Adhesive sheet, reinforcing film, method for producing device with reinforcing film, method for producing device with reinforcing layer, and reinforcing method

Abstract

The adhesive sheet (2) is obtained by forming a photocurable composition, which contains an acrylic base polymer, a photocuring agent having one or more photopolymerizable functional groups, and a photopolymerization initiator, in the form of a layer. The photocurable composition constituting the adhesive sheet contains, as a photocuring agent, a polyfunctional (meth)acrylate having a high homopolymer glass transition temperature. Given the high elastic modulus after photocuring, an adhesive sheet according to the present invention can be applied as a reinforcing layer for reinforcing a device surface. The device surface can also be reinforced by a reinforcing film (10) provided with the adhesive sheet (2) on one main surface of a film substrate (1).

Description

Adhesive sheet, reinforcing film, method for manufacturing a device with a reinforcing film, method for manufacturing a device with a reinforcing layer, and reinforcing method

[0001] The present invention relates to an adhesive sheet and a reinforcing film to be attached to the surface of a device. Furthermore, the present invention relates to a method for manufacturing a device comprising a reinforcing film or reinforcing layer, and a method for reinforcing a device.

[0002] A protective film may be applied to the surface of optical devices such as displays and electronic devices for purposes such as surface protection and impact resistance. Adhesives or adhesives are used to apply the protective film to the device surface.

[0003] Patent Document 1 discloses a reinforcing film comprising an adhesive layer made of a photocurable adhesive composition on a film substrate. When the adhesive is photocured while this reinforcing film is temporarily attached to the surface of a device, the adhesive strength increases and it adheres firmly, so the film substrate of the reinforcing film functions as a surface protective film.

[0004] Japanese Patent Publication No. 2020-41113

[0005] As electronic devices become thinner, greater reinforcing capabilities are required, and there is a demand for more elastic adhesives to bond surface protective films. One method for achieving high elasticity is to use liquid adhesives, but because they are liquid, they are less easy to handle than conventional adhesives.

[0006] Adhesives tend to become more elastic by increasing the amount of crosslinking agents and polyfunctional monomers used to increase their hardness. However, there is generally a trade-off relationship between the elastic modulus of an adhesive and its adhesive strength, and adhesives with a high elastic modulus tend to have low tack (viscosity) and low adhesive strength. When such adhesives are used, bonding with the substrate becomes difficult, or they tend to peel off from the substrate in the device's operating environment, and therefore cannot function as a reinforcing film.

[0007] In view of the above, the present invention aims to provide an adhesive sheet that achieves both high adhesive strength and high modulus of elasticity, and a reinforcing film equipped with the adhesive sheet.

[0008] The present invention relates to an adhesive sheet in which a photocurable composition comprising an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator is formed in layers, and to a reinforcing film in which the adhesive sheet is fixedly laminated on one main surface of a film substrate.

[0009] The acrylic-based polymer contains one or more constituent monomers selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers. A cross-linked structure is introduced into the acrylic-based polymer. The photocuring agent is a compound having a photopolymerizable functional group.

[0010] In the first embodiment of the present invention, the photocurable composition constituting the adhesive sheet includes an acrylic base polymer, a photocuring agent, and a photopolymerization initiator, in addition to an acrylic oligomer, and the photocuring agent includes a polyfunctional (meth)acrylate having an alicyclic structure. The glass transition temperature of the acrylic base polymer may be -60°C or higher.

[0011] In the first embodiment of the present invention, the content of the photocuring agent in the photocurable composition may be 20 to 100 parts by weight per 100 parts by weight of the acrylic base polymer. The content of the polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent may be 10 to 100 parts by weight per 100 parts by weight of the acrylic base polymer.

[0012] The acrylic oligomer preferably has a weight-average molecular weight of 1,000 to 30,000 and a glass transition temperature of 0°C or higher. The acrylic oligomer may also contain an alkyl (meth)acrylate having an alicyclic alkyl group as a constituent monomer component.

[0013] In the first embodiment of the present invention, the content of the acrylic oligomer in the photocurable composition is preferably 20 to 150 parts by weight per 100 parts by weight of the acrylic base polymer. The content of the acrylic oligomer in the photocurable composition may be 0.7 to 2.5 times by weight relative to the polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent.

[0014] In the first embodiment of the present invention, the shear storage modulus of the photocured adhesive sheet at 25°C is preferably 5.0 MPa or higher.

[0015] In a second embodiment of the present invention, the acrylic-based polymer contains, as a constituent monomer component, one or more selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, in addition to an aromatic ring-containing (meth)acrylic acid ester. The acrylic-based polymer may further contain a nitrogen-containing monomer as a constituent monomer component. The glass transition temperature of the acrylic-based polymer may be -40°C or higher.

[0016] In a second embodiment of the present invention, the photocurable composition constituting the adhesive sheet contains a polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher as a photocuring agent. The content of the polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher as a photocuring agent may be 10 to 150 parts by weight per 100 parts by weight of the acrylic base polymer. An example of a polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher is a polyfunctional (meth)acrylate having an alicyclic structure.

[0017] In the second embodiment of the present invention, the photocurable composition constituting the adhesive sheet may also contain an acrylic oligomer.

[0018] In the second embodiment of the present invention, the shear storage modulus of the photocured adhesive sheet at 25°C is preferably 50 MPa or higher.

[0019] By laminating the above-mentioned adhesive sheet onto the surface of a device and curing it with light, the device can be reinforced to increase its rigidity. The above-mentioned adhesive sheet can also be used as a reinforcing film laminated with a base film and laminated onto the surface of a device.

[0020] The adhesive sheet of the present invention exhibits high adhesion to the adherend and high storage modulus upon photocuring. By laminating the adhesive sheet or a reinforcing film equipped with the adhesive sheet onto a film substrate to the surface of the adherend to be protected, and then photocuring the adhesive sheet, high protective performance can be achieved.

[0021] This is a cross-sectional view showing the laminated structure of an adhesive sheet with release liners temporarily attached to both sides. This is a cross-sectional view showing the laminated structure of a reinforcing film. This is a cross-sectional view showing the laminated structure of a reinforcing film. This is a cross-sectional view showing a device to which a reinforcing film has been attached. This is a cross-sectional view showing a device to which an adhesive sheet has been temporarily attached to the surface. This is a cross-sectional view showing the laminated structure of a device with a reinforcing layer.

[0022] The present invention relates to an adhesive sheet in which a curable composition is formed in layers. As shown in Figure 1, the adhesive sheet 2 may have release liners 5 and 7 temporarily attached to one or both sides. As an example of how the adhesive sheet of the present invention can be used, as shown in Figure 2, a reinforcing film is formed in which the adhesive sheet 2 is fixedly laminated on one main surface of a film substrate 1. As shown in Figure 3, a release liner 5 may be temporarily attached to the surface of the adhesive sheet 2 of the reinforcing film. Figure 4 is a cross-sectional view showing a state in which the reinforcing film 10 is attached to the surface of a device 20.

[0023] The release liner 5 is peeled off from the surface of the adhesive sheet 2 of the reinforcing film shown in Figure 3, and the exposed surface of the adhesive sheet 2 is bonded to the surface of the device 20, thereby attaching the reinforcing film 10 to the surface of the device 20. By photocuring the adhesive sheet 2 in this state, the device 20 and the reinforcing film 10 are firmly bonded together. In addition, as the elastic modulus of the adhesive sheet 2 increases with photocuring, the protective performance of the device surface is improved.

[0024] [[Adhesive Sheet]] The adhesive sheet 2 consists of a photocurable composition comprising an acrylic-based polymer, a photocuring agent, and a photopolymerization initiator.

[0025] The thickness of the adhesive sheet 2 is, for example, about 1 to 300 μm. The greater the thickness of the adhesive sheet 2, the better the adhesion to the substrate tends to be. On the other hand, if the thickness of the adhesive sheet 2 is excessively large, the fluidity before photocuring is high, which may make handling difficult. For this reason, the thickness of the adhesive sheet 2 is preferably 3 to 100 μm, more preferably 5 to 50 μm, even more preferably 6 to 40 μm, and particularly preferably 8 to 30 μm. From the viewpoint of thinning, the thickness of the adhesive sheet 2 may be 25 μm or less, 20 μm or less, or 18 μm or less.

[0026] When used in optical devices such as displays, the total light transmittance of the adhesive sheet 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the adhesive sheet 2 is preferably 2% or less, more preferably 1% or less, even more preferably 0.7% or less, and particularly preferably 0.5% or less.

[0027] In the first embodiment of the present invention, the photocurable composition constituting the adhesive sheet 2 comprises an acrylic oligomer in addition to an acrylic base polymer, a photocuring agent, and a photopolymerization initiator, and is characterized by comprising a polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent. In the second embodiment of the present invention, the photocurable composition constituting the adhesive sheet 2 comprises an acrylic base polymer containing an (meth)acrylic acid ester having an aromatic ring as a constituent monomer component, and a polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher as the photocuring agent.

[0028] [First Form of Adhesive Sheet] First, the preferred forms of each component of the photocurable composition (adhesive composition) that constitutes the first form of adhesive sheet will be described in order.

[0029] <Base Polymer> The base polymer is the main component of the adhesive composition. Acrylic polymers are used as the base polymer of the adhesive composition because they have excellent adhesion to the adherend and high transparency. Preferably, 30% by weight or more of the adhesive composition is made up of acrylic polymer.

[0030] Acrylic-based polymers contain alkyl (meth)acrylate as the main monomer component. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0031] As the alkyl (meth)acrylate ester, an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group is preferably used. The alkyl (meth)acrylate ester may have branched alkyl groups or may have cyclic alkyl groups (alicyclic alkyl groups).

[0032] Specific examples of alkyl (meth)acrylate esters having a chain-like alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (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, isooctyl (meth)acrylate, and (meth) Examples include nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0033] Specific examples of alkyl (meth)acrylate esters having an alicyclic alkyl group include cycloalkyl (meth)acrylate esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylate esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylate esters having three or more aliphatic hydrocarbon rings such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. Alkyl (meth)acrylate esters having an alicyclic alkyl group may also have substituents on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. Furthermore, the alkyl (meth)acrylate ester having an alicyclic alkyl group may also be a (meth)acrylate ester containing a fused ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0034] Among the example alkyl (meth)acrylate esters, C (meth)acrylate is selected because it exhibits adhesive strength to the substrate over a wide temperature range. １－９ Alkyl esters are preferred, and from the viewpoint of increasing the elastic modulus of the adhesive sheet after photocuring, those with a homopolymer glass transition temperature of -60°C or higher are preferred. From the viewpoint of achieving both excellent adhesive strength and high elastic modulus, butyl acrylate (homopolymer glass transition temperature: -55°C) is particularly preferred.

