Adhesive composition and polarizing plate using the same

Abstract

To provide a polarizing plate which does not cause coloring of a polarizer due to polyene formation when exposed to a high-temperature environment and in which a protective film and the polarizer stuck together via an adhesive do not peel off even in a high-temperature and high-humidity environment.SOLUTION: An adhesive composition used for laminating a polarizer composed of a polyvinyl alcohol-based resin film on which iodine or a dichroic dye is adsorbed and oriented and a protective film, wherein the adhesive composition contains an isocyanate compound and a (meth) acrylic compound, and a content of an isocyanate group in the total amount of the adhesive composition is 5% by weight or more and 16% by weight or less, and a polarizing plate obtained by laminating a protective film on one surface or both surfaces of a polarizer using the adhesive composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition having high resistance to high temperatures and humidity and adhesiveness, and a polarizing plate obtained by laminating a protective film on one or both sides of a polarizer using the adhesive composition. [Background technology]

[0002] In recent years, the applications of various liquid crystal display devices have expanded, and they are now used not only in mobile devices such as mobile phones and tablet terminals, but also in in-vehicle image display devices such as car navigation devices and rear monitors. Accordingly, the image display devices are required to have higher durability in harsher environments (for example, high-temperature environments) than conventional requirements.

[0003] Polarizing plates are useful as one of the optical components that make up liquid crystal display devices. Polarizing plates usually have a structure in which protective films are laminated on both sides of a polarizer, and are incorporated into liquid crystal display devices for use. Until now, triacetyl cellulose film has been used as most of the protective films. Triacetyl cellulose has high moisture permeability, and polarizing plates to which it is attached as a protective film have had problems such as deterioration under humid and hot conditions, such as a temperature of 85°C and a relative humidity of 85%.

[0004] Therefore, a method for solving this problem by using a resin film having lower moisture permeability than a triacetyl cellulose film as a protective film has been proposed, and for example, it is known to use an amorphous polyolefin resin as the protective film. Specifically, Patent Document 1 describes laminating a thermoplastic saturated norbornene resin sheet as a protective film on at least one surface of a polarizer.

[0005] When such a protective film having low moisture permeability is laminated using conventional equipment, so-called wet lamination, in which an adhesive containing water as the main solvent, for example, an aqueous polyvinyl alcohol solution, is used to laminate the protective film to a polyvinyl alcohol-based polarizer and then the solvent is dried, has had problems such as insufficient adhesive strength being obtained and poor appearance, etc. This is because films having low moisture permeability are generally more hydrophobic than triacetyl cellulose films and the low moisture permeability makes it difficult to sufficiently dry the water solvent.

[0006] Therefore, Patent Document 2 discloses an adhesive whose main component is an epoxy resin that does not contain an aromatic ring, and proposes an adhesion method that uses cationic polymerization by heating or irradiation with active energy rays. However, although these adhesives improve adhesive strength due to the effect of the generated cations, they have the problem that the polarizer turns brown during durability tests due to polyenization.

[0007] Furthermore, Patent Document 3 discloses an adhesive using a hydroxyl group-containing acrylate and an isocyanate compound, which can prevent discoloration of a polarizer due to polyenation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-51117 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-245925 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-8928 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the adhesive composition described in Patent Document 3 has a problem in that the protective film and polarizer bonded together via the adhesive peel off in a high-temperature, high-humidity environment.

[0010] An object of the present invention is to provide a polarizing plate that does not cause coloration of a polarizer due to polyenation when exposed to a high-temperature environment, and that prevents peeling of a protective film and a polarizer that are bonded together via an adhesive even in a high-temperature, high-humidity environment. [Means for solving the problem]

[0011] The present inventors have conducted extensive research and found that by bonding a polarizer and a protective film with an adhesive composition containing specific amounts of an isocyanate compound and a (meth)acrylic compound as essential components, the adhesive strength can be maintained even under high temperature and high humidity conditions, and the polarizer made of a polyvinyl alcohol-based resin film is not discolored, thereby completing the present invention. That is, the present invention relates to the following items [1] to [7].

[0012] [1] An adhesive composition used for bonding a polarizer made of a polyvinyl alcohol-based resin film having iodine or a dichroic dye adsorbed and oriented thereon to a protective film, comprising: An adhesive composition comprising an isocyanate compound and a (meth)acrylic compound, wherein the content of isocyanate groups in the total amount of the adhesive composition is 5% by weight or more and 16% by weight or less. [2] The adhesive composition according to the above item [1], wherein the (meth)acrylic compound is a urethane (meth)acrylate. [3] The adhesive composition according to the above item [1], further comprising a polyester resin. [4] The adhesive composition according to any one of the preceding items [1] to [3], wherein the isocyanate compound is at least one selected from the group consisting of an isocyanurate of hexamethylene diisocyanate, an adduct of hexamethylene diisocyanate, and a biuret of hexamethylene diisocyanate. [5] The adhesive composition according to any one of the above items [1] to [3], further comprising a photoradical polymerization initiator. [6] A polarizing plate characterized by laminating a protective film to one or both sides of a polyvinyl alcohol-based resin film on which iodine or a dichroic dye is adsorbed and oriented using the adhesive composition described in any one of the preceding items [1] to [3]. [7] The polarizing plate according to item [6] above, wherein the protective film is a film of at least one resin selected from the group consisting of amorphous polyolefin resins, polyester resins, acrylic resins, polycarbonate resins, polysulfone resins, and alicyclic polyimide resins, and is bonded to one or both surfaces of the polarizer. [Effects of the Invention]

[0013] By using the adhesive composition of the present invention to prepare a polarizing plate, the protective film and the polarizer have sufficient adhesive strength, and the polarizing plate can ensure high durability even in a high-temperature, high-humidity environment.

[0014] Hereinafter, embodiments according to the present invention will be described in detail. Note that the following embodiments are examples of some typical embodiments of the present invention, and various modifications can be made within the scope of the present invention.

