TWI381031B - Optically compensated acrylic pressure-sensitive adhesive composition, polarizing plate and liquid crystal display device containing the same - Google Patents

Description

Optically compensated pressure sensitive acrylic adhesive composition, polarizing plate and liquid crystal display device therewith

The present invention relates to a pressure sensitive acrylic adhesive composition for a polarizing plate. More specifically, the present invention relates to pressure sensitivity of a polarizing plate which has excellent properties of low light leakage and which is not changed under high temperature or high temperature and high humidity conditions (e.g., long-term reliability and usability). The adhesive composition, and the polarizing plate and the liquid crystal display including the same.

In general, when preparing a liquid crystal display device, it is basically necessary to contain liquid crystal cells of a liquid crystal and a polarizing plate, and they must be bonded using a suitable adhesive layer or a pressure sensitive adhesive layer. Further, in order to improve the function of the liquid crystal display device, a phase retardation plate, a compensation plate for a wide viewing angle, a brightness enhancement film, and the like may be used, which are additionally adhered to the polarizing plate.

Generally, a main structure for forming a liquid crystal display device includes a liquid crystal layer uniformly arranged; a polarizing plate having a multilayer structure which is doped with a pressure-sensitive adhesive layer or an adhesive layer to be made of a transparent glass plate or a plastic sheet material containing a transparent electrode layer/ The constituent liquid crystal cells are based; phase retardation plates; and additional functional film layers and the like.

The structure of the polarizing plate includes an iodine compound or a dichroic polarizing material arranged in a certain direction. To protect these polarizing components, a protective film (for example, triethylenesulfonyl cellulose (TAC)) is used to form a plurality of layers on both sides. Further, the polarizing plate may further comprise a phase retardation film or a wide viewing angle compensation film (for example, a liquid crystal type film) having a shape of a unidirectional molecular arrangement.

The foregoing films are made from materials having different molecular structures and compositions, and thus have different physical properties. In particular, at high temperatures, or under conditions of high temperature and high humidity, dimensional stability is insufficient according to shrinkage or expansion of a material having a unidirectional molecular arrangement. Therefore, if the polarizing plate is fixed with a pressure-sensitive adhesive, at a high temperature or under high temperature and high humidity conditions, stress may concentrate on the TAC layer due to shrinkage or expansion, which may cause birefringence and light leakage. Happening. Here, negative birefringence is typically caused on the layer due to the contracted TAC.

At the same time, pressure-sensitive adhesive layers require high cohesive strength at high temperatures to maintain long-lasting reliability, and therefore, partially cross-linked viscoelastic materials are used. When the partially crosslinked structure is introduced into the pressure sensitive layer, the pressure sensitive layer has residual stress at a specified stress and the polymer in the crosslinked structure is aligned to a specific phase to develop a birefringence condition. Under this arrangement, in general, an alkylacrylic pressure sensitive adhesive develops negative birefringence as in the case of TAC.

At the same time, the screen sizes of computers and the like are getting larger and larger, and the demand for LCD TVs using polarizers has recently increased rapidly. As the panel becomes larger and larger, the polarizing plate becomes larger and larger, and therefore, the residual stress of the TAC layer and the pressure-sensitive adhesive becomes higher and higher, thereby increasing the negative birefringence and thus causing a large increase in light leakage.

In a method of reducing light leakage as much as possible under such residual stress, a method can be considered which minimizes the total birefringence value (including the TAC layer and the pressure sensitive adhesive) under residual stress. From adding (blending) materials exhibiting positive birefringence to final pressure sensitivity The adhesive layer is copolymerized with an acrylic monomer having positive birefringence.

KR Patent Application Publication No. 2003-0069461 discloses a pressure sensitive adhesive which is corrected for a negative value of birefringence exhibited by a pressure sensitive acrylic adhesive layer under residual stress, which is 0.01 to 40 parts by weight under residual stress. A low molecular weight material exhibiting a positive birefringence material is incorporated into the pressure sensitive acrylic adhesive layer. However, in the pressure sensitive adhesive, the modulus of the pressure sensitive adhesive is lowered because of the incorporation of a low molecular weight material therein. Therefore, there is a problem in the customization of the nature when processing the polarizing plate. In addition, the possibility of moving low molecular weight materials into the interface and phase separation from pressure sensitive acrylic adhesives during long-term storage is also a problem.

A method of copolymerizing a monomer having negative birefringence under residual stress with a monomer having positive birefringence to minimize the birefringence value is also known (refer to Applied Optics (1997)). In a specific example, birefringence at a specific stress can be adjusted by copolymerizing an acrylic monomer having an alkyl side chain (negative birefringence) and an acrylic monomer having an aryl side chain (positive birefringence). value.

Japanese Laid-Open Patent Publication No. 2002-332468 describes a method of improving the plastic resistance of a pressure-sensitive adhesive layer by introducing an acrylic monomer having a side chain-containing aryl group. In addition, U.S. Patent No. 6,663,978 and Japanese Patent Laid-Open Publication Nos. 2002-173656 and 2003-013029 describe a method of adjusting the refractive index of a pressure-sensitive adhesive layer by introducing an acrylic monomer having a side chain-containing aryl group. In addition, Japanese Laid-Open Patent Publication No. 2005-053976 describes the introduction of an acrylic group containing an aryl group by a side chain. The method of improving the adhesion performance of a lower polarizing film.

