Adhesive sheet, optical film with adhesive, and image display device

Abstract

The invention relates to an adhesive sheet, an optical film with an adhesive, and an image display device. The adhesive sheet (5) has a shear storage modulus at 80 DEG C of 3 * 104 Pa or more. The absolute value [Delta] G'of the difference between the shear storage modulus at 25 DEG C after a weather test performed by irradiating light from a xenon lamp having an irradiation intensity of 0.63 W / cm2 at a wavelength of 340 nm for 500 hours and the shear storage modulus at 25 DEG C before the weather test is 5 * 104 Pa or less. It is preferable that the amount of increase [Delta] b * of transmitted light b * before and after a weather test of the adhesive sheet be 0.5 or less.

Description

[0001] This application is a divisional application of the Chinese patent application with the application date of September 28, 2021, application number 202111143296.9, and invention name: Adhesive sheet, optical film with adhesive, and image display device. Technical Field

[0002] The present invention relates to a pressure-sensitive adhesive sheet, an optical film with a pressure-sensitive adhesive, and an image display device. Background Art

[0003] Liquid crystal display devices and organic electroluminescent (EL) display devices are widely used as various image display devices such as mobile phones, smartphones, car navigation systems, personal computer monitors, and televisions. To prevent damage to the image display panel caused by external impact, a front transparent plate (also called a "cover window") such as a transparent resin plate or glass plate is provided on the visible side of the image display device. The cover window is attached to the visible side of the image display panel via an adhesive sheet (see, for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-237965 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] The adhesive sheet placed on the visible side of an image display panel is susceptible to external light, and changes in its properties can lead to image quality degradation. Furthermore, in-vehicle displays, such as car navigation systems, are often exposed to high temperatures for extended periods of time. When outgassing from foreign matter at the bonding interface occurs, bubbles can become trapped there, impairing visibility.

[0009] Means used to solve problems

[0010] The shear storage modulus of the pressure-sensitive adhesive sheet according to one embodiment of the present invention at 80°C is 3×10 4 The absolute value ΔG' of the difference between the shear storage modulus at 25°C after the weathering test and the shear storage modulus at 25°C before the weathering test of the pressure-sensitive adhesive sheet is 5×10 4 Pa or less. Transmitted light b before and after the weathering test of the adhesive sheet * The increase Δb * The weathering test shows that the irradiation intensity at a wavelength of 340 nm is 0.63 W / cm2 for 500 hours. 2 It is carried out with the light of a xenon lamp.

[0011] The shear storage modulus of the pressure-sensitive adhesive sheet at 25°C may be 1 to 8 times the shear storage modulus at 80°C.

[0012] The pressure-sensitive adhesive sheet may contain an acrylic polymer as a base polymer, and the amount of the nitrogen-containing monomer is preferably 5 parts by weight or less relative to 100 parts by weight of the total amount of monomer components constituting the acrylic base polymer.

[0013] The pressure-sensitive adhesive sheet is used, for example, in an image display device in which a cover window is provided on the visible side surface of the image display panel to bond the image display panel to the cover window.

[0014] Effects of the Invention

[0015] The adhesive sheet of the embodiment of the present invention has the ability to prevent outgassing from foreign matter, etc., thereby suppressing the accumulation of bubbles at the bonding interface. In addition, due to the minimal change in properties after weathering testing and excellent weather resistance, it is also suitable for use in automotive displays, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a cross-sectional view showing a structural example of a pressure-sensitive adhesive sheet with a release film.

[0017] Figure 2 It is a cross-sectional view showing a structural example of an image display device.

[0018] Figure 3 It is a cross-sectional view showing an example of a laminated structure of an optical film with a pressure-sensitive adhesive.

[0019] Figure 4 It is a cross-sectional view showing an example of a laminated structure of an optical film with a pressure-sensitive adhesive.

[0020] Label Description

[0021] 5 adhesive sheet

[0022] 1.2 Release film

[0023] 3 polarizing plates

[0024] 4 adhesive sheets

[0025] 6 Image display unit

[0026] 10 Image display panel

[0027] 7 Overlay Window

[0028] 100 Image display device DETAILED DESCRIPTION

[0029] One embodiment of the present invention is an adhesive sheet for attaching a cover window to a viewing side surface of an image display panel in an image display device.

