Optical film and liquid crystal display

1. An optical film comprising

a polarizer,

a uniaxially elongated film disposed directly on the polarizer and comprising a polymer, the polymer having a glass transition temperature of greater than about 100° C. and comprising a structural unit derived from styrene or a styrene derivative, and

a compensation film disposed on the uniaxially elongated film and having a refractive index satisfying Relationship Equations 1 and 2,

wherein the uniaxially elongated film has an in-plane retardation satisfying Relationship Equation 3 and a thickness direction retardation satisfying Relationship Equation 4, and the compensation film has an in-plane retardation satisfying Relationship Equation 5 and a thickness direction retardation satisfying Relationship Equation 6, and

wherein the optical film has a contrast ratio of greater than 26° as measured at a polar angle/azimuthal angle of 60°/45°:

n x2 >n z2   Relationship Equation 1

n y2 >n z2   Relationship Equation 2

wherein, in Relationship Equations 1and 2,

n x2 is a refractive index at a slow axis of the compensation film,

n y2 is a refractive index at a fast axis of the compensation film, and

n z2 is a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film;

110 nm≤ R o1 (550 nm)<180 nm  Relationship Equation 3

−100 nm≤ R th1 (550 nm)<−20 nm  Relationship Equation 4

wherein, in Relationship Equations 3 and 4,

R o1 (550 nm) is in-plane retardation of the uniaxially elongated film at a 550 nm wavelength, and

R th1 (550 nm) is thickness direction retardation of the uniaxially elongated film at a 550 nm wavelength;

−10 nm≤ R o2 (550 nm)≤10 nm  Relationship Equation 5

30 nm≤ R th2 (550 nm)<110 nm  Relationship Equation 6

wherein, in Relationships Equations 5 and 6,

R o2 (550 nm) is in-plane retardation of the compensation film at a 550 nm wavelength, and

R th2 (550 nm) is thickness direction retardation of the compensation film at a 550 nm wavelength.

2. The optical film of claim 1 , wherein the uniaxially elongated film has a refractive index satisfying Relationship Equation 7:

n y1 <n x1 =n z1   Relationship Equation 7

wherein, in Relationship Equation 7,

n x1 is a refractive index at a slow axis of the uniaxially elongated film,

n y1 is a refractive index at a fast axis of the uniaxially elongated film, and

n z1 is a refractive index in a direction perpendicular to the slow axis and the fast axis of the uniaxially elongated film.

3. The optical film of claim 1 , wherein the styrene derivative comprises a substituted or unsubstituted C1 to C20 alkyl styrene, a substituted or unsubstituted C6 to C20 aryl styrene, a halogenated styrene, a substituted or unsubstituted C1 to C5 alkoxy styrene, a substituted or unsubstituted nitro styrene, a substituted or unsubstituted amino styrene, a substituted or unsubstituted carboxyl styrene, a substituted or unsubstituted C1 to C6 carbonyl styrene, or a combination thereof.

4. The optical film of claim 1 , wherein the polymer further comprises a structural unit derived from maleimide, maleic anhydride, (meth)acrylonitrile, acrylonitrile, a derivative thereof, or a combination thereof.

5. The optical film of claim 4 , wherein the polymer further comprises a structural unit derived from a (meth)acrylate or a derivative thereof.

6. The optical film of claim 1 , wherein the polymer is a terpolymer consisting essentially of

a structural unit derived from styrene or a styrene derivative,

a structural unit derived from maleimide, maleic anhydride, (meth)acrylonitrile, acrylonitrile, or a derivative thereof, and

a structural unit derived from a (meth)acrylate or a derivative thereof.

7. The optical film of claim 1 , wherein the polymer has a glass transition temperature of about 110° C. to about 150° C.

8. The optical film of claim 1 , wherein the uniaxially elongated film is uniaxially elongated about 1.1 times to about 5.0 times.

9. The optical film of claim 1 , wherein in-plane retardation (R o1 ) of the uniaxially elongated film at 450 nm, 550 nm, and 650 nm wavelengths satisfies Relationship Equation 8 or Relationship Equation 9:

R o1 (450 nm)> R o1 (550 nm)≥ R o1 (650 nm)  Relationship Equation 8

R o1 (450 nm)≥ R o1 (550 nm)> R o1 (650 nm)  Relationship Equation 9

wherein, in Relationship Equations 8 and 9,

R o1 (450 nm) is in-plane retardation of the uniaxially elongated film at a 450 nm wavelength,

R o1 (550 nm) is in-plane retardation of the uniaxially elongated film at a 550 nm wavelength, and

R o1 (650 nm) is in-plane retardation of the uniaxially elongated film at a 650 nm wavelength.

