Patent GB-119328-A (GB)
Title: Process for Preparing Printing Plates.
Inventor: HAIN ALBERT JUSTICE
IPC: G03F7/115
Filed: 1917-11-07
Abstract: 119,328. Hain, A.J. Nov. 7, 1917 Drawings to Specification. Photo-mechanical printing-surfaces. - In the preparation of etched photo-mechanical printing- surfaces, the printing plates are provided with isolated uniform areas of hardened gelatine which are light sensitive, or are associated with a sensi. tized emulsion, and are treated so as to increase their size laterally in accordance with the tones of the images to be printed. The following methods of procedure may be employed. (1) The areas are produced by depositing a film of gelatine sensitized with potassium bi-chromate either directly on to the plate or on to a layer of etching resist thereon, exposing the film to light beneath a screen having spaced openings or transparent areas, and washing out the soft gelatine. Other methods of producing isolated areas may be employed, if desired. The areas are sensitized with silver bromide or other metallic salt, and the spaces between the areas are filled with soft gelatine, the plate being then immersed in a solution comprising 10 grains of potassium ferricyanide and 10 grains of potassium bichromate in 1 ounce of water. A positive print is squeegeed into contact with the plate after it has been immersed in water left for about 15 minutes and removed. The contact, with the print causes chemical reaction which hardens the soft gelatine in the neighbourhood of the areas so that they are increased in size in accordance with the tones of the print. The still soluble gelatine is then dissolved out with hot water. (2) The steps up to and including the sensitizing with a metallic salt and the filling in of the spaces with soft gelatine are carried out as in (1) and the plate is exposed under a negative. The plate is then immersed in a solution comprising 10 grains each of bromide, ferricyanide, and bichromate of potassium in 1 ounce of water, and the soft gelatine is re moved as before. (3) The solution employed in method (2) is replaced by a solution of pyrogallic and citric acids, 3 grains each, and 15 drops of 20 grain silver nitrate solution, in 2 ounces of water, the plate after treatment with this solution being immersed in a 5 per cent solution of potassium bichromate and afterwards treated to remove the soft gelatine. (4) The isolated areas are produced and sensitized as in (1) and the plate is exposed beneath a negative or in a camera, developed, and fixed, being then immersed in a solution of lead nitrate 100 grains, potassium ferricyanide 150 grains, and acetic acid 25 minims, in 5 ounces of water. This treatment deposits lead on the isolated areas in accordance with the amount of metallic silver contained therein, and approximately increases their size. (5) The gela. tine film first deposited as in (1) contains in addition manganous chloride, and after treatment as in (1) to produce isolated areas, the plate is flowed with gelatine-bromide emulsion which surrounds and covers the isolated areas. After exposure under a negative, the plate is immersed for about two minutes in a solution of 10 grains each of bromide, ferricyanide, and bichromate of potassium in 2 ounces of water and 1 minim of sulphuric acid. drained, allowed to lie for 15 minutes, and then washed to remove the soft gelatine. In all cases in which the areas are deposited on an etching resist, the plate is treated to a solvent for the resist after treatment bv one of the above methods and then etched. When the areas are deposited directly on the plate they are burnt into the plate to form an enamel before etching.