KR20130130927A - Adhesive composition and adhesive layer - Google Patents

Abstract

The present invention relates to an adhesive composition and an adhesive layer, and more particularly, an acrylic copolymer, a crosslinking agent, a polyfunctional (meth) acrylate monomer, a first photoinitiator having a maximum absorption wavelength of 200 to 300 nm, and a maximum absorption wavelength. By including the second photoinitiator of 340 to 500nm, it is possible to relieve the stress caused by the shrinkage of the polarizing plate when used for a long time under high temperature and high humidity conditions, to improve the light leakage phenomenon, even in harsh conditions (high temperature and high humidity) adhesion durability It is related with this excellent adhesive composition and an adhesive layer.

Description

Adhesive composition and adhesive layer {ADHESIVE COMPOSITION AND ADHESIVE LAYER}

The present invention relates to a pressure-sensitive adhesive composition and pressure-sensitive adhesive layer excellent in adhesion durability and at the same time improved light leakage phenomenon.

In general, a liquid crystal display device (LCD) includes a liquid crystal cell and a polarizing plate containing liquid crystal, and various optical films (phase difference plate, viewing angle magnification film, Brightness enhancement film, etc.) is used.

In order to bond such a polarizing plate and an optical film to a liquid crystal cell, an appropriate adhesive is used. The pressure-sensitive adhesive is previously formed an adhesive layer on one surface of the polarizing plate and the optical film in order not to perform a drying process for fixing.

The pressure sensitive adhesive is often used an acrylic pressure sensitive adhesive using an acrylic polymer having excellent adhesiveness and transparency as a base. Crosslinking of the acrylic pressure sensitive adhesive utilizes a crosslinking agent or a combination of an acrylic polymer and a functional monomer.

Since the liquid crystal display device can be installed in various environments such as high temperature and high humidity conditions, high durability that does not inhibit display quality is required even under such an environment.

In addition, when the polarizing plate is fixed by the pressure-sensitive adhesive, strain stress due to shrinkage or expansion of the polarizing plate under high temperature and high humidity conditions remains. As a result, the pressure-sensitive adhesive layer is also deformed, and the residual stress causes the polymer in the crosslinked structure to be oriented in a specific direction, thereby exhibiting birefringence. Under this orientation, the general alkyl acrylic pressure sensitive adhesive exhibits negative birefringence, and light leakage occurs due to the birefringence difference.

Accordingly, Korean Laid-Open Patent Publication No. 2011-98692 includes an acrylic polymer having an alkylene oxide group and an ultraviolet absorber, and includes an interpenetrating polymer network structure having the acrylic polymer in a crosslinked state in a cured state, and curing into a sheet shape. The adhesive composition which shows the peeling force which differs on both surfaces of the said sheet form when it exists is proposed.

The pressure-sensitive adhesive composition is to control the degree of curing using a UV absorber to prevent light leakage and to improve the durability, but the UV absorber was discharged under the conditions of high temperature and high humidity, causing a non-uniform stress, there was a limit in improving the durability.

An object of the present invention is to provide a pressure-sensitive adhesive composition and pressure-sensitive adhesive layer which is excellent in adhesion durability under high temperature and high humidity conditions, and can improve light leakage by relieving stress caused by shrinkage of a polarizing plate.

In order to achieve the above object, the present invention provides an acrylic copolymer, a crosslinking agent, a polyfunctional (meth) acrylate monomer, a first photoinitiator having a maximum absorption wavelength of 200 to 300 nm, and a maximum absorption wavelength of 340 to 500 nm. It provides a pressure-sensitive adhesive composition comprising a second photoinitiator, wherein the first photoinitiator and the second photoinitiator in a ratio of 0.1: 10 to 1: 2 by weight.

Preferably, the first photopolymerization initiator may have a maximum absorption wavelength of 230 to 280 nm.

Preferably, the second photopolymerization initiator may have a maximum absorption wavelength of 350 to 490 nm.

