Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, optical member, and display device produced using the same

Abstract

The present invention relates to a pressure-sensitive adhesive composition containing an acrylic copolymer having a refractive index of 1.55 to 1.70, and a pressure-sensitive adhesive sheet, an optical member, and a display device produced using the same.

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet, an optical member, and a display device produced using the same. [Background technology]

[0002] Flat panel displays include liquid crystal displays (LCDs), plasma display panels (PDPs), organic electroluminescence displays (OLEDs), etc. Flat panel displays include a display panel and optical films. The optical films include polarizing films, retardation films, anti-glare films, wide viewing angle compensation films, brightness enhancement films, etc. When these optical films are laminated on top of each other or attached to a display panel, optically clear adhesives (OCAs) or pressure sensitive adhesives (PSAs) are used.

[0003] The optical adhesive must have high transmittance and low haze, and must satisfy physical properties such as adhesion to various substrates, and durability such as heat resistance and moisture resistance. In addition, reworkability is also required for easy replacement when defects occur on the surface of the display panel or optical film.

[0004] Meanwhile, with the recent development of technology, a touch screen panel (hereinafter referred to as "touch panel"), which is an optical display element, is formed on the display surface of the above-mentioned flat panel display device, and a combination of the display device and a device that recognizes coordinate axes on the spot and performs input has been developed. This has made it possible to realize various operability in combination with the display device and software.

[0005] There are various driving methods for touch panels, including resistive film and capacitive touch panels. The capacitive touch panel, which is made up of two conductive ITO (Indium Tin Oxide) layers, detects signals through electromagnetic changes rather than physical contact between the upper and lower electrodes. Compared to resistive film touch panels, the capacitive touch panel has a faster response speed and provides a better operational feel, so it is widely used these days.

[0006] The optical pressure sensitive adhesive can also be used to bond the two elements together by being provided between a touch panel and an optical member.

[0007] However, the ITO (Indium Tin Oxide) layer used to realize capacitive touch panels has steps that occur during patterning, which causes problems with visibility due to differences in refractive index.

[0008] In order to solve such problems, a separate highly refractive pattern layer for improving visibility by correcting the refractive index has been conventionally provided between the electrode pattern and the optical member.

[0009] However, when a separate high refractive index pattern layer is provided, an adhesive layer for attaching other members must be separately coated on the top surface of the high refractive index pattern layer, which is disadvantageous in terms of process economy.

[0010] To solve these problems, Korean Patent Publication No. 10-2016-0045199 discloses an adhesive film that contains highly refractive nanoparticles, which has a higher refractive index than that of general adhesives (1.48) and excellent adhesion between various substrates. However, when the adhesive film contains nanoparticles, there are problems in that the haze characteristics become poor, and when nanoparticles of 100 nm or less are used, the viscosity of the prepared solution increases. Thus, there is a need for an adhesive composition that solves these problems. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Republic of Korea Patent Publication No. 10-2016-0045199 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a pressure-sensitive adhesive composition having an improved refractive index. Another object of the present invention is to provide a pressure-sensitive adhesive composition having improved level difference absorbency.

[0013] Another object of the present invention is to provide a pressure-sensitive adhesive composition having improved haze properties.

[0014] Another object of the present invention is to provide a pressure-sensitive adhesive sheet produced using the pressure-sensitive adhesive composition.

[0015] Another object of the present invention is to provide an optical member comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

[0016] Another object of the present invention is to provide a display device including the optical member. [Means for solving the problem]

[0017] The present invention relates to a pressure-sensitive adhesive composition containing an acrylic copolymer having a refractive index of 1.55 to 1.70.

[0018] In a first aspect of the present invention, the acrylic copolymer may contain a repeating unit derived from a high refractive index acrylic monomer having a refractive index of 1.58 or more for the homopolymer.

[0019] In a second aspect of the present invention, the high refractive index acrylic monomer having a refractive index of 1.58 or more of the homopolymer may include one or more selected from the group consisting of pentabromophenyl (meth)acrylate, 2-(naphthalene-2-yloxy)ethyl (meth)acrylate, 2-(naphthalene-2-ylthio)ethyl (meth)acrylate, biphenylmethyl (meth)acrylate, and 1-pyrenemethyl (meth)acrylate.

[0020] In a third aspect of the present invention, the high refractive index acrylic monomer having a homopolymer refractive index of 1.58 or more may be contained in an amount of 10 to 70% by weight based on the total weight of the acrylic copolymer.

[0021] In a fourth aspect of the present invention, the acrylic copolymer may further contain at least one of a repeating unit derived from an acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms and a repeating unit derived from a polymerizable monomer having a crosslinkable functional group.

[0022] In a fifth aspect, the present invention provides a method for producing a acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms, the acrylic monomer being selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, It may contain one or more selected from the group consisting of isobornyl acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentafluorooctyl acrylate, 2-ethylhexyl diglycol acrylate, nonylphenol (modified with 4 mol of ethylene oxide) acrylate, and 6-(1-naphthyloxy)-1-hexyl acrylate.

