KR100784995B1 - Acrylic Pressure-Sensitive Adhesive Composition for the Polarizing Film - Google Patents

Abstract

The present invention includes a (meth) acrylic copolymer containing an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl, the gel fraction is 10-55%, the expansion ratio is 30-110, The acrylic pressure-sensitive adhesive composition for a polarizing plate, characterized in that the weight average molecular weight of the solvent (Sol) eluted with ethyl acetate in the final adhesive is at least 800,000, the molecular weight distribution is 2.0 ~ 7.0, a polarizing plate comprising a composition according to the present invention And the liquid crystal display including the same, exhibits excellent adhesion durability under high temperature or high temperature and high humidity conditions, and effectively provides high modulus and stress relaxation characteristics, thereby providing excellent workability in producing polarizers and improving light leakage. .

Polarizer, acrylic pressure sensitive adhesive, gel content, expansion ratio, light leakage, modulus, stress

Description

Acrylic pressure-sensitive adhesive composition for polarizing plate {Acrylic Pressure-Sensitive Adhesive Composition for the Polarizing Film}

1 is a graph showing the relationship between the gel fraction and expansion ratio of the acrylic pressure-sensitive adhesive composition according to an embodiment of the present invention

The present invention relates to an acrylic pressure-sensitive adhesive composition for a polarizing plate, and more particularly, a pressure-sensitive adhesive composition for a polarizing plate having excellent durability and low light leakage characteristics under high temperature or high temperature and high humidity conditions, and greatly improving workability of the polarizing plate, including the same. It relates to a polarizing plate and a liquid crystal display device.

In general, in order to manufacture a liquid crystal display, a liquid crystal cell and a polarizing plate including a liquid crystal are basically required, and an appropriate adhesive layer or adhesive layer for bonding the liquid crystal display should be used. In addition, in order to improve the function of the liquid crystal display, a retardation plate, a wide viewing angle compensation plate, or a brightness enhancement film may be additionally attached to the polarizing plate.

The main structure for forming the liquid crystal display device includes a liquid crystal layer that is constantly arranged; A polarizing plate having a multilayer structure including an adhesive layer or an adhesive layer; Retardation plate; And further functional film layers and the like.

At this time, the polarizing plate is a structure containing an iodine-based compound or a dichroic polarizing material arranged in a predetermined direction, using a protective film such as a triacetyl cellulose (TAC) system on both sides in order to protect these polarizing elements It constitutes a multilayer. In addition, the polarizing plate may additionally include a retardation film of a shape having a unidirectional molecular array, a wide viewing angle compensation film such as a liquid crystal film.

Each of the above-mentioned films has different physical properties because they are made of materials having different molecular structures and compositions. In particular, under high temperature or high temperature and high humidity conditions, dimensional stability due to shrinkage or expansion of materials having a unidirectional molecular arrangement is insufficient. Therefore, when the polarizing plate is fixed by the pressure-sensitive adhesive, the deformation stress due to shrinkage or expansion of the polarizing plate under high temperature or high temperature and high humidity conditions remains. As a result, light leakage occurs in a portion where stress is concentrated.

In order to improve the light leakage phenomenon, it is necessary to reduce the shrinkage of the polarizing plate under high temperature or high temperature and high humidity conditions, but to remove the stress generated in the liquid crystal panel with polarizing plates composed of materials having different physical properties. It is very difficult to do. Another method of improving the light leakage phenomenon is a method of imparting excellent stress relaxation function to the pressure-sensitive adhesive layer for fixing the polarizing plate to the liquid crystal panel. In general, the pressure-sensitive adhesive is rubber, acrylic, silicone, etc. Among these, the acrylic pressure-sensitive adhesive is most widely used in the production of a pressure-sensitive adhesive composition for polarizing plates because it is advantageous in terms of adhesive properties, optical properties, durability, or weather resistance.

Conventional pressure-sensitive adhesive design for imparting the stress relaxation function to the pressure-sensitive adhesive layer is designed so that the amount of creep is large and easy to deform with respect to external stress. A typical method is to mix a multifunctional crosslinking agent with a high molecular weight polymer including a reactive crosslinking functional group and a low molecular weight polymer containing or not containing a small amount of a crosslinkable functional group to provide excellent pressure and stress relief to the pressure-sensitive adhesive composition under high temperature or high temperature and high humidity conditions. How to grant.

For example, Korean Patent Publication No. 1998-079266 discloses 100 parts by weight of a high molecular weight acrylic copolymer having a weight average molecular weight of 1 million or more, 20 to 200 parts by weight of a low molecular weight acrylic copolymer having a weight average molecular weight of 30,000 or less, and multifunctionality. The crosslinking agent compound 0.005 to 5 parts by weight of the pressure-sensitive adhesive composition through the pressure-sensitive adhesive composition for polarizing plate to improve the light leakage phenomenon.

Japanese Laid-Open Patent Publication No. 2002-47468 discloses 100 parts by weight of a high molecular weight acrylic copolymer having a functional group having a weight average molecular weight of 800,000 to 2 million, a functional group having a weight average molecular weight of 50,000 or less and a dispersion degree of 1.0 to 2.5. The low-molecular weight acrylic copolymer having 5 to 50 parts by weight, the cross-linking agent and the silane compound to provide a stress relaxation property through the pressure-sensitive adhesive composition for a polarizing plate.