[0030] The shear storage modulus of the adhesive sheet at 80°C is preferably 3×10 4 Pa or more. A PSA sheet having a large shear storage modulus at 80°C has the ability to prevent outgassing from foreign matter attached to the adherend in a high-temperature environment, thereby suppressing the accumulation of bubbles at the bonding interface with the adherend.

[0031] The adhesive sheet was irradiated for 500 hours with an irradiation intensity of 0.63 W / cm at a wavelength of 340 nm. 2 In a weathering test using xenon lamp light, the change in shear storage modulus ΔG' of the adhesive sheet at 25°C before and after the weathering test is preferably 5×10 4 Pa or less. b after weathering test of adhesive sheet * The increase Δb * The PSA sheet with minimal change in properties after weathering testing is suitable for laminating a cover window to the visible side surface of an image display panel, and is particularly suitable for in-vehicle displays requiring high weather resistance (light resistance).

[0032] [Adhesive composition]

[0033] <Base polymer>

[0034] The adhesive composition constituting the adhesive sheet generally contains a base polymer, which may be acrylic polymers, polysiloxanes, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxies, fluoropolymers, rubbers, and the like.

[0035] In particular, acrylic adhesives containing an acrylic polymer as a base polymer are preferred due to their excellent optical transparency and adhesive properties. Acrylic base polymers contain an alkyl (meth)acrylate as a primary monomer component. It should be noted that, in this specification, "(meth)acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0036] As the alkyl (meth)acrylate, preferably used are those having an alkyl group with 1 to 20 carbon atoms. The alkyl group of the alkyl (meth)acrylate may have a branched chain, or the alkyl (meth)acrylate may have a cyclic alkyl group (alicyclic alkyl group).

[0037] Specific examples of the (meth)acrylate alkyl ester having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-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, (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, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like.

[0038] Specific examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylates having a dicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; and (meth)acrylates having three or more aliphatic hydrocarbon rings such as tetrahydrodicyclopentadienyl (meth)acrylate, tetrahydrodicyclopentadienyloxyethyl (meth)acrylate, tetrahydrotricyclopentadienyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate. Alkyl (meth)acrylates having an alicyclic alkyl group may be alkyl (meth)acrylates having a substituent on the ring such as 3,3,5-trimethylcyclohexyl (meth)acrylate. The alkyl (meth)acrylate having an alicyclic alkyl group may be a (meth)acrylate containing a condensed ring of an alicyclic structure and a ring structure having an unsaturated bond, such as dihydrodicyclopentadienyl (meth)acrylate.

[0039] 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 base polymer.

[0040] The acrylic base polymer may contain an acrylic monomer having a crosslinkable functional group as a comonomer component. The base polymer having a crosslinkable functional group can enhance the cohesive force of the adhesive by reacting the base polymer with a crosslinking agent, thereby improving the adhesive reliability.

[0041] Examples of acrylic monomers having crosslinkable functional groups include hydroxyl-containing monomers and carboxyl-containing monomers. For example, when using an isocyanate crosslinking agent, a crosslinking structure is introduced through the reaction of hydroxyl groups with isocyanate groups. When using an epoxy crosslinking agent, a crosslinking structure is introduced through the reaction of carboxyl groups with epoxy groups.

[0042] Examples of hydroxyl-containing monomers include (meth)acrylates such as 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-hydroxymethylcyclohexyl)methyl acrylate. Among these, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred because they contribute significantly to improving adhesive strength and can suppress white turbidity of the PSA sheet in high humidity environments.

[0043] The amount of the hydroxyl 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 monomer components constituting the acrylic base polymer.

[0044] Examples of the carboxyl group-containing monomer include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate; and itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0045] The acrylic base polymer may contain monomer components other than those mentioned above. For example, the acrylic base polymer may contain a vinyl ester monomer, an aromatic vinyl monomer, an epoxy group-containing monomer, a vinyl ether monomer, and the like as monomer components.

[0046] The acrylic base polymer may contain a nitrogen-containing monomer as a monomer component. Examples of the nitrogen-containing monomer include N-vinyl pyrrolidone, methyl vinyl pyrrolidone, vinyl pyridine, vinyl piperidone, vinyl pyrimidine, vinyl piperazine, vinyl pyrazine, vinyl pyrrole, vinyl imidazole, vinyl oxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinylcarboxylic acid amides, N-vinylcaprolactam, etc.

