GB1473383A - Liquid crystal display device - Google Patents

Abstract

1473383 Controlling light RANK ORGANISATION Ltd 9 April 1975 [11 April 1974] 16085/74 Heading G2F In an electro-optic cell exhibiting variable optical rotatory power and comprising a layer of liquid crystal material with positive dielectric arisotropy between parallel walls, the liquid crystal material is mainly nematic but contains at least some cholesteric component in order to provide a twisted molecular structure with a uniform sense of twist throughout in the absence of an electric field, and the molecules adjacent each wall are uniformly inclined thereto but at a different angle for each wall such that no place intermediate and parallel to the walls consists of molecules aligned parallel to the walls, whereby when a field is applied across the thickness of the layer all the liquid crystal molecules are rotated in the same sense to the parallel with the field. The formation of domains with opposite twist in the absence of a field, and of domains of anti-parallel molecules with different birefringence in the presence of a field which leads to inhomogeneity colour fringes in a display when the cell is between polarizers, is thereby avoided. As described, the molecules are caused to lie at 20-30 degrees to one wall and substantially parallel to the other wall by vapour deposition on the wall surfaces at 5 and 30 degrees respectively. The cholesteric component may be cholesteryl nonanoate, 0À25 wt. per cent based on the nematic component.