Double-sided adhesive tape

Abstract

To provide a double-sided adhesive tape capable of suppressing cracking at corners of an adherend caused by external impacts such as dropping.SOLUTION: A double-sided adhesive tape comprises a foam substrate, and acrylic adhesive layers provided on both surfaces of the foam substrate, where the double-sided adhesive tape has a shear elastic modulus of 90 MPa or more and 300 MPa or less when measured at -30°C and a shear rate of 1000 mm / min, and a tensile elastic modulus of 3.0 MPa or more when measured at -30°C and a tensile rate of 1000 mm / min.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a double-sided pressure-sensitive adhesive tape. [Background technology]

[0002] Foam-based adhesive tapes are sometimes used inside electronic devices such as semiconductor devices to fill gaps between components. Because foams have appropriate flexibility, the foam-based adhesive tape can be compressed while bonding components together, thereby effectively fixing the components and filling the gaps between them.

[0003] Examples of foams that can be used include polyolefin foams, polyurethane foams, etc. As pressure-sensitive adhesive tapes using such foams as a substrate, for example, Patent Documents 1 and 2 describe impact-absorbing tapes in which an acrylic pressure-sensitive adhesive layer is integrally laminated on at least one surface of a substrate layer, and the substrate layer is a cross-linked polyolefin resin foam sheet having a specific degree of cross-linking 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] Foam-based adhesive tapes are used to secure the back panels that protect the interior of electronic devices such as smartphones. These back panels are prone to cracking due to external impacts such as being dropped, so adhesive tapes used to secure the back panels must have high adhesiveness and impact resistance. Furthermore, in addition to inexpensive resin materials, glass is sometimes used for such back panels to give them a luxurious feel. However, when the back panel is made of glass, it is particularly prone to cracking due to external impacts such as being dropped, and therefore adhesive tapes are required to have even higher adhesion and impact resistance, which has been difficult to meet with conventional adhesive tapes based on foam.

[0006] An object of the present invention is to provide a double-sided pressure-sensitive adhesive tape that can prevent corners of an adherend from cracking due to an external impact such as being dropped. [Means for solving the problem]

[0007] Disclosure 1 relates to a double-sided pressure-sensitive adhesive tape having a foam substrate and acrylic pressure-sensitive adhesive layers on both sides of the foam substrate, wherein the double-sided pressure-sensitive adhesive tape has a shear modulus of 90 MPa or more and 300 MPa or less, measured at -30°C and a shear rate of 1000 mm / min, and a tensile modulus of 3.0 MPa or more, measured at -30°C and a tensile rate of 1000 mm / min. Disclosure 2 describes that the double-sided adhesive tape has a volume storage modulus (K') of 2.1 x 10 at -40°C measured in a compression mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz. 7 The double-sided pressure-sensitive adhesive tape of Disclosure 1 has a compressive strength of 50 kPa or more and 200 kPa or less at 25%. In the present disclosure 3, the foam substrate has an expansion ratio of 5.0 cm 3 / g or less and the aspect ratio of the cells is less than 1.0. Disclosure 4 is the double-sided pressure-sensitive adhesive tape of Disclosure 1, 2, or 3, wherein the double-sided pressure-sensitive adhesive tape has an overall thickness of 250 μm or more and 450 μm or less. Disclosure 5 is the double-sided pressure-sensitive adhesive tape of Disclosure 1, 2, 3, or 4 used for fixing a glass rear panel in an electronic device. The present invention will be described in detail below.

[0008] The present inventors have investigated adjusting the shear modulus and tensile modulus of a double-sided pressure-sensitive adhesive tape using a double-sided pressure-sensitive adhesive tape having acrylic pressure-sensitive adhesive layers on both sides of a foam substrate, and have found that it is possible to obtain a double-sided pressure-sensitive adhesive tape that can suppress cracking at corners of an adherend due to external impact, such as being dropped, and have completed the present invention.

[0009] The double-sided pressure-sensitive adhesive tape of the present invention has a foam substrate. By having a foam substrate, the double-sided pressure-sensitive adhesive tape of the present invention can exhibit high impact resistance, making it less likely to peel off or damage to the object to be fixed when subjected to an impact such as a fall. The foam substrate may have a single layer structure or a multilayer structure.

[0010] The foam substrate may have an open-cell structure or a closed-cell structure, but preferably has a closed-cell structure. The closed-cell structure of the foam substrate increases the strength of the foam substrate, making it possible to further suppress deformation and breakage, and as a result, to further suppress cracking of the adherend due to external impact. The cell structure can be confirmed by observing the film using an optical microscope (for example, Keyence Corporation's "VHX-6000") at a magnification of 150 to 200 times.

[0011] The foam substrate is not particularly limited, and examples thereof include substrates having a polyurethane foam layer, a polyolefin foam layer, a rubber-based foam layer, an acrylic foam layer, etc. Among these, substrates having a polyurethane foam layer or a polyolefin foam layer are preferred, and substrates having a polyolefin foam layer are more preferred, as they can exhibit excellent stress relaxation properties and strength.

[0012] Examples of the substrate having a polyolefin foam layer include substrates having a foam layer made of a resin such as a polyethylene-based resin, a polypropylene-based resin, or a polybutadiene-based resin. Among these, substrates having a foam layer made of a polyethylene-based resin are preferred because a substrate having a flexible polyolefin foam layer is easily obtained. Examples of the substrate having a foam layer made of a polyethylene-based resin include substrates having a foam layer made of low-density polyethylene, high-density polyethylene, linear low-density polyethylene, an ethylene-α-olefin copolymer, a mixture thereof, or the like.

[0013] From the viewpoint of flexibility and impact absorption, the ethylene-α-olefin copolymer is preferably a linear low-density polyethylene obtained by copolymerizing ethylene with a small amount of α-olefin as required. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene.

[0014] Examples of the substrate having a polyurethane foam layer include a substrate having a polyurethane foam layer composed of a urethane resin composition derived from polyisocyanate and polyol. Such a substrate having a polyurethane foam layer can be produced by, for example, heat-curing the urethane resin composition.

[0015] The preferred upper limit of the expansion ratio of the foam substrate is 5.0 cm 3 / g. The foam base material has an expansion ratio of 5.0 cm 3 / g or less, the strength of the foam substrate is increased, and deformation and destruction due to impact can be further suppressed, so that the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as dropping. A more preferable upper limit of the expansion ratio of the foam substrate is 4.5 cm 3 / g, and a more preferable upper limit is 4.0 cm 3 / g. The preferred lower limit of the expansion ratio of the foam substrate is 1.8 cm 3 The foam base material has an expansion ratio of 1.8 cm 3 / g or more, the foam substrate can have appropriate flexibility. As a result, it is possible to prevent external impacts such as a fall from concentrating near the interface with the adherend, and it is possible to further suppress peeling of the adherend. A more preferable lower limit of the expansion ratio of the foam substrate is 2.0 cm 3 / g, and a more preferable lower limit is 2.5 cm 3 / g. The expansion ratio of the foam layer can be determined as the reciprocal of the density of the foam layer. The density of the foam layer can be measured using an electronic hydrometer (e.g., "ED120T" manufactured by Mirage) in accordance with, for example, JIS K 6767 (when polyethylene is used) or JIS K 6401 (when polyurethane is used).

[0016] The average diameter of the cells in the MD direction of the foam substrate is preferably 50 μm at the lower limit and 120 μm at the upper limit. When the average diameter of the cells in the MD direction of the foam substrate is 50 μm or more, the flexibility of the foam substrate is increased, and the impact resistance is further improved, thereby making it possible to further suppress cracking of the adherend due to external impact such as dropping. When the average diameter of the cells in the foam substrate is 120 μm or less, the strength of the foam substrate is increased, making it possible to further suppress deformation and interlayer fracture, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as dropping. The average diameter of the cells in the MD direction of the foam substrate is more preferably 60 μm at the lower limit, more preferably 110 μm at the upper limit, and even more preferably 70 μm at the lower limit.

[0017] The average diameter of the cells in the TD direction of the foam substrate is preferably 70 μm at the lower limit and 120 μm at the upper limit. When the average diameter of the cells in the TD direction of the foam substrate is 70 μm or more, the flexibility of the foam substrate is increased, and the impact resistance is further improved, thereby making it possible to further suppress cracking of the adherend due to external impact such as dropping. When the average diameter of the cells in the TD direction of the foam substrate is 120 μm or less, the strength of the foam substrate is increased, and deformation and interlayer fracture can be further suppressed. Therefore, the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as dropping. The average diameter of the cells in the TD direction of the foam substrate is more preferably 75 μm at the lower limit and more preferably 110 μm at the upper limit, and even more preferably 80 μm at the lower limit and even more preferably 105 μm at the upper limit.

