Polyethylene resin multi-layer extruded foam sheet

Abstract

To provide a multilayer extrusion expanded sheet having extremely suppressed migration of low-molecular-weight components, etc., to articles to be packed, excellent anti-static performance, excellent slipperiness, and good appearance.SOLUTION: A polyethylene-based resin multilayer extrusion expanded sheet includes a polyethylene-based resin foamed layer and a resin layer laminated by coextrusion, wherein the resin layer includes an anti-static layer and a non-anti-static layer, the anti-static layer includes a polyethylene-based resin (B) and an ionomer resin, the ionomer resin forms a disperse phase dispersed in a layer in a specified vertical cross-section (a) in a continuous phase of the polyethylene-based resin (B), an average layer number of the disperse phase is 3 or more layers per 1 μm in a thickness direction, the non-anti-static layer includes a polyethylene-based resin (C) and substantially does not include an anti-static agent, an average thickness of the non-anti-static layer is in a specified range, and a surface resistivity of the multilayer extrusion expanded sheet is 1×1012 Ω or under.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a multi-layer extruded polyethylene-based resin foam sheet, and more particularly to a multi-layer extruded polyethylene-based resin foam sheet that can be used as an insert sheet or packaging material for electronic devices and the like, and that has a good appearance, excellent antistatic properties, and extremely little migration of low-molecular-weight components into packaged items and the like. [Background technology]

[0002] Multilayer extruded foam sheets, in which a resin layer made of a polyethylene-based resin is laminated on a foam sheet made of a polyethylene-based resin, are lightweight and have excellent cushioning properties. Therefore, they are widely used in the packaging of electronic devices and their materials, such as slip sheets to be placed between glass plates used in liquid crystal panels for packaging.

[0003] In such applications, multi-layer extruded polyethylene resin foam sheets (hereinafter simply referred to as "multi-layer extruded foam sheets" or "foam sheets") are usually imparted with antistatic properties in order to prevent adhesion of dust, dirt, etc. One method for imparting antistatic properties to multi-layer extruded foam sheets is to blend a polymeric antistatic agent with a resin melt for forming a resin layer, and then co-extrude the resulting mixture to form a resin layer containing the polymeric antistatic agent, when producing a multi-layer extruded foam sheet by co-extrusion (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-204227 Summary of the Invention [Problem to be solved by the invention]

[0005] When the multilayer extruded foam sheet is used as an interleaf, etc., it is required that it not only have excellent antistatic properties but also not contaminate packaged items such as glass plates. In addition, in recent years, for multilayer extruded foam sheets used as interleaf sheets for glass plates in electronic devices, etc., there has been a demand for multilayer extruded foam sheets that further suppress the migration of contaminants, such as low-molecular-weight components derived from polymeric antistatic agents, to the packaged items in order to further suppress contamination of the packaged items.

[0006] In order to reduce the amount of migration of low-molecular-weight components, it is conceivable to use a polymeric antistatic agent with a low content of low-molecular-weight components, such as an ionomer resin.

[0007] However, in the past, when a multi-layer extruded foam sheet was produced by co-extruding a polyethylene-based resin layer (hereinafter also simply referred to as a resin layer) containing an ionomer resin on a polyethylene-based resin foam layer, it was difficult to stably achieve desired antistatic properties, and it was difficult to stably produce a multi-layer extruded foam sheet having good antistatic performance.

[0008]

[0005] Furthermore, multi-layer extruded foam sheets containing ionomer resins tend to have poor slip properties, which may reduce workability when packaging an item with the multi-layer extruded foam sheet depending on the application. Furthermore, when a multi-layer extruded foam sheet is produced by a co-extrusion method, increasing the amount of ionomer resin blended into the resin layer reduces the slip properties of the multi-layer extruded foam sheet, which may cause wavy patterns when the multi-layer extruded foam sheet is taken up, making it difficult to take up, or may leave traces that impair the appearance of the foam sheet.

[0009] Furthermore, even when an ionomer resin is used as an antistatic agent, small amounts of low-molecular-weight components contained in the ionomer resin may migrate to the packaged goods. Therefore, depending on the application, there is a demand for a multi-layer extruded foam sheet in which the migration of low-molecular-weight components to the packaged goods is extremely suppressed.

[0010] An object of the present invention is to solve the above problems and to provide a multi-layer extruded foam sheet that is highly inhibited from migrating low-molecular-weight components and the like into packaged items, and that has excellent antistatic properties, excellent slip properties, and a good appearance. [Means for solving the problem]

[0011] According to the present invention, there is provided the following multi-layer extruded foam sheet. [1] A foamed layer made of a polyethylene resin (A) and a resin layer laminated by coextrusion on at least one side of the foamed layer. Polyethylene Resin A multi-layer extruded foam sheet, the resin layer has an antistatic layer and a non-antistatic layer located on a surface of the multi-layer extruded foam sheet, the antistatic layer contains a polyethylene resin (B) and an ionomer resin antistatic agent, and in a vertical cross section (a) of the multi-layer extruded foam sheet perpendicular to the width direction, the ionomer resin antistatic agent forms a dispersed phase in the form of layers in a continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase is 3 or more per 1 μm in the thickness direction of the multi-layer extruded foam sheet; the ionomer resin in the antistatic layer Antistatic agent The content of the polyethylene resin (B) and the ionomer resin is 30 to 80% by weight. Antistatic agent The total of these is 100% by weight. The non-antistatic layer contains a polyethylene resin (C), and the content of the antistatic agent in the non-antistatic layer is 3% by weight or less, the average thickness of the non-antistatic layer is 0.5 to 15 μm, The surface resistivity of the resin layer side of the multi-layer extruded foam sheet is 1×10 12 A multi-layer extruded polyethylene resin foam sheet having a modulus of elasticity of Ω or less. [2] The method according to item 1, characterized in that the average aspect ratio of the dispersed phase in the vertical cross section (a) is 2 or more. Polyethylene Resin Multi-layer extruded foam sheet. [3] In the vertical cross section (a), the median dispersion area based on the number of dispersed phases is 1 × 10 2 ~5×10 5 nm 23. The multi-layer extruded polyethylene resin foam sheet according to 1 or 2 above, wherein [4] The multi-layer extruded polyethylene resin foam sheet according to any one of [1] to [3], wherein in the vertical cross section (a), the median dispersed diameter in the horizontal direction based on the number of dispersed phases is 200 to 3,000 nm. [5] The multi-layer extruded polyethylene resin foam sheet according to any one of items 1 to 4, wherein in the vertical cross section (a), the dispersed phase occupies an average area of ​​30 to 80 area% in a rectangular region having a thickness length of 500 nm and a width length of 1500 nm in a central part of the antistatic layer. [6] The multi-layer extruded polyethylene resin foam sheet according to any one of the above items 1 to 5, wherein the antistatic layer contains a polyalkylene glycol in an amount of 0.3 to 6 parts by weight per 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin antistatic agent. [7] The surface resistivity is 1×10 10 7. The multi-layer extruded polyethylene resin foam sheet according to any one of the above items 1 to 6, having a modulus of less than Ω. [Effects of the Invention]

[0012] The multi-layer extruded polyethylene resin foam sheet of the present invention has a foam layer and a resin layer, and the resin layer has an antistatic layer and a non-antistatic layer that is substantially free of an antistatic agent. Furthermore, the antistatic layer contains an ionomer resin-based antistatic agent with a specific morphology, and the non-antistatic layer has a thickness within a specific range, thereby providing the foam sheet with excellent antistatic properties. Furthermore, despite the antistatic layer containing the ionomer resin-based antistatic agent, the non-antistatic layer has a thickness within a specific range, thereby significantly suppressing the migration of low-molecular-weight components in the ionomer resin to the packaged product, etc. Furthermore, the presence of the non-antistatic layer provides the foam sheet with excellent slip properties and a good appearance. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a drawing showing an example of a cross-sectional view of the multi-layer extruded foam sheet of the present invention. [Figure 2] FIG. 2 is an electron microscope photograph (magnification: 17,500 times) of the vertical cross section (a) of the multi-layer extruded foam sheet obtained in Example 1. [Figure 3] FIG. 2 is an electron microscope photograph (magnification: 70,000 times) of a vertical cross section (a) of the multi-layer extruded foam sheet obtained in Example 1. [Figure 4] FIG. 2 is an electron microscope photograph (magnification: 17,500 times) of the vertical cross section (a) of the multi-layer extruded foam sheet obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The multi-layer extruded polyethylene resin foam sheet of the present invention (hereinafter simply referred to as the multi-layer extruded foam sheet or foam sheet) will be described in detail below. The multilayer extruded foam sheet of the present invention is a multilayer extruded foam sheet having a foam layer composed of a polyethylene-based resin (A) and a resin layer laminated by coextrusion on at least one side of the foam layer. Furthermore, the resin layer has an antistatic layer and a non-antistatic layer. Therefore, the multilayer extruded foam sheet has at least a three-layer structure (non-antistatic layer / antistatic layer / foam layer). If resin layers are laminated on both sides of the foam layer, as shown in Figure 1, the multilayer extruded foam sheet has a five-layer structure (non-antistatic layer / antistatic layer / foam layer / antistatic layer / non-antistatic layer). The antistatic layer and the non-antistatic layer are laminated and bonded by coextrusion. In Figure 1, 1 denotes the multilayer extruded foam sheet, 2 denotes the foam layer, 3 denotes the resin layer, 3a denotes the antistatic layer, and 3b denotes the non-antistatic layer. It should be noted that a six-layer structure or even a seven-layer structure can be formed by providing another layer between one or both of the resin layers and the foam layer (not shown).

[0015] First, the components constituting the foam layer will be described. In the multi-layer extruded foam sheet of the present invention, the foam layer is composed of a polyethylene resin (A). That is, the foam layer contains the polyethylene resin (A) as a main component. In this specification, the term "main component" means that the content of that component is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more.

