adhesive tape

Abstract

To provide an adhesive tape that has excellent conformability to unevenness and can suppress deflection that occurs when a foamed resin sheet is transported during production. [Solution] An adhesive tape having a foamed resin sheet containing a polyolefin resin and an adhesive layer laminated on at least one side of the foamed resin sheet, wherein the polyolefin resin contains high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), the foamed resin sheet has a gel fraction of 20% by weight or more and 60% by weight or less, and the adhesive tape satisfies the following formula (1): 2≦(MD×TD) / (ZD) 2 (1) In formula (1), MD, TD, and ZD represent the average cell diameters in the MD, TD, and ZD directions of the foamed resin sheet, respectively.

Description

[Technical Field]

[0001] The present invention relates to an adhesive tape that has excellent conformability to unevenness and can suppress deflection that occurs when a foamed resin sheet is transported during production. [Background technology]

[0002] Adhesive tapes having an adhesive layer have been widely used to fix components in electronic devices, vehicles, houses, and building materials. Specifically, adhesive tapes are used, for example, to bond a cover panel for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or to bond a touch panel module to a display panel module.

[0003] Adhesive tape is sometimes crushed when used to secure two parts together, so it is required to be highly flexible so that it can conform to uneven surfaces such as the uneven shapes of the parts. As an adhesive tape having excellent conformability to unevenness, for example, an adhesive tape using a highly flexible foamed resin sheet as a substrate is used. Patent Documents 1 and 2 describe an impact absorbing tape in which an acrylic adhesive layer is laminated and integrated onto at least one surface of a substrate layer, and the substrate layer is a crosslinked polyolefin resin foam sheet having a specific degree of crosslinking and a specific aspect ratio of cells. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-242541 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-258274 Summary of the Invention [Problem to be solved by the invention]

[0005] Polyolefin resins such as those described in Patent Documents 1 and 2 are used as raw materials for foamed resin sheets. Among these, linear low-density polyethylene (LLDPE) is widely used because it has an appropriate density, can achieve a high degree of both flexibility and strength, and can easily form thin foamed resin sheets. However, foamed resin sheets made of linear low-density polyethylene (LLDPE) have the problem that they are prone to deflection when transported during the production of pressure-sensitive adhesive tapes, and wrinkles occur when pressure-sensitive adhesive layers are laminated on them.

[0006] An object of the present invention is to provide an adhesive tape that has excellent conformability to unevenness and can suppress deflection that occurs when a foamed resin sheet is transported during production. [Means for solving the problem]

[0007] The present invention provides an adhesive tape having a foamed resin sheet containing a polyolefin resin and an adhesive layer laminated on at least one surface of the foamed resin sheet, wherein the polyolefin resin contains high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), the foamed resin sheet has a gel fraction of 20% by weight or more and 60% by weight or less, and the adhesive tape satisfies the following formula (1): 2≦(MD×TD) / (ZD) 2 (1) In formula (1), MD, TD, and ZD represent the average cell diameters in the MD, TD, and ZD directions of the foamed resin sheet, respectively. The present invention will be described in detail below.

[0008] The present inventors have investigated the use of high-pressure low-density polyethylene (LDPE) in addition to linear low-density polyethylene (LLDPE) as the polyolefin resin in an adhesive tape having a foamed resin sheet containing a polyolefin resin and an adhesive layer laminated on at least one side of the foamed resin sheet. Furthermore, the present inventors have found that, in such an adhesive tape, by adjusting the gel fraction of the foamed resin sheet to a specific range and adjusting the average cell diameter to satisfy a specific formula, it is possible to maintain excellent conformability to uneven surfaces while suppressing deflection that occurs when the foamed resin sheet is transported during the production of the adhesive tape. This has led to the completion of the present invention.

[0009] The pressure-sensitive adhesive tape of the present invention comprises a foamed resin sheet containing a polyolefin resin, and a pressure-sensitive adhesive layer laminated on at least one surface of the foamed resin sheet. By using the foamed resin sheet as a substrate, the pressure-sensitive adhesive tape can have excellent conformability to uneven surfaces.

[0010] The polyolefin resin includes high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). High-pressure low-density polyethylene (LDPE) is a polyethylene with a long-chain branching structure and a density of 0.930 g / cm 3 Linear low density polyethylene (LLDPE) refers to a polyethylene resin with a density of 0.930 g / cm or less, in which an appropriate number of short chain branches are introduced into a linear backbone polymer, and the molecular chain is substantially linear. 3 Linear low-density polyethylene (LLDPE) can be prepared, for example, by copolymerizing ethylene with a small amount (about 1 to 10 mol %) of an α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or 4-methyl-1-pentene through an ionic polymerization reaction under medium to low pressure. When the polyolefin resin contains high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), the adhesive tape has excellent conformability to uneven surfaces, and the tensile modulus of the foamed resin sheet is increased, thereby suppressing deflection that occurs when the foamed resin sheet is transported during the production of the adhesive tape.

[0011] The high-pressure low-density polyethylene (LDPE) may consist solely of petroleum-derived LDPE, but preferably contains bio-derived LDPE. In recent years, the depletion of petroleum resources and carbon dioxide emissions from the combustion of petroleum-derived products have become a problem. The use of biologically derived materials is preferable from the viewpoint of saving petroleum resources. Furthermore, since biologically derived materials are originally produced by absorbing carbon dioxide from the atmosphere, their combustion is not expected to increase the total amount of carbon dioxide in the atmosphere. Therefore, the use of biologically derived materials is also preferable from the viewpoint of reducing carbon dioxide emissions. An example of the biologically-derived LDPE is LDPE made from sugarcane.

[0012] The melt flow rate (MFR) of the high-pressure low-density polyethylene (LDPE) is not particularly limited, but a preferred lower limit is 0.1 g / 10 min and a preferred upper limit is 20 g / 10 min. If the MFR is 0.1 g / 10 min or more, the high-pressure low-density polyethylene (LDPE) has increased fluidity when melted, facilitating molding and processing. If the MFR is 20 g / 10 min or less, the strength of the adhesive tape will be increased. A more preferred lower limit of the MFR is 1 g / 10 min and a more preferred upper limit is 10 g / 10 min. The MFR can be measured by the method specified in JIS K 7210:1999.

