Method for producing polyethylene-based resin multilayer foam sheet and polyethylene-based resin multilayer foam sheet

Abstract

To provide a method for producing a multilayer foam sheet which has less environmental loads, and is excellent in appearance, and a polyethylene-based resin multilayer foam sheet.SOLUTION: A polyethylene-based resin multilayer foam sheet includes a polyethylene-based resin foam layer and a polyethylene-based resin layer stacked on and bonded to at least one surface of the foam layer, by co-extrusion of a foamable resin molten material for foam layer formation obtained by kneading a polyethylene-based resin A and a physical foaming agent, and a resin molten material for resin layer formation obtained by kneading a polyethylene-based resin B. There is provided a method for producing a polyethylene-based resin multilayer foam sheet having density of 300 kg / m3 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a polyethylene resin multilayer foam sheet and a polyethylene resin multilayer foam sheet.

Background Art

[0002] Foam sheets having a polyethylene resin as a base resin are known. Such foam sheets are used in various applications such as cushioning materials and packaging materials. In recent years, products that consider the environment have been demanded. From such a viewpoint, foam sheets using plant-derived polyethylene having a predetermined biomass degree as a raw material are known.

[0003] For example, Patent Document 1 discloses a polyethylene resin foam sheet including a foam layer containing low-density polyethylene containing natural-derived ethylene as a constituent unit at a predetermined ratio.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-described foam sheet, from the viewpoint of further reducing the environmental load, a foam sheet having a lower density may be desired. On the other hand, when a foam sheet having a low density is produced by using plant-derived polyethylene as a resin raw material for the foam layer as in Patent Document 1, the appearance of the obtained foam sheet tends to deteriorate. The present invention has been made in view of such problems, and an object thereof is to provide a polyethylene resin multilayer foam sheet having a small environmental load and excellent appearance.

Means for Solving the Problems

[0006] [1] A polyethylene resin foamable melt for forming a foam layer, which is obtained by kneading a polyethylene resin A and a physical foaming agent, and a resin melt for forming a resin layer, which is obtained by melt-kneading a polyethylene resin B, are co-extruded to provide a polyethylene resin foam layer and a polyethylene resin layer laminated and adhered to at least one side of the foam layer, having a density of 300 kg / m 3 The following method for producing a polyethylene resin multilayer foam sheet, wherein the polyethylene resin A contains polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, the polyethylene resin B contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the total blending amount Bb of plant-derived polyethylene b-PE B in the polyethylene Y is 40% by mass or more, and the total blending amount Ab of plant-derived polyethylene b-PE A in the polyethylene X is 40% by mass or less (including 0), and the difference (Bb - Ab) between the total blending amount Bb of the plant-derived polyethylene b-PE B and the total blending amount Ab of the plant-derived polyethylene b-PE A is 20% by mass or more. A method for producing a polyethylene resin multilayer foam sheet.

[0007] [2] The biomass degree of the plant-derived polyethylene b-PE A and the plant-derived polyethylene b-PE B measured by ASTM D 6866 is 80% or more respectively. The method for producing a polyethylene resin multilayer foam sheet according to [1].

[0008] [3] The polyethylene Y contains plant-derived low-density polyethylene b-LD B and the melt flow rate of the plant-derived low-density polyethylene b-LD B measured at a temperature of 190 °C and a load of 2.16 kg is 0.1 g / 10 min or more and 25 g / 10 min or less. The method for producing a polyethylene resin multilayer foam sheet according to [1] or [2].

[0009] [4] The polyethylene Y is a plant-derived low-density polyethylene b-LD B and a linear low-density polyethylene LL B and is composed of a mixture thereof. The mass ratio of the plant-derived low-density polyethylene b-LD B to the linear low-density polyethylene LL B (b-LD B :LL B ) is 1:0.1 to 1:1. The method for producing a polyethylene-based resin multilayer foamed sheet according to any one of [1] to [3].

[0010] [5] The linear low-density polyethylene LL B contains a linear low-density polyethylene that is a copolymer of ethylene and octene. The method for producing a polyethylene-based resin multilayer foamed sheet according to [4].

[0011] [6] The resin melt for forming the resin layer further contains a polymer type antistatic agent ASP. The polyethylene Y contains a plant-derived low-density polyethylene b-LD B . The mass ratio of the plant-derived low-density polyethylene b-LD B to the polymer type antistatic agent ASP (b-LD B :ASP) is 1:0.05 to 1:3. The method for producing a polyethylene-based resin multilayer foamed sheet according to any one of [1] to [5].

[0012] [7] The mass ratio of the resin layer per side to the foamed layer is 0.01 to 0.4. The method for producing a polyethylene-based resin multilayer foamed sheet according to any one of [1] to [6].

[0013] [8] The biomass degree D of the multilayer foamed sheet measured by ASTM D 6866 is 5% or more and 60% or less. The method for producing a polyethylene-based resin multilayer foamed sheet according to any one of [1] to [7].

[0014] [9] A polyethylene-based resin foamed layer and a polyethylene-based resin layer laminated and adhered to at least one side of the foamed layer, with a density of 300 kg / m 3The following is a polyethylene resin multi-layer foamed sheet, where the polyethylene resin foamed layer contains polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the polyethylene resin layer contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene. The total blending amount Bb of plant-derived polyethylene b-PE B in the polyethylene Y is 40% by mass or more, and the total blending amount Ab of plant-derived polyethylene b-PE A in the polyethylene X is 40% by mass or less (including 0), and the difference (Bb - Ab) between the total blending amount Bb of the plant-derived polyethylene b-PE B and the total blending amount Ab of the plant-derived polyethylene b-PE A is 20% by mass or more. A polyethylene resin multi-layer foamed sheet.

Advantages of the Invention

[0015] The polyethylene resin multi-layer foamed sheet of the present invention has a small environmental load and excellent appearance. According to the manufacturing method of the polyethylene resin multi-layer foamed sheet of the present invention, a polyethylene resin multi-layer foamed sheet with a small environmental load and excellent appearance can be provided.

Brief Description of the Drawings

[0016]

Figure 1

Modes for Carrying Out the Invention

[0017] [Manufacturing Method of Multi-Layer Foamed Sheet] The manufacturing method of the polyethylene resin multilayer foamed sheet (hereinafter also referred to as "multilayer foamed sheet") according to the present invention is to co-extrude a foaming resin melt for forming a foamed layer (hereinafter also referred to as "foaming resin melt") obtained by kneading a polyethylene resin A and a physical foaming agent, and a resin melt for forming a resin layer obtained by melt-kneading a polyethylene resin B, to obtain a polyethylene resin foamed layer (hereinafter also referred to as "foamed layer") and a polyethylene resin layer (hereinafter also referred to as "resin layer") laminated and adhered to at least one side of the foamed layer, with a density of 300 kg / m 3 It is a method for manufacturing the following multilayer foamed sheet. The present invention includes an embodiment in which the resin layer is adhered only to one side of the foamed layer, and an embodiment in which the resin layer is adhered to each of one surface and the other surface of the foamed layer. FIG. 1 exemplifies an embodiment in which the resin layer is adhered to each of one surface and the other surface of the foamed layer.

[0018] In the manufacturing method of the present invention, the polyethylene resin A contains polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, and the polyethylene resin B contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene. The total blending amount Bb of the plant-derived polyethylene b-PE B in the polyethylene Y is 40% by mass or more, and the total blending amount Ab of the plant-derived polyethylene b-PE A in the polyethylene X is 40% by mass or less (including 0), and the difference (Bb - Ab) between the total blending amount Bb of the plant-derived polyethylene b-PE B and the total blending amount Ab of the plant-derived polyethylene b-PE A is 20% by mass or more.

[0019] Hereinafter, the manufacturing method of the present invention will be described in detail. In the method for manufacturing a multilayer foamed sheet according to the present invention, a known extrusion device used in the field of extrusion foaming can be employed. Specifically, for example, an extruder for forming a foamed layer configured to extrude a foamed resin melt, an extruder for forming a resin layer configured to extrude a resin melt for forming a resin layer, and a co-extrusion die configured to laminate the foamed resin melt and the resin melt for forming a resin layer on the downstream side of these extruders are provided. A multilayer foamed sheet can be manufactured using a co-extrusion device. Note that the co-extrusion die is attached to the downstream side of the extruder for forming a foamed layer, and the downstream side of the extruder for forming a resin layer and the co-extrusion die are connected, so that the foamed resin melt and the resin melt for forming a resin layer can be laminated and co-extruded.

[0020] When performing co-extrusion using a co-extrusion device, the foamed resin melt formed in the extruder for forming a foamed layer and the resin melt for forming a resin layer formed in the extruder for forming a resin layer are guided to a co-extrusion die and extruded in layers from the discharge port of the co-extrusion die. As the co-extrusion die, for example, a flat die having a linear discharge port may be used, but from the viewpoint of facilitating stable production of a wide foamed sheet, it is preferable to use an annular die having an annular discharge port. When using an annular die, after the resin melt for forming a resin layer is laminated on the outer surface side and / or the inner surface side of the foamed resin melt flowing in a cylindrical shape inside the die, a laminate of the foamed resin melt and the resin melt for forming a resin layer is extruded in a cylindrical shape from the discharge port of the die. When such a laminate is extruded into a lower pressure atmosphere (for example, in the air) than inside the extruder, the foamed resin melt foams to form bubbles, and a laminated foam is formed. Then, the extruded cylindrical laminated foam is cut while being pulled along a cylindrical expanding device (for example, a mandrel) equipped with a cooling mechanism, whereby a multilayer foamed sheet including a foamed layer and a resin layer laminated and adhered to the foamed layer can be obtained.