[0023] In a sixth aspect of the present invention, the polymerizable monomer having a crosslinkable functional group may include one or more selected from the group consisting of a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a cyano group-containing monomer, a vinyl ester monomer, an aromatic vinyl monomer, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer and an ether group-containing monomer.

[0024] In a seventh aspect of the present invention, the pressure-sensitive adhesive composition may further comprise at least one of a photoinitiator, a thermal curing agent, and nanoparticles.

[0025] In an eighth aspect of the present invention, the heat curing agent may include an isocyanate-based crosslinking agent.

[0026] In a ninth aspect of the present invention, the nanoparticles may comprise one or more selected from the group consisting of titanium oxide, zinc oxide, zirconium oxide, magnesium oxide, zirconium titanate, zirconium silicate, strontium titanate, aluminum titanate, silicon ferrite, nickel ferrite, cobalt ferrite, barium carbonate, silicon carbide, yttrium carbide, magnesium silicate, zinc sulfate, and barium sulfate.

[0027] In a tenth aspect of the present invention, the pressure-sensitive adhesive composition may have a glass transition temperature (Tg) of -10°C or lower.

[0028] In an eleventh aspect, the present invention may provide a pressure-sensitive adhesive layer produced from the pressure-sensitive adhesive composition, which has a refractive index of 1.58 or more.

[0029] In a twelfth aspect of the present invention, a pressure-sensitive adhesive layer produced from the pressure-sensitive adhesive composition may have a haze of less than 2%.

[0030] The present invention also relates to a pressure-sensitive adhesive sheet produced using the pressure-sensitive adhesive composition. In a thirteenth aspect of the present invention, the pressure-sensitive adhesive sheet may have a refractive index of 1.58 or more.

[0031] The present invention also relates to an optical member comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. Furthermore, the present invention relates to a display device including the optical member. Effect of the Invention

[0032] The pressure-sensitive adhesive composition according to the present invention has a higher refractive index than conventional pressure-sensitive adhesive compositions, and therefore visibility can be improved without the need for a separate high refractive pattern layer.

[0033] Furthermore, the pressure-sensitive adhesive composition according to the present invention has improved step absorbency compared to conventional pressure-sensitive adhesive compositions, and can exhibit excellent reliability over a wide temperature range.

[0034] In addition, the pressure-sensitive adhesive composition according to the present invention has improved haze properties compared to conventional pressure-sensitive adhesive compositions, and is therefore particularly suitable for use as an optical pressure-sensitive adhesive.

[0035] Furthermore, the pressure-sensitive adhesive composition of the present invention can prevent an increase in viscosity of the prepared solution, as compared with conventional pressure-sensitive adhesive compositions, and the processability can be further improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The present invention provides a pressure-sensitive adhesive composition comprising an acrylic copolymer having a refractive index of 1.55 to 1.70, and a pressure-sensitive adhesive sheet, an optical member, and a display device produced using the same.

[0037] The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer having a refractive index of 1.55 to 1.70, and thus can improve the refractive index, haze properties and reliability of the pressure-sensitive adhesive layer.

[0038] The term "(meth)acrylate" described in the present invention is defined as a concept including both acrylate and methacrylate.

[0039] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer and may further contain at least one of a photoinitiator, a heat curing agent, and nanoparticles, if necessary.

[0040] The pressure-sensitive adhesive composition of the present invention preferably has a glass transition temperature (Tg) of −10° C. or lower. In this case, the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition can exhibit good adhesive properties.

[0041] The pressure-sensitive adhesive layer produced by the pressure-sensitive adhesive composition of the present invention may have a refractive index of 1.58 or more, more preferably 1.58 to 1.70, and most preferably 1.60 to 1.70. In this case, visibility can be improved in a display device including a touch panel without including a separate high refractive index pattern layer. In particular, the pressure-sensitive adhesive layer produced by the pressure-sensitive adhesive composition of the present invention can exhibit a high refractive index without including excessive nanoparticles, and is advantageous in terms of optical properties.

[0042] In addition, the adhesive layer produced from the adhesive composition of the present invention may have a haze of less than 2%, which improves light transmittance and is particularly suitable for use as an optical adhesive in display devices and the like.

[0043] Acrylic Copolymer The pressure-sensitive adhesive composition according to the present invention contains an acrylic copolymer to exhibit adhesive properties and durability.

[0044] The acrylic copolymer preferably has a refractive index of 1.55 to 1.70. When the refractive index of the acrylic copolymer is 1.55 to 1.70, it is close to the target refractive index of the adhesive layer or adhesive sheet. Therefore, a high refractive index of the adhesive layer can be achieved without containing additional nanoparticles, which is advantageous in terms of processability and light transmittance, and the elastic modulus is improved to prevent a decrease in durability. In addition, by further containing nanoparticles with a high refractive index as necessary, a refractive index further improved compared to conventional adhesive compositions can be exhibited.

