Foam sheet and adhesive tape

Abstract

Provided is a foam sheet which has a tensile strength of 1-9 MPa, a breaking strength of 3.5 MPa or less when an interlayer strength measurement is performed, does not break when the interlayer strength measurement is performed, and has a thickness of 0.05-0.9 mm as a whole.

Description

Technical Field

[0001] This invention relates to foam sheets and adhesive tapes based on said foam sheets. Background Technology

[0002] In recent years, with the rapid development of larger displays and the widespread adoption of OLED technology in information terminals such as smartphones, tablets, personal computers, and televisions, the temporary disassembly and subsequent repair of display panels used in these applications has become increasingly common. These display panels are typically fixed to the casing of electronic devices using adhesive tape.

[0003] As a specific example of adhesive tape, Patent Document 1 discloses an adhesive sheet that is a photocurable adhesive sheet formed from a resin composition containing a (meth)acrylic acid copolymer (A), a crosslinking agent (B), and a photopolymerization initiator (C). This adhesive sheet has photocurability and meets specified requirements for shape retention, self-adhesion, and viscosity. Furthermore, Patent Document 1 discloses that since adhesive tape cannot absorb strain applied to the display panel based on unevenness or other irregularities present in the adhered material, unevenness in the display panel can occur. As a result, by improving the flexibility of the aforementioned adhesive sheet, unevenness in the display can be improved.

[0004] Furthermore, many adhesive tapes based on foam sheets have been proposed in the past. For example, Patent Document 2 discloses a multilayer foam sheet having a substrate layer composed of a foam layer and a surface layer composed of a foam layer or a resin film laminated on at least one side of the substrate layer, and an adhesive tape having an adhesive material provided on at least one side of the multilayer foam sheet. In addition, Patent Document 3 discloses a multilayer foam sheet having a resin layer and foam layers on both sides of the resin layer, and an adhesive tape having an adhesive material on at least one side of the multilayer foam sheet.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2016 / 194957

[0008] Patent Document 2: International Publication No. 2022 / 080219

[0009] Patent Document 3: International Publication No. 2022 / 030649 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] However, with the increasing size of TVs and the widespread adoption of devices equipped with advanced OLED panels, the need for temporarily disassembling display panels has increased, such as when recovering undamaged display panels from malfunctioning devices for reuse in other devices, or when repairing these devices to enable them to be used again. Furthermore, in recent years, from a design perspective, the trend towards thinner TVs and other devices has led to a demand for thinner adhesive tape used to secure the display panels inside the TV.

[0012] Therefore, adhesive tapes require the ability to be easily peeled off without leaving residue on the display panel, even when they are thin. To facilitate easy peeling of the adhesive tape, the inventors considered, for example, cracking the interior of the tape substrate along the surface direction to create a so-called "mid-crack," and then peeling off the remaining tape.

[0013] However, if conventional adhesive tapes are used for split-crack peeling, it is not designed for split-crack peeling, making it impossible to peel off easily without adhesive residue on the panel. Specifically, adhesive tapes using foam with a low expansion ratio as the substrate cannot cause the substrate to split along the surface direction. In addition, they compromise the required level of conformability (flexibility), making them unsuitable for use in panel fixing applications such as televisions. On the other hand, adhesive tapes using foam with a high expansion ratio as the substrate can cause the substrate to split along the surface direction, but when peeling off the foam with adhesive residue on the display panel, the low tensile strength causes the foam to be pulled by the adhesive, resulting in tearing or breakage during peeling, making it difficult to peel off smoothly.

[0014] Therefore, the objective of this invention is to provide a foam sheet that is thin and allows for easy peeling of the adhesive material without leaving any residue on the adhered material.

[0015] Methods for solving problems

[0016] The inventors conducted in-depth research and found that the above-mentioned problems can be solved by ensuring that the tensile strength and interlaminar strength of the foam sheet are both below a certain value and that the overall thickness is within a specified range.

[0017] That is, the present invention provides the following [1]~

[13] .

[0018] [1] A foam sheet having a tensile strength of 1 to 9 MPa and a breaking strength of less than 3.5 MPa when the interlaminar strength is measured, and the overall thickness of the foam sheet is 0.05 to 0.9 mm.

[0019] [2] According to the foam sheet described in [1], the 25% compressive strength of the foam sheet is less than 150 kPa.

[0020] [3] According to the foamed sheet described in [1], the overall density of the foamed sheet is 0.07~0.60 g / cm³. 3 .

[0021] [4] The foam sheet according to any one of [1] to [3] has a core layer and outer layers respectively disposed on both sides of the core layer, wherein the core layer is a foam and the outer layers are foams with a foaming ratio lower than that of the core layer or are non-foams.

[0022] [5] According to the foamed sheet described in [4], the foaming ratio of the core layer is 5 to 20 times.

[0023] [6] According to the foam sheet described in [4] or [5], the thickness ratio of the core layer to the outer layer (the thickness of the core layer / the average thickness of the outer layer) is 2 or more.

[0024] [7] The foam sheet according to any one of [4] to [6] has an independent bubble rate of 90% or more in the core layer.

[0025] [8] The foam sheet according to any one of [4] to [7] has an outer layer thickness of 5 μm or more.

[0026] [9] The foam sheet according to any one of [4] to [8] has an average bubble diameter of 20 to 500 μm in the core layer.

[0027]

[10] The foam sheet according to any one of [4] to [9], wherein the core layer is a cross-linked foam.

[0028]

[11] According to the foam sheet described in

[10] , the gel fraction of the core layer is 20 to 50% by mass.

[0029]

[12] The foam sheet according to any one of [4] to

[11] , wherein the resin constituting the core layer is selected from at least one of polyolefin resins, polyurethane resins, acrylic resins, and elastic resins.

[0030]

[13] An adhesive tape comprising a foam sheet as described in any one of [1] to

[12] and an adhesive material disposed on at least one side of the foam sheet.

[0031] Invention Effects

[0032] According to the present invention, a foam sheet can be provided that not only has good conformability to elevation differences, but also has a thin thickness and can be easily peeled off without leaving adhesive material residue on the adhered object. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating an example of the structure of the foamed sheet of the present invention.

[0034] Figure 2 This is a schematic diagram illustrating an example of the structure of the adhesive tape of the present invention.

[0035] Figure 3 This is a schematic diagram of a device for measuring fracture strength. Detailed Implementation

[0036] [Effervescent tablets]

[0037] The foam sheet of the present invention has a tensile strength of 1 to 9 MPa and a breaking strength (hereinafter also referred to as "breaking strength") of 3.5 MPa or less when the interlaminar strength is measured, and the overall thickness of the foam sheet is 0.05 to 0.9 mm. By having the above-described structure, the foam sheet of the present invention, for example, when used as a substrate for adhesive tape, allows for easy removal of the adhesive tape from the adhered material by using a cutter or similar tool to split the foam sheet along its surface when peeling off the adhesive tape, thereby removing a portion of the adhesive tape remaining on the adhered material.

[0038] The following is a more detailed explanation of foam tablets.

[0039] Tensile Strength

[0040] If the tensile strength of the foam sheet is less than 1 MPa, the foam sheet will break due to the pulling of the adhesive material during peeling, making it difficult to peel the foam sheet cleanly. Furthermore, if the tensile strength exceeds 9 MPa, the breaking strength is significantly higher than specified, making it difficult to cause the foam sheet to crack along the surface direction before peeling. Additionally, reduced flexibility can sometimes decrease the ability to follow contour changes. Based on these considerations, a tensile strength of 1.2 to 8.5 MPa is preferred, and more preferably 1.3 to 5 MPa.

