US2984566A - Method of preparing a printing surface - Google Patents

Description

May 16, 1961 R. H. CAINE METHOD OF PREPARING A PRINTING SURFACE FiledApril 10, 1957 2 Sheets-Sheet 1 May 16, 1961 R. H. CAINE METHOD OF PREPARING A PRINTING SURFACE Filed April 10, 1957 2 SheetsSheet 2 f7? fizz for? KOZZQIZd/ (Q5726 m, i zzw United States Patent Rolland H. Caine, Park Ridge, Ill., 'assignor to R. R.

Donnelley & Sons Company, a corporation of Delaware Filed Apr. 10, 1957, Ser. No. 651,915

3 Claims. (Cl. 96-38) This invention relates to a method of preparing a printing surface of a subject and in particular it relates to a method of producing a printing surface which combines the characteristics of conventional gravure and half-tone dot structure.

A number of different methods have been devised for incorporating the feature of variable size printing dots into a gravure printing surface. The oldest, and perhaps the best known of such methods is that disclosed in Dultgen Patent No. 2,096,794.

The present invention is directed to a novel and very simple way of producing a gravure printing surface which includes certain advantages of half-tone printing. The final plate is similar to that produced by Dultgen, but the present method is much simpler.

The principal object of the invention is to form a photographic image of varying dot areas ranging from representing a light tone, to approximately 56% representing a solid, and in which the dots form a conventional gravure pattern in the solid, i.e. with their sides adjacent.

A further object of the invention is to form the image from a corrected positive transparency of the subject.

Yet another object of the invention is to form such an image without the aid of a camera or lens.

Practice of the present invention requires only a modified vacuum hold down table, together with a positive gravure screen transparency mounted in a suitable spacing frame to position the gravure screen a predetermined distance above the hold down surface, and a flood light in a lamp house. The vacuum table and the screen spacing frame are provided with suitable pins and indexing notches by means of which to assure proper angular disposition of the gravure screen and to obtain the desired angular shifts of the screen for various colors.

In the accompanying drawings,

Fig. 1 is a plan view of a gravure screen supporting frame mounted on top of a suitable vacuum hold down table;

Fig. 2 is a fragmentary section on an enlarged scale taken as indicated along the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary section similar to Fig. 2, but on a greatly enlarged scale, diagrammatically illustrating the position of the components for a first exposure of a high contrast emulsion;

Fig. 4 is a view similar to Fig. 3, showing the arrangement of components during a second exposure;

Fig. 5 is a fragmentary, generally diagrammatic view on a greatly enlarged scale of representative dot areas in a negative produced by an exposure such as that shown in Fig. 3;

Fig. 6 is a positive produced from the negative of Fig. 5;

Fig. 7 is a view similar to Fig. 5 of a negative produced from the exposure illustrated in Fig. 4;

Fig. 8 is a positive produced from the negative of Fig. 7; and j I Fig. 9 is a composite positive produced from a negative which is obtained by superimposing a latent image such as that which would develop to make the negative of Fig. 5 upon a latent image such as that which would develop to make the negative of Fig. 7, and developing the two latent images simultaneously.

The method of the present invention requires that a high contrast emulsion be prepared for developing which has on it two latent images, the first being produced by exposing the emulsion through a continuous tone, corrected positive transparency of the subject and through a gravure screen; and the second being a sharp image of the gravure screen superimposed on the first image.

The present invention is most conveniently practiced by using a vacuum hold down table, indicated generally at 10, having a top 11 in which is a vacuum manifold 12 provided with a nipple 13 to receive a vacuum line 14. The top surface of table top 11 is adapted to be placed in communication with the vacuum manifold 12, and this may be accomplished by means of a series of bores 15 extending from the top surface to the manifold, or as is common in the art, by a crisscross pattern of shallow grooves which communicate with the manifold as through a group of bores similar to the bores 15. A peripheral vacuum channel 16 communicates by a bore 17 with the manifold 12, and takes the form of a rectangular frame which completely surrounds the central portion of the table top 11. Thus, both a high contrast film or emulsion N and a continuous tone positive transparency P may be positioned on top of vacuum table 16 as seen in Figs. 2 and 3, the positive transparency P being about an inch larger than the high contrast film N in both length and breadth. The system of vacuum bores 15 will hold the film N firmly flat upon the table top, while the rectangular channel frame 16 will hold the positive P firmly against the film N.

