Claims
- 1. A twisted nematic liquid crystal display capable of displaying an image to a viewer, said display comprising:
- a pair of electrodes sandwiching a twisted nematic liquid crystal layer therebetween, said pair of electrodes for applying a voltage across said liquid crystal layer;
- first and second orientation means disposed adjacent said liquid crystal layer on opposite sides thereof, said first orientation means defining a first orientation or buffing direction and said second orientation means defining a second orientation or buffing direction, said first and second orientation directions for aligning the liquid crystal molecules of said liquid crystal layer in a predetermined manner;
- a positively birefringent uniaxial retardation film having a retardation value "d.multidot..DELTA.n" in the range of about 100-200 nm, where "d" is the thickness of said retardation film and ".DELTA.n" is its birefringent value, wherein said retardation film is disposed on the same side of said liquid crystal layer as said first orientation means, said retardation film being oriented such that its optical axis is substantially parallel plus or minus about 25.degree. to the second orientation or buffing direction of said second orientation means thereby enabling said liquid crystal display to display to the viewer an image with improved contrast ratios and reduced inversion.
- 2. The display of claim 1, wherein said optical axis of said retardation film is rotated relative to said second orientation or buffing direction, whereby said rotation of said optical axis shifts the display's high contrast ratio viewing zone or envelope vertically so as to allow the viewer to view said image at increased vertical viewing angles and wherein the display is of the normally white type and the thickness of said liquid crystal layer is from about 4.8-6.0 .mu.m and the An of said liquid crystal layer is from about 0.075 to 0.095 at room temperature.
- 3. The display of claim 2, wherein said optical axis of said retardation film is rotated from about 2.degree.-20.degree. relative to said second orientation or buffing direction, and wherein said retardation value of said retardation film is from about 120-160 nm, and wherein said first and second directions are substantially perpendicular to one another.
- 4. The display of claim 3, wherein said retardation film and said first orientation means are disposed on the viewer side of said liquid crystal layer, and said optical axis of said retardation film is rotated clockwise relative to said second orientation or buffing direction so that the high contrast viewing zone is shifted to a position in the positive or upper vertical viewing region in order to enable viewers at high positive viewing angles to view images of high contrast, and wherein said liquid crystal layer twists at least one visible wavelength of light less than about 100.degree. when said liquid crystal layer is in the off-state.
- 5. The display of claim 4, wherein the display outputs contrast ratios to the viewer of at least about 10:1 or 10 at viewing angles of about +20.degree. vertical, .+-.45.degree. horizontal when a driving voltage of greater than or equal to about 6 volts is applied to said liquid crystal layer.
- 6. The display of claim 5, wherein said display outputs a contrast ratio of at least about 30:1 at viewing angles at about +15.degree. vertical over a total horizontal range of about 75.degree. when greater than about a 6 driving voltage is applied to said liquid crystal layer; and
- wherein said optical axis of said retardation film is rotated from about 5.degree.-10.degree. in the clockwise direction relative to second orientation or buffing direction when viewed from the viewer side of said display.
- 7. A method of shifting the high contrast ratio viewing zone of a twisted nematic normally white liquid crystal display upward into the positive or upper vertical viewing zone, said method comprising the steps of:
- a) sandwiching a twisted nematic liquid crystal layer between a pair of electrodes, said liquid crystal layer having a thickness of from about 4.5-6.5 .mu.m;
- b) orienting the liquid crystal molecules on a first side of said liquid crystal layer in a first direction;
- c) orienting the liquid crystal molecules on a second side of said liquid crystal layer in a second direction, said first and second directions being different from one another in a manner such that said liquid crystal layer when in the off-state twists at least one visible wavelength of light less than about 100.degree. ;
- d) providing a retardation film having a retardation value "d.multidot..DELTA.n", in the range of about 100-250 nm on said first side of said liquid crystal layer, wherein "d" is the thickness of said retardation film and ".DELTA.n" is its birefringence;
- e) rotating the optical axis of said retardation film from about 2.degree.-20.degree. relative to said second direction, said rotating of said optical axis shifting the high contrast viewing zone vertically so that viewers at such viewing angles may see a high contrast image with reduced inversion.
