Patent GB-573771-A (GB)
Title: Improvements in the production of photographic relief images
IPC: G03F7/004
Filed: 1943-11-16
Abstract: 573,771. Photographic wash-out relief images. KODAK, Ltd. (Eastman Kodak Co., and Staehle, H. C.). Nov. 16, 1943, No. 19101. [Class 98 (ii)] A photographic wash-out relief image is made by exposing a layer of a bichromated hydrophilic colloid binder (giving an aqueous dispersion capable of forming a smooth water-soluble film becoming when bichromated less soluble on exposure) in which is incorporated a soft resin or other polymerized substance such as a cellulose derivative which is completely waterinsoluble but is compatible with the hydrophilic colloid, the mixture being such as to comply with the test given in the Specification, and then washing away the exposed portions with aqueous liquid. The hydrophilic colloid may be glue, gelatine, gum arabic, or polyvinyl alcohol, and the resin an aqueous dispersion of polymethyl or polyethyl acrylate or mixtures thereof, and the cellulose derivative an aqueous dispersion of cellulose nitrate. The layer is coated more thickly than normal bichromated glue. and is given a less exposure. The layer may contain a pigment such as titanium oxide, lithopone, carbon black, cobalt blue, or yellow ochre, a wetting agent such as " Gardinol " (Registered Trade Mark) or Duponol, a plasticiser such as glycerol or ethylene glycol, and an antifoaming agent such as butyl or octyl alcohol. The wash-out resist may be used as an etching resist and then removed or may be used as a permanent image on a support. The resist may be used in the preparation of intaglio plates on copper, zinc, and anodised aluminium, in the preparation of deep-etched plates for offset lithography, and in the preparation of cellulose hydrate surfaces on cellulose ester films. Metal plates may be first coated with a resin subbing layer. Etching may be performed with acid or alkali, sand-blast, or electrolytically. The layer may be applied by spraying, whirling, brushing, dipping, or by ordinary emulsion coating technique. The resist image may be protected by a. lacquer coating. In example 1, glass or other support is coated with a composition comprising gelatin,. Rhoplex ER (an aqueous dispersion of an acrylate resin), ammonium dichromate, and ammonium hydroxide and after formation of a wash-out relief image the glass is sand-blasted. In example 2, a dispersion formed by grinding together titanium oxide, fish glue, and water is added to an aqueous dispersion of Rhoplex W66 (comprising a mixture of polymethyl and polyethyl acrylate), and the light-sensitive coating composition is completed by the addition of aqueous ammonia, " Gardinol " (Registered Trade Mark), Tamol, and ammonium dichromate. In example 3, the composition comprises gelatine, water, titanium dioxide, Rhoplex W66, Rhoplex ER, ammonium dichromate, and ammonium hydroxide. In example 4, the composition comprises titanium dioxide, water, gelatine, Rhoplex ER, and ammonium dichromate solution. In example 5, the composition comprises an aqueous dispersion of polystyrene, gelatine, Rhoplex ER, and ammonium dichromate. In example 6, the composition comprises silver halide gelatine emulsion, Rhoplex ER, water, ammonium dichromate, and ammonia solution. After production of the washout relief, the material 'is developed in an ordinary developer to give a black image or in a colour developer followed by Farmer's reducer to give a coloured image. The support may be glass, steel, wood, aluminium, hard or soft rubber, cellulose ester, synthetic resin, or ceramic material. The subbing layer may comprise a resin, and may be formed on a phenol-formaldehyde resin by wiping with turpentine. Coumarone or alkyd resins, a cellulose ester such as plasticised cellulose nitrate, or oxidized drying oils may also be used. Development is effected by immersion in or spraying with water. A hardening agent, e.g. alum, a swelling agent, e.g. ammonium hydroxide, an acid, e.g. acetic acid, or a solvent, e.g. alcohol may be added. The image may be hardened by heating or by treatment with a swelling agent, e.g. alcohol or toluene, followed by thorough drying, or by treatment with formalin followed by drying, or by treatment with ammonium dichromate solution followed by exposure to strong light. The composition may be applied to a metal sheet for use in the production of templates or structural parts. Specification 355,573, [Group IV], is referred to.