In addition, Japanese Patent Laid-Open Publication No. 2003-49141 discloses a high molecular weight acrylic copolymer containing a functional group having a weight average molecular weight of 1 million to 2 million, and a medium molecular weight acrylic air containing less than 2 functional groups having a weight average molecular weight of 30,000 to 300,000. In order to improve the light leakage phenomenon by imparting stress relaxation characteristics through a pressure-sensitive adhesive composition for a polarizing plate composed of a low molecular weight acrylic copolymer and a crosslinking agent having no functional group, which have a weight average molecular weight of 1,000 to 20,000 (dispersion degree 1.0 to 2.5). It was.

The patent publications implement the technical idea of softening the final adhesive in order to improve stress relaxation of the adhesive. That is, it is designed to reduce the modulus of the pressure-sensitive adhesive due to the added low molecular weight material to increase the amount of deviation from external stress and to easily deform, thereby to relieve the local stress caused by shrinkage or expansion of the polarizing plate. However, when a soft adhesive is realized through the addition of a low molecular weight, the modulus of the final adhesive layer is lowered, so when the polarizing plate is stored in a roll shape in a polarizing plate manufacturing process, it is easy to cause a poor adhesive pressure (Pit), and to cut the manufactured polarizing plate. In this case, there is a problem in that the pressure-sensitive adhesive protrudes from the end face of the polarizing plate to be cut (sticking out of the adhesive) or the polarizing plate is easily contaminated by the protruding pressure-sensitive adhesive. In addition, since the added low molecular weight is easy to move to the interfacial layer of the glass of the liquid crystal panel and the TAC, the degradation of durability is likely to be accompanied at high temperature or high temperature and high humidity conditions.

Another method for adding the stress relaxation function to the pressure-sensitive adhesive layer is a method of maintaining a very low gel content of the final pressure-sensitive adhesive made of a high molecular weight containing a crosslinking functional group. This method has the advantage that the modulus of the pressure-sensitive adhesive does not significantly decrease, but it is very difficult to reproduce it in order to maintain a uniform low gel content, and the time (cure period or Aging time) until the polarizing plate can be cut after crosslinking the pressure-sensitive adhesive There is a long disadvantage, there is a disadvantage that the durability is greatly reduced under high temperature or high temperature and high humidity.

Japanese Patent Application Laid-Open No. 60-207101 can be used as a method for reproducibly producing an adhesive having a low gel content composed of the above high molecular weight. In this publication, an acrylic copolymer (A) containing a crosslinkable functional group, an acrylic copolymer (B) not containing a crosslinkable functional group and a multifunctional crosslinking agent of two or more functional groups are mixed so that the weight ratio of A / B is 1 /. The invention which manufactures an adhesive in 4-4 / 1 area is disclosed. However, this publication shows a technical idea that the long-term storage property of the polarizing plate manufactured by adding a corresponding polyfunctional crosslinking agent amount to the amount of crosslinkable functional groups at the time of crosslinking does not remain free functional groups, but the molecular weight of the acrylic polymer used The technical idea of the conditions for the crosslinked structure and its crosslinked structure is not expressed, and in particular, the technical idea of the stress relaxation property of the pressure-sensitive adhesive related to the light leakage phenomenon is not described.

Therefore, the light leakage phenomenon can be suppressed while minimizing the decrease in the workability of the polarizing plate by minimizing the decrease in the modulus of the final pressure-sensitive adhesive, as well as the main characteristics of the polarizing plate products such as the durability reliability that can occur during long-term use as well as at high temperature or high temperature and high humidity conditions. The development of this improved pressure-sensitive adhesive for polarizing plates and a polarizing plate to which the applied is urgently required.

In order to solve the conventional problems as described above, an object of the present invention is not to significantly reduce the modulus of the pressure-sensitive adhesive, without changing the main characteristics such as adhesion durability reliability that can occur under high temperature or high temperature, high humidity conditions, the operation of the polarizing plate It is to provide an acrylic pressure-sensitive adhesive composition for a polarizing plate that improves the light leakage phenomenon while suppressing the degradation of the properties.

Another object of the present invention is to provide a polarizing plate using an acrylic pressure-sensitive adhesive composition having the above characteristics.

Still another object of the present invention is to provide a liquid crystal display device including a polarizing plate manufactured from an acrylic pressure-sensitive adhesive composition having the above characteristics.

In order to achieve the above object, the present invention includes a (meth) acrylic copolymer containing an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl,

The gel fraction represented by the following formula (1) is 10 to 55%,

The expansion ratio represented by the following formula (2) is 30 to 110,

The weight average molecular weight of Sol eluted with ethyl acetate in the final pressure-sensitive adhesive is 800,000 or more,

Molecular weight distribution (ratio of weight average molecular weight and number average molecular weight) provides 2.0-7.0 acrylic adhesive composition characterized by the above-mentioned.

Gel fraction (%) = B / A x 100 (1)

Expansion ratio = C / B (2)

In the formula (1) or (2),

A represents the acrylic pressure-sensitive adhesive composition, B represents the dry mass of the insoluble fraction of the acrylic pressure-sensitive adhesive composition after 48 hours of immersion with ethyl acetate at room temperature, and C is insoluble expanded by ethyl acetate after 48 hours of immersion with ethyl acetate at room temperature. The mass of the sea ash (acrylic adhesive insoluble content mass + mass of the solvent infiltrated) is shown.

