US3287131A

US3287131A - Method of producing a positive assemblage suitable for the preparation of a rotogravure plate

Info

Publication number: US3287131A
Application number: US247979A
Authority: US
Inventors: Jemseby Anton Wilhelm
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-01-05
Filing date: 1962-12-28
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22
Also published as: GB1034111A; SE319975B; DE1447906A1; CH463278A

Description

3,287,131 FOR THE Nov. 22, 1966 A. w. JEMsl-:BY

METHOD OF PRODUCING A POSITIVE ASSEMBLAGE SUITABLE PREPARATION OF' A ROTOGRAVURE PLATE 2 Sheets-Sheet l Filed DeC. 28, 1962 FIGJ FIGO

Nov. 22, 1966 A. w. JEMSEBY 3,287,131

METHOD OF PRODUCING A POSITIVE ASSEMBLAGE SUITABLE FOR THE Filed Dec. 28, 1962 PREPARATION OF' A ROTOGRAVURE PLATE 2 Sheets-Sheet 2 United States Patent 3,287,131 METHOD OF PRODUCING A POSITIVE ASSEM- BLAGE SUITABLE FOR THE PREPARATION OF A ROTOGRAVURE PLATE Anton Wilhelm Jemseby, Allfarvagen 29, Taby, Sweden Filed Dec. 28, 1962, Ser. No. 247,979 Claims priority, application Sweden, Jan. 5, 1962, 134/62 7 Claims. (Cl. 96-45) In the printing technique use is made in principle of two different main processes for the reproduction of continuous tone images by means of printing plates etched by making use of photographic methods. One such process, which may be termed the halftone process, resides in dividing the image into a great number of halftone dots usually of the same spacing, which in principle are printed with the same intense inking, the various tones of the printed reproduction being Iobtained by the varying size of the surfaces of the halftone dots. The other main process, which may be termed the intaglio process, consists in etching a printing plate in such a way that the depth of etch varies in relation to the tones of the image, the various tones of the printed reproduction being obtained by a differently intense inking (ink layer of varying thickness) of the various surface portions of the reproduction. The intaglio process yields reproductions of considerably higher quality than docs the halftone process, but the preparation of the printing plate is more diicult and more expensive.

In the intaglio process the printing plate is first inked in excess whereupon the excess ink is removed to the level of the printing plate surfaces that shall not give any ink impression and which may thus be designated as the image-free surfaces, so that ink remains only in the printing plate recesses produced by the etching. The predominating intaglio process is the rotogravure process in which the excess ink is wiped off by means of a doctor engaging the image-free surfaces of the printing plate. As the tones of the reproduction are determined in actual rotogravure by variation of the inking degree, i.e. the thickness of the ink layer, it is important that the doctor wipes off the excess ink precisely at a level with the imagefree surfaces of the printing plate. Since the doctor due to its resilence tends to enter the recesses of the printing plate, image-free surfaces must be arranged also within the image areas to support the doctor, and said surfaces must be so shaped and dimensioned as not to disturb the visual image impression given by the reproductions. Although there have been suggested a great many methods of providing such doctor-supporting image-free surfaces within the image areas the procedure now most generally applied is to print in the image, when effecting the photographic operations permitting etching the image on the printing plate surface, a so-ca-lled rotogravure or doctor screen usually made up of a grid of relatively widely spaced thin lines which after etching appear on the printing plate as line-shaped image-free surfaces traversing the image areas and dividing them into a large number of spaced minute cavities or wells.

For a correct understanding of the following account it should be realized that the doctor screen screendivides the continuous-tone image but does not produce a halftone image composed of halftone dots according to the halftone process, i.e. the said cavities of the printing plate have a depth that is in a certain relation to the tones within the portion in question of the image so that the tones of the reproductions are still determined by the inking intensity (thickness of the ink layer), which is in opposition to the image composition of a halftone image wherein the intensity is -constant but the surtace size of the 3,287,131 Patented Nov. 22, 1966 ICC halftone dots varies relatively to the tones of the image. In the following there will thus be made a severe distinction between the term screen-divided continuous-tone image and the term halftone image according to the explanation given hereinbefore.