100 parts by weight of the acrylic copolymer, 0.1 to 15 parts by weight of a crosslinking agent, 5 to 25 parts by weight of a multifunctional (meth) acrylate monomer, and 0.01 to 10 parts by weight of the first photoinitiator and the second photoinitiator.

In addition, the present invention provides a pressure-sensitive adhesive layer that the pressure-sensitive adhesive composition is cured, the difference in storage modulus of the core and the surface is 0.1MPa or more.

Preferably, the difference in storage modulus may be 0.1 to 0.4 MPa.

The pressure-sensitive adhesive composition of the present invention can adjust the degree of curing of the surface and the core, there is an advantage that the elastic gradient is given to the cured product (adhesive layer).

In addition, the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer of the present invention is effective in improving the light leakage phenomenon by relieving the stress caused by the shrinkage of the polarizing plate when used for a long time under high temperature and high humidity conditions.

In addition, the pressure-sensitive adhesive composition of the present invention is excellent in adhesion durability even under severe conditions (high temperature and high humidity), and can be used as an adhesive as well as an adhesive.

The present invention relates to a pressure-sensitive adhesive composition and pressure-sensitive adhesive layer excellent in adhesion durability and at the same time improved light leakage phenomenon.

Hereinafter, the present invention will be described in detail.

The pressure-sensitive adhesive composition of the present invention is an acrylic copolymer, a crosslinking agent, a polyfunctional (meth) acrylate monomer, a first photoinitiator having a maximum absorption wavelength of 200 to 300 nm, and a second photoinitiator having a maximum absorption wavelength of 340 to 500 nm. It includes.

The first photopolymerization initiator and the second photopolymerization initiator are contained in a weight ratio of 0.1: 10 to 1: 2.

It is preferable that the acryl-type copolymer of this invention contains the polymerizable monomer which has a functional group which can be bridge | crosslinked with the (meth) acrylate monomer which has a C1-C12 alkyl group. Here, (meth) acrylate means acrylate and methacrylate.

Examples of the (meth) acrylate monomer having an alkyl group having 1-12 carbon atoms include n-butyl (meth) acrylate, 2-butyl (meth) acrylate, (Meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (Meth) acrylate, n-butyl acrylate, nonyl (meth) acrylate, decyl (meth) acrylate and lauryl Or a mixture thereof. These can be used individually or in mixture of 2 or more types.

The polymerizable monomer having a crosslinkable functional group is a component for reinforcing the cohesive force or adhesive strength of the pressure-sensitive adhesive composition by chemical bonding and imparting durability and cutting property, such as a monomer having a hydroxy group, a monomer having a carboxyl group, a monomer having an amide group, The monomer etc. which have a tertiary amine group are mentioned, These can be used individually or in mixture of 2 or more types.

As a monomer which has a hydroxyl group, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 2-hydroxyethylene glycol (meth) acrylate, 2-hydroxypropylene glycol (meth) acrylate, hydroxyalkylene glycol having 2 to 4 carbon atoms of an alkylene group ( Meta) acrylate, 4-hydroxybutyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, 7-hydroxyheptyl vinyl ether, 8-hydroxyoctyl vinyl ether, 9-hydroxynonyl Vinyl ether, 10-hydroxydecyl vinyl ether, etc. are mentioned, Among these, 4-hydroxybutyl vinyl ether is preferable.

Examples of the monomer having a carboxyl group include monovalent acids such as (meth) acrylic acid and crotonic acid; Dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and monoalkyl esters thereof; 3- (meth) acryloylpropionic acid; A succinic anhydride ring-opening addition adduct of 2-hydroxyalkyl (meth) acrylate in which the alkyl group has 2 to 4 carbon atoms, anhydrous succinic ring opening adduct of a hydroxyalkylene glycol (meth) acrylate having 2 to 4 carbon atoms in the alkylene group , And compounds obtained by ring-opening addition of succinic anhydride to a caprolactone adduct of 2-hydroxyalkyl (meth) acrylate in which the alkyl group has 2-3 carbon atoms. Of these, (meth) acrylic acid is preferable.