[0021] <Foamed resin melt> The foaming resin melt is obtained by kneading a polyethylene-based resin A and a physical foaming agent. By foaming the foaming resin melt, a polyethylene-based resin foamed layer is formed. The polyethylene-based resin A in the present invention refers to a resin containing 50 mol% or more of structural units derived from ethylene. For example, as the polyethylene-based resin A, polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), or an ethylene-based copolymer containing 50 mol% or more of structural units derived from ethylene such as ethylene-vinyl acetate copolymer (EVA) (however, excluding ethylene-based ionomers) can be mentioned. Note that the low-density polyethylene in the present invention has a long-chain branched structure and a density of 0.910 g / cm 3 or more and less than 0.930 g / cm 3 refers to polyethylene. Low-density polyethylene is indicated by the abbreviation "PE-LD" in "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties" of JIS K 6899-1:2015. Also, low-density polyethylene can be said to be high-pressure method low-density polyethylene.

[0022] In the present invention, polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene is used as the polyethylene-based resin A for forming the foamed layer. As the low-density polyethylene used as polyethylene X, plant-derived low-density polyethylene b-LD A and petroleum-derived low-density polyethylene p-LD A can be mentioned. These polyethylenes can be used in combination of two or more, and a foaming resin melt can be formed by melt-kneading the polyethylene-based resin A containing polyethylene X and a physical foaming agent. From the perspective of enhancing the extrusion foaming property, the proportion of low-density polyethylene in polyethylene X is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Further, the polyethylene-based resin A used for forming the foamed layer preferably has low-density polyethylene as the main component. Specifically, the proportion of low-density polyethylene in the polyethylene-based resin A is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0023] (Plant-derived polyethylene b-PE A , plant-derived low-density polyethylene b-LD A ) The above polyethylene X may contain plant-derived polyethylene b-PE A . As the plant-derived polyethylene b-PE A , low-density polyethylene or linear low-density polyethylene produced by polymerizing monomers containing bioethylene produced from plants such as sugarcane, corn, and beet can be used. When the polyethylene X contains plant-derived polyethylene b-PE A , it preferably contains plant-derived low-density polyethylene b-LD A . The proportion of plant-derived low-density polyethylene b-LD A in the plant-derived polyethylene b-PE A is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. A Examples of commercially available plant-derived low-density polyethylene include plant-derived low-density polyethylene such as SEB853, SPB681, and STN7006 manufactured by Braskem.

[0024] Plant-derived polyethylene b-PE AThe biomass content measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Also, plant-derived low-density polyethylene b-LD A The biomass content measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Note that the biomass content measured by 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.

[0025] Plant-derived low-density polyethylene b-LD A The melting point of 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. Plant-derived low-density polyethylene b-LD A When the melting point of plant-derived low-density polyethylene b-LD is within the above range, a foamed layer having a good cell structure can be stably obtained.

[0026] Plant-derived low-density polyethylene b-LD A The melting point of plant-derived low-density polyethylene b-LD can be measured based on JIS K 7121-1987. Using a test piece conditioned according to the conditions of Condition (2) of the test piece of JIS K 7121-1987 (however, the cooling rate is 10°C / min.), the melting peak is obtained by heating at 10°C / min, and the temperature at the peak of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the temperature at the peak of the melting peak with the largest area is taken as the melting point.

[0027] Plant-derived low-density polyethylene b-LD A The melt flow rate of plant-derived low-density polyethylene b-LD 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. Plant-derived low-density polyethylene b-LD AWhen the melt flow rate is within the above range, it becomes easier to stably manufacture the desired multilayer foamed sheet.

[0028] Also, the melt flow rate of the plant-derived low-density polyethylene b-LD A may exceed 1.0 g / 10 min. When the melt flow rate of the plant-derived low-density polyethylene b-LD A is relatively high, it tends to be difficult to obtain a foamed sheet with a low density and good appearance. On the other hand, in the present invention, even when using the plant-derived low-density polyethylene b-LD A having the above melt flow rate, a foamed sheet with good appearance can be stably manufactured in a wide density range.

[0029] The melt flow rate of the plant-derived low-density polyethylene b-LD A is a value measured at a temperature of 190 °C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0030] In addition, when using a plurality of types of plant-derived low-density polyethylene as the plant-derived low-density polyethylene b-LD A at the time of manufacturing the foamed layer, by preparing a measurement kneaded product in which each resin is melt-kneaded by an extruder or the like at the blending ratio of each plant-derived low-density polyethylene, and performing various measurements on the measurement kneaded product, the melting point and melt flow rate of the plant-derived low-density polyethylene b-LD A can be determined.

[0031] The total amount Ab of the plant-derived polyethylene b-PE A in the polyethylene X is 40% by mass or less (including 0). The plant-derived polyethylene b-PE ABy setting the total amount Ab of the compounding amounts within the above range, in the foaming resin melt, it becomes easier to increase the compounding amount of petroleum-derived polyethylene that is likely to enhance the extrusion foaming property, and it becomes easier to stably manufacture a multilayer foamed sheet with excellent appearance. From the above viewpoints, the total amount Ab of the compounding amounts is more preferably 30% by mass or less, further preferably 25% by mass or less, and particularly preferably 20% by mass or less. Also, from the viewpoint of making it easier to increase the biomass degree of the multilayer foamed sheet and making it easier to reduce the environmental load, the plant-derived polyethylene b-PE in the polyethylene X A The total amount Ab of the compounding amounts is preferably 2% by mass or more, more preferably 5% by mass or more, and further preferably 10% by mass or more.

[0032] (Petroleum-derived polyethylene p-PE A , Petroleum-derived low-density polyethylene p-LD A ) The polyethylene X preferably contains petroleum-derived polyethylene p-PE A . As the petroleum-derived polyethylene p-PE A , Low-density polyethylene or linear low-density polyethylene derived from fossil fuel resources produced using fossil fuels such as naphtha can be used. As the petroleum-derived polyethylene p-PE A When it contains petroleum-derived low-density polyethylene p-LD A , As the petroleum-derived low-density polyethylene p-LD A , The petroleum-derived low-density polyethylene used in the production of conventional polyethylene-based resin foams can be used. From the viewpoint of enhancing the extrusion foaming property, the proportion of petroleum-derived low-density polyethylene p-LD A in the petroleum-derived polyethylene p-PE A is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 80% by mass or more.

[0033] Petroleum-derived low-density polyethylene p-LD AThe melting point 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. Petroleum-derived low-density polyethylene p-LD A By setting the melting point of A within the above range, it becomes easier to stably obtain a foamed layer having a good cell structure.

[0034] Petroleum-derived low-density polyethylene p-LD A The melt flow rate of A is preferably 0.1 g / 10 min or higher and 12 g / 10 min or lower, and more preferably 0.2 g / 10 min or higher and 10 g / 10 min or lower. Petroleum-derived low-density polyethylene p-LD A By having the melt flow rate of A within the above range, it becomes easier to stably manufacture a desired multilayer foamed sheet.

[0035] Petroleum-derived low-density polyethylene p-LD A The melting point and melt flow rate of A are measured in the same manner as the melting point and melt flow rate of plant-derived low-density polyethylene b-LD A When a plurality of types of petroleum-derived low-density polyethylene are used as A , a measurement kneaded product in which each resin is melt-kneaded by an extruder or the like is prepared at the blending ratio of each petroleum-derived low-density polyethylene during the production of the foamed layer, and various measurements are performed on the measurement kneaded product, whereby the melting point and melt flow rate of petroleum-derived low-density polyethylene p-LD

[0036] Note that when a plurality of types of petroleum-derived low-density polyethylene are used as A , a measurement kneaded product in which each resin is melt-kneaded by an extruder or the like is prepared at the blending ratio of each petroleum-derived low-density polyethylene during the production of the foamed layer, and various measurements are performed on the measurement kneaded product, whereby the melting point and melt flow rate of petroleum-derived low-density polyethylene p-LD A can be determined. A can be determined.

[0037] The total blending amount Ap of petroleum-derived polyethylene p-PE in polyethylene X A is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Petroleum-derived polyethylene p-PE A By setting the total blending amount Ap of A within the above range, it becomes easier to stably manufacture a multilayer foamed sheet having a good appearance in a wide density range. Further, in the foamed resin melt, the plant-derived low-density polyethylene b-LD A The ratio (Ap-LD / Ab-LD) of the blending amount Ap-LD of the petroleum-derived low-density polyethylene p-LD A to the blending amount Ab-LD is preferably 1 or more and 5 or less, and more preferably 2 or more and 4 or less. In this case, while reducing the environmental load, it becomes easier to stably manufacture a multilayer foamed sheet with good appearance in a wide density range.

[0038] (Linear low-density polyethylene LL A ) The polyethylene-based resin A for forming the foamed resin melt may contain linear low-density polyethylene LL A . As the linear low-density polyethylene LL A , for example, an ethylene copolymer which is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms can be mentioned. When the foamed resin melt further contains linear low-density polyethylene LL A , at the time of extrusion foaming, the collapse of the bubbles of the foam is easily suppressed, and the closed-cell ratio of the obtained multilayer foamed sheet is easily increased. Thereby, it becomes easier to obtain a multilayer foamed sheet with good appearance. In addition, the rigidity of the multilayer foamed sheet can be easily increased, and a multilayer foamed sheet that is less likely to sag can be obtained.

[0039] Examples of the α-olefin having 4 to 10 carbon atoms include butene (4 carbon atoms), hexene (6 carbon atoms), octene (8 carbon atoms), and the like. Among these, linear low-density polyethylene LL C8 which is a copolymer of ethylene and octene (α-olefin having 8 carbon atoms) and contains linear low-density polyethylene LL A as a main component, it is possible to stably obtain a multilayer foamed sheet with a high closed-cell ratio and low sag. Note that octene includes isomers of octene such as 1-octene and isooctene. Linear low-density polyethylene LL A in the linear low-density polyethylene LLC8 The proportion is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 80% by mass or more.

[0040] In the present invention, linear low-density polyethylene LL A has a linear shape, and its density is preferably 0.910 g / cm 3 or more and 0.935 g / cm 3 or less. Linear low-density polyethylene is indicated by the abbreviation "PE-LLD" in "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Characteristics" of JIS K 6899-1:2015. Further, linear low-density polyethylene LL A may contain plant-derived components (naturally derived components). From the viewpoint of supply stability in the market, linear low-density polyethylene derived from fossil fuel resources (petroleum-derived linear low-density polyethylene) produced from fossil fuels as raw materials can be preferably used.

