Resin foam sheet and adhesive tape

Abstract

A resin foam sheet comprising a first resin layer that is a foamed resin layer, and a second resin layer that is either a foamed resin layer or a resin film layer provided on at least one side of the first resin layer, the contact angle of at least one surface being 36-95° and the 25% compressive strength being 250 kPa or lower.

Description

[Technical Field]

[0001] The present invention relates to a resin foam sheet and an adhesive tape including the resin foam sheet. [Background technology]

[0002] Foam sheets have been widely used as substrates for pressure-sensitive adhesive tapes. Known foam sheets include polyolefin resin foam sheets obtained by foaming a foamable polyolefin resin sheet containing a thermally decomposable foaming agent.

[0003] In recent years, attempts have been made to make resin foam sheets multilayered in order to impart various functions. For example, Patent Document 1 discloses a multilayer foam sheet in which non-foam layers are provided on both surfaces of a foam layer in order to improve flexibility and mechanical strength. Furthermore, Patent Document 2 discloses a multilayer foam sheet in which outer layers, each composed of a foam layer having a lower expansion ratio than the middle layer, are provided on both surfaces of a foam layer constituting a middle layer in order to improve reworkability, flexibility, and waterproofness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-54961 [Patent Document 2] International Publication No. 2020 / 158886 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, foam sheets are sometimes used as the substrate of adhesive tapes for fixing wall hangers. Adhesive tapes for fixing wall hangers are required to have high shear holding strength so that they do not peel off from members such as wall surfaces even when a shear load is applied. In addition, foam sheets used as the substrate of adhesive tapes for fixing wall hangers are also required to have flexibility in order to ensure adhesion to the wall surface, ability to conform to the shape of the wall surface, and ease of peeling when peeling the adhesive tape from the wall surface.

[0006] However, conventional polyolefin resin foam sheets generally have a surface made of polyethylene resin, which can be difficult to adhere to depending on the type of adhesive, such as a silicone adhesive, making it difficult to increase shear strength. On the other hand, if an acrylic resin or the like is used in the foam sheet, adhesion to the silicone adhesive is also high, but it is difficult to achieve a high expansion ratio when foamed, making it difficult to increase flexibility.

[0007] Therefore, an object of the present invention is to provide a resin foam sheet that can enhance both shear holding strength and flexibility when used as a tape substrate for an adhesive tape using an adhesive such as a silicone-based adhesive. [Means for solving the problem]

[0008] The present inventors have found that the above-mentioned problems can be solved by adjusting both the surface contact angle and the 25% compressive strength of a resin foam sheet within predetermined ranges, and have completed the present invention as described below. That is, the gist of the present invention is as follows: [1] to

[18] [1] A first resin layer which is a foamed resin layer, and a second resin layer which is either a foamed resin layer or a resin film layer and is provided on at least one surface of the first resin layer, A resin foam sheet having a contact angle of 36 to 95° on at least one surface and a 25% compressive strength of 250 kPa or less. [2] The resin foam sheet according to the above [1], wherein the thickness of the resin foam sheet is 0.1 to 3.0 mm. [3] The foaming ratio of the resin foam sheet is 1.5 to 20 cm 3 / g. [4] The resin foam sheet according to any one of the above [1] to [3], which has a closed-cell structure. [5] The resin foam sheet according to any one of the above [1] to [4], comprising a middle layer made of the first resin layer, and outer layers (second resin layers) provided on both sides of the middle layer and made of either a foamed resin layer or a resin film layer. [6] The foaming ratio of the outer layer is 1 to 3 cm 3 / g, and the expansion ratio of the middle layer is 3 to 20 cm 3 / g. [7] The resin foam sheet according to [5] or [6] above, wherein the middle layer contains a polyolefin-based resin, and the outer layer contains at least one resin selected from the group consisting of a polyolefin-based resin, a modified polyolefin-based resin, and an acrylic-based resin. [8] The resin foam sheet according to any one of the above [5] to [7], wherein all of the outer layers are resin film layers. [9] The resin foam sheet according to any one of the above [5] to [8], wherein the oxygen atom content of each of the outer layers is 3.5% by mass or more.

[10] The resin foam sheet according to any one of the above [1] to [9], which is used as a substrate for an adhesive tape for fixing a wall hanger.

[11] The resin foam sheet according to any one of the above [1] to

[10] , which exhibits a retention time of 5 minutes or more in the following hanging test. <Hanging test> A wall hanger with a hook is attached to the resin foam sheet attached to the wall surface using a silicone double-sided adhesive tape under a load of 1 kg for 5 seconds to attach the wall hanger to the resin foam sheet. After that, a 1.1 kg weight is hung on the hook of the wall hanger and left to stand, and the time until the wall hanger peels off the resin foam sheet is measured and taken as the retention time.

[12] The resin foam sheet according to any one of the above [1] to

[11] , wherein the ratio of the thickness of each of the second resin layers to the thickness of the first resin layer (each second resin layer / first resin layer) is 0.001 to 0.5.

[13] The resin foam sheet according to any one of the above [1] to

[12] , wherein the resin constituting the first resin layer is a polyolefin resin.

[14] The resin foam sheet according to any one of the above [1] to

[13] , wherein the resin constituting the second resin layer comprises at least one selected from the group consisting of an acrylic olefin resin, an ethylene vinyl acetate copolymer, and a modified polyolefin resin.

[15] The resin foam sheet according to the above [7] or

[14] , wherein the modified polyolefin resin is an acid-modified polyolefin resin.

[16] The resin foam sheet according to the above [7] or

[15] , wherein the modified polyolefin resin is at least one selected from the group consisting of unsaturated carboxylic acid-modified polyethylene resins and epoxy group-modified polyethylene resins.

[17] The resin foam sheet according to the above [7],

[14] ,

[15] or

[16] , wherein the modification amount based on the total amount of the second resin layer is 0.02 to 10% by mass.

[18] A pressure-sensitive adhesive tape comprising the resin foam sheet according to any one of the above [1] to

[17] and an adhesive material on at least one surface of the resin foam sheet. [Effects of the Invention]

[0009] According to the present invention, a resin foam sheet can be provided that is excellent in both shear strength and flexibility when used as a tape substrate for pressure-sensitive adhesive tapes using various pressure-sensitive adhesives including silicone-based pressure-sensitive adhesives. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a resin foam sheet according to one embodiment of the present invention. [Figure 2] FIG. 10 is a schematic cross-sectional view showing an example of use of the double-sided adhesive tape for fixing a wall hanger. [Figure 3] FIG. 10 is a schematic cross-sectional view showing a test method for a hanging test. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Resin foam sheet] The resin foam sheet of the present invention has a surface contact angle of 36 to 95° and a 25% compressive strength of 250 kPa or less. The resin foam sheet, having the above-described structure, can ensure high adhesiveness and high shear strength even when used with various adhesives, including silicone-based adhesives. Therefore, even when used as a substrate for an adhesive tape for fixing a wall hanger and subjected to high shear loads, it can be prevented from peeling off from a wall surface. Furthermore, high flexibility can be ensured, ensuring, for example, adhesion to the wall surface, flexibility to the wall surface shape, and ease of peeling when peeling the adhesive tape from the wall surface.

[0012] <Contact angle> The resin foam sheet of the present invention has a surface contact angle of 36 to 95°. If the contact angle is greater than 95°, the wettability with silicone-based adhesives and the like may be poor, which may result in poor adhesion to the adhesive. Therefore, when a high shear load is applied to an adhesive tape using a resin foam sheet as a substrate, problems such as the adhesive peeling from the resin foam sheet and the adherend peeling off together with the adhesive, or the adhesive peeling from the resin foam sheet leaving the adhesive on the adherend, causing residue of the adhesive tape to fall off, are likely to occur. Furthermore, if the contact angle is less than 36°, it becomes difficult to practically produce a resin foam sheet. From the above viewpoints, the contact angle is preferably 50° or more, more preferably 60° or more, and even more preferably 80° or more, and the contact angle is preferably 93° or less, and even more preferably 91° or less.

