Foam sheet

Abstract

To provide a foam sheet having cushioning, vibration-proof, and low-dielectric properties.SOLUTION: A foam sheet has at least one glass transition temperature (Tg) of 0-40°C, a loss tangent (tanδ) peak value of 0.30 or more at the glass transition temperature (Tg), a 25% compression strength of 1000 kPa or less, and a relative dielectric constant of 2 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a foam sheet, for example, a foam sheet used as a cushioning material for displays. [Background technology]

[0002] In portable electronic devices such as notebook personal computers, mobile phones, smartphones, and tablets, cushioning materials are often placed on the backside of the display devices to prevent damage or malfunction. High flexibility is required for the cushioning materials, and foam sheets have been widely used. A foam sheet may be used inside an electronic device as an adhesive tape by applying an adhesive to at least one surface thereof. Conventionally, a crosslinked polyolefin resin foam sheet obtained by foaming and crosslinking an expandable polyolefin resin sheet containing a thermal decomposition type foaming agent has been known as a foam sheet used in such applications (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-28925 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, as electronic devices have become more sophisticated, the acoustic capabilities of portable electronic devices such as smartphones have improved. This has led to the problem of increased vibration in portable electronic devices, particularly when glass or polycarbonate materials are used for the back cover for wireless power supply. Specifically, foam sheets are used as cushioning materials between the battery and the back glass, etc., to provide shock-absorbing properties, and these foam sheets are required to have vibration-damping properties. In addition, as smartphones are increasingly being converted to 5G, low dielectric properties are required for foam sheets to reduce communication delays. Therefore, an object of the present invention is to provide a foam sheet that has vibration-proofing properties and low dielectric properties in addition to the cushioning properties that have been conventionally required of foams. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the above problems can be solved by setting the glass transition temperature (Tg), loss tangent (tanδ), and compressive strength within certain ranges and setting the relative dielectric constant to a certain value or less, and have completed the present invention. That is, the present invention provides the following [1] to

[16] .

[0006] [1] A foam sheet having at least one glass transition temperature (Tg1) of 0 to 40°C, a peak value of loss tangent (tanδ) at the glass transition temperature (Tg1) of 0.30 or more, a 25% compressive strength of 1000 kPa or less, and a relative dielectric constant of 2 or less. [2] The foam sheet according to [1] above, which has a 25% compressive strength of 800 kPa or less. [3] The foam sheet according to the above [1] or [2], which has a thickness of 0.03 to 2 mm. [4] The foam sheet according to any one of the above [1] to [3], which has a breaking strength at 23°C of 5 N / 10 mm or more. [5] The foam sheet according to any one of the above [1] to [4], which has a closed cell rate of 80% or more. [6] The foam sheet according to any one of the above [1] to [5], wherein the average cell diameter is 20 to 400 μm. [7] The foam sheet according to any one of the above [1] to [6], which has a gel fraction of 30 to 80% by mass. [8] Apparent density: 0.05 to 0.70 g / cm 3 The foam sheet according to any one of the above [1] to [7], wherein [9] Water vapor transmission rate (WVTR) is 400g / m 2The foam sheet according to any one of the above [1] to [8], wherein the average daily limit is 10 days or less.

[10] The foam sheet according to any one of the above [1] to [9], which has a glass transition temperature (Tg2) of −40° C. or lower.

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

[10] , which has an elongation at break of 200% or more at 23°C.

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

[11] , wherein the resin constituting the foam sheet contains a polyolefin resin.

[13] The foam sheet according to

[12] above, wherein the resin constituting the foam sheet further contains an elastomer.

[14] The foam sheet according to the above

[13] , wherein the mass ratio of the elastomer to the polyolefin resin is 90:10 to 15:85.

[15] An adhesive tape comprising the foam sheet according to any one of [1] to

[14] above and an adhesive material provided on at least one surface of the foam sheet.

[16] A roll made of the foam sheet according to any one of [1] to

[14] above. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a foam sheet that has not only shock-absorbing properties but also vibration-proof properties and low dielectric properties. DETAILED DESCRIPTION OF THE INVENTION

[0008] The foam sheet of the present invention will be described in more detail below. [Foam sheet] The foam sheet of the present invention is characterized by having at least one glass transition temperature (hereinafter sometimes referred to as "Tg") of 0 to 40°C, a peak value of loss tangent (tanδ) at the glass transition temperature (Tg1) of 0.30 or more, a 25% compressive strength of 1000 kPa or less, and a relative dielectric constant of 2 or less.

[0009] [Glass transition temperature and loss tangent] The foam sheet of the present invention has at least one glass transition temperature (Tg1) in the range of 0 to 40°C, and the peak value of the loss tangent (tanδ) at Tg1 is 0.30 or higher. When Tg1 and tanδ are within the above ranges, the foam sheet of the present invention exhibits excellent vibration-proofing properties. In the present invention, the Tg is defined as the temperature at the peak top of the loss tangent (tanδ) obtained by viscoelasticity measurement. In addition, in this specification, a Tg in the range of 0 to 40°C may be referred to as Tg1. Tan δ is the ratio (G" / G') of the storage shear modulus (G') to the loss shear modulus (G"), and is an index showing how much energy a material absorbs (converts to heat) when it deforms. The foam sheet of the present invention has a glass transition temperature (Tg1) in the range of 0 to 40°C, which is close to room temperature, and the peak value of tan δ at the glass transition temperature is 0.30 or more, thereby improving energy loss in the low frequency range and, as a result, exhibiting excellent vibration-damping properties. From the above viewpoints, the peak value of tan δ is preferably 0.35 or more, more preferably 0.37 or more, even more preferably 0.39 or more, and particularly preferably 0.40 or more. The glass transition temperature (Tg) and loss tangent (tan δ) are values ​​measured by the method described in the examples. Here, when two or more Tg points are observed, it is preferable that at least one Tg point is in the range of 0 to 40° C., and the peak value of tan δ at that Tg is within the above range.