[0035] The content of alkyl (meth)acrylate is preferably 40 parts by weight or more, more preferably 50 parts by weight or more, even more preferably 60 parts by weight or more, and may also be 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more, based on 100 parts by weight of the total monomer components constituting the acrylic base polymer. The amount of butyl acrylate relative to 100 parts by weight of the total monomer components constituting the acrylic base polymer may also be within the above range.

[0036] Acrylic-based polymers contain, as constituent monomer components, alkyl (meth)acrylate esters and monomers having crosslinkable functional groups. Examples of monomers having crosslinkable functional groups include hydroxyl group-containing monomers and carboxyl group-containing monomers. Acrylic-based polymers may contain both hydroxyl group-containing monomers and carboxyl group-containing monomers as copolymer components, or they may contain only one of them. The introduction of a crosslinked structure into the acrylic-based polymer improves cohesive strength and thus improves adhesion to the adherend.

[0037] Examples of monomers containing a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-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-(hydroxymethyl)cyclohexylmethyl (meth)acrylate.

[0038] Examples of carboxyl group-containing monomers include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. Among these, acrylic acid and methacrylic acid are preferred, with acrylic acid being particularly preferred, because they tend to improve adhesive strength and adhesive retention by increasing the cohesiveness of the adhesive.

[0039] The total amount of hydroxyl group-containing monomers and carboxyl group-containing monomers per 100 parts by weight of the total monomer components constituting the acrylic base polymer is preferably 0.5 to 30 parts by weight, more preferably 1 to 25 parts by weight, and may be 1.5 to 20 parts by weight, 2 to 15 parts by weight, or 2.5 to 10 parts by weight.

[0040] The acrylic base polymer may contain monomer components other than those described above. When the acrylic base polymer contains a high Tg monomer as a constituent monomer component, the elastic modulus of the pressure-sensitive adhesive sheet after photo-curing tends to be improved. A high Tg monomer is a monomer whose homopolymer has a high glass transition temperature (Tg), and those having a glass transition temperature of 0°C or higher for the homopolymer are preferred. For the high Tg monomer, those having a glass transition temperature of 10°C or higher for the homopolymer are more preferred, and those having 20°C or higher are particularly preferred.

[0041] Examples of high Tg monomers include monomers having an aromatic ring. As the monomer having an aromatic ring, (meth)acrylic acid esters are preferred. Specific examples include phenyl (meth)acrylate, naphthyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl (meth)acrylate, phenoxy (meth)acrylate, biphenyl (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, phenol ethylene oxide-modified (meth)acrylate, 2-naphthoyl (meth)acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, and the like.

[0042] Examples of high Tg monomers other than aromatic group-containing monomers include (meth)acrylic acid esters having an alicyclic structure such as cyclohexyl methacrylate (Tg: 83°C), tetrahydrofurfuryl methacrylate (Tg: 60°C), dicyclopentanyl methacrylate (Tg: 175°C), dicyclopentanyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 155°C), isobornyl acrylate (Tg: 97°C), 1-adamantyl methacrylate (Tg: 250°C), 1-adamantyl acrylate (Tg: 153°C); acid monomers such as methacrylic acid (Tg: 228°C), acrylic acid (Tg: 106°C); and methyl methacrylate (Tg: 105°C), and the like.

[0043] The amount of the high Tg monomer may be 1 part by weight or more, 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more, relative to 100 parts by weight of the total monomer components constituting the acrylic base polymer. If the proportion of the high Tg monomer is excessively high, the adhesive strength may decrease. The amount of the high Tg monomer may be 60 parts by weight or less, 50 parts by weight or less, 40 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less, relative to 100 parts by weight of the total monomer components constituting the acrylic base polymer.

[0044] The acrylic base polymer may contain nitrogen-containing monomers as constituent monomer components, such as N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-acryloylmorpholine, N-vinylcarboxylic acid amides, and N-vinylcaprolactam.

[0045] The acrylic base polymer may contain, as constituent monomer components, a (meth)acrylic acid ester having an alkylene oxide chain, such as methoxyethyl acrylate, phenoxyethyl acrylate, ethoxyethoxyethyl acrylate, and methoxytriethylene glycol acrylate.

[0046] Examples of monomer components other than those listed above include vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers.

[0047] From the viewpoint of increasing the elastic modulus of the pressure-sensitive adhesive sheet after photo-curing, the glass transition temperature of the acrylic base polymer is preferably -60°C or higher, more preferably -55°C or higher. On the other hand, from the viewpoint of improving adhesiveness, the glass transition temperature of the acrylic base polymer is preferably 50°C or lower, more preferably 40°C or lower, and may be 35°C or lower, 30°C or lower, or 25°C or lower.

[0048] Generally, when the glass transition temperature of the base polymer is high, the tackiness of the adhesive tends to decrease, resulting in poor adhesion to the substrate. On the other hand, in the first embodiment of the present invention, the adhesive composition contains a photocuring agent, and since the photocuring agent is in liquid form in the adhesive composition before photocuring, the adhesive exhibits tackiness even when the glass transition temperature of the acrylic base polymer is high. When the adhesive is photocured, it exhibits high adhesion and an increase in elastic modulus as the photocuring agent hardens.

[0049] The glass transition temperature is the temperature at which the loss tangent tanδ in viscoelastic measurements is maximized (peak top temperature). Instead of the glass transition temperature obtained by viscoelastic measurements, the theoretical Tg calculated by Fox's equation may be applied. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the acrylic-based polymer. ｉ And the weight fraction W of each monomer component ｉ Therefore, it is calculated by the following Fox formula: 1 / Tg = Σ(W ｉ / Tg ｉ )

[0050] Tg is the glass transition temperature of the polymer chain (unit: K), W ｉ This is the weight fraction (weight-based copolymerization ratio) of monomer component i that constitutes the segment, Tg ｉ is the glass transition temperature (in K) of the homopolymer of monomer component i. The values ​​listed in the Polymer Handbook, 3rd edition (John Wiley & Sons, Inc., 1989) can be used as the glass transition temperature of the homopolymer. For homopolymers of monomers not listed in the above literature, the peak top temperature of tanδ obtained by dynamic viscoelasticity measurement can be used.

[0051] Acrylic polymers as base polymers are obtained by polymerizing the above monomer components using various known methods such as solution polymerization, emulsion polymerization, and bulk polymerization. Solution polymerization is preferred from the viewpoint of balancing properties such as adhesive strength and holding power of the adhesive, as well as cost. Ethyl acetate, toluene, etc. are used as solvents for solution polymerization. The solution concentration is usually about 20 to 80% by weight. Various known polymerization initiators such as azo-based and peroxide-based ones can be used for solution polymerization. Chain transfer agents may be used to adjust the molecular weight. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

[0052] The weight-average molecular weight of the acrylic base polymer is preferably 100,000 to 3,000,000, more preferably 200,000 to 2,500,000, and even more preferably 300,000 to 2,300,000. Note that when a cross-linked structure is introduced into the acrylic base polymer, the molecular weight of the acrylic base polymer refers to the molecular weight before the introduction of the cross-linked structure.

[0053] <Crosslinking Agent> As mentioned above, a crosslinked structure is introduced into the acrylic-based polymer. For example, a crosslinked structure is introduced by adding a crosslinking agent to the solution after polymerization of the acrylic-based polymer and heating as necessary. The crosslinking agent has two or more crosslinkable functional groups per molecule. The crosslinking agent may also have three or more crosslinkable functional groups per molecule.

[0054] Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents react with functional groups such as hydroxyl groups and carboxyl groups introduced into the acrylic base polymer to form a crosslinked structure. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxyl groups and carboxyl groups of the acrylic base polymer and facilitate the introduction of crosslinked structures. Isocyanate-based crosslinking agents are preferred when the acrylic base polymer has hydroxyl groups as crosslinkable functional groups, and epoxy-based crosslinking agents are preferred when the acrylic base polymer has carboxyl groups as crosslinkable functional groups.

[0055] As isocyanate crosslinking agents, polyisocyanates having two or more isocyanate groups in one molecule are used. Isocyanate crosslinking agents may also have three or more isocyanate groups in one molecule. Examples of isocyanate crosslinking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; and trimethylolpropane / tri- Examples of isocyanate adducts include diisocyanate trimer adducts (e.g., Mitsui Chemicals' "Takenate D101E"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate HL"), xylylene diisocyanate trimethylolpropane adducts (e.g., Mitsui Chemicals' "Takenate D110N"), and hexamethylene diisocyanate isocyanurates (e.g., Tosoh's "Coronate HX"). As isocyanate crosslinking agents, isocyanate compounds having a biuret group (e.g., Asahi Kasei's "Duranate 24A-100") or isocyanate compounds having an allophanate group may be used.

[0056] As the epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy crosslinking agent may also have three or more or four or more epoxy groups in one molecule. The epoxy groups of the epoxy crosslinking agent may be glycidyl groups. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether. As epoxy crosslinking agents, commercially available products such as "Denacol" from Nagase ChemteX and "Tetrad X" and "Tetrad C" from Mitsubishi Gas Chemical may be used.

[0057] The amount of crosslinking agent used can be appropriately adjusted depending on the composition and molecular weight of the acrylic base polymer. The amount of crosslinking agent used is approximately 0.01 to 5 parts by weight per 100 parts by weight of the acrylic base polymer, preferably 0.02 to 1 part by weight, more preferably 0.03 to 0.5 parts by weight, and may also be 0.04 to 0.3 parts by weight or 0.05 to 0.2 parts by weight.

[0058] A crosslinking catalyst may be used to promote the formation of crosslinked structures. Examples of crosslinking catalysts include organometallic compounds such as organometallic complexes (chelates), compounds of metals and alkoxy groups, and compounds of metals and acyloxy groups; as well as tertiary amines. In particular, organometallic compounds are preferred from the viewpoint of suppressing the progress of the crosslinking reaction in a solution state at room temperature and ensuring the pot life of the adhesive composition. Examples of metals in organometallic compounds include iron, tin, aluminum, zirconium, zinc, titanium, lead, and cobalt. The amount of crosslinking catalyst used is generally 0.5 parts by weight or less per 100 parts by weight of the acrylic base polymer.

[0059] <Photocuring Agent> The photocurable adhesive composition constituting the adhesive sheet 2 includes a photocuring agent in addition to an acrylic-based polymer. The photocuring agent is a compound having a photopolymerizable functional group (photocurable monomer). The photocuring agent may be a monofunctional monomer having one photopolymerizable functional group in one molecule, or a polyfunctional monomer having two or more photopolymerizable functional groups. The adhesive composition containing the photocuring agent is photocurable, and by performing photocuring after bonding to the adherend, the adhesive strength to the adherend is improved and the elasticity is increased.

