Adhesive layer and adhesive sheet

Abstract

To provide an adhesive layer and a pressure sensitive adhesive sheet capable of reducing environmental load while excellent in impact resistance and layer thinning.SOLUTION: An adhesive layer 1 includes a dried product of a water dispersion type adhesive composition. The water dispersion type adhesive composition contains a water dispersion type polymer, water, and a polyacrylic acid. A content of the polyacrylic acid is over 0.1 pt.mass to 7 pts.mass or less, based on 100 pts.mass of the water dispersion type polymer. Thickness of the adhesive layer 1 is 10 μm or more to 40 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive layer and an adhesive sheet.

Background Art

[0002] In recent years, in various technical fields, adhesive sheets provided with an adhesive layer have been used.

[0003] As such an adhesive sheet, for example, a double-sided adhesive tape including a polyester film (release film), an adhesive layer, a support, an adhesive layer, and a polyester film (release film) in this order has been proposed (see, for example, Patent Document 1). Further, such an adhesive layer is obtained by applying an acrylic adhesive obtained by dissolving an acrylic copolymer in ethyl acetate (organic solvent) onto a polyester film to form a coating film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, in Patent Document 1, an organic solvent is used in the preparation of an adhesive composition (acrylic adhesive). When an organic solvent is used, there is a problem that the environmental load increases because the organic solvent volatilizes when the adhesive composition is applied.

[0006] In addition, depending on the use and purpose, the adhesive sheet is required to have impact resistance and be thinned.

[0007] The present invention provides an adhesive layer and an adhesive sheet that reduce the environmental load and are excellent in impact resistance and thinning. )

Means for Solving the Problems

[0008] The present invention [1] is an adhesive layer comprising a dried product of a water-dispersible adhesive composition, wherein the water-dispersible adhesive composition contains a water-dispersible polymer, water, and polyacrylic acid, the content of the polyacrylic acid is more than 0.1 parts by mass but 7 parts by mass or less per 100 parts by mass of the water-dispersible polymer, and the thickness of the adhesive layer is 10 μm or more and 40 μm or less.

[0009] The present invention [2] further comprises the adhesive layer described in [1] above, wherein the water-dispersible adhesive composition further comprises a leveling agent.

[0010] The present invention [3] includes the adhesive layer described in [2] above, wherein the leveling agent content is 1 part by mass or more per 100 parts by mass of the water-dispersible polymer.

[0011] The present invention [4] comprises an adhesive layer according to any one of the above [1] to [3], wherein the viscosity of the water-dispersible adhesive composition at 25°C is less than 1.5 Pa·s.

[0012] The present invention [5] includes an adhesive sheet comprising a base material and an adhesive layer according to any one of the above [1] to [4] in order toward one side in the thickness direction, wherein the base material is a foam.

[0013] The present invention [6] includes an adhesive sheet comprising a base material and an adhesive layer according to any one of the above [1] to [4] in order toward one side in the thickness direction, wherein the base material is a polymer film. [Effects of the Invention]

[0014] The water-dispersible adhesive composition for forming the adhesive layer of the present invention contains a water-dispersible polymer, water, and polyacrylic acid. In the adhesive layer, which is the dried product of such a water-dispersible adhesive composition, the polyacrylic acid segregates at the interface of the water-dispersible polymer particles. This allows the water-dispersible polymer to maintain its microparticle shape. Furthermore, because such a water-dispersible polymer relieves stress, the adhesive layer has excellent impact resistance.

[0015] Furthermore, the polyacrylic acid content in the water-dispersible adhesive composition is within a predetermined range. Therefore, the adhesive layer, which is the dried product of this water-dispersible adhesive composition, exhibits excellent impact resistance.

[0016] Furthermore, water-dispersible adhesive compositions do not contain organic solvents and do contain water. Therefore, they can reduce environmental impact.

[0017] Furthermore, the thickness of the adhesive layer is between 10 μm and 40 μm. Therefore, it is possible to achieve a thinner layer while maintaining impact resistance.

[0018] The adhesive sheet of the present invention comprises the adhesive layer of the present invention. Therefore, it reduces environmental impact and has excellent impact resistance and thinness. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic cross-sectional view of one embodiment of the adhesive layer of the present invention. [Figure 2] Figures 2A and 2B are schematic diagrams showing one embodiment of a method for manufacturing an adhesive layer (adhesive sheet). Figure 2A shows the first step of preparing a release film. Figure 2B shows the second step of forming an adhesive layer on one side of the release film in the thickness direction. [Figure 3] Figure 3 is a schematic cross-sectional view of one embodiment of the adhesive sheet of the present invention. [Figure 4] Figure 4 shows a transmission electron microscope image of the adhesive layer of Example 1. [Modes for carrying out the invention]

[0020] Referring to FIG. 1, an embodiment of the adhesive layer of the present invention will be described.

