Adhesive sheet, optical film with adhesive and image display device

Abstract

To provide an adhesive sheet having excellent durability even when used for an on-vehicle display.SOLUTION: There is provided an adhesive sheet (5) which contains an acrylic base polymer and has a shear storage modulus at 80°C of 3×104 Pa or more. The acrylic base polymer has 60 pts.wt or more of a (meth) acrylic acid alkyl ester based on 100 pts.wt. of the total amount of the constituent monomer components and contains butyl acrylate and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group as a (meth)acrylic acid alkyl ester, the glass transition temperature of the homopolymer is 10°C or more and the amount of the (meth)acrylic acid alkyl ester having an alicyclic alkyl group is 20 to 40 pts.wt. The acrylic base polymer has 20 to 40 pts.wt. of a hydroxyl group-containing monomer and 5 pts.wt. or less of a nitrogen-containing monomer based on 100 pts.wt. of the total amount of the constituent monomer components.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, an optical film with an adhesive, and an image display device.

Background Art

[0002] As various image display devices such as mobile phones, smartphones, car navigation devices, monitors for personal computers, and televisions, liquid crystal display devices and organic EL display devices are widely used. On the viewing-side surface of the image display device, a front transparent plate (also referred to as a "cover window"), such as a transparent resin plate or a glass plate, is provided for the purpose of preventing damage to the image display panel due to impact from the outer surface. The cover window is bonded to the viewing-side surface of the image display panel via an adhesive sheet (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The adhesive sheet disposed on the viewing-side surface of the image display panel is susceptible to the influence of external light, and the change in its characteristics can cause factors such as image quality degradation. In addition, in-vehicle displays such as car navigation devices are often exposed to a high-temperature environment for a long time. When outgassing occurs from foreign substances or the like present at the bonding interface, bubbles may remain at the bonding interface, and the visibility may be impaired.

Means for Solving the Problems

[0005] The adhesive sheet according to an embodiment of the present invention has a shear storage modulus of 3×10 4 Pa or more at 80°C.

[0006] The adhesive sheet may have a shear storage modulus at 25°C that is 1 to 8 times the shear storage modulus at 80°C.

[0007] The adhesive sheet may contain an acrylic polymer as a base polymer. The amount of the nitrogen-containing monomer is preferably 5 parts by weight or less with respect to 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer.

[0008] The adhesive sheet is used, for example, for bonding an image display panel and a cover window in an image display device in which a cover window is disposed on the viewing-side surface of the image display panel.

Advantages of the Invention

[0009] The adhesive sheet according to the embodiment of the present invention has resistance to outgas generated from foreign substances or the like, and thus can suppress the retention of bubbles at the bonding interface. In addition, since the change in characteristics after the weather resistance test is small and the weather resistance is excellent, it can also be suitably used for in-vehicle displays and the like.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] One embodiment of the present invention is an adhesive sheet used for bonding a cover window to the viewing-side surface of an image display panel in an image display device.

[0012] The adhesive sheet has a shear storage modulus at 80°C of 3×104 It is preferably Pa or more. Since the pressure-sensitive adhesive sheet having a large shear storage modulus at 80°C has resistance to outgassing generated from foreign substances or the like adhered to the adherend in a high-temperature environment, it can suppress the retention of bubbles at the bonding interface with the adherend.

[0013] The pressure-sensitive adhesive sheet is irradiated with light from a xenon lamp with an irradiation intensity of 0.63 W / cm at a wavelength of 340 nm for 500 hours. When a weather resistance test is performed, the change ΔG' in the shear storage modulus at 25°C before and after the weather resistance test is 5×10 2 It is preferably Pa or less. The pressure-sensitive adhesive sheet has an increase Δb in b 4 after the weather resistance test. * is preferably 0.5 or less. Thus, a pressure-sensitive adhesive sheet with little change in characteristics after the weather resistance test is preferably used for bonding the cover window to the visual side surface of the image display panel, and is particularly suitable for in-vehicle displays that require high weather resistance (light resistance). *

[0014] [Pressure-sensitive adhesive composition] <Base polymer> The pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet generally contains a base polymer. Examples of the base polymer include polymers such as acrylic, silicone, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy, fluorine-based, and rubber-based polymers.

[0015] In particular, an acrylic pressure-sensitive adhesive containing an acrylic polymer as the base polymer is preferred because of its excellent optical transparency and adhesiveness. The acrylic base polymer contains an alkyl (meth)acrylate as the main constituent monomer component. In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0016] As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or may have a cyclic alkyl group (alicyclic alkyl group).