[0045] The structure of the acrylic copolymer is not particularly limited as long as the refractive index is 1.55 to 1.70, but it is preferable that the acrylic copolymer contains a repeating unit derived from a high refractive acrylic monomer having a homopolymer refractive index of 1.58 or more.

[0046] The high refractive index acrylic monomer having a homopolymer refractive index of 1.58 or more may include, for example, one or more selected from the group consisting of pentabromophenyl(meth)acrylate, 2-(naphthalen-2-yloxy)ethyl(meth)acrylate, 2-(naphthalen-2-ylthio)ethyl(meth)acrylate, biphenyl methyl(meth)acrylate, and 1-pyrene methyl(meth)acrylate, but is not limited thereto, as described above.

[0047] The content of the high refractive acrylic monomer having a homopolymer refractive index of 1.58 or more is not particularly limited as long as it can improve the refractive index and elastic modulus of the matrix, but it is preferably 10 to 70 wt % relative to the total weight of the acrylic copolymer, and more preferably 15 to 60 wt %. If the content of the high refractive acrylic monomer having a homopolymer refractive index of 1.58 or more is less than 10 wt %, the effect of improving the refractive index and elastic modulus is slight, and if it exceeds 70 wt %, the adhesive properties and durability of the pressure-sensitive adhesive composition itself may be reduced.

[0048] In one embodiment of the present invention, the acrylic copolymer may further include at least one of a repeating unit derived from an acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms and a repeating unit derived from a polymerizable monomer having a crosslinkable functional group.

[0049] The acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms is preferably a (meth)acrylate monomer, but is not limited thereto.

[0050] The hydrocarbon group may include an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The hydrogen atom contained in the hydrocarbon group may be substituted with an alkyl group, a halogen atom, an alkoxy group, a phenoxy group, or the like, and the -CH2- contained in the hydrocarbon group may be substituted with a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, or with -(CH2CH2O)m-. In this case, the m may be 1 to 4.

[0051] The acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms is not particularly limited as long as it imparts adhesive properties or cohesive strength to the pressure-sensitive adhesive composition.

[0052] In one or more embodiments, the acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms is methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl acrylate, n-nonyl (meth)acrylate, or n-butyl (meth)acrylate. ) acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentafluorooctyl acrylate, 2-ethylhexyl diglycol acrylate, nonylphenol (modified with 4 mol of ethylene oxide) acrylate, and 6-(1-naphthyloxy)-1-hexyl acrylate. In terms of availability, the acrylate may include one or more selected from the group consisting of 2-ethylhexyl (meth)acrylate.

[0053] When the acrylic copolymer has a repeating unit derived from an acrylic monomer having a hydrocarbon group with 1 to 20 carbon atoms, the acrylic monomer having a hydrocarbon group with 1 to 20 carbon atoms is preferably contained in an amount of 30 to 90% by weight, more preferably 30 to 60% by weight, based on the total weight of the acrylic copolymer. If the content of the acrylic monomer having a hydrocarbon group with 1 to 20 carbon atoms is less than 30% by weight, the adhesive strength may be slightly reduced, and if it exceeds 90% by weight, the cohesive strength may be slightly reduced.

[0054] The polymerizable monomer having a crosslinkable functional group is not particularly limited as long as it reacts with a crosslinking agent to impart cohesive strength or adhesive strength through chemical bonds so that the adhesive does not break down due to cohesive force under high temperature or humidity conditions.

[0055] In one or more embodiments, the polymerizable monomer having a crosslinkable functional group may include one or more monomers selected from the group consisting of a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a cyano group-containing monomer, a vinyl ester monomer, an aromatic vinyl monomer, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer, and an ether group-containing monomer.

[0056] Examples of the sulfonic acid group-containing monomer include styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, and sodium vinylsulfonate.

[0057] An example of the phosphate group-containing monomer is 2-hydroxyethyl acryloyl phosphate, and an example of the cyano group-containing monomer is (meth)acrylonitrile.

[0058] Examples of the vinyl ester monomer include vinyl acetate, vinyl propionate, and vinyl laurate. Examples of the aromatic vinyl monomer include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes.

[0059] Examples of the carboxyl group-containing monomer include monovalent acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate; divalent acids such as maleic acid, itaconic acid, and fumaric acid, and monoalkyl esters thereof; ring-opening adducts of 2-hydroxyalkyl (meth)acrylates having an alkyl group with 2 to 3 carbon atoms with succinic anhydride, ring-opening adducts of hydroxyalkylene glycol (meth)acrylates having an alkyl group with 2 to 4 carbon atoms with succinic anhydride, and compounds obtained by ring-opening addition of succinic anhydride to caprolactone adducts of 2-hydroxyalkyl (meth)acrylates having an alkyl group with 2 to 3 carbon atoms, and among these, (meth)acrylic acid is preferred.