[0041] It should be noted that tensile strength can be measured using the methods described in the examples.

[0042] <Thickness>

[0043] When the overall thickness of the foam sheet exceeds 0.9 mm, the foam sheet is too thick and difficult to use inside thin electronic devices. Furthermore, if the overall thickness is less than 0.05 mm, sufficient clearance for a cutter to penetrate the foam sheet cannot be ensured, thus preventing it from splitting along the surface and hindering the imparting of excellent peelability to the foam sheet. Based on these considerations, the overall thickness is preferably 0.07 to 0.8 mm, more preferably 0.12 to 0.5 mm.

[0044] <Tension Strength>

[0045] As described above, the foam sheet of the present invention has a tensile strength of 3.5 MPa or less. If the tensile strength exceeds 3.5 MPa, the foam sheet cannot crack along the surface direction, making it difficult to impart excellent peelability to the foam sheet. From this point of view, the tensile strength is preferably 3.2 MPa or less, and more preferably 3 MPa or less.

[0046] Furthermore, from the viewpoint of imparting a certain mechanical strength to the foam sheet and preventing the panel fixed by the tape from falling when used as a substrate for adhesive tape, the aforementioned breaking strength is preferably 0.1 MPa or more, more preferably 0.3 MPa or more, and even more preferably 0.5 MPa or more.

[0047] It should be noted that the fracture strength can be measured during the interlaminar strength determination using the method described in the examples.

[0048] <25% compressive strength>

[0049] The 25% compressive strength of the foam sheet of the present invention is preferably 150 kPa or less, more preferably 100 kPa or less, and even more preferably 70 kPa or less. When the compressive strength is below the aforementioned upper limit, the foam sheet exhibits good flexibility and excellent height tolerance. Furthermore, even when the foam sheet is sandwiched between components inside electronic devices such as televisions, the load applied to the components is reduced, making it easier to prevent malfunctions in the electronic devices.

[0050] On the other hand, from the viewpoint of imparting a certain mechanical strength to the foam sheet, the 25% compressive strength is preferably 10 kPa or more, more preferably 15 kPa or more, and even more preferably 20 kPa or more.

[0051] It should be noted that the 25% compressive strength can be determined using the method described in the examples.

[0052] <Density>

[0053] The overall density of the foam sheet is preferably 0.07~0.60 g / cm³. 3 More preferably, it is 0.10~0.50 g / cm³. 3Further preferably, it is 0.20~0.45 g / cm³. 3 If the overall density of the foam sheet is above the lower limit mentioned above, then the foam sheet is given a certain tensile strength, making it less likely to be torn by the adhesive material during peeling.

[0054] On the other hand, if the overall density of the foam sheet is below the aforementioned upper limit, the breaking strength of the foam sheet will be below a certain level, making it easy for the core layer to crack along the surface direction before the foam sheet is peeled off. Additionally, it is easy to impart excellent height-difference tracking properties to the foam sheet.

[0055] It should be noted that the density referred to here includes the overall density mentioned above, and refers to the apparent density. Furthermore, the apparent density can be determined together with the foaming ratio described later using the methods described in the examples.

[0056] <Structure>

[0057] The foam sheet of the present invention can be composed solely of a core layer made of foam, or it can have an outer layer on at least one side of the core layer, which is a foam. When an outer layer is included, it can be a multilayer body with an outer layer on only one side of the core layer, or it can be a multilayer body with outer layers on both sides of the core layer, but... Figure 1 As shown, the preferred embodiment is a multilayer body 1 having outer layers B and C on both sides of the core layer A.

[0058] By providing outer layers on both sides of the core layer, the tensile strength of the foam sheet can be easily improved. Therefore, when using the foam sheet as a substrate for adhesive tape, it prevents tape breakage during peeling after the core layer is cracked along the surface direction, exhibiting excellent peelability. Furthermore, excellent peelability is maintained even when adhesive material is applied to both sides of the foam sheet.

[0059] In addition, the outer layer is preferably laminated directly relative to the core layer, but it can also be laminated via an adhesive layer or the like.

[0060] The outer layer can be a foamed layer composed of foamed materials or a non-foamed layer composed of non-foamed materials. It should be noted that when the outer layer is a foamed layer, the foaming ratio can be lower than that of the foamed layer constituting the core layer. In this invention, the outer layer is preferably a non-foamed material. By using a non-foamed material, the tensile strength of the foamed sheet is increased, preventing breakage during peeling and easily exhibiting excellent peelability.

[0061] [Core layer (foam)]

[0062] The foam that makes up the core layer will be explained in more detail below.

[0063] <Expansion Ratio>

[0064] The foaming ratio of the core layer is preferably 5 to 20 times, more preferably 5.2 to 15 times, and even more preferably 6 to 8.5 times. When the foaming ratio is above the lower limit mentioned above, the breaking strength of the foam sheet is below a certain value, making it easy for the core layer to crack along the surface direction before the foam sheet is peeled off. In addition, it is easy to impart excellent height difference tracking to the foam sheet.

[0065] On the other hand, when the foaming ratio is below the aforementioned upper limit, the foam sheet is given a certain tensile strength and is not easily torn by the adhesive material during peeling. In addition, when the foam sheet has an outer layer, during its manufacturing process, the outer layer is sometimes compressed and stretched due to the foaming of the foaming composition that serves as the raw material for the core layer. However, by keeping the foaming ratio below the aforementioned upper limit, this stretching is suppressed, making it easier to ensure that the overall tensile strength of the foam sheet is above a certain level.

[0066] <Average bubble diameter>

[0067] The average bubble diameter of the core layer is preferably 20-500 μm, more preferably 30-300 μm, and even more preferably 35-200 μm. If the average bubble diameter is above the lower limit mentioned above, it is easy to impart excellent peelability and contour following properties to the foam sheet. In addition, it is easy to crack along the surface direction.

[0068] On the other hand, if the average bubble diameter is below the aforementioned upper limit, the foam sheet is endowed with a certain tensile strength, thereby easily imparting excellent peelability to the foam sheet. Additionally, it facilitates the thinning of the foam sheet's walls.

[0069] It should be noted that the average bubble diameter in this invention is the maximum value among the average bubble diameter in the MD (Machine Direction) direction, the average bubble diameter in the TD (Transverse Direction) direction, and the average bubble diameter in the ZD (perpendicular to both MD and TD) direction.

[0070] Furthermore, in the core layer, the average bubble diameter in the MD direction is preferably 15-450 μm, more preferably 25-250 μm, and even more preferably 30-150 μm. Additionally, the average bubble diameter in the TD direction is preferably 20-500 μm, more preferably 30-300 μm, and even more preferably 35-200 μm. Furthermore, the average bubble diameter in the ZD direction is preferably 5-100 μm, more preferably 10-70 μm, and even more preferably 15-50 μm.

[0071] It should be noted that the average bubble diameter described above can be measured using the method described in the examples.

[0072] <Independent bubble rate>

[0073] The independent bubble rate of the core layer is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. Furthermore, the upper limit of the independent bubble rate is not particularly limited, and is 100%. By ensuring the independent bubble rate is above the aforementioned lower limit, excellent height difference tracking is easily achieved. Additionally, the shear strength of the core layer is increased, thus, when used inside electronic devices such as televisions, it has the advantage of preventing defects such as core layer cracking and panel drop.

[0074] It should be noted that the independent bubble rate can be determined using the method described in the examples.

[0075] <Degree of crosslinking>

[0076] The core layer is preferably a cross-linked foam. Specifically, the degree of cross-linking (gel fraction) of the core layer is preferably 20-50% by mass, more preferably 30-45% by mass. By keeping the degree of cross-linking of the core layer within the above range, the mechanical strength, softness, and shock absorption of the foam sheet are easily improved. Furthermore, foaming in the core layer can be appropriately performed. It should be noted that the method for determining the degree of cross-linking is as follows.

