DE331745C - Process to increase the shelf life of negative tracing papers - Google Patents

Description

Process for increasing the shelf life of negative tracing papers. Under The iron oxide salts used in the cyanotype include the citric acid iron oxide ammonia in the first place, but it is flawed. For example, it cannot in crystalline form and can therefore only be produced with difficulty in a pure and constant manner Composition can be obtained. Furthermore, it is very hygroscopic and therefore dissolves soon when stored and cannot be sent in bulk. Also stands it is higher in price than other double salts used in the cyanotype.

Of the latter, the oxalic acid double salts are often used. In contrast to the citric acid salt, they do not show any of the deficiencies mentioned above, however, provide tracing papers with a poor durability.

It has now been found that one can also use the iron oxide double salts the oxalic acid can produce negative tracing papers, which in terms of durability not only reach the papers prepared with the citric acid iron oxide ammonia, but even surpass it. This effect is achieved by adding to the emulsion those from a solution of potassium ferricyanide, oxalic iron oxide salts, potassium dichromate and a binding agent, still adds a certain amount of inert salts, who are neither photosensitive nor take part in the reaction that occurs as a result of exposure occurs between the reduced iron oxide salts and the potassium ferricyanide.

This observation is already in the patent 3ao98r specifically for the neutral oxalic acid alkalis. In contrast to this patent It was established that not only the neutral, but also the acidic salts this favorable cause comes. Yes, it turned out that depending on what you wanted Effect the acidic salts are preferable to the neutral ones. The blue of the negative breaks becomes livelier and more fiery when the acidic oxalic acid salts are used. Particularly What is striking is the difference in the effect that the acid salts compared to the neutral or even basic salts achieve when using the phosphoric acid Salts. While the primary ammonium phosphate produces the described effect, this cannot by any means be said of the secondary and tertiary ammonium phosphate. On the contrary, the addition of the latter two salts has a direct, non-partisan effect the emulsion .-- a. Example. 9 kg of sodium oxalate and 3 kg of acid oxalic acid ammonium are dissolved in 5o 1 water. This solution is mixed with another solution of r kg of potassium ferricyanide in 5 1 of water containing as much gelatin and potassium dichromate is added as required by the nature of the paper will.

The paper is coated with this emulsion in the known manner and is ready to use after drying. It is very sensitive to light, it persists but also very good. Show even after several months of storage the pauses made with it are pure white lines on a dark blue background.

Claims (1)

Vgahr @ - # F @ .y4e4üng the shelf life of negative tracing papers with the iron oxide salts of oxalic acid are prepared, characterized in that one indifferent to the photosensitive emulsion, neither photosensitive nor an the reaction that occurs as a result of exposure between the reduced iron oxide salts and the ferricyankali enters, participating salts, with the exception of the neutral oxalic acids Alkalis, adds.