[0013] As will be described later, the contact angle can be appropriately adjusted depending on the type of resin used in the resin foam sheet, more specifically, by appropriately selecting the type of resin used in the second resin layer (outer layer). That is, it is preferable that the surface of the resin foam sheet constituted by the second resin layer (outer layer) described later has a contact angle in the above range. Furthermore, it is preferable that the contact angle of at least one surface of the resin foam sheet is within the above range, but it is preferable that the contact angles of both surfaces of the sheet are within the above range. When the contact angles of both surfaces of the sheet are within the above range, the sheet can be suitably used as a substrate for a double-sided pressure-sensitive adhesive tape. The contact angle is the contact angle with pure water, as described in the examples.

[0014] <25% compressive strength> The 25% compressive strength of the resin foam sheet of the present invention is 250 kPa or less. If the 25% compressive strength is greater than 250 kPa, the flexibility of the resin foam sheet decreases, which may result in a decrease in adhesion to an adherend such as a wall surface, conformability to the shape of the wall surface, and releasability when peeling the pressure-sensitive adhesive tape from an adherend such as a wall surface. From the viewpoint of further increasing the flexibility of the resin foam sheet, the 25% compressive strength of the resin foam sheet of the present invention is preferably 200 kPa or less, more preferably 150 kPa or less, and even more preferably 90 kPa or less. The 25% compressive strength of the resin foam sheet is not particularly limited, but is preferably 10 kPa or more, more preferably 20 kPa or more, from the viewpoint of imparting a certain level of mechanical strength to the resin foam sheet.

[0015] <Closed bubble structure> The resin foam sheet of the present invention preferably has a closed-cell structure. The closed-cell structure of the resin foam sheet ensures flexibility while improving shear strength, making it easier to improve shear retention. The term "having a closed cell structure" means that the cells in the resin foam sheet are mostly closed cells, and the closed cell ratio of the resin foam sheet is, for example, 70% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 92% or more. The upper limit of the closed cell ratio is not particularly limited, and is 100%. The closed cell ratio can be measured by the method described in the Examples.

[0016] <Thickness> The thickness of the resin foam sheet is preferably 0.1 to 3 mm. When the thickness of the resin foam sheet is within the above range, the flexibility and mechanical strength of the resin foam sheet are easily improved. Furthermore, the thickness required for an adhesive tape substrate, particularly an adhesive tape substrate for fixing a wall hanger, can be sufficiently ensured, and the tape substrate can be prevented from becoming thicker than necessary. From this perspective, the thickness of the resin foam sheet is more preferably 0.3 to 2 mm, and even more preferably 0.5 to 1.6 mm.

[0017] <Expansion ratio> The expansion ratio of the resin foam sheet of the present invention is preferably 1.5 to 20 cm 3 / g. The expansion ratio is 1.5 cm 3 / g or more, the flexibility of the resin foam sheet is increased, and the above-mentioned 25% compressive strength can be easily reduced. 3 By setting the expansion ratio to 5 to 19 cm / g or less, the mechanical strength of the resin foam sheet is improved, and the above-mentioned shear holding power and the like are also likely to be improved. 3 / g, and 10 to 18 cm 3 / g is more preferred. The expansion ratio is expressed as the reciprocal of the apparent density, and the expansion ratio of a resin foam sheet can be determined by measuring the apparent density of the entire resin foam sheet and calculating the reciprocal. The apparent density can be measured in accordance with JIS K7222.

[0018] <Retention time> The resin foam sheet of the present invention preferably has a retention time of 5 minutes or more in the following hanging test. When the retention time is 5 minutes or more, the resin foam sheet of the present invention is less likely to suffer from problems such as peeling off even when used to fasten a wall hanger. <Hanging test> A wall hanger with a hook is attached to the resin foam sheet attached to the wall surface using a silicone double-sided adhesive tape under a load of 1 kg for 5 seconds to attach the wall hanger to the resin foam sheet. After that, a 1.1 kg weight is hung on the hook of the wall hanger and left to stand, and the time until the wall hanger peels off from the resin foam sheet is measured and taken as the retention time.

[0019] <Layer structure of resin foam sheet> The resin foam sheet includes at least a foamed resin layer made of a foam. In the present invention, the resin foam sheet includes a foamed resin layer (hereinafter sometimes referred to as a first resin layer) and an outer layer (hereinafter sometimes referred to as a second resin layer) provided on at least one surface of the foamed resin layer. As shown in FIG. 1, a preferred resin foam sheet is a resin foam sheet 10 including a middle layer (first resin layer) 11 made of a foamed resin layer and outer layers (second resin layers) 12A and 12B provided on both surfaces of the middle layer 11. The provision of the outer layers 12A and 12B in the resin foam sheet 10 makes it easier to adjust the contact angles of both surfaces within a desired range. In the resin foam sheet, the outer layer (second resin layer) preferably constitutes the surface of the resin foam sheet.

[0020] The outer layer is either a resin film layer or a foamed resin layer. Here, a foamed resin layer is a layer made of a foam, and a resin film layer is a layer made of a non-foamed material. Both outer layers 12A, 12B may be resin film layers, both may be foamed resin layers, or one may be a resin film layer and the other a foamed resin layer. Of these, it is preferable that both outer layers 12A, 12B are resin film layers. When both outer layers 12A, 12B are resin film layers, the shear holding strength tends to be high, and even when used as a tape base for fixing a wall hanger, problems such as peeling off are less likely to occur.

[0021] (Expansion Ratio of First and Second Resin Layers) In the resin foam sheet, the expansion ratio of the first resin layer (middle layer) is preferably 3 to 20 cm 3 The expansion ratio of the first resin layer is 3 cm / g. 3 / g or more, the flexibility of the resin foam sheet is increased, and the above-mentioned 25% compressive strength can be easily reduced. 3 By setting the expansion ratio to 6 to 19 cm / g or less, the mechanical strength of the resin foam sheet is improved. 3 / g, and 10 to 18 cm 3 / g is more preferred.

[0022] The expansion ratio of each second resin layer (outer layer) is preferably lower than that of the first resin layer (middle layer). By making the expansion ratio of the second resin layer lower than that of the first resin layer, it becomes easier to ensure the mechanical strength of the resin foam sheet. From the viewpoint of making it easier to ensure the mechanical strength and shear strength of the resin foam sheet, the expansion ratio of the second resin layer is 1 to 3 cm. 3 / g, and 1 to 2 cm 3 / g, and more preferably 1 to 1.5 cm 3 / g is more preferred. The expansion ratio of the first resin layer and the second resin layer can be calculated by measuring the apparent density of each layer and calculating the reciprocal of the apparent density. Therefore, the second resin layer may be a non-foamed material, but even in such a case, the second resin layer is considered to have an expansion ratio. The expansion ratio of a non-foamed material is approximately 1 cm. 3 / g.

[0023] (Thickness of first and second resin layers) The thickness of the first resin layer (middle layer) in the resin foam sheet is preferably 0.05 to 2.9 mm. When the thickness of the first resin layer is within the above range, flexibility is easily ensured. Furthermore, the thickness required for an adhesive tape substrate, particularly an adhesive tape substrate for fixing a wall hanger, can be sufficiently ensured, and the tape substrate can be prevented from becoming thicker than necessary. From this perspective, the thickness of the first resin layer is more preferably 0.25 to 1.9 mm, and even more preferably 0.4 to 1.5 mm.

