adhesive tape

Abstract

The purpose of the present invention is to provide an adhesive tape that has excellent heat resistance retention and does not easily peel when subjected to loads at high temperatures. The present invention is an adhesive tape that includes a substrate and an adhesive layer that is layered on at least one surface of the substrate, the relaxation time (TL25) of the L component as measured by the Hahn Echo method at 25°C using pulse NMR being no more than 0.9 miliseconds. The present invention is also an adhesive tape that includes a substrate and an adhesive layer that is layered on at least one surface of the substrate, the relaxation time (TL85) of the L component as measured by the Hahn Echo method at 85°C using pulse NMR being no more than 3.3 miliseconds.

Description

[Technical Field]

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

[0002] Adhesive tapes are used for assembly of portable electronic devices such as mobile phones and personal digital assistants (PDAs) (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 off even when subjected to impact. On the other hand, in recent years, portable electronic devices, in-vehicle electronic devices, etc. tend to have more complex shapes as they become more highly functional, and therefore adhesive tapes are sometimes 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.

[0005] Known pressure-sensitive adhesive tapes having excellent flexibility and impact resistance include, for example, pressure-sensitive adhesive tapes using a foam substrate obtained by foaming a polyolefin resin, etc. However, in recent years, electronic devices have increasingly been used for long periods of time at higher temperatures than before due to harsher usage conditions and applications in the field of car electronics, etc., and pressure-sensitive adhesive tapes using conventional foam substrates have a problem in that they tend to peel when a load is applied in the shear direction, etc., at high temperatures.

[0006] An object of the present invention is to provide an adhesive tape that has excellent heat-resistance retention and is resistant to peeling when a load is applied at high temperatures. [Means for solving the problem]

[0007] The present invention provides a pressure-sensitive adhesive tape having a substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate, wherein the relaxation time (T L25 The present invention also provides a pressure-sensitive adhesive tape having a substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate, wherein the relaxation time (T) of the L component measured by the Hahn Echo method at 85°C using pulse NMR is 0.9 milliseconds or less. L85 ) is an adhesive tape having a delay time of 3.3 milliseconds or less. The present invention will be described in detail below.

[0008] The present inventors have discovered that a pressure-sensitive adhesive tape having a substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate: 1 The analysis was carried out using pulsed NMR, which measures the H nucleus. 1 The free induction decay curve of the spin-spin relaxation of H nuclei can be separated into multiple components, and the "relaxation time" of each component can be obtained, allowing the molecular mobility of that component to be evaluated. The present inventors measured the relaxation time (T L25) to a specific value or less, it has been found that an adhesive tape with excellent heat resistance and retention properties, which is resistant to peeling when a load is applied at high temperatures, can be obtained. In addition, the present inventors have found that the relaxation time (T L85 ) to a specific value or less, it has been found that an adhesive tape having excellent heat resistance and retention properties that is resistant to peeling when a load is applied at high temperatures can be obtained, and this has led to the completion of the present invention.

[0009] The pressure-sensitive adhesive tape of the present invention has a substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate.

[0010] The pressure-sensitive adhesive tape of the present invention has a relaxation time (T L25 Alternatively, the pressure-sensitive adhesive tape of the present invention has an upper limit of the relaxation time (T L85 ) has an upper limit of 3.3 milliseconds.

[0011] Here, "the L component obtained by measurement using pulse NMR at 25°C by the Hahn Echo method" means the L component obtained by measurement using pulse NMR at 25°C by the Hahn Echo method. 1 This refers to the component with the longest relaxation time when the free induction decay curve of the spin-spin relaxation of H nuclei is separated into three components in order of shortest relaxation time. The separation into the three components (S component, M component, and L component in order of shortest relaxation time) is performed by analyzing the free induction decay curve using the least squares method.