However, in the above-mentioned disclosure, the following technical idea is not proposed: an attempt is made to adjust the optically sensitive manner when preparing a pressure-sensitive adhesive composition for a polarizing plate by introducing an acrylic monomer having a side chain containing an aryl group. The birefringence value under residual stress improves the light leakage phenomenon.

The present invention has been made in an effort to solve the aforementioned conventional problems, and an object of the present invention is to provide a pressure-sensitive adhesive composition for a polarizing plate having extremely low light leakage properties by adjusting a birefringence value such that it is under residual stress Has a positive value and does not change the main properties under high temperature or high temperature and high humidity conditions (eg, long-term reliability and usability), using a (meth) acrylate copolymer with the most adaptive release properties, the copolymer contains An optically compensated acrylic copolymer (A) having a crosslinkable functional group, an optically compensated acrylic copolymer (B) having no crosslinkable functional group, and a polyfunctional crosslinking agent (C) as a pressure Sensitive adhesive layer.

Another object of the present invention is to provide a polarizing plate which uses a pressure sensitive acrylic adhesive composition having this property.

Another object of the present invention is to provide a liquid crystal display device comprising a polarizing plate obtained by a pressure-sensitive acrylic adhesive composition having such characteristics.

The present invention relates to a pressure-sensitive acrylic adhesive composition comprising an acrylic copolymer (A) comprising i) 50 to 75 parts by weight of an alkyl (meth)acrylate monomer, and an alkyl group of the alkyl ester having 2 to 14 carbon atoms, ii) 25 to 50 parts by weight of an acrylate monomer including an aryl group copolymerizable with the acrylic monomer, and iii) 0.1 to 10 parts by weight of an ethylene or acrylate monomer including a crosslinkable functional group Acrylic copolymer (B) comprising i) 50 to 75 parts by weight of an alkyl (meth) acrylate monomer, an alkyl group of an alkyl ester having 2 to 14 carbon atoms, and ii) 25 to 50 parts by weight An acrylate monomer comprising an aryl group copolymerizable with the acrylic monomer; and a polyfunctional crosslinking agent (C) crosslinkable with an acrylate monomer comprising the crosslinkable group of the above iii).

In order to improve the light leakage phenomenon, a method of providing a pressure-sensitive adhesive to release stress is generally used, that is, by adding a plasticizer or a low molecular weight material to a high molecular weight copolymer, or adjusting a crosslinked structure. However, it is generally difficult to completely suppress the light leakage phenomenon of the polarizing plate only by stress release. This is because the partially crosslinked structure should be able to be introduced into the adhesive to maintain the long-term reliability of the pressure sensitive adhesive for the polarizing plate, but the crosslinked structure exhibits a pressure sensitive residual in the adhesive layer. The stress cannot be completely removed. Therefore, negative birefringence exists in the pressure-sensitive acrylate alkyl ester adhesive layer commonly used under this residual stress (this is impossible to further improve light leakage). The main reason), and negative birefringence, exists in the constrained TAC layer. To compensate for this negative birefringence in the pressure-sensitive adhesive layer, an acrylic monomer (which contains an aryl group) copolymerized with the pressure-sensitive adhesive layer and exhibits positive birefringence can be introduced into the pressure-sensitive adhesive layer. Acrylic monomer). However, when the optical leakage is improved by simply using the optical compensation effect, a large amount of aryl group-containing acrylic monomer is required, and thus there is a side effect of greatly increasing the adhesion strength of the pressure sensitive adhesive. This has a negative effect on the re-release property of the main action of the pressure-sensitive adhesive for the polarizing plate. Therefore, in order to suppress light leakage of the polarizing plate as much as possible, and to maintain long-lasting reliability and re-release property as a main function of the adhesive for the polarizing plate, it is necessary to simultaneously achieve optical compensation to an appropriate degree and make pressure sensitivity The stress release effect of the adhesive is maximized, which is achieved by introducing an optimum crosslinked structure.

Accordingly, the present invention is characterized by having an optimum cross-linking structure to minimize light leakage and to maintain the main function of a pressure-sensitive adhesive using an optically compensated acrylic copolymer containing a crosslinkable functional group ( A) and a mixture of optically compensated acrylic copolymer (B) which does not contain a crosslinkable functional group.

In order to obtain the optimum crosslinked structure of the pressure-sensitive acrylic adhesive composition according to the present invention, the weight ratio of the acrylic copolymer (A) to the acrylic copolymer (B) is preferably from 1:9 to 4:1.

When the ratio of the acrylic copolymer (A) is lower than that of the acrylic copolymer (B), it is difficult to obtain sufficient cohesive strength. Therefore, the ratio is suitably more than 1:9, more preferably more than 1:4. In addition, when acrylic copolymer When the ratio of (A) to the acrylic copolymer (B) exceeds 4:1, the proportion of the crosslinkable copolymer increases. As a result, it is difficult to control the degree of crosslinking and improve the light leakage by the stress release of the pressure sensitive adhesive combined with the optical compensation effect.