[0018] The aspect ratio of the cells in the foam substrate is preferably less than 1.0. When the aspect ratio of the cells in the foam substrate is less than 1.0, the strength of the foam substrate is increased, deformation and interlayer fracture can be further suppressed, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as being dropped. The upper limit of the aspect ratio of the cells in the foam substrate is more preferably 0.98, and even more preferably 0.95. The preferred lower limit of the aspect ratio of the cells in the foam substrate is 0.7. When the aspect ratio of the cells in the foam substrate is 0.7 or more, the cells in the foam substrate are flattened, which increases the flexibility of the foam substrate and improves the impact resistance, thereby making it possible to further suppress cracking of the adherend due to external impact such as dropping. The preferred lower limit of the aspect ratio of the cells in the foam substrate is 0.75, and the more preferred lower limit is 0.8. In this specification, the "aspect ratio of bubbles" means the value obtained by dividing the average diameter of bubbles in the MD direction by the average diameter of bubbles in the TD direction (average diameter of bubbles in the MD direction / average diameter of bubbles in the TD direction).

[0019] The average diameter of the cells in the MD direction of the foam substrate, the average diameter of the cells in the TD direction of the foam substrate, and the aspect ratio of the cells in the foam substrate can be determined, for example, as follows. Specifically, a razor (manufactured by Feather Corporation) was used to slice the foam substrate along a plane parallel to the MD and thickness directions to obtain a cut sample. The resulting cut sample was then photographed using a digital microscope (e.g., Keyence Corporation's "VHX-6000") at a magnification of 200x and a measurement screen size of 1.8mm x 1.3mm. From the resulting photographed image, the bubble with the largest MD radius and the bubble with the second largest MD radius were selected, and the MD and TD radii of these bubbles were measured to calculate the aspect ratio. This procedure was repeated for three photographed images, and the average values ​​of the MD radius, TD radius, and aspect ratio of a total of six bubbles were determined as the average MD cell diameter, average TD cell diameter, and aspect ratio of the foam substrate, respectively.

[0020] The interlaminar strength of the foam substrate is preferably 1.5 MPa (lower limit) and 7.0 MPa (upper limit). Having the interlaminar strength of the foam substrate within the above range makes it easier to achieve both flexibility and impact resistance. The interlaminar strength of the foam substrate is more preferably 1.7 MPa (lower limit), 5.0 MPa (upper limit), 1.9 MPa (even more preferred lower limit), and 4.5 MPa (upper limit). The interlaminar strength of the foam substrate can be determined by measuring the peel strength in the ZD direction. Specifically, for example, a foam substrate cut into a size of 10 mm x 10 mm is attached to a SUS plate with a cyanoacrylate instant adhesive, and then pulled at a speed of 100 mm / min in a direction perpendicular to the lamination direction of the SUS plate at 23°C. For example, a precision universal testing machine such as the AUTOGLAPH AGS-X (manufactured by Shimadzu Corporation) can be used for this test. A stress-strain curve is obtained from the measurement results, and the stress (MPa) at the point where the stress is maximum is taken as the interlaminar strength of the foam substrate.

[0021] The thickness of the foam substrate is preferably 150 μm at minimum and 350 μm at maximum. When the foam substrate is 150 μm or thicker, the foam substrate exhibits sufficient flexibility and impact resistance, thereby enabling the double-sided pressure-sensitive adhesive tape of the present invention to better prevent cracking of the adherend due to external impact, such as being dropped. When the foam substrate is 350 μm or thicker, deformation of the double-sided pressure-sensitive adhesive tape when subjected to external impact, such as being dropped, can be suppressed, thereby further preventing cracking of the adherend due to deformation of the double-sided pressure-sensitive adhesive tape. The thickness of the foam substrate is more preferably 170 μm at minimum and 300 μm at maximum, with a still more preferred lower limit and a still more preferred upper limit of 200 μm and 250 μm, respectively. In this specification, the thickness can be measured using a dial thickness meter (for example, "ABS Digimatic Indicator" manufactured by Mitutoyo Corporation).

[0022] The preferred lower limit of the ratio of the foam substrate thickness to the overall thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 50%, and the preferred upper limit is 90%. When the foam substrate thickness ratio is 50% or more, the double-sided pressure-sensitive adhesive tape of the present invention can further enhance the properties of the foam substrate, i.e., flexibility and impact resistance, and can further suppress cracking and peeling of the adherend due to external impact such as being dropped. When the foam substrate thickness ratio is 90% or less, deformation of the double-sided pressure-sensitive adhesive tape when external impact such as being dropped can be suppressed, and cracking of the adherend due to deformation of the double-sided pressure-sensitive adhesive tape can be further suppressed. The more preferred lower limit of the foam substrate thickness ratio is 53%, and the more preferred upper limit is 85%, and the even more preferred lower limit is 55%, and the even more preferred upper limit is 80%.

[0023] The method for producing the foam substrate is not particularly limited, and can be any conventionally known method. Specifically, for example, a foamable composition for forming the foam substrate is first introduced into an extruder for extrusion molding, and extruded to obtain a foam sheet. Examples of compositions for forming the foam sheet include compositions containing a polyethylene resin or the like and a thermally decomposable foaming agent, as described above. The expansion ratio of the final foam substrate can be adjusted by changing the type and amount of the thermally decomposable foaming agent. The expansion ratio of the final foam substrate can also be adjusted by applying a foaming gas during the production of the foam substrate or by incorporating hollow spheres into the foamable composition. Next, at least one surface of the obtained foamed sheet is irradiated with ionizing radiation to crosslink the polyethylene resin, etc. By changing the degree of crosslinking of the polyethylene resin, etc., the expansion ratio of the finally obtained foam layer can be adjusted.

[0024] The pressure-sensitive adhesive tape of the present invention has acrylic pressure-sensitive adhesive layers on both sides of the foam substrate. The acrylic pressure-sensitive adhesive layers may be laminated directly adjacent to the foam substrate, or may not be laminated directly adjacent to the foam substrate with another layer interposed therebetween. The composition, physical properties, thickness, etc. of the acrylic pressure-sensitive adhesive layers on both sides may be the same or different.

[0025] In the present specification, the term "acrylic pressure-sensitive adhesive layer" means a pressure-sensitive adhesive layer containing a (meth)acrylic copolymer. In addition, in this specification, "(meth)acrylic" means acrylic or methacrylic.

[0026] The (meth)acrylic copolymer preferably contains at least one structural unit selected from the group consisting of structural units derived from n-butyl(meth)acrylate and structural units derived from 2-ethylhexyl(meth)acrylate, from the viewpoints of improving initial tack and thereby improving ease of application at low temperatures, and of increasing the glass transition temperature (Tg) of the (meth)acrylic copolymer, thereby further improving the cohesive strength of the bulk of the acrylic pressure-sensitive adhesive layer and enabling the double-sided pressure-sensitive adhesive tape of the present invention to better suppress cracking of the adherend due to external impact such as dropping.More preferably, the (meth)acrylic copolymer contains both structural units derived from n-butyl(meth)acrylate and structural units derived from 2-ethylhexyl(meth)acrylate. In this specification, the term "(meth)acrylate" means acrylate or methacrylate.

[0027] The content of the structural units derived from n-butyl (meth)acrylate in the (meth)acrylic copolymer is preferably 30% by mass at the lower limit and 80% by mass at the upper limit. By setting the content of the structural units derived from n-butyl acrylate within this range, the resulting double-sided pressure-sensitive adhesive tape can achieve both high adhesive strength and tackiness, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as being dropped. The content of the structural units derived from n-butyl (meth)acrylate is more preferably 35% by mass at the lower limit and 75% by mass at the upper limit, and even more preferably 40% by mass at the lower limit and 70% by mass at the upper limit.

[0028] The content of the structural units derived from 2-ethylhexyl (meth)acrylate in the (meth)acrylic copolymer is preferably 20% by mass at the lower limit and 60% by mass at the upper limit. By setting the content of the structural units derived from 2-ethylhexyl (meth)acrylate within this range, the cohesive strength of the bulk of the acrylic pressure-sensitive adhesive layer is further improved, the resulting double-sided pressure-sensitive adhesive tape is able to exhibit higher adhesive strength, and the double-sided pressure-sensitive adhesive tape of the present invention is able to further suppress cracking of the adherend due to external impact, such as being dropped. The more preferred lower limit of the content of the structural units derived from 2-ethylhexyl (meth)acrylate is 25% by mass, the more preferred upper limit is 55% by mass, the even more preferred lower limit is 30% by mass, and the even more preferred upper limit is 50% by mass.

