Adhesive tape

Abstract

The present invention aims to provide an adhesive tape with excellent repeated impact resistance. The adhesive tape of the present invention is an adhesive tape having: a multilayer substrate, and an adhesive layer laminated to at least one surface of the multilayer substrate, the multilayer substrate having a substrate layer, and a resin layer laminated to at least one surface of the substrate layer, the substrate layer having a storage elastic modulus E' of 2.0 MPa or more and 21 MPa or less in dynamic viscoelasticity measurement at 10°C, the resin layer having a Young's modulus of 500 MPa or more at 23°C, the adhesive layer having an elongation at break of 30% or more in shear adhesion force measurement at 23°C, and a storage elastic modulus G' of 0.13 MPa or more and 7.0 MPa or less in dynamic viscoelasticity measurement at 10°C.

Description

Technical Field

[0001] This invention relates to adhesive tape. Background Technology

[0002] Adhesive tape is used for assembly in portable electronic devices such as mobile phones and portable information terminals (Personal Digital Assistants, PDAs) (e.g., Patent Documents 1 and 2). Adhesive tape is also used to fix automotive electronic device components, such as automotive panels, to the vehicle body.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-242541

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-258274 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Adhesive tapes used for securing components in portable and automotive electronic devices require high adhesive strength and impact resistance to prevent peeling even under impact. Furthermore, recent portable and automotive electronic devices have become increasingly complex in shape due to their higher functionality; therefore, adhesive tapes are sometimes used to adhere to surfaces with height differences, corners, or non-planar surfaces. In such cases, the adhesive tape must possess excellent flexibility to conform to the shape of the object being adhered to.

[0009] Adhesive tapes, which are known for their excellent flexibility and impact resistance, include those using foamed substrates obtained by foaming polyolefin resins, for example. However, in recent years, due to the increasingly stringent and diverse operating conditions for electronic devices, there is a requirement to withstand repeated impacts (continuous impacts). Existing adhesive tapes using foamed substrates have the following problems: even if they do not peel off due to a single impact, they may peel off or cause damage to the adhered material when subjected to repeated impacts such as drops.

[0010] The purpose of this invention is to provide an adhesive tape with excellent repeatability and impact resistance.

[0011] means for solving problems

[0012] This invention relates to an adhesive tape comprising: a multilayer substrate and an adhesive layer laminated on at least one side of the multilayer substrate, wherein the multilayer substrate has a substrate layer and a resin layer laminated on at least one side of the substrate layer, wherein the storage modulus E' of the substrate layer in a dynamic viscoelasticity test at 10°C is 2.0 MPa or more and 21 MPa or less, the young's modulus of the resin layer at 23°C is 500 MPa or more, the elongation at break of the adhesive layer in a shear adhesion test at 23°C is 30% or more, and the storage modulus G' of the adhesive layer in a dynamic viscoelasticity test at 10°C is 0.13 MPa or more and 7.0 MPa or less.

[0013] The present invention will now be described in detail.

[0014] The inventors have discovered that by using a multilayer substrate having a substrate layer and a resin layer having at least one side of the substrate in an adhesive tape having a substrate and an adhesive layer having at least one side of the substrate layer, the resin layer can disperse stress when subjected to impact, thereby improving the repeated impact resistance of the adhesive tape.

[0015] The inventors further analyzed the factors affecting the repeated impact resistance of such adhesive tapes. As a result, they discovered that by adjusting the storage modulus E' of the substrate layer in a dynamic viscoelasticity test at 10°C, the Young's modulus of the resin layer at 23°C, the elongation at break in a shear bond strength test of the adhesive layer at 23°C, and the storage modulus G' of the dynamic viscoelasticity test at 10°C to specific ranges, the repeated impact resistance of the adhesive tape can be significantly improved. Thus, the present invention is completed.

[0016] The adhesive tape of the present invention comprises: a multilayer substrate and an adhesive layer laminated on at least one side of the multilayer substrate.

[0017] The aforementioned multilayer substrate comprises: a substrate layer and a resin layer laminated on at least one side of the substrate layer. By having such a multilayer substrate, the resin layer disperses stress upon impact, enabling the adhesive tape of the present invention to exhibit excellent repeated impact resistance. The resin layer may be laminated on only one side of the substrate layer or on both sides, but preferably only on one side of the substrate layer.

[0018] The lower limit of the energy storage modulus E' in the dynamic viscoelasticity test of the above-mentioned substrate layer at 10°C is 2.0 MPa and the upper limit is 21 MPa.

[0019] By setting the energy storage elastic modulus E' at 10°C to 2.0 MPa or higher, the substrate layer can possess moderate hardness, and the adhesive tape of the present invention can exhibit excellent repeated impact resistance. By setting the energy storage elastic modulus E' at 10°C to 21 MPa or lower, the flexibility of the substrate layer is improved, and when subjected to impact, it can prevent the substrate layer from being too hard to disperse stress, thus the adhesive tape of the present invention can exhibit excellent repeated impact resistance. The preferred lower limit of the energy storage elastic modulus E' at 10°C is 2.1 MPa, the preferred upper limit is 12.0 MPa, the more preferred lower limit is 2.2 MPa, the more preferred upper limit is 11.5 MPa, the even more preferred lower limit is 2.5 MPa, and the even more preferred upper limit is 9.6 MPa.

[0020] It should be noted that the storage modulus E' of the substrate layer in the dynamic viscoelasticity determination at 10°C can be obtained as follows: using a viscoelastic spectrometer (e.g., IT Measurement & Control Co., Ltd., DVA-200, etc.), the dynamic viscoelastic spectrum from -40°C to 140°C is measured under constant-rate heating and stretching mode at 5°C / min, strain 0.1%, and frequency 10Hz, and is obtained in the form of the storage modulus E' at 10°C at this time.

[0021] There is no particular limitation on the method for adjusting the energy storage elastic modulus E' at 10°C to the range described above. For example, the following methods can be used: adjusting the gel fraction of the substrate layer; adjusting the type or amount of foaming particles when the substrate layer is a foam substrate layer; or using a copolymer having a structure derived from vinyl aromatic monomers and a structure derived from (meth)acrylic monomers as described below for the substrate layer.

[0022] The aforementioned substrate layer is not particularly limited as long as the storage modulus E' at 10°C meets the aforementioned range. Preferably, it contains copolymers having structures derived from (meth)acrylic monomers, and more preferably, it contains copolymers having structures derived from both vinyl aromatic monomers and (meth)acrylic monomers. By including these copolymers in the substrate layer, the storage modulus E' at 10°C can be easily adjusted to the aforementioned range, further improving the repeatability and impact resistance of the adhesive tape.

[0023] Examples of the aforementioned vinyl aromatic monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, 1-ethyl-2-vinylbenzene, 1-ethyl-3-vinylbenzene, vinylnaphthalene, and chlorostyrene. These vinyl aromatic monomers can be used alone or in combination of two or more. From the perspective of further improving the repeated impact resistance of the adhesive tape, styrene is preferred. It should be noted that, in this specification, the structure derived from the vinyl aromatic monomer refers to the structure shown in the following general formulas (1) and (2).

[0024] [Chemical Formula 1]

[0025]

[0026] In general formulas (1) and (2), R 1 This indicates a substituent having an aromatic ring. R is a substituent having an aromatic ring. 1 Examples include phenyl, methylphenyl, and chlorophenyl.

