US2004144A - Process for photographically producing printing plates - Google Patents

Description

UNITED STATES PATENT (OFFICE PROCESS FOR PHOT This invention relates OGRAPHICALLY PRO- DUCING PRINTING PLATES William J.,Wilkinson, Great Neck, N. Y., assignmof one-half to The Miehle Printing Press and Manufacturing Company, Chicago, 111., a corporation of Illinoi N0 Drawing.

4 n 6 Claims. to processes for photographically producing printing plates,.and more particularly to processes for producing the photographic plates from which-the final metal printing plates are to be made.

In the graphic or I printing arts photographic reproductions of originals by the photo-engraving, photo-lithography or photo-gravure process. 1

Where the original is to be reproduced in colors,

it is usually plates which series of negatives are color filters,

photographed on made through different each of which negatives is used to.

make a different printing plate, and each of these plates when printed in the proper color and superimposed results in a reproduction of the original in colors.

, Theoretically, it is tions in all colors .to means of three printing low, another to print re possible to print reproducmatch the originals by plates, one to print yeld, and another to print blue. In practice, however, due to limitations of printing inks and the photographic process, a a black printing plate is usually added in the photoengraving and photo-lithographic processes.

Yellow, red and blue ink the proper proportions,

s, when superimposed in will produce all colors and black. A pure yellow area in an original will be reproduced by printing such area in yellow from the yellow printing plate and by superimposing substantially no color thereon from the red and blue printing plates.

redis produced by the In a similar Way red printing plate, and

blue by the blue printing plate. Green, which is a combination of yellow and blue, will therefore be produced by the superimposing of inks fromthe yellow and which is a combination blue printing plates.

of yellow and red, will be produced by the yellow and red printing plates, and violet or purplewhich is'a combination of blue and red will be produced bythe blue and red printing plates. imposing yellow, red and d from the corresponding printing plates.

intermediate colors will imposing all three of the colors appearing printed from fin plate. 4

C In the photo-engraving process, for example, photographing the origa negative is made by inal through a violet or filter permits the red 9. the original to pass thr Black is produced by superblue inks in full strength Certain be produced by supercolors, but with one or more light by virtue of being half-tone dots of the printing purple color filter. This nd blue color values of ough the filter and act Application November 19, Serial No. 576,014

panchromatic dry are sensitized for all colors, and a on the negative while the yellow light or value of the original is absorbed by the filter and is thus shut off from the negative. When a positive is made from this negative the fact that the yellow value'did not acton the negative and therefore left such areas of the negative light or transparent results in these areas being dense or dark on the positive, while-the blue and red values which acted on the negative and were therefore darkthereon will be light on the positive. Inasmuch asthe metalplate which is used to-do the actual printing is a positive, the dark portion on the positive is what represents the printing surface which will be used for printing in yellow ink. For, this reason the negatve from which this positive is made is called the yellow plate or negativeor separation negative. In a similar way, the red separation negative is made through a green filter which shuts off red and transmits yellow and blue, and the blue separation negative through an orange filter which shuts offblue and transmits yellow and red. The black separation negative has sometimes been made heretofore through a yellow filter.

If itwere attempted to produce the yellow, red, blue and black printing plates solely and entirely by photographic methods without handwork, when the various colors were printed in superposed relation to produce would .be found that the printedreproduction would look but little like the original andwould not be satisfactory. Where there were bright blues, reds, yellows, etc. in the originalfithe printed reproduction would tend to dullness,

somberness, and in parts to blackness. This is largely due to failure to secure correct and full color separation on the different printing plates -by photography alone. ,Where a pure yellow should appear, for example, it would be masked by too much red, blue and black from the corre- And inasmuch as yel- The defects inherent in the photographic process are largely due to there being too little the finished picture it process. This hand correction byexperts is expensive, not

can be automatically and photographically produced so that when the different colors are printed in superposed relation to these plates, the

printed reproduction will be a substantial duplicate of the original.

Another object of this invention is to provide an improved process for automatically and photographically producing dots of proper size and denstiy in the printing plates.

The above and other objects and advantages will appear from the following description and appended claims forming a part of this specification.

In carrying out my improved process, a yellow separation negative may be made through a violet filter on a panchromatic photographic plate which is sensitized for all colors. In a similar way, the red separation negative is made through a. green filter, and the blue separation negative is made through an orange filter. As hereinbefore explained, these separation negatives, if used as they are, would not give the true color values. The yellow plate is approximately 60% correct, the red plate 4050% correct, and the blue plate approximately 85% correct.

In order to correct the yellow separation negative the yellow value should be retained in its light or transparent condition, and the red and blue values should be made darker to get greater contrast between the yellow valueon the one hand, and the blue and red on the other, since the light portions of the negative which represent the yellow will be dark in the positive to represent the yellow printing value, whereas the red and blue values must be eliminated from or made light in the positive so that yellow ink will not be printed in any substantial depth of color on the final, picture where only red and blue values should be printed. In a similar way, the red value should be dark in the red positive, and the yellow andblue values should be made lighter. In the blue positive, the blue valueshould be dark, and the yellow and red values should be made lighter.

