Adhesive sheet

Abstract

The present invention provides an adhesive sheet having both excellent reworkability and adhesive force despite having a single-layer structure. The adhesive sheet according to the present invention is used for bonding optical members to each other, and contains an acrylic polymer that contains at least one type of structural unit F selected from the group consisting of structural units having a hydroxyl group and structural units having an amide group, the structural units having at least one type of structural unit F being selected from the group consisting of structural units having a hydroxyl group and structural units having an amide group, and the structural units having at least one type of structural unit F being selected from the group consisting of structural units having a hydroxyl group and structural units having an amide group. The content of the structural unit F is 10% by mass or more, the stress relaxation value of the adhesive sheet when a load of 1 N is applied for 1 minute is 0.55 N / 25 mm or more, and the adhesive sheet has a single-layer structure.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet. Background Art

[0002] An adhesive sheet is used to bond various optical components such as a touch panel and a liquid crystal display (LCD), and is an indispensable material in manufacturing a display device or an input device. Such an adhesive sheet is known, for example, to be formed mainly of an acrylic polymer.

[0003] When using an adhesive sheet to bond optical components to each other, the following operation may be performed: after bonding two components to each other, in order to perform position adjustment or to remove inadvertently mixed foreign matter, the optical component is temporarily peeled off from the adhesive sheet and bonded again (so-called reprocessing operation). In such a case, if the adhesive sheet and the optical component are too strongly adhered, when the optical component is peeled off from the adhesive sheet, the adhesive sheet will be peeled off and remain on a part of the optical component. Therefore, the adhesive sheet is required to have the following property: it is easy to peel off immediately after bonding or after a certain period of time has passed since bonding. That is, in order to easily perform position adjustment between optical components, it is important for the adhesive sheet to have excellent peelability after bonding, that is, so-called reprocessability. On the other hand, it is also important to have the property of firmly bonding optical components to each other after position adjustment, that is, so-called adhesive strength.

[0004] In Patent Documents 1 to 3, an adhesive sheet with improved reprocessability is disclosed. For example, in Patent Document 1, a double-sided adhesive sheet including a rubber-based adhesive layer and an acrylic-based adhesive layer is disclosed. According to this double-sided adhesive sheet, it is said that excellent unevenness compliance, reprocessability, and low water vapor permeability can be completely achieved. Background Art Documents Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-155139 Summary of the Invention Problems to be Solved by the Invention

[0006] However, since the double-sided adhesive sheet disclosed in Patent Document 1 has a multilayer structure, compared with a double-sided adhesive sheet having a single-layer structure, there is a problem that the manufacture of the adhesive sheet is likely to become complicated. Further, in recent years, since devices using optical components have become more miniaturized and sophisticated, there is sometimes a demand for a double-sided adhesive sheet to have higher reprocessability and adhesive strength than in the past. From this viewpoint, it is urgently necessary to develop an adhesive sheet having excellent reprocessability and adhesive strength although it has a single-layer structure.

[0007] The present invention has been completed in view of the above circumstances, and an object thereof is to provide an adhesive sheet that has excellent reworkability and adhesiveness despite being a single-layer structure. Means for Solving the Problem

[0008] The inventors of the present invention repeatedly conducted research to achieve the above object, and as a result, found that the above object can be achieved by forming an acrylic polymer having a specific structure and adjusting the stress relaxation value within a specified range, and finally completed the present invention.

[0009] That is, the present invention includes, for example, the subjects described in the following items. Item 1 An adhesive sheet for bonding optical members to each other, The adhesive sheet contains an acrylic polymer, The acrylic polymer contains at least one structural unit F selected from the group consisting of a structural unit having a hydroxyl group and a structural unit having an amide group, In the acrylic polymer, the structural unit F contains 10% by mass or more, When a load of 1 N is applied to the adhesive sheet for 1 minute, the stress relaxation value is 0.55 N or more, and it has a single-layer structure. Item 2 The adhesive sheet according to Item 1, wherein the adhesive force to glass is 10 N / 25 mm or more. Item 3 The adhesive sheet according to Item 1 or 2, which is used for an image display device. Advantages of the Invention

[0010] The adhesive sheet of the present invention has excellent reworkability and adhesiveness despite being a single-layer structure. Detailed Description of the Invention Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. Furthermore, in this specification, the expressions "containing" and "comprising" include the concepts of "containing", "comprising", "substantially consisting of", and "consisting only of".

[0012] The adhesive sheet of the present invention is used for bonding optical members to each other. The adhesive sheet contains an acrylic polymer, has a stress relaxation value of 0.55 N or more when a load of 1 N is applied for 1 minute, and has a single-layer structure. In particular, in the adhesive sheet of the present invention, the acrylic polymer contains at least one structural unit F selected from the group consisting of a structural unit having a hydroxyl group and a structural unit having an amide group, and in the acrylic polymer, the structural unit F contains 10% by mass or more.

[0013] Since the pressure-sensitive adhesive sheet of the present invention contains a specific acrylic polymer and has a specified stress relaxation value, it has excellent reprocessability and adhesiveness despite being a single-layer structure. Therefore, the pressure-sensitive adhesive sheet of the present invention is suitable for use in bonding optical members to each other.

[0014] (Acrylic polymer) The pressure-sensitive adhesive sheet of the present invention may contain an acrylic polymer as a main component. As described above, in this acrylic polymer, at least one structural unit F selected from the group consisting of a structural unit having a hydroxyl group and a structural unit having an amide group is contained in an amount of 10% by mass or more based on the total mass of the acrylic polymer.

[0015] The acrylic polymer is, for example, a polymer composed of (meth)acrylic monomer units. The acrylic polymer contained in the pressure-sensitive adhesive sheet of the present invention may also form a crosslinked product described later. That is, the acrylic polymer contained in the pressure-sensitive adhesive sheet of the present invention may also be a crosslinked product of an acrylic polymer. As described later, this crosslinked product can be formed by the reaction of an acrylic polymer (more specifically, a crosslinkable acrylic polymer) and a crosslinking agent, or can also be formed by a polyfunctional monomer.

[0016] In this specification, "(meth)acrylic acid" means "acrylic acid" or "methacrylic acid", "(meth)acrylate" means "acrylate" or "methacrylate", and "(meth)allyl" means "allyl" or "methallyl".

[0017] The type of the acrylic polymer is not particularly limited as long as it has a specified amount of the structural unit F. For example, in addition to the structural unit F, the acrylic polymer may also contain a (meth)acrylate unit. Therefore, examples of the acrylic polymer include a polymer containing at least a (meth)acrylate unit and the aforementioned structural unit F other than the (meth)acrylate. Here, the (meth)acrylate unit means a structural unit formed by polymerization of a (meth)acrylate monomer. However, the (meth)acrylate unit does not include the aforementioned structural unit F.

