adhesive tape

Abstract

To provide an adhesive tape which is hardly deformed at a low temperature and has excellent waterproofness even when used with a narrow width.SOLUTION: There is provided an adhesive tape which has a foam substrate and adhesive layers on both sides of the foam substrate, wherein the foam substrate has a closed-cell structure and contains a block copolymer having a hard block containing a structure derived from a vinyl aromatic monomer and a soft block containing a structure derived from a (meth)acrylic monomer, the block copolymer has the hard block having a glass transition temperature Tg of 50°C or more and the soft block having a glass transition temperature Tg of -60°C or more and 10°C or less and contains a structure derived from a monomer having a crosslinkable functional group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive tape. [Background technology]

[0002] Adhesive tapes are used for the assembly of portable electronic devices such as mobile phones, personal digital assistants (PDAs), tablet devices, smartphones, and smartwatches (for example, Patent Documents 1 and 2). Adhesive tapes are also used to fix in-vehicle electronic device components such as in-vehicle panels to the vehicle body. [Prior art documents] [Patent documents]

[0003] [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]

[0004] Adhesive tapes used to fix portable electronic device components, in-vehicle electronic device components, etc., are required to have high adhesive strength and impact resistance so that they do not peel even when subjected to impact. Meanwhile, in recent years, portable electronic devices, in-vehicle electronic devices, etc., have tended to have more complex shapes as their functionality has increased, and therefore adhesive tapes are sometimes used by being attached to steps, corners, non-flat surfaces, etc. In such cases, the adhesive tape is required to have excellent flexibility so that it can conform to the shape of the adherend, and further, to have excellent waterproof properties so that it can conform to the shape of the adherend and thereby prevent moisture from penetrating into the electronic device.

[0005] As an adhesive tape having excellent flexibility, for example, an adhesive tape using a foam substrate obtained by foaming a polyolefin resin or the like is known. However, in recent years, in electronic devices, the width of the outer frame (frame) of the display has been narrowed, so-called narrow frame, and the width of the adhesive tape used in such a narrow area has become narrower than before. When used in a narrow width, an adhesive tape using a foam substrate is likely to deform in the planar direction when subjected to an impact, particularly a high-speed impact such as a drop, which causes problems such as peeling of the adhesive tape or damage to the adherend.

[0006] An object of the present invention is to provide a pressure-sensitive adhesive tape that is resistant to deformation at low temperatures and has excellent waterproof properties even when used in a narrow width. [Means for solving the problem]

[0007] The present invention provides a pressure-sensitive adhesive tape comprising a foam substrate and pressure-sensitive adhesive layers on both sides of the foam substrate, wherein the foam substrate has a closed-cell structure and contains a block copolymer having a hard block containing a structure derived from a vinyl aromatic monomer and a soft block containing a structure derived from a (meth)acrylic monomer, wherein the block copolymer has a glass transition temperature Tg of 50°C or higher and a glass transition temperature Tg of the soft block of -60°C or higher and 10°C or lower, and further contains a structure derived from a monomer having a crosslinkable functional group. The present invention will be described in detail below.

[0008] The present inventors have investigated the use of a foam substrate having a closed-cell structure and containing a specific block copolymer having hard blocks and soft blocks in a pressure-sensitive adhesive tape having a foam substrate and pressure-sensitive adhesive layers on both sides of the foam substrate, and have found that by using such a foam substrate, a pressure-sensitive adhesive tape that is resistant to deformation at low temperatures and has excellent waterproof properties can be obtained, even when used in a narrow width, and have completed the present invention.

[0009] The pressure-sensitive adhesive tape of the present invention comprises a foam substrate and pressure-sensitive adhesive layers on both sides of the foam substrate. By including the foam substrate, the pressure-sensitive adhesive tape of the present invention can have excellent flexibility and can also conform to the shape of the adherend, thereby preventing moisture from penetrating into the interior of an electronic device and providing excellent waterproofing. The foam substrate may have a single-layer structure or a multi-layer structure. The pressure-sensitive adhesive tape of the present invention, which has a foam substrate and pressure-sensitive adhesive layers on both sides of the foam substrate, may have a configuration in which pressure-sensitive adhesive layers are laminated on both surfaces of the foam substrate, or may have a configuration in which a layer other than the pressure-sensitive adhesive layer is laminated between the foam substrate and the pressure-sensitive adhesive layer. Examples of the layer other than the pressure-sensitive adhesive layer include a resin layer. The pressure-sensitive adhesive layers on both sides of the foam substrate may have the same composition and physical properties, or may have different compositions and physical properties.

[0010] The foam substrate has a closed-cell structure. When the foam substrate has the closed cell structure rather than the open cell structure, moisture is less likely to penetrate into the foam substrate, and the pressure-sensitive adhesive tape of the present invention can have excellent waterproof properties. The closed-cell structure of a foam substrate can be confirmed by the following method. First, the foam substrate is cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut using a razor blade along a plane perpendicular to the thickness direction of the foam substrate. Next, a magnified photograph of the cut surface is taken at 200x magnification using a digital microscope (e.g., Keyence's VHX-900). If the magnified photograph shows a structure in which each bubble is not connected to other bubbles, the foam substrate can be determined to have a closed-cell structure. If multiple areas in which adjacent bubbles are connected are confirmed, the foam substrate can be determined to have an open-cell structure.

[0011] The foam substrate contains a block copolymer (hereinafter also simply referred to as "block copolymer") having a hard block containing a structure derived from a vinyl aromatic monomer and a soft block containing a structure derived from a (meth)acrylic monomer. Because the foam substrate contains the block copolymer, the pressure-sensitive adhesive tape of the present invention has an excellent balance between hardness and flexibility, and is less likely to deform at low temperatures (i.e., has high deformation resistance) even when used in a narrow width, thereby achieving excellent waterproofing. Furthermore, even when used in a narrow width, the tape exhibits excellent processability. The deformation resistance at low temperatures corresponds to the deformation resistance upon high-speed impact (time-temperature conversion rule), and by examining the deformation resistance at low temperatures, the deformation resistance upon high-speed impact can be determined.

[0012] The block copolymer is a copolymer having the hard block having a rigid structure and the soft block having a flexible structure. The two blocks of the block copolymer are poorly compatible with each other, and the block copolymer may have a heterogeneous phase-separated structure in which islands formed by aggregation of the hard block are scattered among a sea of ​​the soft block. The islands serve as pseudo-crosslinking points, imparting rubber elasticity to the block copolymer. Therefore, the pressure-sensitive adhesive tape of the present invention has an excellent balance of hardness and flexibility, and is resistant to deformation at low temperatures even when used in a narrow width, and can have excellent waterproofing properties. Introducing a crosslinkable functional group, as described below, into the hard block makes the pressure-sensitive adhesive tape more resistant to deformation at low temperatures and further improves waterproofing properties.

