adhesive tape

Abstract

To provide an adhesive tape having excellent repeated impact resistance.SOLUTION: An adhesive tape has an adhesive layer on at least one side of a foam substrate. The foam substrate has at least one peak in each of the 50-100°C range and the -100°C-10°C range in DSC measurement at a temperature increase rate of 10°C / min, in the temperature range of -100°C to 200°C, and at one cycle number.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] As an adhesive tape with excellent flexibility and impact resistance, adhesive tapes using a foam substrate made from a foamed polyolefin resin are known. On the other hand, in recent years, portable electronic devices, in-vehicle electronic devices, etc., are required to be able to withstand repeated impacts due to the increasingly severe and diverse conditions of use. However, while conventional adhesive tapes do not peel after a single impact, they sometimes peel or damage the adherend when subjected to repeated drop impacts.

[0006] An object of the present invention is to provide a pressure-sensitive adhesive tape having excellent repeated impact resistance. [Means for solving the problem]

[0007] The present invention provides a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on at least one surface of a foam substrate, The foam substrate is an adhesive tape characterized in that when DSC measurement is performed under the conditions of a temperature rise rate of 10°C / min, a temperature range of -100°C to 200°C, and one cycle, the foam substrate has at least one peak in the range of 50 to 100°C and at least one peak in the range of -100°C to 10°C. The present invention will be described in detail below.

[0008] The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer on at least one surface of a foam substrate. By using the foam substrate, the pressure-sensitive adhesive tape of the present invention can exhibit excellent flexibility and impact resistance. The foam substrate may have an open-cell structure or a closed-cell structure, but a closed-cell structure is preferred. The foam substrate may have a single-layer structure or a multi-layer structure.

[0009] When the foam substrate is subjected to DSC (differential scanning calorimetry) measurement under the conditions of a temperature rise rate of 10°C / min, a temperature range of -100°C to 200°C, and one cycle, it has at least one peak in the range of 50 to 100°C and at least one peak in the range of -100°C to 10°C. When the foam exhibits at least one peak in the 50 to 100°C region and at temperatures below 10°C when measured by DSC, the foam has a phase-separated structure formed by a copolymer containing a rigid structure (hereinafter also referred to as hard segments) and a flexible structure (hereinafter also referred to as soft segments). The phase-separated structure is a structure (sea-island structure) in which the hard segments aggregate, resulting in the aggregated hard segments being scattered like islands in a sea of ​​soft segments. It is believed that such a phase-separated structure imparts rubber elasticity to the copolymer, as the islands of hard segments act as pseudo-crosslinking points, thereby imparting high repeated impact resistance to the resulting pressure-sensitive adhesive tape. To further enhance repeated impact resistance, the foam substrate preferably exhibits at least one peak in the 50 to 100°C region and the -100 to 0°C region when measured by DSC (differential scanning calorimetry) at a temperature range of -100 to 200°C and with one cycle. The peak region can be adjusted by adjusting the type of monomers used for the hard and soft segments. The DSC measurement is performed using a differential scanning calorimeter (for example, a product name "220C" manufactured by Seiko Instruments Inc.) for 100 mg of foam in air at a heating rate of 10°C / min, in a temperature range of -100°C to 200°C, and with one cycle.

[0010] The foam substrate preferably has an island structure with a maximum major axis of 60 nm or less. The island structure is an island-like structure formed by the aggregation of the hard portions. The small maximum diameter of the island structure, i.e., the finely formed sea-island structure, can improve the repeated impact resistance. The reason why the finely formed sea-island structure improves the repeated impact resistance is unclear, but it is thought that the finer sea-island structure increases the interfacial area between the island structure and the sea structure, allowing for better dispersion and absorption of impact. The maximum diameter can be calculated based on TEM (transmission electron microscope) images. More specifically, TEM observation is performed at 5000x magnification to obtain an observation image of a 4.3 μm × 4.3 μm area. The obtained image is then automatically binarized using image analysis software (e.g., Avizo, version 2019.4, manufactured by Thermo Fisher Scientific, etc.). The long diameter of each island structure (dark area) is measured from the binarized image, and the arithmetic average of these values ​​is used as the maximum diameter. Details of the above automatic binarization method are based on a known document ("Automatic Threshold Selection Method Based on Discrimination and Least Squares Criterion," Otsu, Nobuyuki, IEICE Transactions on Electronics, Information and Communication Engineers, Vol. J63-D, No. 4, pp. 349-356).

