Protective film for a polarizer, a polarizing plate comprising the same, and a display device with the polarizing plate
View Patent ↗Disclosed are a protective film for a polarizer with superior optical and mechanical properties, a polarizing plate including the same and a display device including the same.
1. A protective film for a polarizer, the protective film comprising polyethylene terephthalate (PET),
wherein the protective film satisfies the in-plane phase difference and phase difference in the thickness direction conditions of (1) and (2) at a wavelength of 550 nm:
(1) 10 nm≤in-plane phase difference (R o )≤350 nm
(2) 16,000 nm≥phase difference in thickness direction (R th )≥6,000 nm,
the protective film experiences change in the phase difference in the thickness direction with respect to the width change within the effective width (|ΔR th |/|Δx|) of less than 1.5 nm/mm,
the protective film experiences variation in the phase difference in the thickness direction within the effective width (R th,max −R th,min ) of 1,500 nm/m or less, and
the protective film has a degree of crystallization (X c ) of 35-55%.
2. The protective film for a polarizer according to claim 1 , which has a phase difference in the thickness direction (R th ) at the width center of 6,800 nm or more.
3. The protective film for a polarizer according to claim 1 , which has a ratio (R th /R o ) of the phase difference in the thickness direction (R th ) with respect to the in-plane phase difference (R o ) at the width center of 60 or larger and 1,600 or smaller.
4. The protective film for a polarizer according to claim 1 , which has an in-plane phase difference (R o ) at the width center of 200 nm or less.
5. The protective film for a polarizer according to claim 1 , which has an in-plane phase difference (R o ) within ±500 mm from the width center along the width direction of 250 nm or less.
6. The protective film for a polarizer according to claim 1 , which has an in-plane phase difference (R o ) within ±1000 mm from the width center along the width direction of 300 nm or less.
7. The protective film for a polarizer according to claim 1 , which experiences variation in the in-plane phase difference (R o,max −R o,min ) within the effective width of 250 nm/m or less.
8. The protective film for a polarizer according to claim 1 , which experiences change in the in-plane phase difference with respect to the width change (|ΔR o |/|Δx|) within the effective width of less than 0.3 nm/mm.
9. The protective film for a polarizer according to claim 1 , which has a stretching ratio in the length direction (MD) of 2.8-3.5 times and a stretching ratio in the width direction (TD) of 2.9-3.7 times.
10. The protective film for a polarizer according to claim 1 , which has a ratio (MD/TD) of a stretching ratio in the length direction (MD) with respect to a stretching ratio in the width direction (TD) of 0.9-1.1.
11. The protective film for a polarizer according to claim 1 , which has a thickness of 20-60 μm.
12. The protective film for a polarizer according to claim 1 , which is stretched in the length direction and the width direction and then heat-treated at 160-230° C.
13. A polarizing plate comprising:
a polarizer; and
the protective film for a polarizer according to claim 1 , the protective film being adjacent to at least one of the upper side and the lower side of the polarizer.
14. A display device comprising:
a display panel; and
the polarizing plate according to claim 13 , the polarizing plate being disposed on at least one of the upper side and the lower side of the display panel.
15. The protective film for a polarizer according to claim 1 , wherein the degree of crystallization (X c ) is calculated by:
X c [%]= d c ( d−d a )/ d ( d c −d a )*100
where d c is density (g/cm 3 ) of crystalline region, d a is density (g/cm 3 ) of amorphous region, and d is density (g/cm 3 ) at measured site.
16. The protective film for a polarizer according to claim 15 , wherein d c is about 1.455 g/cm 3 and d a is about 1.335 g/cm 3 .
17. A polarizing plate comprising:
a polarizer;
a first protective film for a polarizer according to claim 1 , the first protective film being adjacent to the upper side of the polarizer; and
a second protective film for a polarizer according to claim 1 , the second protective film being adjacent to the lower side of the polarizer.
18. A display device comprising:
a display panel;
a first polarizing plate according to claim 17 , the first polarizing plate being disposed on the upper side of the display panel; and
a second polarizing plate according to claim 17 , the second polarizing plate being disposed on the lower side of the display panel.
19. A display device comprising:
a display panel; and
the polarizing plate according to claim 17 , the polarizing plate being disposed on at least one of the upper side and the lower side of the display panel.