Adhesive composition for polarizing plate, adhesive film for polarizing plate prepared using the same, polarizing plate comprising the same and optical display comprising the same
An adhesive composition for polarizing plates includes a (meth)acrylic copolymer, an isocyanate crosslinking agent, and a silane coupling agent. The molar ratio (A) of the number of moles of hydroxyl groups in the (meth)acrylic copolymer may be about 2.5 mol % to about 4 mol %, the molar ratio (B) of the number of moles of alkoxy silane groups in the silane coupling agent may be about 50 mol % to about 80 mol %, and the molar ratio (C) of the number of moles of isocyanate groups of the isocyanate crosslinking agent may be about 20 mol % to about 50 mol %, based on the total number of moles of alkoxy silane groups of the silane coupling agent and isocyanate groups of the isocyanate crosslinking agent. An adhesive film is formed from the adhesive composition, a polarizing plate includes the adhesive film, and an optical display includes the polarizing plate.
1. An adhesive composition for polarizing plates, the adhesive composition comprising a (meth)acrylic copolymer, an isocyanate crosslinking agent, and a silane coupling agent,
wherein:
a molar ratio A of a number of moles of hydroxyl groups in the (meth)acrylic copolymer is about 2.5 mol % to about 4 mol % as calculated using Equation 1,
a molar ratio B of a number of moles of alkoxy silane groups in the silane coupling agent is about 50 mol % to about 80 mol % as calculated using Equation 2, and
a ratio C of a number of moles of isocyanate groups in the isocyanate crosslinking agent is about 20 mol % to about 50 mol % as calculated using Equation 3:
molar ratio A= ( a 2/ a 1)×100 Equation 1
wherein a 1 denotes a total number of moles of monomers included in a monomer mixture for forming the (meth)acrylic copolymer, and a2 denotes a number of moles of hydroxyl group-containing (meth)acrylic monomers in the monomer mixture;
molar ratio B={b/ ( b+c )}×100 Equation 2
molar ratio C={c/ ( b+c )}×100 Equation 3
wherein b denotes (a number of moles of the silane coupling agent in the adhesive composition)×(a number of moles of alkoxy silane groups contained in one molecule of the silane coupling agent), and c denotes (a number of moles of the isocyanate crosslinking agent in the adhesive composition)×(a number of moles of isocyanate groups contained in one molecule of the isocyanate crosslinking agent).
2. The adhesive composition according to claim 1 , wherein the (meth)acrylic copolymer has an acid value of about 0.5 mg KOH/g or lower.
3. The adhesive composition according to claim 1 , wherein the (meth)acrylic copolymer is a copolymer of a monomer mixture comprising: a hydroxyl group-containing (meth)acrylic monomer; and at least one of an alkyl group-containing (meth)acrylic monomer, a hetero ring-containing (meth)acrylic monomer, an aromatic group-containing (meth)acrylic monomer, or an alicyclic group-containing (meth)acrylic monomer.
4. The adhesive composition according to claim 3 , wherein the (meth)acrylic copolymer is a copolymer of a monomer mixture comprising about 96.0 mol % to about 97.5 mol % of an unsubstituted C 1 to C 20 alkyl group-containing (meth)acrylic acid ester, and about 2.5 mol % to about 4.0 mol % of a C 2 to C 20 alkyl group-containing (meth)acrylic acid ester having a hydroxyl group.
5. The adhesive composition according to claim 3 , wherein the (meth)acrylic copolymer is a copolymer of a monomer mixture comprising about 76.0 mol % to about 97.4 mol % of a C 1 to C 20 alkyl group-containing (meth)acrylic acid ester; about 2.5 mol % to about 4.0 mol % of a C 2 to C 20 alkyl group-containing (meth)acrylic acid ester having a hydroxyl group; and about 0.1 mol % to about 20.0 mol % of at least one of the hetero ring-containing (meth)acrylic monomer, the alicyclic group-containing (meth)acrylic monomer, or the aromatic group-containing (meth)acrylic monomer.
6. The adhesive composition according to claim 1 , wherein the (meth)acrylic copolymer has a glass transition temperature of about −52° C. to about −27° C.
7. The adhesive composition according to claim 1 , wherein the silane coupling agent comprises a mercapto group-containing silicon compound.
8. The adhesive composition according to claim 1 , wherein the isocyanate crosslinking agent comprises an end capped isocyanate crosslinking agent.
9. The adhesive composition according to claim 1 , comprising: about 0.1 parts by weight to about 10 parts by weight of the isocyanate crosslinking agent based on 100 parts by weight of the (meth)acrylic copolymer, and about 0.1 parts by weight to about 10 parts by weight of the silane coupling agent based on 100 parts by weight of the (meth)acrylic copolymer.
10. An adhesive film for polarizing plates formed from the adhesive composition for polarizing plates according to claim 1 .
11. The adhesive film for polarizing plates according to claim 10 , the adhesive film for polarizing plates having an adhesive strength to a polarizer of about 1,000 gf/inch or greater.
12. A polarizing plate comprising:
a polarizer,
an adhesive layer on one surface of the polarizer, the adhesive layer comprising the adhesive film for polarizing plates according to claim 10 , and
a protective film on another surface of the polarizer.
13. An optical display comprising the polarizing plate according to claim 12 .