US2316645A - Deep etching lithographic plate - Google Patents

Description

Patented Apr. 13,,1943.

UNITED STATES PATENT" 1 OFFICE I near fiomncrirfifeflkmc mm I Philip Zeiger, New York, N. Y.

No Drawing. Application February 25, 1942,

I Serial No. 432,239

1 Glaim. (cur-41,5)

This invention relates to improvements in theart of deep etching lithographic plates.

In the common procedure of making deep etch lithographic plates, the plate is first freed of oxide fllm by treatment with-counteretch solution, after which the plate is coated with alightsensitive dichromated gum solution and the desired design is then photographically exposed on the sensitized coating, thereby hardening the portions of the coating exposed to the action of light. other areas which it is. not desired to have appear in the print ultimately made from the plate, are stopped out with shellac solution or other appropriate material. The exposed design is then developed with -a suitable developing solution and the spent developing solution is re moved with simultaneous removal of the unhardened portions of the gum coating, after which the plate is ready for deep etching. The etching of the plate is then accomplished by treating the uncovered portions thereof with a suitable etching solution, afterwhich the plate is washed with water-free denatured alcohol to remove the etching solution as well as the stopout shellac. Following the washing operation, the plate is dried of all alcohol, after which a coating of laquer is applied evenly and thinly over its entire surface. Next, the plate is coated with developing ink and dusted with powdered talc. Following this, the hardened gum stencil, together with the developing ink adhering thereto is removed by scrubbing with water while the developing ink remains on the etched portion of the plate. .After drying, the plate is ready for use. This procedure requires "a considerable quantity of alcohol for the purpose of removing the stop-out shellac and thoroughly cleaning the plate of all developing and etching solution.

An object of this invention is a deep etching technique for producing lithographic plates which eliminates the use of alcohol, thereby eiiecting a substantial reduction in expense, as well as elim-. inating any difliculty arising from a shortage of alcohol.

According to the present invention, a lithographic plate to be deep etched is first counteretched and then coated with light-sensitive dichromated gum solution in the usual manner and is photographically exposed to the desired design as heretofore. Instead of stopping out the unchromated gum coating unhardened by exposure to light are immediately removed from the plate The unexposed border of the plate and through the use of suitable developing solution as formerly. After the developing step, the uncovered portions of the plate are treated with etching solution as formerly except in the absence of stopout medium. Following the etching operation, the plate is thoroughly rinsed in hot water (approximately boiling temperature) thereby removing the developing and etching solutions, as well as removing the hardened or light-exposed portions of the dichromated gum coating except for a very thin film adhering to the portions of the plate corresponding to the exposed portions of the dichromated gum coating, which film inherently adheres to the plate. The major portion of the rinsing operation is preferably eflected in a. tank of hot water followed by treating the plate with running water. The plate is then immediately dried preferably by blotting with clean news stock or water-leaf blotting paper and changing the paper two or three times. The border and undesired portions are now stopped out with regular desensitizing plate etch which is soluble in water. After the drying of the stop-out medium, the entire plate is lacquered as formerly and dried with the lacquer coating being applied evenly and thinly. On the surface of the dried lacquer, deep etch ink is applied and the ink film dusted with asphaltum if desired. Following this treatment, the plate is subjected to running water which washes ofi the lacquer together with the adhering ink from the portions of the plate coated on the parts corresponding to the light-hardened portions of the dichromated gum coating with the previously mentioned film as well as the stop-out medium while leaving the ink on the etched portions of the plate. The lacquer and excess ink may also be removed by immersing the plate in a tank of warm, but not hot, water and wiping oil with absorbent cotton. Following the drying of the plate subsequent to the operation of removing the excess ink and lacquer, the plate is ready for 'use in the usual manner.

The technique above described is carried on without the use of alcohol. The alcohol can be dispensed with due to the fact that shellac is not used as the stop-out medium. Instead of using shellac as the stop-out medium, water-soluble plate etch is used as the stop-out medium after the etching step so that it is not subjected to the washing operation following the completion of the etching step but is applied just prior to the application of lacquer.

I claim:

The method of deep etching a plate which consists in coating the same with light-sensitive dithe entire surface or the p te including said s op-o m coating said lacquer mm with ink and washing of! said stop-out medium together with lacquer and adhering ink from the 5 unetched portions or the plate while leaving ml:

in the etched portions of the plate.

PHILIP ZEIGER.