[0011] The maximum major axis is more preferably 55 nm or less, even more preferably 50 nm or less, even more preferably 40 nm or less, and particularly preferably 30 nm or less. In particular, the maximum major axis is preferably so small that the sea-island structure cannot be confirmed with the naked eye when the TEM observation is performed. By constructing a sea-island structure so fine that it cannot be confirmed by the TEM observation, repeated impact resistance can be further improved. Even if the sea-island structure cannot be confirmed with the naked eye in the TEM image, if the DSC measurement shows at least one peak in the 50 to 100°C region and at least one peak in the -100 to 10°C region, it can be confirmed that a phase-separated structure exists and a fine sea-island structure is constructed. The lower limit of the maximum major axis is not particularly limited, and the smaller the better as long as the DSC measurement shows peaks in the above regions, the better. The maximum major axis is preferably, for example, 0.5 nm or more. The maximum major axis can be adjusted by the content of hard segments in the copolymer.

[0012] Here, the sea-island structure will be explained. Figure 1 shows a TEM photograph of the foam substrate of the present invention. As shown in Figures 1(a) and 1(b), a copolymer having hard and soft segments has a heterogeneous phase-separated structure (sea-island structure) in which islands of aggregated hard segments (black areas in the photograph) are scattered in a sea of ​​soft segments (bright areas in the photograph) because the hard and soft segments are not easily miscible. In Figure 1(a), it can be seen that the long diameter of each island structure is on the order of several nanometers. On the other hand, in Figure 1(b), the long diameter of the island structure reaches several tens of nanometers.

[0013] The material constituting the foam substrate is not particularly limited as long as it has a peak in the above region when the DSC measurement is performed, i.e., is a copolymer having hard and soft segments, and examples thereof include block copolymers, graft polymers, random copolymers, etc. Among these, block copolymers are preferred because they can impart high flexibility and impact resistance to the resulting pressure-sensitive adhesive tape and also have excellent repeated impact resistance. Examples of block copolymers include diblock copolymers, triblock copolymers, and graft copolymers. Among these, from the viewpoint of the formation of phase separation, diblock copolymers and triblock copolymers are preferred, and triblock copolymers having a structure in which a block consisting of the soft segment is sandwiched between blocks consisting of the hard segment are more preferred.

[0014] The hard segment is not particularly limited as long as it has a rigid structure. When the copolymer is a block copolymer, the hard segment may be a polymer of a single monomer having a rigid structure, or may be a copolymer composed of multiple monomers including a monomer having a rigid structure. Examples of the monomer having a rigid structure include vinyl aromatic compounds, compounds having a cyclic structure, and compounds with short side chain substituents. Among these, it is more preferable that the copolymer has a structure derived from a vinyl aromatic compound monomer as the hard segment, since this further improves impact resistance. Examples of the vinyl aromatic compound monomer include styrene, alpha-methylstyrene, para-methylstyrene, and chlorostyrene. Among these, styrene is preferred because it further improves impact resistance. In this specification, the structure derived from a vinyl aromatic compound monomer refers to a structure such as that shown in the following general formulas (1) and (2).

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

[0016] When the copolymer has a structure derived from the vinyl aromatic compound monomer, the content of the structure derived from the vinyl aromatic compound monomer in the copolymer is preferably 0.5% by weight or more and 30% by weight or less. When the content of the structure derived from the vinyl aromatic compound monomer is within the above range, a sea-island type phase separation structure can be formed, and flexibility, impact resistance, and repeated impact resistance can be further improved. The lower limit of the content of the structure derived from the vinyl aromatic compound monomer is more preferably 0.5 wt%, even more preferably 1 wt%, particularly preferably 2 wt%, and especially preferably 2.5 wt%, and the upper limit is more preferably 19 wt%, even more preferably 16 wt%, particularly preferably 8 wt%, and especially preferably 5 wt%.

[0017] The hard portion preferably has a structure derived from a monomer having a crosslinkable functional group. When the hard segment has a crosslinkable functional group, the crosslinking enhances the rubber elasticity of the copolymer, thereby further improving flexibility and impact resistance. The crosslinkable functional group may be crosslinked or not. Even if the structure remains uncrosslinked, the cohesive force of the hard segment is improved by the interaction between the functional groups, thereby improving flexibility and impact resistance. However, crosslinking is more preferable. In this specification, the structure derived from a monomer having a crosslinkable functional group refers to a structure such as that shown in the following general formulas (3) and (4).

