GB1208308A - Electroluminescent display devices - Google Patents

Abstract

1,208,308. Electroluminescence. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 20 Oct., 1967 [27 Oct., 1966 (6)], No. 47922/67. Heading C4S. The pattern displayed by an electroluminescent sign is determined by applying a layer of a conductive substance, e.g. water, to the display surface whereupon the portions so coated glow. The device comprises an element 3 (e.g. ZnS: Cu Al in plastic binder such as urea resin) which luminesces according to the electric field strength applied thereto and electrodes for supplying power, one W wire electrode 5 being exposed and having a plurality of parts separated spatially but connected together electrically. The electrode 5 forms, in effect, one of the plates of a capacitor, and applying a conductive layer increases its effective area, causing the element 3 to glow in the vicinity of said layer. Electrode 5 comprises either a plurality of spaced parallel wires or a reticular structure. It is mounted on a dielectric layer 4 of epoxy resin for instance. Either the layer 4 or the electrode 2 and base 1 are transparent, allowing the pattern to be viewed. The device may operate on D.C., Fig. 3 (not shown), including as luminescent material SiC, CdS or thin film evaporated ZnS: Cu, Mn, but then the resistivity of dielectric layer 4 must be lower. Fig. 2 (not shown), illustrates the provision of a high insulation polyester film layer (9) between layers 4 and 3, to prevent breakdowns. The layer may be powdery barium titanate in a plastic binder and reflective. Figs. 4 and 5 (not shown), illustrate embodiments comprising two sets of electrodes 5 arranged on either side of a common base: in Fig. 4, there are two electroluminescent layers, one for each electrode, permitting display in two colours; in Fig. 5 there is one common electroluminescent layer which can be arranged to glow solely at the intersection points of the two electrodes. Fig. 6 includes green and orange emitting layers 14 and 16 of ZnS: Cu, Al and ZnCdS: Ag, respectively. Fig. 7 shows an arrangement having three electrodes, of which 15 and 19 are of the composite type, two sources of power 23, 24, and two luminescent layers 14, 16, which may emit different colours. By selecting appropriate voltages, currents I 1 and I 2 can be made to cancel, thus eliminating the residual ("dark") luminescence of the device; application of a pattern-forming droplet 25 causes a current I<SP>1</SP> 1 to flow, the resulting glow contrasting strongly with the background. The embodiment of Fig. 8 has three electroluminescent layers 14, 16, 25 for different colours, and electrodes 12, 15, 19, and is generally similar to that of Fig. 7. A range of materials is disclosed for the pattern-forming conductive layer which may be permanent or temporary, and in the latter case can be applied by a brush and removed by wiping off.