[0029] The (meth)acrylic copolymer may optionally contain structural units derived from other copolymerizable polymerizable monomers other than n-butyl(meth)acrylate and 2-ethylhexyl(meth)acrylate. Examples of the other copolymerizable polymerizable monomers include alkyl(meth)acrylates having an alkyl group with 1 to 3 carbon atoms, alkyl(meth)acrylates having an alkyl group with 13 to 18 carbon atoms, and functional monomers. Examples of the alkyl (meth)acrylate in which the alkyl group has 1 to 3 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of the alkyl (meth)acrylate in which the alkyl group has 13 to 18 carbon atoms include tridecyl methacrylate and stearyl (meth)acrylate. Examples of the functional monomer 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 cohesive strength of the bulk of the acrylic pressure-sensitive adhesive layer, hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylate and glycerin dimethacrylate are preferred. Specific examples of the hydroxyalkyl (meth)acrylate include 2-hydroxyethyl (meth)acrylate. These copolymerizable other polymerizable monomers may be used alone or in combination of two or more kinds.

[0030] The weight-average molecular weight (Mw) of the (meth)acrylic copolymer preferably has a lower limit of 400,000. When the weight-average molecular weight of the (meth)acrylic copolymer is 400,000 or more, the bulk cohesive strength of the acrylic pressure-sensitive adhesive layer is further improved, and the double-sided pressure-sensitive adhesive tape of the present invention is more able to prevent the adherend from cracking due to external impact, such as being dropped. The weight-average molecular weight of the (meth)acrylic copolymer more preferably has a lower limit of 450,000, and even more preferably has a lower limit of 500,000. The upper limit of the weight-average molecular weight of the (meth)acrylic copolymer is preferably 1,000,000. When the weight-average molecular weight of the (meth)acrylic copolymer is 1,000,000 or less, the acrylic pressure-sensitive adhesive layer does not become too hard, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact such as being dropped. The upper limit of the weight-average molecular weight of the (meth)acrylic copolymer is more preferably 900,000, even more preferably 800,000, and even more preferably 700,000.

[0031] In this specification, the weight average molecular weight (Mw) is the weight average molecular weight measured by GPC (Gel Permeation Chromatography) in terms of standard polystyrene. Specifically, the resulting acrylic copolymer solution is diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution is filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The resulting filtrate is fed to a gel permeation chromatograph (Waters, 2690 Separations Model) and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C to measure the polystyrene-equivalent molecular weight of the (meth)acrylic copolymer, which is taken as the weight-average molecular weight (Mw) of the (meth)acrylic copolymer. Examples of columns used include GPC KF-806L (Showa Denko), and examples of detectors include a differential refractometer.

[0032] The (meth)acrylic copolymer can be obtained by radically reacting a monomer mixture containing n-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, and other copolymerizable monomers in the presence of a polymerization initiator. The method for radically reacting the monomer mixture, i.e., the polymerization method, can be any conventionally known method, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, or bulk polymerization.

[0033] The acrylic pressure-sensitive adhesive layer may further contain a tackifying resin from the viewpoint of improving adhesive strength.

[0034] 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, C5-C9 copolymer petroleum resins, etc. Among these, from the viewpoint of compatibility with the base polymer, rosin resins or terpene resins are preferred, and rosin resins having hydroxyl groups or terpene resins having hydroxyl groups are more preferred. These tackifier resins may be used alone or in combination of two or more kinds.

[0035] Examples of the rosin resin having a hydroxyl group include Pencel D-135 and Superester A-75 (both manufactured by Arakawa Chemical Industries, Ltd.). Examples of the terpene resin having a hydroxyl group include YS Polystar G150 and YS Polystar T160 (both manufactured by Yasuhara Chemical Co., Ltd.).

[0036] The softening point of the tackifier resin preferably has a lower limit of 70°C and an upper limit of 170°C. If the softening point of the tackifier resin is 70°C or higher, the double-sided pressure-sensitive adhesive tape of the present invention can better prevent the adherend from cracking due to external impact, such as being dropped. If the softening point of the tackifier resin is 170°C or lower, the acrylic pressure-sensitive adhesive layer does not become too hard, so the double-sided pressure-sensitive adhesive tape of the present invention can better prevent the adherend from cracking due to external impact, such as being dropped. A more preferred lower limit of the softening point of the tackifier resin is 120°C. In this specification, the "softening point of the tackifier resin" means the softening temperature measured according to JIS K2207 (ring and ball method).

[0037] The tackifier resin preferably has a lower limit of 25 mgKOH / g for its hydroxyl value. Having a hydroxyl value of 25 mgKOH / g or more improves adhesion to glass and metals, which are commonly used as adherends, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking of the adherend due to external impact, such as being dropped. The lower limit of the hydroxyl value of the tackifier resin is more preferably 30 mgKOH / g, and even more preferably 35 mgKOH / g. The upper limit of the hydroxyl value of the tackifier resin is not particularly limited. In this specification, the hydroxyl value of the tackifier resin can be measured according to JIS K1557 (phthalic anhydride method).

[0038] The content of the tackifier resin relative to 100 parts by mass of the (meth)acrylic copolymer is preferably 5 parts by mass at the lower limit and 60 parts by mass at the upper limit. By keeping the content of the tackifier resin within this range, the adhesive strength of the resulting double-sided pressure-sensitive adhesive tape becomes more sufficient. The lower limit of the content of the tackifier resin is more preferably 10 parts by mass, more preferably 50 parts by mass at the upper limit, even more preferably 15 parts by mass, and even more preferably 40 parts by mass at the upper limit.

[0039] The acrylic pressure-sensitive adhesive layer may contain a crosslinking agent to form a crosslinked structure between the main chains of the resins (e.g., the (meth)acrylic copolymer, the tackifier resin, etc.) that constitute the acrylic pressure-sensitive adhesive layer. Adjusting the type and amount of the crosslinking agent makes it easier to adjust the shear storage modulus, gel fraction, etc. of the acrylic pressure-sensitive adhesive layer. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an aziridine-based crosslinking agent, an epoxy-based crosslinking agent, a metal chelate-based crosslinking agent, etc. Among these, an isocyanate-based crosslinking agent is preferred from the viewpoint of adhesion to the foam substrate.

[0040] The acrylic pressure-sensitive adhesive layer may contain a silane coupling agent to further improve adhesive strength. Examples of the silane coupling agent include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

[0041] The acrylic pressure-sensitive adhesive layer may contain a colorant to impart light-shielding properties. Examples of the colorant include carbon black, aniline black, titanium oxide, etc. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable.

[0042] The acrylic 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.

[0043] The acrylic pressure-sensitive adhesive layer preferably has a glass transition temperature measured in compression mode in dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter simply referred to as "glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in compression mode") of -10°C or higher, and a preferred upper limit of 20°C. When the acrylic pressure-sensitive adhesive layer has a glass transition temperature measured in compression mode of -10°C or higher, the double-sided pressure-sensitive adhesive tape of the present invention has improved impact resistance, and is more able to prevent cracking or lifting of the surface of the back panel of an adherend due to external impact such as dropping. When the acrylic pressure-sensitive adhesive layer has a glass transition temperature measured in compression mode of 20°C or lower, the double-sided pressure-sensitive adhesive tape of the present invention has improved flexibility, and is more able to prevent cracking or lifting of the surface of the back panel of an adherend due to external impact such as dropping. The glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in compression mode is more preferably -5°C or higher, and more preferably 18°C ​​or higher, and even more preferably 0°C or higher, and even more preferably 15°C. It is more preferable that the glass transition temperature of the acrylic pressure-sensitive adhesive layers on both sides of the double-sided pressure-sensitive adhesive tape of the present invention, measured in compression mode, falls within the above-mentioned range.

[0044] The acrylic pressure-sensitive adhesive layer has a volume storage modulus K′ at −40° C. measured in a compression mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter, may be simply referred to as “the volume storage modulus of the acrylic pressure-sensitive adhesive layer at −40° C.”) of preferably 2.0×10 8 Pa, the preferred upper limit is 2.5 × 10 8 The volume storage modulus of the acrylic pressure-sensitive adhesive layer at −40° C. is 2.0×10 Pa. 8 When the double-sided pressure-sensitive adhesive tape of the present invention has a volume storage modulus of 2.5 × 10 Pa or more, the impact resistance is further improved, and cracking or lifting of the surface of the back panel of the adherend due to an external impact such as being dropped can be further suppressed. 8The double-sided pressure-sensitive adhesive tape of the present invention can be deformed appropriately by being 1.2 × 10 Pa or less. This makes it possible to further suppress cracking or lifting of the surface of the back panel of the adherend due to an external impact such as a fall. A more preferable lower limit of the volume storage modulus at −40° C. of the acrylic pressure-sensitive adhesive layer is 2.2 × 10 8 Pa, and a more preferable upper limit is 2.4 × 10 8 Pa, and a more preferable lower limit is 2.3 × 10 8 Pa, and a more preferable upper limit is 2.35 × 10 8 It is Pa. It is more preferable that the volume storage modulus of the acrylic pressure-sensitive adhesive layers on both sides of the double-sided pressure-sensitive adhesive tape of the present invention at −40° C. satisfies the above-mentioned range.

