adhesive tape

Abstract

To provide an adhesive tape that is flexible and protects a part fixed therewith against damage due to drop impacts.SOLUTION: An adhesive tape contains a foam substrate, and an adhesive layer laminated on at least one side of the foam substrate. In the adhesive tape, an inclination of shear adhesion relative to an amount of displacement found by measurement of shear adhesion at -20°C is 1500 N / mm or more. In the foam substrate, a storage elastic modulus E' in dynamic viscoelasticity measurement at -10°C is 200 MPa or more and 550 MPa or less.SELECTED DRAWING: None

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 that are excellent in flexibility and impact resistance include, for example, pressure-sensitive adhesive tapes that use a foam substrate obtained by foaming a polyolefin resin, etc. However, pressure-sensitive adhesive tapes that use a foam substrate have a problem in that when an electronic device is subjected to an impact, such as when dropped, even if the pressure-sensitive adhesive tape does not peel off, the fixed component, such as a glass panel or a housing, may be damaged.

[0006] An object of the present invention is to provide an adhesive tape that is highly flexible and can prevent damage to a component to be fixed thereto even when subjected to an impact such as being dropped. [Means for solving the problem]

[0007] The present invention provides an adhesive tape having a foam substrate and an adhesive layer laminated on at least one surface of the foam substrate, wherein the adhesive tape has a slope of shear adhesive strength versus displacement obtained by shear adhesive strength measurement at -20°C of 1500 N / mm or more, and the foam substrate has a storage modulus E' of 200 MPa or more and 550 MPa or less when measured by dynamic viscoelasticity measurement at -10°C. The present invention will be described in detail below.

[0008] The present inventors have investigated adjusting the slope of the shear adhesive strength versus displacement of a pressure-sensitive adhesive tape having a foam substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the foam substrate by measuring the shear adhesive strength of the pressure-sensitive adhesive tape at -20°C. Such a pressure-sensitive adhesive tape exhibits a sufficiently small displacement upon exposure to shear force at low temperatures (i.e., the displacement upon exposure to shear force at high speed), making it less likely to deform even upon impact, such as being dropped, and thus preventing the fixed component from moving significantly and colliding with surrounding components, the floor, the ground, etc., resulting in damage. However, such a pressure-sensitive adhesive tape has the problem of insufficient flexibility. In response to this, the present inventors have found that by adjusting the storage modulus E' of the foam substrate in dynamic viscoelasticity measurement at -10°C to a specific range in addition to the slope of the shear adhesive strength of the adhesive tape at -20°C, it is possible to obtain an adhesive tape that can suppress damage to a fixed component even when subjected to an impact such as being dropped, without impairing flexibility. This has led to the completion of the present invention.

[0009] The pressure-sensitive adhesive tape of the present invention comprises a foam substrate and a pressure-sensitive adhesive layer laminated on at least one surface of the foam substrate. By including the foam substrate, the pressure-sensitive adhesive tape of the present invention can exhibit excellent flexibility and can sufficiently conform to the shape of an adherend, such as unevenness, corners, and non-flat surfaces.

[0010] The pressure-sensitive adhesive tape of the present invention has a lower limit of 1500 N / mm for the slope of the shear adhesive strength versus displacement measured at -20°C. When the slope of the shear adhesive strength at -20°C is 1500 N / mm or more, the pressure-sensitive adhesive tape of the present invention has a sufficiently small displacement when subjected to shear force at low temperatures (i.e., the displacement when subjected to shear force at high speed). Therefore, the pressure-sensitive adhesive tape of the present invention is less likely to deform even when subjected to an impact such as a fall, and can prevent the fixed component from moving significantly and colliding with surrounding components, the floor, the ground, etc., resulting in damage. A preferred lower limit for the slope of the shear adhesive strength at -20°C is 2000 N / mm, and a more preferred lower limit is 2500 N / mm. There is no particular limitation on the upper limit of the slope of the shear adhesive strength at -20°C. However, if it is too large, the adhesive tape may not be able to fully disperse the stress when subjected to an impact such as being dropped, which may result in interfacial peeling. Therefore, a preferred upper limit is 3500 N / mm, and a more preferred upper limit is 3000 N / mm.