[0027] In the copolymers described above, which have structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, the content of the structures derived from vinyl aromatic monomers is not particularly limited, but is preferably 1% by weight or more and 30% by weight or less. By setting the content of the structures derived from vinyl aromatic monomers within the above range, the repeatability and impact resistance of the adhesive tape are further improved. A more preferred lower limit for the content of the structures derived from vinyl aromatic monomers is 1.5% by weight, a further preferred lower limit is 2% by weight, a further more preferred lower limit is 3% by weight, a particularly preferred lower limit is 3.5% by weight, a more preferred upper limit is 15% by weight, and a further preferred upper limit is 8% by weight.

[0028] The copolymers described above having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers preferably also have structures derived from monomers having crosslinking functional groups.

[0029] If the copolymer having structures derived from vinyl aromatic monomers and (meth)acrylic monomers has crosslinking functional groups, the rubber elasticity of the copolymer is improved through crosslinking. Therefore, the storage modulus E' at 10°C can be easily adjusted to the range described above, and the repeated impact resistance of the adhesive tape is further improved. The crosslinking functional groups can be crosslinked or uncrosslinked, but crosslinking is more preferred. However, even when maintaining an uncrosslinked structure, the cohesive force within the hard or soft blocks (especially hard blocks) described later is increased due to the interaction between functional groups, making it easy to adjust the storage modulus E' at 10°C to the range described above, and further improving the repeated impact resistance of the adhesive tape. It should be noted that, in this specification, the structure derived from monomers having crosslinking functional groups refers to the structure shown in the following general formulas (3) and (4).

[0030] [Chemical Formula 2]

[0031]

[0032] In general formulas (3) and (4), R 2 This indicates a substituent containing at least one functional group. Examples of functional groups include: carboxyl, hydroxyl, epoxy, double bond, triple bond, amino, amide, nitrile, etc. It should be noted that the substituent R containing at least one functional group... 2 It may contain alkyl, ether, carbonyl, ester, carbonate, amide, carbamate and other groups as its constituent elements.

[0033] The monomers with crosslinking functional groups mentioned above are not particularly limited, and examples include: monomers containing carboxyl groups, hydroxyl groups, epoxy groups, double bonds, triple bonds, amino groups, amide groups, and nitrile groups. These monomers with crosslinking functional groups can be used alone or in combination of two or more. From the perspective of further improving the repeated impact resistance of the adhesive tape, it is preferable to select at least one monomer from the group containing carboxyl groups, hydroxyl groups, epoxy groups, double bonds, triple bonds, and amide groups.

[0034] Examples of carboxyl-containing monomers include (meth)acrylic acid and other (meth)acrylic acid monomers. Examples of hydroxyl-containing monomers include 4-hydroxybutyl (meth)acrylic acid and 2-hydroxyethyl (meth)acrylic acid. Examples of epoxy-containing monomers include glycidyl (meth)acrylic acid. Examples of monomers containing double bonds include allyl (meth)acrylic acid and hexanediol di(meth)acrylic acid. Examples of monomers containing triple bonds include propargyl (meth)acrylic acid. Examples of monomers containing amide groups include (meth)acrylamide. From the perspective of further improving the repeated impact resistance of the adhesive tape, carboxyl-containing monomers and hydroxyl-containing monomers are preferred. Furthermore, (meth)acrylic acid monomers containing carboxyl groups and (meth)acrylic acid monomers containing hydroxyl groups are more preferred, and (meth)acrylic acid, 4-hydroxybutyl (meth)acrylic acid, and 2-hydroxyethyl (meth)acrylic acid are even more preferred.

[0035] In the copolymers having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, the content of the structure derived from the monomer with crosslinking functional groups is not particularly limited, but is preferably 0.1% by weight or more and 30% by weight or less. By setting the content of the structure derived from the monomer with crosslinking functional groups within the above range, the repeatability and impact resistance of the adhesive tape are further improved. A more preferred lower limit for the content of the structure derived from the monomer with crosslinking functional groups is 0.5% by weight, a further preferred lower limit is 1% by weight, a more preferred upper limit is 25% by weight, and a further preferred upper limit is 20% by weight.

[0036] The aforementioned (meth)acrylic acid monomers can be a single monomer or multiple monomers. It should be noted that, in this specification, the structure derived from the (meth)acrylic acid monomer refers to the structure shown in the following general formulas (5) and (6).

[0037] [Chemical Formula 3]

[0038]

[0039] In general formulas (5) and (6), R 3 Represents a sidechain. As a sidechain R 3 Examples include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, lauryl, isostearyl, etc.

[0040] Examples of the aforementioned (meth)acrylate monomers include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, dodecyl methacrylate, lauryl methacrylate, and isostearyl methacrylate. These (meth)acrylate monomers can be used alone or in combination of two or more. From the perspective of further improving the repeated impact resistance of the adhesive tape, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate are preferred, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl methacrylate are even more preferred.

[0041] Furthermore, it is preferable to use (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains as the aforementioned (meth)acrylic monomers. Using (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains increases the entanglement of the copolymer chains, improves cohesion, makes it easier to adjust the storage modulus E' at 10°C to the aforementioned range, further improves the repeated impact resistance of the adhesive tape, and also improves its heat resistance.

[0042] Examples of (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains include methyl methacrylate and ethyl methacrylate, with methyl acrylate and ethyl acrylate being particularly preferred.

[0043] In the copolymers described above having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, the content of the structures derived from (meth)acrylic monomers is not particularly limited, as long as the effects of the present invention are achieved; preferably, it is 30% by weight or more and 99% by weight or less. More preferably, the content of the structures derived from (meth)acrylic monomers is 40% by weight or more and 98% by weight or less, and even more preferably 50% by weight or more and 97% by weight or less.

[0044] Furthermore, in the copolymers having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, the content of the (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains is not particularly limited, but a preferred lower limit is 5% by weight, and a preferred upper limit is 90% by weight. When the content of the (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains is 5% by weight or more, it is easy to exhibit an effect of improved cohesion. When the content of the (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains is 90% by weight or less, it is possible to prevent the cohesion from becoming too high, the flexibility from becoming low, and the loss of flexibility as an adhesive tape. A more preferred lower limit for the content of the (meth)acrylic monomers with 2 or fewer carbon atoms in their side chains is 10% by weight, a further preferred lower limit is 20% by weight, a further more preferred lower limit is 25% by weight, a particularly preferred lower limit is 30% by weight, a more preferred upper limit is 85% by weight, a further preferred upper limit is 80% by weight, a further more preferred upper limit is 75% by weight, and a particularly preferred upper limit is 70% by weight.

[0045] The copolymers having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers are not particularly limited as long as they have the structures described above; they can be random copolymers or block copolymers. From the viewpoint of further improving the flexibility of the substrate layer, random copolymers are preferred, while from the viewpoint of further improving the balance between the hardness and flexibility of the substrate layer, block copolymers are preferred.

[0046] The aforementioned block copolymer refers to a copolymer containing a rigid structure (hereinafter also referred to as "hard block") and a flexible structure (hereinafter also referred to as "soft block").