[0077] Approximately 100 mg of the test sample was collected from the core layer, and its weight A (mg) was accurately measured. Next, the test sample was immersed in xylene at 120°C for 30 cm. 3 After being placed in the solution for 24 hours, the solution is filtered through a 200-mesh metal mesh. The insoluble components on the mesh are collected, vacuum dried, and the weight B (mg) of the insoluble components is accurately measured. The degree of crosslinking (mass %) is calculated from the obtained value using the following formula.

[0078] Degree of crosslinking (mass%) = 100 × (B / A)

[0079] The thickness of the core layer is preferably 0.03 to 0.7 mm, more preferably 0.05 to 0.5 mm, and even more preferably 0.08 to 0.3 mm. If the core layer thickness is above the lower limit, sufficient clearance for cutting tools and the like is ensured, allowing for cracking along the surface direction and easily imparting excellent peelability to the foam sheet. Conversely, if the core layer thickness is below the upper limit, the overall thickness of the foam sheet can be thin, facilitating its appropriate use inside thin electronic devices and the like.

[0080] <Resin>

[0081] The resin constituting the core layer of the present invention is preferably selected from at least one of polyolefin resins, polyurethane resins, acrylic resins, and elastic resins.

[0082] (Polyolefin resins)

[0083] Examples of polyolefin resins include polyethylene resin, polypropylene resin, and ethylene-vinyl acetate copolymer, with polyethylene resin being preferred. Examples of polyethylene resins include those polymerized using Ziegler-Natta compounds, metallocene compounds, chromium oxide compounds, etc., with polyethylene resins polymerized using metallocene compound catalysts being preferred.

[0084] Furthermore, linear low-density polyethylene (LLDPE) is preferred as the polyethylene resin. By using LLDPE, high flexibility can be imparted to the foam sheet, and thin-walled foam sheets can be achieved. Moreover, LLDPE is more preferably obtained by copolymerizing ethylene (e.g., 75% by mass or more, preferably 90% by mass or more, relative to the total monomer content) with a small amount of α-olefin as needed.

[0085] Examples of α-olefins include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene, with α-olefins having 4 to 10 carbon atoms being preferred.

[0086] The density of the polyethylene resin, such as the linear low-density polyethylene described above, is preferably 0.870~0.910 g / cm³. 3 More preferably, it is 0.875~0.907 g / cm³. 3 More preferably, it is 0.880~0.905 g / cm³. 3 As a polyethylene resin, various polyethylene resins can be used, and polyethylene resins outside the density range mentioned above can also be added.

[0087] (metallocene compounds)

[0088] As metallocene compounds, examples include bis(cyclopentadienyl) metal complexes, which have a structure in which an unsaturated compound with a π-electron system sandwiches a transition metal. More specifically, examples include compounds in which one or more cyclopentadienyl rings or their analogues serve as ligands (ligands) on tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum.

[0089] The active sites of such metallocene compounds are uniform in nature, and each active site possesses the same level of activity. Polymers synthesized using metallocene compounds exhibit high uniformity in molecular weight, molecular weight distribution, composition, and compositional distribution. Therefore, when crosslinking sheets containing polymers synthesized using metallocene compounds is performed, crosslinking occurs uniformly. The uniformly crosslinked sheets foam uniformly, thus facilitating property stability. Furthermore, because uniform stretching is possible, the thickness of the foamed sheets can be made uniform.

[0090] Examples of ligands include cyclopentadienyl rings and indenyl rings. These cyclic compounds can be substituted with hydrocarbon groups, substituted hydrocarbon groups, or hydrocarbon-substituted metalloid groups. Examples of hydrocarbon groups include methyl, ethyl, various propyl, various butyl, various pentyl, various hexyl, 2-ethylhexyl, various heptyl, various octyl, various nonyl, various decyl, various cetyl, phenyl, etc. It should be noted that "various" refers to various isomers including n-, sec-, tert-, and iso-.

[0091] Alternatively, substances formed by polymerizing cyclic compounds into oligomers can be used as ligands.

[0092] Furthermore, in addition to unsaturated compounds with π-electron systems, monovalent anionic ligands such as chlorine and bromine, or divalent anionic chelating ligands, hydrocarbons, alkoxides, aryl amides, aryl oxides, amides, aryl amides, phosphides, aryl phosphides, etc., can also be used.

[0093] Examples of metallocene compounds containing tetravalent transition metals and ligands include cyclopentadienyl tris(dimethylamide)titanium, methylcyclopentadienyl tris(dimethylamide)titanium, bis(cyclopentadienyl)titanium dichloride, and dimethylsilyltetramethylcyclopentadienyl-tert-butylamide zirconium dichloride.

[0094] Metallocene compounds act as catalysts in the polymerization of various olefins by combining with specific co-catalysts (pro-catalysts). Examples of specific co-catalysts include methylaluminoxane (MAO) and boron compounds. It should be noted that the ratio of the co-catalyst to the metallocene compound is preferably 10 to 1,000,000 molar ratios, more preferably 50 to 5,000 molar ratios.

[0095] When using linear low-density polyethylene (LDPE) as a polyolefin resin, it can be used alone or in combination with other polyolefin resins besides LLDPE. For example, it can be used in combination with polyolefin resins other than the polyethylene resin described below. When using other polyolefin resins in combination, the proportion of the other polyolefin resin relative to the linear low-density polyethylene (100% by mass) is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0096] Examples of ethylene-vinyl acetate copolymers used as polyolefin resins include those containing 50% by mass or more of ethylene.

[0097] In addition, examples of polypropylene resins include homopolymer polypropylene and propylene-α-olefin copolymers containing, for example, 70% or more by mass of propylene, more preferably 90% or more by mass of propylene. One of these resins may be used alone, or two or more may be used in combination.

[0098] Examples of α-olefins constituting propylene-α-olefin copolymers include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene, with α-olefins having 6 to 12 carbon atoms being preferred.

[0099] Furthermore, when using a polyolefin resin as the resin, the resin may be a polyolefin resin alone, or it may include a resin other than a polyolefin resin. The proportion of the polyolefin resin relative to the total amount of resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. As for the resin other than the polyolefin resin used in conjunction with the polyolefin resin, any resin other than the polyolefin resin mentioned above may be used, but an elastic system resin is preferred.

[0100] (Polyurethane-based resin)

[0101] As a polyurethane resin, a reaction product of polyol and polyisocyanate can be preferred.

[0102] There are no particular restrictions on the types of polyols used; they can be selected appropriately according to the purpose. Examples include polyester polyols, polyether polyols, and polycarbonate polyols. A single type can be used, or two or more can be used in combination.

[0103] Examples of polyester polyols include polyesters obtained by esterification of low molecular weight polyols with polycarboxylic acids, polyesters obtained by ring-opening polymerization of cyclic ester compounds such as ε-caprolactone, and their copolyesters.

[0104] As low molecular weight polyols that can be used in the manufacture of polyester polyols, examples include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, 1,3-butanediol and other aliphatic alkylene glycols, cyclohexanediol and others, with a weight average molecular weight of approximately 50 to 300.

[0105] Examples of polycarboxylic acids include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid; and their anhydrides or esters.

[0106] Examples of polyether polyols include substances formed by the addition polymerization of alkyl epoxides using one or more compounds having two or more active hydrogen atoms as initiators.

[0107] As a polycarbonate polyol, for example, a substance obtained by reacting carbonate and / or phosgene with a low molecular weight polyol described below can be used.