Further, preferably, according to the pressure-sensitive acrylic adhesive composition of the present invention, the weight average molecular weight of the acrylic copolymer (A) and the acrylic copolymer (B) are each independently from 800,000 to 2,000,000.

If the weight average molecular weight is less than 800,000, the cohesive strength is impaired to make the durability reliability poor. If the weight average molecular weight is higher than 2,000,000, the effect of stress release is impaired to a slight effect on the effect of light leakage.

Each component of the present composition is specifically explained below.

Acrylic copolymers (A) and (B) i) (meth)acrylic acid alkyl ester monomer According to the invention, the acrylic copolymer (A) and the acrylic copolymer (B) as the main resin include i) 50 to 75 parts by weight of an alkyl (meth)acrylate monomer, wherein the alkyl group of the alkyl ester has 2 Up to 14 carbon atoms. The i) (meth)acrylic acid alkyl ester monomers included in the acrylic copolymer (A) and the acrylic copolymer (B) may be the same or different.

If the amount of the i) alkyl (meth) acrylate monomer exceeds 75 parts by weight, the final pressure-sensitive adhesive exhibits high negative birefringence under residual stress, and therefore, the effect of improving the optical light leakage is slight. . Further, if the amount of the i) alkyl (meth) acrylate monomer is less than 50 parts by weight, the balance of the adhesive property of the final pressure-sensitive adhesive is impaired, and the adhesive is High positive birefringence is exhibited under residual stress, and thus the effect of improving optical light leakage is impaired.

The i) alkyl (meth)acrylate monomer, wherein the alkyl group of the alkyl ester has 2 to 14 carbon atoms, and is selected from the group consisting of ethyl (meth)acrylate and n-propyl (meth)acrylate, Isopropyl methacrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, second butyl (meth) acrylate, amyl (meth) acrylate, (meth) acrylate 2-ethylhexyl ester, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate and tetradecyl (meth)acrylate One or more of the groups consisting of alkyl esters are preferred. If the carbon number of the alkyl group is out of the above range, the glass transition temperature (Tg) of the pressure sensitive adhesive is increased, or the adhesive property is difficult to adjust. Therefore, the carbon number is limited to the range of 2-14.

Ii) aryl-containing (meth)acrylic monomer According to the present invention, the acrylic copolymer (A) and the acrylic copolymer (B) are monomers which exhibit positive birefringence under stress, which are used to compensate for the inclusion of an alkyl (meth)acrylate monomer (wherein an alkyl ester) The alkyl group has a negative birefringence in an acrylic copolymer having 2 to 14 carbon atoms, and includes ii) 25 to 50 parts by weight including the acrylic monomer (alkyl (meth) acrylate monomer) Copolymerized aryl acrylate monomer. Ii) The acrylate monomer containing the aryl group contained in the acrylic monomer (A) and the acrylic monomer (B) may be the same or different.

The aryl group-containing (meth) acrylate single in all the monomers The amount of the body is suitably from 25 to 50 parts by weight. If the amount of the aryl group-containing alkyl (meth) acrylate monomer is less than 25 parts by weight in all the monomers, the final pressure-sensitive adhesive exhibits a large negative birefringence under residual stress and thus The effect of improving optical light leakage is slight. If the amount exceeds 50 parts by weight, the balance of the adhesive properties of the final pressure-sensitive adhesive is impaired. In particular, the adhesion strength is greatly increased, and the re-release property of the polarizing plate is further impaired.

Preferably, the compound of formula 1 is used according to the (meth) acrylate monomer containing a copolymerizable aryl group according to the present invention:

Wherein R ₁ represents hydrogen or methyl, R ₂ represents an alkylene group having 1 to 12 carbon atoms, n represents an integer of 0 to 3, preferably 0 or 1, and X represents an oxygen atom, a sulfur atom or has 1 The alkylene group to 4 carbon atoms and Ar represent an aryl group which is unsubstituted or substituted with a halogen (particularly bromine or chlorine) or an alkyl group of 1 to 12 carbon atoms.

Preferred examples of the compound of the formula 1 include, but are not limited to, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, 2-phenylthio-1-ethyl (meth)acrylate, (meth)acrylic acid 6-(4,6- Dibromo-2-isopropylphenoxy)-1-hexyl ester, 6-(4,6-dibromo-2-t-butylphenoxy)-1-hexyl (meth)acrylate, ( 2,6-dibromo-4-decylphenyl methacrylate, 2,6-dibromo-4-dodecyl phenyl (meth)acrylate, 2-(1-(meth)acrylate Naphthyloxy)-1-ethyl ester, 2-(2-naphthyloxy)-1-ethyl (meth)acrylate, 6-(1-naphthyloxy)-1-hexyl (meth)acrylate, 6-(2-naphthyloxy)-1-hexyl (meth)acrylate, 8-(1-naphthalenyloxy)-1-octyl (meth)acrylate and 8-(2-(2-)2-(meth)acrylate Naphthyloxy)-1-octyl ester. The compound of the formula 1 can be used singly or in the form of a mixture thereof.

More preferably, the compound of the formula 1 is phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, 2-phenylthio-1-ethyl acrylate, 8-(2-naphthyloxy)acrylate. -1-octyl ester, 2-(1-naphthyloxy)-1-ethyl acrylate and mixtures thereof; optimally, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate Or a mixture of them.

