Patent GB-985089-A (GB)
Title: Data display device
IPC: G03C1/73
Filed: 1961-01-26
Abstract: <FORM:0985089/C4-C5/1> A data display device comprises a screen including two photochromic materials differing from each other in their response to exciting radiation and light projection means so constructed that at least one of the photochromic materials can be written on and/or erased independently of the other photochromic material. At least one of the photochromic materials can be converted into its coloured form by writing-light having a spectral range from blue to ultra-violet and restored to its colourless form by erasing light having a spectral range from green to infra-red.  In the arrangement shown in Fig. 1 a support 20, which passes visible light and infra-red light if of glass, and ultra-violet light if of polymethyl methacrylate, has a coating 21 on one side of dye solution which turns red under the influence of ultra-violet light and becomes colourless under the influence of infra-red light and has a coating 22 on the other side which turns blue when exposed to ultra-violet light, and becomes colourless when exposed to erasing-light.  The coatings 21 and 22 can be continuous films containing droplets of the dye used or can be of the capsular type.  Different colour-responsive or colour-persistent droplets or capsules can be used in the same coating.  A standard I has universally mounted on it an incandescent lamp 23 and projector 24, the lamp having attached to it a bracket 25 on which is pivoted a frame 26 in which are mounted two filter elements, one 31 passing writing-light and the other 39 passing erasing-light. A similar arrangement is mounted on the Standard II. The writings on the coatings are viewed in visible light or in darkness if the dyes fluoresce under the writing-light.  An anaglyph effect can be obtained owing to the support 20 between the coatings 21 and 22. Variable intensity of coloration or amount of erasure of a given area of the screen can be effected by controlling the duration and intensity of the writing or erasing light, or of applied thermal excitation which can also effect erasing.  The coatings can be spaced apart so as to allow the insertion of slides, stencils or filters.  A filter sheet can be positioned between the two coatings which substantially absorbs at least some colours in the range from infra-red to ultra-violet. At least one of the coatings can absorb most or all of the writing-light.  In other arrangements the two coatings can be superimposed <PICT:0985089/C4-C5/1> and supported between two glass plates, or a glass plate can have a coating on each side, one of the sides being covered with a transparent film having data thereon of material which will not pass writing-light.  The screen can be such as not to scatter or diffuse substantially any of the incident visible light or can be translucent so as to scatter at least a substantial proportion of the incident visible light, or can be treated to reflect visible light. In the arrangement shown in Fig. 8 a light scattering support screen 60a is provided so that an image 61 can be formed thereon by a projector 62.  The screen is provided with two adjacent layers 63 of dye solutions, and a trace 64 can be made on the layers, with the projected image as background, by writing beams from two lamps 23.  A fluorescent material can be embodied in the whole or some portions of the screen to give an immediate visual indication on the incidence of writing-light.  The screen can comprise a support on which are located flexible films with adhesive coatings, on one or both sides, which contain in the film and coating the light-responsive dye and which, after being treated with writing-light, can be stripped from the support and attached adhesively to another support.  A screen layer can consist of a mesh of woven filaments having capillary openings holding a solution of the photochromic dye, or can be a translucent layer having randomly-disposed capillary pores holding the solution, or can be a translucent fibrous layer the interstitial spaces of which hold the solution.  The screen can comprise a support having both internal capillary channels and an external capillary comb in which the solutions are held. The screen layers can be erased by using blotting paper to remove the liquid, by rolling or squeegeeing, by blowing, by dipping in washing liquids, or by evaporation of the solvent.  The photochromic dyes can be as described in Specifications 845,939, 887,958 and 889,186, preferably 61-nitro-spiropyan derivatives.  Many solvents are specified. Specifications 646,926 and 751,600 also are referred to.