[0024] The thickness of each second resin layer (outer layer) is preferably 3 to 300 μm. When the thickness of the second resin layer is 3 to 300 μm, it is easy to improve the adhesiveness to various pressure-sensitive adhesives such as silicone-based pressure-sensitive adhesives while ensuring a certain level of mechanical strength and flexibility. From this viewpoint, the thickness of each second resin layer is more preferably 5 to 200 μm, even more preferably 10 to 100 μm, and even more preferably 15 to 70 μm.

[0025] The thickness ratio of each second resin layer (outer layer) to the first resin layer (middle layer) (each second resin layer / first resin layer) is preferably 0.001 to 0.5. When the thickness ratio is within this range, the flexibility and mechanical strength of the resin foam sheet are ensured, while also making it easier to achieve good adhesion to various pressure-sensitive adhesives such as silicone-based pressure-sensitive adhesives. The thickness ratio is more preferably 0.005 to 0.4, even more preferably 0.01 to 0.3, and even more preferably 0.015 to 0.15.

[0026] (Oxygen atom content) The resin foam sheet preferably has an oxygen atom content of 3.5% by mass or more in the second resin layer (outer layer). An oxygen atom content of 3.5% by mass or more improves adhesion to various adhesives such as silicone-based pressure-sensitive adhesives, thereby improving the shear holding strength of the pressure-sensitive adhesive tape. From the viewpoint of improving adhesion to silicone-based pressure-sensitive adhesives, the oxygen atom content is more preferably 4% by mass or more, and even more preferably 6% by mass or more. The oxygen atom content is not particularly limited, but is, for example, 15% by mass or less. The oxygen atom content can be appropriately adjusted depending on the type of resin used in the resin foam sheet, as described later, and preferably can be adjusted by appropriately selecting the type of resin used in the outer layer, as described later. The resin foam sheet may have an oxygen atom content of at least one outer layer within the above range, but it is preferable that the oxygen atom contents of both outer layers are within the above range. When the oxygen atom contents of both outer layers are within the above range, the resin foam sheet can be suitably used as a substrate for a double-sided pressure-sensitive adhesive tape.

[0027] (Composition of the first resin layer) In the resin foam sheet of the present invention, the foamed resin layer is made of a foam. The type of resin constituting the foamed resin layer is not particularly limited, but any known resin used as a foam may be used. As described above, the first resin layer is composed of a foamed resin layer. From the viewpoints of flexibility and processability, the resin constituting the first resin layer (middle layer) is preferably a thermoplastic resin, and more preferably a polyolefin resin. By using a polyolefin resin, it becomes easier to increase shear strength while maintaining flexibility, and it is easy to improve shear retention force, etc. The polyolefin resin may be a polyolefin resin such as a polyethylene resin or a polypropylene resin, or an olefin copolymer resin such as an ethylene-vinyl acetate copolymer, but among these, a polyethylene resin is preferred from the viewpoints of flexibility and shear strength. Examples of the polyethylene resin include polyethylene resins polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene catalyst, or a chromium oxide compound, and preferably polyethylene resins polymerized with a metallocene catalyst are used.

[0028] (Metallocene catalyst) Examples of metallocene catalysts include compounds such as bis(cyclopentadienyl) metal complexes, which have a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, examples include compounds in which one or more cyclopentadienyl rings or analogs thereof exist as ligands on a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, or platinum. Such metallocene catalysts have uniform properties of active sites, and each active site has the same activity. Polymers synthesized using metallocene catalysts have high uniformity in molecular weight, molecular weight distribution, composition, composition distribution, etc., so when a sheet containing a polymer synthesized using a metallocene catalyst is crosslinked, the crosslinking proceeds uniformly. A uniformly crosslinked sheet is foamed uniformly, making it easier to stabilize its physical properties. In addition, since it can be stretched uniformly, the thickness of the foam can be made uniform.

[0029] Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted with a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon-substituted metalloid group. Examples of hydrocarbon groups include a methyl group, an ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various cetyl groups, and a phenyl group. Note that "various" refers to various isomers including n-, sec-, tert-, and iso-. Alternatively, a cyclic compound may be polymerized as an oligomer and used as the ligand. Furthermore, in addition to the π-electron unsaturated compounds, monovalent anionic ligands such as chlorine and bromine, or divalent anionic chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, arylphosphides, and the like may also be used.

[0030] Examples of metallocene catalysts containing a tetravalent transition metal or a ligand include cyclopentadienyltitanium tris(dimethylamide), methylcyclopentadienyltitanium tris(dimethylamide), bis(cyclopentadienyl)titanium dichloride, and dimethylsilyltetramethylcyclopentadienyl-t-butylamide zirconium dichloride. Metallocene catalysts, when combined with a specific cocatalyst (promoter), function as a catalyst during the polymerization of various olefins. Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron-based compounds. The ratio of the cocatalyst to the metallocene catalyst is preferably 100,000 to 1,000,000 moles, and more preferably 50 to 5,000 moles.

[0031] As polyethylene resin, low-density polyethylene (LDPE: density 0.925 g / cm 3 below), medium density polyethylene (MDPE: density 0.925g / cm 3 Super 0.945g / cm 3 below), high density polyethylene (HDPE: density 0.945g / cm 3 Among these, linear low density polyethylene is preferred. The linear low-density polyethylene is preferably a linear low-density polyethylene obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more, based on the total amount of monomers) with a small amount of an α-olefin as needed. Specific examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Of these, α-olefins having 4 to 10 carbon atoms are preferred. The density of linear low-density polyethylene is 0.870 to 0.925 g / cm3 from the viewpoint of flexibility. 3 is preferable, and 0.890 to 0.925 g / cm 3 More preferably, 0.910 to 0.925 g / cm 3 As the polyethylene resin, one type may be used alone, or a plurality of polyethylene resins may be used.

[0032] The polyolefin resin is preferably the main component of the first resin layer (middle layer), and the specific content of the polyolefin resin is, for example, 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, based on the total amount of resin contained in the first resin layer. The foamed resin layer constituting the first resin layer may be composed solely of a polyolefin resin as the resin component, but may also contain a resin other than the polyolefin resin as long as the effects of the present invention are not impaired.

[0033] (Composition of the second resin layer) The second resin layer (outer layer) is a resin film layer or a foamed resin layer as described above. The type of resin constituting the second resin layer is not particularly limited, but it is preferable to select a resin that has a surface contact angle within the above range. Furthermore, the resin used for each second resin layer is preferably a thermoplastic resin from the viewpoint of processability, but may also be a curable resin such as a thermosetting resin or a photocurable resin.

[0034] Resins used in each second resin layer (outer layer) include polyolefin resins, modified polyolefin resins such as acid-modified polyolefin resins, and acrylic resins. These resins may be used alone or in combination of two or more. Using these resins in the second resin layer makes it easier to adjust the contact angle on the surface of the resin foam sheet within a predetermined range. As described above, it is preferable that the second resin layer is provided on each of both sides of the intermediate layer, but the resins contained in the multiple second resin layers may be the same as or different from each other.

[0035] The polyolefin resin used in the second resin layer is preferably an olefin copolymer resin, which is a copolymer of an olefin and a monomer other than an olefin, such as vinyl acetate or (meth)acrylate. The olefin used in the olefin copolymer resin is, for example, an α-olefin having about 2 to 12 carbon atoms, such as ethylene, propylene, butene, or methylpentene-1, and is preferably ethylene. Preferred examples of the olefin copolymer resin include acrylic olefin resins and ethylene-vinyl acetate copolymers. Preferred specific examples of the acrylic olefin resin include acrylic ethylene resins such as ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-butyl acrylate copolymer (EBA), and ethylene-methyl methacrylate copolymer (EMMA). By using the above-mentioned olefin copolymer resins in the second resin layer, the contact angle on the surface of the resin foam sheet can be suitably adjusted, and the oxygen atom content can be easily adjusted within a desired range. Among these, acrylic olefin resins are preferred, and acrylic ethylene resins are more preferred.