[0016] In this specification, the polyethylene resin means a resin containing 50 mol% or more of ethylene units. Examples of the polyethylene resin (A) include low-density polyethylene (LDPE), ethylene-vinyl acetate copolymer (EVA), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), and mixtures thereof. Low-density polyethylene includes polyethylene having a long-chain branched structure and a density of 910 kg / m 3 More than 930kg / m 3 The linear low-density polyethylene is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms, and has a substantially linear molecular chain and a density of 910 kg / m 3 More than 930kg / m 3 The high density polyethylene is preferably an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms, and has a density of 930 kg / m 3 The above polyethylene resins are preferred.

[0017] The polyethylene resin (A) constituting the foam layer is preferably low-density polyethylene, since it has excellent foaming properties and the extruded multi-layer foam sheet has excellent cushioning properties.

[0018] The melting point of the polyethylene resin (A) is preferably 100 to 135°C. A polyethylene resin (A) having a melting point within this range has excellent extrusion foamability and can stably form a foamed layer with excellent cushioning properties. For these reasons, the melting point of the polyethylene resin (A) is preferably 100 to 130°C, more preferably 100 to 120°C, and even more preferably 100 to 115°C.

[0019] The melting point of the polyethylene resin (A) in this specification is a value determined by heat flux differential scanning calorimetry in accordance with JIS K7121-1987. Specifically, in this measurement, a test specimen conditioned under the conditions of JIS K7121-1987, 3. Conditioning of test specimen (2) (with the exception of a cooling rate of 10°C / min) is used, and a melting peak is obtained by raising the temperature at a rate of 10°C / min, and the melting point is the temperature at the apex of the obtained melting peak. However, when two or more melting peaks appear, the melting point is the temperature at the apex of the melting peak with the largest area.

[0020] The melt flow rate (MFR) of the polyethylene resin (A) is preferably 0.1 to 20 g / 10 min, more preferably 0.1 to 10 g / min, and even more preferably 0.1 to 5 g / 10 min, because of its excellent foamability. Furthermore, it is more preferable to use a polyethylene resin (A) having a melt flow rate (MFR) of 0.1 to 1.5 g / 10 min, because this allows the foamed sheet to have a higher closed cell content. The melt flow rate (MFR) in this specification is a value measured in accordance with JIS K7210-1 (2004) Method A at a test temperature of 190°C and a load of 2.16 kg.

[0021] The polyethylene resin (A) constituting the foamed layer may be blended with other polymers such as resins other than the polyethylene resin (A) or elastomers, if necessary. When blending other polymers, the blending amount is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less, per 100 parts by weight of the polyethylene resin constituting the foamed layer.

[0022] In addition, additives such as cell regulators, nucleating agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, antibacterial agents, shrinkage inhibitors, and inorganic fillers may be added to the foam layer within a range that does not impair the objects and effects of the present invention.

[0023] Next, the components constituting the resin layer will be described. The resin layer has an antistatic layer (1) and a non-antistatic layer (2). The antistatic layer (1) contains a polyethylene resin (B) and an ionomer resin-based antistatic agent, and the non-antistatic layer (2) contains a polyethylene resin (C) and is substantially free of an antistatic agent.

[0024] The antistatic layer (1) contains a polyethylene resin (B). The polyethylene resins exemplified as the polyethylene resin (A) can be used as the polyethylene resin (B). Among them, it is preferable to use the same type of polyethylene resin as the polyethylene resin (A) because it has excellent adhesion to the foam layer. Specifically, low-density polyethylene is preferred. However, a different type of polyethylene resin can also be used.

[0025] The polyethylene resin (B) constituting the antistatic layer may be blended with other polymers such as resins other than the polyethylene resin (B) or elastomers, if necessary. When blending other polymers, the blending amount is preferably 20 parts by weight or less per 100 parts by weight of the polyethylene resin (C) constituting the non-antistatic layer.

[0026] The melting point of the polyethylene resin (B) is preferably 100 to 120°C. By setting the melting point within this range, the adhesion between the resin layer and the foam layer is improved, and a homogeneous antistatic layer is formed, resulting in good antistatic performance throughout the multi-layer extruded foam sheet. For these reasons, the melting point is more preferably 102 to 115°C. The melting point of the polyethylene resin (B) can be determined by the same method as for the polyethylene resin (A).

[0027] The antistatic layer (1) contains the ionomer resin-based antistatic agent (hereinafter simply referred to as ionomer resin). The ionomer resin is a polymeric antistatic agent with low surface resistivity, and therefore can impart good antistatic properties to the multi-layer extruded foam sheet. Furthermore, since the ionomer resin has a low content of low molecular weight components, it has excellent contamination prevention properties and can suppress contamination of packaged items due to migration of low molecular weight components to the packaged items.

[0028] The ionomer resin is a resin in which the molecules of a copolymer of an olefin such as ethylene or propylene and a carboxylic acid such as acrylic acid, methacrylic acid, or maleic acid are intermolecularly crosslinked with a metal ion, and examples of the metal ion include alkali metal ions such as lithium ions, sodium ions, and potassium ions, and alkaline earth metal ions such as calcium ions. Among these, an ethylene-based potassium ionomer resin, which is a copolymer of ethylene and an unsaturated carboxylic acid and uses potassium ions as the metal ion, is preferred because it can impart good antistatic properties to the multi-layer extruded foam sheet.

[0029] The melting point of the ionomer resin-based antistatic agent is preferably about 80 to 110° C., more preferably 85 to 100° C. The melting point of the ionomer resin can be determined by the same method as for the melting point of the polyethylene resin (A).

[0030] The surface resistivity of the ionomer resin is 1×10 12Surface resistivity is preferably less than 1×10 Ω. 12 By forming an antistatic layer using an ionomer resin with a surface resistivity of less than Ω, a multi-layer extruded foam sheet with excellent antistatic properties can be stably obtained. 11 It is more preferable that the resistance is Ω or less, and even more preferable that the resistance is 1×10 10 Ω or less, and particularly preferably 1×10 9 It is less than Ω. The surface resistivity of the ionomer resin can be measured in accordance with the method of JIS K6271 (2001).

[0031] Specific examples of the ionomer resin include those commercially available under the trade names "Entira SD100" and "Entira MK400" manufactured by DuPont-Mitsui Polychemicals Co., Ltd.

[0032] The antistatic layer of the present invention preferably contains a polyalkylene glycol. When a multi-layer extruded foam sheet is produced by co-extrusion, the antistatic layer containing a polyalkylene glycol can disperse the ionomer resin well in layers in the continuous phase of the polyethylene resin (B), more reliably forming the specific dispersion state (morphology) described below, and can stably produce a multi-layer extruded foam sheet with superior antistatic performance. Furthermore, when the resin layer contains polyalkylene glycol, the humidity dependency of the antistatic performance is reduced, and a multi-layer extruded foam sheet that exhibits good antistatic performance even under low humidity conditions can be obtained.

[0033] The polyalkylene glycol preferably has an HLB value of 8 or more. Examples of such polyalkylene glycols include polyethylene glycol, polyoxyethylene polyoxypropylene glycol, etc. Two or more types of polyalkylene glycols may be used in combination. Among these, it is preferable to use polyethylene glycol, since it allows the ionomer resin to be stably dispersed in the polyethylene resin (B), and also allows the humidity dependency of the antistatic performance to be further reduced while improving the antistatic performance.

[0034] In the present invention, the HLB value is a value determined by the Griffin method (equation (1)). HLB = 20 × molecular weight of hydrophilic group / molecular weight of entire hydrophilic compound (1)

[0035] In the present specification, when the HLB value of a polyalkylene glycol is determined by the Griffin method, the procedure is specifically as follows. For example, when a polyalkylene glycol is composed of a copolymer of polyethylene glycol and other polyalkylene glycols, the polyethylene glycol is regarded as the hydrophilic group portion, and the other polyalkylene glycols are determined as either hydrophilic or hydrophobic group portions in consideration of their lipophilicity and hydrophilicity, and the HLB value is calculated by the Griffin method. In the case of polyethylene glycol, since all of the polyethylene glycols are hydrophilic group portions, the upper limit of the HLB value of the polyalkylene glycol is 20. In order to disperse the ionomer resin well in the polyethylene resin, the HLB value is preferably 10 or more, and more preferably 15 or more.

[0036] When polyethylene glycol is used as the polyalkylene glycol, its number average molecular weight is preferably 100 to 10,000, more preferably 150 to 1,000, and even more preferably 200 to 600. By setting the molecular weight of the polyethylene glycol within the above range, a multi-layer extruded foam sheet exhibiting excellent antistatic properties can be stably obtained. The number average molecular weight of polyethylene glycol can be determined by a well-known method calculated from the hydroxyl value.

[0037] The content of the polyalkylene glycol in the antistatic layer is preferably 0.3 to 8 parts by weight, more preferably 0.3 to 6 parts by weight, per 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin. By adjusting the content within this range, a multi-layer extruded foam sheet with excellent antistatic properties can be stably obtained. Furthermore, when polyethylene glycol is used as the polyalkylene glycol, the content thereof is preferably 0.3 to 6 parts by weight, more preferably 0.5 to 5 parts by weight, even more preferably 0.8 to 4 parts by weight, and particularly preferably 1 to 4 parts by weight, per 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin.

[0038] In the antistatic layer, the weight ratio of the polyalkylene glycol to the ionomer resin is preferably 0.03 to 0.5, which allows the ionomer resin to be more satisfactorily dispersed in the polyethylene resin. From this viewpoint, the weight ratio is more preferably 0.04 to 0.4, further preferably 0.05 to 0.3, and particularly preferably 0.05 to 0.1.

[0039] As described above, the antistatic layer (1) of the present invention contains a polyethylene resin (B) and an ionomer resin, and the ionomer resin-based antistatic agent forms a dispersed phase in the form of layers in the continuous phase of the polyethylene resin (B), forming a morphology in which the average number of dispersed phase layers is 3 or more per μm in the thickness direction. In this specification, this specific morphology is also referred to as an antistatic morphology structure. The multilayer extruded foam sheet of the present invention has an antistatic network formed by the formation of this antistatic morphology structure, and has a surface resistivity of 1×10 12 It is believed that excellent antistatic properties of Ω or less are exhibited.