[0041] Linear low-density polyethylene LL A preferably has a melting point of 116°C or higher and 130°C or lower, and more preferably 118°C or higher and 126°C or lower. When the melting point of linear low-density polyethylene LL A is within the above range, it is easy to suppress the bursting of bubbles during extrusion foaming, and it is easy to stably obtain a multilayer foamed sheet with a high closed cell ratio.

[0042] Linear low-density polyethylene LL A preferably has a melt flow rate of 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. When the melt flow rate of linear low-density polyethylene LL A is within the above range, it is easy to suppress the bursting of bubbles during extrusion foaming, and it is easy to stably obtain a multilayer foamed sheet with a high closed cell ratio.

[0043] Linear low-density polyethylene LL AThe melting point and melt flow rate of the plant-derived low-density polyethylene b-LD A are measured in the same manner as the melting point and melt flow rate of A .

[0044] In addition, when using a plurality of types of linear low-density polyethylene as the linear low-density polyethylene LL A during the production of the foamed layer, by preparing a kneaded product for measurement in which each resin is melt-kneaded by an extruder or the like at the blending ratio of each linear low-density polyethylene, and performing various measurements on the kneaded product for measurement, the melting point and melt flow rate of the linear low-density polyethylene LL A can be determined.

[0045] When blending the linear low-density polyethylene LL A into the foaming resin melt, the blending amount AL of the linear low-density polyethylene LL A in the polyethylene X 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. By setting the blending amount AL of the linear low-density polyethylene LL A within the above range, even when obtaining a multilayer foamed sheet with a relatively low density, it becomes easier to stably suppress the foam breakage of bubbles during extrusion foaming.

[0046] Further, when blending the petroleum-derived low-density polyethylene p-LD A and the plant-derived low-density polyethylene b-LD A and the linear low-density polyethylene LL A as the polyethylene X, when blending the plant-derived low-density polyethylene b-LD A and the petroleum-derived low-density polyethylene p-LD A the total of the blending amounts (Ab-LD + Ap-LD) of the plant-derived low-density polyethylene b-LD and the petroleum-derived low-density polyethylene p-LD, and the linear low-density polyethylene LL AThe mass ratio to the blending amount AL (Ab+Ap:AL) is preferably 1:0.05 to 1:0.4, more preferably 1:0.1 to 1:0.3. By setting the mass ratio (Ab-LD+Ap-LD:AL) within the above range, even when obtaining a multilayer foamed sheet with a relatively low density while increasing the biomass degree of the multilayer foamed sheet, it becomes easier to stably suppress the defoaming of bubbles during extrusion foaming.

[0047] (Melt flow rate ratio (p-LD A / b-LD A )) The melt flow rate ratio (p-LD A of petroleum-derived low-density polyethylene p-LD A to the melt flow rate of plant-derived low-density polyethylene b-LD A / b-LD A ) is preferably 0.01 or more and 3 or less, more preferably 0.05 or more and 2 or less. By having the melt flow rate ratio (p-LD A / b-LD A ) within the above range, it is possible to stably manufacture a multilayer foamed sheet with excellent appearance. Also, even when the melt flow rate of plant-derived low-density polyethylene b-LD A exceeds 1.0 g / 10 min, it is possible to stably manufacture a multilayer foamed sheet with excellent appearance.

[0048] (Difference in melting point between b-LD A and p-LD A ) The difference in melting point between the melting point of plant-derived low-density polyethylene b-LD A and the melting point of petroleum-derived low-density polyethylene p-LD A (melting point of b-LD A - melting point of p-LD A ) is preferably within 5°C, more preferably within 3°C, from the viewpoint of enhancing extrusion stability.

[0049] (Physical foaming agent) As the physical foaming agent used for the foaming resin melt, an organic physical foaming agent or an inorganic physical foaming agent can be used. Examples of the organic physical foaming agent 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.

[0050] Examples of the inorganic physical foaming agent include oxygen, nitrogen, carbon dioxide, air, water, etc. These physical foaming agents can be used by mixing two or more of them. Among these, from the viewpoint of excellent extrusion foamability and take - up stability of the multilayer foam sheet, it is preferable to use an organic physical foaming agent, and it is more preferable to use butane. As butane, normal butane, isobutane, or a mixture thereof can be used.

[0051] The addition amount of the physical foaming agent is adjusted according to the type of the physical foaming agent, the density and basis weight of the target multilayer foam sheet. For example, when using 30% by mass of isobutane and 70% by mass of normal butane as the physical foaming agent, the addition amount of the physical foaming agent 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 with respect to 100 parts by mass of the polyethylene - based resin A.

[0052] (Other additives) In addition to the polyethylene - based resin A and the physical foaming agent, various other additives may be added to the foaming resin melt. Examples of the other additives include a cell regulator, an anti - shrinkage agent, an antioxidant, a heat stabilizer, a weathering agent, an ultraviolet absorber, a flame retardant, an inorganic filler, an antibacterial agent, a colorant, etc.

[0053] As the bubble regulator, inorganic powder or chemical blowing agent can be used. Examples of the inorganic powder include talc, zeolite, silica, calcium carbonate, etc. Examples of the chemical blowing agent include azodicarbonamide, hydrazodicarbonamide, azobisisobutyronitrile, sodium hydrogen carbonate (baking soda), and baking soda-citric acid-based chemical blowing agents which are mixtures of sodium hydrogen carbonate and a monoalkali metal salt of citric acid such as citric acid or sodium citrate. The addition amount of the bubble regulator is preferably 0.01 part by mass or more and 3 parts by mass or less, more preferably 0.2 part by mass or more and 2 parts by mass, based on 100 parts by mass of the polyethylene-based resin A for forming the foaming resin melt, because it becomes easy to stably adjust the bubble diameter of the foaming layer within a desired range.

[0054] Also, within the range that can achieve the intended effect of the present invention, other resins and elastomers other than the polyethylene-based resin A specified in the present invention may be blended. When blending other resins and elastomers, 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, based on 100 parts by mass of the polyethylene-based resin A.

[0055] In the formation of the foaming resin melt, for example, the polyethylene-based resin A, the physical blowing agent, and additives added as necessary are supplied to an extruder for forming the foaming layer. Then, by melt-kneading these in the extruder for forming the foaming layer, a foaming resin melt can be formed.

[0056] <Resin melt for forming the resin layer> The resin melt for forming the resin layer is obtained by melt-kneading the polyethylene-based resin B as a resin raw material for forming the resin layer. The polyethylene-based resin layer is formed by the resin melt for forming the resin layer. The polyethylene-based resin B in the present invention refers to a resin containing 50 mol% or more of structural units derived from ethylene. For example, as the polyethylene-based resin B, polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and ethylene-based copolymers containing 50 mol% or more of structural units derived from ethylene such as ethylene-vinyl acetate copolymer (EVA) (however, excluding ethylene-based ionomers) can be mentioned. As the polyethylene-based resin B, polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene is used. As the low-density polyethylene used as polyethylene Y, plant-derived low-density polyethylene b-LD B , petroleum-derived low-density polyethylene p-LD B can be mentioned. Further, two or more of these polyethylenes can be used in combination. In addition, the low-density polyethylene in the present invention has a long-chain branched structure and a density of 0.910 g / cm 3 or more and less than 0.930 g / cm 3 . Low-density polyethylene is indicated by the abbreviation "PE-LD" in "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties" of JIS K 6899-1:2015. In addition, low-density polyethylene can also be said to be high-pressure method low-density polyethylene. In addition, the resin raw material for forming the resin melt for forming the resin layer may contain, in addition to the polyethylene-based resin B, a polystyrene-based resin, a polymer type antistatic agent, and the like.

[0057] In the present invention, the polyethylene-based resin layer is a resin layer containing the polyethylene-based resin B. Specifically, the proportion of the polyethylene-based resin B in the polyethylene-based resin layer is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 50% by mass or more. Also, the proportion of low-density polyethylene in polyethylene resin B is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Also, the proportion of low-density polyethylene in polyethylene Y is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0058] (Plant-derived polyethylene b-PE B , plant-derived low-density polyethylene b-LD B ) The polyethylene Y contains plant-derived polyethylene b-PE B . Plant-derived polyethylene b-PE B As the plant-derived polyethylene b-PE A , similar to the plant-derived polyethylene b-PE Plant-derived polyethylene b-PE B When containing plant-derived low-density polyethylene b-LD B , the proportion of plant-derived low-density polyethylene b-LD B in the plant-derived polyethylene b-PE B is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0059] The biomass content measured by ASTM D 6866 in the plant-derived polyethylene b-PE B is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Also, the plant-derived polyethylene b-LD BThe biomass content measured by ASTM D 6866 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. When the biomass content is within the above range, the environmental load is small, and it becomes easier to stably obtain a multilayer foamed sheet having a good appearance.

[0060] Plant-derived low-density polyethylene b-LD B The melting point of 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 102°C or lower. Plant-derived low-density polyethylene b-LD B When the melting point of is within the above range, a multilayer foamed sheet having a good appearance can be stably manufactured.

[0061] Plant-derived low-density polyethylene b-LD B The melting point of is the same as that of plant-derived low-density polyethylene b-LD A and can be measured based on JIS K 7121-1987.

[0062] Plant-derived low-density polyethylene b-LD B The melt flow rate of is preferably 0.1 g / 10 min or more and 30 g / 10 min or less, more preferably 0.1 g / 10 min or more and 25 g / 10 min or less, even more preferably 0.5 g / 10 min or more and 20 g / 10 min or less, and even more preferably more than 1.0 g / 10 min and 15 g / 10 min or less. Plant-derived low-density polyethylene b-LD B When the melt flow rate of is within the above range, at the time of extrusion foaming, the resin layer can be well laminated on the foamed layer, and it becomes easier to improve the appearance of the multilayer foamed sheet. Also, when the resin layer is well laminated at the time of extrusion foaming, the addition efficiency of the physical foaming agent blended in the foamed resin melt can be increased. As a result, the foamed resin melt can be foamed to a low density without excessively blending the physical foaming agent, so that the foaming of the bubbles is suppressed, and a multilayer foamed sheet with a good appearance can be stably obtained.