[0060] Examples of the acid anhydride-containing monomer include maleic anhydride, itaconic anhydride, and anhydrides thereof. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl acrylate, N-methylol (meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, and 2-acryloyloxyethyl-2-hydroxyethyl phthalate.

[0061] Examples of the amide group-containing monomer include (meth)acrylamide, N-isopropylacrylamide, N-tertiary butylacrylamide, 3-hydroxypropyl(meth)acrylamide, 4-hydroxybutyl(meth)acrylamide, 6-hydroxyhexyl(meth)acrylamide, 8-hydroxyoctyl(meth)acrylamide, and 2-hydroxyethylhexyl(meth)acrylamide.

[0062] Examples of the amino group-containing monomer include N,N-(dimethylamino)ethyl (meth)acrylate, N,N-(diethylamino)ethyl (meth)acrylate, and N,N-(dimethylamino)propyl (meth)acrylate. Examples of the imido group-containing monomer include cyclohexylmaleimide and isopropylmaleimide.

[0063] Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate, and examples of the ether group-containing monomer include 3-methoxybutyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-methoxybutyl (meth)acrylate, methoxypolyethylene glycol acrylate having an added mole number of oxyethylene in the range of 1 to 15, ethoxy-diethylene glycol (meth)acrylate, and ethyl carbitol (meth)acrylate.

[0064] When the acrylic copolymer has a repeating unit derived from a polymerizable monomer having a crosslinkable functional group, the polymerizable monomer having a crosslinkable functional group is preferably contained in an amount of 0.05 to 10% by weight, more preferably 1 to 10% by weight, based on the total weight of the acrylic copolymer. When the content of the polymerizable monomer having a crosslinkable functional group is less than 0.05% by weight, the cohesive strength of the pressure-sensitive adhesive composition decreases and the durability decreases, and when it exceeds 10% by weight, the adhesive strength and durability may decrease slightly.

[0065] The acrylic copolymer may further contain, in addition to the monomer, other monomers that are commonly used in the technical field to which the present invention pertains, within the range that does not reduce the adhesive strength, and may further contain, for example, 10 wt % or less of the total weight of the acrylic copolymer.

[0066] The acrylic copolymer may have a weight average molecular weight (polystyrene equivalent; Mw) of 500,000 to 2,000,000 as measured by gel permeation chromatography (GPC), and more preferably 700,000 to 1,700,000. If the weight average molecular weight of the acrylic copolymer is less than 500,000, the chain structure in the structure of the adhesive film after ultraviolet polymerization and curing is simple and short, which is disadvantageous in terms of reliability, such as the generation of bubbles, and the deterioration of durability due to discoloration, etc. occurs. If it exceeds 2,000,000, the viscosity of the adhesive resin composition during the production of the adhesive film is excessively high, and a large amount of monomer dilution is required to adjust the appropriate viscosity required for production, which requires high energy during ultraviolet polymerization and curing, or unreacted monomers may remain.

[0067] The method for producing the acrylic copolymer is not particularly limited. For example, methods commonly used in the technical field to which the present invention pertains, such as bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, and UV polymerization, can be used, and preferably solution polymerization or UV polymerization can be used.

[0068] Photoinitiators The pressure-sensitive adhesive composition of the present invention may further include a photoinitiator to efficiently induce a photocuring reaction even with light in the UV range, for example, with a wavelength of 400 nm or less.

[0069] The photoinitiator is not particularly limited as long as it is a component that can initiate a photocuring reaction when irradiated with actinic rays, and any conventional or later developed photoinitiator can be used.

[0070] In one or more embodiments, the photoinitiator of the present invention may include one or more selected from the group consisting of acetophenone-based, benzophenone-based, triazine-based, thioxanthone-based, oxime-based, benzoin-based, and biimidazole-based compounds.

[0071] Examples of the acetophenone-based compounds include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, and oligomers of 2-hydroxy-2-methyl[4-(1-methylvinyl)phenyl]propan-1-one.

[0072] Examples of the benzophenone compounds include benzophenone, 2,2'-hydroxy-4,4'-dimethoxybenzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 2,4,6-trimethylbenzophenone.

[0073] Examples of the triazine-based compound include 2,4-bis(trichloromethyl)-6-(4-methoxyphenyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxynaphthyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(4-methoxystyryl)-1,3,5-triazine, and 2,4-bis(trichloromethyl)-6-[2-(5-methylfuran-2-yl)ethyl]-1,3,5-triazine. [2-(3,4-dimethoxyphenyl)ethenyl]-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-[2-(furan-2-yl)ethenyl]-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-[2-(4-diethylamino-2-methylphenyl)ethenyl]-1,3,5-triazine, and 2,4-bis(trichloromethyl)-6-[2-(3,4-dimethoxyphenyl)ethenyl]-1,3,5-triazine.

