Polyethylene resin multilayer foamed sheet, interlayer paper for glass plate, and method for manufacturing polyethylene resin multilayer foamed sheet

Abstract

The multilayer foam sheet has a polyethylene resin foam layer and a resin layer laminated on at least one of the two surfaces of the foam layer. The resin layer has a multilayer structure formed by a surface layer and an intermediate layer. Both the surface layer and the intermediate layer contain polyethylene resin and a polymer antistatic agent. The polymer antistatic agent is included in the intermediate layer in a ratio of 30-70 weight % (inclusive). The polymer antistatic agent is included in the surface layer in a ratio of at least 5 weight % to less than 30 weight %.

Description

Technical Field

[0001] The present invention relates to a multilayer foamed sheet, and more particularly, to a polyethylene-based resin multilayer foamed sheet that can be used as an interlayer sheet for glass plates and the like and a packaging material for electronic devices and the like. Background Art

[0002] Polyethylene resin multilayer foamed sheets are widely used in the field of packaging electronic devices or materials thereof because of their light weight and excellent cushioning properties. For example, such multilayer foamed sheets are used as interlayer sheets inserted between glass plates used as liquid crystal panels for packaging them.

[0003] In such applications, in order to suppress the adhesion of dust, dirt, etc. to a polyethylene-based resin multilayer foamed sheet (hereinafter also referred to simply as a multilayer foamed sheet or foamed sheet), antistatic properties are generally imparted to the multilayer foamed sheet. As a multilayer foamed sheet imparted with antistatic properties, for example, Patent Document 1 discloses a multilayer foamed sheet composed of a polyolefin-based resin foam layer and a resin layer laminated on at least one surface of the foam layer, wherein the resin layer contains a polymer antistatic agent.

[0004] Depending on its application, there may be a case where a multilayer foamed sheet is required to have higher antistatic performance. In order to cope with this requirement, Patent Document 2 discloses a multilayer foamed sheet having a surface resistivity of less than 1.0×10 9 A multi-layer foamed sheet comprising a polyethylene-based resin foam layer and a surface layer laminated on at least one surface of the foam layer, wherein the surface layer is composed of 25 wt % or more and less than 70 wt % of a thermoplastic resin and more than 30 wt % and 75 wt % or less of a polymer antistatic agent (the total of the two is 100 wt %).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Unexamined Patent Publication No. 2004-181933

[0008] Patent Document 2: WO2012 / 105237 Summary of the invention

[0009] Problems to be solved by the present invention:

[0010] In recent years, there are cases where a multilayer foamed sheet is required to be not only excellent in antistatic performance but also not to contaminate products packaged therewith or objects in contact therewith. That is, since a small amount of low molecular weight components contained in the polymer antistatic agent itself is found to migrate into the packaged products, there is a need to develop a low-pollution polyethylene-based resin foamed sheet with which the amount of low molecular weight components migrating into the packaged products is even smaller, depending on the application.

[0011] However, in conventional multilayer foamed sheets, since a large amount of polymer antistatic agent needs to be incorporated into the surface layer to obtain an increased surface resistivity, it is difficult to suppress the migration of low molecular weight components to the products packaged therewith. On the other hand, when the blending amount of the polymer antistatic agent is reduced in order to suppress the migration of low molecular weight components derived from the polymer antistatic agent, high antistatic performance cannot be obtained. Therefore, high antistatic performance and excellent low pollution performance are contradictory issues, and it has been difficult to achieve both at a high level so far.

[0012] In view of the above problems, an object of the present invention is to provide a polyethylene-based resin multilayer foamed sheet having both high antistatic performance and low staining properties, in which the amount of low molecular weight components migrating to articles packaged therewith is extremely small.

[0013] Means of solving the problem:

[0014] According to one aspect of the present invention, there is provided the following multi-layer foamed sheet.

[0015] [1] A multi-layer foamed sheet comprising a foam layer containing a polyethylene-based resin (PE2) and a resin layer laminated on at least one of both sides of the foam layer,

[0016] The resin layer comprises a surface layer located on the outermost side of the multi-layer foamed sheet and containing a polyethylene-based resin (PE4) and a polymer antistatic agent (AS4), and an intermediate layer located between the foam layer and the surface layer and containing a polyethylene-based resin (PE3) and a polymer antistatic agent (AS3),

[0017] wherein the polymer antistatic agent (AS3) is contained in the intermediate layer in an amount of 30 wt % or more and 70 wt % or less based on the weight of the intermediate layer, and the polymer antistatic agent (AS4) is contained in the surface layer in an amount of 5 wt % or more and less than 30 wt % based on the weight of the surface layer.

[0018] [2] The multilayer foamed sheet according to [1] above, wherein the polymer antistatic agent (AS3) is present in an amount of 1 m 2 The amount of the intermediate layer 1-5g A [g / m 2 ] is included in the intermediate layer.

[0019] [3] The multilayer foamed sheet according to [1] or [2] above, wherein the polymer antistatic agent (AS4) is present in an amount of 1 m 2 The amount of the surface layer 0.05-0.8g B [g / m 2 ] is contained in the surface layer.

[0020] [4] The multilayer foamed sheet according to the above [3], wherein the ratio B / A of the amount B of the polymer antistatic agent (AS4) to the amount A of the polymer antistatic agent (AS3) is 0.03 to 0.3.

[0021] [5] The multilayer foamed sheet according to any one of [1] to [4] above, wherein the basis weight of the surface layer is 0.5 to 10 g / m 2 .

[0022] [6] The multilayer foamed sheet according to any one of [1] to [5] above, wherein the surface layer contains the polystyrene resin in an amount of 3 to 35% by weight based on the weight of the surface layer.

[0023] [7] The multilayer foamed sheet according to any one of [1] to [6] above, wherein the polymer antistatic agent (AS3) and the polymer antistatic agent (AS4) are ionomer resins that are the same as or different from each other.

[0024] [8] The multilayer foamed sheet according to any one of [1] to [7] above, wherein the surface resistivity of the surface layer is less than 1×10 9 Ω.

[0025] According to another embodiment of the present invention, there is provided:

[0026] [9] Use of the multilayer foamed sheet according to any one of [1] to [8] above as an interlayer sheet for a glass plate.

[0027] According to yet another embodiment of the present invention, there is provided:

[0028]

[10] A method for producing a polyethylene-based resin multilayer foamed sheet having a multilayer structure in which a surface layer, an intermediate layer, and a foam layer are laminated in this order, the method comprising the steps of:

[0029] providing a foamable melt M2 for forming a foam layer containing a polyethylene-based resin (PE2) and a physical foaming agent, a melt M3 for forming an intermediate layer containing a polyethylene-based resin (PE3) and a polymer antistatic agent (AS3), and a melt M4 for forming a surface layer containing a polyethylene-based resin (PE4) and a polymer antistatic agent (AS4),

[0030] laminating melts M2, M3 and M4 in this order in a mold to form a laminated material, and coextruding the laminated material from the mold to foam the foamable melt M2,

[0031] wherein a polymer antistatic agent (AS3) is contained in the melt M3 for forming the intermediate layer in an amount of 30 wt % or more and 70 wt % or less based on the weight of the M3, and

[0032] The polymer antistatic agent (AS4) is contained in the melt M4 for forming the surface layer in an amount of 5 wt% or more and less than 30 wt% based on the weight of the M4.

[0033] Effects of the present invention:

[0034] The multilayer foamed sheet of the present invention is provided with a resin layer having a surface layer and an intermediate layer, and is provided on at least one side of the foam layer. The intermediate layer contains 30% by weight or more and 70% by weight or less of a polymer antistatic agent, and the surface layer contains 5% by weight or more and less than 30% by weight of a polymer antistatic agent. As a result of this configuration, the multilayer foamed sheet has a high antistatic property and has such a low-pollution property that migration of low molecular weight components, etc. to products packaged therewith is extremely small. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a cross-sectional view schematically showing an example of the multilayer foamed sheet of the present invention. DETAILED DESCRIPTION

[0036] refer to Figure 1 , reference numeral 1 represents a multilayer foam sheet of the present invention (hereinafter also referred to as a foam sheet). The foam sheet 1 has a foam layer 2 and a resin layer 5 laminated on at least one of both sides of the foam layer 2. The resin layer 5 has a multilayer structure consisting of a surface layer 4 located on the outermost surface side of the multilayer foam sheet 1 and an intermediate layer 3 located between the surface layer 4 and the foam layer 2. That is, Figure 1 The multilayer foam sheet 1 specifically shown in the figure has a five-layer structure consisting of a resin layer 5 (surface layer 4 / intermediate layer 3) / foam layer 2 / resin layer 5 (intermediate layer 3 / surface layer 4). The foam sheet of the present invention is not necessarily limited to such a five-layer structure. As long as the gist and effect of the present invention are not adversely affected, the foam sheet 1 may have a three-layer structure in which a resin layer 5 (intermediate layer 3 / surface layer 4) is provided only on one side of the foam layer 2. In addition, although not shown, an additional layer made of another polymer (e.g., a resin) may be provided between the foam layer 2 and the resin layer 5 provided on one or both sides of the foam layer 2.