[0011] The shear adhesive strength of the adhesive tape at -20°C can be measured in accordance with JIS-Z-0237 using a tabletop precision universal testing machine (e.g., Shimadzu Corporation, Autograph AGS-X series, etc.) as follows. A test specimen was prepared by cutting adhesive tape to a length of 12.5 mm and a width of 25 mm. Two 55 mm x 65 mm x 1 mm thick polycarbonate plates were then attached to both sides of the test specimen, and a pressure of 5 kg was applied for 10 seconds to bond the two polycarbonate plates. The specimen was then left at 23°C for 24 hours to obtain a test sample. The test sample was then stretched in the longitudinal direction of the specimen at a rate of 10 mm / min at -20°C using the above-mentioned apparatus, and the shear adhesive strength was measured. Measuring shear adhesive strength at a low temperature of -20°C allowed us to examine the behavior of the specimen when subjected to high-speed shear forces. The slope of the shear adhesive strength versus displacement was calculated by plotting the displacement (mm) obtained from the shear adhesive strength measurement on the horizontal axis and the shear adhesive strength (N) on the vertical axis, and calculating the average slope (N / mm) of the shear adhesive strength versus displacement over a displacement range of 0.1 to 0.5 mm.

[0012] The method for adjusting the slope of the shear adhesive strength at -20°C to fall within the above range is not particularly limited, and examples include a method for adjusting the storage modulus of the foam substrate at low temperatures to fall within a specific range, a method for laminating a resin layer on at least one surface of the foam substrate, a method for adjusting the gel fraction and storage modulus at low temperatures of the pressure-sensitive adhesive layer to fall within a relatively high range, and a method for reducing the ratio of the thickness of the pressure-sensitive adhesive layer to the thickness of the entire pressure-sensitive adhesive tape. More specifically, examples of methods for adjusting the storage modulus of the foam substrate at low temperatures 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 foam substrate, as described below.

[0013] The foam substrate has a storage modulus E' measured at -10°C in dynamic viscoelasticity such that the lower limit is 200 MPa and the upper limit is 550 MPa. When the storage modulus E' at -10°C is 200 MPa or more, the pressure-sensitive adhesive tape of the present invention is less likely to deform even when subjected to an impact such as a drop, and can prevent the fixed component from moving significantly and colliding with surrounding components, the floor, the ground, etc., resulting in damage. When the storage modulus E' at -10°C is 550 MPa or less, the pressure-sensitive adhesive tape of the present invention can appropriately distribute stress when subjected to an impact such as a drop, thereby preventing the fixed component from peeling off and exhibiting excellent flexibility, allowing it to fully conform to the shape of the adherend, such as steps, corners, and non-flat surfaces. That is, when the storage modulus E' at -10°C is within the above range, the pressure-sensitive adhesive tape of the present invention has high flexibility and can prevent the fixed component from being damaged when subjected to an impact such as a drop. The preferred lower limit of the storage modulus E' at -10°C is 220 MPa, and the preferred upper limit is 500 MPa, with a more preferred lower limit being 250 MPa and a more preferred upper limit being 450 MPa. The storage modulus E' of the foam substrate in dynamic viscoelasticity measurement at -10°C can be obtained as the storage modulus E' at -10°C when the dynamic viscoelasticity 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 a constant temperature rise tensile mode of 5°C / min, a strain of 0.1%, and a frequency of 10 Hz.

[0014] The method for adjusting the storage modulus E' at -10°C to fall within the above range is not particularly limited, and examples thereof include a method in which a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer, as described below, is used as the foam base material.

[0015] The foam substrate may have an open-cell structure or a closed-cell structure, preferably a closed-cell structure. The foam substrate may have a single-layer structure or a multi-layer structure. The foam substrate preferably contains a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer. When the foam substrate contains such a copolymer, it becomes easy to adjust the slope of the shear adhesive strength at −20° C. and the storage modulus E′ at −10° C. to fall within the above ranges, and the adhesive tape has higher flexibility and can further prevent damage to the fixed part when subjected to an impact such as being dropped.

[0016] 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 can further prevent damage to the fixed part when the pressure-sensitive adhesive tape is subjected to an impact such as being dropped. In this specification, the structure derived from a vinyl aromatic monomer refers to a structure such as that shown in the following general formulas (1) and (2).

[0017] [ka]

[0018] 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.