[0018] [ka] where 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. 2may 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.

[0019] 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. Among these, at least one selected from the group consisting of hydroxyl group-containing monomers, carboxyl group-containing monomers, epoxy group-containing monomers, amide group-containing monomers, double bond-containing monomers, and triple bond-containing monomers is preferred, as it provides improved flexibility and impact resistance. Examples of the hydroxyl group-containing monomer include 4-hydroxybutyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate. Examples of the carboxyl group-containing monomer include (meth)acrylic acid. Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate. Examples of the amide group-containing monomer include (meth)acrylamide. Examples of the double bond-containing monomer include allyl (meth)acrylate and hexanediol di(meth)acrylate. Examples of the triple bond-containing monomer include propargyl (meth)acrylate. Among these, carboxyl group-containing monomers and hydroxyl group-containing monomers are preferred because they can impart superior flexibility and impact resistance to the pressure-sensitive adhesive tape, and (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.

[0020] When the hard segment is a copolymer of the monomer having the rigid structure and the monomer having the crosslinkable functional group, the hard segment preferably contains 0.1% by weight or more and 30% by weight or less of the structure derived from the monomer having the crosslinkable functional group. When the content of the structure derived from the monomer having a crosslinkable functional group in the hard portion is within the above range, flexibility and impact resistance can be further improved. The lower limit of the content of the structure derived from the monomer having a crosslinkable functional group is more preferably 0.5 wt %, even more preferably 1 wt %, and more preferably 25 wt %, even more preferably 20 wt %.

[0021] The soft portion constituting the copolymer is not particularly limited as long as it has flexibility exhibiting rubber elasticity, but it preferably has a structure derived from a (meth)acrylic monomer. By forming the soft portion from a (meth)acrylic monomer, the resulting pressure-sensitive adhesive tape can be imparted with heat resistance, and deformation and peeling of the pressure-sensitive adhesive tape can be suppressed even when exposed to high temperatures for a long period of time. The (meth)acrylic monomer may be a single monomer, or multiple monomers may be used. Furthermore, monomers other than (meth)acrylic monomers may be used as long as the effects of the present invention are not lost. 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).

[0022] [ka] where 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.

[0023] Examples of (meth)acrylic monomers that serve as raw materials for the soft portion 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. Among these, methyl acrylate, ethyl acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred because they easily achieve both heat resistance and flexibility, and methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are more preferred.

[0024] The content of the structure derived from the (meth)acrylic monomer in the copolymer is not particularly limited as long as the effects of the present invention are exhibited, but 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.

[0025] As the (meth)acrylic monomer serving as a raw material for the soft portion, it is preferable to use a (meth)acrylic monomer having two or less carbon atoms in the side chain. When a (meth)acrylic monomer having two or less carbon atoms in the side chain is used, the entanglement of the resulting polymer chains increases and the cohesive strength improves, thereby further improving the heat resistance and impact 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.

[0026] The preferred lower limit of the content of the (meth)acrylic monomer having two or less side chain carbon atoms in the soft segment is 5% by weight. By including this lower limit, the cohesive strength improving effect described above is more likely to be achieved. A more preferred lower limit is 10% by weight, an even more preferred lower limit is 20% by weight, an especially preferred lower limit is 25% by weight, and an especially preferred lower limit is 30% by weight. The preferred upper limit of the content of the (meth)acrylic monomer having two or less side chain carbon atoms in the soft segment is 90% by weight. By keeping the content below this upper limit, the cohesive strength does not become too high, and the flexibility of the adhesive tape can be further improved. A more preferred upper limit is 85% by weight, an even more preferred upper limit is 80% by weight, an especially preferred upper limit is 75% by weight, and an especially preferred upper limit is 70% by weight.

[0027] The copolymer preferably contains 1% by weight or more and 40% by weight or less of the hard segment. By setting the content of the hard segment within the above range, a foam base material excellent in flexibility, impact resistance, and repeated impact resistance can be formed. From the viewpoint of further improving flexibility, impact resistance, and heat resistance, the lower limit of the content of the hard segment is more preferably 2% by weight, even more preferably 2.5% by weight, and particularly preferably 3% by weight, and more preferably 30% by weight, even more preferably 26% by weight, even more preferably 20% by weight, even more preferably 17% by weight, particularly preferably 8% by weight, and particularly preferably 5% by weight.