[0013] The density of the high-pressure low-density polyethylene (LDPE) is 0.910 g / cm 3 More than 0.930g / cm 3 It is preferable that the density is less than 0.910 g / cm 3If the density is 0.930 g / cm or more, the strength of the adhesive tape will be higher. 3 If the density is less than 0.915 g / cm, the adhesive tape will have better conformability to uneven surfaces. 3 , and a more preferable upper limit is 0.925 g / cm 3 is. The density can be measured in accordance with JIS K 6767 using an electronic densimeter (for example, "ED120T" manufactured by Mirage).

[0014] Commercially available high-pressure low-density polyethylene (LDPE) includes, for example, SEB853 (manufactured by Braskem), LF640MA (manufactured by Japan Polyethylene Co., Ltd.), LF440HB (manufactured by Japan Polyethylene Co., Ltd.), and LF448K (manufactured by Japan Polyethylene Co., Ltd.). These high-pressure low-density polyethylenes (LDPE) may be used alone or in combination of two or more. Among these, SEB853 (manufactured by Braskem) is preferred because it is a biological material.

[0015] The content of the high-pressure low-density polyethylene (LDPE) in the polyolefin resin is not particularly limited, but a preferred lower limit is 20% by weight and a preferred upper limit is 80% by weight. If the content is 20% by weight or more, the tensile modulus of the foamed resin sheet becomes higher, and deflection that occurs when the foamed resin sheet is conveyed during the production of the pressure-sensitive adhesive tape can be more effectively suppressed. If the content is 80% by weight or less, the pressure-sensitive adhesive tape can have a higher ability to conform to unevenness, and the foamed resin sheet can be stretched well, making it easier to adjust the average cell diameter. A more preferred lower limit of the content is 35% by weight and a more preferred upper limit is 65% by weight.

[0016] The linear low-density polyethylene (LLDPE) may be composed of ethylene alone, or may be composed of ethylene and an α-olefin other than ethylene. The α-olefin other than ethylene is not particularly limited, and examples thereof include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. These α-olefins may be used alone or in combination of two or more. The linear low-density polyethylene (LLDPE) is preferably a linear low-density polyethylene (LLDPE) obtained using a metallocene catalyst. Use of the metallocene catalyst narrows the molecular weight distribution of the linear low-density polyethylene (LLDPE), thereby increasing the strength of the pressure-sensitive adhesive tape.

[0017] The melt flow rate (MFR) of the linear low-density polyethylene (LLDPE) is not particularly limited, but a preferred lower limit is 0.1 g / 10 min and a preferred upper limit is 20 g / 10 min. If the MFR is 0.1 g / 10 min or more, the fluidity of the linear low-density polyethylene (LLDPE) when melted increases, facilitating molding and processing. If the MFR is 20 g / 10 min or less, the strength of the adhesive tape increases. A more preferred lower limit of the MFR is 1 g / 10 min and a more preferred upper limit is 10 g / 10 min.

[0018] The density of the linear low-density polyethylene (LLDPE) is 0.870 g / cm 3 More than 0.930g / cm 3 It is preferable that the density is less than 0.870 g / cm 3 If the density is 0.930 g / cm or more, the strength of the adhesive tape will be higher. 3 If the density is less than 0.910 g / cm, the adhesive tape will have better conformability to uneven surfaces. 3 , and a more preferable upper limit is 0.925 g / cm 3 is.

[0019] Commercially available linear low-density polyethylene (LLDPE) products include, for example, Exact 3027 (manufactured by Exxon Chemical Co.), UF240 (manufactured by Japan Polyethylene Co., Ltd.), UF641 (manufactured by Japan Polyethylene Co., Ltd.), and UF943 (manufactured by Japan Polyethylene Co., Ltd.) These linear low-density polyethylenes (LLDPE) may be used alone or in combination of two or more types.

[0020] The content of the linear low-density polyethylene (LLDPE) in the polyolefin resin is not particularly limited, but a preferred lower limit is 20% by weight and a preferred upper limit is 80% by weight. If the content is 20% by weight or more, the adhesive tape will have higher conformability to unevenness, and the foamed resin sheet can be stretched well, making it easier to adjust the average cell diameter. If the content is 80% by weight or less, the foamed resin sheet will have a higher tensile modulus, and deflection that occurs when the foamed resin sheet is transported during adhesive tape production can be more effectively suppressed. A more preferred lower limit of the content is 35% by weight and a more preferred upper limit is 65% by weight.

[0021] The foamed resin sheet has a gel fraction of 20% by weight at the lower limit and 60% by weight at the upper limit. When the gel fraction of the foamed resin sheet is within this range, the pressure-sensitive adhesive tape can have excellent conformability to uneven surfaces, and deflection that occurs when the foamed resin sheet is transported during the production of the pressure-sensitive adhesive tape can be suppressed. The foamed resin sheet preferably has a gel fraction of 25% by weight at the lower limit and 55% by weight at the upper limit, more preferably 30% by weight at the lower limit and 50% by weight at the upper limit. The gel fraction of the foamed resin sheet can be measured by the following method. A test piece is prepared by cutting a foamed resin sheet into a flat rectangular shape of 50 mm x 100 mm. The test piece is immersed in xylene at 120°C for 24 hours, then removed from the xylene and vacuum dried. The weight of the dried test piece is measured, and the gel fraction is calculated using the following formula (2). No release film is laminated on the test piece. Gel fraction (wt%) = 100 × W2 / W1(2) (W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

[0022] The method for adjusting the gel fraction of the foamed resin sheet to fall within the above range is not particularly limited, but a method for adjusting the degree of crosslinking of the foamed resin sheet by adjusting the amount of electron beam irradiation during production of the foamed resin sheet is preferred. More specifically, the degree of crosslinking of the foamed resin sheet can be adjusted by adjusting the amount of electron beam irradiation, by increasing the intensity of electron beam irradiation or by lengthening the time of electron beam irradiation.

[0023] The foamed resin sheet satisfies the following formula (1). 2≦(MD×TD) / (ZD) 2 (1) In formula (1), MD, TD, and ZD represent the average cell diameters in the MD, TD, and ZD directions of the foamed resin sheet, respectively. The MD (Machine Direction) direction is the flow direction of the foamed resin sheet when it is molded into a sheet shape, the TD (Transverse Direction) direction is the direction perpendicular to the MD direction, and the ZD direction is the thickness direction of the foamed resin sheet.