[0037] The following description is mainly made for the multilayer foam sheet having the above-mentioned five-layer structure as the most preferred embodiment of the present invention, but the description is also applicable to multilayer foam sheets having other layer structures. In addition, although for the sake of simplicity, the resin layer 5 provided on one side of the foam layer 2 is described, when the resin layer 5 is provided on both sides of the foam layer 2, the description is also applicable to the resin layer 5 provided on the other side. In addition, it should be noted that as long as the requirements described in detail below are met, a pair of resin layers 5 provided on both sides of the foam layer 2 can have the same or different structures. For example, the type and amount of the resin component, additives, etc. of one of the two surface layers 4 and the physical property value (such as basis weight) can be the same or different from that of the other surface layer 4.

[0038] The middle layer and the surface layer are usually laminated and bonded by coextrusion. According to coextrusion, a thin layer with such a thickness that cannot be formed by the heat-pressing bonding of heat lamination can be formed. In addition, since the middle layer and the surface layer can adhere to each other on their entire surface, an antistatic effect can be stably exhibited. In addition, coextrusion makes it easy to obtain such a multilayer foamed sheet: wherein the foam layer, the middle layer and the surface layer are laminated together, and wherein the resin layer consisting of the middle layer and the surface layer is laminated on one side or both sides of the foam layer.

[0039] In the present invention, the foam layer contains a polyethylene resin (polyethylene resin PE2) as a main component, and the resin layer (intermediate layer and surface layer) contains a polyethylene resin (polyethylene resin PE3 and PE4). As used herein, a polyethylene resin refers to a polyethylene resin containing 50 mol% or more of an ethylene component. Specific examples of polyethylene resins include low-density polyethylene (PE-LD), linear low-density polyethylene (PE-LLD), high-density polyethylene (PE-HD), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate (EEAK) and mixtures thereof. The low-density polyethylene preferably has a long-chain branched structure and a density of 910 kg / m 3 or more and less than 930kg / m 3 The linear low-density polyethylene is preferably a polyethylene-based resin that is a copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms, has a substantially linear molecular chain, and has a density of 910 kg / m 3 or more and less than 930kg / m 3 The high-density polyethylene is preferably a polyethylene-based resin that is 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 or more.

[0040] The foam layer is composed of a base polymer containing polyethylene resin PE2. That is to say, the foam layer contains polyethylene resin PE2. Specifically, the content of polyethylene resin PE2 in the foam layer is 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and particularly preferably 90% by weight. As used herein, the term "base polymer" is intended to mean any polymer, resin or composition that can form a foam with multiple cells by extrusion foaming. In the above-mentioned polyethylene resin, polyethylene resin PE2 is preferably a mixed resin of low-density polyethylene or low-density polyethylene and linear low-density polyethylene, more preferably low-density polyethylene, because of its excellent foamability and excellent flexibility. In the case of a mixed resin, based on the total amount of 100% by weight of low-density polyethylene and linear low-density polyethylene, the blending amount of linear low-density polyethylene is preferably 5-20% by weight, more preferably 8-15% by weight.

[0041] In addition, as the polyethylene-based resin PE3 contained in the intermediate layer, among the above-mentioned polyethylene-based resins, it is preferable to use a polyethylene-based resin of the same kind as the polyethylene-based resin PE2 because it is excellent in adhesion to the foam layer. Specifically, a low-density polyethylene or a mixed resin of a low-density polyethylene and a linear low-density polyethylene is preferred, among which a low-density polyethylene is more preferred. However, a polyethylene-based resin of a different kind from the polyethylene-based resin PE2 may also be used.

[0042] As the polyethylene-based resin PE4 contained in the surface layer, among the above-mentioned polyethylene-based resins, it is preferred to use a low-density polyethylene, a linear low-density polyethylene or a mixed resin of a low-density polyethylene and a linear low-density polyethylene. Low-density polyethylene is more preferred. When the surface layer contains a linear low-density polyethylene, the migration amount of low-molecular-weight components can be further reduced. Since the adhesion between the intermediate layer and the surface layer is excellent and production becomes easy, the polyethylene-based resin PE4 contained in the surface layer is preferably a polyethylene-based resin of the same type as the polyethylene-based resin PE3 contained in the intermediate layer. However, polyethylene-based resins of different types from the polyethylene-based resin PE3 can also be used.

[0043] The base polymer constituting the foam layer may be mixed with other polymers as needed, such as thermoplastic elastomers or thermoplastic resins other than polyethylene resins. When such other polymers are mixed, the mixing amount is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight based on 100 parts by weight of the base polymer of the foam layer. It is particularly preferred that the base polymer of the foam layer is composed only of polyethylene resin. As long as the purpose and effect of the present invention are not adversely affected, the foam layer may be added with additives such as cell control agents, nucleating agents, antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, antibacterial agents, shrinkage inhibitors and inorganic fillers.

[0044] In the multilayer foamed sheet of the present invention, the intermediate layer and the surface layer each contain a polymer antistatic agent (polymer antistatic agent AS3 or AS4). Examples of the polymer antistatic agent include polyether, polyether ester amide, block copolymers of polyether and polyolefin, ionomer resin, etc. Among them, block copolymers of polyether and polyolefin and ionomer resin are preferred, and ionomer resin is particularly preferred.

[0045] As the block copolymer, there may be mentioned those having a structure in which polyolefin blocks and polyether blocks are repeatedly and alternately bonded via bonds such as ester bonds, amide bonds, ether bonds, urethane bonds, and imide bonds.

[0046] Ionomer resins are resins in which molecules of copolymers of olefins such as ethylene or propylene and carboxylic acids such as acrylic acid, methacrylic acid and maleic acid are crosslinked with metal ions. Examples of metal ions include alkali metal ions such as lithium ions, sodium ions and potassium ions, and alkaline earth metal ions such as calcium ions. Among them, ionomer resins using potassium ions as metal ions are preferred, particularly potassium-containing ionomer resins as copolymers of ethylene and unsaturated carboxylic acids, because they can impart good antistatic properties to the multilayer foamed sheet.

[0047] The surface resistivity of these polymer antistatic agents is preferably less than 1×10 9 Ω, more preferably 5×10 8 Ω or less, and more preferably 1×10 8 Ω or less. The surface resistivity can be measured according to the method of JIS K6271 (2001).

[0048] Specific examples of the polymer antistatic agent include those commercially available under, for example, the following trade names: "Perestat 300", "Perestat 230", "Perestat HC250", "Perectron PVH", "Pelectron PVL", "Pelectron HS", "Pelectron LMP", etc. manufactured by Sanyo Kasei Kogyo Co., Ltd. as block copolymers of polyether and polyolefin, and "Entila SD100", "Entira MK400", etc. manufactured by Mitsui DuPont Polychemical Co., Ltd. as ionomer resins.

[0049] In the present invention, as described above, the resin layer has a multilayer structure consisting of an intermediate layer and a surface layer, and further, the intermediate layer and the surface layer each contain a specific amount of a polymer antistatic agent. As a result of this configuration, the multilayer foamed sheet of the present invention can achieve both antistatic performance and low-pollution properties at a high level. That is, the multilayer foamed sheet can stably exhibit a surface resistivity of less than 10 9 The high antistatic performance of Ω, and further, the amount of low molecular weight components migrating to the products packaged therewith is extremely small, that is, the packaged items are hardly contaminated.

[0050] Next described is the content of the polymer antistatic agent in each of the intermediate layer and the surface layer.Based on the weight of the intermediate layer, the intermediate layer contains the polymer antistatic agent AS3 with 30 wt % or more and 70 wt % or less.When the intermediate layer contains the polymer antistatic agent AS3 within the range, the polymer antistatic agent AS3 forms a conductive network structure, and therefore stably shows excellent antistatic properties.When the content of the polymer antistatic agent AS3 is too little, there is the possibility that high antistatic performance may not be obtained.On the other hand, when the content is too large, there is the possibility that the low molecular weight components derived from the polymer antistatic agent in the intermediate layer may migrate and contaminate the products packaged with it.In addition, its adhesion to the surface layer and the foam layer is reduced, so that there is the possibility that a good multilayer foamed sheet may not be obtained.From this point of view, the lower limit of the content of the polymer antistatic agent AS3 is preferably 35 wt %, more preferably 40 wt %.The upper limit of the content is preferably 65 wt %, more preferably 60 wt %.

[0051] The content ([wt %]) of the polymer antistatic agent AS3 based on the weight of the intermediate layer and the ... 2 The content of the polymer antistatic agent AS3 in the middle layer (A[g / m 2 ]) can be calculated from the blending amount of each raw material during manufacturing.