[0012] "Relaxation time" refers to the time it takes for electron spins to return from an excited state to the ground state after a magnetic field is applied, and the longer the "relaxation time," the higher the molecular mobility. That is, the S component is a hard component with the shortest relaxation time, whose magnetization intensity decays quickly, and whose molecular mobility is relatively low. The M component is a component with a relaxation time and molecular mobility intermediate between the S component and the L component. The L component is a soft component with the longest relaxation time, whose magnetization intensity decays slowly, and whose molecular mobility is relatively high. The relaxation time of the L component at 25°C (T L25 If the relaxation time (T) of the L component at 25°C is 0.9 milliseconds or less, the molecular mobility of the L component, which has relatively high molecular mobility, is suppressed at 25°C, and the adhesive tape of the present invention is therefore less likely to peel when a load is applied at high temperatures. L25 The preferred upper limit of the relaxation time (T) of the L component at 25°C is 0.8 milliseconds, more preferably 0.6 milliseconds, and even more preferably 0.4 milliseconds. L25 The lower limit of ) is not particularly limited, but from the viewpoint of ensuring the flexibility of the adhesive tape, the lower limit is preferably 0.05 milliseconds, and more preferably 0.1 milliseconds. The relaxation time of the L component at 25°C (T L25 ) can be measured by the Hahn Echo method at 25°C using a pulse NMR device (e.g., the minispec mq20, manufactured by BRUKER) and analysis software (e.g., TD-NMRA, manufactured by BRUKER), with an adhesive tape as a measurement sample.

[0013] In addition, the term "L component obtained by measurement using pulse NMR at 85°C by the Hahn Echo method" refers to the L component obtained by measurement using pulse NMR at 85°C by the Hahn Echo method. 1 This refers to the L component when the free induction decay curve of the spin-spin relaxation of H nuclei is separated into two components, the S component and the L component, in order of shortest relaxation time. The separation into the two components is performed by analyzing the free induction decay curve using the least squares method.

[0014] The relaxation time of the L component at 85°C (T L85If the relaxation time (T) of the L component at 85°C is 3.3 milliseconds or less, the molecular mobility of the L component, which has relatively high molecular mobility, is suppressed at 85°C, and the adhesive tape of the present invention is therefore less likely to peel when a load is applied at high temperatures. L85 The upper limit of the relaxation time (T) of the L component at 85°C is more preferably 3 milliseconds, and even more preferably 2.5 milliseconds. L85 The lower limit of the time t is not particularly limited, but from the viewpoint of ensuring the flexibility of the adhesive tape, the lower limit is preferably 0.5 milliseconds, and more preferably 1 millisecond.

[0015] The relaxation time of the L component at 25°C (T L25 ), and the relaxation time of the L component at 85°C (T L85 The method for adjusting the molecular weight (Mw) within the above range is not particularly limited, and examples thereof include a method of using a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer as the substrate, as described below. Other examples include a method of adjusting the weight-average molecular weight (Mw) of such a copolymer, and a method of adjusting the content of foamed particles in the substrate. Still other examples include a method of adjusting the composition of the pressure-sensitive adhesive layer and a method of adjusting the weight-average molecular weight (Mw) of the resin constituting the pressure-sensitive adhesive layer. More specifically, methods for shortening the relaxation time include introducing a structure derived from a vinyl aromatic monomer into the substrate or the pressure-sensitive adhesive layer, increasing the content of the hard block described below in the block copolymer, introducing a crosslinked structure or increasing the degree of crosslinking, etc. Further examples include increasing intermolecular entanglement in the substrate or the pressure-sensitive adhesive layer (i.e., increasing the amount of monomers with short side chains or decreasing the amount of monomers with long side chains), reducing the mobility of molecular chains (e.g., introducing an alicyclic structure), and increasing polar interactions (e.g., introducing an acid or hydroxyl group or increasing its amount). Further examples include selecting raw material monomers to increase the glass transition temperature (Tg) of the substrate or the pressure-sensitive adhesive layer, increasing the molecular weight, adding a filler, etc.

[0016] The substrate is not particularly limited, but preferably contains a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer. When the substrate contains such a copolymer, the relaxation time (T L25 ), and the relaxation time of the L component at 85°C (T L85 ) can be easily adjusted to fall within the above range, and the adhesive tape becomes less likely to peel when a load is applied at high temperatures.

[0017] Examples of the vinyl aromatic monomer include styrene, alpha-methylstyrene, para-methylstyrene, and chlorostyrene. These vinyl aromatic monomers may be used alone or in combination of two or more. Among them, styrene is preferred because it makes the adhesive tape less likely to peel when a load is applied at high 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).

