Patent GB-655274-A (GB)
Title: Improvements in processes of photographic reproduction
IPC: G03B15/00
Filed: 1948-04-15
Abstract: 655,274. Photographic processes. KODAK, Ltd. (Eastman Kodak Co., Yutzy, H. C., and Yackel, E. C.). April 15, 1948, No. 10545. [Class 98 (ii)] A method of photographic reproduction comprises exposing to an object or image a substantially unhardened light-sensitive silver salt emulsion layer, developing the exposed layer in the presence of a tanning, developing agent, and transferring in the presence of moisture at least a thin stratum of the unexposed and unhardened parts of the emulsion layer to a support, which may be absorbent. The emulsion binder may be gelatin, polyvinyl alcohol, a hydrolysed cellulose ester, or an imagewise hardenable resin (e.g. polyacrylamide) and may contain a pigment, e.g. metallic silver, carbon black, or Monastral Fast Blue BWD. The tanning developing agent may be incorporated in the emulsion layer as in Specification 655,273, and development effected by means of an alkaline solution. Alternatively, the exposed material may be treated with a solution of a tanning developing agent and then with an alkaline solution, or the exposed material may be treated with the solution of a tanning developing agent and then placed in contact with the receiving support with a layer of alkaline solution between. The absorbent support may be paper, wood, or cloth, and after contacting the moist emulsion layer with such support, an outer thin stratum of the unexposed and unhardened portion of the emulsion layer is caused to adhere thereto by the application of pressure, and, if necessary, heat. After stripping, the differentially hardened layer may be rewetted with the alkaline solution and additional transfers similarly made. The optical density of the transferred image may be increased by treatment with a sulphide (e.g. sodium or zinc sulphide), alkaline thiourea, or a metal salt, or the transferred image may be further exposed and, if desired, heated and treated with a reducing agent or developed in an alkaline solution which may contain a developing agent. If the layer contained a developing agent before exposure, the density may be increased by exposing and heating the print. The transferred image may be colour developed, or a coupling component, with or without a colour developing agent of lower developing rate than the tanning developing agent, may be incorporated in the emulsion. The receiving support may be coated with a sulphide or thiourea, with alkali, with citric acid to facilitate stripping from the receiving support, and with sulphite, bisulphite, or ascorbic acid. The colloidal binder of the transferred image may be hardened with alum or chromium salts. Development may be commenced by treating with ammonia solution or by fuming with ammonia. The preparation of a gelatino silver chloride emulsion containing as a tanning developing agent 3 : 4-dihydroxydiphenyl, and slightly hardened with formaldehyde, is described. In an example, the emulsion is exposed by contact or projection printing, is treated in a sodium carbonate bath and excess alkaline solution removed by squeegeeing, and a sheet of paper is rolled into contact with the emulsion and immediately removed. On exposure to light, the transferred image develops to a positive image, development being accelerated by heat. Further transfers may be effected by re-wetting the negative with alkaline solution, squeegeeing off excess, and rolling into contact with paper. Six to eight copies may be made. With an emulsion not containing a developing agent, the exposed material is immersed in aqueous hydroquinone solution prior to treatment in the sodium carbonate solution, which includes a small amount of sulphite. A diazo compound and/or an azo coupling component may be incorporated in the emulsion, the remaining component (if any) being incorporated in the receiving support. An azo dye image is formed in the transferred area. The negative image remaining on the support may be treated with a reducing agent (sodium sulphite) and then squeezed into contact with a support carrying a layer of dye bleachable with sulphite (e.g. Malachite Green) to give a direct positive image of the original subject in dye. An ink or pigment may be rolled into the matrix remaining after transfer of the soft unhardened emulsion, and the ink or pigment transferred on to a support. With a gelatin emulsion, the developing solution may contain formamide, ethylene chlorhydrin, urea, sodium nitrate, or glycerol to facilitate transfer. A stencil may be prepared by coating the emulsion on a porous support such as cloth, silk, or highly porous paper and transfer the unhardened image after exposure or processing in one or more transfers until the support becomes pervious to a printing ink in the unhardened area. By the selection or preparation of an emulsion layer of suitable softness or thickness, or a suitable temperature or pressure during transfer, substantially all of the unhardened gelatin may be transferred in one operation. Specification 655,275 also is referred to,