Liquid crystal cells – elements and systems – Particular structure – Interconnection of plural cells in series
Patent
1996-05-17
1998-06-02
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Interconnection of plural cells in series
349 76, 349117, 349183, 428 1, G02F 11335, G02F 11347
Patent
active
057608598
DESCRIPTION:
BRIEF SUMMARY
The invention is in the field of retardation layers comprising high-molecular weight liquid-crystalline material. Such retardation layers are used in displays. FIG. 1 is a schematic depiction of the construction of a display.
FIG. 1 shows a cross-section of a display comprising an active twisted layer (4), the active cell, which can be switched on and off by means of transparent electrodes (6), and a retardation layer (3), with substrates (2) disposed on either side of the two layers (3) and (4). At the outer sides of the two outermost substrates there are polarisers (1), and underneath the polariser situated under the active twisted layer is positioned a mirror (5).
DESCRIPTION OF THE RELATED ART
In practice, the mirror can be omitted in some displays. The invention is directed in particular to the retardation layer (3) of a display. Retardation layers serve to compensate for the undesirable birefringence effect that occurs in the active cell in the display. For the retardation layer use may be made of a twisted nematic layer composed of low-molecular weight liquid-crystalline material such as is described in, e.g., Kirk Othmer's Encyclopedia of Technology, 3rd ed. (New York: Wiley & Sons) Vol. 7, p. 728. Although low-molecular weight liquid-crystalline material gives good compensation when used, it is attended with the drawback of being low-viscous. For that reason, the low-molecular weight material is sealed between inflexible substrates by means of spacers in order to attain a twisted, form-retaining structure. In other words, a closed, rigid cell has to be made.
Alternatively, use may be made of birefringent films, e.g., a film of drawn polymer such as a birefringent polycarbonate film. Such a birefringent polycarbonate film is described in Jap. J. Appl. Physics, Vol. 30, No. 4 (April 1991), 682-686. By using birefringent polycarbonate films a liquid-crystalline display of reduced thickness and weight may be obtained. However, said birefringent polycarbonate films fail to provide optimum contrast. birefringence effect that occurs in the active cell of a display. This birefringence effect depends on the retardation value, the angle of twist, and the direction of twist of the layer of liquid-crystalline molecules in the active cell of the display. The retardation of a birefringent layer is defined as the product of the birefringence value (.DELTA.n) and the layer thickness. At a given wavelength, the birefringence effect of the active cell of the display can be completely compensated for by using a retardation layer that has equal retardation, and an equal as well as an opposite angle of rotation compared with the active cell. For full compensation these conditions should apply for the entire visible part of the wavelength spectrum. This requirement can only be realised if the dependence of the birefringence on the wavelength, also known as the dispersion, of the material of the retardation layer is equal to that of the LC material used in the active cell of the display. This is not the case for birefringent polycarbonate films. The dispersion of birefringent polycarbonate films is lower than liquid crystalline active cells which are commercially used. Therefore, their retardation can only be set (by setting the layer thickness) to match the retardation of the active cell at 550 nm. As a consequence, over the rest of the visible wavelength area the retardation fails to match that of the active cell of the display, especially in the wavelength area o f 400-550 nm the dispersion appears to be too low. This results in a less than optimal contrast.
In DE 39 25 382 A1 it is acknowledged that the optical properties of the compensating film (i.e., the retardation layer) should have a wavelength dependency which is substantially identical to that of the liquid-crystalline layer used for displaying information ( i.e. the active liquid-crystalline cell). Further, DE 39 25 382 teaches that a retardation layer containing a liquid-crystalline polymer is more suitable than a layer consisting of stretched polycarbo
REFERENCES:
patent: 4954288 (1990-09-01), East
patent: 5142393 (1992-08-01), Okumura et al.
patent: 5308535 (1994-05-01), Scheuble et al.
patent: 5380459 (1995-01-01), Kanemoto et al.
patent: 5519523 (1996-05-01), Madokoro et al.
patent: 5576077 (1996-11-01), Bosma et al.
International Search Report in PCT/EP94/03246 dated Jan. 31, 1995.
W.H. deJeu, Physical Properties of Liquid Crystals, p. 23 (1st ed. 1980).
Jun-ichi Hirakata, et al., "A Monochromatic Black and White Supertwisted Nematic Liquid Crystal Display with a Single Cell and a Birefringent Film" 30 Japanese J. of Applied Physics, pp. 682-686 (Apr. 1991).
Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 7, pp. 728-730 (3rd ed. 1979).
E.P. Raynes, "The Optical Properties of Supertwisted Liquid Crystal Layers" 4 Molecular Crystals & Liquid Crystals Letters, pp. 69-75 (Feb. 1987).
Bosma Martin
Mohlmann Gustaaf Ronald
Picken Stephen James
Venema Jan-Willem
Akzo Nobel nv
Duong Tai V.
Miraglia Loretta A.
Morris Louis A.
Sikes William L.
LandOfFree
Retardation layer having a dispersion adapted to the active liqu does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Retardation layer having a dispersion adapted to the active liqu, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Retardation layer having a dispersion adapted to the active liqu will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1466491