[0024] Above (MD × TD) / (ZD) 2 is the product of the ratio of the average cell diameter in the MD direction to the average cell diameter in the ZD direction of the foamed resin sheet (MD / ZD) and the ratio of the average cell diameter in the TD direction to the average cell diameter in the ZD direction of the foamed resin sheet (TD / ZD) [(MD / ZD) × (TD / ZD)]. 2 The larger the value of (MD×TD) / (ZD), the smaller the average cell diameter in the ZD direction is compared to the average cell diameters in the MD and TD directions, i.e., the more the cells in the foamed resin sheet are crushed in the thickness direction. 2When the value of (MD×TD) / (ZD) is 2 or more, the pressure-sensitive adhesive tape can have excellent conformability to unevenness, and can suppress deflection that occurs when the foamed resin sheet is transported during the production of the pressure-sensitive adhesive tape. 2 A preferred lower limit for the value is 3.5. Above (MD × TD) / (ZD) 2 Although there are no particular limitations on the upper limit of the value, a preferred upper limit is 25, and a more preferred upper limit is 20, since the strength of the foamed resin sheet is sufficiently exhibited when the adhesive tape is peeled off. The average bubble diameters in the MD, TD, and ZD directions of a foamed resin sheet can be measured using a digital microscope (Keyence Corporation, product name VHX-900 or equivalent). More specifically, for example, a foamed resin sheet is cut into 50 mm squares to serve as a measurement sample. This measurement sample is then immersed in liquid nitrogen for 1 minute and cut into thickness directions along the MD and TD directions with a razor blade. A 200x magnification photograph of the cut surface is taken using a digital microscope (Keyence Corporation, product name VHX-900 or equivalent), and the bubble diameters of all bubbles present in a 2 mm long region in each of the MD and TD directions are measured. This procedure is repeated five times. The bubble diameters in all MD and TD directions are measured, and the number-average bubble diameters in the MD and TD directions are calculated, which are defined as the average bubble diameters in the MD and TD directions. Furthermore, the bubble diameters in the ZD direction of all measured bubbles are measured, and the number-average bubble diameter is calculated, which is defined as the average bubble diameter in the ZD direction.

[0025] Above (MD × TD) / (ZD) 2 Although the method for adjusting the value of to within the above range is not particularly limited, a method for adjusting the production conditions of the foamed resin sheet is preferred. Specific examples thereof include a method for adjusting the stretching conditions when the foamed resin sheet is stretched after being molded during the production of the foamed resin sheet.

[0026] The average cell diameters in the MD and TD of the foamed resin sheet are not particularly limited, but are preferably 20 μm or more and 350 μm or less in both directions. When the average cell diameters in the MD and TD are within the above ranges, the maximum cell diameter is also small, and the 25% compressive strength of the foamed resin sheet can be adjusted to a desired range while improving performance such as impact resistance and impact absorption. From these viewpoints, the average cell diameters in the MD and TD of the foamed resin sheet are more preferably 30 μm or more and 250 μm or less, even more preferably 50 μm or more and 200 μm or less, and even more preferably 60 μm or more and 140 μm or less. The average bubble diameter in the ZD direction of the foamed resin sheet is not particularly limited, but from the viewpoint of ensuring the impact resistance, impact absorption, etc. of the foamed resin sheet, it is preferably 5 μm or more and 250 μm or less, more preferably 10 μm or more and 140 μm or less, even more preferably 15 μm or more and 100 μm or less, and even more preferably 20 μm or more and 60 μm or less.

[0027] The expansion ratio of the foamed resin sheet is not particularly limited, but the preferred lower limit is 1.5 cm 3 / g, with a preferred upper limit of 20 cm 3 / g. The foaming ratio of the foamed resin sheet is 1.5 cm 3 / g or more, the step-following ability of the adhesive tape is improved. 3 When the expansion ratio of the foamed resin sheet is 2 cm / g or less, the strength of the pressure-sensitive adhesive tape is sufficient, and the foamed resin sheet can be prevented from becoming too thick, so that the deflection that occurs when the foamed resin sheet is transported during the production of the pressure-sensitive adhesive tape can be further suppressed. 3 / g, and a more preferable upper limit is 15 cm 3 / g. The expansion ratio of the foamed resin sheet can be calculated by measuring the density of the foamed resin sheet in accordance with JIS K 7222 and calculating the reciprocal thereof.

[0028] The content of bio-derived carbon in the foamed resin sheet is not particularly limited, but is preferably 20% by weight or more. A bio-derived carbon content of 20% by weight or more is preferable from the viewpoint of reducing the burden on the environment, i.e., from the viewpoint of saving petroleum resources and reducing carbon dioxide emissions. From this viewpoint, the content of bio-derived carbon is more preferably 40% by weight or more, even more preferably 50% by weight or more, and even more preferably 60% by weight or more. The upper limit of the content of bio-derived carbon is not particularly limited, but from the viewpoint of the strength, flexibility, production cost, etc. of the foamed resin sheet, it is preferably 90% by weight or less, more preferably 82% by weight or less, even more preferably 75% by weight or less, and even more preferably 68% by weight or less. While carbon derived from living organisms contains a certain percentage of the radioactive isotope C-14, petroleum-derived carbon contains almost no C-14. Therefore, the content of carbon derived from living organisms can be calculated by measuring the concentration of C-14 in the sample. Specifically, this can be measured in accordance with ASTM D6866-20, a standard used in many bioplastic industries.

[0029] The thickness of the foamed resin sheet is not particularly limited, but a preferred lower limit is 0.05 mm and a preferred upper limit is 1.5 mm. If the thickness of the foamed resin sheet is 0.05 mm or more, the strength of the adhesive tape will be sufficient. If the thickness of the foamed resin sheet is 1.5 mm or less, deflection that occurs when the foamed resin sheet is transported during adhesive tape production can be further suppressed. A more preferred lower limit of the thickness of the foamed resin sheet is 0.1 mm and a more preferred upper limit is 1.0 mm.

[0030] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer laminated on at least one surface of the foamed resin sheet. The pressure-sensitive adhesive layer may be laminated on only one surface of the foamed resin sheet, or on both surfaces thereof. The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive layer, a rubber-based pressure-sensitive adhesive layer, a urethane pressure-sensitive adhesive layer, a silicone-based pressure-sensitive adhesive layer, etc. Among these, an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer and a tackifying resin is preferred because it is relatively stable against light, heat, moisture, etc. and can adhere to a variety of adherends (it has low adherend selectivity).