In addition, the present invention provides a pressure-sensitive polarizing plate comprising a pressure-sensitive adhesive layer formed of the acrylic pressure-sensitive adhesive composition for the polarizing plate on one side or both sides of the polarizing film.

In addition, the present invention provides a liquid crystal display device comprising a liquid crystal panel for bonding the adhesive polarizing plate prepared above to one side or both sides of the liquid crystal cell.

The present invention maintains the durability in high temperature or high temperature and high humidity conditions by controlling the gel content, expansion ratio, molecular weight and molecular weight distribution of the sole eluted by the solvent, and the modulus of the final adhesive to the level of workability of the polarizing plate It is characterized in that the light leakage is improved by improving the stress relaxation characteristics of the pressure-sensitive adhesive while maintaining.

Typically, when the final pressure-sensitive adhesive is adjusted to a low gel content and deposited by a solvent, the amount of expansion of the gel by the solvent (swelling index) increases significantly. In the case of an adhesive having such a crosslinked structure, a very loose crosslinked structure is formed. Therefore, when the stress is loaded from the outside, the amount of displacement is large and easily deformed, so the stress relaxation property of the pressure-sensitive adhesive is very excellent and light leakage can be improved, but durability is very poor at high temperature or high temperature and high humidity.

The present inventors have studied to solve the above problems, and when the adhesive is designed to have a low expansion ratio and low gel content of the final adhesive, the adhesive has excellent stress relaxation characteristics and maintains durability at high temperature or high temperature and high humidity. The present invention has been completed. Although not theoretically limited, the adhesive having a low gel content and low expansion ratio forms a relatively dense crosslinked structure, and the crosslinked structure of the adhesive is connected to each other to provide durability and stress relaxation characteristics. Can be satisfied at the same time. Therefore, control of the crosslinking structure is very important in the present invention. If the crosslinked structure becomes very dense even with similar gel content, the durability of the uncrosslinked polymer is difficult to penetrate between the crosslinked structures. On the other hand, if the crosslinked structure is too loose, the uncrosslinked polymer can easily penetrate between the crosslinked structures, but when the force is applied to the pressure-sensitive adhesive, the uncrosslinked polymer is easily pulled out between the crosslinked structures, which also lowers durability.

The pressure-sensitive adhesive composition for polarizing plates of the present invention can be applied to various types of optically used adhesives and adhesive materials such as acrylic, silicone, rubber, urethane, polyester, epoxy, etc. without limitation, but acrylic adhesives are preferred. Do.

Hereinafter, the present invention will be described in more detail.

The present invention includes a (meth) acrylic copolymer containing an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl,

The gel fraction represented by the following formula (1) is 10 to 55%,

The expansion ratio represented by the following formula (2) is 30 to 110,

The weight average molecular weight of Sol eluted with ethyl acetate in the final pressure-sensitive adhesive is 800,000 or more,

It provides the acrylic pressure-sensitive adhesive composition, wherein the ratio (hereinafter, molecular weight distribution) of the weight average molecular weight and the number average molecular weight is 2.0 to 7.0.

Gel fraction (%) = B / A x 100 (1)

Expansion ratio = C / B (2)

In the formula (1) or (2), A, B and C are as described above.

In the acrylic pressure-sensitive adhesive composition according to the present invention, the gel fraction is preferably 15 to 45%, in which case the gel fraction and the expansion ratio more preferably satisfy the following formula (3):

In Formula (3), x represents a gel fraction and y represents an expansion ratio.

The gel content of the acrylic pressure-sensitive adhesive composition according to the present invention is 10 to 55%, preferably 15 to 45%, more preferably 15 to 35% of range.

When the gel fraction exceeds 55%, the stress relaxation property of the pressure-sensitive adhesive is greatly degraded. When the gel fraction is less than 10%, durability and reliability under high temperature or high temperature and high humidity conditions become very poor.

At the same time, when the expansion ratio measured by the gel is less than 30, the crosslinked structure is too dense so that the stress relaxation property of the pressure-sensitive adhesive is insufficient, and when it exceeds 110, the crosslinked structure is too loose and the durability is poor.

In addition, when the molecular weight of the sole eluted by the solvent is less than 800,000, each cross-linked structure is not sufficiently connected by the sole part, so durability is poor.

On the other hand, when the molecular weight distribution of the sole is less than 2, the stress relaxation characteristics are insufficient, and if it exceeds 7, there is a problem in durability. Therefore, the molecular weight distribution of the sol is preferably 2.0 to 7.0, most preferably adjusted to 3 to 5.5.

The (meth) acrylic copolymer according to the present invention preferably contains 80 to 99.8 parts by weight of an alkyl (meth) acrylic acid ester monomer having an alkyl group of 2 to 14 and 0.01 to 5 parts by weight of a crosslinkable monomer crosslinkable with a polyfunctional crosslinking agent.

The alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of the alkyl may be ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylic As a rate and isononyl (meth) acrylate, lauryl (meth) acrylate or tetradecyl (meth) acrylate etc. are mentioned. When the number of carbon atoms of the alkyl is outside the above range, the glass transition temperature (Tg) of the pressure-sensitive adhesive becomes high, or because the adhesion is difficult to control, it is limited to the range of 2 to 14. The alkyl (meth) acrylic acid esters may be used alone, or two or more kinds may be used in combination. It is preferable to use within the range of 80-99.8 parts by weight of the alkyl (meth) acrylic acid ester monomer having 2 to 14 alkyl groups in the total monomer components for controlling adhesion and cohesion.