[0017] Specific examples of the (meth)acrylic acid alkyl ester having a linear 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, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate and the like.

[0018] Specific examples of the alkyl (meth)acrylate having an alicyclic alkyl group include cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate; (meth)acrylate esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; (meth)acrylate esters having an alicyclic hydrocarbon ring of three or more rings such as dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may have a substituent on the ring, such as 3,3,5-trimethylcyclohexyl (meth)acrylate. Further, the alkyl (meth)acrylate having an alicyclic alkyl group may be a (meth)acrylate ester containing a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dicyclopentenyl (meth)acrylate.

[0019] The amount of the alkyl (meth)acrylate is preferably 60 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the total amount of the monomer components constituting the acrylic-based polymer.

[0020] The acrylic-based polymer may have a crosslinkable functional group as a copolymer monomer component. By having a crosslinkable functional group in the base polymer, the base polymer and a crosslinking agent can be reacted to increase the cohesive force of the adhesive and improve the adhesion reliability.

[0021] Examples of acrylic monomers having crosslinkable functional groups include hydroxy group-containing monomers and carboxy group-containing monomers. For example, when an isocyanate-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between the hydroxy group and the isocyanate group. When an epoxy-based crosslinking agent is used, a crosslinked structure is introduced by the reaction between the carboxy group and the epoxy group.

[0022] Examples of hydroxy group-containing monomers include (meth)acrylic acid 2-hydroxyethyl, (meth)acrylic acid 2-hydroxypropyl, (meth)acrylic acid 4-hydroxybutyl, (meth)acrylic acid 6-hydroxyhexyl, (meth)acrylic acid 8-hydroxyoctyl, (meth)acrylic acid 10-hydroxydecyl, (meth)acrylic acid 12-hydroxylauryl, and (meth)acrylic acid esters such as (4-hydroxymethylcyclohexyl)-methyl acrylate. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they greatly contribute to improving the adhesive strength and can suppress the clouding of the pressure-sensitive adhesive sheet in a high-humidity environment.

[0023] The amount of the hydroxy group-containing monomer is preferably 0.1 to 40 parts by weight, more preferably 1 to 35 parts by weight, based on 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer.

[0024] Examples of carboxy group-containing monomers include acrylic monomers such as (meth)acrylic acid, (meth)acrylic acid carboxyethyl, (meth)acrylic acid carboxypentyl, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0025] The acrylic base polymer may contain monomer components other than those described above. The acrylic base polymer may contain, as monomer components, for example, vinyl ester monomers, aromatic vinyl monomers, epoxy group-containing monomers, vinyl ether monomers, and the like.

[0026] The acrylic-based polymer may contain a nitrogen-containing monomer as a monomer component. Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, N-vinylcaprolactam, and the like.

[0027] When the acrylic-based polymer contains a nitrogen-containing monomer as a monomer component, the cohesive force tends to be improved and the adhesive force tends to be enhanced. On the other hand, the C-N bond has a bond energy of about 290 kJ / mol (= 3.0 eV; corresponding to a wavelength of 410 nm), which is smaller than that of the C-C bond and the C-O bond (bond energy of about 350 kJ / mol), and the bond is easily cleaved by light with a wavelength of 350 nm to 410 nm. Therefore, a base polymer with a high C-N bond content is likely to deteriorate upon light irradiation, and there are large changes in the shear storage modulus and color change (yellowing) of the pressure-sensitive adhesive sheet due to the weather resistance test.

[0028] By reducing the amount of the nitrogen-containing monomer in the monomer component constituting the base polymer, the amount of the C-N bond contained in the base polymer is small, and a pressure-sensitive adhesive sheet excellent in weather resistance can be obtained. The amount of the nitrogen-containing monomer is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and may be 1 part by weight or less, 0.5 part by weight or less, 0.1 part by weight or less, or 0.05 part by weight or less with respect to 100 parts by weight of the total amount of the monomer components constituting the acrylic-based polymer. The acrylic-based polymer may not contain a nitrogen-containing monomer as a monomer component.

[0029] From the viewpoint of enhancing the cohesive force and adhesive reliability of the acrylic-based polymer with a small amount of the nitrogen-containing monomer, it is preferable that the acrylic-based polymer does not contain a C-N bond and contains a high-Tg monomer having a glass transition temperature (Tg) of 10°C or higher of the homopolymer.