[0060] As the photopolymerizable functional group, one that has polymerizability by photoradical reaction is preferred, and as the photocuring agent, a compound having an ethylenically unsaturated bond is preferred, and (meth)acrylic acid esters are preferred due to their high compatibility with acrylic-based polymers. The (meth)acrylic acid ester may be monofunctional or a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups. A typical polyfunctional (meth)acrylate is an ester of a polyol and (meth)acrylic acid.

[0061] In the first embodiment of the present invention, a polyfunctional (meth)acrylate having an alicyclic structure is used as the photocuring agent. The (meth)acrylate having an alicyclic structure has an alicyclic structure in its molecular structure and may have a chain-like structure between the alicyclic ring and the (meth)acryloyl group. The alicyclic ring may be a fused ring.

[0062] Specific examples of polyfunctional (meth)acrylates having an alicyclic structure include tricyclodecanedimethanol di(meth)acrylate, hydrogenated bisphenol A type epoxy(meth)acrylate, hydrogenated bisphenol F type epoxy(meth)acrylate, hydrogenated bisphenol E type epoxy(meth)acrylate, hydrogenated phthalate type epoxy(meth)acrylate, hydrogenated terpenephenol(meth)acrylate, and 1,4-cyclohexanedimethanol diglycidyl ether(meth)acrylate.

[0063] The adhesive composition contains a polyfunctional (meth)acrylate having an alicyclic structure as a photocuring agent, resulting in an adhesive sheet exhibiting a high modulus of elasticity after photocuring. The adhesive composition, containing a polyfunctional (meth)acrylate having an alicyclic structure as a photocuring agent and also containing the acrylic oligomer described later, allows the adhesive sheet to achieve both high modulus of elasticity and strong adhesive strength after photocuring.

[0064] Polyfunctional (meth)acrylates having an alicyclic structure, whether acrylate or methacrylate, can contribute to increased elasticity. Using polyfunctional methacrylate with an alicyclic structure as a photocuring agent tends to result in higher adhesive strength of the photocured adhesive sheet compared to using acrylate. One possible reason for this increased adhesive strength is that methacrylate has a higher homopolymer glass transition temperature than acrylate.

[0065] From the viewpoint of increasing the elasticity of the adhesive sheet, among the polyfunctional (meth)acrylates having an alicyclic structure exemplified above, tricyclodecanedimethanol di(meth)acrylate is particularly preferred, and from the viewpoint of increasing adhesive strength, tricyclodecanedimethanol dimethacrylate is particularly preferred.

[0066] As a photocuring agent, a polyfunctional (meth)acrylate having an alicyclic structure and other photopolymerizable compounds may be used in combination. As mentioned above, (meth)acrylate is preferred as the photocuring agent.

[0067] Examples of monofunctional (meth)acrylates include those previously exemplified as constituent monomers of acrylic-based polymers. Other specific examples of monofunctional (meth)acrylates include carboxypolycaprolactone mono(meth)acrylate, monohydroxyethyl phthalate (meth)acrylate, and N-acryloyloxyethyl hexahydrophthalimide.

[0068] Specific examples of polyfunctional (meth)acrylates that do not have an alicyclic structure include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and tri Examples include methylolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, urethane(meth)acrylate, epoxy(meth)acrylate, butadiene(meth)acrylate, isoprene(meth)acrylate, etc.

[0069] From the viewpoint of increasing the elasticity of the adhesive after photocuring, the content of the photocuring agent in the adhesive composition is preferably 20 parts by weight or more, more preferably 25 parts by weight or more, even more preferably 30 parts by weight or more, and may also be 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the acrylic base polymer. The greater the amount of photocuring agent, the higher the storage modulus of the adhesive sheet after photocuring tends to be, and the storage modulus tends to be particularly high when the amount of polyfunctional (meth)acrylate is large. From the viewpoint of increasing the elasticity of the adhesive after photocuring, it is preferable that the amount of polyfunctional (meth)acrylate in the adhesive composition is within the above range.

[0070] If the amount of photocuring agent is excessively high, bleed-out of the photocuring agent may occur in the adhesive before photocuring, and handling may become difficult due to its high liquidity. Also, if the amount of photocuring agent is excessively high, the viscosity of the adhesive after photocuring may be low, resulting in insufficient adhesion to the substrate. For this reason, the amount of photocuring agent in the adhesive composition is preferably 100 parts by weight or less, more preferably 80 parts by weight or less, even more preferably 75 parts by weight or less, and may also be 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, or 55 parts by weight or less, per 100 parts by weight of the acrylic base polymer.

[0071] From the viewpoint of making the adhesive highly elastic after photocuring, the content of polyfunctional (meth)acrylate having an alicyclic structure as a photocuring agent is preferably 10 parts by weight or more, more preferably 15 parts by weight or more, even more preferably 20 parts by weight or more, and may also be 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the acrylic base polymer. From the viewpoint of the handling properties of the adhesive sheet before photocuring and the adhesive strength after photocuring, the content of polyfunctional (meth)acrylate having an alicyclic structure as a photocuring agent is preferably 100 parts by weight or less, more preferably 80 parts by weight or less, even more preferably 75 parts by weight or less, and may also be 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, or 55 parts by weight or less, per 100 parts by weight of the acrylic base polymer.

[0072] <Photopolymerization Initiator> A photopolymerization initiator generates active species upon irradiation with active light, thereby accelerating the curing reaction of the photocuring agent. It is preferable to use a photoradical polymerization initiator (photoradical generator) as the photopolymerization initiator.

[0073] Preferred photo-radical polymerization initiators are those that generate radicals upon irradiation with visible light or ultraviolet light with a wavelength shorter than 450 nm, and include hydroxyketones, benzyldimethylketals, aminoketones, acylphosphine oxides, benzophenones, and trichloromethyl group-containing triazine derivatives. Photo-polymerization initiators may be used alone or in combination of two or more.

[0074] The content of the photopolymerization initiator in the adhesive composition is preferably 0.01 to 5 parts by weight, more preferably 0.02 to 3 parts by weight, and even more preferably 0.03 to 2 parts by weight, per 100 parts by weight of the base polymer. The content of the photopolymerization initiator in the adhesive sheet 2 is preferably 0.02 to 20 parts by weight, more preferably 0.05 to 10 parts by weight, and even more preferably 0.1 to 7 parts by weight, per 100 parts by weight of the photocuring agent.

[0075] <Oligomer> The adhesive composition contains an acrylic oligomer with a lower molecular weight than the acrylic base polymer described above. By including an oligomer in addition to the base polymer, the adhesive strength to substrates such as glass and resin films is increased.

[0076] The weight molecular weight of the acrylic oligomer is approximately 1,000 to 30,000. If the molecular weight of the acrylic oligomer is excessively large, the compatibility with the acrylic base polymer tends to decrease. The weight-average molecular weight of the acrylic oligomer is preferably 20,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less. The weight-average molecular weight of the acrylic oligomer may also be 1,500 or more, 2,000 or more, or 2,500 or more.

[0077] The glass transition temperature of the acrylic oligomer is preferably 0°C or higher, more preferably 20°C or higher, even more preferably 40°C or higher, and may be 50°C or higher or 60°C or higher. Including an acrylic oligomer with a high glass transition temperature in the adhesive composition tends to increase the adhesive strength of the adhesive and increase the elastic modulus of the adhesive sheet after photocuring. There is no particular upper limit to the glass transition temperature of the acrylic oligomer, but it is generally 200°C or lower, and may be 150°C or lower, 120°C or lower, or 100°C or lower. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

[0078] Acrylic oligomers contain alkyl (meth)acrylate as the main constituent monomer component. The content of alkyl (meth)acrylate in the constituent monomer component of the acrylic oligomer is more preferably 50% by weight or more, more preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, or 90% by weight or more, based on the total amount of constituent monomer component of the acrylic oligomer.

[0079] Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having a linear alkyl group (linear alkyl (meth)acrylate) and alkyl (meth)acrylates having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of these alkyl (meth)acrylates are as previously exemplified as constituent monomers of acrylic-based polymers.

[0080] From the viewpoint of increasing the glass transition temperature, it is preferable that the acrylic oligomer contains a monomer component as an alkyl (meth)acrylate ester whose homopolymer has a glass transition temperature of 40°C or higher. Among alkyl (meth)acrylate esters whose homopolymer has a glass transition temperature of 40°C or higher, alicyclic alkyl (meth)acrylates are particularly preferred.

[0081] The acrylic oligomer may have alicyclic alkyl (meth)acrylate as its main constituent monomer. The amount of alicyclic alkyl (meth)acrylate per 100 parts by weight of the total constituent monomer components of the acrylic oligomer may be 50 parts by weight or more, 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more. The amount of alicyclic alkyl (meth)acrylate per 100 parts by weight of the total constituent monomer components of the acrylic oligomer may be 99 parts by weight or less, 97 parts by weight or less, or 95 parts by weight or less.

[0082] Acrylic oligomers whose main constituent monomer is alicyclic alkyl (meth)acrylate may also contain monomer components other than alicyclic alkyl (meth)acrylate. Examples of monomers other than alicyclic alkyl (meth)acrylate include linear alkyl (meth)acrylate, hydroxyl group-containing monomers, carboxyl group-containing monomers, nitrogen-containing monomers, and the like.

[0083] An example of an acrylic oligomer having alicyclic alkyl (meth)acrylate as the main constituent monomer is one that mainly consists of alicyclic alkyl (meth)acrylate with two or fewer rings, and contains 1 to 10 parts by weight of a carboxyl group-containing monomer such as acrylic acid as a copolymer monomer. Another example of an acrylic oligomer having alicyclic alkyl (meth)acrylate as the main constituent monomer is one that mainly consists of alicyclic alkyl (meth)acrylate with three or more rings, and contains 10 to 50 parts by weight of a chain-like alkyl (meth)acrylate, such as methyl methacrylate, whose homopolymer glass transition temperature is 40°C or higher, as a copolymer monomer.

[0084] Acrylic oligomers are obtained by polymerizing the above monomer components using various polymerization methods. Various polymerization initiators may be used during the polymerization of acrylic oligomers. Chain transfer agents may also be used to adjust the molecular weight.

[0085] The content of acrylic oligomers in the adhesive composition is preferably 20 to 150 parts by weight, more preferably 25 to 100 parts by weight, even more preferably 30 to 80 parts by weight, and may also be 35 to 70 parts by weight or 40 to 60 parts by weight, per 100 parts by weight of the acrylic base polymer. When the oligomer content in the adhesive composition is within the above range, the adhesive strength of the adhesive sheet to the adherend after photocuring tends to be higher.