The (meth) acrylic copolymer according to the present invention may copolymerize a crosslinkable monomer crosslinkable with a polyfunctional crosslinking agent, for example, a vinyl-based and / or acrylic crosslinkable monomer including a hydroxyl group or a carboxyl group to control adhesion and cohesion. have. Examples of the crosslinkable monomer are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyethylene glycol (meth) acrylic Acrylate, 2-hydroxypropylene glycol (meth) acrylate, acrylic acid, methacrylic acid, acrylic acid duplex, itaconic acid, maleic acid or maleic anhydride and the like, and the like. When there is too much quantity of the crosslinkable monomer crosslinkable with the said polyfunctional crosslinking agent in an acryl-type copolymer, since adhesiveness falls and peeling force falls, use of 0.01-5 weight part in all the monomer components is preferable.

The (meth) acrylic copolymer according to the present invention further comprises 0 to 20 parts by weight of the vinyl monomer of the general formula (1) relative to the total monomer weight as an optional component in order to adjust the glass transition temperature of the pressure-sensitive adhesive or to impart other functionality. It is desirable to.

Where

R ₄ represents hydrogen or alkyl,

R ₃ represents cyano, alkyl substituted or unsubstituted phenyl, acetyloxy, or COR ₅ , wherein R ₅ represents amino or glycidyloxy unsubstituted or substituted with alkyl.

In the formula, alkyl in the definition of R ₃ to R ₅ preferably denotes lower alkyl having 1 to 6 carbon atoms, more preferably methyl or ethyl.

Examples of the compound of Formula 1 include styrene monomers such as styrene and alpha methyl styrene; Carboxylic acid vinyl esters such as vinyl acetate; Nitrogen containing vinyl monomers, such as (meth) acrylamide and N-butoxy methyl (meth) acrylamide, etc. are mentioned. When the quantity of the said vinylic monomer in the said acryl-type copolymer is too large, since the flexibility of an adhesive composition falls and peeling force falls, use of 20 weight part or less in all the monomer components is preferable.

The polyfunctional crosslinking agent used in the case of crosslinking an acrylic copolymer having an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms as a main component increases the cohesion of the adhesive by reacting with the carboxyl group and the hydroxyl group of the acrylic polymer. do. The crosslinking agent may be at least one selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal chelate compound.

Examples of the isocyanate-based crosslinking agent include polyols such as tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoform diisocyanate, tetramethylxylene diisocyanate, naphthalene diisocyanate, or trimethylolpropane thereof. And reactants. Moreover, as an epoxy type crosslinking agent, ethylene glycol diglycidyl ether, triglycidyl ether, trimethol propane triglycidyl ether, N, N, N ', N'- tetraglycidyl ethylenediamine, or glycerin digly Cyl ether, and the like. Examples of the aziridine-based crosslinking agent include N, N'-toluene-2,4-bis (1-aziridinecarboxide) and N, N'-diphenylmethane-4,4`-bis (1-aziridinecarboxes). Id), triethylenemelamine, bisisoprotaloyl-1- (2-methylaziridine), or tri-1-aziridinylphosphine oxide. Examples of the metal chelate crosslinking agent include compounds in which polyvalent metals such as aluminum, iron, zinc, tin, titanium, antimony, magnesium, or vanadium are coordinated with acetylacetone or ethyl acetoacetate.

In the pressure-sensitive adhesive composition of the present invention, the multifunctional crosslinking agent is preferably used in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the (meth) acrylic copolymer.

In addition, the composition of the present invention may further include a silane coupling agent, which may improve the adhesion stability when the adhesion to the glass plate to further improve the heat and moisture resistance characteristics. The silane coupling agent serves to improve the adhesion reliability, especially when left for a long time under high temperature and high humidity, the content may be used in 0.005 to 5 parts by weight based on 100 parts by weight of the acrylic copolymer. Examples of the silane coupling compound include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, and 3-mercapto propyl trimethoxysilane , Vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltrie Methoxysilane, 3-isocyanatepropyltriethoxysilane, or γ-acetoacetatepropyltrimethoxysilane, and the like, and these may be used alone or in combination.

In addition, the present invention may further add a tackifying resin in order to adjust the adhesive performance, the content thereof may be used in the range of 1 to 100 parts by weight based on 100 parts by weight of the acrylic copolymer. At this time, if the tackifying resin is used in an excessive amount, it may reduce the compatibility or cohesion of the pressure-sensitive adhesive should be added properly with caution. Examples of the tackifying resin include (hydrogenated) hydrocarbon resins, (hydrogenated) rosin resins, (hydrogenated) rosin ester resins, (hydrogenated) terpene resins, (hydrogenated) terpene phenol resins, polymerization rosin resins, or polymerization furnaces. Gin ester resin etc. can be used, These can be used individually or in mixture of 2 or more types.

In addition, the present invention may be used by mixing a plasticizer, an epoxy resin, a curing agent, and the like for a specific purpose, and a UV stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, an antifoaming agent, a surfactant, and the like may be appropriately added according to a general purpose. Can be.