[0018] Examples of the (meth)acrylate include: (meth)acrylates having a linear, branched, or cyclic alkyl group, or (meth)acrylates having an aromatic ring. When the (meth)acrylate has a linear, branched, or cyclic alkyl group, the number of carbon atoms thereof may be, for example, 1 to 20, preferably 1 to 10. When the (meth)acrylate has an aromatic ring, the number of carbon atoms thereof may be, for example, 5 to 20, preferably 6 to 10. Specific examples of the (meth)acrylate monomer include: methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isopropyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and the like.

[0019] Among them, the (meth)acrylate is preferably an alkyl (meth)acrylate and / or a cycloalkyl (meth)acrylate. Specifically, examples include one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isopropyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. In this case, an adhesive sheet having a relatively high adhesive strength and excellent reprocessability can be easily obtained. In terms of the stress relaxation value being easily 0.55 N or more when a load of 1 N is applied for 1 minute as described later, the alkyl (meth)acrylate in which the alkyl group directly connected to the ester bond in the (meth)acrylate has 2 to 10 carbon atoms is preferred, the alkyl (meth)acrylate having 3 to 9 carbon atoms is more preferred, and the alkyl (meth)acrylate having 3 to 8 carbon atoms is even more preferred.

[0020] The (meth)acrylate unit contained in the acrylic polymer may be a single type, or may be two or more types. The (meth)acrylate unit contained in the acrylic polymer may also contain two or more of a (meth)acrylate having a linear alkyl group, a (meth)acrylate having a branched chain, and a (meth)acrylate having a cyclic alkyl group.

[0021] On the other hand, as described above, the aforementioned structural unit F contained in the acrylic polymer is at least one selected from the group consisting of a structural unit having a hydroxyl group and a structural unit having an amide group.

[0022] Examples of the structural unit having a hydroxyl group include a (meth)acrylate unit having a hydroxyl group. The (meth)acrylate unit having a hydroxyl group refers to a structural unit formed by polymerization of a (meth)acrylic acid monomer containing a hydroxyl group.

[0023] A structural unit having an amide group, for example, a (meth)acrylic unit having an amide group can be cited. The (meth)acrylic unit having an amide group refers to a structural unit formed after polymerization of a (meth)acrylic monomer containing an amide group.

[0024] Regarding the aforementioned (meth)acrylic monomer containing a hydroxyl group, (meth)acrylic monomers having one or more hydroxyl groups in the molecule can be widely cited. For example, they can include: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2,2-dimethyl-2-hydroxyethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and other (meth)acrylic hydroxyalkyl esters.

[0025] Among them, the (meth)acrylic monomer containing a hydroxyl group is preferably one or more selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. In this case, it is easy to obtain an adhesive sheet that has an excellent reprocessability and adhesiveness despite being a single-layer structure.

[0026] The (meth)acrylic ester unit having a hydroxyl group as the structural unit F contained in the acrylic polymer can be a single type, or can also be two or more types.

[0027] Regarding the aforementioned (meth)acrylic monomer containing an amide group, (meth)acrylic monomers having one or more amide groups in the molecule can be widely cited. For example, they can include: (meth)acrylamide, (meth)acrylamide derivatives, and (meth)acrylic esters containing an amide group. Regarding (meth)acrylamide derivatives, they can include: N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N,N-diethylaminopropylmethacrylamide, etc. Regarding (meth)acrylic esters containing an amide group, they can include: N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate, etc.

[0028] In terms of easily obtaining an adhesive sheet having an excellent reprocessability and adhesiveness despite being a single-layer structure, the (meth)acrylic monomer containing an amide group is preferably (meth)acrylamide and its derivatives, and (meth)acrylate containing an amide group. More preferably, it is at least one selected from the group consisting of (meth)acrylamide derivatives and (meth)acrylate containing an amide group. Even more preferably, it is at least one selected from the group consisting of N,N-dimethylacrylamide, N,N-dimethylaminoethyl acrylate, and N,N-diethylaminoethyl acrylate. Particularly preferably, it is N,N-dimethylacrylamide.

[0029] The (meth)acrylic acid unit having an amide group as the structural unit F contained in the acrylic polymer may be a single type, or may be two or more types.

[0030] The structural unit F may also have both a hydroxyl group and an amide group in one structural unit. Examples of the structural unit F having both a hydroxyl group and an amide group in one structural unit include structural units formed from monomers such as N-hydroxypropyl (meth)acrylamide and the like by hydroxyalkyl (meth)acrylamide and the like.

[0031] The structural unit F contained in the acrylic polymer may be a single type, or may be two or more types. Further, the acrylic polymer may also contain both the structural unit F having a hydroxyl group and the structural unit F having an amide group.

[0032] The structural unit F contained in the acrylic polymer can react with a crosslinking agent described later, and thereby a crosslinked product of the acrylic polymer can also be formed. The reason is that the hydroxyl group or amide group in the structural unit F can react with the crosslinking agent. Therefore, the acrylic polymer containing the structural unit F is a crosslinkable acrylic polymer (crosslinkable acrylic polymer).

[0033] The acrylic polymer may also have other monomer units other than the aforementioned (meth)acrylate unit and the aforementioned structural unit F.

[0034] Regarding the monomer for forming other monomer units, (meth)acrylic monomers having a carboxyl group, an amino group, an epoxy group, a thiol group, an isocyanate group, etc. can be cited. Regarding this monomer, for example, (meth)acrylic acid can be cited. The other monomer units contained in the acrylic polymer may be a single type, or may be two or more types.

[0035] In the acrylic polymer, the total content ratio of the aforementioned structural unit F is 10% by mass or more relative to the total mass of the aforementioned acrylic polymer. Thereby, the adhesive sheet of the present invention can be a single-layer structure and also have excellent reprocessability and adhesiveness.

[0036] The total content ratio of the aforementioned structural unit F may also be 12% by mass or more, preferably 15% by mass or more, more preferably 18% by mass or more, still more preferably 20% by mass or more, and particularly preferably 25% by mass or more, based on the total mass of the aforementioned acrylic polymer. Further, the upper limit of the total content ratio of the aforementioned structural unit F is not particularly limited. For example, based on the total mass of the aforementioned acrylic polymer, it is preferably 80% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less, and particularly preferably 40% by mass or less. Moreover, when the acrylic polymer contains two types of structural units F, namely a structural unit F having a hydroxyl group and a structural unit F having an amide group, the ratio of the two can be set within any range.