Examples of the monomer having an amide group include (meth) acrylamide, N-isopropylacrylamide, N-tert-butylacrylamide, 3-hydroxypropyl (meth) acrylamide, 4-hydroxybutyl (meth) acrylamide, 6 -Hydroxyhexyl (meth) acrylamide, 8-hydroxyoctyl (meth) acrylamide, 2-hydroxyethylhexyl (meth) acrylamide, etc. are mentioned, Among these, (meth) acrylamide is preferable.

Examples of the monomer having a tertiary amine group include N, N- (dimethylamino) ethyl (meth) acrylate, N, N- (diethylamino) ethyl (meth) Methacrylate, and the like.

The polymerizable monomer having a crosslinkable functional group is preferably contained in an amount of 0.05 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, based on 100 parts by weight of the (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms. . If the content is less than 0.05 parts by weight, the cohesive force of the pressure-sensitive adhesive may be reduced, the durability may be lowered. If the content is more than 10 parts by weight, the adhesive strength is lowered by a high gel fraction may cause problems in durability.

The acrylic copolymer may further contain other polymerizable monomers other than the above monomers in a range of not lowering the adhesive strength, for example, 10 wt% or less with respect to the total amount.

The method for producing the copolymer is not particularly limited and can be produced by methods such as bulk polymerization, solution polymerization, emulsion polymerization or suspension polymerization, which are commonly used in the art, and solution polymerization is preferable. In addition, a solvent, a polymerization initiator, a chain transfer agent for molecular weight control and the like which are usually used in polymerization can be used.

The acrylic copolymer preferably has a weight average molecular weight (polystyrene equivalent, Mw) measured by gel permeation chromatography (GPC) of 50,000 to 2 million, more preferably 200,000 to 2 million. When the weight-average molecular weight is less than 50,000, cohesion between co-polymers may be insufficient, which may cause problems in adhesion durability. If the weight average molecular weight is more than 2,000,000, a large amount of a diluting solvent may be required in order to ensure fairness in coating.

A crosslinking agent can improve adhesiveness and durability, and can maintain the reliability and shape of an adhesive at high temperature.

An isocyanate type, an epoxy type, a peroxide type, a metal chelate type, an oxazoline type, etc. can be used for a crosslinking agent, and can use 1 type, or 2 or more types. Double isocyanate type is preferred.

Specifically, diisocyanate compounds, such as tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, 2, 4- or 4, 4- diphenylmethane diisocyanate; And adducts to polyhydric alcohol-based compounds such as trimethylolpropane of diisocyanate can be used.

Further, in addition to the isocyanate crosslinking agent, melamine derivatives such as hexamethyrolmelamine, hexamethoxymethylmelamine, hexabutoxymethylmelamine and the like; Polyepoxy compounds such as bisphenol A and epichlorohydrin condensate epoxy compounds; One or more crosslinking agents selected from the group consisting of polyglycidyl ethers of polyoxyalkylene polyols, glycerin di- or triglycidyl ethers, tetraglycidyl xylenediamine and the like can be further added and used together.

Such a crosslinking agent may be contained in an amount of 0.1 to 15 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the acrylic copolymer based on the solid content. If the content is less than 0.1 part by weight, the cohesive force may be reduced due to insufficient crosslinking degree, thereby impairing the adhesive durability and the cleavage property. If the content is more than 15 parts by weight, problems may occur in reducing residual stress due to excessive crosslinking reaction.

The polyfunctional (meth) acrylate monomer forms a first crosslinked structure in which isocyanate groups and a polymer functional group are thermoset and a second crosslinked structure crosslinked by radical reaction according to UV curing, thereby hardening the adhesive during curing. ) State. This can improve the durability degradation problem caused by the use of the acrylic copolymer while at the same time can secure the desired storage modulus (G ') and can also suppress the peeling force of the release film. Moreover, it is a component which makes coating easy by diluting a solvent-free adhesive composition and adjusting a viscosity.