In printing the doctor slides against the doctor-supporting image-free surfaces which dene the image surface cavities from each other, and wears away said surfaces, which implies that the ink-receiving cavities become shallower. This wear will be substantially equally large within all image areas but the effect on the image quality becomes different for the different tones in the image. When the level of the image-free doctor-supporting surfaces has been changed by the wear over a certain distance the latter is a larger percentual portion of the depth of the initially shallow cavities corresponding to the bright tones of the image, than the depth of the initially deep cavities corresponding to the dark tones of the image so that in the course of the printing there arises a relatively rapid manifest deterioration of the bright tones of the reproductions toward a larger brightness.,

It has been tried to overcome this disadvantage in several ways. It has thus been suggested to control the etch of the printing plate by means `of a pure halftone image. In this process, however, the tones of the image are not built up by varying inking intensity (thickness of the ink layer) but by a varying surface size of equally intensely inked halftone dots. As a result, the printing plate will certainly have an excellent wearing strength since all cavities are equally deep and the image-free doctor-supporting printing plate surfaces become very large within the bright portion of the image because the halftone dots which are arranged with the same spacing throughout the image, have a small cross-sectional surface in said bright portions and are thus surrounded by large image-free surface areas, but the advantage of actual rotogravure of giving a good image quality is lost while the disadvantage of the rotogravure, e.g. a higher cost of production for the printing plate, remains. The best method which is known at present of counteracting the quality deterioration of the bright tones of the image in rotogravure is to superpose, in effecting the photographic operations for permitting etching of the image on the printing plate, a normal continuous-tone image screen-divided by a doctor screen, and a pure halftone image prepared by a reproduction camera. In this method each cavity in the printing plate within the image areas having bright tones is designed in principle as a comparatively shallow cavity rotogravure cavity surrounded by the doctor-supporting image-free surfaces generated by the doctor screen, and the bottom of said rotogravure cavity at one point has a recess halftone dot cavity which extends to the same depth under the doctor-supporting image-free printing plate surfaces in all cavities and the cross-sectional surface of which corresponds to the cross-sectional surface of the corresponding halftone dot in the pure halftone image employed at the preparation of the plate. The line of thoughts underlying this method is that the reduction in volume of a printing plate cavity within an image portion having a bright tone, which reduction arises after a certain wear of the doctor-supporting image-free surfaces, shall not become percentually as large as in a pure rotogravure process because the volume of the cavity is composed of the rotogravure cavity on one hand and the considerably deeper halftone dot cavity on the other. The last-mentioned method, however, suffers from serious drawbacks. For a given bright tone in the image the rotogravure cavity on one hand is shallower than in normal rotogravure, while the ink amount required for the tone is accommodated to a considerable proportion by the halftone dot cavity, and the doctor-supporting image-free surfaces on the other hand are not larger than in normal rotogravure, which implies that the importance of the rotogravure cavity to the quality of the reproduction upon wear of the doctor-supporting image-free surfaces decreases more rapidly ythan in normal rotogravure so that one very soon obtains reproductions in which the bright tones lare built up almost exclusively of the halftone dot cavities, i.e. of the lower quality of the halftone process.

The present invention suggests Ia novel and better solution of the problem outlined above of a deteriorated image quality within the bright tone lareas of the image, and in certain aspects the invention may be considered as a further development of the last-mentioned method whereby larger doctor-supporting image-free surfaces are obtained in the bright areas of the image so that the wear of these surfaces is reduced, and besides deeper rotogravure cavities than both in normal rotogravure and in the lastmentioned prior-art process for one and the same bright tone of the image, which implies that the wear of the doctor-supporting image-free surfaces less rapidly reduces the contribution of the rotogravure cavities to the image quality. In addition, the method according t'o the invention offers the possibility of a cheaper and more rapid production of the printing plates as well as increased possibilites of modifying the tones of the image, whichis of particular importance in multieolour printing.