Iii) crosslinkable monomer In the acrylic copolymer (A) according to the present invention, iii) an ethylene or acrylate single system containing a crosslinkable functional group for adjusting the adhesion strength and cohesive strength of the acrylic copolymer, and preferably, the structure thereof This includes acid groups or hydroxyl groups.

The acid group-containing ethylene monomer used herein is a component which reacts with a crosslinking agent and a component which imparts agglomeration strength to a pressure sensitive adhesive by chemical bonding. Therefore, the agglomeration of the adhesive does not fail when the temperature is raised.

The acid group-containing copolymerizable monomer includes one of a group consisting of a copolymerizable monomer selected from a carboxyl group or an anhydride thereof, a copolymerizable monomer containing a sulfonic acid group, and a copolymerizable monomer containing a phosphoric acid group. Or more.

The carboxyl group-containing copolymerizable monomer is (meth)acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid or crotonic acid; the anhydride of the carboxyl group-containing copolymerizable monomer is Maleic anhydride or itaconic anhydride; the sulfonic acid group-containing copolymerizable monomer is styrenesulfonic acid, allylsulfonic acid, 2-(methyl)acrylamido-2-methylpropanesulfonic acid, (methyl a acrylamide propyl sulfonic acid, sulfopropyl (meth) acrylate, (meth) propylene phthaloxy naphthalene sulfonic acid; and a copolymerizable monomer containing a phosphoric acid group may be selected from 2-hydroxy phenyl methacrylate Ester and similar, but not limited to this.

Further, preferably, the hydroxyl group-containing ethylene or acrylic monomer is selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. One or more of a group consisting of 2-hydroxyethylene glycol (meth)acrylate and 2-hydroxypropylene glycol (meth)acrylate.

When the amount of the acid or hydroxyl group-containing ethylene or acrylic monomer in the acrylic copolymer (A) is too large, the adhesiveness is lowered and the release strength is lowered. Therefore, the amount thereof in all the monomers is preferably in the range of 0.01 to 10 parts by weight.

Iv) functional monomer To adjust the glass transition temperature of the pressure sensitive adhesive or to provide other functionalities, preferably, the (meth)acrylic copolymers (A) and (B) according to the present invention are independently further included in total monomer weight. From 0 to 20 parts by weight of iv) of the functional monomer of formula 2 is selected as the optional component.

Wherein R ₄ represents hydrogen or alkyl, R ₃ represents cyano, unsubstituted or alkyl substituted phenyl, ethoxylated or COR ₅ , wherein R ₅ represents unsubstituted or alkyl substituted amine Base or glycidoxy.

In the above formula, the alkyl group in R ₃ to R ₅ is preferably a lower alkyl group representing 1 to 6 carbon atoms, more preferably a methyl group or an ethyl group.

Examples of the compound of the formula 2 may include, but are not limited to, a styrene monomer such as styrene or α-methylstyrene; a vinyl carboxylate monomer such as vinyl acetate; a nitrogen-containing ethylene monomer, For example, acrylonitrile, (meth) acrylamide, N-methyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide or glycidyl (meth) acrylate. The monomer may be used singly or in combination of two or more of them.

If the amount of the functional monomer iv) of the formula 2 is too high, the elasticity and the peeling strength of the pressure-sensitive adhesive are lowered. Therefore, preferably, the use is low 20 parts by weight of the total monomer component.

v) The polymerization method is not specifically limited to the method for preparing the acrylic copolymers (A) and (B) according to the present invention, and the (meth)acrylic copolymer may be by solution polymerization, photopolymerization, bulk polymerization, suspension polymerization. Or by emulsion polymerization. Preferably, it is prepared by using a solution polymerization method. The polymerization temperature is preferably from 50 to 140 ° C, and the initiator is preferably added in a state in which the monomers are uniformly mixed.

The polymerization initiator may use an azo-based polymerization initiator (for example, azobisisobutyronitrile and azobiscyclohexanecarbonitrile) or a peroxide (for example, benzoquinone peroxygen). And acetonitrile peroxy), used alone or in a mixture.

Polyfunctional crosslinking agent (C) To crosslink the acrylic copolymer (A), the pressure sensitive adhesive composition of the present invention may comprise 0.01 to 10 parts by weight of the polyfunctional crosslinking agent (C) based on 100 parts by weight of the (meth)acrylic copolymer. . Preferred physical properties are provided within the foregoing ranges.

The polyfunctional crosslinking agent (C) reacts with a carboxyl group and a hydroxyl group and the like to increase the cohesive strength of the pressure sensitive adhesive.

Preferably, the polyfunctional crosslinking agent is selected from one or more of the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal-clamping compound. Among them, isocyanate compounds are easily used for this purpose.