[0108] Examples of carbonates include methyl carbonate, dimethyl carbonate, ethyl carbonate, diethyl carbonate, cyclic carbonates, and diphenyl carbonate.

[0109] Examples of low molecular weight polyols that can react with carbonates and / or phosgene and can be used in the manufacture of polycarbonate polyols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, and 1,7-heptanediol. Alcohols, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, 1,4-cyclohexanediol, hydroquinone, resorcinol, bisphenol A, bisphenol F, 4,4'-biphenol, etc.

[0110] There are no particular restrictions on the types of polyisocyanates used; they can be selected appropriately according to the purpose. For example, alicyclic polyisocyanates, aliphatic polyisocyanates, aromatic polyisocyanates, etc., can be used. Examples include alicyclic polyisocyanates. They can be used alone or in combination of two or more.

[0111] Examples of alicyclic polyisocyanates include isophorone diisocyanate, 1,3-bis(isocyanate-methyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, 2,4-methylcyclohexane diisocyanate, 2,6-methylcyclohexane diisocyanate, cyclohexene diisocyanate, methylcyclohexene diisocyanate, bis(2-isocyanate-ethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, 2,6-norbornane diisocyanate, dimer acid diisocyanate, and dicycloheptane triisocyanate. They can be used individually or in combination of two or more.

[0112] (Acrylic resin)

[0113] As an acrylic resin, polymers containing (meth)acrylate monomer units, optionally further containing other monomer units, can be used.

[0114] It should be noted that, in this invention, "polymer containing monomer units" means "polymer obtained using the monomer contains repeating units derived from the monomer." Additionally, in this invention, "(meth)acrylate" refers to acrylates and / or methacrylates.

[0115] Here, the (meth)acrylate monomer unit is a repeating unit derived from (meth)acrylate monomers. There are no particular limitations on the (meth)acrylate monomer; examples include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, n-heptyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-dodecyl methacrylate, and other alkyl methacrylate monomers, as well as alkoxyalkyl methacrylate monomers such as 2-methoxyethyl methacrylate, 3-methoxypropyl methacrylate, 3-methoxybutyl methacrylate, and ethoxymethyl methacrylate.

[0116] It should be noted that (meth)acrylate monomers can be used alone or in combination with two or more. Furthermore, in this invention, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0117] Other monomer units are not particularly limited, and examples include repeating units from unsaturated carboxylic acid monomers, repeating units from vinyl cyanide monomers, and repeating units from alkenyl aromatic monomers.

[0118] (Elastic system resin)

[0119] Examples of resins used in elastic systems include acrylonitrile butadiene rubber, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), natural rubber, polybutadiene rubber, polyisoprene rubber, styrene rubber, silicone rubber, and acrylic rubbers. As for styrene rubber, any polymer of styrene and a conjugated diene compound can be a random copolymer or its hydride. Specifically, examples include styrene-butadiene copolymer (SBR) or its hydride (HSBR).

[0120] As an elastic system resin, thermoplastic elastomers can also be listed. Examples of thermoplastic elastomers include olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyurethane-based thermoplastic elastomer resins, polyester-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

[0121] The elastomer can use one of the above-mentioned components alone, or it can use two or more components in combination. Thermoplastic elastomers are preferred. Furthermore, from the viewpoint of easily adjusting the tensile storage modulus, the rate of change of tensile storage modulus, and the sheet recovery rate to the above-mentioned ranges, silicone rubber, olefin-based thermoplastic elastomers, and styrene-based thermoplastic elastomers are more preferred. Additionally, the above-mentioned rubbers and elastomers can be mixed with each other, or compatible thermoplastic resins can be mixed as described later.

[0122] As olefin-based thermoplastic elastomers, examples include mixed-type, dynamically cross-linked, and polymeric thermoplastic elastomers. More specifically, examples include thermoplastic elastomers that use thermoplastic crystalline polyolefins such as polypropylene and polyethylene in the hard segments and rubbers that are fully or partially vulcanized in the soft segments.

[0123] Examples of thermoplastic crystalline polyolefins include homopolymers of α-olefins having 1 to 4 carbon atoms or copolymers of two or more α-olefins, with polyethylene or polypropylene being preferred. Examples of soft-segment components include butyl rubber, halogenated butyl rubber, EPDM, EPM, acrylonitrile / butadiene rubber, NBR, natural rubber, etc., with EPDM being preferred.

[0124] As the olefin-based thermoplastic elastomer used in this invention, an olefin-based thermoplastic elastomer that can be manufactured through dynamic crosslinking is preferred, and an olefin-based thermoplastic elastomer in which EPDM micro-island phases are formed in the polypropylene phase. The reasons for using such an olefin-based thermoplastic elastomer are not yet clear, but in either the case of crosslinking of the resin foam sheet or the case of no crosslinking, the aforementioned sheet recovery rate and, consequently, the rate of change of tensile storage modulus can be adjusted to the aforementioned specified range. Commercially available examples of such thermoplastic elastomers include, for example, "Plain TPO" manufactured by Premium Polymer Co., Ltd., and "EXCELINK 4700P" manufactured by JSR Co., Ltd.

[0125] In addition, block copolymers can also be cited as olefin-based thermoplastic elastomers. Examples of block copolymers include substances having crystalline blocks and soft-chain blocks; more specifically, crystalline olefin block-ethylene / butene copolymer-crystalline olefin block copolymer (CEBC) can be exemplified. In CEBC, the crystalline olefin block is preferably a crystalline ethylene block, and commercially available examples of such CEBCs include "DYNARON 6200P" manufactured by JSR Corporation.

[0126] Examples of styrene-based thermoplastic elastomers include block copolymers containing styrene polymer or copolymer blocks and conjugated diene compounds. Examples of conjugated diene compounds include isoprene and butadiene.

[0127] The styrene-based thermoplastic elastomer used in this invention may or may not be hydrogenated. If hydrogenation is performed, it can be carried out using known methods.

[0128] As a styrene-based thermoplastic elastomer, it is usually a block copolymer, and examples include styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene / butene-styrene block copolymer (SEBS), styrene-ethylene / propylene-styrene block copolymer (SEPS), styrene-ethylene / butene block copolymer (SEB), styrene-ethylene / propylene block copolymer (SEP), and styrene-ethylene / butene-crystalline olefin block copolymer (SEBC).

[0129] As the aforementioned styrene-based thermoplastic elastomers, block copolymers are preferred, with SEBS and SEBC being more preferred.

[0130] It should be noted that commercially available styrene-based thermoplastic elastomers include those manufactured by JSR Corporation under the trade names "DYNARON 8600P" (15% styrene content by mass), "DYNARON 4600P" (20% styrene content by mass), and "DYNARON 1321P" (10% styrene content by mass).

[0131] As for the resin constituting the foam sheet of the present invention, it is more preferably selected from at least one of polyolefin resins, polyurethane resins, and elastic resins, further preferably polyolefin resins, even more preferably ethylene resins, and particularly preferably ethylene resins polymerized from metallocene compounds. By using a polyolefin resin in the core layer, the generation of resin debris is suppressed when the foam sheet is cracked in the surface direction, and it is easy to prevent foreign matter from being mixed in due to debris, thus avoiding malfunctions in electronic devices. In addition, by using these specific types of resins, it is also effective to easily and cleanly peel off the foam sheet during peeling. Furthermore, it is also easy to improve the performance of high-low gradients.

[0132] <Foaming Agent>

[0133] The foamed sheet of the present invention is preferably a foamed body obtained by foaming a foaming composition comprising the above-mentioned resin and foaming agent. The foamed body obtained by foaming is composed of a foamed body having a plurality of cells formed by air bubbles inside, with a resin monomer or a resin mixed with additives as required as the matrix resin.