[0074] Examples of the thioxanthone compounds include 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone.

[0075] Examples of the oxime compounds include 1-[4-(phenylthio)phenyl]-heptane-1,2-dione 2-(O-benzoyloxime), 1-[4-(phenylthio)phenyl]-octane-1,2-dione 2-(O-benzoyloxime), 1-[4-(benzoyl)phenyl]-octane-1,2-dione 2-(O-benzoyloxime), 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-ethanone 1-(O-acetyloxime), 1-[9-ethyl-6-(3 ... -methylbenzoyl)-9H-carbazol-3-yl]-ethanone 1-(O-acetyloxime), 1-(9-ethyl-6-benzoyl-9H-carbazol-3-yl)-ethanone 1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydrofuranylbenzoyl)-9.H-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydropyranylbenzoyl)-9.H-carbazol-3-yl]- ]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-5-tetrahydrofuranylbenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-5-tetrahydropyranylbenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-{2-methyl-4-(2,2-dimethyl-1,3-dioxolanyl)benzoyl}-9.H.-carbazol Ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydrofuranylmethoxybenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-4-tetrahydropyranylmethoxybenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-5-tetrahydrofuranylmethoxybenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-(2-methyl-5-tetrahydropyranylmethoxybenzoyl)-9.H.-carbazol-3-yl]-1-(O-acetyloxime), ethanone-1-[9-ethyl-6-{2-methyl-4-(2,2-dimethyl-1,3-dioxolanyl)methoxybenzoyl}-9.H.-carbazol-3-yl]-1-(O-acetyloxime), and the like.

[0076] Examples of the benzoin-based compounds include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoisobutyl ether.

[0077] Examples of the biimidazole-based compound include 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetrakis(4-ethoxycarbonylphenyl)-1,2'-biimidazole, 2,2'-bis(2-bromophenyl)-4,4',5,5'-tetrakis(4-ethoxycarbonylphenyl)-1,2'-biimidazole, 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, and 2,2'-bis(2,4-dichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole. 2,2'-bis(2,4,6-trichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2-bromophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4-dibromophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4,6-tribromophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, and the like.

[0078] The photoinitiator may be contained in an amount of preferably 0.3 to 3 wt % based on the total weight of the acrylic copolymer, and more preferably 0.5 to 2 wt %. In this case, when the pressure-sensitive adhesive composition is treated with ultraviolet light having a specific wavelength range, illuminance and amount of light, the photoinitiator can effectively initiate polymerization or crosslinking reaction of monomers, and can exhibit durability and excellent variability.

[0079] Heat Curing Agent The pressure-sensitive adhesive composition of the present invention may further include a heat curing agent to enhance the cohesive strength of the pressure-sensitive adhesive.

[0080] The thermosetting agent is not particularly limited as long as it is a component that can appropriately crosslink the acrylic copolymer to strengthen the cohesive strength of the pressure-sensitive adhesive, but is preferably an isocyanate-based crosslinking agent.

[0081] Examples of the isocyanate crosslinking agent include, but are not limited to, tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, 2,4-diphenylmethane diisocyanate, 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, naphthalene diisocyanate, and addition trimers such as 2,4-toluene diisocyanate addition trimer, or isocyanurate trimers.

[0082] The thermosetting agent is preferably contained in an amount of 0.1 to 1 wt % based on the total weight of the acrylic copolymer, and more preferably 0.1 to 0.5 wt %. If the content of the thermosetting agent is less than 0.1 wt %, the adhesive strength or cohesive strength of the adhesive composition may be slightly decreased, and if it exceeds 1 wt %, the compatibility may be slightly decreased, surface migration may occur, and the crosslinking reaction may proceed excessively, resulting in a slightly decreased adhesive strength.

[0083] Nanoparticles The pressure-sensitive adhesive composition of the present invention can improve the refractive index without containing nanoparticles by containing the above-mentioned acrylic copolymer, but is not limited to further containing nanoparticles as necessary, for example, for the purpose of further improving the refractive index.

[0084] The nanoparticles are not particularly limited as long as they can exhibit high refractive index properties, and conventional or later developed nanoparticles can be used.

[0085] In one or more embodiments, the nanoparticles of the present invention may comprise one or more selected from the group consisting of titanium oxide, zinc oxide, zirconium oxide, magnesium oxide, zirconium titanate, zirconium silicate, strontium titanate, aluminum titanate, silicon ferrite, nickel ferrite, cobalt ferrite, barium carbonate, silicon carbide, yttrium carbide, magnesium silicate, zinc sulfate, and barium sulfate.

[0086] The average particle size of the nanoparticles is preferably 1 to 100 nm, more preferably 50 to 100 nm, in order to realize high refractive index properties. If the average particle size of the nanoparticles is less than 1 nm, it is difficult to disperse them in the pressure-sensitive adhesive composition, inhibiting light transmittance, whereas if the average particle size exceeds 100 nm, the particle size may inhibit light transmittance of visible light.