[0030] Examples of high-Tg monomers include styrene (Tg: 80°C), methyl methacrylate (Tg: 105°C), cyclohexyl acrylate (Tg: 15°C), cyclohexyl methacrylate (Tg: 66°C), 3,3,5-trimethylcyclohexyl acrylate (Tg: 52°C), dicyclopentanyl methacrylate (Tg: 175°C), dicyclopentanyl acrylate (Tg: 120°C), dicyclopentenyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 173°C), isobornyl acrylate (Tg: 97°C), 1-adamantyl methacrylate (Tg: 250°C), 1-adamantyl acrylate (Tg: 153°C), and the like. Among these high-Tg monomers, acrylate esters are preferred because they have excellent copolymerizability with low-Tg monomers such as butyl acrylate and 2-ethylhexyl acrylate. In addition, since both acrylate esters and methacrylate esters can exhibit a high Tg, (meth)acrylate esters having an alicyclic structure are preferred as high-Tg monomers. Among them, acrylate esters having an alicyclic structure such as cyclohexyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, isobornyl acrylate, and 1-adamantyl acrylate are preferred. The glass transition temperature of the homopolymer of the high-Tg monomer may be 13°C or higher or 15°C or higher.

[0031] With respect to 100 parts by weight of the total amount of monomer components constituting the acrylic-based polymer, the amount of the high-Tg monomer is preferably 3 to 40 parts by weight, more preferably 5 to 35 parts by weight, and even more preferably 10 to 30 parts by weight.

[0032] The glass transition temperature of the acrylic-based base polymer is preferably from -55°C to 10°C, more preferably from -50°C to 0°C. When the glass transition temperature of the base polymer is -55°C or higher, the difference in the shear storage elastic modulus between normal temperature (25°C) and high temperature (80°C) of the pressure-sensitive adhesive sheet becomes smaller, and the retention of bubbles caused by outgassing from foreign substances or the like in a high-temperature environment can be suppressed. Further, when the glass transition temperature of the base polymer is 10°C or lower, the pressure-sensitive adhesive sheet exhibits appropriate viscosity in the use environment and can exhibit excellent adhesiveness to the adherend.

[0033] The glass transition temperature of the polymer is the peak top temperature of the loss tangent (tanδ) by dynamic viscoelasticity measurement. The glass transition temperature can also be obtained from the theoretical Tg. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the constituent monomer components of the acrylic-based base polymer i and the weight fraction W of each monomer component i and is calculated by the following Fox's formula. 1 / Tg = Σ(W i / Tg i )

[0034] Tg is the glass transition temperature of the polymer chain (unit: K), W i is the weight fraction of the monomer component i constituting the segment (copolymerization ratio on a weight basis), Tg i is the glass transition temperature of the homopolymer of the monomer component i (unit: K). As the glass transition temperature of the homopolymer, the values described in Polymer Handbook, 3rd Edition (John Wiley & Sons, Inc., 1989) can be adopted. For the Tg of the homopolymer of a monomer not described in the above literature, the peak top temperature of tanδ by dynamic viscoelasticity measurement may be adopted.

[0035] <Crosslinked structure of the base polymer> The base polymer, which is the main component of the pressure-sensitive adhesive sheet, preferably has a crosslinked structure. By introducing a crosslinked structure into the base polymer, the cohesive force of the adhesive is enhanced, and a high adhesive force to the adherend is exhibited. Further, by introducing a crosslinked structure, the shear storage modulus at high temperature increases, and the retention of bubbles due to outgassing from foreign substances or the like tends to be suppressed. It can be adjusted.

[0036] As a method for introducing a crosslinked structure into the base polymer, (1) a method of adding a crosslinking agent to a base polymer having a functional group capable of reacting with the crosslinking agent after polymerization and reacting the base polymer with the crosslinking agent; and (2) a method of introducing a branched structure (crosslinked structure) into the polymer chain by including a polyfunctional compound in the polymerization components of the base polymer, and the like can be mentioned. These may be used in combination to introduce a plurality of types of crosslinked structures into the base polymer.

[0037] In the method of reacting the base polymer and the crosslinking agent of the above (1), a crosslinked structure is introduced into the base polymer by adding a crosslinking agent to the base polymer after polymerization and heating if necessary. Examples of the crosslinking agent include compounds that react with functional groups such as hydroxy groups and carboxy groups contained in the base polymer. Specific examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, metal chelate-based crosslinking agents, and the like.