[0021] In FIG. 1, the vertical direction of the paper surface is the vertical direction (thickness direction). Also, the upper side of the paper surface is the upper side (one side of the thickness direction). Also, the lower side of the paper surface is the lower side (the other side of the thickness direction). Also, the left-right direction and the depth direction of the paper surface are surface directions orthogonal to the vertical direction. Specifically, it conforms to the direction arrows in each figure.

[0022] The adhesive layer 1 has a film shape. The adhesive layer 1 is composed of a dried product of a water-dispersible adhesive composition.

[0023] <Water-dispersible adhesive composition> The water-dispersible adhesive composition contains a water-dispersible polymer, water, and polyacrylic acid.

[0024] [Water-dispersible polymer] Examples of the water-dispersible polymer include a water-dispersible acrylic polymer, a water-dispersible urethane-based polymer, a water-dispersible polyaniline-based polymer, and a water-dispersible polyester-based polymer. Preferably, a water-dispersible acrylic polymer is mentioned.

[0025] The water-dispersible acrylic polymer is a polymer of a monomer component.

[0026] The monomer component mainly contains an alkyl (meth)acrylate. Here, (meth)acrylic acid is defined as acrylic acid and / or methacrylic acid.

[0027] Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having linear or branched alkyl groups with 1 to 20 carbon atoms. Examples of such alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, and i Examples include sooctyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridodecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Preferably, alkyl acrylates have an alkyl group with 1 to 12 carbon atoms, and more preferably, methyl acrylate and 2-ethylhexyl acrylate.

[0028] Alkyl (meth)acrylates can be used alone or in combination of two or more. Preferably, they are used in combination with methyl acrylate and an alkyl acrylate having an alkyl group with 2 to 8 carbon atoms, and more preferably with methyl acrylate and 2-ethylhexyl acrylate.

[0029] The proportion of alkyl (meth)acrylate is, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and also, for example, 99.5% by mass or less, preferably 99% by mass or less, relative to the monomer component.

[0030] Furthermore, the monomer component may include one or more functional group-containing vinyl monomers copolymerizable with alkyl (meth)acrylate. Functional group-containing vinyl monomers are useful for modifying acrylic polymers, such as ensuring the cohesive strength of the acrylic polymer and introducing crosslinking points into the acrylic polymer.

[0031] Examples of functional group-containing vinyl monomers include carboxyl group-containing vinyl monomers, acid anhydride vinyl monomers, hydroxyl group-containing vinyl monomers, sulfo group-containing vinyl monomers, phosphate group-containing vinyl monomers, cyano group-containing vinyl monomers, and glycidyl group-containing vinyl monomers.

[0032] Examples of carboxyl group-containing vinyl monomers include acrylic acid, methacrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid, with acrylic acid and / or methacrylic acid being preferred. If the carboxyl group-containing vinyl monomer is acrylic acid and / or methacrylic acid, the adhesive properties and mechanical stability of the emulsion particles are excellent.

[0033] Examples of acid anhydride vinyl monomers include maleic anhydride and itaconic anhydride.

[0034] Examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

[0035] Examples of sulfo group-containing vinyl monomers include styrene sulfonic acid, allyl sulfonic acid, sodium vinyl sulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid.

[0036] Examples of phosphate-containing vinyl monomers include 2-hydroxyethyl acryloyl phosphate.

[0037] Examples of cyano group-containing vinyl monomers include acrylonitrile and methacrylonitrile.

[0038] Examples of glycidyl group-containing vinyl monomers include glycidyl (meth)acrylate and 2-ethylglycidyl ether (meth)acrylate.

[0039] Preferred functional group-containing vinyl monomers include carboxyl group-containing vinyl monomers. In other words, the monomer component preferably includes a carboxyl group-containing vinyl monomer.

[0040] The proportion of functional group-containing vinyl monomer is, for example, 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 1.5% by mass or more, relative to the monomer component. The proportion of functional group-containing vinyl monomer in the monomer component is, for example, 30% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0041] Functional group-containing vinyl monomers can be used alone or in combination of two or more.

[0042] Water-dispersible acrylic polymers can be obtained, for example, by emulsion polymerization of the above-mentioned monomer components. In emulsion polymerization, for example, first, a mixture containing monomer components, an emulsifier, and water is stirred to prepare a monomer emulsion. Next, a polymerization initiator is added to the monomer emulsion to start the polymerization reaction. A chain transfer agent may be used in this polymerization reaction to adjust the molecular weight of the acrylic polymer. Additives such as coupling agents and preservatives can also be used. The polymerization method may be dropwise polymerization or batch polymerization. The polymerization time is, for example, 0.5 hours or more, or, for example, 10 hours or less. The polymerization temperature is, for example, 50°C or more, or, for example, 80°C or less.

[0043] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, and radical polymerizable emulsifiers (reactive emulsifiers).

[0044] Examples of anionic emulsifiers include sodium polyoxyethylene lauryl sulfate, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate.

[0045] Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers.