[0010] Furthermore, the foam sheet of the present invention preferably has a glass transition temperature of -40°C or lower. By having a Tg of -40°C or lower, flexibility can be ensured even in cold regions, and cracking of the foam sheet can be prevented. In this specification, a Tg of -40°C or lower may be referred to as Tg2. Tg2 is more preferably -60°C or lower, and even more preferably -80°C or lower. There is no particular lower limit to Tg2, but it is preferably -150°C or higher, more preferably -140°C or higher, and even more preferably -130°C or higher.

[0011] [Compression strength] The foam sheet of the present invention has a 25% compressive strength of 1000 kPa or less. If the compressive strength exceeds 1000 kPa, the flexibility is insufficient, which may cause damage to internal components of portable electronic devices. Furthermore, insufficient flexibility results in poor conformability, and when used as a tape substrate, for example, the adhesive strength during bonding is insufficient. From these viewpoints, the 25% compressive strength is more preferably 900 kPa or less, even more preferably 800 kPa or less, and particularly preferably 600 kPa or less. There is no particular restriction on the lower limit of the 25% compressive strength, but it is usually about 10 kPa, and preferably 20 kPa or more. The 25% compressive strength is a value measured at a temperature of 23°C using a measurement method in accordance with JIS K6767.

[0012] [Dielectric constant] The foam sheet of the present invention has a relative dielectric constant of 2 or less. If the relative dielectric constant exceeds 2, communication delays may occur, and communication delays are particularly likely to occur when the foam sheet is used in 5G-compatible electronic devices. Furthermore, if the relative dielectric constant exceeds 2, it may cause operational errors in the electronic devices. From the above viewpoints, the relative dielectric constant is preferably 1 to 1.80, more preferably 1 to 1.70, and even more preferably 1 to 1.55. The relative dielectric constant is a value measured by the method described in the examples. The relative dielectric constant can be adjusted appropriately by changing the type of resin constituting the foam sheet, the apparent density, and the like.

[0013] Thickness The thickness of the foam sheet of the present invention is preferably 0.03 to 2 mm. When the thickness is 0.03 mm or more, it is easy to ensure the cushioning properties of the foam sheet. Furthermore, when the thickness is 2 mm or less, it becomes possible to make the foam sheet thinner, and it is suitable for use in thin electronic devices such as smartphones and tablets. Furthermore, it is easy to ensure the flexibility of the foam sheet. From these viewpoints, the thickness of the foam sheet is more preferably 0.1 to 1.8 mm, even more preferably 0.15 to 1.6 mm, and even more preferably 0.15 to 0.7 mm. The thickness was measured using a dial gauge.

[0014] [Breaking strength] The strength at break of the foam sheet of the present invention at 23°C is preferably 5 N / 10 mm or more. When the strength at break is 5 N / 10 mm or more, good impact resistance is obtained. From the above viewpoints, the strength at break is more preferably 5.5 N / 10 mm or more, even more preferably 6 N / 10 mm or more, and even more preferably 7 N / 10 mm or more. There is no particular upper limit to the strength at break, but it is usually about 50 N / 10 mm, and preferably 40 N / 10 mm or less. The strength at break is a value measured by the method described in the examples.

[0015] [Elongation at break] The foam sheet of the present invention preferably has an elongation at break of 200% or more at 23°C. When the elongation at break is 200% or more, good impact resistance is obtained. From the above viewpoints, the elongation at break is more preferably 300% or more, and even more preferably 400% or more. There is no particular upper limit to the elongation at break, but it is usually about 800%, preferably 600% or less. The elongation at break is a value measured by the method described in the examples.

[0016] [Closed bubble rate] The foam sheet of the present invention preferably has a closed cell ratio of 80% or more. A closed cell ratio of 80% or more improves cushioning properties and impact resistance, and the foam sheet tends to maintain its original elasticity even after heating or cooling. Another advantage is that the rate of change in compressive strength tends to be low. From the above viewpoints, it is more preferable that the closed cell ratio of the foam sheet is 90% or more. The higher the closed cell ratio, the better, but it is sufficient as long as it is 100% or less. The closed cell ratio was measured by the method described in the examples.

[0017] [Average bubble diameter] The foam sheet of the present invention preferably has an average cell diameter of 20 to 400 μm. When the average cell diameter is within the above range, the impact resistance is good. From the above viewpoints, the average cell diameter is more preferably 50 to 350 μm, even more preferably 70 to 300 μm, and even more preferably 70 to 220 μm. The average cell diameter in the present invention is the larger of the average cell diameter in the machine direction (MD) and the average cell diameter in the direction perpendicular to the MD (TD). The average cell diameter was measured by the method described in the examples.

[0018] [Crosslinking degree (gel fraction)] The foam sheet of the present invention is preferably crosslinked, and the degree of crosslinking, expressed as gel fraction, is preferably 30 to 80% by mass. By setting the degree of crosslinking within this range, the foam sheet tends to have good impact resistance while ensuring a certain level of flexibility and cushioning properties. From the above viewpoints, the gel fraction is more preferably 35 to 70% by mass, and even more preferably 38 to 65% by mass. The gel fraction was measured by the method described in the examples.