[0086] As mentioned above, the inclusion of a polyfunctional (meth)acrylate with an alicyclic structure as a photocuring agent in the adhesive composition results in a high modulus of elasticity after photocuring. Furthermore, the inclusion of an acrylic oligomer in the adhesive composition improves the adhesive strength, thus achieving both high adhesive strength and high modulus of elasticity. In other words, the combination of an acrylic oligomer and a polyfunctional (meth)acrylate with an alicyclic structure as a photocuring agent makes it possible to achieve both high adhesive strength and high modulus of elasticity, which are generally in a trade-off relationship.

[0087] In order to achieve both high adhesive strength and high modulus of elasticity, it is preferable that the content of the photocuring agent and the acrylic oligomer in the adhesive composition be within the aforementioned ranges, and that the ratio of the content of the photocuring agent to the acrylic oligomer be within a predetermined range. From the viewpoint of increasing the adhesive strength to the adherend while making the adhesive sheet after photocuring highly modulus of elasticity, the content of the acrylic oligomer in the adhesive composition is preferably 0.7 to 2.5 times, more preferably 1.0 to 2.3 times, even more preferably 1.3 to 2.1 times, and may also be 1.4 to 2.0 times or 1.5 to 1.9 times, relative to the polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent.

[0088] <Other Components> As described above, in the first embodiment, the photocurable adhesive composition constituting the adhesive sheet 2 includes an acrylic base polymer, a photocuring agent, a photopolymerization initiator, and an acrylic oligomer. In addition to these, the adhesive composition may also contain additives such as antistatic agents, silane coupling agents, tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, UV absorbers, antioxidants, and surfactants, to the extent that they do not impair the properties of the present invention.

[0089] The adhesive composition constituting the adhesive sheet 2 may contain organic or inorganic fine particles (fillers). The inclusion of fillers tends to increase the elastic modulus of the adhesive sheet. On the other hand, adding fillers to increase the elastic modulus may increase the haze of the adhesive sheet and impair its transparency. From the viewpoint of ensuring the transparency of the adhesive sheet, the adhesive composition preferably contains 10 parts by weight or less of fillers per 100 parts by weight of acrylic base polymer, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, and may contain 1 part by weight or less or 0.5 parts by weight or less. The adhesive composition may also not contain fillers. As described above, since the adhesive sheet exhibits a high elastic modulus after photocuring due to the inclusion of a predetermined photocuring agent in the adhesive composition, high elasticity is possible even without fillers.

[0090] <Formation of Adhesive Sheet> The above adhesive composition is applied to a substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, etc., and an adhesive sheet is formed by drying and removing the solvent as necessary. As for the drying method, an appropriate method may be used as appropriate. The heating drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and even more preferably 10 seconds to 10 minutes.

[0091] If the adhesive composition contains a crosslinking agent, it is preferable to promote crosslinking by heating or aging simultaneously with or after the drying of the solvent. The heating temperature and heating time are set appropriately depending on the type of crosslinking agent used, and crosslinking is usually carried out by heating for about 1 minute to 7 days in the range of 20°C to 160°C. Heating to dry and remove the solvent may also serve as heating for crosslinking.

[0092] Even after a cross-linked structure is introduced into the polymer using a cross-linking agent, the photocuring agent remains unreacted. Therefore, the adhesive sheet 2 contains an acrylic-based polymer with a cross-linked structure, a photocuring agent, a photopolymerization initiator, and an acrylic oligomer.

[0093] <Storage Modulus of Adhesive Sheet> In the first embodiment, the shear storage modulus of the photocured adhesive sheet 2 at 25°C is preferably 5.0 MPa or higher, more preferably 7.0 MPa or higher, even more preferably 9.0 MPa or higher, and may be 10 MPa or higher, or 11 MPa or higher. A high modulus of elasticity in the photocured adhesive sheet enhances the protective properties for the adherend.

[0094] The upper limit of the shear storage modulus at 25°C of the adhesive sheet 2 after photocuring is not particularly limited, but if the modulus is excessively large, the adhesive strength to the adherend tends to be low. In the first embodiment of the adhesive sheet, the shear storage modulus at 25°C after photocuring is preferably 1000 MPa or less, more preferably 800 MPa or less, and may be 600 MPa or less, 500 MPa or less, 400 MPa or less, 300 MPa or less, 200 MPa or less, 100 MPa or less, or 50 MPa or less.

[0095] The shear storage modulus of an adhesive sheet (hereinafter simply referred to as "storage modulus") is determined by performing a viscoelastic measurement under the conditions of a frequency of 1 Hz and a heating rate of 5°C / min, in accordance with the method described in JIS K7244-1 "Plastics - Test methods for dynamic mechanical properties," and reading the value at a predetermined temperature.

[0096] [Second Form of Adhesive Sheet] Next, the preferred forms of each component of the photocurable composition (adhesive composition) constituting the second form of adhesive sheet will be described in order. In the second form, the preferred forms and their contents of the crosslinking agent and photopolymerization initiator constituting the adhesive composition are the same as in the first form. To avoid duplication, the following descriptions of the crosslinking agent and photopolymerization initiator will be omitted and the descriptions of the first form above will be referenced. Furthermore, for components other than the crosslinking agent and photopolymerization initiator that are common with the first form, the descriptions of the first form will be referenced.

[0097] <Base Polymer> Similar to the first embodiment described above, the adhesive sheet in the second embodiment also contains an acrylic polymer as the base polymer. Preferably, 30% by weight or more of the adhesive composition is an acrylic polymer. In the second embodiment, the acrylic base polymer contains an (meth)acrylic acid ester having an aromatic ring as a monomer component, and further contains a monomer having a crosslinkable functional group.

[0098] Specific examples of (meth)acrylic acid esters having an aromatic ring are the same as those described above in the first form, and include phenyl (meth)acrylate, naphthyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl (meth)acrylate, phenoxy (meth)acrylate, biphenyl (meth)acrylate, ethylene oxide-modified nonylphenol (meth)acrylate, phenolethylene oxide-modified (meth)acrylate, 2-naphthoethyl (meth)acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, and the like.

[0099] The (meth)acrylic acid ester having an aromatic ring is preferably one in which the glass transition temperature of the homopolymer is 0°C or higher. The (meth)acrylic acid ester having an aromatic ring may also have a glass transition temperature of 5°C or higher or 10°C or higher. When an acrylic-based polymer contains an (meth)acrylic acid ester having an aromatic ring as a constituent monomer component, the glass transition temperature of the polymer is increased, and the elastic modulus of the adhesive sheet tends to increase.

[0100] From the viewpoint of increasing the elastic modulus of the adhesive sheet after photocuring, the amount of (meth)acrylic acid ester having an aromatic ring relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer is preferably 20 parts by weight or more, more preferably 30 parts by weight or more, even more preferably 40 parts by weight or more, and particularly preferably 50 parts by weight or more. The amount of (meth)acrylic acid ester having an aromatic ring relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer may be greater than 60 parts by weight, and may be 65 parts by weight or more, 70 parts by weight or more, 75 parts by weight or more, or 80 parts by weight or more.

[0101] The amount of (meth)acrylic acid ester having an aromatic ring relative to 100 parts by weight of the total constituent monomer components of the acrylic base polymer may be 99.5 parts by weight or less, 99 parts by weight or less, 98 parts by weight or less, 97 parts by weight or less, or 96 parts by weight or less.

[0102] Generally, increasing the proportion of high-Tg monomers in the constituent monomers of acrylic-based polymers tends to increase the elastic modulus of the adhesive sheet, but also decrease its adhesive strength. On the other hand, (meth)acrylic acid esters with aromatic rings maintain high adhesive strength even when their proportion is increased, thus providing an adhesive sheet that combines high elastic modulus and adhesive strength.

[0103] The acrylic-based polymer contains, as constituent monomer components, (meth)acrylic acid esters having aromatic rings, as well as monomers having crosslinkable functional groups. As described above for the first embodiment, examples of monomers having crosslinkable functional groups include hydroxyl group-containing monomers and carboxyl group-containing monomers. Specific examples of hydroxyl group-containing monomers and carboxyl group-containing monomers are the same as those described above for the first embodiment. By introducing a crosslinked structure into the acrylic-based polymer, the cohesive force is improved, and the adhesion to the adherend is enhanced.

[0104] The total amount of hydroxyl group-containing monomers and carboxyl group-containing monomers per 100 parts by weight of the constituent monomer components of the acrylic-based polymer is preferably 0.5 to 30 parts by weight, more preferably 1 to 25 parts by weight, and may be 1.5 to 20 parts by weight, 2 to 15 parts by weight, or 2.5 to 10 parts by weight.

[0105] The acrylic-based polymer may contain monomer components other than those mentioned above. The inclusion of nitrogen-containing monomers as constituent monomer components in the acrylic-based polymer tends to increase the adhesive strength of the adhesive sheet after photocuring. Specific examples of nitrogen-containing monomers are the same as those described above for the first embodiment.

[0106] When an acrylic-based polymer contains nitrogen-containing monomers as constituent monomers, the amount of nitrogen-containing monomers relative to 100 parts by weight of the total constituent monomer components may be 0.5 to 25 parts by weight, 1 to 20 parts by weight, 2 to 15 parts by weight, 3 to 10 parts by weight, or 4 to 8 parts by weight.

[0107] The acrylic-based polymer may contain alkyl (meth)acrylate as a constituent monomer component. Specific examples of alkyl (meth)acrylate are the same as those described above for the first embodiment.

[0108] When an acrylic-based polymer contains an alkyl (meth)acrylate as a constituent monomer, the amount of alkyl (meth)acrylate relative to 100 parts by weight of the total constituent monomer components may be 0.5 to 50 parts by weight, 1 to 40 parts by weight, 3 to 40 parts by weight, 5 to 30 parts by weight, or 10 to 25 parts by weight.

[0109] The acrylic-based polymer does not necessarily have to contain alkyl (meth)acrylate as a constituent monomer. Even if the acrylic-based polymer does contain alkyl (meth)acrylate as a constituent monomer, it is preferable that the amount of aromatic ring-containing (meth)acrylate in the constituent monomers of the acrylic-based polymer is greater than the amount of alkyl (meth)acrylate, from the viewpoint of increasing the glass transition temperature of the polymer and increasing the elastic modulus of the adhesive sheet.

[0110] On the other hand, from the viewpoint of adjusting the glass transition temperature of acrylic-based polymers, it can be useful to include alkyl (meth)acrylate as a constituent monomer. For example, when an acrylic-based polymer contains nitrogen-containing monomers in addition to (meth)acrylate with an aromatic ring as a constituent monomer, the glass transition temperature of the polymer tends to be higher. By incorporating low-Tg alkyl (meth)acrylate such as butyl acrylate or 2-ethylhexyl acrylate as a constituent monomer component, the glass transition temperature of the polymer can be lowered, which can improve adhesive strength at low temperatures.

