Optical film, polarizing plate and liquid crystal display device

Abstract

An optical film, which has a photoelastic coefficient in a longitudinal direction and a photoelastic coefficient in a direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two photoelastic coefficients by greater one is 0.8 or below; an optical film, which has a value of 1.2 or above obtained by dividing greater one of a velocity of sound in a longitudinal direction and a velocity of sound in a direction approximately orthogonal to the longitudinal direction by smaller one; and an optical film, which has a coefficient of linear thermal expansion in a longitudinal direction and a coefficient of linear thermal expansion in a width direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two coefficients of linear thermal expansion by greater one is from 0.1 to 0.5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a diagrammatic sketch for explaining a configuration example of a VA-mode liquid crystal display device currently in use;

FIG. 2 illustrates a diagrammatic sketch for explaining a configuration example of a VA-mode liquid crystal display device currently in use;

FIG. 3 illustrates a diagrammatic sketch for explaining a configuration example of a liquid crystal display device according to an aspect of the invention;

FIG. 4 illustrates a graph showing optical characteristics of an exemplary example of an optical compensation film used in the invention;

FIG. 5 illustrates a schematic diagram of a Poincaré sphere used for illustrating a change in polarized state of light entering into a liquid crystal display device according to an aspect of the invention;

FIG. 6 illustrates a schematic diagram of a Poincaré sphere used for illustrating a change in polarized state of light entering into an example of a liquid crystal display device currently in use;

FIG. 7 illustrates a diagram showing schematically another exemplary example of the cross-section structure of a polarizing plate according to an aspect of the invention; and

FIG. 8 illustrates a diagram showing a configuration example of a liquid crystal display device according to an aspect of the invention,

wherein 70 denotes polarizing plate; 71 denotes polarizer; 72 and 73 denote protective films; 81 denotes functional film; 101 denotes polarizing film; 102 denotes absorption axis; 103a denotes protective film; 104a denotes in-plane slow axis; 105 denotes optical compensation film; 105a denotes in-plane slow axis; 106 denotes substrate; 107 denotes liquid crystal molecule; 108 denotes substrate; 109 denotes optical compensation film; 109a denotes in-plane slow axis; 203a denotes protective film; 204a denotes in-plane slow axis; 201 denotes polarizing film; and 202 denotes absorption axis.

Claims

1. An optical film, which has a photoelastic coefficient in a longitudinal direction of the optical film and a photoelastic coefficient in a direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two photoelastic coefficients by greater one of the two photoelastic coefficients is 0.8 or below.

2. The optical film according to claim 1, wherein values of in-plane retardation Re and thickness-direction retardation Rth at wavelengths 450 nm, 550 nm and 650 nm satisfy the following relations (I) to (III): 0.4<{(Re(450)/Rth(450))/(Re(550)/Rth(550))}<0.95 and1.05<{(Re(650)/Rth(650))/(Re(550)/Rth(550))}<1.9  Relation (I)0.1<(Re(450)/Re(550))<0.95  Relation (II)1.03<(Re(650)/Re(550))<1.93  Relation (III)wherein Re(λ) represents an in-plane retardation Re value, expressed in the unit nm, at a wavelength λ nm; andRth(λ) represents a thickness-direction retardation Rth value, expressed in the unit nm, at a wavelength λ nm.

3. A method of manufacturing an optical film, which comprises: casting a dope solution on to a support; thendrying the dope solution at a temperature of from 40° C. to 60° C., so as to form a film; thenstretching the film; andshrinking the film.

4. The optical film produced by the method according to claim 3, wherein the optical film has a photoelastic coefficient in a longitudinal direction of the optical film and a photoelastic coefficient in a direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two photoelastic coefficients by greater one of the two photoelastic coefficients is 0.8 or below.

5. An optical film, which has a value of 1.2 or above obtained by dividing greater one of a velocity of sound in a longitudinal direction of the optical film and a velocity of sound in a direction approximately orthogonal to the longitudinal direction by smaller one of the two velocities.

6. An optical film, which has a value of 1.1 or above obtained by dividing greater one of a velocity of sound in a longitudinal direction of the optical film and a velocity of sound in a direction approximately orthogonal to the longitudinal direction by smaller one of the two velocities, wherein values of in-plane retardation Re and thickness-direction retardation Rth at wavelengths 450 nm, 550 nm and 650 nm satisfy the following relations (I) to (III): 0.4<{(Re(450)/Rth(450))/(Re(550)/Rth(550))}<0.95 and1.05<{(Re(650)/Rth(650))/(Re(550)/Rth(550))}<1.9  Relation (I)0.1<(Re(450)/Re(550))<0.95  Relation (II)1.03<(Re(650)/Re(550))<1.93  Relation (III)wherein Re(λ) represents an in-plane retardation Re value, expressed in the unit nm, at a wavelength λ nm; andRth(λ) represents a thickness-direction retardation Rth value, expressed in the unit nm, at a wavelength λ nm.

7. A method of manufacturing an optical film, which comprises: stretching a film; andshrinking a film,wherein the shrinking is performed at a shrink speed of 10% to 100% per minute.

8. The optical film produced by the method according to claim 7, wherein the optical film has a value of 1.2 or above obtained by dividing greater one of a velocity of sound in a longitudinal direction of the optical film and a velocity of sound in a direction approximately orthogonal to the longitudinal direction by smaller one of the two velocities.