[0013] Examples of the vinyl aromatic monomer include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, 1-ethyl 2-vinylbenzene, 1-ethyl 3-vinylbenzene, vinylnaphthalene, and chlorostyrene. These vinyl aromatic monomers may be used alone or in combination of two or more. Among these, styrene is preferred because it makes the pressure-sensitive adhesive tape harder and less likely to deform at low temperatures. In this specification, the structure derived from a vinyl aromatic monomer refers to a structure such as those shown in the following general formulas (1) and (2).

[0014] [ka]

[0015] In general formulas (1) and (2), R 1 represents a substituent having an aromatic ring. 1 Examples of the phenyl group include a phenyl group, a methylphenyl group, and a chlorophenyl group.

[0016] In the block copolymer, the content of the structure derived from the vinyl aromatic monomer is not particularly limited, but is preferably 1% by weight or more and 30% by weight or less. When the content of the structure derived from the vinyl aromatic monomer is within the above range, the pressure-sensitive adhesive tape becomes less susceptible to deformation at low temperatures and the waterproofing is further improved. The lower limit of the content of the structure derived from the vinyl aromatic monomer is more preferably 1.5% by weight, even more preferably 2% by weight, particularly preferably 2.5% by weight, more preferably 25% by weight, even more preferably 19% by weight, particularly preferably 16% by weight, and particularly preferably 8% by weight.

[0017] The block copolymer further contains a structure derived from a monomer having a crosslinkable functional group. When the block copolymer has a crosslinkable functional group, the rubber elasticity of the copolymer is enhanced by crosslinking, and therefore the pressure-sensitive adhesive tape of the present invention has an excellent balance between hardness and flexibility, is resistant to deformation at low temperatures even when used in a narrow width, and can have excellent waterproof properties. Furthermore, even when used in a narrow width, the pressure-sensitive adhesive tape has excellent processability. The crosslinkable functional group may be crosslinked or uncrosslinked, but crosslinking is more preferable. However, even if the structure remains uncrosslinked, the interaction between the functional groups improves the cohesive force within the hard block or soft block (particularly the hard block), making the pressure-sensitive adhesive tape less resistant to deformation at low temperatures and further improving waterproof properties. The structure derived from the monomer having the crosslinkable functional group may be contained in either the hard block or the soft block of the block copolymer, but is preferably contained in the hard block. In this specification, the structure derived from the monomer having a crosslinkable functional group refers to structures such as those shown in the following general formulas (3) and (4).

[0018] [ka]

[0019] In general formulas (3) and (4), R 2 represents a substituent containing at least one functional group. Examples of the functional group include a carboxyl group, a hydroxyl group, an epoxy group, a double bond, a triple bond, an amino group, an amide group, and a nitrile group. The substituent R containing at least one functional group 2 may contain, as its constituent elements, an alkyl group, an ether group, a carbonyl group, an ester group, a carbonate group, an amide group, a urethane group, or the like.

[0020] The monomer having a crosslinkable functional group is not particularly limited, and examples thereof include carboxyl group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, double bond-containing monomers, triple bond-containing monomers, amino group-containing monomers, amide group-containing monomers, and nitrile group-containing monomers. These monomers having a crosslinkable functional group may be used alone, or two or more types may be used in combination. Among these, at least one selected from the group consisting of carboxyl group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, double bond-containing monomers, triple bond-containing monomers, and amide group-containing monomers is preferred, as this makes the pressure-sensitive adhesive tape less susceptible to deformation at low temperatures and further improves waterproofing. Examples of the carboxyl group-containing monomer include (meth)acrylic acid-based monomers such as (meth)acrylic acid. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, etc. Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate, etc. Examples of the double bond-containing monomer include allyl (meth)acrylate, hexanediol di(meth)acrylate, etc. Examples of the triple bond-containing monomer include propargyl (meth)acrylate, etc. Examples of the amide group-containing monomer include (meth)acrylamide, etc. Among these, carboxyl group-containing monomers and hydroxyl group-containing monomers are preferred because they make the pressure-sensitive adhesive tape even more resistant to deformation at low temperatures and further improve waterproofing. Furthermore, (meth)acrylic acid-based monomers containing a carboxyl group and (meth)acrylic acid-based monomers containing a hydroxyl group are more preferred, with (meth)acrylic acid, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate being even more preferred.

[0021] In the block copolymer, the content of the structure derived from the monomer having a crosslinkable functional group is not particularly limited, but is preferably 0.1 wt% or more and 30 wt% or less. When the content of the structure derived from the monomer having a crosslinkable functional group is within the above range, the pressure-sensitive adhesive tape becomes even less susceptible to deformation at low temperatures and further improves waterproofing. The lower limit of the content of the structure derived from the monomer having a crosslinkable functional group is more preferably 0.5 wt%, even more preferably 1 wt%, and even more preferably 25 wt%, even more preferably 20 wt%.

[0022] The (meth)acrylic monomer may be a single monomer or a plurality of monomers. In this specification, the structure derived from a (meth)acrylic monomer refers to a structure such as those shown in the following general formulas (5) and (6).

[0023] [ka]

[0024] In general formulas (5) and (6), R 3 represents a side chain. Side chain R 3 Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, a dodecyl group, a lauryl group, and an isostearyl group.

[0025] Examples of the (meth)acrylic monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, isostearyl (meth)acrylate, etc. These (meth)acrylic monomers may be used alone or in combination of two or more. Among these, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, as they make the adhesive tape less susceptible to deformation at low temperatures and further improve waterproofing, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are more preferred.

[0026] Furthermore, as the (meth)acrylic monomer, it is preferable to use a (meth)acrylic monomer having two or less carbon atoms in its side chain. When the (meth)acrylic monomer having two or less carbon atoms in its side chain is used, the entanglement of the resulting copolymer chains increases, the cohesive force improves, the pressure-sensitive adhesive tape becomes less likely to deform at low temperatures, and the waterproof property and heat resistance are improved. Examples of the (meth)acrylic monomer having two or less carbon atoms in the side chain include methyl (meth)acrylate and ethyl (meth)acrylate, with methyl acrylate and ethyl acrylate being particularly preferred.

