Quarter wave plate comprising two optically anisotropic layers

• US 20020159005A1
• Filed: 04/10/2002
• Published: 10/31/2002
• Est. Priority Date: 11/06/1998
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Ken Kawata, Kohei Arakawa, Mitsuyoshi Ichihashi
• Inventors: Ichihashi, Mitsuyoshi, Arakawa, Kohei, Kawata, Ken
• Granted Patent: US 6,593,984 B2
• Time in Patent Office: Days
• US Class Current: 349/96
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528
• CPC Class Codes: G02F 1/133541 Circular polarisers
• CPC Class Codes: G02F 1/133637 characterised by the wavelength dispersion
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n

Abstract

A circularly polarizing plate comprises a linearly polarizing membrane and a quarter wave plate. The quarter wave plate comprises an optically anisotropic layer A and an optically anisotropic layer B. The quarter wave plate has such an optical characteristic that a retardation value essentially is a quarter of a wavelength when the retardation value is measured at the wavelength of 450 nm, 550 nm and 650 nm. One of the optically anisotropic layers A and B is a layer made from liquid crystal molecules, and the other is a polymer film or a layer made from liquid crystal molecules.

Claims

1. A circularly polarizing plate which comprises a linearly polarizing membrane and a quarter wave plate comprising an optically anisotropic layer A and an optically anisotropic layer B, said quarter wave plate having such an optical characteristic that a retardation value essentially is a quarter of a wavelength when the retardation value is measured at the wavelength of 450 nm, 550 nm and 650 nm, wherein one of the optically anisotropic layers A and B is a layer made from liquid crystal-molecules, and the other is a polymer film or a layer made from liquid crystal molecules.

2. The circularly polarizing plate as defined in. claim 1, wherein one of the optically anisotropic layers A and B is a layer made from discotic liquid crystal molecules.

3. The circularly polarizing plate as defined in claim 2, wherein each of the optically anisotropic layers A and B is a layer made from discotic liquid crystal molecules.

4. The circularly polarizing plate as defined in claim 2, wherein one of the optically anisotropic layers A and B is a layer made from discotic liquid crystal molecules, and the other is a polymer film.

5. The circularly polarizing plate as defined in claim 2, wherein the discotic liquid crystal molecules are aligned at an average inclined angle in the range of 50°

to 90°

, said inclined angle being an angle between a plane of a discotic core of the discotic liquid crystal molecule and a surface plane of the optically anisotorpic layer.

6. The circularly polarizing plate as defined in claim 1, wherein each of the optically anisotropic layers A and B has a slow axis in plane, and wherein an angle between the slow axis of the optically anisotropic layer A and the slow axis of the optically anisotropic layer B is in the range of 75°

to 105°

.

7. The circularly polarizing plate as defined in claim 6, wherein the optically anisotropic layer A has retardation values of Re450A and Re550A when the values are measured at the wavelengths of 450 nm and 550 nm respecptively, and the optically anisotropic layer B has retardation values of Re450B and Re550B when the values are measured at the wavelengths of 450 nm and 550 nm respectively, and wherein the values of Re450A, Re550A, Re450B and Re550B satisfy the formulas (1) and (2).

Re550A<

Re550B 

 

(1) Re450B/Re550B<

Re450A/Re550A 

 

(2)

8. The circularly polarizing plate as defined in claim 7, wherein the values of Re550A and Re550B satisfy the formula (1a). nm<

Re550B−

Re550A<

180 nm 

 

(1a)

9. The circularly polarizing plate as defined in claim 7, wherein the values of Re450A, Re550A, Re450B and Re550B satisfy the formula (2a).

Re450A/Re550A−

Re450B/Re550B>

0.08 

 

(2a)

10. The circularly polarizing plate as defined in claim 6, wherein the linearly polarizing membrane has a polarizing axis, and wherein an angle between the polarizing axis and the slow axis of the optically anisotropic layer A is in the range of 40°

to 50°

, and an angle between the polarizing axis and the slow axis of the optically anisotropic layer B is in the range of 40°

to 50°

.

11. The circularly polarizing plate as defined in claim 6, wherein the quarter wave plate further comprises a transparent support having a lengthwise direction, and wherein an angle between the lengthwise direction and the slow axis of the optically anisotropic layer A is in the range of 40°

to 50°

, and an angle between the lengthwise direction and the slow axis of the optically anisotropic layer B is in the range of 40°

to 50°

.

12. The circularly polarizing plate as defined in claim 1, wherein each of the optically anisotropic layers A and B has a slow axis in plane, and wherein an angle between the slow axis of the optically anisotropic layer A and the slow axis of the optically anisotropic layer B is in the range of 50°

to 70°

.

13. The circularly polarizing plate as defined in claim 12, wherein the optically anisotropic layer A has a retardation value in the range of 150 to 350 nm when the value is measured at the wavelength of 550 nm, and the optically anisotropic layer B has a retardation value in the range of 60 to 170 nm when the value is measured at the wavelength of 550 nm.

14. The circularly polarizing plate as defined in claim 13, wherein the optically anisotropic layer A has a retardation value in the range of 210 to 300 nm when the value is measured at the wavelength of 550 nm, and. the optically anisotropic layer B has a retardation value in the range of 115 to 150 nm when the value is measured at the wavelength of 550 nm.

15. The circularly polarizing plate as defined in claim 13, wherein the optically anisotropic layer A is a layer made from liquid crystal molecules, said liquid crystal molecules being twisted at a twist angle in the range of 3°

to 45°

.

16. The circularly polarizing plate as defined in claim 12, wherein the linearly polarizing membrane has a polarizing axis, and wherein an angle between the polarizing axis and the slow axis of one of the optically anisotropic layers A and B is in the range of 60°

to 80°

, and an angle between the polarizing axis and the slow axis of the other is in the range of 10°

to 30°

.

17. The circularly polarizing plate as defined in claim 12, wherein the quarter wave plate further comprises a transparent support having a lengthwise direction, and wherein an angle between the lengthwise direction and the slow axis of one of the optically anisotropic layers A and B is in the range of 60°

to 80°

, and an angle between the lengthwise direction and the slow axis of the other is in the range of 10°

to 30°

.