Patent GB-626501-A (GB)
Title: A screened transparent light sensitive sheet for diazotype reflectography processes
IPC: G03C1/52
Filed: 1946-10-25
Abstract: 626,501. Photographic reflex printing. CHEMISCHE FABRIEK L. VAN DER GRINTEN. Oct. 25, 1946, Nos. 31789, 31790 and 31791. Convention dates, Nov. 1, 1945, April 23, 1946 and April 23, 1946. [Class 98 (ii)] Screened light sensitive sheets for the positive diazotype reflex printing process which incorporate opaque and transparent areas without intermediate transitions are characterized in that the substance forming the opaque areas is deposited in cavities present in the sheets, and in one embodiment in cavities formed in the sensitive layer itself. The opaque areas may, individually, have a size of 80 mu. and may occupy 80 per cent of the area of the sheets, and after exposure and development the opaque substance is removed and this results, in the case where the cavities are formed in the sensitive layer, in a positive copy with a dull or relief surface which can be written on. Removal is effected by causing the opaque substance to adhere to a covering transparent skin, which forms one layer of the original sheet, more strongly than it adheres to the light sensitive layer and then removing this transparent skin along with the opaque substance, or by use of an opaque substance which owes its opacity to its finely divided condition, such as powdered thiourea, which is soluble in the developing liquid. Fig. 4 is a sectional view of a complete sensitive sheet lying on the surface of a drum used to form the sheet as by application of a solution of nitrocellulose in acetone to the grooved surface 2 of the drum 1 to form a cavitied skin 6 to which an opaque substance such as a paste of carbon black in gum arabic solution is applied, and this forms opaque areas 10 ; excess of paste is doctored off, an extremely thin layer 16 as of rubber latex is placed over the opaque areas and the latter is loosely united to the sensitive side 15 of an acetyl cellulose film 14. The product is laid with its lower side on an original and exposed through the skin 6, after which layers 6, 10 and 16 are stripped off with aid of adhesive paper or suction treatment and the film 15, 16 is developed as usual. In the embodiment in which opaque areas are formed in the sensitive layer itself, an acetyl cellulose film may be softened on one surface by means of acetone, pressed against a relief mould to form the cavities and then surface saponified and sensitized and the cavities filled with opaque substance, which latter may be removed by brushing with developer, or it may be further treated with a solution of acetyl cellulose in acetone which makes the particles of opaque substance sufficiently coherent to enable removal by pressing them, after exposure, on to an adhesive layer of latex and then removing the film. Suitable diazo compounds for producing the light sensitive layers, developers for the same, and additional types of opaque pastes are described. The Specification as open to inspection under Sect. 91 comprises also the production of a half-tone screen by a method similar to that used for making the reflex printing sheets, and states that half-tone images suitable for production of cliches in relief and flat printing can be made by copying images produced on the reflex printing sheets of the invention on to sensitized layers. This subject-matter does not appear in the Specification as accepted.