[0063] Plant-derived low-density polyethylene b-LD B Its melt flow rate is the value measured at a temperature of 190°C and a load of 2.16 kg in accordance with JIS K7210-1:2014.

[0064] In addition, when using multiple types of plant-derived low-density polyethylene as plant-derived low-density polyethylene b-LD B by the blending ratio of each plant-derived low-density polyethylene during the production of the resin layer, a kneaded mixture for measurement is prepared by melting and kneading each resin with an extruder or the like, and various measurements are performed on the kneaded mixture for measurement, whereby the melting point and melt flow rate of plant-derived low-density polyethylene b-LD B can be determined.

[0065] The total blending amount Bb of plant-derived polyethylene b-PE in polyethylene Y B is 40% by mass or more. By forming the resin layer with the total blending amount Bb of plant-derived polyethylene b-PE B within the above range, it becomes easier to increase the biomass degree of the multilayer foamed sheet. From this viewpoint, the total blending amount Bb is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Note that the total blending amount Bb of plant-derived polyethylene b-PE B may be 100% by mass.

[0066] Furthermore, in the present invention, the difference (Bb - Ab) between the total blending amount Bb of plant-derived polyethylene b-PE B and the total blending amount Ab of plant-derived polyethylene b-PE A is 20% by mass or more. By having the total blending amount Bb be a specific value or more and the difference (Bb - Ab) between the total blending amount Bb and the total blending amount Ab be a specific value or more, while increasing the biomass degree of the multilayer foamed sheet, petroleum-derived low-density polyethylene p-LD which is easy to increase the extrusion foamability is added to the foaming resin melt AThe blending ratio of etc. can be increased. As a result, a multilayer foamed sheet with a small environmental load and good appearance in a wide density range can be obtained. From the above viewpoints, the difference (Bb - Ab) between the total blending amount Bb and the total blending amount Ab is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. From the viewpoint of easily increasing the biomass degree of the multilayer foamed sheet, the difference (Bb - Ab) between the total blending amount Bb and the total blending amount Ab may be 90% by mass or less, or may be 80% by mass or less.

[0067] (Linear low-density polyethylene LL B ) The polyethylene-based resin B for forming the resin melt for forming the resin layer may contain linear low-density polyethylene LL B . When the resin melt for forming the resin layer contains linear low-density polyethylene LL B , during extrusion foaming, the resin layer can easily follow and stretch along with the foamed layer, and a better resin layer can be easily formed. In addition, when the resin layer is laminated well during extrusion foaming, the addition efficiency of the physical foaming agent blended in the foaming resin melt can be increased. As a result, the foaming resin melt can be foamed to a low density without excessively blending the physical foaming agent, so that the bubbles in the foamed layer can be more effectively suppressed from bursting, and the effect of more stably obtaining a multilayer foamed sheet with excellent appearance becomes remarkable.

[0068] Linear low-density polyethylene LL B can be, for example, an ethylene-based copolymer that is a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms. Examples of the α-olefin having 4 to 10 carbon atoms include butene (4 carbon atoms), hexene (6 carbon atoms), octene (8 carbon atoms), and the like. Among these, linear low-density polyethylene LL which is a copolymer of ethylene and octene (α-olefin having 8 carbon atoms) C8By using linear low-density polyethylene containing as the main component, a multilayer foamed sheet with a high closed-cell ratio can be stably obtained. Note that octene includes isomers of octene such as 1-octene and isooctene. Linear low-density polyethylene LL B The linear low-density polyethylene LL in C8 The proportion is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0069] In the present invention, linear low-density polyethylene LL B has a linear shape, and its density is 0.910 g / cm 3 or more and 0.935 g / cm 3 or less. Linear low-density polyethylene is indicated by the abbreviation "PE-LLD" in "Plastics - Symbols and Abbreviations - Part 1: Basic Polymers and Their Properties" of JIS K 6899-1:2015. Also, linear low-density polyethylene LL B may contain plant-derived components (naturally derived components). From the perspective of supply stability in the market, linear low-density polyethylene derived from fossil fuel resources (petroleum-derived linear low-density polyethylene) produced from fossil fuels as raw materials can be preferably used.

[0070] Linear low-density polyethylene LL B The melting point of is preferably 116°C or more and 130°C or less, and more preferably 118°C or more and 126°C or less. By setting the melting point of linear low-density polyethylene LL B within the above range, it becomes easier to stably obtain a multilayer foamed sheet with good appearance.

[0071] Linear low-density polyethylene LL B The melt flow rate of 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. Linear low-density polyethylene LL BWhen the melt flow rate is within the above range, it becomes easier to suppress the bursting of bubbles during extrusion foaming, and it becomes easier to stably obtain a multilayer foamed sheet with a high closed cell ratio.

[0072] Linear low density polyethylene LL B The melting point and melt flow rate of are measured in the same manner as those of plant-derived low density polyethylene b-LD B

[0073] In addition, when using a plurality of types of linear low density polyethylene as linear low density polyethylene LL B at the compounding ratio of each linear low density polyethylene during the production of the resin layer, a kneaded product for measurement in which each resin is melt-kneaded by an extruder or the like is prepared, and various measurements are performed on the kneaded product for measurement, whereby the melting point and melt flow rate of linear low density polyethylene LL B can be determined.

[0074] When linear low density polyethylene LL B is blended into the resin melt for forming the resin layer, the blending amount of linear low density polyethylene LL B in polyethylene Y is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, and even more preferably 12% by mass or more and 30% by mass or less. By setting the blending amount of linear low density polyethylene LL B within the above range, a multilayer foamed sheet having a relatively low density and a high closed cell ratio can be stably produced.

[0075] Also, the mass ratio (b-LD B : LL B ) between plant-derived low density polyethylene b-LD B and linear low density polyethylene LL B is preferably 1:0.05 to 1:1, more preferably 1:0.08 to 1:0.6, and even more preferably 1:0.1 to 1:0.5. The ratio (b-LD B : LL B ​By setting [[ID=]], a multilayer foamed sheet having a relatively low density and a good appearance can be stably produced.

[0076] (Ratio of melt flow rate (LL B / b-LD B )) The ratio of the melt flow rate of linear low-density polyethylene LL B to that of plant-derived low-density polyethylene b-LD B (LL B / b-LD B ) is preferably 0.01 or more and 5 or less, and more preferably 0.05 or more and 1 or less. By the ratio of the melt flow rate (LL B / b-LD B ) being within the above range, a multilayer foamed sheet with excellent appearance can be stably produced. Also, even when the melt flow rate of plant-derived low-density polyethylene b-LD A exceeds 1.0 g / 10 min, a multilayer foamed sheet with excellent appearance can be stably produced.

[0077] (Difference in melting point (T_LL B -T_b-LD B )) The difference (T_LL - T_b-LD B ) between the melting point T_LL B of linear low-density polyethylene LL B and the melting point T_b-LD B of plant-derived low-density polyethylene b-LD B ) is preferably 5°C or more and 25°C or less, and more preferably 8°C or more and 20°C or less, from the viewpoint of enabling good lamination of the resin layers and facilitating the production of a multilayer foamed sheet with a high closed-cell ratio.

[0078] (Ratio of melt flow rate (b-LD B / p-LD A ), difference in melting point (T_p-LD A -T_b-LD B )) Also, from the viewpoint of facilitating the production of the desired multilayer foamed sheet, the melt flow rate of the plant-derived low-density polyethylene b-LD A with respect to the melt flow rate of the petroleum-derived low-density polyethylene p-LD B is preferably from 0.1 to 30, more preferably from 1 to 25. B / p-LD A ) Also, from the viewpoint of enhancing extrusion stability, the difference (T_p-LD A -T_b-LD A ) between the melting point T_p-LD of the petroleum-derived low-density polyethylene p-LD B and the melting point T_b-LD of the plant-derived low-density polyethylene b-LD B is preferably within 5°C, more preferably within 3°C. A -T_b-LD B )

[0079] (Polymeric antistatic agent ASP) The resin melt for forming the resin layer may further contain a polymeric antistatic agent ASP. When the resin melt for forming the resin layer contains the polymeric antistatic agent ASP, the resin layer also functions as an antistatic layer.

[0080] Examples of the polymeric antistatic agent ASP include polyethers, polyether ester amides, block copolymers of polyethers and polyolefins, ionomer resins, and the like. Among these, block copolymers of polyethers and polyolefins and / or ionomer resins are preferred, and ionomer resins are particularly preferred. Also, when the resin melt for forming the resin layer contains an ionomer resin, it becomes easier to obtain a multilayer foamed sheet with excellent appearance. Although the reason for this is not clear, it is considered that when the resin layer contains an ionomer resin, the addition efficiency of the physical foaming agent blended in the foaming resin melt can be increased, making it easier to obtain a multilayer foamed sheet with a high closed cell ratio.

[0081] Examples of the block copolymer include those having a structure in which a block of polyolefin and a block of polyether are repeatedly and alternately bonded via a bond such as an ester bond, an amide bond, an ether bond, a urethane bond, or an imide bond.

[0082] As the ionomer resin, an ethylene-based ionomer can be preferably used. The ethylene-based ionomer is a resin in which intermolecular cross-linking is performed with metal ions between molecules of a copolymer of ethylene and an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, and maleic acid. Examples of the metal ions include ions of alkali metals such as lithium ions, sodium ions, and potassium ions, or ions of alkaline earth metals such as calcium ions. Among these, an ethylene-based potassium ionomer, which is an ionomer in which a copolymer of ethylene and an unsaturated carboxylic acid is intermolecularly cross-linked with potassium ions, can be preferably used because it can impart good antistatic performance to the multilayer foam sheet.

[0083] The surface resistivity of the polymer type antistatic agent ASP is preferably less than 1×10 12 Ω, more preferably 5×10 11 Ω or less, and even more preferably 1×10 10 Ω or less. The surface resistivity can be measured based on JIS K6271-1:2015.

