US2037716A - Process for the graining and surfacing of metal photolithographic and offset press plates - Google Patents

Description

Patented Apr. 21, 1936 UNI-T ED STATES.

PATENT OFFICE John a. San mm, Tu.

No Tm flan March 9,1935.

Serial No. 10.140 Claims. (01. 41-41.:5)

(Granted under act of March 3, 1888, as

amended April 30, 1928; 370 O. G- 157) The invention described herein may be manufactured and used by, or for, the Government for governmental purposes, without the payment to me of any royalty thereon.

I This invention relates to a process for-graining and surfacing, with a grease repellent surface, the metal photolithographic and oilset press plates.

This new process of surfacing. graining and i protecting the metal photolitho and oilset press plates is accomplished by first washingboth surfaces of the metal plate, 1. e., the work surface and the back surface, with benzole, turpentine or other grease solvent, to remove all oil and i grease. The plate is wiped to remove excess solvent and the remaining solvent allowed to evaporate until the plate surfaces are dry.

The second step in the process is to select one surface of the plate as the work surface and coat :0 it with a solution of gum arabic containing hydrofluoric acid or other acid which has the effect of producing a grease repellent surface on metal. This coating is allowed to dry. Y a

The plates are now in condition for the third 25 operation which is the graining of the work surface. Several plates are piled in the grainer with the coated or work surface up. The coating of gum on the work surface prevents the abrasive from working between the piled platesand this is ll a distinct advantage as it permits removing the top plate and proceeding to grain the next plate without cleaning the grainer. The graining marbles are placed on the plate surface and a solution of gum arable containing hydrofluoric or 86 other acid poured over marbles and upper or work surface of plate and the. abrasive is sprinkled on the marbles after which the grainer is set in motion. The length of time required in the grainer varies with the abrasive used. The solution 40 of gum arabic containing acid forms a desensitizing solution that is constantly being worked against the plate surface during the entire graining operation with the result that the clean metal is being rendered grease repellent.

45 The fourth operation consists of removing the plate from graining washing the work surface and back surface clean and free from abrasive under running water and without permitting the work surface to dry after washing it is coated U .with a solution of gum arable containing a small tion and contact with other surfaces.

amount of hydrofluoric acid or other acid. This coating is smoothed with sponge or cloth and dried on the work surface thereby preventing the bare dry metal of the work surface from contact with the atmosphere. Contact with the atmos- 5 phere will result in a film of grease forming over the entire work surface of the plate and this sum arabic coating prevents this deposit on the bare metal surface. The plate when completely dry is ready for storage or for use.

The fifth operation or operation necessary to put the plate into photolitho use requires that the plate be washed clean under running water and the work surface again coated; with gum arabic and acid solution which is immediately removed with running water and. the light sensitive coating (egg albumen and bichromate solution) is applied and allowed to dry without heating above 120 F. The application of solutions of cyanide or counteretches must be avoided.

This new process of preparing and surfacing the metal plates for photolitho and offset press use, creates and maintains a grease repellent property on the work surface of the plate and protects this work surface from atmospheric 8.0-

A study of the development, evolution or unfolding of the lithographic industry reveals a constant struggle against a scum or false tint that occurs on the blank surfaces of stones and plates. The methods and solutions used to combat, this scum destroy the brilliance of.-ink colors and eventually wear the'design 01f the plate for the simple reason that this scum foundation was imbedded in the work surface of the plate before the design was created thereon and this 'new method of preparing the plate surface has been developed to prevent this formation.

The method in common use today is the same method for preparing plate surfaces that has 40 been in use since metal plates were adopted to the lithographic industry. The plate is washed, given a bath with cyanide or lye solution washed clean and counteretched with a solution of alum, nitric acid, hydrochloric acid or acetic acid or some acid that acts as a counteretch. This counteretch renders the plate surface very sensitive to grease and it goes into the grainer where only-water and an abrasive are used with the graining marbles. The plate is taken from the so grainer and washedelean under running water and dried and after drying it is stored away for future use. This plate surface is extremely sensitivetogrease andisexpoeedbareanddry.

'l'hefactiswell knownthatathinillmygrease coating is deposited by the atmosphere on every bare dry surfaceand the resultis that (lithe grease sensitive work surface of the metal photoiitho plate the atmosphere is depositing and building up a grease illm that is constantly gettingstronger anditisthisnlmthatisthe foundation for false tint and scum that causes trouble in later operations. 7.

Having described nLv invention claim isnew andwishtosecur ehyLettersl'ateutis:

1. The method of preparing metal plates for photolithography which comprises graining the plates in the presence of solution of gum-arable and an acid. A

2. The method of preparing metal plates for photolithography which comprises graining the plates in the presence of solution of gum arable 5 and hydrofluoric acid.

3. In the preparation of metal plates for photolithography the imt" which comprises 'carryingoutallofthegrainingandsuriacing operation in the presence of a protective coating 10 remnprising gum arabic and an acid,

4. In the preparation of metal plates for photolithography the improvement which comprises carrying out'all of the graining and surfacing operation in the presence or a protective coating 15 comprising hydrofluoric acid. V

. JOHN G. GOEDIKE.