Electro-optic passive display cell

Claim 1

An electro-optic display cell comprising: A. two plates arranged adjacent one another and providing a space therebetween, at least one of the plates being transparent and both plates having an inner surface arranged adjacent the other; B. electrodes carried on the inner surfaces of the plates to form display zones, in which display zones, electric fields may be created; C. a layer of a mixture of a nematic liquid crystal having a positive dielectric anisotropy, an optically active component and dichroic molecules, the mixture filling the space between the plates and having a median zone, the mixture having a critical thickness in the presence of a homeotropic alignment layer on each of the inner surfaces of the plates such that for a thickness of the mixture less than this critical thickness, the molecules of the mixture have a homeotropic structure through the whole structure of the mixture and for a thickness of the mixture greater than the critical thickness, the molecules of the mixture have a helicoidal structure in the median zone, and the mixture having a homeotropic structure in the presence of an electric field; D. in the areas of the inner surface situated outside the display zones there is a homeotropic alignment layer on each of the inner surfaces of the plates and the thickness of the mixture is less than the critical thickness so that the molecules of the mixture have a homeotropic structure through the whole thickness of the mixture and the mixture is transparent; and E. in the display zones, in the absence of any electric field, the molecules of the mixture have a helicoidal structure and are absorbent, while in the presence of an electric field, the molecules of the mixture have a homeotropic structure and are transparent so that the non-activated display zones are dark on a transparent background.