US2412889A - Printing process - Google Patents

Description

1946- E. JAHODA 2,412,889

PRINTING PROCESS Filed Feb. 16, 1945 Molar Pandas s' ms 6 40::

4 INVENTOR. 'W ;M BY

Patented Dec. 17, 1946 PRINTING PROCESS Edward Jahoda, Detroit, Mich'., "am; to Walter M. Fuchs, Detroit, Mich.

Application February 16, 1945, Serial No. 578,187

This application relates to the art of printing, using the retro-gelatin printing process.

In that process, an original whose image lines contain a primary chemical, such as potassium dichromate, is caused toengage a moist gelatin coated plate, the coating being sensitized by the inclusion therein of a secondary chemical, such as ferrous sulphate. The contact of the original image with the ferrogelatin coating causes the engaged portions of the ferrogelatin coating to be chemically aflected or hardened selectively and superficially, that is, only on the surface, to form against the unaflected parts of the ferrogelatin coating, which remain soft or unhardened, a superficial image whose lines are oxidized or dulled or hardened. 'I'he hardening which forms the image is merely superficial and selective, that is to say, the hardening occurs only at points where the markings of the original,

containing the primary chemical, make contact with the gelatin, but is sufficient to have a greater affinity for greasy printer's ink than the background which, when sufllciently moist, has no such affinity. It is known that, in printing with a ferrogelatin coated plate so affected by an original image, hereafter known as a printing plate, it is desirable to keep the gelatin coating surface moist, that is, to maintain what is technically called a water "balance" for such surface.

One way of maintaining such water balance I is to provide a high humidity for the room. This has obvious disadvantages, but is an accepted practice.

Another way of maintaining water balance, is to apply water to the printing surface by spraying or otherwise wetting it directly. This is not desirable, because it has been discovered that when water is applied directly to the printing surface, it has a tendency to spread unevenly, and also to emulslfy with.the ink.

A third way is to load the gelatin with a hygroscopic material such as glycerine. This is also undesirable since glycerine coated materials are dificult to handle and store.

In commercial practice, particularly where a gelatin coating is spread on a supporting table in a humid room, it is common practice to scrape oil or otherwise remove the gelatin coating fairly frequently, let us say, after a few hours of use,

and to spread a new and fresh coating. This has obvious disadvantages but it has been accepted as part of the practice in this art.

Now, I have contemplated using, as the gelatin printing plate, a paper sheet coated with gelatin.

1 Claim. (01. 101-1493) 2 However, I observed that if the gelatin coating were to be used at ordinary room temperatures, which in warm weather may exceed 975 F., good reproduction results would be diillcult to obtain. Consequently, in warm weather, it would be necessary to maintain low room temperatures and this would be costly and diilicult and annoying. Therefore, I contemplated loading the gelatin with a body hardener or tanning agent, such as formaldehyde, or chrome alum, but this also would be unsatisfactory. Ii little tanning agentwere used, the gelatin coating would not become sufficiently tanned except after being aged" or "cured by storing the coated paper for a long time, to attain sufllcient tanning. Thereafter the coated paper would be usable, provided not too long a time elapsed before use: otherwise the coating would become excessively water repellant. It is observed that excessively tanned coatings would not function well inthe process, primarily because, of the lack of capacity to absorb suflicient water for good reproduction. On the other hand, if much tanning ag nt were used, the coating would tan quickly, but this would require immediate use of the paper, and this, would not always be feasible. In addition, the use of tanning agents would reduce the quality and ease of reproduction.

In this application, I disclose a solution to the problem of maintaining water balance, now encountered in the art of printing by the i'errogelatin process. Briefly, it may be character.- ized as using a paper printing plate and wetting it from the back, the moisture passing through the plate to the printing surface. This way of maintaining water balance is extremely effective and desirable. Using this way, it is unnecessary to control the humidity of the room in which the printing is being done, nor is it necessary to wet the printing surface from the front, and run the risk of emulsifying the ink.

The invention may be practiced by providing, as the printing plate, a thin sheet of water absorbent, wet strength paper, coated with gelatin and laid down on a moist smooth rubbing pad. The paper sheet provides an economical, renewable, inexpensive to discard, stable, printing plate, which is not only superior to presently known plates because it may be wetted from the back, but in addition, can be renewed quickly, inexpensively, and very conveniently, after its gelatin coatinghas had its effectiveness destroyed by the changes whichhave taken place in it during the printing operation.

The present invention is also directed to the auaase problems of making the printing plate, that is,

coated paper to be stored indefinitely, used whenever desired, and used at ordinary room temperatures even in warm weathen and to the use of such coated paper for reproduction, at ordinary room temperature, even in warm weather.

Briefly, the coating herein disclosed is substantially untanned, having little or no tanning agent. Kept dry, it may be stored indefinitely. Paper coated with untanned gelatin, may be packaged in cut sheet or roll form, and if protected against moisture, as by being wrapped in waxed paper, may be stored.

In use, the paper may be wetted from the back. I have discovered, however, that when the wetting pad II is made of a porous stone block, moisture is evaporated, and such evaporation functions to cool the gelatin coating sufficiently to enable untanned coatings to be used at ordinary room temperatures with good results.

It seems, therefore, that a solution to all problems is offered by the adoption of back wetting, by the use of a porous stone block as the wetting block or pad, and by the use of untanned-gelatin for the coating.

For a further understanding of theinvention hereof, reference should be had to the appended drawing which shows a plate ID in the form r of a sheet of water absorbent wet strength paper,

coated on its upper surface with untanned gelatin, and disposed upon a moist porous stone block or pad II. A suitable moisture suppl for the pad may be provided, if needed, to maintain the pad ll continuously moist.

