US848833A - Method for preparing half-tone printing-plates. - Google Patents

Description

No. 843,833. PATBNTBD APR. 2, 1907.

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METHOD POR PREPARING HALF TONE PRINTING PLATES.

- APPLCATION FILED FEB. a. 190e.

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LAWRENCE KERN, OF DAYTON, KENTUCKY.

METHOD FOR PREPARING-HALF-TONE PRiNTlNG-PLATES.

Specification of Letters Patent.

Patented .April 2, 1907.

Application filed February 8, 1906. Serial No. 300,043.

To a/ZZ whom t may concern.-

Be it known that I, LAWRENCE KERN, a citizen of the United States, and residing at Dayton, Campbell county, State of Kentucky, have invented a certain new and useful Method for Preparing Half-Tone Printing- Plates; and I do declare the following to be a clear, full, and exact description of the invention, attention being called to the accompanying drawings, with the reference characters marked thereon, which form also a part of this specification.

The desideratum in the various processes in half-tone printing is to attain the proper effects and contrasts in dark and lights, as well as a proper soft blending from one into the other. Absolute high lights-that is, clear white imprinted spaces-are difficult to obtain under present methods and with the printing-plates now used, and expensive methods using so-called overlays and underlays are resorted to, which give, however, only limited results.

The obj ect of my invention is to produce a a printing-plate which gives absolutely clear high lights and self-blending vignettes, as well as properly-blended effects, without the use of overlays or other auxiliary means.

In the following speciiication, and particularly pointed out in the claim at the end thereof, is found a full description of my invention, together with its manner of use and method of preparation, which latter is also illustrated in the accompanying drawings, a half-tone plate being used for purpose of illustration, and in which- Figure l shows a cross-section of a printing-plate in the first stage of its preparation. Fig. 2 shows the same in a later stage of such preparation. Fig. 3 shows the same at` a still later stage. Fig. 4 illustrates a printing-plate prepared according to my process.

Fig. 5 shows the die-plate I use in the preparation of my improved printing-plate. Fig. 6 shows in cross-section both the printingplate and the die-plate shown in Fig. 5 on top of the printing-plate and for the purpose of acting upon the latter. Fig. 7 shows a crosssection of the completed printing-plate. Fig.

8 showsa portion' of the preceding figure onl a larger scale. y

In order to make myself better understood, I will now briefly recite the usual present method of producing a half-tone printingplate. A negative on a sensitized glass plate is first produced by the usual photographing process through a screen, the latter being used to obtain the dots necessary to produce an ink-transmitting printing-surface or printing-face on the plate. With the aid of this negative a photographic print is made on a sensitized metal plate intended to form the half-tone printing-plate. This plate is shown in section in Fig. l, in which A indicates the metallic plate, and B its light-'sensitive coating, all considerably enlarged. The process under which this photographic 'print is made causes certain parts of this coating to become fixed on the plate, subject to the ac-l tion of the light, and the non-exposed parts of the coating remaining soluble are washed away, leaving the plate as shown in Fig. 2, in which b indicates those parts of the coating which remain after the soluble parts have been washed away, a indicating the intermediate parts where the printing-plate, is now exposed. A printing depth is now obtained by means of chemical etching, whereby the plate is subjected to the action of a chemical in form of a suitable acid solution and Whereby the exposed parts are eaten away, as shown at a in Fig. 3. This causes parts b,

protected by the non-soluble coating, to rei main, such parts producing the so-called "dots, which constitute the printing-face of this plate. Contrasts in light and shade exist in such a photo-engraved reproduction by reason of the color value of the original copy, which has been proportionally transmitted through the screen on the negative; but because the natureof the half-tone plate makes it necessary to make printing possible to'hold a dot even in its lightest portion, where it only prints an unsatisfactory gray tone, the present half-tone is faulty and unsatisfactory. This is by reason that the dots which constitute the printing-face are all on a level and equally subjected to the action of the .press-roller and equally affected thereby IOO engravers tools, routing-machines, &c., does not entirely overcome this defect. My method proposes to dispense with all such make-ready devices and relies solely on the printing-plate itself to obtain these desired effects, the printing-plate being prepared in a certain manner accordingly.