[0015] [Adhesive composition] The adhesive composition of the present invention is an adhesive used for bonding a polarizer made of a polyvinyl alcohol-based resin film on which iodine or a dichroic dye has been adsorbed and oriented to a protective film, and is characterized by containing an isocyanate compound and a (meth)acrylic compound as essential components.

[0016] The adhesive composition of the present invention contains an isocyanate compound, and as a result, the isocyanate group reacts with the hydroxy group of the polyvinyl alcohol used in the polarizer, thereby exhibiting high adhesiveness. Furthermore, when a hydroxy group-containing (meth)acrylate is added to the adhesive composition, the isocyanate group also reacts with the hydroxy group of the compound, resulting in a high crosslink density and high durability.

[0017] The isocyanate compound is a compound having at least one isocyanate group in the molecule, and specific examples thereof include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, and 1,6-hexanediisocyanate. Examples of suitable isocyanates include diisocyanates, isophorone diisocyanate, methylene bis(4-cyclohexyl isocyanate), 2,2,4-trimethylhexamethylene diisocyanate, bis(2-isocyanatoethyl) fumarate, 6-isopropyl-1,3-phenyl diisocyanate, 4-diphenylpropane diisocyanate, lysine diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, tetramethylxylylene diisocyanate, 2,5 (or 6)-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane, and acryloyl alkyl isocyanates. Polyisocyanates, which are modified isocyanates, can also be used. Specific examples include adducts, isocyanurates, biurets, and allophanates modified with polyhydric alcohols such as trimethylolpropane and pentaerythritol.

[0018] Among these, 1,6-hexane diisocyanate isocyanurate, 1,6-hexane diisocyanate adduct, and 1,6-hexane diisocyanate biuret are particularly preferable. Specific product names include Asahi Kasei Corporation's Duranate TPA-100 (1,6-hexane diisocyanate isocyanurate), Duranate TUL-100 (1,6-hexane diisocyanate isocyanurate), Duranate E402-100 (1,6-hexane diisocyanate adduct), and Duranate 24A-100 (1,6-hexane diisocyanate biuret).

[0019] Furthermore, when an isocyanate compound containing an acryloyl or methacryloyl group is used, the acryloyl or methacryloyl group reacts with other components containing acryloyl or methacryloyl groups, resulting in a high crosslink density and high durability. Specific product names include Karenz AOI, Karenz MOI, and Karenz MOI-EG manufactured by Resonac.

[0020] The adhesive composition of the present invention has an isocyanate group content of 5% by weight or more and 16% by weight or less, preferably 6% by weight or more and 15% by weight or less, more preferably 7% by weight or more and 14% by weight or less, and even more preferably 8% by weight or more and 13% by weight or less, based on the total amount of the adhesive composition. If the isocyanate group content is less than 5% by weight, the adhesive composition has a low isocyanate group content, resulting in reduced adhesion. Furthermore, as the crosslink density decreases, the polarizer peels off from the protective film and shrinks during a durability test, leaving only the protective film visible at the edge. Furthermore, if the isocyanate group content is greater than 16% by weight, the crosslink density of the adhesive layer similarly decreases, potentially reducing durability. Furthermore, the adhesive composition rapidly increases in viscosity over time, making it unsuitable for processability.

[0021] The content (wt %) of isocyanate groups in the total amount of the adhesive composition can be calculated using the following formula.

[0022] Isocyanate group content (wt%) = Isocyanate compound content (parts by weight) × Isocyanate group content in isocyanate compound (wt%) / Total amount of adhesive composition (parts by weight)

[0023] Here, the content (wt %) of isocyanate groups in the isocyanate compound is the amount of isocyanate groups in the isocyanate compound expressed as a weight fraction, and can be measured in accordance with JIS K 1603-1.

[0024] A (meth)acrylic compound is a compound having at least one (meth)acryloyl group in the molecule, and specific examples thereof include hydroxy group-containing (meth)acrylates, monofunctional (meth)acrylates, polyfunctional (meth)acrylates, (meth)acrylamides, urethane (meth)acrylates, epoxy (meth)acrylates, polyester (meth)acrylates, tris(acryloxyethyl) isocyanurate, (meth)acrylic acid, etc. In the present invention, "(meth)acrylic" refers to acrylic and / or methacrylic, "(meth)acrylate" refers to acrylate and / or methacrylate, and "(meth)acryloyl" refers to acryloyl and / or methacryloyl.

[0025] The hydroxy group-containing (meth)acrylate is a (meth)acrylate having a hydroxy group in the molecule, and specifically, 2-hydroxyethyl (meth)acrylate or 1-hydroxyethyl (meth)acrylate or 2-hydroxypropyl (meth)acrylate or 3-hydroxypropyl (meth)acrylate or 1-hydroxypropyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate or 3-hydroxybutyl (meth)acrylate or 2-hydroxybutyl (meth)acrylate or 1-hydroxybutyl (meth)acrylate or 5-hydroxypropyl (meth)acrylate. Examples of suitable hydroxyl groups include hexapentyl (meth)acrylate or 6-hydroxyhexyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, N-(2-hydroxyethyl) (meth)acrylamide, 1,6-hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)]bisacrylate, EO-modified isocyanuric acid di(meth)acrylate, 1-(acryloyloxy)-3-(methacryloyloxy)-2-propanol, glycerol di(meth)acrylate, glycerin dimethacrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate. The hydroxyl group-containing (meth)acrylate not only enhances the adhesive strength of the adhesive, but also reduces the viscosity of the adhesive composition, improving its applicability to protective films. Furthermore, the hydroxyl groups of these hydroxyl-containing (meth)acrylates react with the isocyanate groups of the isocyanate compound to form an adhesive layer with high crosslinking density, making it possible to provide a polarizing plate with high adhesive strength and excellent durability. Among hydroxyl-containing (meth)acrylates, appropriately combining hydroxyl-containing (meth)acrylates whose alkyl groups have 2 to 6 carbon atoms is preferred in terms of adjusting the wettability of the coating liquid with the polarizing film or protective film and the plasticity of the cured product after photocuring. 4-hydroxybutyl acrylate, which has 4 carbon atoms, is particularly preferred from the perspective of film processing because it can increase the adhesiveness immediately after curing.Furthermore, when a (meth)acrylate containing two or more hydroxy groups is added to the adhesive composition, the crosslinking density becomes higher, thereby improving durability. However, since the viscosity of the adhesive composition increases rapidly over time, it is preferable to add the (meth)acrylate in an amount of 50% by weight or less.