[0040] Next, the antistatic morphological structure (hereinafter also simply referred to as the morphological structure) will be described. The morphology can be confirmed in a vertical cross section (a) perpendicular to the width direction of the multi-layer extruded foam sheet. That is, the morphology is such that the ionomer resin forms a dispersed phase in the form of layers in the continuous phase of the polyethylene resin (B), and the average number of dispersed phase layers is 3 or more per μm in the thickness direction. Here, "dispersed phase in the form of layers" means a dispersed phase with an aspect ratio of 2 or more.

[0041] Examples of the antistatic morphology structure are shown in Figures 2 and 3. Figures 2 and 3 are electron microscope photographs of a vertical cross section (a) perpendicular to the width direction of the multi-layer extruded foam sheet obtained in Example 1. The magnification of the electron microscope photograph in Figure 2 is 17,500 times, and the magnification of the electron microscope photograph in Figure 3 is 70,000 times.

[0042] 2 and 3, it can be seen that an antistatic morphology structure has been formed in which the polyethylene resin (B) forms a continuous phase 4 and the ionomer resin forms a dispersed phase 5 dispersed in layers within the continuous phase. In addition, in FIGS. 2 and 3, the darker black parts are the dispersed phase 5, and the lighter black and whitish parts are the continuous phase 4.

[0043] In the antistatic morphology structure, the average number of layers of the dispersed phase must be 3 or more per 1 μm in the thickness direction. If the average number of layers is 3 or more, the surface resistivity is 1×10 12 When the average number of layers is less than 3, the surface resistivity is 1×10 12 If the number of layers is more than 20, the antistatic property of Ω or less may not be achieved. Therefore, the average number of layers is preferably 4 or more, more preferably 5 or more, 6 or more, 7 or more, and even more preferably 8 or more. The upper limit is approximately 20 layers.

[0044] The polyethylene resin (B) forms a continuous phase in the antistatic layer, thereby improving the flexibility of the multi-layer extruded foam sheet of the present invention. Meanwhile, as described above, the ionomer resin is dispersed in layers within the continuous phase of the polyethylene resin (B), and the dispersed phase layers overlap each other so that the average number of layers is 3 or more per μm in the thickness direction. Therefore, unlike conventional multi-layer extruded foam sheets, the multi-layer extruded foam sheet of the present invention exhibits excellent antistatic properties despite the use of an ionomer resin as a polymeric antistatic agent. This is thought to be because the ionomer resin forms a dispersed phase, and the dispersed phase is stretched into layers, thereby forming a network of the polymeric antistatic agent. Specifically, an excellent network is formed when the dispersed phase is stretched into layers so that its aspect ratio is 2 or greater. The aspect ratio will be described later.

[0045] In the present invention, in the vertical cross section (a), the median dispersion area based on the number of the dispersed phase is 1 × 10 2 ~5×10 5 nm 2 It is preferable that the ionomer resin is dispersed so as to satisfy the following conditions. The median of the dispersed area is the value located in the middle of the total number of dispersed phases (50% of the total number of dispersed phases) when the number of dispersed phases and the cross-sectional area (dispersed area) of each dispersed phase are measured for the morphology appearing in the vertical cross section (a) and the measured cross-sectional areas of each dispersed phase are sorted in order of size. By using the median, the dispersed state of the ionomer resin, which contributes to antistatic performance, can be appropriately evaluated.

[0046] The median dispersed area within the above range means that the dispersed phase of the ionomer resin has a small dispersed diameter, and many small dispersed phases are dispersed in the continuous phase of the polyethylene-based resin (B). The formation of such dispersed phases improves the antistatic properties of the multi-layer extruded foam sheet. This is thought to be because the dispersed phase of the ionomer resin with a small dispersed diameter is dispersed in large numbers in the continuous phase (the median dispersed area is small), which more reliably forms a conductive network structure of the ionomer resin in the polyethylene-based resin. In order to further improve the antistatic performance of the multi-layer extruded foam sheet, the lower limit of the median value is 5 × 10 2 nm 2 is preferable, and more preferably 1×10 3 nm 2 , particularly preferably 1 × 10 4 nm 2 The upper limit of the median is 1 × 10 5 nm 2 is preferably 7×10 4 nm 2 is.

[0047] In addition, in the vertical cross section (a), the median B of the horizontal dispersion diameter of the dispersed phase of the ionomer resin is preferably 200 to 3,000 nm. The median B within this range means that the dispersed phase of the ionomer resin is elongated in the horizontal direction, making it easier to form an excellent antistatic network. From this perspective, the median B of the horizontal dispersion diameter is more preferably 300 to 2,000 nm, and even more preferably 500 to 1,500 nm.

[0048] In addition, in the vertical cross section (a), the average aspect ratio of the dispersed phase of the ionomer resin is preferably 2 or more. The average aspect ratio is calculated by dividing the median dispersed diameter B in the horizontal direction by the median dispersed diameter A in the thickness direction. A large average aspect ratio means that the dispersed phase composed of the ionomer resin is present in a layered, elongated state. Therefore, when the above range is satisfied, a conductive network structure of the ionomer resin is easily formed, and a multi-layer extruded foam sheet exhibiting excellent antistatic performance can be more reliably obtained. From this viewpoint, the aspect ratio is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The upper limit of the aspect ratio is about 20, and preferably 15. The dispersed phase is preferably stretched at least in the extrusion direction, and more preferably in the width direction as well, which is perpendicular to the extrusion direction and the thickness direction of the multi-layer extruded foam sheet.

[0049] In addition, in the vertical cross section (a), the central portion of the antistatic layer has a thickness direction length of 500 nm, Extrusion In a rectangular area having a length in the thickness direction of 1500 nm, the average area ratio of the dispersed phase of the ionomer resin-based antistatic agent is preferably 30 to 80 area %. Extrusion When a rectangular area having a directional length of 1500 nm is set, the average area ratio occupied by the dispersed phase of the ionomer resin-based antistatic agent is preferably 30 to 80 area %.

[0050] The average ratio is a numerical value representing the percentage of the total area of ​​the dispersed phase of the ionomer resin within a range along the extrusion direction, including a 500-nm section centered at the thickness center of the antistatic layer, in the vertical cross section (a). This average value is considered to reflect the weight ratio of the ionomer resin in the antistatic layer. That is, the larger the average value, the greater the weight ratio of the ionomer resin in the antistatic layer. In conventional techniques, particularly when the ionomer resin is blended at a high concentration, the slipperiness is significantly reduced, which can lead to poor workability, for example, when the extruded multilayer foam sheet is interposed between glass plates for packaging. Furthermore, during production, the extruded multilayer foam sheet is difficult to remove, resulting in poor appearance, such as waviness. When the average value is within the above range, the antistatic layer contains a high concentration of ionomer resin, resulting in particularly excellent antistatic properties. Furthermore, the multi-layer extruded foam sheet of the present invention has a non-antistatic layer that does not contain an antistatic agent, and the non-antistatic layer is located on the surface of the resin layer of the multi-layer extruded foam sheet so as to cover the antistatic layer. Furthermore, because the non-antistatic layer has a thickness within a specific range, the sheet exhibits good slip properties despite the high concentration of ionomer resin. Furthermore, migration of low-molecular-weight components to the packaged goods is effectively prevented. The non-antistatic layer will be described later.

[0051] To achieve a higher level of antistatic properties in the extruded multi-layer foam sheet, the average area ratio is more preferably 35% or more. In order to improve the slipperiness of the extruded multi-layer foam sheet and more reliably suppress the migration of low-molecular-weight components, the average area ratio is more preferably 70% or less, and even more preferably 60% or less.

[0052] The median dispersed area based on the number of dispersed phase particles, the median dispersed diameter A in the thickness direction based on the number of dispersed phase particles, the median dispersed diameter B in the horizontal direction of the dispersed phase particles, and the average area ratio of the dispersed phase within the predetermined range can be calculated based on photographs obtained by cutting a vertical cross section perpendicular to the width direction of the multi-layer extruded foam sheet, preparing ultrathin sections including the resin layer portion, staining the ultrathin sections, and then photographing the stained ultrathin sections using a transmission electron microscope. Specific measurement methods will be described in detail in the Examples.

[0053] As shown in FIG. 1, the resin layer constituting the multi-layer extruded foam sheet of the present invention includes a non-antistatic layer 3b located on the surface of the multi-layer extruded foam sheet. Specifically, the resin layer 3 includes an antistatic layer 3a and a non-antistatic layer 3b. The antistatic layer 3a is located in contact with the foam layer 2, and the non-antistatic layer 3b is located on the surface of the multi-layer extruded foam sheet and covers the antistatic layer 3a. The non-antistatic layer contains a polyethylene resin (C) but is substantially free of an antistatic agent. Therefore, the non-antistatic layer does not contaminate the packaged items with low-molecular-weight components derived from the antistatic agent. Furthermore, because the non-antistatic layer does not contain an ionomer resin, the slipperiness of the multi-layer extruded foam sheet is prevented from decreasing, ensuring easy handling during use. Furthermore, the occurrence of waviness during production of the multi-layer extruded foam sheet is prevented, resulting in a multi-layer extruded foam sheet with excellent appearance.

[0054] A non-antistatic layer is shown in the multi-layer extruded foam sheet shown in Figures 2 and 3. In Figures 2 and 3, the portion designated by reference numeral 3a is the antistatic layer in which the antistatic morphology structure unique to the present invention is formed, and the portion designated by reference numeral 3b is the non-antistatic layer.

[0055] In this specification, "not containing an antistatic agent" means that the content of the antistatic agent in the non-antistatic layer is 3% by weight or less, preferably 2% by weight or less, more preferably 1% by weight or less, even more preferably 0.5% by weight or less, and particularly preferably 0.