[0111] In addition to the above, the acrylic-based polymer may also contain, as monomer components, high Tg monomers other than (meth)acrylic acid esters having an aromatic ring, (meth)acrylic acid esters having an alkylene oxide chain, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, sulfo group-containing monomers, phosphate group-containing monomers, acid anhydride group-containing monomers, and the like.

[0112] From the viewpoint of increasing the elastic modulus of the adhesive sheet after photocuring, the glass transition temperature of the acrylic base polymer is preferably -40°C or higher, more preferably -20°C or higher, even more preferably -10°C or higher, and may also be -5°C or higher or 0°C or higher. On the other hand, from the viewpoint of improving adhesion, the glass transition temperature of the acrylic base polymer is preferably 50°C or lower, more preferably 40°C or lower, and may also be 35°C or lower, 30°C or lower or 25°C or lower.

[0113] Generally, when the glass transition temperature of the base polymer is high, the tackiness of the adhesive decreases, and the adhesion to the substrate tends to be poor. On the other hand, in the present invention, the adhesive composition contains a photocuring agent, and the photocuring agent is in liquid form in the adhesive composition before photocuring. Therefore, even when the glass transition temperature of the acrylic base polymer is high, the adhesive exhibits tackiness. When the adhesive is photocured, it exhibits high adhesion and an increase in elastic modulus as the photocuring agent hardens. In the second embodiment, the glass transition temperature of the acrylic base polymer is higher than in the first embodiment, and the adhesive sheet after photocuring exhibits a greater elastic modulus. The adhesive sheet of the second embodiment exhibits little to no tackiness after photocuring.

[0114] The polymerization method for the acrylic polymer is the same as described above for the first embodiment. The weight-average molecular weight of the acrylic base polymer is preferably 100,000 to 3,000,000, more preferably 200,000 to 2,500,000, and even more preferably 300,000 to 2,300,000.

[0115] <Photocuring Agent> In the second form, a polyfunctional (meth)acrylate with a homopolymer glass transition temperature of 25°C or higher is used as the photocuring agent. By adding a high Tg acrylic base polymer containing an aromatic ring-containing (meth)acrylic acid ester as a constituent monomer component, and using a high Tg photocuring agent, the adhesive sheet after photocuring can achieve both high elastic modulus and adhesive strength.

[0116] Examples of polyfunctional (meth)acrylates having a glass transition temperature of 25°C or higher include polyfunctional (meth)acrylates having an alicyclic structure. Specific examples of polyfunctional (meth)acrylates having an alicyclic structure are the same as those described in the first embodiment, and include tricyclodecanedimethanol di(meth)acrylate, hydrogenated bisphenol A type epoxy(meth)acrylate, hydrogenated bisphenol F type epoxy(meth)acrylate, hydrogenated bisphenol E type epoxy(meth)acrylate, hydrogenated phthalate type epoxy(meth)acrylate, hydrogenated terpenephenol(meth)acrylate, and 1,4-cyclohexanedimethanol diglycidyl ether(meth)acrylate.

[0117] From the viewpoint of increasing the elasticity of the adhesive sheet, among the polyfunctional (meth)acrylates having an alicyclic structure exemplified above, tricyclodecanedimethanol di(meth)acrylate is particularly preferred, and from the viewpoint of increasing adhesive strength, tricyclodecanedimethanol dimethacrylate is particularly preferred.

[0118] Polyfunctional (meth)acrylates with a homopolymer glass transition temperature of 25°C or higher are not limited to those having an alicyclic structure. Examples of difunctional (meth)acrylates with a homopolymer glass transition temperature of 25°C or higher and without an alicyclic structure include polyethylene glycol di(meth)acrylate (with an average chain length n of EO of 5 or less), polypropylene glycol di(meth)acrylate (with an average chain length n of PO of 5 or less), trimethylolpropane tri(meth)acrylate, isocyanuric acid EO-modified di(meth)acrylate, bisphenol A type epoxy(meth)acrylate, bisphenol F type epoxy(meth)acrylate, and bisphenol E type epoxy(meth)acrylate.

[0119] Furthermore, many (meth)acrylates with three or more functions, such as trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-modified tri(meth)acrylate, trimethylolpropane PO-modified tri(meth)acrylate, pentaerythritol tri(meth)acrylate, isocyanuric acid EO-modified tri(meth)acrylate, isocyanuric acid PO-modified tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, exhibit a homopolymer glass transition temperature of 25°C or higher, even if they do not have an alicyclic structure. For polyfunctional (meth)acrylates, the glass transition temperature of the homopolymer tends to increase as the number of (meth)acryloyl functional groups increases. On the other hand, the greater the number of (meth)acryloyl functional groups per molecule of the photocuring agent, the greater the curing shrinkage of the adhesive sheet during photocuring, which can cause peeling due to stress strain at the adhesive interface. Therefore, the number of functional groups in the polyfunctional (meth)acrylate is preferably four or less, and more preferably two or three functional groups.

[0120] The higher the glass transition temperature of the photocuring agent homopolymer, the more likely the adhesive sheet will have a higher modulus of elasticity after photocuring. The glass transition temperature of the photocuring agent homopolymer is preferably 30°C or higher, more preferably 50°C or higher, even more preferably 75°C or higher, and may be 100°C or higher, 125°C or higher, 150°C or higher, or 175°C or higher. There is no particular upper limit to the glass transition temperature of the photocuring agent homopolymer, but if the glass transition temperature is excessively high, the adhesive strength may decrease. The glass transition temperature of the photocuring agent homopolymer is preferably 300°C or lower, and may be 250°C or lower, 230°C or lower, 210°C or lower, or 200°C or lower.

[0121] From the viewpoint of making the adhesive highly elastic after photocuring, the content of the polyfunctional (meth)acrylate, which has a glass transition temperature of 25°C or higher as a photocuring agent, is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more, and may also be 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the acrylic base polymer. From the viewpoint of the handling properties of the adhesive sheet before photocuring and the adhesive strength after photocuring, the content of the polyfunctional (meth)acrylate, which has a glass transition temperature of 25°C or higher as a photocuring agent, is preferably 150 parts by weight or less, more preferably 100 parts by weight or less, even more preferably 80 parts by weight or less, and may also be 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, or 55 parts by weight or less, per 100 parts by weight of the acrylic base polymer.

[0122] As a photocuring agent, a polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher may be used in combination with other photopolymerizable compounds. Examples of other photopolymerizable compounds include monofunctional (meth)acrylates or polyfunctional (meth)acrylates having a homopolymer glass transition temperature of less than 25°C. Specific examples of such photocuring agents are the same as those described in the first embodiment.

[0123] From the viewpoint of making the adhesive highly elastic after photocuring, the content of the photocuring agent in the adhesive composition (total of polyfunctional (meth)acrylates having a homopolymer glass transition temperature of 25°C or higher and other photopolymerizable compounds) is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more, and may also be 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the acrylic base polymer.

[0124] From the viewpoint of suppressing bleed-out of the photocuring agent and ensuring the handling properties of the adhesive sheet before photocuring and the adhesive strength to the substrate, the content of the photocuring agent in the adhesive composition is preferably 150 parts by weight or less, more preferably 100 parts by weight or less, even more preferably 80 parts by weight or less, and may also be 75 parts by weight or less, 70 parts by weight or less, 65 parts by weight or less, 60 parts by weight or less, or 55 parts by weight or less, per 100 parts by weight of the acrylic base polymer.

[0125] <Oligomer> The adhesive composition may contain an acrylic oligomer with a lower molecular weight than the acrylic base polymer described above. The weight molecular weight of the acrylic oligomer is approximately 1,000 to 30,000. The weight-average molecular weight of the acrylic oligomer is preferably 20,000 or less, more preferably 10,000 or less, and even more preferably 5,000 or less. The weight-average molecular weight of the acrylic oligomer may be 1,500 or more, 2,000 or more, or 2,500 or more.

[0126] The glass transition temperature of the acrylic oligomer is preferably 0°C or higher, more preferably 20°C or higher, even more preferably 40°C or higher, and may be 50°C or higher or 60°C or higher. Including an acrylic oligomer with a high glass transition temperature in the adhesive composition tends to increase the adhesive strength of the adhesive. There is no particular upper limit to the glass transition temperature of the acrylic oligomer, but it is generally 200°C or lower, and may be 150°C or lower, 120°C or lower, or 100°C or lower.

[0127] Acrylic oligomers contain alkyl (meth)acrylate as the main constituent monomer component. The content of alkyl (meth)acrylate in the constituent monomer component of the acrylic oligomer is more preferably 50% by weight or more, more preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, or 90% by weight or more, based on the total amount of constituent monomer component of the acrylic oligomer.

[0128] From the viewpoint of increasing the glass transition temperature, it is preferable that the acrylic oligomer contains a monomer component as an alkyl (meth)acrylate ester whose homopolymer has a glass transition temperature of 40°C or higher. Among alkyl (meth)acrylate esters whose homopolymer has a glass transition temperature of 40°C or higher, alicyclic alkyl (meth)acrylates are particularly preferred.

[0129] The acrylic oligomer may have alicyclic alkyl (meth)acrylate as its main constituent monomer. The amount of alicyclic alkyl (meth)acrylate per 100 parts by weight of the total constituent monomer components of the acrylic oligomer may be 50 parts by weight or more, 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more. The amount of alicyclic alkyl (meth)acrylate per 100 parts by weight of the total constituent monomer components of the acrylic oligomer may be 99 parts by weight or less, 97 parts by weight or less, or 95 parts by weight or less. Specific examples of acrylic oligomers having alicyclic alkyl (meth)acrylate as the main constituent monomer are the same as those described above in the first embodiment.

[0130] The adhesive tends to have greater adhesion to substrates such as glass and resin films when it contains acrylic oligomers in addition to the acrylic base polymer. In the second embodiment, high adhesion can be achieved by including (meth)acrylic acid esters having aromatic rings as constituent monomer components in the acrylic base polymer, so acrylic oligomers are not an essential component.

[0131] When the adhesive composition contains an acrylic oligomer, the content of the acrylic oligomer is preferably 1 to 100 parts by weight, more preferably 1.5 to 50 parts by weight, and may be 2 to 30 parts by weight, 2.5 to 20 parts by weight, 3 to 19 parts by weight, or 4 to 15 parts by weight, per 100 parts by weight of the acrylic base polymer.

[0132] <Other Components> As described above, in the second embodiment, the photocurable adhesive composition constituting the adhesive sheet 2 comprises an acrylic base polymer, a photocuring agent, and a photopolymerization initiator, and may further contain an acrylic oligomer. In addition to these, the adhesive composition may contain additives such as antistatic agents, silane coupling agents, tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, UV absorbers, antioxidants, and surfactants, to the extent that they do not impair the properties of the present invention.