[0028] The weight average molecular weight of the copolymer is preferably 50,000 to 800,000. When the weight-average molecular weight of the copolymer is within the above range, flexibility, impact resistance, and heat resistance can be further improved. A more preferred lower limit of the weight-average molecular weight of the copolymer is 75,000, and a more preferred upper limit is 600,000. The weight-average molecular weight can be measured, for example, by GPC using a Water's "2690 Separations Module" as a measuring instrument, a Showa Denko "GPC KF-806L" column, ethyl acetate as a solvent, a sample flow rate of 1 mL / min, and a column temperature of 40°C.

[0029] The method for producing the copolymer is not particularly limited. For example, when the copolymer is a block copolymer, the raw material monomers for the hard and soft segments can be radically reacted in the presence of a polymerization initiator to obtain the hard and soft segments, respectively, and then the two can be reacted. Alternatively, after the hard segment is obtained by the above method, the raw material monomer for the soft segment can be subsequently added and copolymerized. When the copolymer is a random copolymer, a solution containing raw material monomers for the hard and soft segments, and optionally other monomers, can be radically reacted in the presence of a polymerization initiator. The method for causing the radical reaction, i.e., the polymerization method, can be any conventionally known method, such as solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, or bulk polymerization.

[0030] 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.

[0031] The foam substrate has an apparent density of 0.3 g / cm 3 More than 0.75g / cm 3 It is preferable that: By setting the apparent density of the foam substrate within the above range, it is possible to obtain a pressure-sensitive adhesive tape that is more excellent in flexibility and impact resistance while maintaining strength. From the viewpoint of further improving the strength, flexibility and impact resistance of the pressure-sensitive adhesive tape, a more preferable lower limit of the foam substrate is 0.33 g / cm 3 , and a more preferable upper limit is 0.73 g / cm 3 and a more preferable lower limit is 0.35 g / cm 3 , and a more preferable upper limit is 0.71 g / cm 3 is. The apparent density can be measured in accordance with JIS K 7222 using an electronic densimeter (for example, "ED120T" manufactured by Mirage).

[0032] The foam substrate preferably has a gel fraction of 95% or less. By ensuring that the gel fraction of the foam substrate is within the above range, the impact resistance of the resulting pressure-sensitive adhesive tape can be further improved. From the viewpoint of further improving the impact resistance of the pressure-sensitive adhesive tape, the upper limit of the gel fraction is more preferably 90%, and even more preferably 85%. The lower limit of the gel fraction is not particularly limited, but is, for example, 10% or more, particularly 20% or more, and particularly 35% or more. The gel fraction can be adjusted by crosslinking at least one of the hard segment and the soft segment. The gel fraction can be measured by the following method. 0.1 g of the foam substrate alone was removed from the resulting 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)

[0033] The foam substrate preferably contains a crosslinking agent to form a crosslinked structure between the main chains of the resin constituting the foam substrate. Forming a crosslinked structure between the main chains of the resin constituting the foam substrate can disperse intermittently applied peel stress, thereby further improving the heat resistance and impact resistance of the pressure-sensitive adhesive tape. The crosslinking agent is not particularly limited and can be appropriately selected depending on the functional groups possessed by 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 containing alcoholic hydroxyl groups or carboxyl groups, which can further improve flexibility and impact resistance. The isocyanate-based crosslinking agent crosslinks between the alcoholic hydroxyl groups or carboxyl groups in the resin constituting the foam substrate and the isocyanate groups of the crosslinking agent. The epoxy-based crosslinking agent crosslinks between the carboxyl groups in the resin constituting the foam substrate and the epoxy groups of the crosslinking agent. 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 that is the main component of the foam base material.

[0034] The foam substrate preferably has bubbles with an average diameter of 80 μm or less. When the average cell diameter of the foam substrate is within the above range, the balance between strength, flexibility and impact resistance of the resulting pressure-sensitive adhesive tape can be further improved. The average cell 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 tape flexibility, it is preferably 20 μm or more, and more preferably 30 μm or more. The average cell diameter can be measured by the following method. First, the foam substrate was cut into 50 mm squares and immersed in liquid nitrogen for 1 minute. Then, a razor blade was used to cut the foam substrate along a plane perpendicular to its thickness. Next, a digital microscope (e.g., Keyence VHX-900) was used to take a magnified photograph of the cut surface at 200x magnification, and the longest cell diameter (cell diameter) of all cells present within a thickness x 2 mm area was measured. This procedure was repeated five times, and the average cell diameter was calculated by averaging all the obtained cell diameters.