[0037] The acrylic polymer preferably contains 50% by mass or more of the aforementioned (meth)acrylate unit and the aforementioned structural unit F, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The acrylic polymer may also be composed only of the aforementioned (meth)acrylate unit and the aforementioned structural unit F.

[0038] The acrylic polymer can be produced, for example, by polymerizing a monomer mixture for forming each structural unit by a known polymerization method. Regarding this polymerization method, for example, solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. can be adopted. Moreover, the ratio of each structural unit in the acrylic polymer corresponds to the usage ratio of each monomer used during polymerization.

[0039] When polymerizing the acrylic polymer, a solvent can be used as needed. The type of the solvent is not particularly limited. For example, known organic solvents for polymerization can be widely used. For example, it can include: ester compounds such as ethyl acetate and butyl acetate; ketones such as acetone and methyl ethyl ketone; hydrocarbons such as hexane; aromatic compounds such as toluene, xylene, and benzene. The usage amount of the solvent used in the aforementioned polymerization reaction is not particularly limited.

[0040] When polymerizing the acrylic polymer, a polymerization initiator, a chain transfer agent, a polymerization accelerator, etc. can also be used. Regarding the polymerization initiator, for example, known polymerization initiators used in general polymerization can be widely used. Regarding the polymerization initiator, for example, it can include: azobisisobutyronitrile, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 1,1'-azobis(cyclohexanecarbonitrile), di-tert-butyl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, ammonium persulfate, photoinitiators (Irgacure or Omnirad (registered trademark) series, etc.). The usage amount of the polymerization initiator is not particularly limited. For example, it can be appropriately adjusted according to the target molecular weight.

[0041] The polymerization time and temperature of the acrylic polymer are not limited either, and can be appropriately set according to the type, amount used, and polymerization reactivity of the monomers used. For example, the polymerization reaction can be carried out under the conditions of 20 to 100 °C for 1 to 24 hours. The polymerization can be appropriately carried out in an inert gas environment such as nitrogen.

[0042] The weight-average molecular weight of the acrylic polymer is not particularly limited. However, for example, from the viewpoint of not easily reducing the adhesive strength in the adhesive sheet, it can be set to 100,000 to 2,000,000, preferably 200,000 to 1,000,000.

[0043] Furthermore, the weight-average molecular weight referred to in the present invention is the weight-average molecular weight converted to polystyrene measured by gel permeation chromatography (GPC) method. The GPC apparatus used in the GPC method is not particularly limited, and a commercially available GPC measuring machine can be used. For example, the LC-2000Plus series manufactured by JASCO Corporation, RI-2031Plus, UV-2075Plus, etc. as detectors. At this time, for example, a GPC column formed by connecting four of "Shodex KF801", "Shodex KF803L", "Shodex KF800L", and "Shodex KF800D" manufactured by Showa Denko K.K. can be used. The column temperature can be set to 40 °C. Tetrahydrofuran can be used as the eluent, and the measurement can be carried out at a flow rate of 1.0 ml / min. Usually, a calibration curve can be made using standard polystyrene, and the weight-average molecular weight (Mw) can be obtained by converting to polystyrene.

[0044] The acrylic polymer can be a random copolymer, or can also have other structures such as block polymers.

[0045] (Adhesive sheet) The adhesive sheet of the present invention can be manufactured, for example, from an adhesive composition containing the aforementioned acrylic polymer.

[0046] In addition to containing the aforementioned acrylic polymer, the adhesive composition can also contain, for example, a crosslinking agent, a silane coupling agent, a monofunctional monomer, a polyfunctional monomer, a photoinitiator, a solvent, etc.

[0047] The crosslinking agent can be widely exemplified by components that can cause crosslinking of the acrylic polymer. In particular, the crosslinking agent can be widely exemplified by components that can react with hydroxyl groups, carboxyl groups, amino groups, etc. in the acrylic polymer. The crosslinking agent can be widely exemplified by known crosslinking agents, and isocyanate crosslinking agents, epoxy crosslinking agents, etc. can be cited.

[0048] The types of isocyanate crosslinking agents are not particularly limited, and known compounds can be widely used. Examples of isocyanate crosslinking agents include: polymethylene polyphenyl isocyanate such as tolylene diisocyanate, chlorotolylene diisocyanate, diphenylmethane diisocyanate, butylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate. The isocyanate crosslinking agent can be used alone or in combination of two or more different ones. Moreover, it is preferably to use trifunctional derivatives such as adducts, allophanate bodies, biuret bodies obtained from the above-mentioned diisocyanates as the isocyanate crosslinking agent.

[0049] The types of epoxy crosslinking agents are not particularly limited, and known compounds can be widely used. Examples of epoxy crosslinking agents include: ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl) cyclohexanone, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, etc.

[0050] Silane coupling agents can be widely used as known compounds, for example. Examples of silane coupling agents include: γ-acryloyloxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyl dialkoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrialkoxysilane, γ-methacryloyloxypropyltrialkoxysilane, γ-chloropropyltrialkoxysilane, γ-methacryloyloxypropyl dialkoxysilane, γ-mercaptopropyltrialkoxysilane, vinyltrialkoxysilane, etc. The silane coupling agent can also be an oligomer of other various alkoxysiloxanes. These silane coupling agents can all be obtained from commercially available products.

[0051] The type of the monofunctional monomer is not particularly limited. For example, monomers the same as the monomer units constituting the acrylic polymer can be cited. The monofunctional monomer preferably includes all monomers (usually a mixture) used to form the monomer units constituting the (meth)acrylic polymer. The monofunctional monomer contained in the adhesive composition is preferably a mixed monomer, and the ratio of the mixed monomer to each monomer constituting the acrylic polymer contained in the adhesive composition is the same. When the adhesive composition contains a monofunctional monomer, a solution (so-called syrup) in which the acrylic polymer is dissolved in the monofunctional monomer can be formed.

[0052] Examples of the polyfunctional monomer include compounds having two or more polymerizable double bonds in the molecule. Among the polyfunctional monomers, the number of polymerizable double bonds is two or more, preferably two or more and less than five, and more preferably two or more and less than four.