[0019] 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 flexibility of the pressure-sensitive adhesive tape is increased, and damage to the fixed part when subjected to an impact such as a drop can be further suppressed. 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, and especially preferably 4% by weight. The upper limit of the content of the structure derived from the vinyl aromatic monomer is more preferably 25% by weight, even more preferably 19% by weight, particularly preferably 16% by weight, and especially preferably 8% by weight.

[0020] 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 a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer has a crosslinkable functional group, the rubber elasticity of the copolymer is enhanced by crosslinking, making it easy to adjust the slope of the shear adhesive strength at −20°C and the storage modulus E′ at −10°C within the above ranges. This increases the flexibility of the pressure-sensitive adhesive tape and further reduces damage to the fixed component when subjected to impact, such as dropping. The crosslinkable functional group may be crosslinked or uncrosslinked, but is preferably crosslinked. 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), as described below, thereby increasing the flexibility of the pressure-sensitive adhesive tape and further reducing damage to the fixed component when subjected to impact, such as dropping. In this specification, a structure derived from a monomer having a crosslinkable functional group refers to a structure represented by the following general formulas (3) and (4).

[0021] [ka]

[0022] 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.

[0023] 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 increases the flexibility of the pressure-sensitive adhesive tape and can further reduce damage to the fixed component when subjected to an impact such as being dropped. 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 further increase the flexibility of the pressure-sensitive adhesive tape and further reduce damage to the fixed component when subjected to impact, such as being dropped. Furthermore, (meth)acrylic acid-based monomers containing a carboxyl group and (meth)acrylic acid-based monomers containing a hydroxyl group are more preferred, with acrylic acid, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate being even more preferred.

[0024] 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 flexibility of the pressure-sensitive adhesive tape is increased and damage to the fixed part when subjected to an impact such as being dropped can be further suppressed. 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, more preferably 25% by weight, and even more preferably 20% by weight.

[0025] 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).

[0026] [ka]

[0027] 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.

[0028] 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 further increase the flexibility of the adhesive tape and can further reduce damage to the fixed part when subjected to an impact such as being dropped, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are more preferred.

[0029] Furthermore, it is preferable to use a (meth)acrylic monomer having two or less carbon atoms in its side chain as the (meth)acrylic monomer. 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, improving the cohesive strength and making it easier to adjust the slope of the shear adhesive strength at -20°C and the storage modulus E' at -10°C within the above ranges. This makes it possible to further reduce damage to the fixed component when the adhesive tape is subjected to an impact, such as being dropped, and also improves heat resistance. 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.

[0030] 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.

[0031] 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%.

[0032] 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 of the structures described above, and may be a random copolymer or a block copolymer. From the viewpoint of further improving flexibility, a random copolymer is preferred, and from the viewpoint of achieving both flexibility and the ability to suppress damage to the fixed part, a block copolymer is preferred.

[0033] 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 heterogeneous phase-separated structure in which islands formed by aggregation of the hard block are scattered among a sea of ​​the soft block. These islands serve as pseudo-crosslinking points, imparting rubber elasticity to the block copolymer, thereby increasing the flexibility of the adhesive tape and further reducing damage to the fixed part when subjected to an impact, such as being dropped. Introducing the above-described crosslinkable functional groups into the hard block further increases the flexibility of the adhesive tape and further reduces damage to the fixed part when subjected to an impact, such as being dropped. 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 pressure-sensitive adhesive tape has high flexibility and can prevent damage to the fixed part even when subjected to an impact such as being dropped. This is thought to be because interactions similar to those of the phase separation structure described above are at work on an extremely small scale, such as the nano-level or molecular level.

[0034] 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. 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.

[0035] 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 increases the flexibility of the pressure-sensitive adhesive tape and can further reduce damage to the fixed part when it is subjected to an impact, such as being dropped. 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.

[0036] 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. Having the hard block content within this range increases the flexibility of the adhesive tape, further reduces damage to the fixed component when subjected to impact such as dropping, and improves heat resistance. From the viewpoint of further improving flexibility, the ability to prevent damage to the fixed component, and heat resistance, 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 26% by weight, even more preferably 20% by weight, particularly preferably 17% by weight, and particularly preferably 8% by weight.