[0035] 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, the pressure-sensitive adhesive tape of the present invention can be suitably used for fixing portable electronic device components, in-vehicle electronic device components, etc. From the viewpoint of being more suitably used for fixing the above components, the more preferred lower limit of the thickness of the foam substrate is 60 μm, a more preferred upper limit is 1900 μm, an even more preferred lower limit is 80 μm, an even more preferred upper limit is 1400 μm, a particularly preferred lower limit is 100 μm, and a particularly preferred upper limit is 1000 μm.

[0036] The foam substrate may have a cellular structure, and the manufacturing method is not particularly limited. Examples of manufacturing methods include a method of manufacturing the foam substrate by the action of a foaming gas or a method of blending hollow spheres into a raw material matrix. Foams manufactured by the latter method are called syntactic foams, and are preferred for the foam substrate because they have superior impact resistance and heat resistance. Using a syntactic foam as the foam substrate results in a closed-cell foam with a uniform size distribution of the foamed bubbles, thereby making the density of the entire foam substrate more consistent and improving impact resistance. Furthermore, syntactic foams are less likely to irreversibly collapse under high temperatures and pressures than other foams, and therefore exhibit higher heat resistance. Syntactic foams include those having a foam structure composed of hollow inorganic particles and those having a foam structure composed of hollow organic particles. From the perspective of flexibility, syntactic foams having a foam structure composed of hollow organic particles are preferred.

[0037] Examples of the hollow organic fine particles include the Expancel DU series (manufactured by Nippon Phillite Co., Ltd.) and the Advancel EM series (manufactured by Sekisui Chemical Co., Ltd.) Among these, Expancel 461-20 (average cell diameter after foaming under optimal conditions: 20 μm), Expancel 461-40 (average cell diameter after foaming under optimal conditions: 40 μm), Expancel 043-80 (average cell diameter after foaming under optimal conditions: 80 μm), and Advancel EML101 (average cell diameter after foaming under optimal conditions: 50 μm) are preferred because the cell diameter after foaming can be easily designed to a more effective range.

[0038] 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.

[0039] 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.

[0040] The acrylic copolymer constituting the acrylic pressure-sensitive adhesive layer 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.

[0041] 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 3 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 3 carbon atoms in the alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, etc. Examples of (meth)acrylic acid alkyl esters having 13 to 18 carbon atoms in the alkyl group include tridecyl methacrylate and stearyl (meth)acrylate, etc. 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, fumaric acid, etc.

[0042] 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.

[0043] The weight-average molecular weight (Mw) of the acrylic copolymer is preferably 400,000 at its lower limit and 1,500,000 at its upper limit. 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, the weight-average molecular weight is more preferably 500,000 at its lower limit and 1,400,000 at its upper limit. The weight average molecular weight (Mw) is the weight average molecular weight determined by GPC (Gel Permeation Chromatography) in terms of standard polystyrene.

[0044] 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.

[0045] 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.

[0046] 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, a decrease in the adhesive strength of the pressure-sensitive adhesive layer can be suppressed. 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.

[0047] The pressure-sensitive adhesive layer preferably contains a crosslinking agent, which forms a crosslinked structure between the main chains of the resins (e.g., the acrylic copolymer, the tackifier resin, etc.) that constitute the pressure-sensitive adhesive layer. The crosslinking agent is not particularly limited, and examples include isocyanate-based crosslinking agents, aziridine-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-type crosslinking agents. Of these, isocyanate-based crosslinking agents are preferred. Adding 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 resins (e.g., the acrylic copolymer, the tackifier resin, etc.) that constitute the pressure-sensitive adhesive layer, thereby crosslinking the pressure-sensitive adhesive layer. Formation of a crosslinked structure between the main chains of the resins that constitute the pressure-sensitive adhesive layer allows the pressure-sensitive adhesive layer to disperse intermittently applied peel stress, further improving the adhesive strength of the pressure-sensitive adhesive tape. 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.

[0048] 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.