[0134] Examples of foaming agents include thermally decomposable foaming agents. Both organic and inorganic foaming agents can be used as thermally decomposable foaming agents. Thermally decomposable foaming agents typically use substances with a decomposition temperature higher than the melting temperature of the resin; for example, substances with a decomposition temperature of 140~270℃ can be used.

[0135] Specific examples of organic foaming agents include azodicarbonamide, metal salts of azodicarboxylic acid (such as barium azodicarboxylic acid), azobisisobutyronitrile and other azo compounds, nitroso compounds such as N,N'-dinitrospentamethylenetetramine, hydrazine dicarboxamide, hydrazine derivatives such as 4,4'-oxobis(benzenesulfonylhydrazine) and toluenesulfonylhydrazine, and aminourea compounds such as toluenesulfonylaminourea.

[0136] Examples of inorganic foaming agents include ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous sodium citrate.

[0137] From the perspectives of obtaining fine bubbles, as well as economy and safety, azo compounds are preferred, and azodicarbonamide is particularly preferred. These thermally decomposable foaming agents can be used alone or in combination of two or more.

[0138] The amount of thermally decomposable foaming agent in the foaming composition is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, and even more preferably 1 to 10 parts by weight relative to 100 parts by weight of the resin.

[0139] When using polyolefin resins, acrylic resins, or elastic resins as the resin, the aforementioned thermally decomposable blowing agent is preferred as the blowing agent. However, blowing agents other than thermally decomposable blowing agents can also be used. For example, when using polyurethane resins, water, organohalogen compounds, etc., are preferred as the blowing agent. Examples of organohalogen compounds include organochlorine compounds and organofluorine compounds, with organofluorine compounds being preferred. Examples of organofluorine compounds include hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs), which may further contain chlorine atoms.

[0140] Alternatively, physical blowing agents can be used as blowing agents. As physical blowing agents, high-pressure inert gases are preferred. There are no particular limitations on the inert gas, as long as it is inert to the resin composition and capable of impregnation; examples include carbon dioxide, butane gas, nitrogen, and air. These gases can also be mixed. From the viewpoint of easily increasing the foaming ratio of the foam, carbon dioxide and butane gas are preferred. The inert gas used for impregnation is preferably in a supercritical or subcritical state.

[0141] <Other Additives>

[0142] In foamed sheets or foamed compositions, additives commonly used in foams, such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, and decomposition temperature regulators, may be mixed in as needed. Among these, antioxidants and decomposition temperature regulators are preferred.

[0143] Specific compounds that can be used as decomposition temperature regulators include zinc oxide, zinc stearate, and urea. The content of the decomposition temperature regulator relative to 100 parts by weight of the resin is preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight.

[0144] [Outer layer]

[0145] When the outer layer is non-foamed, it can be a non-foamed resin layer or a layer other than a resin layer such as paper. As for the resin constituting the outer layer, there are no particular limitations as long as it can prevent the foam sheet from breaking during peeling; polyolefin resins, polyester resins such as polyethylene terephthalate, styrene-acrylate resins, elastic resins, acrylic resins, etc., can be used.

[0146] In the above description, polyolefin resins and polyester resins are preferred, with polyolefin resins being more preferred. As explained above regarding the foam, polyethylene resins are more preferred. It should be noted that the polyolefin resin used in the core layer and the polyolefin resin used in the outer layer can be the same or different, but using the same polyolefin resin is preferred. Using the same material easily improves the adhesive strength between the core layer and the outer layer, preventing interfacial delamination. Furthermore, when manufacturing the foam sheet using the first manufacturing method described later, the resin constituting the outer layer is preferably a polyolefin resin, and more preferably a polyethylene resin.

[0147] Furthermore, in the foam sheet manufactured by the second manufacturing method, the resin used in the outer layer is preferably a polyolefin resin or a polyester resin, and more preferably a polyethylene resin, a polypropylene resin, or polyethylene terephthalate.

[0148] In the foam sheet manufactured by the second manufacturing method, the resin layer used for the outer layer can be an oriented film or a non-oriented film. For example, when using acrylic resin, OPP film is also preferred.

[0149] When the outer layer is a foamed material, the foaming ratio of the foamed material constituting the outer layer should be lower than that of the foamed material constituting the core layer. Specifically, the foaming ratio is preferably greater than 1 and less than 5, more preferably 1.1 to 4, and even more preferably 1.1 to 2.

[0150] When the outer layer is a foam, the resin constituting the outer layer is the same as the resin constituting the core layer described above, and its description is omitted. Furthermore, it is preferable that the independent bubble rate and degree of crosslinking are also the same as those for the core layer described above.

[0151] Alternatively, additives can be appropriately blended into the resin of the outer layer. The same additives used in the core layer can be used as the additives employed in the outer layer.

[0152] (Thickness of the outer layer)

[0153] The thickness of the outer layer of the foam sheet of the present invention is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 10 μm or more. Furthermore, the thickness of the outer layer is preferably 300 μm or less, more preferably 100 μm or less, and even more preferably 40 μm or less. If the thickness of the outer layer is at or above the aforementioned lower limit, the outer layer imparts tensile strength to the foam sheet, preventing the foam sheet from tearing during peeling from the adhered object, and easily imparting excellent peelability to the foam sheet. Additionally, when the thickness of the outer layer is at or below the aforementioned upper limit, the overall thickness of the foam sheet is thin, making it easily suitable for use in thin electronic devices.

[0154] It should be noted that when the foam sheet has an outer layer on both sides of the core layer, the thickness of the outer layer refers to the thickness of each individual outer layer. For example, if the thickness of each outer layer is 5 μm or more, then all outer layers are 5 μm or more. Furthermore, when the foam sheet has an outer layer on both sides of the core layer, any outer layer is preferably within the above-mentioned range.

[0155] When a foam sheet has an outer layer on both sides, the thickness of the two outer layers can be the same or different, but it is preferred that they are the same.

[0156] When the foam sheet of the present invention is a multilayer body having outer layers, from the viewpoint of maximizing the conformability of the height difference and the peelability of the foam sheet, the ratio of the thickness of the core layer to the thickness of the outer layers (thickness of the core layer / thickness of each outer layer) is preferably 2.0 or more, more preferably 3.0 or more, even more preferably 5.0 or more, even more preferably 8.0 or more, and preferably 50 or less, more preferably 30 or less, even more preferably 20 or less. It should be noted that when the core layer has outer layers on both sides of the multilayer body, the thickness of the outer layers when calculating the above thickness ratio is the average of the thicknesses of the outer layers on both sides.

[0157] <Manufacturing Method of Foamed Sheets>;

[0158] The manufacturing methods for the case where the foamed sheet is a multilayer body having a core layer and an outer layer will be described below using the first manufacturing method and the second manufacturing method.

[0159] (First Manufacturing Method)

[0160] The foamed sheet of the present invention is not particularly limited, and can be manufactured, for example, by means of: for a layer formed of a foaming composition, an outer layer is laminated on one or both sides of the layer to obtain a laminated sheet, and then the laminated sheet is foamed to obtain the sheet (hereinafter also referred to as the "first manufacturing method").

[0161] More specifically, manufacturing method 1 includes the following steps I to II.

[0162] (I) A process of obtaining a laminated sheet having a layer formed of a foaming composition and an outer layer formed on one or both sides of the layer.

[0163] (II) A process of foaming the layers of a laminated sheet formed by a foaming composition to obtain a foamed sheet.

[0164] The following is a description of each process.

[0165] (Process (I))

[0166] There are no particular limitations on the method for obtaining the laminated sheet in step (I), but co-extrusion molding is preferred.