[0046] Examples of radically polymerizable emulsifiers (reactive emulsifiers) include emulsifiers obtained by introducing radically polymerizable functional groups such as vinyl groups, propenyl groups, isopropenyl groups, vinyl ether groups, and allyl ether groups into the above-mentioned anionic emulsifiers and nonionic emulsifiers. Specifically, ammonium-α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene is an example. When a reactive emulsifier is used, the acrylic polymer, which is a water-dispersible polymer obtained by emulsion polymerization, contains monomer units derived from the reactive emulsifier.

[0047] The proportion of the emulsifier is, for example, 0.2 parts by mass or more, and for example, 10 parts by mass or less, per 100 parts by mass of the monomer component.

[0048] Emulsifiers can be used alone or in combination of two or more types.

[0049] Examples of polymerization initiators include azo polymerization initiators and peroxide polymerization initiators.

[0050] Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane}n hydrate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine).

[0051] Examples of peroxide-based polymerization initiators include benzoyl peroxide, t-butyl hydroperoxide, and hydrogen oxide.

[0052] Preferably, the polymerization initiator is an azo polymerization initiator, and more preferably, 2,2'-azobis{2-[N-(2-carboxyethyl)amidino]propane}n hydrate.

[0053] The proportion of the polymerization initiator is, for example, 0.01 parts by mass or more, and for example, 2 parts by mass or less, per 100 parts by mass of the monomer component.

[0054] Polymerization initiators can be used alone or in combination of two or more.

[0055] Examples of chain transfer agents include glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, t-lauryl mercaptan, t-dodecanethiol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol, with t-dodecanethiol being preferred.

[0056] The proportion of the chain transfer agent is, for example, 0.001 parts by mass or more, and for example, 0.5 parts by mass or less, per 100 parts by mass of the monomer component.

[0057] Chain transfer agents can be used alone or in combination of two or more types.

[0058] Through this emulsion polymerization, the water-dispersible acrylic polymer is prepared as an aqueous dispersion, specifically, an aqueous dispersion (emulsion) in which the water-dispersible acrylic polymer is dispersed in water. In other words, the aqueous dispersion contains the water-dispersible polymer and water.

[0059] The weight-average molecular weight (Mw) of the resulting water-dispersible acrylic polymer is, for example, 100,000 or more, preferably 300,000 or more, and also, for example, 5,000,000 or less, preferably 3,000,000 or less. The weight-average molecular weight of the acrylic polymer is measured by gel permeation chromatography (GPC) and calculated on a polystyrene basis (the same applies hereinafter).

[0060] [Polyacrylic acid] Polyacrylic acid is added to improve the impact resistance of adhesive layer 1.

[0061] The proportion of polyacrylic acid is more than 0.1 parts by mass per 100 parts by mass of the water-dispersible polymer, preferably 0.15 parts by mass or more, more preferably 0.25 parts by mass or more, even more preferably 0.8 parts by mass or more, particularly preferably 1.5 parts by mass or more, most preferably 2.5 parts by mass or more, even more preferably 3.3 parts by mass or more, even more preferably 3.8 parts by mass or more, and also 7 parts by mass or less, preferably 5 parts by mass or less. Note that the proportion of polyacrylic acid is the amount of polyacrylic acid contained in the water-dispersible adhesive composition (the same applies hereinafter).

[0062] If the proportion of polyacrylic acid exceeds or is equal to the lower limit mentioned above, the impact resistance of the adhesive layer 1 can be improved.

[0063] On the other hand, if the proportion of polyacrylic acid is below or less than the above lower limit, the impact resistance of the adhesive layer 1 cannot be improved.

[0064] Furthermore, if the proportion of polyacrylic acid is below the above upper limit, the impact resistance of the adhesive layer 1 can be improved.

[0065] On the other hand, if the proportion of polyacrylic acid exceeds the above upper limit, the elasticity of the adhesive layer 1 increases, making it less likely to adhere to the substrate and reducing its drop impact resistance. In addition, a high proportion of water-absorbing polymer reduces the drying efficiency during the manufacture of the adhesive layer 1, significantly decreasing productivity. Similarly, the adhesive layer 1 (adhesive sheet 3) also absorbs moisture during storage, causing the adhesive layer 1 itself to soften and reducing its adhesive properties.

[0066] Such polyacrylic acid can be intentionally added in the above proportions, or it can be generated during the polymerization process.

[0067] The weight-average molecular weight of polyacrylic acid is, for example, 50,000 or more, preferably 100,000 or more, preferably 150,000 or more, and also, for example, 300,000 or less, preferably 250,000 or less.

[0068] [Leveling agent] The water-dispersible adhesive composition preferably further contains a leveling agent.

[0069] Leveling agents are added to improve the applicability of the water-dispersible adhesive composition. As will be explained in more detail later, improving the applicability of the water-dispersible adhesive composition improves the impact resistance of the adhesive layer 1.