The present invention also provides a step of preparing a structural acrylic polymer for crosslinking by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl and a crosslinkable monomer crosslinkable with a polyfunctional crosslinking agent;

Preparing an uncrosslinked structural acrylic polymer by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl; And

Method for producing an acrylic pressure-sensitive adhesive composition for polarizing plates according to the present invention comprising the step of mixing the acrylic polymer for crosslinking structure and the acrylic polymer for uncrosslinked structure, or

A first step of preparing an acrylic polymer containing a crosslinking structure by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl and a crosslinkable monomer crosslinkable with a polyfunctional crosslinking agent; And

According to the present invention comprising a second step of providing an uncrosslinked structure by further reacting the alkyl (meth) acrylic ester monomer having 2 to 14 carbon atoms of alkyl in the presence of the cross-linked acrylic polymer obtained in the first step The manufacturing method of the acrylic adhesive composition for polarizing plates is related.

The method for producing an acrylic pressure-sensitive adhesive composition according to the present invention as described above is embodied by the following.

In order to have a crosslinked structure suitable for the present invention, the acrylic pressure-sensitive adhesive is prepared by preparing two separate acrylic polymers, that is, a polymer to form a crosslinked structure and a polymer to form an uncrosslinked structure, and then mixed in a constant weight ratio or sequentially in a reactor. Two acrylic polymers may be prepared and then reacted with a multifunctional crosslinking agent. The polymer to form the crosslinked structure necessarily contains a crosslinkable functional group, and if the amount of the crosslinked functional group is too large, the crosslinked structure is too dense so that the polymer to form the uncrosslinked structure becomes very difficult to penetrate between the crosslinked structures, resulting in high durability. It is lowered and the gel fraction and expansion ratio of the present invention cannot be achieved. On the other hand, when the crosslinking functional group is less than a certain content in the polymer to form the crosslinked structure, the crosslinked structure is too loose, so that the polymer to form the uncrosslinked structure is easily penetrated between the crosslinked structures, but when the force is applied to the adhesive, the uncrosslinked structure is formed. The polymer is easily released from the crosslinked structure, resulting in poor durability. On the other hand, if the composition of the polymer that will form the crosslinked structure and the polymer that will form the uncrosslinked structure is significantly different, a similar composition is preferred as much as possible because complete mixing between the two polymers is difficult. In addition, in terms of mixing the two polymers, the crosslinking functional group is more advantageous than the carboxyl group. The polymer which will form the uncrosslinked structure preferably does not contain a cross-linking functional group (hydroxyl group or carboxyl group), but is not necessarily contained.

The method for producing the acrylic copolymer is not particularly limited, and may be prepared by a solution polymerization method, a photopolymerization method, a bulk polymerization method, a suspension polymerization method or an emulsion polymerization method. Preferably, the acrylic copolymer is prepared using a solution polymerization method, the polymerization temperature is preferably 50 ℃ to 140 ℃, it is preferable to add the initiator in a state in which the monomers are uniformly mixed.

Such a polymerization initiator can be used singly or in combination with an azo polymerization initiator such as azobisisobutyronitrile and azobiscyclohexanecarbonitrile and a peroxide such as benzoyl peroxide and acetyl peroxide.

The manufacturing method of the adhesive composition of this invention is not specifically limited, It can obtain by mixing the above-mentioned acrylic copolymer and a crosslinking agent by a conventional method.

At this time, the multifunctional crosslinking agent may be uniformly coated only when the functional group crosslinking reaction of the crosslinking agent is hardly generated in the compounding process for forming the adhesive layer. After the coating operation is finished and the drying and aging process, a cross-linked structure is formed to obtain an elastic adhesive layer having a strong cohesive force.

In addition, the present invention provides a polarizing plate comprising the acrylic pressure-sensitive adhesive composition as an adhesive layer of the polarizing film.

The polarizing plate of this invention contains the adhesive layer formed from the said adhesive composition in one or both surfaces of a polarizing film, The polarizing film or polarizing element which comprises a polarizing plate is not specifically limited.

Preferably, examples of the polarizing film include a film obtained by adding a polarizing component such as iodine or a dichroic dye to a film made of polyvinyl alcohol-based resin and stretching the film, and the thickness of these polarizing films is also particularly limited. It is not possible to form a conventional thickness. At this time, the polyvinyl alcohol-based resin may be used polyvinyl alcohol, polyvinyl formal, polyvinyl acetal and ethylene, saponified vinyl acetate copolymer.

On both sides of the polarizing film, a cellulose-based film such as triacetyl cellulose, a polycarbonate film, a polyester-based film such as polyethylene terephthalate, a polyethersulfone-based film, a polyethylene, a polypropylene, a cyclo-based or a polyolefin-based having a norbornene structure And a multilayer film in which protective films such as polyolefins such as ethylene propylene copolymer are laminated. At this time, the thickness of these protective films is also not particularly limited, and may form a conventional thickness.

In the present invention, the method of forming the pressure-sensitive adhesive layer on the polarizing film is not particularly limited, and the method of applying and drying the pressure-sensitive adhesive using a bar coater or the like directly on the surface of the polarizing film, or applying the pressure-sensitive adhesive on the surface of the peelable substrate once After drying, the pressure-sensitive adhesive layer formed on the surface of the peelable base material may be transferred onto the surface of the polarizing film and then aged.