[0053] Regarding the polyfunctional monomer, for example, in the case of a difunctional monomer (a monomer having two polymerizable double bonds), examples include: polyethylene glycol diacrylate, polypropylene glycol diacrylate, alkyl diacrylate, polytetramethylene glycol diacrylate, polypropylene glycol diacrylate, dioxane diacrylate, tricyclodecanol diacrylate, fluorene diacrylate. Further, regarding the polyfunctional monomer, in the case of monomers having three or more functional groups, examples include: alkoxylated trimethylolpropane triacrylate, alkoxylated glycerol triacrylate, caprolactone-modified isocyanurate triacrylate, neopentyl glycol acrylate, alkoxylated neopentyl glycol acrylate, (alkoxylated) neopentyl glycol acrylate, (alkoxylated) di-trimethylolpropane acrylate, (alkoxylated) di-neopentyl glycol acrylate, (ethoxylated) polyglycerol acrylate, etc.

[0054] The polyfunctional monomer is preferably a polyfunctional monomer having an alkylene glycol group in one molecule. At this time, the number of alkylene glycol groups in one molecule is preferably 1 to 20. Regarding such a polyfunctional monomer, for example, polyethylene glycol diacrylate, propylene oxide-modified trimethylolpropane triacrylate, etc. can be cited.

[0055] Commercially available products can be used as the polyfunctional monomer. Regarding commercially available products, examples include: "A-200" (polyethylene glycol #200 diacrylate), "A-400" (polyethylene glycol #400 diacrylate) of the NK ester series which are difunctional polyethylene glycol acrylates manufactured by Shin-Nakamura Chemical Co., Ltd., trifunctional monomer M310 (propylene oxide-modified trimethylolpropane triacrylate) or trifunctional monomer M321 (propylene oxide-modified trimethylolpropane triacrylate) manufactured by Toagosei Co., Ltd., difunctional monomer M211B (bisphenol A EO-modified diacrylate) manufactured by Toagosei Co., Ltd., etc.

[0056] The polyfunctional monomer may also have a bisphenol skeleton in one molecule. By using a polyfunctional monomer having a bisphenol skeleton in one molecule, the hardness of the adhesive sheet can be more effectively increased, and the processability of the adhesive sheet can be easily improved. Examples of such polyfunctional monomers include: diacrylate of bisphenol A diglycidyl ether, diacrylate of propoxylated bisphenol A, diacrylate of bisphenol F diglycidyl ether, and the like.

[0057] When the adhesive composition contains a polyfunctional monomer, the adhesive composition is cured by UV irradiation, and the acrylic polymer can form a crosslinked structure, whereby the adhesive sheet can easily have excellent adhesiveness.

[0058] As the photoinitiator, for example, well-known photoinitiators can be widely used, and among them, acetophenone-based photoinitiators or acylphosphine oxide-based photoinitiators are preferably used.

[0059] Specific examples of acetophenone-based initiators include: diethoxyacetophenone, benzyl dimethyl ketal, oligomer(2-hydroxy-2-methyl-1-[4-(1-methylethenyl)phenyl]propanone), 2,2-dimethoxy-2-phenylacetophenone, (1-hydroxycyclohexyl-phenone, 2-hydroxy-2-methyl-1-phenylpropanone, and the like. Specific examples of benzoin ether-based initiators include: benzoin, benzoin methyl ether, and the like.

[0060] Specific examples of acylphosphine oxide-based initiators include: phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and the like.

[0061] In addition, examples of photoinitiators also include: benzoin ether-based initiators, benzophenone-based initiators, hydroxyalkyl phenyl ketone-based initiators, thioxanthone-based initiators, amine-based initiators, and the like.

[0062] The adhesive composition for manufacturing the adhesive sheet contains at least an acrylic polymer, and may further contain at least one selected from the group consisting of a crosslinking agent, a silane coupling agent, a monofunctional monomer, a polyfunctional monomer, a photoinitiator, a solvent, and various other additives as needed. In one aspect of the adhesive composition, it may contain at least an acrylic polymer and a crosslinking agent, and contain a solvent and / or a silane coupling agent as needed. This aspect of the adhesive composition may not contain a monofunctional monomer, a polyfunctional monomer, or a photoinitiator. In another aspect of the adhesive composition, it may contain at least an acrylic polymer, a monofunctional monomer and / or a polyfunctional monomer, and a photoinitiator. In this aspect, a crosslinking agent may or may not be contained. In yet another aspect of the adhesive composition, for example, it may contain at least the aforementioned slurry (monofunctional monomer solution of acrylic polymer) and a photoinitiator.

[0063] When the adhesive composition contains a crosslinking agent, its content ratio is not particularly limited. For example, 0.01 to 5 parts by mass, preferably 0.05 to 1 part by mass, can be used relative to 100 parts by mass of the acrylic polymer. When the adhesive composition contains a crosslinking agent, one type of crosslinking agent can be used alone or two or more types can be used in combination.

[0064] When the adhesive composition contains a silane coupling agent, the content ratio of the silane coupling agent can be 0.1 to 5 parts by mass relative to 100 parts by mass of the aforementioned (meth)acrylic polymer. When the adhesive composition contains a crosslinking agent, one type of silane coupling agent can be used alone or two or more types can be used in combination.

[0065] When the adhesive composition contains a polyfunctional monomer, its content ratio is not particularly limited. For example, 0.01 to 20 parts by mass, preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, can be used relative to 100 parts by mass of the acrylic polymer. When the adhesive composition contains a polyfunctional monomer, one type of polyfunctional monomer can be used alone or two or more types can be used in combination.

[0066] When the adhesive composition contains a photoinitiator, its content ratio is not particularly limited. For example, 0.05 to 10 parts by mass, preferably 0.1 to 5 parts by mass, can be used relative to 100 parts by mass of the acrylic polymer. One type of photoinitiator can be used alone or two or more types can be used in combination.

[0067] When the adhesive composition contains a monofunctional monomer, its content ratio is not particularly limited. For example, per 100 parts by mass of the total mass of the aforementioned acrylic polymer and the monofunctional monomer, the monofunctional monomer can be 3 to 1000 parts by mass, preferably 5 to 700 parts by mass, more preferably 25 to 500 parts by mass, and particularly preferably 30 to 400 parts by mass.

[0068] When the adhesive composition contains a solvent, its content is not particularly limited. For example, its content can be 25 to 500 parts by mass, preferably 30 to 400 parts by mass, relative to 100 parts by mass of the acrylic polymer. Also, the content of the solvent is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, relative to the total mass of the adhesive composition. One type of solvent can be used alone or two or more types can be used in combination. When two or more types are used in combination, the total mass should be within the above range. Furthermore, when the adhesive composition contains a solvent, the coating property is good.

