Polarizing plate protective cellulose triacetate film

Details Polarizing plate protective cellulose triacetate film Polarizing plate protective cellulose triacetate film

2000-02-29

2001-11-20

Brunsman, David (Department: 1755)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbohydrates or derivatives

C536S080000, C106S168010, C106S171100, C428S001400, C428S532000, C349S096000

Reexamination Certificate

active

06320042

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a protective film for a polarizing plate, which is employed for liquid crystal display and the like, and particularly to a cellulose triacetate film which is suitable for such a protective film.
BACKGROUND OF THE INVENTION
Cellulose triacetate exhibits less double refraction. Due to its appropriate double refraction, said cellulose triacetate has frequently been employed for production of a protective film which is used for the polarizing plate of liquid crystal displays.
Commonly, the polarizing plate has such a structure that a polarizing film comprised of a polyvinyl alcohol film and the like, in which iodine or dyes are absorbed and oriented, is laminated on both sides with transparent resin layers. Frequently employed as said transparent resin layer is a protective film comprised of cellulose triacetate film.
In recent years, development of liquid crystal displays, to achieve a large-sized image screen as well as high image quality, has increasingly been made to produce monitors which is used in lieu of the conventional CRT. In conjunction with this, requirements for a protective film for the polarizing plate for a liquid crystal display have become more stringent. Specifically, it is strongly desired to overcome problems with the surface quality as well as the optical isotropy caused by the surface roughness of the protective film. Further, it is or also desired to improve the machine adaptability of the film, specifically the cutting properties when during production, the film is cut into the desired shape. Still further, it is strongly demanded to minimize foreign particles which are called glittering point of foreign particles observed under the arrangement of polarizing plates at the right angle.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problem of fluctuation. Another object of the present invention is to improve the machine adaptability of said film, specifically the cutting properties of said film when during production, said film is cut into a desired shape. Still another object of the present invention is to minimize foreign particles which are called glittering point of foreign particles observed under the arrangement of polarizing plates at the right angle.
The present invention is described.
A protective film for a polarizing plate comprising cellulose ester film wherein the cellulose ester film comprises cellulose ester having a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.0 to 5.0.
1. A protective film for a polarizing plate comprising cellulose ester having a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.0 to 5.0.
2. The protective film wherein the cellulose ester is cellulose triacetate.
3. The protective film wherein the cellulose ester is prepared by employing cotton liter as the raw material and has a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.4 to 4.5.
4. The protective film wherein the cellulose ester is prepared by employing wood pulp as the raw material and has a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.5 to 5.0.
5. The protective film wherein the cellulose ester has a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.3 to 4.5.
6. The protective film wherein the cellulose ester has a degree of polymerization of 230 to 300.
7. The protective film wherein the cellulose triacetate is prepared by employing cotton linter as the raw material and has a degree of polymerization of 250 to 300.
8. The protective film wherein the cellulose triacetate is prepared by employing wood pulp as the raw material and has a degree of polymerization of 230 to 280.
9. The protective film wherein the content of Fe component in the protective film is not more than 1 ppm.
10. The protective film wherein the content of Ca component in the protective film is not more than 60 ppm.
11. The protective film wherein the content of Ca component in the protective film is not more than 30 ppm.
12. The protective film wherein the content of Mg component in the protective film is 15 to 70 ppm.
13. The protective film wherein the cellulose ester has a 6 percent viscosity of 100 to 250 cp.
14. The protective film wherein absolute retardation value in plane (Ro) of the protective film is not more than 30 nm.
15. The protective film wherein the cellulose ester is a cellulose triacetate having degree of acetylation from 59 percent to 62.5 percent.
16. The protective film wherein the protective film satisfies condition:
R
0
≦1/(−4.1×10
−4
Z
2
+b×Z−
0,015)
wherein R
0
represents the retardation within the surface in nm, Z represents the axis dislocation angle in degree of the protective film for a polarizing plate, b is a value selected from a group consisting of 0.044, 0.06, 0.1, 0.2 and 0.3.
17. The protective film wherein number of glittering points having a diameter of at least 0.01 mm on the polarizing plates is not more than 100/cm
2
, which is counted by that two polarizing plates are arranged in cross Nicol, and the protective film is placed between them and other surface of the polarizing plates are irradiated with light.
18. A polarizing plate comprising a first protective film, a polarizer and a second protective film wherein at least one of the first protective film and the second protective film comprises cellulose ester having a value of weight average molecular weight Mw
umber average molecular weight Mn of 3.0 to 5.0.


REFERENCES:
patent: 5434707 (1995-07-01), Dalzell et al.
patent: 5705632 (1998-01-01), Shimoda et al.
patent: 5753140 (1998-05-01), Shigemura
patent: 5962677 (1999-10-01), Murakami et al.
patent: 0 761 788 A1 (1997-03-01), None
Patent Abstracts of Japan, vol. 015, No. 430, Oct. 31, 1991 of JP 03 177801 A, 1(Aug. 1991).

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