[0019] [Apparent Density] The apparent density of the foam sheet of the present invention is 0.05 g / cm 3 ~0.70g / cm 3 It is preferable that the density is 0.06 g / cm 3 ~0.65g / cm 3 More preferably, it is 0.07 g / cm 3 ~0.60g / cm 3More preferably, it is 0.10 g / cm 3 ~0.45g / cm 3 It is particularly preferred that: When the apparent density is within the above range, the flexibility, cushioning properties, dielectric constant, etc. of the foam sheet are likely to be good. In addition, a certain level of mechanical strength is imparted to the foam sheet, and impact resistance, handling properties, etc. are likely to be good. The apparent density is a value measured in accordance with JIS K7222 (2005).

[0020] [Moisture permeability] The foam sheet of the present invention has a water vapor transmission rate (WVTR) of 400 g / m 2 ·day or less. 2 ·day or less, it is possible to prevent moisture from entering the inside of electronic devices, etc. From the above viewpoint, the moisture permeability is set to 200 g / m 2 ·day or less is preferable, 100g / m 2 ·day or less is more preferable, 80g / m 2 ·days or less is particularly preferable. There is no particular limit on the lower limit, but it is usually 5 g / m 2 It is about a day. The moisture permeability is a value measured by the method described in the examples.

[0021] [Component resin] The resin constituting the foam sheet of the present invention preferably contains a polyolefin resin. The inclusion of a polyolefin resin can impart strength to the foam sheet. Furthermore, the constituent resin preferably contains an elastomer, and the constituent resin preferably contains an elastomer (A) and a polyolefin resin (B). The use of an elastomer and a polyolefin resin can improve the foamability and other properties while also improving flexibility, impact resistance, and dielectric constant.

[0022] The elastomer according to the present invention preferably has a maximum peak temperature of tan δ measured by dynamic viscoelasticity measurement of 0 to 40°C. When the maximum peak temperature of tan δ is close to room temperature, sound absorption properties are improved and vibration damping properties are likely to be improved. From the above viewpoints, the maximum peak temperature of tan δ of the elastomer is more preferably 5 to 35°C, and even more preferably 10 to 30°C. In this specification, the "maximum peak temperature of tan δ" refers to a value measured using a dynamic viscoelasticity measuring device in a tensile mode at a temperature rise rate of 10°C / min and a frequency of 10 Hz. Examples of dynamic viscoelasticity measuring devices that can be used for the measurement include the "Rheovibron DDV-III" manufactured by Orientec Co., Ltd.

[0023] (Elastomer (A)) Examples of the elastomer (A) include thermoplastic elastomers, ethylene-α-olefin copolymer rubbers, and amorphous 4-methyl-1-pentene copolymers. Examples of the thermoplastic elastomer include olefin thermoplastic elastomers, styrene thermoplastic elastomers, vinyl chloride thermoplastic elastomers, polyurethane thermoplastic elastomers, polyester thermoplastic elastomers, and polyamide thermoplastic elastomers. The elastomer (A) may be used alone or in combination of two or more of these components. Among these, olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, and ethylene-α-olefin-based copolymer rubbers are preferred, styrene-based thermoplastic elastomers and ethylene-α-olefin-based copolymer rubbers are more preferred, and styrene-based thermoplastic elastomers are even more preferred.

[0024] <Olefin-based thermoplastic elastomer> Olefin-based thermoplastic elastomers (TPO) generally have polyolefins such as polyethylene and polypropylene as hard segments and rubber components such as butyl rubber, halobutyl rubber, EPDM (ethylene-propylene-diene rubber), EPM (ethylene-propylene rubber), NBR (acrylonitrile-butadiene rubber), and natural rubber as soft segments. Any of the blend, dynamic crosslink, and polymerization types of olefin-based thermoplastic elastomers (TPO) can be used. Specific examples of suitable rubber components include the above-mentioned EPM and EPDM, with EPDM being particularly preferred. EPDM includes ethylene-propylene-5-ethylidene-2-norbornene copolymer rubber and ethylene-propylene-dicyclopentadiene copolymer rubber, with ethylene-propylene-dicyclopentadiene copolymer rubber being preferred.

[0025] Further, olefin-based thermoplastic elastomers include block copolymer types. Block copolymer types include those having a crystalline block and a soft segment block, and more specifically, crystalline olefin block-ethylene-butylene copolymer-crystalline olefin block copolymer (CEBC). In CEBC, the crystalline olefin block is preferably a crystalline ethylene block, and commercially available CEBCs include "DYNARON 6200P" manufactured by JSR Corporation.

[0026] <Styrene-based thermoplastic elastomer> Examples of styrene-based thermoplastic elastomers include block copolymers having a styrene polymer or copolymer block and a conjugated diene compound polymer or copolymer block, such as isoprene and butadiene. The styrene-based thermoplastic elastomer used in the present invention may or may not be hydrogenated, but is preferably hydrogenated. When hydrogenated, the hydrogenation can be carried out by a known method.

[0027] Styrene-based thermoplastic elastomers are usually block copolymers, such as styrene-isoprene block copolymer (SI), styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene block copolymer (SB), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene / butylene-styrene block copolymer (SEBS), styrene-ethylene / propylene-styrene block copolymer (SEPS), styrene-ethylene / ethylene / propylene-styrene block copolymer (SEEPS), styrene-ethylene / butylene block copolymer (SEB), styrene-ethylene / propylene block copolymer (SEP), and styrene-ethylene / butylene-crystalline olefin block copolymer (SEBC). As the styrene-based thermoplastic elastomer, a block copolymer is preferred, and among them, SIS, SEBS, SEPS, SEEPS and SEBC are more preferred, SEEPS and SEBS are further preferred, and SEBS is particularly preferred. Commercially available SEBS products include the Tuftec (registered trademark) series and the SOE (registered trademark) series manufactured by Asahi Kasei Corporation.