[0052] Based on the weight of the surface layer, the surface layer contains 5 wt % or more and less than 30 wt % of the polymer antistatic agent AS4. When the surface layer contains the polymer antistatic agent AS4 within the range, it shows a high antistatic effect. The reason is believed to be that the conductive network structure of the above-mentioned polymer antistatic agent extends to the surface of the multilayer foamed sheet by containing a specific amount of polymer antistatic agent not only in the intermediate layer but also in the surface layer. On the other hand, when the content is too large, there is a possibility that the low molecular weight components derived from the polymer antistatic agent in the surface layer may migrate and contaminate the products packaged therewith. From this point of view, the lower limit of the content of the polymer antistatic agent AS4 is preferably 7 wt %, more preferably 10 wt %. The upper limit of the content is preferably 25 wt %, more preferably 20 wt %.

[0053] It is preferred that the content W3 ([wt%]) of the polymer antistatic agent AS3 based on the weight of the intermediate layer is higher than the content W4 ([wt%]) of the polymer antistatic agent AS4 based on the weight of the surface layer by at least 10 wt% (W3-W4≧10 [wt%]), more preferably at least 20 wt% (W3-W4≧20 [wt%]). From the perspective of effectively obtaining high antistatic properties and low contamination properties of the foamed sheet, (W3-W4) within this range is preferred.

[0054] The content ([wt%]) of the polymer antistatic agent AS4 based on the weight of the surface layer and the content ([wt%]) of the polymer antistatic agent AS4 per 1 m 2 The content of polymer antistatic agent AS4 in the surface layer (B[g / m 2 ]) can be calculated from the blending amount of each raw material during manufacturing.

[0055] Since the content of the polymer antistatic agent AS4 in the surface layer is less than 30% by weight, the low molecular weight components derived from the polymer antistatic agent in the surface layer are less likely to migrate, thereby suppressing contamination of the packaging product. In addition, the presence of the surface layer also suppresses contamination of the packaging product due to migration of low molecular weight components derived from the polymer antistatic agent in the intermediate layer.

[0056] In the present invention, preferably every 1m 2 The content (A) of the polymer antistatic agent AS3 in the middle layer is 1-5 g / m 2 The content (A) represents the absolute amount of the polymer antistatic agent contained in the interlayer per unit area on each side. When the content (A) is 1 g / m 2 When the content (A) is 5 g / m 2 When the content (A) is less than 1.5 g / m2, the exudation of organic substances such as low molecular weight components derived from the polymer antistatic agent AS3 contained in the intermediate layer to the surface of the multilayer foamed sheet can be suppressed. For the above reasons, the lower limit of the content (A) is more preferably 1.5 g / m2. 2 , still more preferably 2g / m 2 , and the upper limit of the content (A) is more preferably 4 g / m 2 , more preferably 3.5g / m 2 , particularly preferably 3g / m 2 .

[0057] It is also preferred that every 1m 2 The content of the polymer antistatic agent AS4 in the surface layer (B) is 0.05-0.8 g / m 2The content (B) represents the absolute amount of the polymer antistatic agent AS4 contained in the surface layer per unit area on each side. When the content (B) is 0.05 g / m 2 When the content (B) is 0.8 g / m 2 or less, the exudation of organic substances such as low molecular weight components derived from polymer antistatic agents contained in the surface layer to the surface of the multilayer foamed sheet is further suppressed. For these reasons, the lower limit of the content (B) is more preferably 0.08 g / m 2 , and more preferably 0.1 g / m 2 , particularly preferably 0.15 g / m 2 , and the upper limit of this content is more preferably 0.7g / m 2 , and more preferably 0.6 g / m 2 , particularly preferably 0.5 g / m 2 .

[0058] In the present invention, since the content (B) is less than the content (A), the multilayer foamed sheet has an excellent balance between high antistatic performance and low contamination properties. 2 The content of polymer antistatic agent AS4 in the surface layer (B) and the 2 The content (A) of the polymer antistatic agent AS3 in the intermediate layer preferably has a ratio B / A of 0.03 to 0.3.

[0059] When ratio B / A is 0.03 or more, relative to the content of the polymer antistatic agent of per unit area middle layer, the content of the polymer antistatic agent of per unit area surface layer is not too small, so that high antistatic performance is more stably shown.When ratio B / A is 0.3 or less, relative to the content of the polymer antistatic agent of per unit area middle layer, the content of the polymer antistatic agent of per unit area surface layer is not too large, so that the oozing out of organic substances such as low molecular weight components derived from the polymer antistatic agent contained in the surface layer is more reliably suppressed.For these reasons, the lower limit of ratio B / A is more preferably 0.05, and more preferably 0.07, and the upper limit of ratio B / A is more preferably 0.25, and more preferably 0.2.In this specification, numerical range "X to Y" includes lower limit "X" and upper limit "Y", and therefore with "X or more and Y or less" synonymous.

[0060] As described above, the content (A) is the absolute amount of the polymer antistatic agent AS3 contained in the intermediate layer per unit area on each side, and can therefore be determined from the product of the content (weight %) of the polymer antistatic agent AS3 in the intermediate layer and the basis weight of the intermediate layer with appropriate unit conversion. Therefore, the content (A) can be controlled by changing the content of the polymer antistatic agent AS3 in the intermediate layer or changing the basis weight of the intermediate layer.

[0061] Similarly, the content (B) is the absolute amount of the polymer antistatic agent AS4 contained in the surface layer per unit area on each side, and can therefore be determined from the product of the content (weight %) of the polymer antistatic agent AS4 in the surface layer and the basis weight of the surface layer with appropriate unit conversion. Therefore, the content (B) can be controlled by changing the content of the polymer antistatic agent AS4 in the surface layer or changing the basis weight of the surface layer.

[0062] The basis weight of the middle layer is preferably 1-10 g / m 2 When the basis weight is within this range, the balance of antistatic performance and low contamination performance related to the migration of low molecular weight components is good. For this reason, the basis weight of the intermediate layer is more preferably 2 / m 2 or more, still more preferably 3 g / m 2 , and the upper limit of the basis weight of the middle layer is more preferably 8g / m 2 , and still more preferably 6 g / m 2 .

[0063] The basis weight of the surface layer is preferably 0.5-10 g / m 2 When the basis weight is within this range, the balance between antistatic performance and low contamination performance related to the migration of low molecular weight components is good. 2 When the basis weight is 10 g / m or more, a surface layer having a uniform thickness is easily formed, and uniform antistatic properties can be exhibited over the entire foamed sheet. 2 For these reasons, the lower limit of the basis weight of the surface layer is more preferably 0.8 g / m 2 , and more preferably 1 g / m 2 , particularly preferably 1.5 g / m 2 , most preferably 2g / m 2 The upper limit of the basis weight of the surface layer is more preferably 8 g / m 2 , more preferably 6g / m 2 , particularly preferably 4g / m 2 .

[0064] The basis weight of the resin layer (total basis weight of the surface layer and the intermediate layer) is preferably 1-20 g / m 2 When the basis weight is within this range, the cushioning properties and light weight of the multilayer foamed sheet can be ensured. In addition, when the resin layer (intermediate layer and surface layer) is laminated on the foam layer by coextrusion described later in this article, a foam layer with a good cell structure can be formed. From this point of view, the upper limit of the basis weight of the resin layer is more preferably 15 g / m 2 , and more preferably 12 g / m 2 , particularly preferably 10g / m2 The lower limit of the basis weight of the resin layer is more preferably 2 g / m 2 , still more preferably 3g / m 2 .

[0065] When the resin layer consisting of the surface layer and the middle layer is laminated on both sides of the foam layer, the basis weights of the above-mentioned resin layer, the surface layer and the middle layer refer to the basis weights of the resin layer, the surface layer and the middle layer laminated on one side of both sides of the foam layer, respectively. Among the two resin layers, the two surface layers and the two surface layers laminated on both sides of the foam layer, the basis weight of one layer is preferably equal to the basis weight of the other corresponding layer, although they may be different from each other.

[0066] In the multilayer foamed sheet of the present invention, as described above, it is preferred to use an ionomer resin as the polymer antistatic agent. That is, it is preferred that the polymer antistatic agent AS3 contained in the intermediate layer is an ionomer resin-based antistatic agent, and the polymer antistatic agent AS4 contained in the surface layer is an ionomer resin-based antistatic agent. By using an ionomer resin as the polymer antistatic agent, the low-pollution property of the multilayer foamed sheet can be further improved.

[0067] When an ionomer resin is used as a polymer antistatic agent, polyalkylene glycol is preferably incorporated into at least one of the surface layer and the intermediate layer, preferably both, because excellent antistatic performance can be exhibited in a stable manner. That is, when a multilayer foamed sheet is produced by coextrusion, and when the melt to be extruded for forming the surface layer and / or the intermediate layer contains polyalkylene glycol, the ionomer resin can be satisfactorily dispersed in the continuous phase of the polyethylene-based resin, and thus a multilayer foamed sheet having excellent antistatic performance can be stably obtained.