[0036] The modified polyolefin resin may be an acid-modified polyolefin resin that has been acid-modified with at least one of an unsaturated carboxylic acid and an anhydride thereof, specifically, a polyolefin resin that has been chemically bonded to an unsaturated carboxylic acid or the like by an addition reaction, a graft reaction, or the like. In the acid-modified polyolefin resin, examples of the unsaturated carboxylic acid that modifies the polyolefin resin include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and anhydrides thereof, and among these, maleic acid or its anhydride is preferred.

[0037] Furthermore, the modified polyolefin resin is not limited to acid-modified resins such as the above-mentioned carboxylic acid-modified resins that act as Bronsted acids, but may be modified in a manner other than acid-modified resins, or may be resins that act as Bronsted bases. The resin that functions as a Bronsted base is preferably a resin containing an epoxy group, and therefore, the modified polyolefin resin is preferably an epoxy group-modified polyolefin resin.

[0038] Examples of polyolefin resins include homopolymers or copolymers of α-olefins having about 2 to 12 carbon atoms, such as ethylene, propylene, butene, and methylpentene-1. Of these, polyethylene resins and polypropylene resins are preferred, with polyethylene resins being particularly preferred. Therefore, the modified polyolefin resin is preferably a modified polyethylene resin. Furthermore, the acid-modified polyolefin resin is preferably an acid-modified polyethylene resin. Furthermore, the acid-modified polyolefin resin may contain structural units derived from components other than olefins, unsaturated carboxylic acids, and their anhydrides, and may contain structural units derived from vinyl acetate or various (meth)acrylates.

[0039] Modified polyolefin resins such as acid-modified polyolefin resins may contain olefin-derived structural units as the main component, and may contain, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 70% by mass or more of olefin relative to the total amount of monomers. Examples of acid-modified polyolefin resins include those obtained by graft copolymerizing at least one of unsaturated carboxylic acid and its anhydride onto a polyolefin resin such as a polyethylene resin. Further examples include copolymers of an olefin such as ethylene with an unsaturated carboxylic acid or anhydride thereof such as maleic anhydride, maleic acid, or (meth)acrylic acid, and other components used as needed. In this case, maleic anhydride is preferred as the unsaturated carboxylic acid or anhydride thereof. Further, examples of epoxy group-modified polyethylene resins include copolymers of an olefin such as ethylene, an epoxy group-containing compound such as glycidyl (meth)acrylate, and other components that are used as needed. Specific examples of preferred modified polyolefin resins include unsaturated carboxylic acid-modified polyethylene resins such as maleic anhydride-modified polyethylene resins, maleic acid-modified polyethylene resins, and (meth)acrylic acid-modified polyethylene resins, and epoxy group-modified polyethylene resins. As the modified polyolefin resin, from the viewpoint of increasing the shear holding strength, unsaturated carboxylic acid-modified polyethylene resins and the like are preferred, and specifically, maleic anhydride-modified polyethylene resins and maleic acid-modified polyethylene resins are more preferred, and maleic anhydride-modified polyethylene resins are particularly preferred.

[0040] The modification amount of the modified polyolefin resin (the acid modification amount in the case of the modified polyolefin resin) is not particularly limited, but is, for example, 0.1 to 25 mass %, preferably 0.5 to 20 mass %, more preferably 1 to 15 mass %. The modification amount here is expressed as the mass % of the structural units derived from the modifying group-containing monomer, such as the unsaturated carboxylic acid or the epoxy group-containing compound, in the modified polyolefin resin.

[0041] The acrylic resin used in the second resin layer may be an acrylic polymer obtained by polymerizing a monomer component (a) containing an acrylic monomer component. The monomer component (a) is a monomer component having one addition-polymerizable double bond, preferably a monomer component having one vinyl group. The monomer component (a) is not particularly limited, but preferably contains an alkyl(meth)acrylate as the acrylic monomer component. In this specification, (meth)acrylate refers to acrylate or methacrylate, and the same applies to other similar terms.

[0042] Examples of alkyl(meth)acrylates include alkyl(meth)acrylates having a linear or branched alkyl group, and the alkyl group has, for example, 1 to 18 carbon atoms, preferably 1 to 14 carbon atoms, more preferably 1 to 10 carbon atoms, and even more preferably 1 to 8 carbon atoms. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, and n-tetradecyl (meth)acrylate.

[0043] The alkyl(meth)acrylate is preferably contained in the monomer component (a) constituting the acrylic polymer in an amount of 50% by mass or more, more preferably 60% by mass to 100% by mass, even more preferably 75% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass. By using an alkyl(meth)acrylate in an amount equal to or greater than these lower limits, it becomes easier to impart the required mechanical strength to the foamed resin layer. Furthermore, the monomer component (a) may entirely be alkyl(meth)acrylate.

[0044] Furthermore, the monomer component (a) may contain, in addition to the alkyl (meth)acrylate, a monomer component other than the alkyl (meth)acrylate. Examples of the monomer component other than the alkyl (meth)acrylate include a carboxyl group-containing monomer or anhydride thereof, a hydroxyl group-containing (meth)acrylic monomer, a nitrogen-containing vinyl monomer, and a styrene-based monomer. Examples of the carboxyl group-containing monomer include carboxylic acids containing an addition-polymerizable double bond, such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid. Examples of the hydroxyl group-containing (meth)acrylic monomer include hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone-modified (meth)acrylate, polyoxyethylene (meth)acrylate, and polyoxypropylene (meth)acrylate. Examples of the nitrogen-containing vinyl monomer include acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-propyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N-butyl(meth)acrylamide, and N,N-dibutyl(meth)acrylamide; amino group-containing (meth)acrylic monomers such as aminoethyl(meth)acrylate and t-butylaminoethyl(meth)acrylate; (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinyllaurolactam, (meth)acryloylmorpholine; and dimethylaminomethyl(meth)acrylate. Examples of the styrene-based monomer include styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene. The monomer components other than the alkyl (meth)acrylate may be used singly or in combination of two or more.

[0045] The acrylic polymer may be crosslinked with a crosslinking agent to have a crosslinked structure. When the acrylic polymer is crosslinked with a crosslinking agent, for example, a crosslinking agent may be further blended during polymerization of the monomer component (a), and the monomer component (a) and the crosslinking agent may be copolymerized to crosslink the acrylic polymer with the crosslinking agent. Alternatively, the crosslinking agent may be blended with a partially polymerized product of the monomer component (a), and the resulting mixture may be further polymerized to crosslink the acrylic polymer with the crosslinking agent. The crosslinking agent may be one having two or more addition-polymerizable double bonds, preferably one having two or more vinyl groups, more preferably a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups. Such a crosslinking agent is incorporated into the main chain formed by the monomer component (a) and crosslinks the main chains to form a network. Specific crosslinking agents include hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, ε-caprolactone-modified tris(2-acryloxyethyl)isocyanurate, caprolactone-modified ethoxylated isocyanuric acid triacrylate, ethoxylated trimethylolpropane triacrylate, proxied trimethylolpropane triacrylate, proxied glyceryl triacrylate, neopentyl glycol adipate diacrylate, polyurethane acrylate, epoxy acrylate, polyester acrylate, and liquid hydrogenated 1,2-polybutadiene diacrylate. The crosslinking agents may be used alone or in combination of two or more. The amount of the crosslinking agent to be added is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass, and even more preferably 2 to 6 parts by mass, per 100 parts by mass of the monomer component (a).