9. The optical film according to claim 1, wherein an in-plane retardation Re value at a wavelength of 550 nm is in a range of from 20 to 100 nm and a thickness-direction retardation Rth value at a wavelength of 550 nm is in a range of from 100 to 300 nm.

10. The optical film according to claim 1, which comprises a cellulose acylate.

11. The optical film according to claim 10, wherein substitution degrees of hydroxyl groups with acyl groups at 2-, 3- and 6-positions of a glucose unit in the cellulose acylate satisfy the following relations (IV) and (V): 2.0≦(DS2+DS3+DS6)≦3.0  Relation (IV)DS6/(DS2+DS3+DS6)≧0.315  Relation (V)wherein DS2 represents an acyl substitution degree on the 2-position hydroxyl group;DS3 represents an acyl substitution degree on the 3-position hydroxyl group; andDS6 represents an acyl substitution degree on the 6-position hydroxyl group.

12. The cellulose acylate film according to claim 10, which substantially comprises a cellulose acylate satisfying the following relations (VI) and (VII): 2.0≦A+B≦3.0  Relation (VI)0≦B  Relation (VII)wherein A represents a substitution degree of hydroxyl groups of a glucose unit in the cellulose acylate with acetyl groups; andB represents a substitution degree of hydroxyl groups of a glucose unit in the cellulose acylate with propionyl groups, butyryl groups or benzoyl groups.

13. The optical film according to claim 1, which comprises a retardation developer.

14. A polarizing plate, which comprises: a polarizing film; anda pair of protective films sandwiching the polarizing film,wherein at least one of the pair of protective films is an optical film according to claim 1.

15. A liquid crystal display device, which comprises an optical film according to claim 1.

16. A liquid crystal display device, which comprises a polarizing plate according to claim 14, wherein the liquid crystal display device is of IPS-mode, OCB-mode or VA-mode.

17. A VA-mode liquid crystal display device, which comprises a polarizing plate according to claim 14 on a backlight side.

18. An optical film, which has a coefficient of linear thermal expansion in a longitudinal direction of the optical film and a coefficient of linear thermal expansion in a width direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two coefficients of linear thermal expansion by greater one of the two coefficients is from 0.1 to 0.5.

19. The optical film according to claim 18, wherein one of the two coefficients of linear thermal expansion in the longitudinal direction of the optical film and the width direction approximately orthogonal to the longitudinal direction is 42 or below and the other is 80 or above.

20. The optical film according to claim 18, wherein values of in-plane retardation Re and thickness-direction retardation Rth at wavelengths 450 nm, 550 nm and 650 nm satisfy the following relations (I) to (III): 0.4<{(Re(450)/Rth(450))/(Re(550)/Rth(550))}<0.95 and1.05<{(Re(650)/Rth(650))/(Re(550)/Rth(550))}<1.9  Relation (I)0.1<(Re(450)/Re(550))<0.95  Relation (II)1.03<(Re(650)/Re(550))<1.93  Relation (III)wherein Re(λ) represents an in-plane retardation Re value, expressed in the unit nm, at a wavelength λ nm; andRth(λ) represents a thickness-direction retardation Rth value, expressed in the unit nm, at a wavelength λ nm.

21. A method of manufacturing an optical film, which comprises: stretching a film; andshrinking a film,wherein an ending temperature of the stretching is adjusted to a range of (crystallization temperature of the optical film −10° C.) to (crystallization temperature of the optical film +10° C.).

22. The optical film produced by the method according to claim 21, wherein the optical film has a coefficient of linear thermal expansion in a longitudinal direction of the optical film and a coefficient of linear thermal expansion in a width direction approximately orthogonal to the longitudinal direction, wherein a value obtained by dividing smaller one of the two coefficients of linear thermal expansion by greater one of the two coefficients is from 0.1 to 0.5.

23. The optical film according to claim 18, which comprises a cellulose acylate.

24. The optical film according to claim 23, wherein all acyl substitutents in the cellulose acylate are acetyl groups and a total degree of acyl substitution is from 2.56 to 3.00.

25. The optical film according to claim 23, wherein substitution degrees of hydroxyl groups with acyl groups at 2-, 3- and 6-positions of a glucose unit in the cellulose acylate satisfy the following relations (IV) and (V): 2.0≦(DS2+DS3+DS6)≦3.0  Relation (IV)DS6/(DS2+DS3+DS6)≧0.315  Relation (V)wherein DS2 represents an acyl substitution degree on the 2-position hydroxyl group;DS3 represents an acyl substitution degree on the 3-position hydroxyl group; andDS6 represents an acyl substitution degree on the 6-position hydroxyl group.

26. The optical film according to claim 23, wherein acyl substitutents of the cellulose acylate comprises at least two of acetyl, propionyl, butanoyl and benzoyl groups, and a total degree of acyl substitution is from 2.50 to 3.00

27. The optical film according to claim 18, which comprises a retardation developer.

28. A polarizing plate, which comprises: a polarizing film; anda pair of protective films sandwiching the polarizing film,wherein at least one of the pair of protective films is an optical film according to claims 18.

29. A liquid crystal display device, which comprises an optical film according to claim 18.

30. A liquid crystal display device, which comprises: a pair of polarizing plates; and a liquid crystal cell between the pair of polarizing plates,wherein at least one of the pair of polarizing plates is a polarizing plate according to claim 28, andthe liquid crystal display device is of IPS-mode, OCB-mode or VA-mode.

31. A VA-mode liquid crystal display, which comprises a polarizing plate according to claim 28 on a backlight side.