[0068] Furthermore, when the polyalkylene glycol is contained in the surface layer and / or the intermediate layer, the humidity dependence of the antistatic performance decreases, so that the multilayer foamed sheet exhibits good antistatic performance even under low humidity conditions.

[0069] As the polyalkylene glycol, a polyalkylene glycol having an HLB value of 8 or more can be preferably used. Examples of such polyalkylene glycols include polyethylene glycol, polyoxyethylene polyoxypropylene glycol, and the like. In addition, two or more polyalkylene glycols can be used in combination. In order to satisfactorily disperse the ionomer resin in the polyethylene-based resin, the HLB value of the polyalkylene glycol is more preferably 10 or more, particularly preferably 15 or more.

[0070] Among them, polyethylene glycol is preferably used because it can stably disperse the ionomer resin in the polyethylene-based resin and can further reduce the humidity dependency of the antistatic performance while enhancing the antistatic performance.

[0071] In the present invention, the HLB value is obtained by the Griffin method using the following formula.

[0072] HLB=20×Mh / Mw

[0073] Wherein Mh is the molecular weight of the hydrophilic portion of the hydrophilic compound and Mw is the molecular weight of the entire hydrophilic compound.

[0074] In the present invention, the HLB value is determined as follows. For example, when the polyalkylene glycol is a copolymer of polyethylene glycol and a polyalkylene glycol other than polyethylene glycol, the polyethylene glycol portion is considered to be a hydrophilic portion. The hydrophilicity and lipophilicity of the other polyalkylene glycol portion are checked to determine whether it is a hydrophilic portion or a hydrophobic portion. The HLB value is then determined by the above-mentioned Griffin method. When the polyalkylene glycol is polyethylene glycol, its HLB value is 20 because they are all hydrophilic portions.

[0075] When polyethylene glycol is used as the polyalkylene glycol, its number average molecular weight is preferably 100-10000, more preferably 150-1000, and still more preferably 200-600. By setting the molecular weight of the polyethylene glycol within this range, a multilayer foamed sheet exhibiting excellent antistatic properties can be stably obtained. The number average molecular weight of the polyethylene glycol is determined from its hydroxyl value using a known method.

[0076] When an ionomer resin is used as an antistatic agent, the weight ratio of the polyalkylene glycol to the ionomer resin is 0.03-0.5 because the ionomer resin can be better dispersed in the polyethylene-based resin. From this point of view, the weight ratio is more preferably 0.04-0.4, still more preferably 0.05-0.3, and particularly preferably 0.05-0.1.

[0077] In the multilayer foamed sheet of the present invention, it is preferred that the surface layer contains a polystyrene-based resin because excellent sliding properties can be obtained. In particular, even when the surface layer contains an ionomer resin as a polymer antistatic agent, the inclusion of a polystyrene-based resin suppresses a decrease in sliding properties. As a result, for example, when packaging glass plates using the multilayer foamed sheet as an interlayer sheet inserted between glass plates, the multilayer foamed sheet can be smoothly conveyed and superimposed on the glass plates.

[0078] Examples of polystyrene-based resins include polystyrene (general-purpose polystyrene), rubber-modified polystyrene (impact polystyrene), styrene-α-methylstyrene copolymers, styrene-p-methylstyrene copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-maleic anhydride copolymers, styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, and styrene-acrylonitrile copolymers. Among them, polystyrene or rubber-modified polystyrene is preferred, and polystyrene is more preferred.

[0079] Due to the improved sliding property of the multilayer foamed sheet, the content of the polystyrene-based resin in the surface layer is preferably 3-35% by weight based on the weight of the surface layer. From this point of view, the content of the polystyrene-based resin in the surface layer is more preferably 5% by weight or more. On the other hand, in order to maintain the excellent cushioning properties of the multilayer foamed sheet, the content of the polystyrene-based resin in the surface layer is more preferably 30% by weight or less, still more preferably 25% by weight or less, still more preferably 20% by weight or less, and particularly preferably 12% by weight or less.

[0080] In addition, it is preferred that the ratio PS / PE of the content of the polystyrene-based resin to the content of the polyethylene-based resin PE4 in the surface layer is 0.03-0.6. When the surface layer contains a polystyrene-based resin to provide a PS / PE ratio within this range, the multilayer foamed sheet exhibits better sliding properties while maintaining surface protection efficiency. From this point of view, the upper limit of the above ratio is more preferably 0.4, particularly preferably 0.3, and the lower limit of the PS / PE ratio is more preferably 0.04, particularly preferably 0.1.

[0081] In order to improve the sliding property of the multilayer foamed sheet, it is preferred that the tensile elastic modulus of the polystyrene-based resin contained in the surface layer is 1,000 MPa or more, more preferably 1,500 MPa or more.

[0082] The tensile elastic modulus of the polystyrene-based resin was measured using a test piece punched into a dumbbell shape No. 1 under the condition of a test speed of 500 mm / min in accordance with JIS K6767 (1999), and the calculated value was adopted.

[0083] Preferably, when the surface layer contains a polystyrene-based resin, the surface layer further contains a compatibilizer for the polystyrene-based resin PE4 and the polystyrene-based resin. Since the compatibilizer can improve the film-forming properties of the surface layer, a good surface layer can be formed even when the basis weight of the surface layer is small.

[0084] Examples of the compatibilizer include styrene-butadiene copolymers, styrene-isoprene copolymers, and styrene-based elastomers such as hydrogenated products of these copolymers. The copolymer is preferably a block copolymer.

[0085] Based on the total amount of 100 parts by weight of polyethylene resin PE4, polystyrene resin and compatibilizer, the content of compatibilizer in the surface layer is preferably 1-20 parts by weight. The lower limit of this content is more preferably 2 parts by weight, and 3 parts by weight is even more preferably, and the upper limit is more preferably 15 parts by weight, and 10 parts by weight is even more preferably, and 8 parts by weight is particularly preferred.

[0086] In the multilayer foamed sheet of the present invention, talc is preferably incorporated into the surface layer in order to further enhance the sliding property. The content percentage of talc is preferably 5-30% by weight, more preferably 10-25% by weight, based on the weight of the surface layer.

[0087] Next, the physical properties of the multi-layer foamed sheet of the present invention will be described.

[0088] The multilayer foamed sheet of the present invention having the above-mentioned constitution exhibits excellent antistatic properties. Specifically, the surface resistivity R of the multilayer foamed sheet is preferably less than 1×10 9 Ω, more preferably 9×10 8 Ω or less, still more preferably 8×10 8 Ω or less, particularly preferably 5×10 8 Ω or less. The lower limit of the surface resistivity R is not particularly limited, but is usually 1×10 7 Ω.

[0089] The surface resistivity R of the multilayer foam sheet (i.e., the surface resistivity of the multilayer foam sheet on the surface layer side) was measured in accordance with JIS K6271 (2001). More specifically, a test piece having a length of 100 mm, a width of 100 mm, and the same thickness as the multilayer foam sheet was cut from the multilayer foam sheet. A voltage of 500 V was applied to the surface of the test piece in an atmosphere of 23° C. and 50% relative humidity, and the surface resistivity [Ω] was measured 1 minute after the start of the voltage application.

[0090] The apparent density of the multilayer foamed sheet of the present invention is preferably 15-300 kg / m 3 When the apparent density is within this range, the multilayer foamed sheet has an excellent balance between mechanical properties such as tensile strength, light weight, and cushioning properties. From this point of view, the lower limit of the apparent density is more preferably 20 kg / m 3 , and more preferably 25 kg / m 3 , and the upper limit of the apparent density is more preferably 150kg / m 3 , and more preferably 100 kg / m 3 , particularly preferably 70kg / m 3 or less.

[0091] The thickness of the multilayer foamed sheet is preferably 0.05-3 mm, more preferably 0.1-2.5 mm, and still more preferably 0.2-2 mm. When the thickness of the multilayer foamed sheet is within this range, the balance between cushioning properties and flexibility is good.

[0092] The basis weight of the multilayer foamed sheet of the present invention is preferably 5-100 g / m 2 , more preferably 10-80g / m 2 , still more preferably 20-50g / m 2 When the basis weight of the multi-layer foamed sheet is within this range, the balance between light weight and mechanical properties is good.

[0093] The method for measuring the thickness, basis weight and apparent density of a multilayer foam sheet is as follows. First, the multilayer foam sheet is cut vertically (i.e., in the thickness direction) along its transverse direction (i.e., in the direction perpendicular to the extrusion direction) to obtain a rectangular test piece having a length equal to the full width [mm] of the sheet and a width of 100 mm. Similar operations are repeated at different positions on the foam sheet to obtain a total of 5 test pieces. The thickness of each test piece is measured at intervals of 1 cm in the transverse direction of the multilayer foam sheet. The arithmetic mean of the thickness values ​​obtained is the thickness [mm] of the multilayer foam sheet. In addition, the weight of each test piece is measured. The measured weight is divided by the area of ​​the test piece (i.e., the width [mm] of the sheet × 100 mm (0.1 m)) (accompanied by appropriate unit conversion). The arithmetic mean of the five values ​​obtained is the basis weight [g / m 2 By adjusting the basis weight [g / m 2 ] divided by the thickness of the multilayer foamed sheet obtained above (with appropriate unit conversion) to determine the apparent density of the multilayer foamed sheet [kg / m 3 ].

