Acrylic pressure-sensitive adhesive composition for polarizing plate, containing a photo-initiator group

1. An acrylic pressure-sensitive adhesive composition for polarizing plates, comprising a (meth)acrylic copolymer comprising an alkyl(meth)acrylic acid ester monomer, in which alkyl has 2 to 14 carbon atoms, and a copolymerizable monomer containing a photo-initiator group,

wherein, the composition forms a crosslinked structure through the reaction of the photo-initiator group,

wherein, the composition after forming the crosslinked structure has a gel fraction, represented by Equation 1, of 10 to 55% and a swelling ratio, represented by Equation 2, of 30 to 110, and

wherein, the composition after forming the crosslinked structure comprises a sol that is capable of being eluted with ethyl acetate and that has a weight average molecular weight of 600,000 or more:

Gel fraction(%)= B/A× 100  (1)

Swelling ratio= C/B   (2)

wherein, A represents weight of the composition after forming the crosslinked structure, B represents dry weight of insoluble content after depositing the composition after forming the crosslinked structure in ethyl acetate at ambient temperature for 48 hours, and C represents weight of insoluble content swollen with ethyl acetate after depositing the composition after forming the crosslinked structure in ethyl acetate at ambient temperature for 48 hours.

2. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the (meth)acrylic copolymer comprises 50 to 99.8 parts by weight of (meth)acrylic acid ester monomer, in which alkyl has 2 to 14 carbon atoms, and 0.01 to 3 parts by weight of a monomer containing a photo-initiator group.

3. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the alkyl(meth)acrylic acid ester monomer is one or more selected from the group consisting of 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, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate.

4. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the monomer containing a photo-initiator group is a compound of Formula 1:

X—Y  1

wherein,

X represents a hydrocarbon group containing an ethylenic double bond, and

Y represents a hydrocarbon group that may contain a photo-initiating functional group and a heteroatom.

5. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 4 , wherein

X represents P-Q-, in which P— represents CR 1 R 2 ═CR—CO—, where R 1 , R 2 , and R each represents hydrogen or methyl, and Q represents O or a single bond, and

Y represents a hydrocarbon group containing a benzoyl group, titanocene, camphorquinone, trichloromethyl-triazine or thioxanthene.

6. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the (meth)acrylic copolymer further comprises 0.01 to 5 parts by weight of a polar monomer.

7. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 6 , wherein the polar monomer is one or more selected from the group consisting of 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyleneglycol (meth)acrylate, 2-hydroxypropyleneglycol (meth)acrylate, acrylic acid, methacrylic acid, acrylic acid dimer, itaconic acid, maleic acid, and maleic anhydride.

8. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the (meth)acrylic copolymer further comprises 20 parts by weight or less of a copolymerizable vinyl monomer.

9. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 8 , wherein the vinyl monomer is a compound of Formula 2:

wherein,

R 4 represents hydrogen or alkyl,

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

10. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein it further comprises 0.005 to 5 parts by weight of a silane coupling agent or 1 to 100 parts by weight of a tackifier resin based on 100 parts by weight of the (meth)acrylic copolymer.

11. The acrylic pressure-sensitive adhesive composition for polarizing plates of claim 1 , wherein the acrylic copolymer is prepared by a polymerization method selected from the group consisting of solution polymerization, photo-polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization.

12. An adhesion polarizing plate comprising a pressure-sensitive adhesive layer containing the acrylic pressure-sensitive adhesive composition according to claim 1 and formed on one side or both sides of a polarizing film.

13. The adhesion polarizing plate of claim 12 , 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 wide view angle and a brightness enhancing film.

14. A liquid crystal display device comprising a liquid crystal cell and the pressure-sensitive adhesive polarizing plate according to claim 12 bound to one side or both sides of the liquid crystal cell.

15. A liquid crystal display device comprising a liquid crystal cell and the pressure-sensitive adhesive polarizing plate according to claim 13 bound to one side or both sides of the liquid crystal cell.