[0027] The content of the structure derived from the (meth)acrylic monomer in the block copolymer is not particularly limited as long as the effects of the present invention are exhibited, but it is preferably 30% by weight or more and 99% by weight or less, more preferably 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.

[0028] Furthermore, the content of the (meth)acrylic monomer having two or less side chain carbon atoms in the block copolymer is not particularly limited, but a preferred lower limit is 5 wt %, and a preferred upper limit is 90 wt %. When the content of the (meth)acrylic monomer having two or less side chain carbon atoms is 5 wt % or more, the effect of improving cohesion is more likely to be exhibited. When the content of the (meth)acrylic monomer having two or less side chain carbon atoms is 90 wt % or less, it is possible to prevent the cohesion from becoming too high, resulting in a decrease in flexibility and a decrease in the flexibility and waterproofness of the pressure-sensitive adhesive tape. The lower limit of the content of the (meth)acrylic monomer having two or less side chain carbon atoms is more preferably 10 wt %, even more preferably 20 wt %, even more preferably 25 wt %, and particularly preferably 30 wt %, and more preferably 85 wt %, even more preferably 80 wt %, even more preferably 75 wt %, and particularly preferably 70 wt %.

[0029] The hard block is not particularly limited as long as it has a rigid structure, and in addition to the structure derived from the vinyl aromatic monomer, it may further have, for example, a structure derived from a compound having a cyclic structure, a compound with a short side chain substituent, etc. The soft block may have a structure derived from a monomer other than the (meth)acrylic monomer, as long as the effects of the present invention are not lost.

[0030] The block copolymer may have any structure, such as a diblock structure or a triblock structure, but it is preferable that the block copolymer have a triblock structure having the soft block between the hard blocks, since this makes the pressure-sensitive adhesive tape less susceptible to deformation at low temperatures and further improves waterproofing. The block copolymer may be a graft copolymer in which the hard block and the soft block are separated into a main chain and a side chain. Examples of the graft copolymer include a styrene macromer-(meth)acrylic monomer copolymer.

[0031] The content of the hard block in the block copolymer is not particularly limited, but is preferably 1% by weight or more and 20% by weight or less. When the content of the hard block is within the above range, the pressure-sensitive adhesive tape becomes less susceptible to deformation at low temperatures, and the waterproof property and heat resistance are improved. From the viewpoint of further improving the deformation resistance at low temperatures, the waterproof property, and the heat resistance, the lower limit of the content of the hard block is more preferably 2% by weight, even more preferably 2.5% by weight, and particularly preferably 3% by weight. The upper limit of the hard block is more preferably 17% by weight, even more preferably 8% by weight.

[0032] The weight-average molecular weight (Mw) of the block copolymer is not particularly limited, but is preferably 50,000 or more and 800,000 or less. When the weight-average molecular weight is within the above range, the pressure-sensitive adhesive tape becomes less susceptible to deformation at low temperatures, and waterproofing and heat resistance are improved. The lower limit of the weight-average molecular weight is more preferably 75,000, and the upper limit is more preferably 600,000. The weight-average molecular weight can be determined, for example, by gel permeation chromatography (GPC) in terms of standard polystyrene. More specifically, the measurement can be performed using a Waters 2690 Separations Module as a measuring instrument, a Showa Denko GPC KF-806L column, ethyl acetate as a solvent, at a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0033] In the block copolymer, the lower limit of the glass transition temperature Tg of the hard block is 50°C. The glass transition temperature Tg of the hard block is the glass transition temperature Tg of the peak attributable to the hard block, confirmed when measuring the glass transition temperature Tg of the block copolymer. When the glass transition temperature Tg of the hard block is 50°C or higher, the pressure-sensitive adhesive tape becomes harder and less susceptible to deformation at low temperatures. The lower limit of the glass transition temperature Tg of the hard block is preferably 55°C, and more preferably 60°C. The upper limit of the glass transition temperature Tg of the hard block is not particularly limited, but from the viewpoint of ensuring flexibility and waterproofness of the pressure-sensitive adhesive tape, the upper limit is preferably 110°C, and more preferably 105°C.

[0034] The method for adjusting the glass transition temperature Tg of the hard block within the above range is not particularly limited, but the glass transition temperature Tg tends to increase as the molecular weight of the hard block increases, and vice versa. More specific examples include a method of selecting the type of raw material monomer for the hard block (particularly the vinyl aromatic monomer), a method of adjusting the content of the raw material monomer for the hard block (particularly the vinyl aromatic monomer), and a method of adjusting the weight-average molecular weight (Mw) of the block copolymer. Among the above-mentioned vinyl aromatic monomers, preferred examples of monomers for adjusting the glass transition temperature Tg of the hard block within the above range include styrene, α-methylstyrene, m-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, 1-ethyl-2-vinylbenzene, 1-ethyl-3-vinylbenzene, vinylnaphthalene, and chlorostyrene. Among these, styrene is preferred from the viewpoint of industrial availability. These vinyl aromatic monomers may be used alone or in combination of two or more. The glass transition temperature Tg of the block copolymer can be measured using a differential scanning calorimeter (for example, DSC 2920 manufactured by TA Instruments) under conditions of a temperature range of −40 to 200° C., a heating rate of 10° C. / min, and one cycle.

[0035] In the block copolymer, the lower limit of the glass transition temperature Tg of the soft block is -60°C and the upper limit is 10°C. The glass transition temperature Tg of the soft block is the glass transition temperature Tg of the peak attributable to the soft block, confirmed when measuring the glass transition temperature Tg of the block copolymer. Having a glass transition temperature Tg of the soft block of -60°C or higher improves the handling of the pressure-sensitive adhesive tape when narrowing the width. Having a glass transition temperature Tg of the soft block of 10°C or lower improves the flexibility of the pressure-sensitive adhesive tape and improves its waterproofing. The lower limit of the glass transition temperature Tg of the soft block is preferably -20°C, the upper limit is preferably 0°C, the lower limit is more preferably -10°C, and the upper limit is more preferably -5°C.

[0036] The method for adjusting the glass transition temperature Tg of the soft block within the above range is not particularly limited, but the glass transition temperature Tg tends to increase as the molecular weight of the soft block increases, and vice versa. More specific examples include a method of selecting the type of raw material monomer (particularly, the (meth)acrylic monomer) for the soft block, a method of adjusting the content of the raw material monomer (particularly, the (meth)acrylic monomer) for the soft block, and a method of adjusting the weight average molecular weight (Mw) of the block copolymer. Among the above-mentioned (meth)acrylic monomers, preferred examples of monomers for adjusting the glass transition temperature Tg of the soft block within the above range include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, isostearyl (meth)acrylate, etc. These (meth)acrylic monomers may be used alone, or two or more types may be used in combination.