[0038] Among them, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferable because they have high reactivity with hydroxy groups and carboxy groups of the base polymer and the introduction of a crosslinked structure is easy. These crosslinking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the base polymer to form a crosslinked structure. In the case of an acid-free pressure-sensitive adhesive in which the base polymer does not contain a carboxy group, it is preferable to form a crosslinked structure by the reaction of the hydroxy group in the base polymer with an isocyanate crosslinking agent using an isocyanate-based crosslinking agent.

[0039] In the method of including a polyfunctional monomer in the polymerization components of the base polymer described above (2), the total amount of the monomer components constituting the base polymer and the polyfunctional compound for introducing the crosslinked structure may be reacted all at once, or polymerization may be carried out in multiple steps. As a method of carrying out polymerization in multiple steps, a monofunctional monomer constituting the base polymer is polymerized (prepolymerization) to prepare a partial polymer (prepolymer composition), and a polyfunctional compound such as polyfunctional (meth)acrylate is added to the prepolymer composition, and the prepolymer composition and the polyfunctional monomer are polymerized (main polymerization). The prepolymer composition is a partial polymer containing a polymer of low degree of polymerization and unreacted monomers.

[0040] By performing prepolymerization of the constituent components of the acrylic-based base polymer, branch points (crosslinking points) due to the polyfunctional compound can be uniformly introduced into the base polymer. Further, after applying a mixture of a low molecular weight polymer or partial polymer and an unpolymerized monomer component (adhesive composition) onto a substrate, main polymerization can be carried out on the substrate to form an adhesive sheet. Since a low polymerization composition such as a prepolymer composition has a low viscosity and excellent coatability, according to the method of performing main polymerization on a substrate after applying an adhesive composition which is a mixture of a prepolymer composition and a polyfunctional compound, the productivity of the adhesive sheet can be improved and the thickness of the adhesive sheet can be made uniform.

[0041] Examples of the polyfunctional compound used for introducing the crosslinked structure include compounds containing two or more polymerizable functional groups (ethylenically unsaturated groups) having unsaturated double bonds in one molecule. As the polyfunctional compound, polyfunctional (meth)acrylate is preferable because it is easy to copolymerize with the monomer components of the acrylic-based base polymer. When introducing a branched (crosslinked) structure by active energy ray polymerization (photo polymerization), polyfunctional acrylate is preferable.

[0042] Examples of the polyfunctional (meth)acrylate 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, tricyclodecane dimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(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, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, and the like.

[0043] <Preparation of Base Polymer> The base polymer can be prepared by known polymerization methods such as solution polymerization, UV polymerization, bulk polymerization, emulsion polymerization, etc. From the viewpoints of transparency, water resistance, cost, etc. of the adhesive, the solution polymerization method or the active energy ray polymerization method (for example, UV polymerization) is preferred. Generally, ethyl acetate, toluene, etc. are used as the solvent for solution polymerization.

[0044] When preparing the base polymer, a polymerization initiator such as a photoinitiator or a thermal polymerization initiator may be used according to the type of polymerization reaction. The photoinitiator is not particularly limited as long as it can initiate photopolymerization. For example, benzoin ether-based photoinitiators, acetophenone-based photoinitiators, α-ketol-based photoinitiators, aromatic sulfonyl chloride-based photoinitiators, photoactive oxime-based photoinitiators, benzoin-based photoinitiators, benzyl-based photoinitiators, benzophenone-based photoinitiators, ketal-based photoinitiators, thioxanthone-based photoinitiators, acylphosphine oxide-based photoinitiators, etc. can be used. As the thermal polymerization initiator, for example, azo-based initiators, peroxide-based initiators, redox initiators (e.g., combinations of persulfates and sodium bisulfite, combinations of peroxides and sodium ascorbate, etc.) can be used.

[0045] During polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retarder), etc. may be used for the purpose of molecular weight adjustment, etc. Examples of the chain transfer agent include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimer.

[0046] When introducing a crosslinked structure with an isocyanate-based crosslinking agent or the like, after polymerizing the base polymer by solution polymerization, it is preferable to add the crosslinking agent and perform heating as necessary to introduce a crosslinked structure into the base polymer. When introducing a crosslinked structure with a polyfunctional compound such as polyfunctional (meth)acrylate, it is preferable to polymerize the base polymer or prepare a prepolymer composition by solution polymerization or active energy ray polymerization, add the polyfunctional compound, and then introduce a crosslinked structure formed by the polyfunctional compound by active energy ray polymerization.