[0045] The glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in compression mode and the volume storage modulus of the acrylic pressure-sensitive adhesive layer at −40° C. are measured by dynamic viscoelasticity measurement at a measurement frequency of 10 Hz. Specifically, for example, a sample of only the acrylic pressure-sensitive adhesive layer is prepared, and dynamic viscoelasticity measurement is performed using a dynamic viscoelasticity measurement device (such as the “Dynamic Viscoelasticity Measurement Apparatus DVA-200” manufactured by IT Measurement & Control Co., Ltd.) under conditions of a measurement frequency of 10 Hz, compression mode, a measurement temperature of −40° C. to 140° C., a heating rate of 5° C. / min, and a strain of 0.1%. In this specification, an example of a method for preparing a sample of only the acrylic pressure-sensitive adhesive layer is to separate only the acrylic pressure-sensitive adhesive layer from a double-sided pressure-sensitive adhesive tape and then prepare a sample of the acrylic pressure-sensitive adhesive layer. The method for removing the foam substrate is not particularly limited, so long as it avoids treatment with a solvent, treatment involving a chemical reaction, treatment at high temperature, etc., in order to avoid denaturing the pressure-sensitive adhesive layer. Specific methods that can be selected include a method in which the pressure-sensitive adhesive layers are bonded together, and then an appropriate temperature and peeling speed are selected to peel the foam substrate and the pressure-sensitive adhesive layer, thereby removing the foam substrate, or a method in which the foam substrate is physically ground. Alternatively, a sample may be prepared using a separately prepared sheet having a thickness of about 1.0 mm and consisting of only the pressure-sensitive adhesive layer.

[0046] Examples of methods for adjusting the glass transition temperature measured in compression mode of the acrylic pressure-sensitive adhesive layer and the volume storage modulus at −40° C. of the acrylic pressure-sensitive adhesive layer include a method of changing the composition of the (meth)acrylic copolymer, and a method of changing the type or content of the tackifier resin or crosslinking agent.

[0047] The acrylic pressure-sensitive adhesive layer preferably has a lower limit of -10°C and an upper limit of 15°C for the glass transition temperature measured in shear mode in dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter sometimes simply referred to as "glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in shear mode"). When the acrylic pressure-sensitive adhesive layer has a glass transition temperature measured in shear mode of -10°C or higher, the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking at the corners of the adherend due to external impact such as being dropped. When the acrylic pressure-sensitive adhesive layer has a glass transition temperature measured in shear mode of 15°C or lower, the acrylic pressure-sensitive adhesive layer does not become too hard, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking at the corners of the adherend due to external impact such as being dropped. A more preferred lower limit of the glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in shear mode is -5°C, a more preferred upper limit is 13°C, an even more preferred lower limit is 0°C, and an even more preferred upper limit is 10°C. It is more preferable that the glass transition temperature of the acrylic pressure-sensitive adhesive layers on both sides of the double-sided pressure-sensitive adhesive tape of the present invention, measured in shear mode, falls within the above-mentioned range.

[0048] The acrylic pressure-sensitive adhesive layer has a shear storage modulus G' at -40°C measured in a shear mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter, may be simply referred to as "the shear storage modulus of the acrylic pressure-sensitive adhesive layer at -40°C") of preferably 0.5 × 10 8 Pa, the preferred upper limit is 2.0 × 10 8 The acrylic pressure-sensitive adhesive layer has a shear storage modulus of 0.5×10 Pa at −40° C. 8When the shear storage modulus of the acrylic pressure-sensitive adhesive layer at −40° C. is 2.0×10 Pa or more, the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking at the corners of the adherend due to external impact such as being dropped. 8 By setting the shear storage modulus at -40°C to 1.0 x 10 Pa or less, the acrylic pressure-sensitive adhesive layer does not become too hard, and the double-sided pressure-sensitive adhesive tape of the present invention can further suppress cracking at the corners of the adherend due to external impact such as being dropped. 8 Pa, and a more preferable upper limit is 1.8 × 10 8 Pa, and a more preferable lower limit is 1.3 × 10 8 Pa, and a more preferable upper limit is 1.5 × 10 8 It is Pa. It is more preferable that the shear storage modulus of the acrylic pressure-sensitive adhesive layers on both sides of the double-sided pressure-sensitive adhesive tape of the present invention at −40° C. satisfies the above-mentioned range.

[0049] The glass transition temperature of the acrylic pressure-sensitive adhesive layer measured in shear mode and the shear storage modulus of the acrylic pressure-sensitive adhesive layer at −40° C. are measured by dynamic viscoelasticity measurement at a measurement frequency of 10 Hz. Specifically, for example, a sample of only the acrylic pressure-sensitive adhesive layer is prepared, and dynamic viscoelasticity measurement is performed using a dynamic viscoelasticity measurement device (such as the “Dynamic Viscoelasticity Measurement Apparatus DVA-200” manufactured by IT Measurement & Control Co., Ltd.) under the following conditions: measurement frequency of 10 Hz, shear mode, measurement temperature of −40° C. to 140° C., heating rate of 5° C. / min, and strain of 0.1%.

[0050] Examples of methods for adjusting the glass transition temperature measured in shear mode of the acrylic pressure-sensitive adhesive layer and the shear storage modulus at −40° C. of the acrylic pressure-sensitive adhesive layer include a method of changing the composition of the (meth)acrylic copolymer, and a method of changing the type or content of the tackifier resin or crosslinking agent.

[0051] The acrylic pressure-sensitive adhesive layer preferably has a gel fraction of 10% by mass or less. When the acrylic pressure-sensitive adhesive layer has a gel fraction of 10% by mass or more, the bulk strength of the acrylic pressure-sensitive adhesive layer increases, and the double-sided pressure-sensitive adhesive tape of the present invention is more likely to prevent corners of the adherend from cracking due to external impact, such as being dropped. The acrylic pressure-sensitive adhesive layer more preferably has a gel fraction of 15% by mass or less, and even more preferably has a gel fraction of 20% by mass or less. The upper limit of the gel fraction of the acrylic pressure-sensitive adhesive layer is preferably 80% by mass. By ensuring that the gel fraction of the acrylic pressure-sensitive adhesive layer is 80% by mass or less, the acrylic pressure-sensitive adhesive layer does not become too hard, and the double-sided pressure-sensitive adhesive tape of the present invention can be more effectively prevented from cracking at the corners of the adherend due to external impact, such as being dropped. The upper limit of the gel fraction of the acrylic pressure-sensitive adhesive layer is more preferably 75% by mass, and even more preferably 70% by mass. It is more preferable that the gel fraction of the acrylic pressure-sensitive adhesive layers on both sides of the double-sided pressure-sensitive adhesive tape of the present invention satisfy the above-mentioned range. The gel fraction of the acrylic pressure-sensitive adhesive layer can be measured, for example, by the following method. Specifically, W0 (g) of the acrylic pressure-sensitive adhesive layer for which the gel fraction is to be measured is removed from the double-sided pressure-sensitive adhesive tape, and the removed acrylic pressure-sensitive adhesive layer is immersed in ethyl acetate using a shaker at 23°C and 200 rpm for 24 hours. The ethyl acetate and the acrylic pressure-sensitive adhesive layer that has absorbed the ethyl acetate and swollen with it are then separated using a metal mesh (opening #200 mesh, W1 (g)). The separated acrylic pressure-sensitive adhesive layer is dried at 110°C for 1 hour. The mass W2 (g) of the dried acrylic pressure-sensitive adhesive layer is measured, and the gel fraction (% by mass) of the acrylic pressure-sensitive adhesive layer can be calculated using the following formula (1): Gel fraction (mass%) = 100 × (W2 - W1) / W0 (1) (W0: initial mass of the acrylic adhesive layer, W1: mass of the metal mesh, W2: mass of the acrylic adhesive layer including the metal mesh after immersion and drying)

[0052] The thickness of the acrylic pressure-sensitive adhesive layer preferably has a lower limit of 25 μm and an upper limit of 100 μm. When the thickness of the acrylic pressure-sensitive adhesive layer is 25 μm or more, the adhesive strength of the acrylic pressure-sensitive adhesive layer is sufficient, and the double-sided pressure-sensitive adhesive tape of the present invention can be more effectively prevented from peeling off the adherend due to external impact such as being dropped. When the thickness of the acrylic pressure-sensitive adhesive layer is 100 μm or less, the flexibility of the double-sided pressure-sensitive adhesive tape of the present invention can be more effectively improved, and the adherend can be more effectively prevented from cracking due to external impact such as being dropped. The thickness of the acrylic pressure-sensitive adhesive layer is more preferably 35 μm, more preferably 75 μm, even more preferably 45 μm, even more preferably 55 μm, and even more preferably 50 μm. It is more preferable that the thickness of the acrylic pressure-sensitive adhesive layer on each side of the double-sided pressure-sensitive adhesive tape of the present invention satisfies the above-mentioned range.