[0094] The basis weight of the middle layer and the surface layer can be obtained by the thickness of each layer and the density of the resin composition constituting each layer. More specifically, the multilayer foam sheet is cut vertically (i.e. in the thickness direction) along the transverse direction of the multilayer foam sheet, and the vertical section is taken at ten transversely equally spaced positions on each side of the multilayer foam sheet. When a resin layer is provided on both sides of the foam layer, a total of 20 or more parts of the photos are taken. In each amplified photo, the thickness of the middle layer and the surface layer is measured at intervals of every 1cm (true length) in its transverse direction. The arithmetic mean of each of the obtained middle layer and the surface layer thickness values ​​is the thickness of the middle layer and the surface layer on the corresponding sides of the foam sheet, respectively. The basis weight of the middle layer and the surface layer can be calculated by multiplying their thickness by the density (with appropriate unit conversion) of the resin composition constituting the corresponding layer. As used herein, the term "resin composition" is expected to include not only polyethylene resin components, but also other polymer components and inorganic components used for each layer.

[0095] Alternatively, the basis weight of the intermediate layer and the surface layer can be determined based on the discharge amount of each layer when the multilayer foam sheet is manufactured. Specifically, when the discharge amount X [g / hour] of the intermediate layer, the discharge amount Y [g / hour] of the surface layer, the width W [m] of the multilayer foam sheet, and the winding speed L [m / hour] of the multilayer foam sheet are known, the basis weight can be obtained by the following equation.

[0096] Basis weight of middle layer [g / m 2 ]=[X / (L×W)]

[0097] Basis weight of surface layer [g / m 2 ]=[Y / (L×W)]

[0098] In view of the surface protection of the product to be packaged and appropriate slidability, rigidity, etc., the closed cell content of the multilayer foamed sheet of the present invention is preferably 20% or more, more preferably 30% or more, still more preferably 30% or more, even more preferably 40% or more, particularly preferably 50% or more, and most preferably 55% or more. The upper limit of the closed cell content is not particularly limited, but is generally 90%.

[0099] The closed cell content was measured according to Procedure C of ASTM-D2856-70. Specifically, the true volume Vx of the multilayer foamed sheet (cut sample) was measured using a 930 model air comparative pycnometer from Toshiba Beckman Inc. The closed cell content S (%) was calculated using the obtained Vx by the formula shown below. As a cut sample for measurement, a plurality of samples were cut out from the multilayer foamed sheet, each sample having a thickness of 25 mm × 25 mm × the thickness of the multilayer foamed sheet, and the obtained samples were stacked to obtain a cut sample for measurement having a size of 25 mm × 25 mm × about 20 mm.

[0100] S(%)=(Vx-W / ρ)×100 / (Va-W / ρ)

[0101] in

[0102] Vx represents the actual volume (cm2) of the cut sample measured by the above method. 3 ), which corresponds to the sum of the volume of the resin constituting the cut sample and the total volume of all closed cells in the cut sample,

[0103] Va represents the apparent volume (cm2) of the cut sample measured from the outer dimensions of the cut sample used for measurement. 3 ),

[0104] W is the weight of the cut sample used for measurement (g), and

[0105] ρ is the density of the resin composition constituting the multilayer foam sheet (g / cm 3 ), which is measured after defoaming the multilayer foamed sheet.

[0106] As described above, the multilayer foamed sheet of the present invention has a multilayer structure, wherein the resin layer provided on at least one side of the foam layer is composed of an intermediate layer and a surface layer, wherein the intermediate layer and the surface layer contain a specific amount of a polymer antistatic agent. Through this configuration, both antistatic performance and low-pollution properties are obtained. In other words, in the layer containing the polymer antistatic agent, although the layer located on the most surface side (surface layer) and particularly likely to cause migration to the product to be packaged has a low content of the polymer antistatic agent, it is possible to exhibit high antistatic performance.

[0107] That is, according to another aspect of the present invention, a multi-layer foamed sheet having the following structure is provided.

[0108] A multilayer foamed sheet having a foam layer containing a polyethylene-based resin (PE2) and a resin layer laminated on at least one side of the foam layer, wherein the resin layer has a multilayer structure comprising a surface layer located on the surface side and containing a polyethylene-based resin (PE4) and a polymer antistatic agent (AS4), and an intermediate layer located between the surface layer and the foam layer and containing a polyethylene-based resin (PE3) and a polymer antistatic agent (AS3), and wherein the surface resistivity R (Ω) of the surface layer side of the multilayer foamed sheet and the surface resistivity R (Ω) per 1 m 2 Content of polymer antistatic agent in the surface layer (B) (g / m 2 ) is 5×10 8 (Ωg / m 2 ) or less. In this respect, it is preferred that the requirements described in claim 1 of the present specification are met. Furthermore, it is more preferred that, in addition to the requirements of claim 1, one or more of the requirements of claims 2 to 8 are also met.

[0109] The fact that the product R×B is small means that even when the content of the polymer antistatic agent contained in the surface layer is small, it is possible to sufficiently reduce the surface resistivity value. From this point of view, the product R×B is more preferably 3×10 8 (Ω·g / m 2 ) or less, particularly preferably 2×10 8 (Ω·g / m 2 ) or less. The lower limit of the product R×B is usually 1×10 7 (Ω·g / m 2 ).

[0110] Below, the method for producing the multilayer foam sheet of the present invention will be described.The multilayer foam sheet of the present invention can be produced by known procedures.As its typical preferred procedure, for example, a method can be mentioned, wherein in a coextrusion die, the melt for forming the intermediate layer and the melt for forming the surface layer are laminated in this order on one side and / or both sides of the melt for forming the foam layer, and the melt coextrusion is obtained to foam and expand the melt for forming the foam layer, thereby producing the multilayer foam sheet.However, the multilayer foam sheet can also be laminated by using a coextrusion die to laminate the melt for forming the intermediate layer and the melt for forming the surface layer, to obtain a resin layer with a multilayer structure, and then the resin layer is laminated to one side or both sides of the foam sheet (foam layer) produced separately with the intermediate layer facing the foam sheet and manufactured.

[0111] The multilayer coextrusion method includes (1) a method of coextruding into a sheet using a flat die to form a multilayer foamed sheet, and (2) a method of coextruding into a tubular form using an annular die to produce a tubular multilayer foam body, followed by slitting the obtained tubular multilayer foam body in the extrusion direction to obtain a multilayer foamed sheet. Among the above methods, the multilayer coextrusion method using an annular die can be preferably adopted because it is easy to obtain a wide multilayer foamed sheet having a width of 1,000 mm or more.

[0112] The coextrusion method using an annular die will be described in detail below. First, polyethylene resin PE2 and additives such as cell control agents added as needed are supplied to an extruder to form a foam layer and kneaded under heating, and then a physical foaming agent is injected therein. The contents in the extruder are further kneaded to obtain a foamable melt M2 for a foam layer. At the same time, polyethylene resin PE3, polymer antistatic agent AS3, etc. are supplied to an extruder for forming an intermediate layer, and kneaded under heating to obtain a melt M3 for an intermediate layer. At the same time, further, polyethylene resin PE4, polymer antistatic agent AS4, etc. are supplied to an extruder for forming a surface layer, and kneaded under heating to obtain a melt M4 for a surface layer.

[0113] The obtained foamable melt M2 for the foam layer, the melt M3 for the intermediate layer and the melt M4 for the surface layer are introduced into a co-extrusion annular die, wherein the melt M3 for the intermediate layer and the melt M4 for the surface layer are laminated on one or both sides of the foamable melt M2 flowing in a tubular shape. The resulting laminate is extruded in the atmosphere and foamed to form a tubular foam body. While the tubular foam body is pulled along a widening device (e.g., a mandrel), the tubular foam body is cut to obtain a multilayer foamed sheet.

[0114] The melt flow rate (MFR) of the polyethylene resin PE2 is preferably 0.1-20 g / 10 minutes because of its excellent foaming property. In particular, the MFR of the polyethylene resin PE2 is preferably 0.1-1.5 g / 10 minutes because when a multilayer foamed sheet is produced by coextrusion, the reduction of closed cells in the foam layer can be suppressed.

[0115] Furthermore, when the resin layers are laminated by coextrusion, it is preferred that the MFR of the polyethylene-based resin PE3 and the polyethylene-based resin PE4 are each greater than the MFR of the polyethylene-based resin PE2 from the viewpoint of obtaining a good laminated state. As used herein, MFR refers to a melt mass flow rate measured under the conditions of 190° C. and 2.16 kg load in accordance with JIS K7210-1 (2014).