[0037] The weight-average molecular weight (Mw) of the copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer is not particularly limited, but is preferably 50,000 or more and 800,000 or less. Having the weight-average molecular weight within this range increases the flexibility of the adhesive tape, further reduces damage to the fixed component when subjected to an impact such as being dropped, and improves heat resistance. 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.

[0038] 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.

[0039] 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.

[0040] The foam substrate preferably has at least one peak in the range below 0°C and at least one peak in the range above 50°C when subjected to DSC (differential scanning calorimetry) measurement in air at a temperature increase rate of 10°C / min. When the foam substrate exhibits at least one peak in the region below 0°C and at least one peak in the region above 50°C upon DSC measurement, it can be said that the foam substrate contains a block copolymer having two blocks as described above. From the viewpoint of achieving both flexibility and the ability to suppress damage to the component to be fixed, it is preferable that the foam substrate contains the block copolymer in this manner. In the present invention, the peak in the region below 0°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 foam substrate can be carried out using a differential scanning calorimeter (for example, DSC 2920 manufactured by TA Instruments) under conditions of a temperature range of −100 to 200° C., a temperature rise rate of 10° C. / min, and one cycle.

[0041] The expansion ratio of the foam substrate is not particularly limited, but a preferred lower limit is 1.1 and a preferred upper limit is 10. When the expansion ratio of the foam substrate is within the above range, the balance between strength and flexibility of the pressure-sensitive adhesive tape can be further improved, thereby further increasing the flexibility of the pressure-sensitive adhesive tape and further reducing damage to the fixed component when subjected to an impact such as being dropped. From the viewpoint of further improving flexibility and the ability to further reduce damage to the fixed component, the expansion ratio of the foam substrate is more preferably 1.3 lower limit and more preferably 7 upper limit, and even more preferably 1.4 lower limit and even more preferably 5 upper limit. The expansion ratio of the foam base material is the reciprocal of the foam density, and can be measured using an electronic densimeter (for example, "ED120T" manufactured by Mirage) in accordance with JIS K 7222.

[0042] 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 pressure-sensitive adhesive tape can exhibit superior flexibility and can more fully conform to the shape of the adherend, such as steps, corners, and non-flat surfaces. 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 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, the ethyl acetate and the foam substrate that has absorbed the ethyl acetate and swollen are separated using a metal mesh (opening #200 mesh). 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)

[0043] 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 that constitutes the foam base material, it is possible to disperse intermittently applied stress, thereby further reducing damage to the fixed part when the adhesive tape is subjected to an impact such as being dropped, and also improving heat resistance.

[0044] 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.

[0045] 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 strength and flexibility of the pressure-sensitive adhesive tape can be further improved, thereby increasing the flexibility of the pressure-sensitive adhesive tape and further reducing damage to the fixed component when subjected to an impact such as being dropped. 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.

[0046] 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, ability to prevent damage to the fixed component, heat resistance, handleability, etc. can be obtained, and the adhesive tape can be suitably used for fixing electronic 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 thickness of the foam substrate is more preferably 60 μm in lower limit, more preferably 1900 μm in upper limit, even more preferably 80 μm in lower limit, even more preferably 1400 μm in upper limit, particularly preferably 100 μm in lower limit, and particularly preferably 1000 μm in upper limit.

[0047] The foam substrate may have a cellular structure, and the manufacturing method is not particularly limited. Examples of the manufacturing method of the foam substrate include a method using a foaming gas and a method of blending hollow spheres into a raw material matrix. Among them, a foam substrate manufactured by the latter method is called a syntactic foam, and is superior in strength, flexibility, and heat resistance, so the foam substrate is preferably a syntactic foam.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The pressure-sensitive adhesive layer may be laminated on only one surface of the foam substrate, or may be laminated on both surfaces. When the pressure-sensitive adhesive layer is laminated on both surfaces of the foam 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.

[0052] 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 preferred lower limit of the content of 2-ethylhexyl acrylate in the total monomer mixture is 10% by weight, and the preferred upper limit is 100% by weight. By keeping the content of 2-ethylhexyl acrylate within the above range, high adhesive strength can be exhibited.