[0037] To obtain the block copolymer, raw material monomers for the hard block and the soft block are respectively subjected to a radical reaction in the presence of a polymerization initiator to obtain the hard block and the soft block, and then the two blocks are reacted or copolymerized. Alternatively, after obtaining the hard block, raw material monomers for the soft block may be added and copolymerized. As the method for causing the radical reaction, that is, the polymerization method, a conventionally known method can be used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, and bulk polymerization.

[0038] The foam base material preferably has a crosslinking structure formed between the main chains of the resin constituting the foam base material by adding a crosslinking agent. By forming a crosslinked structure between the main chains of the resin constituting the foam substrate, it is possible to disperse intermittently applied stress, making the pressure-sensitive adhesive tape less susceptible to deformation at low temperatures and improving heat resistance.Furthermore, even when used in a narrow width, the pressure-sensitive adhesive tape has excellent processability.

[0039] The crosslinking agent is not particularly limited and can be appropriately selected depending on the functional groups of the resin constituting the foam substrate. Specific examples include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Among these, epoxy-based crosslinking agents and isocyanate-based crosslinking agents are preferred because they can crosslink resins having alcoholic hydroxyl groups or carboxyl groups, which can further improve flexibility. When the isocyanate-based crosslinking agent is used, crosslinking occurs between the alcoholic hydroxyl groups or carboxyl groups in the resin constituting the foam substrate and the isocyanate groups of the isocyanate-based crosslinking agent. When the epoxy-based crosslinking agent is used, crosslinking occurs between the carboxyl groups in the resin constituting the foam substrate and the epoxy groups of the epoxy-based crosslinking agent. The amount of the crosslinking agent added is not particularly limited, but is preferably 0.01 to 10 parts by weight, more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the resin constituting the foam substrate.

[0040] The foam substrate may contain additives such as antistatic agents, release agents, antioxidants, weathering agents, and crystal nucleating agents, and resin modifiers such as polyolefins, polyesters, polyamides, and elastomers.

[0041] The foam substrate preferably has a gel fraction of 90% by weight or less. When the gel fraction of the foam substrate is within the above range, the flexibility of the pressure-sensitive adhesive tape is further increased and the waterproofness is further improved. From the viewpoint of further improving the waterproofness of the pressure-sensitive adhesive tape, the upper limit of the gel fraction is more preferably 85% by weight, and even more preferably 80% by weight. The lower limit of the gel fraction is not particularly limited, but from the viewpoint of ensuring the deformation resistance of the pressure-sensitive adhesive tape at low temperatures, it is, for example, 10% by weight or more, particularly 20% by weight or more, and particularly 35% by weight or more. The gel fraction can be adjusted by crosslinking the resin constituting the foam substrate. The gel fraction of the foam substrate can be measured using the following method. 0.1 g of the foam substrate alone is removed from the adhesive tape, immersed in 50 mL of ethyl acetate, and shaken in a shaker at 23°C and 120 rpm for 24 hours. After shaking, a metal mesh (opening #200 mesh) is used to separate the ethyl acetate and the foam substrate that has absorbed the ethyl acetate and swollen. The separated foam substrate is dried at 110°C for 1 hour. The weight of the foam substrate including the metal mesh after drying is measured, and the gel fraction of the foam substrate is calculated using the following formula. Gel fraction (wt%) = 100 × (W1 - W2) / W0 (W0: initial foam substrate weight, W1: foam substrate weight including metal mesh after drying, W2: initial weight of metal mesh)

[0042] The storage modulus E' of the foam substrate in dynamic viscoelasticity measurement at 30°C is not particularly limited, but a preferred lower limit is 5.0 × 10 4 Pa, with a preferred upper limit of 5.0 × 10 8 The storage modulus E' at 30°C is 5.0 x 10 4MPa or more, the adhesive tape becomes harder even at low temperatures and becomes less susceptible to deformation. 8 When the storage modulus E' at 30°C is 1.0 x 10 Pa or less, the flexibility of the pressure-sensitive adhesive tape is increased and the waterproof property is further improved. 5 Pa, and a more preferable upper limit is 1.0 × 10 8 It is Pa. The storage modulus E' of the foam substrate in dynamic viscoelasticity measurement at 30°C can be measured in accordance with JIS K 7244 using a dynamic viscoelasticity measuring device (e.g., DVA-200 manufactured by IT Measurement Co., Ltd.) at a temperature rise rate of 5°C / min in the range of -40 to 140°C.

[0043] The storage modulus E' of the foam substrate in dynamic viscoelasticity measurement at -20°C is not particularly limited, but a preferred lower limit is 5.0 × 10 6 Pa, with a preferred upper limit of 1.0 × 10 10 The storage modulus E' at -20°C is 5.0 x 10 6 If the storage modulus E' at -20°C is 1.0 x 10 Pa or more, the adhesive tape becomes harder and is less likely to deform at low temperatures. 10 If the storage modulus E' at -30°C is 1.0 x 10 Pa or less, the flexibility of the adhesive tape is higher and the waterproof property is further improved. 7 Pa, and a more preferable upper limit is 1.0 × 10 9 It is Pa.

[0044] The foam substrate preferably has at least one peak in the range of 10°C or less and at least one peak in the range of 50°C or more when DSC (differential scanning calorimetry) is performed under the conditions of a temperature range of -40 to 200°C, a heating rate of 10°C / min, and one cycle. When the foam substrate is subjected to DSC measurement and has at least one peak in the region below 10° C. and at least one peak in the region above 50° C., it can be said that the foam substrate contains a block copolymer having the above-described two blocks. The peak regions can be adjusted by the types of raw material monomers for the hard block and the soft block. The DSC measurement of the foam substrate can be performed using a differential scanning calorimeter (for example, DSC 2920 manufactured by TA Instruments) under conditions of a temperature range of −40 to 200° C., a temperature rise rate of 10° C. / min, and one cycle.

[0045] The expansion ratio of the foam substrate is not particularly limited, but the preferred lower limit is 1.1 cm 3 / g, with a preferred upper limit of 7.0 cm 3 / g. When the expansion ratio of the foam substrate is in the above range, the balance between hardness and flexibility of the pressure-sensitive adhesive tape can be further improved, so that the pressure-sensitive adhesive tape is less likely to deform at low temperatures and the waterproofing is further improved. From the viewpoint of further improving the deformation resistance and waterproofing at low temperatures, a more preferable lower limit of the expansion ratio of the foam substrate is 1.3 cm 3 / g, and a more preferable upper limit is 5.0 cm 3 / g, and a more preferable lower limit is 1.5 cm 3 / g, and a more preferable upper limit is 3.0 cm 3 / g. The expansion ratio of the foam base material is the reciprocal of the density of the foam base material, and can be measured using an electronic densimeter (for example, "ED120T" manufactured by Mirage) in accordance with JIS K 7222.

