PRODUCTION METHOD OF OPTICAL FILM

Abstract

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.

Claims

1. A method for producing an optical film, comprising: subjecting a polymer film, on a surface of which an optical layer is formed, to a heat-treatment.

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, further comprising: treating the polymer film with steam, of which a temperature is from 50° C. to 150° C., for from 10 seconds to 1 hour before the heat-treatment and forming the optical layer on the surface of the polymer film after the steam treatment.

4. The method for producing an optical film according to claim 1, wherein a shrinkage force of the polymer film before the heat-treatment along a first direction is from 5.5N to 15N.

5. The method for producing an optical film according to claim 4, 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.

6. The method for producing an optical film according to claim 5, 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.

7. The method for producing an optical film according to claim 4, wherein 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.

8. The method for producing an optical film according to claim 1, wherein a shrinkage force of the polymer film after the heat-treatment along a first direction is from 5N to 10N.

9. The method for producing an optical film according to claim 8, wherein 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.

10. The method for producing an optical film according to claim 1, 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.

11. The method for producing an optical film according to claim 1, wherein the heat-treatment is performed for from 10 seconds to 1,000 seconds.

12. A method for producing a polarizing plate, comprising: attaching the optical film produced by the method of claim 1 and a polarizing film having a light absorption axis formed in one in-plane direction.

13. The method for producing a polarizing plate according to claim 12, wherein the optical film is attached to the polarizing film so that a ratio (S.sub.P/S.sub.V) of a shrinkage force (S.sub.P) of the polarizing plate along the light absorption axis of the polarizing film relative to a shrinkage force (S.sub.V) of the polarizing plate along a direction perpendicular to the light absorption axis direction is from 0.7 to 1.5.

14. The method for producing a polarizing plate according to claim 12, 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.

15. The method for producing a polarizing plate according to claim 12, 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.

16. The method for producing a polarizing plate according to claim 12, 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.

17. The method for producing a polarizing plate according to claim 16, 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.

18. The method for producing a polarizing plate according to claim 12, wherein a shrinkage force of the polarizing film along a direction parallel to the light absorption axis is from 0.1 to 15N.

19. The method for producing a polarizing plate according to claim 12, 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.

20. The method for producing a polarizing plate according to claim 12, 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.

Description

MODE FOR INVENTION

[0142] Hereinafter, the present application will be described in detail through Examples, but the scope of the present application is not limited by the following Examples.

[0143] The term MD referred to herein means the machine direction of the stretched film unless otherwise specified, and the TD means the transverse direction of the stretched film unless otherwise specified.

[0144] 1. Measurement of Shrinkage Force

[0145] The shrinkage force of the polarizing film, the optical film, the polymer film or the polarizing plate mentioned herein was measured by the following method using a DMA instrument from TA. A specimen was produced to have a width of about 5.3 mm and a length of about 15 mm, and both ends of the specimen in the longitudinal direction were fixed to the clamp of the measuring instrument and then the contractile force was measured. Here, the length 15 mm of the specimen is the length excluding the portion to be fixed to the clamp. After fixing the specimen to the clamp as above, the specimen was pulled and fixed to maintain strain 0.1% in the state of preload 0N, and then the shrinkage force applied when the strain 0.1% was kept at the elevated temperature of the following temperature condition was measured. As the results of the shrinkage force, values were measured 120 minutes after 80° C. stabilization of the following temperature condition. The shrinkage force was measured at relative humidity maintained at approximately 48% or so.