[0053] The double-sided pressure-sensitive adhesive tape of the present invention may have layers other than the foam substrate and the acrylic pressure-sensitive adhesive layer, if necessary.

[0054] Examples of methods for producing the double-sided pressure-sensitive adhesive tape of the present invention include the following methods. First, a (meth)acrylic copolymer and, if necessary, additives such as a tackifier resin are added to a solvent to prepare a pressure-sensitive adhesive solution. This pressure-sensitive adhesive solution is applied to the release-treated surface of a release film, and the solvent in the solution is dried to remove it, forming an acrylic pressure-sensitive adhesive layer. This acrylic pressure-sensitive adhesive layer is then pressed and bonded to one side of a foam substrate using a rubber roller or the like. In a similar manner, an acrylic pressure-sensitive adhesive layer is bonded to the other side of the foam substrate, resulting in a double-sided pressure-sensitive adhesive tape having acrylic pressure-sensitive adhesive layers on both sides of the foam substrate, with the surfaces of the acrylic pressure-sensitive adhesive layers covered with release films. The release polyethylene terephthalate (PET) film is not necessary.

[0055] The double-sided pressure-sensitive adhesive tape of the present invention has a shear modulus measured at -30°C and a shear rate of 1000 mm / min (hereinafter sometimes simply referred to as "the shear modulus of the double-sided pressure-sensitive adhesive tape at -30°C") of 90 MPa at the lower limit and 300 MPa at the upper limit. External impacts, such as those from a fall, usually act on objects moving at high speed. On the other hand, the elastic modulus and storage modulus of an object subjected to such high-speed force are highly correlated with the elastic modulus and storage modulus at low temperatures, according to the temperature-velocity conversion law. Therefore, when the shear modulus of the double-sided pressure-sensitive adhesive tape at -30°C is 90 MPa or more, the double-sided pressure-sensitive adhesive tape of the present invention can suppress cracking at the corners of an adherend due to external impacts, such as a fall. When the shear modulus of the double-sided pressure-sensitive adhesive tape at -30°C is 300 MPa or less, the double-sided pressure-sensitive adhesive tape of the present invention can easily absorb external impacts, such as a fall, and can easily prevent the impact from being transmitted to the adherend, thereby suppressing cracking at the corners of an adherend due to external impacts, such as a fall. The shear modulus of the double-sided pressure-sensitive adhesive tape at -30°C is preferably 100 MPa (lower limit), 290 MPa (preferably upper limit), 130 MPa (more preferably lower limit), and 280 MPa (more preferably upper limit). The shear modulus of elasticity of the double-sided adhesive tape at −30° C. can be measured by the shear test shown below. A schematic diagram showing a shear test of a double-sided pressure-sensitive adhesive tape is shown in Figure 1. First, a double-sided pressure-sensitive adhesive tape 1 of the present invention is cut into a size of 12.5 mm x 25 mm, and two SUS plates 2 each measuring 30 mm x 50 mm and 1 mm thick are laminated together as shown in Figure 1. This laminate is pressure-bonded at a force of 0.3 MPa for 10 seconds in an environment of 23°C, and then left to stand at 23°C and 50% RH for 24 hours to prepare a test sample in which the two SUS plates 2 are bonded together via the double-sided pressure-sensitive adhesive tape 1. After fixing one SUS plate 2 of the obtained test sample, the upper part of the other SUS plate 2 is pulled at a speed of 1000 mm / min in a direction perpendicular to the lamination direction of the SUS plates (the direction of the arrow in Figure 1) in an environment of -30°C. For this test, for example, a precision universal testing machine such as AUTOGLAPH AGS-X (manufactured by Shimadzu Corporation) can be used. A stress-strain curve is obtained from the measurement results, and the slope (MPa) at a strain of 1 to 2% is taken as the shear modulus of elasticity at -30°C of the double-sided pressure-sensitive adhesive tape.

[0056] Examples of methods for adjusting the shear modulus of elasticity at −30° C. of the double-sided pressure-sensitive adhesive tape include increasing the expansion ratio of the foam substrate and decreasing the glass transition temperature of the acrylic pressure-sensitive adhesive layer.

[0057] The double-sided pressure-sensitive adhesive tape of the present invention has a lower limit of a tensile modulus of elasticity measured at -30°C and a pulling rate of 1000 mm / min (hereinafter sometimes simply referred to as "the tensile modulus of elasticity of the double-sided pressure-sensitive adhesive tape at -30°C") of 3.0 MPa. When the double-sided pressure-sensitive adhesive tape has a tensile modulus of elasticity of 3.0 MPa or more at -30°C, the double-sided pressure-sensitive adhesive tape of the present invention can suppress cracking of the corners of an adherend due to external impact, such as being dropped. The lower limit of the tensile modulus of elasticity of the double-sided pressure-sensitive adhesive tape at -30°C is preferably 3.3 MPa, and more preferably 3.5 MPa. Furthermore, the preferred upper limit of the tensile modulus of elasticity of the double-sided pressure-sensitive adhesive tape at -30°C is 6.0 MPa. When the double-sided pressure-sensitive adhesive tape has a tensile modulus of elasticity of 6.0 MPa or less at -30°C, the double-sided pressure-sensitive adhesive tape of the present invention is more likely to absorb external impacts such as those from a fall, and is more likely to prevent the impact from being transmitted to the adherend, thereby more likely to suppress cracking of the corners of the adherend due to external impacts such as those from a fall. The preferred upper limit of the tensile modulus of elasticity of the double-sided pressure-sensitive adhesive tape at -30°C is 5.5 MPa, and even more preferred is 5.0 MPa. The tensile modulus of elasticity of the double-sided pressure-sensitive adhesive tape at −30° C. is measured by the following method. Specifically, a test piece is prepared by cutting the double-sided adhesive tape into a size of 10 mm × 50 mm. The prepared test piece is subjected to a tensile test in accordance with JIS K 7127 using a tensile tester (such as the "AUTOGLAPH AGS-X" precision universal testing machine manufactured by Shimadzu Corporation) at a gripping distance of 50 mm and a tensile speed of 1000 mm / min in an environment of -30°C. A stress-strain curve is obtained from the measurement results, and the slope (MPa) at a strain of 1% to 2% is taken as the tensile modulus of elasticity at -30°C of the double-sided pressure-sensitive adhesive tape.

[0058] Examples of methods for adjusting the tensile modulus of elasticity at −30° C. of the double-sided pressure-sensitive adhesive tape include increasing the expansion ratio of the foam substrate and decreasing the glass transition temperature of the acrylic pressure-sensitive adhesive layer.

[0059] The double-sided pressure-sensitive adhesive tape of the present invention has a volume storage modulus K′ at −40° C. measured in a compression mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter, may be simply referred to as “volume storage modulus of the double-sided pressure-sensitive adhesive tape at −40° C.”) of preferably 2.1×10 7 The volume storage modulus of the double-sided adhesive tape at −40° C. is 2.1×10 7 By virtue of the double-sided pressure-sensitive adhesive tape having a volume storage modulus of 1.9 × 10 Pa or less, the double-sided pressure-sensitive adhesive tape of the present invention can adequately absorb the impact of a fall, and can further suppress cracking or lifting of the surface of the back panel of the adherend due to an external impact such as a fall. 7 Pa, and a more preferable upper limit is 1.8 × 10 7 It is Pa. The preferred lower limit of the volume storage modulus of the double-sided adhesive tape at −40° C. is 1.0×10 7 The volume storage modulus of the double-sided adhesive tape at −40° C. is 1.0×10 7 The double-sided pressure-sensitive adhesive tape of the present invention has a volume storage modulus of 1.2 × 10 Pa or more, which can further enhance the impact resistance of the double-sided pressure-sensitive adhesive tape of the present invention and can further suppress cracking or lifting of the surface of the back panel of the adherend due to an external impact such as a fall. 7 Pa, and a more preferable lower limit is 1.5 × 10 7 It is Pa.