[0056] The antistatic agent is not limited to ionomer resins, but also includes polymeric antistatic agents such as polyethers, polyether ester amides, and block copolymers of polyethers and polyolefins, as well as surfactants and other components having antistatic properties.

[0057] The non-antistatic layer is located on the surface of the resin layer of the multi-layer extruded foam sheet, extending from the surface of the resin layer in the thickness direction, and is laminated so as to cover the antistatic layer. The average thickness of the non-antistatic layer in the vertical cross section (a) is 0.5 to 15 μm. When the average thickness of the non-antistatic layer is within this range, the desired antistatic properties can be exhibited and migration of low-molecular-weight components derived from the ionomer resin contained in the antistatic agent layer can be suppressed. To more reliably suppress migration of low-molecular-weight components and ensure the slip properties of the multi-layer extruded foam sheet, the lower limit of the average thickness is preferably 0.8 μm, more preferably 1 μm, and even more preferably 1.5 μm. If the average thickness is too large, the desired antistatic properties may not be exhibited. To more reliably exhibit the desired antistatic properties, the upper limit of the average thickness is preferably 13 μm, more preferably 8 μm, and even more preferably 5 μm. The method for measuring the average thickness of the non-antistatic layer in the vertical cross section (a) will be described later.

[0058] The non-antistatic layer is formed mainly from a polyethylene resin (C). The polyethylene resins exemplified as the polyethylene resin (B) can be used as the polyethylene resin (C). Using the same type of polyethylene resin as the polyethylene resin (B) can further enhance adhesion to the antistatic layer. Specifically, low-density polyethylene is preferred. Furthermore, using linear low-density polyethylene as the polyethylene resin (C) can further suppress the migration of low-molecular-weight components. However, different types of polyethylene resins can also be used.

[0059] The melting point of the polyethylene resin (C) is preferably 100 to 120°C. By setting the melting point within this range, the lamination state with the antistatic layer becomes good, and it becomes easier to obtain a multi-layer extruded foam sheet that exhibits good antistatic performance throughout the entire multi-layer extruded foam sheet. For this reason, the melting point is more preferably 102 to 115°C. The melting point of the polyethylene resin (C) can be determined by the same method as for the polyethylene resin (A).

[0060] The polyethylene resin (C) constituting the non-antistatic layer may be blended with other polymers such as resins other than the polyethylene resin (C) or elastomers, if necessary. When blending other polymers, the blending amount is preferably 20 parts by weight or less per 100 parts by weight of the polyethylene resin (C) constituting the non-antistatic layer. By incorporating a polystyrene resin into the non-antistatic layer, the slipperiness can be further improved.

[0061] Additives such as a cell regulator, a nucleating agent, an antioxidant, a heat stabilizer, a weathering agent, an ultraviolet absorber, a flame retardant, an antibacterial agent, a shrinkage inhibitor, and an inorganic filler may be added to the non-antistatic layer and the antistatic layer within a range that does not impair the object and effect of the present invention.

[0062] Next, the physical properties of the extruded multi-layer foam sheet of the present invention will be described. The multi-layer extruded foam sheet of the present invention has the above-mentioned structure and therefore has excellent antistatic properties. Specifically, the surface resistivity of the multi-layer extruded foam sheet is 1×10 12 If the surface resistivity is within the above range, the extruded multi-layer foam sheet has sufficient antistatic properties and can suppress the adhesion of dust and the like. For this reason, the surface resistivity is 1×10 11 It is preferably Ω or less, and more preferably 1×10 10 It is less than Ω. The lower limit of the surface resistivity is not particularly limited, but is generally 1×10 7 It is Ω.

[0063] The surface resistivity in this specification is measured in accordance with JIS K6271-2001. Specifically, a test piece of 100 mm length × 100 mm width × thickness (with the same thickness as the multi-layer extruded foam sheet) cut out from the multi-layer extruded foam sheet is left to stand in an atmosphere of 23°C temperature and 50% relative humidity for 24 hours to condition the test piece, and a voltage of 500 V is applied to the atmosphere under the same conditions (temperature 23°C, relative humidity 50%), and the surface resistivity [Ω] is measured 1 minute after the application, and the obtained value is taken as the surface resistivity.

[0064] The apparent density of the multi-layer extruded foam sheet of the present invention is 15 to 300 kg / m 3 It is preferable that: When the apparent density of the extruded multi-layer foam sheet is within the above range, the extruded multi-layer foam sheet has an excellent balance between mechanical properties such as strength, light weight, and cushioning properties. From this viewpoint, the lower limit of the apparent density is more preferably 18 kg / m 3 , more preferably 20 kg / m 3 On the other hand, the upper limit of the apparent density is more preferably 200 kg / m 3 , more preferably 150 kg / m 3 , particularly preferably 100 kg / m 3 is.

[0065] The total thickness of the extruded multi-layer foam sheet is preferably 0.05 to 2 mm, more preferably 0.1 to 1.8 mm, and even more preferably 0.2 to 1.5 mm. If the thickness of the extruded multi-layer foam sheet is within this range, a good balance between cushioning properties and flexibility will be achieved.

[0066] The overall basis weight of the multi-layer extruded foam sheet is 5 to 100 g / m 2 is preferably 10 to 90 g / m 2 , and more preferably 20 to 80 g / m 2 If the total basis weight is within this range, a good balance between light weight and mechanical properties will be achieved.

[0067] In the present invention, the thickness, basis weight and apparent density of the multi-layer extruded foam sheet are measured as follows. First, a rectangular test piece measuring the total sheet width [mm] × 100 mm was cut out from the multi-layer extruded foam sheet along its width direction, and the thickness of the test piece was measured at equal intervals of 1 cm from one end to the other in the width direction, and the arithmetic mean value of the measured values ​​was taken as the total thickness of the multi-layer extruded foam sheet. Next, the weight [g] of the test piece was measured, and this weight was divided by the area of ​​the test piece (specifically, the total sheet width [mm] × 100 mm), and the basis weight [g / m 2 ] of the multi-layer extruded foam sheet was calculated by unit conversion. 2 Furthermore, the basis weight is divided by the thickness of the entire multi-layer extruded foam sheet obtained above, and the unit conversion is carried out to obtain the apparent density [kg / m 3 ] is required.

[0068] The basis weights of the antistatic layer and non-antistatic layer are determined by multiplying the thickness of each layer by the density of the resin composition constituting each layer and converting the resulting unit. Specifically, the multilayer extruded foam sheet is cut widthwise to form a vertical cross section. Next, enlarged photographs of the front side of the multilayer extruded foam sheet are taken at equal intervals in the width direction, at least 10 points per side (at least 20 points total for both sides). For each enlarged photograph, the thicknesses of the antistatic layer and non-antistatic layer are measured at 1 cm (actual length) intervals in the width direction. The arithmetic mean values ​​obtained are then used as the thicknesses of the antistatic layer and non-antistatic layer for each side. The basis weights of the antistatic layer and non-antistatic layer per side for each side are determined by multiplying the thicknesses by the density of the resin composition and converting the resulting unit. When the antistatic layer or non-antistatic layer contains additives such as inorganic fillers, the density of the resin composition is the density including the additives.

[0069] Alternatively, when the discharge rate X [kg / hour] of the antistatic layer per side, the discharge rate Y [kg / hour] of the non-antistatic layer per side, the width W [m] of the multi-layer extruded foam sheet, and the take-up speed L [m / hour] of the multi-layer extruded foam sheet are known, these values ​​can be used to calculate the tensile strength according to the following equations (2) and (3). Basis weight of antistatic layer per side [g / m 2 ]=[X / (1000×L×W)]···(2) Basis weight per side of non-antistatic layer [g / m 2 ]=[Y / (1000×L×W)]···(3)

[0070] The closed cell content of the extruded multi-layer foam sheet of the present invention is preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more, in consideration of surface protection of the packaged items, appropriate slip properties, stiffness, etc.

[0071] The closed cell content S (%) is calculated using the true volume Vx of the multilayer extruded foam sheet (cut sample) measured using an air comparison hydrometer Model 930 manufactured by Toshiba Beckman Co., Ltd. in accordance with Procedure C of ASTM-D2856-70, using the following formula (4): Note that multiple samples measuring 25 mm x 25 mm x the thickness of the multilayer extruded foam sheet were cut and stacked to prepare cut samples measuring 25 mm x 25 mm x approximately 20 mm.

[0072] S(%)=(Vx-W / ρ)×100 / (Va-W / ρ) (4) Vx: The true volume (cm) of the cut sample measured by the above method 3 ) and corresponds to the sum of the volume of the resin that makes up the cut sample and the total volume of the air bubbles in the closed cell portion within the cut sample. Va: Apparent volume (cm) of the cut sample calculated from the outer dimensions of the cut sample used in the measurement 3 ). W: total weight (g) of the cut sample used for the measurement. ρ: Density of the resin obtained by defoaming the multi-layer extruded foam sheet (g / cm 3 )

[0073] Next, the method for producing the extruded multi-layer foam sheet of the present invention will be described. The multi-layer extruded foam sheet of the present invention can be obtained by the following method: [1] A resin melt for forming a foamed layer obtained by kneading a polyethylene-based resin (A) with a physical foaming agent, a resin melt for forming an antistatic layer obtained by kneading a polyethylene-based resin (B) with an ionomer resin-based antistatic agent, and a resin melt for forming a non-antistatic layer obtained by kneading a polyethylene-based resin (C) are co-extruded, A method for producing a multi-layer extruded foam sheet having a foam layer made of a polyethylene-based resin (A), an antistatic layer laminated and bonded to at least one side of the foam layer, and a non-antistatic layer laminated and bonded to the antistatic layer, comprising: the antistatic layer comprises, in a vertical cross section (a) of the multi-layer extruded foam sheet perpendicular to the width direction, a dispersed phase in which the ionomer resin-based antistatic agent is dispersed in layers in a continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase is 3 or more per 1 μm in the thickness direction; the non-antistatic layer is substantially free of an antistatic agent, is present in the thickness direction from the surface of the multi-layer extruded foam sheet on the resin layer side, and has an average thickness of 0.5 to 15 μm; The surface resistivity of the surface of the resin layer of the multi-layer extruded foam sheet is 1×10 12 The multi-layer extruded foam sheet can be obtained by the method for producing a multi-layer extruded polyethylene resin foam sheet having a hardness of Ω or less. In a more preferred embodiment, the multi-layer extruded polyethylene resin foam sheet can be obtained by the method for producing a multi-layer extruded polyethylene resin foam sheet according to the above item [1], wherein a polyalkylene glycol and / or a volatile plasticizer is added to the molten resin for forming the antistatic layer during co-extrusion.