The isocyanate compound may be selected from the group consisting of toluene diisocyanate, dylyl diisocyanate, diphenyl methyl diisocyanate, hexamethylene diisocyanate, isoform diisocyanate. One or more of a group consisting of tetramethylxyl methacrylate, naphthyl diisocyanate, and a reaction product thereof with a polyol (trimethylolpropane, etc.), the epoxy The compound is selected from the group consisting of ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N, N, N', N'-tetraglycidyl ethylene diamine and glycerol diglycidyl ether One or more of the constituent groups, the aziridine compound may be selected from the group consisting of N,N'-toluene-2,4-bis(1-aziridinecarbonyl), N,N'-diphenylmethane- 4,4'-bis(1-aziridinecarbonyl), triethylenediamine, bis-m-xylylene-1-(2-methylaziridine) and tri-1-aziridine One or more of the groups consisting of oxygen, the metal-clamping compound may be used, but not limited to, selected from polyvalent metals (eg, aluminum, coordinated with ethyl acetonylacetate or ethyl acetoacetate). , Zinc, tin, antimony, magnesium and vanadium) one or more of the group consisting of.

When the functional cross-linking reaction of the cross-linking agent is difficult to combine with the method for forming the pressure-sensitive adhesive layer, the polyfunctional cross-linking agent can be uniformly coated. If drying and aging are carried out after completion of the coating method, a crosslinked structure can be formed to obtain a pressure sensitive adhesive having elasticity and strong cohesive strength.

additive In addition, if the composition is adhered to the glass substrate, it can be further packaged A decane coupling agent is included to improve adhesion stability and thus to modify good heat resistance/moisture resistance. When the glass substrate is exposed to high temperature and high humidity for a long period of time, the decane coupling agent serves to contribute to improvement of adhesion reliability, and may be used in an amount of 0.005 to 5 parts by weight based on 100 parts by weight of all the acrylic copolymer. If the amount is less than 0.005 parts by weight, the adhesion reliability is not improved. If the amount exceeds 5 parts by weight, the durability is lowered.

The decane coupling compound is g-glycidoxypropyltrimethoxydecane, g-glycidoxypropylmethyldiethoxydecane, g-glycidoxypropyltriethoxydecane, 3- Mercaptopropyltrimethoxydecane, vinyltrimethoxydecane, vinyltriethoxydecane, g-methacryloxypropyltrimethoxydecane, g-methylpropenyloxypropyltriethyl Oxydecane, g-aminopropyltriethoxydecane, 3-isocyanatepropyltriethoxydecane or g-acetamidoacetate propyltrimethoxydecane and the like. These can be used alone or in a mixture thereof.

The present invention may further comprise a tacky resin in an amount of from 1 to 100 parts by weight based on 100 parts by weight of the acrylic copolymer (A). If the amount is less than 1 part by weight, the tackiness is poor. If the amount exceeds 100 parts by weight, the compatibility and cohesive strength of the pressure-sensitive adhesive are usually lowered.

As the tackifying resin, a (hydrogenated) hydrocarbon resin, a (hydrogenated) rosin resin, a (hydrogenated) rosin ester resin, a (hydrogenated) terpene resin, a (hydrogenated) terpene phenol resin, a polymerized rosin resin can be used. Or polymerized rosin ester resins and the like. These may be used alone or in combination of two or more of the foregoing resins.

In addition, for special purposes, acrylic low molecular weight polymers, epoxy resins, hardeners, etc. may be additionally mixed and used, and for general purposes, UV stabilizers, antioxidants, colorants, etc. may be appropriately added and used. Strengthening agent, filler, antifoaming agent, surfactant, plasticizer, etc.

Further, the present invention relates to a polarizing plate characterized by comprising a polarizing film; and a pressure-sensitive adhesive layer containing the pressure-sensitive acrylic adhesive composition according to the present invention.

The polarizing film comprises a pressure-sensitive adhesive layer formed of the aforementioned pressure-sensitive adhesive composition on one surface or both surfaces of the polarizing film. The polarizing film or the polarizing means constituting the polarizing plate is not particularly limited.

For example, the polarizing film is a film in which a polarizing component (for example, iodine or a dichroic dye) is contained in a polyvinyl alcohol resin film to extend the obtained product. The thickness of these polarizing films is also not particularly limited, and may be a general thickness. The polyvinyl alcohol resin may be polyvinyl alcohol, polyvinyl formal, polyethylene acetal, and saponified ethylene-vinyl acetate copolymer and the like.

On both surfaces of the polarizing film, a multilayer film may be formed on which a protective layer such as a cellulose film such as triethylsulfonyl cellulose or the like; a polyester film such as polycarbonate or a poly pair may be laminated thereon Ethylene phthalate, etc.; polyether film, such as polyether oxime; polyolefin film, such as polyethylene, polypropylene, polyolefin having a ring or borneol structure or an ethylene-propylene copolymer. The thickness of these protective films is not particularly limited, and may be a general thickness.

In the present invention, a method of forming a pressure-sensitive adhesive layer on a polarizing film is not particularly limited, and a pressure can be applied by using a long coater and the like. The method of applying the sensitive adhesive directly on the surface of the polarizing film, and drying the adhesive; or by applying a pressure sensitive adhesive to the surface of the mold release substrate, drying the adhesive, The pressure-sensitive adhesive layer formed on the mold release substrate is transferred to the surface of the polarizing film and applied in such a manner as to age the layer.

Further, in the polarizing plate of the present invention, one or more layers may be laminated to provide additional functions such as a protective layer, a reflective layer, an anti-glare layer, a phase retardation plate, a compensation film for a wide viewing angle, and a brightness enhancement film. . The pressure sensitive adhesive layer according to the invention may also be attached to the functional layer.