[0026] The content of the hydroxy group-containing (meth)acrylate is preferably 75 wt% or less, more preferably 70 wt% or less, even more preferably 65 wt% or less, and particularly preferably 60 wt% or less, based on the total amount of the adhesive composition. If the content of the hydroxy group-containing (meth)acrylate is greater than 75 wt%, the isocyanate groups of the isocyanate compound will be relatively reduced, which may result in a low crosslink density of the adhesive layer after curing, resulting in reduced durability and reduced adhesion to the polarizer. Furthermore, when the content of the isocyanate compound is taken as 1.0, the content of the hydroxy group-containing (meth)acrylate is preferably 3.6 times or less, more preferably 3.0 times or less, even more preferably 2.0 times or less, and particularly preferably 1.5 times or less. If the content of the hydroxy group-containing (meth)acrylate is greater than 3.6 times, the isocyanate groups of the isocyanate compound will be relatively reduced, which may result in a low crosslink density of the adhesive layer after curing, resulting in reduced durability and reduced adhesion to the polarizer.

[0027] Specific examples of monofunctional (meth)acrylates having one (meth)acryloyl group in the molecule include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. acrylate, 1,4-cyclohexanedimethylol mono(meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, benzyl (meth)acrylate, (meth)acrylate of phenol alkylene oxide adduct, (meth)acrylate of p-cumylphenol alkylene oxide adduct, (meth)acrylate of o-phenylphenol alkylene oxide adduct, (meth)acrylate of nonylphenol alkylene oxide adduct, 2 -Methoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, (meth)acrylate of alkylene oxide adduct of 2-ethylhexyl alcohol, pentanediol mono(meth)acrylate, hexanediol mono(meth)acrylate, diethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate, Propylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, caprolactone-modified tetrahydrofurfuryl (meth)acrylate, (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (2-isobutyl-2-methyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, (1,4-dioxaspiro[4,5]decan-2-yl)methyl (meth)acrylate, glycidyl (meth)acrylate, 3,Examples of the acrylates include 4-epoxycyclohexylmethyl (meth)acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, 2-(meth)acryloyloxyethyl isocyanate, allyl (meth)acrylate, N-(meth)acryloyloxyethyl hexahydrophthalimide, N-(meth)acryloyloxyethyl tetrahydrophthalimide, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, 2-(meth)acryloyloxyethyl acid phosphate, 3-(meth)acryloyloxypropyl trimethoxysilane, 3-(meth)acryloyloxypropyl dimethoxymethylsilane, and 3-(meth)acryloyloxypropyl triethoxysilane.

[0028] Specific examples of polyfunctional (meth)acrylates having two or more (meth)acryloyl groups in the molecule include neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, cyclohexanedimethylol di(meth)acrylate, 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tetramethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tricyclodecane dimethylol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri- or tetra(meth)acrylate, dipentaerythritol penta- or hexa(meth)acrylate, and di(meth)acrylate of hydrogenated bisphenol A, polyethylene glycol (repeating number 8 or more) di(meth)acrylate, polypropylene glycol (repeating number 6 or more) di(meth)acrylate, and di(meth)acrylate of bisphenol A alkylene oxide adduct.

[0029] Specific examples of (meth)acrylamides include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-(3-N,N-dimethylaminopropyl)(meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, N,N-diallyl(meth)acrylamide, and (meth)acryloylmorpholine.

[0030] Examples of urethane (meth)acrylates include urethane (meth)acrylates that are reaction products of polyols such as ethylene glycol, 1,4-butanediol, polytetramethylene glycol, neopentyl glycol, polycaprolactone polyol, polyester polyol, polycarbonate diol, or polytetramethylene glycol with organic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanate, tolylene diisocyanate, xylylene diisocyanate, or 4,4'-diphenylmethane diisocyanate and with hydroxyl group-containing ethylenically unsaturated compounds such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 1,4-butanediol mono(meth)acrylate, an ε-caprolactone adduct of 2-hydroxyethyl (meth)acrylate, or pentaerythritol tri(meth)acrylate. The inclusion of urethane (meth)acrylate is preferable from the viewpoint of film processing, since it can improve adhesiveness immediately after curing. In particular, urethane (meth)acrylates with a homopolymer Tg of 40°C or less are more preferable because they exhibit high adhesiveness.

[0031] Examples of epoxy (meth)acrylates include epoxy (meth)acrylates that are reaction products of polyglycidyl compounds such as bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, trisphenolmethane epoxy resins, polyethylene glycol diglycidyl ether, glycerin polyglycidyl ether, and trimethylolpropane polyglycidyl ether with (meth)acrylic acid. Epoxy (meth)acrylates whose homopolymer Tg is 40°C or less are particularly preferred because they exhibit high adhesiveness.

[0032] Examples of polyester (meth)acrylates include polyester acrylates such as trimethylolpropane tri(meth)acrylate, trimethylolpropane polyethoxy tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and tripentaerythritol octa(meth)acrylate. In particular, polyester acrylates having a homopolymer Tg of 40°C or less are more preferred because they exhibit high adhesiveness.

[0033] Examples of tris(acryloxyethyl) isocyanurate include tris(acryloxyethyl) isocyanurate and trisallyl isocyanurate. In particular, tris(acryloxyethyl) isocyanurate, the homopolymer of which has a Tg of 40° C. or less, is more preferred because it exhibits high adhesiveness.

