Adhesive film for polarizing plate, polarizing plate including the same and optical display including the same
An adhesive film for polarizing plates, a polarizing plate including the same, and an optical display including the same are provided. An adhesive film for polarizing plates is formed of an adhesive composition for polarizing plates, which includes a non-carboxylic acid (meth)acrylic copolymer, an isocyanate curing agent, and an epoxy curing agent, wherein the adhesive film has a modulus at 85° C. of about 0.1 MPa to about 0.8 MPa and a modulus ratio of about 3 or less, as calculated by the equation, Modulus ratio=G′(25° C.)/G′(85° C.), where G′(25° C.) is modulus (unit: MPa) at 25° C. of an adhesive film and G′(85° C.) is modulus (unit: MPa) at 85° C. of the adhesive film.
1. An adhesive film for polarizing plates, the adhesive film being formed of an adhesive composition comprising: a non-carboxylic acid (meth)acrylic copolymer; an isocyanate curing agent; and an epoxy curing agent,
wherein the adhesive film has a modulus at 85° C. of about 0.1 MPa to about 0.8 MPa and a modulus ratio of 3 or less, as calculated by Equation 1:
Modulus ratio= G ′(25° C.)/ G ′(85° C.), Equation 1
where G′(25° C.) is modulus (unit: MPa) at 25° C. of the adhesive film and G′(85° C.) is modulus (unit: MPa) at 85° C. of the adhesive film.
2. The adhesive film according to claim 1 , wherein the adhesive film has a resistance change rate of less than 10%, as calculated by Equation 2:
Resistance change rate=( P 2 −P 1 )/ P 1 ×100, Equation 2
where P 1 is initial resistance (unit: Ω) measured on a specimen in which electrodes are formed at both ends of the adhesive film, and P 2 is resistance (unit: Ω) measured after the specimen is left alone at 60° C. and 95% RH for 250 hours.
3. The adhesive film according to claim 1 , wherein the adhesive film has a modulus at 25° C. of about 0.3 MPa or greater.
4. The adhesive film according to claim 1 , wherein a polarizing plate for durability evaluation, to which the adhesive film for polarizing plates is attached, has a defect rate of about 5% or less, as calculated by Equation 4 after the polarizing plate is left at 85° C. for 500 hours and at 60° C. and 95% RH for 500 hours, wherein Equation 4 is as follows:
Defect rate (%)=|A+B|/T×100, Equation 3
where T is a maximum diagonal length of the polarizing plate for durability evaluation, and A and B are lengths from both end points of a maximum diagonal of the polarizing plate for durability evaluation to defect generation regions on the maximum diagonal, respectively.
5. The adhesive film according to claim 1 , wherein the non-carboxylic acid (meth)acrylic copolymer has a hydroxyl group, and a ratio of an equivalent weight of the isocyanate curing agent to the sum of an equivalent weight of a hydroxyl group-containing (meth)acrylic monomer for the non-carboxylic acid (meth)acrylic copolymer and an equivalent weight of the epoxy curing agent is about 1:0.1 to about 1:1.
6. The adhesive film according to claim 1 , wherein the adhesive composition comprises 100 parts by weight of the non-carboxylic acid (meth)acrylic copolymer, 5 parts by weight or more of the isocyanate curing agent, and about 0.1 parts by weight to about 2 parts by weight of the epoxy curing agent.
7. The adhesive film according to claim 1 , wherein the non-carboxylic acid (meth)acrylic copolymer comprises a copolymer of a monomer mixture comprising about 95 wt % to about 99.9 wt % of an unreactive (meth)acrylic monomer and about 0.1 wt % to about 5 wt % of a hydroxyl group-containing (meth)acrylic monomer.
8. The adhesive film according to claim 7 , wherein the unreactive (meth)acrylic monomer comprises an unsubstituted or substituted C 1 to C 20 alkyl group-containing (meth)acrylic monomer.
9. The adhesive film according to claim 1 , wherein the epoxy curing agent comprises at least one of bisphenol A epichlorohydrin epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, 1,3-bis(N,N-diglycidylaminomethyl)benzene, or N,N,N′,N′-tetraglycidyl-m-xylenediamine.
10. The adhesive film according to claim 1 , wherein a weight ratio of the epoxy curing agent to the isocyanate curing agent in the adhesive composition is about 1:2 to about 1:100.
11. The adhesive film according to claim 1 , wherein the adhesive composition further comprises a silane coupling agent.
12. A polarizing plate comprising the adhesive film for polarizing plates according to claim 1 .
13. An optical display comprising the polarizing plate according to claim 12 .
14. The optical display according to claim 13 , comprising liquid crystals of a twisted nematic (TN) mode.
15. A polarizing plate comprising an optical film, a bonding layer stacked on the optical film, a polarizer stacked on the bonding layer, and an adhesive film stacked on the polarizer,
wherein the adhesive film comprises the adhesive film for polarizing plates according to claim 1 .