The polarizing plate to which the pressure sensitive adhesive of the present invention is applied can be applied to all common liquid crystal display devices, and the type of the liquid crystal display device is not particularly limited. Preferably, the present invention can construct a liquid crystal display device comprising a liquid crystal panel and a pressure sensitive adhesive polarizer bonded to one surface or both surfaces of the liquid crystal cell.

The invention is explained in more detail by the following examples and comparative examples. The examples are intended to facilitate a particular understanding of the invention, but the scope of the invention is not limited by these examples.

Preparation Example 1

In a 1 liter reactor equipped with a cooling system (for refluxing nitrogen and easy to adjust the temperature), 68 parts by weight of n-butyl acrylate (BA), 2.0 parts by weight of hydroxy methacrylate and 30 parts by weight of benzoyl acrylate were added. A monomer mixture composed of esters (the composition of which is shown in Table 1 below). Thereafter, 150 parts by weight of ethyl acetate (EAc) was added thereto as a solvent. Want to remove Oxygen was purged with nitrogen for 60 minutes and the temperature was maintained at 60 °C. 0.03 parts by weight of azobisisobutyronitrile (AIBN) (a reaction initiator) was added thereto and reacted for 8 hours. After the reaction, the obtained product was diluted with ethyl acetate (EAc) to obtain an acrylic copolymer (A-1) having a solid content of 20% by weight, and the weight average molecular weight thereof was 1,200,000.

Preparation 2-8

As shown in Table 1 below, some or a part of each component was not added to Preparation Example 1, and a high molecular weight acrylic copolymer was obtained. Their results are listed in Table 1.

Example 1

<merger> 20 parts by weight of the high molecular weight acrylic copolymer obtained in Preparation Example 1 80 parts by weight of the high molecular weight acrylic copolymer obtained in Preparation Example 5 were uniformly mixed and 0.1 part by weight of trimethylolpropane diisocyanate toluene ester adduct (TDI-1) and 0.1 part by weight were added. Gamma-glycidoxypropyltrimethoxydecane is used as a polyfunctional crosslinking agent. Considering the coating properties, the mixture is diluted to an appropriate concentration and uniformly mixed. The resulting product was coated on a release sheet and dried to obtain a 30 micron uniform pressure sensitive adhesive layer.

<Laminating procedure> The pressure sensitive adhesive layer prepared as described above was adhered to a 185 micron thick iodine polarizing plate. The resulting polarizing plate was cut to an appropriate size and evaluated. The evaluation results of the polarizing plate on which the pressure-sensitive adhesive layer was applied are shown in Table 2 below.

Example 2-3

In the same manner as in Example 1, the acrylic copolymer was subjected to a combination and lamination procedure based on the combination in Example 1, some of which were not combined or partially combined, and the combined ratios are shown in Table 2 below. Thereafter, the durability reliability and the light transmission uniformity were evaluated by the same method as in Example 1 and the results are shown in Table 2 below.

Comparative Example 1-4

In the same manner as in Example 1, the acrylic copolymer was subjected to a combination and lamination procedure based on the combination in Example 1, some of which were not combined or partially combined, and the combined ratios are shown in Table 2 below. After borrowing examples 1 The same method was used to evaluate the long-term reliability and light transmission uniformity and the results are shown in Table 2 below.

Experimental example

Remoulding The pressure sensitive adhesive coated polarizer was cut to a width of 90 mm and a length of 170 mm, and then adhered to an alkali-free glass plate (Corning, Inc.) using a laminator. Thereafter, the glass plate was allowed to stand in a temperature and humidity chamber for 1 hour, heated at 50 ° C for 4 hours, and at room temperature for 1 hour, after which the polarizing plate was released from the glass. The evaluation of re-release property is as follows: ○: easy to detach △: difficult to break away ×: It is difficult to break off and the substrate or glass is broken.

2. Lasting reliability The pressure sensitive adhesive coated polarizing plate (90 mm × 170 mm) prepared in the foregoing Example 1 was attached to both surfaces of a glass substrate (110 mm × 190 mm × 0.7 mm) in a staggered manner in optical absorption axis. on. This glass substrate was subjected to a clean room treatment under a pressure of about 5 kg/cm 2 applied, so that bubbles or impurities could not be formed. To evaluate the moisture-heat resistance of the samples, they were left in an environment at a temperature of 60 ° C and a relative humidity of 90% for 1,000 hours and then observed the formation or release of bubbles. Further, in order to evaluate the heat resistance of the samples, they were left at 80 ° C for 1,000 hours and the formation or release of bubbles was observed thereafter. After 24 hours at room temperature Evaluate their status immediately. Further, the pressure-sensitive adhesive polarizing plate prepared as described above was left for 5 months or longer, and then the reliability was evaluated according to the aforementioned method. The evaluation criteria for long-term reliability are as follows: ○: No bubbles were observed or released △: A little bubble or release appears ×: A large number of bubbles or releases appear