[0053] 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 (meth)acrylic acid alkyl esters having 1 to 3 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having 4 to 12 carbon atoms in the alkyl group include 2-ethylhexyl (meth)acrylate and cyclohexyl (meth)acrylate. Examples of (meth)acrylic acid alkyl esters having 1 to 18 carbon atoms in the alkyl group include tridecyl methacrylate and stearyl (meth)acrylate. 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, and fumaric acid.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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, thereby further reducing damage to the fixed component when the pressure-sensitive adhesive tape is subjected to an impact, such as being dropped, and also 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.

[0060] 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.

[0061] 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.

[0062] The gel fraction of the pressure-sensitive adhesive layer is not particularly limited, but is preferably adjusted to a relatively high range. Adjusting the gel fraction to a relatively high range makes it easy to adjust the slope of the shear adhesive strength at -20°C to the above range, and the pressure-sensitive adhesive tape can further prevent damage to the fixed component when subjected to an impact, such as being dropped. Even if the gel fraction is adjusted to a relatively high range, the pressure-sensitive adhesive tape of the present invention will also have excellent flexibility if the storage modulus E' at -10°C of the foam substrate is within the above range. More specifically, the lower limit of the gel fraction of the pressure-sensitive adhesive layer is preferably 20% by weight, the upper limit is preferably 90% by weight, the more preferable lower limit is 25% by weight, and the more preferable upper limit is 80% 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.

[0063] The storage modulus at low temperatures of the pressure-sensitive adhesive layer is not particularly limited, but is preferably adjusted to a relatively high range. By adjusting the storage modulus at low temperatures to a relatively high range, it becomes easy to adjust the slope of the shear adhesive strength at -20°C to the above range, and the pressure-sensitive adhesive tape can further prevent damage to the fixed part when subjected to an impact such as being dropped. Even if the storage modulus at low temperatures is adjusted to a relatively high range, the pressure-sensitive adhesive tape of the present invention will also have excellent flexibility if the storage modulus E' at -10°C of the foam substrate is within the above range. More specifically, the storage modulus of the pressure-sensitive adhesive layer at 10° C. preferably has a lower limit of 0.1 MPa and an upper limit of 10 MPa, more preferably 1 MPa and an upper limit of 7 MPa. The storage modulus of the pressure-sensitive adhesive layer at 10° C. can be measured in the same manner as for the storage modulus of the foam substrate.

[0064] The total thickness of one or both sides of the pressure-sensitive adhesive layer (i.e., the total thickness of the pressure-sensitive adhesive layer) is not particularly limited, but a preferred upper limit for the ratio of the total thickness of the pressure-sensitive adhesive layer to the total thickness of the pressure-sensitive adhesive tape (total thickness of the pressure-sensitive adhesive layer / thickness of the entire pressure-sensitive adhesive tape) is 0.5. When the total thickness ratio of the pressure-sensitive adhesive layer is 0.5 or less, the pressure-sensitive adhesive tape has a sufficiently small ratio of the total thickness of the pressure-sensitive adhesive layer, which is relatively susceptible to deformation. This makes it easy to adjust the slope of the shear adhesive strength at −20°C to within the above range, and the pressure-sensitive adhesive tape can further prevent damage to the fixed component when subjected to an impact, such as being dropped. A more preferred upper limit for the total thickness ratio of the pressure-sensitive adhesive layer is 0.4, and an even more preferred upper limit is 0.35. The lower limit for the total thickness ratio of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 0.01, and a more preferred lower limit is 0.05, in order to avoid impairing adhesive strength. More specifically, the preferred lower limit of the thickness of one side of the pressure-sensitive adhesive layer is 0.01 mm, the preferred upper limit is 0.1 mm, the more preferred lower limit is 0.015 mm, and the more preferred upper limit is 0.09 mm.

