is low-density polyethylene LD X , or low density polyethylene LD Xand linear low-density polyethylene LL X and polyethylene X, which is a mixture of

[0023] 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, even more preferably 90% by mass or more, and particularly preferably 100% by mass, i.e., the polyethylene resin A is polyethylene X.

[0024] [Low density polyethylene LD X ] Low-density polyethylene LD used as polyethylene X X has a long-chain branched structure and a density of 0.910 g / cm 3 More than 0.930g / cm 3 Low-density polyethylene (LD) refers to polyethylene with a density of less than 100%. X Low-density polyethylene LD X As a material, petroleum-derived low-density polyethylene (p-LD) X and plant-derived low-density polyethylene b-LD X Petroleum-derived low-density polyethylene (p-LD) X and plant-derived low-density polyethylene b-LD X Details will be described later.

[0025] In order to enhance the extrusion foamability of the foamable resin melt A and to obtain a foamed sheet with good cushioning properties, the low-density polyethylene LD in the polyethylene X is X Proportion of low density polyethylene LD X and linear low-density polyethylene LL X Low density polyethylene LD with a total of 100% by mass X The proportion of the total mass of the polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. In addition, the low density polyethylene LD in polyethylene XX The ratio range is: polyethylene X = low density polyethylene LD X In the case of (low density polyethylene LD in polyethylene X) X 100% by mass) and polyethylene X is low-density polyethylene LD X and linear low-density polyethylene LL X When polyethylene X is a mixture of low density polyethylene LD X and linear low-density polyethylene LL X and low density polyethylene LD in polyethylene X. X The proportion of linear low-density polyethylene LL is 50% by mass or more. X The proportion of is 50% by mass or less).

[0026] [Linear low-density polyethylene LL X ] Linear low-density polyethylene LL used in polyethylene X X is a linear ethylene copolymer, a copolymer of ethylene and an α-olefin. Linear low-density polyethylene LL X The density of is 0.910 g / cm 3 More than 0.930g / cm 3 It is preferable that it is less than 10 ...

[0027] Examples of the α-olefin used in the ethylene copolymer include 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). Among these, linear low-density polyethylene LL, which is a copolymer of ethylene and octene (α-olefin having 8 carbon atoms), is C8 Linear low-density polyethylene LL containing as the main component X The use of the octene group makes it easier to increase the rigidity of the foamed sheet. Octene includes octene isomers such as 1-octene and isooctene.

[0028] Linear low-density polyethylene LL XLinear low density polyethylene LL C8 The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0029] Linear low-density polyethylene LL X Examples of such polyethylenes include petroleum-derived linear low-density polyethylene and plant-derived linear low-density polyethylene. Two or more of these polyethylenes can be used in combination. From the viewpoint of supply stability in the market, fossil fuel resource-derived linear low-density polyethylene (petroleum-derived linear low-density polyethylene) produced using fossil fuels as raw materials is preferably used.

[0030] Linear low-density polyethylene LL X The melting point of the linear low-density polyethylene LL having a melting point within the above range is preferably 116°C or higher and 130°C or lower, and more preferably 118°C or higher and 126°C or lower. X By using the above, it becomes easier to prevent cells from breaking during extrusion foaming, and it becomes easier to stably obtain a foamed sheet having a high closed cell content.

[0031] Linear low-density polyethylene LL X The melt flow rate of the linear low density polyethylene LL having a melt flow rate within the above range is preferably 0.1 g / 10 min or more and 15 g / 10 min or less, and more preferably 0.2 g / 10 min or more and 12 g / 10 min or less. X By using the above, it becomes easier to prevent cells from breaking during extrusion foaming, and it becomes easier to stably obtain a foamed sheet having a high closed cell content.

[0032] The melting point and melt flow rate of the linear low-density polyethylene can be measured in the same manner as the melting point and melt flow rate of the polyethylene resin described below.

[0033] In addition, linear low-density polyethylene LL XWhen multiple types of linear low-density polyethylene are used as the foam layer, a test mixture is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each linear low-density polyethylene used in the production of the foam layer, and the melting point and melt flow rate are determined by performing various measurements on the test mixture. X The melting point and melt flow rate are used.

[0034] Expandable resin melt A and linear low-density polyethylene LL X When blending (polyethylene X is low density polyethylene LD X and linear low-density polyethylene LL X When using a mixture of linear low density polyethylene LL in polyethylene X X Amount of blended low density polyethylene LD X and linear low-density polyethylene LL X Linear low-density polyethylene LL with a total of 100% by mass X The proportion of linear low-density polyethylene LL is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. X By setting the blending amount XL within the above range, the rigidity of the foamed sheet can be easily increased, and even in the case of obtaining a foamed sheet having a relatively small thickness and basis weight, the breakage of cells during extrusion foaming can be easily and stably suppressed.

[0035] [Plant-based polyethylene b-PE X ] Polyethylene X is a plant-based polyethylene b-PE X may include:

[0036] Plant-based polyethylene b-PE X As the low-density polyethylene, low-density polyethylene produced by polymerizing a monomer containing bioethylene produced from plants such as sugarcane, corn, and beet, or linear low-density polyethylene can be used. Plant-derived low-density polyethylene b-LD X and linear low-density polyethylene LLX The plant-derived linear low-density polyethylene mentioned above is plant-derived polyethylene b-PE X The commercially available plant-derived low-density polyethylene b-LD is an example. X Examples of such low density polyethylenes include SEB853, SPB681, and STN7006 manufactured by Braskem.

[0037] Polyethylene X is a plant-based polyethylene b-PE X When it contains, plant-derived polyethylene b-PE is used from the viewpoint of making it easier to increase the biomass content of the foam sheet. X The biomass content as measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0038] In the present invention, the biomass ratio measured according to ASTM D 6866 means the proportion 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.

[0039] Plant-based polyethylene b-PE X Plant-derived low-density polyethylene b-LD X When the polyolefin resin contains the plant-derived polyethylene b-PE, the load on the environment is small and it is easy to obtain a foamed sheet with a good appearance. X Plant-derived low-density polyethylene b-LD X The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0040] Plant-derived low-density polyethylene b-LD X The melting point of the plant-derived low-density polyethylene b-LD is preferably 100°C or higher and 115°C or lower, more preferably 102°C or higher and 114°C or lower, and even more preferably 104°C or higher and 112°C or lower. XWhen the melting point is within the above range, a foamed layer A having a good cell structure can be stably obtained.

[0041] Plant-derived low-density polyethylene b-LD X The melting points of polyethylene resins such as those mentioned above can be measured in accordance with JIS K 7121-1987. Test specimens are conditioned under the conditions of JIS K 7121-1987, Test Specimen Conditioning (2) (with the exception of a cooling rate of 10°C / min), and a melting peak is obtained by heating at a rate of 10°C / min. The melting point is determined as the temperature at the apex of the obtained melting peak. When two or more melting peaks appear, the melting point is determined as the temperature at the apex of the melting peak with the largest area.

[0042] Plant-derived low-density polyethylene b-LD X The melt flow rate of the plant-derived low-density polyethylene b-LD 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 even more preferably 0.3 g / 10 min or more and 10 g / 10 min or less. X When the melt flow rate is within the above range, a desired foamed sheet can be easily and stably produced.

[0043] In addition, plant-derived low-density polyethylene b-LD X The melt flow rate of plant-derived low-density polyethylene b-LD may be greater than 1.0 g / 10 min. X In contrast, in the present invention, the plant-derived low-density polyethylene b-LD having the above-mentioned melt flow rate is used. X Even when using the above, a foamed sheet having a good appearance can be stably produced.

[0044] Plant-derived low-density polyethylene b-LD XThe melt flow rate of the polyethylene resins such as those mentioned above is a value measured in accordance with JIS K7210-1:2014 at a temperature of 190°C and a load of 2.16 kg.