3. Light transmission uniformity (light leakage) To study the uniformity of light transmission, a backlight is used in a dark room to observe whether the glass substrate leaks light. The pressure-sensitive adhesive-coated polarizing plates (310 mm × 385 mm) prepared in the foregoing Example 1 were attached to both surfaces of the glass substrate in a staggered manner in optical absorption axes. These samples were stored in an environment at a temperature of 60 ° C and a relative humidity of 90% and at a temperature of 80 ° C for 500 hours, after which the uniformity of light transmission was evaluated. The uniformity of light transmission is evaluated according to the following criteria: ☉: It is difficult for the naked eye to determine the phenomenon of uneven light transmission. ○: A little uneven light transmission exists △: Some light transmission unevenness exists ×: A large amount of uneven light transmission exists

As shown by the results of Table 2, Examples 1 to 3 of the present invention exhibited excellent durability reliability and usability (re-release property), and exhibited excellent low light leakage properties. On the other hand, in Comparative Example 1, the amount of the crosslinkable polymer was so low that the low light leakage property was excellent, but the removability and durability were poor. In Comparative Example 2, the aromatic and acrylate monomers were introduced too much, so that the low light leakage property was excellent, but the removability and durability were poor. Further, in Comparative Example 3, the amounts of the aromatic and acrylate were so low that the light leakage property was poor. In Comparative Example 4, the crosslinkable polymer was used alone, so that the re-release property was very poor.

Industrial utilization

The present invention relates to pressure sensitive acrylic adhesives for polarizing plates The composition, the polarizing plate has excellent low light leakage properties, and does not change main properties such as long-term reliability and reusability under high temperature conditions and high temperature and high humidity conditions. Therefore, if the pressure-sensitive adhesive composition is applied to the polarizing plate of the liquid crystal display device, the light leakage phenomenon after long-term use can be prevented.

The invention has been explained in detail with reference to the system described above. Many modifications and variations are possible within the scope and spirit of the invention. Such modifications and variations are intended to fall within the scope of the appended claims.

Claims (21)