[0065] The pressure-sensitive adhesive tape of the present invention may further have a resin layer laminated on at least one surface of the foam substrate. By having the resin layer, it becomes easy to adjust the slope of the shear adhesive strength at -20°C within the above range, and the adhesive tape can further prevent damage to the fixed part when subjected to an impact such as a drop. Even if the resin layer is included, the adhesive tape of the present invention also has excellent flexibility if the storage modulus E' at -10°C of the foam substrate is within the above range. The resin layer may be laminated on only one surface of the foam substrate or on both surfaces, but it is preferably laminated on only one surface of the foam substrate.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The Young's modulus of the resin layer at 23°C is not particularly limited, but a preferred lower limit is 500 MPa and a preferred upper limit is 5000 MPa. If the Young's modulus at 23°C is 500 MPa or more, the adhesive tape can better prevent damage to the fixed component when subjected to an impact such as being dropped. If the Young's modulus at 23°C is 5000 MPa or less, the adhesive tape will have higher flexibility. A more preferred lower limit of the Young's modulus at 23°C is 1000 MPa and a more preferred upper limit is 4000 MPa. The Young's modulus of the resin layer at 23°C can be measured using a bench-top precision universal testing machine (e.g., Shimadzu Autograph AGS-X Series) in accordance with JIS-K-7161. More specifically, for example, a test piece cut to a width of 10 mm and a length of 100 mm is chucked at 50 mm intervals and stretched at a speed of 200 mm / min, the stress-strain curve is measured, and the Young's modulus can be obtained by calculating the average slope from 1% to 5% strain.

[0070] 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 of the pressure-sensitive adhesive tape and the ability to prevent damage to the fixed component. From the viewpoint of further achieving both easy handling and the ability to prevent damage to the fixed component, a more preferred lower limit of the thickness of the resin layer is 10 μm and a more preferred upper limit is 70 μm.

[0071] 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 range, it is possible to obtain a pressure-sensitive adhesive tape that is excellent in flexibility, ability to prevent damage to fixed components, 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.

[0072] 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.

[0073] The uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but because it is highly flexible and can prevent damage to the part to be fixed (e.g., a glass panel, a housing, etc.) even when subjected to an impact such as being dropped, it is preferably used for assembling or fixing electronic device parts such as portable electronic device parts and in-vehicle electronic device parts. [Effects of the Invention]

[0074] According to the present invention, it is possible to provide an adhesive tape that is highly flexible and can prevent damage to a component to be fixed thereto even when subjected to an impact such as being dropped. [Brief explanation of the drawings]

[0075] [Figure 1] FIG. 10 is a front view schematically showing a method for evaluating the suppression of damage to a fixed part. [Figure 2] FIG. 10 is a side view schematically showing a method for evaluating the suppression of damage to a fixed part. 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] 87 parts by weight of styrene (St), 12 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 monomer 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 50 parts by weight of methyl acrylate (MA), 50 parts by weight of butyl acrylate (BA), 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 8% by weight of hard blocks and 92% 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 monomer and 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 found to be 500,000. The measurement was performed using a Waters 2690 Separations Module as the measuring instrument, 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%. To 100 parts by weight of the block copolymer, 4.4 parts by weight of Advancell EML101 (Sekisui Chemical Co., Ltd.) as a blowing agent (expanded particles) and 0.15 parts by weight of Tetrad C (Mitsubishi Gas Chemical Co., Inc.) as a crosslinking agent were added and thoroughly stirred to obtain a substrate solution. The resulting substrate solution was applied to a polyethylene terephthalate (PET) film (Futamura Chemical Co., Ltd., thickness 23 μm) that would serve as the resin layer and dried at 90°C for 7 minutes to obtain a laminate consisting of an unfoamed substrate and a resin layer. The thickness of the unfoamed substrate was adjusted to 177 μm when the unfoamed substrate was left standing in a 40°C environment for 48 hours and then heated at 130°C for 1 minute.

[0081] (2) Preparation of adhesive solution A reactor equipped with a thermometer, stirrer, and condenser was charged with 78 parts by weight of butyl acrylate, 19 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, 0.2 parts by weight of 2-hydroxyethyl acrylate, and 80 parts by weight of ethyl acetate. The atmosphere was then replaced with nitrogen, and the reactor was heated to initiate reflux. Subsequently, 0.1 parts by weight of azobisisobutyronitrile was added as a polymerization initiator to the reactor. The mixture was refluxed for 5 hours to obtain a solution of an acrylic copolymer (random copolymer). The weight-average molecular weight of the resulting acrylic copolymer was measured by GPC using a Waters "2690 Separations Model" column, and found to be 910,000. To 100 parts by weight of the acrylic copolymer solids contained in the obtained acrylic copolymer solution, 15 parts by weight of a polymerized rosin ester resin with a softening point of 135° C., 10 parts by weight of a terpene phenol resin with a softening point of 160° C., and 10 parts by weight of a rosin ester resin with a softening point of 75° C. were added. Furthermore, 125 parts by weight of ethyl acetate (manufactured by Fuji Chemicals Co., Ltd.) and 2.2 parts by weight of an isocyanate 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 with one side treated with a release agent using a doctor knife to give a dry film thickness of 50 μm. The coating solution was then dried by heating at 110 ° C for 5 minutes to obtain an adhesive layer. Another adhesive layer was then produced using the same procedure, yielding two adhesive layers. The 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 foamed substrate, yielding an adhesive tape.