[0167] Specifically, when an outer layer is formed on both sides of a layer formed from a foaming resin composition, the resin for forming the outer layer and additives to be blended as needed are supplied to a first extruder and a third extruder respectively and melt-blended to obtain a resin composition for forming the outer layer. Additionally, the resin for forming the core layer, a foaming agent such as a thermally decomposable foaming agent, and additives to be blended as needed are supplied to a second extruder and melt-blended to obtain a foaming composition for forming the core layer.

[0168] Next, the compositions supplied from the first to third extruders are combined in such a way that the composition supplied from the second extruder becomes the intermediate layer, and extruded into a sheet using a T-die or the like, thereby obtaining a laminated sheet with a three-layer structure. In the method for obtaining a laminated sheet with a three-layer structure, if the compositions of the two outer layers are the same, it is also possible to use only one extruder instead of two extruders (the first and third extruders), and supply the resin compositions of the two outer layers from this single extruder.

[0169] In the case where the outer layer is formed on one side of a layer formed from a foaming composition, the resin for forming the outer layer and additives to be blended as needed are supplied to a first extruder and melt-blended to obtain a resin composition for forming the outer layer. Separately, the resin for forming the core layer, a foaming agent such as a thermally degradable foaming agent, and additives to be blended as needed are supplied to a second extruder and melt-blended to obtain a foaming resin composition for forming the core layer. Next, the resin composition supplied from the first extruder and the composition supplied from the second extruder are combined and extruded into a sheet using a T-die or the like, thereby obtaining a multilayer laminate sheet with a two-layer structure.

[0170] In co-extrusion molding, either the feed block method or the multi-manifold method can be used, but the feed block method is preferred.

[0171] In the above method, it is preferable to further crosslink the laminated sheet after step (I). As a crosslinking method, there is also a method of pre-mixing an organic peroxide and heating the laminated sheet obtained in step (I) to achieve crosslinking, but it is preferable to crosslink the laminated sheet by irradiating it with ionizing radiation. It should be noted that examples of ionizing radiation include electron beams and beta rays, with electron beams being preferred.

[0172] The preferred dose of ionizing radiation is 1 to 10 Mrad, more preferably 1.5 to 5 Mrad. Crosslinking is preferably performed before step (II).

[0173] (Process (II))

[0174] In step (II), the laminated sheet obtained in step (I) is foamed to foam the layer formed by the foaming composition. The layer formed by the foaming composition can be treated by foaming with a foaming agent; however, if the foaming agent is a thermally decomposable foaming agent, foaming is achieved by heating the laminated sheet. The heating temperature only needs to be above the decomposition temperature of the thermally decomposable foaming agent, for example, around 150~320°C.

[0175] There are no particular limitations on the methods for heating laminated sheets. For example, methods such as heating laminated sheets with hot air, heating with infrared rays, heating with a salt bath, and heating with an oil bath can be used, and these methods can also be combined.

[0176] In addition, laminated sheets can be stretched appropriately during or after foaming.

[0177] It should be noted that the above description illustrates an example where the outer layer is a resin film (non-foamed body). However, in the case where the outer layer is a foamed body, it is preferable to pre-mix a thermally decomposable foaming agent or other foaming agent as an additive into the resin composition used to form the outer layer, and then foam it in step (II).

[0178] (Second manufacturing method)

[0179] The method for manufacturing the foam sheet of the present invention can also be used to manufacture it by other methods. Specifically, a method can be described as follows: a foam layer constituting the core layer is pre-manufactured, and a resin film or foam layer constituting the outer layer is overlapped on one or both sides of the foam layer and bonded together (also known as the "second manufacturing method").

[0180] As a method for obtaining a foamed body in the second manufacturing method, a resin for forming the core layer, a thermally decomposable foaming agent, and additives to be mixed as needed are melt-blended to obtain a foamed composition for forming the core layer, and the foamed composition is then formed into a sheet (foamed composition sheet). The method of melting and blending the foamed composition to form a sheet is not particularly limited, but an extruder is preferably used.

[0181] The resulting foamed composition sheet is preferably further crosslinked before the foaming process described later. As a crosslinking method, there is also a method of pre-mixing an organic peroxide and heating the foamed composition sheet for crosslinking, but it is preferable to crosslink the foamed composition sheet by irradiating it with ionizing radiation. It should be noted that the type and amount of ionizing radiation are as described in the first manufacturing method above.

[0182] Next, it is preferable to foam the foamable composition sheet. The layer formed from the foamable composition can be treated by foaming with a foaming agent; however, if the foaming agent is a thermally decomposable foaming agent, foaming is achieved by heating the laminated sheet. The heating temperature and method are as described in the first manufacturing method above. Furthermore, the foamable composition sheet may be appropriately stretched during or after foaming.

[0183] Then, the separately prepared resin film or foam for the outer layer is overlapped and bonded to one or both sides of the foam layer constituting the substrate layer, thereby obtaining a multilayer. Specifically, this can be achieved by heat pressing using a press or similar method. Alternatively, adhesives or bonding agents can be applied to the bonding surfaces between the foam layer and the surface layer, or double-sided adhesive tape can be used for bonding. The foam for the outer layer can be manufactured using the same method as the foam for the core layer, or it can be manufactured using different methods.

[0184] Adhesive tape

[0185] The present invention also provides an adhesive tape based on the aforementioned foam sheet. The adhesive tape, for example, includes an adhesive material disposed on at least one side of the foam sheet. The adhesive tape can be bonded to other components by means of the adhesive material. The adhesive tape may have adhesive material disposed on both sides of the foam sheet or on one side. The adhesive tape is preferably used for fixing panels on thin electronic devices such as televisions and smartphones.

[0186] Furthermore, when the foam sheet is a multilayer structure, the adhesive material is preferably disposed on the outer layer constituting the multilayer structure. For example, when using a multilayer structure with an outer layer on only one side of the foam sheet as the substrate, such as... Figure 2 As shown, the adhesive tape is preferably composed of a multilayer body 2 consisting of a foam sheet A, an outer layer B, and an adhesive material X, which are sequentially stacked. With this configuration, the overall tensile strength of the adhesive tape is increased due to the outer layer, the foam sheet is less prone to breakage during peeling, and it is easy to peel off without leaving any adhesive material on the adhered object. Furthermore, when the foam sheet has an outer layer on both sides, the adhesive material can be provided on only one side of the foam sheet or on both sides, but it is preferred to provide it on both sides.

[0187] Furthermore, the adhesive material only needs to have at least one adhesive layer. It can be a separate adhesive layer laminated to the surface of the foam sheet, or a double-sided adhesive sheet attached to the surface of the foam sheet, but a separate adhesive layer is preferred. It should be noted that the double-sided adhesive sheet has a substrate and adhesive layers disposed on both sides of the substrate. The double-sided adhesive sheet is used to bond one adhesive layer to the foam sheet and another adhesive layer to other components.

[0188] There are no particular limitations on the adhesive used to form the adhesive layer; for example, acrylic adhesives, polyurethane adhesives, and rubber adhesives can be used. Additionally, release sheets such as release paper can be further bonded to the adhesive material.

[0189] The thickness of the adhesive material is preferably 5~200μm, more preferably 7~150μm, and even more preferably 10~100μm.

[0190] [use]

[0191] The uses of the foam sheet and the adhesive tape containing the foam sheet are not particularly limited, but it is preferred to use it inside electronic devices, such as as a fixing material for panels.

[0192] Examples of electronic devices include televisions, laptop computers, mobile phones, smartphones, tablets, portable music devices, cameras, monitors, game consoles, electronic notebooks, and personal computers.