The kind of polyfunctional (meth) acrylate monomer is not specifically limited, The monomer more than trifunctional is preferable. Specifically, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, propionic acid modified trimethylolpropane tri (meth) acrylate, propylene oxide modified trimethyl 3, such as all propane tri (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, tris (meth) acryloxyethyl isocyanurate, and glycerol tri (meth) acrylate Functional monomers; Tetrafunctional monomers such as diglycerin tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, and tetramethylolpropane tetra (meth) acrylate; Pentafunctional monomers such as dipentaerythritol penta (meth) acrylate and propionic acid-modified dipentaerythritol penta (meth) acrylate; 6-functional monomers, such as dipentaerythritol hexa (meth) acrylate, caprolactone modified dipentaerythritol hexa (meth) acrylate, and isocyanate-modified urethane hexa (meth) acrylate, etc. are mentioned. These can be used individually or in mixture of 2 or more types.

It is preferable that the polyfunctional (meth) acrylate monomer is included in an amount of 5 to 25 parts by weight based on 100 parts by weight of the acrylic copolymer based on the solid content. If the content is less than 5 parts by weight, it may be difficult to suppress durability under high temperature or high temperature and high humidity or to suppress release film peeling force and light leakage, and even if it is more than 25 parts by weight, durability may be reduced.

A photoinitiator is a component for fully advancing hardening of the coated adhesive composition. In the present invention, by using a mixture of the first photoinitiator and the second photoinitiator having different curing properties in a constant ratio, the degree of curing of the surface and the core of the cured body may be different, thereby forming an elastic gradient.

The first photopolymerization initiator serves to cure the surface of the pressure-sensitive adhesive layer to which the pressure-sensitive adhesive composition is applied.

The first photopolymerization initiator has a maximum absorption wavelength of 200 to 300 nm, preferably 230 to 280 nm. Among the photopolymerization initiators currently used, the maximum absorption wavelength of less than 200 nm is almost nonexistent and has a disadvantage of adversely affecting the environment. In addition, when it exceeds 300 nm, there is a problem that the surface hardening effect is insignificant, and it is difficult to form a curing gradient to have a storage modulus in the range desired by the present invention.

In the present invention, the surface refers to the surface of the outermost surface of the pressure-sensitive adhesive composition applied to the surface adhered to the adherend such as Glass. The core portion means a surface of the polarizer that is in contact with the protective film (or retardation film surface) of the polarizer.

These first photoinitiators include 1-hydroxy-cyclohexyl-phenyl-ketone (manufactured by Igacure 184), 2-hydroxy-2-methyl-1-phenyl-propane-1-one (manufactured by Darocur 1173), Igacure 184 50 A mixed initiator of 50% by weight and 50% by weight of benzophenone (manufactured by Igacure 500), methylbenzoylformate (manufactured by Darocur MBF), and the like may be used.

The second photopolymerization initiator serves to cure the core of the pressure-sensitive adhesive layer to which the pressure-sensitive adhesive composition is applied.

The second photopolymerization initiator has a maximum absorption wavelength of 340 to 500 nm, preferably 350 to 490 nm. If the maximum absorption wavelength is less than 340 nm, there is a problem that it is difficult to form a cure gradient that allows the deep curing effect to be insignificant to have a storage modulus of elasticity in the range desired by the present invention. In addition, when it exceeds 500 nm, since it is out of the UV wavelength range, there is a problem that a polymerization reaction is difficult to be formed.

These second photoinitiators include diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide (manufactured by Darocur TPO), phenyl bis (2,4,6-trimethyl benzoyl) (manufactured by Igacure 819), bis (eta5) -2,4-cyclopentadien-1-yl) bis [2,6-difluoro-3- (1H-pyrrol-1-yl) phenyl] titanium (manufactured by Igacure 784) and the like can be used.

The first photopolymerization initiator and the second photopolymerization initiator may be mixed in a range of 0.1: 10 to 1: 2 weight ratio, preferably 0.1: 5 to 1: 3 weight ratio. When the mixing ratio is less than the above range, the surface hardening may not be effectively performed, and thus adhesive properties and durability may be degraded. When the mixing ratio is exceeded, the surface curing may be excessively predominant and light leakage may occur due to the lifting of the substrate, especially glass. have.

