Polarizing plate having specified ratio of polarizing film shrinkage force to protective film shrinkage force

Abstract

The present application relates to a polarizing plate having a polarizing film in which a light absorption axis is formed in one in-plane direction; a protective film formed on one side of the polarizing film; and a pressure-sensitive adhesive layer formed on the other side of the polarizing film, where the total thickness is 200 μm or less, and a ratio of (S.sub.Pro/S.sub.PVA) of a shrinkage force (S.sub.PVA) of the polarizing film in the in-plane direction parallel to the light absorption axis direction and a shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction is in a range of 0.1 to 5. The present application can provide a polarizing plate which does not cause cracks or the like while having a thin thickness, does not induce warping or twisting in itself and does not induce the above problems even when applied to a display device such as an LCD or OLED.

Claims

1. A polarizing plate comprising a polarizing film in which a light absorption axis is formed in one in-plane direction; a protective film formed on one side of the polarizing film; and a pressure-sensitive adhesive layer formed on the other side of the polarizing film, wherein the total thickness is 200 μm or less, a ratio of (S.sub.Pro/S.sub.PVA) of a shrinkage force (S.sub.PVA) of the polarizing film in the in-plane direction parallel to the light absorption axis direction and a shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction is in a range of 0.1 to 5; and a ratio (S/S.sub.Pro) of the shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction of the polarizing film and the shrinkage force (S) of the protective film in the in-plane direction parallel to the light absorption axis direction of the polarizing film is in a range of 2 to 20.

2. The polarizing plate according to claim 1, wherein the ratio (S/S.sub.Pro) of the shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction of the polarizing film and the shrinkage force (S) of the protective film in the in-plane direction parallel to the light absorption axis direction of the polarizing film is in a range of 8 to 20.

3. The polarizing plate according to claim 1, wherein the shrinkage force (S.sub.PVA) of the polarizing film in the light absorption axis direction is in a range of 0.1 N to 15 N.

4. The polarizing plate according to claim 1, wherein the protective film is a polyester film.

5. The polarizing plate according to claim 1, wherein the thickness of the polarizing film is in a range of from 5 μm to 25 μm.

6. The polarizing plate according to claim 1, wherein the thickness of the protective film is in a range of 20 82 m to 250 μm.

7. The polarizing plate according to claim 1, wherein the thickness of the pressure-sensitive adhesive layer is in a range of 5 μm to 100 μm.

8. The polarizing plate according to claim 1, further comprising an adhesive layer between the protective film and the polarizing film.

9. The polarizing plate according to claim 8, wherein the adhesive layer has a thickness in a range of 2 μm to 4 μm.

10. The polarizing plate according to claim 1, further comprising a cured resin layer between the polarizing film and the pressure-sensitive adhesive layer.

11. The polarizing plate according to claim 10, wherein the cured resin layer has a thickness in a range of 4 μm to 10 μm.

12. A display device comprising the polarizing plate of claim 1.

13. A polarizing plate comprising a polarizing film in which a light absorption axis is formed in one in-plane direction; a protective film formed on one side of the polarizing film; and a pressure-sensitive adhesive layer formed on the other side of the polarizing film, wherein the total thickness is 200 μm or less, wherein a ratio of (S.sub.Pro/S.sub.PVA) of a shrinkage force (S.sub.PVA) of the polarizing film in the in-plane direction parallel to the light absorption axis direction and a shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction is in a range of 0.1 to 5, and wherein the protective film has a ratio (S/S.sub.Pro) of a shrinkage force (S.sub.Pro) of the protective film in the in-plane direction perpendicular to the light absorption axis direction of the polarizing film and a shrinkage force (S) of the protective film in the in-plane direction parallel to the light absorption axis direction of the polarizing film is in a range of 2 to 20 wherein an A value in Equation 1 is in a range of 0.01 to 26 N.Math.mm:
A=a×(S.sub.PVA×(T.sub.1+b)+S.sub.Pro×(T.sub.2+b))  [Equation 1] wherein, in Equation 1, S.sub.PVA is the shrinkage force of the polarizing film in the light absorption axis direction, S.sub.Prois a large shrinkage force among a shrinkage force of the protective film in the direction parallel to the light absorption axis direction of the polarizing film and a shrinkage force of the protective film in the direction perpendicular to the light absorption direction, T.sub.1 is a distance (unit:mm) from the lowermost portion of the pressure-sensitive adhesive layer to the center of the polarizing film, T.sub.2 is a distance (unit:mm) from the lowermost portion of the pressure-sensitive adhesive layer to the center of the protective film, a is a number within a range of 0.5 to 2, and b is a number within a range of 0.14 to 0.6.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows an exemplary polarizing plate structure of the present application.

