Patent GB-630874-A (GB)
Title: Improvements in sensitized sheets for positive diazotype screen reflectography processes
IPC: G03C5/20
Filed: 1946-10-25
Abstract: 630,874. Photographic diazotype reflex printing. CHEMISCHE FABRIEK L. VAN DER GRINTEN. Oct. 25, 1946, Nos. 31787 and 31788. Convention dates, Nov. 1, 1945, and April 23, 1946. [Class 98 (ii)] A transparent film sensitized with a diazo compound is united to a skin having a screen pattern consisting of a myriad of minute transparent and opaque areas without intermediate transitions, the screen pattern being in the immediate vicinity of the sensitive layer of the film. Union between the sensitized film and the skin may be effected by pressure alone or may be facilitated by wetting or by use of adhesive. The assembly may be exposed to an opaque original during its transport through an exposing apparatus which has frictional resistance, the skin stripped off dry from the sensitive film, and when a two-component diazotype sensitizer is used, development may be effected with ammonia vapour only. The skin may have local screenless portions and may not be adhered to the sensitized film at a corner or other places so as to facilitate its removal from the sensitized film, and such removal may be effected by contacting the skin with an adhesive surface to which it has greater adhesion. than to the sensitized film, and then removing this surface, together with the skin, from the sensitized film. As shown in Fig. 1 an adhesive paper strip 5 from roll 4 is pressed on to the skin side of the assembly 7 between cylinders 1 and 2 and separation is effected at the edge 8 of frame 3, at which point the paper carrying the skin is caused to make a sharp bend downwards to roll 6, while the sensitized film is stiff enough to continue straight on. In Fig. 2 an internal vacuum applied at point 11 of the surface of rotating cylinder 15 is caused to suck the skin 17 away from the travelling film 7. Example 1 describes a skin of acetyl-cellulose of 35 grams per square metre which is unilaterally saponified, sensitized with a solution containing p-diazo-o-chloro-dimethylaniline chloride, oxalic acid and phenol, exposed under a dot screen such as that described in Specification 540,178 and developed in ammonia vapour, to produce the skin having a screen pattern; and this skin is united to a dulled and superficially saponified acetyl-cellulose film of 70 grams per square metre, which has been sensitized with para-diazoethylbenzyl-aniline, by a thin layer of rubber latex; the screen side of the skin to the sensitized side of the film. This assembly is subjected to reflex exposure, the skin is removed and the film developed with alkaline phloroglucinol. Example 2 describes a similar assembly but one in which thiourea and phloroglucinol are present in the sensitive layer, permitting development with ammonia only; and example 3 an assembly in which the screen skin is of 15 grams per square metre only and is adhered to the sensitized film by means of a solution of rubber in benzene and subsequently removed therefrom by use of a paper treated with a solution of rubber and colophony in benzene. Specifications 425,126 and 540,178 are referred to.