[0146] <Measurement Temperature Condition and Time>

[0147] Temperature: 25° C. start.fwdarw.75° C. after 3 minutes.fwdarw.80° C. stabilization (no acceleration condition) after 7 minutes

[0148] Measurement time: 120 minutes

Production Example 1. Production of PVA-Based Polarizing Film (A)

[0149] After a PVA (poly(vinyl alcohol)) film (Nippon Synthetic Chemical Co., Ltd., polymerization degree of about 3,000 or so) with a thickness of about 45 μm or so used in manufacturing a polarizing film was swelled in a pure solution at a temperature ranging from about 20° C. to 30° C., a dyeing process was performed for about 10 seconds to 30 seconds or so in an iodine solution at a temperature of 30° C. to 40° C. or so. Thereafter, a cleaning process was performed for about 20 seconds with a boric acid solution (concentration: about 2 wt %) at a temperature of about 40° C. or so, and then the film was stretched about 6 times in a boric acid solution at a temperature of 50° C. to 60° C. and a concentration of about 4.0 wt %, and after stretching, a complementary color process was performed in a KI solution at a concentration of about 2 to 4 wt % and dried to produce a polarizing film having a thickness of about 17 μm. As a result of measuring the shrinkage force (hereinafter, MD shrinkage force) of the manufactured PVA-based polarizing film in the light absorption axis direction, it was approximately 8 to 10 N or so.

Example 1

[0150] Heat Treatment of Polymer Film

[0151] For a PET (polyethylene terephthalate) polymer film (SRF film, thickness: 80 μm, manufacturer: Toyobo, product name: TA055, glass transition temperature: 80° C., shrinkage force in TD direction before heat-treatment: about 7.53 N, shrinkage direction in MD direction: in a range of about 0.1 to 0.5N), heat-treatment was performed in the following manner. First, a flattening process was performed by exposing the SRF film to steam having a temperature of approximately 80° C. to 100° C. or so for a time (about 20 seconds to 60 seconds) to improve flatness. Subsequently, an antiglare layer (AG layer) as an optical layer was formed on one side of the SRF film. The antiglare layer was formed by using a curable composition, in which organic particles (manufacturer: Sekisui, average diameter: 2 μm) having a refractive index in a level of about 1.555 (reference wavelength: 550 nm) and a hydroxyl group on the surface were mixed to a urethane acrylate binder (Kyoeisha, PE3A) in a weight ratio of 20:1 (urethane acrylate binder: organic particles). The binder was crosslinked and polymerized by coating the curable composition on one side of the SRF film and irradiating it with ultraviolet rays in a light quantity of 150 mJ/cm.sup.2, thereby forming an optical layer, where the antiglare layer thus formed had a thickness of approximately 4 μm or so.

[0152] Subsequently, the SRF film on which the optical layer was formed was maintained at a temperature of approximately 40° C. or so for 30 seconds to 90 seconds to perform heat-treatment. After the heat-treatment process, the shrinkage force of the SRF film in the TD (transverse direction) direction was about 7.18N or so, and the shrinkage force in the MD direction was in a level of about 0.2 to 0.35N or so.

[0153] Manufacture of Polarizing Plate

[0154] The heat-treated SRF film was applied as a protective film to produce a polarizing plate in the following manner. First, the SRF film was attached to one side of the PVA polarizing film (MD shrinkage: 8 to 10 N, thickness: 17 μm) produced in Production Example 1 using an epoxy-based ultraviolet curable adhesive (thickness: 2 μm to 3 μm). Upon the attachment, they were attached such that the TD (transverse direction) direction of the SRF film and the MD direction (absorption axis direction) of the PVA polarizing film were approximately perpendicular to each other, where the surface on which the optical layer was not formed was attached to the PVA polarizing film. Subsequently, an epoxy-based hard coating layer was formed to a thickness of about 5 to 7 μm or so on the surface of the PVA polarizing film to which the SRF film was not attached. Thereafter, an acrylic pressure-sensitive adhesive layer having a thickness of about 25 μm was formed on the lower part of the hard coating layer to produce a polarizing plate. The shrinkage force of the entire polarizing plate as manufactured above along the MD direction of the polarizing film was approximately 8N, and the shrinkage force along the TD direction of the polarizing film was approximately 9.5N or so. As a result of obtaining the A value of Equation 1 above on the manufactured polarizing plate, it was approximately 3.94 Nmm to 6.41 Nmm or so. The lower limit of the A value range was obtained by applying 0.78 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 7.18N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1. In addition, the upper limit of the A value range was obtained by applying 1.27 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 7.18N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