The invention thus relates to a method of photographically producing from a transparent continuous-tone negative a positive assemblage suited for the preparation of a rotogravure plate and comprising halftone and continuous-tone separations of the continuous-tone negative, said different components of the positive assemblage being made on a single photosensitive material or on several photosensitive materials. It is pointed out that the expression rotogravure plate is used in the following disclosure as including both flat plates and cylindrical plates. The method according to the invention is characterized by the fact that the continuous-tone negative in preparing the continuous-tone separation or each continuous-tone separation is printed together with a screen, a dividing screen, by which the image surface of the separation is divided into individual continuous-tone image surface portions each of which has a smaller area than the area of one of the mutually equally large screen apertures of the doctor screen, used in reproducing the positive assemblage on the rotogravure plate.

For better understanding the invention will be described more in detail in the following with reference to the accompanying drawings which illustrates some possibilities of applying the invention. In the drawings:

FIG. l shows a lenticular screen from one face on a heavily magnified scale;

FIG. 2 in the same manner shows a dividing screen;

FIG. 3 in the same manner shows a doctor screen;

FIG. 4 shows a cross-sectional view and on a magnified scale the arrangement of different elements in preparing a halftone separation;

FIG. 5 in the same manner as FIG. 4 shows the arrangement of the elements in producing a continuoustone separation;

FIGS. 6 and 7 schematically show on a magnified scale the appearance of two different positive assemblages produced by application of different embodiments of the method according to the invention.

FIG. 1 shows from one side face a lenticular screen illustrated in cross section in FIGS. 4 and 5. This lenticular screen has transparent screen elements 1 in the form of small positive lenses arranged with the same spacing in relatively perpendicular rows and surrounded by a nontransparent background portion 2. The total surface of the lens elements is at most half and preferably a much smaller proportion of the total surface of the screen, and in the example illustrated the total surface of the lens elements is a fourth of the entire surface of the screen, which is the most suitable dimensioning. While the lenticular screen can be made in several different ways, for instance according to U.S. Patent 1,849,036 to V. C. Ernst. In other words the lenticular screen has a transparent film backing 3 on which a photosensitive silver halide emulsion layer has been exposed with a suitable screen pattern and then developed while producing a heavy Ross effect so that the exposed silver halide of the emulsion has been developed to black silver forming the background 2 While non-exposed emulsion portions through the Ross effect have been caused lenticularly to project from the background 2 to form the lens elements 1.

FIG. 2 shows a screen which is employed in certain embodiments of the invention and which on a non-transparent background 4 has transparent screen elements 5 which are arranged in the same way and with the same spacing as the lens elements 1 in the lenticular screen according to FIG. 1. The screen elements 5 are circular like the lens elements 1 but are not lenticular. The total surface of the screen elements 5 in FIG. 2 is approximately half that of the entire surface of the screen. Like the screen in FIG. l, the screen shown in FIG. 2 may be a contact print of an original screen, i.e. have a film backing with a silver halide emulsion layer thereon, which after printing-exposure has been developed while avoiding a Ross effect so that the transparent screen elements 5 have not be-come lenticular.

FIG. 3 shows an ordinary doctor screen which has a square grid of non-transparent lines 6 which define mutually equally large screen apertures 7. Although the spacing of the doctor screen could be identical to that of the screens in FIGS l and 2 it is, however, considerably more advantageous that the spacing of the doctor screen is greater than that of the screens in FIGS. 1 and 2. In any case it is essential that each transparent frame 7 has a considerably larger area than the area of one of the

transparent screen elements

1, 5 in the screens shown in FIGS. 1 and 2. The doctor screen according to FIG. 3 can be made as a contact print of an original screen so that it has a trans-parent film backing 8 (ser: FIGS. 4 and 5) with non-transparent black silver lines and transparent emulsion portions therebetween.