[0070] Examples of leveling agents include "Surfinol 420" (acetylene glycol ethylene oxide-based surfactant, manufactured by Nisshin Chemical Industry Co., Ltd.), "Perex OT-P" (sodium dialkyl sulfosuccinate, manufactured by Kao Corporation), "Neocol P" (sodium dialkyl sulfosuccinate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "Nopco Wet 50" (sulfonic acid-based anionic surfactant, manufactured by Sunnopco Co., Ltd.), "SN Wet 126" (modified silicone / special polyether-based surfactant, manufactured by Sunnopco Co., Ltd.), "SN Wet FST2" (nonionic humectant of polyoxyalkyleneamine, manufactured by Sunnopco Co., Ltd.), "SN Wet S" (nonionic humectant of polyoxyalkyleneamine ether, manufactured by Sunnopco Co., Ltd.), and "SN Wet 125" (modified silicone-based surfactant, manufactured by Sunnopco Co., Ltd.).

[0071] Preferred leveling agents include sodium dialkyl sulfosuccinate.

[0072] Furthermore, the number of carbon atoms in sodium dialkyl sulfosuccinate is, for example, 4 or more, preferably 6 or more, more preferably 8 or more, and also, for example, 20 or less, preferably 13 or less, more preferably 10 or less.

[0073] The blending ratio of the leveling agent is, for example, 1 part by mass or more, preferably 1.5 parts by mass or more, and for example, 3.5 parts by mass or less, preferably 2.5 parts by mass or less, per 100 parts by mass of the water-dispersible polymer, from the viewpoint of improving the applicability of the water-dispersible adhesive composition. Note that the blending ratio of the leveling agent refers to the amount of leveling agent contained in the water-dispersible adhesive composition (the same applies hereinafter).

[0074] Furthermore, the blending ratio of the leveling agent is, for example, 10 parts by mass or more, and for example, 500 parts by mass or less, per 100 parts by mass of polyacrylic acid.

[0075] More specifically, if the blending ratio of polyacrylic acid is more than 0.1 parts by mass but less than 2.5 parts by mass per 100 parts by mass of the water-dispersible polymer, the blending ratio of the leveling agent is, for example, 150 parts by mass or more, preferably 250 parts by mass or more, more preferably 350 parts by mass or less, and also, for example, 500 parts by mass or less, preferably 450 parts by mass or less, per 100 parts by mass of polyacrylic acid. Also, if the blending ratio of polyacrylic acid is 2.5 parts by mass or more but 7 parts by mass or less per 100 parts by mass of the water-dispersible polymer, the blending ratio of the leveling agent is, for example, 10 parts by mass or more, preferably 30 parts by mass or more, and also, for example, less than 150 parts by mass, preferably 120 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of polyacrylic acid.

[0076] If the proportion of the leveling agent is above the lower limit or below the upper limit, the applicability of the water-dispersible adhesive composition can be improved.

[0077] Leveling agents can be used alone or in combination of two or more types.

[0078] [Other ingredients] The water-dispersible adhesive composition may also contain other components. These other components may include, for example, tackifiers, release agents, silane coupling agents, thickeners, crosslinking agents (e.g., 3-methacryloxypropyltrimethoxysilane), fillers, antioxidants, surfactants, and antistatic agents.

[0079] Examples of tackifiers include various tackifier resins such as rosin resins, rosin derivative resins, petroleum resins, terpene resins, phenolic resins, and ketone resins. Preferably, rosin resins and terpene resins are used, and more preferably, terpene resins.

[0080] The content of the tackifier is, for example, 5 parts by mass or more, preferably 15 parts by mass or more, more preferably 25 parts by mass or more, even more preferably 33 parts by mass or more, or, for example, 50 parts by mass or less, preferably 45 parts by mass or less, more preferably 38 parts by mass or less, per 100 parts by mass of the water-dispersible polymer.

[0081] Other ingredients can be used alone or in combination of two or more.

[0082] [Organic solvents] Water-dispersible adhesive compositions do not contain organic solvents. Therefore, they can reduce environmental impact.

[0083] [Preparation of water-dispersible adhesive compositions]

[0084] A water-dispersible adhesive composition can be prepared, for example, by adding polyacrylic acid and various components (leveling agents as needed, and other components as needed) to an aqueous dispersion of a water-dispersible polymer (the aqueous dispersion contains the water-dispersible polymer and water). Furthermore, the solid content concentration of the water-dispersible adhesive composition can be adjusted by increasing or decreasing its water content.

[0085] The solid content concentration of the water-dispersible adhesive composition is, for example, 10% by mass or more, preferably 20% by mass or more, and for example, 60% by mass or less, preferably 45% by mass or less.

[0086] The viscosity (viscosity at 25°C) of the water-dispersible adhesive composition is, from the viewpoint of improving the applicability of the water-dispersible adhesive composition, for example, less than 1.5 Pa·s, preferably 1.0 Pa·s or less, more preferably 0.8 Pa·s or less, even more preferably 0.6 Pa·s or less, and for example, 0.4 Pa·s or more.

[0087] Viscosity, as will be described in detail in the examples below, can be measured using a Type B viscometer at a measurement temperature of 25°C.

[0088] <Method for manufacturing an adhesive layer> An embodiment of the method for manufacturing the adhesive layer 1 (adhesive sheet 3) will be described with reference to Figures 2A and 2B.