[0018] [ka]

[0019] 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.

[0020] In the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer, 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 likely to peel when a load is applied at high temperatures. 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, even more preferably 2.5% by weight, particularly preferably 3% by weight, especially preferably 4% by weight, more preferably 25% by weight, even more preferably 20% by weight, especially preferably 15% by weight.

[0021] The copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer preferably further has a structure derived from a monomer having a crosslinkable functional group. When the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer has a crosslinkable functional group, the cohesive force of the copolymer is increased by crosslinking, and therefore the relaxation time (T L25 ), and the relaxation time of the L component at 85°C (T L85 ) within the above range. This makes it easier to adjust the crosslinkable functional group within the above range. This makes it more difficult for the adhesive tape to peel when a load is applied at high temperatures. The crosslinkable functional group may be crosslinked or not, but it is more preferable for it to be crosslinked. However, even if the crosslinked structure remains uncrosslinked, the interaction between the functional groups improves the cohesive force within the hard block or soft block (particularly the hard block) described below, making it more difficult for the adhesive tape to peel when a load is applied at high temperatures. In this specification, a structure derived from a monomer having a crosslinkable functional group refers to a structure such as those shown in the following general formulas (3) and (4).

[0022] [ka]

[0023] 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.

[0024] 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 it makes the pressure-sensitive adhesive tape less likely to peel when a load is applied at high temperatures. 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 it even more difficult for the pressure-sensitive adhesive tape to peel when a load is applied at high temperatures. 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.

[0025] In the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer, the content of the structure derived from the monomer having a crosslinkable functional group is not particularly limited, but is preferably 0.1% by weight or more and 30% by weight 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 less likely to peel when a load is applied at high temperatures. The lower limit of the content of the structure derived from the monomer having a crosslinkable functional group is more preferably 0.5% by weight, even more preferably 1% by weight, and even more preferably 25% by weight, and even more preferably 20% by weight.

[0026] 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).

[0027] [ka]

[0028] 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.

[0029] 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 because they make it more difficult for the adhesive tape to peel when a load is applied at high temperatures, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are more preferred.

[0030] Furthermore, it is preferable to use a (meth)acrylic monomer having two or less carbon atoms in the side chain as the (meth)acrylic monomer. When the (meth)acrylic monomer having two or less carbon atoms in the side chain is used, the entanglement of the resulting copolymer chains increases, the cohesive force improves, and the relaxation time (T L25 ), and the relaxation time of the L component at 85°C (T L85 ) can be easily adjusted to fall within the above range, and the adhesive tape becomes less likely to peel when a load is applied at high temperatures. 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.

[0031] In the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer, the content of the structure derived from the (meth)acrylic monomer 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.

[0032] Furthermore, in the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer, the content of the (meth)acrylic monomer having two or less side chain carbon atoms 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 loss of flexibility as an 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%.

[0033] The copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer is not particularly limited as long as it has each structure as described above, and may be a random copolymer or a block copolymer. From the viewpoint of further improving the flexibility of the substrate, a random copolymer is preferred, and from the viewpoint of further improving the balance between the heat resistance retention and flexibility of the substrate, a block copolymer is preferred.

[0034] The block copolymer is a copolymer containing a rigid structure (hereinafter also referred to as a "hard block") and a flexible structure (hereinafter also referred to as a "soft block"). The two blocks of the block copolymer are poorly compatible with each other, and the block copolymer may have a non-uniform phase-separated structure in which islands formed by aggregation of the hard block are scattered among a sea of ​​the soft block. These islands act as pseudo-crosslinking points, imparting rubber elasticity to the block copolymer, making the adhesive tape less likely to peel when a load is applied at high temperatures. Introducing the above-described crosslinkable functional groups into the hard block makes the adhesive tape even less likely to peel when a load is applied at high temperatures. In addition, even when the copolymer having the structure derived from the vinyl aromatic monomer and the structure derived from the (meth)acrylic monomer is a random copolymer, the resulting adhesive tape has excellent heat resistance and is resistant to peeling when a load is applied at high temperatures. This is thought to be because interactions similar to those of the phase separation structure are at work on an extremely small scale, such as the nano or molecular level.