[0047] The prepolymer composition can be prepared, for example, by subjecting a composition obtained by mixing a monomer component constituting an acrylic-based polymer and a polymerization initiator (referred to as "composition for prepolymer formation") to partial polymerization (prepolymerization). The monomers in the composition for prepolymer formation are preferably monofunctional monomer components such as alkyl (meth)acrylate esters and monomers containing polar groups. The composition for prepolymer formation may contain a polyfunctional monomer in addition to the monofunctional monomer. For example, a part of the polyfunctional monomer may be contained in the composition for prepolymer formation, and the remainder of the polyfunctional monomer component may be added after prepolymerization to carry out bulk polymerization.

[0048] The polymerization rate of the prepolymer is not particularly limited, but from the viewpoint of having a viscosity suitable for coating on a substrate, 3 to 50% by weight is preferable, and 5 to 40% by weight is more preferable. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photoinitiator, the irradiation intensity and irradiation time of actinic rays such as UV light, and the like.

[0049] <Preparation of the pressure-sensitive adhesive composition> A pressure-sensitive adhesive composition is prepared by mixing an acrylic-based polymer (or prepolymer composition) with a crosslinking agent and / or polyfunctional compound for introducing the degree of crosslinked structure, and other additives. If necessary, the remainder of the monomer components constituting the acrylic-based polymer may be added to the pressure-sensitive adhesive composition. For the purpose of viscosity adjustment or the like, a thickening additive or the like may be used.

[0050] When the pressure-sensitive adhesive composition contains a prepolymer composition and a polyfunctional compound or the like, the pressure-sensitive adhesive composition preferably contains a photoinitiator for bulk polymerization. After prepolymerization, a polymerization initiator for bulk polymerization may be added to the prepolymer composition. When the polymerization initiator during prepolymerization remains without being deactivated in the prepolymer composition, the addition of the polymerization initiator for bulk polymerization may be omitted. The pressure-sensitive adhesive composition may contain a chain transfer agent.

[0051] The content of the acrylic-based polymer (or prepolymer composition) in the total amount of non-volatile components in the adhesive composition is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and particularly preferably 90% by weight or more.

[0052] For the purpose of adjusting the adhesive strength, a silane coupling agent may be added to the adhesive composition. When a silane coupling agent is added to the adhesive composition, the addition amount is usually about 0.01 to 5.0 parts by weight, preferably about 0.03 to 2.0 parts by weight, based on 100 parts by weight of the base polymer.

[0053] In addition to the components exemplified above, the adhesive composition may contain various additives such as various oligomers, tackifiers, plasticizers, softeners, anti-degradants, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, etc.

[0054] [Formation of Adhesive Sheet] An adhesive sheet is formed on a substrate by applying an adhesive composition onto the substrate and, if necessary, drying and removing the solvent and / or subjecting it to bulk polymerization by irradiation with active light. As the substrate used for forming the adhesive sheet, any suitable substrate can be used. As the substrate, a release film having a release layer on the contact surface with the adhesive sheet may also be used.

[0055] As the film base material of the release film, films made of various resin materials are used. Examples of the resin materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl alcohol resins, polyarylate resins, polyphenylene sulfide resins, etc. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the film base material is preferably 10 to 200 μm, more preferably 25 to 150 μm. Examples of the material for the release layer include silicone-based release agents, fluorine-based release agents, long-chain alkyl-based release agents, fatty acid amide-based release agents, etc. The thickness of the release layer is generally about 10 to 2000 nm.

[0056] As the coating method of the adhesive composition onto the base material, various methods such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brush, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coater, etc. are used.

[0057] When the base polymer of the adhesive composition is a solution polymerized polymer, it is preferable to dry the solvent after coating. As the drying method, an appropriate method can be adopted as appropriate according to the purpose. The heat drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, and particularly preferably 70°C to 170°C. The drying time can be an appropriate time adopted as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

[0058] When the pressure-sensitive adhesive composition contains a crosslinking agent, a crosslinking reaction may be carried out after the pressure-sensitive adhesive composition is applied onto the substrate. When crosslinking, heating may be carried out as necessary. The temperature of the crosslinking reaction is usually in the range of 20°C to 160°C, and the time of the crosslinking reaction is about 1 minute to 7 days. After the pressure-sensitive adhesive composition is applied, the heating for drying the solvent may also serve as the heating for crosslinking. After the solvent is dried, it is preferable to attach a cover sheet to protect the surface of the pressure-sensitive adhesive sheet. As the cover sheet, it is preferable to use a release film having a release layer on the contact surface with the pressure-sensitive adhesive sheet, similar to the base film.