[0046] Among the above, the resin used for each second resin layer is preferably a resin selected from the group consisting of an olefin copolymer resin, a modified polyolefin resin, and an acrylic resin, from the viewpoint of easily adjusting the contact angle within a desired range. Among these, when the first resin layer (middle layer) contains an olefin resin, from the viewpoint of adhesion to the first resin layer, an olefin copolymer resin or an acid-modified polyolefin resin is more preferred, and an acid-modified polyolefin resin is even more preferred. These resins may be used alone or in combination of two or more.

[0047] Furthermore, a resin selected from the group consisting of an olefin copolymer resin, a modified polyolefin resin, and an acrylic resin is preferably the main component of each second resin layer, and is contained in an amount of preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total amount of the second resin layer. Furthermore, in each second resin layer, a resin selected from these may be used in combination with other resins, for example, a polyolefin resin other than an olefin copolymer resin or a modified polyolefin resin.

[0048] Furthermore, when a modified polyolefin resin is used in the second resin layer, the modified polyolefin resin does not need to be the main component, and the content may be appropriately adjusted so that the modification amount falls within a certain range. Specifically, the modified polyolefin resin may be contained in the second resin layer so that the modification amount based on the total amount of the second resin layer is, for example, 0.02 to 10 mass%, preferably 0.05 to 8 mass%, more preferably 0.1 to 6 mass%, and even more preferably 0.2 to 6 mass%. The modification amount based on the total amount of the second resin layer refers to the proportion (mass%) of structural units derived from a modifying group-containing monomer, such as an unsaturated carboxylic acid or an epoxy group-containing compound, relative to the total amount of the second resin layer. The modification amount based on the total amount of the second resin layer can be calculated from the blending amounts of each component, but it can also be determined by, for example, XPS measurement of the surface of the resin foam sheet.

[0049] When a modified polyolefin resin is used in the second resin layer, a polyolefin resin can be used in combination with the modified polyolefin resin. The polyolefin resin may be a polyolefin resin such as a polyethylene resin or a polypropylene resin, or an olefin copolymer resin such as an ethylene-vinyl acetate copolymer, with a polyethylene resin being preferred. Details of the polyethylene resin used in the second resin layer are as described above for the first resin layer, and therefore will not be described here. The polyolefin resin used in combination with the modified polyolefin resin in the second resin layer may be a different type from the polyolefin resin used in the first resin layer, but it is preferable that the same type be used. Therefore, if the resin used in the first resin layer is a polyethylene resin, it is preferable that the resin used in combination with the modified polyolefin resin in the second resin layer is also a polyethylene resin. Furthermore, if the resin used in the first resin layer is LLDPE, it is preferable that the resin used in combination with the modified polyolefin resin in the second resin layer is also LLDPE.

[0050] When a modified polyolefin resin is used in the second resin layer, the content of the modified polyolefin resin in the second resin layer is, for example, 5 to 100 mass%, preferably 10 to 100 mass%, and more preferably 15 to 40 mass%, based on the total amount of the second resin layer.

[0051] (foaming agent) The foamed resin layer is preferably obtained by foaming a foamable composition for the foamed resin layer, which contains the resin and a foaming agent. The foaming agent is preferably a thermal decomposition type foaming agent. When an additive is to be contained in the foamed resin layer, the foamable composition may further contain various additives. The thermal decomposition type blowing agent may be an organic blowing agent or an inorganic blowing agent. Examples of the organic blowing agent include azo compounds such as azodicarbonamide, azodicarboxylic acid metal salts (e.g., barium azodicarboxylate), and azobisisobutyronitrile, nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, hydrazine derivatives such as hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide), and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonylsemicarbazide. Examples of inorganic foaming agents include ammonium carbonate, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, and anhydrous monosodium citrate. Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, azo compounds are preferred, and azodicarbonamide is more preferred. The thermal decomposition type foaming agents may be used alone or in combination of two or more.

[0052] The amount of foaming agent in the foamable composition for the foamed resin layer may be adjusted appropriately depending on the desired expansion ratio. For example, in the foamable composition for the foamed resin layer constituting the first resin layer, the content of the foaming agent is preferably 1 to 20 parts by mass, more preferably 3 to 18 parts by mass, and even more preferably 5 to 15 parts by mass, per 100 parts by mass of the resin. By adjusting the amount of foaming agent to be equal to or greater than these lower limits, the flexibility of the resin foam sheet is improved. Furthermore, by adjusting the amount of foaming agent to be equal to or less than these upper limits, the first resin layer is prevented from expanding more than necessary, and the mechanical strength of the resin foam sheet can be improved. In addition, in the foamable composition for the foamed resin layer constituting the second resin layer, the content of the foaming agent is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, per 100 parts by mass of the resin. By adjusting the amount of the foaming agent to be equal to or greater than these lower limits, the expansion ratio of the second resin layer can be maintained at a certain level or higher. By adjusting the amount of the foaming agent to be equal to or less than these upper limits, the foam can be prevented from expanding more than necessary, thereby improving the mechanical strength of the resin foam sheet. As described above, the second resin layer is preferably a resin film layer (i.e., a non-foamed body), and therefore the second resin layer is preferably formed from a resin composition that does not contain a foaming agent.

[0053] (additives) The resin foam sheet may contain additives other than the resin components as appropriate. Examples of additives include additives that are conventionally used in foams and resin films, such as antioxidants, colorants, flame retardants, antistatic agents, fillers, UV absorbers, decomposition temperature regulators, photopolymerization initiators, and crosslinking agents. As described above, the resin foam sheet preferably has a first resin layer and a second resin layer, and each of the first resin layer and the second resin layer may contain an additive as appropriate. Among the above, the resin foam sheet preferably contains an antioxidant. When the resin foam sheet is composed of multiple layers, the antioxidant may be contained in each layer. For example, when the resin foam sheet has a first resin layer and a second resin layer, the antioxidant may be contained in each of the first resin layer and the second resin layer. Examples of the antioxidant include phenol-based antioxidants such as 2,6-di-t-butyl-p-cresol, sulfur-based antioxidants, phosphorus-based antioxidants, and amine-based antioxidants. The content of the antioxidant in each layer is, for example, 0.01 to 5 parts by mass relative to 100 parts by mass of the resin contained in each layer.

[0054] The foamable composition (i.e., foamed resin layer) may also contain a decomposition temperature regulator. The decomposition temperature regulator is blended to lower the decomposition temperature of the thermally decomposable foaming agent or to accelerate or adjust the decomposition rate, and specific examples of such compounds include zinc oxide, zinc stearate, and urea. The decomposition temperature regulator is blended in each foamed resin layer in an amount of, for example, 0.01 to 5 parts by mass per 100 parts by mass of the resin.

[0055] (adhesive layer) In the resin foam sheet, the second resin layer (outer layer) and the first resin layer (middle layer) are preferably laminated directly to each other, but may be laminated via another layer. An example of such another layer is an adhesive layer. A known adhesive, pressure-sensitive adhesive, or the like may be used as the adhesive layer. Alternatively, a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of a substrate may be used. The adhesive layer may have a thickness that does not significantly affect the physical properties of the resin foam sheet, such as mechanical strength, flexibility, etc. Therefore, the thickness of the adhesive layer that bonds the outer layer and the foamed resin layer is preferably thinner than the outer layer, and more preferably 1 / 2 or less of the thickness of the outer layer.

[0056] <Method of manufacturing resin foam sheet> The method for producing a resin foam sheet is not particularly limited. A multilayer resin foam sheet can be produced by a method (hereinafter also referred to as "production method 1") in which a plurality of resin layers are laminated to obtain a multilayer sheet, and then at least one of the resin layers in the multilayer sheet is foamed.