[0087] The nanoparticles are preferably contained in an amount of 0.1 to 30% by weight based on the total weight of the acrylic copolymer. If the content of the nanoparticles is less than 0.1% by weight, the change rate of the refractive index is small and the refractive index cannot be improved, whereas if the content of the nanoparticles is more than 30% by weight, the viscosity of the prepared solution increases, and the adhesive properties decrease, which may result in poor reliability.

[0088] In addition to the above-mentioned components, the pressure-sensitive adhesive composition according to the present invention may further contain additives such as an ultraviolet (UV) blocking agent, a silane coupling agent, an antioxidant, a corrosion inhibitor, an antifoaming agent, a filler, and an antistatic agent, if necessary, within the scope of the object of the present invention.

[0089] <Adhesive sheets, optical members and display devices> One embodiment of the present invention relates to a pressure-sensitive adhesive sheet comprising a cured product of the pressure-sensitive adhesive composition described above.

[0090] The pressure-sensitive adhesive sheet may include a base film and a pressure-sensitive adhesive layer laminated on at least one surface of the base film. For example, the pressure-sensitive adhesive layer may be formed from the pressure-sensitive adhesive composition according to the present invention on the base film, or the pressure-sensitive adhesive layer may be interposed between two base films and the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to the present invention.

[0091] The substrate film can be any substrate that is commonly used in the industry without any particular limitations, and is preferably a film that is excellent in transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, and the like. In one or more embodiments, the substrate film may be a film made of a thermoplastic resin such as a polyester-based resin such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, or polybutylene terephthalate; a cellulose-based resin such as diacetyl cellulose or triacetyl cellulose; a polycarbonate-based resin; an acrylic resin such as polymethyl (meth)acrylate or polyethyl (meth)acrylate; a styrene-based resin such as polystyrene or an acrylonitrile-styrene copolymer; a polyolefin-based resin such as polyethylene, polypropylene, a polyolefin having a cyclo- or norbornene structure, or an ethylene-propylene copolymer; a vinyl chloride-based resin; an amide-based resin such as nylon or an aromatic polyamide; an imide-based resin; a sulfone-based resin; a polyethersulfone-based resin; a polyetheretherketone-based resin; a polyphenylene sulfide-based resin; a vinyl alcohol-based resin; a vinylidene chloride-based resin; a vinyl butyral-based resin; an arylate-based resin; a polyoxymethylene-based resin; or an epoxy-based resin. A film made of a blend of the above thermoplastic resins may also be used. In addition, a film made of a thermosetting resin or an ultraviolet-curable resin such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone resin may be used, and according to an embodiment of the present invention, a polyimide resin can be used, which has excellent durability against repeated bending and can be more easily applied to a flexible image display device.

[0092] In some embodiments, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer laminated on one side of a base film, and a hard coat layer formed on the other side of the base film on which the pressure-sensitive adhesive layer is not laminated. If necessary, a separator is formed on the one side of the pressure-sensitive adhesive layer.

[0093] The method for producing the pressure-sensitive adhesive sheet is not particularly limited, but for example, the pressure-sensitive adhesive sheet can be produced by applying the above-mentioned pressure-sensitive adhesive composition to one or both sides of a base film at a temperature of about 40° C. to form a pressure-sensitive adhesive layer, and curing the pressure-sensitive adhesive layer by photocuring. In one embodiment, the pressure-sensitive adhesive composition may be applied to the surface of a base film that has been subjected to a surface release treatment with silicone, fluorine, or the like, and then heated and dried to form a pressure-sensitive adhesive layer.

[0094] If necessary, the surface of the base film may be subjected to a corona discharge treatment, a plasma treatment, a blast treatment, a chemical etching treatment, a primer treatment or the like in order to improve adhesion to the pressure-sensitive adhesive layer.

[0095] The coating can generally be performed using a knife coater, roll coater, calendar coater, comma coater, etc. Depending on the coating thickness and the viscosity of the adhesive composition, the coating can also be performed using a gravure coater, rod coater, etc. The adhesive layer can be formed to a thickness of, for example, 5 to 80 μm. If the thickness of the adhesive layer is within the above range, it has excellent adhesive strength and is advantageous in terms of light transmittance, reliability, and step absorbency.

[0096] The pressure-sensitive adhesive sheet may have a refractive index of 1.58 or more, more preferably 1.58 to 1.70, and most preferably 1.60 to 1.70. In this case, visibility can be improved in a display device including a touch panel without including a separate high refractive index pattern layer. In particular, the pressure-sensitive adhesive sheet according to the present invention can exhibit a high refractive index without including excess nanoparticles, which is advantageous in terms of optical properties.