[0060] The double-sided pressure-sensitive adhesive tape of the present invention preferably has a loss tangent (tan δ) measured in compression mode in dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter simply referred to as the "loss tangent of the double-sided pressure-sensitive adhesive tape measured in compression mode") of 0.1 or more, and a preferred upper limit of 0.5. When the loss tangent measured in compression mode of the double-sided pressure-sensitive adhesive tape is 0.1 or more, the double-sided pressure-sensitive adhesive tape of the present invention can be made more flexible, and external impacts such as dropping can be adequately absorbed, thereby more effectively preventing peeling at the surface of the back panel of the adherend. When the loss tangent measured in compression mode of the double-sided pressure-sensitive adhesive tape is 0.5 or less, deformation of the double-sided pressure-sensitive adhesive tape of the present invention can be more effectively prevented, and cracking or lifting of the surface of the back panel of the adherend due to external impacts such as dropping can be more effectively prevented. The loss tangent measured in compression mode of the double-sided pressure-sensitive adhesive tape of the present invention is more preferably 0.15, and a more preferred upper limit is 0.4, and an even more preferred lower limit is 0.2, and an even more preferred upper limit is 0.3.

[0061] The double-sided pressure-sensitive adhesive tape of the present invention preferably has a glass transition temperature of 0°C or higher, measured in compression mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz (hereinafter sometimes simply referred to as "glass transition temperature of the double-sided pressure-sensitive adhesive tape measured in compression mode"), with a lower limit of 0°C and an upper limit of 20°C. When the glass transition temperature of the double-sided pressure-sensitive adhesive tape measured in compression mode is 0°C or higher, the impact resistance of the double-sided pressure-sensitive adhesive tape of the present invention is improved, thereby making it possible to further suppress cracking and lifting of the surface of the back panel of an adherend due to external impact such as being dropped. When the glass transition temperature of the double-sided pressure-sensitive adhesive tape of the present invention is 20°C or lower, the flexibility of the double-sided pressure-sensitive adhesive tape of the present invention is improved and deformation can be further suppressed, making it possible to further suppress cracking and lifting of the surface of the back panel of an adherend due to external impact such as being dropped. The glass transition temperature of the double-sided pressure-sensitive adhesive tape measured in compression mode is more preferably 5°C, more preferably 18°C, even more preferably 10°C, and even more preferably 16°C.

[0062] The volume storage modulus of the double-sided pressure-sensitive adhesive tape at −40° C., the loss tangent measured in compression mode of the double-sided pressure-sensitive adhesive tape, and the glass transition temperature measured in compression mode of the double-sided pressure-sensitive adhesive tape are measured by dynamic viscoelasticity measurement at a measurement frequency of 10 Hz. Specifically, for example, the double-sided pressure-sensitive adhesive tape is cut into a sample having a width of 10 mm and a length of 10 mm, and the sample is subjected to dynamic viscoelasticity measurement using a dynamic viscoelasticity measurement device (such as the “Dynamic Viscoelasticity Measurement Apparatus DVA-200” manufactured by IT Measurement & Control Co., Ltd.) under the following conditions: a measurement frequency of 10 Hz, a measurement temperature of −40° C. to 140° C., a heating rate of 5° C. / min, and a strain of 0.1%.

[0063] Examples of methods for adjusting the volume storage modulus at −40° C. of the double-sided pressure-sensitive adhesive tape, the loss tangent measured in compression mode of the double-sided pressure-sensitive adhesive tape, and the glass transition temperature measured in compression mode of the double-sided pressure-sensitive adhesive tape include a method of increasing the expansion ratio of the foam substrate and a method of changing the composition of the acrylic pressure-sensitive adhesive layer.

[0064] The double-sided pressure-sensitive adhesive tape of the present invention has a 25% compressive strength of preferably 50 kPa (lower limit) and 200 kPa (upper limit). When the double-sided pressure-sensitive adhesive tape has a 25% compressive strength of 50 kPa or more, the double-sided pressure-sensitive adhesive tape of the present invention can have improved impact resistance, and can be more effectively prevented from cracking or lifting on the surface of the back panel of an adherend due to external impact such as being dropped. When the double-sided pressure-sensitive adhesive tape has a 25% compressive strength of 200 kPa or less, the tape can be more effectively flexible, and can be more effectively prevented from peeling on the surface of the back panel of an adherend. Since deformation of the double-sided pressure-sensitive adhesive tape of the present invention can be more effectively prevented, the double-sided pressure-sensitive adhesive tape can be more effectively prevented from cracking or lifting on the surface of the back panel of an adherend due to external impact such as being dropped. The double-sided pressure-sensitive adhesive tape's 25% compressive strength is more preferably 60 kPa (lower limit), more preferably 150 kPa (upper limit), even more preferably 70 kPa (lower limit), and even more preferably 100 kPa (upper limit). The 25% compressive strength of the double-sided pressure-sensitive adhesive tape can be determined by measuring as follows in accordance with JIS K 6767:2016. Double-sided adhesive tape is cut into 20 mm x 20 mm pieces and stacked to create a sample approximately 5 mm x 20 mm x 20 mm thick. The sample is compressed in the compression direction at a speed of 10 mm / min, and the pressure (N) at the point of 25% compression is measured. The 25% compressive strength (kPa) of the double-sided adhesive tape is calculated from the obtained pressure using the following formula (2). Note that the thickness of the sample is considered to be 100, and when it is compressed 25% (when the thickness of the sample is 75), it is considered to be 25% compressed. Compressive strength (kPa) = pressure (N) / 0.4 (2)

[0065] Examples of methods for adjusting the 25% compressive strength of the double-sided pressure-sensitive adhesive tape include increasing the expansion ratio of the foam substrate and changing the resin that constitutes the foam substrate.

[0066] The preferred lower limit of the overall thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 250 μm, and the preferred upper limit is 450 μm. When the overall thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 250 μm or more, the adhesive strength of the resulting double-sided pressure-sensitive adhesive tape is sufficient, and the double-sided pressure-sensitive adhesive tape of the present invention can better suppress cracking or lifting of the surface of the back panel of the adherend due to external impact such as being dropped. When the overall thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 450 μm or less, the resulting double-sided pressure-sensitive adhesive tape can achieve sufficient adhesion and fixation, and the double-sided pressure-sensitive adhesive tape of the present invention can be more flexible and have improved impact resistance, which can better suppress cracking or lifting of the surface of the back panel of the adherend due to external impact such as being dropped. A more preferred lower limit of the overall thickness of the double-sided pressure-sensitive adhesive tape of the present invention is 300 μm, and a more preferred upper limit is 400 μm.

[0067] The uses of the double-sided pressure-sensitive adhesive tape of the present invention are not particularly limited, but since the double-sided pressure-sensitive adhesive tape of the present invention can suppress cracking at the corners of the adherend due to external impact such as dropping, it can be used to fix the back panel of the adherend, and is particularly suitable for fixing the back panel that protects the inside of an electronic device. The double-sided pressure-sensitive adhesive tape of the present invention can also be suitably used for fixing a glass rear panel in an electronic device. Use of the double-sided pressure-sensitive adhesive tape of the present invention makes it easy to prevent cracking of corners of a glass rear panel due to external impact, such as a drop, which was difficult to achieve with conventional pressure-sensitive adhesive tapes. Examples of the electronic device include display devices such as televisions and monitors, and portable electronic devices such as smartphones. Among these, portable electronic devices such as smartphones are preferred, and smartphones are more preferred. [Effects of the Invention]

[0068] According to the present invention, it is possible to provide a double-sided pressure-sensitive adhesive tape that can suppress cracking at corners of an adherend due to an external impact such as being dropped. [Brief explanation of the drawings]

[0069] [Figure 1] FIG. 1 is a schematic diagram showing a shear test of a double-sided adhesive tape. DETAILED DESCRIPTION OF THE INVENTION

[0070] The following examples will explain the present invention in more detail, but the present invention is not limited to these examples.

[0071] (Preparation of Acrylic Copolymer A) A reactor equipped with a thermometer, stirrer, and condenser was charged with 80 parts by weight of ethyl acetate as a solvent and 42 parts by weight of n-butyl acrylate, 55 parts by weight of 2-ethylhexyl acrylate, 3.0 parts by weight of acrylic acid, and 0.2 parts by weight of 2-hydroxyethyl acrylate as structural unit monomers. After nitrogen substitution, the reactor was placed in a water bath set at 60°C and heated to initiate reflux. Thirty minutes after the start of reflux, 0.050 parts by weight of azobisisobutyronitrile as a polymerization initiator was added to the reactor and allowed to react for 6 hours. Ethyl acetate was then added to the reactor to dilute and cool, yielding a solution of acrylic copolymer A. The resulting solution of acrylic copolymer A was diluted 50-fold with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The resulting filtrate was fed to a gel permeation chromatograph (Waters, 2690 Separations Model) and subjected to GPC measurement at a sample flow rate of 1 mL / min and a column temperature of 40°C. The polystyrene-equivalent molecular weight of acrylic copolymer A was measured, and the weight-average molecular weight (Mw) was calculated. The weight-average molecular weight (Mw) was 1.4 million. A GPC KF-806L (Showa Denko) column was used, and a differential refractometer was used as the detector.

