Production method of optical film
The present application relates to an optical film and a method for producing a polarizing plate. The present application can provide an optical film satisfying optical and mechanical durability required in a polarizing plate effectively and capable of forming a polarizing plate without causing bending when applied to a display device, and a method for producing a polarizing plate to which the optical film is applied. The present application can provide an optical film capable of realizing the required optical and mechanical durability without causing bending even in a polarizing plate applied to a thin display device and/or a thin polarizing plate, and a method for producing a polarizing plate to which the optical film is applied.
1. A method for producing an optical film, comprising:
treating a polymer film with steam, of which a temperature is from 50° C. to 150° C., for from 10 seconds to 1 hour before a heat-treatment,
forming an optical layer on a surface of the polymer film after the steam treatment,
subjecting the polymer film, on the surface of which the optical layer is formed, to a heat-treatment to adjust an asymmetry property of the polymer film,
wherein the heat-treatment is performed for from 10 seconds to 1,000 seconds,
wherein a shrinkage force of the polymer film before the heat-treatment along a first direction is from 5.5N to 15N,
wherein a ratio (S1/S2) of the shrinkage force (S1) of the polymer film before the heat-treatment along the first direction relative to a shrinkage force (S2) of the polymer film before the heat-treatment along a second direction perpendicular to the first direction is 10 or more,
wherein the heat-treatment is performed at a temperature satisfying Equation 2 below
( Tg− 60° ° C.)≤ T ≤( Tg+ 50° ° C.) [Equation 2]
wherein, Tg is a glass transition temperature of the polymer film, T is a temperature of the heat-treatment, and each of units of the glass transition temperature and the temperature of the heat-treatment is ° C.
2. The method for producing an optical film according to claim 1 , wherein the optical layer comprises a hard-coating layer, an antireflection layer, an antiglare layer or an antistatic layer.
3. The method for producing an optical film according to claim 1 ,
wherein, in the step of treating a polymer film with steam, positioning the polymer film on a flat surface, or positioning the polymer film in a direction parallel to a gravity direction, or positioning the polymer film at another position where a flatness may be secured and then exposing all or part of the polymer film to steam.
4. The method for producing an optical film according to claim 1 , wherein the shrinkage force (S2) of the polymer film before the heat-treatment along a second direction perpendicular to the first direction is from 0.01N to 2N.
5. The method for producing an optical film according to claim 1 , wherein the heat treatment is performed to adjust the asymmetry property of the polymer film, so that a ratio (SB/SA) of a shrinkage force (SB) of the polymer film before the heat-treatment along the first direction relative to a shrinkage force (SA) of the polymer film after the heat-treatment along the first direction is more than 1.
6. The method for producing an optical film according to claim 1 , wherein the heat treatment is performed to adjust the asymmetry property of the polymer film, so that a shrinkage force of the polymer film after the heat-treatment along a first direction is from 5N to 10N.
7. The method for producing an optical film according to claim 6 , wherein the heat treatment is performed to adjust the asymmetry property of the polymer film, so that a ratio (S1/S2) of the shrinkage force (S1) of the polymer film after the heat-treatment along the first direction relative to a shrinkage force (S2) of the polymer film after the heat-treatment along a second direction perpendicular to the first direction is 13 or more.
8. A method for producing a polarizing plate, comprising:
producing the optical film according to the method of claim 1 ;
attaching the optical film and a polarizing film having a light absorption axis formed in one in-plane direction.
9. The method for producing a polarizing plate according to claim 8 , wherein the optical film is attached to the polarizing film so that a ratio (S P /S V ) of a shrinkage force (S P ) of the polarizing plate along the light absorption axis of the polarizing film relative to a shrinkage force (S V ) of the polarizing plate along a direction perpendicular to the light absorption axis direction is from 0.7 to 1.5.
10. The method for producing a polarizing plate according to claim 8 , wherein the optical film is attached to the polarizing film so that a shrinkage force of the polarizing plate along a direction parallel to the light absorption axis of the polarizing film is from 6.5N to 15N.
11. The method for producing a polarizing plate according to claim 8 , wherein the optical film is attached to the polarizing film so that a shrinkage force of the polarizing plate along a direction perpendicular to the light absorption axis is from 6.0N to 15N.
12. The method for producing a polarizing plate according to claim 8 , wherein a shrinkage force of the optical film along a first direction of the polymer film is from 5N to 10N and wherein the polarizing film and the optical film are attached so that the first direction and the light absorption axis of the polarizing film are perpendicular to each other.
13. The method for producing a polarizing plate according to claim 12 , wherein a ratio (S1/S2) of a shrinkage force (S1) along a first direction of the polymer film relative to a shrinkage force (S2) along a second direction perpendicular to the first direction is 13 or more.
14. The method for producing a polarizing plate according to claim 8 , wherein a shrinkage force of the polarizing film along a direction parallel to the light absorption axis is from 0.1 to 15N.
15. The method for producing a polarizing plate according to claim 8 , wherein the smallest angle among angles formed by one side of the polarizing film and the light absorption axis of the polarizing film is from 0 to 10 degrees or from 80 to 100 degrees.
16. The method for producing a polarizing plate according to claim 8 , wherein the smallest angle among angles formed by one side of the polarizing film and the light absorption axis of the polarizing film is from 35 to 55 degrees or from of 125 to 145 degrees.