[0116] It is preferred that a volatile plasticizer is added to each of the melt M3 for the middle layer and the melt M4 for the surface layer. A plasticizer is used as a volatile plasticizer: it has the function of reducing the melt viscosity of the melt, and it volatilizes from the middle layer and the surface layer after forming the resin layer (middle layer and surface layer), and is not present in the middle layer and the surface layer. By incorporating a volatile plasticizer into each melt, the extrusion temperature of the melt M3 for the middle layer and the melt M4 for the surface layer can be close to the extrusion resin temperature of the foamable melt for the foam layer when the foaming sheet is co-extruded, and in addition, the melt stretchability of the resin layer of the middle layer and the surface layer in a molten state can be significantly improved. Therefore, the cells of the foam layer are less likely to be thermally destroyed by the resin layer (middle layer and surface layer) during foaming, and further, the resin layer can be easily stretched as the foam layer stretches during its foaming.

[0117] As the volatile plasticizer, it is preferred to use one or two or more selected from aliphatic hydrocarbons or 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. When a low-volatile substance such as a so-called lubricant is used instead of a volatile plasticizer, the lubricant may remain in the resin layer and contaminate the surface of the product to be packaged. Relatively speaking, a volatile plasticizer is preferred because it effectively plasticizes the resin in the resin layer and because it hardly remains in the obtained resin layer.

[0118] The boiling point of the volatile plasticizer is preferably 120°C or lower, more preferably 80°C or lower, because it is easy to volatilize from the resin layer. When the boiling point of the volatile plasticizer is within the above range, and when the foamed sheet obtained by coextrusion is allowed to stand after coextrusion, the volatile plasticizer spontaneously volatilizes and is removed from the resin layer (intermediate layer and surface layer) by the heat remaining therein immediately after coextrusion or by subsequent gas permeation at room temperature. The lower limit of the boiling point of the volatile plasticizer is generally -50°C.

[0119] The volatile plasticizer is preferably added to each of the melts M3 and M4 in an amount of 5 to 50 parts by weight, based on 100 parts by weight of the melt.

[0120] When an ionomer resin is used as the above-mentioned polymer antistatic agent, it is preferable to use one or two or more selected from alcohols having a boiling point of 120° C. or lower, saturated hydrocarbons having 3 to 5 carbon atoms and / or dialkyl ethers having 1 to 3 carbon atoms in their alkyl chains in the volatile plasticizer because the dispersion state of the ionomer resin can be further improved.

[0121] In addition, various additives may be added to the melts M3 and M4 as long as the purpose of the present invention is not adversely affected. Examples of various additives include antioxidants, heat stabilizers, weathering agents, ultraviolet absorbers, flame retardants, fillers, and antibacterial agents. In this case, the amount added is appropriately determined depending on the type, 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 based on 100 parts by weight of each melt.

[0122] When the resin layer 5 is provided on each side of the foam layer 2, the two resin layers 5 preferably have the same structure for easy manufacturing, but may have different compositions as required. Therefore, in this case, the composition (resin component, type and amount of additives, etc.) of the melt M3 used for one of the two intermediate layers 3 may be the same as or different from that of the other intermediate layer. Similarly, the composition (resin component, type and amount of additives, etc.) of the melt M4 used for one of the two surface layers 4 may be the same as or different from that of the other surface layer.

[0123] Examples of physical foaming agents added to the foamable melt M2 for the foam layer include: organic physical foaming agents, such as aliphatic hydrocarbons (e.g., propane, n-butane, isobutane, n-pentane, isopentane, n-hexane and isohexane), alicyclic hydrocarbons (e.g., cyclopentane and cyclohexane), chlorinated hydrocarbons (e.g., methyl chloride and ethyl chloride) and fluorocarbons (e.g., 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 may also be used. Two or more of the above-mentioned physical foaming agents may be used in combination. Among them, organic physical foaming agents are preferred because they are excellent in compatibility and foamability with polyethylene resins, and among them, those containing n-butane, isobutane or a mixture thereof as the main component are preferred.

[0124] The amount of the physical foaming agent added is controlled according to the type of the foaming agent and the desired apparent density. In order to obtain a multilayer foamed sheet having the above-mentioned apparent density range using, for example, a mixed butane consisting of 30 wt% isobutane and 70 wt% normal butane as a foaming agent, the amount of the mixed butane added is preferably 3-30 wt%, more preferably 4-20 wt%, and even more preferably 6-18 wt%, per 100 wt% of the base polymer.

[0125] Cell control agents are usually added to the foamable melt M2 as its main additive. As cell control agents, organic or inorganic types can be used. As inorganic cell control agents, metal borates (such as zinc borate, magnesium borate and borax), sodium chloride, aluminum hydroxide, talc, zeolite, silicon dioxide, calcium carbonate and sodium bicarbonate can be mentioned, for example. As organic cell control agents, 2,2-methylenebis (4,6-tert-butylphenyl) sodium phosphate, sodium benzoate, calcium benzoate, aluminum benzoate and sodium stearate can be mentioned. In addition, a combination of citric acid and sodium bicarbonate, and a combination of citric acid basic salt and sodium bicarbonate can also be used as a cell control agent. Two or more of these cell control agents can be used in combination. For every 100 parts by weight of base polymer, the addition amount of the cell control agent is preferably 0.01-3 parts by weight, more preferably 0.03-1 parts by weight.

[0126] As the production apparatus such as an annular die and an extruder, known apparatuses conventionally used in the field of extrusion foaming can be used.

[0127] The multilayer foamed sheet of the present invention has excellent cushioning properties and antistatic properties, and the amount of low molecular weight components that may migrate to the products packaged therewith is also extremely low. Therefore, the foamed sheet can be suitably used as a packaging material for electronic devices, such as an interlayer sheet for glass plates.

[0128] Example:

[0129] The present invention will be described in more detail based on Examples. However, the present invention is not limited to the Examples.

[0130] The polyethylene-based resin, polystyrene-based resin, polymer antistatic agent, compatibilizer and cell control agent used in the Examples and Comparative Examples are as follows.

[0131] Polyethylene-based resin:

[0132] (1) Abbreviation "LDPE1": Low-density polyethylene "NS-1s", manufactured by NUC Corporation (density 922 kg / m 3 , MFR 0.4g / 10min, melting point 110°C, melt viscosity 1,468Pa / s, melt tension 199mN)

[0133] (2) Abbreviation "LDPE2": Low-density polyethylene "NUC8321", manufactured by NUC Corporation., Ltd. (density 922 kg / m 3 , MFR 2.4g / 10min, melting point 112°C, melt viscosity 818Pa / s, melt tension 64mN)

[0134] Polystyrene resin

[0135] (1) Abbreviation "GPPS1": General purpose polystyrene "680", manufactured by PS Japan Corporation (density 1,050 kg / m 3 , MFR 7.0g / 10min, Vicat softening temperature 98°C, tensile modulus 3,200MPa)

[0136] (2) Abbreviation "HIPS1": High-impact polystyrene "408", manufactured by PS Japan Corporation (density 1,040 kg / m 3 , MFR 7.0g / 10min, Vicat softening temperature 92℃)

[0137] Polymer antistatic agent:

[0138] Abbreviation "SD100": Vinyl potassium ionomer resin "ENTILA SD100", manufactured by Mitsui DuPont Polychemicals Company Ltd. (MFR 5 g / 10 min, melting point 92°C, surface resistivity 1.0×10 7 Ω)

[0139] Compatibilizer:

[0140] Abbreviation "H1041": Hydrogenated styrene-based thermoplastic elastomer "TUFTEC H1041", manufactured by Asahi Kasei Corporation, rubber content 70%

[0141] Cell control agent:

[0142] Abbreviation "Talc MB": Use a low-density polyethylene

[0143] A cell control agent masterbatch of 20% talc (talc "HIGH FILLER #12", manufactured by Matsumura Sangyo Co., Ltd.) in PTFE ("LA500M", manufactured by Japan Polyethylene Corporation).

[0144] Sliding property improver:

[0145] Abbreviation "Talc MB": The same cell control agent as above was used.

[0146] Polyalkylene glycol:

[0147] Abbreviation "PEG1": polyethylene glycol "PEG300", manufactured by Sanyo Chemical Industries, Ltd. (number average molecular weight 300)

[0148] Physical foaming agent:

[0149] Isobutane

[0150] Volatile plasticizers:

[0151] Mixed butane (a mixture of 35 wt% n-butane and 65 wt% isobutane)

[0152] instrument:

[0153] The apparatus was made using a multi-layer foamed sheet equipped with the following extruder and die.

[0154] Extruder for forming the foam layer: a first extruder having a barrel inner diameter of 115 mm.

[0155] Extruder for forming the middle layer: a second extruder having a barrel inner diameter of 65 mm.

[0156] Extruder for forming the surface layer: a third extruder having a barrel inner diameter of 50 mm.