[0089] The method for manufacturing the adhesive layer 1 (adhesive sheet 3) comprises a first step of preparing a release film 2 and a second step of forming the adhesive layer 1 on one side of the release film 2 in the thickness direction.

[0090] [1st step] In the first step, the release film 2 is prepared as shown in Figure 2A.

[0091] The release film 2 is a film that covers and protects the adhesive layer 1. The release film 2 has a film shape.

[0092] The release film 2 is a plastic substrate (plastic film), and examples include polyester sheets (polyethylene terephthalate (PET) sheets), polyolefin sheets (e.g., polyethylene sheets, polypropylene sheets), polyvinyl chloride sheets, polyimide sheets, and polyamide sheets (nylon sheets). The surface of the release film 2 (one side in the thickness direction) may be treated with a surface treatment such as silicone treatment.

[0093] The thickness of the release film 2 is, for example, 1 μm or more, and for example, 100 μm or less.

[0094] [Second process] In the second step, as shown in Figure 2B, an adhesive layer 1 is formed on one side of the release film 2 in the thickness direction.

[0095] Specifically, a water-dispersible adhesive composition is applied to one side of the release film 2 in the thickness direction to form a coating film. The coating film is then dried to form an adhesive layer 1, which is a dried product of the water-dispersible adhesive composition. Since the water-dispersible adhesive composition does not contain organic solvents, the environmental impact can be reduced.

[0096] This forms an adhesive layer 1 on one side of the release film 2 in the thickness direction.

[0097] The thickness of the adhesive layer 1 is 10 μm or more, and 40 μm or less, preferably 30 μm or less.

[0098] If the thickness of the adhesive layer 1 is greater than or equal to the lower limit mentioned above, impact resistance can be improved.

[0099] On the other hand, if the thickness of the adhesive layer 1 is less than the lower limit mentioned above, the impact resistance will decrease.

[0100] Furthermore, if the thickness of the adhesive layer 1 is less than or equal to the above upper limit, it is possible to make it thinner.

[0101] On the other hand, if the thickness of the adhesive layer 1 exceeds the above upper limit, the effect of thinning the layer while maintaining impact resistance is reduced.

[0102] In other words, by setting the thickness of the adhesive layer 1 within the above range, it is possible to achieve excellent impact resistance while also making the layer thinner.

[0103] As described above, an adhesive layer 1 is manufactured, and an adhesive sheet 3 is manufactured which has a release film 2 and an adhesive layer 1 arranged sequentially on one side in the thickness direction.

[0104] The thickness of the adhesive sheet 3 is, for example, 500 μm or less, preferably 400 μm or less, more preferably 300 μm or less, more preferably 200 μm or less, and also, for example, 10 μm or more, more preferably 30 μm or more, more preferably 50 μm or more.

[0105] <Effects and Effects> The water-dispersible adhesive composition that forms the adhesive layer 1 contains a water-dispersible polymer, water, and polyacrylic acid.

[0106] Figure 4 shows a transmission electron microscope image of the adhesive layer 1, which is the dried product of such a water-dispersible adhesive composition (more specifically, Figure 4 is a transmission electron microscope image of the adhesive layer of Example 1, which will be described later).

[0107] As shown in Figure 4, in the adhesive layer 1, polyacrylic acid segregates at the interface 5 of the particles of the water-dispersible polymer 4 (dotted line in Figure 4). This allows the water-dispersible polymer 4 to maintain its microparticle shape. Furthermore, because such water-dispersible polymer 4 relieves stress, the adhesive layer 1 has excellent impact resistance.

[0108] Furthermore, in the water-dispersible adhesive composition, the proportion of polyacrylic acid is within a predetermined range. Therefore, the adhesive layer 1 has excellent impact resistance.

[0109] Furthermore, water-dispersible adhesive compositions do not contain organic solvents and do contain water. Therefore, they can reduce environmental impact.

[0110] Furthermore, the water-dispersible adhesive composition preferably further contains a leveling agent. The inclusion of a leveling agent in the water-dispersible adhesive composition improves its applicability.

[0111] On the other hand, if the water-dispersible adhesive composition has poor applicability, it may not be possible to form a smooth adhesive layer 1 on the substrate 11 (described later). If the adhesive layer 1 cannot be formed smoothly, the adhesion of the adhesive layer 1 to the substrate 11 (described later) will decrease, and as a result, the impact resistance may decrease.

[0112] In contrast, in this adhesive layer 1, the water-dispersible adhesive composition preferably contains a leveling agent, which improves the applicability of the water-dispersible adhesive composition. As a result, the adhesive layer 1 can be formed smoothly on the substrate 11 (described later). Consequently, the adhesion of the adhesive layer 1 to the substrate 11 (described later) is improved, and the impact resistance of the adhesive layer 1 can be further improved.

[0113] Furthermore, the thickness of the adhesive layer 1 is between 10 μm and 40 μm. Therefore, it is possible to achieve a thin layer while maintaining impact resistance.