[0047] The two blocks of the aforementioned block copolymer are not easily compatible, sometimes forming a heterogeneous phase-separated structure where the soft blocks are interspersed with islands formed by the aggregation of the hard blocks. Furthermore, these islands act as potential crosslinking points, thereby imparting rubber-like elasticity to the block copolymer and further improving the repeated impact resistance of the adhesive tape. By introducing the crosslinking functional groups described above into the hard blocks, the repeated impact resistance of the adhesive tape is further improved.

[0048] It should be noted that even when the copolymers described above, which have structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, are random copolymers, the adhesive tape still exhibits excellent repeatable impact resistance. This is believed to be because, at such extremely small scales as the nanoscale and molecular scale, the same interactions as those in the aforementioned phase-separated structures are at play.

[0049] Regarding the block copolymers described above, it is preferred that the structures derived from vinyl aromatic monomers are included in the hard blocks, and the structures derived from (meth)acrylic monomers are included in the soft blocks.

[0050] The hard blocks described above are not particularly limited as long as they have a rigid structure. In addition to the structures derived from vinyl aromatic monomers, they can also have structures derived from compounds with cyclic structures, compounds with short side-chain substituents, etc. Without sacrificing the effects of the present invention, the soft blocks described above can also have structures derived from monomers other than the (meth)acrylic monomers described above.

[0051] The block copolymers described above can take any structure, such as a diblock structure or a triblock structure. From the perspective of further improving the repeatability and impact resistance of the adhesive tape, a triblock structure with soft blocks between the hard blocks is preferred.

[0052] Furthermore, the aforementioned block copolymer can be a graft copolymer in which the aforementioned hard block and the aforementioned soft block exist separately in the main chain and side chain. Examples of such graft copolymers include styrene macromonomer-(meth)acrylic acid monomer copolymers.

[0053] In the aforementioned block copolymer, the content of the hard block is not particularly limited, but is preferably 1% by weight or more and 40% by weight or less. By setting the content of the hard block within the aforementioned range, the repeatability of the adhesive tape is further improved, and its heat resistance is also improved. From the viewpoint of further improving repeatability and heat resistance, a more preferred lower limit for the content of the hard block is 2% by weight, a more preferred lower limit is 2.5% by weight, and a particularly preferred lower limit is 3% by weight. A more preferred upper limit for the content of the hard block is 35% by weight, a more preferred upper limit is 30% by weight, a more preferred upper limit is 26% by weight, a more preferred upper limit is 20% by weight, a particularly preferred upper limit is 17% by weight, and an especially preferred upper limit is 8% by weight.

[0054] The weight-average molecular weight (Mw) of the copolymers having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers is not particularly limited, but is preferably 50,000 or more and 800,000 or less. By setting the weight-average molecular weight within the above range, the repeatability of the adhesive tape is further improved, and its heat resistance is also improved. A more preferred lower limit for the weight-average molecular weight is 75,000, and a more preferred upper limit is 600,000.

[0055] It should be noted that the weight-average molecular weight can be determined, for example, using GPC (Gel Permeation Chromatography) and conversion to standard polystyrene. More specifically, for example, a Waters "2690 Separations Module" can be used as the analytical instrument, a Showa Denko "GPC KF-806L" column can be used as the chromatographic column, ethyl acetate can be used as the solvent, and the determination can be performed at a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0056] To obtain the copolymer having structures derived from vinyl aromatic monomers and (meth)acrylic acid monomers, the raw material monomers of the hard block and the soft block are subjected to free radical reactions in the presence of a polymerization initiator. After obtaining the hard block and the soft block, they are then reacted or copolymerized. Alternatively, after obtaining the hard block, the raw material monomers of the soft block can be added to perform copolymerization. In the case of a random copolymer, a solution containing the raw material monomers is subjected to a free radical reaction in the presence of a polymerization initiator.

[0057] As a method for carrying out the above-mentioned free radical reaction, i.e., a polymerization method, existing known methods can be used, such as solution polymerization (boiling point polymerization or isothermal polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0058] The aforementioned substrate layer may contain additives such as antistatic agents, release agents, antioxidants, weathering agents, and crystal nucleating agents, as well as resin modifiers such as polyolefins, polyesters, polyamides, and elastomers.

[0059] The aforementioned substrate layer preferably exhibits at least one peak in the region below 10°C and in the region above 50°C when subjected to DSC (differential scanning calorimetry) in the atmosphere at a heating rate of 10°C / min.

[0060] When the aforementioned substrate layer exhibits at least one peak in both the region below 10°C and the region above 50°C during DSC measurement, it can be said that the substrate layer contains a block copolymer with two blocks as described above. From the viewpoint of further improving the balance between the hardness and flexibility of the aforementioned substrate layer, it is preferable, as described above, that the aforementioned substrate layer contains the aforementioned block copolymer. In this invention, peaks in the region below 10°C during DSC measurement can be referred to as peaks originating from the aforementioned soft blocks, and peaks in the region above 50°C can be referred to as peaks originating from the aforementioned hard blocks. The regions of the aforementioned peaks can be adjusted by the types of raw material monomers for the aforementioned hard blocks and the aforementioned soft blocks.

[0061] It should be noted that the DSC measurement of the substrate layer can be performed using a differential scanning calorimeter (e.g., TA Instruments DSC 2920, etc.) under the conditions of a temperature range of -100 to 200°C, a heating rate of 10°C / min, and one cycle.

[0062] The aforementioned substrate layer can be a single-layer structure or a multi-layer structure.

[0063] The aforementioned substrate layer is preferably a foamed substrate layer. By making the aforementioned substrate layer a foamed substrate layer, flexibility is improved, and it is possible to prevent the substrate layer from being too hard to disperse stress upon impact. As a result, the repeated impact resistance of the adhesive tape is further improved. The aforementioned foamed substrate layer may have a continuous bubble structure or an independent bubble structure, but an independent bubble structure is preferred.

[0064] The foaming ratio of the aforementioned foamed substrate layer is not particularly limited, but a preferred lower limit is 1.1 times and a preferred upper limit is 10 times. By setting the foaming ratio within the aforementioned range, the balance between the hardness and flexibility of the aforementioned foamed substrate layer can be further improved, thus further enhancing the repeated impact resistance of the adhesive tape. From the viewpoint of further improving repeated impact resistance, a more preferred lower limit of the aforementioned foaming ratio is 1.3 times, a more preferred upper limit is 7 times, a further preferred lower limit is 1.5 times, and a further preferred upper limit is 5 times.

[0065] It should be noted that the foaming ratio of the foam substrate layer refers to the reciprocal of the density of the foam substrate layer, which can be measured based on JIS K 7222 using an electronic hydrometer (e.g., MIRAGE, ED120T, etc.).

[0066] The average bubble diameter of the aforementioned foam substrate layer is not particularly limited, but is preferably 80 μm or less. By setting the average bubble diameter to 80 μm or less, the balance between the hardness and flexibility of the aforementioned foam substrate layer can be further improved, thus further enhancing the repeated impact resistance of the adhesive tape. More preferably, the average bubble diameter is 60 μm or less, and even more preferably 55 μm or less.

[0067] The lower limit of the average bubble diameter is not particularly limited, but from the viewpoint of ensuring the softness of the foam substrate layer, it is preferably 20 μm or more, and more preferably 30 μm or more.