[0046] The average bubble diameter of the foam substrate is not particularly limited, but is preferably 80 μm or less. By having the average bubble diameter of the foam substrate be 80 μm or less, the balance between hardness and flexibility of the pressure-sensitive adhesive tape can be further improved, making the pressure-sensitive adhesive tape less susceptible to deformation at low temperatures and further improving waterproofing. The average bubble diameter of the foam substrate is more preferably 60 μm or less, and even more preferably 55 μm or less. There is no particular lower limit to the average cell diameter of the foam substrate, but from the viewpoint of ensuring flexibility of the pressure-sensitive adhesive tape, it is preferably 20 μm or more, and more preferably 30 μm or more. The average bubble diameter of the foam substrate can be measured by the following method. First, the foam substrate is cut into 50 mm squares, immersed in liquid nitrogen for 1 minute, and then cut using a razor blade along a plane perpendicular to the thickness direction of the foam substrate. Next, a magnified photograph of the cut surface is taken at 200x magnification using a digital microscope (e.g., Keyence's "VHX-900"), and the longest bubble diameter (bubble diameter) is measured for all bubbles present within a thickness x 2 mm range. This procedure is repeated five times, and the average bubble diameter is calculated by averaging all the obtained bubble diameters.

[0047] The thickness of the foam substrate 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 foam substrate within the above range, an adhesive tape excellent in flexibility, waterproofness, deformation resistance at low temperatures, heat resistance, handleability, etc. can be obtained, and the adhesive tape can be suitably used for fixing electronic device components such as portable electronic device components and in-vehicle electronic device components. From the viewpoint of being more suitably used for fixing the above components, the more preferred lower limit of the thickness of the foam substrate is 60 μm, a more preferred upper limit is 1900 μm, an even more preferred lower limit is 80 μm, an even more preferred upper limit is 1400 μm, a particularly preferred lower limit is 100 μm, and a particularly preferred upper limit is 1000 μm.

[0048] The foam substrate may be produced by any method as long as it has the closed-cell structure. Examples of the method for producing the foam substrate include a method using a foaming gas and a method incorporating hollow spheres into a raw material matrix. Among these, a foam substrate produced by the latter method is called a syntactic foam, and is therefore preferably a syntactic foam because it has superior strength, flexibility, and heat resistance.

[0049] When the foam substrate is a syntactic foam, the foam becomes a closed-cell foam with a uniform size distribution, resulting in a more consistent density throughout the foam substrate, and improved strength, flexibility, and heat resistance. Furthermore, syntactic foams are less likely to undergo irreversible collapse under high temperatures and pressures than other foams, and therefore exhibit higher heat resistance. Syntactic foams include those having a foamed structure made of hollow inorganic particles and those having a foamed structure made of hollow organic particles. From the viewpoint of flexibility, syntactic foams having a foamed structure made of hollow organic particles are preferred.

[0050] Examples of the hollow organic particles include the Expancel DU series (manufactured by Nippon Phillite Co., Ltd.) and the Advancel EM series (manufactured by Sekisui Chemical Co., Ltd.) Among these, Expancel 461-20 (average cell diameter after foaming under optimal conditions: 20 μm), Expancel 461-40 (average cell diameter after foaming under optimal conditions: 40 μm), Expancel 043-80 (average cell diameter after foaming under optimal conditions: 80 μm), and Advancel EML101 (average cell diameter after foaming under optimal conditions: 50 μm) are preferred because the cell diameter after foaming can be easily designed to a more effective range.

[0051] When the foam substrate is made of a foam other than the syntactic foam, the foaming agent is not particularly limited, and any conventionally known foaming agent such as a thermal decomposition type foaming agent can be used.

[0052] The pressure-sensitive adhesive layer is not particularly limited, and examples thereof include an acrylic pressure-sensitive adhesive layer, a rubber-based pressure-sensitive adhesive layer, a urethane pressure-sensitive adhesive layer, a silicone-based pressure-sensitive adhesive layer, etc. Among these, an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer is preferred because it has excellent heat resistance and can be adhered to a wide variety of adherends.

[0053] The acrylic copolymer is preferably obtained by copolymerizing a monomer mixture containing butyl acrylate and / or 2-ethylhexyl acrylate, and more preferably by copolymerizing a monomer mixture containing butyl acrylate and 2-ethylhexyl acrylate, from the viewpoint of improving initial tack and thereby improving ease of application at low temperatures. The preferred lower limit of the content of the 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 the butyl acrylate in the above range, both high adhesive strength and tackiness can be achieved. The content of 2-ethylhexyl acrylate in the total monomer mixture is preferably 10% by weight at the lower limit, 100% by weight at the upper limit, 30% by weight at the lower limit, 80% by weight at the upper limit, 50% by weight at the lower limit, and 60% by weight at the upper limit. By keeping the content of 2-ethylhexyl acrylate within the above range, high adhesive strength can be exhibited.

[0054] The monomer mixture may contain other copolymerizable polymerizable monomers other than butyl acrylate and 2-ethylhexyl acrylate, as needed. Examples of the other copolymerizable polymerizable monomers include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 18 carbon atoms, functional monomers, and the like. Examples of the (meth)acrylic acid alkyl esters having an alkyl group of 1 to 18 carbon atoms 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 functional monomers include hydroxyalkyl (meth)acrylate, alkoxyalkyl (meth)acrylate, glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, etc.

[0055] To obtain the acrylic copolymer by copolymerizing the monomer mixture, the monomer mixture may be subjected to a radical reaction in the presence of a polymerization initiator. As a method for radically reacting the monomer mixture, i.e., a polymerization method, a conventionally known method may be used, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0056] The weight-average molecular weight (Mw) of the acrylic copolymer is not particularly limited, but a preferred lower limit is 400,000 and a preferred upper limit is 1,500,000. By setting the weight-average molecular weight of the acrylic copolymer within the above range, high adhesive strength can be exhibited. From the viewpoint of further improving adhesive strength, a more preferred lower limit of the weight-average molecular weight is 500,000 and a more preferred upper limit is 1,400,000.