FIG. 4 shows how a halftone separation is produced from a continuous-tone negative which is the original for the production of .a rotogravure plate. Although photographic glass plates may naturally be employed it is presupposed here for the sake of simplicity that photographic film is used. FIG. 4 shows at the bottom a photographic film which consists of a backing 9 with a photosensitive layer 10 thereon. This film 9, 10 shall form a positive assemblage from which a rotogravure plate is to be made in the usual manner. Disposed on top of the photosensitive layer 10 of the film 9, 10 is the doctor screen according to FIG. 3 with the non-transparent screen lines 6 next to the layer 10. Placed upon the 4backing 8 of the doctor screen is the original negative which has a backing 11 and a developed emulsion layer 12 with the original image. The layer 12 is applied against the backing 8 ofl the doctor screen. Superposed on the Ibacking 11 of the negative is the lenticular screen according to FIG. l with the lens elements 1 in contact with the backing 11 of the negative. Exposure is effected with very -obliquely incident light from different directions, e.g. four directions so that a hard gradation is obtained. The lamps used at the exposure shall be arranged at such a distance from the screen 1-3 that the lens elements 1 collect the light in focal points lying approximately on the photosensitive layer 10, although said focal points may in principle lie slightly above said layer 10, i.e. in the doctor screen 6-8. As the light in the selected example falls very obliquely from four different lamps one obtains at least within the brightest portions of the positive four individual halftone dots for each lens element 1 while the four halftone dots from each lens element coincide at least partly Within the darkest portions of the positive image, as will appear from FIG. 6 where the halftone dots are indicated by means of black circles 13. The black lines 6 of the doctor screen partly shield the light of exposure from the photosensitive layer 10, as will appear from the positive image in FIG. 6.

After exposure of the halftone separation, the lenticular screen 1-3 and the negative 11, 12 are caused t-o change places so that t-he arrangement according to FIG.

5 is obtained. Thereafter exposure is again effected with perpendicularly incident parallel light or by means `of a punctiform light source situated directly above and at a considerable distance from the negative 11, 12. Since the lens elements 1 now are very close to the photosensitive layer they cannot any longer produce halftone dots but merely serve for screen-dividing the image of the continuous-tone negative so that this second exposure yields a continuous-tone separation positive of the negative, which separation positive is broken up or divided by the screen. In this second exposure there are thus obtained circles 14 (FIG. 6) the density of which is inversely proportional to that of the negative at the corresponding points of the image surface. In this second exposure also, the non-transparent lines 6 of the doctor screen partly shield the light from the photosensitive layer 10, as will be seen from FIG. 6. Since each lens element 1 has a considerably smaller surface than the surface of the transparent screeny apertures 7 of the doctor screen the` positivelimage, as will'appear from FIG. 6, will have image-free .surfaces not only in the area of the non-transparent lines 6 of the doctor screen but also at their points in the area of the transparent screen apertures 7 ofthe doctor screen within the brighter portions of the positive. The exposures according to FIGS. 4 and 5 shall be so pronounced that the tones of the image are correct although image-free surfaces occur also in the range of the screen apertures 7 of the doctor screen 6, i.e. the image circles 14 of the continuous-tone separation shall be darker than if the image surfaces entirely filled out the surface portions of the positive corresponding to the apertures 7 of the doctor screen. It is presupposed in FIG. 6 that the lens elements 1 have occupied the same positions within the image surface in both exposuresaccording to FIGS. 4 and 5 so that' the continuous-tone surface .porti-ons 14 of the continuous-tone separation are arranged substantially symmetrically relative to the screen elements 13 of the halftone separation, but the lens elements 1 can also occupy different positions in the image surface tarea at the exposures according to FIGS. 4 and 5, e.g. by the screen 1-3 being displaced in parallel or turned as is well known.

A positive assemblage according to FIG. 6 is particularly useful for a black separation positive in colour printing. When on the other hand the production of a rotogravure plate for a monochrome image or for the colour separation plates in multicolour printing is concerned it is more suitable to make a positive assemblage according to FIG. 7. This is produced by first making a halftone separation according to FIG. 4 and then a continuous-tone separation according to FIG. 5 whereupon the lenticular screen 1-3 in FIG. 5 is replaced by the screen according to FIG. 2 and a new exposure is made so that a further continuous-tone separation is obtained, the circularcontinuous-tone image surface portions of which are larger than the continuous-tone image surface portions provided by means of the lenticular screen 1-3. In this third exposure the screen according to FIG. 2 should be offset to the position of the lenticular screen 1-3 in the exposures according to FIGS. 4 and 5. In FIG. 7 the halftone dots are indicated by black circles 13, the continuous-tone image surface portions obtained by means of the lenticular screen 1-3 by hatched circles 14 and the continuous-tone image surface portions obtained by means of the screen according to FIG. 2 by hatched circles 15. As is seen from FIG. 7, the

circles

14, 15 should partly'overlap. It

is assumed in FIG. 7 that the doctor screen 6-8 has been used in all exposures but it may possibly be dispensed with in exposing either of or both continuous-tone separations Whereas the doctor screen shall always be used in exposing the halftone separation according to FIG. 4.