[0069] Within the range that does not impair the effects of the present invention, the adhesive composition can contain various additives for adhesives other than those described above. Regarding such additives, for example, they can be selected as needed from plasticizers, antioxidants, metal antiseptics, adhesion imparting agents, ultraviolet absorbers, light stabilizers such as hindered amine compounds, etc. Also, dyes or pigments can be added for coloring purposes.

[0070] The method for preparing the adhesive composition is not particularly limited. For example, the adhesive composition can be prepared by mixing a pre-synthesized acrylic polymer and components contained as needed in a specified ratio.

[0071] By using the above-mentioned adhesive composition, the adhesive sheet of the present invention can be manufactured. The method for manufacturing the adhesive sheet using the adhesive composition is not particularly limited. For example, the adhesive composition can be cured by a known method to form an adhesive layer, and the adhesive layer is obtained as the adhesive sheet. The adhesive layer is a cured product of the adhesive composition.

[0072] Specifically, the adhesive layer can be formed by a method including a step of coating the adhesive composition on a substrate to form a coating film and a step of heat-treating the coating film. Alternatively, the adhesive layer formed by curing the adhesive composition can be formed by a method including a step of coating the adhesive composition on a substrate to form a coating film and a step of irradiating the coating film with active energy rays. The coating of the adhesive composition can be carried out using a known coating device. Examples of the coating device include a doctor blade coater, an air knife coater, a roll coater, a bar coater, an intaglio coater, a micro intaglio coater, a rod doctor blade coater, a die coater, a die coater, a curtain coater, etc.

[0073] When coating the adhesive composition, the substrate used is not particularly limited. For example, the adhesive composition can be coated on various substrates such as a resin substrate and a glass substrate. When the substrate has a release sheet described later, the adhesive composition can also be coated on the release sheet. Further, the adhesive composition can also be directly coated on a member to be adhered. The thickness after coating the adhesive composition is not particularly limited and can be appropriately set according to the thickness of the target adhesive layer.

[0074] The step of heat-treating the coating film can adopt, for example, the same steps as known methods. By this heat treatment, the adhesive composition is cured and volatile components disappear, becoming a cured product. For example, when the adhesive composition contains the aforementioned crosslinking agent, the reaction between the acrylic polymer and the crosslinking agent also occurs, forming a crosslinked product of the acrylic polymer. Thereby, the strength of the adhesive layer can be increased, and the adhesive force can also be increased.

[0075] In the step of heat-treating the coating film, the heating temperature can be set to, for example, 50°C or higher and 150°C or lower, and the heating time can be appropriately set according to the heating temperature or the residual solvent concentration of the target adhesive layer. For example, it can be set to 1 to 30 minutes. This heat treatment can be carried out using a known heating device such as a heating furnace and an infrared lamp. After the heat treatment, the cured product can be aged in a specified environment as needed.

[0076] The step of irradiating the coating film with active energy rays can be carried out, for example, in the same manner as known methods. By this step, for example, the photo-polymerizable components in the adhesive composition are cured to form a cured product. For example, when the adhesive composition contains the aforementioned monofunctional monomer, the aforementioned polyfunctional monomer and a photoinitiator, the polymerization reaction of the polyfunctional monomer and the monofunctional monomer also occurs. Thereby, the strength of the adhesive layer can be increased, and the adhesive force can also be increased. Regarding the active energy rays, examples include ultraviolet rays, electron beams, visible light, X-rays, ion beams, etc., which can be appropriately selected according to the photoinitiator contained in the adhesive layer. Among them, in terms of versatility, ultraviolet rays or electron beams are preferable, and ultraviolet rays are particularly preferable. Regarding the light source of ultraviolet rays, for example, chemical lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, carbon arc lamps, xenon arc lamps, electrodeless ultraviolet lamps, etc. can be used. The irradiation output of ultraviolet rays is preferably such that the cumulative light amount is 100 to 10,000 mJ / cm 2 , preferably the cumulative light amount is 200 to 5,000 mJ / cm 2 .

[0077] The adhesive layer formed as described above can be obtained as the adhesive sheet of the present invention. The thickness of the adhesive sheet can be appropriately set according to the use and is not particularly limited. For example, it is preferably 10 to 1,000 μm, more preferably 20 to 500 μm, and still more preferably 100 to 400 μm. Furthermore, in order to adjust the thickness of the adhesive layer (adhesive sheet), the same type of adhesive composition can also be coated in multiple layers (that is, after forming a coating film of the adhesive composition, the adhesive composition is further coated on this coating film to laminate the coating films). The adhesive sheet formed in this way is also a single-layer structure as described later.

[0078] The adhesive sheet of the present invention is formed of a single-layer structure. That is, the adhesive layer formed from the aforementioned adhesive composition is a single layer. Since the adhesive sheet is formed of a single-layer structure, the manufacture of the adhesive sheet becomes easy, and the bonding of optical members also becomes easy. Also, since the adhesive sheet has a single-layer structure, the reprocessing property immediately after bonding is improved, and the adhesive force after bonding the optical members is also easily maintained. Furthermore, just in case, the so-called single-layer structure means a structure in which the adhesive sheet is formed of one layer, and a structure in which two or more different types of layers are laminated is not included in the single-layer structure. However, only a laminate of two or more identical types of layers can be included in the single-layer structure. Therefore, the so-called single-layer structure means a structure formed of only one single type of layer or a structure formed by laminating two or more single types of layers. From this viewpoint, the adhesive sheet obtained by overlapping and coating the same type of adhesive composition as described above has a single-layer structure.

[0079] The adhesive sheet of the present invention has a stress relaxation value of 0.55 N or more when a load of 1 N is applied for 1 minute. Thereby, the adhesive sheet of the present invention can have excellent reprocessability. The stress relaxation value of the adhesive sheet of the present invention when a load of 1 N is applied for 1 minute is preferably 0.58 N or more, more preferably 0.60 N or more, and still more preferably 0.62 N or more. Also, for example, in terms of the fact that the adhesion between optical members after performing the reprocessing operation is easily improved, the upper limit of the stress relaxation value of the adhesive sheet of the present invention when a load of 1 N is applied for 1 minute is preferably 0.90 N or less.

[0080] Here, the aforementioned stress relaxation value of the adhesive sheet of the present invention is a value measured by the following method. The adhesive sheet with a thickness of 200 μm is cut into a width of 60 mm and evenly rolled along a direction perpendicular to the width direction to form a cylindrical shape, thereby obtaining a measurement sample. When producing the cylindrical sample, the length of the adhesive sheet is appropriately adjusted in advance so that the area of the circular cross-section becomes 5 mm 2 . The distance between the chucks is set to 3 mm, and the obtained cylindrical sample is fixed and stretched at 300 mm / min. After maintaining this state for 1 minute at the time point when the load reaches 1 N, the stress value of the adhesive sheet is measured. This measured value is set as the "stress relaxation value when a load of 1 N is applied for 1 minute". This stress relaxation value can be measured using the RTC-1210 (TENSILON universal material testing machine) of ORIENTIC Co., Ltd.