[0035] In the block copolymer, it is preferable that the hard block contains a structure derived from the vinyl aromatic monomer, and the soft block contains a structure derived from the (meth)acrylic monomer. 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., and may also have a structure derived from the (meth)acrylic monomer as long as the effects of the present invention are not lost. The soft block may also 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.

[0036] The block copolymer may have any structure, such as a diblock structure or a triblock structure, but it preferably has a triblock structure having the soft block between the hard blocks, since this makes it more difficult for the adhesive tape to peel when a load is applied at high temperatures. 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.

[0037] The content of the hard block in the block copolymer is not particularly limited, but is preferably 1% by weight or more and 40% by weight or less. When the content of the hard block is within the above range, the adhesive tape becomes less likely to peel when a load is applied at high temperatures. From the viewpoint of further improving heat resistance retention and flexibility, the lower limit of the hard block content 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 content is more preferably 35% by weight, even more preferably 30% by weight, even more preferably 25% by weight, even more preferably 20% by weight, and particularly preferably 15% by weight.

[0038] The weight-average molecular weight (Mw) of the copolymer having a structure derived from the vinyl aromatic monomer and a structure derived from the (meth)acrylic monomer is not particularly limited, but is preferably 50,000 or more and 800,000 or less. When the weight-average molecular weight is in the above range, the pressure-sensitive adhesive tape becomes less likely to peel when a load is applied at high temperatures. 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 Water Corporation "2690 Separations Module" measuring instrument, a Showa Denko Corporation "GPC KF-806L" column, ethyl acetate as a solvent, a sample flow rate of 1 mL / min, and a column temperature of 40°C.

[0039] To obtain a copolymer having a structure derived from the vinyl aromatic monomer and a structure derived from the (meth)acrylic monomer, the raw material monomers for the hard block and the soft block may be radically reacted in the presence of a polymerization initiator to obtain the hard block and the soft block, respectively, and then the two may be reacted or copolymerized. Alternatively, after the hard block is obtained, the raw material monomers for the soft block may be added and copolymerized. In the case of a random copolymer, a solution containing the mixed raw material monomers may be radically reacted in the presence of a polymerization initiator. 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.

[0040] The 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 above 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 subjected to DSC (differential scanning calorimetry) measurement at a temperature rise rate of 10°C / min in a temperature range of -80 to 200°C. When the substrate exhibits at least one peak in the region below 10°C and at least one peak in the region above 50°C upon DSC measurement, it can be said that the substrate contains a block copolymer having two blocks as described above. From the viewpoint of achieving both heat resistance retention and flexibility, it is preferable that the substrate contains the block copolymer in this manner. In the present invention, the peak in the region below 10°C upon DSC measurement can be called the peak derived from the soft block, and the peak in the region above 50°C can be called the peak derived from the hard block. 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 substrate can be carried out on 100 mg of the substrate using a differential scanning calorimeter (for example, 220C manufactured by Seiko Instruments Inc.).

[0042] The substrate may have a single layer structure or a multilayer structure. The substrate is preferably a foam substrate. When the substrate is a foam substrate, the relaxation time (T L25 ), and the relaxation time of the L component at 85°C (T L85 ) can be easily adjusted to fall within the above range, and the adhesive tape becomes less likely to peel when a load is applied at high temperatures. The foam substrate may have an open-cell structure or a closed-cell structure, but preferably has a closed-cell structure.

[0043] When the substrate is a foam substrate, the expansion ratio is not particularly limited, but the preferred lower limit is 1.1 cm 3 / g, with a preferred upper limit of 5 cm 3 / g. When the expansion ratio is in the above range, the balance between heat resistance retention and flexibility of the pressure-sensitive adhesive tape can be further improved. From the viewpoint of further improving the balance between heat resistance retention and flexibility, a more preferable lower limit of the expansion ratio is 1.2 cm 3 / g, and a more preferable upper limit is 4.5 cm 3 / g, and a more preferable lower limit is 1.3 cm 3 / g, and a more preferable upper limit is 4 cm 3 / g. The expansion ratio of the substrate can be calculated from the reciprocal of the density of the substrate, and can be measured using an electronic densimeter (for example, "ED120T" manufactured by Mirage) in accordance with JIS K 7222.