[0072] (Preparation of Acrylic Copolymers B to D) Solutions of acrylic copolymers B to D were prepared in the same manner as for acrylic copolymer A, except that the parts by mass of the structural unit monomers were changed as shown in Table 1, and the weight-average molecular weights of acrylic copolymers B to D were measured. The results are shown in Table 1.

[0073] [Table 1]

[0074] (Preparation of foam substrate A) The foamable composition used to form the foam base material was a composition consisting of 100 parts by mass of linear low-density polyethylene resin, 3.0 parts by mass of azodicarbonamide as a thermal decomposition type foaming agent, 1.0 part by mass of zinc oxide as a decomposition temperature regulator, and 0.5 parts by mass of 2,6-di-t-butyl-p-cresol as an antioxidant. The foamable composition forming the foam base material was fed to an extruder for extrusion molding and melt-kneaded at 130° C. After melt-kneading, a long sheet-like foam raw material having a thickness of about 0.06 mm and comprising a layer made of the foamable composition forming the foam base material was extruded. Next, both sides of the long sheet-like foam raw material were crosslinked by irradiating with 8.8 Mrad of electron beams at an accelerating voltage of 150 kV. The crosslinked foam raw material was continuously fed into a foaming furnace maintained at 250°C by hot air and an infrared heater, and heated to foam, thereby obtaining foam substrate A. Furthermore, the thickness and density of the foam substrate A were measured in accordance with JIS K 7222, and the expansion ratio was calculated using the obtained density. The results are shown in Table 2.

[0075] (Preparation of foam substrates B to E) Foam substrates B to E were prepared in the same manner as foam substrate A, except that the amount of foaming agent added was adjusted to 1.5 to 4.0 parts by mass and the electron beam dose during crosslinking was adjusted to 3.0 to 10.5 Mrad, and the thicknesses and expansion ratios of foam substrates B to E were measured. The results are shown in Table 2.

[0076] (Preparation of foam substrate F) (1) Preparation of block copolymers 0.902 g of 1,6-hexanedithiol, 1.83 g of carbon disulfide, and 11 mL of dimethylformamide were added to a two-neck flask and stirred at 25°C. 2.49 g of triethylamine was added dropwise over 15 minutes and the mixture was stirred at 25°C for 3 hours. 2.75 g of methyl-α-bromophenylacetate was then added dropwise over 15 minutes and stirred at 25°C for 4 hours. The reaction mixture was then extracted with 100 mL of extraction solvent (n-hexane:ethyl acetate = 50:50) and 50 mL of water. The organic layers obtained from the first and second extractions were combined and washed sequentially with 50 mL of 1 M hydrochloric acid, 50 mL of water, and 50 mL of saturated saline. The washed organic layer was dried over sodium sulfate, filtered, and the filtrate was concentrated using an evaporator to remove the organic solvent. The resulting concentrate was purified by silica gel column chromatography to obtain the RAFT agent.

[0077] 93 parts by mass of styrene (St), 6 parts by mass of acrylic acid (AAc), 1 part by mass of hydroxyethyl acrylate (HEA), 1.9 parts by mass of the RAFT agent obtained by the method described above, and 0.2 parts by mass of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) were placed in a two-necked flask, and the flask was heated to 85°C while being purged with nitrogen gas. The mixture was then stirred at 85°C for 6 hours to carry out a polymerization reaction (first-stage reaction). After the reaction was completed, 4,000 parts by mass of n-hexane was added to the flask and stirred to precipitate the reaction product. The unreacted monomers (St, AAc, HEA) and RAFT agent were then filtered off, and the reaction product was dried under reduced pressure at 70°C to obtain a copolymer (hard block).

[0078] A mixture containing 49.5 parts by mass of methyl acrylate (MA), 49.5 parts by mass of butyl acrylate (BA), 1 part by mass of acrylic acid (AAc), 0.058 parts by mass of ABN-E, and 50 parts by mass of ethyl acetate, along with the copolymer (hard block) obtained above, was placed in a two-neck flask, and the flask was heated to 85°C while purging with nitrogen gas. The mixture was then stirred at 85°C for 6 hours to carry out a polymerization reaction (second-stage reaction), yielding a reaction solution containing a block copolymer formed from hard blocks and soft blocks. The blending ratios of the mixture were adjusted so that the resulting block copolymer contained 3% by mass of hard blocks and 97% by mass of soft blocks. A portion of the reaction liquid was collected, and 4,000 parts by mass of n-hexane was added thereto and stirred to precipitate the reaction product. After that, the unreacted monomers (MA, BA, AAc) and the solvent were filtered off, and the reaction product was dried under reduced pressure at 70°C to obtain a block copolymer. The glass transition temperature (Tg) of the resulting block copolymer was measured. The glass transition temperature (Tg) of the peak derived from the hard block was 60°C, and the glass transition temperature (Tg) of the peak derived from the soft block was -10°C. The glass transition temperature (Tg) of the block copolymer was measured using a differential scanning calorimeter (e.g., TA Instruments, DSC 2920) at a temperature range of -40 to 200°C, a heating rate of 10°C / min, and one cycle. The weight-average molecular weight (Mw) of the resulting block copolymer was measured by GPC, which was 400,000. The measurement was performed using a Waters "2690 Separations Module," a Showa Denko "GPC KF-806L" column, ethyl acetate as the solvent, a sample flow rate of 1 mL / min, and a column temperature of 40°C.

[0079] (2) Manufacturing of foam substrate The resulting block copolymer was dissolved in ethyl acetate to a solids content of 35%, and 3.3 parts by mass of Advancell EML101 (Sekisui Chemical Co., Ltd.) as a blowing agent (expanded particles) and 0.15 parts by mass of Tetrad C (epoxy crosslinking agent, Mitsubishi Gas Chemical Co., Inc.) as a crosslinking agent were added to 100 parts by mass of the block copolymer, followed by thorough stirring to obtain a substrate solution. The resulting substrate solution was applied to the release-treated surface of a 50 μm polyethylene terephthalate (PET) film with a release treatment on one side, and dried at 90°C for 7 minutes to obtain an unfoamed substrate. The unfoamed substrate was left to stand in a 40°C environment for 48 hours, and then heated at 130°C for 1 minute to foam the unfoamed substrate to produce foamed substrate F. The thickness and expansion ratio of foamed substrate F were measured. The results are shown in Table 2.

[0080] Example 1 (1) Preparation of adhesive solution To the solution of acrylic copolymer A obtained in the above-mentioned "(Preparation of acrylic copolymer)", 15 parts by mass of polymerized rosin ester resin, 8 parts by mass of terpene phenol resin, and 8 parts by mass of rosin ester resin were added as tackifier resins, 1.0 part by mass of an isocyanate-based crosslinking agent as a crosslinking agent, and 30 parts by mass of ethyl acetate as a solvent, per 100 parts by mass of the solid content of the acrylic copolymer, and the mixture was thoroughly stirred to obtain a pressure-sensitive adhesive solution.

[0081] (2) Preparation of double-sided adhesive tape The prepared adhesive solution was applied to the release-treated surface of a 23 μm-thick release polyethylene terephthalate (PET) film and dried at 110°C for 5 minutes to produce two adhesive sheets with a 50 μm-thick acrylic adhesive layer. One adhesive sheet was bonded to one side of the foam substrate A obtained by the method described above, and the other adhesive sheet was bonded to the other side of the foam substrate with the adhesive sheet bonded to one side, and the resulting mixture was cured by heating at 40°C for 48 hours. This produced a double-sided adhesive tape having a foam substrate and acrylic adhesive layers on both sides of the foam substrate.

[0082] (3) Measurement of the average cell diameter in the MD direction, the average cell diameter in the TD direction, and the aspect ratio of the cells of the foam substrate Using a razor (manufactured by Feather Corporation), foam substrate A was sliced ​​in planes parallel to the MD and thickness directions to obtain cut samples. The resulting cut samples were photographed using a digital microscope (Keyence Corporation, "VHX-6000") at a magnification of 200x and a measurement screen size of 1.8 mm x 1.3 mm. From the photographed images, the bubble with the largest MD radius and the bubble with the second largest MD radius were selected, and the MD and TD radii of these bubbles were measured to calculate the aspect ratio. This procedure was repeated for three photographed images, and the average values ​​of the MD radius, TD radius, and aspect ratio of the six bubbles were used as the average MD cell diameter, average TD cell diameter, and aspect ratio of the foam substrate, respectively. The results are shown in Table 2.

[0083] (4) Measurement of interlaminar strength of foam substrate A 10mm x 10mm piece of foam substrate was bonded to a SUS plate using a cyanoacrylate instant adhesive, and then the peel strength in the ZD direction was measured using a precision universal testing machine (Shimadzu Corporation, "AUTOGLAPH AGS-X") at 23°C by pulling the plate perpendicular to the lamination direction at a rate of 100mm / min. A stress-strain curve was obtained from the measurement results, and the stress (MPa) at the point where the stress was maximum was taken as the interlaminar strength of foam substrate A. The results are shown in Table 2.