[0047] Acrylic base polymers containing nitrogen-containing monomers tend to improve cohesive and adhesive strength. However, the bond energy of a CN bond is approximately 290 kJ / mol (3.0 eV; equivalent to a wavelength of 410 nm), which is lower than that of CC and CO bonds (bond energies of approximately 350 kJ / mol). CN bonds are easily broken by light with a wavelength of 350 to 410 nm. Therefore, base polymers containing a high content of CN bonds are susceptible to degradation by light exposure, resulting in significant changes in the shear storage modulus and color change (yellowing) of the PSA sheet during weathering tests.

[0048] By reducing the amount of nitrogen-containing monomers in the monomer components constituting the base polymer, a PSA sheet with low C-N bonds and excellent weather resistance can be obtained. The amount of nitrogen-containing monomers is preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and may also be 1 part by weight or less, 0.5 parts by weight or less, 0.1 parts by weight or less, or 0.05 parts by weight or less, relative to 100 parts by weight of the total monomer components constituting the acrylic base polymer. The acrylic base polymer does not necessarily contain nitrogen-containing monomers as a monomer component.

[0049] From the viewpoint of increasing the cohesive strength of the acrylic base polymer having a small amount of nitrogen-containing monomers and improving the adhesive reliability, the acrylic base polymer preferably contains a high Tg monomer having no CN bonds and a homopolymer glass transition temperature (Tg) of 10° C. or higher.

[0050] 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), tetrahydrodicyclopentadienyl methacrylate (Tg: 175°C), tetrahydrodicyclopentadienyl acrylate (Tg: 120°C), dihydrodicyclopentadienyl acrylate (Tg: 120°C), isobornyl methacrylate (Tg: 173°C), isobornyl acrylate (Tg: 97°C), 1-adamantyl methacrylate (Tg: 250°C), and 1-adamantyl acrylate (Tg: 153°C). Among these high-Tg monomers, acrylic acid esters are preferred due to their excellent copolymerizability with low-Tg monomers such as butyl acrylate and 2-ethylhexyl acrylate. Furthermore, since both acrylates and methacrylates can exhibit high Tg, (meth)acrylates having an alicyclic structure are preferred as high Tg monomers. Among these, preferred are alicyclic acrylates such as cyclohexyl acrylate, tetrahydrodicyclopentadienyl acrylate, dihydrodicyclopentadienyl acrylate, isobornyl acrylate, and 1-adamantyl acrylate. The glass transition temperature of the homopolymer of the high Tg monomer can be 13°C or higher, or 15°C or higher.

[0051] 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, based on 100 parts by weight of the total monomer components constituting the acrylic base polymer.

[0052] The glass transition temperature of the acrylic base polymer is preferably -55°C to 10°C, more preferably -50°C to 0°C. A base polymer glass transition temperature of -55°C or higher reduces the difference between the shear storage modulus of the PSA sheet at room temperature (25°C) and at high temperature (80°C), thereby suppressing the accumulation of bubbles caused by outgassing from foreign matter, etc., in high-temperature environments. Furthermore, a base polymer glass transition temperature of 10°C or lower ensures that the PSA sheet exhibits moderate tack in its intended use environment, demonstrating excellent adhesion to adherends.

[0053] The glass transition temperature of a polymer is the peak temperature of the loss tangent (tan δ) obtained by dynamic viscoelasticity measurement. The glass transition temperature can also be calculated from the theoretical Tg. The theoretical Tg is the glass transition temperature Tg of the homopolymer of the monomer components constituting the acrylic base polymer. i and the weight fraction W of each monomer component i Calculated according to the following Fox formula.

[0054] 1 / Tg=Σ(W i / Tg i )

[0055] Tg is the glass transition temperature of the polymer chain (unit: K), W i is the weight fraction of monomer component i constituting the segment (copolymerization ratio based on weight), Tg i is the glass transition temperature (unit: K) of the homopolymer of monomer component i. The glass transition temperature of the homopolymer can be the value listed in the Polymer Handbook, 3rd edition (John Wiley & Sons, Inc., 1989). For homopolymers of monomers not listed in the above literature, the Tg of tan δ obtained by dynamic viscoelasticity measurement can be used.

[0056] <Crosslinking structure of base polymer>

[0057] The base polymer, the main component of the adhesive sheet, preferably has a cross-linked structure. By incorporating a cross-linked structure into the base polymer, the cohesive force of the adhesive is enhanced, resulting in high adhesion to adherends. Furthermore, the inclusion of a cross-linked structure increases the shear storage modulus at high temperatures, tending to suppress the retention of bubbles caused by outgassing from foreign matter, etc.