[0084] The melt flow rate of the polymer type antistatic agent ASP is preferably 1 g / 10 min or more and 40 g / 10 min or less, and more preferably 2 g / 10 min or more and 35 g / 10 min or less. When using an ionomer resin in particular, an ionomer resin having a melt flow rate of 1 g / 10 min or more and 10 g / 10 min or less can be preferably used. When the melt flow rate of the polymer antistatic agent ASP is within the above range, a resin layer can be formed well. The melt flow rate of the polymer antistatic agent ASP is a value measured under the conditions of a temperature of 190°C and a load of 2.16 kg based on JIS K 7210-1:2014.

[0085] Specific examples of the polymer antistatic agent ASP include, for example, block copolymers of polyether and polyolefin such as "Pelestat 300", "Pelestat 230", "Pelestat HC250", "Perektron PVH", "Perektron PVL", "Perektron HS", "Perektron LMP" manufactured by Sanyo Chemical Industries, Ltd., and ionomer resins such as "Entira SD100", "Entira MK400" manufactured by Mitsui Dow Polychemical Co., Ltd., which are commercially available under these trade names.

[0086] When the polymer antistatic agent ASP is blended into the resin melt for forming the resin layer, from the viewpoint of forming a good resin layer, the blending amount of the polymer antistatic agent ASP is preferably 5% by mass or more and 60% by mass or less, more preferably 5% by mass or more and 50% by mass or less, still more preferably 6% by mass or more and 40% by mass or less, and particularly preferably 8% by mass or more and 30% by mass or less, with the total of the blending amount of the polyethylene-based resin B and the blending amount of the polymer antistatic agent ASP being 100% by mass.

[0087] Also, from the viewpoint of increasing the biomass degree of the multilayer foamed sheet and forming a good resin layer, the ratio (b-LD B :ASP) of the blending amount of the plant-derived low-density polyethylene b-LD B to the blending amount of the polymer antistatic agent ASP is preferably 1:0.05 to 1:3, more preferably 1:0.05 to 1:2, still more preferably 1:0.05 to 1:1, particularly preferably 1:0.08 to 1:0.6, and most preferably 1:0.1 to 1:0.4.

[0088] In addition, as long as it is within the range capable of achieving the intended effect of the present invention, other resins such as polystyrene resins or elastomers may be blended in the resin melt for forming the resin layer. When blending a polystyrene resin in the resin melt for forming the resin layer, polystyrene (GPPS) or high-impact polystyrene (HIPS) can be used as the polystyrene resin. Note that high-impact polystyrene is a rubber-modified polystyrene containing a rubber component, and is obtained, for example, by polymerizing styrene in the presence of rubber-like polymer particles such as polybutadiene. By blending a polystyrene resin in the resin melt for forming the resin layer, it becomes easier to take out the foam extruded from the extruder along the mandrel, and it becomes easier to disperse the ionomer resin well in the polyethylene resin. From such a viewpoint, the blending amount of the polystyrene resin is preferably 3 parts by mass or more and 30 parts by mass or less, and more preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyethylene resin B.

[0089] (Other Additives) Various other additives may be added to the resin melt for forming the resin layer. Examples of the additives include volatile plasticizers, anti-shrinking agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, antibacterial agents, colorants, and the like. Examples of the volatile plasticizer include alcohols having a boiling point of 120°C or lower, saturated hydrocarbons having 3 to 5 carbon atoms, dialkyl ethers having 1 to 3 carbon atoms in the alkyl chain, and the like.

[0090] In the production of the resin melt for forming the resin layer, for example, the resin raw material for forming the resin layer and other additives added as necessary are supplied to the extruder for forming the resin layer. Then, by melt-kneading these in the extruder for forming the resin layer, a resin melt for forming the resin layer can be obtained.

[0091] In manufacturing a multilayer foamed sheet having a desired apparent density or the like, mainly by adjusting the take-up speed of the multilayer foamed sheet, the discharge amounts of the foaming resin melt and the resin melt for forming the resin layer, and the blow-up ratio (diameter expansion ratio) of the multilayer foamed sheet during the production of the multilayer foamed sheet, a desired multilayer foamed sheet can be obtained. Specifically, it is preferable that the blow-up ratio of the tubular multilayer foam extruded from the extruder is 2.0 or more and 4.5 or less, and more preferably 2.1 or more and 4.0 or less. The blow-up ratio means the ratio of the diameter of the annular die (discharge port diameter) to the diameter of the mandrel (blow-up ratio: diameter of mandrel / diameter of the lip portion of the annular die). Also, it is preferable that the take-up speed of the tubular multilayer foam extruded from the extruder is 10 m / min or more and 120 m / min or less, and more preferably 20 m / min or more and 100 m / min or less. Also, although it depends on the size of the extruder and the length in the width direction of the multilayer foamed sheet to be obtained, it is preferable that the discharge amount of the foaming resin melt extruded from the extruder is 50 kg / hr or more and 300 kg / hr or less, and more preferably 60 kg / hr or more and 260 kg / hr or less. Also, it is preferable that the discharge amount of the resin melt for forming the resin layer extruded from the extruder is 5 kg / hr or more and 60 kg / hr or less, and more preferably 10 kg / hr or more and 50 kg / hr or less.

[0092] Also, it is preferable to co-extrude the foaming resin melt and the resin melt for forming the resin layer so that the mass ratio of the resin layer per side to the foaming layer (resin layer / foaming layer) is 0.01 to 0.4. By satisfying the relationship between the foaming resin melt and the resin melt for forming the resin layer and co-extruding the foaming resin melt and the resin melt for forming the resin layer with the above mass ratio relationship, while increasing the biomass degree of the multilayer foamed sheet, a multilayer foamed sheet with good appearance can be stably manufactured in a wide density range. Also, particularly when laminating resin layers on both sides of the foaming layer, the addition efficiency of the foaming resin melt during extrusion can be further increased, and a multilayer foamed sheet having a low density, a high closed cell ratio, and excellent appearance can be more stably manufactured. From the viewpoint of facilitating the stable production of a multilayer foam sheet having a desired biomass content and density, it is more preferable that the mass ratio of the resin layer per side to the foam layer (resin layer / foam layer) is 0.02 to 0.3, and even more preferably 0.03 to 0.2.

[0093] The mass ratio of the resin layer per side to the foam layer can be determined, for example, as the ratio of the basis weight of the resin layer per side to the basis weight of the foam layer (basis weight of the resin layer per side / basis weight of the foam layer). Here, the basis weight of the resin layer [g / m 2 can be determined by substituting the discharge amount X [g / hour] of the resin layer, the width W [m] of the obtained multilayer foam sheet, and the length L [m / hour] of the multilayer foam sheet extruded per unit time into the following formula (1). When the resin layer is laminated on both sides of the foam layer, the basis weight of the resin layer on each side can be determined from the relationship between the total basis weight of the resin layer and the discharge amount of each resin layer. Total basis weight of the resin layer [g / m 2 = [X / (L×W)] ···(1)

[0094] According to the manufacturing method described above, it is an object to provide a multilayer foam sheet with a small environmental load and excellent appearance. In the case of producing a foamed sheet by extrusion foaming, when attempting to obtain a foamed sheet with a low density, the production of the foamed sheet tends to become difficult. On the other hand, in the case of plant-derived polyethylene, compared to petroleum-derived polyethylene, since the types of resins that can be selected are fewer, the degree of freedom in producing the foamed sheet tends to decrease. For these reasons, in order to obtain a foamed sheet having a desired thickness and density and a desired biomass content, when producing a foamed sheet with a high biomass content by blending plant-derived polyethylene and petroleum-derived polyethylene as a single-layer foamed sheet, the production of the desired foamed sheet may become difficult. In particular, when obtaining a foamed sheet with a low density, since the bubbles of the foam tend to break easily during extrusion foaming, even when the obtained foamed sheet is cured, the influence of shrinkage caused by the dissipation of the foaming agent cannot be eliminated, and the foamed sheet may have wrinkles or the like remaining. In contrast, in the production method according to the present invention, a multilayer foamed sheet is produced such that it includes a specific resin layer containing a relatively large amount of plant-derived polyethylene, and the difference between the total blending amount of plant-derived polyethylene contained in the resin layer and the total blending amount of plant-derived polyethylene contained in the foamed layer is equal to or greater than a specific value. Thereby, while ensuring the biomass content in the entire multilayer foamed sheet, it is possible to increase the blending ratio of petroleum-derived low-density polyethylene or the like that easily enhances the extrusion foaming property in the foaming resin melt for forming the foamed layer. Even when obtaining a foamed sheet with a low density, it becomes easier to suppress the occurrence of bubble breakage in the foam during extrusion foaming. As a result, it is possible to obtain a multilayer foamed sheet that has a small environmental load and a good appearance in a wide density range.

[0095] [Multilayer foamed sheet] The multilayer foamed sheet produced by the production method described above includes a polyethylene-based resin foamed layer and a polyethylene-based resin layer laminated and adhered to at least one side of the foamed layer, with a density of 300 kg / m 3 It is the following polyethylene-based resin multilayer foamed sheet. The multilayer foamed sheet of the present invention includes a specific resin layer, and by satisfying a specific relationship between the resin layer and the foamed layer, it becomes a multilayer foamed sheet with a reduced environmental load and a good appearance.

[0096] <Foam layer> The foam layer contains polyethylene X made of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene. As the polyethylene resin A forming the foam layer, polyethylene X and the like described in the production method of the present invention can be used. For example, plant-derived low-density polyethylene b-LD A , petroleum-derived low-density polyethylene p-LD A , linear low-density polyethylene LL A and the like can be used. These polyethylene resins can be used in combination of two or more. In addition, the foam layer is mainly composed of polyethylene X. Specifically, the blending amount of polyethylene X in the foam layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Further, the proportion of low-density polyethylene in polyethylene X is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Regarding the properties (such as melting point and melt flow rate) of low-density polyethylene and the like forming the foam layer, the blending amounts of each resin, the relationship between the properties of each resin, etc., the properties of low-density polyethylene and the like, the blending amounts of each resin, and the relationship between the properties of each resin described in the production method of the present invention can be appropriately referred to.