[0059] When the pressure-sensitive adhesive composition is a photopolymerizable composition containing a prepolymer composition, a polyfunctional compound, etc., after the pressure-sensitive adhesive composition is applied in layers on the substrate, photocuring is carried out by irradiating active light rays. When performing photocuring, it is preferable to attach a cover sheet to the surface of the coating layer and irradiate the active light rays in a state where the pressure-sensitive adhesive composition is sandwiched between two sheets to prevent polymerization inhibition by oxygen.

[0060] The active light rays may be selected according to the types of polymerizable components such as monomers and polyfunctional (meth) acrylates, the types of photoinitiators, etc. Generally, ultraviolet rays and / or short-wavelength visible light are used. The integrated light quantity of the irradiated light is preferably about 100 to 5000 mJ / cm 2 ². The light source for light irradiation is not particularly limited as long as it can irradiate light in the wavelength range to which the photoinitiator contained in the pressure-sensitive adhesive composition is sensitive. LED light sources, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, xenon lamps, etc. are preferably used.

[0061] By laminating the release films 1 and 2 on the surface of the pressure-sensitive adhesive sheet 5, a pressure-sensitive adhesive sheet with release films temporarily attached to both sides can be obtained as shown in FIG. 1. The base material and the cover sheet at the time of forming the pressure-sensitive adhesive sheet may be used as the release films 1 and 2 as they are.

[0062] When the release films 1 and 2 are provided on both sides of the adhesive sheet 5, the thickness of one release film 1 and the thickness of the other release film 2 may be the same or different. The peeling force when peeling the release film temporarily attached to one surface from the adhesive sheet 5 and the peeling force when peeling the release film temporarily attached to the other surface from the adhesive sheet 5 may be the same or different.

[0063] [Physical properties of the adhesive sheet] The total light transmittance of the adhesive sheet is preferably 85% or more, more preferably 90% or more. The haze of the adhesive sheet is preferably 1.5% or less, more preferably 1% or less.

[0064] The thickness of the adhesive sheet is not particularly limited and may be appropriately adjusted according to the type of adherend and the like. From the viewpoint of increasing the adhesive strength of the adhesive sheet, the thickness is preferably 10 μm or more. From the viewpoints of processability and handleability, etc., the thickness of the adhesive sheet is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less.

[0065] As described above, from the viewpoint of providing resistance to outgassing generated from foreign substances, etc. and suppressing the retention of bubbles, the shear storage modulus G' of the adhesive sheet at 80 °C 80 is preferably 3×10 4 Pa or more. G' 80 may be 4×10 4 Pa or more or 5×10 4 Pa or more. The upper limit of G' 80 is not particularly limited, but from the viewpoint of imparting followability to the printing step, etc., G' 80 is 5×10 5 Pa or less, 4×10 5 Pa or less, 3×10 5 Pa or less, or 2×10 5 Pa or less may be acceptable.

[0066] From the viewpoint of achieving both adhesiveness and handleability, the shear storage modulus G' of the adhesive sheet at 25 °C 25 is 5×10 4 ~5×10 5Pa is preferred, 8×10 4 ~3×10 5 Pa is more preferable, 1×10 5 ~2×10 5 It may be Pa.

[0067] From the viewpoint of achieving both adhesiveness at room temperature and resistance to outgassing at high temperatures, the G' of the adhesive sheet 25 and G' 80 The ratio G' 25 / G' 80 is preferably 1 to 8, more preferably 1.2 to 5, and may be 1.4 to 4. As described above, by increasing the glass transition temperature of the base polymer, the temperature dependence of the shear storage modulus (G' 25 / G' 80 ) becomes smaller, and G' 80 The shear storage modulus G' of a pressure-sensitive adhesive sheet is determined by viscoelasticity measurement at a frequency of 1 Hz.

[0068] As mentioned above, the PSA sheet has a G' value after the weather resistance test. 25 The change in ΔG' is 5×10 4 It is preferable that ΔG' is 4×10 Pa or less. 4 Pa or less is preferable, 3.5×10 4 ΔG' is the G' of the pressure sensitive adhesive sheet before the weather resistance test. 25 and G' of the adhesive sheet after weather resistance test 25 The absolute value of the difference between the G' of the adhesive sheet was 25 When the bond is broken by light irradiation, the generated radicals recombine with the polymer chain (curing deterioration), and after weathering test, G' 25 often increases.

