Production method of polarizing plate

Abstract

The present application relates to a polymer film and a method for producing a polarizing plate. The present application can provide a polymer 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 polymer film is applied. The present application can provide a polymer 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 polymer film is applied.

Claims

1. A method for producing a polarizing plate, comprising: steaming a polyester polymer film by exposing the polymer film to steam while a temperature of the steam is in a range of 50° C. to 150° C. for 10 seconds to 1 hour, water-treating the polymer film by immersing the polymer film in water having a temperature in a range of 10° C. to 30° C. for 5 to 1000 seconds, heat-treating the polymer film, wherein the polymer film before the heat treatment has a shrinkage force in a first direction in a range of 5.5N to 15N, wherein the polymer film after the heat treatment has a shrinkage force in the first direction in a range of 5N to 10N, a ratio (S1/S2) of the shrinkage force (S1) of the polymer film after the heat treatment in the first direction to a shrinkage force (S2) in a second direction perpendicular to the first direction is 13 or more; the heat treatment is performed at a temperature satisfying Equation 2 below:
(Tg−60)° C.≤T≤(Tg+50)° C.  [Equation 2]  the Tg is a glass transition temperature of the polymer film, the T is the heat treatment temperature and the unit of the glass transition temperature and the heat treatment temperature is ° C.; attaching the heat-treated polymer film to a polarizing film having a light absorption axis formed in one direction, wherein the polymer film and the polarizing film are attached such that the first direction forms an angle in a range of 80 degrees to 100 degrees with the light absorption axis of the polarizing film, wherein a ratio (S.sub.Pro/S.sub.PVA) of a shrinkage force (S.sub.PVA) of the polarizing film in a direction parallel to the light absorption axis direction and the shrinkage force (S.sub.Pro) of the polymer film in the first direction is in a range of 0.1 to 5.5; and forming a pressure-sensitive adhesive layer on, a surface of a side opposite to a surface of the polarizing film on which the polymer film is attached and wherein thicknesses of the polarizing film, the polymer film and the, pressure-sensitive adhesive layer are adjusted so as to satisfy Equation 1 below:
0.01 to 26 N.Math.mm=a×(S.sub.PVA×(T.sub.1+b)+S.sub.Pro×(T.sub.2+b))  [Equation 1] wherein, the T1 is a distance (unit: mm) from the lowermost portion of the pressure-sensitive adhesive layer to the center of the polarizing film, the T2 is a distance (unit: mm) from the lowermost portion of the pressure-sensitive adhesive layer to the center of the polymer film, the a is a number within a range of 0.5 to 2, and the b is a number within a range of 0.14 to 0.6.

2. The method for producing a polarizing plate according to claim 1, wherein the shrinkage force (S2) of the polymer film before the heat treatment in the second direction is from 0.01N to 2N.

3. The method for producing a polarizing plate according to claim 1, wherein a ratio (SB/SA) of the shrinkage force (SB) of the polymer film before the heat treatment in the first direction relative to a shrinkage force (SA) of the polymer film after the heat treatment in the first direction is more than 1.

4. The method for producing a polarizing plate according to claim 1, wherein the heat treatment is performed for 10 to 1,000 seconds.

5. The method for producing a polarizing plate according to claim 1, wherein the polymer film is attached to the polarizing film so that a ratio (SP/SV) of a shrinkage force (SP) of the polarizing plate in the light absorption axis direction to a shrinkage force (SV) of the polarizing plate in a direction perpendicular to the light absorption axis direction is in a range of 0.78 to 1.5.

6. The method for producing a polarizing plate according to claim 5, wherein the polymer film is attached to the polarizing film so that a shrinkage force of the polarizing plate in a direction parallel to the light absorption axis of the polarizing film is in a range of 6.5N to 15N.

7. The method for producing a polarizing plate according to claim 5, wherein the polymer film is attached to the polarizing film so that a shrinkage force of the polarizing plate in a direction perpendicular to the light absorption axis is in a range of 6.0N to 15N.

8. The method for producing a polarizing plate according to claim 1, wherein a shrinkage force of the polarizing film in a direction parallel to the light absorption axis is in a range of 0.1 to 15N.

9. The method for producing a polarizing plate according to claim 1, wherein an 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 of 80 to 100 degrees.

10. The method for producing a polarizing plate according to claim 1, wherein an 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 125 to 145 degrees.

Description

PRODUCTION EXAMPLE 1

Production of PVA-Based Polarizing Film (A)

(1) 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

(2) Heat Treatment of Polymer Film

(3) 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), a water treatment process was first performed and then heat treatment was performed. First, the water treatment process was performed by immersing the SRF film in water maintained at approximately 20° C. to 30° C. so that the whole was submerged therein, and then maintaining it for about 10 seconds to 20 seconds. Subsequently, the heat treatment was performed by maintaining the SRF film at a temperature of approximately 50° C. for about 10 seconds to 60 seconds or so. After the heat treatment process, the shrinkage force of the SRF film in the TD (transverse direction) direction was about 7N or so, and the shrinkage force in the MD direction was in a level of about 0.2 to 0.35N or so.

(4) Manufacture of Polarizing Plate

(5) 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. 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.

(6) The shrinkage force of the manufactured 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 9.0N or so.

(7) As a result of obtaining the A value of Equation 1 above on the manufactured polarizing plate, it was approximately 3.89 Nmm to 6.34 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 7N 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 7N 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

(8) Heat treatment was performed by maintaining the SRF film subjected to the water treatment in the same manner as in Example 1 at a temperature of approximately 100° C. or so for 10 seconds to 60 seconds or so. After the heat treatment process, the shrinkage force of the SRF film in the TD (transverse direction) direction was about 6.6N 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 8.6N or so. As a result of obtaining the A value of Equation 1 above on the manufactured polarizing plate, it was approximately 4.17 Nmm to 5.68 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 6.6N 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 6.6N 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.

COMPARATIVE EXAMPLE 1

(9) A polarizing plate was produced in the same manner as in Example 1, except that the heat treatment was not performed on the SRF film. The shrinkage force of the manufactured 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 10.4N or so.

(10) Bending Characteristic Evaluation

(11) The polarizing plates manufactured in Examples and Comparative Example 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.).

(12) TABLE-US-00001 TABLE 1 Initial After 2 hours After 6 hours Flatness Flatness Variation Flatness Variation Example 1 1.9 2.8 0.9 2.6 0.7 Example 2 1.4 2.6 1.2 2.4 1 Comparative 2.3 3.2 0.9 3.1 0.8 Example 1