Adhesive film, optical member including same, and optical display device including same
Provided are an adhesive film, an optical member including the same, and an optical display device including the same, the adhesive film being formed from a monomer mixture comprising an alkyl group-containing acrylate and a hydroxyl group-containing acrylate, wherein the adhesive film has a modulus of 80 kPa or less at −20° C., and the adhesive film has a value of 40% to 140% in equation 1 at 25° C.
1. An adhesive film formed of an adhesive composition comprising: a monomer mixture comprising an alkyl group-containing acrylate and a hydroxyl group-containing acrylate; and an initiator, the adhesive film having a modulus of 80 kPa or less at −20° C. and a value of 40% to 140% at 25° C., as calculated by Equation 1:
(Stretched length of adhesive film)/(Initial thickness of adhesive film)×100,
wherein the stretched length of the adhesive film (unit: μm) is measured on a specimen, the specimen being prepared by attaching one end of a first polyimide film (length×width×thickness, 45 mm×15 mm×50 μm) to one end of a second polyimide film (length×width×thickness, 45 mm×15 mm×50 μm) via the adhesive film (length×width×thickness, 15 mm×15 mm×50 μm) in a structure of one end of the first polyimide film/adhesive film/one end of the second polyimide film to have a stepped cross-sectional shape , and the stretched length of the adhesive film is obtained by subtracting an initial length (unit: mm) of the adhesive film from a final length of the adhesive film (unit: mm) (final length of the adhesive film (unit: mm)−initial length (unit: mm) of the adhesive film) and converting to unit of micrometers when the other end of the second polyimide film is pulled at 0.6 mm/min under a load of 500 gf at 25° C. for 10 minutes, with the other end of the first polyimide film of the specimen secured to a tester; and
the initial thickness of the adhesive film (unit: μm) is a thickness of the adhesive film before preparation of the specimen,
wherein the alkyl group-containing acrylate comprises a mixture of a first alkyl group-containing acrylate and a second alkyl group-containing acrylate,
the first alkyl group-containing acrylate being a non-alkylene glycol-based acrylate having a glass transition temperature of −20° C. to −55° C. in a homopolymer phase and free from an alkylene glycol group, and
the second alkyl group-containing acrylate being an alkylene glycol-based acrylate having a glass transition temperature of −55° C. to −90° C. in a homopolymer phase and containing an alkylene glycol group.
2. The adhesive film according to claim 1 , wherein the adhesive film has a ratio of modulus at 80° C. to modulus at −20° C. of 1:1 to 1:10.
3. The adhesive film according to claim 1 , wherein the adhesive film has a modulus of 10 kPa to 200 kPa at 80° C.
4. The adhesive film according to claim 1 , wherein the adhesive film has a peel strength of 700 gf/in or more at 25° C.
5. The adhesive film according to claim 1 , wherein the first alkyl group-containing acrylate comprises at least one of 2-ethylhexyl acrylate, n-butyl acrylate, and iso-octyl acrylate.
6. The adhesive film according to claim 1 , wherein the second alkyl group-containing acrylate comprises at least one of methoxypolyethylene glycol acrylate and ethylhexyldiethylene glycol acrylate.
7. The adhesive film according to claim 1 , wherein the hydroxyl group-containing acrylate has a glass transition temperature of 0° C. to −40° C. in a homopolymer phase.
8. The adhesive film according to claim 1 , wherein the monomer mixture comprises 10 wt % to 40 wt % of the hydroxyl group-containing acrylate and 60 wt % to 90 wt % of the alkyl group-containing acrylate.
9. The adhesive film according to claim 1 , wherein the adhesive composition further comprises organic nanoparticles, the organic nanoparticles having an average particle diameter of 10 nm to 400 nm.
10. The adhesive film according to claim 9 , wherein the organic nanoparticles have a core-shell structure, the core and the shell satisfying Equation 2:
Tg ( c )< Tg ( s ) <Equation 2>
wherein 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.
11. The adhesive film according to claim 9 , wherein the organic nanoparticles are present in an amount of 0.1 parts by weight to 20 parts by weight relative to 100 parts by weight of the hydroxyl group-containing acrylate and the alkyl group-containing acrylate.
12. The adhesive film according to claim 1 , wherein the adhesive composition further comprises a crosslinking agent having a glass transition temperature of 40° C. to −60° C. in a homopolymer phase.
13. The adhesive film according to claim 12 , wherein the crosslinking agent comprises polyethylene glycol diacrylate.
14. An optical member comprising an optical film and an adhesive film formed on at least one surface of the optical film,
wherein the adhesive film comprises the adhesive film according to claim 1 .
15. The optical member according to claim 14 , wherein the optical member is a three-layer film laminate comprising a first optical film, a second optical film, and the adhesive film interposed 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 is formed of at least one resin selected from among a polyester resin, a polycarbonate resin, a polyimide resin, a polyacrylate 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 10 μm to 100 μm and the adhesive film has a thickness of 10 μm to 100 μm.
18. A window film comprising: the optical member according to claim 14 ; and a window coating layer formed on the optical member.
19. An optical display comprising the optical member according to claim 14 .