In addition, the polarizing plate of the present invention may be laminated with one or more layers providing additional functions such as a protective layer, a reflective layer, an antiglare layer, a retardation plate, a wide viewing angle compensation film, and a brightness enhancement film.

The polarizing plate to which the pressure-sensitive adhesive of the present invention is applied can be applied to all conventional liquid crystal display devices, and the kind of the liquid crystal panel is not particularly limited. Preferably, the present invention may comprise a liquid crystal display device including a liquid crystal panel in which the adhesive polarizing plate is bonded to one or both surfaces of a liquid crystal cell.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, which are intended to help a concrete understanding of the present invention, and the scope of the present invention is not limited to these Examples.

EXAMPLE

Preparation Example 1 : Acrylic copolymer (A1) manufacture

98 parts by weight of n-butylacrylate (BA), 2.0 parts by weight of hydroxy methacrylate, as shown in Table 1, in a 1L reactor equipped with a refrigeration system to allow nitrogen gas to reflux and to facilitate temperature control. A mixture of monomers consisting of parts was added. Then, 120 parts by weight of ethylacetate (EAc) was added as a solvent. After purging with nitrogen gas for 60 minutes to remove oxygen, the temperature was maintained at 60 ° C, 0.03 parts by weight of azobisisobutyronitrile (AIBN), a reaction initiator, and reacted for 8 hours. After the reaction, the mixture was diluted with ethyl acetate (EAc) to prepare an acrylic copolymer (A-1) having a solid content of 15% by weight, a weight average molecular weight of 1.6 million, and a molecular weight distribution of 4.9.

Preparation Example 2 , 3: acrylic copolymer A-2, A-3

In Preparation Example 1, as shown in Table 1, some of the components were not added or partially added based on the composition of the high molecular weight acrylic copolymer A-1 to prepare high molecular weight acrylic copolymers A-2 and A-3. The results are shown in Table 1.

Preparation Example 4 , 5,6: acrylic copolymer B-1, B-2, B- 3 manufacturing

In Preparation Example 1, as shown in Table 1, some of the components were not added or partially added based on the composition of the high molecular weight acrylic copolymer A-1 to prepare high molecular weight acrylic copolymers B-1 and B-2. The results are shown in Table 1.

Preparation Example 7 : Low molecular weight  Manufacture of Acrylic Copolymer L-1

In Preparation Example 1, as shown in Table 1 below, part of each component was not added or partially added based on the composition of the high molecular weight acrylic copolymer A-1 to prepare a low molecular weight acrylic copolymer L-1. The results are shown in Table 1.

Preparation Example 8 , 9: acrylic copolymer I-1, I- 2 manufacturing

In the composition containing the hydroxyl group-containing monomer in a one-step reaction as shown in Table 2 below, the hydroxyl group-containing high molecular weight acrylic copolymer was first prepared under the same conditions as in Preparation Example 1, and then, in the presence of the polymer prepared in the first step, The final high molecular weight acrylic polymer was obtained after the reaction as described in Table 2 and the reaction under the same conditions.

Example 1

<Mixing>

To 20 parts by weight of the high molecular weight acrylic copolymer A-1 solids obtained in the above preparation step, the high molecular weight acrylic copolymer B-1 was mixed so as to be 80 parts by weight of solids. Toly of isocyanate trimethylolpropane was used as a polyfunctional crosslinking agent. 0.1 parts by weight of rendiisocyanate adduct (TDI-1) was added, diluted to an appropriate concentration in consideration of coating properties, uniformly mixed, coated on a release paper, dried, and a 30 micron uniform adhesive layer was obtained.

<Plywood process>

The pressure-sensitive adhesive layer prepared above was adhesively processed on an iodine-based polarizing plate having a thickness of 185 microns. The obtained polarizing plate was cut to an appropriate size and used for evaluation, and the results of the following evaluation with respect to the polarizing plate to which the pressure-sensitive adhesive was applied are shown in Table 3a below.

Example 2-7

As shown in Table 3 below, by mixing or partially blending a part of the formulation of Example 1, the acrylic copolymer was blended and plywooded in the same manner as in Example 1. Then, durability and light transmission uniformity were evaluated in the same manner as in Example 1, and the results are shown in Table 3a.

[Comparative Example 1-6]

As shown in the following Table 2, the acrylic copolymer was blended and plywooded in the same manner as in Example 1 by not blending or partially blending a part of the formulation of Example 1. Then, durability and light transmission uniformity were evaluated in the same manner as in Example 1, and the results are shown in Table 3b.

[Test Example]

Durability Reliability

The pressure-sensitive adhesive coated polarizing plate (90 mm × 170 mm) prepared in Example 1 was attached to a glass substrate (110 mm × 190 mm × 0.7 mm) in a state where the optical absorption axis was crossed on both sides. At this time, the applied pressure was about 5㎏ / ㎠ to clean the room so that no bubbles or foreign matter. The specimens were left for 1000 hours at a temperature of 60 ° C. and a relative humidity of 90% in order to determine the heat and moisture resistance of the specimens. The heat resistance was observed for 1000 hours at the temperature of 80 ℃ after the occurrence of bubbles or peeling. Immediately after evaluating the state of the specimen was performed at room temperature for 24 hours. In addition, after leaving the pressure-sensitive adhesive polarizing plate prepared for 5 months or more, the reliability was evaluated by the above method. The evaluation criteria for reliability are as follows.