[0045] In addition, plant-derived low-density polyethylene b-LD X When multiple types of plant-derived low-density polyethylene are used, a test mixture is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each plant-derived low-density polyethylene used in the production of the foam layer, and the melting point and melt flow rate are determined by performing various measurements on the test mixture. X The melting point and melt flow rate are used.

[0046] 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.

[0047] Plant-based polyethylene b-PE in polyethylene X X The total blending amount Xb of the petroleum-derived low-density polyethylene p-LD, which is likely to improve extrusion foamability, is less than 25% by mass (including 0). By making the total blending amount Xb less than 25% by mass, the foamable resin melt A can be easily filled with the petroleum-derived low-density polyethylene p-LD, which is likely to improve extrusion foamability. X The blending ratio of the plant-derived polyethylene b-PE in polyethylene X can be increased, and by co-extruding the foamable resin melt A and the foamable resin melt B described below to produce a multilayer foamed sheet, it is possible to obtain a foamed sheet with a low basis weight and good appearance, which has a low environmental impact. In particular, even when a foamed sheet with a low basis weight, a thin thickness, and a low density is obtained, a foamed sheet with a good appearance can be obtained. From the above viewpoints, the plant-derived polyethylene b-PE in polyethylene X can be used. X The total amount Xb of these components is more preferably 20 mass % or less (including 0).

[0048] From the viewpoint of making it easier to increase the biomass content of foam sheets and reduce environmental impact, the plant-derived polyethylene b-PE in polyethylene X isX The total amount Xb of the blending amounts of the above is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0049] [Petroleum-derived polyethylene (p-PE) X ] Polyethylene X is petroleum-derived polyethylene (p-PE) X It is preferable that the polyethylene (p-PE) be petroleum-derived polyethylene. X As the low-density polyethylene, low-density polyethylene derived from fossil fuel resources such as naphtha and linear low-density polyethylene can be used. X and linear low-density polyethylene LL X The petroleum-derived linear low-density polyethylene mentioned above is petroleum-derived polyethylene p-PE X The petroleum-derived low-density polyethylene p-LD is an example. X As the polyethylene foam, petroleum-derived low-density polyethylene, which is used in the production of conventional polyethylene-based resin foams, can be used.

[0050] Petroleum-derived polyethylene (p-PE) X Petroleum-derived low-density polyethylene (p-LD) X When the foamable resin melt A contains petroleum-derived polyethylene p-PE, the extrusion foamability of the foamable resin melt A can be easily improved. X Petroleum-derived low-density polyethylene (p-LD) X The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0051] Petroleum-derived low-density polyethylene (p-LD) XThe melting point of the petroleum-derived low-density polyethylene is preferably 100° C. or higher and 115° C. or lower, more preferably 102° C. or higher and 114° C. or lower, and even more preferably 104° C. or higher and 112° C. or lower. Use of a petroleum-derived low-density polyethylene having a melting point within the above range facilitates stable formation of a foamed layer A having a good cell structure, and makes it easier to obtain a foamed sheet having a low basis weight and good appearance.

[0052] Petroleum-derived low-density polyethylene (p-LD) X The melt flow rate of the petroleum-derived low-density polyethylene p-LD having a melt flow rate in the above range is preferably 0.1 g / 10 min or more and 12 g / 10 min or less, and more preferably 0.2 g / 10 min or more and 10 g / 10 min or less. X By using the above, it becomes easier to stably produce a desired foamed sheet.

[0053] Petroleum-derived low-density polyethylene (p-LD) X The melting point and melt flow rate of plant-based low-density polyethylene b-LD X Similarly, it can be measured by the above-mentioned method for measuring the melting point and melt flow rate of polyethylene resins.

[0054] In addition, petroleum-derived low-density polyethylene (p-LD) X When multiple types of petroleum-derived low-density polyethylene are used, the respective resins are melt-kneaded in an extruder or the like at the blending ratio of each petroleum-derived low-density polyethylene when the foam layer is manufactured to prepare a kneaded product for measurement, and the melting point and melt flow rate obtained by performing various measurements on the kneaded product for measurement are used for petroleum-derived low-density polyethylene p-LD. X The melting point and melt flow rate are used.

[0055] Polyethylene X is a petroleum-derived low-density polyethylene (p-LD). X and plant-derived low-density polyethylene b-LD X When using the above, the plant-derived low-density polyethylene b-LD in the foamable resin melt A XThe blending amount of Xb-LD and petroleum-derived low-density polyethylene p-LD X The ratio of the blending amount Xp-LD (Xp-LD / Xb-LD) of Xp-LD is preferably 2 or more and 5 or less, and more preferably 3 or more and 4 or less. In this case, it becomes easier to stably produce a multi-layer foamed sheet having a good appearance over a wide range of densities while reducing the environmental load.

[0056] In addition, polyethylene X is a petroleum-derived low-density polyethylene (p-LD). X and plant-derived low-density polyethylene b-LD X and linear low-density polyethylene LL X When using plant-derived low-density polyethylene b-LD X and petroleum-derived low-density polyethylene (p-LD) X The total amount of (Xb-LD + Xp-LD) and linear low-density polyethylene LL X The mass ratio (Xb-LD+Xp-LD:XL) of the amount of LD to the amount of XL is preferably 1:0.05 to 1:0.4, and more preferably 1:0.1 to 1:0.3. By keeping the mass ratio (Xb-LD+Xp-LD:XL) within the above range, it becomes easier to stably suppress cell breakage during extrusion foaming, even when a foamed sheet having a relatively thin thickness and low basis weight is obtained, while increasing the biomass content of the foamed sheet.

[0057] [Physical foaming agent] The physical foaming agent used to form the foamable resin melt A may be an organic physical foaming agent or an inorganic physical foaming agent. Examples of organic physical blowing agents that can be used include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal 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. Examples of inorganic physical foaming agents that can be used include oxygen, nitrogen, carbon dioxide, air, and water. These physical foaming agents can be used in combination of two or more. Among them, organic physical foaming agents are preferred from the viewpoint of excellent extrusion foamability and take-up stability of the multilayer foamed sheet, and butane is more preferred. As butane, normal butane, isobutane, or a mixture thereof can be used.

[0058] The amount of the physical foaming agent added is adjusted depending on the type of the physical foaming agent and the density and basis weight of the desired multi-layer foamed sheet. For example, when 30% by mass of isobutane and 70% by mass of normal butane are used as the physical foaming agents, the amount of the physical foaming agent added is preferably 3 to 35 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 6 to 25 parts by mass, per 100 parts by mass of polyethylene resin A.

[0059] [Other additives] 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 the other additives include a cell regulator, a shrinkage inhibitor, an antioxidant, a heat stabilizer, a weather resistance agent, an ultraviolet absorber, a flame retardant, an inorganic filler, an antibacterial agent, and a colorant.

[0060] The cell regulator may be an inorganic powder or a chemical foaming agent. Examples of inorganic powders include talc, zeolite, silica, and calcium carbonate. Examples of chemical foaming agents include azodicarbonamide, hydrazodicarbonamide, azobisisobutyronitrile, sodium bicarbonate (sodium bicarbonate), and sodium bicarbonate-citric acid-based chemical foaming agents, which are mixtures of sodium bicarbonate and citric acid or a monoalkali metal citrate such as monosodium citrate. The amount of the cell regulator added is preferably 0.01 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, relative to 100 parts by mass of the polyethylene resin A used to form the foamable resin melt A, because this makes it easier to stably adjust the cell diameter of the foamed layer within the desired range.

[0061] Furthermore, as long as the desired effects of the present invention can be achieved, other resins or elastomers than the polyethylene resin A specified in the present invention may be blended. When other resins or elastomers are blended, the blending amount 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, per 100 parts by mass of the polyethylene resin A.