Surmounting the vacuum table 10 is a separate supporting and spacing frame 18 for a gravure screen S. Frame 18 includes an annular base member 19 provided with a spacing flange 20 upon which is supported a sandwich, indicated generally at 21, consisting of a glass base plate 22 on which is carried a photographic image comprising gravure screen S, and a superimposed glass cover plate 23. In order to minimize diffraction, glass cover plate 23 is cemented to the screen S with Canada balsam in the usual Way. Screen S may have the normal 3 to l gravure ruling. The spacing provided by the flange 20 and base plate 22 are selected to produce a predetermined amount of undercutting of the areas behind the opaque parts of the screen, thereby to determine the range of dot sizes in the image on the high contrast film N. The sandwich 21 is suitably held in place in frame 18 by an annular top member 24 which may be screwed to the annular base 19.

The combined thickness of the spacing flange 20 and the bottom glass 22 equals 0.180 inch, so as to maintain that spacing between the gravure screen 5 and the top 11 of the vacuum table.

As seen in Fig. l, the vacuum table top 11 is provided with a pair of indexing pins 11a and 11b, and the gravure screen mounting frame 18 is provided around its margin with a group of indexing notches, numbered 18a to 18e, inclusive. The indexing notches on the pins are suitably positioned to permit the gravure screen to be indexed at different angles for the different color plates of a set, in accordance with common practice in the art.

As previously stated, the method of the present invention contemplates the production of a high contrast negative which is a composite of a modified half-tone image of the subject being reproduced, and an image of a gravure screen. This is accomplished through the use of the apparatus previously described, in combination with a lamp house having two apertures of different sizes placed 48 inches from the surface of the gravure screen, and normal to the center thereof. The lamp house contains a No. 1 photofiood, and is arranged to provide a uniform light source for the illumination of the high contrast film.

A first exposure is made through a 1% inch opening in the manner shown in Fig. 3, with the continuous tone positive transparency P overlying the high contrast film or emulsion N and the gravure screen in place. This exposure produces a modified half-tone latent image of the subject.

The continuous tone transparency is then removed from between the screen and the high contrast emulsion and a supplemental exposure of about three minutes duration is made through a inch diameter aperture. The gravure screen is in precisely the same position for the two exposures. This produces two superimposed latent images on the emulsion.

Figs. to 9, inclusive, illustrate the types of negatives and positives producible by the different exposures shown in Figs. 3 and 4. If the latent image resulting from the exposure of Fig. 3 were developed a negative would result which would present generally the appearance shown in Fig. 5 as to the areas of varying darkness and lightness in the original subject. Thus, the fragment A of Fig. 5 represents the darkest area of the subject, while the fragment B represents an area of intermediate tone, and the fragment C represents one of the lightest areas. Thus, it is seen that the intermediate area B and the light area C have substantially conventional half-tone dot representations B1 and C1, respectively; while the darkest area A has very large, nearly square dots A1 which have convex sides that nearly merge.

Conversely, a positive produced from the negative of Fig. 5, which is illustrated in Fig. 6, has a fragment A3 containing large dark areas A2 which correspond to the areas A1 in the negative, a fragment B3 containing intermediate size dark areas B2 which correspond to the light areas B1 in the negative, and a fragment C3 con taining small dark areas C2 which correspond with the light areas C1 in the negative.

The supplemental exposure illustrated in Fig. 4 is produced by exposing the high contrast emulsion to light emanating from a hole the size of which is correlated with the distance of the hole from the gravure screen S as to produce a sharp image of the gravure screen upon the emulsion N. Thus, as seen in Fig. 7, the image produced by the exposure of Fig. 4 results in a negative image having a distinct grid G which isolates substantially square gravure screen dot areas G1. Conversely, of course, a positive produced from the negative of Fig. 7, which is illustrated in Fig. 8, has a light grid G2 which segregates the positive film surface into nearly square gravure dot areas G3.

