US1982967A - Printing element and process of making same - Google Patents

Description

Dec. 4, 1934.V B. L. SITES 1,982,967

PRINTING ELEMENT AND PROCESS 0F MAKING' SAME Filed oct. 9, 1951 Patented nDec. 4, 1934 UNITED STATES PRINTING ELEMENT AND PROCESS F MAKING SAME Benjamin L. Sites, Chicago, Ill., assignor to The Miehle Printing Press & Mfg. Company, Chicago, Ill., a corporation of Illinois Application October 9,

Claims.

My invention pertains to printing surfaces and more specically relates to a process of producing printing elements such as are used in rotov 0 is to say, the deep tones of a print will be produced by those cells which carry most ink, while the lighter tones are represented by the shallow, less ink carrying cells.

Heretofore intaglio printing surfaces were prof duced by the delicate and cumbersome carbon tissue method according to which method a carbon tissue, such as regular commercial carbon paper, after it has been sensitized, is exposed through a screen and through a photographic transparency. The exposed tissue is then squeegeed onto a carefully prepared base such as a sheet of copper, whereupon the base is subjected to a dissolution treatment and etching process as is well known in the art.

The principal object of my invention is to eliminate the use of carbon tissue and to thereby very substantially simplify the old methods of producing intaglio printing elements.

According to my invention, it will also be possible to correct errors that might occur during the preparation of a printing element, or to change designs by retaining the same base, a feature which it was impossible to accomplish heretofore. In order to attain these and other objects which will become apparent from the following description and appended claims, I conceived a scheme of providing the surface of a printing elementwith ink carrying cells which are all of the same, or approximately the same, depth, and to then determine the in k carrying capacity of the cells by applying thereto a material different' from that of which the base itself is made, preferably a photographic emulsion which, after having been exposed and developed, will leave in the cells deposits of unequal depth corresponding to the various color tones required.

According to my invention I propose to proceed for example by flowing a printing base such as a sheet of copper or a copper cylinder with a lm of bichromated gelatin or bichromated albumen, generally termed bichromated colloid, which film I subsequently expose through a rotogravure screen and then develop it with warm water in thev usual manner, so that a screen image will remain on the base. Preferably the developed screen image is then baked so as to form a permanent resist. Thereupon I etch the base with ferric chloride which will produce ink 1931, Serial N0. 567,776

retaining cells, all of which are of approximately the same depth.

It will be readily understood that instead of providing the screen image on the printing base by the etching method as explained above, the same result could be accomplished mechanically such as by impressing `or rolling a screen image into the surface of the base. If produced in this manner, the walls of the cells become hardened by the physical contact of the tool used for this purpose.

This would afford a decided advantage over the etching process because thereby the surface of the printing element will be rendered more resistant to the wear of the doctor blade which is generally used. for scraping the surplus ink off the printing surface of the element prior to effecting the impression.

The cells of the screen image are then flowed with a silver bromide gelatin photographic emulsion in a dark room and squeegeed off so that the emulsion will remain in the cells only. 'I'his emulsion will then be shrunk and thus solidified by dryingor by any other practical method so that eventually its level will be below the plane of the screen image.

After this silver bromide gelatin emulsion is shrunk i. e. solidied, I expose it through a design carrying-transparency such as'by contact in a vacuum frame, which exposure requires but a few seconds.

After exposure the emulsion in the cells of the copper plate orthe like will be developed by any desired method, for instance in a photographic developer so that the emulsion remaining in the cells will be of varying thickness in proportion to the exposure received, and after developing the emulsion which remains in the cells will be swelled either with an alkaline or an acid solution. I have found that the swelled condition of the silver bromide gelatin emulsion can be rendered permanent by immersing the `plate i. e. exposed surface into` a solution of alcohol, alum and formaline. drying of the surface by heat will cause the swelled emulsion to 'become hardened. By this swelling process the emulsion in those cells which correspond with the high lights ofthe sibject, will completely fill said cells, so that no ink retaining depth will be provided in these cells.

Another method whereby the swelling of the emulsion can be arrested i. e. rendered per. manent is that of saturating the swelled emulsion with a solution of sodium silicate and subsequently precipitating silica in the gelatin with acid; or, saturating the swelled emulsion i. e. gelatin with a solution of a salt and subsequently.

precipitating an insoluble compound by the addition of a precipitating agent.

In Figures 1 to 9 of the accompanying draw- Subsequent ing, I have illustrated one manner of carrying coating 11 of bichromated gelatin or bichromated albumen, see Figure 2, whereupon thiscoating 11 is exposed through a rotogravure screen 12 having transparent portions 13, see Figure 3.