[0083] (4) Measurement of foaming ratio of foam base material In accordance with JIS K 7222, the density of the foam base material was measured using an electronic densimeter (manufactured by Mirage, ED120T), and the expansion ratio was calculated by taking the reciprocal of the density.

[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] (6) Measurement of storage modulus E' of foam substrate at -10°C The dynamic viscoelasticity spectrum was measured from -40 to 140°C using a viscoelasticity spectrometer (IT Measurement and Control, DVA-200) under conditions of a constant temperature rise tensile mode of 5°C / min, strain of 0.1%, and frequency of 10 Hz, and the storage modulus E' at -10°C was obtained.

[0086] (7) Measurement of the slope of the shear adhesive force of adhesive tape at -20°C In accordance with JIS-Z-0237, the shear adhesive strength of the adhesive tape was measured at -20°C using a tabletop precision universal testing machine (Shimadzu Corporation, Autograph AGS-X series) as follows. Test specimens were prepared by cutting adhesive tape into 12.5 mm long x 25 mm wide pieces. Two 55 mm x 65 mm x 1 mm thick polycarbonate plates were then attached to both sides of the test specimen, and a pressure of 5 kg was applied for 10 seconds to bond the two polycarbonate plates. The test specimens were then left at 23°C for 24 hours to obtain test samples. The test specimens were then stretched in the longitudinal direction of the specimen at a rate of 10 mm / min at -20°C using the above-mentioned apparatus, and the shear adhesive strength was measured. The slope of the shear adhesive strength versus displacement was calculated by plotting the displacement (mm) obtained from the shear adhesive strength measurement on the horizontal axis and the shear adhesive strength (N) on the vertical axis, and calculating the average slope (N / mm) of the shear adhesive strength versus displacement over a displacement range of 0.1 to 0.5 mm.

[0087] (8) DSC measurement of foam substrate Using a differential scanning calorimeter (TA Instruments, DSC 2920), DSC measurements (differential scanning calorimetry) of the foam substrate were performed under the conditions of a temperature range of -100 to 200°C, a heating rate of 10°C / min, and one cycle, and the number of peaks in the range below 0°C and above 50°C was confirmed.

[0088] (Examples 2 to 5, Comparative Examples 1, 3 to 4) An adhesive tape was obtained in the same manner as in Example 1, except that the foam substrate, adhesive layer, and resin layer were changed as shown in Table 1. The raw materials in the table are as follows.

[0089] Foaming agent (foam particles) Expancel 461-DU-20 (461DU20) (manufactured by Nippon Phillite Co., Ltd.) Expancel 461-DU-40 (461DU40) (manufactured by Nippon Phillite Co., Ltd.)

[0090] ·Foam base material monomer 2EHA (2-ethylhexyl acrylate) AA (acrylic acid)

[0091] (Comparative Example 2) (1) Preparation of foam substrate Volara H0180015 (polyethylene resin, manufactured by Sekisui Chemical Co., Ltd., thickness 150 μm) was used as the foam substrate.

[0092] (2) Manufacturing of adhesive tapes Except for using the obtained foam substrate, a pressure-sensitive adhesive tape was obtained in the same manner as in Example 1. The obtained pressure-sensitive adhesive tape was subjected to the various measurements in the same manner as in Example 1.

[0093] <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.

[0094] (1) Flexibility (adhesion strength at low pressure) The flexibility of the adhesive tape was evaluated by measuring the PUSH adhesive strength when applied with low pressure. PUSH adhesive strength is the adhesive strength when force is applied in a direction perpendicular to the adhesive surface. PUSH adhesive strength varies depending on the pressure applied, even for the same adhesive tape. This is because the degree of adhesion between the adhesive surface of the adhesive tape and the surface of the adherend changes depending on the pressure. Therefore, the higher the pressure applied, the higher the degree of adhesion and the higher the PUSH adhesive strength. In other words, the more flexible the adhesive tape, the less the degree of adhesion between the adhesive surface and the surface of the adherend will be compromised even when it is applied with low pressure, and the higher the PUSH adhesive strength can be. Therefore, measuring the PUSH adhesive strength when applied with low pressure can be used as an indicator of the flexibility of the adhesive tape.