[0062] In forming the foamable resin melt A, for example, the polyethylene resin A, the physical foaming agent, and additives added as needed are supplied to an extruder for forming the foam layer A. Then, by melt-kneading these in the extruder for forming the foam layer A, the foamable resin melt A can be formed.

[0063] <Foamable resin melt B> The foamable resin melt B can be formed by melt-kneading a polyethylene resin B and a physical foaming agent. The foamable resin melt B is foamed to form a foam layer B.

[0064] 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. Examples of the polyethylene resin B include one or a combination of two or more of polyethylenes such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), and ethylene copolymers containing 50 mol % or more of structural units derived from ethylene, such as ethylene-vinyl acetate copolymer (EVA).

[0065] The polyethylene resin B used to form the foamable resin melt B is low-density polyethylene LD Y , or low density polyethylene LD Y and linear low-density polyethylene LL Y and polyethylene Y, which is a mixture of

[0066] 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, even more preferably 90% by mass or more, and particularly preferably 100% by mass, i.e., the polyethylene resin B is polyethylene Y.

[0067] [Low density polyethylene LD Y ] Low density polyethylene LD used as polyethylene Y Y has a long-chain branched structure and a density of 0.910 g / cm 3 More than 0.930g / cm 3 Low-density polyethylene (LD) refers to polyethylene with a density of less than 100%. Y Low-density polyethylene LD Y As a material, plant-derived low-density polyethylene b-LD Y and petroleum-derived low-density polyethylene. Plant-derived low-density polyethylene b-LD Y Details will be described later.

[0068] In order to enhance the extrusion foamability of the foamable resin melt B and to obtain a foamed sheet with good cushioning properties, the low density polyethylene LD in the polyethylene Y is Y Ratio of low density polyethylene LD Y and linear low-density polyethylene LL Y Low density polyethylene LD with a total of 100% by mass Y The proportion of the total mass of the polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. In addition, the low density polyethylene LD in polyethylene Y Y The ratio range of polyethylene Y is low density polyethylene LD Y When (low density polyethylene LD in polyethylene Y) Y 100% by mass) and polyethylene Y is low-density polyethylene LD Yand linear low-density polyethylene LL Y When polyethylene Y is a mixture of low density polyethylene LD Y and linear low-density polyethylene LL Y and low density polyethylene LD in polyethylene Y. Y The proportion of linear low-density polyethylene LL is 50% by mass or more. Y The proportion of is 50% by mass or less).

[0069] [Linear low-density polyethylene LL Y ] Linear low-density polyethylene LL used in polyethylene Y Y is a linear ethylene copolymer, a copolymer of ethylene and an α-olefin. Linear low-density polyethylene LL Y The density of is 0.910 g / cm 3 More than 0.930g / cm 3 It is preferable that it is less than 10 ...

[0070] Linear low-density polyethylene LL Y Examples of the α-olefins used in the present invention include α-olefins having 4 to 10 carbon atoms. Examples of α-olefins having 4 to 10 carbon atoms include butene (having 4 carbon atoms), hexene (having 6 carbon atoms), and octene (having 8 carbon atoms). Among these, linear low-density polyethylene LL, which is a copolymer of ethylene and octene (α-olefin having 8 carbon atoms), is preferred. C8 Linear low-density polyethylene LL containing as the main component Y The use of the octene group makes it easier to increase the rigidity of the foamed sheet. Octene includes octene isomers such as 1-octene and isooctene.

[0071] Linear low-density polyethylene LL Y Linear low density polyethylene LL C8 The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0072] Linear low-density polyethylene LL Y As the polyethylene, plant-derived linear low-density polyethylene and petroleum-derived linear low-density polyethylene can be used. Two or more of these polyethylenes can be used in combination. From the viewpoint of supply stability in the market, fossil fuel resource-derived linear low-density polyethylene (petroleum-derived linear low-density polyethylene) produced using fossil fuel as a raw material can be preferably used.

[0073] Linear low-density polyethylene LL Y The melting point of the linear low-density polyethylene LL having a melting point in the above range is preferably 116°C or higher and 130°C or lower, and more preferably 118°C or higher and 126°C or lower. Y By using the above, it becomes easier to prevent cells from breaking during extrusion foaming, and it becomes easier to stably obtain a foamed sheet having a high closed cell content.

[0074] Linear low-density polyethylene LL Y The melt flow rate of the linear low density polyethylene LL having a melt flow rate in the above range is preferably 0.1 g / 10 min or more and 15 g / 10 min or less, and more preferably 0.2 g / 10 min or more and 12 g / 10 min or less. Y By using the above, it becomes easier to prevent cells from breaking during extrusion foaming, and it becomes easier to stably obtain a foamed sheet having a high closed cell content.

[0075] 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.

[0076] In addition, linear low-density polyethylene LL Y When multiple types of linear low-density polyethylene are used as the foam layer, a test mixture is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each linear low-density polyethylene used in the production of the foam layer, and the melting point and melt flow rate are determined by performing various measurements on the test mixture. YThe melting point and melt flow rate are used.

[0077] Expandable resin melt B and linear low-density polyethylene LL Y When blending (polyethylene Y, low density polyethylene LD Y and linear low-density polyethylene LL Y When using a mixture of linear low density polyethylene LL in polyethylene Y Y Amount of blended low density polyethylene LD Y and linear low-density polyethylene LL Y Linear low-density polyethylene LL with a total of 100% by mass Y The proportion of linear low-density polyethylene LL is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less. Y By setting the blending amount YL within the above range, the rigidity of the foamed sheet can be easily increased, and even in the case of obtaining a foamed sheet having a relatively small thickness and basis weight, the breakage of cells during extrusion foaming can be easily and stably suppressed.

[0078] [Plant-based polyethylene b-PE Y ] Plant-based polyethylene b-PE Y As for the material, plant-based polyethylene b-PE X Similarly, low-density polyethylene and linear low-density polyethylene produced by polymerizing monomers containing bioethylene produced from plants such as sugarcane, corn, and beets can be used. Plant-derived low-density polyethylene b-LD Y and linear low-density polyethylene LL Y The plant-derived linear low-density polyethylene mentioned above is plant-derived polyethylene b-PE Y This is an example of:

[0079] From the viewpoint of making it easier to increase the biomass content of foam sheets, plant-derived polyethylene b-PE YThe biomass content as measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0080] From the viewpoint of minimizing the burden on the environment and making it easier to stably obtain foamed sheets with good appearance, plant-derived polyethylene b-PE Y Plant-derived low-density polyethylene b-LD Y The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0081] Plant-derived low-density polyethylene b-LD used as polyethylene Y Y The melting point of the plant-derived low-density polyethylene is preferably 100° C. or higher and 115° C. or lower, more preferably 102° C. or higher and 114° C. or lower, and even more preferably 104° C. or higher and 112° C. or lower. Use of a plant-derived low-density polyethylene having a melting point within the above range facilitates stable formation of a foamed layer B having a good cell structure, and makes it easier to obtain a foamed sheet having a low basis weight and good appearance.

[0082] Plant-derived low-density polyethylene b-LD Y The melt flow rate of the plant-derived low-density polyethylene b-LD having a melt flow rate within the above range 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, even more preferably 0.3 g / 10 min or more and 20 g / 12 min or less, and even more preferably more than 1.0 g / 10 min and 10 g / 10 min or less. YBy using the foam layer A, the foam layer B can be well laminated during extrusion foaming, which makes it easier to improve the appearance of the foamed sheet. Furthermore, by well laminating the foam layer B during extrusion foaming, the addition efficiency of the physical foaming agent blended into the foamable resin melt A can be increased. This allows the foamable resin melt A to be foamed to a low density without blending an excessive amount of physical foaming agent, which suppresses cell breakage and makes it possible to stably obtain a foamed sheet with a good appearance.

[0083] Plant-derived low-density polyethylene b-LD Y The melting point and melt flow rate of plant-based low-density polyethylene b-LD X As such, it can be measured in the same manner as the melting point and melt flow rate of the polyethylene resin described above.