[0114] As described above, the adhesive layer 1 reduces environmental impact and has excellent impact resistance and thinness, making it particularly suitable for use in the manufacture of electronic devices.

[0115] More specifically, in recent years, electronic devices (such as mobile phones, portable game consoles, and wearable devices) are often carried around and used on the go. In such cases, impact resistance against drops is required for these electronic devices. Furthermore, such electronic devices are required to be thin.

[0116] On the other hand, the adhesive layer 1 has excellent impact resistance and thinness, thus satisfying the requirements for impact resistance and thinness in electronic devices.

[0117] Hereinafter, with reference to Figure 3, an embodiment of the adhesive sheet of the present invention, preferably used in electronic devices, will be described.

[0118] The double-sided tape 10 comprises an adhesive layer 1, a base material 11, and another adhesive layer 1, arranged in order toward one side in the thickness direction. Specifically, the double-sided tape 10 comprises an adhesive layer 1, a base material 11 directly positioned on the upper surface (one side in the thickness direction) of the adhesive layer 1, and another adhesive layer 1 directly positioned on the upper surface (one side in the thickness direction) of the base material 11. In other words, the double-sided tape 10 comprises a base material 11 and an adhesive layer 1, arranged in order toward one side in the thickness direction.

[0119] The adhesive layer 1 is a dried product of the above-mentioned water-dispersible adhesive composition.

[0120] From the viewpoint of impact resistance, the base material 11 can be a foam. Examples of foams include ethylene-propylene-diene rubber foam (EPDM foam), ethylene-propylene foam (EPM foam), polyurethane foam, polystyrene foam, polyolefin foam, and chloroprene foam.

[0121] The thickness of the substrate 11 is preferably thicker than the adhesive layer 1, for example, exceeding 40 μm, preferably 60 μm or more, more preferably 80 μm or more, and also, for example, 120 μm or less, preferably 100 μm or less.

[0122] The double-sided tape 10 is manufactured by applying a water-dispersible adhesive composition to one surface in the thickness direction and the other surface in the thickness direction of the base material 11, and then drying it.

[0123] Because such double-sided tape 10 includes the adhesive layer 1, it reduces environmental impact and offers excellent impact resistance and thinness.

[0124] <Variation> In the modified examples, the same reference numerals are used for components and processes as in the first embodiment, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and advantages as the first embodiment, unless otherwise specified. Moreover, the first embodiment and the modified examples can be combined as appropriate.

[0125] In the above explanation, a foam is used as the base material 11, but a polymer film can also be used instead of the foam. By using the adhesive layer 1, even when a polymer film is used as the base material 11, good adhesion can be achieved, and a double-sided tape 10 (adhesive sheet) can be obtained that exhibits excellent impact resistance similar to that of a foam, while being significantly thinner.

[0126] Examples of polymer film materials include olefin resins, polyester resins, (meth)acrylic resins (acrylic resins and / or methacrylic resins), polycarbonate resins, polyethersulfone resins, polyarylate resins, melamine resins, polyamide resins, polyimide resins, cellulose resins, and polystyrene resins. Examples of olefin resins include polyethylene, polypropylene, and cycloolefin polymers. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of (meth)acrylic resins include polymethacrylate. Preferably, the material for the base material 1 is a polyester resin, more preferably polyethylene terephthalate (PET).

[0127] The thickness of the polymer film is, for example, 1 μm or more, preferably 3 μm or more, and for example, 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less.

[0128] Furthermore, in the above description, the double-sided tape 10 has adhesive layers 1 on both sides of the base material 11 (one side in the thickness direction and the other side in the thickness direction), but it is also possible to have adhesive layers 1 on only one side of the base material 11 (one side in the thickness direction or the other side in the thickness direction). [Examples]

[0129] The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited in any way to the examples and comparative examples. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than or equal to") of the blending ratios (content ratios), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0130] <Details of each ingredient> Details of each component are as follows: Aqualon KH1025: Ammonium-α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene, emulsifier, manufactured by Daiichi Kogyo Seiyaku Co., Ltd. VA-057: 2,2'-Azobis{2-[N-(2-carboxyethyl)amidino]propane}n-hydrate, polymerization initiator, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. KBM-503: 3-Methacryloxypropyltrimethoxysilane, crosslinking agent, manufactured by Shin-Etsu Chemical Co., Ltd. Aron A-10H: Polyacrylic acid, weight-average molecular weight 200,000, manufactured by Toagosei Co., Ltd. Perex OT-P: Sodium dialkyl sulfosuccinate (8 carbon atoms), leveling agent, manufactured by Kao Corporation. Tamanoru E-200NT: Terpene resin, tackifier, manufactured by Arakawa Chemical Industries, Ltd. KE-802: Polymerized rosin, tackifier, manufactured by Arakawa Chemical Industries, Ltd. NS-100H: Rosin ester, tackifier, manufactured by Arakawa Chemical Industries, Ltd. YS Polystar S145: Terpene phenol resin, tackifier, softening point 145°C, manufactured by Yasuhara Chemical Co., Ltd. Pencel D-125: Polymerized rosin ester resin, softening point 125°C, manufactured by Arakawa Chemical Industries, Ltd. Coronate L: Isocyanate-based crosslinking agent, manufactured by Tosoh Corporation. TETRAD-C: Epoxy-based crosslinking agent, manufactured by Mitsubishi Gas Chemical Company.