[0031] From the viewpoint of improving initial tackiness and thus improving ease of application at low temperatures, the acrylic copolymer preferably contains at least one selected from the group consisting of structural units derived from butyl acrylate and structural units derived from 2-ethylhexyl acrylate, and more preferably contains both structural units derived from butyl acrylate and structural units derived from 2-ethylhexyl acrylate. The content of the structural units derived from butyl acrylate in the acrylic copolymer is preferably 40% by weight at the lower limit and 80% by weight at the upper limit. By setting the content of the structural units derived from butyl acrylate within this range, the adhesive strength of the pressure-sensitive adhesive layer can be further increased. The content of the structural units derived from 2-ethylhexyl acrylate in the acrylic copolymer is preferably 10 wt% at the lower limit and 100 wt% at the upper limit, more preferably 30 wt%, more preferably 80 wt%, even more preferably 50 wt%, and even more preferably 60 wt%. By keeping the content of the structural units derived from 2-ethylhexyl acrylate within this range, the adhesive strength of the pressure-sensitive adhesive layer is further increased.

[0032] The acrylic copolymer may contain, as necessary, a structural unit derived from another copolymerizable polymerizable monomer other than the structural unit derived from butyl acrylate and the structural unit derived from 2-ethylhexyl acrylate. Examples of the other copolymerizable polymerizable monomer include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms, (meth)acrylic acid alkyl esters having an alkyl group with 13 to 18 carbon atoms, and functional monomers. Examples of (meth)acrylic acid alkyl esters having 1 to 3 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc. Examples of (meth)acrylic acid alkyl esters having 13 to 18 carbon atoms in the alkyl group include tridecyl methacrylate and stearyl (meth)acrylate, etc. Examples of the functional monomers include hydroxyalkyl (meth)acrylate, glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc. Among these, from the viewpoint of increasing the bulk strength and elastic modulus at high temperatures of the pressure-sensitive adhesive layer, hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylate and glycerin dimethacrylate are preferred.

[0033] The acrylic copolymer preferably contains a structural unit derived from at least one selected from the group consisting of n-heptyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, decyl (meth)acrylate, and isostearyl (meth)acrylate. These biologically derived monomers are relatively easy to obtain, and their use can reduce carbon dioxide emissions. Furthermore, since the glass transition temperatures of the homopolymers of these monomers are relatively low, a pressure-sensitive adhesive layer containing an acrylic copolymer containing structural units derived from such monomers is likely to exhibit adhesive properties. Therefore, by using a relatively large amount of these monomers to increase the content of biologically derived carbon in the entire pressure-sensitive adhesive layer, and optionally combining other non-biologically derived monomers, a pressure-sensitive adhesive layer that can exhibit sufficient adhesive strength can be obtained. In particular, it is more preferable that the acrylic copolymer contains a structural unit derived from n-heptyl (meth)acrylate, since this allows excellent adhesive strength to be exerted on both smooth and rough surfaces. The content of the structural units derived from these monomers in the acrylic copolymer is not particularly limited, but the lower limit is preferably 25% by weight, the upper limit is preferably 99% by weight, the lower limit is more preferably 48% by weight, the upper limit is more preferably 97% by weight, the lower limit is even more preferably 60% by weight, and the lower limit is even more preferably 80% by weight.

[0034] To obtain the acrylic copolymer, a monomer mixture containing the above-mentioned monomers may be copolymerized. To obtain the acrylic copolymer by copolymerizing the monomer mixture, the monomer mixture may be subjected to a radical reaction in the presence of a polymerization initiator. As a method for radically reacting the monomer mixture, i.e., a polymerization method, a conventionally known method may be used, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0035] The weight-average molecular weight (Mw) of the acrylic copolymer has a preferred lower limit of 300,000 and a preferred upper limit of 2,000,000. By setting the weight-average molecular weight of the acrylic copolymer within this range, the adhesive strength of the pressure-sensitive adhesive layer is further increased. The weight-average molecular weight more preferably has a lower limit of 400,000 and a more preferred upper limit of 1,900,000, an even more preferred lower limit of 500,000 and a still more preferred upper limit of 1,800,000, an even more preferred lower limit of 600,000 and a still more preferred upper limit of 1,750,000. The weight-average molecular weight (Mw) is the weight-average molecular weight measured by gel permeation chromatography (GPC) in terms of standard polystyrene. Specifically, the acrylic copolymer is diluted 50 times with tetrahydrofuran (THF), and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore size: 0.2 μm) to prepare a measurement sample. This measurement sample is fed to a gel permeation chromatograph (Waters, trade name "2690 Separations Model" or equivalent) and subjected to GPC measurement under conditions of a sample flow rate of 1 ml / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of the acrylic copolymer is measured, and this value is taken as the weight-average molecular weight.

[0036] The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic copolymer has a preferred lower limit of 1.05 and an upper limit of 5.0. When Mw / Mn is 5.0 or less, the proportion of low-molecular-weight components is suppressed, and the adhesive strength of the pressure-sensitive adhesive layer is further increased. The upper limit of Mw / Mn is more preferably 4.5, even more preferably 4, and even more preferably 3.5.

[0037] Examples of the tackifying resin include rosin resins, rosin ester resins, hydrogenated rosin resins, terpene resins, terpene phenol resins, coumarone-indene resins, alicyclic saturated hydrocarbon resins, C5 petroleum resins, C9 petroleum resins, and C5-C9 copolymer petroleum resins. These tackifying resins may be used alone or in combination of two or more. Among these, rosin resins or terpene resins are preferred, and rosin resins or terpene resins having a hydroxyl group are more preferred.

[0038] The softening temperature of the tackifier resin preferably has a lower limit of 70°C and an upper limit of 170°C. If the softening temperature is 70°C or higher, the pressure-sensitive adhesive layer can be prevented from becoming too soft and easily peeling. If the softening temperature is 170°C or lower, the pressure-sensitive adhesive layer can be prevented from having poor interface wettability, resulting in interfacial peeling. A more preferred lower limit of the softening temperature is 120°C. The softening temperature is measured by the ring and ball method according to JIS K2207.

[0039] The tackifier resin preferably has a hydroxyl value of 25 (lower limit) and 55 (upper limit). When the hydroxyl value is within the above range, interfacial peeling due to poor wettability at the interface of the pressure-sensitive adhesive layer can be suppressed. The hydroxyl value is more preferably 30 (lower limit) and 50 (upper limit). The hydroxyl value can be measured according to JIS K1557 (phthalic anhydride method).