[0097] The total blending amount Ab of the plant-derived polyethylene b-PE A in polyethylene X is 40% by mass or less (including 0). The plant-derived polyethylene b-PE ABy setting the total amount Ab of the blending amounts within the above range, a multilayer foamed sheet with excellent appearance can be stably obtained. From the above viewpoints, the total amount Ab of the blending amounts is more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less. In the multilayer foamed sheet of the present invention, the "blending amount" can be read as "content". Further, the blending amount of each resin such as low-density polyethylene in the multilayer foamed sheet of the present invention corresponds to the blending amount of each resin such as low-density polyethylene blended during the production of the multilayer foamed sheet. Also, from the viewpoint of easily increasing the biomass degree of the multilayer foamed sheet and easily reducing the environmental load, the plant-derived polyethylene b-PE A the total amount Ab of the blending amounts is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more.

[0098] <Resin layer> The resin layer contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene. The resin layer is, as described in the production method of the present invention, plant-derived low-density polyethylene b-LD B , petroleum-derived low-density polyethylene p-LD B , linear low-density polyethylene, polystyrene resin, polymer type antistatic agent, etc. may be included. In the present invention, the polyethylene-based resin layer is a resin layer containing polyethylene Y. Specifically, the blending amount of polyethylene Y in the resin layer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more. Also, the ratio of low-density polyethylene in polyethylene Y is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Examples of each resin constituting the resin layer, properties of each resin (such as melting point and melt flow rate), compounding amount of each resin, relationship between properties of each resin, etc. can be appropriately referred to the descriptions of examples of each resin, properties of each resin (such as melting point and melt flow rate), compounding amount of each resin, relationship between properties of each resin, etc. described in the manufacturing method of the present invention.

[0099] Plant-derived polyethylene b-PE in polyethylene Y B The total compounding amount Bb of is 40% by mass or more. Plant-derived polyethylene b-PE B By forming the resin layer with the total compounding amount Bb of within the above range, it becomes easier to increase the biomass degree of the multilayer foamed sheet. From such a viewpoint, the total compounding amount Bb is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Incidentally, the total compounding amount Bb of plant-derived polyethylene b-LD B may be 100% by mass.

[0100] In the present invention, the total compounding amount Bb of plant-derived polyethylene b-PE in the resin layer B and the total compounding amount Ab of plant-derived polyethylene b-PE in the foamed layer A The difference (Bb - Ab) between is 20% by mass or more. The total compounding amount Bb of b-PE B is a specific value or more, and the difference (Bb - Ab) between the total compounding amount Bb and the total compounding amount Ab is a specific value or more, so that while increasing the biomass degree of the multilayer foamed sheet, a multilayer foamed sheet with a high closed cell ratio can be stably manufactured. Thereby, a multilayer foamed sheet with a small environmental load and good appearance in a wide density range can be obtained. From the above viewpoints, the difference (Bb - Ab) between the total compounding amount Bb and the total compounding amount Ab is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. Incidentally, from the viewpoint of being easy to increase the biomass degree of the multilayer foamed sheet, the difference (Bb - Ab) between the total compounding amount Bb and the total compounding amount Ab may be 90% by mass or less, or 80% by mass or less.

[0101] The mass ratio of the resin layer per side to the foamed layer (resin layer / foamed layer) is preferably from 0.01 to 0.4, more preferably from 0.02 to 0.3, and even more preferably from 0.03 to 0.2. When the mass ratio (resin layer / foamed layer) is within the above range, a multilayer foamed sheet with good appearance can be obtained in a wide density range while increasing the biomass degree. In particular, when the resin layer is laminated on both sides of the foamed layer, a multilayer foamed sheet with a high closed cell ratio and low sag can be obtained.

[0102] [Physical properties of multilayer foamed sheet] <Grammage> The grammage of the multilayer foamed sheet is preferably 10 g / m 2 or more and 200 g / m 2 or less. When the grammage is within the above range, a low-grammage multilayer foamed sheet can be obtained, which can be suitably used as a cushioning material for logistics. From the perspective of making a lighter multilayer foamed sheet, the grammage is preferably 150 g / m 2 or less, more preferably 100 g / m 2 or less, and even more preferably 80 g / m 2 or less. The grammage can be obtained by measuring the area (m 2 ) and mass (g) of the multilayer foamed sheet cut out to a predetermined size (for example, 1000 mm × 250 mm), and dividing the mass (g) by the area (m 2 ).

[0103] Also, the grammage of the resin layer per side is preferably 0.5 g / m 2 or more and 20 g / m 2 or less from the perspective of easily obtaining a multilayer foamed sheet with good appearance in a wide density range while increasing the biomass degree. More preferably, it is 1 g / m 2 or more and 10 g / m 2 or less. Incidentally, as described above, the basis weight of the resin layer can be determined from the relationship between the discharge amount X of the resin layer, the width W [m] of the obtained multilayer foam sheet, and the length L [m / hour] of the multilayer foam sheet extruded per unit time, for example, during the production of the multilayer foam sheet. Also, for example, it can be determined by multiplying the thickness of the resin layer by the density of the resin composition constituting the resin layer and performing unit conversion. Specifically, it can be measured as follows. First, cut the multilayer foam sheet along the width direction of the multilayer foam sheet to form a vertical cross-section. Next, in the vertical cross-section, take more than 10 magnified photographs of the surface side of the multilayer foam sheet at equal intervals in the width direction. In the magnified photograph of each point, measure the thickness of the resin layer at 1 cm intervals in the width direction, and use the arithmetic mean value of the obtained values as the thickness of the resin layer for each surface. By multiplying the obtained thickness by the density of the resin composition and performing unit conversion, the basis weight of the resin layer for each surface can be determined.

[0104] <Density> The density of the multilayer foam sheet is 300 kg / m 3 The following. By setting the density of the multilayer foam sheet within the above range, a lightweight and excellent shock-absorbing multilayer foam sheet can be obtained, and it can be more preferably used as a shock-absorbing material for logistics. From the above viewpoints, the density is preferably 10 kg / m 3 or more and 200 kg / m 3 or less, more preferably 12 kg / m 3 or more and 100 kg / m 3 or less, and even more preferably 15 kg / m 3 or more and 80 kg / m 3 or less.

[0105] Incidentally, the density can be obtained by dividing the basis weight (g / m 2 ) of the multilayer foam sheet by the average thickness of the multilayer foam sheet described below, and further performing unit conversion to (kg / m 3 ).

[0106] <Average thickness> The average thickness of the multilayer foam sheet is preferably 0.1 mm or more and 5 mm or less. By setting the thickness of the multilayer foam sheet within the above range, the loading efficiency can be increased when used as interleaving paper for flat plates. In particular, when used for interleaving paper applications, the average thickness of the multilayer foam sheet is preferably 3 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. Also, from the perspective of enhancing cushioning properties, the average thickness of the multilayer foam sheet is preferably 0.2 mm or more, and preferably 0.3 mm or more.

[0107] The average thickness can be determined by measuring the thickness at 1 cm intervals across the entire width of the multilayer foam sheet in the width direction perpendicular to the extrusion direction of the multilayer foam sheet, and calculating the arithmetic mean of the measured thicknesses. The thickness can be measured using an offline thickness measuring instrument "TOF-4R" manufactured by Yamabun Electric Co., Ltd. The multilayer foam sheet used for measurement shall be conditioned for 24 hours or more under the conditions of a temperature of 23 ± 5°C and a relative humidity of 50%.

[0108] <Biomass content> The biomass content of the multilayer foam sheet measured by ASTM D 6866 is 5% or more and 60% or less. From the perspective of further reducing the environmental load, the biomass content of the multilayer foam sheet is preferably 8% or more, more preferably 10% or more, and even more preferably 15% or more. Also, the biomass content of the multilayer foam sheet may be 50% or less, 45% or less, or 40% or less.

[0109] The biomass content Df of the foam layer measured by ASTM D 6866 is preferably 40% or less (including 0), more preferably 30% or less, and even more preferably 25% or less. Also, the biomass content Dr of the resin layer measured by ASTM D 6866 is preferably 30% or more, more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more.

[0110] The difference (Dr - Df) between the biomass degree Dr of the resin layer and the biomass degree Df of the foamed layer is preferably 10% or more, more preferably 20% or more, still more preferably 25% or more, and particularly preferably 30% or more. When the difference in biomass degree (Dr - Df) is within the above range, it becomes easier to obtain a multilayer foamed sheet with a high biomass degree and a good appearance in a wide density range while increasing the biomass degree of the multilayer foamed sheet.

[0111] The biomass degree can be measured according to ASTM D 6866. Also, it can be calculated from the biomass degree measured according to ASTM D 6866, such as plant-derived low-density polyethylene (b-LD A , b-LD B ), etc., used in the production of the multilayer foamed sheet, and the blending ratio in each layer such as the plant-derived low-density polyethylene.

[0112] <Closed cell ratio> The closed cell ratio of the multilayer foamed sheet is preferably 40% or more, more preferably 50% or more, and still more preferably 60% or more. When the closed cell ratio of the multilayer foamed sheet is within the above range, it becomes easier to obtain a multilayer foamed sheet with excellent appearance. Also, appropriate rigidity can be imparted to the multilayer foamed sheet, and the multilayer foamed sheet can be made less likely to sag.

[0113] To measure the closed cell ratio, cut samples are prepared by randomly cutting the multilayer foamed sheet into 25 mm × 25 mm × sheet thickness (the thickness of the multilayer foamed sheet). A plurality of cut samples are stacked so that the total sum of the sheet thicknesses is closest to 20 mm to form a test piece. Next, according to Procedure C of ASTM-D2856-70, using an air comparison type pycnometer 930 type or the like of Toshiba Beckman Co., Ltd., the true volume Vx of the test piece is measured, and the closed cell ratio S (%) is calculated by the following formula (2). The above measurement is performed using 5 test pieces, and the arithmetic mean value is taken as the closed cell ratio of the multilayer foamed sheet. S(%) = (Vx - W / ρ) × 100 / (Va - W / ρ) ··· (2) Vx: The true volume (cm 3 ) of the test piece measured by the above method, which corresponds to the sum of the volume of the resin constituting the multilayer foam sheet and the total volume of the bubbles in the independent bubble portion within the test piece. Va: The apparent volume (cm 3 ) of the test piece calculated from the outer dimensions of the test piece used for the measurement. W: The total mass (g) of the cut samples used for the measurement. ρ: The density (g / cm 3 ) of the resin composition constituting the multilayer foam sheet.