[0084] In addition, plant-derived low-density polyethylene b-LD Y When multiple types of plant-derived low-density polyethylene are used, a test mixture is prepared by melt-kneading each resin using an extruder or the like at the blending ratio of each plant-derived low-density polyethylene used in the production of the foam layer, and the melting point and melt flow rate are determined by performing various measurements on the test mixture. Y The melting point and melt flow rate are used.

[0085] Plant-derived low-density polyethylene b-LD Y The biomass content as measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0086] Plant-based polyethylene b-PE in polyethylene Y Y The total amount of Yb blended is the plant-derived polyethylene b-PE in polyethylene X. XThe foamable resin melt A and the foamable resin melt B are formed so that the total compounding amount Xb is a specific value or less and the total compounding amount Yb is greater than the total compounding amount Xb, and the petroleum-derived low-density polyethylene p-LD, which is easy to improve extrusion foamability in the foamable resin melt A, is used. X By increasing the blending ratio of the biomass component B in the foamable resin melt while increasing the blending ratio of the plant-derived polyethylene in the foamable resin melt B, and then foaming them by co-extrusion, it is possible to increase the biomass content of the foamed sheet as a whole while improving extrusion foamability. This makes it possible to obtain a foamed sheet having a predetermined biomass content and good appearance, even when obtaining a foamed sheet with a relatively low basis weight. In particular, it is possible to obtain a foamed sheet with good appearance, even when obtaining a foamed sheet with a low basis weight, thin thickness, and low density.

[0087] From the viewpoint of easily obtaining a foamed sheet with a desired 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 X The difference Yb-Xb between the total amount of each of the components Yb and the total amount of each of the components Xb is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and even more preferably 50% by mass or more. From the viewpoint of easily increasing the biomass content of the foamed sheet, the difference Yb-Xb between the total amount of each of the components Yb and the total amount of each of the components Xb may be 90% by mass or less, or may be 80% by mass or less.

[0088] Plant-based polyethylene b-PE in polyethylene Y Y The total amount Yb of the blending amounts of the above is preferably 30% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, even more 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 foamed sheet.

[0089] [Physical foaming agent] As the physical foaming agent used to form the foamable resin melt B, the physical foaming agents explained as the physical foaming agents used to form the foamable resin melt A can be used. From the viewpoint of excellent extrusion foamability and take-up stability of the resulting multilayer foamed sheet, it is preferable to use an organic physical foaming agent, and it is more preferable to use butane, which can be normal butane, isobutane, or a mixture thereof.

[0090] The amount of the physical foaming agent added is adjusted depending on the type of the physical foaming agent and the density and basis weight of the desired multi-layer foamed sheet. For example, when 30% by mass of isobutane and 70% by mass of normal butane are used as the physical foaming agents, the amount of the physical foaming agent added is preferably 3 to 35 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 6 to 25 parts by mass, per 100 parts by mass of the polyethylene resin B.

[0091] [Other additives] 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 the other additives include a cell regulator, a shrinkage inhibitor, an antioxidant, a heat stabilizer, a weather resistance agent, an ultraviolet absorber, a flame retardant, an inorganic filler, an antibacterial agent, and a colorant.

[0092] The cell control agent may be an inorganic powder or a chemical foaming agent. Examples of inorganic powders include talc, zeolite, silica, and calcium carbonate. Examples of chemical foaming agents include azodicarbonamide, hydrazodicarbonamide, azobisisobutyronitrile, sodium bicarbonate (sodium bicarbonate), and sodium bicarbonate-citric acid-based chemical foaming agents, which are mixtures of sodium bicarbonate and citric acid or a monoalkali metal citrate such as monosodium citrate. The amount of the cell control agent added is preferably 0.01 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the polyethylene resin B used to form the foamable resin melt, since this makes it easier to stably adjust the cell diameter of the foamed layer within the desired range.

[0093] As long as the desired effects of the present invention can be achieved, other resins or elastomers than the polyethylene resin B specified in the present invention may be blended. When other resins or elastomers are blended, the blending amount 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, per 100 parts by mass of the polyethylene resin B.

[0094] In forming the foamable resin melt B, for example, the polyethylene resin B, the physical foaming agent, and additives added as needed are supplied to an extruder for forming the foam layer B. Then, by melt-kneading these components in the extruder for forming the foam layer B, the foamable resin melt B can be formed.

[0095] [Melt flow rate ratio (b-LD Y / p-LD X )] From the viewpoint of making it easier to obtain the desired foamed sheet, petroleum-derived low-density polyethylene p-LD X Melt flow rate of bio-based low density polyethylene b-LD Y The ratio of the melt flow rate (b-LD Y / p-LD X ) is preferably 0.1 or more and 30 or less, and more preferably 1 or more and 25 or less.

[0096] [Melting point difference (T_p-LD X -T_b-LD Y) ] From the viewpoint of improving extrusion stability, petroleum-derived low-density polyethylene p-LD X Melting point T_p-LD X and plant-derived low-density polyethylene b-LD Y Melting point T_b-LD Y Difference between (T_p-LD X -T_b-LD Y ) is preferably within 5°C, more preferably within 3°C.

[0097] In producing a foamed sheet having a desired basis weight, etc., the desired foamed sheet can be obtained mainly by adjusting the take-up speed of the foamed sheet, the discharge amounts of the foamable resin melt A and the foamable resin melt B, the blow-up ratio (diameter expansion ratio) of the foamed sheet, etc. during the production of the foamed sheet.

[0098] Specifically, the blow-up ratio of the tubular laminated foam extruded from the extruder is preferably 2.0 to 4.5, more preferably 2.1 to 4.0. The blow-up ratio refers to the ratio of the diameter of the annular die (discharge orifice diameter) to the diameter of the mandrel (blow-up ratio: mandrel diameter / annular die lip diameter). The take-up speed of the tubular laminated foam extruded from the extruder is preferably 10 to 120 m / min, more preferably 20 to 100 m / min.

[0099] Although it depends on the size of the extruder and the widthwise length of the foamed sheet to be obtained, the total output rate of the foamable resin melt A and the foamable resin melt B extruded from the extruder is preferably 50 kg / hr to 300 kg / hr, more preferably 60 kg / hr to 260 kg / hr. The ratio of the output rate of the foamable resin melt B to the output rate of the foamable resin melt A is preferably 0.01 to 5, more preferably 0.1 to 2.

[0100] In addition, when multiple layers of foamable resin melt A are formed, the total amount of extrusion of these foamable resin melt A is considered to be the amount of extrusion of foamable resin melt A, and when multiple layers of foamable resin melt B are formed, the total amount of extrusion of these foamable resin melt B is considered to be the amount of extrusion of foamable resin melt B.

[0101] It is preferable to co-extrude the foamable resin melt A and the foamable resin melt B so that the mass ratio of foam layer B to foam layer A (foam layer B / foam layer A) is 0.1 or more and 2 or less. By satisfying the relationship between the foamable resin melt A and the foamable resin melt B and co-extruding the foamable resin melt A and the foamable resin melt B in the above-mentioned mass ratio relationship, it is possible to stably produce a foamed sheet that has a thin thickness, a small basis weight, and a good appearance while increasing the biomass content. Furthermore, particularly in the case where one foamed layer is laminated on both sides of the other foamed layer, it is possible to further increase the efficiency of adding the physical foaming agent to the foamed resin melt for forming the foamed layer located at the center in the thickness direction, and it is possible to more stably produce a foamed sheet that has a low basis weight, a thin thickness, a low density, a high closed cell content, and a good appearance. From the viewpoint of facilitating the stable production of a multi-layer foamed sheet that has a desired biomass content, a low basis weight, and an excellent appearance, the mass ratio of foamed layer B to foamed layer A (foamed layer B / foamed layer A) is more preferably 0.2 or more and 1 or less, and even more preferably 0.3 or more and 0.8 or less.