[0068] It should be noted that the average bubble diameter of the foam substrate layer can be determined using the following method. First, cut the foam substrate layer into 50mm squares, immerse them in liquid nitrogen for 1 minute, and then use a razor to cut the foam substrate layer perpendicular to its thickness direction. Next, using a digital microscope (e.g., KEYENCE VHX-900), take a magnified photograph of the cut surface at 200x magnification, and measure the diameter of the longest bubble (the diameter of the bubble) within a thickness × 2mm range. Repeat this operation 5 times, and average the obtained bubble diameters to calculate the average bubble diameter.

[0069] The gel fraction of the above-mentioned substrate layer is preferably 90% by weight or less.

[0070] By setting the gel fraction of the substrate layer within the aforementioned range, the repeatability of the adhesive tape is further improved. From the viewpoint of further improving repeatability, a more preferred upper limit for the gel fraction is 85% by weight, and a more preferred upper limit is 80% by weight. The lower limit of the gel fraction is not particularly limited, but is, for example, 10% by weight or more, particularly 20% by weight or more, and especially 35% by weight or more. The gel fraction can be adjusted by crosslinking the resin forming the substrate layer.

[0071] It should be noted that the gel fraction of the substrate layer can be determined using the following method. Only 0.1 g of the substrate layer is taken from the adhesive tape and immersed in 50 mL of ethyl acetate. The mixture is then shaken for 24 hours at 23°C and 120 rpm. After shaking, the ethyl acetate is separated from the swollen substrate layer using a metal mesh (200 mesh). The separated substrate layer is then dried at 110°C for 1 hour. The weight of the dried substrate layer, including the metal mesh, is measured, and the gel fraction of the substrate layer is calculated using the following formula.

[0072] Gel fraction (wt%) = 100 × (W1 - W2) / W0

[0073] (W0: Initial substrate layer weight, W1: Dried substrate layer weight including metal mesh, W2: Initial weight of metal mesh)

[0074] The aforementioned substrate layer is preferably cross-linked by adding a cross-linking agent to form a cross-linked structure between the main chains of the resin forming the substrate layer.

[0075] By forming a cross-linked structure between the main chains of the resin that forms the above-mentioned substrate layer, the intermittently applied stress can be dispersed, the repeated impact resistance of the adhesive tape can be further improved, and the heat resistance can also be improved.

[0076] The crosslinking agent is not particularly limited and can be appropriately selected based on the functional groups of the resin forming the substrate layer. Specifically, examples include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Among these, epoxy-based or isocyanate-based crosslinking agents are preferred from the perspective of being able to crosslink resins with alcoholic hydroxyl and carboxyl groups that can further improve flexibility. It should be noted that when using the isocyanate-based crosslinking agent, crosslinking occurs between the alcoholic hydroxyl and carboxyl groups in the resin forming the substrate layer and the isocyanate groups in the isocyanate-based crosslinking agent. Similarly, when using the epoxy-based crosslinking agent, crosslinking occurs between the carboxyl groups in the resin forming the substrate layer and the epoxy groups in the epoxy-based crosslinking agent.

[0077] The amount of the crosslinking agent is not particularly limited, but is preferably 0.01 parts by weight or more and 10 parts by weight or less, more preferably 0.1 parts by weight or more and 7 parts by weight or less, relative to 100 parts by weight of the resin forming the substrate layer.

[0078] The thickness of the aforementioned substrate layer is not particularly limited, but a preferred lower limit is 40 μm and a preferred upper limit is 2900 μm. By setting the thickness of the substrate layer within the aforementioned range, an adhesive tape with excellent flexibility, repeated impact resistance, heat resistance, and processability can be manufactured, and the adhesive tape can be suitable for fixing electronic device components such as portable electronic device components and automotive electronic device components. From the viewpoint of being more suitable for fixing the aforementioned components, a more preferred lower limit of the thickness of the substrate layer is 60 μm, a more preferred upper limit is 1900 μm, a further preferred lower limit is 80 μm, a further preferred upper limit is 1400 μm, a particularly preferred lower limit is 100 μm, and a particularly preferred upper limit is 1000 μm.

[0079] The manufacturing method of the aforementioned substrate layer is not particularly limited. Examples of manufacturing methods for the aforementioned foamed substrate layer include: a method using foaming gas; and a method using hollow spheres incorporated into a raw material matrix. The foamed substrate layer manufactured by the latter method is referred to as a composite foam plastic, and from the perspective of superior strength, flexibility, and heat resistance, the aforementioned foamed substrate layer is preferably a composite foam plastic.

[0080] By making the aforementioned foam substrate layer a composite foam plastic, a foam with a uniform size distribution of independent air bubbles is formed. Therefore, the overall density of the aforementioned foam substrate layer is more constant, and its strength, flexibility, and heat resistance are further improved. Furthermore, compared to other foams, composite foam plastics are less prone to irreversible disintegration under high temperature and pressure, thus exhibiting higher heat resistance. Composite foam plastics include those with a foam structure containing hollow inorganic particles and those with a foam structure containing hollow organic particles; however, from the viewpoint of flexibility, composite foam plastics with a foam structure containing hollow organic particles are preferred.

[0081] Examples of hollow organic particles mentioned above include the Expancel DU series (manufactured by Japan Fillite Co., Ltd.) and the Advancell EM series (manufactured by Sekisui Chemicals Co., Ltd.). Among these, from the perspective of easily designing the bubble diameter after foaming to achieve a higher level of effectiveness, Expancel 461-DU-20 (average bubble diameter after foaming under optimal conditions: 20 μm), Expancel 461-DU-40 (average bubble diameter after foaming under optimal conditions: 40 μm), Expancel 043-80 (average bubble diameter after foaming under optimal conditions: 80 μm), and Advancell EML101 (average bubble diameter after foaming under optimal conditions: 50 μm).

[0082] The content of the hollow organic particles is not particularly limited, but relative to 100 parts by weight of the resin forming the foamed substrate layer, the preferred lower limit is 0.1 parts by weight, the preferred upper limit is 10 parts by weight, the more preferred lower limit is 0.3 parts by weight, and the more preferred upper limit is 7 parts by weight. By keeping the content of the hollow organic particles within the above range, the foaming ratio of the foamed substrate layer can be adjusted to an appropriate range.

[0083] When the foam substrate layer contains foams other than the aforementioned composite foam plastic, the foaming agent is not particularly limited, and existing known foaming agents such as thermally decomposable foaming agents can be used.

[0084] The lower limit of the Young's modulus of the above resin layer at 23°C is 500 MPa.

[0085] By achieving a Young's modulus of 500 MPa or more at 23°C, the resin layer can disperse stress upon impact, thus enabling the adhesive tape of the present invention to exhibit excellent repeated impact resistance. The preferred lower limit for the Young's modulus at 23°C is 1000 MPa, and a more preferred lower limit is 2000 MPa.

[0086] There is no particular upper limit to the Young's modulus at 23°C, but from the point of view of ensuring softness, the preferred upper limit is 4000 MPa, and the more preferred upper limit is 3000 MPa.

[0087] It should be noted that the Young's modulus of the resin layer at 23°C can be determined based on JIS-K-7161 using a benchtop precision universal testing machine (e.g., Shimadzu Corporation, Autograph AGS-X series, etc.). More specifically, for example, by clamping test pieces cut to a width of 10 mm and a length of 100 mm at 50 mm intervals, measuring the stress-strain curve when subjected to tension at a speed of 200 mm / min, and calculating the average slope from 1% to 5% strain, the Young's modulus can be obtained.