In order to accomplish this automatically and photographically, I make a thin positive from the yellow negative and a thin positive from the blue negative. The density of these positives will be varied by the operator in accordance with the conditions encountered and will be referred to as positive overlaysl,

To correct the yellow negative, the positive overlay made from the blue plate is placed in register over the yellow negative and a corrected positive is made by photographing through the negative and positive overlay. Inasmuch as the blue negative was made through an orange filter which transmits yellow and red rays, the yellow values will be dark in the blue negative and there: fore light or transparent in the blue positive overlay. Thus, light readily passes through the areas which represent strong yellow values in the yellow separation negative andthe blue positive overlay, to record the yellow values dark in the.

corrected positive made from the yellow negative. And since the blue values are dark in the blue positive overlay. this will lighten the blue values in the yellow corrected positive. In practice, it is found that by the above procedure the red values are also reduced sufficiently in the yellow corrected positive. Thus, in the yellow corrected positive, the yellows have been retained dark and at full strength to represent the printing surface in the final metal printing plate to be made, whereas the red and blue values have been eliminated or lightened to the extent desired. In a similar way, a red corrected positive is made from the red separation negative placed in register with the blue positive overlay, and a blue corrected positive is made from the blue separation negative with the yellow positive overlay placed in register therewith.

The positive overlays may be made either on glass photographic plates or on films. Ordinarily, glass overlays are preferable where the corrected positives are to be made in the camera, since glass gives more perfect "register. Film overlays, however, give fairly satisfactory registry and at the same time are much thinner than those of glass and are therefore advantageous in making corrected positives by the contact method in the printing frame, since the film overlay being much thinner than a glass plate permits the separation negative to be closer to the sensitized plate, thus producing a sharper image on the sensitized plate.

I prefer to make the black separation plate by giving a partial exposure to a sensitized plate through one colored filter at one time and another colored filter subsequently. These colored filters may be respectively green and orange, and the amount of each exposure will be determined by the operator in accordance with the black values in the original-which is to be reproduced. By correct exposure of the-black separation negative, it can be made quite correct and requires little, if any, retouching.

In case'it is desired toreproduce an original by printingin more than four colors in photolithography, the additional colors, which are usually-pink, light blue and grey, are printed in corresponding colored inks. The pink and light blue printing plates are made from corrected posi tives of the red and blue separation negatives, respectively, in the manner described above, and the grey printing plate is made from the black separation negative, the positives being given longer or shorter exposures and being reduced or intensified to get the proper strength for these additional colors.

This process which I have developed, in a great many instances enables retouching to be entirely done away with and, in some instances, reduces the amount of retouching required by 85-95%. The corrected positives may be produced either by the printing frame or camera. To produce a corrected positive in the printing frame, a glass half-tone screen is placed in a vacuum printing frame and on this half-tone screen is placed the separation negative with the proper positive film overlay on top of the negative and secured in register therewith in any suitable way, as, for example, by pieces of gummed paper. Next, a sensitized photographic plate is placed with its sensitized surface in contact with the film overlay, and light is passed through the half-tone screen, separation negative and positive overlay to produce the desired corrected positive on the sensitized plate. In-order to produce dots of the proper size'and density on the corrected positive, a contrast plate is preferably used. I find that several feet away from excellent results are produced by carrying out this operation in a dark room with a beam of light thrown upon the printing frame from a concentrated source of light placed the printing frame. In particular, I have found it advantageousto use a projector provided with a concentrated-light source and condenser lens means and preferably also having a reflector behind the concentrated light source. A- projector of this naturewhich gives satisfactory results is the Bausch & Lomb projector provided with a suitable lens andpri-f' marily manufactured to be used to throw enlarge ments of transparencies on a screen; I preferably place the projector about '7 to 8 feet fromthe printing frame and give a suitable length of exposure which ordinarily is a fraction of a second. As the described sends the light from a concentrated source in a beam sufiiciently divergent to properly cover a photographic plate,good dot formation is produced in the corrected positive. The re sulting corrected positive is examined for correct 1 density, detail and proper. dot'size anddensity,

and may be intensified or reduced by chemical treatment as required. I have found that additional contrast may be obtained by placing a clean transparent glass plate of suitable thickness, such, for example, as the thickness of a photographic plate, between the half-tone screen and the separation negative, since this causes the light to be so diffracted as to increase the size of the large ha1f-tone dots more than the small half-tone dots.

Instead of producing a half-tone corrected positive direct from the separation negative and positive overlay, the half-tone glass screen may be omitted from the process just described, and a continuous-tone corrected positive will then be produced. This continuous-tone positive permits hand retouching which is not practical in a half-tone positive. The continuous-tone correctcd positive, retouched if desired, is then placed in the printing frame between a glass half-tone screen and a sensitized photographic plate and a half-tone negative is then produced by means of the projector in the way above-described.