[0057] The upper limit of the ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic copolymer is preferably 10.0. When Mw / Mn is 10.0 or less, the proportion of low-molecular-weight components is suppressed, and the pressure-sensitive adhesive layer is prevented from softening at high temperatures, resulting in a decrease in bulk strength and a decrease in adhesive strength. From the same viewpoint, the upper limit of Mw / Mn is more preferably 5.0, and even more preferably 3.0.

[0058] The pressure-sensitive adhesive layer may contain a tackifying resin. Examples of the tackifying resin 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, C5-C9 copolymer petroleum resins, etc. These tackifying resins may be used alone or in combination of two or more.

[0059] The content of the tackifier resin is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 60 parts by weight per 100 parts by weight of the resin (e.g., acrylic copolymer) that is the main component of the pressure-sensitive adhesive layer. When the content of the tackifier resin is 10 parts by weight or more, the pressure-sensitive adhesive layer can exhibit high adhesive strength. When the content of the tackifier resin is 60 parts by weight or less, a decrease in adhesive strength or tackiness due to hardening of the pressure-sensitive adhesive layer can be suppressed.

[0060] It is preferable that a crosslinking agent be added to the pressure-sensitive adhesive layer to form a crosslinked structure between the main chains of the resin (e.g., the acrylic copolymer, the tackifying resin, etc.) that constitutes the pressure-sensitive adhesive layer. The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred. Addition of an isocyanate-based crosslinking agent to the pressure-sensitive adhesive layer causes the isocyanate groups of the isocyanate-based crosslinking agent to react with alcoholic hydroxyl groups in the resin constituting the pressure-sensitive adhesive layer (e.g., the acrylic copolymer, the tackifying resin, etc.), thereby crosslinking the pressure-sensitive adhesive layer. Formation of a crosslinked structure between the main chains of the resin constituting the pressure-sensitive adhesive layer makes it possible to disperse intermittently applied stress, making the pressure-sensitive adhesive tape less susceptible to deformation at low temperatures and improving heat resistance. 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, per 100 parts by weight of the resin (for example, the acrylic copolymer) that is the main component of the pressure-sensitive adhesive layer.

[0061] The pressure-sensitive adhesive layer may contain a silane coupling agent to improve adhesive strength. The silane coupling agent is not particularly limited, and examples thereof include epoxy silanes, acrylic silanes, methacrylic silanes, amino silanes, and isocyanate silanes.

[0062] The pressure-sensitive adhesive layer may contain a colorant to impart light-blocking properties. The colorant is not particularly limited, and examples thereof include carbon black, aniline black, titanium oxide, etc. Among these, carbon black is preferred because it is relatively inexpensive and chemically stable. The pressure-sensitive adhesive layer may contain conventionally known particles and additives, such as inorganic particles, conductive particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, as needed.

[0063] The pressure-sensitive adhesive layer preferably has a gel fraction of 5% by weight at the lower limit and 90% by weight at the upper limit. If the gel fraction is 5% by weight or more, the pressure-sensitive adhesive tape becomes harder and less susceptible to deformation at low temperatures. If the gel fraction is 90% by weight or less, the pressure-sensitive adhesive tape becomes more flexible and more waterproof. A more preferred lower limit of the gel fraction is 10% by weight, and an even more preferred lower limit is 20% by weight. A more preferred upper limit of the gel fraction is 80% by weight, an even more preferred upper limit is 70% by weight, and an especially preferred upper limit is 60% by weight. The gel fraction of the pressure-sensitive adhesive layer can be measured in the same manner as the gel fraction of the foam substrate.

[0064] The pressure-sensitive adhesive layer has a storage modulus G' of 5.0 x 10 4 Pa, with a preferred upper limit of 5.0 × 10 7 The storage modulus G at 10°C is 5.0 x 10 4 If the storage modulus G' at 10°C is 5.0 x 10 Pa or more, the adhesive tape becomes harder and is less likely to deform at low temperatures. 7 When the storage modulus G' of the pressure-sensitive adhesive layer at 10°C is 1.0 × 10 Pa or less, the flexibility of the pressure-sensitive adhesive tape is further increased and the waterproof property is further improved. 5 Pa, and a more preferable upper limit is 1.0 × 10 7 It is Pa. The storage modulus G' of the pressure-sensitive adhesive layer at 10°C can be measured in the same manner as the storage modulus of the foam substrate.

[0065] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 0.01 mm, a preferred upper limit is 0.1 mm, a more preferred lower limit is 0.015 mm, and a more preferred upper limit is 0.09 mm. By setting the thickness of the pressure-sensitive adhesive layer within the above range, a pressure-sensitive adhesive tape excellent in flexibility, waterproofness, deformation resistance at low temperatures, heat resistance, handleability, etc. can be obtained, and the pressure-sensitive adhesive tape can be suitably used for fixing electronic device parts such as portable electronic device parts and in-vehicle electronic device parts.

[0066] The pressure-sensitive adhesive tape of the present invention may further have a resin layer on at least one surface of the foam substrate. The resin layer may be laminated on only one surface of the foam substrate, or on both surfaces of the foam substrate, but is preferably laminated on only one surface of the foam substrate.

[0067] The resin constituting the resin layer preferably has heat resistance. Examples of the resin constituting the resin layer having heat resistance include polyester resins such as polyethylene terephthalate, acrylic resins, silicone resins, phenolic resins, polyimides, polycarbonates, etc. Among these, acrylic resins and polyester resins are preferred, and polyethylene terephthalate is more preferred, as they provide a pressure-sensitive adhesive tape with excellent flexibility.

[0068] The resin layer may be colored. By coloring the resin layer, it is possible to impart light-blocking properties to the pressure-sensitive adhesive tape. The method for coloring the resin layer is not particularly limited, and examples thereof include a method of kneading particles of carbon black, titanium oxide, or the like, or fine bubbles into the resin constituting the resin layer, and a method of applying ink to the surface of the resin layer.

[0069] The resin layer may contain, as necessary, conventionally known particles and additives such as inorganic particles, conductive particles, plasticizers, tackifiers, ultraviolet absorbers, antioxidants, foaming agents, organic fillers, and inorganic fillers.

[0070] The Young's modulus of the resin layer at 23°C is not particularly limited, but a preferred lower limit is 1000 MPa and a preferred upper limit is 3000 MPa. If the Young's modulus at 23°C is 1000 MPa or more, the pressure-sensitive adhesive tape becomes harder and less likely to deform at low temperatures. If the Young's modulus at 23°C is 3000 MPa or less, the pressure-sensitive adhesive tape becomes more flexible and its waterproofing is further improved. A more preferred lower limit of the Young's modulus at 23°C is 1200 MPa and a more preferred upper limit is 2500 MPa. The Young's modulus of the resin layer at 23°C can be measured in accordance with JIS K 7161 by measuring the tension of a test piece 10 mm wide and 30 mm high at 200 mm / min using a tabletop precision universal testing machine (e.g., Shimadzu Corporation, Autograph AGS-X series, etc.).