[0028] The styrene-based thermoplastic elastomer contains structural units derived from styrene, which allows the foam sheet to have good impact resistance. The styrene content in the styrene-based thermoplastic elastomer is preferably 5 to 50% by mass. By setting the styrene content within this range, excellent impact resistance can be obtained. Furthermore, by setting the styrene content to the above upper limit or less, compatibility with the polyolefin resin (B), which will be described in detail later, is improved, and crosslinkability and foamability tend to be good. From these viewpoints, the styrene content in the styrene-based thermoplastic elastomer is more preferably 7 to 40% by mass, and even more preferably 7 to 30% by mass.

[0029] The number average molecular weight of the styrene-based thermoplastic elastomer is not particularly limited, but from the viewpoints of breaking strength and processability, it is preferably 30,000 to 800,000, more preferably 120,000 to 180,000. The number average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0030] <Ethylene-α-olefin copolymer rubber> Examples of the α-olefin used in the ethylene-α-olefin copolymer rubber include one or more α-olefins having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms, such as propylene, 1-butene, 2-methylpropylene, 3-methyl-1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Among these, propylene and 1-butene are preferred, and 1-butene is more preferred. The ethylene-α-olefin copolymer rubber used here is an amorphous or low-crystalline rubber-like substance in which two or more olefin monomers are copolymerized substantially randomly.

[0031] The ethylene-α-olefin copolymer rubber may have other monomer units in addition to the ethylene units and α-olefin units. Examples of monomers that form the other monomer units include conjugated dienes having 4 to 8 carbon atoms, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene; non-conjugated dienes having 5 to 15 carbon atoms, such as dicyclopentadiene, 5-ethylidene-2-norbornene, 1,4-hexadiene, 1,5-dicyclooctadiene, 7-methyl-1,6-octadiene, and 5-vinyl-2-norbornene; vinyl ester compounds, such as vinyl acetate; unsaturated carboxylic acid esters, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and ethyl methacrylate; and unsaturated carboxylic acids, such as acrylic acid and methacrylic acid. These monomers may be used alone or in combination of two or more. Among these, non-conjugated dienes having 5 to 15 carbon atoms are preferred, and from the viewpoint of availability, 5-ethylidene-2-norbornene, 1,4-hexadiene, and dicyclopentadiene (DCPD) are more preferred.

[0032] The ethylene unit content of the ethylene-α-olefin copolymer rubber is usually 30 to 85 mass%, preferably 40 to 80 mass%, more preferably 45 to 75 mass%. The content of α-olefin units having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms, such as propylene, is usually 10 to 60 mass%, preferably 15 to 50 mass%. The content of other monomer units, such as non-conjugated dienes, is usually 0 to 20 mass%, preferably 1 to 10 mass%.

[0033] The ethylene-α-olefin copolymer rubber is preferably a terpolymer such as EPDM (ethylene-propylene-diene rubber) or EBDM (ethylene-butene-1-diene rubber). Examples of the ethylene-α-olefin copolymer include "EBT K-9330" manufactured by Mitsui Chemicals, Inc.

[0034] <Amorphous 4-methyl-1-pentene copolymer> Examples of amorphous 4-methyl-1-pentene copolymers include copolymers of 4-methyl-1-pentene and an α-olefin other than 4-methyl-1-pentene. Examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, preferably ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-decene, and more preferably ethylene and propylene. Among these, a 4-methyl-1-pentene / propylene copolymer is preferred. An example of the amorphous 4-methyl-1-pentene copolymer is "EP1001" manufactured by Mitsui Chemicals, Inc.

[0035] (Polyolefin resin (B)) Polyolefin resins are thermoplastic resins, and specific examples thereof include polyethylene resins, polypropylene resins, polybutene resins, and ethylene-vinyl acetate copolymers. Among these, polyethylene resins are preferred. By using polyethylene resins, it is easy to reduce the relative dielectric constant and moisture permeability. As the polyethylene resin, low-density polyethylene (LDPE) is preferred, and linear low-density polyethylene (LLDPE) is more preferred. Therefore, it is particularly preferred to use a styrene-based thermoplastic elastomer as the elastomer (A) and LLDPE as the polyolefin resin (B). Furthermore, examples of the polyethylene resin include polyethylene resins polymerized with a polymerization catalyst such as a Ziegler-Natta catalyst, a metallocene catalyst, or a chromium oxide compound, and polyethylene resins polymerized with a metallocene catalyst are preferably used.

[0036] (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.

[0037] 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, phosphides, arylphosphides, etc. may also be used.

[0038] 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.

[0039] Moreover, the polyethylene resin is preferably a linear low-density polyethylene. The linear low-density polyethylene is more 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 the polyethylene resin, for example, the linear low-density polyethylene described above, is 0.870 to 0.925 g / cm 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, a plurality of polyethylene resins may be used, and a polyethylene resin having a density outside the above range may be added.

[0040] The ethylene-vinyl acetate copolymer used as the polyolefin resin is, for example, an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene. Examples of polypropylene resins include homopolypropylene and propylene-α-olefin copolymers containing 50% by mass or more of propylene. These may be used alone or in combination of two or more. Specific examples of α-olefins constituting the propylene-α-olefin copolymers include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Of these, α-olefins having 6 to 12 carbon atoms are preferred. Examples of polybutene resins include homopolymers of butene-1 and copolymers with ethylene or propylene.

[0041] [Mass ratio of elastomer (A) to polyolefin resin (B)] The mass ratio of the elastomer (A) to the polyolefin resin (B) is preferably 90:10 to 15:85. Within this range, a foam sheet that exhibits the effects of the present invention can be easily produced. From the viewpoint of obtaining a foam sheet with even greater effects, the mass ratio of the (A) component to the (B) component is more preferably within the range of 80:20 to 20:80, and even more preferably 80:20 to 30:70.