[0088] There are no particular limitations on the method for adjusting the Young's modulus at 23°C to the range described above. For example, methods for selecting the resin that forms the resin layer can be cited. More specifically, it is preferable to select a resin with rigid components such as aromatic rings in the main chain.

[0089] The resin forming the above-mentioned resin layer preferably has heat resistance. Examples of heat-resistant resins for forming the above-mentioned resin layer include polyester resins such as polyethylene terephthalate, acrylic resins, silicone resins, phenolic resins, polyimide, polycarbonate, and polyolefin resins. Among these, from the perspective of further improving the repeated impact resistance of the adhesive tape, polyester resins, polyimide, and polyolefin resins are preferred, polyester resins are more preferred, and polyethylene terephthalate is even more preferred.

[0090] The resin layer described above can be colored. By coloring the resin layer, the adhesive tape can be given light-blocking properties.

[0091] There is no particular limitation on the method of coloring the above-mentioned resin layer. Examples include: mixing carbon black, titanium oxide particles or microbubbles into the resin forming the above-mentioned resin layer; coating the surface of the above-mentioned resin layer with ink, etc.

[0092] The resin layer may contain, as needed, existing and known particles and additives such as inorganic particles, conductive particles, plasticizers, tackifiers, ultraviolet absorbers, antioxidants, foaming agents, organic fillers, and inorganic fillers.

[0093] The thickness of the resin layer is not particularly limited, but a preferred lower limit is 5 μm and a preferred upper limit is 100 μm. By setting the thickness of the resin layer within the above range, both the processability and repeated impact resistance of the adhesive tape can be considered. From the viewpoint of further balancing processability and repeated impact resistance, a more preferred lower limit of the thickness of the resin layer is 10 μm and a more preferred upper limit is 70 μm.

[0094] The adhesive layer may be laminated on only one side of the multilayer substrate or on both sides. When the adhesive layer is laminated on both sides of the multilayer substrate, the adhesive layers on both sides may have the same composition and properties or different compositions and properties.

[0095] The lower limit of the elongation at break in the shear adhesion test of the above-mentioned adhesive layer at 23°C is 30%. By achieving an elongation at break of 30% or more at 23°C, breakage due to deformation of the adhesive layer upon impact is less likely to occur, thus the adhesive tape of the present invention exhibits excellent repeatable impact resistance. The preferred lower limit of the elongation at break at 23°C is 35%.

[0096] There is no particular limit to the upper limit of the elongation at break at 23°C, but from the point of view of ensuring strength, the preferred upper limit is 80%, and the more preferred upper limit is 70%.

[0097] It should be noted that the elongation at break in the shear bond strength test of the adhesive layer at 23°C can be calculated based on JIS-Z-0237 using a benchtop precision universal testing machine (e.g., Shimadzu Corporation, Autograph AGS-X series, etc.) as described below.

[0098] Prepare test pieces by cutting adhesive tape into 5mm long and 35mm wide sections. Next, adhere two 55mm × 65mm × 1mm thick polycarbonate sheets to both sides of the test piece, applying 10kg of pressure for 10 seconds to bond the two polycarbonate sheets together. Then, allow the sample to stand at 23°C for 3 hours to obtain the test sample. Using the above apparatus, stretch the test sample along its length at 500mm / min at 23°C, recording the tensile elongation at break. Calculate the elongation at break of the adhesive layer in the shear bond strength test at 23°C as the elongation relative to the length of the test piece.

[0099] It should be noted that, for elongation at break in shear adhesion testing, when the laminate is the test object, the influence of the most easily elongated layer is dominant. Even if the laminate contains layers with minimal shear elongation, their presence will not significantly affect the overall value. Therefore, when adjusting the test piece is difficult, the elongation at break of the most easily elongated layer can be estimated by performing the same measurement on the laminate itself.

[0100] The preferred lower limit for the gel content of the adhesive layer is 10% by weight, and the preferred upper limit is 90% by weight. If the gel content is 10% by weight or more, the adhesive layer is less prone to deformation upon impact, further improving the repeated impact resistance of the adhesive tape. If the gel content is 90% by weight or less, the flexibility of the adhesive layer is improved, preventing the adhesive layer from becoming too stiff and unable to disperse stress upon impact. This further improves the repeated impact resistance of the adhesive tape. A more preferred lower limit for the gel content is 20% by weight, and a more preferred upper limit is 80% by weight.

[0101] It should be noted that the gel fraction of the adhesive layer can be determined using the same method as that used for the gel fraction of the substrate layer.

[0102] The lower limit of the storage modulus G' of the adhesive layer in the dynamic viscoelasticity test at 10°C is 0.13 MPa, and the upper limit is 7.0 MPa. If the storage modulus G' at 10°C is 0.13 MPa or higher, the adhesive layer is less prone to deformation upon impact, further improving the repeated impact resistance of the adhesive tape. If the storage modulus G' at 10°C is 7.0 MPa or lower, the flexibility of the adhesive layer is improved, preventing the adhesive layer from becoming too stiff and unable to disperse stress upon impact. This further improves the repeated impact resistance of the adhesive tape. The preferred lower limit of the storage modulus G' of the adhesive layer at 10°C is 0.25 MPa, the preferred upper limit is 5.0 MPa, the more preferred lower limit is 0.3 MPa, and the more preferred upper limit is 4.0 MPa.

[0103] It should be noted that the energy storage elastic modulus G' of the adhesive layer at 10°C can be measured using the same method as that of the substrate layer, in addition to the constant rate heating shear mode.

[0104] The method for adjusting the elongation at break at 23°C, the gel fraction, and the storage modulus G' at 10°C to the aforementioned ranges is not particularly limited; for example, methods for selecting the resin and additives used to form the adhesive layer can be cited. More specifically, as the adhesive layer, an acrylic adhesive layer containing the acrylic copolymer, tackifying resin, and crosslinking agent described below is preferably used.

[0105] The adhesive layer is not particularly limited, and examples include acrylic adhesive layers, rubber-based adhesive layers, urethane adhesive layers, and silicone-based adhesive layers. Among these, acrylic adhesive layers containing acrylic copolymers are preferred from the perspective of excellent heat resistance and the ability to bond to a wide variety of substrates.

[0106] From the viewpoint that the improved initial tack results in better adhesion at low temperatures, the aforementioned acrylic copolymer is preferably obtained by copolymerizing a monomer mixture containing butyl acrylate and / or 2-ethylhexyl acrylate. More preferably, it is obtained by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate.

[0107] The preferred lower limit for the content of butyl acrylate in the total monomer mixture is 40% by weight, and the preferred upper limit is 80% by weight. By setting the content of butyl acrylate within the above range, both high adhesion and tackiness can be achieved.

[0108] The preferred lower limit for the content of 2-ethylhexyl acrylate in the total monomer mixture is 10% by weight, and the preferred upper limit is 100% by weight. By setting the content of 2-ethylhexyl acrylate within the above range, high adhesive strength can be achieved.

[0109] The monomer mixture described above may, as needed, include other copolymerizable monomers besides butyl acrylate and 2-ethylhexyl acrylate. Examples of such other copolymerizable monomers include alkyl (meth)acrylates with alkyl groups having 1 to 18 carbon atoms, functional monomers, etc.

