The 'Paintable LCD' approach allows the preparation of an LCD on a single substrate by the sequential coating and curing of a stack of tailored organic layers. This revolutionary new technology for the manufacturing of liquid crystal displays (LCDs) provides freedom in display design as well as in production methodology. In fact, displays can be prepared on any substrate. The key process that enables layer stacking on top of the liquid crystal (LC) layer is called photo-enforced stratification (PES). It comprises a two-step photopolymerisation-induced phase-separation of an LC blend and a polymer precursor. In these polymerization steps, the single thin layer (a homogeneous mixture of an LC blend and a polymer precursor) very accurately phase-separates in a hard polymer top coat and a pure LC layer underneath. Directionality with respect to the phase-separation can be achieved by using the absorption of one of the compounds in the mixture which provides a UV intensity gradient over the layer thickness. As a result, the photopolymerisation predominantly takes place where the UV intensity is the highest i.e. near the film surface that is directed towards the UV source. Also other optical layers, like polarisers or retarders, can be deposited by simple coating techniques, so that the complete display can be made using one, very simple and versatile, technology.
The contrast and color saturation of cathode ray tube (CRT) and plasma display images is negatively affected by the reflection of ambient light at the white phosphor dots. A variable photochromic transmission filter reversibly darkens upon exposure to sunlight, and could offer the optimal compromise between contrast and brightness of the image under a range of illumination conditions. The photochromic transmission filter that we present here consists of a soft polymer layer doped with a photochromic dye that has been sandwiched between the CRT screen and a front glass panel. The fabrication process of such a photochromic laminate involves the in-situ polymerization of a resin in the presence of the dye. For this purpose we have studied the radical polymerization of several (meth)acrylates in the presence of a photochromic dye, and evaluated the optical properties of the dye in the resulting polymer films. In this way a photochromic laminate has been developed that upon irradiation turns from a transparent state to an almost neutrally colored state and exhibits sufficiently fast coloration and decoloration kinetics. The photochromic laminate significantly improves the daylight contrast of the CRT under high illumination conditions (e.g. direct sunlight), while at the same time the brightness of the CRT is retained under low illumination conditions.
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