In the practice of the invention as previously described, by the production of a double exposure on the high contrast emulsion N, neither the negative of Fig. 5 nor the negative of Fig. 7 ever is developed as a single image. Instead, the two superimposed latent images on the high contrast emuls on N are developed to provide a negative 7 which is a composite of the negative shown in Fig. 5

and the negative shown in Fig. 7; and this composite negative is then used to make a composite positive in which the varying dot areas have the appearance shown in Fig. 9. Thus, in the positive of Fig. 9 the darkest areas of the original subject are represented by the fragment X, which corresponds to the fragment A of the negative of Fig. 5, While the intermediate fragment Y corresponds to the fragment B of the negative of Fig. 5 and the fragment Z corresponds to the fragment C of the negative of Fig. 5. The darkest areas of the original subject have a dot size of about 56%, representing a solid, and the dot has approximately a square shape with a dot to line ratioof substantially 3:1.

In the practice of the invention the dot sizes may be adjusted by changing the explosures. The small dot is decreased by increasing the exposure illustrated in Fig. 3, that is, the exposure through the screen plus the continuous tone transparency; and the large dot may be de 1:reased by increasing the exposure through the screen on y.

The composite negative from which the positive of Fig. 9 is prepared is developed in a conventional Kodalith developer at 68 degrees F., while agitating the developer bath to give maximum uniformity. The positive from this composite negative is also on high contrast film and is developed in the same Way. The entire process is controlled to form, as much as possible, hard dots without fringe.

In the preparation of a printing plate, the conventional gravure screen is replaced by the dot image of Fig. 9, in the form of a positive screen transparency, as a means of preparing a printing surface of isolated cells of ink. Accordingly, the positive represented in Fig. 9 is used to form a carbon tissue etching resist in the usual way, i.e., by exposing the resist first through the dot image of Fig. 9 and then through the continuous tone positive. In this double exposure, of course, the variable dot image and the continuous tone positive must be maintained in perfect register, so that the areas X2 register with the densest areas of the positive, the areas Y2 with the corresponding areas of the positive, and so on. The resulting resist is used in the normal Way for etching the printing plate.

The resulting plate has isolated cells of ink, and the cross section of the cells varies so that the cell volume changes with area as well as with depth. This is especially desirable in the cells of minimum volume, since the depth does not become infinitesimal as is true in conventional gravure.

The larger minimum depth for the smallest cells removes the lightest printing tone from a supercritical condition found in conventional gravure processes, so that in etching the surface, in correcting it, and in printing, less precision is required; or correlatively, greater uniformity of tone may be obtained.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. In the preparation of a modified gravure printing plate of a subject, the steps of: exposing a high contrast photographic emulsion to a relatively Wide angle, uniform light source through a continuous tone positive transparency in contact with the emulsion and through a gravure screen which is in a predetermined plane between said light source and said positive transparency to produce on said emulsion a first latent image in which the size of the exposed image area at various parts of the emulsion varies inversely with the density of the positive transparency overlying each part; exposing said emulsion to light from a narrow angle source through said screen only to produce on said emulsion a sharp latent image of the screen which is in register with said first latent image, and thereby modify the exposed image area at certain parts of the emulsion; developing said emulsion to provide a negative screen transparency; producing a positive screen transparency from said negative screen transparency; forming a gravure etching resist by exposing a light sensitive resist material separately through said positive screen transparency and through the continuous tone transparency to produce registering latent images on said resist material, and then developing said resist; and using said resist in the etching of said printing surface .to produce a gravure plate in which the depth and the area of the recesses in the plate both vary in accordance with the density of tone of the subject.

2. In the preparation of a modified gravure printing surface of a subject, the steps of: forming on a high contrast emulsion a composite latent image, said latent image including a first latent image produced by an unfocused image of a positive gravure screen modified by interposing between the screen and the high contrast emulsion a continuous tone positive transparency of the subject, and a second latent image in register with said first latent image produced by a sharp image of said screen on said emulsion to modify the exposed image areas at certain parts of the emulsion; developing said composite latent image to provide a negative screen transparency; and producing a positive screen transparency from said negative screen transparency; forming a gravure etching resist by exposing a light sensitive resist material separately through said positive screen transparency and through the continuous tone transparency to produce registering latent images on said resist material, and then developing said resist; and using said resist in the etching of said printing surface to produce a gravure plate in which the depth and the area of the recesses in the plate both vary in accordance with the density of tone of the subject.

