Claims
- 1. A normally white liquid crystal display comprising:
- a rear, light-entrance polarizer having a transmission axis oriented in a first direction;
- a front, light-exit polarizer having a transmission axis oriented in a second direction with respect to said first direction so as to define a normally white display;
- first and second positively birefringent uniaxial retardation films both disposed between a twisted nematic liquid crystal layer and one of: (i) said rear, light-entrance polarizer; and (ii) said front, light-exit polarizer;
- wherein said liquid crystal layer in the off state twists at least one normally incident visible wavelength of light less than about 110.degree. as it passes therethrough, and said first and second uniaxial retardation films each have retardation values of from about 80-200 nm; and
- wherein the transmission axes of said polarizers and optical axes of said retardation films are so arranged each with respect to the others so as to achieve high contrast ratios over a large range of predetermined viewing angles.
- 2. The display of claim 1, wherein said first and second retardation films each have retardation values of from about 100-170 nm.
- 3. The display of claim 2, wherein said first and second retardation films each have retardation values of from about 120-160 nm.
- 4. The display of claim 2, wherein said liquid crystal layer is from about 4.8-6.5 .mu.m thick with a birefringence of from about 0.075-0.095 at room temperature.
- 5. The display of claim 4, wherein said liquid crystal layer is sandwiched between rear and front orientation means for aligning molecules of said liquid crystal material, said rear orientation means having a buffing or orientation direction substantially parallel to the transmission axis of said rear polarizer, and said front orientation means having a buffing or orientation direction substantially parallel to the transmission axis of said front polarizer.
- 6. The display of claim 4, wherein said display has a white light contrast ratio of at least about 10:1 when about a 6 volt driving voltage is applied thereto at viewing angles of about 0.degree. vertical, .+-.50.degree. horizontal.
- 7. The display of claim 4, wherein certain contrast ratio contours of said display extend further in one horizontal direction than the other such that said display has about a 10:1 contrast ratio when about a 6 volt driving voltage is applied thereto at a viewing angle of one of about: (i) 0.degree. vertical, 55.degree. horizontal; and (ii) 0.degree. vertical, -55.degree. horizontal.
- 8. The display of claim 4, wherein an angle of from about 80.degree.-100.degree. is defined between the respective optical axes of said first and second retardation films.
- 9. The display of claim 8, wherein an angle of from about 85.degree.-95.degree. is defined between said optical axes of said first and second retardation films such that said optical axis of said first retardation film is substantially parallel to the transmission axis of said front polarizer and said optical axis of said second retardation film is substantially parallel to the transmission axis of said rear polarizer.
- 10. A normally white liquid crystal display comprising:
- a rear, light-entrance polarizer having a transmission axis oriented in a first direction;
- a front, light-exit polarizer having a transmission axis oriented in a second direction wherein said first and second directions are oriented so as to define a normally white display;
- first and second biaxial retardation films both disposed between a twisted nematic liquid crystal layer and one of said rear and front polarizers, wherein said liquid crystal layer in the off state twists at least one wavelength of normally incident visible light at least about 85.degree. as it passes therethrough; and
- wherein said first and second biaxial retardation films each have the following retardation values:
- d.multidot..DELTA.n.sub.ZX =from about -100 to -200 nm
- d.multidot..DELTA.n.sub.ZY =from about -10 to -100 nm
- wherein n.sub.X >n.sub.Y >n.sub.Z and "d" is the thickness of the film such that the viewing zone of said display has high contrast ratios and reduced inversion throughout an enlarged range of viewing angles.
- 11. The display of claim 10, wherein the optical axis having the largest index of refraction n.sub.X of the biaxial retardation film disposed closest to said liquid crystal layer is aligned substantially parallel to the buffing or orientation direction of an adjacent orientation film, said orientation film being disposed between said liquid crystal layer and said first and second biaxial retardation films.
- 12. The display of claim 11, wherein said buffing or orientation direction is substantially parallel to the polarizer transmission axis disposed on the same side of said liquid crystal layer.
- 13. The display of claim 11, wherein said first and second retardation films have retardation values d.multidot..DELTA.n.sub.ZX of from about -140 to -180 nm.
- 14. The display of claim 10, wherein said first and second retardation films each have the following retardation values:
- d.multidot..DELTA.n.sub.ZX =from about -120 to -180 nm
- d.multidot..DELTA.n.sub.ZY =from about -40 to -80 nm.
- 15.
- 15. A normally white twisted nematic liquid crystal display comprising:
- a plurality of pixels, each said pixel including electrode means and a twisted nematic liquid crystal layer for twisting at least one normally incident visible wavelength of light passing therethrough from about 80.degree. to 100.degree. when the liquid crystal layer is in the off state;
- a rear light-entrance polarizer having a transmission axis oriented in a first direction;
- a front, light-exit polarizer or analyzer having a transmission axis oriented in a second direction with respect to said first direction thereby defining a twisted nematic normally white display;
- a first retardation film;
- a second retardation film; and
- wherein the transmission axes of said rear and front polarizers and the optical axes of said first and second retardation films are so arranged with respect to the others so as to achieve a white light contrast ratio of at least about 10:1 over a horizontal angular span, at a predetermined vertical angle, of at least about 120.degree. and over a vertical angular span of greater than about 50.degree. at a predetermined horizontal angle.
- 16. The display of claim 15, wherein said display has a contrast ratio of at least about 10:1 over a horizontal angular span of at least about 120.degree. and over a vertical angular span of greater than about 60.degree. when about 6.0 volts is applied to said display.
- 17. The display of claim 16, wherein said display has a contrast ratio of at least about 30:1 over a horizontal angular span of at least about 80.degree. and over a vertical angular span of greater than about 30.degree..
- 18. The display of claim 15, wherein said first and second retardation films have retardation values, positive or negative, of from about 80-200 nm.
- 19. The display of claim 15, wherein said first and second retardation films are on the same side of said liquid crystal layer.
- 20. A normally white twisted nematic liquid crystal display comprising:
- a twisted nematic liquid crystal layer which twists at least one normally incident visible wavelength of light from about 80.degree.-100.degree. as it passes therethrough when the liquid crystal is in the off state;
- electrode means for applying voltage to said liquid crystal layer so as to selectively display image data to a viewer;
- a first negative retardation film having a retardation value of from about -80 to -200 nm;
- a second negative retardation film having a retardation value of from about -80 to -200 nm; and
- wherein the optical axes of said first and second negative retardation films are oriented relative to one another so as to achieve a high contrast ratio over a predetermined range of viewing angles.
- 21. The display of claim 20, wherein the optical axes of each of said first and second retardation films are substantially parallel to the normal viewing axis.
- 22. The display of claim 20, wherein the display has a contrast ratio of at least about 10:1 over a horizontal angular span of at least about 120.degree. and a vertical angular span of greater than about 60.degree. when about 6.0 volts is applied to the display.
- 23. The display of claim 20, wherein the indices of refraction of each of said first and second negative retarders are characterized by the equations:
- d.multidot..sup..DELTA. n.sub.ZX =d.multidot..sup..DELTA. n.sub.ZY
- and
- n.sub.X >n.sub.Z.
RELATED APPLICATION
This is a continuation-in-part of Ser. No. 08/167,652 filed Dec. 15, 1993, pending the disclosure of which is hereby incorporated herein by reference.
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EPX |
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Non-Patent Literature Citations (2)
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
167652 |
Dec 1993 |
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