[0058] Examples of methods for introducing a crosslinked structure into a base polymer include: (1) polymerizing a base polymer having functional groups that react with a crosslinking agent, then adding the crosslinking agent and reacting the base polymer with the crosslinking agent; and (2) introducing a branched structure (crosslinked structure) into the polymer chain by including a polyfunctional compound in the polymer components of the base polymer. These methods can be used in combination to introduce multiple crosslinked structures into the base polymer.

[0059] In the method of reacting a base polymer with a crosslinking agent in (1) above, a crosslinking agent is added to the polymerized base polymer and heated as needed, thereby introducing a crosslinking structure into the base polymer. Examples of the crosslinking agent include compounds that react with functional groups such as hydroxyl groups and carboxyl groups contained in the base polymer. Specific examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, Oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, etc.

[0060] Among them, isocyanate crosslinking agents and epoxy crosslinking agents are preferred because they are highly reactive with the hydroxyl and carboxyl groups in the base polymer and can easily introduce a crosslinked structure. These crosslinking agents react with functional groups such as the hydroxyl and carboxyl groups introduced into the base polymer to form a crosslinked structure. For acid-free adhesives that do not contain carboxyl groups in the base polymer, isocyanate crosslinking agents are preferably used, and a crosslinked structure is formed by the reaction of the hydroxyl groups in the base polymer with the isocyanate crosslinking agent.

[0061] In the method (2) of including a polyfunctional monomer in the polymerization components of the base polymer, the entire amount of the monomer components constituting the base polymer and the polyfunctional compound for introducing a cross-linking structure may be reacted at once, or the polymerization may be carried out in multiple steps. As a method of carrying out polymerization in multiple steps, the following method is preferred: a monofunctional monomer constituting the base polymer is polymerized (prepolymerization) to prepare a partial polymer (prepolymer composition), a polyfunctional compound such as a 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 with a low degree of polymerization and unreacted monomers.

[0062] By prepolymerizing the constituents of the acrylic base polymer, the branching points (crosslinking points) formed by the multifunctional compound can be uniformly introduced into the base polymer. In addition, a mixture (adhesive composition) of a low molecular weight polymer or a partially polymerized polymer and an unpolymerized monomer component can be applied to a substrate, and then a main polymerization is performed on the substrate to form an adhesive sheet. Since the viscosity of low polymer compositions such as prepolymer compositions is low and the coating property is excellent, the method of performing the main polymerization on the substrate after applying the adhesive composition as a mixture of the prepolymer composition and the multifunctional compound can improve the productivity of the adhesive sheet and make the thickness of the adhesive sheet uniform.

[0063] Examples of polyfunctional compounds for introducing a crosslinked structure include compounds containing two or more polymerizable functional groups (ethylenically unsaturated groups) having unsaturated double bonds in one molecule. Polyfunctional (meth)acrylates are preferred as polyfunctional compounds due to their ease of copolymerization with the monomer components of the acrylic base polymer. When introducing a branched (crosslinked) structure by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferred.

[0064] Examples of the polyfunctional (meth)acrylate include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polybutylene 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 isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, and the like. (meth)acrylate, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane) tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol multi(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerol di(meth)acrylate, epoxy (meth)acrylate, butadiene (meth)acrylate, isoprene (meth)acrylate, and the like.

[0065] Preparation of base polymer

[0066] The base polymer can be prepared by known polymerization methods such as solution polymerization, UV polymerization, bulk polymerization, and emulsion polymerization. In view of the transparency, water resistance, and cost of the adhesive, solution polymerization or active energy ray polymerization (e.g., UV polymerization) is preferred. Ethyl acetate, toluene, etc. are commonly used as solvents for solution polymerization.

[0067] When preparing the base polymer, polymerization initiators such as photopolymerization initiators and thermal polymerization initiators can be used depending on the type of polymerization reaction. As the photopolymerization initiator, there is no particular limitation as long as it is a substance that initiates photopolymerization. For example, benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketol photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, etc. can be used. As the thermal polymerization initiator, for example, azo initiators, peroxide initiators, and redox initiators obtained by combining a peroxide with a reducing agent (for example, a combination of persulfate and sodium bisulfite, a combination of peroxide and sodium ascorbate, etc.) can be used.