[0049] 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 fine particles and additives, such as inorganic fine particles, conductive fine particles, antioxidants, foaming agents, organic fillers, and inorganic fillers, as needed.

[0050] The thickness of the pressure-sensitive adhesive layer is not particularly limited, but a preferred lower limit is 0.01 mm and a preferred upper limit is 0.1 mm. By setting the thickness of the pressure-sensitive adhesive layer within the above range, the pressure-sensitive adhesive tape of the present invention can be suitably used for fixing portable electronic device components, in-vehicle electronic device components, etc. From the viewpoint of being more suitably used for fixing the above components, a more preferred lower limit of the thickness of the pressure-sensitive adhesive layer is 0.015 mm and a more preferred upper limit is 0.09 mm.

[0051] The pressure-sensitive adhesive tape of the present invention preferably has a resin layer on at least one surface of the foam substrate. The resin layer between the foam substrate and the pressure-sensitive adhesive layer improves the strength of the resulting pressure-sensitive adhesive tape, thereby further increasing impact resistance, and in particular improving durability (tumble resistance) when subjected to repeated impacts. The resin layer may be formed on one or both sides of the foam substrate, but is preferably formed on one side of the foam substrate.

[0052] The resin constituting the resin layer preferably has heat resistance. Examples of the heat-resistant resin constituting the resin layer 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.

[0053] 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.

[0054] The resin layer may contain conventionally known fine particles and additives, such as inorganic fine particles, conductive fine particles, plasticizers, tackifiers, ultraviolet absorbers, antioxidants, foaming agents, organic fillers, and inorganic fillers, as needed.

[0055] 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 handleability and impact resistance of the pressure-sensitive adhesive tape. From the viewpoint of further achieving both handleability and impact resistance, a more preferred lower limit of the thickness of the resin layer is 10 μm and a more preferred upper limit is 70 μm.

[0056] The pressure-sensitive adhesive tape of the present invention may have layers other than the foam substrate, the pressure-sensitive adhesive layer, and the resin layer, as necessary.

[0057] In the pressure-sensitive adhesive tape of the present invention, the ratio of the thickness of the pressure-sensitive adhesive layer to the thickness of the foam substrate (pressure-sensitive adhesive layer thickness / foam substrate thickness) is preferably 0.1 or more and 2 or less. When the thickness ratio of the pressure-sensitive adhesive layer to the foam substrate is within the above range, the strength of the entire pressure-sensitive adhesive tape obtained is improved, and therefore impact resistance can be further enhanced. The ratio of the thickness of the pressure-sensitive adhesive layer to the thickness of the foam substrate is more preferably 0.15 or more and more preferably 1.2 or less. The thickness of the pressure-sensitive adhesive layer refers to the sum of the thicknesses of the pressure-sensitive adhesive layers on both sides.

[0058] The thickness of the 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 pressure-sensitive adhesive tape of the present invention within the above range, the pressure-sensitive adhesive tape can be made to have excellent handleability.

[0059] The method for producing the pressure-sensitive adhesive tape of the present invention is not particularly limited, and examples thereof include the following methods. First, a pressure-sensitive adhesive solution is applied to a release film and dried to form a pressure-sensitive adhesive layer, and a second pressure-sensitive adhesive layer is formed in the same manner. Next, an unfoamed substrate is produced by the above method, and the resin layer is laminated on the unfoamed substrate to form a laminate. Thereafter, the pressure-sensitive adhesive layers obtained are bonded to both sides of the obtained laminate, and the unfoamed substrate is foamed by heating, thereby producing a pressure-sensitive adhesive tape.

[0060] 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.

[0061] The uses of the pressure-sensitive adhesive tape of the present invention are not particularly limited, but since it has excellent flexibility, repeated impact resistance, and heat resistance, it can be suitably used as an impact-resistant pressure-sensitive adhesive tape for fixing electronic components such as portable electronic device components and in-vehicle electronic device components. [Effects of the Invention]

[0062] According to the present invention, a pressure-sensitive adhesive tape having excellent repeated impact resistance can be provided. [Brief explanation of the drawings]

[0063] [Figure 1] 1 is a TEM photograph of a foam substrate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0064] The following examples will explain the present invention in more detail, but the present invention is not limited to these examples.

[0065] 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.