[0102] When a plurality of foam layers A are formed, the sum of the basis weights of these foam layers A is the basis weight of foam layer A, and when a plurality of foam layers B are formed, the sum of the basis weights of these foam layers B is the basis weight of foam layer B. Therefore, the mass ratio of foam layer B to foam layer A can be calculated, for example, as the ratio of the sum of the basis weights of foam layer B to the sum of the basis weights of foam layer A.

[0103] Basis weight of each foam layer [g / m 2 The basis weight of each foam layer can be calculated by substituting the discharge rate X [g / hr] of each foam layer during the production of the foam sheet, the width W [m] of the resulting foam sheet, and the length L [m / hr] of the foam sheet extruded per unit time into the following formula (1). When a plurality of foam layers are formed, the total discharge rate of the corresponding foam layers is used as the discharge rate of each foam layer to calculate the basis weight of each foam layer. Basis weight of each foam layer [g / m 2 ]=〔X / (L×W)〕 (1)

[0104] The basis weight of the foam layer A is 5 g / m 2 More than 90g / m 2Preferably, it is 10 g / m or less. 2 More than 60g / m 2 More preferably, it is: The basis weight of the foam layer B is 5 g / m 2 More than 90g / m 2 Preferably, it is 10 g / m or less. 2 More than 60g / m 2 More preferably, it is:

[0105] According to the production method described above, it is possible to provide a foamed sheet that has a small load on the environment, a small basis weight, and an excellent appearance.

[0106] When a foam sheet is produced by extrusion foaming, it tends to be difficult to produce a foam sheet having a low basis weight, particularly when a foam sheet having a low basis weight, a thin thickness, and a low density is to be produced.

[0107] On the other hand, plant-derived polyethylene has a smaller range of resins to choose from than petroleum-derived polyethylene, which tends to reduce the flexibility in the production of foamed sheets. For this reason, when a single-layer foamed sheet is produced by blending plant-derived polyethylene and petroleum-derived polyethylene to obtain a foamed sheet with a high biomass content and desired physical properties such as basis weight, it can be difficult to produce the desired foamed sheet. In particular, when a foamed sheet with a low basis weight, thin thickness, and low density is obtained, the foam cells tend to break easily during extrusion foaming. Even when the resulting foamed sheet is cured, the effects of shrinkage caused by the dissipation of the blowing agent cannot be eliminated, resulting in a foamed sheet with wrinkles or the like.

[0108] In contrast, the production method of the present invention produces a multilayer foam sheet by coextrusion, including a specific foam layer A containing a relatively large amount of petroleum-derived polyethylene, and by configuring the amount of plant-derived polyethylene contained in foam layer B to be greater than the amount of petroleum-derived polyethylene contained in foam layer A. Forming a multilayer foam sheet by coextrusion facilitates stable extrusion conditions, such as extrusion temperature, during extrusion foaming of each foamable resin melt, facilitating stable production of a foam sheet. In addition, foam layer B ensures the biomass content of the entire foam sheet, while foam layer A, which contains a high proportion of petroleum-derived low-density polyethylene and the like, which tends to improve extrusion foamability, suppresses cell breakdown during extrusion foaming, facilitating the production of a foam sheet with a desired foaming state. As a result, a foam sheet with a small basis weight, good appearance, and low environmental impact can be obtained.

[0109] (2) Foam sheet The present invention uses a material having a basis weight of 100 g / m 2 and a biomass content of 5% or more as measured by ASTM D 6866, the foam sheet comprising a polyethylene-based resin foam layer A and a polyethylene-based resin foam layer B, the polyethylene-based resin foam layer A containing polyethylene X made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene-based resin foam layer B containing polyethylene Y made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the polyethylene X containing plant-derived polyethylene b-PE. X The total amount of the plant-derived polyethylene b-PE in polyethylene Y is less than 25% by mass (including 0). Y The total amount of Yb in polyethylene X is the plant-derived polyethylene b-PE X The polyethylene resin foam sheet contains a content greater than the total amount Xb of the above.

[0110] Such a foamed sheet has a specific foamed layer A and a specific relationship between the foamed layer A and the foamed layer B, thereby reducing the environmental load, providing a multilayer foamed sheet with a small basis weight and good appearance. Such a polyethylene-based resin foamed sheet can be preferably produced by the above-mentioned production method.

[0111] The foam sheet according to the present invention includes at least one foam layer A and at least one foam layer B. A schematic diagram of a preferred lamination form of the foam sheet (a cross section in the thickness direction of the foam sheet according to the present embodiment) is shown in FIG. 1. The foam sheet according to (a) in FIG. 1 has a configuration including a foam layer B and a foam layer A laminated and bonded to both sides of the foam layer B (a configuration in which the foam layer B is sandwiched between the two foam layers A). The foam sheet according to (b) in FIG. 1 has a configuration including a foam layer A and a foam layer B laminated and bonded to both sides of the foam layer A (a configuration in which the foam layer A is sandwiched between the two foam layers B). The foam sheet according to (c) in FIG. 1 has a configuration including a foam layer A and a foam layer B laminated and bonded to one side of the foam layer A. From the viewpoint of easily obtaining a foamed sheet having a good appearance while reducing the basis weight, it is preferred that the foamed sheet is a multi-layer foamed sheet including a foamed layer B and a foamed layer A laminated and bonded to both sides of the foamed layer B.

[0112] The foam sheet of the present invention may further include layers other than foam layer A and foam layer B, as long as the intended object of the present invention can be achieved. For example, the foam sheet may be an antistatic foam sheet in which an antistatic layer is laminated and bonded to one or both sides of a multilayer foam sheet including one or more foam layers A and one or more foam layers B. In this case, the antistatic layer may be formed, for example, from a polyethylene resin composition obtained by kneading the above-mentioned polyethylene resin with a known polymeric antistatic agent or the like that is used in the production of conventional antistatic foam sheets having an antistatic layer.

[0113] <Foam layer A> Foam layer A is made of low density polyethylene LD X , or low density polyethylene LD Xand linear low-density polyethylene LL X It includes polyethylene X, which is a mixture of polyethylene X and low-density polyethylene LD, which is used as polyethylene X. X and linear low-density polyethylene LL X Regarding this, please refer to the explanation of polyethylene X in foamable resin melt A and the low-density polyethylene LD used as polyethylene X in foamable resin melt A. X and linear low-density polyethylene LL X The explanations in the above can be referred to as appropriate.

[0114] From the viewpoint of obtaining a foamed sheet having a small basis weight and good cushioning properties, the proportion of low-density polyethylene in the foamed layer A is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0115] Plant-based polyethylene b-PE in polyethylene X X The total amount of the blended amount of the plant-derived polyethylene b-PE in the polyethylene X is less than 25% by mass (including 0). A foamed sheet comprising such a foamed layer A and a foamed layer B described below has a small environmental impact, a thin thickness, a low basis weight, and a good appearance. From this viewpoint, the plant-derived polyethylene b-PE in the polyethylene X is X The total amount Xb of these components is more preferably 20 mass % or less (including 0).

[0116] From the viewpoint of making it easier to obtain a foamed sheet with high cushioning properties, the foamed layer A is made of petroleum-derived low-density polyethylene p-LD X The foam layer A contains petroleum-derived low-density polyethylene p-LD. X The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0117] From the viewpoint of making it easier to increase the biomass content of foam sheets and reduce environmental impact, the plant-derived polyethylene b-PE in polyethylene X is XThe total amount Xb of the blending amounts of the above is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0118] In addition, petroleum-derived polyethylene (p-PE) X and plant-based polyethylene b-PE X Regarding the petroleum-derived polyethylene p-PE in foamable resin melt A, X and plant-based polyethylene b-PE X The explanations in the above can be referred to as appropriate.