[0069] As mentioned above, the pressure sensitive adhesive sheet has a transmitted light b * The increase in Δb * It is preferable that is small. * is the chromaticity index b of the CIE1976 color space * Δb *is preferably 0.5 or less, more preferably 0.4 or less, still more preferably 0.3 or less, and may be 0.2 or less.

[0070] As described above, the C-N bond has a small bond energy and is easily cleaved by ultraviolet rays contained in sunlight or fluorescent lamps. Therefore, when the base polymer constituting the pressure-sensitive adhesive sheet does not contain a C-N bond or has a low content of a C-N bond, deterioration of the base polymer due to light irradiation (weather resistance test) is suppressed, and ΔG’ and Δb * tend to be small.

[0071] [Image display device] The pressure-sensitive adhesive sheet of the present invention can be used for bonding various transparent members and opaque members. The type of adherend is not particularly limited, and examples thereof include various resin materials, glass, and metal. Since the pressure-sensitive adhesive sheet of the present invention has high transparency, it is suitable for bonding optical members such as image display devices. In particular, since the pressure-sensitive adhesive sheet of the present invention has excellent weather resistance, it is preferably used for bonding a transparent member to the visual side surface of an image display device, and can also be applied to in-vehicle displays such as car navigation devices.

[0072] FIG. 2 is a cross-sectional view showing an example of a laminated structure of an image display device in which a cover window 7 is bonded to the visual side surface of an image display panel 10 via a pressure-sensitive adhesive sheet 5. The image display panel 10 includes a polarizing plate 3 bonded to the visual side surface of an image display cell 6 such as a liquid crystal cell or an organic EL cell via a pressure-sensitive adhesive sheet 4. The cover window 7 is made of, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate. The cover window may have a touch panel function. As the touch panel, any type of touch panel such as a resistive film method, a capacitance method, an optical method, or an ultrasonic method can be used.

[0073] The polarizing plate 3 provided on the surface of the image display panel 10 and the cover window 7 are bonded together via the adhesive sheet 5. The bonding order is not particularly limited, and the adhesive sheet 5 may be bonded to the image display panel 10 first, or the adhesive sheet 5 may be bonded to the cover window 7 first. Also, the bonding of both can be performed simultaneously.

[0074] [Optical Film with Adhesive Sheet] In addition to the form in which the release films are temporarily attached to both sides as shown in FIG. 1, the adhesive sheet of the present invention can also be used as an optical film with an adhesive in which the adhesive sheet is fixed to an optical film such as a polarizing plate. For example, in the form shown in FIG. 3, the release film 1 is temporarily attached to one surface of the adhesive sheet 5, and the polarizing plate 3 is fixed to the other surface of the adhesive sheet 5. In the form shown in FIG. 4, an adhesive sheet 4 is further provided on the polarizing plate 3, and the release film 2 is temporarily attached thereon.

[0075] Thus, in the form in which an optical film such as a polarizing plate is bonded to the adhesive sheet in advance, the release film 1 temporarily attached to the surface of the adhesive sheet 5 may be peeled off and bonded to a cover window or the like.

Examples

[0076] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0077] [Production of Adhesive Sheet] [Polymerization of Prepolymer] As a monomer component for forming a prepolymer, monomers in the ratios shown in Table 1 (total 100 parts by weight), and 0.10 part by weight of "Omnirad 184" manufactured by IGM Resins as a photopolymerization initiator were blended, and polymerization was carried out by irradiating with ultraviolet rays to obtain a prepolymer composition (polymerization rate: about 10%).

[0078] In Table 1, the monomers are described by the following abbreviations. 2EHA: 2-Ethylhexyl acrylate BA: Butyl acrylate ISA: Isostearyl acrylate CHA: Cyclohexyl acrylate IBXA: Isobornyl acrylate 4HBA: 4-Hydroxybutyl acrylate NVP: N-Vinyl-2-pyrrolidone

[0079] <Preparation of Adhesive Composition> To 100 parts by weight of the above prepolymer composition, as post-added components, a polyfunctional monomer (1,6-hexanediol diacrylate; HDDA), a silane coupling agent (''KBM403'' manufactured by Shin-Etsu Chemical Co., Ltd.), and a chain transfer agent (α-thioglycerol) in the amounts shown in Table 1 were added, and then uniformly mixed to prepare an adhesive composition.