A pressure sensitive acrylic adhesive composition comprising an acrylic copolymer (A) comprising i) 50 to 75 parts by weight of an alkyl (meth)acrylate monomer, the alkyl group of the alkyl ester having 2 to 14 carbon atoms , ii) 25 to 50 parts by weight including an aryl group-containing acrylate monomer copolymerizable with the (meth)acrylic acid alkyl ester monomer, and iii) 0.1 to 10 parts by weight of ethylene including a crosslinkable functional group or An acrylate monomer; an acrylic copolymer (B) comprising i) 50 to 75 parts by weight of an alkyl (meth) acrylate monomer, an alkyl group of an alkyl ester having 2 to 14 carbon atoms, and ii) 25 to 50 parts by weight of an aryl group-containing acrylate monomer copolymerizable with the (meth)acrylic acid alkyl ester monomer; and a polyfunctional crosslinking agent (C) which is compatible with the crosslinkable functional group including the above iii) The ethylene or acrylate monomer is crosslinked. A pressure-sensitive acrylic adhesive composition according to claim 1, wherein the weight ratio of the acrylic copolymer (A) to the acrylic copolymer (B) is from 1:9 to 4:1. The pressure-sensitive acrylic adhesive composition according to claim 1, wherein the weight average molecular weight of the acrylic copolymer (A) and the acrylic copolymer (B) are each independently from 800,000 to 2,000,000. The pressure-sensitive acrylic adhesive composition according to claim 1, wherein i) the alkyl (meth)acrylate monomer in the acrylic copolymer (A) and the acrylic copolymer (B) are each independently Selected from From ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, (methyl) Dibutyl acrylate, amyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, (meth) acrylate One or more of a group consisting of decyl ester, lauryl (meth) acrylate, and tetradecyl (meth) acrylate. A pressure-sensitive acrylic adhesive composition according to claim 1, wherein ii) the acrylate-containing acrylate monomer in the acrylic copolymer (A) and the acrylic copolymer (B) are each independently 1 compound: Wherein R ₁ represents hydrogen or methyl, R ₂ represents an alkylene group having 1 to 12 carbon atoms, n represents an integer of 0 to 3, and X represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 4 carbon atoms. The group, and Ar represents an aryl group which is unsubstituted or substituted with a halogen or an alkyl group of 1 to 12 carbon atoms. A pressure sensitive acrylic adhesive composition according to claim 5, wherein the compound of the formula 1 is selected from the group consisting of benzene (meth)acrylate Oxyethyl ester, benzyl (meth)acrylate, 2-phenylthio-1-ethyl (meth)acrylate, 6-(4,6-dibromo-2-isopropyl (meth)acrylate Phenoxy)-1-hexyl ester, 6-(4,6-dibromo-2-t-butylphenoxy)-1-hexyl (meth)acrylate, 2,6-(meth)acrylate Dibromo-4-mercaptophenyl ester, 2,6-dibromo-4-dodecylphenyl (meth)acrylate, 2-(1-naphthalenyloxy)-1-ethyl (meth)acrylate Ester, 2-(2-naphthyloxy)-1-ethyl (meth)acrylate, 6-(1-naphthalenyloxy)-1-hexyl (meth)acrylate, 6-((meth)acrylate) 2-naphthyloxy)-1-hexyl ester, 8-(1-naphthalenyloxy)-1-octyl (meth)acrylate and 8-(2-naphthyloxy)-1-octyl (meth)acrylate One or more of the group consisting of esters. The pressure-sensitive acrylic adhesive composition of claim 1, wherein iii) of the acrylic copolymer (A) comprises an acid or a hydroxyl group in the structure of the ethylene or acrylate monomer having a crosslinkable functional group. . The pressure-sensitive acrylic adhesive composition according to claim 7, wherein the ethylene or acrylate single system containing an acid group is selected from the group consisting of (meth)acrylic acid, acrylic acid dimer, carboxyethyl acrylate, and carboxylic acid carboxy pentane. Ester, itaconic acid, maleic acid, fumaric acid, crotonic acid, maleic anhydride, itaconic anhydride, styrenesulfonic acid, allylsulfonic acid, 2-(methyl)propenylamine-2-methyl a group consisting of propanesulfonic acid, (meth) acrylamide, propanesulfonic acid, sulfopropyl (meth) acrylate, (meth) propylene decyl naphthalene sulfonic acid and 2-hydroxyethyl methacrylate One or more. Pressure sensitive acrylic adhesive as claimed in item 7 of the patent application The composition wherein the ethylene or acrylate monosystem containing a hydroxyl group is selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, One or more of a group consisting of 2-hydroxyethylene glycol (meth)acrylate and 2-hydroxypropylene glycol (meth)acrylate. The pressure-sensitive acrylic adhesive composition according to claim 1, wherein the acrylic copolymer (A) and the acrylic copolymer (B) each independently further comprise 0-20 parts by weight based on the total monomer weight. Functional monomer of formula 2: Wherein R ₄ represents hydrogen or an alkyl group having 1 to 6 carbon atoms, and R ₃ represents a cyano group, a phenyl group which is unsubstituted or substituted with an alkyl group having 1 to 6 carbon atoms, an ethoxy group or a COR ₅ , wherein R ₅ represents an amino group or a glycidoxy group which is unsubstituted or substituted with an alkyl group having 1 to 6 carbon atoms. A pressure sensitive acrylic adhesive composition according to claim 10, wherein the functional single system of Formula 2 is selected from the group consisting of acrylonitrile, (meth) acrylamide, N-methyl (meth) acrylamide And one or more of the group consisting of N-butoxymethyl (meth) acrylamide, styrene, methyl styrene, glycidyl (meth) acrylate and vinyl acetate. The pressure-sensitive acrylic pressure-sensitive adhesive composition according to the first aspect of the invention, wherein the polyfunctional crosslinking agent (C) is contained in an amount of from 0.01 to 10 parts by weight based on the acrylic copolymer (A). The pressure-sensitive acrylic adhesive composition according to claim 12, wherein the polyfunctional crosslinking agent (C) is selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal compounding compound. One or more of them. The pressure sensitive acrylic adhesive composition according to claim 13, wherein the polyfunctional crosslinking agent (C) is selected from the group consisting of toluene diisocyanate, dylyl diisocyanate, and diisocyanate. Phenylmethyl ester, hexamethylene diisocyanate, isoform diisocyanate, tetramethyl xylyl diisocyanate, naphthyl diisocyanate and their reaction products with polyol One or more isocyanate compounds in the group. The pressure-sensitive adhesive composition of claim 1, which further comprises 0.005 to 5 parts by weight of a decane coupling agent based on 100 parts by weight of the total acrylic copolymer. A pressure sensitive acrylic adhesive composition according to claim 15 wherein the decane coupling agent is selected from the group consisting of g-glycidoxypropyltrimethoxydecane, g-glycidoxypropylmethyldiethoxylate Baseline, g-glycidoxypropyltriethoxydecane, 3-mercaptopropyltrimethoxydecane, vinyltrimethoxydecane, vinyltriethoxydecane, g-methacryloxyloxy Propyltrimethoxydecane, g-methacryloxypropyltriethoxydecane, g-aminopropyltriethoxydecane, 3- One or more of the group consisting of isocyanatopropyltriethoxydecane and g-acetamidoacetate propyltrimethoxydecane. A pressure-sensitive acrylic adhesive composition according to claim 1, which further comprises from 1 to 100 parts by weight of a tackifier resin with respect to 100 parts by weight of the total acrylic copolymer. A pressure-sensitive acrylic adhesive composition according to claim 17, wherein the tacky resin is selected from the group consisting of (hydrogenated) hydrocarbon resins, (hydrogenated) rosin resins, (hydrogenated) rosin ester resins, (hydrogenated) One or more of a group consisting of a terpene resin, a (hydrogenated) terpene phenol resin, a polymerized rosin resin, and a polymerized rosin ester resin. A polarizing plate comprising a polarizing film; and a pressure-sensitive adhesive layer comprising the pressure-sensitive acrylic adhesive composition according to any one of claims 1 to 16. The polarizing plate of claim 19, further comprising one or more layers selected from the group consisting of a protective layer, a reflective layer, a phase retardation plate, a compensation film for a wide viewing angle, and a brightness enhancement film. A liquid crystal display device comprising a liquid crystal panel comprising a polarizing plate of claim 19 attached to a surface or both surfaces of a liquid crystal cell.