US1897828A - Process for photochemical production of aluminum printing forms - Google Patents

Description

Patented Feb. 14, 1933 UNITED STATES PATENT OFFICE MAX THIMANN, OF BERLIN-WILMERSDORF, GERMANY, ASSIGNOR TO THE FIRM DR. IBEKK & KAULEN CHEMISCHE FABRIK G. 11.3. 11., OF BERLIN-LICHTERFELDE, GER- MANY' PROCESS FOR PEOTOCHEMICAL PRODUCTION OF ALUMINUM PRINTING FORMS v No Drawing. Application filed March 12, 1931, Serial No. 522,186, and in Germany March 17; 1930.

While it is easy in the photochemical production of zinc printing forms to remove the colloid coating fromthe exposed parts of the plate after having exposed,'developed and etched the cleared parts of the plate before such removal is being made, for example by means of alkali, this removal of the hardened colloid coating makes difiiculties when aluminum printing forms are used.

Alkali cannot here be used for the removal before applying the sensitized colloid coat-- ing to the plate. Especially suitable for this purpose are the sulphates of aluminum,

' chrome, iron and the like, and in first line the alums, such as potassic aluminum alum,

iron ammonium alum, chrome potassium alum and so on.

By first treating the aluminum plate or similar aluminum printing form with such a salt solution it is possible, easily to remove or wash oil the parts of the coating hardened by exposure from the plate or the like, which after said treatment with the salt solution has been covered with the sensitized colloid coating, exposed, developed and etched. This removing of the hardened coating can be easily and quickly done with suitable acids, especially phosphoric acid. Thereby as a rule it is not dissolving of the hardened coating which takes place, but

loosening of it from the metal plate or the like, so that the coating can be rinsed off the plate, either as a whole or in large pieces.

To attain the said effect it is, ior example, sufiicient to pour a diluted, say 1% solution of alum salt on to the clear metal plate, to leave it standing therewith for a short time,

then to'pour' ofi the said solution and to water the plate or the like and to coat in.

the usual way with a sensitized colloidcoating.

The further treatment, exposing, developing and, if desired, etching of the plate can be done in the usual way, wherein for etching the clear-laid parts of the aluminum plate or the like, preferably phosphoric acid, mixed with concentrated ferric-chloride can be used. By using the said mixture of phosphoric acid and ferric-chloride, for the preparation of which a ferric-{chloride solution of at least contents should be used, and which therefore has either the consistency of a paste or of a viscid fluidity, one attains, that the etching medium only acts on the clear-lying parts of the plate and does not go to the exposedparts of the plate through the hardened coating which may be covered with a varnish or,resi= n layer, if required.

To remove the coating from the etched plate, a diluted phosphoric acid, e. g. a watery 10% phosphoric acid may expediently be used, whereby the loosening of the sensitized colloid coating from the plate previously treated with alum or the like, in the way above stated, is easily attained.

- If the plate, which has first been treated inthe said way with salt solutions, then spread with the sensitized colloidcoating, exposed and developed, is to be etched, the parts of the plate to be protected from the action of the etching medium must be covered in known way with a suitable coatin In the above stated case, for an especia y suitable cover-coating a mixture of tannable organic substances, such as copying-glue, and

tanning means, such as chrome alum are to be considered. The plate hereinis treated for instance in that way, that a fresh mixture of about equal parts of copying-glue and a solution containing 5% chrome alum is brought on to the parts of the'developed plate to be protected. Here the mixture stifiens after some time owing to tanning setting in. The

stifiening may be quickened by heating the plate. The thus formed covercoating protects the parts of the plate below it from the action of the etching means, for example from the above indicated mixture of phosphoric acid and iron chloride. The removal of the coatings on the plate after the etching by means of phosphoric acid can then be done forthwith, the protective coating formed from tannable substances and tanning means being dissolved from the plate with the hardened gelatine coating in so far as the protective coating is arranged on the gelatine coating, but on the other hand also from those par of the plate where the protective coating is situated directly on the metal of the plate, it

is directly dissolved without further ado by the action of the prosphoric acid.

Having now particularly described and ascertained the nature of my said inyention,

i I declare that what I claim is 1. A process for the photochemical production of aluminum printing-forms, comprising treating the aluminum body with an acid-free solution of a salt of a tri-valent metal, coating a sensitized-colloid coating onto the plate, exposing, developing, and

etching the plate, and then removing the hardeiied colloid-coating.

2. which the salt for treating the aluminum body,'prior to applying the sensitized colloid-coating, consists of an acid-free solution of ,a sulphate of a tri -valent metal.

3. A process according to claim 1, in which the salt for treating the aluminum body, loid-coating, consists-of an acid-free solution of an alum.

1 4. process for the photochemical production of aluminum printing-forms, comprising treating the aluminum body with an acid-free solution of a salt of a tri-valent metal, coating a sensitized-colloid coating onto the plate, exposing, developing, and etching the plate, and then removing the process according to claim 1 inv before applying the sensitized col acid and highly concentrated ferric-chloride, and removing the hardened colloidcoamg from the metal by dilute phosphoric acl 8. A process for the photochemical production of aluminum printing-forms, comprising treating the aluminum body with an my hand.

1 -MAX THIMANN.

hardenedcolloid-coating by means of a dilute acid.

5. A process according to claim 4-, in ;which the hardened colloid-coating remover is a water solution of phosphoric acid.

6. process for the photochemical production of aluminum printingiorms, comprising treating the aluminum body with an r acid-free solution of a-salt of a tri-valent metal, applying a sensitized colloid-coating thereover, exposing and developing the plate, etching the clear-lying parts of. the plate with phosphoric acid, and removing the hardened colloid-coating from the metal 7 with dilute phosphoric acid.

thereover.

process for the photochemical production of aluminum printing-forms, comprising treating the aluminum body with an I acid-free solution of a salt of a tri-valent meta-l, applying a sensitized colloid-coating exposing and developing the plate, etching the clear-lying parts of the plate by means of a mixture of phosphoric acid-free solution of a salt of a tri-valent