The range proposed in the present invention provides a hard characteristic by improving the degree of hardening of the core of the cured body as compared with the related art, and forms an elastic gradient by imparting soft characteristics by lowering the degree of curing of the surface of the cured body. .

By such an elastic gradient, the adhesion durability at high temperature and high humidity is excellent, and the light leakage phenomenon can be improved by relieving the stress caused by shrinkage of the polarizing plate.

Such first and second photopolymerization initiators may be contained in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the acrylic copolymer. If the content is less than 0.01 parts by weight, the curing speed may be slow and sufficient curing may be difficult to progress. If the content is more than 10 parts by weight, the physical properties of the pressure-sensitive adhesive may decrease due to the remaining components after the reaction, and yellowing may occur.

The pressure-sensitive adhesive composition of the present invention may further contain a silane coupling agent.

The kind of the silane coupling agent is not particularly limited, and for example, vinylchlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxy Propyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-metha Krilloxypropyl triethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyl diethoxysilane, 3-acryloxypropyl trimethoxysilane , N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropyl Methyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethylbutylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyl Dimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis (triethoxysilylpropyl) tetrasulfide, 3-isocyanatopropyltriethoxysilane, and the like. These can be used individually or in mixture of 2 or more types.

The silane coupling agent may be contained in an amount of 0 to 10 parts by weight, preferably 0.005 to 5 parts by weight, based on 100 parts by weight of the acrylic copolymer based on the solid content. If the content is more than 10 parts by weight, durability may be reduced.

In addition to the above components, the pressure-sensitive adhesive composition is a tackifying resin, antioxidant, corrosion inhibitor, leveling agent, surface lubricant, dye, pigment in order to adjust the adhesion, cohesion, viscosity, modulus, glass transition temperature, etc. required according to the application It may further contain additives such as antifoaming agents, fillers, light stabilizers, antistatic agents.

In addition, the present invention can harden the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer has a difference in storage modulus of the core portion and the surface thereof is 0.1 MPa or more, preferably 0.1 to 0.4 MPa. In consideration of the durability and stress relaxation effect according to the elastic gradient, the storage modulus of the surface is more preferably 0.1 to 0.4 MPa, and the storage modulus of the core is 0.2 to 0.6 MPa.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Manufacturing example : Acrylic Copolymer

N-butyl acrylate (BA) 90 parts by weight, methyl acrylate (MA) 5 parts by weight, 2-hydroxyethyl acrylate (2) -HEA) 4 parts by weight of a monomer mixture consisting of 4 parts by weight of acrylic acid (AA) was added, and then 100 parts by weight of ethyl acetate (EAc) was added as a solvent. Then, after purging nitrogen gas for 1 hour to remove oxygen, it was maintained at 62 ℃. After homogenizing the mixture, 0.07 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator, and reacted for 6 hours to prepare an acrylic copolymer having a weight average molecular weight of about 800,000.

Example  1-6 and Comparative Example  1-4

As shown in Table 1 below, an acrylic copolymer, a crosslinking agent, a polyfunctional (meth) acrylate monomer, a first photoinitiator, a second photoinitiator, and a silane coupling agent were mixed, and then diluted in an organic solvent to prepare an adhesive composition. It was.