[0042] [Additives] The foam sheet of the present invention is preferably obtained by foaming a foamable composition containing the above-mentioned resin and a foaming agent, preferably a thermally decomposable foaming agent. 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.

[0043] The amount of foaming agent in the foamable composition is preferably 1 part by mass or more and 20 parts by mass or less, more preferably 1.5 parts by mass or more and 15 parts by mass or less, and even more preferably 3 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the resin. By using a foaming agent amount of 1 part by mass or more, the foamable sheet is foamed appropriately, making it possible to impart appropriate flexibility and impact absorption to the foam sheet. Furthermore, by using a foaming agent amount of 20 parts by mass or less, the foam sheet is prevented from foaming more than necessary, making it possible to improve the mechanical strength of the foam sheet.

[0044] The foamable composition may contain a decomposition temperature regulator. The decomposition temperature regulator is added to have a regulating function, such as lowering the decomposition temperature of the thermally decomposable foaming agent or accelerating the decomposition rate. Specific examples of the decomposition temperature regulator include zinc oxide, zinc stearate, and urea. The decomposition temperature regulator is added in an amount of, for example, 0.01 to 5 parts by mass per 100 parts by mass of the resin in order to adjust the surface condition of the foam sheet.

[0045] The foamable composition may contain an antioxidant. 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 antioxidant is blended in an amount of, for example, 0.01 to 5 parts by mass per 100 parts by mass of the resin. In addition to the above, the foamable composition may contain additives that are generally used in foams, such as heat stabilizers, colorants, flame retardants, antistatic agents, and fillers.

[0046] In the foam sheet, the elastomer (A) and the polyolefin resin (B) are the main components, and the total content of the (A) component and the (B) component is, for example, 70 mass % or more, preferably 80 mass % or more, and more preferably 90 mass % or more, based on the total amount of the foam sheet.

[0047] [Method of manufacturing foam sheet] The foam sheet of the present invention is not particularly limited, but can be produced by heating a foamable sheet made of a foamable composition containing at least a resin and a thermally decomposable foaming agent to foam the thermally decomposable foaming agent. Preferably, the foamable sheet is crosslinked and the crosslinked foamable sheet is heated to foam. More specifically, the method for producing a foam sheet preferably includes the following steps (1) to (3). Step (1): A step of forming a foamable sheet from a foamable composition containing at least a resin and a thermally decomposable foaming agent. Step (2): A step of irradiating the foamable sheet with ionizing radiation to crosslink the foamable sheet. Step (3): A step of heating the crosslinked expandable sheet to expand the thermally decomposable foaming agent, thereby obtaining a foam sheet.

[0048] In step (1), the method for forming the foamable sheet is not particularly limited, but may be, for example, by feeding the resin and additives to an extruder, melt-kneading them, and extruding the foamable composition from the extruder into a sheet. Alternatively, the foamable sheet may be formed by pressing the foamable composition. The forming temperature of the foamable sheet (i.e., the temperature during extrusion or pressing) is preferably 50°C or higher and 250°C or lower, more preferably 80°C or higher and 180°C or lower.

[0049] In step (2), the foamable composition is crosslinked by irradiating the foamable sheet with ionizing radiation such as electron beams, α-rays, β-rays, γ-rays, etc. The dose of the ionizing radiation may be adjusted so that the degree of crosslinking of the resulting foam sheet falls within the desired range, and is preferably 1 to 12 Mrad, more preferably 1.5 to 10 Mrad.

[0050] In step (3), the heating temperature when the foamable composition is heated to foam the thermally decomposable foaming agent may be equal to or higher than the foaming temperature of the thermally decomposable foaming agent, but is preferably 200 to 300° C., more preferably 220 to 280° C. In step (3), the foamable composition is foamed to form bubbles, resulting in a foam.

[0051] In the present production method, the foam sheet may be thinned by rolling, stretching, or the like.

[0052] However, the present production method is not limited to the above, and a foam sheet may be obtained by a method other than the above. For example, instead of irradiating with ionizing radiation, crosslinking may be performed by a method in which an organic peroxide is blended in advance with the foamable composition, and the foamable sheet is heated to decompose the organic peroxide. If crosslinking is not required, step (2) may be omitted, and in that case, in step (3), the uncrosslinked expandable sheet may be heated to expand it.

[0053] [Adhesive tape] The foam sheet of the present invention may be used in an adhesive tape using the foam sheet as a substrate. The adhesive tape, for example, comprises a foam sheet and an adhesive material provided on at least one surface of the foam sheet. The adhesive tape can be adhered to other members such as a support member via the adhesive material. The adhesive tape may have adhesive materials provided on both surfaces of the foam sheet or on one surface. The adhesive material may be any material that includes at least a pressure-sensitive adhesive layer, and may be a single pressure-sensitive adhesive layer laminated on the surface of a foam sheet, or a double-sided pressure-sensitive adhesive sheet attached to the surface of a foam sheet, but is preferably a single pressure-sensitive adhesive layer. 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 is used to adhere one pressure-sensitive adhesive layer to a foam sheet and the other pressure-sensitive adhesive layer to another member.

[0054] The adhesive constituting the adhesive layer is not particularly limited, and for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, etc. Furthermore, a release sheet such as release paper may be further attached onto the adhesive material. The thickness of the pressure-sensitive adhesive layer is preferably 5 to 200 μm, more preferably 7 to 150 μm, and even more preferably 10 to 100 μm.

