Protective film for a polarizer, a polarizing plate comprising the same, and a display device with the polarizing plate

• US 10,088,606 B2
• Filed: 06/19/2017
• Issued: 10/02/2018
• Est. Priority Date: 06/20/2016
• Status: Active Grant

• Current Assignee: SK Microworks Company Limited
• Original Assignee: SKC Company Limited
• Inventors: Lee, Se Chul, Heo, Young Min, Jeong, Da Woo, Kang, Ho Chun, Lee, Jang Won
• Primary Examiner(s): Cherry, Euncha
• Application Number:
  US15/626,240
• Publication Number:
  US 20170363778A1
• Time in Patent Office: 470 Days
• Field of Search: 359507
• CPC Class Codes: C08L 67/02 Polyesters derived from dicarboxylic acids and dihydroxy compounds C08L67/06 takes precedence
• CPC Class Codes: G02B 1/04 made of organic materials, e.g. plastics G02B1/08 takes precedence
• CPC Class Codes: G02B 1/14 Protective coatings, e.g. hard coatings
• CPC Class Codes: G02B 5/3025 Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state G02B5/3008, G02B5/3016 take precedence
• CPC Class Codes: G02F 1/133502 Antiglare, refractive index matching layers
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 2201/501 Blocking layers, e.g. against migration of ions
• CPC Class Codes: H10K 50/86 Arrangements for improving contrast, e.g. preventing reflection of ambient light
• CPC Class Codes: H10K 59/8791 Arrangements for improving contrast, e.g. preventing reflection of ambient light

Abstract

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.

Claims

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 in-plane phase difference with respect to the width change within the effective width (|Δ

R_o|/|Δ

x|) of less than 5 nm/cm,

the protective film experiences variation in the in-plane phase difference within the effective width (R_o,max−

R_o,min) of 250 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 an in-plane phase difference (R_o) at the width center of 200 nm or less.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. The protective film for a polarizer according to claim 1, which has a thickness of 20-60 μ

m.

9. 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.

10. 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.

11. A display device comprising:

a display panel; and

the polarizing plate according to claim 10, the polarizing plate being disposed on at least one of the upper side and the lower side of the display panel.

12. 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/cm³) of crystalline region, d_a is density (g/cm³) of amorphous region, and d is density (g/cm³) at measured site.

13. The protective film for a polarizer according to claim 12, wherein d_c is about 1.455 g/cm³ and d_a is about 1.335 g/cm³.

14. 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.

15. A display device comprising:

a display panel;

a first polarizing plate according to claim 14, the first polarizing plate being disposed on the upper side of the display panel; and

a second polarizing plate according to claim 14, the second polarizing plate being disposed on the lower side of the display panel.

16. A display device comprising:

a display panel; and

the polarizing plate according to claim 14, the polarizing plate being disposed on at least one of the upper side and the lower side of the display panel.