(2) FIGS. 2 to 4 are views showing evaluation results of liquid crystal panels of Examples.

MODE FOR INVENTION

(3) Hereinafter, the present application will be specifically described by way of Examples, but the scope of the present application is not limited by the following examples.

(4) The term MD mentioned herein means the machine direction unless otherwise specified, and TD means the transverse direction unless otherwise specified.

(5) 1. Measurement of Shrinkage Force

(6) The shrinkage force of the polarizing film or protective film 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.

(7) As the results of the shrinkage force, values were measured 120 minutes after 80° C. stabilization of the following temperature condition.

(8) <Measurement Temperature Condition and Time>

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

(10) Measurement time: 120 minutes

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

(11) After a PVA (poly(vinyl alcohol)) film (Nippon Synthetic Chemical Co., Ltd., polymerization degree of about 3,000 or so) having a thickness of about 45 μm used for 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 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., 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 produced PVA-based polarizing film in the light absorption axis direction, it was about 8 to 10 N.

Production Examples 2 to 5. Preparation of Protective Film

(12) A PET (polyethylene terephthalate) film (product name: SRF Film, thickness: 80 μm, manufacturer: Toyobo) (PET film (A), glass transition temperature: about 90° C.) was prepared as a protective film to be applied to the polarizing plate. The PET film (A) was heat-treated at a temperature condition of 90° C. to 100° C. for about 30 to 40 seconds to prepare a PET film (B), and the PET film (A) was heat-treated at a temperature condition of 100° C. to 110° C. for about 30 to 40 seconds to prepare a PET film (C).

(13) The shrinkage force for each PET film was summarized in Table 1 below

(14) TABLE-US-00001 TABLE 1 MD Shrinkage force TD Shrinkage force PET(A) 0~1N 7~8N PET(B) 0~1N 5~6N PET(C) 0~1N 3~4N

Example 1

(15) A polarizing plate was produced in the following manner. First, using an epoxy-based ultraviolet curable adhesive (thickness: 2 μm to 3 μm), the PET film (A) (MD shrinkage force: 0 to 1N, TD shrinkage force: 7 to 8N, thickness: 80 μm) of Production Example was attached to one side of the PVA polarizing film (MD shrinkage force: 8 to 10 N, thickness: 17 μm) produced in Production Example 1. Upon the attachment, the TD direction of the PET film and the MD direction (absorption axis direction) of the PVA polarizing film were attached so as to be substantially perpendicular to each other. Subsequently, a hard coating layer was formed to a thickness of about 5 to 7 μm using a material containing an epoxy compound and an oxetane compound on the surface of the PVA polarizing film to which the PET 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.

(16) As a result of obtaining the A value of Equation 1 above for the produced polarizing plate, it was about 4.02 Nmm to 6.55 Nmm.

(17) The lower limit of the A value range was obtained by applying 0.78 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 7.5N as S.sub.Pro, and 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 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 T.sub.2.

(18) Furthermore, the upper limit of the range of the A value was obtained by applying 1.27 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 7.5N as S.sub.Pro, and 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 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 T.sub.2.