[0055] [Foam sheet roll] The foam sheet of the present invention can be made into a roll. By making it into a roll, it is easy to store and convenient to transport. When used, it can be unwound from the roll.

[0056] [Uses of foam sheets] The foam sheet may be used as a cushioning material for a display device, although the foam sheet is not particularly limited thereto. Specifically, the foam sheet may be placed on the rear side of a display panel in various electronic devices to cushion shocks acting on the display panel. In this case, the foam sheet may be placed on a support member placed on the rear side of the display panel. The support member may be, for example, a part of the housing of the electronic device. It is also preferable to use it as a cushioning material between the battery and the back cover of a mobile electronic device such as a smartphone, as it can effectively suppress vibrations that occur in the back cover. The foam sheet may be provided with an adhesive material as described above, and may be attached to a display panel, a support member, a back cover material, or the like by the adhesive material. Furthermore, since the foam sheet of the present invention has a peak of tan δ near room temperature, it can exhibit vibration-damping properties and is particularly effective for electronic devices such as smartphones whose back cover material is glass, etc. Electronic devices have built-in acoustic components such as speakers, and the back cover material made of glass, etc. is prone to vibration due to these acoustic components, but the foam sheet of the present invention has excellent vibration-damping properties in the low-frequency band and can effectively prevent vibration. Furthermore, because the foam sheet of the present invention has a low dielectric constant, it does not cause communication delays when used in portable electronic devices such as smartphones, and this effect is particularly pronounced when used in high-speed communication devices such as fifth-generation mobile communication systems (5G). [Example]

[0057] The present invention will be described below with reference to examples, but the present invention is not limited to these examples in any way. The methods for measuring the various physical properties and the methods for evaluating the foam sheets are as follows.

[0058] [Physical properties after molding] (1) Glass transition temperature (Tg) and loss tangent (tanδ) Using a tensile storage modulus measuring device manufactured by IT Measurement Control Co., Ltd., trade name "DVA-200 / L2", Tg and tan δ were determined under the following measurement conditions. (Measurement conditions) Gauge length: 2.5cm Sample width: 0.5cm Sample thickness: Thickness of foam sheet Deformation mode: tension Static / dynamic stress ratio: 1.5 Set distortion: 1.0% Set temperature rise rate: 10℃ / min Measurement frequency 10Hz Temperature range: -150℃~100℃

[0059] (2) Breaking strength and breaking elongation The foamed sheets produced in each of the Examples and Comparative Examples were cut into a dumbbell No. 1 shape as specified in JIS K6251 4.1. Using these as samples, they were subjected to tension in the MD direction at a measurement temperature of 23°C and a speed of 500 mm / min using a tensile tester (product name: Tensilon RTF235, manufactured by A&D Co., Ltd.), and the tensile strength at break (strength at break, unit: N / 10 mm) and tensile elongation (elongation at break, unit: %) were measured.

[0060] (3) Degree of crosslinking (gel fraction) A test piece of about 100 mg was taken from the foam sheet, and the mass A (mg) of the test piece was precisely weighed. Next, this test piece was immersed in 30 cm of xylene at 120°C. 3 After immersion for 24 hours, the insoluble matter on the wire mesh was filtered through a 200-mesh mesh and collected, and then vacuum-dried. The mass B (mg) of the insoluble matter was precisely weighed. The degree of crosslinking (mass%) was calculated from the obtained value using the following formula: Gel fraction (mass%) = 100 × (B / A)

[0061] (4) Closed cell ratio A flat square test piece with a side length of 5 cm was cut out from the foam sheet. The thickness of the test piece was measured to calculate the apparent volume V1 of the test piece, and the mass W1 of the test piece was also measured. Next, the volume V2 occupied by the cells was calculated using the following formula. The density of the test piece 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

[0062] (5) Average bubble diameter The foam sheet was cut in the thickness direction along both the MD and TD, and a 200x magnified photograph was taken using a digital microscope (Keyence Corporation, product name "VHX-900"). In the enlarged photograph, the MD and TD cell diameters of all bubbles present in a 2 mm-long cut surface in each of the MD and TD were measured, and this procedure was repeated five times. The average values ​​of the cell diameters of all bubbles in each of the MD and TD were taken as the average cell diameters in the MD and TD. Here, MD means machine direction and is a direction that coincides with the extrusion direction, etc. TD means transverse direction and is a direction that is perpendicular to MD and parallel to the foam sheet.

[0063] (6) 25% compressive strength Measurement was performed at a temperature of 23°C using a measurement method in accordance with JIS K6767. (7) Apparent density and expansion ratio The apparent density of the foam was measured in accordance with JIS K7222, and the reciprocal thereof was taken as the expansion ratio. (8) Thickness The measurement was carried out using a dial gauge.

[0064] (9) WVTR At a temperature of 40°C, the foam sheets produced in each Example and Comparative Example were cut into pieces of approximately 10 cm x 10 cm, and placed in the measurement section of a water vapor transmission rate measuring device (MOCON, PERMATRAN-W 1 / 50), after which the water vapor transmission rate was measured under conditions of 40°C and 90% RH. The evaluation criteria are as follows: 〇: Moisture permeability (WVTR) is 400g / m 2 ·day or less ×: Water vapor permeability (WVTR) is 400g / m 2 ·day super

[0065] (10) Dielectric constant Using an LCR (impedance) analyzer "PSM3750" manufactured by Iwasaki Electric Co., Ltd., the frequency range from 100 mHz to 10 MHz was divided into logarithmic scales and measured at 33 points for one cycle at room temperature in the air, and the relative permittivity at a frequency of 1 MHz was calculated by reading the resulting waveform.