[0034] The content of the (meth)acrylic compound is preferably 75 wt% or less, more preferably 70 wt% or less, even more preferably 65 wt% or less, and particularly preferably 60 wt% or less, based on the total amount of the adhesive composition. If the content of the (meth)acrylic compound is greater than 75 wt%, the isocyanate groups of the isocyanate compound will be relatively reduced, which may result in a low crosslink density of the adhesive layer after curing, resulting in reduced durability and reduced adhesion to the polarizer. Furthermore, when the content of the isocyanate compound is taken as 1.0, the content of the (meth)acrylic compound is preferably 3.6 times or less, more preferably 3.0 times or less, even more preferably 2.0 times or less, and particularly preferably 1.5 times or less. If the content of the (meth)acrylic compound is greater than 3.6 times, the isocyanate groups of the isocyanate compound will be relatively reduced, which may result in a low crosslink density of the adhesive layer after curing, resulting in reduced durability and reduced adhesion to the polarizer.

[0035] The adhesive composition of the present invention can contain a polyester resin. Specific product names include Vylon 200, Vylon GK-360, Vylon 600, Vylon GK-810, Vylon 630, and Vylon GK-680 manufactured by Toyobo Co., Ltd., and Teslac 2455, Teslac 2460, Teslac 2461, Teslac 2462, Teslac 2464, and Teslac TA22-981 manufactured by Resonac Corporation. Polyester resins with a homopolymer Tg of 40°C or less are particularly preferred because they exhibit high adhesive properties. Furthermore, polyester resins with a number-average molecular weight of 10,000 or less are preferred from the standpoint of processability because they can maintain a low viscosity of the adhesive composition.

[0036] The adhesive composition of the present invention may contain a photoradical polymerization initiator. Specific examples include 4'-phenoxy-2,2-dichloroacetophenone, 4'-tert-butyl-2,2-dichloroacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 1-hydroxycyclohexyl phenyl ketone, α,α-diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, and 1-(4-isopropylphenyl)-2-hydroxycyclohexylphenyl ketone. acetophenone-based photopolymerization initiators such as 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one; benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isopropyl ether; benzoin ether-based photopolymerization initiators such as butyl ether; benzophenone-based photopolymerization initiators such as benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, and 2,4,6-trimethylbenzophenone; thioxanthone-based photopolymerization initiators such as 2-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, and 1-chloro-4-propoxythioxanthone; 2 Acylphosphine oxide photoinitiators such as 4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; oxime ester photoinitiators such as 1,2-octanedione, 1-[4-(phenylthiophenyl)]-, 2-(O-benzoyloxime); camphorquinone, etc.

[0037] The photoradical polymerization initiator can be used alone or in combination of two or more types depending on the desired performance. When a photoradical polymerization initiator is used, the content is preferably 20 parts by weight or less, more preferably 0.1 to 10 parts by weight, and even more preferably 0.1 to 5 parts by weight, based on the total weight of the composition. By setting the content of the photoradical polymerization initiator within the above range, sufficient adhesive strength can be obtained and excellent curability can also be achieved.

[0038] Furthermore, as long as the effects of the present invention are not impaired, the adhesive composition may contain other additives, such as ion trapping agents, antioxidants, antioxidants, stabilizers, chain transfer agents, sensitizers, tackifiers, thermoplastic resins, fillers, flow modifiers, plasticizers, defoamers, organic solvents, dyes, pigments, processing agents, and UV screeners. Ion trapping agents include, for example, powdered inorganic compounds such as bismuth, antimony, magnesium, aluminum, calcium, and titanium, as well as mixtures thereof. Antioxidants include, for example, hindered phenol antioxidants. Tackifying resins include, for example, rosins such as rosin acid, polymerized rosin acid, and rosin acid esters; terpene resins; terpene phenol resins; aromatic hydrocarbon resins; aliphatic saturated hydrocarbon resins; and petroleum resins.

[0039] The adhesive composition of the present invention can be produced by stirring and mixing the above-mentioned components according to a conventional method. In this case, heating can be performed if necessary. The heating temperature and time can be appropriately set depending on the composition used, the substrate, the purpose, etc., but a temperature of 30 to 80°C for about 30 minutes to 2 hours is preferred.

[0040] The viscosity of the composition is preferably from 10 to 1500 mPa·s, more preferably from 10 to 1000 mPa·s, and even more preferably from 10 to 700 mPa·s, in terms of excellent coatability onto substrates.

[0041] The thickness of the adhesive layer of the polarizing plate is preferably in the range of 0.05 to 100 μm. If it is less than 0.05 μm, the adhesive strength will be weak. On the other hand, if it exceeds 100 μm, there is a risk of a decrease in transmitted light, distortion of the transmitted image, and deterioration of optical properties. For applications where optical properties are important, the thinner the adhesive layer, the more suppressed distortion of the polarizing plate and the improved optical properties will be. Therefore, it is preferable to make it as thin as possible within an acceptable range of deterioration in adhesive strength. The thickness is preferably 5 μm or less, more preferably 2.5 μm or less, even more preferably 1 μm or less, and most preferably 0.5 μm or less. The adhesive of the present invention can be made thin because it can reduce viscosity. Furthermore, for applications requiring a certain level of strength in the polarizing plate, a thick adhesive layer is preferable. The thickness is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 25 μm or more, and most preferably 50 μm or more. The adhesive of the present invention can be made thick because it can increase viscosity.

[0042] [Polarizing plate] The polarizing plate according to the present invention comprises a polarizer having a dichroic dye adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film, and a protective film laminated to one or both sides of the polarizer. The polyvinyl alcohol-based resin constituting the polarizer is obtained by saponifying a polyvinyl acetate-based resin. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol-based resin is typically 85 to 100 mol%, preferably 98 to 100 mol%. The polyvinyl alcohol-based resin may be further modified; for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may also be used. The degree of polymerization of the polyvinyl alcohol resin is usually in the range of 1,000 to 10,000, and preferably in the range of 1,500 to 10,000.

[0043] A polarizing plate is manufactured through the steps of uniaxially stretching such a polyvinyl alcohol-based resin film, dyeing the polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye, treating the polyvinyl alcohol-based resin film with the adsorbed dichroic dye with an aqueous boric acid solution, washing with water after the treatment with the aqueous boric acid solution, and laminating a protective film to the uniaxially stretched polyvinyl alcohol-based resin film with the adsorbed and oriented dichroic dye that has been subjected to these steps.

