Quarter wave plate comprising two optically anisotropic layers

• US 6,593,984 B2
• Filed: 04/10/2002
• Issued: 07/15/2003
• Est. Priority Date: 11/06/1998
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Ichihashi, Mitsuyoshi, Arakawa, Kohei, Kawata, Ken
• Primary Examiner(s): Ngo, Julie
• Application Number:
  US10/119,149
• Publication Number:
  US 20020159005A1
• Time in Patent Office: 461 Days
• Field of Search: 349/75, 349/117-121, 349/123
• US Class Current: 349/117
• 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 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 discotic liquid crystal molecules, and the other is a polymer film or a layer made from liquid crystal molecules, and 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 molecules and a surface plane of the optically anisotropic layer.

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

3. The quarter wave 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, and the other is a polymer film.

4. 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, 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°

, 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°

.

5. The quarter wave plate as defined in claim 4, 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 respectively, 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, wherein the values of Re450A, Re550A, Re450B and Re550B satisfy the formulas (1) and (2):

6. The quarter wave plate as defined in claim 4, wherein the values of Re550A and Re550B satisfy the formula (1a):

7. The quarter wave plate as defined in claim 4, wherein the values of Re450A, Re550A, Re450B and Re550B satisfy the formula (2a):

8. 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 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°

, 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°

.

9. The quarter wave plate as defined in claim 8, 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.

10. The quarter wave plate as defined in claim 9, 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.

11. The quarter wave plate as defined in claim 9, 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°

.