Patent GB-690093-A (GB)
Title: Improvements in or relating to methods of developing images in photographic layers to form developed images consisting of metal
IPC: G03C1/62
Filed: 1948-10-12
Abstract: 690,093. Physical development processes. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. Oct. 12, 1948 [Oct. 15, 1947], No. 26500/48. Class 98 (ii). A process for forming photographically metal images by physical development of exposed material comprises preparing a continuous supply of developer from constituent parts, allowing a continuous supply of exposed material to absorb sufficient freshly prepared developer to produce the metal images in a time less than the development time and less than the keeping period of the developer, development of the material then being allowed to proceed solely with the developer so absorbed for a period longer than the keeping period of the developer. The developer may be freshly prepared continuously by mixing together two component solutions, the amount available at any time being small compared with the quantity absorbed by the exposed material during a period equal to the keeping time of the developer, or a stock solution of a developer stabilized by cooling, dilution, or addition of acid may be used, development in either case being accelerated by heating. All the steps necessary to provide a support with a photographic metal image, viz. sensitizing, conditioning, exposing, developing, fixing if necessary, washing and drying, may be performed as a continuous process or at least all those steps after exposing may be so performed. Thus a film of regenerated cellulose may be soaked in a sensitizer comprising 1-hydroxy 2-diazonium 6-methyl benzene 4-sulphonic acid, mercurous nitrate and nitric acid, dried, and exposed, a paper support may be similarly sensitized by passage over a roller dipping into a sensitizing bath, cut to size, dried and contact printed on an exposure roller, or both sides of a paper support may be sensitized by passing vertically through a sensitizing bath between two rotating rollers and exposed by contact or projection printing, the printing light being in all cases a H.P.M.V. lamp. To avoid fogging due to the spontaneous decomposition of the physical developer comprising a metal salt and a reducing agent the exposed material is treated with freshly-prepared developer, either from a sprayer whose reservoir of small capacity is fed continuously with solutions of metol and tartaric acid and of silver nitrate which are mixed in the reservoir by means of a stream of nitrogen, or upon a roller on to which the separate solutions are poured, mixing taking place before the developer is applied to the exposed material. Alternatively there may be employed a physical developer stabilized by acidifying to a pH of less than 1, cooling, or dilution such as a metolsilver nitrate developer acidified with nitric acid, a hydroquinone-tartaric acid-silver nitrate developer, to which glycerol is added to prevent freezing, cooled to below 0‹ C., or a diluted hydroquinone-silver nitrate, the developer being applied to the exposed material by immersion therein, by passage over a developer-moistened roller, or for a support exposed on both sides by passing vertically through a bath of developer between two rollers. The development of the material is then preferably accelerated by heating it as by means of a heated drum, preferably covered with a porous layer and having a belt covering the material to stop excessive loss of water, a current of steam or hot air, infra-red radiation, high-frequency field heating or, in the case of paper sheets, by passing a heating current through the metal belt covering them, followed by washing with hot water. Alternatively the heating and washing may be combined as a single step by passing the material into a bath of hot water, while in the case of a stabilized developer applied by means of a roller, this itself may be heated while the main supply of developer is unheated. Specifications 439,005 and 545,901 are referred to. As open to inspection under Sect. 91, the Specification describes a further example in which a film of regenerated cellulose is sensitized by successively soaking it in a solution of silver nitrate and a solution of potassium bromide and nitric acid containing some free bromine, developed by applying to it a continuously freshly prepared metol - tartaric acid - silver nitrate developer and heating the film with steam, fixed, washed, and dried. This subjectmatter does not appear in the Specification as accepted.