[0157] Die: Annular die with an outlet diameter of 96 mm for coextrusion

[0158] Examples 1-5 and Comparative Example 3

[0159] Preparation of melt M2 for foam layer:

[0160] 100 parts by weight of LDPE1 as polyethylene-based resin PE2 and 2 parts by weight of talc MB as a cell control agent were fed to the first extruder and kneaded at about 200°C. Subsequently, isobutane was injected into the kneaded material as a physical foaming agent and further kneaded. In the case of Examples 1, 2, 3 and 5 and Comparative Example 3, the amount of isobutane injected was 9.8 parts by weight based on 100 parts by weight of LDPE, and in the case of Example 4, the amount of isobutane injected was 13.8 parts by weight based on 100 parts by weight of LDPE. The kneaded product obtained was adjusted to the resin temperature shown in Table 3 in the first extruder to obtain a melt M2 for a foam layer. The melt M2 for a foam layer used in Examples 1-3 and 5 and Comparative Example 3 was also used in Comparative Examples 1 and 2 described below.

[0161] Preparation of melt M3 for the middle layer:

[0162] The polyethylene resin PE3 of the kind and amount shown in Tables 1 and 2, the polymer antistatic agent AS3 of the kind and amount shown in Tables 1 and 2, and the polyalkylene glycol PAG of the kind and amount shown in Tables 1 and 2 were fed to the second extruder and kneaded at about 200° C. Next, the mixed butane (n-butane / isobutane=65 wt % / 35 wt %) as a volatile plasticizer in the amount shown in Tables 1 and 2 was injected therein and kneaded. The kneaded product obtained was adjusted to the resin temperature shown in Table 3 in the second extruder to obtain a melt M3 for the intermediate layer. The amounts of the polyethylene resin PE3, the polymer antistatic agent AS3, and the polyalkylene glycol PAG shown in Table 1 are each weight percentage based on the weight of the intermediate layer, and the amount of the mixed butane as the volatile plasticizer in Table 1 is parts by weight based on 100 parts by weight of the polyethylene resin PE3 and the polymer antistatic agent AS3 in the intermediate layer in total.

[0163] Preparation of melt M4 for surface layer:

[0164] The polyethylene resin PE4 of the kind and amount shown in Tables 1 and 2, the polystyrene resin PS of the kind and amount shown in Tables 1 and 2, the compatibilizer of the kind and amount shown in Tables 1 and 2, the polymer antistatic agent AS4 of the kind and amount shown in Tables 1 and 2, the polyalkylene glycol PAG of the kind and amount shown in Tables 1 and 2, and the talc MB as a slip improver of the kind and amount shown in Tables 1 and 2 were fed to the third extruder and kneaded at about 200° C. Subsequently, a mixed butane (n-butane / isobutane=35 wt % / 65 wt %) of the amount shown in Tables 1 and 2 was injected as a volatile plasticizer and kneaded. The kneaded product obtained was adjusted to the resin temperature shown in Table 3 to obtain a melt M4 for the surface layer. The amounts of the polyethylene-based resin PE4, the polystyrene-based resin PS, the compatibilizer, the polymer antistatic agent AS4, the polyalkylene glycol PAG and the sliding property improver in Tables 1 and 2 are each weight percentage based on the weight of the surface layer, while the amount of the mixed butane as the volatile plasticizer in Tables 1 and 2 is parts by weight based on 100 parts by weight in total of the polyethylene-based resin PE4, the polystyrene resin PS, the compatibilizer, the polymer antistatic agent AS4, the polyalkylene glycol PAG and the sliding property improver of the surface layer.

[0165] Preparation of multi-layer foamed sheets:

[0166] Each of the melt M2 for foam layer, the melt M3 for the intermediate layer and the melt M4 for the surface layer is introduced into the coextrusion annular die with the extrusion amount shown in Table 3, wherein the melt M3 is combined and laminated on both the inner surface and the outer surface of the melt M2, and further, the melt M4 is combined and laminated on both the inner surface and the outer surface of the melt M3. The laminate obtained is coextruded by annular die, to form a tubular multilayer foam with three materials, a five-layer structure, wherein the intermediate layer is laminated and bonded to both the inner surface and the outer surface of the foam layer, and further, the surface layer is laminated and bonded to each intermediate layer. The tubular multilayer foam of extrusion is expanded on the cylindrical widening device (mandrel) of 333mm in diameter, and is pulled with the pulling speed shown in Table 3 so that its basis weight (basis weight) is as shown in Table 4 and Table 5. At the same time, the tubular laminated foam was cut in the extrusion direction to obtain a multilayer foamed sheet having a five-layer structure consisting of resin layer (surface layer / middle layer) / foam layer / resin layer (middle layer / surface layer).

[0167] Comparative Examples 1 and 2

[0168] By laminating the surface layer on both sides of the foam layer without forming an intermediate layer, a multilayer foamed sheet having a two-material, three-layer structure consisting of the surface layer / foam layer / surface layer is produced. The production method is the same as in Example 1 except that the melt M3 for the intermediate layer is not used and the composition of the melt M4 for the surface layer becomes as shown in Table 1.

[0169] Incidentally, in Examples 1-5 and Comparative Examples 1-3, since the composition and physical properties of the two surface layers and the composition and physical properties of the two intermediate layers provided on both sides of the foam layer of the multilayer foamed sheet are respectively the same as each other, only the composition and physical properties of one layer are shown in Tables 1-5 below. In Tables 1 and 2, "%" and "parts" are "% by weight" and "parts by weight", respectively.

[0170] Table 1

[0171]

[0172]

[0173] Table 2

[0174]

[0175]

[0176] Table 3

[0177]

[0178] The multilayer foamed sheets obtained in Examples and Comparative Examples were measured for their physical properties and evaluated for their antistatic properties and low staining properties. The measurement and evaluation results of Examples are shown in Table 4, and the measurement and evaluation results of Comparative Examples are shown in Table 5.

[0179] Table 4

[0180]

[0181]

[0182] Table 5

[0183]

[0184] The multilayer foamed sheets obtained in Examples 1 to 5 exhibited high antistatic properties and extremely suppressed contamination of articles packaged therewith. In addition, the surface of the foamed sheet had low static friction and excellent slidability.

[0185] The multilayer foam sheet of Comparative Example 1 is a foam sheet of a three-layer structure without an intermediate layer. The obtained foam sheet having a three-layer structure has excellent antistatic properties, but a large amount of haze change and poor low-fouling properties. In addition, the static friction of the surface of the foam sheet is high, and therefore the sliding property is also poor.

[0186] The multilayer foamed sheet of Comparative Example 2 is a three-layer foamed sheet similar to Comparative Example 1, but the content of the polymer antistatic agent in its surface layer is less than that in Comparative Example 1. The obtained foamed sheet having a three-layer structure has a slightly higher haze variation and a slightly poor antistatic property. That is, both the antistatic property and the low-pollution property cannot be achieved at a high level. In addition, the static friction of the surface of the foamed sheet is high, and therefore the sliding property is also poor.

[0187] The multilayer foamed sheet of Comparative Example 3 is a foamed sheet having a five-layer structure similar to Example 1, but the content of the polymer antistatic agent in the middle layer is greater than that in Example 1. The surface layer thereof does not contain the polymer antistatic agent. The obtained multilayer foamed sheet exhibits high antistatic properties, but has a large haze variation and poor low-pollution properties.

[0188] The measurement and evaluation of each physical property in Tables 4 and 5 were performed as follows.

[0189] (1) Thickness, basis weight and apparent density of multilayer foam sheets:

[0190] The thickness, basis weight and apparent density of the multilayer foam sheet are determined by the aforementioned method. Specifically, first, the multilayer foam sheet is cut vertically (i.e., in the thickness direction) along its transverse direction (i.e., in the direction perpendicular to the extrusion direction) to obtain a rectangular test piece with a length equal to the total width [mm] of the sheet and a width of 100 mm. Repeat the same operation at different positions on the foam sheet to obtain a total of 5 test pieces. The thickness of each test piece over the entire width is measured at intervals of 1 cm in the transverse direction of the multilayer foam sheet. The arithmetic mean of the thickness values ​​obtained is defined as the total thickness [mm] of the multilayer foam sheet. The weight of each test piece is also measured. The measured weight is divided by the area of ​​the test piece (i.e., the width [m] of the sheet × 0.1m (100mm)). The arithmetic mean of the five values ​​obtained is the basis weight [g / m 2 By adjusting the basis weight [g / m 2 ] divided by the thickness [m] of the foamed sheet obtained above (with appropriate unit conversion) to obtain the apparent density [kg / m 3 ].

[0191] (2-1) Basis weight of surface layer and middle layer and thickness of resin layer:

[0192] The basis weights of the surface layer and the middle layer are determined by the above method from the extrusion rate of each of the surface layer and the middle layer (i.e., the extrusion rate of the melt M4 for the surface layer and the melt M3 for the middle layer). Specifically, the basis weights [g / m] of each side of the middle layer are calculated by the following formula shown below from the extrusion rate X [g / hour] of the middle layer on each side, the extrusion rate Y [g / hour] of the surface layer on each side, the width W [m] of the multilayer foamed sheet, and the winding speed L [m / hour]. 2 ]. The basis weight of the resin layer is the sum of the basis weight of the intermediate layer and the basis weight of the surface layer. Incidentally, since the multilayer foamed sheet is manufactured under the same conditions as the basis weight of the surface layer and the intermediate layer in one surface side thereof and the basis weight of the surface layer and the intermediate layer in the other surface side thereof, only the basis weight of one side thereof is shown in Tables 4 and 5.