[0193] As described above, the foamed sheet and the adhesive tape incorporating the foamed sheet of the present invention exhibit excellent peelability and good contour tracking. Therefore, the adhesive tape incorporating the foamed sheet is preferably used in displays, particularly large displays, specifically, displays larger than 20 inches. It should be noted that the display can be a liquid crystal display or an organic EL display. Furthermore, when the adhesive tape incorporating the foamed sheet is used in a display, it is applied to the back or bezel of the display, preferably to the bezel. Moreover, as described above, the adhesive tape of the present invention exhibits excellent contour tracking; therefore, when the adhesive tape of the present invention is used in a display, it can follow the contours of the display housing, thereby reducing the area of ​​the gap between the adhesive tape and the housing.

[0194] Furthermore, the adhesive tape with the foamed sheet can be peeled off after splitting along the surface direction. Therefore, in the aforementioned applications, such as when it is necessary to peel off components inside electronic devices during repair, peeling can be performed without relying on the operator's peeling skills, without putting load on the components inside the electronic devices, and without leaving adhesive material on the components. As a result, the reuse of components such as displays becomes easier.

[0195] Example

[0196] The invention will be described in more detail by way of examples, but the invention is not limited by these examples.

[0197] [Determination Method]

[0198] The methods for determining and evaluating each physical property are described below.

[0199] <Thickness of core and outer layers>

[0200] The cross-section of the foam sheet was photographed using a digital microscope (manufactured by KEYENCE Co., Ltd., product name VHX-900), and the thickness of the core layer and outer layer was determined from the photographed image.

[0201] Overall thickness (thickness of the foam sheet)

[0202] The thickness of the foam sheet is the sum of the thickness of the core layer and the thickness of the outer layer.

[0203] <Apparent density and foaming ratio>

[0204] Apparent density was determined according to JIS K7222. Additionally, apparent density (g / cm³) was measured. 3 The reciprocal of ) is the foaming ratio (times).

[0205] <Gel fraction>

[0206] Approximately 100 mg of the test piece was collected from the foam that constitutes the core layer, and its mass A (mg) was accurately weighed. Next, the test piece was immersed in xylene at 120°C for 30 cm. 3 After being placed in the solution for 24 hours, the sample was filtered through a 200-mesh metal mesh. The insoluble components on the mesh were collected, vacuum dried, and the mass B (mg) of the insoluble components was accurately weighed. The gel fraction (mass %) was calculated from the obtained value using the following formula. It should be noted that the test pieces were collected evenly along the thickness direction of the foam that constitutes the core layer.

[0207] Gel fraction (mass%) = 100 × (B / A)

[0208] <Average bubble diameter>

[0209] The foam forming the core layer was cut into 50mm square pieces, immersed in liquid nitrogen for 1 minute, and then cut along the thickness direction along both the MD and TD axes. A 200x magnified photograph was taken using a digital microscope (KEYENCE VHX-900, manufactured by KEYENCE Co., Ltd.). For each 2mm section of the foam in the photographed image, the bubble diameters of MD and ZD, and the bubble diameters of TD and ZD were measured for all air bubbles present in the cut surface. This operation was repeated 5 times. The average bubble diameter of MD and TD for all air bubbles was then set as the average bubble diameter of MD and TD, and the average bubble diameter of ZD measured through the above operation was set as the average bubble diameter of ZD.

[0210] <Independent bubble rate>

[0211] The determination was performed according to the method of ASTM D2856 (1998).

[0212] Specifically, the measurement should be performed according to the following guidelines.

[0213] First, a square test piece with a side length of 5 cm was cut from the foam that constitutes the core layer. Then, the thickness of the test piece was measured, the apparent volume V1 of the test piece was calculated, and the weight W1 of the test piece was measured.

[0214] Next, the volume V2 occupied by the air bubble is calculated based on the following formula. It should be noted that the density of the matrix resin constituting the test piece is set as ρ (g / cm³). 3 ).

[0215] The volume occupied by the bubble is V2 = V1 - W1 / ρ

[0216] 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. Then, the pressure was released in the water, and after standing for 1 minute, the test piece was removed from the water, the water adhering to the surface of the test piece was removed, and the weight W2 of the test piece was measured. The continuous bubble rate F1 and the independent bubble rate F2 were calculated based on the following formula.

[0217] Continuous bubble rate F1(%) = 100 × (W2 - W1) / V2

[0218] Independent bubble rate F2 (%) = 100 - F1

[0219] <25% compressive strength>

[0220] The determination was performed at a temperature of 23°C, following the method described in JIS K 6767.

[0221] Tensile Strength

[0222] The foam sheets prepared in each embodiment and comparative example were cut into dumbbell-shaped No. 1 shapes as specified in JIS K62514.1. These were used as test specimens and subjected to tensile testing using a tensile testing machine (Tensilon RTF235, manufactured by A&D) at a test temperature of 23°C and a speed of 500 mm / min along the MD direction.

[0223] <Tension Strength>

[0224] Figure 3The diagram shows a schematic of a test apparatus used to evaluate fracture strength as interlaminar strength. After applying a primer (CEMEDINE Co., Ltd.'s "PPX Primer") to a 25mm square area of ​​the foam sheet 11 obtained in the various embodiments and comparative examples, a 5mm diameter adhesive 12 (CEMEDINE Co., Ltd.'s "PPX") is dropped into the center of the coated area. Immediately afterward, a 25mm square aluminum clamp 13 is placed on the adhesive-added area, and the foam sheet and clamp 13 are pressed together. Then, the foam sheet is cut along the size of the clamp 13. Primer is applied to the unbonded surface of the cut foam sheet, and a 5mm diameter adhesive 12 is dropped into the center of the coated area. Immediately afterward, a 10mm square aluminum clamp 14 is placed on the adhesive-added area, and the foam sheet and clamp 14 are pressed together. After wiping away the adhesive that has overflowed onto the periphery of the clamp 14, cuts 15 are made on the foam sheet along the size of the clamp 14. The sheet is then left at room temperature for 30 minutes to allow the adhesive to cure, thus preparing a sample for fracture strength testing.

[0225] Next, a 1kN force sensor was installed in a testing machine (Tensilon Universal Testing Machine manufactured by A&D Corporation) equipped with a constant temperature bath for conducting tests within the bath. The sample for fracture strength testing was then mounted on the testing machine with the surface of the foam sheet perpendicular to the tensile direction. The temperature of the constant temperature bath was set to 23°C, and the sample was left to reach 23°C. Then, one side of the clamp was stretched vertically upwards at a speed of 100 mm / min, causing only a 1cm square area of ​​the foam sheet to peel off. The fracture strength at this point was measured and recorded as the first measurement result. The same operation was repeated three times, and the average value was taken as the fracture strength at 23°C.

[0226] <Intermediate cracking>

[0227] After applying adhesive to the foam sheets produced in the various embodiments and comparative examples, the foam sheets were clamped in place with an SUS plate. The blade of a cutter (manufactured by OLFA, trade name "folding blade cutter") was placed on the side of the foam sheet in the MD direction, and the cutter was slid along the MD direction to cut the foam sheet (mid-splitting). Mid-splitting performance was evaluated based on the degree of progress of the cutter at this point. The evaluation criteria are as follows.

[0228] (Evaluation Criteria)

[0229] A: Excellent (no resin debris is produced, and the cutter moves to the end, causing the foam sheet to completely split into two).

[0230] B: Good (The cutter moved to the end, causing the foam sheet to completely split into two, but producing resin debris).

[0231] C: The cutter did not proceed to the end, failing to completely split the foam sheet into two.