division
(Parts by weight) Acrylic
Copolymer Cross-linking agent Multifunctionality (meta)
Acrylate monomer Photopolymerization initiator Silane
couple
Ring agent A-1 A-2 B-1 B-2 C Example 1 100 0.3 10 0.02 - 0.18 - - 0.3 Example 2 100 0.3 10 0.04 - 0.16 - - 0.3 Example 3 100 0.3 10 0.2 - One - - 0.3 Example 4 100 0.3 10 0.1 - 0.7 - - 0.3 Example 5 100 0.3 10 0.02 - - 0.18 - 0.3 Example 6 100 0.3 10 - 0.02 - 0.18 - 0.3 Comparative Example 1 100 0.3 10 0.2 - - - - 0.3 Comparative Example 2 100 0.3 10 - - 0.2 - - 0.3 Comparative Example 3 100 0.3 10 0.1 - 0.1 - - 0.3 Comparative Example 4 100 0.3 10 - - 0.18 - 0.02 0.3 Crosslinking agent: Cor-L, Coronate-L, Nippon Polyurethane Co., Ltd.
Polyfunctional (meth) acrylate monomers: trimethylolpropane triacrylate, M300 product, Miwon Specialty Chemical
A-1: 1-hydroxy-cyclohexyl phenyl- ketone, Igacure 184, CIBA company, maximum absorption wavelength about 240 nm
A-2: Igacure 500 product, 50% by weight of Igacure 184 and 50% by weight of benzophenone, initiator, CIBA, maximum absorption wavelength about 250nm
B-1: diphenyl (2,4,6-trimethylbenzoyl) -phosphine oxide, product of Darocur TPO, CIBA company, maximum absorption wavelength about 380 nm
B-2: Phenyl bis (2,4,6-trimethyl benzoyl), Igacure 819, CIBA, maximum absorption wavelength about 380 nm
C: bis [2,6-difluoro-3- (1H-pyrrol-1-yl) phenyl] titanium, manufactured by Igacure 784, CIBA, maximum absorption wavelength about 400 nm
Silane coupling agent: 3-glycidoxypropyltrimethoxysilane, KBM-403, Shin-Etsu Corp.

The pressure-sensitive adhesive composition prepared above was applied on a release film coated with a silicone release agent to have a thickness of 30 μm, dried at 100 ° C. for 1 minute to form an adhesive layer, and then irradiated with ultraviolet rays using a high pressure mercury lamp (roughness). : 250 mW / c, light quantity: 300 mJ / cm 2) to form an adhesive layer between two release PET films.

Furthermore, the adhesive layer prepared above was laminated | stacked on the 185-micrometer-thick iodine type polarizing plate by the adhesion process, and the polarizing plate with an adhesive layer was manufactured. The prepared polarizing plate was stored under curing conditions at 23 ° C. and 60% RH.

Test Example

The physical properties of the pressure-sensitive adhesive composition and pressure-sensitive adhesive polarizing plate prepared in Examples and Comparative Examples were measured by the following method, and the results are shown in Table 2 below.

1. Durability (heat resistant, Wet heat )

The pressure sensitive adhesive polarizing plate was cut into 90 mm x 170 mm, and the release film was peeled off, and then attached to both surfaces of the glass substrate (110 mm x 190 mm x 0.7 mm) so that the absorption axes of the polarizing plates were perpendicular to each other. At this time, the applied pressure was 5kg / cm ² to prepare a specimen by performing a clean room operation so that no bubbles or foreign matter.

The heat resistance of the specimen was observed for 1000 hours at a 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. The moisture resistance characteristics of the specimens were observed for 1000 hours under the conditions of a temperature of 60 ° C and a humidity of 90% RH, and then the occurrence of bubbles or peeling was observed.

<Evaluation Criteria>

No bubbles or peeling: ⓞ

Less than 5 bubbles or exfoliation: ○

5 or more bubbles or peelings less than 10: △

10 or more bubbles or peelings: ×

2. Adhesive force (N / 25㎜)

The prepared polarizer with a pressure-sensitive adhesive was cut into a size of 25 mm x 100 mm, and the release film was peeled off. The release film was laminated to a glass substrate (# 1737, Corning) at a pressure of 0.25 MPa and autoclaved.

After room temperature adhesiveness was left for 24 hours under 23 ° C and 50% RH conditions, the room temperature adhesive force was allowed to stand for 48 hours under 50 ° C and 50% RH conditions, then the universal tensile tester (UTM, Instron) The pressure-sensitive adhesive layer was peeled off at a peeling rate of 300 mm / min and a peeling angle of 180 ° using to measure the adhesive strength. At this time, measurement was carried out under conditions of 23 캜 and 50% RH.