[0097] One embodiment of the present invention relates to an optical member including the above-mentioned pressure-sensitive adhesive sheet or pressure-sensitive adhesive layer. Specifically, the pressure-sensitive adhesive sheet or pressure-sensitive adhesive layer may be an optical adhesive film (OCA).

[0098] Examples of the optical member include a touch panel, a window, a polarizing plate, a color filter, a retardation film, an elliptical polarizing film, a reflective film, an anti-reflection film, a compensation film, a brightness enhancing film, an alignment film, a light diffusing film, a glass shatterproof film, a surface protective film, a plastic LCD substrate, and a transparent electrode film such as ITO (indium tin oxide), FTO (fluorinated tin oxide), AZO (aluminum dopped zinc oxide), CNT (carbon nanotube), Ag nanowire, and graphene.

[0099] The method for producing the optical member can be easily carried out by a person having ordinary skill in the art to which the present invention pertains.

[0100] An embodiment of the present invention relates to a display device including the optical member described above. The display device is not limited to the above as long as it includes the optical member including the adhesive sheet or adhesive layer described above, and may be, for example, a liquid crystal display (LCD), an electroluminescent (EL) display, a plasma display panel (PDP), a field emission display (FED), an organic light emitting diode (OLED) display, etc.

[0101] The display device may include any configuration commonly known in the art, except for including the optical members described above.

[0102] The present invention will be described in more detail below based on examples, but the embodiments of the present invention disclosed below are merely illustrative, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is set forth in the claims, and includes all modifications within the scope and meaning equivalent to the claims. In the following examples and comparative examples, the "%" and "parts" indicating the content are based on mass unless otherwise specified. EXAMPLES

[0103] <Examples and Comparative Examples> Example 1 A monomer mixture consisting of 40 parts by weight of pentabromophenyl acrylate, 15 parts by weight of 2-ethylhexyl acrylate, 40 parts by weight of nonylphenol (ethylene oxide 4 mol modified) acrylate, and 5 parts by weight of 2-hydroxyethyl acrylate was added to a 1L reactor equipped with a cooling device to allow nitrogen gas to flow back and to facilitate temperature control, and then 300 parts by weight of methyl ethyl ketone was added as a solvent. After that, nitrogen gas was added for 1 hour to remove oxygen, and the temperature was maintained at 70°C. After the monomer mixture was uniformly stirred, 0.07 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator and reacted for 8 hours to produce an acrylic copolymer with a weight average molecular weight of 1.53 million, and 0.5 parts by weight of an isocyanate crosslinking agent (AK75) was added to produce a pressure-sensitive adhesive composition. The adhesive composition was coated on a 75 μm-thick polyethylene terephthalate (PET) film that had been subjected to a coating solution release treatment using a bar coater, and then dried at 100° C. for 1 minute and aged at room temperature for 7 days to prepare an adhesive sheet with an adhesive layer thickness of 25 μm.

[0104] Example 2 An adhesive sheet was produced using the adhesive composition of Example 2 in the same manner as in Example 1, with the components and amounts shown in Table 1 below.

[0105] Example 3 An adhesive composition containing 60 parts by weight of 2-(naphthalene-2-ylthio)ethyl acrylate, 35 parts by weight of 2-ethylhexyl diglycol acrylate, 5 parts by weight of 2-acryloyloxyethyl 2-hydroxyethyl phthalate, and 0.5 parts by weight of (1-hydroxycyclohexyl)phenyl ketone (Irgacure®-184) was prepared, and the glass transition temperature of the adhesive composition was measured to be -13°C (measurement device: DSC8000, PerkinElmer Inc.). The adhesive composition was coated on a polyethylene terephthalate (PET) film having a thickness of 75 μm and having been subjected to a coating liquid release treatment using a bar coater. Thereafter, the adhesive was irradiated with ultraviolet light using a UV lamp for 10 minutes to cure the adhesive, thereby producing an adhesive sheet having an adhesive layer thickness of 25 μm.

[0106] Examples 4 and 5 and Comparative Examples 1 to 4 Pressure-sensitive adhesive sheets were produced using the pressure-sensitive adhesive compositions of Examples 4 and 5 and Comparative Examples 1 to 4 in the same manner as in Example 3, with the components and amounts shown in Table 1 below.

[0107] [Table 1]

[0108] <Experimental Example> (1) Transparency assessment The adhesive layers according to the examples and comparative examples were peeled off from the release film and bonded to a slide glass (manufactured by Matsunami Glass Industry Co., Ltd., model number: S1111), and the haze value (%) was measured in accordance with JISK-7136 using a "Reflectance / Transmittance Meter HR-100" manufactured by Murakami Color Research Laboratory Co., Ltd. in an atmosphere of 25° C. The haze value of the adhesive layer was evaluated by subtracting the haze value of the slide glass (0.2%) from the haze value, and the evaluation results are shown in Table 2 below.