[0119] <Foam layer B> Foam layer B is made of low density polyethylene LD Y or low density polyethylene LD Y and linear low-density polyethylene LL Y Polyethylene Y and low-density polyethylene LD, which are used as polyethylene Y, are also included. Y and linear low-density polyethylene LL Y Regarding polyethylene Y in the foamable resin melt B and low-density polyethylene LD used as polyethylene Y, Y and linear low-density polyethylene LL Y The explanations in the above can be referred to as appropriate.

[0120] From the viewpoint of obtaining a foamed sheet having a small basis weight and good cushioning properties, the proportion of low-density polyethylene in the foamed layer B is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0121] Plant-based polyethylene b-PE in polyethylene Y Y The total amount of Yb blended is the plant-derived polyethylene b-PE in polyethylene X. X The amount of the foamed sheet including the foamed layer B and the foamed layer A is larger than the total amount Xb of the foamed sheet. Even when the foamed sheet has a relatively low basis weight, the foamed sheet has a predetermined biomass degree and a good appearance.

[0122] From the viewpoint of easily obtaining a foamed sheet with a desired 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 X The difference Yb-Xb between the total amount of each of the components Xb and the total amount of each of the components Yb-Xb is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and even more preferably 50% by mass or more. From the viewpoint of easily increasing the biomass content of the foamed sheet, the difference Yb-Xb between the total amount of each of the components Xb and the total amount of each of the components Yb-Xb may be 90% by mass or less, or may be 80% by mass or less.

[0123] From the viewpoint of making it easier to increase the biomass content of foam sheets, the plant-derived polyethylene b-PE in polyethylene Y is Y The total amount of Yb blended is preferably 30% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0124] From the viewpoint of minimizing the environmental impact and stably obtaining foamed sheets with good appearance, the plant-derived low-density polyethylene b-LD in the foam layer B is Y The proportion of is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0125] In addition, petroleum-derived polyethylene (p-PE) Y and plant-based polyethylene b-PE Y Regarding the petroleum-derived polyethylene p-PE in foamable resin melt B, Y and plant-based polyethylene b-PE Y The explanations in the above can be referred to as appropriate.

[0126] (3) Physical properties of foam sheets <Basic weight> The basis weight of the foam sheet is 100 g / m2 When the basis weight is within the above range, the foam sheet has a low basis weight and can be suitably used as a cushioning material for logistics. From the viewpoint of obtaining a lighter foam sheet, the basis weight is 90 g / m or less. 2 More preferably, it is 80 g / m or less. 2 The basis weight is the area (m ) of a foamed sheet cut into a predetermined size (for example, 1000 mm × 250 mm). 2 ) and mass (g), and calculate the mass (g) to the area (m 2 ) can be calculated by dividing by

[0127] The mass ratio of foam layer B to foam layer A (foam layer B / foam layer A) is preferably 0.1 or more and 2 or less, more preferably 0.2 or more and 1 or less, and even more preferably 0.3 or more and 0.8 or less, from the viewpoints of increasing the biomass content, achieving a thin thickness and a small basis weight, and improving the appearance.

[0128] As described above, the basis weight of each foam layer can be determined, for example, from the relationship between the extrusion rate X of each foam layer during the production of a 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. Alternatively, the basis weight of each foam layer can be determined, for example, by multiplying the thickness of each foam layer by the density of the resin composition constituting each foam layer and converting the result into units.

[0129] <Thickness> The average thickness of the foam sheet is preferably 0.05 mm or more and 5 mm or less. By setting the thickness of the foam sheet within this range, the foam sheet can be suitably used for various cushioning applications such as cushioning materials for logistics, and when used as slip sheets for plate-like objects, loading efficiency can be improved. The average thickness of the foam sheet is preferably less than 2 mm, and more preferably 1 mm or less.

[0130] The average thickness of a foam sheet can be determined by measuring the thickness at 1cm intervals across the entire width of the foam sheet in the width direction perpendicular to the extrusion direction of the foam sheet and calculating the arithmetic mean of the measured thicknesses. Thickness can be measured using an offline thickness measuring instrument such as the TOF-4R manufactured by Yamabun Denki Co., Ltd. The foam sheet used for measurement should be conditioned for at least 24 hours at a temperature of 23±5°C and a relative humidity of 50%.

[0131] <density> The density of the foam sheet is 300 kg / m 3 By setting the density of the foam sheet within the above range, the foam sheet becomes lightweight and has excellent cushioning properties, and can be more suitably used as a cushioning material for logistics, etc. From the above viewpoints, the density is preferably 10 kg / m or less. 3 More than 200kg / m 3 It is preferable that the saturation is 12 kg / m or less. 3 More than 100kg / m 3 More preferably, it is 15 kg / m or less. 3 More than 80kg / m 3 It is even more preferable that: The density of the foam sheet is determined by the basis weight (g / m 2 ) is divided by the average thickness of the foam sheet, and then (kg / m 3 ) can be calculated by converting the unit.

[0132] Furthermore, when a foam sheet is provided with a foam layer A and a foam layer B laminated and bonded to both sides 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 2 or more and 5 or less. In this case, the foam layer A, which is easy to extrusion foam, can be foamed at a relatively high expansion ratio, while the foam layer B located on the surface side can be formed at a relatively low expansion ratio, thereby providing a multilayer foam sheet with excellent surface properties while maintaining a low density as a whole. In addition, when a foamed sheet is provided with a foamed layer B and a foamed layer A laminated and bonded to both sides of the foamed layer B, the ratio of the density of the foamed layer B to the density of the foamed layer A can be set to 1 or more and 10 or less. In this case, by foaming the foamed layer A, which is easy to extrusion foam, at a relatively high expansion ratio and positioning it on the surface side, it is possible to obtain a multilayer foamed sheet having a relatively soft surface layer portion while reducing the density of the foamed sheet as a whole. Furthermore, when a foam sheet is provided with a foam layer B and a foam layer A laminated and bonded to both sides of the foam layer B, the density of the foam layer B can be made lower than the density of the foam layer A. In this case, by foaming the foam layer B at a relatively high expansion ratio and positioning the foam layer A, which is easy to extrusion foam, on the surface side, it is possible to obtain a multilayer foam sheet having excellent surface properties while reducing the density of the foam sheet as a whole.

[0133] <Biomass ratio> The foam sheet has a biomass degree of 5% or more as measured by ASTM D 6866. From the viewpoint of further reducing the burden on the environment, the biomass degree of the foam sheet is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and even more preferably 25% or more. The biomass degree of the foam sheet may be 60% or less, 50% or less, 45% or less, or 40% or less.

[0134] Biomass content D of foam layer A measured according to ASTM D 6866 A is preferably less than 25% (including 0), more preferably 20% or less. B is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more.

[0135] Biomass content D of foam layer B B and the biomass degree D of the foam layer A The difference between (D B -D A) is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. B -D A ) within the above range, it becomes easier to obtain a foamed sheet that has a high biomass content, a low basis weight, and a good appearance.

[0136] The biomass content of the foam sheet and each foam layer can be determined by measuring the radioactive carbon concentration of the foam sheet and each foam layer based on ASTM D 6866. In addition, the biomass content of the plant-derived low-density polyethylene (b-LDPE) used in the production of the foam sheet can be determined by measuring the radioactive carbon concentration of the foam sheet and each foam layer based on ASTM D 6866. X , b-LD Y It can also be calculated from the biomass ratio measured according to ASTM D 6866, such as that of the plant-derived low-density polyethylene, and the blending ratio of the plant-derived low-density polyethylene or the like in each foam layer.