[0074] Next, a specific method for producing the extruded multi-layer foam sheet of the present invention will be described. The multi-layer extruded foam sheet can be produced by any conventionally known method, and a representative preferred method is a multi-layer co-extrusion method in which a molten resin for forming a resin layer is laminated on one or both sides of a molten resin for forming a foam layer in a co-extrusion die, and these are co-extruded while foaming the molten resin for forming a foam layer to produce a multi-layer extruded foam sheet. Furthermore, in the present invention, the resin layer must be co-extruded as a laminate of the antistatic layer 3a and the non-antistatic layer 3b. Specifically, the molten resins for forming the resin layers are separately extruded using separate extruders to form the molten resin for forming the antistatic layer and the molten resin for forming the non-antistatic layer. The molten resin for forming the antistatic layer is formed to have a specific antistatic morphology by using a polyethylene-based resin (B), an ionomer resin, and, if necessary, a polyalkylene glycol and / or a volatile plasticizer. Simultaneously, the molten resin for forming the non-antistatic layer is formed using the polyethylene-based resin (C) or the like. Next, the molten resin for forming the antistatic layer and the molten resin for forming the non-antistatic layer are introduced into a co-extrusion die, and the molten resin for forming the antistatic layer and the molten resin for forming the non-antistatic layer are laminated in this order on one or both sides of the molten resin for forming the foam layer. These are co-extruded, and the molten resin for forming the foam layer is foamed and taken up, thereby obtaining the multilayer extruded foam sheet of the present invention.

[0075] Multilayer coextrusion methods include (1) coextrusion using a flat die to form a sheet to produce a multilayer extruded foam sheet, and (2) coextrusion using an annular die to form a tubular multilayer foam, which is then slit open along the extrusion direction to produce a multilayer extruded foam sheet. Of these, the multilayer coextrusion method using an annular die is preferred because it is easy to produce wide multilayer extruded foam sheets with a width of 1000 mm or more.

[0076] The coextrusion method using the annular die is described in detail below. First, the polyethylene resin (A) and optional additives such as a cell control agent are fed into an extruder for forming a foam layer, where they are heated and kneaded. Then, a physical foaming agent is injected into the extruder and further kneaded to form a resin melt for forming a foam layer. At the same time, the polyethylene resin (B), the ionomer resin antistatic agent, and optional polyalkylene glycol and / or volatile plasticizer are fed into an extruder for forming an antistatic layer, where they are heated and kneaded to form a resin melt for forming an antistatic layer. At the same time, the polyethylene resin (C) and other components are fed into an extruder for forming a non-antistatic layer, where they are heated and kneaded to form a resin melt for forming a non-antistatic layer. The resulting foam layer-forming resin melt, antistatic layer-forming resin melt, and non-antistatic layer-forming resin melt are introduced into a co-extrusion annular die, laminated, and co-extruded to be extrusion-foamed into the atmosphere to obtain a tubular foam, which is then drawn along a widening device such as a mandrel and slit open to obtain a multi-layer extruded foam sheet.

[0077] The difference [Tm(B)-Tm(i)] between the melting point Tm(B) of the polyethylene resin (B) used in the resin melt for forming the antistatic layer and the melting point Tm(i) of the ionomer resin is preferably 5 to 30°C, more preferably 8 to 28°C, and more preferably 10 to 25°C.

[0078] The multi-layer extruded foam sheet of the present invention exhibits excellent antistatic properties due to the antistatic morphology structure formed by the polyethylene resin and the ionomer resin. However, in the past, when a polyethylene-based resin extruded foam sheet was produced by coextrusion using an ionomer resin as a polymeric antistatic agent in the antistatic layer, it was difficult to form the above-mentioned morphology. Specifically, when producing a multilayer extruded foam sheet by coextrusion, the temperature conditions for extruding the resin melt for forming the antistatic layer must usually be set at a sufficiently high temperature in order to disperse the ionomer resin in the resin constituting the continuous phase. However, in order to maintain a good cell structure in the foam layer, the temperature of the resin melt for forming the antistatic layer cannot be set at a sufficiently high temperature. Furthermore, at low temperatures sufficient for forming a good foam layer, the melt viscosity of the ionomer resin tends to increase. Therefore, in the past, when a polyethylene-based resin and an ionomer resin were used as resins for forming the antistatic layer, it was difficult to disperse the ionomer resin in the polyethylene-based resin because of the difference in melting points between them. In contrast, by adding a polyalkylene glycol and / or a volatile plasticizer to the molten resin for forming the antistatic layer during co-extrusion, the ionomer resin can be dispersed in the polyethylene resin even when there is a difference in melting point within the above-mentioned range, and a multi-layer extruded foam sheet exhibiting excellent antistatic performance over the entire surface thereof can be stably obtained.

[0079] The polyalkylene glycol may be any of the polyalkylene glycols described above. When polyethylene glycol is used as the polyalkylene glycol, the amount added is preferably 0.3 to 6 parts by weight, more preferably 0.5 to 5 parts by weight, even more preferably 0.8 to 4 parts by weight, and particularly preferably 1 to 4 parts by weight, per 100 parts by weight of the total of the polyethylene resin (B) and the ionomer resin.

[0080] The volatile plasticizer used has the function of reducing the melt viscosity of the resin melt and volatilizes from the resin layer after the resin layer is formed, eliminating its presence in the resin layer. Specifically, one or more selected from aliphatic hydrocarbons and alicyclic hydrocarbons having 3 to 7 carbon atoms, aliphatic alcohols having 1 to 4 carbon atoms, and aliphatic ethers having 2 to 8 carbon atoms are preferably used. When a low-volatility lubricant is used instead of a volatile plasticizer, the lubricant may remain in the resin layer and contaminate the surface of the packaged object. In contrast, a volatile plasticizer is preferred because it efficiently plasticizes the resin in the resin layer and is less likely to remain in the resulting resin layer (antistatic layer and non-antistatic layer). To improve the dispersion state of the ionomer resin, it is preferable to use these volatile plasticizers in combination with the polyalkylene glycol.

[0081] The boiling point of the volatile plasticizer is preferably 120°C or lower, more preferably 80°C or lower, because it readily volatilizes from the resin layer. If the boiling point of the volatile plasticizer is within the above range, the volatile plasticizer will naturally volatilize and be removed from the resin layer by the heat immediately after co-extrusion and by gas permeation during subsequent storage of the foam sheet at room temperature if the resulting extruded multi-layer foam sheet is left standing. The lower limit of the boiling point of the volatile plasticizer is generally -50°C.

[0082] Among the volatile plasticizers, it is preferable to use one or more selected from an alcohol having a boiling point of 120°C or less and a saturated hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having an alkyl chain with 1 to 3 carbon atoms, because this improves the dispersion state of the ionomer resin. In particular, when an alcohol having a boiling point of 120°C or less and a saturated hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having an alkyl chain with 1 to 3 carbon atoms are used in combination as the volatile plasticizer, a good antistatic morphology structure can be stably formed even without using the polyalkylene glycol.

[0083] It is preferable that a volatile plasticizer be added to both the resin melt for forming the antistatic layer and the resin melt for forming the non-antistatic layer. By adding a volatile plasticizer to the resin melt, when producing a multi-layer extruded foam sheet by co-extrusion, the extrusion temperatures of the resin melt for forming the antistatic layer and the resin melt for forming the non-antistatic layer can be made closer to the extrusion temperature of the resin melt for forming the foam layer, and the melt elongation of the softened antistatic layer and the non-antistatic layer can be significantly improved. This makes it difficult for the bubbles in the foam layer (the antistatic layer and the non-antistatic layer) to be destroyed by the heat of the resin layer during foaming, and furthermore, the elongation of the resin layer can more easily follow the elongation of the foam layer during foaming. In this case, the antistatic morphology structure is more likely to be formed stably.

[0084] The volatile plasticizer is preferably added in an amount of 5 to 50 parts by weight, more preferably 8 to 30 parts by weight, and particularly preferably 10 to 25 parts by weight, per 100 parts by weight of the total of the polyethylene resin and the polymeric antistatic agent added as needed, in each of the resin melts for forming the antistatic layer and the non-antistatic layer.

[0085] The amount of the ionomer resin in the antistatic layer is preferably 30 to 80% by weight (where the total of the polyethylene resin (B) and the ionomer resin is 100% by weight). When the amount is within this range, the antistatic morphology structure becomes stronger, resulting in particularly excellent antistatic properties. Since the multi-layer extruded foam sheet of the present invention has the non-antistatic layer, it exhibits excellent slip properties and prevents migration of low-molecular-weight components, even when the ionomer resin is added at a high concentration. To further improve the antistatic properties of the multi-layer extruded foam sheet, the amount is more preferably 35% by weight or more. To achieve the effects of improving the slip properties of the multi-layer extruded foam sheet and more reliably suppressing migration of low-molecular-weight components, the amount is more preferably 70% by weight or less, and even more preferably 60% by weight or less.

[0086] Various additives may be added to the resins forming the melt for forming the antistatic layer and the melt for forming the non-antistatic layer, as long as the object of the present invention is not impaired. Examples of various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, antibacterial agents, etc. In this case, the amount added is determined appropriately depending on the purpose and effect of the additive, but is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less, of each additive per 100 parts by weight of the total of the polyethylene resin and the polymeric antistatic agent added as needed.