[0114] <Surface resistivity> When the resin layer in the multilayer foam sheet contains a polymer type antistatic agent, the surface resistivity of the multilayer foam sheet is preferably 1×10 13 Ω or less, more preferably 5×10 12 Ω or less, and even more preferably 1×10 12 Ω or less. If the surface resistivity is within the above range, a multilayer foam sheet with sufficient antistatic performance can be obtained, and the adhesion of dust and the like can be suppressed. When resin layers are laminated on both sides of the multilayer foam sheet, it is more preferable that the surface resistivity of each side of the multilayer foam sheet is within the above range. The lower limit of the surface resistivity is not particularly limited, but is generally 1×10 7 Ω. The surface resistivity of the multilayer foam sheet can be obtained by cutting out a plurality of test pieces with a predetermined size (for example, 100 mm in length × 100 mm in width × thickness: sheet thickness) from the multilayer foam sheet, applying a voltage of 500 V to this test piece in accordance with JIS K6271-1:2015, measuring the surface resistance value 1 minute after the application, and taking the average value of the obtained measurement values. As the measuring device for the surface resistivity, for example, those manufactured by Takeda Riken Kogyo Co., Ltd., model: TR8601, etc. can be used.

Examples

[0115] Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the examples.

[0116] In the examples and comparative examples, the following apparatuses were used.

[0117] In the production of the multilayer foam sheet of the example, first, as an extruder for forming the foam layer, a first extruder with a barrel inner diameter of 115 mm was prepared. A coextrusion annular die was attached to the downstream side of the extruder, and a mandrel (cooling pipe) with a diameter of 380 mm was arranged on the downstream side of the annular die. Further, as an extruder for forming the resin layer, a second extruder with a barrel inner diameter of 50 mm was prepared, and the downstream side of the second extruder and the coextrusion annular die were connected. The extrusion apparatus thus prepared was used for the production of the multilayer foam sheet.

[0118] In the production of the foam sheet of the comparative example, as an extruder for forming the foam layer, a first extruder with a barrel inner diameter of 115 mm was prepared. An annular die was attached to the downstream side of the extruder, and a mandrel (cooling pipe) with a diameter of 380 mm was arranged on the downstream side of the annular die. The extrusion apparatus thus prepared was used for the production of the foam sheet.

[0119] Table 1 and Table 2 show the details of the polyethylene-based resins used in the examples and comparative examples. Table 1 shows the polyethylene-based resin A used for forming the foam layer, and Table 2 shows the polyethylene-based resin B used for forming the resin layer. The linear low-density polyethylene "5110G" in Table 1 and Table 2 is an ethylene copolymer of ethylene and octene, and the linear low-density polyethylene "25100J" in Table 2 is an ethylene copolymer of ethylene and hexene.

[0120]

Table 1

[0121]

Table 2

[0122] The multilayer foamed sheet of the example was manufactured as follows using the extrusion apparatus described above. In the example, a multilayer foamed sheet having resin layers laminated on both sides of the foamed layer was manufactured.

[0123] To form the foamed layer, a total of 100 parts by mass of each polyethylene-based resin A having the raw material formulation shown in Table 3 and 1 part by mass of talc (High Filler #12 manufactured by Matsumura Sangyo Co., Ltd.) as a foam regulator were supplied to the first extruder, heated, melted, and kneaded to obtain a resin melt. Next, a physical foaming agent (isobutane) was injected into the resin melt so as to obtain a multilayer foamed sheet having a desired density, and after further kneading, the temperature was adjusted to about 200°C to obtain a foamable resin melt. The blending amount of the physical foaming agent in the foamable resin melt was adjusted in the range of 18% by mass to 21% by mass in Examples 1, 3 to 10, about 13% by mass in Example 2, and about 15% by mass in Example 11. Next, on the downstream side of the extruder, the temperature of the foamable resin melt was adjusted to about 111°C.

[0124] On the other hand, to form the resin layer, each polyethylene-based resin B and components added as necessary were supplied to the second extruder according to the formulation shown in Table 3, heated, melted, and kneaded to obtain a resin melt. Then, a predetermined volatile plasticizer was added and further kneaded to obtain a resin melt for forming the resin layer. In Table 3, "SD100" in the ASP column is an ionomer resin ("SD100" manufactured by Mitsui Dow Polychemical Co., Ltd., melt flow rate 5 g / 10 min measured under the conditions of temperature 190°C and load 2.16 kg). "LMP" in the ASP column is a block copolymer of polyether and polyolefin ("Pelektron LMP" manufactured by Sanyo Chemical Industries, Ltd., melt flow rate 30 g / 10 min measured under the conditions of temperature 190°C and load 2.16 kg). "HIPS" in the HIPS column is high impact polystyrene ("408" manufactured by PS Japan Co., Ltd., melt flow rate 7 g / 10 min measured under the conditions of temperature 200°C and load 5 kg). In Examples 1 to 4 and Example 9, as the volatile foaming agent, a mixed butane of 70 mol% of normal butane and 30 mol% of isobutane and ethanol were used. In Examples 5 to 8, 10, and 11, as the volatile foaming agent, a mixed butane of 70 mol% of normal butane and 30 mol% of isobutane was used. Further, in Examples 1 to 4 and Example 9, the addition amount of the mixed butane in the resin melt for forming the resin layer was adjusted to 17% by mass, and the addition amount of ethanol in the resin melt for forming the resin layer was adjusted to 0.5% by mass. In Examples 5 to 8, 10, and 11, the addition amount of the mixed butane in the resin melt for forming the resin layer was adjusted to 17% by mass.

[0125] The foaming resin melt and the resin melt for forming the resin layer were laminated in a co-extrusion annular die, and the foaming resin melt was foamed by extruding it from the co-extrusion annular die into the atmosphere, thereby forming a multilayer foam having resin layers on the outer surface and the inner surface of the tubular foam. While widening this multilayer foam with a tubular widening device (mandrel), it was taken up by a take-up machine so as to have a predetermined thickness and density, and further, the multilayer foam was cut along the extrusion direction, thereby manufacturing a multilayer foam sheet of the examples shown in Table 3 with a width of about 1 m. In addition, in Examples 1 and 3 to 10, the discharge amount of the foaming resin melt was 115 kg / hr, the discharge amount of the resin melt for forming the resin layer was 17 kg / hr, and the take-up speed was 90 m / min. In Examples 2 and 11, the discharge amount of the foaming resin melt was 120 kg / hr, the discharge amount of the resin melt for forming the resin layer was 20 kg / hr, and the take-up speed was 70 m / min.

[0126] The single-layer foam sheet of the comparative example was manufactured in the same manner as in Example 6, except that using the above-described extrusion device, a resin layer was not formed, and only the foam layer was formed with the raw material formulation shown in Table 3.

[0127] Regarding the multilayer foam sheet obtained in the examples and the foam sheet obtained in the comparative example, the average thickness, basis weight, basis weight of the resin layer, density, closed cell ratio, and biomass degree were calculated.

[0128] <Average thickness> The average thickness of the multilayer foamed sheet was determined by measuring the thickness at 1 cm intervals for the entire width of the multilayer foamed sheet in the width direction perpendicular to the extrusion direction of the multilayer foamed sheet, and calculating the arithmetic mean of the measured thicknesses. The thickness was measured using an offline thickness measuring machine "TOF-4R" manufactured by Yamamoto Electric Co., Ltd. The multilayer foamed sheet used for the measurement was conditioned for 24 hours or more under the conditions of a temperature of 23 ± 5°C and a relative humidity of 50%.

[0129] <Grammage> The grammage of the entire multilayer foamed sheet was measured by cutting out a multilayer foamed sheet to a predetermined size (for example, 1000 mm × 250 mm), measuring the area (m 2 ) and mass (g) of the multilayer foamed sheet, and dividing the mass (g) by the area (m 2 ) to obtain the grammage (g / m 2 ).

[0130] The grammage of the resin layer per side was obtained from the relationship between the discharge amount X [g / hour] of the resin layer, the width W [m] of the obtained multilayer foamed sheet, and the length L [m / hour] of the multilayer foamed sheet extruded per unit time at the time of manufacturing the multilayer foamed sheet according to the following formula (1), and then obtained from the relationship between the grammage of the entire resin layer and the discharge amount of each resin layer. Since the ratio of the discharge amounts of each resin layer was 1:1, the grammage of the resin layer per side was obtained by dividing the grammage of the entire resin layer by 2. Grammage of the entire resin layer [g / m 2 = [X / (L × W)] ··· (1)

[0131] <Density> The density of the multilayer foamed sheet was obtained by dividing the grammage (g / m 2 ) of the multilayer foamed sheet by the average thickness of the multilayer foamed sheet, and further converting the unit to (kg / m 3 ).

[0132] <Closed cell ratio> The closed-cell ratio of the multilayer foam sheet was measured as follows. First, cut samples measuring 25 mm × 25 mm × sheet thickness (the thickness of the multilayer foam sheet) were randomly cut from the multilayer foam sheet. A plurality of cut samples were stacked so that the total sum of the sheet thicknesses was closest to 20 mm to form a test piece. Next, in accordance with Procedure C of ASTM-D2856-70, using an air comparison pycnometer model 930 of Toshiba Beckman Co., Ltd., etc., the true volume Vx of the test piece was measured, and the closed-cell ratio S(%) was calculated using the following formula (2). The above measurement was performed using 5 test pieces, and the arithmetic mean value was taken as the closed-cell ratio of the multilayer foam sheet. S(%)=(Vx-W / ρ)×100 / (Va-W / ρ)···(2) Vx: The true volume of the test piece measured by the above method (cm 3 ), which corresponds to the sum of the volume of the resin constituting the multilayer foam sheet and the total volume of the bubbles in the closed-cell portion within the test piece. Va: The apparent volume of the test piece calculated from the outer dimensions of the test piece used for the measurement (cm 3 ). W: The total mass (g) of the cut samples used for the measurement. ρ: The density of the resin constituting the multilayer foam sheet (g / cm 3 ).