10. A display device including the optical film of claim 1 .

11. A liquid crystal display comprising

a light source,

a liquid crystal display panel disposed on the light source, and

an optical film disposed on the liquid crystal display panel,

wherein the optical film comprises

a first polarizer,

a uniaxially elongated film disposed directly under the first polarizer and comprising a polymer, the polymer having a glass transition temperature of greater than about 100° C. and comprising a structural unit derived from styrene or a styrene derivative, and

a compensation film disposed under the uniaxially elongated film and having a refractive index satisfying Relationship Equations 1 and 2,

wherein the uniaxially elongated film has an in-plane retardation satisfying Relationship Equation 3 and a thickness direction retardation satisfying Relationship Equation 4, and the compensation film has an in-plane retardation satisfying Relationship Equation 5 and a thickness direction retardation satisfying Relationship Equation 6 and

wherein the liquid crystal display has a contrast ratio of greater than 26° as measured at a polar angle/azimuthal angle of 60°/45°:

n x2 >n z2   Relationship Equation 1

n y2 >n z2   Relationship Equation 2

wherein, in Relationship Equations 1 and 2,

n x2 is a refractive index at a slow axis of the compensation film,

n y2 is a refractive index at a fast axis of the compensation film, and

n z2 is a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film;

110 nm≤ R o1 (550 nm)<180 nm  Relationship Equation 3

−100 nm≤ R th1 (550 nm)<−20 nm  Relationship Equation 4

wherein, in Relationship Equations 3 and 4,

R o1 (550 nm) is in-plane retardation of the uniaxially elongated film at a 550 nm wavelength, and

R th1 (550 nm) is thickness direction retardation of the uniaxially elongated film at a 550 nm wavelength;

−10 nm≤ R o2 (550 nm)≤10 nm  Relationship Equation 5

30 nm≤ R th2 (550 nm)<110 nm  Relationship Equation 6

wherein, in Relationships Equations 5 and 6,

R o2 (550 nm) is in-plane retardation of the compensation film at a 550 nm wavelength, and

R th2 (550 nm) is thickness direction retardation of the compensation film at a 550 nm wavelength.

12. The liquid crystal display of claim 11 , wherein the uniaxially elongated film has a refractive index satisfying Relationship Equation 7:

n y1 <n x1 =n z1   Relationship Equation 7

wherein, in Relationship Equation 7,

n x1 is a refractive index at a slow axis of the uniaxially elongated film,

n y1 is a refractive index at a fast axis of the uniaxially elongated film, and

n z1 is a refractive index in a direction perpendicular to the slow axis and the fast axis of the uniaxially elongated film.

13. The liquid crystal display of claim 11 , wherein the styrene derivative comprises a substituted or unsubstituted C1 to C20 alkyl styrene, a substituted or unsubstituted C6 to C20 aryl styrene, a halogenated styrene, a substituted or unsubstituted C1 to C5 alkoxy styrene, a substituted or unsubstituted nitro styrene, a substituted or unsubstituted amino styrene, a substituted or unsubstituted carboxyl styrene, a substituted or unsubstituted C1 to C6 carbonyl styrene or a combination thereof.

14. The liquid crystal display of claim 11 , wherein the polymer further comprises a structural unit derived from maleimide, maleic anhydride, (meth)acrylonitrile, acrylonitrile, a derivative thereof, or a combination thereof.

15. The liquid crystal display of claim 14 , wherein the polymer further comprises a structural unit derived from a (meth)acrylate or a derivative thereof.

16. The liquid crystal display of claim 11 , wherein the polymer is a terpolymer consisting essentially of

a structural unit derived from styrene or a styrene derivative,

a structural unit derived from maleimide, maleic anhydride, (meth)acrylonitrile, acrylonitrile, or a derivative thereof, and

a structural unit derived from (meth)acrylate or a derivative thereof.

17. The liquid crystal display of claim 11 , wherein the polymer has a glass transition temperature of about 110° C. to about 150° C.

18. The liquid crystal display of claim 11 , in-plane retardation (R o1 ) of the uniaxially elongated film at 450 nm, 550 nm, and 650 nm wavelengths satisfies Relationship Equation 8 or Relationship Equation 9:

R o1 (450 nm)> R o1 (550 nm)≥ R o1 (650 nm)  Relationship Equation 8

R o1 (450 nm)≥ R o1 (550 nm)> R o1 (650 nm)  Relationship Equation 9

wherein, in Relationship Equations 8 and 9,

R o1 (450 nm) is in-plane retardation of the uniaxially elongated film at a 450 nm wavelength,

R o1 (550 nm) is in-plane retardation of the uniaxially elongated film at a 550 nm wavelength, and

R o1 (650 nm) is in-plane retardation of the uniaxially elongated film at a 650 nm wavelength.

19. The liquid crystal display of claim 11 , further comprising a second polarizer interposed between the light source and the liquid crystal display panel.

20. The liquid crystal display of claim 11 , wherein the liquid crystal display panel comprises:

a pair of display panels facing each other, and

a liquid crystal layer disposed between the pair of display panels and comprising liquid crystals rotated in an in-plane direction of the display panels when in the presence of an electric field.