[0040] The content of the tackifier resin is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 60 parts by weight per 100 parts by weight of the acrylic copolymer. If the content of the tackifier resin is 10 parts by weight or more, the adhesive strength of the pressure-sensitive adhesive layer will be higher. If the content of the tackifier resin is 60 parts by weight or less, the pressure-sensitive adhesive layer can be prevented from becoming too hard and losing its adhesive strength.

[0041] The pressure-sensitive adhesive layer preferably contains a crosslinking agent to form a crosslinked structure between the main chains of the resins (e.g., the acrylic copolymer, the tackifying resin, etc.) that constitute the pressure-sensitive adhesive layer. By adjusting the type and amount of the crosslinking agent, it becomes easier to adjust the gel fraction of the pressure-sensitive adhesive layer. The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, etc. Of these, isocyanate-based crosslinking agents are preferred. The amount of the crosslinking agent added is preferably 0.01 parts by weight at the lower limit and 10 parts by weight at the upper limit, more preferably 0.1 parts by weight and 3 parts by weight at the upper limit, per 100 parts by weight of the acrylic copolymer.

[0042] The content of bio-derived carbon in the pressure-sensitive adhesive layer is not particularly limited, but is preferably 10% by weight or more. A bio-derived carbon content of 10% by weight or more is an indicator of a "bio-based product." A bio-derived carbon content of 10% by weight or more is preferable from the perspective of reducing the burden on the environment, i.e., from the perspective of saving petroleum resources and reducing carbon dioxide emissions. A more preferred lower limit of the bio-derived carbon content is 30% by weight, and an even more preferred lower limit is 60% by weight. The upper limit of the bio-derived carbon content is not particularly limited, and may be 100% by weight. The content of bio-derived carbon in the pressure-sensitive adhesive layer can be measured in the same manner as in the case of the foamed resin sheet.

[0043] The pressure-sensitive adhesive layer may contain a silane coupling agent to improve adhesive strength. The silane coupling agent is not particularly limited, and examples thereof include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

[0044] The pressure-sensitive adhesive layer may contain a colorant to impart light-blocking properties. The colorant is not particularly limited, and examples thereof include carbon black, aniline black, titanium oxide, etc. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

[0045] The pressure-sensitive adhesive layer may contain conventionally known fine particles and additives, such as inorganic fine particles, conductive fine particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, as needed.

[0046] The gel fraction of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 1 wt% and a preferred upper limit is 80 wt%. If the gel fraction is 1 wt% or more, the bulk strength and elastic modulus at high temperatures of the pressure-sensitive adhesive layer increase, resulting in higher adhesive strength. If the gel fraction is 80 wt% or less, the pressure-sensitive adhesive layer will have poor interface wettability, thereby preventing interfacial peeling. A more preferred lower limit of the gel fraction is 10 wt%, a more preferred upper limit is 75 wt%, an even more preferred lower limit is 20 wt%, an even more preferred upper limit is 70 wt%, an even more preferred lower limit is 30 wt%, and an even more preferred upper limit is 65 wt%. The gel fraction of the pressure-sensitive adhesive layer can be measured by the following method. The adhesive layer is cut from the adhesive tape into a flat rectangular shape of 50 mm x 100 mm to prepare a test specimen. The test specimen is immersed in ethyl acetate at 23°C for 24 hours, then removed from the ethyl acetate and dried at 110°C for 1 hour. The weight of the dried test specimen is measured, and the gel fraction is calculated using the following formula (3). No release film to protect the adhesive layer is laminated on the test specimen. Gel fraction (wt%) = 100 × (W4 - W0) / (W3 - W0) (3) (W0: weight of substrate, W3: weight of test piece before immersion, W4: weight of test piece after immersion and drying)

[0047] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but the preferred lower limit of the thickness of the pressure-sensitive adhesive layer on one side is 20 μm, and the preferred upper limit is 100 μm. If the thickness of the pressure-sensitive adhesive layer is 20 μm or more, the pressure-sensitive adhesive layer will have sufficient adhesive strength. If the thickness of the pressure-sensitive adhesive layer is 100 μm or less, the flexibility of the foamed resin sheet can sufficiently contribute to the flexibility of the pressure-sensitive adhesive tape as a whole. The more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 25 μm, and the more preferred upper limit is 80 μm, and the even more preferred lower limit is 30 μm, and the even more preferred upper limit is 70 μm, and the even more preferred lower limit is 35 μm, and the even more preferred upper limit is 65 μm. The thickness of the adhesive layer can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation or an equivalent product).

[0048] The pressure-sensitive adhesive tape of the present invention may further include a resin sheet that is integrated with the foamed resin sheet and is separate from the foamed resin sheet. By using the resin sheet, it is possible to prevent the foamed resin sheet from stretching and breaking during handling, and it is also possible to impart reworkability to the pressure-sensitive adhesive tape. The resin sheet may be laminated on only one surface of the foamed resin sheet, or on both surfaces thereof. The resin constituting the resin sheet is not particularly limited, and examples thereof include polyester resins such as polyethylene terephthalate, polyethylene resins, polypropylene resins, polyvinyl chloride, epoxy resins, silicone resins, phenolic resins, polyimides, polyesters, polycarbonates, etc. Among these, polyethylene resins, polypropylene resins, and polyester resins are preferred because of their excellent flexibility. Among polyester resins, polyethylene terephthalate is preferred.

[0049] The thickness of the resin sheet is not particularly limited, but a preferred lower limit is 10 μm and a preferred upper limit is 100 μm. If the thickness of the resin sheet is 10 μm or more, the resin sheet is less likely to break even when pulled. If the thickness of the resin sheet is 100 μm or less, a decrease in the step-following ability of the adhesive tape can be suppressed.

[0050] The resin sheet may be colored. By coloring the resin sheet, it is possible to impart light-blocking properties to the pressure-sensitive adhesive tape. The method for coloring the resin sheet is not particularly limited, and examples thereof include a method of kneading particles of carbon black, titanium oxide, or the like, or fine bubbles into the resin that constitutes the resin sheet, and a method of applying ink to the surface of the resin sheet.