[0133] The adhesive composition constituting the adhesive sheet 2 may contain organic or inorganic fine particles (fillers), but from the viewpoint of ensuring the transparency of the adhesive sheet, the filler content per 100 parts by weight of acrylic base polymer is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, and may be 1 part by weight or less or 0.5 parts by weight or less. The adhesive composition may also not contain fillers. In the second embodiment, the adhesive sheet after photocuring exhibits an even higher modulus of elasticity than in the first embodiment, and high elasticity is possible even without fillers.

[0134] <Formation of Adhesive Sheet> The method for forming the second form of adhesive sheet is not particularly limited, and an adhesive sheet 2 having a cross-linked acrylic base polymer, a photocuring agent, and a photopolymerization initiator can be obtained by the same method as described above for the first form. The second form of adhesive sheet may further contain an acrylic oligomer.

[0135] <Storage Modulus of Adhesive Sheet> In the second embodiment, the shear storage modulus of the photocured adhesive sheet 2 at 25°C is preferably 50 MPa or more, more preferably 70 MPa or more, even more preferably 90 MPa or more, and particularly preferably 100 MPa or more. The high modulus of the photocured adhesive sheet enhances the protective properties to the adherend. The shear storage modulus of the second embodiment adhesive sheet at 25°C after photocuring may be 1000 MPa or less, 800 MPa or less, 600 MPa or less, 500 MPa or less, 400 MPa or less, or 300 MPa or less.

[0136] The shear storage modulus at 85°C of the second form of adhesive sheet after photocuring is preferably 0.5 MPa or higher, and may be 0.7 MPa or higher, 0.9 MPa or higher, 1.0 MPa or higher, or 1.1 MPa or higher. The high elastic modulus at high temperatures of the photocured adhesive sheet tends to suppress peeling at high temperatures. Furthermore, the high elastic modulus at high temperatures provides high protection to the adherend even in high-temperature processes. The shear storage modulus at 85°C of the second form of adhesive sheet after photocuring may be 10 MPa or less, 8 MPa or less, 6 MPa or less, 5 MPa or less, 4 MPa or less, 3 MPa or less, or 2 MPa or less.

[0137] [[Reinforcement Film]] The adhesive sheet 2 may be provided as a substrate-less adhesive sheet as shown in Figure 1, or as an adhesive film (reinforcement film) in which the adhesive sheet 2 is fixedly laminated on a film substrate 1 as shown in Figure 2.

[0138] A reinforcing film is obtained by laminating a photocurable adhesive sheet 2 onto a film substrate 1. The adhesive sheet 2 may be formed on the film substrate 1 by applying an adhesive composition to the film substrate 1, or an adhesive sheet 2 formed on another substrate may be transferred onto the film substrate 1. For example, an adhesive composition can be applied to a release liner to create a substrate-less adhesive sheet with release liners 5 and 7 temporarily attached to both sides of the adhesive sheet, as shown in Figure 1. The release liner 7 on one side of the adhesive sheet 2 is then peeled off, and the film substrate 1 is bonded to the exposed surface of the adhesive sheet 2, thereby obtaining a reinforcing film with a release liner 5 temporarily attached to the surface of the adhesive sheet 2, as shown in Figure 3.

[0139] <Film Substrate> A flexible plastic film is used as the film substrate 1 of the reinforcing film 10. In order to fix the film substrate 1 and the adhesive sheet 2, it is preferable that the surface of the film substrate 1 to which the adhesive sheet 2 is attached is not treated with a release agent.

[0140] The thickness of the film substrate 1 is, for example, about 4 to 300 μm. From the viewpoint of reinforcing the device by providing rigidity and mitigating impact, the thickness of the film substrate 1 is preferably 5 μm or more, more preferably 12 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. From the viewpoint of giving flexibility to the film substrate 1, the thickness of the film substrate is preferably 200 μm or less, more preferably 150 μm or less, and may be 125 μm or less or 100 μm or less.

[0141] Examples of plastic materials constituting the film substrate 1 include polyester resins, polyolefin resins, cyclic polyolefin resins, polyamide resins, polyimide resins, polyetheretherketones, polyethersulfones, polyarylate resins, aramid resins, thermosetting elastomers, and thermoplastic elastomers. In the case of reinforcing films for optical devices such as displays, the film substrate 1 is preferably a transparent film. Furthermore, when photocuring the adhesive sheet 2 by irradiating it with active light from the film substrate 1 side, it is preferable that the film substrate 1 has transparency to the active light used for curing the adhesive. Polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, transparent polyimides, and transparent aramids are preferably used because they possess both mechanical strength and transparency. When irradiating with active light from the adherend side, it is sufficient that the adherend has transparency to the active light, and the film substrate 1 does not need to be transparent to the active light.

[0142] The surface of the film substrate 1 may be provided with functional coatings such as an easy-adhesion layer, an easy-slip layer, a release layer, an antistatic layer, a hard coat layer, or an anti-reflective layer. As mentioned above, in order to fix the film substrate 1 and the adhesive sheet 2 together, it is preferable that no release layer is provided on the surface of the film substrate 1 to which the adhesive sheet 2 is attached.

[0143] <Release Liner> When forming an adhesive sheet 2 on a film substrate 1, it is preferable to attach a release liner 5 to the adhesive sheet 2 for the purpose of protecting the adhesive sheet 2. The substrate used to form the adhesive sheet may be used as the release liner 5 as is.

[0144] As the release liners 5 and 7, plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film are preferably used. The thickness of the release liner is usually 3 to 200 μm, preferably about 10 to 100 μm. The contact surfaces of the release liners 5 and 7 with the adhesive sheet 2 are preferably treated with a release agent such as silicone-based, fluorine-based, long-chain alkyl-based, or fatty acid amide-based, or silica powder. In the embodiment shown in Figure 3, because the surface of the release liner 5 is treated with a release agent, when the release liner 5 is peeled off from the film substrate 1, peeling occurs at the interface between the adhesive sheet 2 and the release liner 5, and the state in which the adhesive sheet 2 is fixed to the film substrate 1 is maintained. The release liners 5 and 7 may have an antistatic treatment applied to either the release-treated surface or the untreated surface, or both. By applying an antistatic treatment to the release liners 5 and 7, static charge can be suppressed when the release liner is peeled off from the adhesive sheet.

[0145] [[Use of Adhesive Sheet and Reinforcement Film]] The adhesive sheet 2 described above is used for bonding various components. In one embodiment, the adhesive sheet 2 is used to bond a protective member such as a glass plate or film to the surface of a device or its components. By bonding a flexible film to the surface of a device or its components, appropriate rigidity is provided, and effects such as improved handling and impact resistance can be expected for components with a small thickness. As described above, by using a reinforcement film 10 in which the adhesive sheet 2 is pre-laminated onto a film substrate 1, the workability of bonding can be improved.

[0146] The substrate to which the reinforcing film is bonded is not particularly limited and can include various electronic devices, optical devices and their components. The reinforcing film may be bonded to the entire surface of the substrate, or it may be selectively bonded only to the part that requires reinforcement (the area to be reinforced).

[0147] The adhesive sheet before photocuring has moderate tackiness and excellent adhesion to the substrate. The adhesive strength (initial adhesive strength) between the adhesive sheet 2 before photocuring and the substrate is preferably 0.05 N / 25 mm or more, more preferably 0.1 N / 25 mm or more, even more preferably 0.3 N / 25 mm or more, and may be 0.5 N / 25 mm or more, 0.7 N / 25 mm or more, 1.0 N / 25 mm or more, or 1.5 N / 25 mm or more. The adhesive strength is determined by a peel test using a polyimide film as the substrate at a tensile speed of 300 mm / min and a peel angle of 180°. Unless otherwise specified, the adhesive strength is measured at 25°C.

[0148] After the reinforcing film is attached to the adherend, the adhesive sheet 2 is irradiated with active light to photocur the adhesive composition constituting the adhesive sheet 2. Examples of active light include ultraviolet light, visible light, infrared light, X-rays, alpha rays, beta rays, and gamma rays. Ultraviolet light is preferred as the active light because it can suppress hardening of the adhesive during storage and is easy to cure. The irradiation intensity and irradiation time of the active light can be appropriately set according to the composition, thickness, etc. Irradiation of the adhesive sheet 2 with active light may be carried out from either the film substrate 1 side or the adherend side, or from both sides.

[0149] As the adhesive sheet is photocured, the adhesive strength of the adhesive sheet to the substrate tends to increase. From the viewpoint of adhesive reliability during practical use of the device, the adhesive strength between the photocured adhesive sheet 2 and the substrate is preferably 2 N / 25 mm or more, more preferably 3 N / 25 mm or more, even more preferably 5 N / 25 mm or more, and may be 7 N / 25 mm or more, 9 N / 25 mm or more, or 10 N / 25 mm or more. It is preferable that the reinforcing film 10 has an adhesive strength within the above range of the photocured adhesive sheet 2 to the polyimide film.

[0150] As described above, in the first embodiment, the shear storage modulus of the photocured adhesive sheet 2 at 25°C is preferably 5.0 MPa or higher, more preferably 7.0 MPa or higher, even more preferably 9.0 MPa or higher, and may be 10 MPa or higher, or 11 MPa or higher. As described above, in the second embodiment, the shear storage modulus of the photocured adhesive sheet 2 at 25°C is preferably 50 MPa or higher, more preferably 70 MPa or higher, even more preferably 90 MPa or higher, and may be 100 MPa or higher, or 110 MPa or higher. The high modulus of elasticity of the photocured adhesive sheet enhances the protective properties for the adherend.

[0151] As described above, by laminating the film substrate 1 to the surface of the adherend 20 via the adhesive sheet 2 of the present invention, or by laminating a reinforcing film 10 in which the adhesive sheet 2 and the film substrate 1 are laminated, and then photocuring the adhesive sheet 2, rigidity is imparted to the adherend. Therefore, even if external forces are unexpectedly applied, such as when the device is dropped, heavy objects are placed on the device, or flying objects collide with the device, damage or scratches to the device can be prevented. Furthermore, since the adhesive sheet is firmly adhered to the device after photocuring, the film substrate 1 is less likely to peel off even after long-term use, resulting in excellent reliability.

[0152] [[Use as a reinforcing layer for adhesive sheets]] Because the adhesive sheet of the present invention has a high elastic modulus after photocuring, it can be used as a reinforcing layer even as a standalone adhesive sheet (substrate-less adhesive sheet) without a film substrate. In particular, the second form of the adhesive sheet has a high storage elastic modulus after photocuring and exhibits little to no tackiness despite being firmly adhered to the adherend, so it can function as a reinforcing layer even without a film substrate.