[0081] The method for adjusting the stress relaxation value of the adhesive sheet is not particularly limited. For example, the stress relaxation value of the adhesive sheet can be adjusted by appropriately selecting the type of acrylic polymer, the weight average molecular weight, etc. Specifically, the stress relaxation value of the adhesive sheet can be adjusted by appropriately selecting the type of (meth)acrylic monomer used to form the acrylic polymer. In particular, after setting the content ratio of the aforementioned structural unit F in the aforementioned acrylic polymer to 10% by mass or more, when appropriately selecting other monomer types (such as the types of the aforementioned (meth)acrylate), it is easy to adjust the stress relaxation value of the adhesive sheet within the above range.

[0082] The glass adhesion of the adhesive sheet of the present invention is 10 N / 25 mm or more. Thereby, the adhesive sheet of the present invention can bond optical members to each other with high adhesion. That is, the adhesive sheet of the present invention has excellent reprocessability and is not likely to cause peeling or position deviation between optical members after bonding. The glass adhesion of the adhesive sheet of the present invention is preferably 20 N / 25 mm or more, more preferably 25 N / 25 mm or more, and still more preferably 30 N / 25 mm or more. Also, the upper limit of the glass adhesion of the adhesive sheet of the present invention is not particularly limited. For example, it is preferably 50 N / 25 mm or less.

[0083] The adhesive force of the adhesive sheet to glass is the value measured by the following method. One adhesive surface of the adhesive sheet is adhered to a 100-μm-thick polyester film (A4300 manufactured by Toyobo Co., Ltd.) that has been subjected to easy adhesion treatment, and cut so that the bonding portion to the adherend (float glass described later) has a width of 25 mm and a length of 80 mm to obtain a measurement sample. The other adhesive surface of this sample is adhered to a 1-mm-thick, 115-mm-wide, and 75-mm-long float glass with a width of 25 mm and a length of 50 mm, and then pressed with a 2-kg roller reciprocally 2 times. Then, after treating in an autoclave for 30 minutes in an environment of a temperature of 30°C and a pressure of 0.5 MPa, it is left standing for 1 day in an environment of atmospheric pressure, a temperature of 23°C, and a humidity of 50%. Next, using Shimadzu Corporation's AGX-500NX, while holding the non-adhered portion of the adhesive sheet, the sample including the adherend is stretched in the 180°C direction at a stretching speed of 300 mm / min, and the adhesive force is measured. The value obtained by the above measurement is used as the adhesive force of the adhesive sheet to glass.

[0084] The adhesive sheet of the present invention can be suitably used as an adhesive for bonding optical members to each other, and is particularly suitable for use in image display devices. The types of optical members are not particularly limited, and for example, the adhesive sheet of the present invention can be widely applied to known optical members.

[0085] Regarding optical members, examples include each constituent member in optical products such as touch panels or image display devices. Regarding the constituent members of a touch panel, for example, an ITO film provided with an ITO film on a transparent resin film, ITO glass provided with an ITO film on the surface of a glass plate, a transparent conductive film coated with a conductive polymer on a transparent resin film, a hard coat film, a fingerprint-resistant film, etc. can be listed. Regarding the constituent members of an image display device, for example, an antireflection film, an alignment film, a polarizing film, a retardation film, a brightness enhancement film, etc. for a liquid crystal display device can be listed. Further, the adhesive sheet of the present invention can also be used for bonding between modules such as a liquid crystal module and a touch panel module. Optical members can be formed of materials such as glass, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyimide, and acetylated cellulose.

[0086] Regarding the aforementioned optical members, a touch panel can be suitably used. When bonding a touch panel using the adhesive sheet of the present invention, reprocessing can be easily performed even in the case of reprocessing operations. Therefore, when bonding optical members to each other using the adhesive sheet of the present invention, at least one of the aforementioned optical members can be a touch panel.

[0087] The pressure-sensitive adhesive sheet of the present invention can also be a pressure-sensitive adhesive sheet having a base material such as a release sheet on one or both sides. Examples of the release sheet include a releasable laminated sheet having a base material for the release sheet and a release agent layer provided on one side of the base material for the release sheet, or a polyolefin film such as a polyethylene film or a polypropylene film as a low-polarity base material. As the base material for the release sheet in the releasable laminated sheet, paper or a polymer film can be used. As the release agent constituting the release agent layer, for example, a general addition-type or condensation-type polysiloxane-based release agent or a compound containing a long-chain alkyl group can be used. As for the releasable laminated sheet, commercially available products can also be used. For example, a heavy release film made of a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films, or a light release film made of a release-treated polyethylene terephthalate film manufactured by Teijin DuPont Films can be cited.

[0088] When the pressure-sensitive adhesive sheet of the present invention has a base material on one or both sides, the base material is not particularly limited. For example, known base materials that can be used for optical pressure-sensitive adhesive sheets can be widely used. For example, various transparent base materials can be cited. As the transparent base material, general films used in the optical field such as a polyethylene terephthalate film, an acrylic film, a polycarbonate film, a triacetyl cellulose film, and a cycloolefin polymer film can be used. Further, an easy-adhesion layer can be provided on the adhesive layer side of these transparent base materials. Furthermore, functional layers such as a hard coat layer, an antireflection layer, an antifouling layer, and an ultraviolet absorption layer can be provided on the surface of the transparent base material opposite to the adhesive layer.

[0089] When specifying the inventions included in this disclosure, the respective components (properties, structures, functions, etc.) described in each embodiment of this disclosure can be combined in any manner. That is, this disclosure includes all the subject matters constituted by all the combinations of the respective components that can be combined as described in this specification. Examples

[0090] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the modes of these examples.

[0091] Solvent system (Production Example 1) In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 100 parts by mass of a mixed monomer having a mass ratio of 2-ethylhexyl acrylate (2EHA), 4-hydroxybutyl acrylate (4HBA), and N,N-dimethylacrylamide (DMAA) of 74:20:6 was polymerized by heating to 65°C in 77 parts by mass of ethyl acetate as a polymerization solvent in the presence of 0.1 part by mass of ABVN (azobisvaleronitrile). Thereby, an acrylic polymer having a weight average molecular weight of 300,000 was obtained.