[0109] <Transparency evaluation criteria> ○: Haze value is less than 2% X: Haze value is 2% or more (2) Refractive index evaluation The adhesive layers according to the above examples and comparative examples were irradiated with sodium D rays in an atmosphere of 25° C., and the refractive index was measured using an Abe refractometer (DMM4, manufactured by ATAGO Corporation). The measurement results are shown in Table 2 below.

[0110] <Refractive index evaluation criteria> ◎: Refractive index 1.60 or higher ○: Refractive index 1.58 or more and less than 1.60 X: Refractive index less than 1.58

[0111] [Table 2]

[0112] Referring to the contents of Table 2, the pressure-sensitive adhesive layers produced using the pressure-sensitive adhesive compositions of Examples 1 to 5 exhibit excellent transparency and a high refractive index of 1.58 or more.

[0113] On the other hand, it can be seen that the pressure-sensitive adhesive layers produced using the pressure-sensitive adhesive compositions of Comparative Examples 1 to 3 have poorer refractive indexes than the Examples, and the pressure-sensitive adhesive layer produced using the pressure-sensitive adhesive composition of Comparative Example 4 has poorer transparency than the Examples.

[0114] Therefore, it can be seen that the pressure-sensitive adhesive composition according to the present invention is particularly suitable for producing a pressure-sensitive adhesive layer that exhibits excellent optical properties and reliability while improving visibility in display devices including touch panels without including a separate high refractive pattern layer.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic copolymer having a refractive index of 1.55 to 1.

70.

2. The pressure-sensitive adhesive composition according to claim 1 , wherein the acrylic copolymer contains a repeating unit derived from a high refractive acrylic monomer having a refractive index of 1.58 or more.

3. The pressure-sensitive adhesive composition according to claim 2, wherein the high refractive index acrylic monomer having a refractive index of 1.58 or more of the homopolymer includes at least one selected from the group consisting of pentabromophenyl (meth)acrylate, 2-(naphthalene-2-yloxy)ethyl (meth)acrylate, 2-(naphthalene-2-ylthio)ethyl (meth)acrylate, biphenylmethyl (meth)acrylate, and 1-pyrenemethyl (meth)acrylate.

4. The pressure-sensitive adhesive composition according to claim 2, wherein the high refractive index acrylic monomer having a homopolymer refractive index of 1.58 or more is contained in an amount of 10 to 70% by weight based on the total weight of the acrylic copolymer.

5. The pressure-sensitive adhesive composition according to claim 2, wherein the acrylic copolymer further comprises at least one of a repeating unit derived from an acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms and a repeating unit derived from a polymerizable monomer having a crosslinkable functional group.

6. The acrylic monomer having a hydrocarbon group having 1 to 20 carbon atoms includes methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and isobornyl acrylate.

6. The pressure-sensitive adhesive composition according to claim 5, comprising at least one selected from the group consisting of n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, pentafluorooctyl acrylate, 2-ethylhexyl diglycol acrylate, nonylphenol (modified with 4 mol of ethylene oxide) acrylate and 6-(1-naphthyloxy)-1-hexyl acrylate.

7. 6. The pressure-sensitive adhesive composition according to claim 5, wherein the polymerizable monomer having a crosslinkable functional group comprises at least one selected from the group consisting of a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a cyano group-containing monomer, a vinyl ester monomer, an aromatic vinyl monomer, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, a hydroxyl group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, an imide group-containing monomer, an epoxy group-containing monomer, and an ether group-containing monomer.

8. The pressure-sensitive adhesive composition according to claim 1 , further comprising at least one of a photoinitiator, a thermal curing agent, and nanoparticles.

9. The pressure-sensitive adhesive composition according to claim 8 , wherein the heat curing agent comprises an isocyanate-based crosslinking agent.

10. The pressure-sensitive adhesive composition according to claim 8, wherein the nanoparticles include at least one selected from the group consisting of titanium oxide, zinc oxide, zirconium oxide, magnesium oxide, zirconium titanate, zirconium silicate, strontium titanate, aluminum titanate, silicon ferrite, nickel ferrite, cobalt ferrite, barium carbonate, silicon carbide, yttrium carbide, magnesium silicate, zinc sulfate, and barium sulfate.

11. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition has a glass transition temperature (Tg) of -10°C or lower.

12. The pressure-sensitive adhesive composition according to claim 1 , wherein a pressure-sensitive adhesive layer produced from the pressure-sensitive adhesive composition has a refractive index of 1.58 or more.

13. The pressure-sensitive adhesive composition according to claim 1 , wherein a pressure-sensitive adhesive layer produced from the pressure-sensitive adhesive composition has a haze of less than 2%.

14. A pressure-sensitive adhesive sheet produced using the pressure-sensitive adhesive composition according to any one of claims 1 to 13.

15. The pressure-sensitive adhesive sheet according to claim 14 , wherein the pressure-sensitive adhesive sheet has a refractive index of 1.58 or more.

16. An optical member comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 13.

17. A display device comprising the optical member according to claim 16.

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