[0153] For example, by peeling off the release liner 7 from one side of the substrate-less adhesive sheet 2 shown in Figure 1, and bonding the exposed side of the adhesive sheet 2 to the surface of the adherend 20 (for example, a polyimide film substrate of an organic EL element), a laminate is obtained in which the adhesive sheet 2 is bonded to the surface of the adherend 20, as shown in Figure 5. After irradiating the adhesive sheet 2 of this laminate with active light to photocure it, the release liner 5 is peeled off from the photocure adhesive sheet 2 (reinforcement layer 12), as shown in Figure 6, a reinforced layer device is obtained in which the reinforcement layer 12, which is a photocured product of the adhesive sheet, is attached to the surface of the adherend 20.

[0154] The adhesive sheet 2 has tackiness before photocuring and exhibits adhesion to the adherend 20. The reinforcing layer 12 formed by photocuring of the adhesive sheet 2 adheres firmly to the adherend 20, but does not exhibit tackiness, so even after peeling off the release liner 5, it does not adhere to the conveying device or other components. Furthermore, since the reinforcing layer 12 can have a high storage modulus of about 100 MPa at room temperature, it can impart rigidity to the adherend even without a film substrate on its surface, and is highly reliable as it is difficult to peel off from the adherend even after long-term use.

[0155] The first and second embodiments of the present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to these embodiments.

[0156] [[Examples and Comparative Examples of the First Embodiment]] [Example 1] <Preparation of Acrylic-Based Polymer> In a reaction vessel equipped with a thermometer, stirrer, reflux condenser and nitrogen gas inlet tube, 95 parts by weight of butyl acrylate (BA) and 5 parts by weight of acrylic acid (AA) were added as monomers, 0.2 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 233 parts by weight of ethyl acetate as a solvent. Nitrogen gas was then introduced, and the mixture was purged with nitrogen for about 1 hour while stirring. After that, the mixture was heated to 60°C and reacted for 7 hours to obtain a solution of acrylic polymer A (glass transition temperature -53°C) with a weight-average molecular weight of 600,000.

[0157] <Preparation of Acrylic Oligomers> In a reaction vessel equipped with a thermometer, stirrer, reflux condenser, and nitrogen gas inlet tube, 95 parts by weight of cyclohexyl methacrylate (CHMA) and 5 parts by weight of acrylic acid (AA) were added as monomers, 10 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, 10 parts by weight of α-methylstyrene dimer as a chain transfer agent, and 119 parts by weight of toluene as a solvent. Nitrogen gas was then introduced, and the mixture was purged with nitrogen while stirring for about 1 hour. After that, the mixture was heated to 85°C and reacted for 4 hours to obtain a solution of acrylic oligomer P (glass transition temperature 68°C) with a weight-average molecular weight of 3600.

[0158] <Preparation of Adhesive Composition> An adhesive composition was prepared by adding 25 parts by weight of acrylic oligomer P (solids content) per 100 parts by weight of polymer solids, 40 parts by weight of photocuring agent (tricyclodecanedimethanol dimethacrylate, "NK Ester DCP-M" manufactured by Shin Nakamura Chemical Industry Co., Ltd.), 0.07 parts by weight of crosslinking agent (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd.), and 0.3 parts by weight of photopolymerization initiator ("Omnirad 651" manufactured by IGM RESINS) to a solution of acrylic polymer A and mixing the mixture.

[0159] <Preparation of Reinforcement Film> The above adhesive composition was applied to a 75 μm thick polyethylene terephthalate film using a fountain roll so that the thickness after drying was 20 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated side of a release liner (a 25 μm thick polyethylene terephthalate film with a silicone release treatment on its surface) was bonded to the adhesive-coated surface. Subsequently, an aging treatment was carried out in a 25°C atmosphere for 4 days to promote crosslinking, and a reinforcement film was obtained in which a photocurable adhesive sheet was fixedly laminated on the film substrate, with the release liner temporarily attached on top of it.

[0160] [Examples 2 to 11, Comparative Examples 1 to 13] In the preparation of the pressure-sensitive adhesive composition, a reinforcing film was produced in the same manner as in Example 1, except that the addition amount of the acrylic oligomer, and the type and addition amount of the photocuring agent were changed as shown in Table 1. In Comparative Examples 6 to 12, no acrylic oligomer was added. In Comparative Example 13, neither a photocuring agent nor a photopolymerization initiator was added.

[0161] [Evaluation] The following evaluations were performed on the reinforcing films obtained in the above Examples 1 to 11 and Comparative Examples 1 to 13.

[0162] <Storage Modulus of Pressure-Sensitive Adhesive Sheet> On a release liner, the pressure-sensitive adhesive composition was applied and crosslinked in the same manner as in each of the above Examples and Comparative Examples, to produce a pressure-sensitive adhesive sheet (before photocuring). A release liner was attached to the surface of the pressure-sensitive adhesive sheet before photocuring to shield it from oxygen, and the sheet was irradiated with 4000 mJ / cm ２ of ultraviolet rays using a 365 nm LED lamp to be photocured. The photocured pressure-sensitive adhesive sheets were laminated to prepare a measurement sample having a thickness of about 0.8 mm. Dynamic viscoelasticity measurement was performed under the following conditions using a rotational rheometer ("Discovery-HR2" manufactured by TA Instruments), and the value of shear storage modulus G' at a predetermined temperature was read. For the pressure-sensitive adhesive sheet of Comparative Example 13 having no photocurability, the measurement was performed without performing photocuring. Deformation mode: torsion Measurement frequency: 1 Hz Temperature increase rate: 5°C / min Measurement temperature: -50 to 150°C Shape: parallel plate, 8.0 mm diameter

[0163] <Adhesive Strength> A 25 μm-thick polyimide film ("UPILEX 25S" manufactured by UBE) was attached to a glass plate via a double-sided adhesive tape ("No.531" manufactured by Nitto Denko Corporation), to obtain a polyimide film substrate for measurement. The release liner was peeled and removed from the surface of the reinforcing film cut into a size of 25 mm width × 100 mm length, and the reinforcing film was bonded to the polyimide film substrate for measurement using a hand roller, and irradiated with 4000 mJ / cm from the reinforcing film side (PET film substrate side) using a 365 nm LED lamp ２The test sample was an adhesive sheet that had been photocured by irradiation with ultraviolet light. Using this test sample, the end of the film substrate of the reinforcing film was held with a chuck, and the reinforcing film was peeled 180° at a tensile speed of 300 mm / min, and the peel strength was measured. For Comparative Example 13, the measurement was performed without photocuring the adhesive sheet.

[0164] <Haze> The photocured adhesive sheets were prepared in the same manner as the samples prepared for measuring the storage modulus described above. The adhesive sheets were bonded to a glass plate, and the haze of the adhesive sheets was measured in accordance with JIS K7136 by irradiating light from the adhesive sheet side using a haze meter (NDH-5000, manufactured by Nippon Denshoku Industries). The adhesive sheets of Examples 1 to 11 and Comparative Examples 1 to 13 all had a haze of 0.5% and exhibited high transparency. The adhesive sheets of Examples 21 to 29 and Comparative Examples 21 to 23, described later, also had a haze of 0.5% and exhibited high transparency.

[0165] [Evaluation Results] Table 1 shows the composition of the adhesive in the reinforcing films of Examples 1 to 11 and Comparative Examples 1 to 13 (amount of acrylic oligomer added, and type and amount of photocuring agent), as well as the evaluation results of the storage modulus and adhesive strength of the adhesive at 25°C after photocuring. The amounts of acrylic oligomer and photocuring agent in Table 1 are relative to 100 parts by weight of solids of the acrylic base polymer. Details of the photocuring agents shown in Table 1 and Table 3 described later are as follows.

[0166] DCP-M: Tricyclodecane dimethanol dimethacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester DCP" DCP-A: Tricyclodecane dimethanol diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester A-DCP" A200: Polyethylene glycol #200 diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester A-200" A400: Polyethylene glycol #400 diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester A-400" A600: Polyethylene glycol #600 diacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester A-600" TMPT: Trimethylolpropane trimethacrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester TMPT" 701A: 2-Hydroxy-3-methacrylate propyl acrylate, manufactured by Shin-Nakamura Chemical Industry Co., Ltd. as "NK Ester 701A" EBECRYL225: Aliphatic urethane acrylate with a weight-average molecular weight of 1200 and 10 functional groups, manufactured by Daicel Ornex. EBECRYL1290: Aliphatic urethane acrylate with a weight-average molecular weight of 1000 and 6 functional groups, manufactured by Daicel Ornex.

[0167]

[0168] In Comparative Examples 6-8, where the adhesive composition did not contain an acrylic oligomer, increasing the amount of photocuring agent (DCP-M) increased the storage modulus, but tended to decrease the adhesive strength, making it impossible to achieve both high modulus and adhesive strength. The same was true for Comparative Examples 9-11.

[0169] Comparative Examples 1 to 4, in which the adhesive composition contained an acrylic oligomer and used a polyfunctional acrylate without an alicyclic structure as the photocuring agent, exhibited high adhesive strength in the photocured adhesive sheets, but had low storage modulus and poor reinforcing properties for the adherend. Comparative Example 13, which contained an acrylic oligomer but did not contain a photocuring agent (i.e., was not photocurable), showed similar results.

[0170] Examples 1 to 10, in which the adhesive composition contained an acrylic oligomer and a polyfunctional (meth)acrylate having an alicyclic structure was used as the photocuring agent, showed that the adhesive sheets after photocuring achieved both high elastic modulus and high adhesive strength.

[0171] Comparative Example 5, which contained a small amount of acrylic oligomer, showed a high modulus of elasticity, but lacked sufficient adhesive strength. A comparison of Comparative Example 5 with Examples 2 and 3 shows that the acrylic oligomer contributes to the increase in adhesive strength. A comparison of Examples 4 and 6 also showed a tendency for adhesive strength to increase with increasing amounts of acrylic oligomer. On the other hand, in Examples 9 and 10, which contained even larger amounts of acrylic oligomer, the adhesive strength decreased with increasing amounts of acrylic oligomer.

[0172] A comparison of Examples 5 to 7 showed that the storage modulus of the adhesive sheet after photocuring tended to increase with increasing amounts of the photocuring agent (DCP-M). However, in Example 8, which contained 40 parts by weight of the photocuring agent, the adhesive strength was lower compared to Examples 5 to 7.

[0173] Example 11, which used a polyfunctional acrylate (DCP-A) having an alicyclic structure as the photocuring agent, achieved both high modulus of elasticity and high adhesive strength, similar to Examples 1 to 10 which used a polyfunctional methacrylate (DCP-M). A comparison of Example 6 and Example 11 shows that using a polyfunctional methacrylate tends to result in higher adhesive strength of the adhesive sheet after photocuring.