[0131] <Manufacturing of water-dispersible polymers> Manufacturing Example 1 In a reaction vessel equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, 0.07 parts by mass of Aqualon KH1025 (emulsifier) ​​and 61.1 parts by mass of distilled water were added, and the mixture was purged with nitrogen at room temperature (25°C) for 1 hour while stirring. Then, 0.1 parts by mass of VA-057 (polymerization initiator) was added, and the temperature was raised to 60°C.

[0132] Next, 85 parts by mass of 2-ethylhexyl acrylate, 13 parts by mass of methyl acrylate, 1.25 parts by mass of acrylic acid, 0.75 parts by mass of methacrylic acid, 0.025 parts by mass of t-dodecanethiol (chain transfer agent), 0.02 parts by mass of KBM-503 (crosslinking agent), and 1.93 parts by mass of Aqualon KH1025 (emulsifier) ​​were emulsified with 28 parts by mass of distilled water, and polymerized by dropwise addition at 60°C for 4 hours. After cooling to room temperature, the pH was adjusted to 6 using 10% aqueous ammonia as a pH adjuster to produce a water-dispersible polymer.

[0133] <Manufacturing of acrylic polymers> Manufacturing Example 2 In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 95 parts by mass of butyl acrylate, 5 parts by mass of acrylic acid, 2,2'-azobisisobutyronitrile (AIBN) (polymerization initiator), and ethyl acetate (polymerization solvent) were charged, and solution polymerization was carried out at 60°C for 6 hours to obtain a solution of acrylic polymer. The weight-average molecular weight of the acrylic polymer was 60 × 10⁶. 4 That was the case.

[0134] Manufacturing Example 3 In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 70 parts by mass of butyl acrylate, 30 parts by mass of 2-ethylhexyl acrylate, 3 parts by mass of acrylic acid, 0.05 parts by mass of 4-hydroxybutyl acrylate, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) (polymerization initiator), and toluene (polymerization solvent) were charged, and solution polymerization was carried out at 60°C for 6 hours to obtain a solution of acrylic polymer. The weight-average molecular weight of the acrylic polymer was 55 × 10⁶. 4 That was the case.

[0135] Example 1 [Manufacturing of water-dispersible adhesive compositions] To 100 parts by mass of the water-dispersible polymer from Production Example 1, 30 parts by mass of Tamanol E-200NT (tackifier), 3 parts by mass of Aron A-10H (polyacrylic acid), and 1 part by mass of Perex OT-P (leveling agent) were added. The mixture was then diluted and neutralized with distilled water and 10% aqueous ammonia to produce a water-dispersible adhesive composition (solid content concentration 25% by mass).

[0136] [Manufacturing of adhesive layers (adhesive sheets)] (1st step) A release film (product name "Diafoil MRF #38", manufactured by Mitsubishi Chemical Corporation) was prepared.

[0137] (2nd process) A water-dispersible adhesive composition was applied to one side of the release film in the thickness direction to form a coating. The coating was then dried to produce an adhesive layer (10 μm thick) and an adhesive sheet, which are dried products of the water-dispersible adhesive composition.

[0138] Example 2 Examples 6-8, 11, 12, and 14 ~Example 21 ,ratio Comparison Examples 1 to 4 and Comparative Examples 14 to 19 The adhesive layer and adhesive sheet were manufactured in the same manner as in Example 1. However, the formulation and the thickness of the adhesive layer were changed according to Tables 1 and 2. In addition, the solid content concentration and viscosity were adjusted with distilled water and aqueous ammonia.

[0139] Example 22 Using the water-dispersible adhesive composition of Example 1, an adhesive layer and an adhesive sheet were manufactured in the same manner as in Example 1. However, instead of a release film, a polyethylene terephthalate (PET) resin film (polymer film) (manufactured by Mitsubishi Chemical Corporation, trade name "K880-4.5W", 4.5 μm) was used. Furthermore, adhesive layers were formed on both sides of the polymer film.

[0140] Comparative Example 5 To 100 parts by mass of the acrylic polymer from Production Example 2, 20 parts by mass of YS Polystar S145 (tackifier), 2 parts by mass of Coronate L (isocyanate-based crosslinking agent), and 0.01 parts by mass of TETRAD-C (epoxy-based crosslinking agent) were added and stirred to prepare an adhesive composition.

[0141] Next, using the above adhesive composition, an adhesive layer and an adhesive sheet were manufactured in the same manner as in Example 1.

[0142] Comparative Examples 6 and 7 The adhesive layer was manufactured in the same manner as in Comparative Example 5. However, the thickness of the adhesive layer was changed according to Table 3. In addition, the solid content concentration and viscosity were adjusted with distilled water and aqueous ammonia.