[0084] (5) Measurement of the glass transition temperature of the acrylic adhesive layer measured in compression mode and the volume storage modulus at -40°C A sample containing only the acrylic adhesive layer was prepared by overlapping the acrylic adhesive layers to a thickness of 1 mm, and dynamic viscoelasticity measurements were performed using a dynamic viscoelasticity measuring device (IT Measurement & Control Co., Ltd., "Dynamic Viscoelasticity Measurement Apparatus DVA-200") under the following conditions: measurement frequency 10 Hz, compression mode, measurement temperature -40°C to 140°C, heating rate 5°C / min, and strain 0.1%. The glass transition temperature (°C) and volume storage modulus (Pa) at -40°C were measured in compression mode for the acrylic adhesive layer. The results are shown in Table 2.

[0085] (6) Measurement of the glass transition temperature of the acrylic adhesive layer measured in shear mode and the shear storage modulus at -40°C The glass transition temperature (°C) of the acrylic pressure-sensitive adhesive layer measured in shear mode and the shear storage modulus (Pa) at -40°C were measured in the same manner as in "(5) Measurement of the glass transition temperature (°C) of the acrylic pressure-sensitive adhesive layer measured in compression mode and the volume storage modulus at -40°C" above, except that the dynamic viscoelasticity measurement was performed by changing the compression mode to shear mode. The results are shown in Table 2.

[0086] (7) Measurement of shear modulus of double-sided adhesive tape at -30°C A schematic diagram showing a shear test of double-sided adhesive tape is shown in Figure 1. First, the obtained double-sided adhesive tape was cut into a piece measuring 12.5 mm x 25 mm, and two SUS plates 2 measuring 30 mm x 50 mm and 1 mm thick were laminated together as shown in Figure 1. This laminate was pressed at 0.3 MPa for 10 seconds in an environment of 23°C to bond the two plates, and then left to stand at 23°C and 50% RH for 24 hours to produce a test sample in which two SUS plates 2 were bonded together via the double-sided adhesive tape 1. After fixing one of the SUS plates 2 of the obtained test sample, the upper part of the other SUS plate 2 was pulled at a speed of 1000 mm / min in a direction perpendicular to the stacking direction of the SUS plates (the direction of the arrow in Figure 1) using a precision universal testing machine AUTOGLAPH AGS-X (manufactured by Shimadzu Corporation) in an environment of -30°C. A stress-strain curve was obtained from the measurement results, and the slope (MPa) at strains of 1 to 2% was taken as the shear modulus. The results are shown in Table 3.

[0087] (8) Measurement of the tensile modulus of elasticity of double-sided adhesive tape at -30°C The obtained double-sided adhesive tape was cut into a size of 10 mm × 50 mm to prepare a test piece. The prepared test piece was subjected to a tensile test in accordance with JIS K 7127 using a tensile tester (Shimadzu Corporation, "AUTOGLAPH AGS-X" precision universal testing machine) at a gripping distance of 50 mm and a tensile speed of 1000 mm / min in an environment of -30°C. A stress-strain curve was obtained from the measurement results, and the slope (MPa) at a strain of 1% to 2% was taken as the tensile modulus of elasticity. The results are shown in Table 3.

[0088] (9) Measurement of the volume storage modulus of the double-sided adhesive tape at -40°C, the loss tangent measured in compression mode, and the glass transition temperature measured in compression mode The resulting double-sided adhesive tape was cut into a 10 mm wide x 10 mm long sample. Dynamic viscoelasticity measurements were performed on the resulting sample using a dynamic viscoelasticity measuring device (IT Measurement & Control Co., Ltd., "Dynamic Viscoelasticity Measurement Apparatus DVA-200") under the following conditions: measurement frequency 10 Hz, compression mode, measurement temperature -40°C to 140°C, heating rate 5°C / min, and strain 0.1%. The loss tangent measured in compression mode, glass transition temperature (°C) measured in compression mode, and volume storage modulus (Pa) at -40°C were measured for the double-sided adhesive tape. The results are shown in Table 3.

[0089] (10) Measurement of 25% compressive strength of double-sided adhesive tape The resulting double-sided adhesive tape was cut into 20 mm x 20 mm pieces and stacked to create samples approximately 5 mm x 20 mm x 20 mm thick. The resulting samples were compressed in the compression direction at a rate of 10 mm / min, and the pressure (N) measured at 25% compression was measured. The 25% compression strength (kPa) of the double-sided adhesive tape was calculated from the obtained pressure using the following formula (2). The results are shown in Table 3. Compressive strength (kPa) = pressure (N) / 0.4 (2)

[0090] (Examples 2 to 3, Comparative Examples 1 to 8) Double-sided pressure-sensitive adhesive tapes were prepared and various measurements were carried out in the same manner as in Example 1, except that the type and thickness of the foam substrate and the composition and thickness of the acrylic pressure-sensitive adhesive layer were changed as shown in Tables 1 and 2. The results are shown in Tables 2 and 3.

[0091] <Evaluation> The double-sided pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 3.

[0092] (1) Preparation of smartphone samples for evaluation A commercially available smartphone was prepared and the back panel was separated from the smartphone by heating it with a heat gun. A mold was then created with the same shape as the tape that had been used to secure the inside of the smartphone to the back panel. Using this mold, double-sided adhesive tape was punched out to the same shape as the tape that had been used to secure the inside of the smartphone to the back panel. This was then used to bond the inside of the smartphone to the back panel, thereby producing a smartphone sample for evaluation.

[0093] (2) Evaluation of cracks at corners A corner drop test was conducted on the smartphone sample for evaluation prepared in the above-mentioned "(1) Preparation of test sample" in which a specific corner was positioned vertically downward and dropped from a height of 1 m onto a concrete slab. The corner drop test described above was repeated for three evaluation smartphone samples until the corner of the evaluation smartphone sample cracked. The corner cracking was evaluated as follows: if the average number of times the corner drop test was performed until the corner of the evaluation smartphone sample cracked was more than 4.0 times, it was marked as "○", if it was more than 3.5 times but not more than 4.0 times, it was marked as "△", and if it was 3.5 times or less, it was marked as "×".

[0094] (3) Evaluation of cracks and lifting on the back surface A back drop test was conducted on the smartphone sample for evaluation prepared in the above-mentioned "(1) Preparation of test sample" in which the back was aligned parallel to the drop point and dropped from a height of 1 m onto a concrete slab. The above-mentioned back drop test was repeated for three evaluation smartphone samples until the back of the evaluation smartphone sample cracked or the back surface lifted. If the average number of back drop tests performed before the back of the evaluation smartphone sample cracked or the back surface lifted was 6 or more, it was marked as "○", if it was 5 or more but less than 6 times, it was marked as "△", and if it was less than 5 times, it was marked as "×". Even if the evaluation is "X", the double-sided pressure-sensitive adhesive tape of the present invention can be used without any problems depending on the application.

[0095] [Table 2]

[0096] [Table 3] [Industrial Applicability]

[0097] According to the present invention, it is possible to provide a double-sided pressure-sensitive adhesive tape that can suppress cracking at corners of an adherend due to an external impact such as being dropped. [Explanation of symbols]

[0098] 1 double-sided adhesive tape 2 SUS board

Claims

1. A double-sided pressure-sensitive adhesive tape having a foam substrate and acrylic pressure-sensitive adhesive layers on both sides of the foam substrate, The double-sided pressure-sensitive adhesive tape has a shear modulus of 90 MPa or more and 300 MPa or less, measured at −30° C. and a shear rate of 1000 mm / min, and The tensile modulus of elasticity measured at -30°C and a tensile speed of 1000 mm / min is 3.0 MPa or more. A double-sided adhesive tape characterized by:

2. The double-sided adhesive tape has a volume storage modulus (K') of 2.1 x 10 at -40°C as measured in a compression mode in a dynamic viscoelasticity measurement at a measurement frequency of 10 Hz. ７ Pa or less, and 2. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the 25% compressive strength is 50 kPa or more and 200 kPa or less.

3. The foam substrate has an expansion ratio of 5.0 cm ３ / g or less, and The aspect ratio of the bubbles is less than 1.0 The double-sided pressure-sensitive adhesive tape according to claim 1 or 2.

4. 3. The double-sided pressure-sensitive adhesive tape according to claim 1, wherein the thickness of the double-sided pressure-sensitive adhesive tape is 250 [mu]m or more and 450 [mu]m or less.

5. 3. The double-sided pressure-sensitive adhesive tape according to claim 1, which is used for fixing a glass back panel in an electronic device.

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