Adhesive composition, protective film for a polarizing plate, polarizing plate, and liquid crystal display

1. A polarizer comprising:

a polarizing film or polarizing element; and

a protective film attached to a side or both sides of the polarizing film or polarizing element,

wherein the protective film comprises:

a base film, and

a pressure sensitive adhesive layer on a side or both sides of the base film,

wherein the pressure sensitive adhesive layer comprises a cured product of a pressure-sensitive adhesive composition satisfying a condition of General Formula 1 given below:

Δ X ≦2 nm,  [General Formula 1]

wherein ΔX represents an absolute value of a phase retardation (R in ) in a surface-direction, the phase retardation being measured by an equation, R in ={(n x −n y )×d}, when a sheet-shaped pressure-sensitive adhesive that has a width of 10 mm and a length of 20 mm and that is prepared by using the pressure-sensitive adhesive composition is elongated by 500 μm in a longitudinal direction at 23° C.,

wherein n x represents a refractive index along a horizontal axis in a surface of the sheet-shaped pressure-sensitive adhesive, n y represents a refractive index along a vertical axis in the surface of the sheet-shaped pressure-sensitive adhesive, and d represents a thickness of the sheet-shaped pressure-sensitive adhesive,

wherein the base film is a saturated cycloolefin film; an olefin thermoplastic resin film having a substituted or unsubstituted imide group in its side chain; a thermoplastic resin film having a substituted or unsubstituted phenyl group and nitrile group in its side chain; or an acrylic film,

wherein a stress optical coefficient of the saturated cycloolefin film; the olefin thermoplastic resin film having a substituted or unsubstituted imide group in its side chain; the thermoplastic resin film having a substituted or unsubstituted phenyl group and nitrile group in its side chain is 6 brewster or less, and the stress optical coefficient of the acrylic film is 3 brewster or less, and

wherein the pressure sensitive adhesive composition comprises a compound having a positive stress optical coefficient expressed by Formula 3 or Formula 4:

where B represents a single bond, —CH═N—, —N═N—, —N═N(O)—, —COO—, —CH 2 O—, —C(R 7 ) 2 —CO—, —COO—CH 2 —, —CH═CH—, —C≡C—, —S—, —SO 2 —, -φ(R 7 )—, —CH═N-φ(R 7 )—N═CH—, —CH═CH-φ(R 7 )—N═CH—, —CH═CH-φ(R 7 )—CH═CH—, —CH═CH-φ(R 7 )-φ(R 8 )—CH═CH—, —CH═N-φ(R 7 )(R 8 )—N═CH—, —CH═N-φ(R 7 )-φ(R 8 )—CH═CH—, —N═N-φ(R 7 )—N═CH—, —C(═O)—O-φ(R 7 )—C(CH 3 ) 2 —, a naphthalene core, or an anthracene core, X, Y, R 7 , and R 8 represent independently hydrogen, halogen, cyano, amino, hydroxy, alkyl, alkoxy, aryl, dialkylamine, and cumyl, a represents an integer of 0 to 3, and b represents an integer of 1 to 3 when a is 0, and an integer of 0 to 3 when a is an integer of 1 to 3,

Z is C—W or N;

Q 1 to Q 16 and W are independently hydrogen, halogen, cyano, perfluoroalkyl, perfluoroalkyloxy, —R 9 , —OR 9 , —NHR 9 , —N(R 9 ) 2 , —C(═O)R 9 , —SR 9 , —SOR 9 , —SO 2 R 9 , —C(═O)NR 9 , —NR 9 C(═O)R 9 , —C(═O)OR 9 , —OC(═O)R 9 , or —OC(═O)OR 9 ;

R 9 is hydrogen, alkyl, alkenyl, alkynyl, or —(R 10 O) q R 11 , R 10 is alkylene, R 11 is alkyl, and q is an integer of 1 to 5;

l, m, n, and o are independently an integer of 0 to 2, and l+m+n+o is an integer greater than 2;

E and F are independently hydrogen, halogen, cyano, —R 9 , —OR 9 , —NHR 9 , —N(R 9 ) 2 , —NCO, —NCS, —C(═O)R 9 , or —Si(R 90 ) 3 ; and

G 1 , G 2 and G 3 , are independently a single bond, —O—, —R 10 O—, —NR 10 —, —S—, —SO—, —SO 2 —, alkylene, alkenylene, alkynylene, or —U-T-V—, U and T are independently a single bond, —S—, —NR 10 —, —O(CH 2 ) p —, carbonyl or —O—, V is a single bond, —O—, carbonyl, —NR 10 —, —S—, —(CH 2 ) p —, —O(CH 2 ) p —, or —(CH 2 ) p O—, and p is an integer of 0 to 5.

2. The polarizer of claim 1 , wherein the pressure-sensitive adhesive composition further comprises a base resin having a weight average molecular weight of 500,000 or more.