[0057] More specifically, production method 1 includes the following steps I and II. (I) A step of obtaining a multilayer sheet having a layer made of a foamable composition for forming a first resin layer and a layer for forming a second resin layer. (II) A step of foaming the multilayer sheet to obtain a resin foam sheet

[0058] Each step will be described below. (Process (I)) The method for obtaining the multilayer sheet in step (I) is not particularly limited, but is preferably performed by coextrusion molding. Specifically, a resin for forming the first resin layer (middle layer), a foaming agent such as a thermally decomposable foaming agent, and optional additives are fed into an extruder and melt-kneaded to obtain a resin composition (foamable composition) for the first resin layer. A resin for forming the second resin layer (outer layer), and optional foaming agents and additives are fed into another extruder and melt-kneaded to obtain a resin composition for the second resin layer. The resin compositions fed from the extruders are then joined and extruded into a sheet using a T-die or the like to obtain a multilayer sheet. In coextrusion molding, either a feedblock method or a multimanifold method may be used, but the feedblock method is preferred. The multilayer sheet obtained in step (I) may include a layer for forming the first resin layer and a layer for forming the second resin layer, but is preferably a multilayer sheet in which layers for forming the second resin layer are laminated on both sides of a layer for forming the first resin layer. The layer for forming the second resin layer may be a layer made of a foamable composition containing a foaming agent, or may be a layer made of a resin composition containing no foaming agent.

[0059] In step (I), it is preferable to further crosslink the multilayer sheet obtained above. As a crosslinking method, an organic peroxide is previously blended as a crosslinking agent, and the multilayer sheet obtained in step (I) is heated to crosslink, but it is preferable to crosslink the multilayer sheet by irradiating it with ionizing radiation. Examples of ionizing radiation include electron beams and β rays, and electron beams are preferred. The dose of ionizing radiation is preferably 1 to 10 Mrad, more preferably 1.5 to 5 Mrad.

[0060] (Step (II)) In step (II), the multilayer sheet obtained in step (I) is subjected to a foaming treatment to foam the layer comprising the foamable composition. The layer comprising the foamable composition may be treated so that the foaming agent foams, but when the foaming agent is a thermally decomposable foaming agent, the multilayer sheet is heated to foam it. The heating temperature may be equal to or higher than the temperature at which the thermally decomposable foaming agent decomposes, and is, for example, about 150 to 320°C. The method for heating the multilayer sheet is not particularly limited, and examples thereof include a method for heating the multilayer sheet with hot air, a method for heating with infrared rays, a method for heating in a salt bath, a method for heating in an oil bath, and the like, and these may be used in combination. The multilayer sheet may be stretched as appropriate during or after foaming. In step (II), the layer for forming the first resin layer is preferably foamed, and if the layer for forming the second resin layer is a foamable composition, the second resin layer is also preferably foamed.

[0061] (Second manufacturing method) The multilayer resin foam sheet can also be produced by another method, specifically, a method (also referred to as a "second production method") in which a foam constituting the first resin layer is produced in advance, and a resin film or foam (outer layer) is superimposed on one or both sides of the foam (first resin layer) to bond them together.

[0062] In the second production method, a foam can be obtained by melt-kneading a resin for forming a foamed resin layer, a thermally decomposable foaming agent, and additives blended as necessary to obtain a foamable composition for the foamed resin layer, and then molding the foamable composition into a sheet (foamable composition sheet). The method for melt-kneading the foamable composition and molding it into a sheet is not particularly limited, but it is preferably carried out using an extruder.

[0063] The obtained foamable composition sheet is preferably further crosslinked before foaming, as described below. A crosslinking method may involve blending an organic peroxide in advance and heating the foamable composition sheet to crosslink it, but it is preferred to crosslink the foamable composition sheet by irradiating it with ionizing radiation. The type and dose of ionizing radiation are as described in the first production method above.

[0064] Next, the foamable composition sheet may be foamed. When the foaming agent is a thermally decomposable foaming agent, the foamable composition sheet is heated to foam it. The heating temperature and heating method are as described in the first production method above. The foamable composition sheet may be appropriately stretched during or after foaming. In this way, a foamed resin layer (foam) is obtained.

[0065] Thereafter, a separately prepared resin film or foam for constituting the outer layer is superimposed on and bonded to the foamed resin layer (foam), thereby obtaining a resin foam sheet. Specifically, the foamed resin layer (foam) may be heated and pressurized using a press or the like to achieve thermocompression bonding. Alternatively, the foamed resin layer and the outer layer may be bonded together by applying a pressure-sensitive adhesive, adhesive, or the like to the bonding surface between them, or by applying a double-sided adhesive tape.

[0066] (Third manufacturing method) The multilayer resin foam sheet can also be produced by the following third production method. Specifically, a foam constituting the first resin layer may be produced in advance, and the resin composition for forming the second resin layer may be applied to one or both sides of the foam (first resin layer). The third production method is suitable when the second resin layer is formed from a curable resin. For example, when the second resin layer is an acrylic resin, a resin composition containing a monomer component (a) and a crosslinking agent, or a partially cured product of the resin composition, may be applied to the first resin layer, and then cured to form the second resin layer.

[0067] The method for obtaining a resin foam sheet, which is a multilayer laminate, has been described above. However, when obtaining a resin foam sheet consisting only of a foamed resin layer, it is preferable to obtain a foamable composition sheet as described in the second production method above, and then obtain a foamed resin layer (foam) in the same manner as in the second production method above. Furthermore, in the above explanation, the resin foam sheet of the present invention has been described on the assumption that bubbles are formed by a foaming agent, but bubbles do not necessarily have to be formed by a foaming agent. For example, a resin foam sheet may be formed by incorporating hollow particles inside the resin foam sheet.

[0068] [Adhesive tape] The resin foam sheet of the present invention is preferably used as a pressure-sensitive adhesive tape substrate. The pressure-sensitive adhesive tape comprises the resin foam sheet of the present invention and a pressure-sensitive adhesive material provided on at least one surface of the resin foam sheet. The pressure-sensitive adhesive tape can be adhered to other members via the pressure-sensitive adhesive material. The pressure-sensitive adhesive tape may be a resin foam sheet with pressure-sensitive adhesive materials provided on both sides or one side, but is preferably a double-sided pressure-sensitive adhesive tape with pressure-sensitive adhesive materials on both sides.

[0069] The adhesive is a layer having pressure-sensitive adhesive properties and may include at least a pressure-sensitive adhesive layer. It may be a single pressure-sensitive adhesive layer laminated on the surface of a resin foam sheet, or a double-sided pressure-sensitive adhesive sheet attached to the surface of a resin foam sheet, but a single pressure-sensitive adhesive layer is preferred. The double-sided pressure-sensitive adhesive sheet includes a substrate and pressure-sensitive adhesive layers provided on both sides of the substrate. The double-sided pressure-sensitive adhesive sheet constituting the adhesive is used to adhere one pressure-sensitive adhesive layer to the resin foam sheet and the other pressure-sensitive adhesive layer to another member. A release sheet such as release paper may be further attached onto the adhesive material. The thickness of the adhesive material is preferably 5 to 200 μm, more preferably 7 to 150 μm, and even more preferably 10 to 100 μm.

[0070] Examples of adhesives that can be used to form the adhesive layer include acrylic adhesives, urethane adhesives, rubber adhesives, and silicone adhesives, with silicone adhesives being preferred among these. When using a silicone-based pressure-sensitive adhesive, it is generally difficult to achieve excellent adhesion to a tape substrate made of a resin foam sheet. However, in the present invention, by using a resin foam sheet having a specific contact angle as described above, it is possible to achieve excellent adhesion of the tape substrate (the resin foam sheet of the present invention) to the silicone-based pressure-sensitive adhesive.