[0044] When the substrate is a foam substrate, the average cell diameter is not particularly limited, but is preferably 80 μm or less. By having the average cell diameter of 80 μm or less, the balance between heat resistance and flexibility of the pressure-sensitive adhesive tape can be further improved. The average cell diameter 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, but from the viewpoint of ensuring flexibility of the pressure-sensitive adhesive tape, it is preferably 10 μm or more, and more preferably 20 μm or more. The average bubble diameter of the substrate can be measured by the following method. First, the 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 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.

[0045] The substrate preferably has a gel fraction of 90% by weight or less. When the gel fraction of the substrate is within the above range, the pressure-sensitive adhesive tape can exhibit better flexibility. From the viewpoint of further increasing the flexibility 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 making the pressure-sensitive adhesive tape less likely to peel when a load is applied at high 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 substrate. The gel fraction of the substrate can be measured using the following method. 0.1 g of the 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 substrate that has absorbed the ethyl acetate and swollen. The separated substrate is dried at 110°C for 1 hour. The weight of the substrate including the metal mesh after drying is measured, and the gel fraction of the substrate is calculated using the following formula. Gel fraction (wt%) = 100 × (W1 - W2) / W0 (W0: initial substrate weight, W1: substrate weight including metal mesh after drying, W2: initial weight of metal mesh)

[0046] It is preferable that a crosslinking agent be added to the base material to form a crosslinked structure between the main chains of the resin constituting the base material. By forming a crosslinked structure between the main chains of the resin constituting the substrate, it is possible to disperse intermittently applied stress, making it more difficult for the adhesive tape to peel off when a load is applied at high temperatures.

[0047] The crosslinking agent is not particularly limited and can be appropriately selected depending on the functional groups possessed by the resin constituting the 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 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 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 base material.

[0048] The thickness of the 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 substrate within the above range, an adhesive tape excellent in flexibility, heat resistance retention, 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 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.

[0049] The method for producing the substrate is not particularly limited. 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 substrate produced by the latter method is called a syntactic foam, and is excellent in strength, flexibility, and heat resistance, so the substrate is preferably a syntactic foam.

[0050] When the substrate is a syntactic foam, the resulting foam is a closed-cell foam with a more uniform size distribution, resulting in a more consistent density throughout the substrate, and improved strength, flexibility, and heat resistance. Furthermore, compared to other foams, syntactic foams are less likely to undergo irreversible collapse under high temperatures and pressures, 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.

[0051] 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-DU-20 (average cell diameter after foaming under optimal conditions: 20 μm), Expancel 461-DU-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. The content of the hollow organic particles is not particularly limited, but since this makes it more difficult for the adhesive tape to peel when a load is applied at high temperatures, the preferred lower limit is 0.1 parts by weight and the preferred upper limit is 10 parts by weight relative to 100 parts by weight of the resin constituting the substrate, and more preferably the lower limit is 0.3 parts by weight and the more preferred upper limit is 7 parts by weight.

[0052] When the 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.

[0053] The pressure-sensitive adhesive layer may be laminated on only one surface of the substrate, or may be laminated on both surfaces. When the pressure-sensitive adhesive layer is laminated on both surfaces of the substrate, the pressure-sensitive adhesive layers on both surfaces may have the same composition and physical properties, or may have different compositions and physical properties. 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.

[0054] 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.

[0055] 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 8 carbon atoms, (meth)acrylic acid alkyl esters having an alkyl group with 13 to 18 carbon atoms, and functional monomers. Examples of (meth)acrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having 13 to 18 carbon atoms in the alkyl group include tridecyl methacrylate and stearyl (meth)acrylate. Examples of the functional monomers include hydroxyalkyl (meth)acrylate, glycerin dimethacrylate, glycidyl (meth)acrylate, 2-methacryloyloxyethyl isocyanate, (meth)acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, and fumaric acid.

[0056] 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.