3. The polarizer of claim 2 , wherein the base resin is a polymer of a monomer mixture comprising 80 to 99.8 parts by weight of a (meth)acrylic acid ester monomer; and 0.01 to 10 parts by weight of a crosslinking monomer.

4. The polarizer of claim 3 , wherein the (meth)acrylic acid ester monomer is one or more selected from a group consisting of methyl (meth)acrylate, 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, 2-ethylbutyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, and tetradecyl (meth)acrylate.

5. The polarizer of claim 3 , wherein the crosslinking monomer is one or more selected from a group consisting of a hydroxy group-containing monomer, a carboxyl group-containing monomer, and a nitrogen-containing monomer.

6. The polarizer of claim 3 , wherein the monomer mixture further comprises a monomer expressed by:

where R 1 to R 3 independently represent hydrogen or alkyl, and R 4 represents cyano; phenyl unsubstituted or substituted with alkyl; acetyloxy; or COR 5 , in which R 5 represents glycidyloxy or amino unsubstituted or substituted with alkyl or alkoxy alkyl.

7. The polarizer of claim 3 , wherein the monomer mixture further comprises a compound expressed by:

where R 6 represents hydrogen or alkyl, A represents an alkylene, n represents an integer of 0 to 3, Q represents a single bond, —O—, —S—, or an alkylene, and P represents a substituted or unsubstituted aromatic group.

8. The polarizer of claim 2 , wherein the pressure sensitive adhesive composition further comprises 0.1 to 10 parts by weight of a crosslinking agent relative to 100 parts by weight of the base resin.

9. The polarizer of claim 8 , wherein the crosslinking agent is one or more selected from a group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal chelate compound.

10. The polarizer of claim 2 , wherein the pressure-sensitive adhesive composition further comprises 0.01 to 10 parts by weight of a silane coupling agent relative to 100 parts by weight of the base resin.

11. The polarizer of claim 1 , wherein the acrylic film comprises an acrylic resin; and a graft copolymer containing a conjugated diene rubber.

12. The polarizer of claim 1 , further comprising one or more selected from a group consisting of a protective layer, a reflective layer, an anti-glare layer, a phase retardation film, a compensation film for wide view angle, and a brightness enhancement film.

13. A liquid crystal display comprising a liquid crystal panel in which the polarizer according to claim 1 is attached on a face or both faces of a liquid crystal cell.

14. The polarizer of claim 1 , wherein the ΔX of the General Formula 1 is 1.5 nm or less.

15. The polarizer of claim 1 , wherein the ΔX of the General Formula 1 is 1 nm or less.

16. A polarizer comprising:

a polarizing film or polarizing element; and

a protective film attached to a side or both sides of the polarizing film or polarizing element,

wherein the protective film comprises:

a base film disposed on the polarizing film or polarizing element, and

a pressure sensitive adhesive layer disposed on a side of the base film opposite to the polarizing film or polarizing element,

wherein the pressure sensitive adhesive layer is a cured product of a pressure-sensitive adhesive composition satisfying a condition of General Formula 1 given below:

Δ X ≦2 nm,  [General Formula 1]

wherein ΔX represents an absolute value of a phase retardation (R in ) in a surface-direction, the phase retardation being measured by an equation, R in ={(n x −n y )×d}, when a sheet-shaped pressure-sensitive adhesive that has a width of 10 mm and a length of 20 mm and that is prepared by using the pressure-sensitive adhesive composition is elongated by 500 μm in a longitudinal direction at 23° C., wherein n x represents a refractive index along a horizontal axis in a surface of the sheet-shaped pressure-sensitive adhesive, n y represents a refractive index along a vertical axis in the surface of the sheet-shaped pressure-sensitive adhesive, and d represents a thickness of the sheet-shaped pressure-sensitive adhesive,

wherein the base film is a saturated cycloolefine film, an olefine thermoplastic resin film having a substituted or unsubstituted imide group in its side chain; a thermoplastic resin film having a substituted or unsubstituted phenyl group and nitrile group in its side chain; or an acrylic film,

wherein a stress optical coefficient of the saturated cycloolefine film, the olefine thermoplastic resin film having a substituted or unsubstituted imide group in its side chain; or the thermoplastic resin film having a substituted or unsubstituted phenyl group and nitrile group in its side chain is 6 brewster or less and a stress optical coefficient of the acrylic film is 3 brewster or less,

wherein the pressure-sensitive adhesive composition comprises: a base resin that is a polymer of a monomer mixture including a (meth)acrylic acid ester monomer, a crosslinking monomer and a compound expressed by Formula 2 given below; and a crosslinking agent crosslinking the base resin:

where R 6 represents hydrogen or alkyl, A represents an alkylene, n represents an integer of 0 to 3, Q represents a single bond, —O—, —S—, or an alkylene, and P represents a substituted or unsubstituted aromatic group, and

wherein the crosslinking agent is one or more selected from the group consisting of an isocyanate compound, an epoxy compound, an aziridine compound, and a metal chelate compound.

17. The polarizer of claim 16 , wherein the protective film comprises only one base film.