[0051] The adhesive strength of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but the lower limit of the 180° peel strength against polycarbonate measured in accordance with JIS Z 0237 is preferably 2 N / 25 mm, more preferably 5 N / 25 mm. If the 180° peel strength against polycarbonate is 2 N / 25 mm or more, the step-following ability of the pressure-sensitive adhesive tape will be improved. There is no particular upper limit for the 180° peel strength, and the higher the better, but it is substantially about 25 N / 25 mm. The method for adjusting the 180° peel strength from the polycarbonate to fall within the above range is not particularly limited, and examples thereof include methods for adjusting the composition, thickness, etc. of the pressure-sensitive adhesive layer. The 180° peel strength can be measured by the following method. A test piece was prepared by cutting the adhesive tape to a width of 25 mm and a length of 75 mm. The test piece was then placed on a polycarbonate sheet with the adhesive layer facing the polycarbonate, and then laminated by rolling a 2 kg rubber roller back and forth on the test piece at a speed of 300 mm / min. The test piece was then aged for 20 minutes at 23°C and 50% humidity. According to JIS Z 0237, the test piece was peeled in a 180° direction at a pulling rate of 300 mm / min at 23°C and 50% humidity, and the peel force (N / 25 mm) was measured. For double-sided adhesive tapes with adhesive layers on both sides, a 23 μm-thick polyethylene terephthalate film (e.g., FE2002 or equivalent, manufactured by Futamura Chemical Co., Ltd.) was attached to the surface of the adhesive layer not being measured before laminating the tape to the polycarbonate sheet.

[0052] The pressure-sensitive adhesive tape of the present invention has a total thickness of preferably 3 μm at its lower limit and 1200 μm at its upper limit, and more preferably 500 μm at its upper limit.

[0053] The content of bio-derived carbon in the pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably 10% by weight or more. A bio-derived carbon content of 10% by weight or more is an indicator of a "bio-based product." A bio-derived carbon content of 10% by weight or more is preferable from the viewpoint of reducing the burden on the environment, i.e., from the viewpoint of saving petroleum resources and reducing carbon dioxide emissions. A more preferred lower limit of the bio-derived carbon content is 40% by weight, and an even more preferred lower limit is 60% by weight. The upper limit of the bio-derived carbon content is not particularly limited, and may be 100% by weight. The content of bio-derived carbon in a pressure-sensitive adhesive tape refers to the weight proportion of bio-derived carbon in the weight of the pressure-sensitive adhesive tape. The pressure-sensitive adhesive tape referred to here does not include release films, release papers, release liners, etc. More specifically, for example, the content of bio-derived carbon in a pressure-sensitive adhesive tape can be determined as follows. That is, the content of bio-derived carbon in each component constituting the pressure-sensitive adhesive tape (typically, the foam resin sheet and the adhesive layer) is determined. The total amount of bio-derived carbon in all components (the sum of the above values) is determined from the value obtained by multiplying the content of bio-derived carbon in each component by the weight ratio of each component (the weight ratio of each component to the total weight of the pressure-sensitive adhesive tape). The content of bio-derived carbon in the pressure-sensitive adhesive tape can be calculated by dividing this sum by the total weight of the pressure-sensitive adhesive tape.

[0054] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and the tape can be produced by a conventionally known production method. For example, in the case of a double-sided pressure-sensitive adhesive tape, the following method can be mentioned. First, a solution of adhesive A is prepared by adding a solvent to an acrylic copolymer and, if necessary, a crosslinking agent, a tackifying resin, etc., and this solution of adhesive A is applied to the surface of a foamed resin sheet, and the solvent in the solution is completely dried and removed to form adhesive layer A. Next, a release film is superimposed on the formed adhesive layer A with its release-treated surface facing the adhesive layer A. Next, a release film separate from the above-mentioned release film is prepared, and a solution of adhesive B prepared in the same manner as above is applied to the release-treated surface of this release film. The solvent in the solution is then completely dried and removed to produce a laminate film in which adhesive layer B is formed on the surface of the release film. The obtained laminate film is overlaid on the back surface of a foamed resin sheet on which adhesive layer A is formed, with adhesive layer B facing the back surface of the foamed resin sheet, to produce a laminate. The laminate is then pressed with a rubber roller or the like to produce a double-sided adhesive tape in which adhesive layers are on both sides of the foamed resin sheet and the surfaces of the adhesive layers are covered with release films.

[0055] Alternatively, two sets of laminate films may be prepared in a similar manner, and these laminate films may be superimposed on both sides of a foamed resin sheet with the pressure-sensitive adhesive layers of the laminate films facing the foamed resin sheet to prepare a laminate, which may then be pressed with a rubber roller, etc. This method also makes it possible to obtain a double-sided pressure-sensitive adhesive tape having pressure-sensitive adhesive layers on both sides of a foamed resin sheet, the surfaces of which are covered with release films.

[0056] The use of the pressure-sensitive adhesive tape of the present invention is not particularly limited, and it can be suitably used on adherends having steps such as uneven shapes of parts. For example, when the pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape in which the pressure-sensitive adhesive layers are laminated on both sides of the foamed resin sheet, it is preferably used for fixing electronic equipment parts or vehicle-mounted parts. Specifically, the pressure-sensitive adhesive tape of the present invention can be suitably used for adhesive fixing of electronic equipment parts in large portable electronic devices, adhesive fixing of vehicle-mounted parts (e.g., vehicle-mounted panels), etc. [Effects of the Invention]

[0057] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent conformability to unevenness and can suppress deflection that occurs when a foamed resin sheet is transported during production. [Brief explanation of the drawings]

[0058] [Figure 1] FIG. 1 is a diagram schematically illustrating a flare measuring device. [Figure 2] FIG. 2 is a diagram schematically illustrating a method for preparing a test sample for evaluating conformability to uneven surfaces. [Figure 3] FIG. 2 is a diagram schematically illustrating a test sample prepared for evaluating conformability to uneven surfaces. DETAILED DESCRIPTION OF THE INVENTION

[0059] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0060] (Preparation of adhesive solution A) A reactor equipped with a thermometer, stirrer, and condenser was charged with 52 parts by weight of ethyl acetate. After purging with nitrogen, the reactor was heated to begin reflux. 30 minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 50 parts by weight of butyl acrylate, 46.5 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate was added dropwise evenly over 1 hour and 30 minutes, allowing the reaction to proceed. 30 minutes after the addition was complete, 0.1 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction continued for an additional 5 hours. The reactor was then cooled while being diluted with ethyl acetate, yielding an acrylic copolymer solution with a solids content of 25% by weight. The weight-average molecular weight of the obtained acrylic copolymer was measured by GPC using a Waters "2690 Separations Model" column, and was found to be 740,000. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) was 5.0. To 100 parts by weight of the solid content of the obtained acrylic copolymer, 14 parts by weight of polymerized rosin ester with a softening point of 150° C., 10 parts by weight of terpene phenol with a softening point of 145° C., and 10 parts by weight of rosin ester with a softening point of 70° C. were added. Furthermore, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemicals Co., Ltd.) and 2.0 parts by weight of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., trade name "Coronate L45") were added and stirred to obtain a pressure-sensitive adhesive solution.

