Adhesive film for polarizing plate, polarizing plate including the same, and optical display including the same

1. An adhesive film for a polarizing plate formed from a composition comprising a (meth)acrylic copolymer and a cross-linking agent, the adhesive film having a peel strength ratio of about 6 or greater, the peel strength ratio being calculated according to Equation 1:

Peel strength ratio= B/A   Equation 1

wherein A is a peel strength in gf/25 mm of the adhesive film when peeled off of a glass substrate at an angle of 180° at 25° C. and at a tensile speed of 300 mm/min using a 30 kgf load cell; and

B is a peel strength in gf/25 mm of the adhesive film when left at 85° C. for 60 minutes, and then peeled off of the glass substrate at an angle of 180° at 85° C. and at a tensile speed of 300 mm/min using a 30 kgf load cell, and

wherein the peel strength A and the peel strength B are measured on a specimen in which a polarizing plate including the adhesive film is formed on a first surface of the glass substrate wherein the adhesive film has a peel strength A of about 200 gf/25 mm to about 500 gf/25 mm, and a peel strength B of about 1500 gf/25 mm to about 3000 gf/25 mm.

2. The adhesive film according to claim 1 , wherein the adhesive film has a gel fraction of about 70% or greater, as calculated by Equation 2:

Gel fraction (%)=( W 3− W 1)/( W 2− W 1)×100   Equation 2

wherein W 1 is a weight of a wire mesh;

W 2 is a first total weight of the wire mesh and an adhesive, wherein the first total weight is obtained by drying the adhesive composition at 120° C. for 3 minutes and leaving the adhesive composition at 35° C. and 45% RH for 1 hour, and then placing the adhesive composition on the wire mesh; and

W 3 is a second total weight of the wire mesh and the adhesive, wherein the second total weight is obtained by drying the adhesive composition at 120° C. for 3 minutes and leaving the adhesive composition at 35° C. and 45% RH for 1 hour, and then placing the adhesive composition and the wire mesh in a sample bottle, followed by adding ethyl acetate into the sample bottle allowing the sample bottle to stand at 25° C. for 1 day, followed by drying at 100° C. for 12 hours.

3. The adhesive film according to claim 1 , wherein the (meth)acrylic copolymer comprises hydroxyl groups and/or carboxylic acid groups uniformly arranged on and connected to a copolymer backbone at intervals.

4. The adhesive film according to claim 1 , wherein the (meth)acrylic copolymer is polymerized by introducing a (meth)acrylic monomer containing a non-reactive functional group, followed by dropwise addition of a (meth)acrylic monomer containing a reactive functional group.

5. The adhesive film according to claim 1 , wherein the (meth)acrylic copolymer has a weight average molecular weight of about 1,000,000 g/mol or less.

6. The adhesive film according to claim 1 , wherein the cross-linking agent comprises a mixture of a modified polyisocyanate cross-linking agent and a metal chelate cross-linking agent.

7. The adhesive film according to claim 6 , wherein the modified polyisocyanate cross-linking agent is prepared by end-capping an isocyanate group of a polyfunctional polyisocyanate cross-linking agent.

8. The adhesive film according to claim 6 , wherein the metal chelate cross-linking agent comprises an aluminum chelate cross-linking agent.

9. The adhesive film according to claim 1 , further comprising about 0.1 wt % to about 10 wt % of a metal selected from the group consisting of aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, zirconium, and combinations thereof.

10. The adhesive film according to claim 6 , wherein a weight ratio of the modified polyisocyanate cross-linking agent to the metal chelate cross-linking agent in the composition is about 1 to about 6.

11. The adhesive film according to claim 6 , wherein a weight ratio of the modified polyisocyanate cross-linking agent to the metal chelate cross-linking agent in the composition is about 3 to about 6.

12. The adhesive film according to claim 1 , wherein the composition further comprises a silane coupling agent.

13. The adhesive film according to claim 1 , wherein the adhesive film has a storage modulus at 30° C. of about 5×10 5 Pa to about 9×10 5 Pa, as measured from 0° C. to 120° C. at a strain of 10% and a frequency of 10 Hz.

14. A polarizing plate comprising the adhesive film for polarizing plates according to claim 1 .

15. An optical display comprising the polarizing plate according to claim 14 .