[0087] Examples of physical foaming agents added to the foam layer-forming resin melt include organic physical foaming agents such as 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; and fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane; and inorganic physical foaming agents such as nitrogen, carbon dioxide, air, and water. In some cases, decomposition-type foaming agents such as azodicarbonamide can also be used. Two or more of the above physical foaming agents can be used in combination. Among these, organic physical foaming agents are preferred due to their excellent compatibility with polyethylene resins and foamability, and those primarily composed of normal butane, isobutane, or a mixture thereof are particularly preferred.

[0088] The amount of the physical foaming agent added is adjusted depending on the type of foaming agent and the desired apparent density. For example, to obtain a multi-layer extruded foam sheet having the above-mentioned apparent density range using isobutane as the foaming agent, the amount of isobutane added is preferably 3 to 30 parts by weight, more preferably 5 to 25 parts by weight, and even more preferably 8 to 20 parts by weight per 100 parts by weight of the polyethylene resin (A) constituting the foam layer.

[0089] The main additive added to the resin melt for forming the foam layer is usually a bubble regulator. Both organic and inorganic bubble regulators can be used. Examples of inorganic bubble regulators include metal borates such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and sodium bicarbonate. Examples of organic bubble regulators include sodium 2,2-methylenebis(4,6-tert-butylphenyl)phosphate, sodium benzoate, calcium benzoate, aluminum benzoate, and sodium stearate. Combinations of citric acid and sodium bicarbonate, or alkali salts of citric acid and sodium bicarbonate, can also be used as bubble regulators. Two or more of these bubble regulators can also be used in combination. The amount of the cell adjusting agent added is preferably 0.01 to 3 parts by weight, more preferably 0.03 to 1 part by weight, per 100 parts by weight of the base resin.

[0090] The manufacturing apparatus such as the circular die and extruder may be any known apparatus that has been conventionally used in the field of extrusion foaming.

[0091] The multi-layer extruded foam sheet of the present invention is a foam sheet that has excellent cushioning properties, excellent appearance, and excellent antistatic properties, and also has an extremely low amount of migration of low-molecular-weight components into the packaged items. Therefore, the multi-layer extruded foam sheet of the present invention can be suitably used as a packaging material for electronic devices, such as an inserting sheet for glass plates. [Example]

[0092] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0093] Next, the raw materials used in the examples and comparative examples will be described. Table 1 shows the polyethylene resins used in the examples and comparative examples.

[0094] [Table 1]

[0095] In Table 1, the melting point, melt flow rate (MFR), melt viscosity (η), and melt tension (MT) were measured as follows. The melting point of the polyethylene resin was determined by heat flux differential scanning calorimetry in accordance with JIS K7121-1987. Specifically, in the measurement, a test specimen conditioned under the conditions of JIS K7121-1987, 3. Conditioning of test specimen (2) (with the exception of a cooling rate of 10°C / min) was used, and the temperature at the apex of the melting peak obtained by heating at a rate of 10°C / min was taken as the melting point.

[0096] The melt flow rate of polyethylene resins was measured at 190°C under a load of 2.16 kg in accordance with JIS K7210-1 (2014).

[0097] The melt viscosity was measured using a Capillograph 1D measuring instrument manufactured by Toyo Seiki Seisakusho Co., Ltd. A cylinder with a diameter of 9.55 mm and a length of 350 mm and an orifice with a nozzle diameter of 1.0 mm and a length of 10 mm were used, and the set temperatures of the cylinder and orifice were set to 190°C. 15 g of the sample to be measured was placed in the cylinder and left for 4 minutes to form a molten resin, and then heated at a shear rate of 100 sec -1 The molten resin was extruded in a string-like shape from the orifice, and the viscosity of the molten resin during extrusion was measured, and this value was taken as the melt viscosity.

[0098] Melt tension (MT) was measured using a Capillograph 1D manufactured by Toyo Seiki Seisakusho, Ltd. Specifically, a cylinder with a diameter of 9.55 mm and a length of 350 mm and a nozzle diameter of 2.095 mm and a length of 8.0 mm were used. The cylinder and orifice were set to a temperature of 190°C. The required amount of sample was placed in the cylinder and allowed to stand for 4 minutes. The piston speed was set to 10 mm / min, and the molten resin was extruded from the orifice in a string-like shape. This string-like material was then placed on a tension detection pulley with a diameter of 45 mm. The take-up speed was increased at a constant rate so that it reached 200 m / min from 0 m / min over 4 minutes, and the maximum tension value immediately before the string-like material broke was obtained. The reason for setting the time required for the take-up speed to reach 200 m / min from 0 m / min to 4 minutes was to suppress thermal degradation of the resin and to improve the reproducibility of the obtained values. The above procedure was repeated 10 times using different samples, and the three largest and three smallest maximum values ​​obtained from the 10 measurements were discarded. The remaining four intermediate maximum values ​​were then averaged to obtain the melt tension (mN).

[0099] Ionomer resin (polymer antistatic agent) Abbreviation "SD100": Ethylene-based potassium ionomer resin "Entira SD100" (density 990 kg / m) manufactured by DuPont-Mitsui Polychemicals Co., Ltd. 3 , MFR 5g / 10min, melt viscosity 823Pa s, melting point 92℃, surface resistivity 1.0×10 7 Ω) The MFR, melt viscosity and melting point of the ionomer resin were determined in the same manner as for the polyethylene resin.

[0100] Polyalkylene glycol Abbreviation "PEG": Polyethylene glycol "PEG300" (number average molecular weight 300) manufactured by Sanyo Chemical Industries, Ltd.

[0101] Physical Foaming Agent Isobutane

[0102] Volatile plasticizers Mixed butane (a mixture of 35% normal butane and 65% isobutane by weight)

[0103] Foam adjuster The cell control agent used was a cell control agent masterbatch containing 80% by weight of low-density polyethylene (Japan Polyethylene Corporation, "LA500M") and 20% by weight of talc (Matsumura Sangyo Co., Ltd., trade name Hifiller #12).

[0104] Device A multi-layer extruded foam sheet manufacturing apparatus equipped with the following extruder and die was used. Extruder for forming foam layer: First extruder with barrel inner diameter of 115 mm Extruder for forming antistatic layer: Second extruder with barrel inner diameter of 65 mm Extruder for forming non-antistatic layer: Third extruder with inner diameter of 50 mm Die: Annular coextrusion die with an outlet diameter of 96 mm

[0105] Examples 1 to 4, Comparative Examples 1 to 4 Polyethylene resin (A) of the type shown in Table 2 (Examples) and Table 3 (Comparative Examples) and 2 parts by weight of a cell control agent masterbatch per 100 parts by weight of polyethylene resin (A) were supplied to a first extruder and kneaded at approximately 200°C, followed by further kneading with pressure-injected isobutane as a physical foaming agent in the amounts shown in Tables 2 and 3. The kneaded mixture was adjusted to the extrusion resin temperature shown in Table 4 (Examples) and Table 5 (Comparative Examples) to form a resin melt for forming a foam layer. At the same time, polyethylene resin (B) of the type and amount shown in Tables 2 and 3, ionomer resin of the type and amount shown in Tables 2 and 3, and polyalkylene glycol of the type and amount shown in Tables 2 and 3 were fed into a second extruder and kneaded at approximately 200°C. Then, mixed butane (normal butane / isobutane = 65 wt% / 35 wt%) shown in Tables 2 and 3 was injected as a volatile plasticizer, and the mixture was further kneaded. The extrusion resin temperature was adjusted to the temperature shown in Tables 4 and 5 to form a resin melt for forming an antistatic layer. At the same time, polyethylene resin (C) of the type and amount shown in Tables 2 and 3, ionomer resin of the type and amount shown in Tables 2 and 3, polyalkylene glycol of the type and amount shown in Tables 2 and 3, and talc masterbatch of the amount shown in Tables 2 and 3 were supplied to a third extruder and kneaded at approximately 200°C. After that, mixed butane (normal butane / isobutane = 35 wt% / 65 wt%) shown in Table 2 was injected as a volatile plasticizer, and the mixture was further kneaded and adjusted to the extrusion resin temperature shown in Tables 4 and 5 to obtain a resin melt for forming a non-antistatic layer.

[0106] The resin melts for forming the foam layer, the resin melts for forming the antistatic layer, and the resin melts for forming the non-antistatic layer were introduced into a co-extrusion annular die at the output rates shown in Table 4 (Examples) and Table 5 (Comparative Examples). The resin melts for forming the antistatic layer were laminated onto both the inner and outer surfaces of the resin melts for forming the foam layer, and the resin melts for forming the non-antistatic layer were laminated onto both the inner and outer surfaces of each of the resin melts for forming the antistatic layer. The laminates were co-extruded through the annular die to form a tubular multilayer foam having a five-layer structure (a three-layer structure in Comparative Examples 1 to 3) in which antistatic layers were laminated and bonded to both the inner and outer surfaces of the foam layer, and a non-antistatic layer was laminated and bonded to each antistatic layer. The extruded tubular multilayer foam was expanded using a cylindrical mandrel with a diameter of 333 mm and taken up at the take-up speeds shown in Tables 4 and 5 to obtain the total basis weights shown in Tables 6 (Examples) and 7 (Comparative Examples). The tubular laminated foam was then slit open along the extrusion direction to obtain a multilayer extruded foam sheet.

[0107] [Table 2]

[0108] [Table 3]

[0109] Tables 2 and 3 show the blending amounts of polyethylene resin, ionomer resin, polyalkylene glycol, etc., and these blending amounts represent the contents of the polyethylene resin, ionomer resin, polyalkylene glycol, etc. constituting the obtained multi-layer extruded foam sheet.

[0110] [Table 4]

[0111] [Table 5]

[0112] The physical properties of the extruded multi-layer foam sheets obtained in the Examples and Comparative Examples are shown in Table 6 for the Examples and Table 7 for the Comparative Examples.