[0133] <Biomass content> The biomass content was calculated from the biomass content measured by ASTM D 6866 of the plant-derived polyethylene used in the production of the multilayer foam sheet and the blending ratio of the plant-derived polyethylene in each layer.

[0134] <Surface resistivity> The surface resistivity of the multilayer foamed sheets obtained in Examples 1, 9, and 10 was measured as follows. Three test pieces (100 mm in length × 100 mm in width × thickness: test piece thickness) were randomly cut out from the obtained multilayer foamed sheets. After conditioning the test pieces, using "TR8601" manufactured by Takeda Riken Kogyo Co., Ltd. as the measuring device, the surface resistivity 1 minute after starting the application to the test pieces at an applied voltage of 500 V was measured for the three test pieces. The measurement of the surface resistivity was performed on one surface of the test piece, and the arithmetic mean value of the obtained measured values was taken as the surface resistivity of the multilayer foamed sheet. As a result, the surface resistivity of the multilayer foamed sheet of Example 1 was 5 × 10 10 Ω, the surface resistivity of the multilayer foamed sheet of Example 9 was 6 × 10 11 Ω, and the surface resistivity of the multilayer foamed sheet of Example 10 was 6 × 10 11 Ω.

[0135] Regarding the multilayer foamed sheets of the examples and the foamed sheets of the comparative examples, the appearance and the stiffness (amount of sag) were evaluated as follows. The evaluation results of the appearance and the stiffness are shown in Table 3.

[0136] <Appearance> As the appearance evaluation of the obtained multilayer foamed sheet, the occurrence status of wrinkles in the surface layer portion of the multilayer foamed sheet (foamed sheet in the comparative example) was evaluated from the following viewpoints. A: Has a good appearance, and almost no wrinkles are confirmed in the multilayer foamed sheet. B: The appearance is not inferior, but wrinkles are scattered in the multilayer foamed sheet. C: A large number of wrinkles are confirmed in the multilayer foamed sheet.

[0137] Note that the above evaluations indicate that "A" and "B" have a good appearance, and "A" indicates a particularly good appearance. In addition, the wrinkles that appeared particularly in the evaluation "C" are considered to have appeared because the bubbles of the foam are likely to burst during extrusion. It is considered that due to the bursting of the bubbles in the foam, the influence of the shrinkage caused by the dissipation of the foaming agent cannot be eliminated even when the foam is cured, and wrinkles and the like remain.

[0138] <Firmness (Amount of Sagging)> The firmness of the foamed sheet was measured as follows. Five randomly selected locations on the multilayer foamed sheet were cut out to obtain MD-direction test pieces with a width of 100 mm and a length of 200 mm such that the extrusion direction of the multilayer foamed sheet was aligned with the longitudinal direction of the test pieces, and TD-direction test pieces with a width of 100 mm and a length of 200 mm such that the width direction of the multilayer foamed sheet was aligned with the short-side direction of the test pieces. Five of each test piece were prepared.

[0139] The test pieces were placed on a horizontal base with 100 mm protruding longitudinally from the edge of the base, and a weight was placed on top of them and fixed. The vertical distance from the upper surface of the base to the lowest part of the test piece that sagged was measured. This measurement was performed for each test piece, and the arithmetic mean value of each measured value was taken as the amount of sagging. Based on the measured amount of sagging, the firmness of the multilayer foamed sheet was evaluated according to the following criteria. A: The amount of sagging is less than 30 mm B: The amount of sagging is 30 mm or more and less than 50 mm C: The amount of sagging is 50 mm or more

[0140] In the above evaluation, "A" and "B" indicate that the firmness is good, and "A" indicates that the firmness is particularly good.

[0141]

Table 3

[0142] In Comparative Examples 1 and 2 without a resin layer, a foamed sheet with poor appearance was obtained. Also, in Comparative Examples 1 and 2, the closed-cell ratio of the foamed sheet was lower than that of the multilayer foamed sheet of the Examples. Further, Comparative Examples 1 and 2 resulted in foamed sheets with low stiffness. In contrast, in Examples 1 to 11, multilayer foamed sheets with good appearance were obtained. Also, Examples 1 to 11 produced multilayer foamed sheets with a higher closed-cell ratio compared to the foamed layers of the Comparative Examples. Moreover, Examples 1 to 11 were able to manufacture multilayer foamed sheets with high stiffness. In particular, in Examples 1 to 5, the resin layer was linear low-density polyethylene LL B By including this, the appearance could be further improved. Furthermore, in Examples 1 to 4, the foamed layer was linear low-density polyethylene LL A By including this, the stiffness could be further improved.

[0143] Also, as Example 12, a multilayer foamed sheet was manufactured as follows. In Example 12, 36 parts by mass of "SEB853", 50 parts by mass of "SD100", 10 parts by mass of "HIPS", and 4 parts by mass of a thermoplastic elastomer were blended as components constituting the resin layer, and except that the addition amount of ethanol in the resin melt for forming the resin layer was changed to 0.9% by mass, a multilayer foamed sheet was manufactured in the same manner as in Example 1. Note that, as the thermoplastic elastomer, "Tuftec H1041" manufactured by Asahi Kasei Corporation was used.

[0144] The multilayer foamed sheet obtained in Example 12 had an average thickness of 1.09 mm, a basis weight of 19 g / m 2 and the basis weight of the resin layer per side was 1.5 g / m 2 The density was 17 kg / m 3 The closed-cell ratio was 80%, the biomass degree of the resin layer was 34%, the biomass degree of the foamed layer was 22%, and the biomass degree (overall) was 24%. Also, the surface resistivity of the multilayer foamed sheet obtained in Example 12 was 7×10 8 Ω, the appearance was "A", and the stiffness was "A".

Claims

1. A foaming resin melt for forming a foamed layer obtained by kneading a polyethylene-based resin A and a physical foaming agent, and a resin melt for forming a resin layer obtained by melt-kneading a polyethylene-based resin B are co-extruded to provide a polyethylene-based resin foamed layer and a polyethylene-based resin layer laminated and adhered to at least one side of the foamed layer, with a density of 300 kg / m 3 The following is a method for manufacturing a polyethylene-based resin multilayer foamed sheet, The polyethylene-based resin A contains polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, The polyethylene-based resin B contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, The total blending amount Bb of the plant-derived polyethylene b-PE in the polyethylene Y is 40% by mass or more, B and The total blending amount Ab of the plant-derived polyethylene b-PE in the polyethylene X is 40% by mass or less (including 0), A and The plant-derived polyethylene b-PE B The total blending amount Bb of the above and the plant-derived polyethylene b-PE A A method for producing a polyethylene-based resin multilayer foamed sheet, wherein the difference (Bb - Ab) between the total blending amount Ab of the above is 20% by mass or more.

2. Said plant-derived polyethylene b-PE measured according to ASTM D 6866 A and said plant-derived polyethylene b-PE B The method for producing a polyethylene resin multilayer foam sheet according to claim 1, wherein the biomass content of each of them is 80% or more.

3. The polyethylene Y contains plant-derived low-density polyethylene b-LD B and The melt flow rate of the plant-derived low-density polyethylene b-LD measured at a temperature of 190 °C and a load of 2.16 kg B is 0.1 g / 10 min or more and 25 g / 10 min or less, and the method for producing a polyethylene resin multilayer foam sheet according to claim 1 or 2.

4. wherein the polyethylene Y is a mixture of plant-derived low-density polyethylene b-LD B and linear low-density polyethylene LL B and consists of a mixture thereof. The plant-derived low-density polyethylene b-LD B and the linear low-density polyethylene LL B The mass ratio thereof (b-LD B : LL B ) is 1:0.1 to 1:

1. The method for producing a polyethylene-based resin multilayer foam sheet according to claim 1 or 2.

5. The linear low density polyethylene LL B A method for producing a polyethylene-based resin multilayer foamed sheet according to claim 4, comprising a linear low density polyethylene which is a copolymer of ethylene and octene.

6. The resin melt for forming the resin layer further contains a polymer type antistatic agent ASP, The polyethylene Y contains plant-derived low-density polyethylene b-LD B and The plant-derived low-density polyethylene b-LD B and the polymer type antistatic agent ASP have a mass ratio (b-LD B :ASP) of 1:0.05 to 1:

3. The method for producing a polyethylene-based resin multilayer foam sheet according to claim 1 or 2.

7. The method for producing a polyethylene-based resin multilayer foam sheet according to claim 1 or 2, wherein the mass ratio of the resin layer per side with respect to the foam layer is 0.01 to 0.

4.

8. The method for producing a polyethylene-based resin multilayer foam sheet according to claim 1 or 2, wherein the biomass degree D of the multilayer foam sheet measured by ASTM D 6866 is 5% or more and 60% or less.

9. A polyethylene resin foam layer and a polyethylene resin layer laminated and adhered to at least one side of the foam layer, with a density of 300 kg / m 3 The following polyethylene resin multilayer foam sheet, The polyethylene-based resin foam layer contains polyethylene X composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, The polyethylene-based resin layer contains polyethylene Y composed of low-density polyethylene or a mixture of low-density polyethylene and linear low-density polyethylene, The total blending amount Bb of the plant-derived polyethylene b-PE in the polyethylene Y is 40% by mass or more, B and The total blending amount Ab of the plant-derived polyethylene b-PE in the polyethylene X is 40% by mass or less (including 0), A and Said plant-derived polyethylene b-PE B The sum Bb of the compounding amounts thereof and the difference (Bb - Ab) between the sum Bb of the compounding amounts and the sum Ab of the compounding amounts of said plant-derived polyethylene b-PE A is 20% by mass or more, a polyethylene-based resin multilayer foamed sheet.

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