[0232] <Evaluation of residual adhesive during peeling>

[0233] After evaluating the crackability as described above, the cracked foam sheet was peeled off from the SUS board used as the adhesive. Based on the amount of residual adhesive material observed when the SUS board was peeled off, the residual adhesive at the time of peeling was evaluated. The evaluation criteria are as follows.

[0234] (Evaluation Criteria)

[0235] A: The adhesive layer was not damaged at the interface between the adhesive layer and the substrate, and the foam sheet after the split was cleanly peeled off from the substrate.

[0236] B: The adhesive layer was damaged several times at the interface between the adhesive layer and the substrate. Part of the adhesive layer remained on the substrate, but the foam sheet after the crack was peeled off to the end.

[0237] C: The adhesive layer is damaged at the interface between the adhesive layer and the adhered object, and the foam sheet after the mid-crack is torn or broken, and is not peeled off to the end.

[0238] <Overall Evaluation>

[0239] A comprehensive evaluation of the physical properties of foamed sheets was conducted based on the following evaluation criteria.

[0240] (Evaluation Criteria)

[0241] A: In the evaluation of cracking properties and residual adhesive during peeling, the evaluation result is not "C".

[0242] B: The evaluation result is "C" in at least one of the evaluation of cracking and the evaluation of residual glue during peeling.

[0243] [Example 1]

[0244] As the resin used to form the core layer of the foam, a linear low-density polyethylene resin (metallocene LLDPE, manufactured by Nippon Polyethylene Co., Ltd., trade name "Kernel KF283") obtained using a metallocene catalyst was prepared; azodicarbonamide was prepared as a thermally decomposable blowing agent. Additionally, zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name "OW-212F") was prepared as a decomposition temperature regulator; and 2,6-di-tert-butyl-p-cresol, a phenolic antioxidant, was prepared as an antioxidant.

[0245] 100 parts by weight of linear low-density polyethylene resin (metallocene LLDPE), 4.5 parts by weight of thermally decomposable foaming agent, 1 part by weight of decomposition temperature regulator and 0.5 parts by weight of antioxidant are fed into a second extruder and melt-blended at 130°C to produce a foamed resin composition for the core layer.

[0246] The resin, decomposition temperature regulator, and antioxidant used for the outer layer are prepared from the same materials as those used for the core layer. 100 parts by weight of linear low-density polyethylene resin (metallocene LLDPE), 1 part by weight of decomposition temperature regulator, and 0.5 parts by weight of antioxidant are supplied to the first extruder and the third extruder, and melt-blended at 130°C to produce the resin composition for the outer layer.

[0247] The foaming resin composition is extruded to 330 μm from a second extruder, and then co-extruded to 220 μm each from a first extruder and a third extruder to obtain an unfoamed laminate sheet having a core layer formed of the foaming resin composition and an outer layer formed of the resin composition laminated on both sides of the core layer.

[0248] Next, the laminated sheet was irradiated with an electron beam of 4.0 Mrad at an accelerating voltage of 550 kV to crosslink it. Then, the crosslinked laminated sheet was continuously fed into a foaming furnace maintained at 250°C using hot air and infrared heaters for heating and foaming. It was then stretched to the target thickness through a stretching process, thereby obtaining the foamed sheet of Example 1 formed by non-foamed body (outer layer) / foamed body (core layer) / non-foamed body (outer layer).

[0249] [Examples 2-3, Comparative Example 2]

[0250] Except for the change in the content of the foaming agent in the foaming resin composition as shown in Table 1, foamed sheets were obtained using the same method as in Example 1.

[0251] [Examples 4-5]

[0252] The thicknesses of the foaming resin composition co-extruded from the second extruder, the resin compositions co-extruded from the first and third extruders, and the content of the foaming agent in the foaming resin composition were changed as shown in Table 1. Otherwise, foamed sheets were obtained by the same method as in Example 1.

[0253] [Example 6]

[0254] The resin used to form the core layer was changed to a styrene-based thermoplastic elastomer (Hybler 7311F manufactured by Kuraray), and the content of the foaming agent in the foaming resin composition was changed as shown in Table 2. Otherwise, a foamed sheet was obtained by the same method as in Example 1.

[0255] [Example 7]

[0256] Except for using an adhesive to bond the polyurethane resin foam (manufactured by INOAC, trade name "PORON") to the non-foamed body (outer layer), the foam sheet was obtained using the same method as in Example 1. It should be noted that the gel fraction of the core layer was not measured in Example 7.

[0257] [Comparative Example 1]

[0258] The thicknesses of the foaming resin composition co-extruded from the second extruder, the resin compositions co-extruded from the first and third extruders, and the content of the foaming agent in the foaming resin composition were changed as shown in Table 2. Otherwise, foamed sheets were obtained by the same method as in Example 1.

[0259] [Comparative Example 3]

[0260] Raw materials were not supplied to the first and third extruders, the resin composition was not laminated on the layer formed by the foaming resin composition used in the core layer, and the thickness of the foaming resin composition co-extruded from the second extruder was changed as shown in Table 2. Otherwise, the core layer was obtained using the same method as in Example 1.

[0261]

[0262]

[0263] As can be seen from the above embodiments, the foam sheet that meets the requirements of the present invention can crack along the surface direction and leaves no adhesive material residue on the adhered object during peeling, thereby exhibiting excellent peelability.

[0264] In contrast, the foam sheets prepared in Comparative Examples 1 and 3 had low tensile strength, resulting in the foam sheets tearing during peeling and adhesive material remaining on the adhered material. Furthermore, the foam sheet prepared in Comparative Example 2 had high fracture strength, therefore it did not crack along the surface direction and did not exhibit excellent peelability.

[0265] Explanation of reference numerals in the attached figures

[0266] 1 multi-layer body

[0267] 2 adhesive sheets

[0268] A. Core layer (foam)

[0269] B, C outer layer

[0270] X adhesive materials

[0271] 11 foaming tablets

[0272] 12 Adhesive

[0273] 13 clamps

[0274] 14 clamps

[0275] 15 incisions.

Claims

1. A foam sheet having a tensile strength of 1-9 MPa and a breaking strength of less than 3.5 MPa as measured during interlaminar strength determination, and the overall thickness of the foam sheet being 0.05-0.9 mm.

2. The foamed sheet according to claim 1, wherein the 25% compressive strength of the foamed sheet is below 150 kPa.

3. The foamed sheet according to claim 1, wherein the overall density of the foamed sheet is 0.07~0.60 g / cm³. 3 .

4. The foamed sheet according to claim 1, comprising a core layer and outer layers respectively disposed on both sides of the core layer, wherein the core layer is a foamed material and the outer layers are foamed materials with a foaming ratio lower than that of the core layer, or non-foamed materials.

5. The foamed sheet according to claim 4, wherein the foaming ratio of the core layer is 5 to 20 times.

6. The foam sheet according to claim 4, wherein the thickness ratio of the core layer to the outer layer, i.e., the ratio of the thickness of the core layer to the average thickness of the outer layer, is 2 or more.

7. The foamed sheet according to claim 4, wherein the independent bubble rate of the core layer is 90% or more.

8. The foam sheet according to claim 4, wherein the thickness of each of the outer layers is 5 μm or more.

9. The foamed sheet according to claim 4, wherein the average bubble diameter of the bubbles in the core layer is 20~500μm.

10. The foam sheet according to claim 4, wherein the core layer is a cross-linked foam.

11. The foamed sheet according to claim 10, wherein the gel fraction of the core layer is 20-50% by mass.

12. The foam sheet according to claim 4, wherein the resin constituting the core layer is selected from at least one of polyolefin resins, polyurethane resins, acrylic resins, and elastic resins.

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

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