[0068] During polymerization, a chain transfer agent, a polymerization inhibitor, etc. may be used for molecular weight adjustment, etc. Examples of the chain transfer agent include mercaptans such as α-thioglycerol, dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol; and α-methylstyrene dimer.

[0069] When introducing a crosslinked structure using an isocyanate crosslinking agent, it is preferred to polymerize the base polymer by solution polymerization, then add the crosslinking agent and, if necessary, heat the base polymer to introduce the crosslinked structure. When introducing a crosslinked structure using a polyfunctional compound such as a polyfunctional (meth)acrylate, it is preferred to polymerize the base polymer or prepare a prepolymer composition by solution polymerization or active energy ray polymerization, then add the polyfunctional compound and then introduce the crosslinked structure formed by the polyfunctional compound by active energy ray polymerization.

[0070] The prepolymer composition can be prepared, for example, by partially polymerizing (prepolymerizing) a composition obtained by mixing monomer components constituting an acrylic base polymer with a polymerization initiator (referred to as a "prepolymer-forming composition"). It should be noted that the monomers in the prepolymer-forming composition are preferably monofunctional monomer components such as (meth) alkyl acrylates and polar group-containing monomers. In addition to monofunctional monomers, the prepolymer-forming composition may also contain polyfunctional monomers. For example, a portion of the polyfunctional monomer may be contained in the prepolymer-forming composition, and the remaining portion of the polyfunctional monomer component may be added after the prepolymerization to perform the main polymerization.

[0071] The polymerization rate of the prepolymer is not particularly limited, but is preferably 3% to 50% by weight, more preferably 5% to 40% by weight, from the perspective of adjusting the viscosity suitable for coating onto a substrate. The polymerization rate of the prepolymer can be adjusted to within a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity and duration of active light such as UV light, and the like.

[0072] <Preparation of Adhesive Composition>

[0073] The adhesive composition is prepared by mixing a crosslinking agent and / or a polyfunctional compound, other additives, etc., for introducing a crosslinked structure, with an acrylic base polymer (or prepolymer composition). The remainder of the monomer components constituting the acrylic base polymer may be added to the adhesive composition as needed. Thickening additives may also be used for purposes such as viscosity adjustment.

[0074] When the adhesive composition comprises a prepolymer composition and a polyfunctional compound, the adhesive composition preferably contains a photopolymerization initiator for the main polymerization. A polymerization initiator for the main polymerization may be added to the prepolymer composition after the prepolymerization. If the polymerization initiator remains in the prepolymer composition without being inactivated during the prepolymerization, the addition of the polymerization initiator for the main polymerization may be omitted. The adhesive composition may contain a chain transfer agent.

[0075] In the PSA composition, the content of the acrylic base polymer (or prepolymer composition) relative to the total non-volatile content is preferably 50 wt % or more, more preferably 70 wt % or more, further preferably 80 wt % or more, and particularly preferably 90 wt % or more.

[0076] A silane coupling agent may be added to the adhesive composition for the purpose of adjusting adhesive strength. When a silane coupling agent is added to the adhesive composition, the amount of the silane coupling agent added is generally about 0.01 to 5.0 parts by weight, preferably about 0.03 to 2.0 parts by weight, relative to 100 parts by weight of the base polymer.

[0077] In addition to the components listed above, the adhesive composition may contain additives such as various oligomers, tackifiers, plasticizers, softeners, anti-degradation agents, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents.

[0078] [Formation of Adhesive Sheet]

[0079] By applying an adhesive composition on a substrate and implementing drying and removing the solvent as needed and / or utilizing the main polymerization of active light irradiation, an adhesive sheet is formed on the substrate. As the substrate used in the formation of the adhesive sheet, any appropriate substrate can be used. As the substrate, it can also be a release film with a release layer on the contact surface with the adhesive sheet.

[0080] As the film substrate of the release film, a film containing various resin materials can be used. As the resin material, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyethersulfone 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. can be listed. Among them, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the film substrate is preferably 10 μm to 200 μm, more preferably 25 μm to 150 μm. As the material of the release layer, polysiloxane release agents, fluorine-containing release agents, long-chain alkyl release agents, fatty acid amide release agents, etc. can be listed. The thickness of the release layer is usually about 10 nm to about 2000 nm.

[0081] As a coating method for applying the adhesive composition to the substrate, various methods can be used, such as roller coating, contact roller coating, gravure coating, reverse coating, roller brushing, spraying, dip roller coating, scraper coating, knife coating, air knife coating, curtain coating, lip die coating, and die coater.