[0110] Examples of alkyl (meth)acrylates having 1 to 18 carbon atoms as the aforementioned alkyl group include: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, tridecyl methacrylate, stearyl (meth)acrylate, etc. Examples of the aforementioned functional monomers include: hydroxyalkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, glyceryl dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylate, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc.

[0111] To copolymerize the above-mentioned monomer mixture to obtain the above-mentioned acrylic copolymer, the monomer mixture is subjected to a free radical reaction in the presence of a polymerization initiator. As a method for causing the above-mentioned monomer mixture to undergo a free radical reaction, i.e., a polymerization method, existing known methods can be used, such as solution polymerization (boiling point polymerization or isothermal polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0112] The weight-average molecular weight (Mw) of the aforementioned acrylic copolymers is not particularly limited, but a preferred lower limit is 400,000 and a preferred upper limit is 1,500,000. High adhesive strength can be achieved by setting the weight-average molecular weight of the aforementioned acrylic copolymers within the above range. From the viewpoint of further improving adhesive strength, a more preferred lower limit of the aforementioned weight-average molecular weight is 500,000, and a more preferred upper limit is 1,400,000.

[0113] The preferred upper limit for the weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio (Mw / Mn) of the aforementioned acrylic copolymer is 10.0. When Mw / Mn is below 10.0, the proportion of low molecular weight components is suppressed, preventing the adhesive layer from softening at high temperatures, resulting in a decrease in bulk strength and bond strength. From the same viewpoint, a more preferred upper limit for Mw / Mn is 5.0, and a further preferred upper limit is 3.0.

[0114] The adhesive layer described above may contain tackifying resin.

[0115] Examples of the aforementioned tackifying resins include 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 can be used alone or in combination of two or more.

[0116] The content of the aforementioned tackifying resin is not particularly limited, but the preferred lower limit is 10 parts by weight and the preferred upper limit is 60 parts by weight relative to 100 parts by weight of the resin (e.g., acrylic copolymer) that forms the main component of the adhesive layer. When the content of the aforementioned tackifying resin is 10 parts by weight or more, the adhesive layer can exhibit high adhesive strength. When the content of the aforementioned tackifying resin is 60 parts by weight or less, the reduction in adhesive strength or tack caused by hardening of the adhesive layer can be suppressed.

[0117] The adhesive layer is preferably formed by adding a crosslinking agent to create a crosslinked structure between the main chains of the resin (e.g., the acrylic copolymer, the tackifying resin, etc.) that forms the adhesive layer.

[0118] The crosslinking agent is not particularly limited, and examples include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Isocyanate-based crosslinking agents are preferred. By adding an isocyanate-based crosslinking agent to the adhesive layer, the isocyanate groups of the isocyanate-based crosslinking agent react with the alcoholic hydroxyl groups in the resin forming the adhesive layer (e.g., the acrylic copolymer, the tackifying resin, etc.), thereby crosslinking the adhesive layer. By forming a crosslinked structure between the main chains of the resin forming the adhesive layer, intermittently applied stress can be dispersed, further improving the repeated impact resistance of the adhesive tape and its heat resistance.

[0119] The amount of the crosslinking agent added is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, relative to 100 parts by weight of the resin (e.g., the acrylic copolymer) that is the main component of the adhesive layer.

[0120] The adhesive layer described above may contain a silane coupling agent to improve adhesion. The silane coupling agent is not particularly limited, and examples include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

[0121] The aforementioned adhesive layer may contain a coloring material for the purpose of providing light-blocking properties. The coloring material is not particularly limited; examples include carbon black, aniline black, and titanium dioxide. Among these, carbon black is preferred from the perspective of being relatively inexpensive and chemically stable.

[0122] The adhesive layer may contain, as needed, existing and known particles and additives such as inorganic particles, conductive particles, antioxidants, foaming agents, organic fillers, and inorganic fillers.

[0123] The thickness of the adhesive layer is not particularly limited, but the preferred lower limit is 0.01 mm, the preferred upper limit is 0.1 mm, the more preferred lower limit is 0.015 mm, and the more preferred upper limit is 0.09 mm. By making the thickness of the adhesive layer within the above range, an adhesive tape with excellent flexibility, repeated impact resistance, heat resistance, and processability can be produced, and the adhesive tape can be suitable for fixing electronic device components such as portable electronic device components and automotive electronic device components.

[0124] The lower limit of the elongation at break in the shear adhesion test of the adhesive tape of the present invention at 23°C is preferably 30%. The elongation at break in the shear adhesion test of the adhesive tape of the present invention at 23°C can be adjusted, for example, by changing the elongation at break of the adhesive layer in the shear adhesion test at 23°C.

[0125] The overall thickness of the adhesive tape of the present invention is not particularly limited, but the preferred lower limit is 0.04 mm, the more preferred lower limit is 0.05 mm, the preferred upper limit is 2 mm, and the more preferred upper limit is 1.5 mm. By making the overall thickness of the adhesive tape of the present invention within the above range, an adhesive tape with excellent flexibility, repeated impact resistance, heat resistance, and processability can be produced.

[0126] The shape of the adhesive tape of the present invention is not particularly limited, and examples include rectangular, frame-shaped, circular, oval, and donut-shaped tapes.

[0127] The method for manufacturing the adhesive tape of the present invention is not particularly limited, and for example, the following method can be cited: First, an adhesive solution is coated on a release film and dried to form an adhesive layer. Next, an unfoamed substrate layer is manufactured, and a resin layer is laminated on the unfoamed substrate layer to form a laminate. Then, the adhesive layer is bonded to both sides of the resulting laminate, and heating is performed, thereby foaming the unfoamed substrate to form a foamed substrate layer, thus manufacturing the adhesive tape.

[0128] The adhesive tape of the present invention is not particularly limited in its application, but due to its excellent repeated impact resistance, it is preferably used for the assembly or fixation of electronic equipment components such as portable electronic equipment components and automotive electronic equipment components.

[0129] Invention Effects

[0130] According to the present invention, an adhesive tape with excellent repeatability and impact resistance can be provided. Detailed Implementation

[0131] The following examples illustrate the invention in more detail, but the invention is not limited to these examples.

[0132] (Example 1)

[0133] (1) Manufacturing of the unfoamed substrate layer

[0134] 0.902 g of 1,6-hexanedithiol, 1.83 g of carbon disulfide, and 11 mL of dimethylformamide were added to a two-necked 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. Next, 2.75 g of methyl-α-bromophenylacetic acid was added dropwise over 15 minutes, and the mixture was stirred at 25 °C for 4 hours. Subsequently, 100 mL of extraction solvent (n-hexane:ethyl acetate = 50:50) and 50 mL of water were added to the reaction mixture for separation extraction. The organic layers obtained from the first and second separation extractions were mixed and washed successively with 50 mL of 1M hydrochloric acid, 50 mL of water, and 50 mL of saturated saline. Sodium sulfate was added to the washed organic layer for drying, and the sodium sulfate was filtered off. The filtrate was concentrated using an evaporator to remove the organic solvent. The concentrate was purified by silica gel column chromatography to obtain the RAFT reagent.

[0135] 93 parts by weight of styrene (St), 6 parts by weight of acrylic acid (AAc), 1 part by weight of hydroxyethyl acrylate (HEA), 2.8 parts by weight of RAFT agent, and 0.35 parts by weight of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) were added to a two-necked flask. The flask was purged with nitrogen while the temperature was raised to 85°C. Then, the mixture was stirred at 85°C for 6 hours to carry out the polymerization reaction (first stage reaction).

