Normally white twisted nematic LCD with positive and negative retarders

• US 5,739,881 A
• Filed: 04/03/1997
• Issued: 04/14/1998
• Est. Priority Date: 12/15/1993
• Status: Expired due to Term

• Current Assignee: Guardian Industries Corporation (KOCH Industries Incorporated)
• Original Assignee: OIS Optical Imaging Systems, Inc. (KOCH Industries Incorporated)
• Inventors: Xu, Gang, VanderPloeg, John A.
• Primary Examiner(s): GROSS, ANITA P
• Application Number:
  US08/826,520
• Time in Patent Office: 376 Days
• Field of Search: 349/118, 349/120, 349/119
• US Class Current: 349/118
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• 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
• CPC Class Codes: G02F 1/133784 by rubbing
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation
• CPC Class Codes: G02F 2413/02 Number of plates being 2
• CPC Class Codes: G02F 2413/04 Number of plates greater than or equal to 4
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation
• CPC Class Codes: G02F 2413/13 Positive birefingence
• CPC Class Codes: G02F 2413/14 Negative birefingence

Abstract

A normally white twisted nematic liquid crystal display is provided for outputting improved viewing characteristics which are defined by high contrast ratios and reduced inversion. The display includes both positive and negative retardation films, the negative films being defined by n_x =n_y >n_z where the "z" direction is substantially perpendicular to the film plane and the "x" and "y" directions are substantially parallel to the film plane. According to certain embodiments, a pair of positive and a pair of negative retardation films are provided such that the two positive retarders sandwich both the liquid crystal layer and the negative retarders therebetween. By providing the positive and negative retarders with specific retardation values and/or ratios, improved viewing characteristics are provided.

Claims

1. A normally white twisted nematic liquid crystal display comprising:

a twisted nematic liquid crystal layer for twisting at least one normally incident visible wavelength of light from about 80°

-100°

as it passes therethrough when said liquid crystal layer is in substantially the off-state thereby defining a twisted nematic normally white display;

a positive retarder having a retardation value of from about 80-200 nm; and

a negative uniaxial retarder means for retarding light passing therethrough, said negative uniaxial retarder means being defined by n_x =n_y >

n_z, where n_x, n_y, and n_z are indices of refraction and the "z" direction is substantially perpendicular to the plane defined by said negative uniaxial retarder means and the "x" and "y" directions are substantially parallel to the plane defined by said negative uniaxial retarder means, and wherein said negative uniaxial retarder means has a retardation value of from about -60 to -220 nm.