Instead of using the vacuum frame to make corrected positives. the camera may be used. On account of the better register attained, the overlays are preferably made of glass in this instance. The negative and glass positive overlay having been joined in perfect the camera and a half-tone positive is made through a half-tone screen of desired size of ruling, preferably on a wet plate. Where the original which is to be reproduced is very large, I find it advantageous and economical to make the corrected positive on a smaller sized plate and with a correspondingly finer screen ruling than ultimately desired on the final negative, the screen ruling used being calculated so as to give the desired size of screen ruling on the final printing plate.

For photo-lithography it is desirable that t I high-light half-tone dots should be eliminated. I

produce the corrected positive; I

size and proper screen ruling, and after very short, usuallyf projector above-'- T register are placed before van tageo'usl'y accomplished both for color ,and monotone reproductions- ,A negative is made of the copy t be reproduced. ,In the case ofcolor reproduction, the separation negatives are what,

are needed. 'In the case .of, av monotone copy.- a

good orthochromaticnegative is needed. -Either;

place the negative before the camera and make a half-tone positive therefrom ina' finer screen and,

in a smaller size thanthe final negative should be, orplacethenegative ,iha vacuum. frame and exposewith the projector lamp as before described have found a way by which ,this, can be very ad;

in order to producea positive on a sensitizedglass plate.

I" have found that'by reducing this glass plate positive by ,chemicaljtreatment, the highlight dotswhich are small can be readily andcompletely eliminated, If, necessary, intensify the positive until the dark portions have satisfactory. H dot formation: Now placeja positive made in this way before the camera in case it has been made,

size, and

on a finer screen and is of a smaller make from it anenlarged negative of the proper exposure intensify or reduce the negativ'eas may sary to get thefinal proper dot formation. case the positive is made required for printing, and to the, right size, the negative may bemade in a contact vacuum frame, preferablyon a Cramercontrast plate, and reduced or intensified as required;

From corrected contact printing in negatives before the camera and half-tone negatives, either on dry or wet photographic plates. By correct exposure and manipulation the proper dot formation may be obtained. From thesefinal half-tone negatives, positives are made on metal for use in printing, as is well known.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention, and the present embodiment of the invention is, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes that come within the range of equivalents of the claims are, therefore, intended to be embraced therein.

I claim:

1. In the art of photographically producing printing plates, the process comprising making yellow, red, blue and black separation negatives, making positive overlays from the yellow and the blue separation negatives, making a corrected positive of the yellow separation negative by photographing through the yellow separation negative and the blue positive overlay, making two corrected positives by photographing through the red separation negative and the blue positive overlay, one corresponding to the red printing plate and the other corresponding to the pink printing plate, making two corrected positives by photographing through the blue sepaand the yellow positive overlay,

printing plates, the process which comprises makpositives obtained, either by the printing frani'eor' by the i, camera znethodnegativesare made'by placing the making final be neces-,,, 1

with the proper screen plate in a vacuum printing frame and exposing to the individual colors required to reproduce the ing a series of separation negatives corresponding original composite coloring making transparent positive'overlays from certain of said separation negatives and making a corrected half-tone posi tive of certain of said negatives by placing a halftone screen, the separation negative, film overlay and a sensitized plate in a vacuum printing frame and exposing the same to light from a projector having a condenser lens.

v 3. In the art of photographically producing printing plates, the process which comprises making a series of separation negatives corresponding to the individual colors required to reproduce the original composite coloring, making transparent positive overlays from certain of said the s'ame'to light from a projectorhaving a condenserlens. I f 1 4. In the art of photographically producing printing plates, the process comprising making yellow, red and blue separation negatives, making a positive overlay from the yellow separation negative having a predetermined density such that when superimposed upon the blueseparation negative the transmitted light possesses the color value required to produce the corrected positive, making a positive overlay from the blue separation negative having a density such that when superimposed on the yellow separation negative and on the red separation negative respec-. tively the transmitted light will have the color values required to produce the corrected positives, making a corrected positive of the yellow separation negative by photographing through the yellow separation negative and the blue positive overlay, making a corrected positive of the red separation negative, ,by photographing through the red separation negative and the blue positive overlay, and making a corrected positive of the blue separation negative by photographing. through the blue separation negative and the yellow positive overlay.

5. In the art of photographically producing printing plates, the process which comprises making a series of separation negatives corresponding to the individual colors required to reproduce the original compositecoloring, making transparent positive overlays from certain of said separation negatives and making a corrected half-tone positive of certain of said negatives by placing a half-tone screen, the separation negative, film overlay and a sensitized plate in a vacu-' um printing frame and exposing the same to light.

,6. In the art of photographically producing printing plates, the process which comprises making a series of separation negatives corresponding to the individual colors required to reproduce the original composite coloring, making