[0082] When the base polymer of the adhesive composition is a solution-polymerized polymer, it is preferred to dry the solvent after application. A suitable drying method can be employed depending on the intended purpose. The heating 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 any suitable time. 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.

[0083] When the adhesive composition contains a crosslinking agent, a crosslinking reaction can be carried out after the adhesive composition is applied to the substrate. During crosslinking, heating can be performed as needed. The temperature of the crosslinking reaction is generally in the range of 20°C to 160°C, and the time of the crosslinking reaction is about 1 minute to about 7 days. After the adhesive composition is applied, the heating for drying the solvent can also serve as the heating for crosslinking. After the solvent is dried, a protective sheet is preferably provided to protect the surface of the adhesive sheet. As the protective sheet, a release film having a release layer on the contact surface with the adhesive sheet is preferably used, as is the case with the substrate film.

[0084] When the adhesive composition is a photopolymerizable composition comprising a prepolymer composition and a polyfunctional compound, the adhesive composition is applied in a layer onto a substrate and then irradiated with active light for photocuring. During photocuring, it is preferred to place a protective sheet on the surface of the coating layer, and irradiate the adhesive composition with active light while sandwiching the protective sheets to prevent polymerization inhibition caused by oxygen.

[0085] The active light can be selected according to the type of polymerizable components such as monomers and multifunctional (meth)acrylates, the type of photopolymerization initiator, etc., and ultraviolet light and / or short-wavelength visible light are usually used. The cumulative light intensity of the irradiated light is preferably about 100 mJ / cm 2 ~about 5000mJ / cm 2 There are no particular restrictions on the light source used for light irradiation as long as it can irradiate light within the wavelength range to which the photopolymerization initiator contained in the adhesive composition has sensitivity. Preferably, an LED light source, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a xenon lamp, or the like is used.

[0086] By laminating the release films 1 and 2 on the surface of the adhesive sheet 5, the following can be obtained: Figure 1 The adhesive sheet shown here has release films temporarily attached to both sides. The base material and protective sheet used to form the adhesive sheet can also be used directly as the release films 1 and 2.

[0087] When release films 1 and 2 are provided on both sides of the adhesive sheet 5, the thickness of one release film 1 may be the same as or different from the thickness of the other release film 2. The peeling force when peeling off the release film temporarily attached to one side of the adhesive sheet 5 may be the same as or different from the peeling force when peeling off the release film temporarily attached to the other side of the adhesive sheet 5.

[0088] [Physical Properties of Adhesive Sheet]

[0089] The total light transmittance of the adhesive sheet is preferably 85% or higher, more preferably 90% or higher. The haze of the adhesive sheet is preferably 1.5% or lower, more preferably 1% or lower.

[0090] The thickness of the adhesive sheet is not particularly limited and can be appropriately adjusted depending on the type of adherend. To improve the adhesive strength of the adhesive sheet, the thickness is preferably 10 μm or greater. To improve processability and operability, 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.

[0091] As mentioned above, from the viewpoint of preventing outgassing from foreign matter and the like and suppressing the retention of bubbles, the shear storage modulus G′ of the PSA sheet at 80° C. 80 Preferably 3×104 Pa above. G' 80 Can be 4×10 4 Pa or above or 5×10 4 Pa above. To G' 80 There is no particular upper limit on the value of G'. 80 It can be 5×10 5 Pa or less, 4×10 5 Pa or less, 3×10 5 Pa or less or 2×10 5 Below Pa.

[0092] From the perspective of achieving a balance between adhesiveness and handleability, the shear storage modulus G' of the PSA sheet at 25°C is 25 Preferably 5×10 4 Pa~5×10 5 Pa, more preferably 8×10 4 Pa~3×10 5 Pa, which can be 1×10 5 Pa~2×10 5 Pa.

[0093] From the perspective of achieving both adhesiveness at room temperature and the ability to prevent outgassing at high temperatures, the G' 25 With G' 80 The ratio G' 25 / G' 80 It is preferably 1 to 8, more preferably 1.2 to 5, and can be 1.4 to 4. As mentioned 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 with this, G' 80 The shear storage modulus G' of the PSA sheet can be determined by viscoelasticity measurement at a frequency of 1 Hz.