[0061] (Preparation of adhesive solution B) Aside from changing the monomer mixture, not adding any tackifying resin, and changing the amount of isocyanate-based crosslinking agent to 5 parts by weight, an adhesive solution was obtained in the same manner as adhesive solution A. The monomer mixture used was a monomer mixture consisting of 50 parts by weight of butyl acrylate, 42 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 5 parts by weight of 4-hydroxyethyl acrylate. The weight-average molecular weight of the obtained acrylic copolymer was measured by GPC using a Waters "2690 Separations Model" column, and was found to be 760,000. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) was 5.2.

[0062] (Preparation of adhesive solution C) An adhesive solution was obtained in the same manner as in adhesive solution B, except that the amount of the isocyanate-based crosslinking agent was changed to 7 parts by weight.

[0063] (Preparation of adhesive solution D) An adhesive solution was obtained in the same manner as in adhesive solution B, except that the amount of the isocyanate-based crosslinking agent was changed to 10 parts by weight.

[0064] (Preparation of Adhesive Solution E) An adhesive solution was obtained in the same manner as for Adhesive Solution A, except that the monomer mixture was changed. The monomer mixture used consisted of 96.9 parts by weight of n-heptyl acrylate, 3 parts by weight of acrylic acid, and 0.1 parts by weight of 2-hydroxyethyl acrylate. n-Heptyl acrylate was prepared by esterifying n-heptyl alcohol, which contains bio-derived carbon, with acrylic acid (manufactured by Nippon Shokubai Co., Ltd.). n-Heptyl alcohol, which contains bio-derived carbon, was obtained by cracking ricinoleic acid derived from castor oil and separating the undecylenic acid from a mixture containing undecylenic acid and heptyl alcohol by distillation. The weight-average molecular weight of the obtained acrylic copolymer was measured by GPC using a Waters "2690 Separations Model" column, and was found to be 750,000. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) was 4.8.

[0065] Example 1 (1) Manufacturing of foam resin sheets As a polyolefin resin, high-pressure low-density polyethylene (LDPE) (manufactured by Braskem, SEB853, density 0.923 g / cm3 ) 20 parts by weight, and linear low-density polyethylene (LLDPE) (Exxon Chemical Company, Exact 3027, density 0.900 g / cm 3 100 parts by weight of polyolefin resin, 2.5 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent, 1 part by weight of zinc oxide as a decomposition temperature regulator, and 0.5 parts by weight of 2,6-di-t-butyl-p-cresol as an antioxidant were fed into an extruder and melt-kneaded at 130°C, and a long sheet-like foam raw material having a thickness of approximately 0.5 mm was extruded. The foam raw sheet was crosslinked by irradiating both sides with 4.0 Mrad of electron beams at an accelerating voltage of 500 kV. The crosslinked foam raw sheet was continuously fed into a foaming furnace maintained at 250°C using hot air and an infrared heater, where it was heated and foamed. During foaming, the foam raw sheet was stretched at 1.4x in MD and 2.5x in TD. This resulted in a foamed resin sheet having the thickness shown in Table 1.

[0066] (2) Measurement of foaming ratio The density of the foamed resin sheet was measured in accordance with JIS K 7222, and the reciprocal thereof was taken as the expansion ratio.

[0067] (3) Measurement of gel fraction The foamed resin sheet was cut into a 50 mm × 100 mm rectangular shape to prepare a test piece. The test piece was immersed in xylene at 120°C for 24 hours, then removed from the xylene and vacuum dried. The weight of the dried test piece was measured, and the gel fraction was calculated using the following formula (2). Gel fraction (wt%) = 100 × W2 / W1(2) (W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

[0068] (4) Measurement of average bubble diameter The foamed resin sheet was cut into 50 mm squares and immersed in liquid nitrogen for 1 minute, then cut with a razor blade along the plane formed by the MD and ZD. A 200x magnified photograph of the cut surface was then taken using a digital microscope (Keyence Corporation, product name VHX-900), and the MD and ZD bubble diameters of all bubbles present in a 2 mm long region of the cut surface in the MD direction were measured. This procedure was repeated five times, and the average of all measured MD bubble diameters was taken as the average MD bubble diameter. In addition, the foamed resin sheet was cut along the plane formed by TD and ZD, and the average cell diameter in TD was determined in the same manner as for the average cell diameter in MD above, except that the measurement was performed over a 2 mm area of ​​the cut surface in the TD direction. The average value of the bubble diameters of all the ZDs measured by the above procedure was taken as the average bubble diameter of the ZDs. From the obtained value, (MD×TD) / (ZD) 2 The value was calculated.

[0069] (5) Manufacture of adhesive tapes A 150 μm-thick release paper was prepared, and the adhesive solution A was applied to the release-treated surface of the release paper. The adhesive solution A was then dried at 100°C for 5 minutes to form an adhesive layer with a thickness of 0.05 mm. This adhesive layer was then bonded to the surface of a foamed resin sheet. Next, a 0.05 mm-thick adhesive layer made of adhesive A was bonded to the other side of the foamed resin sheet in the same manner. The adhesive layer was then cured by heating at 40°C for 48 hours. This resulted in an adhesive tape covered with a 150 μm-thick release paper.

[0070] (6) Peel strength against polycarbonate The peel strength of the adhesive tape in the 180° direction from polycarbonate was measured in accordance with JIS Z 0237. Specifically, one side of the adhesive tape (the side not being measured) was first lined with a 23 μm-thick polyethylene terephthalate film (FE2002, manufactured by Futamura Chemical Co., Ltd.), and then cut to a width of 25 mm and a length of 75 mm to prepare a test specimen. This test specimen was placed on a polycarbonate (PC1600, manufactured by Takiron C.I. Co., Ltd.) with the adhesive layer (the side being measured) facing the polycarbonate, and then bonded to the test specimen by rolling a 2 kg rubber roller back and forth on the test specimen at a speed of 300 mm / min. The test specimen was then aged for 20 minutes at 23°C and 50% humidity. According to JIS Z 0237, the test specimen was peeled in a 180° direction at a pulling rate of 300 mm / min at 23°C and 50% humidity, and the peel force (N / 25 mm) was measured. In Table 1, "peel-off between base layers" means that peeling occurred not at the interface between the adhesive layer of the adhesive tape and the polycarbonate, but due to rupture of the base layer.