3. Light beam  phenomenon

The prepared pressure-sensitive adhesive polarizing plate was bonded to both surfaces of a glass substrate (# 1737, Corning), and then subjected to autoclave treatment at 50 ° C. and 5 atmospheres for 30 minutes to prepare a specimen.

The prepared specimens were left in an 80 ° C. oven for 24 hours and immediately placed on a backlight in a dark room, and photographed by visually confirming the degree of light leakage, and evaluated according to the following criteria.

<Evaluation Criteria>

○: It is difficult to visually identify light leakage

△: Some light leakage phenomenon

×: Light leakage phenomenon is clearly identified

4. Save Modulus of elasticity

After peeling the release film from the prepared pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer having a thickness of 30 μm was laminated to prepare a cylindrical test piece having a thickness of 8 mm Φ × 3 mm, and a dynamic viscoelasticity measuring device (DYNAMIC ANALYZER RDAII, Rheometric Corp.) was used. The storage modulus (G ′) was measured at a frequency of 1 Hz, at a temperature of 23 ° C. and at 80 ° C. by the tosioinal shear method. The storage modulus was measured by measuring the surface A and the core B in the direction of UV irradiation.

division durability Adhesion (N / 25㎜) Light leakage phenomenon Storage modulus (G ', MPa) Heat resistance Wet heat Room temperature Gaon     A B Example 1 ◎ ◎ 2.5 13.8 ○ 0.2 0.35 Example 2 ◎ ◎ 2.2 11.5 ○ 0.22 0.34 Example 3 ◎ ◎ 1.1 8.2 ○ 0.32 0.48 Example 4 ○ ○ 1.3 9.2 ○ 0.30 0.45 Example 5 ◎ ○ 2.1 14.1 ○ 0.21 0.33 Example 6 ○ ◎ 2.3 15.7 ○ 0.19 0.37 Comparative Example 1 × × 0.8 7.4 × 0.37 0.25 Comparative Example 2 △ × 4.5 16.4 △ 0.12 0.39 Comparative Example 3 × × 1.4 8.3 × 0.31 0.29 Comparative Example 4 × × 3.5 18.2 ○ 0.25 0.45

As shown in Table 2, the pressure-sensitive adhesive layer of Examples 1 to 6 containing two kinds of photopolymerization initiators having different maximum absorption wavelengths according to the present invention are different from each other in terms of elastic modulus of elasticity, high temperature and It was confirmed that the light leakage phenomenon is improved when used for a long time under high humidity conditions, and excellent adhesion durability even under severe conditions (high temperature and high humidity).

Claims (6)

An acrylic copolymer, a crosslinking agent, a polyfunctional (meth) acrylate monomer, a first photoinitiator having a maximum absorption wavelength of 200 to 300 nm, and a second photopolymerization initiator having a maximum absorption wavelength of 340 to 500 nm,
The pressure-sensitive adhesive composition containing the first photoinitiator and the second photoinitiator in a weight ratio of 0.1: 10 to 1: 2.
The pressure-sensitive adhesive composition of claim 1, wherein the first photoinitiator has a maximum absorption wavelength of 230 to 280 nm.
The pressure-sensitive adhesive composition of claim 1, wherein the second photopolymerization initiator has a maximum absorption wavelength of 350 to 490 nm.
The method according to claim 1, 100 parts by weight of the acrylic copolymer, 0.1 to 15 parts by weight of a crosslinking agent, 5 to 25 parts by weight of a polyfunctional (meth) acrylate monomer, and 0.01 to 10 parts by weight of the first photoinitiator and the second photoinitiator. Adhesive composition containing.
The pressure-sensitive adhesive layer of any one of claims 1 to 4, wherein the pressure-sensitive adhesive composition is cured, and the difference in storage modulus between the core and the surface is 0.1 MPa or more.
The pressure-sensitive adhesive layer of claim 5, wherein the storage modulus difference is 0.1 to 0.4 MPa.