[0094] As mentioned above, the G' of the adhesive sheet after the weathering test 25 The change ΔG' is preferably 5×10 4 Pa or less. ΔG' is preferably 4×10 4 Pa or less, more preferably 3.5×10 4 Pa or less. ΔG' is the G' of the adhesive sheet before the weathering test 25 G' of the adhesive sheet after weathering test 25 The absolute value of the difference between the two. There is a G' of the adhesive sheet through the weathering test 25 Increased and G' 25When the bond is broken by light irradiation, the generated free radicals re-bond with the polymer chain (curing degradation). In most cases, G' 25 Increase.

[0095] As mentioned above, it is preferred that the transmitted light b of the adhesive sheet after the weathering test * The increase Δb * Small. * is the chromaticity index b of the CIE1976 color space * Δb * It is preferably 0.5 or less, more preferably 0.4 or less, further preferably 0.3 or less, and may be 0.2 or less.

[0096] As mentioned above, the bond energy of CN bonds is small and they are easily broken by sunlight and ultraviolet rays contained in fluorescent lamps. Therefore, by having no CN bonds or a low content of CN bonds in the base polymer constituting the adhesive sheet, the degradation of the base polymer caused by light irradiation (weathering test) can be suppressed, and ΔG' and Δb * Tendency to become smaller.

[0097] [Image Display Device]

[0098] The adhesive sheet of the present invention can be used for laminating various transparent components and opaque components. The type of adherend is not particularly limited, and various resin materials, glass, metal, etc. can be cited. Due to its high transparency, the adhesive sheet of the present invention is suitable for laminating optical components such as image display devices. In particular, due to its excellent weather resistance, the adhesive sheet of the present invention is suitable for laminating transparent components to the visible side surface of image display devices and can also be used in vehicle-mounted displays such as car navigation systems.

[0099] Figure 2 The figure is a cross-sectional view showing an example of a laminated structure of an image display device in which a cover window 7 is attached to the visible side surface of an image display panel 10 via an adhesive sheet 5. The image display panel 10 has a polarizing plate 3, which is attached to the visible side surface of an image display unit 6 such as a liquid crystal unit or an organic EL unit via an adhesive sheet 4. For example, a transparent resin plate made of acrylic resin, polycarbonate resin, or a glass plate can be used for the cover window 7. The cover window can also have a touch panel function. As the touch panel, any touch panel such as a resistive film type, an electrostatic capacitance type, an optical type, or an ultrasonic type can be used.

[0100] 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 order of bonding is not particularly limited, and the adhesive sheet 5 may be bonded to the image display panel 10 first, or to the cover window 7 first. Alternatively, both bonding may be performed simultaneously.

[0101] [Optical film with adhesive]

[0102] The adhesive sheet of the present invention is Figure 1 In addition to the form in which release films are temporarily attached to both sides, it can also be used as an optical film with an adhesive to fix the adhesive sheet to an optical film such as a polarizing plate. Figure 3 In the embodiment shown, a release film 1 is temporarily attached to one surface of an adhesive sheet 5, and a polarizing plate 3 is fixed to the other surface of the adhesive sheet 5. Figure 4 In the illustrated embodiment, a pressure-sensitive adhesive sheet 4 is further provided on the polarizing plate 3 , and a release film 2 is temporarily attached to the pressure-sensitive adhesive sheet 4 .

[0103] In the embodiment where an optical film such as a polarizing plate is previously bonded to the pressure-sensitive adhesive sheet, the release film 1 temporarily bonded to the surface of the pressure-sensitive adhesive sheet 5 can be peeled off before bonding to a cover window or the like.

[0104] [Example]

[0105] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0106] [Preparation of adhesive sheet]

[0107] <Polymerization of prepolymer>

[0108] The monomers (total 100 parts by weight) in the ratios shown in Table 1 as monomer components for forming a prepolymer and 0.10 parts by weight of "Omnirad 184" manufactured by IGM Resins Co., Ltd. as a photopolymerization initiator were mixed and polymerized by irradiation with ultraviolet light to obtain a prepolymer composition (polymerization rate: approximately 10%).

[0109] In Table 1, monomers are represented by the following abbreviations.