[0044] The uniaxial stretching may be carried out before dyeing with a dichroic dye, simultaneously with dyeing with a dichroic dye, or after dyeing with a dichroic dye. When the uniaxial stretching is carried out after dyeing with a dichroic dye, the uniaxial stretching may be carried out before or during the boric acid treatment. Of course, the uniaxial stretching can be carried out in these multiple stages. The uniaxial stretching may be carried out uniaxially between rolls with different peripheral speeds, or may be carried out uniaxially using a heated roll. Furthermore, dry stretching in which stretching is carried out in the atmosphere or wet stretching in which stretching is carried out in a state swollen with a solvent may be used. The stretching ratio is usually about 4 to 8 times.

[0045] To dye a polyvinyl alcohol-based resin film with a dichroic dye, for example, the polyvinyl alcohol-based resin film may be immersed in an aqueous solution containing the dichroic dye. Specific examples of the dichroic dye include iodine and dichroic dyes.

[0046] When iodine is used as the dichroic dye, a dyeing method is typically employed in which a polyvinyl alcohol resin film is immersed in an aqueous solution containing iodine and potassium iodide. The iodine content in this aqueous solution is typically about 0.01 to 0.5 parts by weight per 100 parts by weight of water, and the potassium iodide content is typically about 0.5 to 10 parts by weight per 100 parts by weight of water. The temperature of this aqueous solution is typically about 20 to 40°C, and the immersion time in this aqueous solution is typically about 30 to 300 seconds.

[0047] On the other hand, when a dichroic dye is used as the dichroic pigment, a method of dyeing a polyvinyl alcohol resin film by immersing it in an aqueous solution containing the water-soluble dichroic dye is usually adopted. The content of the dichroic dye in this aqueous solution is usually about 1×10-3 to 1×10-2 parts by weight per 100 parts by weight of water. This aqueous solution may also contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is usually about 20 to 80°C, and the immersion time in this aqueous solution is usually about 30 to 300 seconds.

[0048] The boric acid treatment after dyeing with a dichroic dye is carried out by immersing the dyed polyvinyl alcohol-based resin film in an aqueous boric acid solution. The content of boric acid in the aqueous boric acid solution is usually about 2 to 15 parts by weight, preferably about 3 to 8 parts by weight, per 100 parts by weight of water. When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the aqueous boric acid solution is usually about 2 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of water. The immersion time in the aqueous boric acid solution is usually about 100 to 1200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the aqueous boric acid solution is usually 50°C or higher, preferably 50 to 85°C.

[0049] The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The washing treatment is carried out, for example, by immersing the boric acid treated polyvinyl alcohol resin film in water. After washing with water, a drying treatment is carried out to obtain a polarizer. The water temperature in the washing treatment is usually about 5 to 40°C, and the immersion time is usually about 2 to 120 seconds. The subsequent drying treatment is usually carried out using a hot air dryer or a far-infrared heater. The drying temperature is usually 40 to 100°C. The treatment time in the drying treatment is usually about 120 to 600 seconds.

[0050] In this way, a polarizer made of a polyvinyl alcohol-based resin film on which iodine or a dichroic dye has been adsorbed and oriented is obtained. Next, a protective film is attached to one or both sides of this polarizer using the adhesive composition of the present invention.

[0051] The polarizing plate of the present invention can typically be produced by a method including a coating step of applying the adhesive composition of the present invention in an uncured state to a protective film to form an adhesive-coated surface, a lamination step of laminating a polarizer to the adhesive-coated surface of the protective film, and a curing step of curing the adhesive composition.

[0052] As another method for producing a polarizer in the present invention, a method can be adopted in which the adhesive composition of the present invention is dropped between the polarizer and the protective film in an uncured state, and then the two are pressed together while being uniformly spread with a roll or the like, and then the adhesive composition is cured to form an adhesive layer.

[0053] [Coating process] There are no particular limitations on the method for applying the adhesive composition to the polarizer, and various coating methods can be used, such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater. Since each coating method has its own optimal viscosity range, adjusting the viscosity using a solvent is also a useful technique. The solvent used for this purpose is one that can dissolve the adhesive composition well without deteriorating the optical performance of the polarizer, and there are no particular limitations on the type of solvent. For example, organic solvents such as hydrocarbons typified by toluene and esters typified by ethyl acetate can be used.

[0054] [Lamination process] When the adhesive composition of the present invention is applied to a protective film, a polarizer is then attached to the adhesive-coated surface. When the adhesive composition is applied between a polarizer and a protective film, the two are attached together as is. The protective film used in the polarizing plate of the present invention is typically a transparent film. The protective film is not particularly limited, and specifically, a film of an acetyl cellulose-based resin such as triacetyl cellulose, which is currently the most widely used protective film for polarizing plates, or a film of a transparent resin having lower moisture permeability than triacetyl cellulose can be used. From the viewpoint of improving moist heat resistance, it is preferable to use a film of a transparent resin having low moisture permeability.

[0055] In the polarizing plate of the present invention, typically, a film of an acetyl cellulose-based resin or a film of a transparent resin having lower moisture permeability than triacetyl cellulose can be attached to at least one surface of the polarizer.

[0056] The moisture permeability of the above triacetyl cellulose is approximately 400 g / m 2 When a protective film is attached to both sides of a polarizer, two protective films may be attached to each side in stages, or both sides may be attached in one step.

[0057] Examples of the acetyl cellulose resin film include the above-mentioned triacetyl cellulose film, as well as diacetyl cellulose film and acetyl butyl cellulose film.