[0174] [[Examples and Comparative Examples of the Second Form]] [Preparation of Acrylic-Based Polymers] The amount of monomer used was changed as shown in Table 2. Otherwise, solutions of acrylic polymers B and C were obtained in the same manner as the polymerization of acrylic polymer A. The monomer ratios used and the glass transition temperatures of acrylic polymers A to C are listed in Table 2. The glass transition temperature was calculated from the monomer ratios based on Fox's formula.

[0175] In Table 2, monomers are abbreviated as follows: BA Butyl acrylate BZA Benzyl acrylate NVP N-vinylpyrrolidone AA Acrylic acid

[0176]

[0177] [Example 21] <Preparation of Adhesive Composition> To a solution of acrylic polymer B, 10 parts by weight of a photocuring agent (tricyclodecanedimethanol dimethacrylate, "NK Ester DCP-M" manufactured by Shin Nakamura Chemical Industry Co., Ltd.), 0.05 parts by weight of a crosslinking agent (tetrafunctional epoxy compound, "Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd.), and 1 part by weight of a photopolymerization initiator ("Omnirad 651" manufactured by IGM RESINS Co., Ltd.) were added and mixed to prepare an adhesive composition.

[0178] <Preparation of Adhesive Sheet and Reinforcement Film> The above adhesive composition was applied to the release-treated surface of a release liner using a fountain roll so that the thickness after drying was 30 μm. After drying at 130°C for 1 minute to remove the solvent, the release-treated surface of another release liner was bonded to the adhesive-coated surface. Subsequently, an aging treatment was carried out in an atmosphere of 25°C for 4 days to promote crosslinking, and an adhesive sheet was obtained in which the release liner was temporarily attached to both sides of the photocurable adhesive sheet. The release liner was peeled off one side of the adhesive sheet, and a polyethylene terephthalate film with a thickness of 75 μm was bonded to the adhesive sheet, thereby obtaining a reinforcement film in which the photocurable adhesive sheet was fixedly laminated on the film substrate, and the release liner was temporarily attached on top of it.

[0179] [Examples 22-29, Comparative Examples 21-23] In preparing the adhesive composition, adhesive sheets and reinforcing films were prepared in the same manner as in Example 21, except that the type of acrylic polymer, the type and amount of photocuring agent, and the amounts of crosslinking agent and photopolymerization initiator were changed as shown in Table 3. In Example 29, 5 parts by weight of acrylic oligomer P was added to 100 parts by weight of solids of acrylic polymer C.

[0180] [Evaluation] For the adhesive sheets and reinforcing films obtained in Examples 21-29 and Comparative Examples 21-23 described above, the storage modulus of the adhesive sheet after photocuring, the adhesive strength to the polyimide film, and the haze were measured in the same manner as the evaluations for Examples 1-11 and Comparative Examples 1-13 described above. Furthermore, the release liner was peeled off the adhesive sheet after photocuring, and the presence or absence of tackiness of the adhesive sheet was evaluated by palpation.

[0181] [Evaluation Results] Table 3 shows the evaluation results for the adhesive composition of the adhesive sheets in Examples 21-29 and Comparative Examples 21-23 (type of acrylic polymer, amount of acrylic oligomer added, type and amount of photocuring agent, amount of crosslinking agent and photopolymerization initiator), as well as the storage modulus, adhesive strength, and tackiness of the adhesive after photocuring at 25°C and 85°C. The amounts of acrylic oligomer, photocuring agent, crosslinking agent, and photopolymerization initiator in Table 3 are given in relation to 100 parts by weight of the solids content of the acrylic polymer.

[0182]

[0183] In Comparative Example 21, which used acrylic polymer A, the storage modulus of the adhesive sheet at 25°C after photocuring was 6.5 MPa. In contrast, in Example 22, which used acrylic polymer B containing benzyl acrylate as a constituent monomer, the storage modulus of the adhesive sheet at 25°C after curing was 78 MPa, showing a significant increase in modulus. In Examples 21, 23-25, where the amount of photocuring agent (DCP-M) was changed, the storage modulus of the adhesive sheet at 25°C after photocuring was 50 MPa, and there was a tendency for the modulus to increase as the amount of photocuring agent increased. Furthermore, in these examples, even when acrylic oligomers were not included, the adhesive sheet after photocuring had high adhesive strength to the polyimide film, and when the amount of photocuring agent was up to about 30 parts by weight, there was a tendency for the adhesive strength to increase as the amount of photocuring agent increased.

[0184] In Example 28, which used acrylic polymer C containing benzyl acrylate and the nitrogen-containing monomer NVP as constituent monomer components, the adhesive strength was significantly increased compared to Example 24. In Example 29, which incorporated an acrylic oligomer, a further increase in adhesive strength was observed.

[0185] Examples 26, which used TMPT instead of DCP-M as the photocuring agent, and Example 27, which used A200, exhibited high modulus of elasticity and high adhesive strength, similar to Example 22. On the other hand, Comparative Examples 22, which used A600 as the photocuring agent, and Comparative Example 23, which used A400, showed lower storage modulus of elasticity at 25°C and 85°C after photocuring compared to Examples 21-29.

[0186] These results show that a combination of an acrylic polymer having an aromatic ring as a constituent monomer and a high Tg photocuring agent can yield an adhesive sheet with a high elastic modulus after photocuring and exhibiting high adhesive strength to the adherend. The adhesive sheets of Examples 21 to 29 do not exhibit tackiness after photocuring, and therefore can be used as a reinforcing layer even as an adhesive sheet alone.

[0187] 1 Film substrate 2 Adhesive sheet 12 Reinforcement layer (adhesive sheet after light curing) 10 Reinforcement film 5,7 Release liner 20 Adhesion surface

Claims

1. An adhesive sheet having a layered structure of a photocurable composition comprising an acrylic base polymer, an acrylic oligomer, a photocuring agent having one or more photopolymerizable functional groups, and a photopolymerization initiator, wherein the acrylic base polymer contains one or more constituent monomer components selected from the group consisting of hydroxyl group-containing monomers and carboxyl group-containing monomers, and has a crosslinked structure, the acrylic oligomer has a weight-average molecular weight of 1,000 to 30,000 and a glass transition temperature of 0°C or higher, the photocuring agent contains a polyfunctional (meth)acrylate having an alicyclic structure, and the photocurable composition contains 20 to 150 parts by weight of the acrylic oligomer per 100 parts by weight of the acrylic base polymer.

2. The adhesive sheet according to claim 1, wherein the photocurable composition comprises 20 to 100 parts by weight of the photocuring agent per 100 parts by weight of the acrylic base polymer.

3. The adhesive sheet according to claim 2, wherein the photocurable composition comprises 10 to 100 parts by weight of a polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent, per 100 parts by weight of the acrylic base polymer.

4. The adhesive sheet according to any one of claims 1 to 3, wherein the photocurable composition contains 0.7 to 2.5 times the amount of acrylic oligomer by weight relative to the polyfunctional (meth)acrylate having an alicyclic structure as the photocuring agent.

5. The adhesive sheet according to any one of claims 1 to 3, wherein the acrylic oligomer comprises an alkyl (meth)acrylate having an alicyclic alkyl group as a constituent monomer component.

6. The adhesive sheet according to any one of claims 1 to 3, wherein the glass transition temperature of the acrylic-based polymer is -60°C or higher.

7. The adhesive sheet according to any one of claims 1 to 3, wherein, after photocuring, the shear storage modulus at 25°C is 5.0 MPa or more.

8. A reinforcing film in which an adhesive sheet according to any one of claims 1 to 3 is fixedly laminated on one main surface of a film substrate.

9. A method for manufacturing a device having a reinforcing film laminated to its surface, comprising temporarily attaching the adhesive sheet of the reinforcing film according to claim 8 to the surface of a substrate, and then irradiating the adhesive sheet with active light to photocur the adhesive sheet.

10. A reinforcement method for laminating a reinforcing film onto the surface of an object, comprising: temporarily attaching the adhesive sheet of the reinforcing film described in claim 8 to the surface of the object; and photocuring the adhesive sheet by irradiating it with active light.

11. An adhesive sheet having a layered photocurable composition comprising an acrylic base polymer, a photocuring agent having one or more photopolymerizable functional groups, and a photopolymerization initiator, wherein the acrylic base polymer contains, as constituent monomer components, one or more selected from the group consisting of (meth)acrylic acid esters having aromatic rings, and hydroxyl group-containing monomers and carboxyl group-containing monomers, and has a crosslinked structure introduced, and the photocuring agent contains a polyfunctional (meth)acrylate having a homopolymer glass transition temperature of 25°C or higher.

12. The adhesive sheet according to claim 11, wherein the photocurable composition comprises 5 to 150 parts by weight of a polyfunctional (meth)acrylate having a glass transition temperature of 25°C or higher for the homopolymer used as the photocuring agent, per 100 parts by weight of the acrylic base polymer.

13. The adhesive sheet according to claim 11 or 12, wherein the polyfunctional (meth)acrylate having a glass transition temperature of 25°C or higher is a polyfunctional (meth)acrylate having an alicyclic structure.

14. The adhesive sheet according to claim 11 or 12, wherein the glass transition temperature of the acrylic-based polymer is -40°C or higher.

15. The adhesive sheet according to claim 11 or 12, wherein the acrylic-based polymer further comprises a nitrogen-containing monomer as a constituent monomer component.

16. The adhesive sheet according to claim 11 or 12, wherein the photocurable composition further comprises an acrylic oligomer having a weight-average molecular weight of 1,000 to 30,000 and a glass transition temperature of 0°C or higher.

17. The adhesive sheet according to claim 11 or 12, wherein the shear storage modulus at 25°C after photocuring is 50 MPa or more.

18. A method for manufacturing a device having a reinforcing layer on its surface, comprising: temporarily attaching an adhesive sheet according to claim 11 or 12 to the surface of an object to be attached; and then irradiating the adhesive sheet with active light to photocur the adhesive sheet, thereby forming the reinforcing layer.

19. A reinforcement method for forming a reinforcing layer on the surface of an object, comprising: temporarily attaching an adhesive sheet according to claim 11 or 12 to the surface of the object; and photocuring the adhesive sheet by irradiating it with active light.

20. A reinforcing film in which an adhesive sheet according to claim 11 or 12 is fixedly laminated on one main surface of a film substrate.

21. A method for manufacturing a device having a reinforcing film laminated to its surface, comprising temporarily attaching the adhesive sheet of the reinforcing film according to claim 20 to the surface of a substrate, and then irradiating the adhesive sheet with active light to photocur the adhesive sheet.

22. A reinforcement method for laminating a reinforcing film onto the surface of an object, comprising: temporarily attaching the adhesive sheet of the reinforcing film described in claim 20 to the surface of the object; and photocuring the adhesive sheet by irradiating it with active light.

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