[0071] Furthermore, when the adhesive tape is a double-sided adhesive tape, it is preferable that either one of the adhesive materials provided on both sides of the tape substrate has an adhesive layer formed from a silicone-based adhesive, but it is preferable that both adhesive materials have adhesive layers formed from a silicone-based adhesive. Furthermore, when a double-sided adhesive sheet is used as the adhesive material, it is advisable to form the adhesive layer of the double-sided adhesive sheet constituting the adhesive material that adheres to the resin foam sheet using a silicone-based adhesive, and it is preferable to use a silicone-based adhesive for both adhesive layers.

[0072] The resin foam sheet of the present invention is preferably used as an adhesive tape substrate for fixing a wall hanger. Here, the wall hanger is a component for hanging various items, and examples thereof include a wall hanger 20 having a base 21 and a hanging portion 22 protruding from the base 21, as shown in FIG. 2 . The hanging portion 22 may have any shape, such as a hook, rod, hemisphere, cube, rectangular parallelepiped, or cone. The base 21 is a component for being fixed to a wall surface 25, and as shown in FIG. 2 , it is preferably fixed to the wall surface 25 via a double-sided adhesive tape 15. Therefore, the base 21 preferably has a flat portion 21A to which the double-sided adhesive tape 15 is adhered. The double-sided adhesive tape 15 includes an adhesive tape substrate 10 and adhesive materials 16A and 16B provided on both sides of the substrate 10, and the resin foam sheet of the present invention is preferably used for the adhesive tape substrate 10. Of course, the resin foam sheet of the present invention may be used for purposes other than fixing wall hangers, and may be used as a substrate for any type of adhesive tape, or may be used for purposes other than as a substrate for adhesive tapes. [Example]

[0073] EXAMPLES The present invention will be described below with reference to examples, but is not limited to these examples. The methods for measuring physical properties and the methods for evaluating the resin foam sheet are as follows.

[0074] <Thickness of foamed resin layer and outer layer> The cross section of the resin foam sheet was photographed using a digital microscope (Keyence Corporation, product name VHX-900), and the thickness of the middle layer (first resin layer) and each outer layer (second resin layer) was measured from the photographed image. The sum of the thicknesses of the middle layer and both outer layers was defined as the total thickness of the resin foam sheet.

[0075] <Apparent density and expansion ratio> The apparent density of the resin foam sheets, the first resin layer (middle layer), and the second resin layer (outer layer) obtained in the examples and comparative examples was measured in accordance with JIS K 7222, and the reciprocal thereof was taken as the expansion ratio. In Table 1, the expansion ratio of the resin foam sheets is shown as the total expansion ratio.

[0076] <Closed bubble rate> Planar square test pieces with sides of 5 cm were cut out from the resin foam sheets of the Examples and Comparative Examples. The thickness of the test pieces was measured to calculate the apparent volume V1 of the test pieces, and the mass W1 of the test pieces was also measured. Next, the volume V2 occupied by the bubbles was calculated based on the following formula. The density of the test pieces was ρ (g / cm 3 ) Volume occupied by the bubble V2=V1-W1 / ρ Next, the test piece was submerged in distilled water at 23°C to a depth of 100 mm from the water surface, and a pressure of 15 kPa was applied to the test piece for 3 minutes. After that, the test piece was taken out of the water, and the water adhering to the surface of the test piece was removed. The mass W2 of the test piece was measured, and the closed cell ratio F1 was calculated according to the following formula. Closed cell rate F1 (%) = 100-100 x (W2-W1) / V2

[0077] <25% compressive strength> The 25% compressive strength of the resin foam sheets obtained in the examples and comparative examples was measured in accordance with JIS K6767.

[0078] <Oxygen atom content> Using an energy dispersive X-ray analyzer in a scanning electron microscope (JEOL Ltd.'s "JSM-IT100"), the element distribution on the surface of the resin foam sheet was analyzed and the oxygen atom content (mass%) was measured.

[0079] <Contact angle> The contact angle on the surface of a resin foam sheet was measured in accordance with JIS K6768 using a "DM-701" manufactured by KYOWA Corporation. 5 mL of pure water (wetting tension 73 mN / m) was dropped onto a smooth surface, and the measurement was carried out after it had stabilized.

[0080] <Hanging test> As shown in FIG. 3 , first, resin foam sheet 10 (size: 100 mm × 100 mm) was attached to wall surface 25 via adhesive tape 30. Here, adhesive tape 30 had a shear adhesive strength significantly higher than that of silicone-based double-sided adhesive tape 31, which will be described later. In this hanging test, when wall hanger 20 peeled off, it was designed to peel off at the interface between resin foam sheet 10 and silicone-based double-sided adhesive tape 31. Next, wall hanger 20, which had a hook portion as hanging portion 22, was attached to resin foam sheet 10 via silicone-based double-sided adhesive tape 31 under pressure at a load of 1 kg for 5 seconds, thereby attaching wall hanger 20 to resin foam sheet 10. Thereafter, 1.1 kg weight 32 was hung on the hook portion of wall hanger 20 and allowed to stand. The time until wall hanger 20 peeled off from resin foam sheet 10 was measured and recorded as the holding time. The test was conducted at room temperature (23°C). The wall hanging device 20 and the silicone double-sided adhesive tape 31 are manufactured under the trade name "Command TMThe commercially available product sold as "Hook for Outdoor Use CMO-30" (manufactured by 3M) was used. The silicone double-sided adhesive tape 31 had adhesive layers made of silicone adhesive on both sides of the substrate.

[0081] Example 1 The polyolefin resin for the middle layer was a linear low-density polyethylene resin obtained by a metallocene catalyst (manufactured by Japan Polyethylene Co., Ltd., product name "Kernel KF283", density: 0.921 g / cm 3 ), and azodicarbonamide were prepared as a thermally decomposable foaming agent. Furthermore, zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., product name "OW-212F") was prepared as a decomposition temperature regulator, and 2,6-di-t-butyl-p-cresol, a phenolic antioxidant, was prepared as an antioxidant. 100 parts by mass of polyolefin resin, 8.0 parts by mass of the thermally decomposable foaming agent, 1 part by mass of the decomposition temperature regulator, and 0.5 parts by mass of the antioxidant were each supplied to a second extruder and melt-kneaded at 130°C to produce a foamable composition for the middle layer. Next, an ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, product name "Ultrathene (registered trademark) 626") was prepared as a raw material for the resin composition for the outer layer. 100 parts by mass of the ethylene-vinyl acetate copolymer and 0.5 parts by mass of an antioxidant were supplied to a first extruder and a third extruder, respectively, and melt-kneaded at 130°C to produce a resin composition for the outer layer.

[0082] The foamable composition for the middle layer was co-extruded from the second extruder, and the resin composition for the outer layer was co-extruded from the first extruder and the third extruder, respectively, to obtain an unfoamed multilayer sheet having a layer made of the foamable composition for the outer layer and layers made of the resin composition for the outer layer laminated on both sides of the layer. Next, the multilayer sheet was crosslinked by irradiating it with 2.5 Mrad of an electron beam at an acceleration voltage of 500 kV, and then continuously sent into a foaming furnace maintained at 250°C using hot air and an infrared heater to heat and foam it, thereby obtaining a three-layer resin foam sheet having an outer layer (resin film layer), a middle layer (foamed resin layer), and another outer layer (resin film layer) in that order.

[0083] <Example 2> A resin foam sheet was produced in the same manner as in Example 1, except that the raw material of the resin composition for the outer layer was changed to an acid-modified polyolefin-based resin (Tokyo Materials Co., Ltd., product name "BONDINE TX8030", maleic anhydride-modified polyethylene-based resin, acid modification amount 3% by mass).