[0136] After the reaction was completed, 4000 parts by weight of n-hexane were added to the flask, and the mixture was stirred to precipitate the reactants. The unreacted monomers and RAFT agent were filtered, and the reactants were dried under reduced pressure at 70°C to obtain the copolymer (hard block).

[0137] A mixture comprising 49.5 parts by weight of methyl acrylate (MA), 49.5 parts by weight of butyl acrylate (BA), 1 part by weight of acrylic acid (AAc), 0.058 parts by weight of ABN-E, and 50 parts by weight of ethyl acetate, and the copolymer (hard block) obtained above, was added to a two-necked flask. The flask was purged with nitrogen while the temperature was raised to 85°C. The mixture was then stirred at 85°C for 6 hours to carry out the polymerization reaction (second-stage reaction), yielding a reaction solution containing a block copolymer formed from hard and soft blocks. It should be noted that the proportions of the mixture were adjusted to ensure that the content of hard blocks in the obtained block copolymer was 3% by weight and the content of soft blocks was 97% by weight.

[0138] A portion of the reaction solution was taken, and 4000 parts by weight of n-hexane were added to it. After stirring to precipitate the reactants, the unreacted monomers and solvents were filtered, and the reactants were dried under reduced pressure at 70°C to obtain the block copolymer.

[0139] The weight-average molecular weight of the obtained block copolymer was determined by GPC, and the result was 390,000. It should be noted that a Waters 2690 Separations Module was used as the analytical instrument, a Showa Denko G. KF-806L column was used, ethyl acetate was used as the solvent, and the determination was performed at a sample flow rate of 1 mL / min and a column temperature of 40 °C.

[0140] The obtained block copolymer was dissolved in ethyl acetate to achieve a solids content of 35%. 3.3 parts by weight of Expansionl 461-DU-40 (461DU40) (manufactured by Japan Fillite Co., Ltd.) as a foaming agent (foaming particles) and 0.15 parts by weight of Tetrad C (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent were added to 100 parts by weight of the block copolymer, and the mixture was stirred thoroughly to obtain a foamed substrate layer solution. The obtained foamed substrate layer solution was applied to the corona-treated surface of the resin film (a 23 μm thick polyethylene terephthalate (PET) film with one side corona-treated and a Young's modulus of 2026 MPa at 23°C) as resin layer I, and dried at 90°C for 7 minutes to obtain a laminate of unfoamed substrate layer A and resin layer I. The thickness of the unfoamed substrate layer A was adjusted so that it would become 127 μm after being heated at 130°C for 1 minute after being left to stand at 40°C for 48 hours.

[0141] (2) Preparation of adhesive solution

[0142] In a reactor equipped with a thermometer, stirrer, and condenser, 78 parts by weight of butyl acrylate (BA), 19 parts by weight of 2-ethylhexyl acrylate (2EHA), 3 parts by weight of acrylic acid (AAc), 0.2 parts by weight of 2-hydroxyethyl acrylate (HEA), and 80 parts by weight of ethyl acetate were added. After nitrogen purging, the reactor was heated and refluxed. Next, 0.1 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator was added to the reactor. Reflux was carried out for 5 hours to obtain a solution of acrylic copolymer (random copolymer). The weight-average molecular weight of the obtained acrylic copolymer was determined by GPC using a Waters 2690 Separations Model column, and the result was 910,000.

[0143] Relative to 100 parts by weight of the solid component of the acrylic copolymer contained in the obtained acrylic copolymer solution, 15 parts by weight of a polymeric rosin ester resin with a softening point of 135°C, 10 parts by weight of a terpene phenol resin with a softening point of 160°C, and 10 parts by weight of a rosin ester resin with a softening point of 75°C were added. Further, 125 parts by weight of ethyl acetate (manufactured by Fuji Chemical Co., Ltd.) and 2.2 parts by weight of an isocyanate crosslinking agent (manufactured by Tosoh Co., Ltd., Coronate L45) were added, and the mixture was stirred to obtain a solution of adhesive (1).

[0144] (3) Manufacturing of adhesive tape

[0145] On the demolded surface of a 50 μm polyethylene terephthalate (PET) film that has undergone a demolding treatment, a solution of the obtained adhesive (1) is applied using a scraper to achieve a dry film thickness of 75 μm. The solution is then heated at 110°C for 5 minutes to dry, resulting in an adhesive layer (1). Next, another adhesive layer is manufactured using the same procedure, resulting in two adhesive layers (1). Then, two adhesive layers (1) are bonded to both sides of the laminate of the unfoamed substrate layer A and resin layer I, respectively, and left to stand at 40°C for 48 hours. After 48 hours, the laminate is removed from the 40°C environment and heated at 130°C for 1 minute to foam the unfoamed substrate layer A, thus forming a foamed substrate layer A, resulting in an adhesive tape.

[0146] (4) Preparation of specimens for determining the elongation at break of the adhesive layer

[0147] Instead of the laminate of the unfoamed substrate layer A and the resin layer I, the adhesive layer (1) is bonded to both sides of a 50 μm thick polyethylene terephthalate (PET) film. Otherwise, the same as above (3) is used to obtain a sample for measuring the elongation at break of the adhesive layer.

[0148] (5) Determination of gel fraction of substrate layer

[0149] Only 0.1 g of the substrate layer (foamed substrate layer A) was removed from the adhesive tape and immersed in 50 mL of ethyl acetate. The mixture was shaken for 24 hours at 23°C and 120 rpm. After shaking, the ethyl acetate was separated from the swollen substrate layer using a metal mesh (200 mesh). The separated substrate layer was dried at 110°C for 1 hour. The weight of the dried substrate layer including the metal mesh was measured, and the gel fraction of the substrate layer was calculated using the following formula.

[0150] Gel fraction (wt%) = 100 × (W1 - W2) / W0

[0151] (W0: Initial substrate layer weight, W1: Dried substrate layer weight including metal mesh, W2: Initial weight of metal mesh)

[0152] (6) Determination of the energy storage elastic modulus E' and foaming ratio of the substrate layer at 10℃

[0153] Using a viscoelastic spectrometer (IT Measurement & Control Co., Ltd., DVA-200), dynamic viscoelastic spectra were obtained under constant-rate heating and tensile conditions of 5℃ / min, strain of 0.1%, and frequency of 10Hz, ranging from -40℃ to 140℃. The energy storage modulus E' of the substrate layer (foam substrate layer A) at 10℃ was then measured.

[0154] The expansion ratio of the substrate layer (foam substrate layer A) was determined based on JIS K 7222 and using an electronic hydrometer (MIRAGE, ED120T).

[0155] (7) Determination of the elongation at break of the adhesive layer at 23°C

[0156] The measurements were performed based on JIS-Z-0237 using a benchtop precision universal testing machine (Shimadzu Corporation, Autograph AGS-X series) as described below.

[0157] To prepare a test piece for measuring the elongation at break of the adhesive layer, the sample was cut into pieces with a length of 5 mm and a width of 35 mm. Two polycarbonate sheets, each 55 mm × 65 mm × 1 mm thick, were then bonded to both sides of the test piece under a pressure of 10 kg for 10 seconds. The bonded polycarbonate sheets were then left to stand at 23°C for 3 hours to obtain the test sample. Using the aforementioned apparatus, the test sample was stretched along its length at 500 mm / min at 23°C. The tensile elongation at break was recorded, and the elongation at break of the adhesive layer in the shear bond test at 23°C was calculated as the elongation relative to the length of the test piece.