[0057] 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, making the adhesive tape less likely to peel when a load is applied at high temperatures. From the viewpoint of further improving adhesive strength and heat-resistant retention, a more preferred lower limit of the weight-average molecular weight is 500,000 and a more preferred upper limit is 1,400,000.

[0058] 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, making it more difficult for the pressure-sensitive adhesive tape to peel when a load is applied at high temperatures. From the same viewpoint, the upper limit of Mw / Mn is more preferably 5.0, and even more preferably 3.0.

[0059] 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.

[0060] 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, making the pressure-sensitive adhesive tape less likely to peel when a load is applied at high temperatures. 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.

[0061] 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 (e.g., the acrylic copolymer, the tackifying resin, etc.) that constitutes the pressure-sensitive adhesive layer, resulting in crosslinking of the pressure-sensitive adhesive layer. Formation of a crosslinked structure between the main chains of the resin that constitutes the pressure-sensitive adhesive layer makes it possible to disperse intermittently applied stress, making the pressure-sensitive adhesive tape less susceptible to peeling when a load is applied at high temperatures. 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.

[0062] 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.

[0063] 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.

[0064] The pressure-sensitive adhesive layer preferably has a gel fraction of 10% by weight at the lower limit and 80% by weight at the upper limit. If the gel fraction is within the above range, the pressure-sensitive adhesive tape is less likely to peel when a load is applied at high temperatures. The more preferred lower limit of the gel fraction is 20% by weight, and the more preferred upper limit is 70% by weight. The gel fraction of the pressure-sensitive adhesive layer can be measured in the same manner as the gel fraction of the substrate.

[0065] The pressure-sensitive adhesive layer has a storage modulus G' of 10 5 Pa, with a preferred upper limit of 10 6 When the storage modulus G' at 23°C is within the above range, the pressure-sensitive adhesive tape is less likely to peel when a load is applied at high temperatures. A more preferred lower limit of the storage modulus G' at 23°C of the pressure-sensitive adhesive layer is 2 × 10 5 Pa, a more preferable upper limit is 8 × 10 5 The storage modulus G' at 23°C of the pressure-sensitive adhesive layer can be adjusted by the composition of the raw material monomers of the pressure-sensitive adhesive layer. The storage modulus G' of the pressure-sensitive adhesive layer at 23°C can be obtained as the storage modulus at 23°C when a dynamic viscoelastic spectrum is measured from -40 to 140°C using a viscoelasticity spectrometer (e.g., DVA-200 manufactured by IT Measurement & Control Co., Ltd.) under conditions of 10°C / min and 10 Hz in a constant temperature rise tensile mode.

[0066] 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, heat resistance retention, 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.

[0067] The pressure-sensitive adhesive tape of the present invention may further have a resin layer laminated on at least one surface of the substrate. The resin layer can improve the strength and heat resistance of the pressure-sensitive adhesive tape. The resin layer can be laminated on only one surface of the substrate, or on both surfaces of the substrate, but is preferably laminated on only one surface of the substrate.

[0068] 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.

[0069] 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.

[0070] 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.

[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 easy handling and heat-resistant retention of the pressure-sensitive adhesive tape. From the viewpoint of further achieving both easy handling and heat-resistant retention, 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, a pressure-sensitive adhesive tape excellent in flexibility, heat resistance retention, handleability, etc. can be obtained. The shape of the pressure-sensitive adhesive tape of the present invention is not particularly limited, and examples thereof include rectangular, square, frame-like, circular, oval, and doughnut-like shapes.

[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 uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but since the pressure-sensitive adhesive tape has excellent heat resistance and is resistant to peeling when a load is applied at high temperatures, it is preferably used for assembling or fixing electronic device components such as portable electronic device components and in-vehicle electronic device components. [Effects of the Invention]

[0075] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent heat-resistance retention and is resistant to peeling when a load is applied at high temperatures. [Brief explanation of the drawings]

[0076] [Figure 1] FIG. 1 is a front view schematically showing a holding power test of an adhesive tape. [Figure 2] FIG. 1 is a side view schematically showing a holding power test of an adhesive tape. DETAILED DESCRIPTION OF THE INVENTION

[0077] The following examples further illustrate aspects of the present invention, but the present invention is not limited to these examples.

[0078] 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.

[0079] 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).