[0066] 87 g of styrene (St), 12 g of acrylic acid (AA), 1 g of 2-hydroxyethyl acrylate (HEA), 2.5 g of a RAFT agent, and 0.3 g of 2,2'-azobis(2-methylbutyronitrile) (ABN-E) were placed in a two-necked flask, and the flask was heated to 85°C while being purged with nitrogen gas. The mixture was then stirred at 85°C for 6 hours to carry out the polymerization reaction (first-stage reaction). After the reaction was completed, 4000 g 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 the copolymer (hard portion).

[0067] A mixture containing 49.5 g of butyl acrylate (BA), 49.5 g of methyl acrylate (MA), 1 g of acrylic acid, 0.058 g of ABN-E, and 50 g of ethyl acetate and the copolymer (hard segment) obtained above 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 (second-stage reaction), yielding a reaction solution containing a block copolymer formed from hard segments and soft segments. The blending amounts of the mixture (soft segment) and hard segment were such that the hard segment content in the resulting block copolymer was 3 wt%. A portion of the reaction mixture was collected, 4000 g of n-hexane was added, and the mixture was stirred to precipitate the reaction product. The unreacted monomer and solvent were then filtered off, and the reaction product was dried under reduced pressure at 70°C to isolate the block copolymer (base resin). The weight-average molecular weight of the resulting block copolymer was measured by GPC, which was 398,000. The measurement was performed using a Waters 2690 Separations Module, a Showa Denko GPC KF-806L column, and ethyl acetate as the solvent, with a sample flow rate of 1 mL / min and a column temperature of 40°C.

[0068] The resulting block copolymer was dissolved in ethyl acetate to a solids content of 35%. 3.3 parts by weight of Expancel 461-DU-40 (manufactured by Nippon Phillite Co., Ltd., referred to as 461DU40 in the table) as a blowing agent and 0.12 parts by weight of Tetrad C (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a crosslinking agent were added to 100 parts by weight of block copolymer A and further thoroughly stirred to obtain a substrate solution. The resulting substrate solution was applied to the corona-treated side of a 23 μm polyethylene terephthalate (PET) film that had been corona-treated on one side, and dried at 90 ° C for 7 minutes to obtain an unfoamed substrate. The thickness of the unfoamed substrate was adjusted to 127 μm when the unfoamed substrate was heated to 130 ° C for 1 minute after standing in a 40 ° C environment for 48 hours.

[0069] (2) Preparation of adhesive solution A reactor equipped with a thermometer, stirrer, and condenser was charged with 52 parts by weight of ethyl acetate. After purging with nitrogen, the reactor was heated to begin reflux. Thirty minutes after the ethyl acetate boiled, 0.08 parts by weight of azobisisobutyronitrile was added as a polymerization initiator. A monomer mixture consisting of 70 parts by weight of butyl acrylate, 27 parts by weight of 2-ethylhexyl acrylate, 3 parts by weight of acrylic acid, and 0.2 parts by weight of 2-hydroxyethyl acrylate was added dropwise evenly and gradually over 1 hour and 30 minutes, allowing the reaction to proceed. Thirty minutes after the 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 random copolymer solution with a solids content of 40% by weight. The weight-average molecular weight of the obtained acrylic random copolymer was measured by GPC using a Waters "2690 Separations Model" column, and was found to be 710,000. The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) was 5.5. To 100 parts by weight of the solid content of the obtained acrylic random 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.

[0070] (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 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 then produced using the same procedure, yielding two adhesive layers. The two adhesive layers obtained were then bonded to both sides of the unfoamed substrate obtained above, and the resulting adhesive layer was left standing in a 40 ° C environment for 48 hours. After 48 hours, the substrate was removed from the 40 ° C environment and heated at 130 ° C for 1 minute to foam the substrate, yielding an adhesive tape.

[0071] (4) DSC measurement A measurement sample containing only the foam substrate was prepared using the above method. The obtained measurement sample was measured in air using a differential scanning calorimeter (Seiko Instruments Inc., 220C) under the conditions of a heating rate of 10°C / min, a temperature range of -100°C to 200°C, and one cycle, and the number of peaks in the 50 to 100°C range, -100°C to 0°C range, and -100°C to 10°C range were counted.