[0158] (8) Determination of gel fraction of adhesive layer

[0159] Only 0.1 g of the adhesive layer (adhesive layer (1)) was taken from the adhesive tape, and the gel fraction was determined by the same method as the gel fraction of the substrate layer.

[0160] (9) Determination of the storage elastic modulus G' of the adhesive layer at 10℃

[0161] The energy storage elastic modulus G' was determined using the same method as the energy storage elastic modulus E' of the substrate layer (foam substrate layer A) at 10°C.

[0162] (Examples 2-20, Comparative Examples 1-7)

[0163] The adhesive tape was obtained by modifying the substrate layer (foam substrate layer), adhesive layer, and resin layer as shown in Tables 4 and 5, otherwise the same as in Example 1. Details of the substrate layer (foam substrate layer) are shown in Table 1, details of the adhesive layer are shown in Table 2, and details of the resin layer are shown in Table 3.

[0164] It should be noted that the AS-6S (a styrene macromonomer solution (50% toluene solution) manufactured by Toa Synthetic Co., Ltd.) used in Comparative Example 7 was adjusted to achieve the styrene macromonomer solid content values ​​listed in the table. The raw materials in the table are as follows.

[0165] • Foaming agent (foaming particles)

[0166] Expancel 461-DU-40 (461DU40) (Made by Japan Fillite Co., Ltd.)

[0167] Expancel 461-DU-20 (461DU20) (Made by Japan Fillite Co., Ltd.)

[0168] Advancell EML101 (manufactured by Sekisui Chemicals Co., Ltd.)

[0169] • Raw material monomers for the substrate layer

[0170] AS-6S (Styrene macromolecular monomer solution (50% toluene solution) manufactured by Dong-A Synthetic Co., Ltd.)

[0171] 2EHA (2-Ethylhexyl acrylate)

[0172] · Resin that forms the resin layer

[0173] OPP (polyolefin resin film, 25μm thick, Young's modulus of 689MPa at 23℃)

[0174] PI (polyimide film, 25 μm thick, Young's modulus of 2110 MPa at 23°C)

[0175] Acrylic resin film (23 μm thickness, Young's modulus of 1.3 MPa at 23°C, preparation method shown below)

[0176] (Preparation method of acrylic resin film as resin layer IV)

[0177] The composition was modified as described below, without the addition of foaming particles and curing agent, and the resin solution was applied to the release surface of a 50 μm thick polyethylene terephthalate (PET) film. Otherwise, an acrylic resin film was obtained in the same manner as the manufacturing method of the unfoamed substrate layer A in Example 1.

[0178] • Content ratio of each segment: 20% by weight for hard segments and 80% by weight for soft segments

[0179] • Hard block composition (by weight): St 93%, AAc 12%, HEA 1%

[0180] • Soft segment composition (by weight): MA 50%, BA 50%

[0181] • Weight-average molecular weight: 400,000

[0182] <Evaluation>

[0183] The adhesive tapes obtained in the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 4-5.

[0184] (1) Repeated impact test

[0185] Prepare two pieces of adhesive tape cut to 1mm x 70mm. Next, attach the adhesive tape to each short side of a polycarbonate sheet measuring 72mm in length, 135mm in width, and 1mm in thickness. Overlap the polycarbonate sheet with the adhesive tape attached to it with a polycarbonate sheet measuring 77mm in length, 150mm in width, and 4mm in thickness, with the short sides and long sides facing each other. Apply pressure of 0.7MPa for 15 seconds to bond the two polycarbonate sheets together. Then, allow them to stand at 23°C for 24 hours to obtain the test sample.

[0186] The test sample is placed in the TD-1000A drum-type rotary drop tester (manufactured by Xinrong Electronic Measurement Instrument Co., Ltd.) and rotated at a speed of 12 revolutions per minute under the condition of maintaining a room temperature environment of 23°C, thereby causing the test sample to be dropped repeatedly from a height of 1m.

[0187] The case where the polycarbonate sheet is peeled off after more than 1500 drops is marked as ◎, the case where it is peeled off after more than 1000 drops but less than 1500 drops is marked as ○, and the case where it is peeled off after less than 1000 drops is marked as ×.

[0188]

[0189]

[0190] [Table 3]

[0191]

[0192]

[0193] [Table 5]

[0194]

[0195] Industrial availability

[0196] According to the present invention, an adhesive tape with excellent repeatability and impact resistance can be provided.

Claims

1. An adhesive tape, characterized in that, have: Multilayer substrates, and An adhesive layer laminated on at least one side of the multilayer substrate. The multilayer substrate has a substrate layer and a resin layer laminated on at least one side of the substrate layer. The storage modulus E' of the substrate layer in the dynamic viscoelasticity test at 10°C is above 2.0 MPa and below 21 MPa. The resin layer has a Young's modulus of over 500 MPa at 23°C. The adhesive layer exhibits an elongation at break of ≥30% in the shear adhesion test at 23°C, and a storage modulus G' of ≥0.13 MPa and ≤7.0 MPa in the dynamic viscoelasticity test at 10°C. The substrate layer contains a copolymer having a structure derived from vinyl aromatic monomers and a structure derived from (meth)acrylic monomers. The substrate layer is a foamed substrate layer.

2. The adhesive tape according to claim 1, wherein, In the copolymer having structures derived from vinyl aromatic monomers and structures derived from (meth)acrylic monomers, the content of structures derived from vinyl aromatic monomers is 1.5% by weight or more and 15% by weight or less.

3. The adhesive tape according to claim 1 or 2, wherein, In the copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer, the content of the (meth)acrylic monomer having 2 or fewer carbon atoms in its side chain is 5% by weight or more and 90% by weight or less.

4. The adhesive tape according to claim 1 or 2, wherein, The copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer is a block copolymer.

5. The adhesive tape according to claim 4, wherein, The block copolymer is a copolymer that includes both rigid and flexible structures.

6. The adhesive tape according to claim 1 or 2, wherein, The copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer has a weight-average molecular weight (Mw) of 50,000 or more and 800,000 or less.

7. The adhesive tape according to claim 1 or 2, wherein, The average bubble diameter of the foam substrate layer is above 20 μm and below 80 μm.

8. The adhesive tape according to claim 1 or 2, wherein, The adhesive layer contains an acrylic copolymer obtained by copolymerizing a mixture of monomers comprising butyl acrylate and / or 2-ethylhexyl acrylate.

9. The adhesive tape according to claim 8, wherein, The butyl acrylate accounts for more than 40% by weight and less than 80% by weight in the total monomer mixture.

10. The adhesive tape according to claim 8, wherein, The content of 2-ethylhexyl acrylate in the total monomer mixture is more than 10% by weight and less than 100% by weight.

11. The adhesive tape according to claim 1 or 2, wherein, The adhesive layer is stacked on both sides of the multilayer substrate.

12. The adhesive tape according to claim 1 or 2, wherein, The overall thickness of the adhesive tape is 0.04 mm or more and 2 mm or less.

13. The adhesive tape according to claim 1 or 2, used for assembling or fixing electronic device components.

Images