- 8. The method of claim 7, wherein said retardation value of said retardation film is from about 100-175 nm and said optical axis of said retardation film is rotated from about 4.degree.-15.degree. relative to said second direction.
- 9. The method of claim 8, wherein said first side of said liquid crystal layer is the side closest the viewer and said step e) further includes rotating said film such that said optical axis is rotated from about said 4.degree.-15.degree. in the clockwise direction relative to said second direction so as to position said high contrast viewing zone in the positive or upper vertical viewing direction, said clockwise direction being defined as viewed from the viewer side of said display.
- 10. The method of claim 8, wherein said first side of said liquid crystal layer is the side closest to a corresponding backlight and said step e) further includes rotating said retardation film such that said optical axis is rotated from about said 4.degree.-15.degree. in the counterclockwise direction relative to said second direction so as to position said high contrast viewing zone in the positive vertical viewing direction, said counterclockwise direction being defined as viewed from the viewer side of said display.
- 11. The method of claim 8, further comprising the steps of:
- f) polarizing light emitted from a backlight in a first polarization direction by way of a rear polarizer disposed between said liquid crystal layer and said backlight;
- g) polarizing said light in a second polarization direction as said light proceeds from said liquid crystal layer toward the viewer by way of a front polarizer disposed on the viewer side of said liquid crystal layer; and
- h) orienting said rear and front polarizers such that said first and second polarization directions define a normally white liquid crystal display whose pixels or colored subpixels appear darkened in the "on-state" and substantially light in the "off-state."
- 12. The method of claim 11, wherein said optical axis is rotated from about 6.degree.-10.degree. relative to said second direction so as to allow said display to display an image with good contrast ratios and reduced inversion, and wherein said .DELTA.n of said liquid crystal layer is from about 0.075 to 0.095.
- 13. A method of making a normally white twisted nematic liquid crystal display, the method comprising the steps of:
- a) sandwiching a liquid crystal layer between first and second electrodes, said liquid crystal layer having a thickness "d" of from about 4.5 to 6.5 .mu.m;
- b) providing a first orientation means between said first electrode and said liquid crystal layer, said first orientation means for orienting LC molecules of said LC layer in a first direction adjacent said first orientation means;
- c) providing a second orientation means between said LC layer and said second electrode, said second orientation means for orienting LC molecules in a second direction adjacent said second orientation means;
- d) disposing a positively birefringent uniaxial retardation film on the same side of said LC layer as said first electrode and first orientation means, said retardation film having a retardation value of from about 100-200 nm; and
- e) orienting the optical axis of said uniaxial retardation film substantially parallel .+-. about 20.degree. to said second direction defined by said second orientation means whereby said normally white display exhibits improved contrast ratios and reduced inversion.
RELATED APPLICATIONS
This is a continuation-in-part of U.S. Ser. Nos. 08/167,652 filed Dec. 15, 1993, and 08/235,691 filed Apr. 29, 1994, the disclosures of which are hereby incorporated herein by reference.
US Referenced Citations (41)
Foreign Referenced Citations (2)
Number |
Date |
Country |
55-45037 |
Mar 1980 |
JPX |
3-13916 |
Jan 1991 |
JPX |
Non-Patent Literature Citations (2)
Entry |
"Wide Viewing Angle LCD Using Retardation Films" by Yamagishi et al., Japan Display '89, pp. 316-319. |
"The Symmetry Property of a 90 Degree Twisted Nematic Liquid Crystal Cell" by Lien. |
Related Publications (1)
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Number |
Date |
Country |
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235691 |
Apr 1994 |
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Continuation in Parts (1)
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Number |
Date |
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Parent |
167652 |
Dec 1993 |
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