[0066] [evaluation] (11) Vibration isolation evaluation (frequency vs. loss tangent (tanδ)) A master curve was created using a tensile storage modulus measuring device, product name "DVA-200 / L2" manufactured by IT Measurement & Control Co., Ltd., under the following measurement conditions, and tan δ at each frequency (Hz) was determined. Evaluation was based on the tan δ peak height in the low frequency range (10-1000 Hz) considered effective for vibration. A tan δ peak height of 0.3 or more was considered good (◯), and one below 0.3 was considered poor (×). (Measurement conditions) Gauge length: 2.5cm Sample width: 0.5cm Sample thickness: Thickness of foam sheet Deformation mode: tension Static / dynamic stress ratio: 1.5 Set distortion: 1.0% Set temperature rise rate: 10℃ / min Measurement frequency: Measurements were performed at eight frequencies (0.32, 0.63, 1.25, 2.5, 5, 10, 20, and 40 Hz) in 5°C increments within the temperature range below. Temperature range: -70℃~25℃

[0067] (12) Radio wave interference evaluation The propagation delay time was calculated from the relative dielectric constant using the following formula: If the propagation delay time was less than 4.5 ns / m, it was rated as good (◯), and if it was 4.5 ns / m or more, it was rated as bad (×). In the following formula, ε is the relative dielectric constant, τ is the propagation delay time (ns / m), K is the wavelength shortening rate, and C is the speed of light (3×10 8 m / s).

[0068]

number

[0069] The materials used in the examples and comparative examples are as follows. Elastomer resin (a): SOE (registered trademark) S1609, hydrogenated styrene-based thermoplastic elastomer (SEBS) Elastomer resin (b): EP1001 (Mitsui Chemicals, Inc., 4-methyl-1-pentene / propylene copolymer) Elastomer resin (c): Clarity (registered trademark) LA3320 (manufactured by Kuraray Co., Ltd., acrylic thermoplastic elastomer) Polyolefin resin (a): Kernel (registered trademark) KF283 (Japan Polyethylene Co., Ltd., ethylene / α-olefin copolymer (LLDPE) polymerized with a metallocene catalyst) Polyolefin resin (b): PP-E-333GV (Prime Polymer Co., Ltd., density: 0.9 g / cm 3 , Melt flow rate: 2.4g / 10min) Thermal decomposition type blowing agent: Azodicarbonamide Decomposition temperature regulator: Zinc oxide, manufactured by Sakai Chemical Industry Co., Ltd., product name "OW-212F" Phenolic antioxidant: 2,6-di-t-butyl-p-cresol Crosslinker A: 1,9-nonanediol dimethacrylate Crosslinker B: Trimethylolpropane trimethacrylate

[0070] Example 1 The raw materials used were 40 parts by mass of elastomer resin (a), 60 parts by mass of polyolefin resin (a), 5 parts by mass of a thermally decomposable foaming agent, 1 part by mass of a decomposition temperature regulator, and 0.5 parts by mass of a phenolic antioxidant. These materials were melt-kneaded and then pressed to obtain a foamable resin sheet with a thickness of 0.38 mm. Both sides of the obtained foamable resin sheet were irradiated with 5 Mrad of electron beams at an acceleration voltage of 500 keV to crosslink the foamable resin sheet. Next, the crosslinked foamable resin sheet was heated to 250°C to foam it, resulting in an apparent density of 0.24 g / cm. 3 A foam sheet having a thickness of 0.60 mm was obtained, which was then stretched to an apparent density of 0.24 g / cm. 3 A foam sheet having a thickness of 0.2 mm was obtained. The results of evaluation by the above method are shown in Table 1.

[0071] Example 2 A foam sheet was obtained in the same manner as in Example 1, except that the amount of the thermally decomposable foaming agent was changed to 2.5 parts by mass and the thickness of the foamable resin sheet was changed to 0.36 mm. The apparent density of the foam sheet was 0.48 g / cm. 3 The thickness was 0.45 mm. After that, it was stretched to an apparent density of 0.48 g / cm 3 A foam sheet having a thickness of 0.15 mm was obtained. The evaluation results are shown in Table 1.

[0072] Example 3 A foam sheet was obtained in the same manner as in Example 1, except that the amount of the thermally decomposable foaming agent was changed to 6.5 parts by mass, the thickness of the foamable resin sheet was changed to 0.33 mm, and the electron beam irradiation dose was changed to 4 Mrad. The apparent density of the foam sheet was 0.16 g / cm. 3 The thickness was 0.60 mm. After that, it was stretched to an apparent density of 0.16 g / cm 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0073] Example 4 A foam sheet was obtained in the same manner as in Example 1, except that the amount of the thermally decomposable foaming agent was changed to 7 parts by mass, the thickness of the foamable resin sheet was changed to 0.58 mm, and the electron beam irradiation dose was changed to 5.5 Mrad. The apparent density of the foam sheet was 0.10 g / cm. 3 The thickness was 1.25 mm. After that, it was stretched to an apparent density of 0.10 g / cm 3 A foam sheet having a thickness of 0.5 mm was obtained. The evaluation results are shown in Table 1.

[0074] Example 5 A foam sheet was obtained in the same manner as in Example 1, except that the amount of the thermally decomposable foaming agent was changed to 9 parts by mass, the thickness of the foamable resin sheet was set to 0.61 mm, and the electron beam irradiation dose was set to 6 Mrad. The apparent density of the foam sheet was 0.06 g / cm. 3 The thickness was 1.5 mm. The evaluation results are shown in Table 1.