[0143] Comparative Example 8 To 100 parts by mass of the acrylic polymer from Production Example 3, 30 parts by mass of Pencel D-125 (tackifier) ​​and 3 parts by mass of Coronate L (isocyanate-based crosslinking agent) were added and stirred to prepare an adhesive composition.

[0144] Next, using the above adhesive composition, an adhesive layer and an adhesive sheet were manufactured in the same manner as in Example 1.

[0145] Comparative Examples 9-12 The adhesive layer was prepared in the same manner as in Comparative Example 8. However, the thickness, solid content concentration, and viscosity of the adhesive layer were changed according to Table 3. The solid content concentration and viscosity were also adjusted using distilled water and aqueous ammonia.

[0146] Comparative Example 13 Using the water-dispersible adhesive composition of Comparative Example 8, an adhesive layer and an adhesive sheet were manufactured in the same manner as in Comparative Example 8. However, instead of a release film, a polyethylene terephthalate (PET) resin film (polymer film) (manufactured by Mitsubishi Chemical Corporation, trade name "K880-4.5W", 4.5 μm) was used. Adhesive layers were formed on both sides of the polymer film.

[0147] <Rating> [viscosity] The viscosity (Pa·s) of the water-dispersible adhesive compositions in each example and comparative example was measured using a Type B viscometer (Tokimec Co., Ltd.). The measurement temperature was 25°C, the No. 2 rotor speed was 20 rpm, and the measurement time was 1 minute. The results are shown in Tables 1 to 3.

[0148] [Transmission electron microscope] The adhesive layer of Example 1 was subjected to heavy metal staining, and then the cross-section of the sample was observed using TEM by ultrathin sectioning. For the TEM analysis, for example, a Hitachi TEM (model "H-7650") was used. The results are shown in Figure 4.

[0149] [Impact Resistance] The adhesive sheets of each example and comparative example were punched out in a 2mm wide, 24.5mm square frame shape to serve as evaluation samples. The evaluation samples were placed between a stainless steel plate (25mm square, 3mm thick) with a 20mm x 20mm hole in the center of a 2mm thick, 50mm x 50mm square, and a square stainless steel plate (25mm square, 3mm thick). They were then pressed together under uniform pressure from gravity (62N x 10 seconds), and left to stand at 80°C for 30 minutes. After that, the evaluation samples were removed and returned to 23°C.

[0150] Next, a cylindrical measuring platform measuring 50 mm in length, 49 mm in outer diameter, and 43 mm in inner diameter was placed on the base of a DuPont impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the evaluation sample was placed on top of it with a square stainless steel plate facing downwards.

[0151] Next, a stainless steel impact pin with a tip radius of 3.1 mm was placed on the evaluation sample, and the drop weight and drop height were varied in 50 mm increments from 50 mm to 500 mm with a 50 g weight, then in 50 mm increments from 50 mm to 500 mm with a 100 g weight, then in 50 mm increments from 350 mm to 500 mm with a 150 g weight, then in 50 mm increments from 400 mm to 500 mm with a 200 g weight, and then in 50 mm increments from 350 mm to 500 mm with a 300 g weight, so that the energy increased until peeling occurred. At this time, tests were not conducted for energy levels that had already been evaluated, and the load and height were set so that the amount of energy did not overlap. After that, the energy before peeling was calculated as load × height and the result was obtained. The results are shown in Tables 1 to 3.

[0152] Furthermore, impact resistance was evaluated based on the following criteria. ○: The energy before peeling exceeded 0.2 J. ×: The energy before peeling is 0.2J or less.

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3] [Explanation of Symbols]

[0156] 1. Adhesive layer 11 Base material

Claims

1. An adhesive layer consisting of a dried product of a water-dispersible adhesive composition, The aforementioned water-dispersible adhesive composition contains a water-dispersible polymer, water, polyacrylic acid, a leveling agent, and a tackifier. The polyacrylic acid content is 2.5 parts by mass or more and 7 parts by mass or less per 100 parts by mass of the water-dispersible polymer. The content of the leveling agent is 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the polyacrylic acid. The thickness is between 10 μm and 40 μm. The aforementioned water-dispersible polymer is a water-dispersible acrylic polymer. The adhesive layer contains 5 to 50 parts by mass of the tackifier, with a content of 5 to 50 parts by mass per 100 parts by mass of the water-dispersible polymer.

2. The adhesive layer according to claim 1, wherein the content of the leveling agent is 1 part by mass or more per 100 parts by mass of the water-dispersible polymer.

3. The adhesive layer according to claim 1 or 2, wherein the viscosity of the water-dispersible adhesive composition at 25°C is less than 1.5 Pa·s.

4. The base material and the adhesive layer according to any one of claims 1 to 3 are arranged sequentially toward one side in the thickness direction, An adhesive sheet in which the base material is a foam.

5. The base material and the adhesive layer according to any one of claims 1 to 3 are arranged sequentially toward one side in the thickness direction, An adhesive sheet in which the substrate is a polymer film.

Images