[0110] 2EHA: 2-ethylhexyl acrylate

[0111] BA: Butyl acrylate

[0112] ISA: Isostearyl acrylate

[0113] CHA: Cyclohexyl acrylate

[0114] IBXA: Isobornyl acrylate

[0115] 4HBA: 4-Hydroxybutyl acrylate

[0116] NVP: N-vinyl-2-pyrrolidone

[0117] <Preparation of Adhesive Composition>

[0118] To 100 parts by weight of the prepolymer composition, a polyfunctional monomer (1,6-hexanediol diacrylate; HDDA), a silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., “KBM403”), and a chain transfer agent (α-thioglycerol) were added as post-addition components in the amounts shown in Table 1, and then uniformly mixed to prepare an adhesive composition.

[0119] <Adhesive Sheet Production>

[0120] The 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 a release treatment on one side) to form a coating layer of 50 μm. Another separator was bonded to the coating layer and the coating layer was observed under an illumination of 6.5 mW / cm 2 , Light intensity: 1500mJ / cm 2 The coating layer was photocured by ultraviolet irradiation under conditions of , thereby obtaining a 50 μm thick adhesive sheet.

[0121] [Evaluation of Adhesive Sheet]

[0122] <Shear storage modulus>

[0123] The PSA sheets were stacked to a thickness of about 1.5 mm and used as measurement samples. Dynamic viscoelasticity measurements were performed using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions, and the storage modulus G' at each temperature was read from the measurement results.

[0124] Deformation Mode: Twist

[0125] Measuring frequency: 1Hz

[0126] Heating rate: 5℃ / min

[0127] Shape: Parallel plate 7.9mmφ

[0128] Weathering test

[0129] The separator on one side of the adhesive sheet was peeled off and attached to a glass plate. The separator on the other side of the adhesive sheet was peeled off and attached to a glass plate. This produced a sample with glass plates attached to both sides of the adhesive sheet. The sample was irradiated for 500 hours in a xenon lamp weathering tester at a wavelength of 340 nm and an intensity of 0.63 W / cm 2 The weathering test was carried out under the light of a xenon lamp. The b value of the transmitted light of the sample before the test was obtained. * 0 and b of the transmitted light of the sample after the test * 1 difference Δb * =b * 1-b * 0 and the difference ΔG' between the shear storage modulus of the adhesive sheet before and after the test at a temperature of 25°C. * The measurement was performed using a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, “U4100”).

[0130] The composition of the PSA of each PSA sheet and the evaluation results are shown in Table 1. The numerical values of the prepolymer composition and post-addition components in Table 1 represent weight ratios based on 100 parts by weight of the total monomers used to prepare the prepolymer.

[0131]

[0132] As shown in Table 1, it can be seen that the shear storage modulus of the adhesive sheet of the example at a temperature of 80°C is large, and ΔG' and Δb * Small and excellent weather resistance.

Claims

1. An adhesive sheet, wherein: The adhesive sheet comprises an acrylic base polymer, The glass transition temperature of the acrylic base polymer is -55°C to 10°C, The amount of the nitrogen-containing monomer is 1 part by weight or less relative to 100 parts by weight of the total monomer components constituting the acrylic base polymer. The amount of the high Tg monomer, which is an acrylate or a (meth)acrylate having an alicyclic structure, which does not contain a CN bond and whose homopolymer has a glass transition temperature of 10° C. or higher, is 10 to 30 parts by weight relative to 100 parts by weight of the total amount of the monomer components constituting the acrylic base polymer. The shear storage modulus of the adhesive sheet at 80°C is 3×10 4 Pa or above, and The absolute value of the difference between the shear storage modulus at 25°C after the weathering test and the shear storage modulus at 25°C before the weathering test of the PSA sheet is 5×10 4 Pa or less, the weathering test is carried out by irradiation for 500 hours with an irradiation intensity of 0.63 W / cm at a wavelength of 340 nm. 2 It is carried out by the light of a xenon lamp.

2. The adhesive sheet according to claim 1, wherein Transmitted light b of the adhesive sheet before and after the weathering test * The change in is less than 0.

5.

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

4. The adhesive sheet according to claim 1 or 2, wherein The high Tg monomer is a (meth)acrylate having an alicyclic structure.

5. The adhesive sheet according to claim 1 or 2, wherein The adhesive sheet has a haze of 1.5% or less.

6. An optical film with an adhesive, wherein: The optical film with pressure-sensitive adhesive comprises the pressure-sensitive adhesive sheet according to any one of claims 1 to 5 on one surface of the optical film.

7. An image display device, wherein: The image display device includes a cover window attached to a visible side surface of an image display panel via the adhesive sheet according to any one of claims 1 to 5.

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