It has been described in the foregoing that the halftone separation and the continuous-tone separation or separations areexposed in sequence on one and the same photosensitive material 9, 10, which is advantageous, but the different separations could also be made on different photosensitive materials which after development are then used in the production of the rotogravure plate in the known manner. In making the different separations one may of course also eifect image corrections by masking in any convenient manner.

In the illustrative example chosen the doctor screen has been included in printing the positive assemblage from the original negative but sometimes a better scheme is to postpone the incorporation of the doctor screen until the positive assemblage is printed for making the rotogravure plate. In such a case the doctor screen 6-8 is not used in the printing packages according to FIGS. 4 and 5. In printing according to FIG. 5 (where the lens action of the screen 1-3 is not used) the screen 1-3 can contact the photosensitive layer 10, but in printing according to FIG. 4 the doctor screen 6-8 cannot quite simply be removed but must be replaced by a transparent sheet in order to preserve the lens action of the screen 1-3, as said lens action accounts for obtaining a halftone separation and not a screen-divided continuous-tone separation.

What I claim and desire to secure byLetters Patent is:

1. In a method of photographically producing from a transparent continuous-tone negative a positive image assemblage suited in superposition with a doctor screen image, having mutually equally large screen apertures, for the preparation of a rotogravure plate, the steps of preparing at least one positive halftone separation image of the continuous-tone negative by printing the continuoustone negative on photosensitive material of the positive image assemblage through a halftone screen, and preparing at least one continuous-tone separation image of the continuous-tone negative by dividing, when printing the continuous-tone negative on photosensitive material of the positive image assemblage, the image surface of said continuous-tone separation by means of a dividing screen, printed together with the continuous-tone negative on said material, into individual continuous-tone image surface portions of varying density each having a smaller area than the area of one of the screen apertures of the doctor screen image.

2. In the method according to claim 1, the step of arranging by means of said dividing screen means said continuous-tone image surface portions on said material of the positive image assemblage with a smaller spacing than the spacing of the screen apertures of the doctor screen image.

3. In the method according to claim 1, the step of making by means of said dividing screen means the total area of the continuous-tone image surface portions on said material of the positive image assemblage at most approximately 50% of the entire image frame surface of said material.

4. In a method of photographically producing from a transparent continuous-tone negative a positive image assemblage comprising positive halftone and positive continuous-tone separation images of the continuous-tone negative, and suited in superposition with a doctor screen image, having mutually equally large screen apertures, for the preparation of a rotogravure plate, the steps of exposing photosensitive material of the positive image assemblage at least once by light from different oblique directions through a halftone screen and the continuoustone negative for forming at least one positive halftone separation image of the assemblage, exposing photosensitive material of the positive image assemblage at least once by light from a single light source perpendicularly through the continuous-tone negative and dividing screen means for forming at least one positive continuous-tone separation image of the assemblage, divided by said dividing screen means into individual continuous-tone image surface portions of varying density, each such portion having a smaller area than the area of one of the screen apertures of the doctor screen image.

5. In a method of photographically producing from a transparent continuous-tone negative a positive image assemblage suited for the preparation of a rotogravure plate, the steps of preparing at least one positive halftone separation image of the continuous-tone negative by printing the continuous-tone negative on photosensitive material of the positive image assemblage through a halftone screen and a doctor screen having mutually equally large screen apertures, and preparing at least one continuoustone separation image of the continuous-tone negative by dividing, when printing the continuous-tone negative on photosensitive material of the positive image assemblage, the image surface of said continuous-tone separation by means of a dividing screen printed together with the continuous-tone negative and said doctor screen on said material, into individual continuous-tone image surface portions of varying density, each having a smaller area than the area of one of the screen apertures of said doctor screen.