[0058] Examples of transparent resin films with lower moisture permeability than triacetyl cellulose include films of at least one transparent resin selected from amorphous polyolefin resins, polyester resins such as polyethylene terephthalate, acrylic resins, polycarbonate resins, polysulfone resins, and alicyclic polyimide resins. Among these, films made of amorphous polyolefin resins are particularly preferred. Amorphous polyolefin resins typically contain polymerization units of cyclic olefins such as norbornene or polycyclic norbornene monomers, and may also be copolymers of cyclic olefins and linear olefins. Examples of such amorphous polyolefin resins include thermoplastic saturated norbornene resins. Those with polar groups incorporated therein are also effective. Commercially available amorphous polyolefin resins include "Arton" from JSR Corporation, "ZEONEX" and "ZEONOR" from Nippon Zeon Co., Ltd., and "APO" and "Apel" from Mitsui Chemicals, Inc. When forming a film from an amorphous polyolefin resin, a known method such as a solvent casting method or a melt extrusion method is appropriately used for film formation. These amorphous polyolefin resin films have a film density of approximately 300 g / m 2 / 24hr or less moisture permeability.

[0059] In the present invention, when protective films are attached to both sides of the polarizer, the protective films attached to one side and the other side of the polarizer may be of the same type or different types. When different types of protective films are attached to both sides of the polarizer, for example, one protective film may be a film made of an acetyl cellulose resin, and the other protective film may be a film made of a transparent resin with lower moisture permeability than triacetyl cellulose. Conventionally, wet lamination using a water-based adhesive has been used to bond an acetyl cellulose protective film to a polarizer, but this requires a long and large drying oven. On the other hand, when the adhesive composition of the present invention, which does not use an organic solvent, is used, no drying oven is required. Advantages of this method include, as mentioned above, no investment in a drying oven is required, no thermal degradation of the polarizer and / or adhesive layer occurs, and curling can be suppressed.

[0060] When a protective film having a relatively high moisture permeability, such as an acetyl cellulose-based resin film, is provided on one surface of the polarizer, an adhesive other than the adhesive composition of the present invention, such as a polyvinyl alcohol-based adhesive, may be used on the bonding surface between the protective film and the polarizer.

[0061] The surface of the protective film that will be attached to the polarizer may be subjected to an adhesion-enhancing treatment such as saponification treatment, corona treatment, primer treatment, anchor coating treatment, plasma treatment, or flame treatment prior to attachment to the polarizer. Furthermore, the surface of the protective film opposite to the surface that will be attached to the polarizer may have various treated layers such as a hard coat layer, an antireflection layer, or an antiglare layer. The thickness of the protective film is usually in the range of about 5 to 300 μm, preferably 10 to 200 μm, and more preferably 10 to 100 μm.

[0062] [Curing process] As described above, after the polarizer and the protective film are bonded together via the uncured adhesive composition, the adhesive composition is cured by irradiation with active energy rays, and the protective film is fixed onto the polarizer.

[0063] The light source of the active energy rays is not particularly limited, but is preferably an active energy ray having an emission distribution at a wavelength of 400 nm or less, and specifically, preferred are low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, etc. The light irradiation intensity of the adhesive composition is appropriately determined depending on the composition of the adhesive composition, and is not particularly limited, but is preferably 0.1 to 6000 mW / cm in the wavelength region effective for activating the polymerization initiator. 2 It is preferable that the irradiation intensity is 0.1 mW / cm. 2 If the reaction time is not too long, the output will be 6000mW / cm 2 When the light intensity is less than 10000 mJ / cm, there is little risk of yellowing of the epoxy resin or deterioration of the polarizer due to heat radiated from the light source and heat generated during curing of the adhesive composition. The light irradiation time for the adhesive composition is controlled for each adhesive composition to be cured and is not particularly limited. However, the cumulative light amount, which is expressed as the product of the irradiation intensity and the irradiation time, is 10 to 10,000 mJ / cm. 2 It is preferable that the integrated light dose to the adhesive composition is set to 10 mJ / cm. 2 When the irradiation amount is 10,000 mJ / cm or more, a sufficient amount of active species derived from the polymerization initiator can be generated to more reliably progress the curing reaction, and 2 When the irradiation time is not too long, good productivity can be maintained.

[0064] When the adhesive composition is cured by irradiation with active energy rays, it is preferable to perform the curing under conditions that do not deteriorate the various functions of the polarizing plate, such as the degree of polarization, transmittance, and hue of the polarizer, and the transparency of the protective film.

[0065] The curing step may be performed before the laminating step, and in this case, the adhesive composition cured in the curing step is laminated to the polarizer or the protective film to fix the protective film to the polarizer. The advantage of this method is that it is easy to increase the thickness of the adhesive layer, which is suitable for applications requiring a certain level of strength in the polarizing plate. [Example]

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means parts by weight.

[0067] (Preparation of adhesive composition) [Example 1] 28.8 parts of 4-hydroxybutyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a hydroxy group-containing (meth)acrylate component, and 3.8 parts of Omnirad TPO H manufactured by IGM was added as a photoradical polymerization initiator component, and the mixture was stirred at 25°C for 1 hour. Next, 67.3 parts of 24A-100 manufactured by Asahi Kasei Corporation was added as an isocyanate compound component, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0068] [Examples 2 to 13] Adhesive compositions were obtained in the same manner as in Example 1, except that the formulations were changed as shown in Tables 1 and 2.

[0069] [Example 14] 33.3 parts of 4-hydroxybutyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. as a hydroxy group-containing (meth)acrylate component, 8.8 parts of KAYARAD PET30 manufactured by Nippon Kayaku Co., Ltd. as a polyfunctional (meth)acrylate component, and 3.5 parts of Omnirad TPO H manufactured by IGM as a photoradical polymerization initiator component were added and stirred at 25°C for 1 hour, and then 54.4 parts of 24A-100 manufactured by Asahi Kasei Corporation as an isocyanate compound component were added, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0070] [Examples 15 to 19] An adhesive composition was obtained in the same manner as in Example 14, except that the formulation was changed to that shown in Table 2.

[0071] [Example 20] 36.9 parts of 4-hydroxybutyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a hydroxy group-containing (meth)acrylate component, and 9.2 parts of KAYARAD UX-0937 manufactured by Nippon Kayaku Co., Ltd. was added as a urethane (meth)acrylate component. The mixture was stirred at 60°C for 30 minutes and then cooled at room temperature for 30 minutes. Next, 3.8 parts of Omnirad TPO H manufactured by IGM was added as a photoradical polymerization initiator component, and the mixture was stirred at 25°C for 1 hour. Next, 50.0 parts of 24A-100 manufactured by Asahi Kasei Corporation was added as an isocyanate compound component, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0072] [Examples 21 to 31] An adhesive composition was obtained in the same manner as in Example 20, except that the formulation was changed to that shown in Table 3.