I refer now to Fig. 4, which illustrates a printing-plate produced by means of my process. C may indicate a certain illustration or cut to be printed, and D a vignette surrounding the same. The dots shown are the surfaces indicated at b in Fig. 3, while the intermediate surface portions are the cavities produced by the etching and shownat a in Fig. 3. The varying size of the dots is due to the action of the photographing process first described, subject to the screen, and as the action is modiiied by the light and dark portions of the subject photographed. The larger-sized dots, holding and transmitting more ink, produce the shaded and darkei` portions of the picture and the smaller dots the lighter portions. Pronounced high light effects are, however, not obtainable by reason of the pressure of the press-cylinder, which affects equally all dots of the printing-face, as before stated, including also the smaller dots, where, however, limited pressure only or none at all would be preferable. To overcome this defect, I lower more or less and in a certain manner to be presently described such portions of the printing-face as indicated at c, where I desire to produce high light effects, thus removing such portions beyond the action of the ink-roller and the presscylinder, as well as graduating such action for the purpose of obtaining soft blends at points where dark and light portions merge into each other. Especially around the edges of a vignette such blends enable me to obtain. highly-desirable results without the aid of tools or press make-readies. For the purpose of such lowering I prepare a metallic die-plate E, (see Fig. 5,) having projecting portions e, which in location correspond to such parts in the printing-plate where I desire high lights, as 'at c, (see Fig. 4,) as well as blended effects-as, for instance, around the edge d of the vignette. At the same time the thickness of the intended printing-plate below these spots c where such effects are desired is reduced by the removal of metal thereat, as shown at a2 in Fig. 6, the lower one of the two plates being the printing-plate A in course of preparation. metal is accomplished by a routing-machine or by gouging-tools and is strictly limited to the places mentioned, so that the general thickness of the plate and the straight plane of its back as far as it serves for support remain unimpaired. Next the die-plate E is placed on top of this latter plate, everything eing so arranged that the raised parts e of the die-plate, the high lights c and blended This removal of portions d on one side of the printing-plate, and the reduced parts a2 on its other side register with each other. The printing-plate is now subjected to pressure applied by any suitable means to the die-plate, a suitable protecting medium-as, for instance, a piece of leather F-having first been interposed to prevent injury to the dots which constitute the printing-face of the plate. This pressure is transmitted to the printing-plate by the raised parts c only of the die-plate, and contact between the two is limited to these parts, the action being terminated at proper time, so that the body of the die-plate between these parts e does never come in contact with the face of the printing-plate. The results of this action are illustrated in Fig. 7, which shows the complete printing-plate in section, the high lights c and blended portions d of the face having been depressed, the metal yielding on a gradual uninterrupted curve into the hollowed out portions a2, which resulted' from the previous removal of metal. The extremely fine dots being now within the depressed portion c of the printing-face and on the upwardly-curved surfaces surrounding the same, (see Fig. 8,) it is clear that the pressure of the tympan or roller affects them to a degree varied and graduated by these curves, thus producing highly effective light tones, while at the saine time the gradual transition from the deepest parts of these depressed portions upon the curved surfaces surrounding them to the normal level of the printing-face produces the desirable softly-blended eiiect between extreme contrasts. I have omitted to show the dots in the plate illustrated in Figs. 6 and 7, which in reality are scarcely discernible with the naked eye, and are therefore greatly enlarged in Figs. 2, 3, 4 and also in the enlarged detail, Fig. S, which shows the Yfinal stage of the plate as it appears in Fig. 7 and when made according to the method described. Any cavities which may remain on the under side of the plate after its face has been depressed in the manner stated may be filled with solder or other suitable substance to reestablish thereat a surface even with the back of such plate. This process is equally applicable to any photo-engraved plate or any other printing-plate as may be worked with my method. Vhile copper and zinc are the usual materials used for such plates, I do not limit myself thereto, and any equivalent substances or alloys, as well as electrotypes and stereotypes, may be used.

It is evident that a complete die-plate to produce simultaneously all depressions is not absolutely necessary, and they might be produced in another method and by hand-tools one after the other.

It may be mentioned that my method requires no change in the present way of mounting the plates.

TOO

In conclusion, it will be noted that my method distinguishes sharply against all other processes in which pressure is applied to the entire plate, whereby the delicately-engraved printing dots and lines are always more or less bruised and injured, resulting in a defective'blotchy impression, more or less blurred. In my method I apply pressure only at limited portions of the printing-face and at such portions only which, being depressed below printing contact, do not serve thereafter as any parts of the ink-transferring printing-face. No parts of this latter from which actual printing takes place come in contact with the pressure-exerting medium which depresses the other parts, and they remain, therefore, free from all possible bruises and injuries, which in transmission during printing would result in defective impressions. My process may, therefore, also be carried out in a more positive and direct way and under use of hard-metal implements or hard die-plates, all positively applied at certain limited spots, thus obtaining better and well-defined results, as against the uncertainty of methods working with soft and yielding pressures of tympans, overlays and other surfaces consisting of or built up of soft material. Furthermore, the printing of blended portions is transmitted by curved f parts of the printing-face, whereby a proper evenlygraduated transition from light to shade is obtained. This refers to and is applicable to all parts of the printing-plate, its edges for vignette inish, as well as to the surfaces surrounded by them.

Having described my invention, I claim as new- The method of producing a printing-plate, of the kind here in view, and which method consists of rst decreasing the thickness of the plate from its under side and below such parts only of its printing-face which are intended to produce high lights and blended effects adjacent thereto, and of afterward depressing these parts below the level of the printing-face by applying positive pressure directly against such face, contact of the pressure-exerting means being limited to the deepest portions only of the surface to be depressed, and which portions yare caused to produce absolute high lights by being depressed below printing contact, additional surface portions adjacent to these deepest portions being also .drawn in, the transition from the normal face being on a gradual curve so that the printing on these curved surfaces takes place with an evenly-gradu ated contact, whereby the blended e'ects adjacent to the high lights are produced.

In testimony whereof I hereunto set my hand in presence of two witnesses.

. LAWRENCE KERN. Vitnesses:

ALBERT J. BOWMAN, EDWARD W. BLUM.

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