US2480400A - Method of making gravure printing plates - Google Patents

Description

Aug. 30, l949. A. DULTGEN 2,480,400

METHOD OF MAKING GRAVURE PRINTING PLATES I Filedveo. 30, 1944 SUBJECT eff/wss nssaf army m Fmr:

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Patented Aug. 30, 1949 METHOD or MAK' 1N` G GRAVURE PRiNi G corporation of New York .Y Application December 30, 1944, serial No. `'1,ii4'4" This invention relates `'to a method of making a gravurey printing plate.' L

The invention is directed particularly to preparing gravure printing plates from half-tone printing plates soA as to -take' advantage of the availability of half-tone `plates and the handmade corrections, such as-color corrections, which are customarily present in such plates.

' In preparing half-tone photographs by photographing through ha-l-tone screens, the dot formation formed on-the photographic plate is dependent upon the'screen distance, time of exposure and-the shape of the stop, sothat numerous different half-tonejdot formations are available. In preparing-half-tone printing plates for relief printing-it is usual to obtain the greatest possible tone range by a half-tone dot formation which runs from' a'whitey ground contain-ing minute black dots inthelightest tones to aY black ground containing minute White dotsin the darkest tones; Fonmaking a gravure plate,\it is customary to reduc'ethetonegrange to about onehalf the maximum `tone:range,1so that, While the lightest areas are represented as before, the darkest areas'are `represented by a White eld with large black dots--justlout of contact with one:

another or, in other Words, in the same way that the middle tones are represented .in a halfstone Y of maximum toneran'ge. Prints of such .halftones of redu'cedrange `make resists which may be used in gravure etching because they produce a plate in which evenvthe darkest tones are represented by separate cavities Well adaptedto hold the ink. Gravure plates made-from suchreduced range half-tones of course produce prints of reduced tone ran-ge and are, therefore, unsatisfactory unless the tone rangev of the print is-increased by somev means for causing a variation in the depth of the cavities. Such meansare de-` scribed in my Patent 2,096,79L-issuedv October 26, 1937.

My present invention is directed to making a gravure plate from a full-range half-tonevsuch as a half-tone photograph made for reliefprint'- ingor a print from a half-tone plate. I have found that it is `possible't'oY break up the solid black-areas and the black areas containingisolated White dots Which occur in azfull-range halftone, without modifying the portions of the pictu're which appear as black dots of various sizes on a white background.

In accordance with my invention, this is accomplished by two successive exposures of the resist through Which the plate is to be etched. The rst exposure is made through a full-range positive half-tne transparency of the Subject, While the secondV exposure-is made vthrough a 'positive transparency yhavingV a uniform dotQtoi-rnation consisting of slightly separated-opaque dots-on a transparent ground. VItis=importantthat the transparency with the vuniforml -dot fr'irniat'ion have the-samersci'een size;V as `the half-tne positive. In making the secondexposure of the 'resist, the transparency withltljin'eV uniform dot fore drawings in whlc i f;

`Fig.: 1 is ailowmdlagi'am-of an illustrative meth enc'ymay beprod". print from the-.lhalfrt ,plten a transparent material, vor .m1,photographing@mechanica printfrlfrom the platefmadepn :paperyrv other Opaqueemateliiilrux: riferi: my fr.' an" A positive transparency with a uniform halftonefdot formation;- avingiihe, sameiscreensize as vthe :naifrtcne no Y .ilS- prepareda1-lTI-iis-s throughfafhalf-tnnefscreenin1.a 4ha-lstone. reame era,l making the exposure such asato prnducadis'- connected?dots'.` Aiioontact'pifint ofthe-photo'- graphn'iay #then b-fad, vui`=if1e`cessaiy', order to produce opaque dots on a transparent eld. The dots are of uniform size and just out of contact with each other, such as those which occur at a middle tone of an ordinary half-tone positive. The screen size of this positive is the same 3 as the screen size of the full-range half-tone positive of the original.

The two positives are printed successively on an ordinary carbon tissue, that is to say, the carbon tissue is exposed successively through the fullrange half-tone positive of the subject and through the positive with the uniform dot formation.4 It is important that in making two exposures the dot formations be in register.