[0113] [Table 6]

[0114] [Table 7]

[0115] Comparative Example 1 is an example of a multi-layer extruded foam sheet produced in Example 1 without providing a non-antistatic layer. The multi-layer extruded foam sheet obtained in Comparative Example 1 had excellent antistatic properties due to the formation of an antistatic morphology structure, but lacked a non-antistatic layer, resulting in poor glass stain prevention. Furthermore, the static friction force was high, resulting in insufficient slip properties depending on the application. Furthermore, the multi-layer extruded foam sheet of Comparative Example 1 experienced high friction with the mandrel during sheet take-up, resulting in waviness in the extrusion direction and poor appearance.

[0116] Comparative Example 2 is an example produced by blending talc into the antistatic layer of Comparative Example 1. The multi-layer extruded foam sheet obtained in Comparative Example 2 had improved slip properties due to the blending of talc, but cracks occurred, resulting in poor appearance. In addition, the glass stain prevention properties were significantly reduced.

[0117] Comparative Example 3 is an example of a multi-layer extruded foam sheet produced by changing the amount of ionomer resin in the antistatic layer of Example 1 without providing a non-antistatic layer, and without incorporating polyethylene glycol. In the multi-layer extruded foam sheet obtained in Comparative Example 3, the ionomer resin was not dispersed in layers in the continuous layer of polyethylene resin in the antistatic layer, and the average number of dispersed layers was significantly small. In other words, the sheet did not have an antistatic morphology. Therefore, the desired antistatic properties were not obtained.

[0118] Comparative Example 4 is an example produced by changing the extrusion rate and take-up speed of the resin melt for forming a non-antistatic layer in Example 1. The multi-layer extruded foam sheet obtained in Comparative Example 4 did not have the desired antistatic properties because the thickness of the non-antistatic layer was too large.

[0119] The physical properties in Tables 6 and 7 were measured and evaluated as follows. (1) Apparent density, basis weight, and overall thickness of multi-layer extruded foam sheet Five rectangular test pieces, each measuring the total sheet width [mm] × 100 mm, were cut from the multi-layer extruded foam sheet in the width direction. The thickness of each test piece was measured every 1 cm in the width direction of the multi-layer extruded foam sheet, and the thickness [mm] of each test piece was calculated by arithmetically averaging the thicknesses. The arithmetic mean value of the thicknesses of each test piece was used as the total thickness [mm] of the multi-layer extruded foam sheet. The weight of each test piece was also measured, and the weight was divided by the area of ​​the test piece (specifically, the sheet width [mm] × 100 mm), and the basis weight [g / m ] of each test piece was calculated by unit conversion. 2 The arithmetic mean value of the basis weight of each test piece was calculated as the basis weight [g / m 2 Furthermore, the basis weight was divided by the average thickness, and the result was converted into units to give the apparent density [kg / m3 ] was sought.

[0120] (2) Basis weight of antistatic layer and non-antistatic layer The basis weights of the antistatic layer and the non-antistatic layer were calculated from the respective discharge amounts of the antistatic layer and the non-antistatic layer using the above-mentioned formulas (2) and (3). Note that the multi-layer extruded foam sheets were produced under conditions such that the basis weights of the antistatic layer and the non-antistatic layer on one surface side and the other surface side of the multi-layer extruded foam sheet were the same, so the basis weights of only one surface side are shown in Tables 6 and 7.

[0121] (3) Evaluation of antistatic properties (surface resistivity measurement) Three test pieces measuring 100 mm long x 100 mm wide x thickness (the same thickness as the multilayer extruded foam sheet) were cut from the center and both ends of the multilayer extruded foam sheet. According to JIS K6271-2001, a voltage of 500 V was applied to the test pieces at 23°C and 50% relative humidity, and the surface resistivity of the test pieces was measured one minute after application. Surface resistivity measurements were performed on both sides of the test pieces (three test pieces x both sides: a total of six times), and the surface resistivity was calculated from the arithmetic mean of the measured values. The measurement device used was the "SM-8220" manufactured by Hioki E.E. Corporation. Based on the measured surface resistivity, the antistatic properties were evaluated according to the following criteria. ◎: Surface resistivity is 1.0 x 10 10 Ω or less ○: Surface resistivity is 1.0 × 10 10 Ω, exceeding 1.0×10 12 Ω or less ×: Surface resistivity is 1.0×10 12 exceed

[0122] (4) The closed cell ratio of the extruded multi-layer foam sheet was measured by the above-mentioned method.

[0123] (5) Antistatic morphological structure (5-1) Method for observing antistatic morphology structure First, the multi-layer extruded foam sheet was cut in the widthwise center and near both widthwise ends along the thickness direction and extrusion direction of the multi-layer extruded foam sheet, and three samples having cross sections along the extrusion direction (vertical cross sections (a) perpendicular to the width direction) were cut out. Next, ultrathin sections were prepared from the cross sections of each of the three cut samples, including the entire resin layer (the resin layer on the side of the multilayer extruded foam sheet that was not facing the mandrel). The ultrathin sections were then stained with ruthenium tetroxide to distinguish the polyethylene resin from the ionomer resin by their shades. The stained sections were then observed using a transmission electron microscope (JEOL JEM-1400Plus) at an accelerating voltage of 100 kV, and cross-sectional photographs of the resin layer were taken at magnifications of 17,500x and 70,000x.

[0124] In the cross-sectional photographs, the darker areas represent the dispersed phase (the dispersed phase of the ionomer resin). Figures 2 and 3 show cross-sectional photographs (magnifications: 17,500x and 70,000x) of the multi-layer extruded foam sheet obtained in Example 1, and Figure 4 shows a cross-sectional photograph (magnification: 17,500x) of the multi-layer extruded foam sheet obtained in Comparative Example 1.

[0125] The cross-sectional photographs obtained were subjected to a preparatory process in which the dispersed phase and the portions other than the dispersed phase were color-coded in black and white. Here, the dispersed phase and the portions other than the dispersed phase (continuous phase) were determined based on the shading of the cross-sectional photograph and the presence or absence of a lamellar structure, and the photographs were color-coded. Note that, since ionomer resins typically have more amorphous portions than polyethylene-based resins, they can be determined as portions with less lamellar structure than the continuous phase in the cross-sectional photograph. Furthermore, by color-coding the dispersed phase and the continuous phase, the interface between the two was made clear. Thereafter, using the image processing software "NS2K-pro" manufactured by NanoSystems Co., Ltd., the pre-processed cross-sectional photographs were subjected to image processing and measurement under the following conditions. (1) Monochrome conversion (2) Smoothing filter (processing times 1 to 10) (3) NS method binarization (sharpness 41, sensitivity 10, noise removal, density range 45-255) (4) Feret diameter and area measurement

[0126] (5-2) Average number of layers in the thickness direction of the dispersed phase When a morphology indicating the presence of a layered ionomer resin-based dispersed phase was observed in the cross section obtained by image processing measurement under the conditions (1) to (4), the average number of dispersed phase layers per 1 μm in the thickness direction was measured. Specifically, in the cross-sectional photograph, 10 lines perpendicular to the extrusion direction were drawn at equal intervals in the thickness direction in the portion where the ionomer resin-based antistatic agent was present as a dispersed phase in a layered form in the continuous phase of the polyethylene resin (B). Here, the length of each line corresponds to the thickness of the antistatic layer at the position where the line was drawn. For each of the 10 lines, the number of dispersed phase layers intersecting the line was counted, and the number of dispersed layers per 1 μm in the thickness direction was measured and arithmetically averaged to calculate the number of dispersed phase layers per 1 μm in the thickness direction. Here, 2 Dispersed phases with an aspect ratio of 0.01 or less were not measured. Dispersed phases with an aspect ratio of less than 2 were not measured. Furthermore, black areas in the cross-sectional photographs that are distinguishable from the dispersed phase, such as wrinkles in the slices that occurred during the preparation of the ultrathin sections and the outermost surface of the morphological structure, were not included in the measurement range. This measurement was performed on the three test pieces, and the arithmetic average value for the three test pieces was taken as the average number of layers per 1 μm in the thickness direction of the dispersed phase.

[0127] (5-3) Method for measuring the median dispersion area based on the number of dispersed phases In the image processing measurement under the conditions (1) to (4) above, if a morphology in which a dispersed phase exists appears on the obtained cross section, a measurement range is randomly selected, and the total area of ​​the measurement range is 100 μm 2 Measurements were carried out so that the number and cross-sectional area (dispersed area) of all dispersed phases contained in the measurement range were measured. The dispersed phases that intersect with the boundary of the measurement range were also measured, and the cross-sectional area of ​​the dispersed phases was measured. 2Dispersed phases with a color of 0.01 or less were not included in the measurement. Furthermore, black areas in the cross-sectional photographs that are distinguishable from the dispersed phase, such as wrinkles in the sections that occurred during the preparation of the ultrathin sections and the outermost surface of the morphology, were not included in the measurement range. This measurement was performed on the three test pieces, and the median value of the cross-sectional area of ​​the dispersed phase was calculated based on the number of dispersed phases measured in the three test pieces and the cross-sectional area of ​​each dispersed phase. The median is the value located in the middle of the total number of dispersed phases (50% of the cumulative number of dispersed phases) when the cross-sectional areas of the dispersed phases are arranged in order of size.

[0128] (5-4) Method for determining the presence or absence of an antistatic morphology structure In the vertical cross section (a) of the multilayer extruded foam sheet, when the ionomer resin-based antistatic agent was present as a layered dispersed phase in the continuous polyethylene resin phase, and the dispersed phase was present in an amount of 3 layers / μm or more in the thickness direction, the multilayer extruded foam sheet was judged to have an antistatic morphology structure.