(19) Two polarizing plates produced in the above manner were each attached to upper and lower surfaces of a general 32 inch LCD (liquid crystal display) panel (thickness: about 500 μm) through the pressure-sensitive adhesive layer of the polarizing plate.

(20) Subsequently, after the LCD panel was introduced into a chamber at a temperature of 60° C. for 72 hours, it was taken out, and the panel change amounts at the elapsed time of 2 hours and the elapsed time of 24 hours were measured and summarized in Table 3 below and the results were described in FIG. 2 (flatness after 24 hours). The term flatness in Table 3 below is a difference between the portion of the liquid crystal panel that is most bent toward the upper polarizing plate and the portion of the liquid crystal panel that is most bent toward the lower polarizing plate, and this flatness can be confirmed using a known three-dimensional measuring machine (Dukin Co., Ltd.).

Example 2

(21) A polarizing plate was produced in the same manner as the production of the upper polarizing plate in Example 1, except that a PVA polarizing film (MD shrinkage force: 8 to 10 N, thickness: 17 μm) was used as the polarizing film and the PET film (B) (MD shrinkage force: 0 to 1N, TD shrinkage force: 5 to 6 N, thickness: 80 μm) was used as the PET film.

(22) As a result of obtaining the A value of Equation 1 above for the produced polarizing plate, it was about 3.85 Nmm to 5.23 Nmm.

(23) The lower limit of the A value range was obtained by applying 0.86 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 5.5N as S.sub.Pro, and 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 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 T.sub.2.

(24) Furthermore, the upper limit of the range of the A value was obtained by applying 1.17 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 5.5N as S.sub.Pro, and 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 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.

(25) Two polarizing plates produced in the above manner were each attached to upper and lower surfaces of a general 32 inch LCD (liquid crystal display) panel (thickness: about 500 μm) through the pressure-sensitive adhesive layer of the polarizing plate.

(26) Subsequently, after the LCD panel was introduced into a chamber at a temperature of 60° C. for 72 hours, it was taken out, and the panel change amounts at the elapsed time of 2 hours and the elapsed time of 24 hours were measured and summarized in Table 3 below and the results were described in FIG. 3 (flatness after 24 hours).

Example 3

(27) A polarizing plate was produced in the same manner as the production of the upper polarizing plate in Example 1, except that a PVA polarizing film (MD shrinkage force: 8 to 10 N, thickness: 17 μm) was used as the polarizing film and the PET film (C) (MD shrinkage force: 0 to 1N, TD shrinkage force: 3 to 4 N, thickness: 80 μm) was used as the PET film.

(28) As a result of obtaining the A value of Equation 1 above for the produced polarizing plate, it was about 2.43 Nmm to 5.89 Nmm.

(29) The lower limit of the A value range was obtained by applying 0.64 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 3.5N as S.sub.Pro, and 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 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.

(30) Furthermore, the upper limit of the range of the A value was obtained by applying 1.55 as a and 0.25 mm (=applied LCD panel thickness (mm)/2) as b in Equation 1, applying about 9 N as S.sub.PVA and 3.5N as S.sub.Pro, and 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 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.

(31) Two polarizing plates produced in the above manner were each attached to upper and lower surfaces of a general 32 inch LCD (liquid crystal display) panel (thickness: about 500 μm) through the pressure-sensitive adhesive layer of the polarizing plate.

(32) Subsequently, after the LCD panel was introduced into a chamber at a temperature of 60° C. for 72 hours, it was taken out, and the panel change amounts at the elapsed time of 2 hours and the elapsed time of 24 hours were measured and summarized in Table 3 below and the results were described in FIG. 4 (flatness after 24 hours).

(33) TABLE-US-00002 TABLE 2 At first After 2 hours After 6 hours Flatness Flatness Change amount Flatness Change amount Example 1 1.5 2.8 1.3 2.7 1.2 Example 2 2.2 2.0 0.2 1.8 0.4 Example 3 1.0 −2.7 −3.7 −2.7 −3.7 11: protective film 12: polarizing film 13: pressure-sensitive adhesive layer