[0073] [Example 32] 27.3 parts of 4-hydroxybutyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a hydroxy group-containing (meth)acrylate component, and 9.1 parts of Light Acrylate P2H-A phenoxydiethylene glycol acrylate manufactured by Kyoeisha Chemical Industry Co., Ltd. was added as a monofunctional (meth)acrylate component. Then, 24.3 parts of KAYARAD UX-3204 manufactured by Nippon Kayaku Co., Ltd. was added as a urethane (meth)acrylate component, and the mixture was stirred at 60°C for 30 minutes, then cooled at room temperature for 30 minutes. Next, 5.1 parts of Omnirad TPO H manufactured by IGM was added as a photoradical polymerization initiator component, and the mixture was stirred at 25°C for 1 hour. Next, 34.2 parts of 24A-100 manufactured by Asahi Kasei Corporation was added as an isocyanate compound component, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0074] [Examples 33 to 35] An adhesive composition was obtained in the same manner as in Example 32, except that the formulation was changed to that shown in Table 4.

[0075] [Example 36] 18.2 parts of 4-hydroxybutyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a hydroxy group-containing (meth)acrylate component, 18.2 parts of Viscoat #150 tetrahydrofurfuryl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a monofunctional (meth)acrylate component, then 12.2 parts of KAYARAD HX-620 manufactured by Nippon Kayaku Co., Ltd. was added as a polyfunctional (meth)acrylate, then 12.2 parts of Vylon GK-680 manufactured by Toyobo Co., Ltd. was added as a polyester resin component, and the mixture was stirred at 60°C for 3 hours, then cooled at room temperature for 30 minutes, then 5.1 parts of Omnirad TPO H manufactured by IGM Co., Ltd. was added as a photoradical polymerization initiator component, and the mixture was stirred at 25°C for 1 hour, then 34.2 parts of 24A-100 manufactured by Asahi Kasei Corporation was added as an isocyanate compound component, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0076] [Examples 37 to 40] An adhesive composition was obtained in the same manner as in Example 36, except that the formulation was changed to that shown in Table 4.

[0077] [Example 41] 9.1 parts of KAYARAD R-128H manufactured by Nippon Kayaku Co., Ltd. was added as a hydroxyl group-containing (meth)acrylate component, 27.3 parts of Viscoat #150 tetrahydrofurfuryl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd. was added as a monofunctional acrylate component, and then 18.2 parts of KAYARAD UX-3204 manufactured by Nippon Kayaku Co., Ltd. was added as a urethane (meth)acrylate component. After stirring at 60°C for 30 minutes, 6.1 parts of Vylon GK-680 manufactured by Toyobo Co., Ltd. was added as a polyester resin component, and the mixture was stirred at 60°C for 3 hours. After cooling at room temperature for 30 minutes, 5.1 parts of Omnirad TPO H manufactured by IGM was added as a photoradical polymerization initiator component, and the mixture was stirred at 25°C for 1 hour. Then, 34.2 parts of 24A-100 manufactured by Asahi Kasei Corporation was added as an isocyanate compound component, and the mixture was stirred at 25°C for 5 minutes to obtain an adhesive composition.

[0078] [Examples 42 to 54] Adhesive compositions were obtained in the same manner as in Example 41, except that the formulations were changed as shown in Tables 5 and 6.

[0079] [Comparative Examples 1 to 4] An adhesive composition was obtained in the same manner as in Example 1, except that the components were changed to those shown in Table 7.

[0080] (Fabrication of polarizing element) Based on the description in Example 1 of JP-A-11-218611, the following dyes 1 to 4 were prepared. Then, dyes 1 to 4 and sodium sulfate were dissolved in water to prepare a dyeing solution.

[0081] Dye 1: CIDirect Orange 39 (Kayafect Orange manufactured by Nippon Kayaku Co., Ltd.) nge G) was used.

[0082] Dye 2: CIDirect Red 81 (Red 4BL manufactured by Nippon Chemical Industry Co., Ltd.) was used. Ta.

[0083] Dye 3: The dye having the chemical formula described in JP-A-11-218611 was synthesized according to the same publication.

[0084] [ka]

[0085] Dye 4: A dye having the chemical formula disclosed in Example 38 of JP-A-60-156759 was synthesized according to the same publication.

[0086] [ka]

[0087] Next, a PVA-based resin film (VF-PS#7500 manufactured by Kuraray Co., Ltd.) was immersed in water while uniaxially stretched to swell, and then immersed in the dyeing solution and stretched with a boric acid aqueous solution to orient the dye within the resin film. The total uniaxial stretching ratio between swelling and boric acid treatment was 4 to 5 times. After stretching, the film was dried in a 70°C dryer for 3 minutes while maintaining tension to form a polarizing element. The resulting polarizing element exhibited a grayish color. Measurements using a Hitachi High-Tech Science UH-4150 spectrophotometer revealed the following optical properties: Ys = 60.5%, Py = 47.7%, and the hue in the L*a*b* color space was L*s = 82.1, a*s = 0.4, and b*s = -0.2, respectively.

[0088] (Manufacturing of polarizing plates) [Examples 1 to 27 and Comparative Examples 1 to 5] A 50 μm thick amorphous polyolefin resin film (trade name Zeonor ZF14, manufactured by Zeon Corporation, hereinafter referred to as “ZF14”) was subjected to a corona treatment (Kasuga Electric Co., Ltd. AGF-B10, output 0.3 kW, speed 3 m / min) as an adhesion enhancing treatment.

[0089] Thereafter, each adhesive composition listed in Tables 1 to 4 was applied to the corona-treated surface of "ZF14" using a bar coater with a line count of 4. A polarizer was then laminated onto this, and the laminate film was cured using a high-pressure mercury lamp (HX4000L, manufactured by Harrison Toshiba Lighting Co., Ltd.) at 120 W, 5 m / min, and one pass to obtain a laminate film. Next, the same adhesive composition was applied using a bar coater to a similarly corona-treated "ZF14," and the polarizer side of the resulting laminate film was laminated to the same, followed by curing using a high-pressure mercury lamp under the same conditions to obtain a polarizing plate.