3. In the preparation of a modified gravure printing plate, the steps of: exposing a high contrast photographic emulsion to a relatively Wide angle, uniform light source through a continuous tone positive transparency in contact with the emulsion and through a gravure screen which is in a predetermined plane between said light source and said positive transparency to produce on said emulsion a first latent image in which the size of the 6 I exposed image area at various parts of the emulsion varies inversely with the density of the positive transparency overlying each part; removing said positive transparency and exposing said emulsion to light from a narrow angle source, the angle of said source being correlated with the distance of the gravure: screen from the source and from the emulsion to produce a sharp latent image of the screen on the emulsion in register with the first latent image and thereby modify the exposed image area at certain parts of the emulsion; developing said emulsion to provide a negative screen transparency; and producing a positive screen transparency from said negative screen transparency; forming a gravure etching resist by exposing a light sensitive resist material separately through said positive screen transparency and through the continuous tone transparency to produce registering latent images on said resist material, and then developing said resist; and using said resist in the etching of said printing surface to produce a gravure plate in which the depth and the area of the recesses in the plate both vary in accordance with the density of tone of the subject.

References Cited in the file of this patent UNITED STATES PATENTS 805,244 Szczepanik Nov. 21, 1905 1,167,505 Larsen Jan. 11, 1916 1,563,499 Knudsen Dec. 1, 1925 2,387,408 Alger Oct. 16, 1945 2,446,193 Rice Aug. 3, 1948

Claims (1)

1. IN THE PREPARATION OF A MODIFIED GRAVURE PRINTING PLATE OF A SUBJECT, THE STEPS OF: EXPOSING A HIGH CONTRAST PHOTOGRAPHIC EMULSION TO A RELATIVELY WIDE ANGLE, UNIFORM LIGHT SOURCE THROUGH A CONTINUOUS TONE POSITIVE TRANSPARENCY IN CONTACT WITH THE EMULSION AND THROUGH A GRAVURE SCREEN WHICH IS IN A PREDETERMINED PLANE BETWEEN SAID LIGHT SOURCE AND SAID POSITIVE TRANSPARENCY TO PRODUCE ON SAID EMULSION A FIRST LATENT IMAGE IN WHICH THE SIZE OF THE EXPOSED IMAGE AREA AT VARIOUS PARTS OF THE EMULSION VARIES INVERSELY WITH THE DENSITY OF THE POSITIVE TRANSPARENCY OVERLYING EACH PART; EXPOSING SAID EMULSION TO LIGHT FROM A NARROW ANGLE SOURCE THROUGH SAID SCREEN ONLY TO PRODUCE ON SAID EMULSION A SHARP LATENT IMAGE OF THE SCREEN WHICH IS IN REGISTER WITH SAID FIRST LATENT IMAGE, AND THEREBY MODIFY THE EXPOSED IMAGE AREA AT CERTAIN PARTS OF THE EMULSION; DEVELOPING SAID EMULSION TO PROVIDE A NEGATIVE SCREEN TRANSPARENCY; PRODUCING A POSITIVE SCREEN TRANSPARENCY FROM SAID NEGATIVE SCREEN TRANSPARENCY; FORMING A GRAVURE ETCHING RESIST BY EXPOSING A LIGHT SENSITIVE RESIST MATERIAL SEPARATELY THROUGH SAID POSITIVE SCREEN TRANSPARENCY AND THROUGH THE CONTINUOUS TONE TRANSPARENCY TO PRODUCE REGISTERING LATENT IMAGES ON SAID RESIST MATERIAL, AND THEN DEVELOPING SAID RESIST; AND USING SAID RESIST IN THE ETCHING OF SAID PRINTING SURFACE TO PRODUCE A GRAVURE PLATE IN WHICH THE DEPTH AND THE AREA OF THE RECESSES IN THE PLATE BOTH VARY IN ACCORDANCE WITH THE DENSITY OF TONE OF THE SUBJECT.

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