6. In a method of photographically producing from a transparent continuous-tone negative a positive image assemblage comprising positive halftone and positive continuous-tone separation images of the continuous-tone negative, and suited for the preparation of a rotogravure plate, the steps of exposing photo-sensitive material of the positive image assemblage at least once by light from different directions through a halftone screen, a doctor screen having mutually equally large screen apertures, and the continuous-tone negative for forming at least one positive halftone separation image of the assemblage, exposing photosensitive material of the positive image assemblage at least once by light from a single light source perpendicularly through the continuous-tone negative, said doctor screen, and dividing screen means for forming at least one positive continuous-tone separation image of the assemblage, divided by said dividing screen means into individual continuous-tone image surface portions of varying density, each such portion having a smaller area than the area of one of the screen apertures of the doctor screen.

7. In a method of making a print for controlling the etching of a rotogravure plate, the steps of incorporating in said print by printing an image of a doctor screen, having mutually equally large screen apertures, preparing from a transparent continuous-tone negative a positive image assemblage, comprising positive halftone and positive continuous-tone separation images of the continuoustone negative, by exposing photosensitive material of the positive image assemblage at least once through a halftone screen and the continuous-tone negative for forming at least one positive halftone separation image of the assemblage, exposing photosensitive material of the positive image assemblage at least once through the continuous-tone negative and dividing screen means for forming at least one positive continuous-tone separation image of the assemblage, divided by said dividing screen means into individual continuous-tone image surface portions of varying density, each such portion having a smaller area than the area of one of the screen apertures of the doctor screen, and incorporating in said print by printing an image of said positive image assemblage.

References Cited by the Examiner UNITED STATES PATENTS 1,991,888 2/1935 Ernstr 96-116 2,010,042 8/19315 Stirling 96--38 2,159,588 5/1939 Gorig 96--38 2,201,346 5/1940 Raby et al. 96-38 2,528,007 10/ 1950 Kuberserian 96-38 2,914,405 11/ 1959 Consaul et al. 96-45 2,961,315 11/1960 `Stirling 96-45 3,024,111 3/ 1962 Sportelli 96--38 3,122,436 2/1964 Wattier 96-45 FOREIGN PATENTS 421,529 1/ 1935 Great Britain.

NORMAN G. T-ORCHIN, Primary Examiner. A. D. RICCI, R. H. SMITH, Assistant Examiners.

Claims

1. IN A METHOD OF PHOTOGRAPHICALLY PRODUCING FROM A TRANSPARENT CONTINUOUS-TONE NEGATIVE A POSITIVE IMAGE ASSEMBLAGE SUITED IN SUPERPOSITION WITH A DOCTOR SCREEN IMAGE, HAVING MUTUALLY EQUALLY LARGE SCREEN APERTURES, FOR THE PREPARATION OF A ROTOGRAVURE PLATE, THE STEPS OF PREPARING AT LEAST ONE POSITIVE HALFTONE SEPARATION IMAGE OF THE CONTINUOUS-TONE NEGATIVE BY PRINTING THE CONTINUOUSTONE NEGATIVE ON PHOTOSENTIVE MATERIAL OF THE POSITVE IMAGE ASSEMBLAGE THROUGH A HALFTONE SCREEN, AND PREPARING AT LEAST ONE CONTINUOUS-TONE SEPARATION IMAGE OF THE CONTINUOUS-TONE NEGATIVE BY DIVIDING, WHEN PRINTING THE CONTINUOUS-TONE NEGATIVE ON PHOTOSENSITIVE MATERIAL OF THE POSITIVE IMAGE ASSEMBLAGE, THE IMAGE SURFACE OF SAID CONTINUOUS-TONE SEPARATION BY MEANS OF A DIVIDING SCREEN, PRINTING TOGETHER WITH THE CONTINUOUS-TONE NEGATIVE ON SAID MATERIAL, INTO INDIVIDUAL CONTINUOUS-TONE IMAGE SURFACE PORTION OF VARYING DENSITY EACH HAVING A SMALLER AREA THAN THE AREA OF ONE OF THE SCREEN APERTURES OF THE DOCTOR SCREEN IMAGE.