[0092] (Production Example 2) An acrylic polymer with a weight-average molecular weight of 400,000 was obtained in the same manner as in Production Example 1, except that the mixed monomer was changed to a mixed monomer of butyl acrylate (BA) and 4HBA with a mass ratio of 70:30.

[0093] (Production Example 3) An acrylic polymer with a weight-average molecular weight of 400,000 was obtained in the same manner as in Production Example 1, except that the mixed monomer was changed to a mixed monomer of 2-ethylhexyl acrylate (2EHA), 2-ethylhexyl methacrylate (2EHMA), and 2-hydroxyethyl methacrylate (2HEMA) with a mass ratio of 20:70:10.

[0094] (Example 1) In 100 parts by mass (in terms of solid content) of the acrylic polymer obtained in Production Example 1, 0.3 part by mass of "D-110N" from Mitsui Chemicals, Inc. as a crosslinking agent, 3 parts by mass of "ATM-4PL" from Shin-Nakamura Chemical Co., Ltd. as a polyfunctional monomer, and 0.4 part by mass of "Omnirad184" from IGM RESINS B.V. as a photoinitiator were included in the raw materials. Ethyl acetate was added to make the concentration of the raw materials 46% by mass, and stirring was carried out to prepare Adhesive Composition 1. This Adhesive Composition 1 was uniformly coated on the surface of a polyethylene terephthalate film (First Release Sheet, manufactured by Toyobo, A7100) having a release agent layer treated with a silicone-based release agent using a spreader, and dried at 90°C for 3 minutes to form a 67-μm First Coating Film. On the First Coating Film, the aforementioned Adhesive Composition was further uniformly coated, and a 67-μm Second Coating Film was laminated. Then, on the Second Coating Film, the aforementioned Adhesive Composition was further uniformly coated, and a 67-μm Third Coating Film was laminated to form a coating film with a thickness of 200 μm. Using an air-circulation type constant-temperature oven, a pressure-sensitive adhesive sheet having a coating film with a thickness of 200 μm on the surface of the First Release Sheet was obtained. Next, a 50-μm-thick Second Release Sheet (manufactured by Toyobo, A3800ST) with a different peel strength from that of the First Release Sheet was adhered to the surface of this pressure-sensitive adhesive sheet, and cured under the conditions of 23°C and a relative humidity of 50% for 7 days to obtain a pressure-sensitive adhesive sheet with a release sheet attached.

[0095] (Example 2) In 100 parts by mass (in terms of solid content) of the acrylic polymer obtained in Production Example 2, 0.12 part by mass of "CORONATE L-55E" from Nippon Polyurethane Industry Co., Ltd. as a crosslinking agent and 0.2 part by mass of "X-41-1810" from Shin-Etsu Chemical Co., Ltd. as a silane coupling agent were included in the raw materials. Ethyl acetate was added until a coatable concentration was reached, and stirring was carried out to prepare Adhesive Composition 2. Except for using this Adhesive Composition 2 in place of Adhesive Composition 1, a pressure-sensitive adhesive sheet with a release sheet attached was obtained in the same manner as in Example 1.

[0096] Comparative Example 1 In 100 parts by mass (converted to solid content) of the acrylic polymer obtained in Production Example 3, 0.11 part by mass of "D-110N" of Mitsui Chemicals, Inc. as a crosslinking agent, 0.1 part by mass of "X-41-1810" of Shin-Etsu Chemical Co., Ltd. as a silane coupling agent, 3 parts by mass of "M310" of Toagosei Co., Ltd. as a polyfunctional monomer, and 0.4 part by mass of "Omnirad184" of IGM RESINS B.V. as a photoinitiator were included. Ethyl acetate was added to the raw materials until a coatable concentration was reached, and the mixture was stirred to prepare Adhesive Composition 3. An adhesive sheet with a release sheet was obtained in the same manner as in Example 1, except that Adhesive Composition 3 was used instead of Adhesive Composition 1.

[0097] UV system Production Example 4 100 parts by mass of a mixed monomer with a mass ratio of 2EHA and 4HBA of 70:30 were placed in a 2 L flask equipped with a stirrer, a nitrogen inlet tube, a cooling tube, and a thermometer, and 0.15 g of AIBN was added. The reaction was carried out for 30 minutes while controlling the heat generation, and then the mixture was cooled to obtain a polymer solution. The above-mentioned mixed monomer, that is, a mixed monomer with a mass ratio of 2EHA and 4HBA of 70:30, was added to this solution to obtain an acrylic slurry with a weight average molecular weight of 700,000.

[0098] Production Example 5 An acrylic slurry with a weight average molecular weight of 800,000 was obtained in the same manner as in Production Example 4, except that the mixed monomer was changed to a mixed monomer with a mass ratio of 2EHA and DMAA of 80:20.

[0099] Production Example 6 An acrylic slurry with a weight average molecular weight of 800,000 was obtained in the same manner as in Production Example 4, except that the mixed monomer was changed to a mixed monomer with a mass ratio of 2EHA, DMAA, and 4HBA of 76:20:4.

[0100] Production Example 7 An acrylic slurry with a weight average molecular weight of 800,000 was obtained in the same manner as in Production Example 4, except that the mixed monomer was changed to a mixed monomer with a mass ratio of 2EHA, DMAA, and 4HBA of 86:10:4.

[0101] Production Example 8 An acrylic paste with a weight-average molecular weight of 800,000 was obtained in the same manner as in Production Example 4, except that the mixed monomer was changed to a mixed monomer having a mass ratio of 2EHA, tertiary butyl methacrylate (TBMA), DMAA, acryloylmorpholine (ACMO, registered trademark), and 4HBA of 72:20:2:2:4.

[0102] (Production Example 9) An acrylic paste with a weight-average molecular weight of 800,000 was obtained in the same manner as in Production Example 4, except that the mixed monomer was changed to a mixed monomer having a mass ratio of 2EHA, TBMA, DMAA, and acrylic acid (AAc) of 83:5:4:8.

[0103] (Example 3) 100 parts by mass of the acrylic paste obtained in Production Example 4 was mixed with a mixture composed of 0.5 part by mass of "Omnirad819" of IGM RESINS B.V. and 0.25 part by mass of "TZT" of IGM REGINS as a photoinitiator, thereby preparing Adhesive Composition 4. This Adhesive Composition 4 was coated on a 50-μm polyester film with a thickness of 200 μm, and a polysiloxane release agent was further coated thereon. Then, irradiation was performed using a chemical lamp at a light intensity of 4 mW / cm 2 so that the cumulative light amount became 240 mJ / cm 2 After that, irradiation was performed using a high-pressure mercury lamp at a light intensity of 150 mW / cm 2 so that the cumulative light amount became 2000 mJ / cm 2 Thereby, an adhesive sheet with a thickness of 200 μm was obtained.