[0071] (7) Measurement of the content of biogenic carbon The content of bio-derived carbon in the foamed resin sheet and the adhesive tape was measured in accordance with ASTM D6866-20.

[0072] (Examples 2 to 15, Comparative Examples 1 to 14) An adhesive tape was obtained in the same manner as in Example 1, except that the physical properties of the foamed resin sheet or the adhesive solution were changed as shown in Table 1. The expansion ratio of the foamed resin sheet was changed by adjusting the amount of foaming agent as shown in Table 1. The gel fraction of the foamed resin sheet was changed by adjusting the amount of electron beam irradiation as shown in Table 1. (MD × TD) / (ZD) of the foamed resin sheet 2 The value of was changed as shown in Table 1 by adjusting the stretching conditions.

[0073] <Evaluation> The pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

[0074] (1) Flare measurement (measurement of maximum sagging) The maximum sagging of the foamed resin sheet was measured using the flare measuring device shown in FIG. Specifically, the flare measurement device shown in Figure 1 was first installed on a level floor. This flare measurement device had two 60 mm diameter rolls 2 arranged parallel to each other on a platform 6, with a distance of 2 m between the rolls. A rod-shaped reference point 4 was located midway between the two rolls 2. The reference point 4 was installed in the width direction so that the height of its bottom surface was the same as the height of the top of the rolls 2. One end of a 1 m wide and approximately 4 m long foamed resin sheet 1 was fixed to the floor directly below one of the rolls 2 with fixing tape 3. The other end of the foamed resin sheet 1 was held and positioned so that it passed above the roll 2 on the side where the foamed resin sheet 1 was fixed to the floor, below the reference point 4, and above the other roll 2, in that order. Next, a 2 kg rod-shaped weight 5 was fixed to the end of the foamed resin sheet 1 to apply tension. After the foamed resin sheet 1 came to rest, the distance between the bottom of the reference point 4 and the foamed resin sheet 1 directly below the reference point 4 was measured at 20 points in the width direction. The maximum value among the 20 measured points was taken as the maximum sagging amount (mm). The obtained maximum sagging amount (mm) was evaluated according to the following criteria. ◎: 0mm to 10mm ○: More than 10mm and less than 20mm ×: Larger than 20mm

[0075] (2) Evaluation of step-following ability The conformability to adherends with steps of 10 μm or 20 μm was evaluated. Figure 2 shows a schematic diagram of the method for preparing the test samples, and Figure 3 shows a schematic diagram of the prepared test samples. Specifically, a stepped polycarbonate plate was prepared by attaching a single-sided adhesive tape 9 for forming a step, 10 mm wide, 55 mm long, and 10 μm or 20 μm thick, to the center of a polycarbonate plate 8 measuring 55 mm wide, 65 mm long, and 1 mm thick, so that the length direction of the tape 9 coincided with the width direction of the polycarbonate plate 8. Next, one adhesive layer of adhesive tape 7, which had been punched out into a frame shape (picture frame shape) measuring 46 mm wide, 61 mm long, and 1 mm wide, was attached to the stepped polycarbonate plate. Another polycarbonate plate 8 was prepared and attached to the other adhesive layer of adhesive tape 7. The resulting laminate was pressure-bonded under a load of 20 kg and then left to stand at 23°C for 24 hours to prepare a test sample. The cross section of the test sample was observed using a digital microscope (Keyence Corporation, product name VHX-900), and the peeling distance of the adhesive tape 7 from the edge of the step was measured and evaluated according to the following criteria. ○: Peeling distance from the edge of the step is less than 20 μm ×: Peeling distance from the edge of the step is 20 μm or more

[0076] [Table 1] [Industrial Applicability]

[0077] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent conformability to unevenness and can suppress deflection that occurs when a foamed resin sheet is transported during production. [Explanation of symbols]

[0078] 1 foam resin sheet 2 rolls 3 Fixing tape 4. Rod-shaped reference point 5. Rod-shaped weight 6 units 7 adhesive tape 8 Polycarbonate Plate 9. Single-sided adhesive tape for forming steps

Claims

1. A pressure-sensitive adhesive tape comprising a foamed resin sheet containing a polyolefin resin and a pressure-sensitive adhesive layer laminated on at least one surface of the foamed resin sheet, The polyolefin resin contains high-pressure low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), The foamed resin sheet has a gel fraction of 20% by weight or more and 60% by weight or less, and satisfies the following formula (1): An adhesive tape characterized by: 2≦(MD×TD) / (ZD) ２ (1) In formula (1), MD, TD, and ZD represent the average cell diameters in the MD direction, TD direction, and ZD direction of the foamed resin sheet, respectively.

2. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the polyolefin resin has a content of high-pressure low-density polyethylene (LDPE) of 20% by weight or more and 80% by weight or less, and a content of linear low-density polyethylene (LLDPE) of 20% by weight or more and 80% by weight or less.

3. 3. The adhesive tape according to claim 1, wherein the foamed resin sheet has a thickness of 0.05 mm or more and 1.5 mm or less.

4. The foamed resin sheet has an expansion ratio of 1.5 cm ３ / g or more, 20cm ３ 4. The adhesive tape according to claim 1, wherein the viscosity is 1 / g or less.

5. 5. The adhesive tape according to claim 1, wherein the foamed resin sheet has a content of bio-derived carbon of 20% by weight or more.

6. 6. The adhesive tape according to claim 1, wherein the peel strength in the 180° direction from polycarbonate measured in accordance with JIS Z 0237 is 2 N / 25 mm or more.

7. 7. The pressure-sensitive adhesive tape according to claim 6, wherein the peel strength in the 180° direction from polycarbonate measured in accordance with JIS Z 0237 is 5 N / 25 mm or more.

8. 8. The adhesive tape according to claim 1, wherein the adhesive tape has a content of bio-derived carbon of 10% by weight or more.

9. 9. The adhesive tape according to claim 1, wherein the adhesive layer is laminated on both sides of the foamed resin sheet, and the adhesive tape is used for fixing electronic equipment parts or vehicle-mounted parts.

Images