US2270712A - Etching lithographic plates - Google Patents

Description

To the accomplishment of Patented Jan. 20, 1942 S PATENT OFFICE ETCHIN G IJTHOGRAPHIC PLATES William H. Wood, Bedford, Ohio, assignor to Harris-Seybold-Potter .Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application April 12, 1940,

, Serial No. 329,343

be used to remove the residue of the developer e e 11 Claims.

In'the manufacture of deep-etch lithographic plates it is customary to coat a cleaned and counter-etched zinc or aluminum plate with a resist which is sensitive to light, and the plate is then exposed to light in the form of the subject matter'which is to be reproduced, such that in those areas where no image is desired on the finished plate the resist is hardened; then the unhardened areas of the resist are removed by ,a developing agent so as to leave the image portions of the plate clean.- A so-called deepetching solution is then applied to the plate and allowed to attack the exposed image areas until the metal is etched away to the desired depth, and after drying, the deep etched areas are treated with material, commonly referred to as a lacquer, to render them receptive to inlr. Subsequently the light-hardened areas of the resist, which during etching have served to protect the non-image areas of the plate, are re-' moved by a clean-up solution. The plate is then given a desensitizing etch to make the nonlmage areas receptive to water and is ready for printing. In accordance with the present invention, improved procedure and materials are involved, such as to. afiord more easy manipulation and control, and. more reliable and positive action, and making possible the production of remaining on the, plate.

Following removal of the unhardened portions more rapid in its early stages than is desirable and subsequently diminishes rapidly, thus making it difiicult to control accurately the extent of the etching action. Such solutions also tend .to preserve or emphasize the rough character of the plate surface. In addition, in the case of such iron chloride solution a portion of the iron chloride may crystallize ,out or may form plates having improved longevity, definition,

fidelity and uniformity.

the foregoing and related ends, the invention, then, comprises the features hereinafter fully described, and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative however, of but a few of the various ways in which the principle of the invention may be employed.

In the preparation of plates in accordance with my invention, I may employ any usual or preferred materials, as for instance the well known glue or gum arabic. Such coating material, suitably sensitized with a suitable dichromate or the like as usual, is app ied to the metal plate, as in the well-known practice.

The coated metal plate, (the metal being usual or as preferred, zinc, aluminum, etc), having been exposed to light and the subject matter which is to be reproduced, is treated with the developer, which may be of any usual or pre-- ferred material, for instance a concentrated solution, about 50 B., of calcium chloride confollowing the developer, anhydrous alcohol may ferric hydroxide or metallic iron, thus leaving a deposit on the plate causing the lacquer to lift where it should adhere. In etching in accordance with the present invention however, I apply a saturated solution of magnesium chloride in water to which has been added a small amount, for instance two to five per cent by weight of each of two water-soluble monobasic aliphatic acids, viz. formic and glycollic (the latter also known as hydroxyacetic), or formic and hydracrylic acids. Less advantageously, acetic or propionic acid can be used in lieu of formic acid in some cases. This etching material results in certain new and difierentefiects distinguished by the following characteristics: (1) it has the effect of smoothing out the grain of the etched of the roughened surface to a greater extent than from the valleys; (2) it has a slower and more moderate action than previously known etching solutions, requiring a longer time, such as one and one-half to three minutes, for the completion of a suitable degree of etching, and is therefore more easy to control; (3) it maintains its etching activity for a longer period and etching continues throughout the extent of the time required in normal operation. This deep-etching material may be used on aluminum as well as on zinc, but for best results on aluminum plates it is desirable to include ferric chloride, as in amount of five to twenty per cent in substitution for equivalent amounts of the magnesium chloride.

Having etched the plate by the usual or the preferred etching materials as indicated, the hardened resist is next removed from the nonimage areas of the plate which it has protected during the deep-etching, and for this, I prefer to employ a water solution of gluconic acid, for instance about one to five per cent. Gluconic acid is novel in this relation, and is very useful with known resists, but is particularly desirable where the preferred resists as above described have been employed.

This application is a continuation, in part and as to common subject matter, of my application Serial No. 223,523, filed August 6, 1938.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a process of making lithographic plates, etching the developed plate with a saturated solution of magnesium chloride containing two to five per cent by weight each of formic and glycollic acid.

2. In a process of making lithographic plates,

etching the developed plate witha solution of magnesium chloride containing formic and glycollic acid.

3. In a process of making lithographic plates,

etching the developed plate with a saturated solution of magnesium chloride containing a small per cent of a water-soluble monobasic aliphatic acid. I 4. In a process of making lithographic plates, etching a developed aluminum plate with a solution of magnesium chloride and ferric chloride, containing formic and glycollic acids in amount two to five per cent each.

5. Ina process of making lithographic plates, etching a developed aluminum plate with a solution of magnesium chloride and ferric chloride,

containing formic and glycollic acids.

6. In a process of making lithographic plates,

etching a developed aluminum plate with a solution of magnesium chloride and ferric chloride, containing a small per cent of a water-soluble monobasic aliphatic acid.

7. In a process of making lithographic plates, etching the developed platewith a saturated solution of magnesium chloride containing two to five per cent by weight each of formic and glycollic acid, and then treating the plate with a one to five per cent water solution of gluconic acid.

8. In a process of making lithographic plates, etching the developed plate with a solution of magnesium chloride containing formic and glycollic acid, and then treating the plate with a one to five per cent water solution of gluconic acid.

9. In a process of making lithographic plates, etching the developed plate with a saturated solution of magnesium chloride containing a small per centof a water-soluble monobasic aliphatic acid, and then treating the plate with a one to five per cent water solution of gluconic acid.

10. In a process of making lithographic plates, etching a developed aluminum plate with a solution of magnesium chloride and ferric chloride, containing formic and glycollic acids in amount two to five per cent each, and then treating the plate with a one to five of gluconic acid.

11. In a process of making lithographic plates, etching a developed plate, and then treating the plate with a solution of gluconic acid.

WILLIAM H. WOOD.

per cent water solution;