[0104] (Example 4) 100 parts by mass of the acrylic paste obtained in Production Example 5 was mixed with 0.2 part by mass of "ATM-4PL" of Shin-Nakamura Chemical Co., Ltd. as a polyfunctional monomer, and a mixture composed of 0.5 part by mass of "Omnirad819" of IGM RESINS B.V. and 0.25 part by mass of "TZT" of IGM REGINS as a photoinitiator, thereby preparing Adhesive Composition 5. Except for using this Adhesive Composition 5 in place of Adhesive Composition 4, an adhesive sheet was obtained in the same manner as in Example 3.

[0105] (Example 5) An adhesive sheet was obtained in the same manner as in Example 4, except that the acrylic paste obtained in Production Example 6 was used in place of the acrylic paste obtained in Production Example 5.

[0106] (Example 6) An adhesive sheet was obtained in the same manner as in Example 4, except that the acrylic paste obtained in Production Example 7 was used instead of the acrylic paste obtained in Production Example 5.

[0107] (Comparative Example 2) An adhesive sheet was obtained in the same manner as in Example 3, except that the acrylic paste obtained in Production Example 8 was used instead of the acrylic paste obtained in Production Example 4, and the photoinitiator was changed to a mixture composed of 0.5 parts by mass of "Omnirad 819" from IGM RESINS B.V. and 2 parts by mass of "4MBP" from LAMBSON.

[0108] (Comparative Example 3) An adhesive sheet was obtained in the same manner as in Example 4, except that the acrylic paste obtained in Production Example 9 was used instead of the acrylic paste obtained in Production Example 5.

[0109] (Reworkability evaluation) The adhesive sheets produced in each Example and Comparative Example were cut into a size of 54 mm × 94 mm using a Pinnacle (registered trademark) knife equipped in a blanking machine. Then, one release sheet of the adhesive sheet was peeled off and adhered to optical glass (float glass with a thickness of 1 mm, a width of 115 mm, and a length of 75 mm) to obtain a laminate. After treating this laminate in an autoclave at a temperature of 40°C and a pressure of 0.5 MPa for 30 minutes, it was left standing for 1 day under atmospheric pressure, at a temperature of 23°C, and a humidity of 50%. Then, the other release sheet was peeled off, and while stretching the adhesive sheet from a corner at a peeling angle of 10 to 30° and at a speed of 100 to 300 mm / minute, the adhesive sheet was peeled off from the glass surface, and the time until complete peeling was measured. The reworkability was evaluated based on the following criteria. 〇: The time until complete peeling is less than 20 seconds, and the reworkability is particularly excellent. △: The time until complete peeling is 20 seconds or more and less than 120 seconds, and the reworkability is at a level where there are no practical problems. ╳: The time until complete peeling is 120 seconds or more, and the reworkability is lacking.

[0110] (Stress relaxation value) The stress relaxation value was measured using RTC-1210 from ORIENTIC. Specifically, the 200-μm-thick adhesive sheets produced in each Example and Comparative Example were cut into a width of 60 mm and evenly rolled along the width direction to form a cylindrical shape, thereby obtaining a measurement sample. When producing this cylindrical sample, the length of the adhesive sheet was appropriately adjusted in advance so that the area of the circular cross-section became 5 mm 2Set the distance between the chucks to 3 mm, fix and stretch the obtained cylindrical sample at 300 mm / min. When the load reaches 1 N, maintain the state for 1 minute, and then measure the stress value of the adhesive sheet. Set this measured value as the "stress relaxation value when a load of 1 N is applied for 1 minute".

[0111] (Adhesion to glass) Attach one adhesive surface of the adhesive sheet to a 100-μm-thick polyester film (A4300 manufactured by Toyobo Co., Ltd.) that has been subjected to easy-bonding treatment, and cut it so that the bonded part to the adherend (float glass with a thickness of 1 mm, a width of 115 mm, and a length of 75 mm) becomes a width of 25 mm and a length of 80 mm to obtain a measurement sample. After attaching the other adhesive surface of this sample to a float glass with a thickness of 1 mm, a width of 115 mm, and a length of 75 mm in a manner of 25 mm in width and 50 mm in length, roll it back and forth 2 times with a 2-kg roller for crimping. Then, after treating it in an autoclave at a temperature of 30 °C and a pressure of 0.5 MPa for 30 minutes, leave it standing for 1 day in an environment of atmospheric pressure, a temperature of 23 °C, and a humidity of 50%. Next, using Shimadzu Corporation's AGX-500NX, in the same environment for the sample including the adherend, hold the non-bonded part of the adhesive sheet, and while stretching it in the 180 °C direction at a stretching speed of 300 mm / min, measure the adhesive force. Take the value obtained from the above measurement as the adhesive force of the adhesive sheet to glass.

[0112] Table 1 and Table 2 show the manufacturing conditions of the adhesive sheets and the evaluation results of the adhesive sheets for each example and comparative example. The description of "monomer composition of acrylic polymer (mass%)" in Table 2 refers to the monomer composition of the entire acrylic slurry (acrylic polymer and additional monofunctional monomers). Furthermore, the blank columns in Table 1 and Table 2 mean that the raw material is not used.

[0113] From the results of Table 1 and Table 2, it can be seen that when the adhesive sheet is made of an adhesive composition containing an acrylic polymer and the stress relaxation value is 0.55 N / 25 mm or more, and the acrylic polymer contains a specified amount of structural units having hydroxyl groups and / or structural units having amide groups, the adhesive sheet, although having a single-layer structure, has excellent reprocessability and adhesive force.

[0114] [Table 1]

[0115] [Table 2]

Claims

1. An adhesive sheet for bonding optical members to each other, The adhesive sheet contains an acrylic polymer, The acrylic polymer contains at least one structural unit F selected from the group consisting of a structural unit having a hydroxyl group and a structural unit having an amide group, In the acrylic polymer, the structural unit F contains 10% by mass or more, The stress relaxation value of the adhesive sheet when a load of 1 N is applied for 1 minute is 0.55 N or more, and it has a single-layer structure.

2. The adhesive sheet according to claim 1, having an adhesive force to glass of 10 N / 25 mm or more.

3. The adhesive sheet according to claim 1 or 2, which is used for an image display device.

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