[0129] (5-5) Measurement method for the average thickness of a non-antistatic layer In the cross-sectional photograph of the multi-layer extruded foam sheet showing the morphology, image processing was performed under the conditions (1) to (4) above. The region from the outermost surface of the multi-layer extruded foam sheet to the portion where the morphology was formed was determined to be the non-antistatic layer, and the thickness of the non-antistatic layer was measured. Specifically, at any point in the cross-sectional photograph, a line perpendicular to the extrusion direction was drawn from the outermost surface of the multi-layer extruded foam sheet through the thickness direction, and the distance to the ionomer resin-dispersed phase located at the outermost surface of the multi-layer extruded foam sheet was measured. This measurement was performed at 10 equally spaced locations, and the thickness of the non-antistatic layer was calculated as an arithmetic average. This measurement was performed on the three test pieces, and the arithmetic average of the non-antistatic layer thicknesses calculated for the three test pieces was taken as the average thickness of the non-antistatic layer without the antistatic agent.

[0130] 2 and 3, micrographs of the multi-layer extruded foam sheet obtained in Example 1, show a black dispersed phase dispersed in the white continuous phase, and also show a non-antistatic layer without an ionomer resin dispersed phase. In contrast, in Fig. 4, a micrograph of the multi-layer extruded foam sheet obtained in Comparative Example 1, show a black dispersed phase dispersed in the white continuous phase, but no non-antistatic layer without a dispersed phase.

[0131] (5-6) Measurement method for the average aspect ratio of the dispersed phase In the cross sections obtained by the image processing measurements under the conditions (1) to (4), the vertical Feret diameter and horizontal Feret diameter of all the dispersed phases were measured. Here, the vertical Feret diameter corresponds to the length of the dispersed phase in the thickness direction of the morphological structure (the direction perpendicular to the surface of the foam sheet), and the horizontal Feret diameter corresponds to the length of the dispersed phase in the horizontal direction perpendicular to the thickness direction. Note that the dispersed phases intersecting the boundary of the measurement range were also measured, and the vertical Feret diameter and horizontal Feret diameter of the dispersed phases were measured. This measurement was performed on the three test pieces, and the median value of each Feret diameter on a number basis was calculated from the vertical Feret diameters or horizontal Feret diameters of all the dispersed phases measured on the three test pieces. The median value of the obtained vertical Feret diameters was taken as the median value A of the dispersed diameter in the thickness direction based on the number of dispersed phases, and the median value of the obtained horizontal Feret diameters was taken as the median value B of the dispersed diameter in the horizontal direction perpendicular to the thickness direction based on the number of dispersed phases. The median value means the value located in the middle of the total number of dispersed phases (50% of the total number of dispersed phases) when the Feret diameters of the dispersed phases are arranged in order of size. The average aspect ratio of the dispersed phase in the cross section of the antistatic layer was calculated by dividing the median value B of the dispersed diameter in the horizontal direction perpendicular to the thickness direction based on the number of dispersed phase particles by the median value A of the dispersed diameter in the thickness direction based on the number of dispersed phase particles.

[0132] (5-7) Method for measuring the average value of the area ratio occupied by the dispersed phase In the cross-sectional photograph obtained by the image processing measurement under the conditions (1) to (4) above, a rectangular area measuring 1500 nm in the extrusion direction and 500 nm in the thickness direction was determined at an arbitrarily selected location in the width direction, with the approximate center of the thickness direction of the antistatic layer having the morphology set as the center in the thickness direction, and an enlarged photograph of the rectangular area was taken. Next, the sum of the dispersed areas of all dispersed phases present in the rectangular area was measured, and the ratio of the sum of the dispersed areas of the dispersed phases to the area of ​​the rectangular area was calculated. This measurement was performed on the three test pieces, and the arithmetic mean of the ratios calculated for the three test pieces was taken as the average ratio of the area occupied by the dispersed phase in the specified area.

[0133] (6) Glass stain prevention test Glass for liquid crystal panels was used as the packaged item. Ten sheets of this glass and eleven sheets of the multi-layer extruded foam sheet were stacked to form a glass laminate, and the haze (1) in the thickness direction (glass lamination direction) of the glass laminate was measured using "NDH2000" manufactured by Nippon Denshoku Kogyo Co., Ltd. A sample (the multi-layer extruded foam sheet obtained in the Examples and Comparative Examples) was applied to each glass at a surface pressure of 50 g / cm. 2 The laminate was left to stand for 168 hours at a temperature of 60°C and a relative humidity of 90% while being tightly adhered under a load of 1000 kJ / cm2. The sample was then removed from the glass, and 10 sheets of glass were stacked together. The haze (2) of the glass laminate was measured in the same manner as for haze (1). The haze (1) value was subtracted from the haze (2) value to determine the change in haze (glass haze (%) after test - glass haze (%) before test), and migration was evaluated according to the following criteria. The smaller the change in haze, the less migration of low-molecular-weight components contained in the polymeric antistatic agent in the multilayer extruded foam sheet to the glass. ◎: Haze change is less than 0.5 ○: Haze change is 0.5 or more and less than 1 △: Haze change is 1 or more but less than 2 ×: Haze change is 2 or more

[0134] (7) Slipperiness evaluation: static friction force The static friction force was measured by a method conforming to JIS K7125:1999. First, six 50 mm x 50 mm square test pieces were cut from randomly selected locations on the multilayer extruded foam sheet, with one side aligned with the extrusion direction of the multilayer extruded foam sheet. Next, the test pieces were placed in an atmosphere of 23°C and 50% humidity for 24 hours to condition the test pieces, and then the test pieces were cut into square pieces with a base size of 50 mm x 50 mm and a weight of 125 g (5 g / cm). 2 The test piece was fixed to the bottom of a measuring jig (product number S9112, manufactured by Matsunami Glass Industrial Co., Ltd., product name "Standard Large White Polished Edge No. 2"). The test piece was then placed on a glass slide (product number S9112, manufactured by Matsunami Glass Industrial Co., Ltd.). The extrusion direction of the multilayer extruded foam sheet was aligned with the pulling direction of the measuring jig, and the measuring jig was pulled horizontally at a speed of 100 mm / min, causing the test piece to slide across the glass slide. The first maximum load at this time was recorded as the static friction force (N) of the test piece. The static friction force on the mandrel contact surface was measured for three of the six test pieces, and the static friction force on the surface opposite to the mandrel contact surface was measured for the remaining three. The arithmetic mean value (n = 6) of the static friction forces for each test piece was recorded as the static friction force (N) of the multilayer extruded foam sheet under low load. Based on the measured values ​​of static friction force, the slipperiness was evaluated according to the following criteria. 〇: Static friction force is 2.5N or more but less than 4N ×: Static friction force is 4N or more

[0135] (8) Appearance (8-1) Cracks The resulting extruded multi-layer foam sheet was observed, and the occurrence of cracks was evaluated according to the following criteria. ◯: Visual inspection of the multi-layer extruded foam sheet showed no obvious cracks on the surface. ×: Tears were found on the surface of the multi-layer extruded foam sheet when visually inspected. (8-2) Waviness in the extrusion direction The resulting extruded multi-layer foam sheet was observed, and waviness in the extrusion direction was evaluated according to the following criteria. ◯: When the multilayer extruded foam sheet is visually inspected, there is no obvious waviness (poor appearance) in the extrusion direction. ×: When the multi-layer extruded foam sheet is visually inspected, waviness (poor appearance) occurs in the extrusion direction. [Explanation of symbols]

[0136] 1. Multi-layer extruded foam sheet 2 Foam layer 3 Resin layer 3a Antistatic layer 3b Non-antistatic layer 4. Continuous phase of polyethylene resin (B) 5. Ionomer resin dispersed phase

Claims

1. A multi-layer extruded polyethylene-based resin foam sheet having a foam layer made of a polyethylene-based resin (A) and a resin layer laminated on at least one side of the foam layer by co-extrusion, the resin layer has an antistatic layer and a non-antistatic layer located on a surface of the multi-layer extruded foam sheet, the antistatic layer contains a polyethylene resin (B) and an ionomer resin antistatic agent, and in a vertical cross section (a) of the multi-layer extruded foam sheet perpendicular to the width direction, the ionomer resin antistatic agent forms a dispersed phase in the form of layers in a continuous phase of the polyethylene resin (B), and the average number of layers of the dispersed phase is 3 or more per μm in the thickness direction of the multi-layer extruded foam sheet; the content of the ionomer resin-based antistatic agent in the antistatic layer is 30 to 80% by weight (wherein the total of the polyethylene resin (B) and the ionomer resin-based antistatic agent is 100% by weight); the non-antistatic layer contains a polyethylene resin (C) and the content of an antistatic agent in the non-antistatic layer is 3% by weight or less; the average thickness of the non-antistatic layer is 0.5 to 15 μm; The surface resistivity of the resin layer side surface of the multi-layer extruded foam sheet is 1×10 １２ A multi-layer extruded polyethylene resin foam sheet having a modulus of elasticity of Ω or less.

2. 2. The multi-layer extruded polyethylene resin foam sheet according to claim 1, wherein the dispersed phase has an average aspect ratio of 2 or more in the vertical cross section (a).

3. In the vertical cross section (a), the median dispersion area based on the number of the dispersed phases is 1 × 10 ２ ~5 x 10 ５ nm ２ 3. The multi-layer extruded polyethylene resin foam sheet according to claim 1, wherein

4. The multi-layer extruded polyethylene-based resin foam sheet according to any one of claims 1 to 3, wherein the median dispersed diameter of the dispersed phase in the horizontal direction based on the number of dispersed phase particles in the vertical cross section (a) is 200 to 3,000 nm.

5. 5. The multi-layer extruded polyethylene-based resin foam sheet according to claim 1, wherein in the vertical cross section (a), the dispersed phase occupies an area of ​​30 to 80 area% on average within a rectangular region having a thickness length of 500 nm and a width length of 1500 nm in a central part of the antistatic layer.

6. 6. The multi-layer extruded polyethylene-based resin foam sheet according to claim 1, wherein the antistatic layer contains a polyalkylene glycol in an amount of 0.3 to 6 parts by weight per 100 parts by weight of the total of the polyethylene-based resin (B) and the ionomer resin-based antistatic agent.

7. The surface resistivity is 1×10 １０ The multi-layer extruded polyethylene resin foam sheet according to any one of claims 1 to 6, wherein the modulus of elasticity is less than Ω.

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