[0095] [Method for measuring PUSH adhesive strength when using low pressure] A 1mm-wide frame-shaped test specimen was prepared by punching adhesive tape into a square shape with an outer diameter of 46mm x 61mm and an inner diameter of 44mm x 59mm. The release paper was removed and the test specimen was attached to a 2mm-thick stainless steel plate with a 38mm x 50mm square hole in the center, with the square hole positioned approximately in the center. A 50mm x 70mm, 4mm-thick glass plate was 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 0.05MPa was then applied to the stainless steel plate on top of the test apparatus for 10 seconds to press the stainless steel plate, test specimen, and glass plate together, and the test apparatus was left at room temperature for 24 hours. After leaving the test apparatus, the test apparatus was turned upside down and fixed to a support stand. A 10mm x 10mm stainless steel rod was placed through the square hole in the test piece, and a load was applied slowly at a rate of 10mm / min to the center of the square hole in the test piece. The load value when the test piece and the glass plate were peeled off due to the load was measured and taken as the PUSH adhesive strength. When the PUSH adhesive force was greater than 100N, it was marked as ◯, and when it was 100N or less, it was marked as ×.

[0096] (2) Preventing damage to fixed parts 1 and 2 are front and side views showing a schematic diagram of a method for evaluating the suppression of damage to a fixed part. As shown in Figures 1 and 2, two test pieces 1 were prepared by cutting adhesive tape into 1 mm x 70 mm pieces. Test piece 1 was attached to each short edge of a glass panel 2 measuring 72 mm in length, 135 mm in width, and 0.5 mm in thickness. The surface of the glass panel 2 to which test piece 1 was attached and a polycarbonate plate (polycarbonate housing) 3 were overlapped so that the short edges and long edges of the two plates faced each other, and the two plates were bonded together by applying a pressure of 0.7 MPa for 15 seconds. The plate was then left to stand at 23°C for 24 hours to obtain a test sample. The test sample was repeatedly dropped onto a concrete plate from a height of 1 m in a room temperature environment of 23°C, with the short side of the test sample hitting the concrete plate (in the direction of the arrow in Figure 2). If the number of drops until the glass panel 2 broke or peeled was more than 200 times, it was marked with a ◎, if it was more than 100 but less than 200 times, it was marked with a ○, and if it was 100 times or less, it was marked with an ×.

[0097] [Table 1] [Industrial Applicability]

[0098] According to the present invention, it is possible to provide an adhesive tape that is highly flexible and can prevent damage to a component to be fixed thereto even when subjected to an impact such as being dropped. [Explanation of symbols]

[0099] 1 test piece (adhesive tape) 2 glass panels 3 Polycarbonate plate (polycarbonate housing)

Claims

1. A pressure-sensitive adhesive tape having a foam substrate and pressure-sensitive adhesive layers laminated on both sides of the foam substrate, The pressure-sensitive adhesive tape has a slope of shear adhesive strength versus displacement obtained by shear adhesive strength measurement at −20° C. of 1500 N / mm or more, The foam substrate contains a copolymer having a structure derived from a vinyl aromatic monomer and a structure derived from a (meth)acrylic monomer, and has a storage modulus E' of 200 MPa or more and 550 MPa or less in dynamic viscoelasticity measurement at -10°C. An adhesive tape characterized by:

2. 2. The adhesive tape according to claim 1, wherein the copolymer has a content of the structure derived from the vinyl aromatic monomer of 2% by weight or more and 25% by weight or less.

3. 3. The pressure-sensitive adhesive tape according to claim 1, wherein the foam substrate has at least one peak in a region below 0°C and at least one peak in a region above 50°C when measured by DSC in air at a temperature increase rate of 10°C / min.

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

5. 5. The adhesive tape according to claim 1, wherein the ratio of the total thickness of the adhesive layer to the total thickness of the adhesive tape (total thickness of the adhesive layer / total thickness of the adhesive tape) is 0.5 or less.

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