[0075] Example 6 In Example 1, the apparent density after foaming was 0.24 g / cm. The same procedure as in Example 1 was repeated except that the blending amount of the elastomer resin (a) was 30 parts by mass, the blending amount of the polyolefin resin (a) was 70 parts by mass, and the electron beam irradiation dose was 4 Mrad. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0076] Example 7 In Example 1, the apparent density after foaming was 0.24 g / cm. The same procedure as in Example 1 was repeated except that the blending amount of the elastomer resin (a) was 50 parts by mass, the blending amount of the polyolefin resin (a) was 50 parts by mass, and the electron beam irradiation dose was 4 Mrad. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0077] Example 8 In Example 1, the apparent density after foaming was 0.23 g / cm 3, in the same manner as in Example 1, except that the blending amount of the elastomer resin (a) was 70 parts by mass and the blending amount of the polyolefin resin (a) was 30 parts by mass. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0078] Example 9 The apparent density after foaming was 0.25 g / cm 3 in the same manner as in Example 6, except that the elastomer resin (b) was used instead of the elastomer resin (a) in Example 6 and the electron beam irradiation dose was 6 Mrad. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0079] Example 10 The apparent density after foaming was 0.25 g / cm 3 in the same manner as in Example 7, except that the elastomer resin (b) was used instead of the elastomer resin (a). 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0080] Example 11 The apparent density after foaming was 0.24 g / cm 3 in the same manner as in Example 7, except that polyolefin resin (b) was used instead of polyolefin resin (a) and the electron beam irradiation dose was 2.5 Mrad. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0081] Comparative Example 1 The same procedure as in Example 1 was repeated except that no elastomer resin was used, only 100 parts by mass of polyolefin resin (a) was used, and the electron beam irradiation dose was 4 Mrad. The apparent density after foaming was 0.25 g / cm. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1. Note that Tg1 was not observed under the measurement conditions of the present invention.

[0082] Comparative Example 2 In Example 1, the apparent density after foaming was 0.25 g / cm 3, in the same manner as in Example 1, except that the blending amount of the elastomer resin (a) was 10 parts by mass and the blending amount of the polyolefin resin (a) was 90 parts by mass. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0083] Comparative Example 3 The raw materials used were 100 parts by mass of elastomer resin (c), 5 parts by mass of a thermally decomposable foaming agent, 1 part by mass of a decomposition temperature regulator, 0.5 parts by mass of a phenolic antioxidant, 1.8 parts by mass of crosslinking agent A, and 1.2 parts by mass of crosslinking agent B. These materials were melt-kneaded and then pressed to obtain a foamed resin sheet with a thickness of 0.38 mm. Both sides of the obtained foamed resin sheet were irradiated with 2.5 Mrad of electron beams at an acceleration voltage of 800 keV to crosslink the foamed resin sheet. Next, the crosslinked foamed resin sheet was heated to 250°C to foam it, resulting in a density of 0.27 g / cm. 3 A foam sheet having a thickness of 0.60 mm was obtained, which was then stretched to an apparent density of 0.27 g / cm. 3 A foam sheet having a thickness of 0.2 mm was obtained. The evaluation results are shown in Table 1.

[0084] [Table 1]

[0085] As described above, all of the foam sheets of the examples showed good results in the vibration-damping evaluation, and when used in mobile electronic devices such as smartphones, they can suppress vibrations on the back side. This effect is particularly pronounced when materials such as glass and polycarbonate are used as the backing material. On the other hand, the foam sheet of the comparative example did not have a peak of tan δ near room temperature in the vibration-damping evaluation, and therefore it was found that no vibration-damping effect was obtained. Furthermore, the foam sheet of the present invention exhibited a short delay time and a favorable effect in terms of blocking radio waves.

Claims

1. At least one glass transition temperature (Tg1) is 0 to 40°C, the peak value of the loss tangent (tanδ) at the glass transition temperature (Tg1) is 0.30 or more, the 25% compressive strength is 1000 kPa or less, and the relative dielectric constant is 2 or less, The resin constituting the foam sheet contains a polyolefin-based resin, and the resin further contains an elastomer, the total content of the polyolefin resin and the elastomer is 70% by mass or more based on the total amount of the foam sheet; The foam sheet has a polyolefin resin content of 50% by mass or more based on the total resin amount of the foam sheet.

2. 2. The foam sheet according to claim 1, having a 25% compressive strength of 800 kPa or less.

3. 3. The foam sheet according to claim 1, having a thickness of 0.03 to 2 mm.

4. The foam sheet according to any one of claims 1 to 3, which has a breaking strength at 23°C of 5 N / 10 mm or more.

5. 5. The foam sheet according to claim 1, wherein the closed cell content is 80% or more.

6. The foam sheet according to any one of claims 1 to 5, wherein the average cell diameter is 20 to 400 µm.

7. The foam sheet according to any one of claims 1 to 6, wherein the gel fraction is 30 to 80 mass%.

8. Apparent density of 0.05 to 0.70 g / cm ３ The foam sheet according to any one of claims 1 to 7, wherein

9. Moisture permeability (WVTR) is 400g / m ２ The foam sheet according to any one of claims 1 to 8, wherein the foam sheet has a viscosity of 1000 psi or less.

10. The foam sheet according to any one of claims 1 to 9, which has a glass transition temperature (Tg2) of -40°C or lower.

11. The foam sheet according to any one of claims 1 to 10, which has an elongation at break of 200% or more at 23°C.

12. The foam sheet according to any one of claims 1 to 11, wherein the mass ratio of the elastomer to the polyolefin resin is 90:10 to 15:

85.

13. An adhesive tape comprising the foam sheet according to any one of claims 1 to 12 and an adhesive material provided on at least one surface of the foam sheet.

14. A roll comprising the foam sheet according to any one of claims 1 to 12.

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