[0071] 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, it is possible to achieve both the handleability and the deformation resistance at low temperatures of the pressure-sensitive adhesive tape. From the viewpoint of further achieving both the handleability and the deformation resistance at low temperatures, a more preferred lower limit of the thickness of the resin layer is 10 μm and a more preferred upper limit is 70 μm.

[0072] The thickness of the entire pressure-sensitive adhesive tape of the present invention is not particularly limited, but the lower limit is preferably 0.04 mm, more preferably 0.05 mm, and the upper limit is preferably 2 mm, more preferably 1.5 mm. By setting the thickness of the entire pressure-sensitive adhesive tape of the present invention within the above ranges, it is possible to obtain a pressure-sensitive adhesive tape that is excellent in flexibility, waterproofness, deformation resistance at low temperatures, heat resistance, handleability, etc. The shape of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but examples thereof include a rectangular, frame-like, circular, oval, and doughnut-like shape.

[0073] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and examples thereof include the following method. First, a pressure-sensitive adhesive solution is applied to a release film and dried to form a pressure-sensitive adhesive layer. Next, an unfoamed substrate is produced, and a resin layer is laminated on the unfoamed substrate to form a laminate. Thereafter, pressure-sensitive adhesive layers are attached to both sides of the obtained laminate, and the unfoamed substrate is expanded by heating to form a foamed substrate, thereby producing a pressure-sensitive adhesive tape.

[0074] The applications of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but even when used in a narrow width, it is resistant to deformation at low temperatures and has excellent waterproofing properties. In particular, deformation in the planar direction can be suppressed. The pressure-sensitive adhesive tape of the present invention is also excellent in processability to narrow widths and in workability when applying it to an adherend. For this reason, the pressure-sensitive adhesive tape of the present invention is preferably used for assembling or fixing electronic device components such as portable electronic device components and in-vehicle electronic device components. The pressure-sensitive adhesive tape of the present invention is preferably used in a narrow width, and the width is not particularly limited, but a preferred lower limit is 0.4 mm, a preferred upper limit is 2 mm, a more preferred lower limit is 0.5 mm, a still more preferred upper limit is 1.5 mm, and a particularly preferred upper limit is 1.0 mm. [Effects of the Invention]

[0075] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that is resistant to deformation at low temperatures and has excellent waterproof properties even when used in a narrow width. DETAILED DESCRIPTION OF THE INVENTION

[0076] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0077] Example 1 (1) Manufacturing of unfoamed substrate 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.

[0078] 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 a RAFT agent, and 0.35 parts by weight of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) were placed in a two-neck 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 weight 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).

[0079] A mixture containing 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, 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 weight of hard blocks and 97% by weight of soft blocks. A portion of the reaction liquid was collected, and 4,000 parts by weight of n-hexane was added to it. The mixture was stirred to precipitate the reaction product. The unreacted monomers (MA, BA, AAc) and the solvent were then 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 (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.

[0080] The resulting block copolymer was dissolved in ethyl acetate to a solids content of 35%, and 3.3 parts by weight of Advancell EML101 (manufactured by Sekisui Chemical Co., Ltd.) as a foaming agent (expanded particles) and 0.15 parts by weight of Tetrad C (an epoxy-based crosslinking agent, manufactured by Mitsubishi Gas Chemical Co., Inc.) as a crosslinking agent were added to 100 parts by weight of the block copolymer, followed by thorough stirring to obtain a substrate solution. The resulting substrate solution was applied to a polyethylene terephthalate (PET) film (manufactured by Futamura Chemical Co., Ltd., thickness 23 μm, Young's modulus at 23°C 1800 MPa) that would become the resin layer, and then dried at 90°C for 7 minutes to obtain a laminate consisting of an unfoamed substrate and a resin layer.

[0081] (2) Preparation of adhesive solution A reactor equipped with a thermometer, stirrer, and condenser was charged with 52 parts by weight of ethyl acetate. After purging with nitrogen, the reactor was heated to initiate reflux. Thirty minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 70 parts by weight of butyl acrylate, 27 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.2 parts by weight of 2-hydroxyethyl acrylate was added dropwise evenly and gradually over 1 hour and 30 minutes, allowing the reaction to proceed. Thirty minutes after the dropwise addition was complete, 0.1 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction continued for an additional 5 hours. The reactor was then cooled while being diluted with ethyl acetate, yielding a solution of an acrylic copolymer (random copolymer) with a solids content of 40% by weight. The weight-average molecular weight of the obtained acrylic copolymer was measured by GPC using a Waters "2690 Separations Model" column, and was found to be 710,000. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) was 5.5. To 100 parts by weight of the solid content of the obtained acrylic copolymer, 15 parts by weight of polymerized rosin ester with a softening point of 150° C., 10 parts by weight of terpene phenol with a softening point of 145° C., and 10 parts by weight of rosin ester with a softening point of 70° C. were added. Furthermore, 30 parts by weight of ethyl acetate (manufactured by Fuji Chemicals Co., Ltd.) and 3.0 parts by weight of an isocyanate-based crosslinking agent (Coronate L45, manufactured by Tosoh Corporation) were added and stirred to obtain a pressure-sensitive adhesive solution.

[0082] (3) Manufacture of adhesive tapes The resulting adhesive solution was applied to the release-treated surface of a 50 μm polyethylene terephthalate (PET) film, one side of which had been subjected to a release treatment, using a doctor knife to form a dry film with a thickness of 75 μm. The coating solution was then dried by heating at 110°C for 5 minutes, yielding an adhesive layer. Another adhesive layer was produced using the same procedure. Two adhesive layers were then bonded to both sides of the laminate consisting of the unfoamed substrate and resin layer obtained above, and the laminate was left standing in a 40°C environment for 48 hours. After 48 hours, the laminate was removed from the 40°C environment and heated at 130°C for 1 minute to foam the unfoamed substrate into a foam substrate (thickness 127 μm), yielding an adhesive tape.