○: no bubbles or peeling

△: slight bubble or peeling phenomenon

X: A lot of bubble and peeling phenomenon generate | occur | produce

Light transmission  Uniformity ( Light fountain )

In order to investigate the uniformity of the light transmittance using the same specimen as described above, it was observed whether the light leaked out of the dark room using the backlight. As a method of testing the light transmittance uniformity, the coated polarizing plate (200 mm x 200 mm) was intersected 90 degrees to the glass substrate (210 mm x 210 mm x 0.7 mm) and attached to both sides. The uniformity of light transmittance was evaluated based on the following criteria.

⊙ Unevenness of light transmittance is hard to judge

○: slight light transmittance nonuniformity

△: non-uniformity of light transmittance

X: The light non-uniformity is abundant.

Measurement of Adhesive Press

The pressure drop of the pressure-sensitive adhesive is smaller the higher the elastic modulus of the pressure-sensitive adhesive (the higher the storage modulus of the pressure-sensitive adhesive). The elastic modulus of the pressure-sensitive adhesive was measured using Rheometrics' RMS-800. Using a Parallel Plate fixture with a diameter of 8 mm, the elastic modulus of the adhesive was measured by measuring the storage modulus under a pressure of 1 mm, a strain of 10% and a frequency of 1 rad / sec at a temperature of 30 ° C. at a temperature of 30 ° C. The storage elastic modulus was determined as follows.

5 points | pieces: Very little adhesive deterioration (storage modulus> 1.8x10 ⁴ Pa)

4 points | pieces: There is a little adhesive deterioration (1.4x10 ⁴ Pa <storage modulus <1.7x10 ⁴ Pa)

3 points: that the adhesive pressed slightly poor (1.0x10 ⁴ Pa <Storage Modulus <1.3x10 ⁴ Pa)

2 points | pieces: There are many adhesive depressive defects (0.8x10 ⁴ Pa <storage modulus <1.0x10 ⁴ Pa)

1 point: Very bad adhesive depressed (0.8x10 ⁴ Pa <storage modulus)

Measurement of adhesive sticking out

After cutting the polarizing plate after the said plywood using the Thompson cutter (Thompson), the cut surface of each polarizing plate was observed under the microscope, and the following references | standards evaluated.

3 points | pieces: The adhesive sticking out of the cut surface is good (less than 0.2 mm)

2 points | pieces: The adhesive sticking out of the cut surface is a little bad (0.2-0.5mm)

1 point: The adhesive which protrudes from the cut surface is severe (0.5mm or more)

Gel Fractional  Measure

The pressure-sensitive adhesive dried in the compounding process was left in a constant temperature and humidity (23 ° C., 60% RH) room for about 10 days, and about 0.3 g of the pressure-sensitive adhesive was placed in a # 200 stainless steel wire and immersed in 100 ml of ethyl acetate. After storage for 3 days, the insolubles were separated and the insolubles were dried in an oven at 70 ° C. for 4 hours and then mass was measured.

Measurement of expansion ratio

In the gel content measurement, the insoluble fraction was separated, and then the weight of the insoluble fraction and the solvent (inflated) contained in the insoluble fraction was measured, followed by drying to obtain the expansion ratio by dividing by the mass of the insoluble fraction.

In Tables 1 and 2, abbreviations are as follows.

n-BA: n-butyl acrylate, EHA: ethylhexyl acrylate, 2-HEMA: 2-hydroxyethyl methacrylate, AIBN: azobisisobutyronitrile, EAc: ethyl acetate

In the results of Table 3, in Examples 1-7 of the present invention, both durability and light leakage characteristics are excellent, and pressure-sensitive adhesive squeeze and pressure-related pressure of the pressure-sensitive adhesive are small. On the other hand, in Comparative Example 1, the expansion ratio is very high, so the crosslinked structure is too loose and the durability is insufficient. In Comparative Example 2, the gel content is high, and the expansion ratio is too low, so the crosslinked structure is too dense, and the stress relaxation property is insufficient. The light leakage is not improved. In the case of Comparative Example 3, the molecular weight of the sole is too low and the durability is insufficient, and Comparative Example 4 is a case where the light leakage is improved by mixing a low molecular weight body of the prior art. In this case, the modulus is sharply reduced and the polarizer workability is greatly reduced. In the case of Comparative Example 5 is a case of controlling the low gel content by adding a small amount of the multifunctional crosslinking agent as in the prior art, or when the crosslinking structure is loose, the expansion ratio is very large and the durability is largely insufficient, and in the case of Comparative Example 6 This is a case where the stress relaxation of the pressure-sensitive adhesive is largely insufficient due to general gel content control conditions.

As described above, the present invention is effective in improving the light leakage by relieving the stress caused by the shrinkage of the polarizing plate when used for a long time under high temperature or high temperature and high humidity conditions without changing the main characteristics such as adhesive durability and high modulus of the final adhesive Acrylic adhesive composition for polarizing plates can be provided. Therefore, the present invention can be applied to the polarizing plate of the liquid crystal display device to prevent the light leakage phenomenon due to stress concentration even if used for a long time and can be obtained excellent workability due to high modulus.

