Laminated retardation layer, its fabrication process, and liquid crystal display incorporating the same

• US 20050062917A1
• Filed: 03/31/2004
• Published: 03/24/2005
• Est. Priority Date: 04/07/2003
• Status: Active Grant

• Current Assignee: Dai Nippon Printing Company Limited
• Original Assignee: Dai Nippon Printing Company Limited
• Inventors: Kashima, Keiji
• Granted Patent: US 7,508,474 B2
• Time in Patent Office: Days
• US Class Current: 349/120
• 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: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis

Abstract

The invention relates to a liquid crystal display that incorporates a laminated retardation layer 10 comprising a combination of a negative C-plate having a specific chromatic dispersion and a positive A-plate having a specific chromatic dispersion, used to improve the viewing angle characteristics thereof, thereby presenting high-contrast images with high color reproducibility yet with neither interference variations nor color shifts. The laminated retardation layer 10 is obtained by lamination of a retardation layer 11 having positive index anisotropy and an optical axis in a layer plane and a retardation layer 12 having negative index anisotropy and an optical axis in a normal direction to a layer plane. A stretched polymer film having inverse chromatic dispersion that causes retardation defined by an optical path difference between extraordinary light and ordinary light to become small as wavelength becomes short is used as the retardation layer 11 having positive index anisotropy and an optical axis in a layer plane, and a coating layer having normal chromatic dispersion that causes retardation defined by an optical path difference between extraordinary light and ordinary light to become large as wavelength becomes short is used as the retardation layer 12 having negative index anisotropy and an optical axis in a normal direction to a layer plane.

Claims

1. A laminated retardation layer obtained by lamination of a retardation layer having positive index anisotropy and an optical axis in a layer plane and a retardation layer having negative index anisotropy and an optical axis in a normal direction to a layer plane, wherein a stretched polymer film having inverse chromatic dispersion that causes retardation defined by an optical path difference between extraordinary light and ordinary light to become small as wavelength becomes short is used as said retardation layer having positive index anisotropy and an optical axis in a layer plane, and a coating layer having normal chromatic dispersion that causes retardation defined by an optical path difference between extraordinary light and ordinary light to become large as wavelength becomes short is used as said retardation layer having negative index anisotropy and an optical axis in a normal direction to a layer plane.

2. The laminated retardation layer according to claim 1, wherein a polycarbonate film having a fluorene skeleton, obtained by stretching a liquid crystal-containing polycarbonate film, is used as said stretched polymer film having inverse chromatic dispersion.

3. The laminated retardation layer according to claim 1, wherein a cellulose acetate film, obtained by stretching a cellulose acetate film, is used as said stretched polymer film having inverse chromatic dispersion.

4. The laminated retardation layer according to claim 1, wherein a film, obtained by forming into a film a mixture of an aromatic polyester polymer having normal chromatic dispersion and an aromatic polyester polymer having inverse chromatic dispersion and stretching said film, is used as said stretched polymer film having inverse chromatic dispersion.

5. The laminated retardation layer according to claim 1, wherein a film, obtained by forming into a film a polymer comprising a copolymer containing monomer units capable of yielding polymers having different chromatic dispersions and stretching said film, is used as said stretched polymer film having inverse chromatic dispersion.

6. The laminated retardation layer according to claim 1, wherein a composite film, obtained by lamination of two stretched films having different chromatic dispersions, is used as said stretched polymer film having inverse chromatic dispersion.

7. The laminated retardation layer according to claim 1, wherein a polymerizable chiral nematic (cholesteric) liquid crystal layer is used as said coating layer having normal chromatic dispersion.

8. The laminated retardation layer according to claim 1, wherein a polymerizable discotic liquid crystal of homeotropic orientation is used as said coating layer having normal chromatic dispersion.

9. The laminated retardation layer according to any one of claims 1 to 6, wherein a material that has negative index anisotropy and an optical axis in a normal direction to a layer plane upon coating is used as said coating layer having normal chromatic dispersion.

10. A process for fabrication of a laminated retardation layer as recited in any one of claims 1 to 8, wherein said stretched polymer film having inverse chromatic dispersion is used as a substrate, and a polymerizable liquid crystal layer is coated and oriented on one surface of said substrate for polymerization, thereby forming said polymerizable liquid crystal layer having normal chromatic dispersion into a film.

11. A liquid crystal display comprising a liquid crystal cell having a vertical alignment mode liquid crystal layer and sheet polarizers located on both sides thereof, wherein a laminated retardation layer as recited in claim 1 is interposed between one of said sheet polarizers and said liquid crystal cell.