[0193] Basis weight of middle layer [g / m 2 ]=[X / (L×W)]

[0194] Basis weight of surface layer [g / m 2 ]=[Y / (L×W)]

[0195] (2-2) per 1m 2 The content of the polymer antistatic agent in the middle layer (A) and the amount of the polymer antistatic agent per 1m 2 Content of polymer antistatic agent in surface layer (B):

[0196] According to the formula shown below, the basis weight of the middle layer [g / m 2 ] and the amount x (wt%) of the polymer antistatic agent based on the weight of the intermediate layer, and the content (A) is determined by the basis weight of the surface layer [g / m 2 ] and the amount y (wt %) of the polymer antistatic agent based on the weight of the surface layer to determine the content (B).

[0197] Content (A) = (x / 100) × basis weight of the middle layer [g / m 2 ]

[0198] Content (B) = (y / 100) × basis weight of surface layer [g / m 2 ]

[0199] (3) Evaluation of antistatic properties (measurement of surface resistivity R):

[0200] Three test pieces were cut from the positions near the center and both ends of the multilayer foam sheet in the transverse direction, each of which was 100 mm long, 100 mm wide, and equal to the thickness of the multilayer foam sheet. Each test piece was allowed to stand for 24 hours in an atmosphere of 23°C and 50% relative humidity. Next, according to JIS K6271 (2001), a voltage of 500 V was applied to the test piece at 23°C and 50% relative humidity, and the surface resistivity of the test piece was measured after 1 minute of applying the voltage. The surface resistivity was measured on both sides of the test piece (3 test pieces × both sides: 6 times in total). The arithmetic mean of the measured values ​​obtained was taken as the surface resistivity R. As a measuring device, "SM-8220" manufactured by Hioki Electric Co., Ltd. was used.

[0201] Based on the measured value of the surface resistivity, the antistatic property of the multilayer foamed sheet was evaluated according to the following criteria.

[0202] A: Surface resistivity R is less than 1.0×10 9 Ω

[0203] B: Surface resistivity R is 1.0×10 9 Ω or more and less than 1.0×10 10 Ω

[0204] C: Surface resistivity R is 1.0×10 10 Ω or more

[0205] (4) Migration test (measurement of haze change): evaluation of low-staining properties

[0206] As a migration test, the change in haze was measured.

[0207] Pre-cleaned slide glass manufactured by Matsunami Glass Industries, Ltd. was used as the product to be packaged. Ten slide glass sheets were stacked one after another to obtain a stack of ten glass sheets. The haze (1) of the stack in the thickness direction (glass stacking direction) was measured using "Model NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. Next, the haze was measured at 3.8 g / cm 2 Under pressure, each glass is contacted with the sample (foamed sheet obtained in the embodiment and the comparative example) under pressure, and then it is statically left to stand for 24 hours at a temperature of 60°C and a relative humidity of 90%. Then, the sample is removed from the glass, and the remaining ten sheets of glass are stacked one by one to obtain a glass stack. The haze value (2) of the glass stack is measured in the same manner as above. The haze (1) is subtracted from the haze (2) to obtain the haze change (the haze (%) of the glass after the test minus the haze (%) of the glass before the test). The migration properties (pollution properties) are evaluated based on the standards shown below. The smaller the haze change, the lower the migration of the low molecular weight components contained in the multilayer foamed sheet to the glass, and therefore the more excellent the low pollution properties.

[0208] A: Haze change is less than 1%

[0209] B: Haze change is 1% or more and less than 1.5%

[0210] C: Haze change is 1.5% or more

[0211] (5) Measurement of static friction

[0212] Static friction was measured by a method according to JIS K7125 (1999). First, six square test pieces of 50 mm × 50 mm were cut from randomly selected portions of the multilayer foam sheet so that one side of each test piece was aligned with the extrusion direction of the multilayer foam sheet. Next, the test pieces were placed in an atmosphere of 23°C and 50% humidity for 24 hours to adjust the state of the test pieces. Then, each test piece was fixed to a bottom surface having a size of 50 mm × 50 mm and a weight of 125 g (5 g / cm 2) and placed on a glass slide (manufactured by Matsunami Glass Industry Co., Ltd., product name "Standard Large Sized White Edge Polishing No.2", product number S9112). Then, while aligning the extrusion direction of the multilayer foam sheet with the pulling direction of the measuring fixture, pull the measuring fixture in the horizontal direction at a speed of 100 mm / min so that the test piece slides on the glass slide. The first maximum point load at this time is defined as the static friction force (N) of the test piece. Among the 6 test pieces, the static friction force was measured on the side that had been in contact with the mandrel for 3 of the test pieces, and on the opposite side for the remaining three test pieces. The arithmetic mean (n=6) of the static friction force of each test piece is defined as the static friction force (N) of the multilayer foam sheet under low load.

[0213] (6) Calculation of the product R×B

[0214] Calculate every 1m 2 The content of polymer antistatic agent in the surface layer B (g / m 2 ) and the product of the surface resistivity R (Ω) obtained in (3) R × B (Ω·g / m 2 )

[0215] Explanation of symbols:

[0216] 1: Multi-layer foam sheet

[0217] 2: Foam layer

[0218] 3: Middle layer

[0219] 4: Surface layer

[0220] 5: Resin layer

Claims

1. A multi-layer foamed sheet comprising a foam layer containing a polyethylene-based resin (PE2) and a resin layer laminated on at least one of both sides of the foam layer, The resin layer comprises a surface layer located on the outermost side of the multi-layer foamed sheet and containing a polyethylene-based resin PE4 and a polymer antistatic agent (AS4), and an intermediate layer located between the foam layer and the surface layer and containing a polyethylene-based resin (PE3) and a polymer antistatic agent (AS3), wherein the polymer antistatic agent (AS3) is contained in the intermediate layer in an amount of 30 wt % or more and 70 wt % or less based on the weight of the intermediate layer, and the polymer antistatic agent (AS4) is contained in the surface layer in an amount of 5 wt % or more and less than 30 wt % based on the weight of the surface layer.

2. The multilayer foamed sheet according to claim 1, wherein the polymer antistatic agent (AS3) is present in an amount of 2 The amount A of the intermediate layer 1-5g is contained in the intermediate layer, and the unit of the amount A is g / m 2 .

3. The multilayer foamed sheet according to claim 1 or 2, wherein the polymer antistatic agent (AS4) is present in an amount of 1 m 2 The amount B of 0.05-0.8g of the surface layer is contained in the surface layer, and the unit of the amount B is g / m 2 .

4. The multilayer foamed sheet according to claim 3, wherein the ratio B / A of the amount B of the polymer antistatic agent (AS4) to the amount A of the polymer antistatic agent (AS3) is 0.03 to 0.

3.

5. The multilayer foam sheet according to claim 1 or 2, wherein the basis weight of the surface layer is 0.5-10 g / m 2 .

6. The multilayer foamed sheet according to claim 1 or 2, wherein the surface layer contains the polystyrene resin in an amount of 3 to 35% by weight based on the weight of the surface layer.

7. The multilayer foamed sheet according to claim 1 or 2, wherein the polymer antistatic agent (AS3) and the polymer antistatic agent (AS4) are ionomer resins that are the same as or different from each other.

8. The multilayer foam sheet according to claim 1 or 2, wherein the surface resistivity of the surface layer is less than 1×10 9 Ω.

9. Use of the multilayer foamed sheet according to any one of claims 1 to 8 as an interlayer sheet for a glass plate.

10. A method for producing a polyethylene-based resin multilayer foamed sheet having a multilayer structure in which a surface layer, an intermediate layer and a foam layer are laminated in this order, the method comprising the steps of: providing a foamable melt M2 for forming a foam layer containing a polyethylene-based resin (PE2) and a physical foaming agent, a melt M3 for forming an intermediate layer containing a polyethylene-based resin (PE3) and a polymer antistatic agent (AS3), and a melt M4 for forming a surface layer containing a polyethylene-based resin (PE4) and a polymer antistatic agent (AS4), The melts M2, M3 and M4 are laminated in this order in a mold to form a laminated material, and co-extruding the laminated material from the die to foam the foamable melt M2, wherein a polymer antistatic agent (AS3) is contained in the melt M3 for forming an intermediate layer in an amount of 30 wt % or more and 70 wt % or less based on the weight of the M3, and The polymer antistatic agent (AS4) is contained in the melt M4 for forming the surface layer in an amount of 5 wt% or more and less than 30 wt% based on the weight of the M4.

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