The result of the two exposures of the carbon tissue is shown in Fig. 2. In this figure, the areas with vertical shading are those which are left unexposed when the tissue is exposed through the full-range half-tone positive of the original. For illustrative purposes, it is assumed that the halftone positive shows merely a tone scale extending uniformly from the lightesttone at the top to the darkest tone at the bottom. The areas indicated by horizontal shading are those which are left unexposed when the tissue is exposed through the positive with the uniform dot formation.

The combined result of the two exposures is to expose all parts of the carbon tissue except those which were covered in both exposures and which are represented by cross-line shading in Fig. 2. It will be seen that in thedarker tones shown in the lower part of the figure, the unexposed areas remaining after the two exposures consist of large disconnected dots, as distinguished from the solid unexposed area which remained after the exposure through the half-tone positive and before the second exposure was made. In the lighter tones, on the other hand, the unexposed areas remaining after thel two exposures are the same as those remaining after the first exposure and before the second exposure. The second exposure in no way changes theunexposed dots left in the lighter tones after the first exposure, as each of them is fully covered by one of the larger opaque dots of the uniform dot formation positive, and this will be true even though there is a slight error in registration.

After the two exposures, the carbon tissue may be used as a resist in etching a gravure plate, and will result in producing a plate having disconnected cavities well adapted to hold the ink. Such a plate, however, does not give an accurate representation of the tones of the original. This is apparent from Fig. 2 where it is shown that after the two exposures, the unexposed areas (indicated by cross-line shading) which produce the cavities in the printing plate are of the same size in the darkest tones and in a tone near the middle tone, so that a print made from a plate engraved directly from the resist shown in Fig. 2 would lose those gradations in tone of the original which occur between the middle tone and the darkest tone. This difficulty is remedied according to my invention by printing a continuous-tone positive of the original on the carbon tissue after the full-range half-tone positive and the uniform dot formation positive have been printed on it.

The continuous-tone positive of the original may be merely a positive print of a continuoustone photograph of the original or it may be a slightly blurred photograph of a mechanical print from a half-tone plate in which the dot formation of the print is lost. The effect of the exposure of the tissue through the continuous- 4 tone positive is to produce a graduated exposure of the previously unexposed areas of the tissue so that, on reversing and washing the tissue, the usual multiple-stage etching will produce deeper cavities in the darker areas than in the lighter areas.

My invention is most valuable when used to produce gravure plates from half-tone relief plates so as to obtain the advantage of hand retouching which has been done on such plates. This is particularly important in plates for the three-color or the four-color process. In order to obtain the benefit of such retouching, the fullrange half-tone positive used in my method is produced from a mechanical print from the halftone plate in either of the manners previously described. If this is done, it is not necessary that the continuous-tone positive be also obtained from a mechanical print from the half-tone plate, as the eiect of the retouching is carried into the gravure plate to a sufficient extent if only the half-tone positive is obtained from the relief plate.

Various changes may be made in the specic method which has been described without departing from the scope of my invention. Thus, the order of the successive prints is not important. It is not necessary that the successive prints through the full-range half-tone positive and the uniform dot formation transparency be made directly on a carbon tissue or upon any type of resist. Any light-sensitive material may be exposed successively under the two transparencies and the combined print may thereafter be transferred to a resist. Where the invention is to be used in its best form to produce a plate with cavities differing in depth as well as in area, a carbon tissue should be used at least for the print from the continuous-tone positive.

What I claim is:

The method of making a gravure printing plate, which comprises successively printing in register on a carbon tissue a full-range halftone positive of an original, a uniform half-tone dot formation of the same screen size consisting of disconnected opaque dots on a transparent eld, and a continuous-tone positive of the original, and then producing a gravure plate by multiple-stage etching through said carbon tissue.

ARTHUR DULTGEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,464,140 Sauer Aug. 7, 1923 2,010,042 Stirling Aug. 6, 1935 2,096,794 Dultgen Oct. 26, 1937 2,100,346 Misuraca Nov. 30, 1937 2,134,080 Flader Oct. 25, 1938 2,306,936 Chambers Dec. 29, 1942 2,446,193 Rice Aug. 3, 1948 FOREIGN PATENTS Number Country Date 733,424 France July 11, 1932

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