Claims (17)

A (meth) acrylic copolymer containing an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms, The gel fraction represented by the following formula (1) is 10 to 55%, The expansion ratio represented by the following formula (2) is 30 to 110, The weight average molecular weight of Sol eluted with ethyl acetate in the pressure-sensitive adhesive is 800,000 or more, Acrylic pressure-sensitive adhesive composition for polarizing plates, characterized in that the molecular weight distribution is 2.0 to 7.0: Gel fraction (%) = B / A x 100 (1) Expansion ratio = C / B (2) In the formula (1) or (2), A represents the mass of the acrylic pressure-sensitive adhesive composition, B represents the dry mass of the insoluble fraction of the acrylic pressure-sensitive adhesive composition after 48 hours of immersion with ethyl acetate at room temperature, and C is expanded by ethyl acetate after 48 hours of immersion with ethyl acetate at room temperature. The mass of the insoluble fraction (acrylic adhesive insoluble fraction + mass of infiltrated solvent) is shown. The acrylic pressure-sensitive adhesive composition for polarizing plates according to claim 1, wherein the gel fraction is 15 to 45%. The acrylic pressure-sensitive adhesive composition for polarizing plates according to claim 1, wherein the gel fraction and the expansion ratio further satisfy the conditions of the following formula (3):

In Formula (3), x represents a gel fraction and y represents an expansion ratio. The method of claim 1, (Meth) acrylic copolymer, 80 to 99.8 parts by weight of an alkyl (meth) acrylic acid ester monomer having an alkyl group of 2 to 14; 0.01 to 10 parts by weight of a multifunctional crosslinking agent; And An acrylic pressure-sensitive adhesive composition for a polarizing plate comprising 0.01 to 5 parts by weight of a crosslinkable monomer capable of crosslinking with the crosslinking agent. The method of claim 4, wherein the alkyl (meth) acrylic acid ester monomer is ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t- Butyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, It is an isononyl (meth) acrylate and it is 1 or more types chosen from the group which consists of lauryl (meth) acrylate and tetradecyl (meth) acrylate, The acrylic adhesive composition for polarizing plates characterized by the above-mentioned. The method of claim 4, wherein the crosslinkable monomer is 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyethylene glycol ( Acrylic adhesive composition, characterized in that at least one member selected from the group consisting of meth) acrylate, 2-hydroxypropylene glycol (meth) acrylate, acrylic acid, methacrylic acid, acrylic acid duplex, itaconic acid, maleic acid and maleic anhydride. The acrylic pressure sensitive adhesive composition for polarizing plates according to claim 4, wherein the (meth) acrylic copolymer further comprises 20 parts by weight or less of a copolymerizable vinyl monomer. The acrylic pressure-sensitive adhesive composition for polarizing plates according to claim 4, wherein the multifunctional crosslinking agent is selected from at least one member selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal chelate compound. The acrylic pressure-sensitive adhesive composition of claim 1, further comprising 0.005 to 5 parts by weight of the silane coupling agent and 1 to 100 parts by weight of the tackifier resin based on 100 parts by weight of the acrylic copolymer. The polarizing plate according to claim 1, further comprising at least one additive selected from the group consisting of a plasticizer, an epoxy resin, a curing agent, an ultraviolet stabilizer, an antioxidant, a colorant, a reinforcing agent, a filler, an antifoaming agent, and a surfactant. Acrylic pressure-sensitive adhesive composition. Preparing a crosslinking structural acrylic polymer by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl and a crosslinkable monomer crosslinkable with a multifunctional crosslinking agent; Preparing an uncrosslinked structural acrylic polymer by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl; And Mixing the crosslinked structural acrylic polymer and the uncrosslinked structural acrylic polymer Method for producing an acrylic pressure-sensitive adhesive composition for polarizing plate according to claim 1 comprising a. A first step of preparing an acrylic polymer containing a crosslinking structure by reacting an alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl and a crosslinkable monomer crosslinkable with a polyfunctional crosslinking agent; And A second step of providing an uncrosslinked structure by further reacting the alkyl (meth) acrylic acid ester monomer having 2 to 14 carbon atoms of alkyl in the presence of the acrylic polymer for crosslinking structure obtained in the first step. Method for producing an acrylic pressure-sensitive adhesive composition for polarizing plate according to claim 1 comprising a. The acrylic pressure sensitive adhesive for polarizing plates according to claim 11 or 12, wherein the reaction is made by a polymerization method selected from the group consisting of solution polymerization, photopolymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. Method of preparation of the composition. The method for producing an acrylic pressure-sensitive adhesive composition for polarizing plate according to claim 11 or 12, wherein the crosslinkable monomer contains a hydroxyl group. An adhesive polarizing plate comprising a pressure-sensitive adhesive layer formed of an acrylic pressure-sensitive adhesive composition for polarizing plates according to claim 1 on one or both sides of the polarizing film. The pressure sensitive adhesive plate of claim 15, wherein the pressure sensitive adhesive polarizer further comprises at least one layer selected from the group consisting of a protective layer, a reflective layer, a retardation plate, a wide viewing angle compensation film, and a brightness enhancement film. A liquid crystal display device comprising a liquid crystal panel for bonding the pressure-sensitive adhesive polarizing plate of claim 15 to one side or both sides of a liquid crystal cell.

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