Figure 4 illustrates the printing element after it has been exposed through a screen; the portions 14 representing the exposed areas While the portions 15 show the unexposed areas, which corresponded with the opaque sections of the screen and whichduring the development process will dissolve so that the exposed portions 14 only remain on the base, such as is shown in Figure 5.

After developing, the plate will then be subjected to the) etching process during which the ink carrying cells 16, see Figure 6, wilL be formed. These cells, as explained above, will all be of the same, or approximately the same depth and will then be flowed with a silver emulsion such as a silver bromide gelatin photographic emulsion 17, see Figure '7. lThis emulsion, after having been thoroughly dried and thus solidied, will then be exposed -through a photographic transparency 18, Figure 8, and then developed and swelled as explained above, whereby the high lights i. e. light tones willbe represented by the areas 19, which carry little or no ink at all, whereas the deeper tones will be represented by the more vink carrying cells 20 as shown in Figure 9.

While I prefer to etch all the cells of the screen image to an even depth, it is not essential to devote much care to that part of the process,

i because the ink retaining capacity of each cell is determined by the emulsion as explained', and

therefore minor variations in the depth of these i rotogravure printing elements will oler the following principal advantages:

s 1. The use of carbon tissue will be entirely dispensed with. l

2. Errors may be readily corrected, or new designs applied, by washing out the emulsion in the ink carrying cells and by repeating the flowing of the cells with emulsion and subsequently exposing and developing. This does not destroy the copper cells.

3. The etching of the base does not require the usual skill since a slight variation in thedepth of th cells produced does not result in any defect in the nished plate.

4..,The swelling action of the gelatin can be controlled with less skill than is now required for etching through carbon tissue.

5. The exposure of a plate can be readily accomplished in a step and repeat machine, thereby attaining perfect register for multicolor work.

As an alternative, that is to say, .instead of flowing the ink carrying cells by a silver emulsion and then swelling that emulsion as hereinabove described, I find that equally satisfactory results can be obtained by owing said cells with bichromated gelatin, in which case, however, the

cells would have 'co remain filled, that is to say.,1 the gelatin vin the cells must not be below the' plane of the printing element i. e. screenlimage when the gelatin is dry i. e. solidified'and at thev According to this scheme, instead of the emull swelling and drying the emulsion in said cells.

sion in the cells becoming swelled as explained above, those portions of the screen image which during the exposure through the photographic transparency were not exposed to the light will Qdissolve and wash out so that a printing element identical to that illustrated in Figure 9 will be produced.

It is therefore my intention to cover any such modifications inthe process of making printing elements that will come within the scope and essence of the appended claims.

` 1. The process of making intaglio printing elements, consisting in flowing a metal base with a light sensitive coating capable of producing`an etching resist, exposing. said coating through a screen, developing said coating, drying the screen image remaining on said base, -etching said base to provide ink retaining cells therein, applying a photographic emulsionto said cells, drying said emulsion, exposing said emulsion through a photographic transparency, developing the exposed emulsion to produce varying thickness in said cells in proportion to the exposure received, and drying the emulsion in said cells.

. 2. The process of making intaglio printing elements, consisting in owing a metal base-with a .stantially uniform depth therein, applying a photographic emulsion to said'oells, drying said emulsion, exposing said emulsion through a photographic transparency, developing the exposed ,emulsionl to produce varying thickness in said cells in proportion to the exposure received, and

3. The process of making intaglio printing elements, consisting in flowing a metal base with a light sensitive coating capable of producing an etching resist, exposing said coating through a screen, developing said coating, drying and baking the "creen image remaining on said base, etching id base to provide ink retaining cells therein, applying a photographic emulsion to said cells, drying and-shrinking said emulsion, exposing said emulsion through a photographic transparency, developing the exposed emulsion to produce varying thickness in said cells in proportion to the exposure. received, and swelling and dryingthe emulsion in said cells.

4. The process of making intaglio printing elements, consisting inproviding a metal base with ink retaining `cells of substantially uniform depth, applying a photographic emulsion to said cells, drying said emulsion, exposing said emulsion through a photographic transparency, developing the exposed emulsion to produce varying thickness in said cells in proportion to the.

exposure received, and swelling and drying the emulsion in said cells.

5. Thprocess of making intaglio printing elements, consisting in providing a metal base with ink retaining cells of substantially uniform depth, applying a photographic emulsion to said cells, drying and shrinking said emulsion, exposing said emulsion through a photographic transparency, developing the exposed emulsion to produce varying thickness in said cells in" proportion to the exposure received, and swelling and drying the-emulsion in said cells.

BENJAMIN L. SITES.

.light sensitive coating capable of producing an

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