[0080] 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 and stirred to precipitate the reaction product. After that, the unreacted monomers (MA, BA, AAc) and the solvent were filtered off, and the reaction product was dried under reduced pressure at 70°C to obtain a block copolymer. The weight-average molecular weight of the resulting block copolymer was measured by GPC, which was 391,000. 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.

[0081] The resulting block copolymer was dissolved in ethyl acetate to a solids content of 35%. To 100 parts by weight of the block copolymer, 3.3 parts by weight of Expancel 461-DU-40 (461DU40) (manufactured by Nippon Phillite Co., Ltd.) as a foaming agent (expanded particles) and 0.16 parts by weight of Tetrad C (an epoxy-based crosslinking agent, manufactured by Mitsubishi Gas Chemical Co., Inc.) as a crosslinking agent were added in a solids content ratio and further stirred thoroughly to obtain a substrate solution. The resulting substrate solution was applied to one side of a 23 μm polyethylene terephthalate (PET) film, which had been corona-treated on both sides as a resin layer, and dried at 90 °C for 7 minutes to obtain a laminate of an unfoamed substrate and a resin layer.

[0082] (2) Production of acrylic copolymer A reactor equipped with a thermometer, stirrer, and condenser was charged with 52 parts by weight of ethyl acetate. After purging with nitrogen, the reactor was heated to begin reflux. 30 minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 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. 30 minutes after the addition was complete, 0.1 parts by weight of azobisisobutyronitrile was added, and the polymerization reaction continued for an additional 5 hours. The reactor was then cooled while being diluted with ethyl acetate, yielding an acrylic copolymer solution with a solids content of 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.

[0083] (3) Manufacture of adhesive tapes 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. The resulting adhesive solution was applied to the release-treated surface of a 50 μm polyethylene terephthalate (PET) film with one side treated with a release agent using a doctor knife to a dry film thickness of 75 μm. The coating solution was then dried by heating at 110°C for 5 minutes to obtain an adhesive layer. Another adhesive layer was produced using the same procedure. Subsequently, an adhesive layer was laminated onto each side of the laminate of the unfoamed substrate and resin layer obtained above to obtain a laminate. The laminate was left to stand in a 40°C environment for 48 hours, removed from the 40°C environment after 48 hours, and heated at 130°C for 1 minute to foam the unfoamed substrate into a foam substrate (thickness 127 μm), thereby obtaining an adhesive tape.

[0084] (4) Measurement of the gel fraction of the substrate 0.1 g of the 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 substrate that had absorbed the ethyl acetate and swollen were separated using a metal mesh (opening #200 mesh). The separated substrate was dried at 110°C for 1 hour. The weight of the substrate including the metal mesh after drying was measured, and the gel fraction of the substrate was calculated using the following formula. Gel fraction (wt%) = 100 × (W1 - W2) / W0 (W0: initial substrate weight, W1: substrate weight including metal mesh after drying, W2: initial weight of metal mesh)

[0085] (5) Measurement of the relaxation time of the L component of adhesive tape Approximately 700 mg (height approximately 2 cm) of adhesive tape was introduced into a 10 mm diameter glass sample tube (BRUKER, product number 1824511, 10 mm diameter, 180 mm length, flat bottom). The sample was placed in a pulse NMR device (the minispec mq20, BRUKER) and held at 25°C or 85°C for 10 minutes, after which the Hahn Echo method was performed. 1 The free induction decay curve of the spin-spin relaxation of H nuclei was separated into three curves derived from the three components, S component, M component, and L component, or two curves derived from the two components, S component and L component, and the relaxation time of the L component was determined. The separation was performed by fitting using both Gaussian and exponential types of curves.

[0086] The analysis software "TD-NMRA (Version 4.3 Rev 0.8)" manufactured by BRUKER was used, and according to the product manual, the relaxation curves obtained at 25°C were fitted using a Gaussian type for the S component and an exponential type for the M and L components, while the relaxation curves obtained at 85°C were all fitted using an exponential type. The following equations were used for fitting at 25°C and 85°C, respectively.