The printing plate I is a sheet of wet strength saturating paper, coated on its upper surface with untanned gelatin. It can be manufactured to be sold dry, in cut sheets or rolls, and is perfectly stable under ordinary storing and handling conditions. It is economical, easy to make, and easy and satisfactory to use.

The printing plate hereof may bev and preferably is free of glycerin since it is not required to be hygroscopic, for it is not intended that the water balance for the gelatin surface be maintained'by absorption of moisture from the air, but rather it is intended that the water balance be maintained by the transfer of moisture from the pad ll, through the printing plate itself, to the printing surface. Thus the printing plate hereof is far less affected by storing and handling conditions than plates containing glycerine in which water balance is maintained by the hygroscopic action of the glycerine.

The paper functions as a moisture transfer medium, to transfer moisture from the source, name- 'ly the pad II, to the gelatin surface, and thus is required to be of a character that retains its strength during the moisture transfer. Forthis purpose, it might well be any well known wet strength or saturating or absorbent paper. One paper that has been found suitable is a paper obtained from the Brown Paper Company, and known as No. 201 Aqualized Kraft." Saturating tissue, such as is sold by the Process Manufacturing Company of Chicago, Illinois, has been found satisfactory. Vegetable parchment papers have also been found satisfactory. A paper known as L99, of Byron Weston Co., Dalton, Mass, has also been foundsatisfactory.

The paper need not have any capacity for stor-.

ing moisture, since only its moisture transfer characteristic is relied upon to maintain the water balance.

' 4 With gelatin. the usual plasticizers, filler, etc.,

-all well known to the art, may be and preferably should be incorporated within the coating. Howformed with the secondary chemical of that process, ferro sulphate or its equivalent. Instead, the gelatin may be plain, but it will be sensitized or activated, Just before it is engaged by the original, by dampening or moistening it with a farm sulphate solution. This may be done from the front or the back. Thereafter, the moisture balance for printing is maintained by the transfer of moisture through the printing plate from the back, where the printing plate is in contact with the wet pad. While it is contemplated to apply the sensitizing solution from the front, it is, of course, obvious that if desirable, it also might be applied from the back, but except insofar as the sensitizing is a moistening step, this is not particularly important.

The pad H is a porous stone block. One form of block, now being sold by Filtros Incorporated (formerly General Filtration 00., Inc.) of East Rochester, New York, under the trade-mark Filtros, and described by that company, in a bulletin entitled Filtros Plates," copyright 1944, as a white rigid, porous, mineral substance, composed essentially of silica, and which might be termed as an artificial porous stone has been found satisfactory.

It has been found that maintaining the water balance for printing in the manner herein described, by transfer through the printing plate evenly absorbed by the gelatin, with no excess,

and without drops of water on the surface, and consequently, there is no tendency for the printing ink to spread or emuisify with water.

Further, it has been found that where it is attempted to wet the affected printing plate from the front, great skill, complicated apparatus, considerable time, frequent interruption of production, are required, and even under the best of operating conditions and performances, unevenness of distribution of the moisture occurs, with the result that the ink spreads, or emulsifies, and the unaffected or unhardened or background portions of the gelatin swell unevenly around the chemically aflected or hardened or image portions of the gelatin to cause hills and valleys on that coating, and reproduction is not so satisfactory. Where there is unevenness of distribution of the moisture, either no swelling of the unhardened gelatin background takes place, or else the swelling of the unaffected or unhardened gelatin is accompanied" by a similar swelling of the chemically affected and superficially hardened gelatin image. Where the moisture passes through the paper, entering from the back, as in the present case, the undesirable conditions and factors are eliminated, and, with less difficulty, better reproduction is obtained.

If desired, the paper may be supplied with wetting agents, having a tendency to increase the absorption and transfer qualities of the p per.

These agents might be applied to the paper during the manufacture of the paper, or might be incorporated in the wetting solution.

' Wetting from'the back is of particular value where gelatin coatings are thin, as for example, where the gelatin is in the form of a thin coating, applied to paper, and stored dry. Withsuch plates, the wetting -and maintaining of water balance is a far more delicate operation, and yet is far more important, than under conditions where thick gelatin coatings, frequently renewed, are used in humidity controlledrooms.

Using a wet porous stone block as the wetting pad is of especial importance, inasmuch as it functions to cool the paper, thus enabling papers having untanned gelatin coatings to be used at ordinary room temperatures, with good results,

- and thus enabling coated papers to be stored and kept indefinitely, to be useful for reproduction by the ferrogelatin process. I

Now having described the art of printing herein disclosed, reference should be had to the claim which follows:

I claim:

In the art of printing with moisture repelled, greasy printers ink with anon-hygroscopic, initially untanned gelatin surfaced, thin, water absorbent, wet strength paper printing plate having a superficial printing image of hardened gelatin on and surrounded by an unhardened ferrogelatin background, the image having been produced on the background by surface contact thereof with an original image containing a primary chemical which reacts superficially with the fer- 'rogelatin background to harden the engaged portions thereof to form the selective and superficially hardened image, so that there is unhardened gelatin underlying the image area as well as surrounding it, the step of feeding moisture to the plate from the back thereof, so that the moisture passes through ,the plate to the printing surface thereof, thus maintaining the water balance therefor, and also maintaining a constant .minimum differential of level of the image and non-image areas, by applying the paper to and in contact with a moist porous stone block which wets and cools the paper.

EDWARD JAHODA.

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