[0083] (4) Confirmation of the cell structure of the foam substrate The foam substrate was removed from the adhesive tape, cut into 50 mm squares, and immersed in liquid nitrogen for 1 minute. The foam substrate was then cut perpendicular to the thickness direction using a razor blade. Next, a magnified photograph of the cut surface was taken at 200x magnification using a digital microscope (Keyence Corporation, "VHX-900"). The cell structure of the foam substrate was confirmed as follows: a closed-cell structure was defined when individual bubbles were not connected to other bubbles; an open-cell structure was defined when multiple adjacent bubbles were connected to each other.

[0084] (5) Measurement of gel fraction of foam substrate 0.1 g of the foam substrate alone was removed from the adhesive tape, immersed in 50 mL of ethyl acetate, and shaken in a shaker at 23°C and 120 rpm for 24 hours. After shaking, the ethyl acetate and the foam substrate that had absorbed the ethyl acetate and swollen were separated using a metal mesh (opening #200 mesh). The separated foam substrate was dried at 110°C for 1 hour. The weight of the foam substrate including the metal mesh after drying was measured, and the gel fraction of the foam substrate was calculated using the following formula. Gel fraction (wt%) = 100 × (W1 - W2) / W0 (W0: initial foam substrate weight, W1: foam substrate weight including metal mesh after drying, W2: initial weight of metal mesh)

[0085] (Examples 2 to 8, Comparative Examples 1 to 6) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the foam substrate, resin layer, and pressure-sensitive adhesive layer were changed as shown in Table 1. The raw materials in the table are as follows. In Comparative Example 5, the foam substrate had an open-cell structure in the same manner as in Example 1, except that the base solution was mixed and stirred with nitrogen gas without adding a blowing agent (expanded particles), thereby obtaining a solution containing fine bubbles.

[0086] ·Foam base material monomer MMA (methyl methacrylate)

[0087] <Evaluation> The pressure-sensitive adhesive tapes obtained in the examples and comparative examples were evaluated as follows, and the results are shown in Table 1.

[0088] (1) Measurement of push deformation (surface direction) at -20°C The resulting adhesive tape was punched to an outer diameter of 46 mm wide and 61 mm long, and an inner diameter of 44 mm wide and 59 mm long to prepare a 1 mm wide frame-shaped test specimen. Next, the release paper was peeled off and the test specimen was attached to a 2 mm thick polycarbonate plate with a 38 mm wide and 50 mm long square hole in the center, with the square hole positioned approximately in the center. A 50 mm wide, 75 mm long, and 4 mm thick glass plate was then attached to the top of the test specimen, with the test specimen positioned approximately in the center, to assemble the test apparatus. A pressure of 5 kgf was then applied from the glass plate side located on the top of the test apparatus for 10 seconds to press the polycarbonate plate, test specimen, and glass plate together, and the test apparatus was left at room temperature for 24 hours. The temperature control device of a temperature-controlled benchtop precision universal testing machine (Shimadzu Corporation, Autograph AGS-X series) was set to -20°C, and the fabricated test device was turned upside down and placed on a support stand in the temperature control device for 10 minutes to cool the test device to -20°C. After that, a force was applied through the square hole at a rate of 500 mm / min in a -20°C environment, and the amount of deformation when a force of 30 N was applied to the test device was recorded. When the amount of deformation was less than 700 μm, it was marked with a double circle, when it was 700 μm or more but less than 900 μm, it was marked with a circle, and when it was 900 μm or more, it was marked with an x.

[0089] (2) Waterproof test The obtained adhesive tape was punched out to an outer diameter of 46 mm wide and 61 mm long, and an inner diameter of 45 mm wide and 60 mm long to prepare a narrow, frame-shaped test piece with a width of 0.5 mm (narrow width punching). Next, the test piece with the release paper removed was attached to a polycarbonate plate with a width of 55 mm, a length of 65 mm, and a thickness of 1 mm so that the square hole was located approximately in the center. Then, a polycarbonate plate with a width of 55 mm, a length of 65 mm, and a thickness of 1 mm was attached to the top surface of the test piece so that the test piece was located approximately in the center, and the test apparatus was assembled. Then, a pressure of 2.5 kgf was applied from above the polycarbonate plate of the test apparatus for 10 seconds to press the polycarbonate plate and the test piece together, and the test piece was left at room temperature for 24 hours. The test apparatus was completely immersed in water in a 500 mL polyethylene beaker and placed in an autoclave (Hirayama Manufacturing Co., Ltd., PTU-305VIII). A pressure of 0.5 MPa was applied in the autoclave at 23°C for 30 minutes, and after the pressure was released, water infiltration into the test apparatus was confirmed. A rating of ⊚ was given when no water infiltration was observed and the process of punching the test specimen to the adherend was easy to perform. A rating of ◯ was given when the process of punching the test specimen to the adherend was poor in terms of workability, but the test apparatus could be prepared and no water infiltration was observed. A rating of × was given when the process of punching the test specimen to the adherend was difficult in terms of workability, making it difficult to prepare the test apparatus or when water infiltration was observed.

[0090] [Table 1] [Industrial Applicability]

[0091] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that is resistant to deformation at low temperatures and has excellent waterproof properties even when used in a narrow width.

Claims

1. A pressure-sensitive adhesive tape having a foam substrate and pressure-sensitive adhesive layers on both sides of the foam substrate, The foam substrate has a closed-cell structure, the foam substrate contains a block copolymer having a hard block containing a structure derived from a vinyl aromatic monomer and a soft block containing a structure derived from a (meth)acrylic monomer; the block copolymer has a hard block content of 1% by weight or more and 20% by weight or less; The block copolymer has a glass transition temperature Tg of 50°C or higher for the hard block and a glass transition temperature Tg of -60°C or higher and 10°C or lower for the soft block, and further contains a structure derived from a monomer having a crosslinkable functional group. An adhesive tape characterized by:

2. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the monomer having a crosslinkable functional group is at least one selected from the group consisting of a carboxyl group-containing monomer, a hydroxyl group-containing monomer, an epoxy group-containing monomer, a double bond-containing monomer, a triple bond-containing monomer, and an amide group-containing monomer.

3. 3. The adhesive tape according to claim 1, wherein the block copolymer has a weight average molecular weight of 50,000 or more and 800,000 or less.

4. An adhesive tape as described in claim 1, 2 or 3, characterized in that the glass transition temperature of the hard block is 110°C or less.

5. 5. The adhesive tape according to claim 1, wherein the foam substrate has a gel fraction of 90% by weight or less.

6. 6. The adhesive tape according to claim 1, further comprising a resin layer on at least one surface of said foam substrate.

7. 7. The adhesive tape according to claim 1, 2, 3, 4, 5 or 6, which is used for assembling or fixing electronic device components.

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