Patent GB-929184-A (GB)
Title: Improvements in or relating to fluorescent screens
IPC: G03C5/17
Filed: 1960-01-22
Abstract: 929,184. Luminescent screens. E. I. DU PONT DE NEMOURS & CO. Jan. 22, 1960 [Feb. 20, 1959], No. 2475/60. Class 39 (1). [Also in Group XX] A luminescent screen comprises a flexible support bearing on one surface at least one flexible layer of finely divided particles of an inorganic phosphor dispersed in a polyvinyl butyral binder. The support can be paper or aluminium foil or a film of a macromolecular hydrophobic polymeric material and can be, amongst several examples, a polyethylene terephthalate film. The supporting film can have a substratum of vinylidene chloride/methyl acrylate itaconic acid copolymer. The supporting film can be 0.25 to 30 mils. thick, and the flexible layer containing the phosphor 1 to 20 mils. thick. The phosphor-containing layer can contain up to 50% (on the weight of the polyvinyl butyral) of a non-volatile ester of plasticizing agent such as glycerol monolaurate. The proportion of the polyvinyl butyral binder in the phosphor layer can be 4 to 20% by weight based on the weight of the phosphor particles. A protective layer can be coated over the phosphor-containing layer and a layer containing light-reflecting or light-absorbing pigment particles, such as magnesium oxide, can be placed between the support and the phosphorcontaining layer or mixed with the support. The support can be coated with a layer of aluminium to provide reflection. In a specific example the support film is 0.25 to 30 mils. thick, the reflective pigment layer is 0.3 to 1 mil. thick, the phosphor-containing layer is 4 to 14 mils. thick, and the protective layer is 0.5 to 1.5 mils. thick. The phosphor and polyvinyl butyral binder can be dispersed in various solvents and adjuvants. The phosphor can be calcium tungstate, zinc sulphide (silver activated, magnesium and barium chloride fluxed), zinc cadmium sulphide, zinc orthosilicate or barium sulphate/lead sulphate. The flexible luminescent screens can be used in radiography where it is desirable to bend a cassette or photographic film holder around an object. The flexible screen having the phosphorcontaining layer on a clear or opaque support can be coated, on the phosphor surface, with a pressure-sensitive adhesive and caused to adhere to a photographic film. The combination can be handled in daylight when an opaque support is used. After exposure the screen can be stripped from the film, and re-used. Using a light-opaque support of paper or foil for the phosphor-containing layer a daylight photographic film can be made by applying a sheet of an opaque material to one surface and the opaque screen to the other surface of the photographic film with sufficient overlay at the edges to make the assembly light-tight. The edges can be cemented or heat-sealed. A composite photographic film and intensifying screen can comprise a sheet support, a phosphor-polyvinyl butyral layer and a light-sensitive silver halide layer, e.g. silver chloride, silver bromide-chloride or silver bromoiodide. A substratum layer can be coated on the phosphor-binder layer to aid adhesion to the light-sensitive layer. Several specific embodiments of the invention are described. Specifications 718,422, 727,705, 788,979 and 829,268 are referred to.