Adhesive film, optical member comprising the same and optical display comprising the same
An adhesive film, an optical member including the same, and an optical display including the same are provided. An adhesive film has a tan δ ratio at 25° C. of about 1 to about 2 as calculated by Equation 1 and a tan δ ratio at −20° C. of about 0.1 to about 1.5 as calculated by Equation 2, and is formed of an adhesive composition including a monomer mixture including a hydroxyl group-containing (meth)acrylic acid ester.
1. An adhesive film having a tan δ ratio at 25° C. of about 1 to about 2 as calculated by Equation 1 and a tan δ ratio at −20° C. of about 0.1 to about 1.5 as calculated by Equation 2, the adhesive film being formed of an adhesive composition comprising a (meth)acrylic copolymer formed of monomer mixture comprising a hydroxyl group-containing (meth)acrylic acid ester and an alkyl group-containing (meth)acrylic acid ester, wherein
tan δ ratio at 25° C.=([tan δ] 100/25° C. )/([tan δ] 1/25° C. ), Equation 1
where [tan δ] 1/25° C. is tan δ of the adhesive film at about 1 rad/sec and about 25° C., and
[tan δ] 100/25° C. is tan δ of the adhesive film at about 100 rad/sec and about 25° C., and
Tan δ at −20° C. =([tan δ] 100/−20° C. )/([tan delta] 1/−20° C. ), Equation 2
where [tan δ] 1/−20° C. is tan δ of the adhesive film at about 1 rad/sec and about −20° C., and
[tan δ] 100/−20° C. is tan δ of the adhesive film at about 100 rad/sec and about −20° C., and
wherein the adhesive film has a peel strength at 25° C. of about 700 gf/inch or higher,
wherein the adhesive film has a storage modulus of about 20 kPa to about 70 kPa at 25° C. and 100 rad/sec,
wherein the adhesive film has a storage modulus of about 200 kPa to about 1000 kPa at −20° C. and 100 rad/sec, and
wherein the (meth)acrylic copolymer formed of the monomer mixture has a glass transition temperature Tg of about −150° C. to about −13° C., and
wherein the adhesive film has a glass transition temperature of about −100° C. to less than about −30° C.,
wherein the adhesive composition is obtained by:
mixing the monomer mixture with a first initiator and conducting partial polymerization to prepare a liquid having a viscosity of about 4,000 cP to about 9,000 cP at 25° C., and
mixing the liquid with a second initiator different from the first initiator.
2. The adhesive film according to claim 1 , wherein a homopolymer of the hydroxyl group-containing (meth)acrylic acid ester has a glass transition temperature of about 0° C. or less.
3. The adhesive film according to claim 1 , wherein the hydroxyl group-containing (meth)acrylic acid ester comprises at least one (meth)acrylic acid ester containing a C 4 to C 20 alkyl group having at least one hydroxyl group.
4. The adhesive film according to claim 1 , wherein the monomer mixture comprises about 75 wt % to about 90 wt % of the alkyl group-containing (meth)acrylic acid ester.
5. The adhesive film according to claim 1 , wherein the adhesive film has tan δ of about 0.3 to about 0.7 and a storage modulus of about 50 kPa to about 100 kPa at −20° C. and at 1 rad/sec.
6. The adhesive film according to claim 1 , wherein the adhesive film has tan δ of about 0.1 to about 0.75 and a storage modulus of about 200 kPa to about 1,000 kPa at −20° C. and at 100 rad/sec.
7. The adhesive film according to claim 1 , wherein the adhesive film has a resistance variation rate of about 3% or less as calculated by Equation 4:
Resistance variation rate (%) =(P 2 −P 1 )/P 1 ×100,
where P 1 is initial resistance (unit: Ω) of a specimen having electrodes at both ends of an adhesive film, and P 2 is resistance (unit: Ω) of the specimen as measured after the specimen is left at about 60° C. and about 95% RH for about 250 hours.
8. The adhesive film according to claim 1 , further comprising organic nanoparticles.
9. The adhesive film according to claim 8 , wherein the organic nanoparticles have an average particle diameter of about 10 nm to about 400 nm.
10. The adhesive film according to claim 8 , wherein the organic nanoparticles have a core-shell structure.
11. The adhesive film according to claim 10 , wherein a core and a shell of the core-shell structure satisfy Equation 6:
Tg(c)<Tg(s),
where Tg(c) is a glass transition temperature (unit: ° C.) of the core and Tg(s) is a glass transition temperature (unit: ° C.) of the shell.
12. The adhesive film according to claim 10 , wherein a core of the core-shell structure is formed of at least one of poly(butyl acrylate) and polysiloxane, and a shell of the core-shell structure comprises poly(methyl methacrylate).
13. The adhesive film according to claim 8 , wherein the organic nanoparticles are present in an amount of about 0.1 parts by weight to about 20 parts by weight relative to 100 parts by weight of the monomer mixture.
14. An optical member comprising an optical film and an adhesive film on at least one surface of the optical film, the adhesive film comprising the adhesive film according to claim 1 .
15. The optical member according to claim 14 , wherein the optical member comprises a three-layer film laminate comprising a first optical film, a second optical film, and the adhesive film between the first optical film and the second optical film to attach the first optical film to the second optical film.
16. The optical member according to claim 15 , wherein each of the first optical film and the second optical film comprises at least one resin selected from among a polyethylene terephthalate resin, a polycarbonate resin, a polyimide resin, a poly(meth)acrylate resin, a cyclic olefin polymer resin, and an acrylic resin.
17. The optical member according to claim 15 , wherein each of the first optical film and the second optical film has a thickness of about 10 μm to about 100 μm.
18. A window film comprising:
the optical member according to claim 14 ; and
a window coating layer on the optical member.
19. An optical display comprising the adhesive film according to claim 1 .
20. The adhesive film according to claim 1 , wherein the monomer mixture comprises about 10 wt % to about 25 wt % of the hydroxyl group-containing (meth)acrylic acid ester.
21. The adhesive film according to claim 1 , wherein the adhesive film has a gel fraction of about 70% to about 85%.