Example 2

[0155] Heat treatment was performed by maintaining the SRF film subjected to the steam treatment and the optical layer formation treatment in the same manner as in Example 1 at a temperature of approximately 60° C. or so for 30 seconds to 90 seconds. After the heat-treatment process, the shrinkage force of the SRF film in the TD (transverse direction) direction was about 6.86N or so, and the shrinkage force in the MD direction was in a level of about 0.2 to 0.35N or so. The polarizing plate was produced in the same manner as in Example 1 using the SRF film. The shrinkage force of the produced polarizing plate along the MD direction of the polarizing film was approximately 8N, and the shrinkage force along the TD direction of the polarizing film was approximately 8.18N or so. As a result of obtaining the A value of Equation 1 above on the manufactured polarizing plate, it was approximately 4.25 Nmm to 5.78 Nmm or so. The lower limit of the A value range was obtained by applying 0.86 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 6.86N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1. In addition, the upper limit of the A value range was obtained by applying 1.17 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 6.86N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

Example 3

[0156] Heat treatment was performed by maintaining the SRF film subjected to the steam treatment and the optical layer formation treatment in the same manner as in Example 1 at a temperature of approximately 80° C. for about 30 seconds to 90 seconds. After the heat-treatment process, the shrinkage force of the SRF film in the TD (transverse direction) direction was about 6.08N or so, and the shrinkage force in the MD direction was in a level of about 0.2 to 0.35N or so. The polarizing plate was produced in the same manner as in Example 1 using the SRF film. The shrinkage force of the produced polarizing plate along the MD direction of the polarizing film was approximately 8N, and the shrinkage force along the TD direction of the polarizing film was approximately 7.28N or so.

[0157] As a result of obtaining the A value of Equation 1 above on the manufactured polarizing plate, it was approximately 3 Nmm to 7.25 Nmm or so. The lower limit of the A value range was obtained by applying 0.64 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 6.08N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1. In addition, the upper limit of the A value range was obtained by applying 1.55 as a, applying 0.25 mm (=applied LCD panel thickness (mm)/2) as b, applying about 9 N as S.sub.PVA, applying 6.08N as S.sub.Pro, applying 0.0395 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)/2) as T1, and applying 0.0905 mm (=pressure-sensitive adhesive thickness (25 μm)+hard coating layer thickness (6 μm)+polarizing film thickness (17 μm)+adhesive layer thickness (2.5 μm)+protective film thickness (80 μm)/2) as T2, in Equation 1.

[0158] Bending Characteristic Evaluation

[0159] The polarizing plates manufactured in Examples were each attached to the upper and lower surfaces of a general 32-inch LCD (liquid crystal display) panel (thickness: about 500 μm) through the pressure-sensitive adhesive layers of the polarizing plates, respectively. Subsequently, the flatness (initial flatness) of the LCD panel was measured. Thereafter, the panel was put into a chamber at a temperature of 60° C. for 72 hours, and then taken out, and the panel variations after 2 hours and 24 hours were measured and summarized in Table 1 below. In Table 1 below, the term flatness is a difference between a portion that is bent most toward the upper polarizing plate and a portion that is bent most toward the lower polarizing plate in the liquid crystal panel, where this flatness can be confirmed using a known three-dimensional measuring instrument (Dukin Co., Ltd.).

TABLE-US-00001 TABLE 1 Initial After 2 hours After 6 hours Flatness Flatness Variation Flatness Variation Example 1 2.2 2 −0.2 1.8 −0.4 Example 2 2.5 1.9 −0.6 1.6 −0.9 Example 3 1.7 1.6 −0.1 1.4 −0.3