[0072] (5) Transmission electron microscope (TEM) measurement The foam substrate was prepared by the above method. A small piece of the trimmed foam substrate was stained with a 2% osmic acid solution at 60°C for 12 hours and then washed. A section with a thickness of less than 100 nm was cut out in the thickness direction of the foam substrate using a cryomicrotome (LEICA, ULTRACUT FC7) at a temperature of -100°C. The section was placed on a sheet mesh with a support film attached to it and used as a measurement sample. The obtained measurement sample was observed at 5000x magnification using a transmission electron microscope (JEOL, JEM-2100) in a 4.3 μm × 4.3 μm (square) area. Images observed with the transmission electron microscope were automatically binarized using image analysis software Avizo (ver. 2019.4, Thermo Fisher Scientific). The major axis of each island structure (dark area) in the binarized image was measured, and the maximum major axis of the island structure was calculated from the arithmetic mean value.

[0073] (6) Measurement of gel fraction of foam substrate 0.1 g of the foam substrate alone was removed from the obtained 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)

[0074] (Examples 2 to 5, Comparative Examples 1 and 2) An adhesive tape was obtained in the same manner as in Example 1, except that the compositions of the hard and soft segments and the blending amounts of the expanded microparticles were as shown in Table 1. The obtained adhesive tape was subjected to the same measurements as in Example 1. The AS-6S (manufactured by Toagosei Co., Ltd., styrene macromonomer solution (50% toluene solution)) used in Example 5 was adjusted so that the styrene macromonomer solid content was the value shown in Table 1. In Comparative Example 2, no expanded microparticles were blended, but heating was carried out at 130°C for 1 minute as in the other Examples in order to equalize the thermal history.

[0075] <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.

[0076] (Evaluation of tumbleability) Two pieces of adhesive tape cut to 1 mm x 70 mm were prepared. Next, the adhesive tape was attached to each short edge of a polycarbonate plate measuring 72 mm in length, 135 mm in width, and 1 mm in thickness. The surface of the polycarbonate plate with the adhesive tape attached was then placed on a polycarbonate plate measuring 77 mm in length, 150 mm in width, and 4 mm in thickness, with the short edges of the two polycarbonate plates facing each other and the long edges facing each other. A pressure of 0.7 MPa was applied for 15 seconds to bond the two polycarbonate plates. The test sample was then left to stand at 23°C for 24 hours to obtain a test sample. The obtained test sample was placed in a TD-1000A drum-type rotational drop tester (manufactured by Shin-ei Electronic Measuring Instruments Co., Ltd.) and rotated at a speed of 12 revolutions per minute while maintaining a room temperature environment of 23°C, allowing the measurement sample to be repeatedly dropped from a height of 1 m. The tumble resistance was evaluated by rating "Good" when the number of times of dropping when the polycarbonate plate peeled off was more than 1000, and rating "Poor" when it was 1000 or less.

[0077] [Table 1] [Industrial Applicability]

[0078] According to the present invention, a pressure-sensitive adhesive tape having excellent repeated impact resistance can be provided.

Claims

1. A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer on at least one surface of a foam substrate, the foam substrate contains a copolymer, the copolymer having a hard segment and a soft segment, the hard segment having a structure derived from a vinyl aromatic compound monomer, and the soft segment having a structure derived from a (meth)acrylic monomer; The copolymer contains the hard portion in an amount of 1% by weight or more and 20% by weight or less, The foam substrate has at least one peak in a region of 50 to 100°C and at least one peak in a region of -100°C to 10°C when measured by DSC under the conditions of a temperature rise rate of 10°C / min, a temperature range of -100°C to 200°C, and one cycle.

2. The pressure-sensitive adhesive tape according to claim 1 , wherein the foam substrate has an island structure having a maximum major axis of 60 nm or less.

3. An adhesive tape as described in claim 1 or 2, wherein the content of the structure derived from the vinyl aromatic compound monomer in the copolymer is 0.5% by weight or more and 30% by weight or less.

4. An adhesive tape described in any of claims 1 to 3, wherein the content of the structure derived from the (meth)acrylic monomer in the copolymer is 30% by weight or more and 99% by weight or less.

5. An adhesive tape described in any one of claims 1 to 4, wherein the copolymer has a weight average molecular weight of 50,000 to 800,000.

6. An adhesive tape described in any one of claims 1 to 5, wherein the foam substrate has a gel fraction of 95% or less.

7. The pressure-sensitive adhesive tape according to any one of claims 1 to 6, wherein a resin layer is provided on at least one surface of the foam substrate.

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