US1886556A - Process of making color-printing plates - Google Patents

Description

Patented Nov. 8, 1932 1 menses JOHN Ml REE-NAN, E TORONTO, ONTARIO; CANADA 'IPROCESS OF MAKING COLOR-PRINTING PLATES Ho Drawing.

This invention relates to the production of the half tone plates used in inulti-color lithographing and printing processes. Urdinarily the plates are prepared from negatives 5 taken by photographing the colored subject first through'a green filter, then through a red filter and then through a blue filter, and, in four color works, through a pale amber filter to produce the black plate. Thus color separations are obtained, that is negatives, one of which is supposed to represent all the yellow in the subject, another all thered and another all the blue, While the black," plate represents the Whole of the tones of the original in their proper relation to each other.

Unfortunately, however, it is mainly supposition, as light filters Which Will'pass the rudimentary printing colors in theirproper proportions are unattainable. 2G The result is that, when the plates produced from these color-separation negatives are prepared, a great deal of hand W0; is required to make each plate represent as truly as possible the values of the color which it represents. i

ln the case of photo-engraving this work comprises stopping out or staging parts of the plate which are suficiently etched and re-etching by hand those parts insufificiently etched to loring out the proper value of the color. This Work is done in stages until finished and afterwards proofs must be pulled, with all three or four impressions properly superimposed, in order to determine how accurately the colors of the original are produced. If the results are not satisfactory this goes on till the plates are satisfactory. This hand Work takes a lot of the time of shill-ed and highly paid labor. For instance, from forty-five to sixty hours of time is average for an ordinary job,

My object in the present invention is to obtain proper values the colors the printing plates as ar as possible by photomechanical means, ough some small amount of hand Work may in some oases he necessary -for the finest results, thus eliminating nearly all the hand staging and re-etching non required on the printing plates themselves. 0 This is efi ecteol in the following manner. lt

'colorfilter lets through some redand some Application filed March 26, 1931, "Serial No. 525,609.

appears that thegreen color filter lets through some blue light, that the red color filter also lets througl'r some blue light, that the blue yellow light, and that the blaclr negative, though taken through a pale amber filter does not give the tonal values of the original exactly enough. Therefore, to obtain sub-- stantially correct color values in the final positives, which are used as copy for the making of the color plates, or transparencies for i use in the production of the replicas of the original copy, some means must be provided to cut-out the effects or the intrusive color When preparing a positive from a colorseparation negative This is done by superimposing on the color-separation negative (yellow, red, or blue, as the case may be) a positive, or cut out taken from the complem ntary color separation negative and then, by means of the camera, making a positive lay means oi light transmitted through the combination K This complementary positive or out-out usually remains in position during part only of the time oi exposure and then exposure is completed with light transmitted by the color separation negative only. As the complementary positive or cut-out represents color values complementary to those of the color-separation negative, it cuts down the ellect oi the transparency of the colorseparation negative, Where the complementary color has affected it, so that the positive printed from the combination has cut out of it the eilect of the passage of the complementary color which passes the filter and afiected the original.color-separation negative. In practice employ a cut-out representing blue with a yellow color-separation negative, a cut-out representing blue with color-separation negative, and emloy with a lolue color-separation negative, st a cut-out representing red, and then, reierably, a cut-out representing yellow each for part of the time of exposure), and v ith the blacl? negative all three cut-outs ueoessively (each for part of the time of exosure}, f

the ease of the making of the positives in'rti from the blue and the black color-separation negative the exposure may also be for part time without using a cut-out.

The color separation negatives and positives are, of course, applied face to face so that the films are in substantially the same focal plane.

With the'method of overlaying the colorseparation negatives with cut-out positives, made from complementary color-separation negatives, any tonal efi'ects desired may be produced, as the cut-out efiect is readily varied by varying the ratio of the time exposure of the final positive, with a cutout in position, to the total exposure.

This process demands perfect registration of a color-separation negative, and the cut-out employed and any known apparatus may be employed for this purpose.

The final positives are used in any known manner to produce the printing plates used in makin replicas of the original copy.

What claim as my invention is:

1. In a process of making color-printing plates the steps which consist in making ordinary color-separation negatives from an original representing the three primary printing colors red, yellow and blue; making positives from said negatives; superimposing a positive taken from the blue color separation negative on the yellow color separation negative to serve as a corrective cut-out; superimposing a positive taken from the blue color separation negative on the yellow color-separation negative to serve as a corrective cut-out); superimposing on a blue colorseparation negative a positive taken from a color-separation negative representing light of a longer wave length; and, with a camera, producing a positive of each combination by light transmitted therethroug'h.

2. In a process of making color rinting plates the steps which consist in making ordinary color-separation negatives from an original representing the three primary printing colors red, yellow and blue; making positives from said'negatives; superimposing a positive taken from the blue color-separation negative on the yellow color-separation negative to serve as a corrective cut-out; superimposing a positive taken from the blue color-separation negative on the yellow colorseparation negative to serve as a corrective cut-out; superimposing on ablue colorseparation negative first a positive taken from the yellow color-separation negative and subsequently, after removingthe said positive, a positive taken from the red colorseparation negative; and, with a camera, producing positives from the combinations by light transmitted therethrough, the exposure in the case of the blue color-separation negative being for part time with the yellow cut-out? in place and part time with the red cut-out in place 3. A process of making color printing plates as set forth in claim 2 in which the final positive taken from each color-separation negative is exposed for part time without a cut-out positive superimposed.

4. In a process of making color-printing plates the steps which consist in making ordinary color-separation negativesv from an original representing the three primary printing colors red, yellow and blue and also a so-called black negative; making positives from each color-separation negative -to serve as a corrective cut-out; making final positives from the three color-separation negatives and from the black negative, with a camera by transmitted light; and using said cut-out positives to-correct the color values in the last-mentioned positives by super-imposition on the negatives during exposure.

5. A process according to claim 4 in which the exposure of the final positives is made for part time with the use of the Fcut-out positives and part time without.

6. A process according to claim 4 in which the final positives made from the blue colorseparation negative and the black negative are made, using both the yellow and red cutout positives in the case of the blue colorseparation negative and 'all three cut-out positives in the case of the black negative.

- 7. A process according to claim 4 in which the final positives made from the blue colorseparation negative and the black negative are made, using both the yellow and red cut-out positives in the case of the blue color-separation negative and all three cut-out positives in the case of the black negative and in which the exposure of the final postives is made for part time with the use of the cut-out without.

positives and part time Signed at Toronto, Canada, this 19th day I of January, 1931.

. JOHN M. KEENAN.