[0090] Finally, the resulting polarizing plate was aged by placing it in a dryer at 35°C for 7 days to allow the hydroxyl groups and isocyanate groups in the adhesive layer to react with each other.

[0091] [Example 28] Polarizing plates were obtained in the same manner as in Examples 1 to 27 and Comparative Examples 1 to 5, except that a bar coater with a line count of 2 was used.

[0092] [Examples 29 to 31] Polarizing plates were obtained in the same manner as in Examples 1 to 27 and Comparative Examples 1 to 5, except that the film was cured using a 36-line bar coater with a high-pressure mercury lamp and then attached to a polarizer.

[0093] [Examples 32 to 54] A polarizing plate was obtained in the same manner as in Examples 1 to 27 and Comparative Examples 1 to 5, except that a 125 μm thick polycarbonate resin film (trade name: Panlite PC-2151, manufactured by Teijin Limited) was used instead of the 50 μm thick amorphous polyolefin resin film ZF14.

[0094] The adhesive compositions and polarizing plates obtained were evaluated as follows, and the results are shown in Tables 1 to 7. The components listed by product name in Tables 1 to 7 are as shown in Table 8.

[0095] (viscosity measurement) The viscosity of the adhesive composition was measured in a 25°C environment using an E-type viscometer.

[0096] (Thickness measurement) The thickness of the polarizing plate was measured using a high-precision thickness measuring instrument HKT-1202 manufactured by Fujiwork Co., Ltd., and the thickness of the adhesive layer was calculated using the measured value and the thicknesses of the polarizer and protective film.

[0097] (High temperature and humidity resistance evaluation) The polarizing plate cut into a size of 50 mm x 50 mm was placed in a thermo-hygrostat at 85°C and 85% RH for 1000 hours, and the state of the polarizing plate end face was evaluated according to the following criteria. ◯: The polarizer is not peeled off from the protective film, and the state where only the protective film remains at the edge is not visually observed. ×: The polarizer was peeled off from the protective film and shrunk, and only the protective film was observed at the edge portion by visual inspection.

[0098] (Coloring evaluation) The polarizing plate was placed in a thermo-hygrostat at 85°C and 85% RH and a dryer at 105°C for 1000 hours, and then taken out and visually evaluated for its hue. The evaluation criteria were as follows: 〇: Colorless (no browning of polarizer) ×;Yellow~brown

[0099] (Adhesion evaluation) A cutter blade was inserted between the polarizer of the polarizing plate and the protective film, and the adhesiveness was evaluated according to the following criteria. ◎: Base material destroyed (cutter blade cannot enter) ○: Base material destroyed (cutter blade penetrates) ×: Peel off by hand

[0100] (Adhesion evaluation immediately after curing) Immediately after the adhesive composition was cured by the high-pressure mercury lamp, the polarizer, adhesive layer, and protective film were peeled off by hand to evaluate their adhesion, and the results were evaluated according to the following criteria. ◎: Strong resistance is felt when peeling off ○: There is resistance when peeling off ×: Peels off easily

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] [Table 5]

[0106] [Table 6]

[0107] [Table 7]

[0108] [Table 8]

[0109] As can be seen from Tables 1 to 7, Examples 1 to 54 using the present invention exhibited high resistance to high temperatures and high humidity and high adhesion. Furthermore, no browning due to polyenation was observed even after the durability test. Examples 20 to 54, which used adhesive compositions containing a urethane acrylate compound or a polyester resin, tended to exhibit high adhesion in the adhesion evaluation immediately after curing, thereby demonstrating excellent processability. Furthermore, Example 28, which had an adhesive layer thickness of 1.0 μm, was suitable for applications where optical properties were important because the adhesive layer was thin and distortion as a polarizing plate was suppressed. Examples 29 to 31, which had an adhesive layer thickness of 50 μm or more, were suitable for applications requiring a certain level of strength in the polarizing plate. On the other hand, Comparative Examples 1 to 4, which had an isocyanate group content of less than 5 wt%, all exhibited peeling between the protective film and polarizer after the high-temperature, high-humidity durability test, demonstrating poor resistance to high temperatures and high humidity.

[0110] As described above, by using the adhesive composition of the present invention, it is possible to provide an adhesive composition and a polarizing plate that have high resistance to high temperatures and high humidity, high adhesion, and do not cause discoloration of the polarizer due to polyenation.

Claims

1. An adhesive composition used for bonding a polarizer made of a polyvinyl alcohol-based resin film having iodine or a dichroic dye adsorbed and oriented thereon to a protective film, comprising: An adhesive composition comprising an isocyanate compound and a (meth)acrylic compound, wherein the content of isocyanate groups in the total amount of the adhesive composition is 5% by weight or more and 16% by weight or less.

2. 2. The adhesive composition according to claim 1, wherein the (meth)acrylic compound is a urethane (meth)acrylate.

3. The adhesive composition according to claim 1 , further comprising a polyester resin.

4. 4. The adhesive composition according to claim 1, wherein the isocyanate compound is at least one selected from the group consisting of an isocyanurate of hexamethylene diisocyanate, an adduct of hexamethylene diisocyanate, and a biuret of hexamethylene diisocyanate.

5. 4. The adhesive composition according to claim 1, further comprising a photoradical polymerization initiator.

6. A polarizing plate comprising a protective film attached to one or both sides of a polyvinyl alcohol-based resin film on which iodine or a dichroic dye is adsorbed and oriented, using the adhesive composition according to any one of claims 1 to 3.

7. 7. The polarizing plate according to claim 6, wherein the protective film is a film of at least one resin selected from the group consisting of amorphous polyolefin resins, polyester resins, acrylic resins, polycarbonate resins, polysulfone resins, and alicyclic polyimide resins, and is bonded to one or both surfaces of the polarizer.

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