[0080] <Production of Adhesive Sheet> The above photocurable adhesive composition was applied to the release-treated surface of a separator (a polyethylene terephthalate (PET) film with a thickness of 75 μm and one side release-treated) to a thickness of 50 μm to form a coating layer. Another separator was laminated on this coating layer, and ultraviolet irradiation was performed under the conditions of illuminance: 6.5 mW / cm 2 , light amount: 1500 mJ / cm 2 to photocure the coating layer and obtain an adhesive sheet with a thickness of 50 μm.

[0081] [Evaluation of Adhesive Sheet] <Shear Storage Modulus> An adhesive sheet laminated to a thickness of about 1.5 mm was used as a measurement sample. Using an ''Advanced Rheometric Expansion System (ARES)'' manufactured by Rheometric Scientific, dynamic viscoelasticity measurement was performed under the following conditions, and the storage modulus G' at each temperature was read from the measurement results. Deformation mode: torsion Measurement frequency: 1 Hz Heating rate: 5 °C / min Shape: Parallel plates, 7.9 mm φ

[0082] <Weather resistance test> After peeling off the separator on one side of the adhesive sheet and laminating it on the glass plate, the separator on the other side of the adhesive sheet was peeled off and laminated on the glass plate to prepare a sample in which glass plates were laminated on both sides of the adhesive sheet. In a xenon weather meter, this sample was irradiated with light from a xenon lamp with an irradiation intensity of 0.63 W / cm² at a wavelength of 340 nm for 500 hours to conduct a weather resistance test. The b value of the transmitted light of the sample before the test was b₀, and the difference Δb = b₁ - b₀ between the b value of the transmitted light of the sample after the test and b₀, and the difference ΔG' in the shear storage modulus of the adhesive sheet at a temperature of 25°C before and after the test were determined. The transmitted light b was measured using a spectrophotometer ("U4100" manufactured by Hitachi High-Tech). 2 of the xenon lamp was irradiated for 500 hours to conduct a weather resistance test. The b value of the transmitted light of the sample before the test was b * 0, and the b value of the transmitted light of the sample after the test was b * 1, and the difference Δb * = b * 1 - b * 0, and the difference ΔG' in the shear storage modulus of the adhesive sheet at a temperature of 25°C before and after the test were determined. The transmitted light b * was measured using a spectrophotometer ("U4100" manufactured by Hitachi High-Tech).

[0083] The composition of the adhesive of each adhesive sheet and the evaluation results are shown in Table 1. The numerical values of the prepolymer composition and the post-added components in Table 1 indicate the weight ratio with the total of the monomers used in the preparation of the prepolymer being 100 parts by weight.

[0084]

Table 1

[0085] As shown in Table 1, it can be seen that the adhesive sheets of the examples have a large shear storage modulus at a temperature of 80°C, small ΔG' and Δb, and are excellent in weather resistance. *

Explanation of symbols

[0086] 5 Adhesive sheet 1, 2 Release film 3 Polarizing plate 4 Adhesive sheet 6 Image display cell 10 Image display panel ​7 Cover window 100 Image display device

Claims

1. An adhesive sheet containing an acrylic-based polymer, wherein the acrylic-based polymer has, based on 100 parts by weight of the total amount of the constituent monomer components, an amount of (meth)acrylic acid alkyl ester of 60 parts by weight or more, an amount of hydroxy group-containing monomer of 20 to 40 parts by weight, and an amount of nitrogen-containing monomer of 5 parts by weight or less, the (meth)acrylic acid alkyl ester includes butyl acrylate and (meth)acrylic acid alkyl ester having an alicyclic alkyl group, based on 100 parts by weight of the total amount of the constituent monomer components, the glass transition temperature of the homopolymer is 10°C or more and the amount of (meth)acrylic acid alkyl ester having an alicyclic alkyl group is 20 to 40 parts by weight, The shear storage modulus at 80 °C is 3×10 ４ Pa or more, an adhesive sheet.

2. The adhesive sheet according to Claim 1, wherein the shear storage modulus at 25°C is 1 to 8 times the shear storage modulus at 80°C.

3. An optical film with an adhesive layer, comprising the adhesive sheet according to Claim 1 or 2 on one surface of the optical film.

4. An image display device, wherein a cover window is bonded to the visible side surface of the image display panel via the adhesive sheet according to Claim 1 or 2.

Images