[0137] <Gel fraction of foam sheet> The foamed sheet of the present invention is preferably non-crosslinked. When an attempt is made to produce a low-basis weight, non-crosslinked polyethylene-based resin foam sheet using plant-derived polyethylene without using a crosslinking agent, etc., the foam tends to shrink during foam production, making it difficult to obtain a polyethylene-based resin foam sheet with good appearance. On the other hand, in the present invention, by producing a foam sheet as a multi-layer foam sheet in which foam layer A and foam layer B are laminated and bonded by the above-mentioned production method, it is possible to produce a polyethylene-based resin foam sheet that has a predetermined biomass content, a low basis weight, and excellent appearance. From this viewpoint, the gel fraction of the foamed sheet is preferably 3% or less (including 0), more preferably 2% or less (including 0), even more preferably 1% or less (including 0), and particularly preferably 0. When the gel fraction satisfies the above range, the foamed sheet is a non-crosslinked sheet in which a crosslinked structure is not substantially formed, and the foamed sheet has excellent recyclability. The gel fraction can be measured by the following method. First, weighed approximately 50 mg of foam sheet is immersed in 25 mL of xylene at 130°C for 3 hours, then filtered through a 200-mesh stainless steel wire mesh and washed with acetone. The insoluble matter remaining on the wire mesh is then vacuum-dried, and the mass of this insoluble matter is precisely weighed to calculate the gel fraction as a percentage according to the following formula (2). Gel fraction (%) = {mass of insoluble matter (mg) / mass of weighed foam (mg)} × 100 (2)

[0138] <Closed bubble rate> The closed cell content of the foam sheet is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. When the closed cell content of the foam sheet is within the above range, it becomes easier to obtain a foam sheet with excellent appearance. Furthermore, the foam sheet can be imparted with appropriate rigidity, resulting in a foam sheet that is less likely to sag. To measure the closed cell content, a cut sample measuring 25 mm x 25 mm x sheet thickness (thickness of the foam sheet) is prepared by randomly cutting the foam sheet. A test piece is then prepared by stacking multiple cut samples so that the total sheet thickness is as close to 20 mm as possible. Next, the true volume (Vx) of the test piece is measured using a Toshiba Beckman air comparison hydrometer, Model 930, or similar, according to Procedure C of ASTM-D2856-70, and the closed cell content (S) (%) is calculated using the following formula (3). This measurement is performed on five test pieces, and the arithmetic average value is the closed cell content of the foam sheet. S(%)=(Vx-W / ρ)×100 / (Va-W / ρ)···(3) Vx: The true volume (cm) of the test piece measured by the above method 3 ) and corresponds to the sum of the volume of the resin constituting the foamed sheet and the total volume of the closed cell portion in the test piece. Va: Apparent volume (cm) of the test specimen calculated from the outer dimensions of the test specimen used in the measurement 3 ). W: total mass (g) of the cut sample used in the measurement. ρ: density (g / cm) of the resin composition constituting the foam sheet 3 ). [Example]

[0139] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0140] In the examples and comparative examples, the following devices were used.

[0141] In the production of the foamed sheet of the examples, a first extruder with a barrel inner diameter of 90 mm was prepared as an extruder for forming foamed layer A. A co-extrusion annular die was attached downstream of the extruder, and a mandrel (cooling tube) with a diameter of 380 mm was arranged downstream of the annular die. A second extruder with a barrel inner diameter of 65 mm was prepared as an extruder for forming foamed layer B, and the downstream side of the second extruder was connected to the co-extrusion annular die. The extrusion apparatus prepared in this manner was used to produce a foamed sheet.

[0142] In the production of the foamed sheet of the comparative example, a first extruder with a barrel inner diameter of 90 mm was prepared as an extruder for forming a foamed layer. An annular die was attached downstream of the extruder, and a mandrel (cooling tube) with a diameter of 380 mm was placed downstream of the annular die. The extrusion apparatus thus prepared was used to produce a foamed sheet.

[0143] Table 1 shows details of the polyethylene resins used in the examples and comparative examples. The biomass content is a value measured according to ASTM D 6866. The melt flow rate is a value measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014. The melting point is a value measured based on JIS K 7121-1987.

[0144] [Table 1]

[0145] Table 2 shows the raw material blends for producing the foam sheets of the Examples and Comparative Examples, and the physical properties of the foam sheets obtained in each Example and Comparative Example.

[0146] [Table 2]

[0147] The foamed sheets of the examples were produced using the above-described extrusion apparatus as follows.

[0148] To form foam layer A, a total of 100 parts by mass of polyethylene resin A shown in Table 2 and 1 part by mass of talc (High Filler #12, manufactured by Matsumura Sangyo Co., Ltd.) as a cell adjusting agent were fed into a first extruder, heated, melted, and kneaded to form a resin melt. Next, a physical foaming agent (isobutane) was injected into the resin melt so as to form foam layer A of the desired density, and the mixture was further kneaded, and the temperature was adjusted to about 200°C to form a foamable resin melt A. The amount of physical foaming agent in the foamable resin melt A was adjusted to a range of 10% to 16% by mass. Next, the temperature of the foamable resin melt A was adjusted to about 112°C on the downstream side of the extruder.

[0149] On the other hand, to form foam layer B, polyethylene resin B shown in Table 2 and 1 part by mass of talc (High Filler #12 manufactured by Matsumura Sangyo Co., Ltd.) as a cell adjusting agent were fed into a second extruder, heated, melted, and kneaded to form a resin melt. Next, a physical foaming agent (isobutane) was injected into the resin melt so as to form foam layer B of the desired density, and the mixture was further kneaded, and the temperature was adjusted to about 200°C to form foamable resin melt B. The amount of physical foaming agent in foamable resin melt B was adjusted to a range of 10% to 16% by mass. Next, the temperature of the foamable resin melt B was adjusted to about 112°C on the downstream side of the extruder.

[0150] The foamable resin melt A and the foamable resin melt B were laminated in a co-extrusion annular die, and then extruded from the co-extrusion annular die into the atmosphere, thereby foaming the foamable resin melt A and the foamable resin melt B and forming a foam with a multilayer structure. This multilayer foam was expanded with a cylindrical expanding device (mandrel) and taken up with a take-up machine to have a predetermined thickness, basis weight and density. The multilayer foam was then cut open along the extrusion direction to produce foam sheets of the examples shown in Table 2, each having a width of approximately 1.3 m.

[0151] In Examples 1 to 3, a foamed sheet was produced so as to have a laminated structure of foamable resin melt A / foamable resin melt B / foamable resin melt A, with a total output rate of foamable resin melt A and foamable resin melt B of 120 kg / hr, a ratio of the output rate of foamable resin melt B to foamable resin melt A of 0.50 (foamable resin melt A / foamable resin melt B / foamable resin melt A=1 / 1 / 1), and a take-up speed of 51 m / min, to obtain a multilayer foamed sheet having foamed layer A on both sides of foamed layer B (laminate configuration of FIG. 1(a)).

[0152] In Example 4, a foamed sheet was produced so as to have a laminated structure of foamable resin melt A / foamable resin melt B / foamable resin melt A, with a total output rate of foamable resin melt A and foamable resin melt B of 120 kg / hr, a ratio of the output rate of foamable resin melt B to foamable resin melt A of 1.0 (foamable resin melt A / foamable resin melt B / foamable resin melt A=1 / 2 / 1), and a take-up speed of 38 m / min, to obtain a multilayer foamed sheet having foamed layer A on both sides of foamed layer B (laminate configuration of FIG. 1(a)).

[0153] In Example 5, a foamed sheet was produced so as to have a laminated structure of foamable resin melt A / foamable resin melt B / foamable resin melt A, with a total output rate of foamable resin melt A and foamable resin melt B of 120 kg / hr, a ratio of the output rate of foamable resin melt B to foamable resin melt A of 1.5 (foamable resin melt A / foamable resin melt B / foamable resin melt A=1 / 3 / 1), and a take-up speed of 31 m / min, to obtain a multilayer foamed sheet having foamed layer A on both sides of foamed layer B (laminate configuration in FIG. 1(a)).