[0084] Example 3 A resin foam sheet was produced in the same manner as in Example 1, except that the raw material of the resin composition for the outer layer was changed to an acid-modified polyolefin resin (Tokyo Materials Co., Ltd., product name "OREVAC 18362"), a maleic anhydride-modified polyethylene resin, with an acid modification amount of 0.1% by mass.

[0085] Example 4 A resin foam sheet was produced in the same manner as in Example 1, except that the raw material for the resin composition for the outer layer was changed to an olefin copolymer resin (manufactured by Sumitomo Chemical Co., Ltd., product name "Acryft WH206", ethylene-methyl methacrylate copolymer).

[0086] <Example 5> A resin foam sheet having a three-layer structure having an outer layer (foamed resin layer), a middle layer (foamed resin layer), and another outer layer (foamed resin layer) in this order was obtained in the same manner as in Example 1, except that 1.0 part by mass of a thermally decomposable foaming agent and 1 part by mass of a decomposition temperature regulator were added to the raw materials of the resin composition for the outer layer. A resin foam sheet was produced.

[0087] Example 6 A resin foam sheet was produced in the same manner as in Example 1, except that the raw materials for the resin composition for the outer layer were changed to a mixture of linear low-density polyethylene resin (product name "Kernel KF283") and acid-modified polyolefin resin (product name "BONDINE TX8030") in a mass ratio of 8:2, and the amount of foaming agent was changed as shown in Table 1.

[0088] Example 7 A resin foam sheet was produced in the same manner as in Example 1, except that the raw materials for the resin composition for the outer layer were changed to a 65:35 (mass ratio) mixture of linear low-density polyethylene resin (product name "Kernel KF283") and acid-modified polyolefin resin (product name "BONDINE TX8030").

[0089] Example 8 A resin foam sheet was produced in the same manner as in Example 1, except that the raw materials for the resin composition for the outer layer were changed to a mixture of a linear low-density polyethylene resin (product name "Kernel KF283") and an acid-modified polyolefin resin (Tokyo Materials Co., Ltd., product name "LOTADER AX8900", epoxy group-modified polyethylene resin, modification amount 8% by mass) in a mass ratio of 8:2, and that the amount of foaming agent was changed as shown in Table 1.

[0090] <Examples 9 and 10> The same procedure as in Example 8 was carried out, except that the blending amount of the thermally decomposable foaming agent in the resin layer composition for the middle layer was changed as shown in Table 1.

[0091] Example 11 A resin foam sheet was produced in the same manner as in Example 1, except that the raw materials for the resin composition for the outer layer were changed to a mixture of a linear low-density polyethylene resin (product name "Kernel KF283") and an acid-modified polyolefin resin (manufactured by SK Polymer, product name "Primacor 3440", acrylic acid-modified polyethylene resin, acid modification amount 9% by mass) in a mass ratio of 8:2.

[0092] <Comparative Example 1> A resin foam sheet was produced in the same manner as in Example 1, except that the raw material of the resin composition for the outer layer was changed to a linear low-density polyethylene resin (manufactured by Japan Polyethylene Corporation, trade name "Kernel KF283").

[0093] <Comparative Example 2> A resin foam sheet was produced in the same manner as in Example 1, except that the outer layer was omitted.

[0094] <Comparative Example 3> A syrup-like curable acrylic resin composition with a viscosity of 2000 mPa·s was prepared by mixing 75 parts by weight of methyl acrylate (Nippon Shokubai Co., Ltd.), 25 parts by weight of butyl acrylate (Nippon Shokubai Co., Ltd.), and 0.5 parts by weight of a photopolymerization initiator (BASF Japan Ltd., product name "Irgacure 184") and partially polymerizing it using ultraviolet light. This resin composition was then mixed with 2 parts by weight of a bifunctional crosslinker (product name "NK Ester APG-400"; Shin-Nakamura Chemical Co., Ltd.), 1 part by weight of a trifunctional crosslinker (product name "NK Ester A-9300-3CL"; Shin-Nakamura Chemical Co., Ltd.), and 2 parts by weight of hollow particles (product name "Expancel 920DE80d30"; Nippon Phillite Co., Ltd.) to prepare the final curable acrylic resin composition. This was applied to a release paper at 23°C and irradiated with ultraviolet light to produce a resin foam sheet with a thickness of 200 μm. The ultraviolet light had an illuminance of 4 mW / cm. 2 , Light intensity: 720mJ / cm 2 The irradiation was carried out under the following conditions.

[0095] <Comparative Examples 4 and 5> The same procedure as in Comparative Example 1 was carried out, except that the blending amount of the thermally decomposable foaming agent in the resin layer composition for the middle layer was changed as shown in Table 1.

[0096] [Table 1] *In the hanging test, 3 hours indicates that the wall hanging device did not peel off even after 3 hours and the hanging time was 5 minutes or more.

[0097] As shown in Table 1 above, in each example, a resin foam sheet having first and second resin layers, a contact angle of 36 to 95°, and a 25% compressive strength of 250 kPa or less was used, which enabled high shear strength while maintaining high flexibility. Therefore, as shown in the hanging test, even when the resin foam sheet was used in an adhesive tape for fixing a wall hanger, which uses a silicone adhesive, the wall hanger was prevented from falling. In contrast, in Comparative Examples 1, 2, 4, and 5, a resin foam sheet with a contact angle greater than 95° was used, which failed to increase the shear holding strength, and when used in an adhesive tape for fixing a wall hanger, which uses a silicone adhesive, the wall hanger fell off in a short time.Furthermore, in Comparative Example 3, a resin foam sheet with a compressive strength greater than 250 kPa was used, which failed to ensure the flexibility of the resin foam sheet. [Explanation of symbols]

[0098] 10. Resin foam sheet (adhesive tape base material) 11 First resin layer (middle layer) 12A, 12B Second resin layer (outer layer) 15 double-sided adhesive tape 16A, 16B adhesive material 20 Wall Hanging Device 21 Base 22 Hanging part 25 Wall 30 adhesive tape 31 Silicone double-sided adhesive tape 32 weights

Claims

1. a middle layer formed of a first resin layer which is a foamed resin layer; and outer layers provided on both sides of the middle layer, each of which is formed of a resin film layer; the resin constituting the middle layer contains a polyolefin-based resin, the resin used in the outer layer is at least one resin selected from the group consisting of polyolefin-based resins, modified polyolefin-based resins, and acrylic-based resins, The contact angle of at least one surface is 36 to 95°, 25% compressive strength is 250 kPa or less, and A resin foam sheet having a thickness of 0.1 to 3.0 mm.

2. The resin foam sheet according to claim 1, wherein the resin foam sheet has a thickness of 830 μm to 3.0 mm.

3. The expansion ratio of the resin foam sheet is 1.5 to 20 cm ３ The resin foam sheet according to claim 1 , wherein the elastic modulus is 1 / g.

4. The resin foam sheet according to claim 1 , which has a closed-cell structure.

5. The resin foam sheet according to any one of claims 1 to 4, wherein the oxygen atom content of each of the outer layers is 3.5% by mass or more.

6. The resin foam sheet according to claim 1, which is used as a substrate for an adhesive tape for fixing a wall hanger.

7. The resin foam sheet according to claim 1, which has a retention time of 5 minutes or more in the following hanging test. <Hanging test> A wall hanger having a hook portion is attached to the resin foam sheet attached to the wall surface by pressing the wall hanger with a silicone double-sided adhesive tape under a load of 1 kg for 5 seconds, and then a 1.1 kg weight is hung on the hook portion of the wall hanger and allowed to stand. The time until the wall hanger peels off the resin foam sheet is measured and taken as the retention time.

8. An adhesive tape comprising the resin foam sheet according to claim 1 and an adhesive material on at least one surface of the resin foam sheet.

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