[0087]

number

[0088]

number

[0089] Here, w1 to w3 are Weibull coefficients. At 25°C, w1 is 2, and w2 and w3 are 1. A1 is the component ratio of the S component, B1 is the component ratio of the M component, and C1 is the component ratio of the L component, and T2A is the relaxation time of the S component, T2B is the relaxation time of the M component, and T2C is the relaxation time of the L component. t is time. At 85°C, w1 and w2 take the value of 1. A1 is the component ratio of the S component, B1 is the component ratio of the L component, T2A is the relaxation time of the S component, and T2B is the relaxation time of the L component. t is time.

[0090] [Measurement conditions] Scans:16 Recycle Delay: 1 sec First 90-180 Pulse Separation:0.0082 Final Pulse Separation(ms):5(25℃), 50(85℃) Number of Data Points for Fitting:100

[0091] (Examples 2 to 9, Comparative Examples 1 and 2) Pressure-sensitive adhesive tapes were obtained in the same manner as in Example 1, except that the substrate and resin layer were changed as shown in Table 1. In Examples 8 and 9, no RAFT agent was used, and copolymers were obtained by a one-stage synthesis reaction (random copolymerization) using only ABN-E. In Comparative Example 2, a 30% toluene solution of Septon 2063 (styrene-ethylene-propylene-styrene block polymer resin, manufactured by Kuraray Co., Ltd.) was used, and Tetrad C (epoxy-based crosslinking agent, manufactured by Mitsubishi Gas Chemical Company, Inc.) was not added as a crosslinking agent. The raw materials in the table are as follows.

[0092] Foaming agent (foam particles) Advancell EML101 (manufactured by Sekisui Chemical Co., Ltd.; the unfoamed base material was heated and foamed at 150°C for 1 minute)

[0093] · Raw material monomer for base material 2EHA (2-ethylhexyl acrylate) AS-6S (styrene macromer, manufactured by Toagosei Co., Ltd.) Olefin (Septon 2063, styrene-ethylene-propylene-styrene block polymer resin, manufactured by Kuraray Co., Ltd.)

[0094] <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.

[0095] (1) Evaluation of heat resistance (holding force test) 1 and 2 are diagrams showing a schematic diagram of a holding power test of an adhesive tape. As shown in Figure 1 (front view) and Figure 2 (side view), one side (front surface) of a 25 mm x 25 mm adhesive tape test piece 1 was attached to a SUS plate 2, and a 2 kg rubber roller was rolled back and forth at a speed of 300 mm / min from the other side (back surface) of the test piece 1. Next, an aluminum plate 3 was attached to the back surface of the test piece 1, and a 0.5 kg weight was applied from the aluminum plate 3 side for 10 seconds to compress the test piece, and the test piece was then left to stand in an environment of 23°C and 50% relative humidity for 24 hours to prepare a sample for a holding power test. The holding power test sample was heated to 85°C, and a 1 kg weight 4 was attached to one end of the aluminum plate 3 so that a load was applied horizontally to the test piece 1 and the aluminum plate 3. After one hour, the amount of displacement (length of displacement) of the weight was measured. A case where the amount of displacement was 0 mm (no displacement) was marked with a ◎, a case where the amount of displacement was greater than 0 mm but less than 1 mm was marked with a ○, and a case where the amount of displacement was 1 mm or more or the adhesive tape peeled off and fell.

[0096] [Table 1] [Industrial Applicability]

[0097] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that has excellent heat-resistance retention and is resistant to peeling when a load is applied at high temperatures. [Explanation of symbols]

[0098] 1 test piece (adhesive tape) 2 SUS board 3 Aluminum Plate 4 weights (1 kg)

Claims

1. An adhesive tape having a substrate and adhesive layers laminated on both sides of the substrate, the substrate contains a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer, the substrate is a foam substrate, the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer, The relaxation time (T Ｌ２５ ) is 0.9 milliseconds or less An adhesive tape characterized by:

2. An adhesive tape having a substrate and adhesive layers laminated on both sides of the substrate, the substrate contains a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer, the substrate is a foam substrate, the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic copolymer, The relaxation time (T Ｌ８５ ) is 3.3 milliseconds or less An adhesive tape characterized by:

3. 3. The pressure-sensitive adhesive tape according to claim 1, 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.

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

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