[0154] In Example 6, a foamed sheet was produced so as to have a laminated structure of foamable resin melt B / foamable resin melt A / foamable resin melt B, with a total output rate of foamable resin melt A and foamable resin melt B of 120 kg / hr, a ratio of the output rate of foamable resin melt B to foamable resin melt A of 0.67 (foamable resin melt B / foamable resin melt A / foamable resin melt B = 1 / 3 / 1), and a take-up speed of 31 m / min, to obtain a multilayer foamed sheet having foamed layers B on both sides of foamed layer A (lamination configuration in FIG. 1(b)).

[0155] In Example 7, a foamed sheet was produced so as to have a laminated structure of foamable resin melt A / foamable resin melt B, with the total discharge rate of the foamable resin melt A and the foamable resin melt B being 120 kg / hr, the ratio of the discharge rate of the foamable resin melt B to the foamable resin melt A being 0.83 (foamable resin melt A / foamable resin melt B=1 / 0.83), and the take-up speed being 70 m / min, to obtain a multilayer foamed sheet having a foamed layer B on one side of a foamed layer A (laminate configuration in FIG. 1(c)).

[0156] The single-layer foamed sheet of the comparative example was produced in the same manner as in Example 1, except that the foamed sheet was produced by extruding the foamable resin melt A having the raw material composition shown in Table 2 using the above-mentioned extrusion device so as to form only a single foamed layer.

[0157] The average thickness, basis weight, density, closed cell ratio, and biomass ratio were calculated for the multilayer foamed sheets obtained in each Example and the single-layer foamed sheets obtained in each Comparative Example. The foamed sheets obtained in the Examples and Comparative Examples were non-crosslinked foamed sheets.

[0158] <Average thickness> The average thickness of the foam sheet was determined by measuring the thickness at 1 cm intervals across the entire width of the foam sheet in the width direction perpendicular to the extrusion direction of the foam sheet, and calculating the arithmetic mean of the measured thicknesses. The thickness was measured using an offline thickness measuring instrument such as the TOF-4R manufactured by Yamabun Denki Co., Ltd. The foam sheet used for the measurement had been conditioned for at least 24 hours at a temperature of 23±5°C and a relative humidity of 50%.

[0159] <Basic weight> The basis weight of the entire foam sheet is calculated by dividing the area (m 2 ) and mass (g), and calculate the mass (g) to the area (m 2 ) to get the basis weight (g / m 2 ) was sought.

[0160] The basis weight of each foam layer was calculated from the relationship between the extrusion rate X [g / hour] of each foam layer during production 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, and then the basis weight of the entire foam sheet was calculated from the relationship between the extrusion rate of each foam layer and the basis weight of the entire foam sheet according to the following formula (1). Basis weight of the entire resin layer [g / m 2 ]=〔X / (L×W)〕 (1)

[0161] <density> The density of the foam sheet is determined by the basis weight (g / m 2 ) is divided by the average thickness of the foam sheet, and then (kg / m 3 ) was calculated by converting the units.

[0162] <Closed bubble rate> The closed cell content of the foam sheet was measured as follows. First, a cut sample measuring 25 mm × 25 mm × sheet thickness (thickness of the foam sheet) was prepared by randomly cutting the foam sheet. A plurality of cut samples were stacked to prepare a test piece so that the total sheet thickness was as close to 20 mm as possible. Next, the true volume Vx of the test piece was measured using an air comparison hydrometer Model 930 manufactured by Toshiba Beckman Co., Ltd. according to Procedure C of ASTM-D2856-70, and the closed cell content S (%) was calculated using the following formula (3). The above measurement was performed using five test pieces, and the arithmetic average value was taken as the closed cell content of the foam sheet. S(%)=(Vx-W / ρ)×100 / (Va-W / ρ)···(3) Vx: The true volume (cm) of the test piece measured by the above method 3 ) and corresponds to the sum of the volume of the resin constituting the foamed sheet and the total volume of the closed cell portion in the test piece. Va: Apparent volume (cm) of the test specimen calculated from the outer dimensions of the test specimen used in the measurement 3 ). W: total mass (g) of the cut sample used in the measurement. ρ: Density of the resin that makes up the foam sheet (g / cm 3 ).

[0163] <Biomass ratio> The biomass degree was calculated from the biomass degree of the plant-derived polyethylene used in producing the foam sheet, measured according to ASTM D 6866, and the blending ratio of the plant-derived polyethylene in each foam layer.

[0164] The foamed sheets of the examples and the comparative examples were evaluated for appearance as follows, and the results are shown in Table 2.

[0165] <Appearance> The appearance of the resulting foamed sheet was evaluated based on the following criteria regarding the occurrence of wrinkles on the surface layer of each side of the foamed sheet. A: Almost no wrinkles were observed on the foam sheet on either side, and it had a good appearance. B: Many wrinkles are observed on at least one surface of the foam sheet.

[0166] In the above evaluation, "A" indicates good appearance. The wrinkles that appeared in the evaluation "B" are thought to have occurred because the foam's cells were more likely to break during extrusion. Because the foam's cells had broken, the effects of shrinkage caused by the dissipation of the blowing agent could not be eliminated even after the foam was cured, and wrinkles and other imperfections remained.

[0167] The single-layer foam sheet of the Comparative Example was inferior in appearance. Furthermore, the closed cell ratio of the foam sheet was lower than that of the multilayer foam sheet of the Examples. In contrast, the foam sheets of the Examples had good appearance. Furthermore, the closed cell ratio of the foam sheets was higher than that of the Comparative Example.

Claims

1. Basis weight: 100 g / m ２ 1. A method for producing a polyethylene-based resin foamed sheet having a biomass content of 5% or more as measured in accordance with ASTM D 6866, comprising: The foam sheet is a multi-layer foam sheet in which a polyethylene-based resin foam layer A and a polyethylene-based resin foam layer B are laminated and bonded together, The foam layer A and the foam layer B are formed by co-extruding a foamable resin melt for forming the foam layer A, which is obtained by kneading a polyethylene-based resin A and a physical foaming agent, and a foamable resin melt for forming the foam layer B, which is obtained by kneading a polyethylene-based resin B and a physical foaming agent, the polyethylene resin A contains polyethylene X consisting of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene; the polyethylene resin B includes polyethylene Y consisting of low-density polyethylene or 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 blending amounts of the above is less than 25% by mass (including 0), The plant-derived polyethylene b-PE in the polyethylene Y Ｙ The total amount Yb of the plant-derived polyethylene b-PE in the polyethylene X is Ｘ The method for producing a polyethylene resin foam sheet, wherein the blending amount of the above is greater than the total blending amount Xb.

2. The plant-based polyethylene b-PE measured by ASTM D 6866 Ｘ The biomass ratio is 80% or more, The plant-based polyethylene b-PE measured by ASTM D 6866 Ｙ 2. The method for producing a polyethylene resin foam sheet according to claim 1, wherein the biomass content of the polyethylene resin foam is 80% or more.

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

4. 3. The method for producing a polyethylene resin foam sheet according to claim 1, wherein the ratio of the basis weight of the foam layer B to the basis 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 foam sheet has a thickness of less than 2 mm.

6. Basis weight: 100 g / m ２ A polyethylene-based resin foam sheet having a biomass content of 5% or more as measured by ASTM D 6866, The foam sheet is a multi-layer foam sheet in which a polyethylene-based resin foam layer A and a polyethylene-based resin foam layer B are laminated and bonded together, the polyethylene-based resin foam layer A contains polyethylene X consisting of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene; the polyethylene-based resin foam layer B contains polyethylene Y consisting of low-density polyethylene or 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 blending amounts of the above is less than 25% by mass (including 0), The plant-derived polyethylene b-PE in the polyethylene Y Ｙ The total amount Yb of the plant-derived polyethylene b-PE in the polyethylene X is Ｘ A polyethylene resin foam sheet in which the blending amount is greater than the total blending amount Xb.

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